Hygrothermal Effects on the Tensile Mechanical Properties of Hemp and Coir Fibers

摘要

Plant fibers are becoming more interesting alternatives for glass fiber or synthetic fibers as reinforcement of polymeric based composites, thanks to their renewable origin, relative high specific strength and modulus, light weight and low price [1,2,3]. The objective of this research work was to investigate the effect of the temperature and the humidity on the tensile strength and modulus of elasticity of hemp and coir fibers. Firstly, the glass transition temperature and morphology of these fibers were examined [4]. Secondly, adsorption of humidity into these fibers from ambient air [5] and adsorption of water [6] into these fibers in immersion were studied. Finally, tensile tests of these fibers were conducted in various temperature and humidity conditions [4,7].It was found that, in ambient air (0% < RH < 80%) the moisture content of these fibers decreased with the increase of temperature conformed to the GAB model suggesting a multilayer absorption mechanism. On the contrary, for the fibers immersed in water, the moisture content of the fibers increased with the increase of temperature. The activation of temperature on the diffusion of the water into theses fibers by micro-pores and lumens jointly with the lack of possibility for the imprisoned water to evaporate might be the cause of this effect.The experimental results suggested that temperature and humidity could individually reduce the tensile strength and the modulus of elasticity of these fibers. Their interaction caused even a more harmful effect. Semi empirical and neural networks were used to predict the hygro-thermal effects on the tensile properties of these fibers [7].