The effect of moisture on the modulus of elasticity of several representative individual cellulosic fibers

Understanding the effect of moisture absorption on the mechanical properties of fibers at cellular level is key important to the application of natural fibers in reinforcement composites. This study focused on the variation of the modulus of elasticity (MOE) of several representative individual cellulosic fibers (bamboo, Chinese fir, ramie and Kevlar) under different relative humidity condition (RH: 40 %, 70 %, 90 %), dedicating for the screening of appropriate candidates of fibers used in outdoors. A special custom-designed microtester (SF-I) with the micro humidity control box was devised in order to observe stress-strain behavior of fibers under different humidity condition. Among the fibers investigated, ramie fiber presented the most sensitive to the humidity, Chinese fir and bamboo fiber was followed, and Kevlar fiber showed the bluntest to moisture variation since it belonged to artificial fiber. Compared with the fibers tested at RH of 40 %, the MOE of Bamboo, Chinese fir, Ramie fibers increased at RH 70 %, and decreased at RH 90 %, respectively. The optimal tensile properties were observed for the bamboo fiber among tested single plant fibers, with a MOE value of 26.3-30.7 GPa, and RH of 70-80 % was deduced for obtaining the highest value of MOE under various humidity testing condition.