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.
Depleting fossil fuels and environmental concerns have emphasized the necessity for more sustainable resources for high-performance structural applications. High strength, lightweight, and abundant bioresources make cellulose long filaments (CLFs) an excellent reinforcement for high-performance structural applications. At the same time, high strength and thermally stable vanillin epoxy can efficiently replace petroleum-based epoxies. This study introduces the combination of unidirectional CLFs and vanillin epoxy by using vacuum-assisted resin transfer molding for novel biobased composites. Owing to the low density of CLFs, the proposed composite material possessed very low density, high specific flexural strength, and excellent thermal and hydrophobic properties. The FTIR analysis demonstrated good interfacial adhesion between CLFs and vanillin epoxy. The sustainable resources, hydrophobicity, and good mechanical performance make unidirectional CLFs reinforced Vanillin epoxy composite an excellent candidate for high-performance structural applications.
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.
Polycaprolactone (PCL) is a semicrystalline thermoplastic polymer well-known as a nontoxic and biodegradable material. Due to this nature, PCL has been studied for drug delivery and a bioscaffold in tissue engineering. However, it has incomplete properties as the structural materials such as relatively low mechanical properties, low surface energy, and long degradation rates. Thus, this study aims to complement the previous shortcomings and present the possibility of a more advanced biomaterial by forming nanocomposites with cellulose nanocrystal (CNC), one of the abundant natural polymers with high specific modulus and strength, environmentally-friendliness, and nontoxic. Bulk materials with various concentrations of CNC in PCL matrix were fabricated, and a three-point bending test was conducted. The measured bending modulus was compared with the estimated values based on the rule of mixtures of the nanocomposite and surface morphology was investigated by scanning electron microscopy.
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.
Cellulose nanofibers (CNFs) have attracted attention in a diverse area of applications due to their amazing mechanical properties and lightweight. Recent advances in enhancing the mechanical performance of nanocellulose filaments and films have reported efforts to align the individual cellulose nanofibers using different methods. Among them, the most recent being the use of electrical fields experimentally. It is important to investigate at the molecular level if the application of low electric fields on CNF can induce alignment and what effects these electric fields have on the molecular structure of the CNF. This study reports a molecular dynamics (MD) study of CNF model in a varying electric field (EF) strengths and direction. The MD simulations were conducted in GROningen Machine for Chemical Simulations (GROMACS) and the All-Atom Optimized Potential for Liquid Simulations (OPLS-AA) force field was used. Induced electric field alignment was investigated in terms of how quickly the alignment begins, how long it takes for complete alignment, and the ability to maintain any achieved alignment at different electric fields. To understand the electric field-induced structural changes, the hydrogen bonding network, hydrogen bond length, radius of gyration, and deviation from the original model are critically analyzed. The results show that CNF can be successfully aligned in low electric fields without compromising its molecular structure.
Cellulose, a natural fiber, has been employed vastly for structural components due to its high mechanical strength and young’s modulus. The hydrophilic hydroxyl groups on the surface of cellulose nanofiber enables formation of cellulose-based nanocomposites with high mechanical properties which has been widely studied. The interfacial bonding of the composites between cellulose and other polymers could be improved further by surface modification of cellulose. Aiming to improve the mechanical properties of cellulose nanofiber and its composites as well as functional properties, a bio-inspired approach to coating polydopamine onto cellulose nanofiber was developed. Due to strong adhesion ability and self-polymerization of dopamine in tris buffer, polydopamine could be easily coated on cellulose nanofiber under mild conditions. Prefabricated cellulose nanofiber film and filament were modified by coating with polydopamine. FTIR, XPS, SEM confirmed a homogeneous polydopamine coating on cellulose nanofiber film and filament. The mechanical strength and stiffness of the cellulose-polydopamine fiber and the respective composite materials were investigated. The photostability, antibacterial, and electrical properties of the polydopamine-cellulose nanofiber were also studied.
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.
A continuous fabrication process for high-strength nanocellulose based long-fiber (NLF) has been researched as a key process to fabricate natural fiber-reinforced polymer composites with high specific modulus and strength. The process was custom-designed by utilizing the wet spinning and stretching methods with dry process. First, nanocellulose was isolated from wood pulp by using a combination of chemical and physical methods. Apparatus for the process was self-produced and the process parameters such as the speed, position, number of wheels were experimentally investigated. Among the various designs, two specific setups were chosen and the speed of the wheels was optimized. The success of the process was determined by the sustainability of the setups for more than 30 min. The results were evaluated by using the tensile test and scanning electron microscope.
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