NANOFIBER SHEET, PROCESS FOR PRODUCING THE SAME, AND FIBER-REINFORCED COMPOSITE MATERIAL

摘要

A nanofiber sheet which comprises cellulose fibers sufficiently reduced in size by fibrillation and having a high crystallinity and which can realize a fiber-reinforced composite material which is highly transparent, has a high modulus and a low coefficient of linear thermal expansion, has high heat resistance, and is high in flatness and smoothness. This nanofiber sheet comprises crystalline cellulose as the main component and has a lignin content of from 10 ppm to 10 wt.%. The nanofiber sheet is impregnated with tricyclodecane dimethacrylate and then irradiated with UV at 20 J/cm2 to cure the dimethacrylate and this sheet is heat-treated in vacuum at 160°C for 2 hours to obtain a fiber/resin composite material. When this composite material has a cured tricyclodecane dimethacrylate content of 60 wt.% and a nanofiber content of 40 wt.%, it satisfies the following properties i) to iii). i) The parallel-light transmittance in a 100-mum thickness for light having a wavelength of 600 nm is 70% or higher. ii) The Young's modulus is 5.0 GPa or higher. iii) The coefficient of linear thermal expansion is 20 ppm/K or lower.