Comparison of water absorption and mechanical behaviors of polypropene composites filled with rice husks ash

Composite materials were obtained by filling polypropene with raw and thermally treated rice husks at filler contents from 1 to 20%. The physicochemical properties were determined. A slight increase was observed in the tensile strength of the composites based on white rice husk ash (WRHA) and aerosil (AR) at degree of filling up to 3%. Young's modulus increased and the elongation at break and energy to break point showed a tendency to decrease for all the composites studied. The thermodynamics and kinetics of water absorption at immersion were studied in the temperature interval 25-90 degrees C. The values of the changes in standard free energy, Delta G degrees, enthalpy, Delta H degrees, and entropy, Delta S degrees of adsorption were calculated. Water absorption was found to be thermodynamically difficult due to the diffusion mechanism of the process and it was accompanied by a decrease in the values of Delta H degrees and Delta S degrees with an increase in fillers contents. The effects of the amount of absorbed water, temperature, and treatment time on the composites tensile properties were estimated.