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Abstract
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 30–608 C
under upstream pressures lying in the range 15–76 cm Hg. Permeation and diffusion https://www.51lunwen.org/uk/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.q 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Gas transport; Silicone rubbers; Fillers-Rubber interaction

1. Introduction
The wide industrial use of polysiloxane rubbers arises from the combination of interesting properties presented by these elastomers that include excellent thermal and oxidative stability, good weatherability, good electric isolating properties, a wide interval of temperatures of
use, resistance to oil, solvents, acids, fungi, etc. [1– 5]. Another important aspect of these rubbers is the versatility of their synthesis processes that allows the incorporation of different chemical structures in the chains in proportion large enough to promote interesting changes in the proper-ties of the elastomers [1– 5]. For example, the random
incorporation of vinyl groups in the chains facilitates the vulcanization process, preferentially carried out through these groups by means of peroxides.
In general, the mechanical properties of polysiloxane elastomers are inferior to those of other organic elastomers,such as natural rubber. However, whereas the mechanical properties of polysiloxane elastomers only show a slight dependence on temperature, the properties of natural rubber and other elastomers undergo a great decrease with time at temperatures above 50 8C.

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