However, such a process is highly time and energy consuming. Homogeneous CNF/polymer composites can be prepared by drying a mixture of a plastic and CNF dispersions in organic solvents. Moreover, tailoring the chemical structure of the carboxy groups effectively enables the dispersion of CNFs in various organic solvents. The increased osmotic pressure between the fibrils and mild mechanical treatment in water allow the preparation of CNFs with nanosized widths and good colloidal stability in water. The oxidation selectively introduces carboxylate groups onto the surface of cellulose microfibrils. TEMPO-mediated oxidation is a chemical reaction that enables selective conversion of primary hydroxy groups into carboxylate groups in water. To date, we have sought to develop homogeneously mixed CNF/polymer composites using a CNF prepared through chemical pretreatment termed 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. Therefore, the composition difficulty poses the biggest challenge for the production of such materials. However, obtaining a homogenous composition of CNFs and commodity plastics has been difficult due to the high interfacial energy. To fully elicit the reinforcing effect of CNFs, CNFs must be homogenously dispersed in a composite material. Taking advantage of these characteristics of CNFs, ongoing research has been extensively focused on utilizing them as a reinforcing material for plastics since the mid-1990s. They have been demonstrated to have excellent mechanical and thermomechanical properties, with high strength (2‒6 GPa), high elastic moduli (130‒150 GPa), and low thermal expansion coefficients (4‒6 ppm K −1). In particular, wood-derived CNFs have a characteristic shape and are ~3 nm in width and several micrometers in length. In recent years, cellulose nanofibers (CNFs) have been used as a natural carbon-neutral reinforcing material. However, as the energy demand for the production and discarding of these reinforcing materials is high, plastic reinforcement using environmentally friendly materials has become a priority toward the implementation of a low-carbon society. Common reinforcing materials include glass and carbon fibers hence, composite materials acquire the strength and thermal dimensional stability that plastics cannot attain on their own. Reinforcing materials are often added to these plastics to improve their mechanical properties. Plastics are used for multiple purposes as parts of automobiles, home electrical appliances, food packaging materials, and medical equipment and thus constitute essential materials in our lives.
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