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This paper reports a bio-based vanillin-derived epoxy (VDE) resin for bio-based natural fiber-reinforced composites. VDE monomer was synthesized, and curing agents, namely, 4,4´-diaminodiphenyl methane (DDM) and isophorone diamine, were used. The prepared VDE resins with various curing parameters were characterized using FTIR, NMR, tensile test, bending test and water contact angle. Further, the interfacial adhesion feasibility of VDE resins on cellulose film was studied through the single-lap shear joint examination and compared with a commercial epoxy, DGEBA. The VDE-DDM resin exhibited excellent interfacial adhesion with cellulose than VDE-IPDA and DGEBA-DDM resins. The cured VDE-DDM thermoset showed a tensile strength of 86.0 ± 6.5 MPa, thermal stability of 241.0 °C at T

Over the past decades, glass has been utilized in optoelectronic devices. However, glass has many limitations impeding its use including high coefficient of thermal expansion, glare and shadowing effects. Moreover, various complex nanostructures and inorganic nanoparticles are required to tune the optical properties of glass. For green optoelectronics, cellulose, the most ubiquitous and abundant polymer on planet, is the perfect candidate that could substitute glass. Herein, we modulate light propagation through a random network of cellulose fibers by dramatically tuning the optical properties of cellulose for different applications. We obtained a nano-paper with a high total transmittance >90% and an ultralow haze>0.5% which is suitable for high definition displays. By modifying the morphology of the same cellulose fibers, highly transparent and hazy cellulose film suitable for antiglare windows and solar substrates with a total transmittance >85% and haze >80% is also obtained. These findings offer new possibilities of using cellulose nanofiber to tune the optical properties of glass and other optical materials through blending or coating rather than using toxic nanoparticles.

The development of high-strength nanocellulose long-fiber (CLF) has been required for future composite faced with environmental concerns as well as energy efficiency and biocompatibility towards the high value-added industry. To meet the demand, our research group has studying not only the top-down process, such as the isolation and characterization of nanocellulose from wood pulp, also the bottom-up process which is a continuous fabrication of CLF based on the nanocelluloses. Moreover, high-strength CLF was made via nanocellulose alignment technique by wet spinning and physical stretching. However, the specific modulus and specific strength of currently available CLFs are away behind the technical requirement. Thus, to enhance the mechanical properties, a chemical approach based on increased intermolecular binding through cross-linking induction is attempted with the existing continuous fabrication process. The process parameters and chemical reactions are experimentally investigated, and their effects are evaluated by chemical and mechanical analysis.

In this study, we developed a new type of cross-linked polyvinyl alcohol (PVA)-lignin i.e., esterified PVA-CA-lignin resin by using citric acid (CA) cross-linker. Firstly, hydrogen bonded PVA-CA-lignin resin was prepared by the mixing of PVA, lignin and CA and then esterification of hydrogen bonded PVA-CA-lignin resin was carried out at 180oC. Subsequently, the esterification of PVA-CA-lignin resin was confirmed by FTIR and the morphology of the esterified PVA-CA-lignin resin was examined with the help of scanning electron microscopy.Finally, the effects of CA cross-linker on the properties of esterified PVA-CA-lignin resin, especially the tensile strength and thermal stability were evaluated and analyzed. The results demonstrated that CA was cross-linked in PVA-lignin resin matrix and the content of CAenhances the performance of esterified PVA-CA-lignin resin significantly. The esterified PVA-CA-lignin resin is applicable for the natural fibre reinforced composites.

In the present investigation, we prepared cellulose nanocrystal (CNC)-reinforced polyvinyl alcohol-cellulose (PVA-Cell) physical hydrogels using a simple blending method for actuator application. The prepared hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and the surface and cross-section were studied by scanning electron microscopy. CNCs were well dispersed in the PVA-Cell hydrogel. In the preparation process, surface hydroxyl groups of the CNC and PVA-Cell matrix hydroxyl groups were interacted to produce uniform dispersion of CNCs in the hydrogels. Swelling behavior and compression studies revealed that the increase of the CNCs reinforced the crosslinking. The actuation test of the prepared hydrogels showed that the displacement linearly increased with the voltage, and the immense output displacement was observed at low CNC concentration. The prepared hydrogels are applicable for soft robot actuators and active lens.

This study presents the piezoelectric property test of ultrathin cellulose nanofiber (CNF) film and calculate the piezoelectric coefficient by using piezoresponse force microscopy (PFM). Cellulose is known to have piezoelectric properties. However, its measurement is not easy. The mechanism of PFM is based on detecting the piezoresponse induced by the inverse piezoelectric effect from target sample. We applied the PFM to characterize the piezoelectric properties of ultrathin CNF film which is fabricated by microfabrication method under clean room condition. For characterizing the piezoelectric properties of ultrathin CNF film, the PFM standard sample periodically poled lithium niobite (PPLN) sample was utilized as reference sample. By applying AC voltages through conductive AFM probe to ultrathin CNF film surface, the amplitude data of ultrathin CNF film is recorded and used to calculate the piezoelectric coefficient. Corona poling, electrical in-plane alignment and high magnetic field alignment methods are introduced to align the ultrathin CNF film. According to the different alignment methods, the aligned ultrathin CNF films show different piezoelectric behavior.

This paper reports an ultra-strong, tough and bio-based polyvinyl alcohol-citric acid-lignin resin applicable for all-green fiber-reinforced polymer composites for the first time. Through a facile solution mixing approach, the resin was optimized by varying the cross-linker - citric acid - followed by esterification at 180°C. The treatment dramatically enhanced the tensile strength (269.8%), Young's modulus (273.5%), toughness (1222.8%), and hydrophobicity (48.5%). Moreover, the optimized resin showed an excellent adhesion strength (31.92 MPa) to cellulose. As proof of concept, the wet-spun nanocellulose filament was weaved into mats and utilized in composite fabrication with the resin via hand layup and hot press. The lightweight (1.253±0.0.0613 gcm-3) yet strong structural biocomposite showed a record high bending strength of 363.42 MPa and flexural modulus of 39.89 GPa. Insights from this work offer a promising new avenue for utilizing bio-based resins and nanocellulose to engineer environment-friendly and robust structural composites.

Nanocellulose (NC) has been spotlighted as a new building block of future materials since it has many advantages, such as being lightweight and environment-friendly and having high mechanical properties and heat resistance. However, the use of NC requires an upscale manufacturing process to maintain its advantageous properties. Herein, the process of assembling NC into a macro-scale bulk material was developed through a combination of steam treatment and hot press molding. The steam treatment was applied to an NC paste to energize the hydroxyl groups in the cellulose, followed by two stages of hot press molding, which helped in the self-assembly of NC without adhesives. Cellulose nanocrystals were used as the NC, and circular disk shape specimens were prepared. The mechanical properties of the prepared bulk material were higher than typical engineering plastics. In addition, an end mill machining test of the NC bulk material showed its machinability. This paper showed the processing feasibility of NC bulk material, which can substitute plastics.

Transparent-wood (TW) is an emerging research topic that can be applied to biobased products. However, it is necessary to fill pores in TW with natural substances to prepare all-biobased TW. This paper reports an all-biobased TW by infiltrating cellulose nanofiber (CNF) and chitosan (CTS) suspensions into the bleached wood. CNF was isolated by combining the chemical and physical methods, and CTS was dissolved in acetic acid, and they were infiltrated into the pores of the bleached Fir veneer wood using a vacuum jar. The CNF and chitosan effects on the mechanical properties of the TW were studied, and the morphologies, crystallinity index, water contact angle, antioxidant, thermal degradation, and UV-shielding properties were investigated. The prepared TW showed 80 % total transmittance and 30–60 % haze, suitable for solar cell application. The all-biobased TW showed good thermal stability up to 315 °C and excellent UV shielding property for UV-B and UV-C. The antioxidant property of the CTS-TW significantly increased as compared to the original wood. The CNF-TW showed considerable tensile strength and yield strength of more than 200 % improved from the original wood. The potential for environment-friendly packaging applications was demonstrated by making a bag, medicine packaging, and straw for a drink.

This paper reports an aligned cellulose nanofiber (CNF) composite that exhibits flexibility, transparency, and improved mechanical and piezoelectric properties. The aligned CNF composite was made by electrospinning CNF-polyvinyl alcohol (PVA) blend, followed by casting CNF suspension. The CNF-PVA blend was electrospun to form a CNF-PVA fiber mat, and an optimum CNF-PVA ratio and the spinning parameters were determined by examining CNF alignment. Then, the electrospun CNF-PVA mat was coated with CNF suspension to fabricate the aligned CNF composite. The aligned CNF composite was transparent (85.3%) and had a higher orientation index (α = 0.54) than a neat CNF film. Besides, the composite showed improved mechanical properties. In consequence of CNF alignment, the piezoelectric charge constant, d 31 of the composite was 14.5 pC/N, which was more than double of the neat CNF film. With this piezoelectric behavior, the composite was applied to a vibration energy harvester (VEH), and it showed an output power of 5.43 nW. All about the piezoelectric and mechanical property improvement were explained in this paper. The aligned CNF composite is flexible, lightweight, environment-friendly, and low-cost.