Paper is a very attractive material for many device applications: very low cost, available in almost any size and with versatile surface finishes, portable and flexible/foldable. From an environmental point of view, paper is a renewable resource and is readily disposable (incineration, biodegradable). Applications of paper-based microfluidics¹ and electronics^2,3 currently being considered or investigated include biochips, sensors, communication circuits, batteries, smart packaging, digital displays. The potential advantages of paper-based devices are in many cases very compelling. For extremely low resource environments, lab-on-chip devices fabricated on paper for bio/medical applications utilize the capillary properties of paper and human-eye-based colorimetric detection in order to operate without the need of external pumps, detectors and power sources, greatly simplifying the design and reducing the cost. For applications where higher signal-to-noise and lower limits-of-detection are required, paper microfluidics can be integrated with opto/electronic devices that greatly expand the overall capability and performance. The flow of aqueous and other fluids in paper (porous) media will be first briefly introduced. Next, techniques for the fabrication of paper-based biochips will be reviewed. Finally, examples of paper-based biochips for diagnostic and sensor applications primarily using bodily fluids (such as blood, sweat, etc.) will be discussed.
¹ A. W. Martinez, S. T. Phillips, M. J. Butte, and G. M. Whitesides, “Patterned paper as a platform for inexpensive, low volume, portable bioassays,” Angew. Chem., Int. Ed. 46, 1318 (2007).
² D. Tobjork and R. Osterbacka, “Paper electronics”, Adv Mater23, 1935, doi:10.1002/adma.201004692 (2011).
³ A. J. Steckl, “Circuits on Cellulose”, IEEE Spectrum50 (2) 48, doi:10.1109/MSPEC.2013.6420146 (2013).

There is currently a strong need for the development of inexpensive, flexible, light-weight and environmentally friendly energy storage devices. This has led to the development of a range of new paper-based electrode materials, batteries and supercapacitors. This presentation will focus on the possibilities of using nanocellulose and polypyrrole based composites, manufactured by chemical polymerization of pyrrole on a nanocellulose substrate, as electrodes in charge storage devices, i.e. supercapacitors and batteries [1-3]. The latter paper-based devices combine high charge storage capacities with excellent power capabilities due to the combination of the large surface area (up to 250 m²/g) of the nanocellulose and the thin (i.e. 50 nm) layer of polypyrrole on the nanocellulose fibers. The composite synthesis method and the electrochemical properties of the composites will be discussed, as well as the possibilities of using polypyrrole coated nanocellulose fibers in the manufacturing of free-standing, high active mass paper electrodes [4-7]. With the latter approach, devices with unprecedented cell areal capacitances at high current densities during thousands of cycles in aqueous solutions can be readily realized. The present type of composites provides new exciting possibilities for the development of green and foldable devices for a range of novel applications, many of which are incompatible with conventional batteries and supercapacitors.
References
1) G. Nyström, A. Razaq, M. Stroslash;mme, L. Nyholm, A. Mihranyan, Nano Letters, 9 (2009) 3635.
2) L. Nyholm, G. Nyström, A. Mihranyan, M. Stroslash;mme, Adv. Mater., 23 (2011) 3751.
3) A. Razaq, L. Nyholm, M. Sjödin, M. Stroslash;mme, A. Mihranyan, Adv. Energy Mater, 2 (2012) 445.
4) Z. Wang, P. Tammela, P. Zhang, M. Stroslash;mme, L. Nyholm, J. Mater. Chem. A, 2 (2014) 7711.
5) Z. Wang, P. Tammela, P. Zhang, M. Stroslash;mme, L. Nyholm, J. Mater. Chem. A, 2 (2014) 16761.
6) Z. Wang, P. Tammela, P. Zhang, J. Huo, F. Ericson, M. Stroslash;mme, L. Nyholm, Nanoscale, 6 (2014) 13068.
7) Z. Wang, P. Tammela, M. Stroslash;mme, L. Nyholm, Nanoscale, 7 (2015) 3418.

Nowadays there is a strong demand for smart packaging to provide comfort, welfare and security to owners, vendors and consumers, by allowing them to know the contents and interact with the goods. This is of particular relevance for low cost, fully disposable and recyclable products like identification tags, medical diagnostic tests and devices for analysis and/or quality control in food and pharmaceutical industry^1-3, most of them requiring continuous power which can be addressed by a combined use of a small disposable solid state battery⁴, charged by a disposable solar cells⁵, able to work under indoor lighting.
Presently, the development of non-wafer-based photovoltaics allows supporting thin film solar cells on a wide variety of low-cost recyclable and flexible substrates such as paper; thereby extending PV solutions to a broad range of consumer-oriented indoor disposable applications where autonomous energy harvesting is today a bottleneck issue.
Here, we show a proof-of-concept of the pioneering production of thin-film amorphous silicon (a-Si:H) photovoltaic cells with efficiencies of 4%⁵, by plasma enhanced chemical vapor deposition (PECVD), on packaging cardboard (LPC)⁶ commonly used in the food and beverage industry. Such accomplishment put us one step closer to this revolution, by providing a flexible, renewable and extremely cheap autonomous energy packaging system. Moreover, such Si thin films take advantage of their good performance at low-light levels, which also makes them highly desirable for cheap mobile indoor applications. We also process solar cells on paper coated with a layer of a hydrophilic mesoporous (HM) material, where, as a proof f concept we produce solar cells with a 3.4% efficiency.
The way how cells were produced, the existing challenges and the plethora of electronics^7-10 that they can serve will be presented and discussed in this presentation.
References
[1] R. Martins, L. Pereira, E. Fortunato, SID 2014Frontline Technology: The Future Is Paper Based, p20-24Vol 52 (2014), pp. 50-55
[2] R. Martins, I. Ferreira and E. Fortunato, “Electronics with and on paper”. Physica Status Solidi- Rapid Research Letters, 5 (9) (2011), pp. 332-335.
[3] A. Vicente, H. Águas, T. Mateus, A. Arauacute;jo, A. Lyubchyk, S. Siitonen, E. Fortunato, R. Martins, Solar Cells for Self-Sustainable intelligent Packaging, J. Materials Chemistry A, 2015, DOI 10. 1039/C5TA01752A.
[4] Stora Enso. http://www.storaenso.com. Accessed 15 November 2014.
[5] Martins, R. F. P., Ahnood, A., Correia, N., Pereira, L., Barros, R., Barquinha, P., Costa, R., Ferreira, I. M. M., Nathan, A. & Fortunato, E. Recyclable, Flexible, Low-Power Oxide Electronics. Advanced Functional Materials 23, 2153-2161, doi:10.1002/adfm.201202907 (2013).
[6] Pedro Barquinha, Rodrigo Martins, Luis Pereira, Elvira Fortunato, Transparent Semiconductors: From Materials to Devices. West Sussex: Wiley & Sons (March 2012), ISBN 9780470683736

Cellulose-based PLA/PBAT polymer blends can potentially be a promising class of biodegradable nanocomposites. We show here that this blend can be rendered thermal resistant while maintaining its impact resistance by the formation of an unusually hard surface shell when exposed to flame or high temperature front. In this study, we show that resorcinol diphenyl phosphates (RDP) is easily absorbed by cellulose particles, modifying their surface energy and allowing them to disperse easily in a PLA/PBAT(commercially named Ecoflex) biodegradable polymer blend. Mechanical testing shows that the IZOD impact increased by 14% at a cellulose concentration of 10% since the crack propagation was inhibited by the structure of cellulose. When exposed to flame a hard shell forms on the surface, which, when analyzed with Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, points out that the surface is enhanced in PLA and it is rich in phosphate moieties. The Nanomechanical measurements indicate that the modulus of this shell is nearly 100x higher than that of the unexposed nanocomposites. Subjecting these samples to the UL-94 test indicates that they satisfy the stringent UL94-V0 condition and rapidly self-extinguish without dripping. We utilized Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) to examine the surface segregation of different components as a function of flame exposure time in order to understand the chemistry of the shell layer. The material properties of this blend can be varied such that it can replace conventional polymers such as PS, PE to explore numerous applications for packaging, disposable cutlery, drug delivery etc. and it is a demonstration that cellulose, when modified with phosphate, could serve as a flame retardant and mechanical enhancer in the environmentally responsible nanomaterials.

Plasmonics involves the control of light at nanoscale using surface plasmons. One of the important manifestations of the confinement and control light at the nanoscale is the dramatic enhancement in the electromagnetic field at the surface of plasmonic nanostructures. This electromagnetic field enhancement at the surface of plasmonic nanostructures results in large enhancement of Raman scattering from molecules adsorbed on in close proximity to these nanostructures, which is often termed as surface enhanced Raman scattering (SERS). We demonstrate that a common filter paper can be transformed into a plasmonic sensing platform for highly sensitive and selective detection of trace levels of chemical and biological analytes. Furthermore, plasmonic paper can be transformed into a microfluidic paper-based analytical device (µPAD) using a simple lithography-free process by a simple cut and drop method. Apart from enabling rapid separation of complex analyte mixtures, this design generates a rapid capillary-driven flow capable of dragging liquid samples into a single cellulose microfiber, thereby providing an extremely pre-concentrated and optically active detection spot. We also demonstrate plasmonic calligraphy that enables multiplexed detection of chemical and biological analytes using a simple ball-point pen as a deposition tool and functionalized gold nanorods as ink. Finally, we demonstrate the fabrication of plasmonic aerogels based on bacterial nanocellulose. Plasmonic aerogels, owing to the high density of plasmonic nanostructures, can be harnessed for numerous applications including (i) ultrasensitive chemical detection based on SERS, (ii) highly efficient energy harvesting and steam generation through plasmonic photothermal heating, and (iii) optical control of enzymatic activity by triggered release of biomolecules encapsulated within the aerogel. The design principles and processing methodology of plasmonic paper and aerogels demonstrated here can be broadly applied to realize various other functional materials.

There are many types of energy storage systems based on mechanical, electrochemical, chemical, and electrical principles. Presently, energy storage technologies based on lithium-ion and other advanced secondary batteries are valued for their large energy densities, but are slow to recharge/discharge rate. To address these problems, electrochemical capacitors (ECs) including electrochemical double layer capacitors (EDLCs, also called supercapacitors) are being developed with faster discharge rates and higher power, having properties suitable for super-capacitor applications. Carbon based materials are widely used in this area, including carbon nanotubes and graphene. However most of these artificial materials involve complex, eco-destructive, and resource-consuming processes.
In this work, filter paper (FP), a more natural, abundant and cellulose based carbon material, was converted into high surface area, highly conductive and electrochemical active carbon materials by thermal carbonisation, and then used as supercapacitors. Filter paper carbonised at 1500 #8451; exhibited best electrochemical performance in comparison to other carbonisation temperatures range from 600 to 1700 #8451;. The capacitance was obtained as high as 115 F g^-1, with > 87 % retained after 3000 charge-discharge cycles. This result is very competitive to other raw carbon materials like carbon nanotube or graphene. In order to manufacture FP under milder condition, Ni was further introduced as a catalyst to improve the carbonisation process of FP. A lowered carbonisation temperature of 800 #8451; was achieved. After carbonisation, the Ni particles were etched away by HNO₃ solution, leaving loads of uniformed micro-pores of size about 100 nm on the FP surface. These micro-pores provide more accessible paths for ions and contribute to a even higher capacitance of 278 F g^-1 which is double the value of un-Ni treatment FP sample. The above work has confirmed that natural raw materials such as FP can be used as environmentally friendly sources of advanced high performance materials for application as supercapacitors in energy efficient systems

Transparent paper, composed of cellulose nano fibers, has drawn increasing attention for paper electronics and paper photonics. Different approaches are carried out for high transparency but usually are high cost and time consuming. Here we demonstrate an easily scalable production of transparent paper simply by surface coating. With a thin but dense surface layer coated, the paper becomes transparent (~85% transmittance), mechanically strong (10 times increase in tear resistance), and stable in water for months. Also, the coated paper acquires high transmission haze (~90%), which can be used in solar cell or lighting applications requiring both high light transmission and scattering. We demonstrated solar cells and organic light emitting diodes on these newly developed transparent paper substrates. Importantly, the production is ultra-fast, low cost and fully compatible to roll-to-roll printing. We then demonstrate the currently largest and cheapest transparent paper.

Materials based on nanofibrillated cellulose hold great promise for future mechanical high performance materials, as well as functional materials in fields such as insulation and filtration, transparent gas barriers, or as bioactive materials for tissue engineering, implants and wound dressings. In many of these applications progress will crucially depend on our ability to manipulate shapes and structures on multiple length scales. While nanocellulose itself provides means to structure nano- and mesoscopic length scales via controlled interactions and self-assembly into ordered structures, micro- and macroscopically, these materials are mostly limited to planar films, hydrogels and aerogels.
Advanced, additive fabrication methods such as classical noozle extrusion, 3D inkjet printing or stereolithography may present viable approaches to shape and structure nanocellulose-based materials beyond films to combine the benefits of both worlds.
To this end, we discuss the preparation of nanocellulose fibers, hollow fibers and gyroidal hydrogel scaffolds using a range of additive fabrication methods. We highlight differences in mechanical properties between nanofibrillar cellulose (NFC) and nanofribillar chitin (NFCh) for fibrillar materials. Moreover, we demonstrate how sacrificial templating of stereo-lithographically printed gyroid scaffolds can be used to make gryoid NFC/NFCh hydrogel scaffolds with ordered pores on multiple length scales. We demonstrate their use as instructive plattforms for bone tissue engineering by culturing human mesenchymal stem cells and unravel distinct differences between NFC and NFCh. The approaches serve as first examples, how advanced fabrication methods can be used to shape nanocellulose-based materials beyond films, gels and aerogels and thereby open new fields of applications.
Selected References:
Torres-Rendon, J. G.; Femmer, T.; de Laport, L.; Tigges, T.; Rahimi, K.; Gremse, F.; Zafarnia, S.; Lederle, W.; Ifuku, S.; Wessling, M.; Hardy, J. G.; Walther, A. ”Bioactive Gyroid Scaffolds Formed by Sacrificial Templating of Nanocellulose and Nanochitin Hydrogels as Instructive Platforms for Biomimetic Tissue Engineering” Adv. Mater. doi: 10.1002/adma.201405873 (2015).
Torres-Rendon, J. G.; Schacher, F.; Ifuku, S.; Walther, A.: “Mechanical Performance of Macrofibers of Cellulose and Chitin Nanofibrils Aligned by Wet-Stretching: A Critical Comparison” Biomacromolecules, 15, 2709, (2014).

We report a photolithographic fabrication process for making microelectromechanical systems (MEMS) from cellulose nanocrystal (CNC) films. Aqueous dispersions of sulfuric acid hydrolyzed CNC were blade coated onto patterned photoresist layers on silicon substrates. The properties of the resulting films were controlled by many parameters including the initial dispersion concentration, wet thickness, shear rate, substrate roughness, and drying kinetics. Optimization of these parameters alleviated the well documented difficulties with CNC films cracking during drying. Anchored CNC films were fabricated into the following MEMS testing devices: comb drive resonators (CDR), mechanical strength testers (MST), cantilever beams arrays (CBA) and residual stress testers (RST). Preliminary results based on phase shifting interferometry (PSI), polarized optical microscopy (POM) and scanning electron microscopy (SEM) validated that shear induced alignment of CNC can be used to introduce anisotropic mechanical properties in micromechanical devices. Completely freestanding and mechanically flexible arrays of cantilever beams have been fabricated. Additional device design and fabrication process optimization are needed to enable a broader range of structures. This will enable CNC MEMS to be used for investigating the elastic modulus, fracture strength, surface stiction, and residual stress for CNC devices and the development of CNC MEMS for specific applications.

Fiber mats were prepared by electrospinning solutions of 15-20% hemicellulose solubilized in 1 M acetic acid. The solutions were homogenize at 60°C and 600 rpm for 8-10 h. Water-based-polyvinyl alcohol (25%) was added to the hemicellulose solution in different ratios of 1:2, 2:2 and 2:1. The fiber morphology was studied using scanning electron microscope. Results showed that lower concentration resulted to electrospraying rather than preferred electrospinning. Upon increasing concentration, a mixture of beads and fibers were however obtained. The experimental trial of acetone and dimethylacetamide solvents also resulted in the formation of beads. Experimental set-up variables (such as electric voltage, tip-collector distance, flowrate) and solution parameters (such as concentration/viscosity, solvent choice) are currently under optimization, in order to achieve the fabrication of high quality fiber mats (from beads-free nanofibers) for eventual application in water filtration.

A platform technology that brings together the toughness of cellulose nano-fibers from the plant kingdom, the remarkable elasticity and resilience of resilin that enables flees to jump as high as 400 times their height from the insect kingdom, and the adhesion power of DOPA, the functional molecule of mussels that enable it to bind tightly under water to organic and inorganic matter from the marine kingdom and all that combined with Human Recombinant Type I collagen produced in tobacco plants; super performing biomaterials.
Resilin is a polymeric rubber-like protein secreted by insects to specialized cuticle regions. Resilin binds to the cuticle polysaccharide chitin via a chitin binding domain and is further polymerized through oxidation of the tyrosine residues resulting in the formation of dityrosine bridges and assembly of a high-performance protein-carbohydrate composite material.
Plant cell walls also present durable composite structures made of cellulose, other polysaccharides, and structural proteins. Inspired by the remarkable mechanical properties of insect cuticle and plant cell walls we have developed novel composite materials of resilin and Nano-Crystalline Cellulose (resilin-NCC) that display remarkable mechanical properties combining strength and elasticity. We produced a novel resilin protein with affinity to cellulose by genetically engineering a cellulose binding domain into the resilin. This CBD-Resilin enable, interfacing at the nano-level between the resilin; the elastic component of the composite, to the cellulose, the stiff component. Furthermore, chemical and enzymatic modifications of the composite are developed to produce DOPA- Resilin-NCC which confers adhesive and sealant properties to the composite.
As a central element of the extracellular matrix, collagen is intimately involved in tissue development, remodeling, and repair and confers high tensile strength to tissues. Historically, collagen was always extracted from animal and human cadaver sources, but bare risk of contamination and allergenicity and was subjected to harsh purification conditions resulting in irreversible modifications impeding its biofunctionality. A tobacco plant expression platform has been recruited to effectively express human collagen, along with three modifying enzymes, critical to collagen maturation. The plant extracted recombinant human collagen type I forms thermally stable helical structures, fibrillates, and demonstrates bioactivity resembling that of native collagen. Combining collagen at the nano-scale with resilin to produce fibers resulted in super-performing fibers with mechanical properties which exceed that of natural fibers.

Crystalline nanocellulose (CNC) solid films from evaporated aqueous heterogeneous mixture retain the self-assembled chiral nematic order formed in the suspension. These semi-translucent films are iridescent and reflect or transmit circularly polarized visible light (400-700 nm) due to the birefringence properties of the self-assembly nanostructure. This effect occurs at different wavelengths depending on the pitch of the helical structure. In this paper, CNC films have been fabricated from different recipes to produce various helix pitch. The corresponding optical wavelength shifts have been obtained by means of FTIR measurements. A specific sample has then been investigated for optical polarization effects as function of tilt angles and specific wavelengths by means of ellipsometry and diode lasers. The degree of ellipticity of the circularly polarized light has been found dependant on the tilt angle of the CNC film regarding to the primary laser beam. A pure circular polarization occurs at tilt angles of 00, 360, and 450 degrees for incident wavelengths of 400 nm, 1064 nm and 1550 nm, respectively. From these results, CNC solid films might be envisioned to be used as a broadband passive tunable light polarizer component in the range of 400-1550 nm wavelength. In addition, laser micromachining results on CNC films will be presented proven the feasibility for microfabrication components integration.

Wood, a naturally grown fiber composite possesses outstanding mechanical properties. Its intrinsic hierarchical structure down to the molecular level gives rise to a combination of high stiffness and toughness.
Micro- and nano-fibrillated cellulose materials are frequently used in micro- and nano-composite materials. Due to the high accessibility of the cellulose evolving during the disintegration processes, the cellulose becomes highly suitable for chemical functionalization. However, a significant draw-back is that during the preparation of the material from wood and plant cellulose sources, the intrinsic hierarchical structure is completely lost.
Here we report on the formation of wood derived, highly structured, hierarchical cellulose scaffolds for the assembly of multifunctional materials. We adapt various widely used chemical delignification methods for pulp and paper to bulk wood treatments that preserve the structural organization. A controlled variation of the process conditions, e.g. temperature and treatment duration, allows to control the amount of removed material and tailor the total porosity of the remaining scaffold.
Confocal Raman Spectroscopy Imaging was used for detailed chemical analysis of the samples with high spatial resolution. The decrease in lignin content was visualized, and the impact of the process parameters (reaction duration and temperature) on the scaffold quality and specific anatomical features was studied. SEM and light microscopy of the scaffold backfilled with in situ formed gold nanoparticles helped to visualize the structural differences of the obtained cellulose-based scaffolds and confirmed the preservation of the integrity of the hierarchical anisotropic structure.
The backfilling with gold nanoparticles is as well a first proof of principle for the formation of a new class of multifunctional materials. With the pretreatment of the wood and the gradual liberation of cellulose, the porosity of the modified cell wall and the amount of the newly added material can be tailored according to the desired application needs. Applying various post-functionalization treatments, such as in situ mineralization, metallization and polymerization as well as the infiltration of pre-synthesized nanoparticles, various material combinations with the scaffold can be envisaged.

The use of cellulose nanocrystals (CNCs) in optical materials has been extensively studied. Key in most applications reported to date is the chiral nematic ordering of CNCs. Here, we demonstrate that random packing of silicated CNCs, and sub-micron sized hollow silica rods derived thereof, can also yield materials with interesting optical properties, i.e. highly porous, ultra-low refractive index coatings.
Needle-shaped CNCs with an aspect ratio of 20 were extracted from Avicel, and subsequently covered with a silica layer, yielding a dispersion of CNC-silica core-shell particles in ethanol. In one single dip coating step, highly porous coatings of CNC-silica core-shell particles were deposited on glass slides and silicon wafers. The lowest refractive index achieved was 1.03, which corresponds to a porosity of 94%; the thickness of these coatings ranged from about 100 nm to 500 nm. The dependence of porosity and refractive index on the thickness of the coating was extensively studied. Furthermore, we demonstrated that the refractive index could be tuned between 1.03 and 1.45 through addition of a metal oxide binder.
The substrates, coated with a layer of CNC-silica core-shell particles, were heated to 450°C for two hours. Cellulose was removed through pyrolysis, which resulted in porous coatings of sub-micron sized hollow silica rods. The porosity increase generated through pyrolysis of cellulose, and the decrease in packing porosity due to shrinkage of the coating were studied in detail. The ultra-low refractive index coatings realized in this study can form the base for a series of high tech coatings with advanced functionalities such as quarter-wave antireflective coatings, multi-layer interference stacks, coatings for optical fibers with a high numerical aperture and optical adhesives.

Novel nanomaterials based on renewable resources are attracting a rapidly growing interest for structural and functional applications where extraordinary performance of biological composites like bone, nacre, wood, and butterfly wings is an important inspiration for the development of artificial multifunctional materials. The possibility to isolate and utilize novel forms of cellulose that have at least one dimension in the nanosized range has recently generated a significant research interest. Nanocellulose features an attractive combination of properties that could result in various potential applications where for instance, stiff, rodlike cellulose nanocrystals (CNC) form a chiral nematic liquid crystalline phase with interesting optical behaviour.¹ Full utilization of the intrinsic properties of the CNCs requires a better understanding of their properties and novel processing routes for controlling their assembly at several length scales.
We have investigated the packing of CNC in the anisotropic chiral nematic phase by small angle X-ray scattering and laser diffraction². The separation distance between neighboring CNCs and the pitch of the chiral nematic phase have been determined over the entire isotropic-anisotropic biphasic region, from the onset of the anisotropic phase formation into the high concentration range above 6 vol% where the dispersion is fully liquid crystalline. We show that the twist angle between neighboring CNCs increases as the magnitude of the repulsive interactions between the charged rods increases and the average separation distance decreases.
We have also followed how the internal structure evolves when drying an aqueous CNC droplet immersed in a binary toluene/ethanol mixture. The drying droplets were studied and monitored in-situ by polarized video microscopy, where the influence of the water dissolution rate on the morphology of the resulting microbeads was investigated by scanning electron microscopy.³
1. J. P. F. Lagerwall, C. Schütz, M. Salajkova, J. Noh, J. Hyun Park, G. Scalia, and L. Bergström, NPG Asia Mater., 2014, 6, e80.
2. C. Schütz, M. Agthe, A. B. Fall, K. Gordeyeva, V. Guccini, M. Salajková, T. S. Plivelic, J. P. F. Lagerwall, G. Salazar-Alvarez, L. Bergström, Langmuir2015 DOI: 10.1021/acs.langmuir.5b00924.
3. F. Jativa, C. Schütz, L. Bergström, X. Zhang, B. Wicklein, Soft Matter 2015, DOI: 10.1039/C5SM00886G.

Green electronics are steadily gaining research and commercial interest due to the promise of creating flexible, lightweight, cost efficient, renewable, and biocompatible devices. Nanopaper made from cellulose nanofibers possesses tunable optical properties, mechanical strength, and small surface roughness enabling many types of electronics that were not previously possible using regular paper or plastic substrates. Additionally, the transition from rigid glass to flexible paper substrates enables the creation of flexible and transparent devices that can be produced quickly using established roll-to-roll manufacturing methods. Lowering the cost and improving the performance of devices are essential for making renewable energy feasible for everyday applications. Various nanopaper electronics are demonstrated in our group, including transistors, organic light emitting diodes (OLEDs), touch screens, solar cells, piezoelectric, and antennae.
With the cellulose fiber network as a host, we impregnate other functional materials, like boron nitride and Fe₃O₄, to give the paper good thermal conductivity and magnetic properties. Meanwhile, with strong nanocellulose as building blocks, we fabricated multifunctional fibers with high mechanical strength and excellent electrical conductivity for the application in energy storage, smart textiles, and low density materials in space. The manufacturing of 2D paper and 1D fibers based on earth abundant material have the potential to expand green electronics as well as galvanize a new future for renewable multifunctional materials.

Cellulose is a renewable material with interesting chemical and structural properties. Here I will present our research on developing energy conversion and storage devices utilizing cellulose including nanocellulose. The cellulose offers interesting three-dimensional multi-length scale porous scaffolds for loading conducting nanomaterials and active energy conversion and storage materials and for absorbing liquid electrolyte. We have demonstrated superior performance on supercapacitors and batteries. We have also shown excellent flexibility and stretch ability of these devices. Lastly, novel three-dimensional batteries can be constructed from these materials.

Polymer nanocomposites are currently used in aerospace, electronics and recreation. New uses are being explored in infrastructure, light-weight vehicles, and in alternative energy applications, such as solar and wind. Arguably, the most critical feature of a composite is the interface/interphase. The interphase in a polymer composite is the volume of polymer adjacent to the fiber interface, and it can comprise up to 30 % of the polymer when nano-scale additives are used. The interphase controls the effectiveness with which the nanoparticle and polymer interact to produce enhanced properties, but it remains a poorly characterized phase. Characterization of polymer dynamics in the interphase is necessary to enable development of next generation composite materials. The development of measurements capable of probing polymer dynamics on length scales, comparable to that of the interphase (1 nm -200 nm), is necessary to enable the development of the fundamental structure property and process-property knowledge. This is especially true for emergent materials such as bio-based polymer composites using silk fibers and cellulose nanomaterials. This presentation will highlight recent advancements in applying Förster resonance energy transfer (FRET), mechanochromic dyes, hyperspectral imaging and fluorescence life-time microscopy (FLIM) to imaging the interphase in polymer nanocomposites.

Electrochemically active bacteria (EAB) have the capability to transfer electrons to cell exterior, a feature that is currently explored for important applications in bioremediation and biotechnology fields. However, the number of isolated and characterized EAB species is still very limited regarding their abundance in nature. Colorimetric detection has emerged recently as an attractive mean for fast identification and characterization of analytes based on the use of electrochromic materials. In this work, WO₃ nanoparticles were synthesized by microwave assisted hydrothermal synthesis and used to impregnate non-treated regular office paper substrates. This allowed the production of a paper-based colorimetric sensor able to detect EAB in a simple, rapid, reliable, inexpensive and eco-friendly method. A proof-of-concept allowed the detection of Geobacter sulfurreducens cells at latent phase with an RGB ratio of 1.10 ± 0.04, with a response time of two hours.

Cellulose and chitin are abundant and renewable polymers. However, they leave a large environmental footprint due to the hazardous solvents used during fibre spinning. Like many other fibres, they are currently used for a mono-functional task. In the present work, we have manufactured cellulose and chitin based electrically conducting, multi-functional textile fibres and films by dispersion of up to 10wt% of carbon nanotubes. Ionic liquids were used as environmentally benign solvents to dissolve cellulose and chitin and as medium for dispersion of carbon nanotubes. Due to high degree of alignment of carbon nanotubes during fibres spinning process, cellulose and chitin nanocomposites below 7wt% of carbon nanotubes were not conducting. However, the electrical conductivity at 7wt% of carbon nanotubes was increased by orders of magnitude. Such fibres can find potential applications in smart textiles (electronic textiles) to monitor heart rate and body temperature or as biocompatible and electrically conducting scaffolds for electrical stimulation of neurons and stem cells.

Transparent, strong, but yet flexible bioorganic-inorganic films are of great technological interest for various applications ranging from food packaging (barrier properties), separation membranes to substrates for organic optoelectronic devices. In this regard, cellulose nanofibres (CNF), derived from wood has recently gathered the interest of a wider audience due to its high mechanical properties combined with a sustainable origin of the material (1). Inorganic fillers such as clays, graphene and graphene oxide (GO), etc. are frequently incorporated in such membranes for enhancement of barrier property related characteristics like mechanical strength, swelling behavior, or gas/solvent permeability.
In this work we present the current work in barrier films based on CNF-GO crosslinked with biomimetic agents such as calcium and borate ions. The prepared membranes show improved mechanical strength and reduced permeability towards small molecules emphasizing the potential utility of this novel hybrid system for a wide range of industrial applications. In this talk, we will present also the work done to develop and thermal insulation and fire retardant foams. (2) Our results show that nanoscale engineering can produce foams with a thermal conductivity lower than air and excellent combustion resistance without the need for halogenated compounds.
[1] B. Wicklein, G. Salazar-Alvarez, J. Mater. Chem. A, 1 (2013) 5469.
[2] B. Wicklein, A. Kocjan, G. Salazar-Alvarez, F. Carosio, G. Camino, M. Antonietti, L. Bergström, Nature Nanotech. 10 (2015) 277.

Learning from nature and based on lotus leaves and fish scale, we developed super-wettability system to meet the increasing needs of the advanced community and also to better understand how to imitate biology.^[1-3] Further, we fabricated artificial materials with smart switchable super-wettability,^[4] i.e., nature-inspired binary cooperative complementary nanomaterials (BCCNMs) that consisting of two components with entirely opposite physiochemical properties at the nanoscale, are presented as a novel concept for the building of promising materials.^[5]
The concept of BCCNMs was further extended in to one dimensional system. As one of biomimetic nanodevices, nanochannels or nanopores aroused particular interest because of their potential applications in nanofluidic devices, biosensing, filtration, and energy conversions.^[6-7] Here, inspiration from biological ion channels and ion pump in nature, we developed a series of biomimetic smart nanochanel and ion pump systems by modifying smart molecules or polymers onto the inner surfaces of artificial nanochannels which were prepared by top-down or bottom-up synthetic strategy.^[8] Moreover, we applied those smart nanochannels in energy conversion systems such as photoelectric conversion systems, concentration cell, etc. ^[9-11] Such applications with biomimetic nanochannels can not only help people to know and understand the living processes in nature, but also inspire scientists to study and develop novel nanodevices with better performance for the mankind.
Reference:
1. L. P. Wen, Y. Tian, L. Jiang, 2015, Angew. Chem. Int. Ed. 54, 3387-3399.
2. X. J. Feng, L. Jiang, 2006, Adv. Mater. 18, 3063-3078.
3. Y. Tian, B. Su, L. Jiang, 2014, Adv. Mater. 26, 6872-6897.
4. F. Xia, L. Jiang, 2008, Adv. Mater. 20, 2843-2858.
5. B. Su, W. Guo, L. Jiang, 2015, Small, 11, 1072-1096
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Cellulose is an abundant eco-friendly polymer that can be obtained from wood and plants through mechanical or chemical processes. Also it can be synthesized by algae, bacteria and tunicates (sea animals). Cellulose can be nano scaled as fibrils, which is called cellulose nano/microfibrils (CNF/MFC), bacterial celluloses (BC) or can be as crystals called cellulose nano/microcrystals (CNC/CMC). All types of nanocelluloses have been gaining strong interest due to their abundance, impressive strength properties, their low weight, renewability and biodegradability. Novel materials, high-tech materials, conductors, insulators, transparent films and any kind of nanocomposites which need superb thermal and mechanical properties without increasing the weight of the final product, have been started to be produced using nanocelluloses as matrix or reinforcement materials. A problem is the lack of knowledge on the nanomechanical properties of cellulose nanofibrils, which creates barriers for the scientists and producers to optimize and predict behavior of the final product.
In this research, the behavior of cellulose nanofibrils&’ under nano compression loads were investigated using an Asylum Research MFP-3D Atomic Force Microscope equipped with a nanoindenter. Unloading curves were analyzed using Oliver-Pharr. As a result of 58 successful nanoindents, the average modulus value was estimated as 16.6 GPa with the reduced modulus value of 18.2 GPa for mechanically produced cellulose nanofibrils. The CNF Modulus values vary between 12.4 GPa - 22.8 GPa with 16.9% Coefficient of Variation (COV), and the reduced modulus varies between 13.7 GPa - 24.9 GPa with 16.2 % COV.
This research provides practical knowledge for the nanocellulose producers, researchers and the industry people who focus on nanocellulose reinforce composite materials.

We have shown that nanocellulose can be used as an excellent dispersant for carbon nanotubes (CNTs), which has advantages compared to conventional methods for dispersing CNTs in polymer matrices, that mainly use surfactants or chemical functionalization. These conventional methods can disrupt the nanotube-nanotube contact or the electronic structure of the nanotubes both of which result in decrease in electrical conductivity of the composite.
First, a stable aqueous dispersion of cellulose nanofibrils (CNFs) is prepared. Then, the as-prepared carbon nanotubes are added to the dispersion followed by sonication and centrifugation and the supernatant is collected. The supernatant contains the stable CNF-CNT dispersion and mainly individualized nanotubes. The efficiency of the CNTs stabilization (from amorphous carbon impurities) is analyzed using Raman spectroscopy. The individualization of the CNTs is further analyzed with dynamic light scattering and atomic force microscopy. These different characterization techniques show high degree of de-bundling and stable dispersions that can be utilized into making functional structures. By a vacuum filtration of the dispersions using a sheet forming procedure, nanopapers with very high conductivity and relatively high strength are fabricated. The tensile modulus and strength of these nanopapers are comparable to composites made by surfactant-assisted or chemical functionalization-assisted dispersions of CNTs. The main further challenge in this work is to find out the mechanism behind such dispersive action of the nanocellulose, i.e. the molecular foundation to the interaction between CNF and CNT, which allows for the increase in the conductivity of the nanopaper with increasing CNT concentration and a maintained mechanical performance of the already-strong CNF nanopaper. Moreover, these dispersions have the potential to be used in numerous applications such as transparent conductors and electrodes, supercapacitors, energy storage devices, etc.

We use various lignocellulose sources to prepare thin films by spin coating, Langmuir deposition or convective assembly from dispersed and multiphase media. A combination of different bi-component systems are produced as 2D structures that include bicontinuous morphologies. Such structures are translated into 3D fibrous materials via (electro)spinning. Changes in the surface energy behaviors, morphology and other characteristics are determined as a function of chemical conversion conducted in-situ and capable of producing surface energy switching. This allows for possibilities in the development of new materials and platforms, for example, in sensing, control release and optical devices, some of which will be illustrated. Finally, the manufacture of nanopaper is enable by using ligno-nanocellulose sources and to produce layered structures with different packing density, porosity strength and wettability. The impact of 2D and 3D nanocellulose in the development of new materials will be introduced.

Consumer electronics, such as cell phones, tablets and other portable electronic devices, are made with the consumption of large amount of precious non-renewable natural resources, such as indium and gallium etc. These consumer electronics are frequently upgraded or discarded, leading to serious environmental contamination. Thus, electronic systems consuming the minimum amount of natural resource that could also naturally degrade over a period of time are desirable which can potentially reduce the accumulation of persistent electronic waste disposed of daily. Moreover, today&’s chips in portable electronic devices are made at large amount yet unnecessary consumption of precious materials. In a typical semiconductor electronic chip, the active region comprised in the top thin layer is only a small portion of the chip, whereas the bottom substrate that holds the chip consists of more than 99% of the semiconductor materials. In microwave chips for wireless functions, besides the waste of the bottom substrate, only a tiny fraction of the lateral chip area is used for the needed active transistors/diodes with the rest being used only for carrying other non-active components. Some toxic semiconductor materials like gallium arsenide (GaAs) are widely used in high speed communication devices, such as cell phones and tablets, and can lead to a significant amount of hazardous materials and high cost in applications that require sparse areal coverage, such as monolithic microwave integrated circuits (MMIC). We demonstrate high performance flexible microwave and digital electronics that consume the smallest amount of natural resources on a biobased, biodegradable and microwave compatible cellulose nanofibril (CNF) paper, along with degradation of these electronic systems. Furthermore, we show gallium arsenide (GaAs) microwave devices, the consumer wireless workhorse, in their transferrable thin-film form for the first time, which can greatly reduce the usage of costly and environmentally hazardous materials. Key electrical components, both microwave and digital, including GaAs heterojunction bipolar transistors, Schottky diodes, inductors and capacitors, and silicon-based digital devices with comparable performance with rigid ones are subsequently fabricated on a flexible, transparent, and biodegradable CNF paper. Successful fabrication of microwave composhy;nents with excellent high frequency performance, together with ‘universal&’ logic gates and integrated circuits on a CNF substrate, has fully established the feasibility of creating ecofriendly high performance flexible electronics. Fungal biodegradation tests conducted on the CNF-based electronics indicate that biodegradation can occur with the aid of brown-rot fungi such as Postia placenta, a common inhabitant of the forest ecosystem.

Cellulose nanomaterials represent a promising high-strength sustainable nanoparticle which, when used within polymeric composites, can provide vastly improved mechanical properties. However, given their intrinsic hydrophilicity, surface functionalization at the particle-polymer interface is necessary in order to promote dispersion and interfacial bonding. In this work the role of amine chemistry providing the functional layer between cellulose nanocrystals (CNCs) and polypropylene was studied. Triethylenetetramine (TETA) was combined with polypropylene (PP) and then with CNCs in high-shear mixing. TETA-treatment stiffened the CNC-PP composites increasing elastic modulus by 116% over neat PP and 60% over untreated CNC-PP composites. TETA-treated CNC-PP composites also exhibited a 38% increase in tensile strength at 5.5% strain, over both unfilled PP and CNC-PP composites without TETA treatment. These nanocomposites were prepared without the use of organic solvents using a scalable, high-volume approach. Finally, TETA-treated CNC-PP composites have a lower density than many competitive systems resulting in opportunities to propagate this environmentally-responsible technology to nanocomposites used in additive manufacturing, automotive applications, construction materials and consumer products.

In this study, cellulose acetate nanofibers were electrospuned followed by deacetylation and functionalization to produce anionic cellulose nanofibers. And carbon nanofibers were electrospuned followed by stabilization and calcination. The noble metal nanoparticles (RuNPs and AgNPs) were successfully decorated on the f-cellulose nanofibers and carbon nanofibers by a simple wet reduction method using NaBH4 as a reducing agent. TEM and SEM images of the nanocomposites confirmed that the very fine RuNPs or AgNPs were homogeneously dispersed on the surface of both. The weight percentage of the Ru and Ag in the nanocomposites was found to be 13.29 wt% and 22.60 wt% respectively, as confirmed by SEM-EDS analysis. The usefulness of these nanocomposites was realized from their superior catalytic activity. In the aerial oxidation of benzyl alcohol to benzaldehyde, the RuNPs/Cellulose nanofiber system gave a better yield of 89% with 100% selectivity. Similarly, the AgNPs/Cellulose nanofiber system produced an excellent yield of 99% with 100% selectivity in the aza-Michael reaction of 1-phenylpiperazine with acrylonitrile. Mechanism has been proposed for the catalytic systems. We demonstrated an efficient method for the fabrication of nanocomposites. The advantage of these nanocomposites was proved by their superior catalytic activity towards the organic transformation reactions.

Graphene and other carbon-based materials are often used as electrodes in electrochemical double-layer supercapacitors (EDLCs), due to their ability to store electrical energy. Cellulose nanofibers (CNF) have been proven to be suitable as a dispersion agent and binder in graphite based electrodes for supercapacitor applications, especially due to their capability to improve the wet and dry strength of the electrode. At the same time the capacitance is maintained or even increased with addition of CNF. It is reasonable to believe that the addition of CNF manages to stabilize smaller graphite particles in the dispersion which results in larger internal surface area in the dry material.
When the amount of CNF is around 20 wt%, (in ratio to the total mass of active material), both scanning electron microscopy and XPS analysis showed that the surface is almost completely covered with the nano-cellulose. Even with this isolating layer of cellulose it is interesting to note that the capacitance is as high as 90 F/g, compared to around 50 F/g for the lowest CNF amount of 5 wt%. However, by applying voltage pulses during the galvanostatic cycling procedure for capacitance measurements, an initial transient behavior is observed during the first cycles. Therefore the capacitance is calculated after 4000 charge and discharge curves, when curves are completely stabilized. We found that the electrode structure changes significantly during this capacitance measurement and already after a short pulse of 10 s and 0.3 V the structural change is noticeable. After cycling for 24 hours, a completely new structure emerges where large fiber-like structures are developed with diameters around 20-30 µm. The galvanostatic cycling procedure has created fiber-like cellulose structures around 1000 times larger than the initial size of the nano-cellulose.
Structural properties of the electrode have often been related to the electronic properties in the supercapacitor. Our result shows that due to this change in the CNF structure, the electrode properties after galvanostatic cycling are indeed also of interest to study. This structural change might be critical to device performance and durability.

Current methods of filtering wastewater from everyday dental procedures fail to remove significant amounts of both particles and ions of potentially hazardous materials included in dental amalgam, e.g. mercury, silver, tin and copper. According to the US Environmental Protection Agency, dental offices were responsible for 50 percent of mercury pollution entering public water treatment facilities in 2003. In addition to the potentially hazardous components of dental amalgam, dental sealants are known to contain Bisphenol A (BPA), a monomer linked to a variety of health problems. Nanocellulose, with its high material strength and low density, offers an economic and environmentally friendly alternative to commonly used polypropylene fiber water filters. This work presents an overview of the performance of wastewater filters incorporating nanocellulose. Nanocellulose filters were fabricated by filtering a 0.5% w/w nanocellulose slurry over a spun glass support. The flow rate of water through thin layers of nanocellulose was characterized using both experimental and theoretical models, while the filtration efficiency of nanocellulose was determined by testing with synthetic dental amalgam slurry and ionic solutions of known ionic strength. Nanocelluose filters were characterized through a variety of methods such as confocal imaging, scanning electron microscopy and physical filter testing. The robustness and integrity of these filters were also tested to determine the retention of chemically unmodified nanocellulose on the filters. Furthermore, data is presented indicating that the filtration capabilities of this material increase exponentially with respect to the amount of nanocellulose in each filter. While these filters are being developed for highly efficient dental wastewater filtration, nanocellulose shows strong potential as the material of choice in next-generation wastewater filters of all types as it is effective, readily available, affordable, and sustainable.

Printing is an emerging fabrication paradigm for low cost large area electronics. When the expected market growth of printed, possibly disposable, electronics applications takes place, the concern for environmental loading will also strengthen and call for biodegradable solutions. For this purpose, plastic substrates and not an optimal choice and also their price level can be too high for many applications.
Paper would be a desirable substrate for printed electronics, as there is a very long history of paper making and printing industry and because paper is a much more environmentally friendly substrate than plastics. However, basic paper itself is not well suited for printed electronics devices for which high resolution is needed because the roughness and porosity of paper are typically high as compared to plastics. Furthermore, chemical and dimensional stability of paper is not as good as for plastics. Some of these limitations can be circumvented by using added coating layers.
Special paper-like substrates can be made with modern materials and techniques, for example composite substrates using the micro / nanofibrillated cellulose (MFC/NFC) with suitable inorganic fillers [1]. Also without fillers by adjusting the fibril size and film processing, the substrate can be made very dense, smooth and transparent and they can be used as substrates for solution-processed and printed electronics [2,3,4].
In this work, we present fully printed top-gate and bottom-gate organic thin film transistors using the CNF film as a substrate and commercially available printing inks such as a UV-crosslinkable PMMA derivative for the insulator and Inktec-010 silver precursor ink for the bottom and top electrode layers. The substrate is produced by a roll-to-roll process [5]. The CNF film is coated by gravure printing using a polymer resist in order to decrease the surface average roughness (R_A) down to ~50 nm. The electrical test structures are then deposited printing methods: conductors are inkjet printed while the dielectric and semiconducting active layers are gravure printed. The results show that the substrate is compatible with various materials and methods utilized in printed electronics applications and the obtained TFT performance is comparable to earlier results for similar transistors on plastic substrates [6].
[1] A. Penttilä et al., Cellulose 2013, 20, 1413 - 1424
[2] Y. Fujisaki et al., Adv. Funct. Mater. 2014, 24, 1657-1663
[3] T. Inui et al., Adv. Mater. 2015, 27, 1112-1116
[4] G. Chinga-Carrasco et al., J. Nanopart. Res. 14 (10) (2012), 1213-1223.
[5] T. Tammelin et al., PCT Int. Appl. (2013), WO 2013060934 A2 20130502
[6] T. Hassinen and H. Sandberg, Thin Solid Films 548 (2013) 585-589

In later years composites based on cellulose have been attracting reasonable attention for presenting low cost, easy processing and numerous forms of preparation used to archive composites with new features. In this bias, composites of zirconium oxide and biomass (Passiflora edulis f. flavicarpa) using: Homogeneous precipitation( Method 1) and and solid mixture extrusion (Method 2) with three different ratios of oxide and biomass (1:1, 1:3, 1:5). The thermal decomposition of the materials were investigates to evaluate the influence of the zirconium oxide as well as the correlation of the kinetic models of Ozawa and Kissinger. The analysis were performed in a Shimadzu TG/DTA 50 from 25°C to 800°C in N² atmosphere in three temperature rates (5, 10, 15 °C/min) for the kinetic parameters evaluation. The results for the biomass show two separated events: The first one correlated to the decomposition of the pectin and the cellulose present in the biomass through a reaction of esterification, and the second one correlated to the thermal degradation of the polymeric chains of the compounds at higher temperatures. Comparing the behavior of the composites with ratio of zirconium oxide and biomass 1:1 for the two methods it can be verified that the heating rate has significant influence in the thermograms for both methods and the rate of 15°C/min showed clearer results for the identification of the chemical processes of thermal decomposition. The activation energies of composites thermal degradation were significantly lower than the pure biomass for all the samples studied leading to the conclusion that the zirconium present in the composites was capable of catalyze the esterification and break of polymeric chains due to its elevated acidity. In the method 1 the presence of Zr⁴⁺ ions dislocated the -OH groups of carboxyl present in the pectin causing reduction of its thermal stability, changing the decomposition to a single step lowering the activation energy, this process was especially notable for the 1:3 ratio composite. In the method 2 the activation energies had similar values for the composites and the pure biomass, being so the decomposition of the pectin took place at lower temperature than cellulose, resulting in two clearly independent processes, opposite to the results of method 1. The comparison of the kinetic models showed Ozawa model as the best correlated curve, being more reliable to predict the activation energies, compared to the theory values.

Cellulose nanofibers with high crystallinity were successfully prepared via electrospinning of cellulose/1-ethyl-3-methylimidazolium acetate (EmimOAc)/cosolvent. Two different cosolvents were used in this study; dimethylacetamide (DMAc) and dimethyl formamide (DMF). Observation of electrospinnability and Scanning electron microscopy (SEM) reveal that solution consisting of cellulose/EmimOAc/cosolvent was stably elecrospun. In order to clarify the influences of cosolvent concentration on electrospinning system, the nanofibers were investigated by FT-IR, X-ray diffraction, thermogravimatric analysis. The results of FT-IR spectra indicated that the cosolvent considerably remained in as-spun nanofiber, suggesting that tow solvents (EmimOAc and cosolvent) were competitively diffused during regeneration. This diffusion system significantly improved the growth of cellulose II crystalline exhibiting crystallinity of ~70%. The increasing crystallinity of cellulose nanofiber also improved the thermal stability. Comparing to DMAc, DMF showed more significant influence on the fiber diameter and the crystallinity.

Renewable materials are an important consideration for conversion of fossil resource. A lot of researchers have studied various industrial applications of natural polymers. Cellulose, one of them, has low density, high absorptivity, and biodegradability with cheap cost. In the present study, natural porous cellulose fibers are synthesized by dry jet-wet spinning using non-toxic N-methyl morpholine N-oxide (NMMO) solvents. Air-gap spinning was used at 120#8451; using single hole nozzle with a diameter of 0.3 mm having the length to diameter (L/D) of 1mm. The pore structure was attributed to re-generation of cellulose fibers during the water rinse after jet-wet spinning process. In order to microstructural evolution, morphology and diameter of porous cellulose fibers were observed by a field emission scanning electron microscopy (FE-SEM). Surface area and pore volume were evaluated using the Brunauer-Emmett-Teller (BET). Tensile properties were measured by universal testing machine (UTM). The porous cellulose fiber structure increased the absorption of water due to high density of pores. The physical properties of cellulose fibers and absorptivity were explored in terms of process conditions. Furthermore, it showed structural stability after water sorption test, which will be promising material for eco-friendly sorbent.

Solar steam generation is a solar-energy harvesting technique that can be used in modern power plants, chemical plants, and seawater desalination plants. This approach requires either high optical concentration due to the large heat loss in bulk water or vacuum to reduce heat loss through air. To improve the efficiency of the evaporation process, we demonstrate a novel double layer system comprised of reduced graphene oxide (RGO)-doped bacterial nanocellulose (BNC) and pristine BNC. RGO flakes are incorporated into the bacterial nanocellulose matrix during bacterial cell culture to form the light-to-heat conversion layer which absorbs the solar radiation. Subsequently, an insulating layer of pristine BNC is grown on the RGO-doped BNC layer in a seamless manner. The open porous structure of the pristine BNC layer facilitates the efficient transport of water from the bulk to the light-to-heat conversion layer. Furthermore, the low thermal conductivity of the pristine BNC layer localizes the heat at the surface of the composite structure (i.e., within the RGO-doped BNC layer), which minimizes the bulk heat loss. This biocompatible and reusable novel double layer structure provides a promising approach for harvesting solar energy.

Cellulose, the most abundant biopolymer in nature, is produced by both plants and many microorganisms. In bacteria, the most prolific producer of cellulose is the gram-negative aerobe Gluconacetobacter xylinus. Chemically identical to plant-derived cellulose, bacterial cellulose exhibits higher crystallinity, better mechanical strength, and improved purity due to the absence of hemicellulose and lignin. The cellulose pellicle of G. xylinus forms at the air/medium interface allowing the bacterium to thrive near the oxygen-rich surface while also providing protection from UV light and serving to retain water. Cellulose pellicles form to the confines of the vessel allowing for the material to be shaped during growth. Here we show that the depth of the culture medium during growth directly contributes to the physical properties of the nanocellulose pellicle. By changing the physical growth conditions, the thickness of the nanocellulose pellicles was finely tuned between 500 nm and 10 µm. In addition to the overall thickness of the pellicle, other properties such as porosity and density can be tuned by adjusting the depth of the culture medium. Subsequent characterization of the nanocellulose pellicles by atomic force microscopy showed consistent fibril size, but differing fibril density. Accordingly, the fluid and gas permeation properties of the nanocellulose pellicles were characterized. Following pellicle harvest, the remaining glucose and the pH of the culture medium was measured and shown to be consistent between cultures regardless of the depth, which has possible correlation to oxygen availability. Continued efforts to understand the effect of growth conditions on bacterial nanocellulose production are underway.

Cellulose nanocrystals (also referred to as cellulose nanowhiskers (CNW) have been extensively studied and used as the filler phase in polymer-matrix nanocomposites (PNC), They have been particularly attractive due to their unique properties such as high aspect ratio, high stiffness, high strength, high modulus, good biocompatibility, low density and low cost of manufacturing. In particular, bio-based PNCs reinforced with constitute promising candidates for bioengineering applications, given their bio-affinity, biodegradability and superior mechanical properties. However#65292;if the high stiffness of CNWs is to be fully utilized, there would be a distinct advantage to orient the highly crystalline nanocellulose in the PNC and enhance the anisotropy of the materials. Therefore, we propose to study the decoration of CNWs with magnetic nanoparticles and to orient these fabricated CNWs under a low external magnetic field and embedded in various polymer matrices. Our goal in this research is to orient nanocellulose in various polymer matrices, thus improving the mechanical properties of nanocomposites to act as potential bioengineering materials. In our project, different magnetic nanoparticle candidates including ferrites, coated metal and metal alloys will be investigated and various polymer matrices will be utilized.

Polymer-based nanoparticles have become a research topic of particular interest due to their potential utility in energy, pharmaceutical, medical, and food technology industries. Biopolymers like polysaccharides are biocompatible and robust, possessing exploitable hierarchical structures at both nano and macro scales. Here, we present a systematic investigation of cellulose acetate nanoparticle structure and evaluate encapsulation efficiency using fluorescent dyes as guests. Nanoparticle assembly can be tuned by varying the solvent polarity during nanoprecipitation synthesis to afford nanoparticles of various sizes ranging from 60nm-300nm. The influence of synthesis conditions on nanoparticle crystallinity was examined using Raman spectroscopy, while particle size and morphology was characterized with Dynamic Light Scattering and Electron Microscopy. Fluorescent properties of encapsulated fluorophores were evaluated using steady state and time dependent fluorescence measurements. We show efficient dye entrapment and demonstrate manipulation of encapsulation extent and dye properties through nanoparticle assembly conditions. The ease of processing, control of size and encapsulation efficiency, and bio-compatibility of cellulose acetate makes the present technique promising for application in bio-imaging and drug delivery.

Polymeric composite membranes are leading the reverse osmosis technology market as they are efficient in performance as well as in cost. The choice of membrane material strongly affects the separation efficiency by means of the membrane characteristics in terms of membrane life, solvent-solute flux and rejection rate. Cellulose acetate (CA)/Polyethylene glycol (PEG)/Chitosan membranes doped with 15-30% graphene were fabricated using dissolution casting method. Fourier transform infrared spectroscopy (FTIR) diagram confirmed the interaction of graphene with other polymers. Thermo gravimetric analysis (TGA) and Differential scanning calorimetry (DSC) showed graphene doped membranes are thermally more stable than the membranes grafted without graphene and favored the physical nature of composite membranes. Water swelling index (WSI), ion exchange capacity (IEC) and oxidative stability increased with increase in the amount of graphene filler concentration. Scanning electron microscope (SEM) analysis showed the smooth texture nature of membranes. The salt rejection rates were related to the amount of grafted graphene and chitosan. A maximum of 2251 mL/m²-h permeate flux was observed with salt rejection rate as maximum as 82% at 0.5MPa using 1000 ppm NaCl aqueous solution at 298K. The results are important for the further use of synthesizes membranes.

Phase change materials (PCMs) are attractive because of their huge latent heat during phase change process between liquid state and solid state. One major problem of PCMs as energy storage units is the leakage during the melting process. The encapsulation technology of PCMs is an effective way to solve the problem. In this paper, stable nano-capsules were prepared with nanofibrillated cellulose (NFC) as the shell and paraffin as the core materials confirmed by scanning electron microscope (SEM). The nano-capsules were assembled into nanostructured composites such as films, fibers and aerogels. Melting and crystallization behavior of the composites were investigated by differential scanning calorimeter (DSC), showing obvious phase change and heat of fusion of paraffin. Leakage tests for the composites were performance by thermal gravimetric analysis (TGA), indicating excellent leakage prevention property. The high energy absorption ability and excellent leakage prevention property of the NFC-paraffin nano-capsules composites showed potential applications on temperature management structure materials such as building board, ceiling, textile and so on.

Globally, diarrhea remains the second leading cause of childhood mortality. While purification technologies featuring ultrafiltration membranes can effectively diminish this mortality rate, the costs associated with maintaining high membrane performance prohibits developing countries from generating safe drinking water. Here, we have created a new generation of ultrafiltration membranes that have higher flux, lower operating energy costs, and the potential to reduce biofouling. In this study, we synthesized asymmetric hand-cast polysulfone ultrafiltration membranes that have a pure water permeability that is 80% higher than commercial ultrafiltration membranes. We next optimized electrospinning conditions in order to fabricate polysulfone and cellulose nanofibers with a statistically equivalent average fiber diameter of 1.0 mu;m. Hand-cast and commercial ultrafiltration membranes were coated with a thin (20 mu;m) nanofiber layer, thus creating a new active top-surface. Molecular weight cut-off experiments confirmed that ultrafiltration membranes enhanced with nanofibers exhibited the same retention performance as the unmodified ultrafiltration membranes. After evaluating the cross-flow performance of the hand-cast ultrafiltration membranes at a transmembrane pressure of 1 bar, a 62% and 172% increase in flux was achieved for the ultrafiltration membranes enhanced with a polysulfone and a cellulose nanofiber layer, respectively. In situ experiments that quantify biofouling as a function of nanofiber layer chemistry and time will also be presented. By testing two chemically unique nanofiber layers, polysulfone and cellulose, we have established structure-property relationships of ultrafiltration membranes enhanced with high porosity nanofibers. In addition to improving the performance of membranes for water purification, understanding the materials-biology interface has great implications on the proper functioning of membranes for a broad range of separations, including, beverage clarification, blood filtration, and protein purification.

Microbial nanocellulose (MNC) is a remarkably versatile biomaterial which can be used in a wide variety of applications. [1] Typically produced as a foodstuff in the form of nata de coco, it can be easily grown and processed into large sheet sizes without much technologically elaborate or complex equipment. [2] MNC sheets are flexible, transparent and can be less than 10mu;m thick. They are biodegradable and have good biocompatibility, [3] i.e., they are non-cytotoxic, and provoke minimal foreign body response. Hence, MNC sheets are of particular interest for flexible medical devices, [4] especially for on-site, wear-and-forget, remote body-monitoring applications.
The formation of patterned thin film structures as part of electronic device fabrication on nanocellulose has been achieved via unconventional lithographic processes, such as inkjet printing, imprint lithography and shadow-masking. [5-7] However, despite that photolithography allows for finer and more complex device architectures, reports of conventional photolithographically patterned devices on MNC sheets are rare. The lack of sustained interest to pursue photolithographic developments on MNC is most likely due to concerns about the porous nature of microbial nanocellulose, thereby requiring a protective interfacial layer prior to processing.
In this presentation, we show that, contrary to general expectations, good quality patterned structures, and therefore electronic devices, can be directly formed on MNC sheets via photolithography. Micron resolution and complex architectures, such as Peano electrodes, are demonstrated. Using these better defined structures with potentially better device response, fidelity and repeatability, we have fabricated electronic sensing and wireless devices, such as electrochemical transistors and microwave resonators. Combining such devices can potentially allow us to achieve a medical device which possesses both sensing and data transmission capabilities, ideal for remote body-monitoring applications.
[1] Klemm, D. et al. Nanocelluloses as Innovative Polymers in Research and Application. Polysaccharides II 49-96 (Springer Berlin Heidelberg, 2006).
[2] Phisalaphong, M., Chiaoprakobkij, N. Applications and Products - Nata De Coco. Bacterial NanoCellulose 143-156 (CRC Press, 2012)
[3] Helenius, G. et al. In vivo biocompatibility of bacterial cellulose. J. Biomed. Mater. Res.76A, 431-438 (2006).
[4] Gatenholm, P. & Klemm, D. Bacterial Nanocellulose as a Renewable Material for Biomedical Applications. MRS Bulletin35, 208-213 (2010).
[5] Inui, T. et al. A Miniaturized Flexible Antenna Printed on a High Dielectric Constant Nanopaper Composite. Adv. Mater.27, 1112-1116 (2015).
[6] Hu, L. et al. Transparent and conductive paper from nanocellulose fibers. Energy Environ. Sci.6, 513-518 (2013).
[7] Mäkelä, T. et al. Roll-to-roll printed gratings in cellulose acetate web using novel nanoimprinting device. Microelectron. Eng.88, 2045-2047 (2011).

Application of eco-friendly materials are increase necessarily due to policy. So, cellulose and lignin that most suitable based on non-food materials are studied for substitute oil resources. The composites of petroleum-based polymers with natural materials manufacturing to many studies have been conducted. But those materials have low resistance, durability, poor miscibility with commodity polymer. However, surface chemical modification can make natural polymer with commodity polymer miscible in spite of theirs hydrophilicity and hydrophobicity. Cellulose and lignin are inexpensive natural materials and its composite have a lot of advantage that way to solve environmental regulation.
In this study, silane coupling agent was used interfacial adhesion natural materials with Polypropylene(PP). We find the best proportion of cellulose and lignin respectively, than set on the ratio. Afterwards, it was changed the cellulose/lignin mixture ratio and made the mixture dispersed PP matrix. Modified cellulose and lignin are have slightly different properties each, so, regulating modified cellulose and lignin mixing ratio was best way to find outstanding properties of composites. The chemical modification was confirmed to use FT-IR, XPS, SEM-EDX. Composites thermal and mechanical properties were observed by using DSC, TGA and UTM. Consequently, Modified materials and PP blend has good physical properties than non-modified materials.

Wood is a biological material with outstanding mechanical properties resulting from its hierarchical structure across different scales. While research works have shown that the cellular structure of wood at the micrometer scale is a key factor that renders it excellent mechanical properties at light weight, the mechanical properties of the wood cell wall material itself still needs to be understood comprehensively. The wood cell wall material features a fiber reinforced composite structure where cellulose fibrils act as stiff fibers, and hemicellulose and lignin molecules act as soft matrix, while water molecules can soften the material. With the full atomistic modelling of each component and the interactions between them, the present work provides insights of the deformation mechanisms at the atomistic scale and how the properties of each component contribute to the overall properties. In further, a meso-scale coarse-graining model of wood cell wall material is trained basing on the full atomistic simulation. This enables us to study the wood cell wall at the scale up to microns, where the angle between the fiber direction and the loading direction plays the key role. Our multi-scale modelling of wood cell wall material will provide a full description of the mechanical behavior of wood cell wall material and lead to suggestions to the design of high-performance composite materials.

Crystalline nanocellulose (CNC) is an emerging renewable nanomaterial that is promising for many diverse applications. As a renewable material, nanocellulose and its derivatives have been widely studied, focusing on their biological, chemical, as well as mechanical properties. The electro-optical properties of CNC, however, remain relatively under explored. The birefringence is one of the important properties that make the CNC very attractive for photonic applications. The rode-like nanocellulose fibers dispersed in certain solutions exhibits a specific preferred orientation which depend on their electrical charge, physical dimensions and the type of solutions used to disperse nanocellulose fibers. In recent study of kerr-effect in functionalized CNC solution we demonstrated that it is possible to control the orientation of nanocellulose fibers under an applied electric field. Nanocellulose based spatial light modulator devices were fabricated and characterized. The results obtained showed that the transmittance of the device can be controlled through frequency modulation of the applied electric field. In this paper we present the fabrication and electro-optical characterization of the device and discuss the relevant properties of CNC and future approaches to optimize and improve their characteristics and performance.

In the recent years, we have been observing a rapid and growing interest concerning the utilization of biological materials, such as cellulose, for a wide range of applications not only in the form of raw material mainly for pulp and paper production, but also in the development of advanced materials/products with tailor-made properties, especially the ones based on nanostructures.
Cellulose is the most abundant biopolymer on earth since it is the major component of plant biomass, but also a representative material of microbial extracellular polymers like bacterial cellulose. Bacterial cellulose is a form of cellulose that is produced by bacteria and has an identical molecular structure to that produced by plants. One of the most important features of bacterial cellulose is its chemical purity, which distinguishes from that from plants, which results in an ultrafine reticulated structure exhibiting a higher degree of polymerization as well as a higher crystallinity index. The fibrils of bacterial cellulose are around 100 times thinner than that of plant cellulose making it a highly porous material and in same cases with controlled selectivity.
Bacterial cellulose has demonstrated to be a remarkably versatile biomaterial and can be used in wide variety of applications like: paper, textile, food industry, medicine, cosmetics and more recently in optoelectronic devices.
In this paper we will review the main applications in electronics of bacterial cellulose as either a substrate (passive) on the fabrication of low temperatura amorphous silicon solar cells or as a real electronic material (active) on the production of oxide based thin film transistors, taking into account the expertise as well as the major developments already done at CENIMAT|I3N in the area of bacterial cellulose applied to Paper Electronics: Paper-e.

Biological materials often derive their remarkable mechanical properties from intricate internal hierarchical structures, starting from individual organic molecules, which are wound into fibres and then formed into complex networks, with length scales ranging from a few nanometres all the way up to tens of microns. Such materials naturally possess characteristic length scales derived from this herarchical structure, and mechanical properties that depend on the properties of the individual fibers and the network topology. In order to fully explore the mechanics of such materials, it is desirable to probe over a range of length scales. We demonstrate the use of a novel nanoindentation based mechanical compression testing methodology for the highly repeatable measurement of biomaterial mechanics at mesoscopic length scales and volumes. The testing methodolgy is built upon the compression of a precisely aligned flat probe into the biomaterial layer forming a confined, stationary volume of highly compressed material in a well-defined, invariant geometry. Biomaterials are often inhomogeneous on large length scales, and small-scale compression testing permits material mapping at defined length scales across the sample, which cannot be achieved using bulk tensile testing. Testing is performed at mesoscopic length scales between single fiber and bulk mechanical tests, more closely resembling mechanical interactions such as those of a cell on a collagen scaffold, for example. Furthermore, the probe diameter and film thickness may be varied from nanometers to tens of microns in diameter providing a wide range of length scale tuning. We extract engineering stress versus strain data as a function of loading rate for nanometer to micron thick layers of dehydrated collagen and chitin networks films on high modulus substrates using a flat ended cylindrical indentation probe. Chitin is one of the strongest biological materials, a long chain polymer woven into hierarchical fibrils and networks that gives the exoskeletons of crabs, squid pens and insect cuticles their exceptional strength, while collagen type I is the most prevalent form of collagen in the human body and constitutes the major fibrous protein in the extracellular matrix and connective tissue found in skin, bone, dentin, tendon and sclera for example. Contact moduli are extracted for both collagen and chitin, while viscoelastic behavior is examined by varying loading rates and performing creep tests. A time dependent viscoelastic response is observed in both materials and comparative viscoelastic parameters are extracted.

Optimal design of nanostructured materials require integration of various approaches to synthesize, functionalize, characterize and process the nanosized species for various applications. Here, I will give an overview of recent research on characterization and surface modification of nanocellulose fibrils, and the fabrication of nanocellulose-based hybrid films and super-insulating foams. We have studied the structural features on multiple length scales of rod-like cellulose nanoparticles by applying statistical polymer physics concepts and assessed their physical properties via quantitative nanomechanical mapping. We show clear evidence of a right-handed chirality and statistical analysis of tracked contours shows that the kink angle distribution is inconsistent with a CNF structure consisting of alternating amorphous and crystalline domains. We have chemically modified cellulose nanofibrils (CNF) with polyionic liquids to produce omnidispersable fibrils and and selectively labelled CNF with two different fluorescent probes to create a multi-color labeled material.
We will demonstrate how the microstructure and mechanical, and thermal properties of various inorganic-nanocellulose hybrids can be tailored by controlling the foaming and assembly of nanocellulose and the inorganic nanoparticles. Examples include hybrids based on nanocellulose crystals and amorphous calcium carbonate results in transparent and hard hybrid coatings and hybrids of cellulose nanofibrils and titania nanoparticles that result in transparent and flexible free-standing films with a hardness comparable to concrete. We will also describe recent work on the preparation of thermally insulating and flame retardant nanocellulose hybrid foams. We show that freeze-casting suspensions of cellulose nanofibres, graphene oxide and sepiolite nanorods can produce super-insulating, fire-retardant and strong anisotropic foams. The sepiolite and graphene oxide contribute together with the cross-linker boric acid to the excellent combustion resistance, being significantly better than traditional polymer-based insulating materials.
References:
J. P. F. Lagerwall, C. Schütz, M. Salajkova, J. Noh, J. Hyun Park, G. Scalia, and L. Bergström, NPG Asia Materials, 6, e80 (2014)
I. Usov, G. Nyström, J. Adamcik, S. Handschin, C. Schütz, A. Fall, L. Bergström, R. Mezzenga, Nature Commun., 6, 7564 (2015)
K Grygiel, B Wicklein, Q Zhao, M Eder, T Pettersson, L Bergström, M Antonietti, J Yuan, Chem. Commun., 50, 12486-12489 (2014)
J R. G. Navarro, G Conzatti, Y Yu, A B. Fall, R Mathew, M Edén, L Bergström, Biomacromolecules, 16, 1293-1300 (2015)
B. Wicklein, A. Kocjan, G. Salazar-Alvarez, F. Carosio, G. Camino, M. Antonietti, L. Bergström, Nature Nanotechnology, 10, 277-283 (2015)

Owing to high purity, simple surface chemistry and three-dimensional (3D) nanofibrous structure, the properties of biosynthesized bacterial nanocellulose (BNC) composite are significantly different compared to conventional filter paper. Previously, we demonstrated that conventional laboratory filter paper adsorbed with plasmonic nanostructures can be employed as a flexible surface enhanced Raman scattering (SERS) substrate. In this work, we demonstrate an ultrasmooth BNC-based SERS swab fabricated by simple vacuum-assisted filtration method. The 3D porous structure of BNC provides extraordinarily large surface area facilitating the uniform and dense adsorption of plasmonic nanostructures, which results in significantly higher SERS activity. Furthermore, significantly lower surface roughness of BNC compared to conventional filter paper resulted in an excellent uniformity of SERS activity across the entire substrate, which is far superior compared to filter paper. Harnessing the ultrasmooth surface, we show that BNC-based SERS swab serves as an ideal platform for recognition and detection of bacteria. The 3D plasmonic BNC composites demonstrated here are highly attractive for a broad range of applications including sensing, catalysis, and energy harvesting.

This talk will highlight recent progress toward tuning electromechanical properties of cellulose-based paper through embossing. In particular, embossing is a means to manipulate porosity and morphology for tuning (i) the conductivity of paper-based nanocomposites and (ii) the transient, disintegrating nature of microcrystalline cellulose (MCC)-based electronic substrates. By using embossing, or imprint lithography, as a process for tuning electromechanical properties through the thickness or volume of paper-based electronic substrates, this new process may provide an alternative to transfer printing and additive deposition, which are generally limited to patterning electromechanical properties only on the surfaces of substrates.
To fabricate paper-based nanocomposites with embossing-dependent conductivity, this work describes manual paper-making techniques capable of mixing, sheeting, and drying slurries of water, cellulose fibers, and conductive nanoparticles. With the application of minimal pressure during wet processing, the dried composites are “fluffy” with porosity greater than 90%. This high initial porosity results in nanocomposites with high electrical resistivity as the embedded conductive particles are separated from each other by electrically insulating air and cellulose. By applying large pressures to emboss these fluffy materials, it is then possible to deform the substrates plastically and significantly reduce porosity. Initial results have demonstrated that reductions in porosity can result in large increases in electrical conductivity, which appear to result from the creation of percolating electrical networks.
For tuning the transient disintegration of cellulose-based electronic substrates in aqueous solutions, this work employs techniques similar to those for forming pharmaceutical tablets from powders. Using a punch-and-die system, it is possible to compact or emboss MCC into thin sheets with low porosity. These low porosities limit the penetration of solvents and increase the time for disintegration. To demonstrate the effectiveness of embossing MCC into transient electronic substrates, this work characterizes disintegration of the formed substrates in aqueous solutions. Testing demonstrates the effects of altered porosity on the time for disintegration in both quiescent and agitated flows. Agitated flows result from mechanical inroduction of bubbles/air, and the final demonstration uses a bubbly flow to facilitate the disintegration of button-like, cellulose-based components, which are critical to electronic keypads.

A major part of today`s materials research is driven by inspiration from biological materials. In particular specific features found in nature, such as the hierarchical arrangement of structural components across several length scales, can be transferred to bio-inspired materials and offer the potential to generate high performance materials. Significant progresses have been made in the fabrication of bio-inspired hierarchical materials (e.g. via 3D printing), however it remains very difficult to achieve the biomaterials inherent complexity at the micro and nano-level. Therefore, it would be highly beneficial to directly use readily available biological materials in order to create functional cellular lightweight composite materials. One of the most promising natural hierarchical materials available is wood, with its unique structure at the micro and nano-level.
One approach to the direct use of hierarchical biomaterials is to generate ceramic scaffolds from wood, with the advantage of keeping the complex hierarchical structure intact. However the excellent mechanical properties of wood cannot be retained and in addition, the potential of post functionalization of the scaffolds is rather limited.
Therefore, we follow modification strategies which keep the structure of wood intact and at the same time offer the potential to incorporate new functionalities into the bulk wood structure, in order to overcome limitations in material functionalization and better utilize this renewable resource.
To achieve this, it is necessary to develop modification/functionalization routines which allow for a controlled and selective modification of the wood ultrastructure. We implemented grafting polymerization techniques (FRP, ATRP) within the macromolecular assembly of wood, offering the possibility for a spatially controlled in-situ polymerization within wood cell walls, and for the introduction of new functionalities to the wood ultrastructure (e.g. stimuli responsive behavior). Furthermore, recent results on the combination of stimuli responsive hydrogels with the wood scaffold to create hydrogel-wood hybrid materials will be presented.

This talk will overview a simulation-based approach to enhancing the mechanical properties of novel transparent thin films and nanocomposites by utilizing cellulose minus; the most abundant and renewable structural biopolymer found on our planet. Cellulose nanocrystals (CNCs) exhibit outstanding mechanical properties exceeding that of Kevlar, serving as reinforcing domains in nature&’s toughest hierarchical nanocomposites such as wood. Yet, weak interfaces at the surfaces of CNCs have so far made it impossible to scale these inherent properties to macroscopic systems. A simple analysis on CNC interfaces that accounts for size and geometry effects will be proposed. Our theory and simulations converge on the prediction that the ideal cross-sectional dimensions maximizing the interfacial fracture energy of CNCs must be approximately 5 by 6 nm in dimensions, which intriguingly are very close to the universal dimensions of CNCs found in wood. This study sheds light on a new design principle pertaining to atomically layered bioinspired nanocomposites. Multi-scale studies on nanocellulose interfaces with polymers will be presented to discuss challenges and opportunities for using the nature&’s most common structural building block to achieve property enhancement in nanocomposites. Key importance of interfacial energies, interphase formation, and moisture effects on macroscopic mechanical response will be illustrated. I will conclude with an outlook on how the nascent properties of nanocellulose could be further utilized in polymers through validated systematic multi-scale simulation techniques that marry chemical features with mechanical properties.

The demands from the modern society are driving us towards the use of renewable and biodegradable materials. This development has been propelled by the growing plastic ocean pollution and as of July 1^st 2015 Styrofoam is for example banned for single service food packaging and as packaging fill in New York City. In turn this has increased the interest to use cellulose-based materials since cellulose is renewable, biodegradable and the polymer is also the most common biopolymer on earth. The recent developments in the nano-cellulose area have also opened up new possibilities due to the outstanding chemical and mechanical properties of the cellulose nanofibrils (CNF). It has been shown that high-strength nano-papers (1) and low density aerogels (2) and foams (3) can be prepared from CNF, where the high aspect ratio of the CNF is utilised, together with their excellent mechanical properties, to create these new materials.
In a recent work (4) we have demonstrated that these wet-resilient, low-density materials can be used as templates for Layer-by-Layer (LbL) formation of polyelectrolytes and/or nanoparticles in order to create low density materials with a large variety of functionalities ranging from super-capacitors to anti-bacterial materials. The properties and functionalities of the low density materials are naturally dependant on the selected polyelectrolytes and/or nano-particles, but also on the pre-treatment of the CNF dispersion before foam/aerogel formation. We have also been able to use these aerogels to prepare compressible supercapacitors and batteries simply by covering the interior surfaces of the aerogels with 2 electrodes and a separator LbL structure consisting of 30 bilayers of PEI (polyethyleneimine) and PAA (polyacrylic acid) (5). For the supercapacitor the electrodes consisted of 5 bilayers of PEI and anionically modified carbon nantoubes and for the batteries the cathode was constructed by using copper hexacyanoferrate nanoparticles together with PEI and CNTs.
The current presentation will be focused on the new materials that can be prepared by using the aerogels and foams together with the fast LbL assembly.
References
Berglund, L. A. and Peijs, T. (2010). Cellulose Biocomposites — From Bulk Moldings to Nanostructured Systems. MRS Bulletin, 35(March), 201-208.
Pääkkö, M., Vapaavuori, J., Silvennoinen, R., Kosonen, H., Ankerfors, M., Lindström, T., Berglund, L.A. and Ikkala, O. (2008). Long and entangled native cellulose I nanofibers allow flexible aerogels and hierarchically porous templates for functionalities. Soft Matter, 4(12), 2492.
Cervin, N. T., Andersson, L., Ng, J. B. S., Olin, P., Bergström, L. and Waring;gberg, L. (2013). Lightweight and strong cellulose materials made from aqueous foams stabilized by nanofibrillated cellulose. Biomacromolecules, 14(2), 503-11.
Hamedi, M., Karabulut, E., Marais, A., Herland, A., Nyström, G., & Waring;gberg, L. (2013). Nanocellulose Aerogels Functionalized by Rapid Layer-by-Layer Assembly for High Charge Storage and Beyond. Angewandte Chemie International Edition, 52(46), 12038-12042.
Nyström, G., Marais, A., Karabulut, E., Waring;gberg, L., Cui, Y., and Hamedi, M. M. (2015). Self-assembled three-dimensional and compressible interdigitated thin-film supercapacitors and batteries. Nature Communications, 6(May), 7259.

Nanocellulose, being fully bio-sourced and renewable, with intrinsic high tensile strength and modulus, is considered a viable bio-reinforcement for a wide range of materials and applications, such as concretes, packaging, and bio-composites for additive manufacturing, and a potential strengthening agent in papermaking. New technologies have recently been developed for better controlling size and aspect ratio of nanocellulose products; however, applications that require the dry form of nanocellulose are still cost prohibitive and applications using nanocellulose products in wet form, while favorable in terms of cost, are limited. Dewatering nanocellulose to create useful forms is a current technical challenge. The hydrophilic nature of nanocellulose is also an obstacle to dispersion of cellulosic materials in hydrophobic materials to create composite structures. As a result of these and other issues related to use of nanocellulose, surface modification of nanocellulose is currently receiving a large amount of attention. This paper discusses recent technologies to increase nanocellulose usefulness, including surface modification, and future paths for scale-up and commercialization of nanocellulose for various high volume applications.

Aerogels comprised of organic or inorganic precursors are characterized by open porous structure, extremely low density, large specific strength and surface area, and excellent thermal insulation. Integration of functional nanostructures with aerogels can lead to an extremely powerful class of materials with a wide range of applications such as chemical and biological sensing, catalysis, and energy harvesting. In this work, we demonstrate a surprisingly simple method to create an optically-active aerogel by integrating plasmonic nanostructures with aerogels obtained by freeze-drying bacterial nanocellulose (BNC). Owing to three-dimensional open porous and nanofibrous structure, excellent mechanical properties, high purity and simple surface chemistry, and cost-efficient process, aerogels based on biosynthesized bacterial nanocellulose are highly attractive candidates for functional aerogels. We demonstrate that plasmonic aerogels, a versatile optically-active platform, can be harnessed for numerous applications including (1) ultrasensitive chemical detection based on surface enhanced Raman scattering (SERS), (2) highly efficient energy harvesting and steam generation through plasmonic photothermal heating, (3) optical control of enzymatic activity by triggered release of biomolecules encapsulated within the aerogel. Our results demonstrate that three-dimensional plasmonic aerogels exhibit significantly higher sensing, photothermal, and loading efficiency compared to the two-dimensional counterparts. The design principles and processing methodology of plasmonic aerogels demonstrated here can be broadly applied to realize various other functional aerogels.

Synthetic nanostructures have been widely used to develop novel materials for engineering applications. Carbon-based nanostructures such as graphene and carbon nanotubes (CNTs) have been proven to enhance mechanical and electrical properties in composite materials. For example, an increase of tensile strength, Young&’s modulus and fracture toughness have been reported for polymer-based nanocomposites with graphene inclusions, compared to the pure host polymers. Compared to CNTs or graphite inclusions, graphene typically lead to a bigger enhancement for both mechanical and electrical properties.
Nanobionic materials combining biological constituents and synthetic nanostructures recently opened new pathways in the design of new materials with desired properties.
In our work, we combined undifferentiated plant cells with graphene nanoplatelets to obtain a novel composite material that presents mechanical properties similar to wood but is also electrically conductive.
In this talk, we will present the influence of graphene nanoplatelets on the mechanical and electrical properties of the new material, and analyze the dependence of these properties on the concentration of nanoplatelets. We characterize the structure-function relation using synchrotron X-ray micro-tomography, to investigate the network arrangement of the nanoplatelets at the microscale.
In addition to its remarkable mechanical and electrical properties, the obtained material is workable (like natural wood) but it is also moldable in any shape (like a polymer). It is lightweight and its properties make it suitable for smart building technology and aeronautics applications.

The green aqueous oxidation of cellulose using 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) as a catalyst allows surface- and position-selective modification of 3-nm-wide, crystalline cellulose nanofibrils. All the C6 hydroxyl groups exposed (facing outside) on the nanofibril surfaces can be oxidized to carboxyls, and the microcrystalline structure of the nanofibril is fully preserved irrespective of the reaction conditions such as time and reagent dose. The oxidized nanofibrils are individually dispersed in water, and spontaneously align in a nematic liquid crystalline order. The integration controls of the self-aligned nanofibrils, i.e., careful adjustment of the pH and evaporation of the solvent in the dispersion, produces a wide range of nanostructured bulk materials with outstanding properties. Examples include, transparent and flexible films as strong as steels, and optically translucent yet thermally insulating and tough porous materials.

Since cellulose nanopaper are consisting of only cellulose nanofibers without any additives such as polymer or binders, cellulose nanopaper enhance high mechanical and optical transparency. Moreover, they have high foldability and smooth surface. So the nanopaper is one of the best candidate substrates for flexible electronics. Recently we reported some nanopaper applications in electronic devices of "nanopaper memory", "nanopaper transistor", "high dielectric constant nanopaper", "transparent conductive nanopaper", and "foldable nanopaper antenna". To realize the flexible electronics using cellulose nanopaper, we should overcome some problems in their properties and paper making processes. Some types of cellulose nanopaper are made of mechanically or chemically modified cellulose nanofibers. Among these, nanopapers produced from chemically modified cellulose nanofibers by TEMPO-mediated oxidation or carboxylmethlation are the most promising substrate because of their lower power consumption during fabrication and better optical transparency (lower haze). However, the chemically modified nanopaper had lower thermal durability than mechanically modified nanopaper and some plastics. In this presentation, we will introduce a chemical modification to improve their thermal stability. After the modification, the nanopaper enhanced the high thermal stability while maintaining the high optical transparency and low coefficient of thermal expansion. We will also introduce clear transparent nanopaper from high concentrated nanofiber suspensions, and the ultra-rapid paper making procedure of the transparent nanopaper. We believe that these findings will open the way for further develop of flexible paper electronics using a continuous roll-to-roll process.

Originally introduced in 2007 by the Whitesides&’ laboratory, paper-based microfluidic assays have now been developed for a wide variety of applications. Paper promises to be cheaper than classical lateral flow assay materials such as nitrocellulose, while maintaining capillary movement of fluids, ease of transport, compatibility with a range of chemistries and disposability. However, for paper-based microfluidic assays to make a measurable impact on public health and environmental safety, these assays need to be manufactured, clinically tested and distributed at scale. At Diagnostics for All, we are bringing one of the first paper-based microfluidic assays to market - a point-of-care test for liver function. Here we detail the challenges of commercializing our liver function test, from initial design choices to reduce evaporation and enhance utility, to manufacturing environment selection and quality management. While paper shows strong potential for low-cost diagnostic tests, careful attention is warranted to ensure product repeatability and reproducibility.

Kink-defects in the crystal structure of cellulose fibrils are readily observable by several imaging techniques including Transmission Electron Microscopy and Atomic Force Microscopy. Such defects affect the mechanical properties of cellulose nanomaterials, and are likely important to the production of cellulose nanocrystals as well as cellulose-derive biofuels because kink-defects are suspected to be locations particularly susceptible to hydrolytic depolymerization. I will present our recent investigations into the formation of kink defects in cellulose nanofibrils by molecular dynamics simulation. We have constructed an array of atomic models of cellulose nanofibrils in the I-Beta crystal polymorph using various fibril cross-section geometries. By bending these fibrils in-silico about different crystallographic orientations over a range of curvature magnitudes, we can predict the propensity for kink defects to form as a function of specific nanostructural configurations. These results provide a more holistic understanding of the relationship between the molecular structure and nanoscale architecture of cellulose nanofibrils and offer fundamental insight that may be leveraged to design cellulosic nanomaterials with enhanced mechanical properties as well as biofuel feedstocks with reduced recalcitrance to catalytic transformation.

Strong synthetic fibers have an important role in a wide range of applications from fiber and textile technology to the design of aircraft and wind turbine blades. However, most of the fibers are derived from fossils and petroleum based sources and are expensive, which further limit their potentials for sustainable development. Cellulose nanofibrils (CNF), derived mainly from wood, is a renewable material with diameter in nanoscale and length in microscale. This material has the prospective of being a building block for future high performance composites due to its impressive mechanical properties (elastic modulus of ~140 GPa). Moreover, cellulose based fibers are based on a natural supramolecular load-carrying element that is biodegradable in nature. However, the mechanical properties obtained till now are far away from the values reported for individual cellulose nanofibrils and it can be conjectured that fibrils have to be aligned and assembled in a controlled manner, in order to make the maximum potential out from these fibrils.
There are many fiber production technologies that are based on wet-spinning processes. In these processes, in general, the alignment of polymers is achieved through elongation in the liquid followed by the solidification to obtain a much stronger fiber. The kinetics of solidification depends largely on the diffusion of the solvents, additives and polymer molecules, which make such systems quite complex and differ from a system to another as a function of the specific chemical, physical and structural features of the used material components. By keeping in mind the facts mentioned above, we have recently demonstrated a continuous and potentially industrially scalable approach for the preparation of strong and stiff-CNF based fibers. We have utilized the benefits of flow focusing approach to align the CNF, present inside the colloidal dispersions with the help of elongational flow followed by the solidification using solidifying agents or molecules. In the current study, we have found out that the strength of fibers is not only dependent on the alignment of CNF but also very much dependent on the types of solidifying agents (which will depend on the diffusion and electrostatic interaction between the molecules of solidifying agent and negatively charged CNF) and their concentrations. We have carried out experiments at different concentrations of solidifying agents, which in turn have exhibited direct observable effect on the strength of the fibers. We have also identified the critical concentrations of different solidifying agents, below which the transition of the colloidal dispersions of CNF from liquid to gel is not occurred thus defining the limitation of this process of spinning fibers.

A new paper-based anti-reflection coating for solar cells is presented showing a large reduction in the reflection over the entire solar spectrum for a wide range of angles. This process is simple and inexpensive, requiring no high temperature or vacuum-based processing, and is made from renewable cellulose fibers.
In order to absorb a significant fraction of the incident solar irradiation, a photovoltaic device must incorporate light management techniques. Mechanisms are needed for both incoupling of the light into the device and for ensuring absorption of light that has entered the cell. Here we describe coatings based on an environmentally friendly paper that act as both an anti-reflection coating and an optical scattering structure, which is able to couple light efficiently into the solar cell. We study the effect of this paper-based coating on planar GaAs and Si solar cells as well as textured Si solar cells [1-2]. We find experimentally that a paper-based anti-reflection coating can improve a commercial GaAs cell by 24% and displays angle and wavelength independent behavior over the entire solar spectrum.
[1] Dongheon Ha, Zhiqiang Fang, Liangbing Hu and Jeremy N. Munday, Adv. Energy Mater., 4: 1301804 (2014): i-Cover
[2] Dongheon Ha, Joseph Murray, Zhiqiang Fang, Liangbing Hu, and Jeremy N. Munday, IEEE J. of PV, 5, 577-583 (2015)

The surge in studying cellulosic nano materials as a potential reinforcing material can be attributed primarily to their high intrinsic mechanical properties and their ‘green&’ character. The latter aspect is beneficial from an environmental perspective and the former from a materials perspective. Cellulose nano fibrils (CNF) have a modulus of 60-100 GPa and strength up to 1-6 GPa - this combined with their low density (1.5 g/cm³) makes them a potential alternative for conventional synthetic fibers. In this work, cellulose nano fibrils (CNF) composites with high loading of CNF were investigated as reinforcement for thermosets.
Several works in literature have dealt with low loadings of nano-fillers and have reported significantly improved mechanical properties with addition of small amounts of CNF (typically up to 20 weight %). However, the improvement is rather limited (and sometimes even negative) when higher loading of CNF is used, probably due to extensive CNF agglomeration. In this work, the focus was to prepare composites with high weight fraction on CNF (up to 60 weight %), while maintaining a good dispersion of CNF in the composites so as to exploit the intrinsic properties of the individual fibrils. Materials were prepared by a prepreg approach, where a random-in-plane network of CNF was formed by filtering a dilute hydro-colloidal suspension of CNF. This CNF network was then impregnated with the resin monomers and cured. Special efforts were made during processing steps to create a structure where the nano fibrils do not aggregate and are present as individual nanofibrils in the final materials. This retained nano-structure was characterized by high resolution microscopy and the structure-property relation established by relating to macro-scale properties such as uniaxial tensile tests, dynamic mechanical properties etc. Role of moisture was studied by characterizing the materials at different relative humidities. The characterization results are discussed in terms of the extent of CNF dispersion, the CNF-polymer interface and the characteristic CNF network behavior. Yield strength, strain hardening, ductility, moisture sensitivity are among the different properties discussed in this work.
High performance biocomposites (Modulus: 9.8 GPa and strength 162 MPa) were prepared and characterized with up to 60 weight % of CNF. The results indicated a favorable CNF/polymer interface and their contribution further elucidated by mechanical characterization at high relative humidity. Major drawbacks of biocomposites include brittle character (low strain to failure) and their high moisture sensitivity. Results from this work show that CNF has a distinct advantage in preserving (and even adding) to the ductility of the composite materials provided that the matrix distribution in the CNF network is controlled efficiently. Moreover, CNF based biocomposites which are insensitive to moisture were successfully prepared in this work.

To date, wearable health monitors for sensing electrical and mechanical bio-signals have matured into viable commercial technologies (e.g. WATCH, Fitbit®, BITalino); however, there has been a significant lag in the development of wearable health monitors with biochemical sensing capabilities. Although biophysical signals correspond well to a person&’s state or activity, they provide less information about the person&’s underlying condition or level of function. Sensing, recording and correlating biochemical signals with biophysical signals would provide a better description of the person&’s physiological status.
A biochemical sensor must extract, separate and condition the sample with a suite of fluid-handling tools prior to transduction with the requisite electronics package. Thepossibility of such sensors will be determined by the material properties of the substrate that interfaces the skin and electronics package. These substrates must provide the following: (1) tough and conformal contact with the skin, and (2) transmission of chemical, mechanical or electronic signal from the skin to the electronics package. Polysaccharide composites are ideal for developing epidermal bioelectronics because they can exhibit a high strength/weight ratio, and their functional surface chemistry provides facile routes to tailor electronic activity and analyte transmission across the biological-electronic interface. Demonstrating a capability to fabricate conformal, biocompatible substrates with tunable chemical permeability and electronic properties is essential for truly integrating biology and electronics across the epidermal surface. Our current research is exploring the chemical, mechanical, and electronic properties of conformal circuit boards to develop nanocellulose substrates that enable epidermal bioelectronics. The molecular weight and crystallinity of the nanocellulose are critical components in determining the resultant chemical and mechanical properties of the material. Side-chain modification of the basic nanocellulose fibrils have provided the requisite toughness to form an epidermal substrate — thin enough to adhere by van der Waals forces but robust enough avoid failure of the electronics package due to mechanical deformation. Novel trace architectures and materials are being explored for biochemical sensing.

Layer-by-layer (LbL) assembly was used to fabricate a synthetic analogue of the color producing multilayered structure commonly found in many biological systems, particularly Coleoptera beetles. The resulting iridescent films comprise multiple LbL-deposited stripes designed to control color appearance through the materials&’ refractive indices and individual multilayer stripe thicknesses. The fabricated systems, referred to as Bragg stacks, exhibited very similar optical behavior to the model and the beetle, selectively reflecting the desired color in a narrow visible light band and displaying iridescent behavior.

Porous gold films offer intriguing material properties for potential applications including gas sensors, fuel cells, supercapacitors, and electrochemical sensors. We describe a simple, ambient vacuum filtration method that provides a novel way to rapidly generate porous gold films without the need for sophisticated instruments or clean-room environments. Using this approach, we fabricate a hybrid gold film composed of gold nanoparticles layered atop a matrix of metallic single-walled carbon nanotubes on a mixed cellulose ester filter paper within 25 minutes. This film exhibits excellent conductivity and highly desirable electrochemical properties that are similar to smooth gold films, but with a porous featured surface that lends itself to sensitive analyte detection. As a demonstration, we used the neurotransmitters dopamine and serotonin as benchmark analytes to demonstrate that our porous hybrid gold films can clearly discriminate the presence of both molecules in a mixture with resolution that greatly exceeds smooth gold slides and electrodeposited, paper-based gold films. Importantly, we believe that this promising new approach could readily be generalized for the highly reproducible fabrication of various other metal films at ambient conditions, and could also be used as a prelude to transferring the resulting film to glass or other flexible substrates.

We developed a reactive ball milling method for fabrication of native cellulose nanofibers. These methods can overcome the disadvantage of the traditional acid hydrolysis method, such as environmental pollution, complex process, low yield and low aspect ratio. We found the solvents with different polarity have different effects on the morphological and the structural changes under the ball-milling. My topic include:
1) Cellulose nanofibers dispersed in organic solvent;
2) Cellulose nanofibers dispersed in aqueous solution;
3) Solvent polarity influence on cellulose nanofibers

Chitin (β-(1-4)-poly-N-acetyl-D-glucosamine) is widely distributed in nature and is the second most abundant polysaccharide after cellulose. It is the major structural component in the exoskeleton of crab and shrimp shells and the cell wall of fungi and yeast. Chitin nanofibers are prepared from the exoskeletons of crabs and prawns by a simple mechanical treatment after the removal of proteins and minerals. The obtained nanofibers have fine nanofiber networks with a uniform width of approximately 10 nm and a high aspect ratio. The method used for chitin-nanofiber isolation is also successfully applied to the cell walls of mushrooms. A grinder and a high pressure water jet system are used in the mechanical treatment to convert chitin to nanofibers. Mechanical treatment under acidic conditions is the key to facilitate fibrillation. At pH 3-4, the cationization of amino groups on the fiber surface assists nano-fibrillation by electrostatic repulsive force. Optically transparent chitin nanofiber composites are prepared with 11 different types of acrylic resins. Due to the nano-sized structure, all of the composites are highly transparent. Chitin nanofibers significantly increase the Young&’s moduli and the tensile strengths and decrease the thermal expansion of all acrylic resins due to the reinforcement effect of chitin nanofibers. Moerover, chitin nanofibers have powerful biological activities. For instance, (1) they have anti-inflammatory actions via the suppression of NF-κB and MCP-1 activation, and they suppress fibrosis in an acute ulcerative colitis mouse model. (2) Application of chitin nanofibers to skin improves the epithelial granular layer and increases granular density, resulting in a lower production of TGF-β. (3) The nanofibers can help in healing wounds. The nanofibers induce re-epithelium and proliferation of fibroblasts and collagen tissue. We expect that nano-chitin with the above-mentioned properties will have increased applicability as a novel biomaterial.

A long-standing challenge in material design is to overcome the conflict between strength and toughness, as they are generally mutually exclusive. To address this challenge, we rationally design cellulose-based nanopaper and investigate the dependence of their mechanical properties on constituent cellulose fiber size (PNAS, 2015). Surprisingly, we find that both the strength and toughness of the nanopaper increase simultaneously (40 and 130 times, respectively) as the average diameter of constituent cellulose fibers decreases from 27 micrometers to 11 nanometers, suggesting the promising potential toward an anomalous but highly desirable scaling law: The smaller, the stronger AND the tougher. There are abundant opportunities to utilize the fundamental bottom-up strategy to design a novel class of functional materials that are both strong and tough.

Cellulose Nanocrystals (CNCs) are whisker shaped nanocellulose materials (3-5 nm wide, 50-500 nm in length). Their excellent mechanical, optical properties and biocompatibility have lead a wide range of potential applications including films, substrates for electronics, reinforcing fillers for polymers, biomedical implants and much more. However, one of the challenges of utilizing CNCs is their dispersibility and interfacial compatibility in hydrophobic polymer matrices. In this study, we focused on increasing the hydrophobicity of CNCs via surface esterification reactions. Saturated and unsaturated fatty acids with different hydrocarbon length were used to tune the hydrophobicity of CNCs. The esterification efficiency was evaluated using Fourier transform infrared spectroscopy (FTIR) and ¹³C solid state NMR. The morphology and crystallinity of the modified CNCs were examined by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). By evaluating an array of esterification methods, we were able to discover the best method to attach fatty acids with a certain length of hydrocarbons. Our results could provide other researchers with a guideline on choosing the most efficient method to modify CNCs. In addition, a new method to disperse grafted CNCs in hydrophobic solvents was proposed. Polymer composites with high CNC content were fabricated using solvent casting method. Mechanical and thermal properties of composite films were evaluated with respect to CNC content and the type of moieties grafted on CNCs.

Colloidal dispersions of shape anisotropic particles with high aspect ratios display interesting phase behavior and mechanical properties that are being explored for many industrial applications. Cellulose microfibrils (CMFs) is unique fiber-like nanostructured natural material built of linear aggregates of cellulose molecules. We prepare CMF dispersions from a commercial Nata de Coco source using an ultra-high-energy mechanical deagglomeration process that is able to disperse the microfibrils from the pellicle, in which they are naturally organized in an irregular network. The resulting particles are flexible highly shape-anisotropic with an average length of several microns by electron microscopy and have an average width of 60 nm. Because of the strong attraction between the CMFs, the dispersions remained highly heterogeneous, consisting of fiber bundles, flocs, and voids spanning tens to hundreds of micrometers depending on concentration. The MFC dispersions undergo gel-sol and direct gel-to-colloidal liquid crystalline structure transitions. This is achieved in the presence of an adsorbing polymer sodium carboxymethyl cellulose (CMC). At high CMC content adsorption of the polymer leads to a significant increase in the zeta-potential. The resulting apparent phase diagram shows transitions from aggregates to single microfibril dispersions with increasing CMC/BC weight ratio at low CMF concentrations. At higher concentrations, liquid crystalline ordering was observed and the micro-structure becomes more homogeneous with increasing CMC content. The observed liquid crystalline ordering was found to be reminiscent of nematic gels.

The combination of high strength with elasticity and high toughness in flexible nanocomposites is a vital requirement for the development of advanced engineering materials. However, achieving such a combination is severely restricted by mutually exclusive reinforcing and deformation mechanisms. Most of the engineering materials lie close to the axes of the Ashby plot, which is conventionally referred to as “The Banana Rule,” due to the competition between the reinforcement of the toughness and the Young&’s modulus. Here, we demonstrate exceptionally strong and tough carbon-carbon nanocomposites composed of a cellulose nanocrystal “haystack” network encapsulated into flexible graphene oxide monolayer sheets. The design combines two classical reinforcing components—stiff, high aspect ratio cellulose nanocrystals, and strong, flexible graphene oxide sheets-“glued” together by a polymeric binder. The novel combination of the 1D and 2D nanofillers to form interpenetrating 3D networks is unprecedented and demonstrated to be record-breaking in terms of mechanical properties. These nanomaterials show extremely high ultimate stress of 490 MPa and toughness of 3.9 MJ m^-3 with the Young&’s modulus of 60 GPa. Moreover, an electrochemical post-treatment of the graphene oxide component further increases the elastic moduli of nanocomposites to a record high value of 170 GPa. These mechanical properties with uniquely balanced strength and toughness, benefited from the effective synergistic reinforcement by both the 1D and 2D nanofillers, are by far the highest known for laminated cellulose-based nanomaterials.