Effect of Alkali Treatment on the Tensile and Impact Properties of Ramie Plied Yarn-Reinforced Green Composites

Effect of alkali-treatment on the mechanical properties of a ramie plied yarn reinforced green composite was investigated, using NaOH solutions with various concentrations. The composites reinforced with NaOH-treated yarns decrease in strength and Young's modulus if the concentration of the solution is equal to 12wt% or more. It was proved from X-ray diffraction analysis that these decreases were closely related with a decrease in the index of crystallinity and a crystalline transformation from cellulose I to cellulose II of the yarns. On the other hand, fracture strain of the NaOH-treated yarn composites increased largely, as compared to that of the untreated yarn composite. In this study, furthermore, the effect of liquid ammonia (NH3) treatment on the mechanical properties of the green composite was investigated. The results showed that the NH3-treated yarn composites showed higher tensile strength and fracture strain, as compared to those of the untreated yarn composites, but their Young's modulus decreased. It was considered that such changes were concerned to a change in the yarn structure, as well as a crystalline transformation from cellulose I to cellulose III and the less index of crystallinity.