Diffusion of Bis(2-Ethylhexyl) Phthalate Above and Below the Glass Transition Temperature of Poly(vinyl Chloride)

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Polymers and High Performance Materials


Diffusion coefficients of bis(2-ethylhexyl) phthalate in PVC were measured over the temperature range 60 less-than-or-equal-to T less-than-or-equal-to 100-degrees-C by using a mass-uptake technique. Near and above the unplasticized T(g) of PVC (ca. 81-degrees-C), the values were observed to be in the range 1.29 x 10(-9)-1.10 x 10(-8) cm2/s and to follow approximately an Arrhenius relationship with an activation energy for diffusion of 29 kcal/mol. Within this temperature range, mass uptake vs time 1/2 plots were observed to be curves with a slowly increasing derivative; the initial, approximately linear region yielded the diffusion coefficient in pure (unplasticized) PVC. Below the unplasticized T(g) of PVC, mass uptake vs time 1/2 plots recorded three stages of diffusion: (1) non-Fickian initial behavior constituting essentially an induction period; (2) a brief, approximately Fickian diffusion of plasticizer into glassy PVC; and (3) linear, Fickian diffusion into the plasticized, rubbery polymer. The transition between stages 2 and 3 was characterized by a discontinuity in the mass-uptake plot. Stage 3 diffusion coefficients were calculated to be in the range 3.44 x 10(-10)-1.00 x 10(-9) cm2/s from 65 to 78-degrees-C, respectively, and the activation energy for diffusion within this temperature range was 19 kcal/mol. The value for D at 60-degrees-C was found to be 1.68 x 10(-10) cm2/s, and this value was significantly lower than that predicted by the Arrhenius relation for stage 3 diffusion.

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