Moisture Diffusion in Natural Rubber/Bentonite Nanocomposites: Effect of Clay Filler Treatments

Abstract

This study investigated the effects of clay filler treatments on moisture diffusion in natural rubber (NR)/bentonite nanocomposites. Four types of clay filler treatments were considered: sodium activation using sodium chloride (NaCl), ion exchange using hexadecyldimethylamine (HDA) chloride salt, modification using coco diethanolamide (CDEA), and wet grinding using ethanol as medium. A 24full factorial design of experiment (DOE) was utilized during clay filler treatments. The measured vulcanization characteristics of rubber specimens show the NR nanocomposites to be stiffer than unfilled NR, with very small differences in scorch and curing times. The moisture uptake of rubber specimens at 80°C is linear with square root of immersion time showing Fickian behavior. The rate of moisture uptake (slope of moisture uptake versus square root time) was measured. Determination of factor effects and analysis of variance show all clay filler treatments except for wet grinding significantly increase the rate of moisture uptake of NR nanocomposites. When compared to unfilled NR, only wet grinding of clay is found effective in lowering moisture diffusion.