Radiation effect on the thermal conductivity and diffusivity of ramie fibers in a range of low temperatures by γ rays

Abstract To understand the influence on the thermal conductivity by the length of the molecular chain in the polymer fiber, the thermal conductivity and thermal diffusivity of ramie fibers and those irradiated by γ rays, which induced molecular chain scission of cellulose, were investigated in a range of low temperatures. The degrees of polymerization, crystallinities, and orientation angles of ramie fibers and those irradiated by γ rays (γ‐ray treatment) were measured by the solution viscosity method, solid‐state NMR, and X‐ray diffraction. Only the degree of polymerization decreased with the γ‐ray treatment, and the crystallinities and orientation angles were almost independent of the γ‐ray treatment. The thermal conductivities of the ramie fibers with and without γ‐ray treatments decreased with decreasing temperature. The thermal diffusivities of the ramie fibers and those irradiated by γ rays were almost constant from 250 to 100 K, increased slightly with the temperature decreasing from 100 to 50 K, and increased rapidly with the temperature decreasing below 50 K. The thermal conductivity and thermal diffusivity of the ramie fibers decreased with the γ‐ray treatment. The mean free path of the phonon in the ramie fibers was reduced by the γ‐ray treatment. This decrease of the thermal diffusivity and thermal conductivity was explained by the reduction of the mean free path of the phonon by molecular chain scission with γ rays. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 5007–5018, 2006