Anisotropic Thermal Expansion of Transparent Cellulose Nanopapers
Takayuki Hirano, Kana Mitsuzawa, Shun Ishioka, Kazuho Daicho, Hiroto Soeta, Mengchen Zhao, Masaaki Takeda, Yoshihiro Takai, Shuji Fujisawa, Tsuguyuki Saito
Abstract
We report the anisotropic thermal expansion of a transparent nanopaper structure comprising cellulose nanofibers (CNFs). The coefficient of thermal expansion (CTE) of the nanopaper in the out-of-plane direction was 44.6 ppm/°C in the temperature range of 25-100°C, which is approximately five times larger than its CTE in the in-plane direction in the same temperature range (8.3 ppm/°C). Such a strong anisotropy in thermal expansion is mainly attributable to the anisotropic CTE values of single CNFs in the fiber axis and cross-sectional directions. We observed anisotropic thermal expansion even in a bioplastic composite containing only 2.5% w/w CNFs.