Permeability of Gases Through Filled and Unfilled Rubber Membranes

Abstract

The purpose of this investigation was to study, by way of permeation experiments, structural differences between synthetic polycis 1,4-isoprene (SNR) and natural rubber (NR), as well as differences resulting from filling with carbon black. The study aimed further at testing Frisch's theory of isotope effects in activated diffusion and on the unit size of the free volume in rubbers. -6is about 3.2 x 10 g./g. of rubber, and 8 x 10' g./g. of carbon. The latter is probably completely wetted by rubber.Based on the quantum mechanical treatment of diffusion suggested by H. L. Frisch, the unit free volume in the unfilled rubbers is calculated from the value of UH , i.e., the difference of M for D 2 and H 2 in the same medium to be 51 and 64 respectLvely -for NR and SN.However, Frisch's equation can not be applied to calculate the free volumes in the filled 6&:-ples since NI was found to be positive for this case.The jump length, X, of H 2 in NR and in SNR are found, according to the absolute rate theory, to be almost the sue (about 21 1) in both rubbers, whereas, X, for D is about 26 A in NA and 30 1 in SNA.A semt-quantitative analysis of the diffusion mechanism in che filled samples shows that the data of P, D, and 8 for the filled samples can be related to those of the unfillc samples accounting for the reduction of the cross section of the filler, the imposed tortuosity of the diffusion path, and the increase in the viscosity of the rubber due to the presence of the filler particles.