Progress on Materials Reinforcement using Mechanically Defibrillated Cellulose Nanofibers

Abstract

Cellulose nanofibers (CNFs) are highly crystalline, fibrous materials with a high aspect ratio of long cellulose molecules linked together with strong hydrogen bonds. These long cellulose molecules are incorporated into hemicellulose and lignin, the cell walls of higher plants. The modulus of elasticity of CNF remains constant between −200 °C and +200 °C. However, the linear coefficient of thermal expansion of cellulose fibers was 0.17 ppm/K, which is comparable to that of quartz glass. Further, CNFs have a thermal conductivity in the same order of magnitude as glass. Therefore, they are promising next-generation fiber owing to the excellent mechanical and thermal properties, sustainability, and biodegradability of CNF. Most studies on using CNFs to increase strength have focused on polymer matrix composites, particularly biodegradable polymers. However, it is difficult to increase the strength of materials using CNFs due to the agglomeration of CNFs. Compared to other composite materials, the uniform dispersion of nanosized CNFs is crucial. This article reports that CNFs may behave not as reinforcing fibers but as cross-linking agents to strengthen the polymer when the amount of CNFs is very small in polymer matrix composites, and the addition of CNFs is also effective in strengthening silk yarn and Ti. The mechanical properties of the ceramic green bodies can be increased using CNFs as an auxiliary agent in ceramic slurry. Moreover, the fabrication of composite materials using CNFs is essential for expanding the CNFs applications.