Influence of silica and black rice husk ash fillers on the diffusivity and solubility of gases in silicone rubbers

The preparation of elastomeric compositions based on poly(methylvinyl siloxane) using silica and rice husk ash as fillers is reported. Permeation of oxygen, nitrogen, carbon dioxide and methane across the compositions was measured in the temperature interval 30-60degrees C under upstream pressures lying in the range 15-76 cm Hg. Permeation and diffusion coefficients were independent on the upstream pressure but both parameters were thermal activated processes described by the Arrhenius equation. It was found that the activation energy associated with the diffusion process is larger in the filled than in the unfilled rubbers. The results also showed that the fillers enhance gas solubility in polysiloxane compounds in such a way that in most situations the sorption process is exothermic. The analysis of the solubility and diffusivity of gases in the rubbers suggests very good adherence matrix-fillers that hinder micro-Brownian motions thus impeding the normal development of non-permanent holes through which the diffusive particles can easily jump. Neither the proportion nor the nature of the fillers alters the permselectivity characteristics of polysiloxane based compounds. (C) 2003 Elsevier Science Ltd. All rights reserved.