ANISOTROPIC METHANOL TRANSPORT IN PMMA AFTER MECHANICAL DEFORMATION

Transport of methanol in compressed polymethyl methacrylate (PMMA) (23-34% strain) was found to be anisotropic. It was faster by a factor of two to three in penetration velocity and by a factor of 10 in diffusivity in the direction of compression than in the perpendicular direction. However, the penetration velocity in the slow direction is still a factor of two to five larger than that of the undeformed PMMA (two at 40°C and five at 25°C). The two-dimensional mixed diffusion and case II transport problem was solved analytically so that the diffusivity and the penetration velocity could be obtained from experimental weight gain data. The penetration front was found to correspond approximately to a front of constant concentration of methanol. When methanol was mixed with glycerol to lower the methanol concentration (glycerol does not penetrate PMMA), the penetration velocity was smaller due to reduced swelling but the diffusivity was unchanged as expected.