The influence of thermal and mechanical histories on case II sorption of methanol by PMMA

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Previously published data [6] relating kinetics of the Case II penetration of methanol into PMMA to the thermal history of the samples are discussed in relation to the detailed predictions of a model of the sorption process [4]. It is clear that fast cooling through T g enhances sorption rates through the influence of the thermal history on the rate of mechanical response of the polymer glass. Detailed measurements are reported of the effect of prior plastic deformation of the polymer glass on the Case II kinetics. The results indicate that the sorption rate is enhanced as a consequence of the yielding process itself, irrespective of whether the hydrostatic component of the stress is compressive or tensile. In addition to this “yield factor”, there is another factor which becomes significant at high strains. It is related to the sign of the plastic strain in the glass in the direction normal to the penetrant front. Prior extension normal to the front is found to reduce the penetration rate as a function of strain, and compression to further enhance it. The effect is described as the “retraction factor”.