Symposium EN07—Sustainable Polymeric Materials by Green Chemistry—Degradability and Resilience

Lignocellulosic biomass, particularly the lignin fraction, is an attractive source of diverse, abundant, and inexpensive precursors for macromolecular design. Traditionally, petroleum-based products are designed with functionality being added as needed. Bio-derived molecules, on the other hand, have built-in functionality, which can be exploited to design novel materials with enhanced performance and reduced environmental impact. Bisguaiacols, such as the newly-developed bisguaiacol A (BGA) – an entirely bio-based, methoxy-substituted analogue to bisphenol A (BPA), are robust and potentially safer components for the design of polymeric systems with enhanced properties. We have utilized molecular docking studies to examine the estrogenic activity of these BPA analogues, establishing structure-active relationships. These studies inform application-specific design of polymeric systems – thermoplastics and thermosets. We highlight the design and manufacturing of non-isocyanate polyurethanes (NIPUs) from lignin-derivable bisguaiacols, exploring the role of hydrogen-bonding character on mechanical performance and assembly. As an example, NIPUs display strain-rate dependent mechanics due to the tailorable methoxy functionality of the precursors. We extend this molecular design to acrylate networks and other crosslinked polymers, balancing network architecture and performance characteristics and applying this understading to various form factors. These examples explore the inclusion of diverse lignin sources, synthesis of sustainable building blocks, macromolecular design and characterization, and manufacturing of ‘green’ polymers for a diverse set of applications.

The market for sanitary products is exponentially increasing, reaching over 130 billion USD in 2019. Despite the pandemic, the sanitary industry continued to grow and got net sales of around 7.8 % in the first quarter of 2020 compared with the corresponding period during 2019. About 50% of this market accounts for diapers (adults and babies), and a conservative estimate results in 20 million tons/year waste. A critical aspect is that these sanitary products are single-use and consist of >70% non-biodegradable plastics. The non-biodegradable petroleum-based hygiene products consist of superabsorbent polymer SAP (30 % of the total dry weight) and nonwoven polyethylene/polypropylene (PE/PP) fibers. The material research has focused on decreasing the environmental impact of these products using bio-based PE/PP, which are still non-degradable. At the same time, the absorbent component polymer (SAP) still originates from fossil-based resources. The limited sustainability of the current sanitary products and the growing demand have promoted biobased and sustainable polymeric alternatives in these materials, including the SAP.
We have established a protocol to produce an absorbent and porous sanitary pad article manufactured with protein as the primary protein matrix, using industrial processing techniques (e.g., extrusion + compression molding). The so far performed test at industrial partners has shown that the product resembles properties of a commercial reference product. The results revealed that the porosity and liquid performance were improved compared to techniques found in our previous related works. The bio-based product could even be colored using simple techniques, complying with industrial requirements to commercially such products. A conclusion reached is that the best performing protein matrix was gluten protein, while other protein matrixes (3 tested) showed slightly less mechanical performance. However, one limitation associated with the use of gluten is their amino-acidic profile, which is low lysine as charged amino acid residue, leading to a swelling performance of ca. 40 % compared to the synthetic absorbent core extracted from the commercial sanitary pad. At the same time, the product by itself cannot carry on enough liquid absorption (urine and blood) to compete with other critical hygienic articles in the market, e.g., incontinence/diaper products. An additional limitation of gluten matrixes is that their thermal processing is challenging, and the formation of the porous structure (responsible for the liquid uptake) is non-homogenous. Here, cellulose has been used as a bio-based filler to provide controlled formation of pores in the protein matrixes while increasing the product's mechanical properties and their liquid swelling performance. Our suggested sanitary article has shown biodegradation up to 50% in regular soil after 15 days, whereas the commercial material did not show biodegradability even after 95 days of soil exposure.
Using renewable resources to mass-produce a sustainable thermal processed sanitary article is suggested as a potential alternative to commercial non-sustainable components for the future hygiene industry. Using raw materials based on industrial side-streams and fillers that are innocuous to the environment is currently the only way to promote a non-polluting hygiene industry, contributing to circular bioeconomic principles and the United Nations Sustainable Development Goals 2030.

The global production of thermosets has been increasing in recent years, causing rapid consumption of fossil-based feedstocks and contributing to the plastic waste accumulation in the environment, especially because they cannot be easily reprocessed or recycled at the end of their lifetime. To overcome those issues, dynamic crosslinks capable of exchange reactions can be introduced, enabling network rearrangements, malleability, and reprocessability.[1] Those dynamic thermosets form a new class of materials, called vitrimers, since they flow like a vitreous silica (quartz glass) following the Arrhenius law.[2] At service temperatures they behave like permanently crosslinked polymers but at elevated temperatures the exchange reactions speed up making flow possible while maintaining constant number of chemical bonds and crosslinks. Thanks to that, vitrimers can be repaired, reshaped and reprocessed decreasing significantly the cost and environmental impact.
Facile way to produce biobased vitrimers from vegetable oils and a diboronic ester dithiol vitrimer crosslinker will be presented.[3] The synthesis of the cross-linker and the production process of the vitrimers has been done following green chemistry principles.The developed vitrimer materials can be reprocessed multiple times like a thermoplastic, without compromising its mechanical properties. Moreover they can be conveniently recycled by reversible hydrolysis in 90% ethanol and subsequent solvent evaporation, regenerating the original vitrimer. In case of an accidental release into the environment, the materials are able to biodegrade, solving the problem of waste accumulation.Properties of the final materials can be tuned from soft and flexible to rigid and hard by varying the vegetable oil type and crosslink density. The use of those materials in self-healing coatings, strain sensors and carbon fiber composites will be demonstrated.
1. D. Montarnal, M. Capelot, F. Tournilhac, L. Leibler, Silica-Like Malleable Materials from Permanent Organic Networks. Science, 2011, 334 (6058), 965.
2. W. Denissen, J. M. Winne, F. E.Du Prez, Vitrimers: Permanent Organic Networks With Glass-Like Fluidity, Chemical Science, 2016, 7 (1), 30-38.
3. A. Zych, J. Tellers, L. Bertolacci, L. Ceseracciu, L. Marini, G. Mancini, A. Athanassiou, Biobased, Biodegradable, Self-Healing Boronic Ester Vitrimers from Epoxidized Soybean Oil Acrylate, ACS Applied Polymer Materials, 2021, 3 (2), 1135–1144.

The possibility of using macromolecules from vegetables, with minimal processing, as alternative feedstock to obtain materials capable of substituting plastics in packaging is a very compelling possibility. Succeeding in this strategy will help to mitigate the environmental issues associated with the use of non biodegradable single use plastics and plastic packaging.
Furthermore, the possibility to use byproducts and waste from inedible parts of plants or discarded fruits and vegetables, will generate new value from resources that otherwise will be discarded, wasting also the energy and water used for their production. Using these waste and byproducts as a source of biomaterials will eliminate the controversy associated with the use of foodstuff (e.g. corn, sugars) to produce plastic alternatives such as starch-based plastics, PLA or PHAs.
In this talk we will update on our work on the fabrication of biocomposites from vegetable pomace and waste using a mild hydrolysis in a process carried out only in water, at mild temperature and without the use of harsh chemicals. We successfully obtained films from biomass such as spinach stem, carrot pomace, orange peel, cocoa shells, cauliflower leaves, parsley stems. We were able to correlate the thermo-mechanical properties with the composition and morphology using a combination of techniques: solid state NMR, FTIR, SEM, confocal microscopy, dynamic mechanical thermal analysis and Time Domain NMR. We studied and verified the biodegradability of the final material and the preservation of plant-derived properties such as color and anti oxidant properties; finally we studied the migration of substances from the composite to food simulant. This knowledge allowed us to devise new fabrication techniques, such as hot embossing to obtain complex shapes and to study the materials as mulches for agricultural applications. The proposed production process was studied by Life Cycle Analysis, and compared to traditional plastics and bioplastics like HDPE, PET, PLA and starch. The vegetable biocomposites were more competitive than traditional plastics in terms of global warming potential and cumulative energy demand, and were more competitive than PLA in their water scarcity index.
[1] Perotto G. et al, Green Chemistry, 2018
[2] Perotto G. et al, Polymer, 2020
[3] Simonutti R. et al, Sustainability & Green Polymer Chemistry Volume 2: Biocatalysis and Biobased Polymers 2021
[4] Merino D. et al, Green Chemistry 2021

This presentation will discuss our recent progress in developing sustainable thermoset polymers that are strong, self-healing, malleable, and recyclable by using robust while dynamic boron-oxygen (B–O) and silyl ether (Si–O) bonds. Our goal for this project is to develop a robust and universal strategy for the design of sustainable polymeric materials. Specifically, we aim to combine the excellent attributes of both thermoplastics (reprocessability, recyclability) and thermosets (mechanical strength, creep and solvent resistances) through robust dynamic covalent chemistry. We have particularly focused on developing robust dynamic covalent interactions that can lead to thermosets that are mechanically strong, highly malleable, and fully reprocessable and recyclable. In this talk, I will summarize our recent progress of this project with specific focus on our investigation of sustainable thermosets using boron-oxygen (B–O), silyl ether (Si–O–C), and siloxane (Si–O–Si) exchange reactions. Successful demonstration of robust, malleable, and reprocessable/recyclable thermosets will have major impact on new materials development, polymer recycling and sustainability, and modern technologies including additive manufacturing.

In dynamic covalent polymer networks known as vitrimers, the topology is reconfigured through associative exchange reactions. These materials hold promise as repairable and recyclable thermosets and elastomers. The Kalow Lab combines physical organic approaches and mechanical characterization to interrogate the relationship between the molecular exchange chemistry and flow in reprocessable elastomers. These studies are enabled by the use of crosslinks that exchange via a catalyst-free conjugate addition/elimination pathway. We find that stiffness and stress relaxation rate can be decoupled and independently modulated by synthetically tuning the cross-linker and prepolymer backbone, respectively. Our studies reveal the importance of internal catalysis in accelerating exchange reactions, which has inspired our design of switchable cross-linkers.

Dynamic polymer networks with topology conserving exchange reactions (vitrimers) have emerged as a promising platform for sustainable and reprocessable materials. A major focus thus far has been to understand how the exchange kinetics, crosslink density, and polymer backbone chemistry control the stress relaxation and reprocessability of vitrimers. In contrast, an understanding of crystallization phenomena, particularly how bond exchange affects kinetics, final morphology and melting temperatures (T_m) in vitrimers is currently lacking. With the introduction of dynamic bonds in a network, an additional timescale is generated which may facilitate crystal formation by allowing smaller strands to rearrange rather than an entire polymer chain which can potentially facilitate crystal perfection and growth. While some prior work has focused on semi-crystalline vitrimers based on polyethylene and poly(lactic acid), they did not investigate any temporal evolution of crystallinity or morphology due to dynamic bond rearrangements within the matrix. Knowledge of how dynamic bonds impact crystallization will be critical to the development of new polymers which are easier to recycle and reprocess while still retaining desirable properties. Another key factor in determining crystal structure and melting is the presence of precise motifs. For example, the melting temperatures of telechelic alkanes show a pronounced odd-even effect depending on the number of carbons between functional groups. In polymers, precise polyethylenes and polyacetals have been made as linear polymers, including materials with periodic ionic groups which crystallize and show enhanced conductivity. Precise permanent networks with alkane chain linkers have shown odd-even effects on the glass transition temperature and ionic conductivity. All of these studies point to the potentially critical role of precision on crystallization, which has not been investigated in vitrimers.
Precise ethylene vitrimers with 6 – 12 methylene units between boronic ester junctions were investigated to understand the impact of bond exchange and precision on crystallization kinetics and morphology. Compared to linear polyethylene which has been heavily investigated for decades, a long induction period for crystallization is seen in the vitrimers ultimately taking weeks in the densest networks. An increase in melting temperatures (T_m) of 25-30 K is observed with isothermal crystallization over 30 days. Both C10 and C12 networks initially form hexagonal crystals, while the C10 network transforms to orthorhombic over the 30 day window as observed with wide angle X-ray scattering (WAXS) and optical microscopy (OM). After 150 days of isothermal crystallization, the three linker lengths led to double diamond (C8), orthorhombic (C10), and hexagonal (C12) crystals indicating the importance of precision on final morphology. Control experiments on a precise, permanent network implicate dynamic bonds as the cause of long-time rearrangements of the crystals, which is critical to understand for applications of semi-crystalline vitrimers. The dynamic bonds also allow the networks to dissolve in water and alcohol-based solvents to monomer, followed by repolymerization while preserving the mechanical properties and melting temperatures.

The effectiveness of van der Waals (vdW) interactions formulated the path for the development of fluoro-containing acrylic copolymers that, for well-defined monomer molar ratios, exhibit self-healing. Taking advantage of the large polarizability of copolymer side groups, non-directional vdW interactions between neighboring macromolecular segments are enhanced. Upon mechanical damage macromolecular segments energetically favor before damage inter-chain conformations and return to their initial conformations. Perhaps the most intriguing feature is the acceleration of self-healing in typically hydrophobic copolymers in the presence of confined water molecules. Since dipole-dipole, dipole-induced dipole, and induced-dipole induced dipole interactions significantly impact viscoelastic response controlling macroscopic autonomous multicycle self-healing in acrylic and fluorinated copolymers, the presence of ionic liquid units copolymerized into one macromolecular chain is expected to alter vdW forces. At the same time, the presence of Coulombic interactions provides an opportunity for applying electric fields to accelerate self-healing. These studies show that an interplay of H-bonding, vdW, and Coulombic interactions accelerates self-healing upon mechanical damage in the presence of the electric field. These studies elucidate the molecular origin of processes that lead to autonomous repairs of commodity copolymers.

The features responsible for the desirable mechanical properties of thermosetting materials present challenges to their recycling and reuse. Facilitating the end-of-life management of thermosets while retaining desired properties is largely an unmet challenge. This presentation will discuss efforts towards imparting thermosetting materials with regenerative abilities. Our approach relies on incorporating tailored chemical functionality within thermoset crosslinks to enable crosslink exchange, thereby enabling polymer remolding. Designing our chemical functionality to be compatible with Frontal Ring Opening Metathesis Polymerization (FROMP) enables rapid adoption of this manufacturing technique for the fabrication of materials with regenerative capabilities. We demonstrate these regenerative capabilities by subjecting material to several reprocessing cycles. Material characterization techniques reveal that the performance of the thermoset is preserved over many lifecycles and that reprocessing is enabled by our tailored functionality. Leveraging a chemical approach, we show that thermosets can rapidly and scalably manufactured with functionality that permits regenerative function while minimally compromising material performance over subsequent lifetimes.

Advancements in improving the electronic performance of degradable imine-based semiconducting polymers are pushing the field of transient electronics; however, our understanding of the structure-property relationships of this emerging class of polymers is very limited. Previously, we described a modular approach to prepare degradable semiconducting polymers by Stille cross-couplings. This facile method of polymerization enabled the preparation of both p-type and n-type imine-based donor-acceptor conjugated polymers, expanding the field of existing degradable semiconductors. While degradation studies confirmed the depolymerization into oligomers and monomers, the polymer degradation timescales and lifespans of the corresponding transient devices were not controlled. Comparisons of the degradation behavior across different imine-based semiconducting polymer architectures have also not been closely studied with respect to their morphological and electronic properties. Herein, we use Stille cross-couplings to rapidly prepare imine-based semiconductors with tuned polymer architectures for the systematic exploration of the impact of several molecular design parameters on the degradation lifetimes of these polymers. To rationalize differences in electronic performance and degradation behavior, we characterize the polymers by gel permeation chromatography, ultraviolet-visible (UV-vis) spectroscopy, and grazing-incidence X-ray diffraction. By monitoring degradation via UV-vis, we discover that polymer degradation in solution is aggregation dependent, with accelerated degradation rates facilitated by increasing the hydrophilicity of the polymers. Additionally, the aggregation-dependence of these degradable polymers rely heavily on the solvent used, with a fivefold difference in degradation time depending on solvent. We develop a new method for quantifying the degradation of polymers in the thin film and observe that similar factors and considerations used for designing high-performance semiconductors impact the degradation of imine-based polymer semiconductors. This study provides crucial principles for the molecular design of degradable semiconducting polymers, and we anticipate that these findings will expedite progress toward transient electronics with controlled lifetimes.

The principles of microencapsulation and controlled, in situ release of functional compounds have been exploited extensively in the development of stimuli-responsive materials, such as self-healing composites and coatings with sensing capabilities. In contrast, there are comparatively few examples by which the same principles have been utilized for stimuli-responsive polymer degradation, despite recent evidence that in situ transformations may present new and improved opportunities for remediation of plastic waste. With this context in mind, we illustrate that microencapsulation of alkene metathesis catalysts provides a powerful method to create polybutadiene (PB) elastomers with programmable degradation profiles. Such catalysts, highly active towards depolymerization of PB via ring-closing metathesis, are rendered effectively latent by microencapsulation within a glassy polymer. The micron-sized polymer/catalyst particles are easily compounded into PB resin which is subsequently crosslinked by radical chemistry, yielding particle-loaded elastomers with similar mechanical properties to particle-free controls. Relying on judicious selection and design of the encapsulant or encapsulating system, the catalyst can be released in situ through temperature, time, or light exposure, among other phenomena, thereby initiating rapid depolymerization of the elastomer to soluble products. In situ depolymerization is further demonstrated to be more efficient than the corresponding ex situ reaction involving infusion of catalyst solution into the elastomer. We anticipate that this approach can be expanded to deliver existing and emerging functional compounds for chemical transformation of polymers with reduced resource requirements, as well as precise control over the conditions under which such transformations are effected.

In recent years, plastic pollution has sent out its clearest alarm signals. Micro/nano-plastics were detected in drinking water, snow, and ambient air. To mitigate this threat, biodegradable polymers (BPs) have surfaced as a solution to replace the current single-use ones, but their high cost and off-spec properties regarding both manufacturing and application limit their commercial potential. Herein, we explore the potential for developing photo-bio-degradable polymers with minimal structural and property deviations from the conventional commodity plastics. In this approach, we rely on photooxidation to make further structural modifications toward a BP-like structure, after end of life and under solar radiation. Specifically, we focus on polymer photodegradation (PPD) via singlet oxygen (¹O₂) photosensitization (PPDvSOP), a scheme similar to that proposed by Rabek and Rånby, which however remained less explored and comprehended than the mainstream autooxidation model. We conjecture PPDvSOP has the unique advantage of being specific, where oxidation occurs only at the weaker C—H bonds, for example those vicinal to electronegative heteroatoms in the carbon chain, thereby the desired polymer structures can be obtained more controllably. These yet-to-be-developed thermoplastics are meant to be not biodegradable originally but quickly transform to a biodegradable structure under solar radiation. Unlike in oxo-biodegradation, this transformation does not require pro-oxidants for initiation of radical chain reactions. One needs photostable ¹O₂ photosensitizers, instead. To this end, the present work attains a better understanding of the mechanistic steps and unique aspects of PPDvSOP, which would potentially enable controlling and enhancing the rate of PPD and thereby accelerate biodegradation in certain polymer structures. Such advantageous features of PPDvSOP are: i) ability to control and maximize solar energy coupling to PPD by instrinsic and extrinsic photosensitizers; ii) autocatalytic attribute of the carbonyl (C=O) moieties because of being both products and sensitizers in PPDvSOP; iii) lower activation energy requirement for insertion of ¹O₂ into C—H bonds, vicinal to electronegative heteroatoms in the carbon chain. Indeed, when the heteroatom is O or N, the benefit is twofold. The insertion results in an ester or peptide linkage, respectively, which are active sites for biotic hydrolysis. We express the PPDvSOP mechanistic steps in coupled differential equations with minimal assumptions, and rigorously validate those with measured kinetics of C=O density in thin polymer (with heteroatoms in the carbon chain) films under UV exposure. Additionally, we enrich our simulations with a parallel channel of biodegradation in seawater. We show a hypothetical polymer layer undergoing PPDvSOP and having a thickness of 250 µm, representative of a plastic water bottle, completely biodegrades in seawater in 685 days. The solution of PPDvSOP equations also provides unique insights, which are difficult to gain experimentally alone, such as propagation of PPD front along polymer depth. In a series of experiments, we also validate: the role of C=O as autocatalyst; impact of C₆₀ as a model extrinsic ¹O₂ photosensitizer; the expected effect of initial C=O density; expected influences of oxygen concentration, water (a ¹O₂ quencher), temperature, and excitation spectrum.

Epoxy are an important class of thermosetting polymers for many long-term applications such as adhesives, structural material, and protective coatings. While they provide durable and robust mechanical properties, conventional epoxy products are typically non-recyclable and extremely difficult to remove at the end of their life. To address these limitations, recyclable epoxies through depolymerization are of interest. In this talk, synthesis and characterization of recyclable epoxies crosslinked by the Diels-Alder (DA) reaction will be presented. The recyclable epoxies were synthesized by reactions between two precursors containing maleimide and furan functional groups to form cyclo-adducts. The retro-Diels–Alder (rDA) reaction at elevated temperature can serve as a recycle process through depolymerization of the epoxy network. Various precursors were synthesized by manipulating molecular weights, architecture (e.g., 4-arm or 6-arm), and spacers between functional groups. Different stoichiometric ratios between maleimide and furan precursors were examined to control a crosslinking density of the recyclable epoxy. Thermomechanical behavior of these recyclable epoxies was characterized by calorimetry and rheometry. The epoxies demonstrated a high-temperature (~120 °C) endotherm corresponding to rDA. Moduli of the epoxies dropped at high temperature which indicates depolymerization of the epoxy network through rDA. Plasmonic titanium nitride (TiN) nanoparticles were introduced to trigger the depolymerization through photothermal mechanism. Plasmonic nanoparticles permit localized heating by converting incident light into heat. The generated heat initiates a thermally reversible reaction. The photothermal mechanism offers several benefits compared to the bulk heating because the light allows onset of depolymerization remotely, instantly, and exclusively at a targeted area. Various contents of TiN nanoparticles were loaded to the recyclable epoxy. Removal and recycle processes of these nanocomposite samples were examined by multiple cycles of adhesive tests. Two glass slides were attached using the reversible epoxy/TiN nanocomposites. The sample was then placed under a high-intensity light source. The recyclable epoxy turned soft by depolymerization, consequently, the slides separated under stress. After reattachment of these two glass slides, it could undergo the same stress as before the photothermal test without failing.

Plastic materials are widely used as food packaging. However, the environmental threat caused by their indiscriminate use has reached high levels, since these fossil-oil-based plastics and synthetic polymers are not readily degraded. One alternative to reducing the amount of plastic waste is to use biodegradable and biocompatible materials. Recently, polyhydroxyalkanoates (PHA) have been attracting attention as a biodegradable thermoplastic resin, and the most well-known among them is polyhydroxybutyrate (PHB). PHB has been considered as entirely biodegradable under various natural and biologically active environments, and its properties are similar to those of the conventional petroleum-based polymers such as polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET). On the other hand, the use of pure PHB is limited, due to its inherent brittleness, which renders it too frangible for most practical applications. In particular, the elongation property of pure PHB has been reported in the range of 3–5%, which is very difficult to use for the packaging application, compared to commercial packaging polymers.
In this study, we have studied the degradation of two bio-produced, biodegradable polymers over the 6 weeks: polyhydroxybuterate (PHB) and polyhydroxybuterate-co-polyhydroxyvalerate (PHBV8; 8 wt. percent valerate), in compostable soil. In addition, we propose a new type of biodegradable bioplastic composites bearing green additives to overcome the mechanical instability of PHB and to optimize the film condition.

The sustainability of polymeric materials is strongly tied to end-of-life fate. Large volume thermoplastics such as PET (polyethylene terephthalate), PE (polyethylene), and PP (polypropylene) face numerous challenges in practical recyclability. Techno-economic barriers in end-of-life stages of collection, sorting and mechanical recycling are a consequence of design choices made further upstream in the synthesis and manufacturing stages. We analyze the environmental and economic impact of various green chemistry and design choices made both upstream (synthesis and manufacturing) and downstream (end-of-life). The systems model we have developed combines process-based energy and emissions modeling with market-based supply-demand interaction to estimate and compare different end-of-life processes across sustainability metrics (such as GHG emissions, solid waste diversion, recycled content inclusion, and more) to assess realistic recovery quantity and quality. Our comparative analysis of twelve polymer waste disposal scenarios considers existing large-scale treatment processes such as mechanical recycling, fuel recovery, and energy recovery. The assessment suggests that in the long term, better design for recycling is a powerful lever to synergistically improve net GHG savings and minimize the net cost to the system. We find that quality is a critical parameter driving downstream environmental impact. This finding motivates us to develop data-driven models to inform the quality of recycled blended polymers. We connect chain and additive chemistry, rheological responses, and processing parameters to end-use physical properties to identify new end-use markets for recycled polyolefins and tailor materials-informed sustainability metrics for different polymer products as well as secondary markets. The integration of process-based and market-based models also links technological advances with economic actors and can be used to inform policy actions that can incentivize sustainable polymer design. To realize the benefits of sustainable design, we need to address the collection bottleneck that limits recovery potential significantly. We analyze instances of policy tools, such as extended producer responsibility, in recycled PET markets and show that meeting recycled PET demand by expanding deposit return schemes in the US is cost-effective up to being 75% circular with harmonized container design. As efforts in green chemistry and green design mature, we show that it is important to actively incorporate end-of-life sustainability metrics in upstream decision-making to maximize circularity potential. We believe that lessons from systems modeling of large volume PET and PE waste material streams can help catalyze a sustainable transition to next-generation green polymers.

Aromatic polymers are omnipresent and indispensable to the global economy and modern life. Green pathways for the post-consumer utilization of these materials, via recycling or chemical upcycling, remains a significant challenge as consequence of their intrinsically robust physical properties and recalcitrant aromatic C−H bonds. Here, we demonstrate that homogeneous gold (Au) catalysis offers a practical, mild, and chemoselective means to upcycle high-volume commodity aromatic polymers. Using a Au-catalyzed hydroarylation between a functional alkyne, methyl propiolate, and the arenes within polystyrene (PS) results in the installation of methyl acrylate functional groups onto virgin and waste PS. Methyl acrylate incorporation efficiency is modular as a function of the steric and electronic environment of the catalyst, ion pairing, and means of catalyst activation. The Au-upcycling protocol is broad in scope, allowing for the functionalization of commercial polysulfone and waste polyethylene terephthalate. The functionalized products exhibited significant changes to intrinsic physical properties such as glass transition temperature, modulus, melt viscosity, and wettability. These reactions provide a platform through which to extend the lifespan of commodity aromatic materials, and through which to leverage the unique reactivity of Au toward the upcycling of polymeric materials.

To reach sustainable polymeric materials and a circular plastic economy, the choice of resources and synthetic methodology as well as product consumption, use and the end-of-life handling need to be scrutinized. To add to the complexity, the polymeric material groups portray inherent strengths and weaknesses and, thereby, an array of solutions to reach sustainable polymeric materials are required. Here, examples of our contribution to the field will be presented focusing on the utilization of renewable building-blocks, their polymerization methodologies where the principles of green chemistry are central, and the chemical structure design to achieve both functionality and a predetermined end-of-life handling choice.
Aliphatic polyesters have been identified as valuable examples where chemical recycling to monomer (CRM) is a viable option. This relates to a combination of a possible pathway to revert back to monomer in combination with the appropriate thermodynamic prerequisites for achieving depolymerization using a realistic energy consumption. Yet, achieving a balance of reasonable temperature used for CRM while retaining polymer stability, for example during processing, is difficult. We have demonstrated a methodology to solve this problem by copolymerization and thereby extending the use of naturally occurring 6-membered lactones. When copolymerized with other more thermodynamically stable lactones, the kinetics can be utilized to achieve “end-capping” of the formed polyester, hindering their actual propensity to depolymerize at comparably low temperatures, and at the same time chemical recyclability was achieved.
Thermosets are a group of polymeric materials where the end-of-life handling is inherently challenging, due to their network structure. In this context, the concept of covalently adaptable networks (CANs) is considered a potential future solution, as CANs have mechanical stability and chemical resistance but can, upon applying an external stimulus such as heat, rearrange bonds and thereby portray interesting properties such as self-healing and most importantly - they can be reprocessed. In this area we contribute by utilizing renewable building-blocks and applying the green chemistry principles in the CAN synthesis, achieving functionality and reprocessability for e.g. polyamide networks.

Microfiber pollution presents a global ecological problem. Microfibers which shed from production, laundry and disposal of textiles account for 2.2 million tons of marine pollution yearly. Current solutions to reduce microfiber pollution at the consumer level are labor-intensive and expensive. Materic Group presents fast-biodegrading and scalable sub-micron fibers for use as a replacement to conventional textile yarn. Such fibers biodegrade in soil, compost, and marine environments at ten times the speed of conventional microfibers. By reducing diameter and increasing outer surface area of fibers shed from textiles, biodegradation time upon environmental release is drastically expedited. The presence of polluting fibers in ecosystems can thus be decreased. These results are achieved through needleless electrospinning, a process for manufacturing nonwoven nanofiber mats at production rates of up to 5,000 m² per day. By slitting and twisting the material using conventional yarn production processes, we produce nanofiber yarn that is comfortable and durable like a conventional textile, but biodegrades rapidly upon environmental release. Structure property relationships, processing, and biodegradability will be discussed for PBAT, PCL and PLA nanofibers. Design considerations for sustainable sourcing, enhanced biodegradability, and durability will be assessed compared to properties needed for textile applications. We will discuss possibilities for compounding biodegradable materials with existing polymers for enhanced degradation and performance as well.

The United States generates an estimated 42 million metric tons of plastic waste each year – the most of any country – resulting in pollution and lost chemical and energetic resources. Recycling strategies will play a pivotal role in recapturing this wasted material and ensuring resilient polymer life-cycles. Researchers are actively exploring chemical recycling techniques including pyrolysis, gasification, methanolysis, glycolysis, enzymatic depolymerization and more to supplement traditional mechanical recycling. As the plastic recycling landscape expands, it is crucial to implement these novel technologies in an environmentally and economically beneficial manner, yet there is currently no framework to guide the impartial and holistic making of such decisions.
This work utilizes a rigorous modelling framework combining techno-economic, life cycle and material flows assessments to quantitatively compare current and next generation recycling technologies. The scope includes mechanical, pyrolysis, gasification, depolymerization and dissolution recycling for the top four most widely utilized polymers – high and low density polyethylene (HDPE, LDPE), polypropylene (PP) and polyethylene terephthalate (PET) – as well as biopolymers such as polylactic acid (PLA). The technologies are assessed based on a series of environmental (greenhouse gas emissions, energy use, water and land use, toxicity, waste production), economic (minimum selling price) and technical (technology readiness level, material quality, material retention, impurity and pigment tolerances) metrics to capture key benefits, disadvantages and trade-offs. Multi-criteria decision analysis is subsequently used to highlight preferential applications for the different recycling technologies, and sensitivity analysis allows for the identification of future research directions for improving the viability of these techniques. Through its broad scope, this work provides a baseline for decision-making in the current and upcoming plastic recycling landscape, with an added potential to encompass future recycling breakthroughs.

It is no secret that industrial plastics have become inevitable in nearly every facet of modern life and lifestyle due to their various properties for instance cost-effective production in large volumes. The development of finding new sustainable and reusable strategies for the degradation of omnipresent industrial plastics play a critical role in the future of our planet. (Bio)catalysts such as enzymes offer new pathways for the selective degradation of polymer materials. By the immobilization of such enzymes on nanocarriers enables unique opportunities for selective depolymerization and catalyst recovery. In this study, enzymes (lipase and cutinase) were covalently immobilized on carrier nanoparticles consisting of spherical SiO₂ and ellipsoidal Fe₃O₄@SiO₂ through 3-(aminopropyl)trimethoxysilane and glutaraldehyde linkers forming a stable bond to enzyme molecules. The successful linkage of the enzymes to the surface of the nanocarriers was confirmed by zeta potential and XPS measurements. In terms of degradation activity, high stability (> 144 h) of as-prepared particles in conjunction with their repeatable use shows the promising potential of the controlled decomposition of polymers at room temperature as demonstrated by the conversion of 4-nitrophenyl acetate to 4-nitrophenol.
For the investigation of the enzymatic decomposition (hydrolysis/oxidation), carbon nanofibers of polycaprolactone were electrospun and tested with the enzyme immobilized nanocarriers. The decomposition process of the fibers was verified through morphological (SEM) and weight loss studies, which showed a change in the fiber morphology due to enzymatic degradation and accordingly a weight loss.
The immobilization of the enzymes improves their stability and simplifies their handling such as magnetic-field assisted recovery, which can be achieved by using magnetic carrier particles. Finally, the environmental impact of this approach is given by the stability of immobilized enzymes without compromise of their activity that makes them available for multiple and selective uses.

Despite the degradability and biocompatibility of poly(α-hydroxy acids), their utility remains limited because their thermal and mechanical properties are inferior to those of commodity polyolefins, which can be attributed to the lack of side-chain functionality on the polyester backbone. Attempts to synthesize high-molecular-weight functionalized poly(α-hydroxy acids) from O-carboxyanhydrides have been hampered by scalability problems arising from the need for an external energy source such as light or electricity. Herein, we report an operationally simple, scalable method for the synthesis of stereoregular, high-molecular-weight (>200 kDa) functionalized poly(α-hydroxy acids) by means of controlled ring-opening polymerization of O-carboxyanhydrides mediated by a highly redox reactive manganese complex and a zinc-alkoxide. Mechanistic studies indicated that the ring-opening process likely proceeded via the Mn-mediated decarboxylation with alkoxy radical formation. Gradient copolymers produced directly by this method from mixtures of two O-carboxyanhydrides exhibited better ductility and toughness than their corresponding homopolymers and block copolymers, therefore highlighting the potential feasibility of functionalized poly(α-hydroxy acids) as ductile and resilient polymeric materials.

The use of additive manufacturing for biomedical applications has recently paved the way for new innovations thanks to its high accuracy and precision, fast fabrication and ability to create custom parts. Since non-toxic polymers available for 3D printing are limited, polyurethanes (PUs) play a key role, especially in the medical field due to their biocompatibility. However, their synthesis requires the use of very hazardous isocyanates which are produced with the even more toxic phosgene. In order to avoid their use, more environmental-friendly synthetic routes for PUs have therefore been developed. Among them, the synthesis of poly(hydroxyurethane)s (PHUs) by the polyaddition of bis(cyclocarbonate)s to diamines emerged as one of the most promising routes due to its simplicity and versatility, and the low toxicity of the cyclic carbonate building blocks. Nowadays, five-membered rings bis(cyclocarbonate)s can even be obtained by coupling CO₂ to epoxides (that can be partially or totally biosourced), therefore valorizing CO₂ as a sustainable chemical feedstock. Since it is challenging to achieve reproducible 3D printed PHU materials, only a few research groups reported strategies to 3D print PHUs.
In this work, two curing approaches of PHUs have been developed and compared to find the best candidate PHU materials for 3D printing in terms of curing rate, thermal, mechanical and rheological properties. For that purpose, poly(propylene glycol)-poly(hydroxyurethane) (PPG-PHU) networks were prepared under thermal or photochemical curing conditions. In the thermal crosslinking approach, a poly(propylene glycol) bis(cyclocarbonate), a diamine and a triamine crosslinker were copolymerized in bulk at a moderate temperature. In the UV crosslinking approach, we developed a simple strategy to introduce allyl functions on PPG-PHUs that were then exploited to crosslink the polymer by a thiol-ene reaction with a tri-thiol compound. The influence of the PPG molar mass and the reaction conditions on the polymerization processes and the final network properties were deeply investigated in the two cases, and the type of amine used (aliphatic or aromatic) was also studied in the thermal curing approach. Rheological measurements show that both systems are highly crosslinked network structures but with different curing rates depending on the curing process used, and that PHU networks are formed faster by the second approach, i.e. UV curing. Based on these findings, a UV curable allyl-hydroxyurethane 3D printable resin was prepared in order to create custom objects by photopolymerization.
In this talk, we will thus present the two ways of production of crosslinked PHUs, as well as the impact of the processes and the reaction conditions on the curing of the resins and the final properties of the materials. Finally, we will show how the best system can be exploited for the facile production of 3D printed objects based on PHUs.

Photocatalytic reaction is a fascinating technology for sustainable development, as it can effectively and simply degrade pollutants. Titanium oxide is a well-known material of powerful photocatalytic performance. However, large energy consumption and air pollutant are inevitable for the titanium oxide sintering process. To find an alternative photocatalytic material under green process is an arising issue. Carbon dot is one of the eco-friendly carbon nanomaterials as it can be prepared in mild conditions, from various organic materials. Owing to its unique optical properties, carbon dot can be applied for photocatalyst. However, carbon dot itself showed low photocatalytic performance without metal nanoparticles. Carbon dot needs to be fixed on the metal support to improve the photocatalytic performance and the dimensional stability. It is critical to find a suitable bulk matrix to replace metal nanoparticles. When carbon dot is embedded in a polymer matrix, the surface functional groups of the carbon dot are buried in the matrix, and the photocatalytic effect would be significantly suppressed.
In this study, we solved those two problems by attaching carbon dot at surface of cellulose nanofiber. Via simple and mild in-situ synthesis, carbon dot was chemically linked to the cellulose nanofiber and the functional groups of the carbon dot were exposed to the composite surface. Beyond the role as a matrix, cellulose nanofiber changed the electron recombination pathway and synergetically helped to improve the photocatalytic performance of the carbon dot. The composite degraded 98% of methylene blue molecules within 25 min. The fibrous structure of cellulose nanofiber makes ease of converting the composite morphology into aerogel. Without sacrificing its photocatalytic performance, the aerogel had good re-usability.

Excessive emission of anthropogenic CO₂ in our atmosphere is a major cause of global warming and environmental issues. Climate change is a significant global challenge and causes a serious threat to the planet. Several strategies have been proposed to reduce the emission of anthropogenic CO₂, and to explore the use of CO₂ as an abundant feedstock for the production of sustainable fuels. Thus, capturing CO₂ using a porous polymer and the successful conversion into valuable chemical feedstocks is one of the vital solutions to mitigate this problem.
Crosslinked porous polyimides (pPIs), a type of porous organic polymer (POP), offer a great potential for CO₂ capture and conversion, owing to their porous nature and excellent redox behaviour.^{1, 2} Generally, pPIs are synthesised by polycondensation of dianhydride with multi-amines. However, the incompatibility of solvents during the condensation yields lower surface area and limits total gas uptake. Here we describe in detail how we utilise the Bristol-Xian-Jiaotong (BXJ) approach,^{3, 4} using inorganic salts to tune the porosity and enhance the surface area by tuning the compatibility of the reaction solvent and the growing porous polymer. In this approach, we calculate the Hansen Solubility Parameters (HSPs) of our pPIs, and compare these with the HSPs of a wide range of common reaction solvents to find matching solvents for optimised synthesis conditions. Furthermore, HSPs can be tuned by inorganic salt additives (different ion sizes and concentrations), thus providing a useful method to fine-tune surface area and pore size distribution (PSD) of the polymers. The surface area and PSD of naphthalene-based pPIs acquired from non-BXJ polycondensation reactions have thus been optimised by calculating HSPs to find a suitable solvent for synthesis, and further optimised by salt additives. The surface area of BNPI-1 and BNPI-2 were enhanced from the published values of 16 and 15 m² g^-1 to 846 and 613 m² g^-1, respectively. The BXJ approach provides a simple route to tune the porosity properties in a controlled manner. Moreover, with the improved surface area and enhanced control over the PSD, CO₂ uptake of naphthalene-based pPIs were increased to 14 wt%. Currently we are exploring the use of these naphthalene-based pPIs in the electrocatalytic reduction of CO₂ into valuable chemical feedstock material.
References
1. B. B. Narzary, B. C. Baker, N. Yadav, V. D'Elia and C. F. J. Faul, Polymer Chemistry, 2021, DOI: 10.1039/d1py00997d.
2. Y. Liao, J. Weber and C. F. J. Faul, Macromolecules, 2015, 48, 2064-2073.
3. J. Chen, W. Yan, E. J. Townsend, J. Feng, L. Pan, V. Del Angel Hernandez and C. F. J. Faul, Angew Chem Int Ed Engl, 2019, 58, 11715-11719.
4. J. Chen, T. Qiu, W. Yan and C. F. J. Faul, Journal of Materials Chemistry A, 2020, 8, 22657-22665.

Changes in global plastics recycling landscapes and heightened sensitivity by the general public requires major changes not only in post-consumer plastics recycling logistics but also at the pre-consumer level efforts. In particular, recycling of engineering thermoplastics and high-performance thermoplastics generated from commercial industries are not as robust as that of commodity plastics because of the complexity of the macromolecular structure.
Typical processing of polymeric materials, virgin or recycled, involve melt-state processing by way of compounding, extrusion, and molding. These processes require the molten polymers to have relatively low viscosity to flow through the equipment and molds. However, some polymers, such as ultrahigh molecular weight and crosslinked polyolefins have significantly high melt viscosities that prevent their post-industrial scrap forms from being recycled into the production scheme.
There have been few successful recycling techniques for excessively high mechanical and melt viscosity properties, but these existing mechanical recycling methodologies inadvertently and excessively degrade the polymers, or necessitates the use of additional chemicals such as chain extenders in the materials stream. There is scientific and practical interest in a simple, effective, and environmentally benign processing technique that can be applied to a wide range of difficult-to-recycle polymeric materials.
Solid-State Sheer Pulverization (SSSP) is an alternative processing technique, which uses a continuous twin-screw extruder modified with low-temperature barrels and screws. SSSP processes polymers at a temperature well below the melting and glass transition tempearatures, and the solid-state high shear and compression can yield materials with favorable morphologies such as exfoliated filler structure in composites and sub-micron dispersion of the minor phase in polymer blends. In virgin homopolymers, SSSP has been reported to enhanced the crystallization kinetics and crystallinity through mechanochemical modifications of the molecules.
In this paper, SSSP is applied to two post-industrial, specialty polyethylene materials: ultra-high molecular weight polyethylene (UHMWPE) and crosslinked low density polyethylene (XLLDPE). The effects of SSSP mechanochemistry on each of these polyethylenes are investigated in the context of efficient, large-scale mechanical recycling of high-melt viscosity polymers. The SSSP process is able to effectively reduce the particle size, enhance the melt processability, and enhance the crystallization behavior of the polymers.

Widespread over-farming, exacerbated by the effects of climate change and an ever-growing population, has led to rapid degradation of soil around the globe. Reversing this degradation and protecting soil health, requires methods for in-situ soil health monitoring. The soil microbiome is critical for soil health, and real-time, in-situ, monitoring of soil microbial activity would allow for improved understanding of soil conditions and enable interventions to improve soil health. Here, we demonstrate an approach for monitoring soil microbial activity using printed biodegradable wax-based sensors. Waxes are composed of long-chain alcohols and fatty acids, which can be degraded by bacteria typically found in agricultural soil. With that in mind, we have developed a self-healing conductive wax-based ink that can be used in the fabrication of biodegradable devices for soil health monitoring. By combining a biodegradable wax with the conductive polymer PEDOT:PSS, and by leveraging Direct Ink Writing as a fabrication method, we manufactured microbial activity sensors that utilize the selective biodegradation of the ink to produce variations in electrical properties (resistance and/or capacitance). With these devices, we are able to produce a semi-continuous measure of soil microbial activity, which is then correlated to soil health. Complementary rheological and conductivity measurements are reported here, as well as the transient resistance of the device when tested in soil.

Widespread over-farming, exacerbated by the effects of climate change and an ever-growing population, has led to rapid degradation of soil around the globe. Reversing this degradation and protecting soil health, requires methods for in-situ soil health monitoring. The soil microbiome is critical for soil health, and real-time, in-situ, monitoring of soil microbial activity would allow for improved understanding of soil conditions and enable interventions to improve soil health. Here, we demonstrate an approach for monitoring soil microbial activity using printed biodegradable wax-based sensors. Waxes are composed of long-chain alcohols and fatty acids, which can be degraded by bacteria typically found in agricultural soil. With that in mind, we have developed a self-healing conductive wax-based ink that can be used in the fabrication of biodegradable devices for soil health monitoring. By combining a biodegradable wax with the conductive polymer PEDOT:PSS, and by leveraging Direct Ink Writing as a fabrication method, we manufactured microbial activity sensors that utilize the selective biodegradation of the ink to produce variations in electrical properties (resistance and/or capacitance). With these devices, we are able to produce a semi-continuous measure of soil microbial activity, which is then correlated to soil health. Complementary rheological and conductivity measurements are reported here, as well as the transient resistance of the device when tested in soil.

Changes in global plastics recycling landscapes and heightened sensitivity by the general public requires major changes not only in post-consumer plastics recycling logistics but also at the pre-consumer level efforts. In particular, recycling of engineering thermoplastics and high-performance thermoplastics generated from commercial industries are not as robust as that of commodity plastics because of the complexity of the macromolecular structure.
Typical processing of polymeric materials, virgin or recycled, involve melt-state processing by way of compounding, extrusion, and molding. These processes require the molten polymers to have relatively low viscosity to flow through the equipment and molds. However, some polymers, such as ultrahigh molecular weight and crosslinked polyolefins have significantly high melt viscosities that prevent their post-industrial scrap forms from being recycled into the production scheme.
There have been few successful recycling techniques for excessively high mechanical and melt viscosity properties, but these existing mechanical recycling methodologies inadvertently and excessively degrade the polymers, or necessitates the use of additional chemicals such as chain extenders in the materials stream. There is scientific and practical interest in a simple, effective, and environmentally benign processing technique that can be applied to a wide range of difficult-to-recycle polymeric materials.
Solid-State Sheer Pulverization (SSSP) is an alternative processing technique, which uses a continuous twin-screw extruder modified with low-temperature barrels and screws. SSSP processes polymers at a temperature well below the melting and glass transition tempearatures, and the solid-state high shear and compression can yield materials with favorable morphologies such as exfoliated filler structure in composites and sub-micron dispersion of the minor phase in polymer blends. In virgin homopolymers, SSSP has been reported to enhanced the crystallization kinetics and crystallinity through mechanochemical modifications of the molecules.
In this paper, SSSP is applied to two post-industrial, specialty polyethylene materials: ultra-high molecular weight polyethylene (UHMWPE) and crosslinked low density polyethylene (XLLDPE). The effects of SSSP mechanochemistry on each of these polyethylenes are investigated in the context of efficient, large-scale mechanical recycling of high-melt viscosity polymers. The SSSP process is able to effectively reduce the particle size, enhance the melt processability, and enhance the crystallization behavior of the polymers.

Selective cleavage of C–O bonds in aryl ethers is one of the central challenges for the valorization of lignocellulosic biomass. Efforts to mitigate this challenge have focused on studying organic transformations on a wide range of heterogeneous metal, acid, and multifunctional catalysts under a variety of reaction conditions. Yet, the lack of mechanistic studies of the prevalent pathways limits the general understanding, especially considering the influence of the solvents.
Promising possibilities to achieve the targeted conversion are hydrogenolysis and hydrolysis on supported transition metal catalysts. Aiming at a general description of the reaction routes and mechanisms across different metals and a variety of chemical environments, here we report a study of the reductive conversion of diphenyl ether (Ph₂O) on the noble metals Ru, Rh, Pd, Ir and Pt in water and decalin. The selection of Ph₂O allows to study hydrogenolysis, (reductive) hydrolysis, and hydrogenation (saturation of the aromatic rings without changes in the molecular backbone). We discuss the main reaction mechanisms along these routes and their dependence on reaction parameters. Based on this understanding, we show general strategies to manipulate the reaction networks in C–O bond cleavage.
A series of carbon supported Ru, Rh, Pd, Ir and Pt catalysts with metal loadings ranging from 1 to 5 wt. % were obtained commercially (Sigma Aldrich) or prepared by strong electrostatic adsorption and incipient wetness impregnation. The kinetic data for the reductive conversion of diphenyl ether was recorded in a 100 ml, gradient-less batch reactor (Parr) under H₂ atmosphere (10 - 50 bar), 373 - 473 K, 700 rpm. Catalyst characterization of the materials included, amongst others, elemental analysis, tunneling electron microscopy (TEM) and H₂-chemisorption.
The observed results allow for the identification of three reaction pathways, namely hydrogenation, hydrogenolysis and hydrolysis, which only occurs in water. The generally low isotope effect across all the investigated noble metals for hydrogenolysis indicate that H addition is not involved in the rate determining step (rds). Thus, the C–O bond cleavage, following one or more quasi equilibrated H additions, is hypothesized to be the rds. The resemblance of the reaction orders in H₂ of ~1 for hydrogenation and hydrolysis, as well as similar selectivity trends in the two routes (i.e., Ru ≈ Pt < Ir < Rh < Pd) allow us to conclude that the aromatic ring is partially hydrogenated prior to the hydrolytic C–O bond cleavage. Thus, this cleavage is a reductive hydrolysis that occurs in parallel to hydrogenation. In general, the similar reaction orders in H₂ and the similar selectivity trends, indicate that the reaction mechanisms are identical across the studied metals. The solvent (decalin or water) does not change the mechanisms of Ph₂O hydrogenation and hydrogenolysis.
The overall conversion rates increased in the sequence Pd < Ir < Ru < Pt < Rh for both solvents. The selectivity to hydrogenolysis increased in the order Pd < Rh < Ir < Ru ≈ Pt while the reverse trend was observed for reductive hydrolysis in water. Lower reaction orders in H₂ for hydrogenolysis compared to hydrogenation throughout all the metals as well as trends in H₂ equilibrium adsorption constants (K_Pd > K_Rh > K_Ir > K_Ru ≈ K_Pt) indicate that the selectivity to hydrogenolysis is related to the coverage of the different metals with hydrogen.
The knowledge about the catalytic mechanism of the reductive cleavage of C–O bonds in aryl ethers establishes the possibility to model catalysts and reaction conditions in order to achieve high selectivity towards functionalized cyclic compounds from renewable feedstocks.

There is an increasing demand for sustainable materials derived from renewable resources due to the environmental concerns in our society. Cellulose is one of the promising materials as it is the most abundant natural polymer possessing very intriguing properties. These are associated to its high aspect ratio, excellent mechanical properties and large number of reactive groups available for further functionalization. Over the past decades, a substantial amount of research has focused on extracting cellulose nanofibrils (CNFs) from cellulose fibres and using CNFs in various applications and industries. However, utilising the cellulose fibrils inside the microscopic, porous cellulose fibres directly without converting them to its fibrillated form is still in its infancy.
In this work, we investigate the chemical modification of fibres by means of reactive probes that penetrate throughout the entire fibre wall despite the limited pore size in the fibre network. Reactive probes are synthesised via CDI activation, using Cesium fluoride as the key catalyst to ensure robust, efficient, scalable as well as sustainable esterification. As a result, a unified synthetic strategy is explored for functionalising cellulose fibres with various functional groups that will elevate fibre capabilities without expensive and energy demanding fibrillation and a much more convenient processing due to the microscopic dimensions of the cellulose-rich fibres.

Despite the indispensable use of agricultural fertilizers to achieve current levels of productivity, chemical nutrients have their effectiveness limited by problems such as ammonia (NH₃) volatilization, leaching and/or soil immobilization. One strategy to minimize these problems is to protect the fertilizer with nutrient-release barrier materials. Thus, it is desirable that the formed polymer should have a homogeneous adhesive line on the granule surface and be able to control the diffusion of soluble nutrients through its structure, allowing the barrier to assume an active role and not just that of a physical obstacle, which release would occur by mechanical compromise (fracture) of the polymer. The permeation through a polymer can be significantly reduced by the presence of internal diffusional barriers such as finely dispersed nanoclays (in the nanocomposites form). Thus, we proposed a nanocomposite system based on castor oil-derived polyurethane (PU) for controlling the release of fertilizers by an ion-exchange mechanism. PU coatings modified with less than 5 % montmorillonite, a cation-exchange material, successfully retarded the nitrogen release from urea granules, with less than 50 % of the nutrient released within 18 days of immersion, as confirmed by soil incubation experiments. The same profile was observed for the phosphate release from mono ammonium phosphate (MAP) granules coated with PU modified with hydrotalcite (less than 5 % by weight), an anion-exchange material. The release times were proportional to the contents of the cation- or anion-exchange materials, which exhibited specific correlations with the kind of nutrient released (e.g., cationic or anionic), confirming the diffusion barrier promoted by the PU coating structures. Our results demonstrated that the use of PU nanocomposites can significantly reduce the coating thickness with improved nitrogen and phosphorus release control, opening a new field for the investigation of controlled-release fertilizers.

Polymer foams have an important role in society due to their wide range of densities, and they are extensively used as cushioning, damping, thermal, and sound insulation materials. In 2021, ca. 29.357 thousand tons of polymeric foams were consumed, of which most is used in the packaging, building and construction industry¹. However, foams are mainly obtained from petroleum-based recourses and are not biodegradable. Thus, there is a strong motivation to develop foams using biopolymers from renewable resources for combating their environmental impact. Here, wheat Gluten proteins (WG) is an interesting biopolymer candidate due to their elasticity and foaming properties. The recently demonstrated possibility to develop WG-based foam materials using traditional polymer processing techniques (e.g. extrusion) paves an avenue to substitute conventional petrochemical foams with biopolymers.² However, challenges have raised when extruding WG, primarily because of the protein's sensibility to the high shearing forces and high temperatures, which can impact the protein network structure. Previous work has shown that extruded WG protein foams have resulted in foams having cushioning properties in a similar range as synthetic polyethylene foams².
This project's main objective is to study the effect of different formulations during the extrusion of WG materials towards forming porous materials. An advantage of WG protein concentrate used is that they are obtained as co-streams from the agricultural and food industries. Sodium bicarbonate (NaHCO₃) and ammonium bicarbonate (NH₄)HCO₃ have been used as chemical blowing agents, which provided the extruded material with different foam morphologies. The effect of having glycerol as a plasticizer of the WG has also been studied. Scanning Electron Microscopy has revealed that the most optimal formulation resulting in extruded WG foam structure is based on the use of ammonium bicarbonate (5 wt%). The possibility of producing porous materials using biodegradable and renewable resources is foreseen as an important environmental contribution to replacing petroleum-based foams.
¹Smithers (2021). The future of polymer foams to 2026. Retrieved from https://www.smithers.com/services/market-reports/materials/the-future-of-polymer-foams-to-2025
²George. A; Lacoste. C.; Damien. E . (2018). Effect of formulation and process on the extrudability of starch-based foam cushions. Industrial Crops & Products, 306-314.

In recent years, many researchers believe that global energy consumption can be significantly reduced by passive daytime radiative cooling (PDRC) without any electricity input. Over a decade, PDRC has been developed to enhance solar reflectivity and emissivity in long-wavelength infrared (LWIR) region; however sustainable materials for radiative cooling have not been sufficiently investigated. In the present study, the preparation of an eco-friendly polymer structure for effective radiative cooling via thermally induced phase separation (TIPS) is described. The as-fabricated radiative cooler exhibits reasonable durability for application to buildings and, furthermore, the biodegradable polylactic acid (PLA) is environmentally benign with respect to end-of-life disposal. Moreover, the hierarchically porous PLA exhibits a solar reflectivity of 0.91 and an LWIR emissivity of 0.92, thus realizing high-performance passive radiative cooling without a silver coating for solar reflection. In addition, a radiative cooling power of 99.03 W m^-2 is achieved under direct sunlight along with passive cooling of as much as 9 °C below the ambient temperature. This cooling effect is the highest among all organic-based passive radiation cooling emitters reported so far. The present work provides an ideal passive radiative cooling strategy for creating environmentally-friendly buildings with reduced energy consumption.

Environmental pollution caused by the widespread use of petroleum-based plastics has become a serious problem worldwide. To overcome this problem, many research studies have been conducted to find sustainable and eco-friendly alternatives such as cellulose which is abundantly existing in nature and can be extracted from wood, bacteria, and tunicate. Among them, tunicate cellulose shows great promise due to the high crystalline fiber with lightweight, tensile strength, biocompatibility, biodegradability, straightness, and excellent mechanical properties. However, cellulose has low thermal stability which limits its processability compared to commercial polymers such as polyimide and polytetrafluoroethylene. Therefore, it is necessary to improve the thermal properties of cellulose for partial or complete replacement of commonly used polymers with green alternatives. The thermal stability of cellulose can be modulated by changing the surface functional group with halogen group elements. However, these elements generate toxic gases such as halogen and dioxin during combustion. Modifying the surface group of cellulose with phosphorylation creates a protective layer on cellulose by generating char which reduces oxygen permeability and hence retarding the spread of fire. Since it is a non-toxic flame retardant, we proposed to substitute the surface functional group of cellulose from hydroxyl group to phosphorus group. Different composites can be designed by utilizing these phosphorylated cellulose fibers. Morphology and surface properties of the resultant product were evaluated using scanning electron microscopy and atomic force microscopy. The composition and crystallinity of the composite were analyzed through Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Thermal and mechanical properties were investigated using thermogravimetric analysis (TGA), limiting oxygen index tester (LOI tester), and tensile tester. Phosphorylated cellulose can be utilized in a wide range of fields from flame retardant fabrics to mechanical reinforcement materials and biomedical applications such as catalysts and adsorbents.

As the environmental pollution caused by microplastics deepens, there is increasing interest in environmentally friendly materials that replace conventional persistent plastics. Cellulose is a natural-derived biodegradable material that can be extracted from wood, plant, algae, tunicate, bacteria and the others. Tunicate cellulose has excellent mechanical properties, high crystallinity and high aspect ratio. Nanocellulose has lower density, higher crystallinity, and wider specific surface area than conventional cellulose, while maintaining hydrophilicity and biodegradability with excellent tensile strength and crystallinity. It has attracted great interest in academia and industry. However, thermal decomposition at low temperatures limits the use of nanocellulose. It is known that general cellulose decomposes at 350 degrees C, but in particular, nanocellulose produced by oxidation or strong acid treatment changes the surface functional group of cellulose nanoparticles and exhibits a lower thermal decomposition temperature than pristine cellulose. Tetraethyl orthosilicate (TEOS) was synthesized with Tunicate cellulose-nanofibers (CNFs) aqueous solution via stober process, and the surfaces of CNFs were chemically coated with silica nanoparticles. The fabricated CNF/SiO₂ nanocomposites solution was produced to a film form by vacuum filtration. The morphology, structure, thermal resistance and flame retardance of CNF/SiO₂ nanocomposites were investigated through scanning electron microscopy (SEM), transmission Electron Microscope (TEM), atomic force microscopy (AFM), X-ray diffraction (XRD), thermogravimetry and differential thermal analysis (TG-DTA). The TEM images showed that the silica nanoparticles were thinly coated on the CNFs surfaces. TG-DTA curve reveals the thermal decomposition temperature of the silica-coated CNF nanocomposites is delayed.

Metal recovery from water is important both from the resource development of strategic metals, such as rare earths, and improving the quality of heavy metal contaminated water. One technology that has long been used to remove and concentrate metal cations from solution is functionalized ion exchange resins. Hydrogels with chelate groups are one group of ion exchange resins whose ability to absorb large quantities of water can facilitate metal removal. In this research, hydrogels with biosustainable glycolipid groups have been prepared. Glycolipid biosurfactants can have high metal chelating capacity. The glycolipids are modified with a polymerizable acrylate group. The resulting monomer was characterized by NMR and mass spectrometry to determine its structure and regiochemistry of the acrylate group on the carbohydrate portion of the molecule. The monomer was then copolymerized with acrylamide and bisacrylamide comonomers to afford hydrogels. For example, the acrylate modified glycolipid (19% w/v) was copolymerized with acrylamide (19% w/v) and bis-acrylamide (2% w/v) using N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA) and ammonium persulfate as initiators. Metal chelation was studied with introduction of dry gels and hydrogels into solutions of metal cations to determine the influence of the gel hydration on metal chelation.

Hotmelt adhesives, whether they are used in construction applications or for pressure sensitive adhesives, are not biodegradable. The purpose of this study is to investigate sustainable, alternative materials that are biodegradable under non-specific environmental conditions in less than six months. This PSA must be able to bind for approximately six hours and be durable enough to withstand movement, as well as have the quality of being repositionable (repeatable peeling and unpeeling) while being removable without leaving adhesive residue behind. Our pressure sensitive adhesive formulations show promising results for biodegradation, melt viscosity, and peel strength. Through combining various bio-based polymers, replicating manufacturing conditions to apply the adhesive, and conducting peel strength and biodegradability testing, we hope that the pressure sensitive adhesive developed in this project will have applications in the manufacturing of packaging materials and hygiene products.

Bio-based polymers constructed from naturally occurring monomers such as poly(lactic acid) are excellent alternatives to petroleum-derived plastics due to their renewability and biodegradability. Another desirable attribute for plastic alternatives is a readily available and affordable monomer source. Similar to how lactic acid can be produced cheaply due to the large-scale production of corn and wheat, cannabinoids have become relatively inexpensive due to the proliferation of hemp production in the United States.^1,2 Although they have scarcely been integrated into plastics before, their low cost coupled with their salubrious reputation makes them an interesting candidate for a new class of bio-based polymers. Poly(cannabinoid)s are the first of their kind to include cannabinoids directly in their polymeric backbone. Compared to their phytocannabinoid counterparts, poly(cannabinoid)s have shown a nearly doubled degradation temperature and resistance to prolonged heat exposure. In addition, poly(cannabidiol-adipate) has been drawn into fiber and cast as a film.³ The true potential for the application of poly(cannabinoid)s in a variety of applications is given by the tunability of their thermomechanical properties. This tunability is demonstrated by the copolymerization of cannabidiol (CBD) and cannabigerol (CBG) in varying ratios to form copolymers with a very wide range of glass transition temperatures. Furthermore, due to their ester-containing backbone, these polymers hydrolytically degrade to afford the original cannabinoid and linking monomer, which can be chosen from a family of biologically safe dicarboxylic acids to suit the application. Therefore, poly(cannabinoid) materials can safely deliver a naturally occurring degradation product without the concern for toxicity or wasted material.
References:
1. Robertson, G. L., Food Packaging. In Encyclopedia of Agriculture and Food Systems. Academic Press, 2014, pp. 232-249. https://doi.org/10.1016/B978-0-444-52512-3.00063-2.
2. Rupasinghe, H. P. V.; Zheljazkov, V. D.; Davis, A.; Kumar, S. K.; Murray, B. Industrial Hemp (Cannabis Sativa Subsp. Sativa) as an Emerging Source for Value-Added Functional Food Ingredients and Nutraceuticals. Molecules 2020
3. Sotzing, G. A. PolyCannabinoids, Compounds, Compositions and Methods of Use. US Patent 17/232432, Oct 21, 2021

With an increase of contaminated water sources worldwide, the sequestration of small-molecule contaminants and toxins has become a priority and unique scaffolds are needed which can effectively sequester and remove these contaminants from an aqueous matrix. Polymeric ultrafiltration membranes offer an advantageous scaffold, as they are fabricated from inexpensive materials using facile preparatory techniques and water can pass through them under pressures that can be easily generated using human power. However, given their relatively large pore sizes, they lack the ability to sequester small molecules. To overcome this challenge, we use aptamers which show promise as affinity reagents for binding these toxins. We examine multiple critical components involved in fabricating and functionalizing the membranes, including PEG polymer molecular weight for membrane fabrication, grafting conditions for pMAA attachment, and coupling reagents for aptamer functionalization. Furthermore, and to increase the lifetime of the polymeric material, we attach enzymes capable of degrading small-molecules and contaminants, therefore creating a self-regenerative material that can be used extensively. Our rigorous evaluation resulted in the creation of a functional material which allows the depletion and degradation of multiple small-molecule toxins, contaminants, and microorganisms, demonstrating the potential of biomolecule-functionalized membranes as point-of-use decontamination systems.

In addressing issues of plastic accumulation in the environment and negative impacts of plastic degradation, the development of biobased alternatives is crucial in solving these hazards. Single-use, disposable hygiene products, such as diapers and feminine hygiene, significantly contribute to plastic waste. These products often contain non-biodegradable, synthetic, superabsorbent polymers. In this research, biobased superabsorbent polymers have been designed and synthesized, using biological crosslinker and backbone components to create a hydrogel system, which absorbs water into the polymeric matrix. The hydrogels are synthesized using chitosan and sodium alginate as the backbone foundation and genipin as the crosslinker, which are all commonly found in nature. Through chemical ratio alteration, including the crosslinker to backbone ratio, the superabsorbent polymers successfully absorb and retain water. The characterization of the hydrogels, including the absorbency capacity, absorbency retention, performance under a load, and performance with ion presence, have proven that fully biological superabsorbent polymers are possible.

Designing nature-friendly materials have become the center of attention for the world because of their unharmful properties and can become prime candidates for solving environment-related issues. Aromatic polymers have such characteristics, such as poly(4HCA-co-DHCA)s (4-hydroxycinnamic acid (4HCA) and dihydroxycinnamic acid (DHCA)) were synthesized using phenolic bio monomers, with high thermal, and mechanical performances than conventional aliphatic polyesters. Moreover, these aromatic polymers are proven to be biodegradable.^1,2 Thus, these aromatic polymers qualify for solving one of the environmental related issues of non- degradability in the earth’s environment.
However, the aromatic bioplastics are too rigid to apply in any commercially available flexible applications, and then the poly(butylene succinate) (PBS) was hybridized as flexibility inducer into rigid poly(4HCA-co-DHCA). Since PBS is biodegradable in nature. It degrades into water and carbon dioxide much faster than poly(butylene adipate terephthalate) (PBAT) and poly(lactic acid) (PLAs).³ In this report, we will present the formation protocol for composites of rigid poly(4HCA-co-DHCA) with different weight percent (PBS 0%, PBS 10%, PBS 20%, PBS 25%, PBS 30%, PBS 40%, PBS 50%, and pure PBS) of flexible PBS and in-depth analysis of the composite structure was done using various characterization techniques to study the toughness (PBS 0% 2 MJ/m³, PBS 10% 2 MJ/m³, PBS 20% 7 MJ/m³, PBS 25% 18 MJ/m³, PBS 30% 69 MJ/m³, PBS 40% 76 MJ/m³) and flexibility of the synthesized biocomposite material.
1) T. Kaneko, T.H. Thi, D.J. Shi, M. Akashi Nature Mat. 2006, 5, 966.
2) M. Chauzar, S. Tateyama, T. Ishikura, K. Matsumoto, D. Kaneko, K. Ebitani, T. Kaneko Adv. Funct. Mat. 2012, 16, 3438.
3 M.R. Nobile, A. Crocitti, M. Malinconico, G. Santagata, P. Cerruti AIP Conf. Proc. 2018, 020180.

Three-dimensional (3D) printing has proven to be a suitable technique to face demanding social and technological challenges. In fact, several important fields such as electronics, energy harvesting, environment, and biomedicine, have been benefited from progress in 3D printing. The advantages of 3D printing are numerous, including increased design opportunities, accessibility, process simplification, optimization of resource use, and customization of the final product. However, due to the recency of the 3D printing concept, there are still several areas of opportunity for development, bringing new research paths and market opportunities.
Many technologies can be considered as 3D printing, each with their advantages and disadvantages. Among them, three main groups can be distinguished: photocurable resins, powder sintering, and material extrusion. Due to technological advances many different materials can be processed, including hydrogels, plastics, ceramics, metals, and several intermediate combinations. However, there is still a relatively unexplored area; 3D printing with aqueous media ¹. In this regard, the largest focus has been with 3D bioprinting, however this has a narrow focus to include cells for living biomedical products. In this research, complex microstructures made from aqueous polymers solutions is of technological interest.
To 3D print complex structures from water-based systems, we followed some of the principles established in Melt Electrowriting (MEW). In this way, we use an electrohydrodynamic (EHD) effect to form microfibers, and 3 axis stage for driving fibers accurate deposition². However, in opposition to MEW, we switch from heating thermoplastic materials, to freezing water-based systems. To explore beyond state-of-the-art, we use a cryogenic stage to collect EHD jets, allowing the conservation of fiber shape, allow the 3D growth of structures, and avoid the use of additional components. This new technology has been named cryogenic aqueous electrowriting (Cryo-AEW).
To overview of Cryo-AEW, this study focusses on variables that impact the fabrication of microstructures. Three main areas have been studied: i) solution behavior (viscosity, surface tension and conductivity) and how to control through different materials combination; ii) printer set-up (applied voltage, nozzle dimension, flow rate and collector speed) and how the switch between different parameters allow obtaining different fibers arrangements; and iii) environmental conditions (temperature and humidity), and how them affect the final structure growth.
With the sustainability as a goal, water is the main solvent for all the experiments. With an emphasis on the use of non-toxic, biobased, and renewable materials, silk fibroin obtained from silkworm cocoon is used. Silk fibroin has a unique property to be dissolved in water, and to later become insoluble as a highly water-stable material³. This opens the use for different applications, especially for biomedicine, where silk has been widely used as support material and cell-growth media. Natural thickeners and surfactants (such us polysaccharides and fatty acids) have allowed the control of the solution behavior, for accurate scaffolds development.
With this approach, the suitability of a new type of microstructured and 3D-printed material is achieved, as the time that the complexity and requirements of a new technology are tested. Due to its technological novelty, the work has been approached in a broad way, to first give an overview of the possible effect of all the variables while identifying the guideline for future research and new technology development.

1. Shahrubudin, et al. Procedia Manufacturing 35, 1286-1296, (2019).
2 Kade et al. Polymers for Melt Electrowriting. Adv Healthc Mater 10, 1, 2001232 (2021)
3 Reizabal, et al. Journal of Hazardous Materials 403, 123675,

Thermosetting polymers are a class of high-performance materials with significant industrial applications. However, reclamation of both industrial thermosets matrix and binding matter are significantly challenging. Recently, thermosetting polymers capable with bond exchange reactions provide a new opportunity. Here, we present a method to recycle thermosetting polymers efficiently by a synergistic effect of mixed solvents with a highly efficient organic catalyst at ordinary pressure and mild temperature. The network depolymerization enabled by selective bond cleavage process is substantially enhanced by a good solvent assisted and small molecule participated exchangeable reaction. At 170 ^oC under ambient pressure, we showed the epoxy thermosets can be dissolved in 28 min with 50% mass loss, and 70 min with 95% mass loss. We demonstrate that this method can be used to reclaim carbon fibers from industrial carbon fiber reinforced polymer composites and embedded metal parts from commercial electronic products with undiminished properties at mild temperature (~170^oC) under an ordinary pressure in a short time (1.5 hours). We also developed a modeling framework to probe into the complicated reaction-diffusion coupling and reveal the effect of reinforcement, such as carbon fiber, on the dissolution process of carbon fiber reinforced epoxy.

The decarbonization of the transport and energy sector will accelerate the demand for electrochemical energy storage devices. While past and current research efforts strongly focused on improving the performance of cells (energy density, power density, and stability), little attention has been paid to how these devices are recycled after their end of life, leaving recycling of devices as an afterthought. Thus, to limit the accumulation of electric waste and the depletion of important raw materials for energy storage devices, there is an urgency to develop a circular economy for materials and integrate recyclability in device architectures. In my talk, I will present a new concept where we applied chemical design strategies to develop redox-active materials for a circular economy.[1] We developed solution processible redox-active conjugated polymers that function as binder- and additive-free electrodes with high stability in aqueous electrolytes, achieving >98% retention of the capacity after 500 charging/discharging cycles. The tuning of the local environment of the polymer enables fast charging of micron-thick single-phase electrodes with cell voltages > 1.2 V in aqueous electrolytes. Finally, we demonstrate the recyclability of the devices, achieving >85% capacity retention after recycling (76 % retention after recycling the device twice). Our work provides new ideas for employing material chemistry of redox-active materials to integrate recyclability in electrochemical energy storage devices for a more sustainable future of energy storage devices.
[1] S. T. M. Tan, T. J. Quill, M. Moser, G. LeCroy, X. Chen, Y. Wu, C. J. Takacs, A. Salleo, A. Giovannitti, ACS Energy Lett. 2021, 6, 3450.

The production of conventional crosslinked polymer networks and their composites, i.e., thermosets and thermoset composites, was estimated to consume more than 40 billion kg of polymer in 2020. Unfortunately, thermosets cannot be melt-reprocessed into moderate- to high-value products because permanent crosslinks prevent melt flow. We have developed seven simple one-step or two-step chemistries to produce networks and their composites with dynamic covalent crosslinks that are robust at use conditions but allow for melt-state reprocessing at high temperature. Unique to our research group, we have developed three approaches for melt-state reprocessing of addition-type polymer networks and network composites, including those synthesized directly from monomers containing carbon-carbon double bonds and those synthesized from combined polymer and monomer with both containing carbon-carbon double bonds. These approaches allow for full crosslink density recovery after multiple reprocessing steps. We have also demonstrated for the first time with four dynamic chemistries the ability to make PU and PU-like networks, e.g., polyhydroxyurethane and polythiourethanes networks, reprocessable with full recovery of crosslink density. An “Achilles’ heel” has been identified regarding the application of dynamic covalent networks, i.e., such networks are subject to creep at elevated or sometimes even room temperature, which is often highly undesirable. We have successfully addressed this issue in several ways. Brief highlights of each of these accomplishments will be presented. Implications for making major gains in the sustainability of networks and network composites will be discussed as will the potential benefits of such chemistry even with regards to sustainability.

Current industrial gas separations, such as CO₂ removal from natural gas, rely primarily on energy-intensive and environmentally unfriendly processes. Polymer membranes offer a more sustainable alternative due to their energy-efficiency and ease of operation. However, membranes are infrequently deployed because of separation performance and lifetime limitations of industrial polymers. In this work, the effect of backbone functionalization and polymer packing structure on transport performance was investigated for a high-performance polymer of intrinsic microporosity, PIM-1, and a new microporous polymer based on a poly(aryl ether) (PAE) backbone. Generally, PIMs have shown excellent pure-gas separation performance due to their rigid backbones, inefficient packing, and high free volume. However, their out-of-equilibrium structures make PIMs susceptible to physical aging (i.e., densification of structure overtime) and plasticization (i.e., swelling when in contact with CO₂ or H₂S), and the pure-gas transport performance for PIMs rarely matches mixed-gas performance for industrially relevant conditions.
Recently, we reported on the mixed-gas and high-pressure gas transport properties of six functionalized PIMs for CO₂ capture and purification. Low-pressure mixed-gas tests indicated a relationship between CO₂ sorption affinity and increased CO₂/CH₄ mixed-gas selectivity compared to pure-gas calculations for PIMs considered. The best results were found for amine-functionalized PIM-1 (PIM-NH₂), which shows a 2.4- and 3.5-fold increase in mixed-gas CO₂/CH₄ and CO₂/N₂ selectivity, respectively. PIM-NH₂ also retained high mixed-gas selectivity up to a total mixed-gas pressure of 26 bar. Our results demonstrated the promise of amine functionalization for developing sorption-selective and plasticization-resistant membranes for natural gas separations as well as CO₂ capture. Here, we extend this work as we probe the generalizability of our findings with an amine-functionalized PAE. PAE-NH₂ shows exceptional increases in CO₂/CH₄ and CO₂/N₂ mixed-gas selectivities (compared to pure-gas) similar to those observed for PIM-NH₂. Moreover, pure-gas CO₂ sorption for PAE-NH₂ was significantly higher than that of PAE-CN, which suggests that increases in mixed-gas performance were driven by sorption. The strength of the CO₂-polymer interactions was quantified through calculation of isosteric heats of sorption for CO₂ in PIM-1, PIM-NH₂, PAE-CN, and PAE-NH₂. Amine-functionalized samples showed significantly more exothermic interactions compared to those of nitrile-functionalized analogues, indicating stronger interactions for the amine with CO₂. Notably, PAE-NH₂ also showed exceptional plasticization resistance up to a total mixed-gas pressure of 26 bar.
Finally, to evaluate the performance of the polymers in aggressive toxic-gas conditions, the H₂S sorption capacity as well as pure- and mixed-gas transport of all four samples was tested. Compared to nitrile-functionalized analogues, amine-functionalized samples did not show as strong of an affinity increase with H₂S as was observed with CO₂. Taken together, our results indicate the development of H₂S-resistant and highly CO₂-selective polymers for CO₂ capture and natural gas purification.

Vitrimers, or dynamic polymer networks with associative covalent bonds, provide an ideal platform for sustainability due to their high mechanical strength and facile reprocessability. To utilize vitrimers as reusable materials in many applications, control of their properties will be essential. Tuning viscoelastic properties can be accomplished via chemical versatility. In this work, four different boronic acid crosslinkers were each reacted with silicone diols to form PDMS vitrimers of dynamic boronic esters. Networks with boric acid, phenyl diboronic acid, or biphenyl diboronic acid experienced relaxation times within approximately one order of magnitude at a given temperature, with aromatic groups leading to faster times due to a destabilization of the boronic ester. In contrast, an aromatic diboronic acid with nitrogen neighboring groups led to a four order of magnitude drop in the network relaxation time. For all samples, the modulus remains nearly constant regardless of exchange kinetics, which would be highly useful in applications such as additive manufacturing. All vitrimers show modulus increase with temperature, in line with expectations for networks of conserved topology. Mixing of multiple crosslinker moieties in one network was also investigated. When a single crosslinker is used, only one peak is observed in the rheological relaxation spectra. When two crosslinkers are mixed in the same sample, systems without the nitrogen-bearing boronic acid still show a single relaxation mode dominated by the faster-exchanging crosslinker. When the fastest crosslinker with nitrogen neighboring groups is mixed with another crosslinker, an intermediate relaxation time is observed. Thus, when relaxation times are within an order of magnitude, the faster of two crosslinkers controls the relaxation time, and when modes are further apart, a blending of dynamics occurs. These viscoelastic patterns and mixing rules are essential for controlling vitrimers to be used as sustainable materials in an array of applications.

PET degradation through enzymatic hydrolysis was shown to be promoted at temperatures close to or above the T_g of the PET material, which falls around 70 °C. Given the low thermal stability of relevant enzymes, decreasing T_g of PET by physical means would be an effective strategy to enhance its degradation. Given the interfacial nature of the enzymatic hydrolysis of PET, polymer films with significantly low thicknesses and high surface area could in addition improve the catalysis condition. Langmuir Monolayer Degradation studies (LMD) provide a method for examining the chemical and physical changes in ultrathin polymer films when exposed to the water surface. Various properties can be measured over time: surface tension, rheological properties, infrared molecular fingerprints, and reduction of the area covered by the polymer film.
In this study, PET ultrathin amorphous layers were prepared and characterized at the air-water interface. The films had a thickness of ca. 2.5 nm (at 21°C), and a porous-like structure with heterogeneous micro- and nano-holes (50-250 nm diameter) as evidenced by TEM and AFM. PET films were subjected to heating cycles from 21°C to ~45°C to determine the thermal properties of PET floating on an aqueous subphase. With our system, it was possible to determine the T_g of the films, calculated as the intersection of two tangent lines from the plot of the logarithm of G′ vs. linear temperature as measured by interfacial rheology. It was shown that thin films have a T_g between 40-44 °C, 30 °C lower than that of bulk PET. Furthermore, films were prepared at different initial water temperatures and transferred to solid substrates to measure their thickness by ellipsometer. It was found that films were formed with different thickness, in a temperature-dependent manner, with thicknesses values of 3.22 ± 0.2, 5.22 ± 0.43, and 6.58 ± 0.86 nm at 10, 21, and 42°C, respectively.
Altogether, our results show a direct correlation between temperature, thickness, and the onset of T_g in ultrathin films solely in contact with an aqueous subphase. The reduced T_g of PET films is expected to allow for faster enzymatic degradation and at temperatures lower than those used in traditional bulk PET or micrometric film studies (~70 °C), potentially improving biocatalysis in plastic biorefineries.

Epoxy polymers exhibit excellent mechanical properties and have wide applications ranging from adhesives to structural materials. However, recycling of epoxy is difficult because of their irreversible cross-linked network structure. We have developed a reversible epoxy which can be recycled using visible light. Diels-Alder chemistry is studied to develop thermo-reversible epoxy. At higher temperatures (above~ 120°C), the Diels-Alder reaction reverses, resulting in depolymerization of the epoxy and can polymerize again as it cools down. Photothermal refractory plasmonic titanium nitride (TiN) nanoparticles are incorporated in the reversible epoxy. These nanoparticles can efficiently absorb visible light and convert that to heat to promote the retro Diels-Alder reaction. The nanoscale heating can efficiently break the chemical bonds increasing rate of depolymerization. TiN nanoparticles were well dispersed in the epoxy matrix using optimized probe sonication method. The photothermal reversible epoxy composite was characterized using FTIR, UV-Vis spectroscopy and rheometer. The depolymerization of reversible epoxy could be achieved with 0.1 wt% loading of TiN at light intensity of 1420 W/cm². Funding: U.S. Department of Energy, Office of Basic Energy Sciences, DE-SC0022261.

The waste stream of low-grade wool from the fabric preparation is a keratin-rich material currently underutilized. Therefore, development of appropriate waste employment for added value final products is required. Wool is composed of 95% amount of keratin proteins by weight that have 5-10 mol% cysteine residues. The presence of intra- and intermolecular bonding, including the disulfide bridges formed between cysteine residues, ionic bonds, hydrogen bonds or hydrophobic bonds make the structure of keratin strong but, conversely, difficult to extract and reprocess. Consequently, key to successful keratin extraction is the selection of appropriate chemicals to break these bonds [1]. Moreover, keratin chains contain the sequence leucine-aspartic acid-valine, a well-established cell adhesion motif: this tripeptide is recognized by the cell adhesion molecule α₄β₁ integrin. α₄β₁ integrin can be found in several cells [2]; more specifically, the β₁ integrin subunit plays a crucial role as mechano-sensory receptor in dermal fibroblasts, regulating tissue homeostasis and skin wound healing. This may imply that keratin can potentially act as a tissue regeneration template. Therefore, preparation of keratin micropatterns could become an appropriate strategy for directing cell growth and tissue regeneration. In the present study, we would like to investigate the efficiency of keratin extraction with the high yield target and to explore the possibilities of keratin particles preparation using isoelectric precipitation (IEP). Furthermore, we would like to utilize micro-contact printing (MCP) technique to fabricate keratin-based micropatterns and evaluate their role in the cellular guidance in vitro.
The keratins were extracted from wool using thermo-chemical treatment, such as sulfitolysis, hydrolysis and reduction [3]. These methods were selected due to their high efficiency reported in the literature. Keratin particles were prepared using IEP. The zeta potential as a function of pH, isoelectric point (IP), morphological structures, molecular weights, chemical composition of precipitated keratins and the influence of an anionic surfactant on biocompatibility were investigated. Subsequently, the keratin-based micropatterns were prepared via MCP. Primary human dermal fibroblasts adult cells were plated onto the keratin-patterned surface and cell viability, morphology and adhesion were evaluated by means of immunostaining and the confocal microscope imaging.
The keratins prepared with sulfitolysis and reduction with cysteine showed good compromise between the molecular weights (both protocols produced keratins in the range of 10-60 kDa) and yield (63% and 56%, respectively). Moreover, these methods are based on non-toxic reagents; therefore keratins prepared using these protocols were used in the IEP. The zeta potential values of the surfactant-containing keratins were high and negative at all pH values while the surfactant-free samples showed a typical sigmoidal changes from negative to positive with decreasing pH and a neutral point corresponding to the isoelectric point (the point of minimum solubility). A thick layer of keratin precipitate that settled down at the IP was collected, washed and freeze-dried. IEP produced the globular, tightly packed nano- and microparticles and randomly arranged structures. Characterization techniques indicated that the chemical structure of proteins is retained after treatments. The traces of surfactant that were present in the keratins caused cytotoxicity of the samples, therefore only the surfactant-free samples were used for the keratin-based micro-patterns preparation. Keratin micro-stripes were found supportive in the facilitation of the specific cell adhesion and orientation.
[1] A. Shavandi, et al. Biomaterials science, 2017, 5(9): p. 1699-1735.
[2] V., S. Singh, et al. Comprehensive Biomaterials II, 2017, p. 542-557.
[3] I. Sinkiewicz, et al. Waste and biomass valorization, 2017, 8(4): p. 1043-1048.

A major contributor to the rise of large-scale hemp production in the United States is the harvesting of cannabinoids such as cannabidiol, which can make up more than 18% of the plant’s dry weight.¹ However, the small molecule structure of cannabinoids has limited their incorporation into plastic materials despite their potential as a relatively inexpensive and environmentally safe polymer feedstock. Poly(cannabinoid)s are the first materials to include cannabinoids directly in their polymeric backbone. When compared to cannabidiol (CBD), poly(cannabidiol-adipate) demonstrates a nearly doubled degradation temperature of 361 °C and prevents the conversion of CBD to other cannabinoids such as Δ9-tetrahydrocannabinol. In addition, poly(CBD-adipate) can be drawn into fibers or cast as a semicrystalline film having a broad melting temperature range of 100 to 250 °C. These properties, along with the material’s glass transition temperature of 41 °C, suggest it can be processed into different macrostructures to suit a variety of applications.² The potential of poly(cannabinoid)s as a good alternative to petroleum plastics is further supported by their ester-containing backbone which can be hydrolyzed to produce the original cannabinoid and linking monomer, one of many nontoxic aliphatic dicarboxylic acids chosen to fit the application.


References:
1. VanDolah, H. J.; Bauer, B. A.; Mauck, K. F. Clinicians’ Guide to Cannabidiol and Hemp Oils. Mayo Clin. Proc. 2019, 94 (9), 1840–1851. https://doi.org/10.1016/j.mayocp.2019.01.003.
2. Daniels, R.; Yassin, O.; Mao J.; Mutlu Z.; Jain M.; Valenti J.; Cakmak M; Sotzing G. Poly(Cannabinoid)s. Reconstitution of Cannabis Sativa’s Naturally-Occuring Diols into Thermally Stable, Biodegradable Polyesters. J. Am. Chem. Soc., submitted for publication, 2021.

To comply with green chemistry principles, one can combine renewable biomass with upcycling to form a bio-renewable closed system for the development of recoverable and reusable materials. Experimental study has shown that 2,5-furandicarboxylic acid (FDCA) can be recovered for recycling when incorporated as a building block into photodegradable polymeric systems. Here, we conduct density functional theory (DFT) studies with periodic boundary conditions on sequence of reaction steps and microscopic structures involved in the photodegradation of polymeric chains incorporating FDCA and 2-nitro-1,3-benzenedimethanol. The photodegradation process of polymeric chains is studied by DFT based time-dependent excited-state molecular dynamics (TDESMD) in vacuum and aqueous environment. Changes in the photo-physical features for reaction intermediates are characterized by ground state observables from DFT calculations. Additionally, we calculate the distribution of reaction intermediates and products from TDESMD trajectories using cheminformatics techniques. Our results show that the higher degree of polymeric chain degradation is achieved in vacuum trajectory. Additionally, one finds FDCA molecule is recoverable in aqueous environment, in qualitative agreement with experimental findings.

Slide-ring materials, which are derivatives of polyrotaxanes, are composed of linear polymer guest chains threaded into multiple cyclic molecular hosts that are interconnected to form mechanically-interlocked polymer complexes. The mobility of the host rings along the polymer guest chains makes these specialized polyrotaxanes promising materials in hydrogels, in comparison to energy-dissipating gels that are often difficult to recover to the original state immediately during loading processes. Inspired by previous studies, we developed a series of hydrogels based on slide-ring materials and potentially degradable triblock copolymers. The target hydrogels were synthesized with polyrotaxanes prepared from poly(ethylene glycol)s (PEG) with (2-hydroxypropyl)-α-cyclodextrins (HP-α-CDs) threaded and triblock copolymers incorporating carboxylic acid-modified poly(d-glucose carbonate) and PEG chain segments. The polyrotaxanes and triblock copolymers were then crosslinked through esterification reactions. This presentation will discuss results from investigations of composition-structure-topology-morphology effects on the properties as a function of the polymer parameters, including variation of the PEG main chain length, degree of coverage of α-cyclodextrin, poly(d-glucose carbonate) length, and the concentration of pre-gel solution.
The resulting slide-ring polymer and triblock copolymer networks are expected to contain the following features:
1. High water uptake ability
2. High mechanical properties to help change its volume and retain its structure after water absorption
3. Sustainability with the construction from renewable natural products and in-built degradability

In recent years, the pollution caused by waste plastics including microplastics flowing out into the environment has become a serious problem. In general, common vinyl polymers could not be decomposed in environment in a reasonable time scale since they are composed of only C-C bonds as the main chain, which will remain semi-permanently once discharged to nature and damage our ecosystem. Therefore, there is an urgent requirement for polymer chemists to design new class of polymers that readily degrade with a right trigger to prevent plastic accumulation.
In this talk, I will present our recent attempt for designing degradable polymers, of which the degradation took place by trigger-responsive sites in the skeleton of vinyl polymer side-chain or breaking down the cleavable bonds such as an ester group introduced in the polymer backbone. For examples, we investigated new radically-polymerizable comonomers which can be copolymerized with common olefinic monomers, e.g., (meth)acrylate to result in the vinyl polymers with degradable segments.

The rheological properties of polymeric materials depend on the molecular weight distributions. The mesoscopic coarse-grained models are useful to study rheological properties of polymers. For example, the simple molecular model based on the ideal chain and the Brownian motion can reasonably predict the linear viscoelasticity of polymer melts with relatively low molecular weights (the Rouse model). In most cases, we do not consider the change of the molecular weight distribution is not considered when we consider rheological properties of polymers. However, during the polymer degradation processes, the molecular weight distributions change by the chain scission and cross-linking processes. Therefore the rheological properties change as the degradation proceeds. To understand the effect of the degradation on the rheological properties, mesoscopic coarse-grained models for polymer degradation are useful.
In this work, we consider how to model polymer degradation processes at the mesoscopic scale. If we limit ourselves to the scission processes, the time-evolution of the molecular weight distribution can be straightforwardly modeled as a first-order chemical reaction process. We show that we can analytically calculate the time-dependent molecular weight distributions for any initial conditions, for some simple models. Once the molecular weight distributions are calculated, we can calculate the rheological properties based on the molecular weight distributions. If the average molecular weight of the system is relatively low, the linear rheological properties can be analytically calculated with the Rouse model. Then we can analytically calculate the time-evolution of several rheological quantities. We show some experimental rheological data of degraded polymers and discuss whether we can describe them by the mesoscopic coarse-grained model well.

Organic and polymer encapsulated thermochromic materials have potential use as energy savers in building envelopes, due to the fact their color chromatic behavior changes with temperature. External stimuli, such as solar radiation, often cause degradation in the physicochemical characteristics that impact their optical performance in real-time outdoor applications. The off-the-shelf polymeric encapsulated and three-component thermochromic dyes blended in a sodium silicate binder were prepared as coating materials on glass substrates using a dye-casting process with a film thickness of approximately 300 micrometers. These films have been systematically exposed to extended simulated sunlight environments at ambient conditions. The optical characteristics (UV-Vis absorption and transmission) were evaluated and compared with those of the pristine samples for photodegradation and related processes. We have also attempted to microencapsulate these thermochromic dyes for possible degradation mitigation, these results will also be presented and discussed in this study.

Polyhydroxyalkanoates are a class of bacterially derived polyesters that are known to be readily biodegradable across almost all natural environments, both on land and at sea. They are attractive alternatives to petroleum derived polymers due to their commercially relevant material properties, their thermoplasticity and drop-in processability, and their relatively hydrophobic/water reistant nature, which makes them appealing for applications such as packaging. They are readily subject to enzymatic attack by microorganisms, resulting in hydrolytic chain scission via a surface erosion mechanism. Overall, however, research into the detailed mechanisms and controllers of biodegradation of PHAs has been very disparate and limited in scope to date. Such research often focusses solely on polymer mass loss over time without taking appropriate account of key controlling factors, either at the start or through time. For example, there is often no consideration of initial polymer dimensions, surface area, surface roughness, surface density, crystallinity, molecular weight, morphology, porosity, mechanical properties, voids, local microphase separation, and so on. Likewise, environmental factors such as temperature, pH, dissolved oxygen levels, microbial community concentration and type, nutrient concentrations, salinity and UV exposure are not usually monitored. Frequently, even the initial mass is not recorded. Further, most previous studies have dealt with thin films produced through solvent casting, which poorly represent many commercial plastic products. These studies also do not take into account any aspects of the impacts of additives, fibres or sorbed environmental toxins on biodegradation. This presentation will provide an overview of some of our recent findings on factors that influence polyhydroxyalkanoate lifetimes in the natural environment.

With the growing interest of eco-friendly polymer composites, many researchers employed cellulose as a filler for polymer composites. Especially, microcrystalline cellulose (MCC) has various advantages such as high crystallinity and mechanical properties originating from strong intermolecular hydrogen bonding. However, too strong interaction among MCCs can lead to aggregation of fillers in polymer composites, which can reduce the interfacial areas and reinforcement effects between the polymer matrix and filler. Herein, we employed three different chemically modified microcrystalline cellulose (m-MCC) where hydroxyl groups of MCC were substituted by either methyl (-CH₃) or hydroxypropyl (-CH₂CH(OH)CH₃) groups: (1) low substitution degree with methyl group (HP-0), (2) medium substitution degree with methyl and hydroxypropyl groups (HP-low), and (3) high substitution degree with methyl and hydroxypropyl groups (HP-high). The different types of m-MCCs were compounded with ester type thermoplastic polyurethane (TPU) by an extrusion process. As the chemical substitution of hydroxyl groups can affect the number of hydrogen bonding sites or m-MCC intermolecular distances, both crystallinity of m-MCCs and polymer-filler interaction can also be manipulated. In this presentation, we will discuss structure-property relationships of TPU-MCC composites with focuses on correlation of crystallinity and dispersion of m-MCC with mechanical properties of the TPU-MCC composites.

Traditionally, polymers have been designed to possess irreversible covalent bonds between the repeating monomer units. However more recently, significant interest has been directed toward the synthesis of dynamic polymers that are held together by dynamic (reversible) covalent or non-covalent bonds which can reuse and recycle. Within their structures dynamic polymers contain a reversible bond that can be formed from the monomer units and cleaved back to the monomer units by heat or light. 2π+2πcycloaddition reactions are the dynamic reactions which can be formed and cleaved. A select few molecules are known to possess the ability to undergo this type of reaction such as cinnamine, stilbene, thymine, coumarin and styrylpyrene. The first part of this study focused on the full validation of the potential of these unique reversible reactions, topochemically controlled monomer to polymer transformation techniques using 2π+2π cycloaddition reactions are study to create new materials – such as photo-degradable and photo-reusable polymers and self-healing polymers.
Lignin is the second most abundant biopolymer just after cellulose. Its structure is a complex 3D network of phenol compounds liked by C-C (carbon-carbon) or C-O-C (carbon-oxygen-carbon) bonds, thus representing a promising source of aromatic compounds. The second part of this study focused on the depolymerisation of lignin using the several mechanisms such as a redistribution. We also have developed the novel oxidative degradation of lignin using MnO₂ with blue-light with a formate ionic liquid to produces ethyl acetate and also water soluble depolymerised lignin products. The β-O-4 bonds in lignin were oxidised, which were then depolymerised by a green and recyclable ionic liquid, 2-hydroxy ethylammonium formate, under mild conditions.

We have discovered a new process of polymerizing certain plant-based fatty acids that results in a biopolymer of unusual characteristics and with high potential impact in both the construction and energy sectors. More specifically, it is an iron-based ionomer produced by a carbon-negative process. We call it Polymiron (polymer + iron, po LIM er on). The main ingredients are unsaturated fatty acids and particularly oleic acid that is commonly found in plant oils. The oil is then mixed with metallic iron powder, which can be in the form of waste steel dust, a readily available industrial by-product that is typically not recycled. When carbonic acid (CO₂ dissolved in water) is added to the steel-and-oil slurry, it preferentially adsorbs onto the particles and partially dissolves the iron. This releases Fe(II) ions that replace hydrogens on the carboxyl groups of the fatty acids, which creates bridges and forms dimers. What happens next is not completely understood yet, but apparently the displacement of hydrogens continues up the chains causing more cross-bridging and eventually complete solidification. Due to the oxidation of iron during the curing process, protons are reduced and free H₂ gas is generated as a by-product. The Polymiron production process is thus doubly beneficial for simultaneously capturing a greenhouse gas as well as producing a clean fuel gas. The resulting solid ionomer is electrically conductive and this opens the potential for certain important applications. Our initial practical goal is to develop a self-sensing composite. The conductivity of Polymiron is not a simple metallic type and can vary depending on several factors including intramolecular, like the amount of incorporated iron, and macroscopically, such as the conductivity of embedded fibers in the surrounding polymer matrix. Therefore, we may be able to tune its conductivity so that it is sensitive enough to be correlated with changes in its internal state and especially with strain, cracking, and other damage. If this can be done then it would move Polymiron to the cutting edge of advanced materials for applications in manufacturing and construction where, for example, the integrity of structural components in a building could be monitored continuously in real time. Its conductivity also suggests that it might be re-reduced with photovoltaic DC so that it again reacts with water and CO₂ to create more hydrogen and other fuel gases in an ongoing cycle. If this can be demonstrated, then Polymiron could function as the reactive substrate in a gas conversion reactor that stores excess solar energy by using it to turn water and CO₂ into hydrogen and reduced monocarbon products such as formic acid and methane. There is an intense effort globally to develop biopolymers that are derived from sustainable sources and not petroleum. But these plant-based materials are then typically processed in the usual ways to reach the same product goals. What we have in Polymiron is an entirely new kind of biopolymeric material derived from some of the most readily available and non-toxic materials. The curing process is initiated with nothing more than drinkable seltzer water without heat, pressure, or exotic catalysts. With the increasing interest in green chemistry, this is the kind of promising chemical platform that needs to be fully explored scientifically as well as fully exploited for any practical benefits. Some limited field trials have already been done to test its suitability for simple applications as a thin anti-corrosion coating and a thick, tar-like sealer. Further development is currently underway to find additives and methods to optimize it so that it may function well enough as a resin to replace polyester or epoxy for structural purposes.

Vulcanization is a chemical process that links polymers containing natural rubber and forms tetra-branched crosslinks, creating a three-dimensional (3D) polymer network in which the positions of the constituent polymer chains are fixed. Even when subjected to large deformations, the polymer chains return to their original position when the stress is removed. This is the molecular origin of the elasticity of rubber. Such rubbery materials have become essential in our daily lives, as their elasticity and flexibility provide a functionality range that cannot be supplied by hard materials. Despite the usefulness of these materials, the environmental effect of plastic pollution has been revealed; rubbery materials are a source of microplastic pollutants, and the additives used can also cause environmental pollution. Thus, there is a need to design new rubbery materials that are more environmentally friendly. A methodology for making rubbery materials stronger, without any additives, should help meet this demand.
Although crosslinking is a well-known chemical process, its effect on the ultimate mechanical properties of rubbery materials is still not fully understood. One reason for the poor understanding is the invisibility of the polymer network: it is impossible to visualize the polymer network in rubber because the covalent bonds between the carbon atoms remain almost impossible to visualize using any state-of-the-art microscope. The crowding of the polymer chains also introduced challenges; polymer networks in rubbery materials are far removed from schematic mesh; instead, they resemble entangled spaghetti. In fact, the chain entanglements govern the mechanical properties of the rubber and make it difficult to investigate the effects of the crosslinked structure.
One means of decreasing the number of chain entanglements is adding a diluent to the polymer network. The resultant swollen polymer network is called a polymer gel. In polymer gels, the polymer network architecture plays a vital role in determining the physical properties. Researchers have realized the advantages of such an approach in this century, and many polymer gels with advanced mechanical properties have been developed. These include gels with slidable crosslinks, gels consisting of two coexisting independent networks, homogeneous gels, and self-healing gels. Further, concepts developed in gel science have proven to be translatable, allowing the successful design and fabrication of excellent condensed rubbery materials. In this respect, gel science provides innovative methods for developing advanced rubbery materials.
In this study, we focused on a single simple problem of elucidating how the branching factor—the number of strands connected to each branch—influences the ultimate mechanical properties of polymer networks. Previous studies have been mostly focused on tetra-branched networks, and systematic comparison with other branching factors has been limited to weak deformation regimes. In particular, little is known about tri-branching, which is the lowest branching factor that can form a network. We show that tri-branching, which entails the lowest branching factor, results in a large elastic deformation near the theoretical upper bound. This ideal elastic limit is realized by reversible strain-induced crystallization, providing on-demand reinforcement. The findings indicated that the polymer chain highly orientates along the stretching axis, where enhanced reversible strain-induced crystallization was observed in the tri-branched rather than the tetra-branched network. A mathematical theory of structural rigidity explains the difference in chain orientation. Although tetra-branched polymers have been preferred since the development of vulcanization, we believe that our findings, highlighting the merits of tri-branching, will prompt a paradigm shift in the development of rubbery materials.

Peptides have the potential to contribute significantly to a sustainable society, due to their biomass origin, functionality, and unique properties. The ability to precisely control sequence, length, and stereochemistry in the synthesis of peptides has led to the generation of a variety of materials. However, the diversity of chemical topologies of peptides remains largely unexplored, and cyclic peptides, the simple class of topology, have just been applied to piezoelectric materials and drugs [1,2]. In the field of synthetic polymers, rotaxanes and catenanes have been extensively studied, and their materials with excellent mechanical properties via sliding ring mechanisms have been studied by various groups [3]. In nature, lasso peptides, which adopt a topology similar to that of a threaded lasso or knot, may have therapeutic functions ranging from antimicrobial activity to receptor antagonism and enzyme inhibition [4]. As shown above, peptide topology engineering has the potential to provide a multitude of functional benefits. However, there are still limited examples of the artificial synthesized mechanically interlocked peptide, because the flexible ring skeleton of cyclic peptides and the formation of intramolecular hydrogen bonds prevent cyclic peptides from maintaining an inner diameter large enough for an axial molecule to penetrate. Kimura et al. prepared cyclic hexa-b-peptides composed of b-glucosamino acid. This cyclic peptide has high planarity and large internal pores due to the rigidity derived from the pyranose ring in the side chain, which leads to the synthesis of the polypseudorotaxane with poly(ethylene glycol) [5]. Also, Thomson et al. prepared rotaxanes using cyclo(Pro-Gly)₄, which has a relatively large inner diameter and a planar structure, predominantly in an all-trans conformation in acetonitrile [6]. This cyclic peptide has a solution structure with the glycine carbonyls pointing toward the center and the proline carbonyls directed away, allowing it to interact with cations, which lead to the synthesis of rotaxanes. Therefore, it is important for rotaxane synthesis that the cyclic peptides adopt a solution structure with a large inner diameter. However, the cyclic peptides’ sequence-structure relationships have not been established until now [7].
Here, we aim to establish a guideline for the molecular design of cyclic peptides with a large inner diameter in solution for rotaxane synthesis. Proline, one of our target amino acids, is the only natural amino acid that is N-alkylated and has a five-membered ring at the side chain. Because of the reduction of intramolecular hydrogen bonds and motional restrictions, the presence of proline residue leads to rigid and planer structure and greatly reduces the available conformation of cyclic peptides. Therefore, proline-containing cyclic peptides are potential candidates for cyclic peptides that allow for rotaxane synthesis. In this study, we synthesized cyclic peptides consisting of alternating sequences of L-proline and D-proline and cyclic peptides consisting of alternating sequences of L-proline and glycine by the conventional solid-phase and liquid-phase methods. To clarify the correlation between solution structure and peptide sequence for de novo cyclic peptide designs, the solution structures of the synthesized cyclic peptides were analyzed by circular dichroism measurements and molecular dynamics simulations. In the current presentation, we will present the details of the molecular design and structural information of the resultant cyclic peptides.

[1] T. Kurita, et al. Biomacromolecules 2021, 22, 2815-2821.
[2] D. Price, et al. Chem. Biol. Drug Des. 2013, 81, 136-147.
[3] K. Ito, et al. Adv. Mater. 2001, 13, 485-487.
[4] A. Link, et al. Nat. Prod. Rep. 2012, 29, 996-1006.
[5] S. Kimura, et al. Chemcomun. 2007 10, 1023-1025.
[6] A. Thomson, et al. J. Am. Chem. Soc. 2006, 128, 1784–1785.
[7] Y. Lin, et al. Chem. Rev. 2021, 121, 2292-2324.

To address increasing environmental concerns, green and sustainable materials that promise to replace fossil-based separation materials, and reduce waste generation are attracting considerable research attention. The challenge is multifaceted and lies in finding sufficiently reactive natural monomers that are soluble in green solvents with opposing polarities. On one hand, the monomers need to be reactive to form a highly crosslinked thin film. On the other hand, one of the monomers need to be soluble in polar solvents, while the other monomer need to be soluble in a non-polar solvent, which is immiscible with the selected polar solvent.
Our group has been exploring various green sources to fabricate solvent-resistant nanofiltration membranes. Sustainable thin-film composite (TFC) membranes were designed and fabricated via interfacial polymerization of green building blocks [1]. Chitosan from shrimp-farming waste was derived and turned into a TFC membrane with the plant-based 2,5-furandicarboxaldehyde crosslinker. Moreover, a novel hydrophobic TFC membrane was prepared via interfacial polymerization of plant-based tannic acid and priamine monomers. The cyclohexane, benzene and aliphatic moieties of priamine are suitable to increase the hydrophobicity of the membrane surface, which in turn can result in high permeance of non-polar solvents. In addition, tannic acid is a representative polyphenol compound, which can be extracted from a diverse range of natural materials such as trees, plants, nuts and fruits.
We solubilized date seed biomass (abundantly available from the multimillion-metric-ton date industry) using ionic liquids and dimethyl sulfoxide to fabricate biodegradable nanofiltration membranes [2]. The resultant membranes were coated with mussel-inspired polydopamine via a layer-by-layer deposition method. The obtained membranes demonstrated excellent performance for solvent and oil-in-water separations.
[1] Park et al., Green Chem. 2021, 23, 1175-1184.
[2] Alammar et al., Green Chem. 2022, in press, DOI: 10.1039/D1GC03410C

Poly (citric acid – aspartic acid) copolymer is new material polycarboxylic acid of shale inhibitor was formulated as environmental friendliness, wide sources of raw material, and low-cost additives agents of water-based drilling fluid in oil and gas industry. The formation of the copolymer was verified by Fourier-transform infrared (FTIR) spectroscopy. Thermal degradation of the copolymer was evaluated by Thermal Gravimetric Analysis (TGA) and suggested that the copolymer has good stability. The Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray (EDX) was performed to confirm the morphology of shale before and after copolymer treatment. Shale recovery test, immersion experiment, and anti-swelling measurement were carried out to determine the inhibitor performance in the drilling process. The copolymer showed the highest shale dispersion recovery as compared to common inhibitor (KCl) and water. The anti-swelling and immersion result indicated that the copolymer strongly adsorbed onto the clay surface through electrostatic interactions and hydrogen bonding. Consequently, The hydrophobicity of clay can be increased by producing a hydrophobic film on the clay surface, which decreases the number of hydrogen bonds between water and shale and hence reduces the quantity of water invasion. This study can be suggested the design of permanent green inhibitor for water-based drilling fluid in the larger drilling operation in oil and gas industry.

Keywords: Biodegradable, Poly (citric acid – aspartic acid); Shale Inhibitor; Drilling Fluid; Wellbore Stability

Polyurethanes (PUs) are versatile materials finding applications in many fields including for biomedical applications. Nevertheless, their current synthesis relies on the use of highly toxic isocyanate compounds. Therefore, a strong research activity has recently focused on developing greener production processes and chemistries for PUs. These researches lead today to the emergence of a growing variety of non-isocyanate polyurethanes, so-called NIPUs that should progressively replace conventional polyurethanes.
In that context, we investigated the synthesis of NIPUs by step-growth polyaddition of diamines with CO2-sourced bis(cyclic carbonate)s. We developed novel conceptual routes for the synthesis of such isocyanate-free PUs by valorizing different CO2-sourced building blocks, targeting mild conditions in order to disfavor the occurrence of side reactions. Reactions allowing to introduce CO2 into various cyclic carbonate monomers were studied and optimized allowing the lab-production up to the kg scale of a set of bis-cyclic carbonate monomers. These monomers were designed for the efficient step-growth synthesis of NIPUs and also of polycarbonate for some of them, leading to materials of tunable properties. Adaptation of the reaction conditions notably selecting specific catalysts exhibiting no cytotoxicity allows to produce NIPUs dedicated to biomedical use. The properties of the resulting novel NIPUs materials, e.g. hydroxy-urethane, oxo-urethane, … were then studied and compared to the ones of more conventional PUs.
Beside, a special attention will be dedicated to the synthesis of NIPU hydrogels and their use as drug eluting implants. Finally, the processing of these NIPUs and polycarbonates by 3D-printing and electrospinning will also be briefly described, these technologies being of prime interest for the design of biomedical implants and scaffolds for tissue engineering.

Block copolymers, largely used as thermoplastic elastomers or as compatibilizer of polymer blends, have also actual and potential application in more sofisticated technologies such nanolithography, photonics, nanotechnology and in biomedical field. This contribution will hightlight synthetic strategies for the preparation of sustainable di-block polyesters: the sequential polymerization of lactones and lactides and the emerging chemoselective ter-polymerization of macrolactones, epoxides, and anhydrides.
Aliphatic polyesters are degradable polymers with a reduced environmental impact.¹ The ring-opening polymerization (ROP) of cyclic esters represented the elected method for the production of aliphatic polyesters with controlled composition, microstructures and architecture. Various species have been used as initiators, some having also the ability to initiate a living polymerization.² Aluminum alkyl complexes bearing salicylaldiminato ligands were shown to be efficient and versatile catalysts for the ROP of various cyclic esters. ^3,4 Their catalytic behaviour in the ROP of commercially available cyclic esters, such as ε-caprolactone, L-lactide and rac-lactide, glycolide will be described. Moreover, their use in the ROP of macrolactones, i.e. cyclic esters with large ring-size, and in the ROP of functionalized lactide will be highlighted. By sequential addition of the two monomers, first the L-lactide (or the D,L-lactide) and then the caprolactone, di-block copolymers poly-(L-lactide-block-ε-caprolactone) and poly(D,L-lactide-block-ε-caprolactone) were obtained.⁵ The same class of catalysts was able to copolymerize ε-CL with L-LA and ε-CL with D,L-LA in a random fashion, in the absence of transesterification reactions. The achievement of copolymers having random to block to multiblock structure obtained with ‘non-conventional’ monomers, such as macrolactones⁶ and functionalized monomers will be also discussed.⁷
While the ROP of cyclic esters is limited to the use of available aliphatic lactones, macrolactones and lactides, the alternating ring-opening co-polymerization (ROCOP) of cyclic anhydrides with epoxides recently emerged as a powerful catalytic method for the preparation of structurally diverse polyesters, including aromatic ones. In addition to this, the possibility to combine the ROP and ROCOP processes into the same approach has allowed to further enlarge the avalable combination of monomers and the accessible polymeric structures.⁸ The use of monometallic and bimetallic phenoxyimine aluminum complexes for the ROP of different macrolactones will be described and compared; the same systems were used for the preparation of semi-aromatic polyesters by ROCOP of cyclohexene oxide and phthalic anhydride. The synthesis of diblock polyesters, obtained from the combination of the two processes using a chemoselective “one-pot” procedure, where the semi-aromatic polyester block was formed first, followed by a second chain segment produced by ROP of macrolactones,⁹ will be finally presented.
1 A.-C. Albertsson and M. Hakkarainen, Science (80-. )., 2017, 358, 872–873.
2 O. Dechy-Cabaret, B. Martin-Vaca and D. Bourissou, Chem. Rev., 2004, 104, 6147–6176.
3 T. Fuoco and D. Pappalardo, Catalysts, 2017, 7, 64.
4 M. Strianese, D. Pappalardo, M. Mazzeo, M. Lamberti and C. Pellecchia, Dalt. Trans., 2020.
5 M. Naddeo, A. Sorrentino and D. Pappalardo, Polymers (Basel)., 2021, 13, 1–19.
6 A. Sorrentino, G. Gorrasi, V. Bugatti, T. Fuoco and D. Pappalardo, Mater. Today Commun., 2018, 17, 380–390.
7 T. Fuoco, A. Finne-Wistrand and D. Pappalardo, Biomacromolecules, 2016, 17, 1383–1394.
8 D. C. Romain and C. K. Williams, Angew. Chemie - Int. Ed., 2014, 53, 1607–1610.
9 I. D’Auria, F. Santulli, F. Ciccone, A. Giannattasio, M. Mazzeo and D. Pappalardo, ChemCatChem, 2021, 13, 3303–3311.

COVID-19 pandemic has resulted in an urgent need for personal protective equipment on a daily basis. The use of disposable facemasks significantly contributes to the glut in plastic waste. Asian countries consume approximately 290 billion facemasks annually. Since facemasks are considered as biomedical waste, ideally, they should not be discarded alongside with common solid waste, and therefore the most common treatment of the used masks is incineration. Not much attention has been dedicated to the actual examination of recycling strategies to increase the life cycle of this waste. We have screened sustainable solvents obtained from green sources for the recycling of facemasks. In particular, we selected sustainable experimental parameters in order to recover the polymer constituent of the facemask. In this study, we propose a sustainable process for the recycling of facemasks using versatile dissolution–precipitation method. The selected methodology is scalable and enables the reuse of polypropylene either in microbeads form, or as a freestanding membrane material. The quality of the recycled polymer was assessed through thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The membrane characterization was evaluated via scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle (WCA). The recovered polymer was successfully used in separation processes. We investigated how the fabrication conditions can influence the separation profiles exhibited by the developed membranes. We have proved that the used facemasks can be turned into high-value products using a safe approach, and we expect that our findings will help the world to mitigate the waste issues associated with tackling the current SARS-CoV-2 pandemic.