Diffusion of bis(2-ethylhexyl) phthalate above and below the glass transition temperature of poly(vinyl chloride)

Diffusion coefficients of bis(2-ethylhexyl)phthalate in PVC were measured over the temperature range 60 < = T < = 100 deg C by using a mass-uptake technique. Near and above the unplasticized T sub g of PVC ( approx 81 deg C), the values were observed to be in the range 1.29 x 10 exp --9 -1.10 x 10 exp --8 cm exp 2 /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 exp 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 sub g of PVC, mass uptake vs. time exp 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 exp --10 -1.00 x 10 exp --9 cm exp 2 /s from 65-78 deg C, respectively, and the activation energy for diffusion within this temperature range was 19 kcal/mol. The value for D at 60 deg C was found to be 1.68 x 10 exp --10 cm exp 2 /s, and this value was significantly lower than that predicted by the Arrhenius relation for stage 3 diffusion. Graphs. 17 ref.--AA