Nanocellulose has aroused extensive interests in materials engineering and design owing to its great potential in fabricating robust architectures for diverse applications and functionalities. On the other hand, the sensitivity of cellulose to water results in the deterioration of strength, durability, and functionality thus unsuitable for advanced applications. To address this challenge, we present an efficient, sustainable and scalable strategy to convert cellulose into an advanced biomaterial by integration with a green hydrogen bonded slurry. The resultant cellulose hybrid slurry was cast and cured to fabricate strong and tough biofilms. The hydrogen bonded slurry was revealed to promote tight rapping of the nanofibers resulting to a compact structure with an enhanced performance. The dry and wet tensile characteristics of the cellulose hybrid biofilms (375.1 MPa and 160.0 MPa) were much improved compared to the neat cellulose film. The hybrid biofilms also possess excellent UV shielding characteristics, hydrophobicity and a unique antioxidant activity. Of particular interest, the hybrid biofilms can be readily recycled or biodegraded at end of life, hence promoting a circular
Disposable plastic straws negatively impact the environment and human health while their alternatives such as paper straws are not satisfactory owing to limited mechanical performance and poor user experience. In this report, all-natural and biocompatible straws are fabricated from starch and polyvinyl alcohol slurries respectively. The functionality of the slurries is enhanced by integrating economical resources such as kraft lignin and citric acid. By doctor blading of the slurries followed by subsequent heat treatment, self-bonding straws are fabricated without the use of binders or adhesives. Through heat treatment, our straws achieve excellent strength than paper-based straws. Owing to the strong ester bond network, the straws display superior performance that surpasses commercial plastic counterparts thus meeting the requirements for practical applications. Specifically, the straws are hydro-stable for over 24 hrs. and display a desirable closed-loop degradability aspect making our straws eco-friendly substitutes for synthetic plastic straws.
Continuous production of cost-effective and high-strength nanocellulose long filaments (NCLFs) is critical in the field of natural fiber-reinforced polymer composites (NFRPCs).Herein, we present an integrated wet-spinning system that incorporates a few previously researched filament production processes with the goal of mass fabrication of strong and tough continuous NCLFs.The spinning speed, bobbin winder speed, and NCLF drying conditions were experimentally optimized. The efficacy of the designed wet-spinning system was evaluated by its sustainability in delivering continuous NCLFs for an hour or longer without any interruptions.The two significant parameters considered for calibrating the integrated wet-spinning system are the mechanical characteristics and morphology of the fabricated NCLFs.The study has also incorporated external alignment techniques such as electric field and mechanical stretching of NCLFs to demonstrate the versatility of the designed integrated spinning system.
Developing robust bio-based composites against various kinds of petroleum-derived materials has necessitated the continuous exploration and utilization of natural fiber for high-performance applications, especially those derived from bio-sources. In this scenario, cellulose nanofiber (CNF) can be a vital alternative to replace synthetic fiber commonly used as CNF-reinforced composites. In this regard, we prepared lignin-derived vanillin epoxy resin through the epoxidation of vanillin, and it was cured with a 4,4’-diamino diphenyl methane hardener. Furthermore, the solvent-epoxy mixture was impregnated with CNF film to get the CNF-reinforced vanillin epoxy composites. To confirm the compatibility of epoxy with CNF, we performed FTIR spectroscopy. Further, the bending strength of nanocomposites was evaluated. This research could lead to the manufacture of high-performance and environmentally friendly natural fiber composites that can be potentially useable in numerous applications.
Strong and tough cellulose nanofibers (CNF) are in high demand in the field of polymer composites. Recently, researchers have successfully employed different alignment techniques such as wet spinning, stretching, electric field, and magnetic field alignment to improve the mechanical properties of CNFs. However, none of these techniques were capable to achieve the goal of tensile strength above 600MPa. Herein, we utilize a high-performance bio-based hydrogen-bonded polyvinyl alcohol-citric acid-lignin (H-PCL) resin synthesized by our research group to functionalize CNFs via coating and blending techniques followed by post-heat treatment at 180℃ for esterification of resin. The esterified poly (vinyl alcohol)-citric acid-lignin resin (E-PCL)-CNF fibers were characterized and discovered to exhibit a dramatic increase in mechanical properties. Moreover, E-PCL/CNF fibers also possess high hydrophobicity and high thermal stability. These exceptional and impressive properties of E-PCL/CNF make them an ideal candidate for all-green fiber-reinforced polymer composites and in other structural applications.
The quest for bioderived resins and eco-friendly lightweight materials having remarkable mechanical performance is ubiquitous in scientific reports. In this work, we report a strong and tough biobased resin of esterified Polyvinyl alcohol-Citric acid-Lignin (E-PCL) suitable for nanocellulose fiber-reinforced polymer composites. The mechanical properties of the resin were optimized by varying the volumetric concentration of citric acid and subsequently esterified at 180°C. At 30% citric acid content, the esterified resin showed dramatic improvement in tensile strength (269.8%), toughness (1222.8%), Elastic modulus (273.5%), and hydrophobicity (48.5%). The adhesion strength of the resin to cellulose film was 31.92 MPa making it appropriate for green cellulose-based fiber-reinforced polymer composites. To validate our concept, three wet-spun nanocellulose filament was knit into mats on a loom and applied in composite fabrication through hand-layup and hot press. The lightweight yet strong and stiff structural composite displayed a record high flexural strength of 363.42 MPa and flexural modulus of 39.89 GPa with a water contact angle of 93.4°. Insights from this report offer a promising platform for utilizing environment-friendly resins and nanocellulose to engineer lightweight and robust structural composites for automotive, aerospace, and structural applications.
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.
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.
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.
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.
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