Gas permeation of polymer blends. I. PVC/ethylene–vinyl acetate copolymer (EVA)

Abstract

AbstractThe transport behavior of O2 and N2 were studied for series of physical blends of PVC with EVA having different vinyl acetate (VAc) contents in the EVA (45 and 65 wt‐%) and using different milling temperatures (160° and 185°C). The polymer blends were further characterized by dynamic mechanical measurements, density measurements, and x‐ray diffraction. At higher VAc content in EVA and with higher milling temperature, the rate of permeation (P) and the rate of diffusion (D) decrease, and the activation energy of D (from Arrhenius plots) increases. Furthermore, the experimental density values of PVC/EVA‐45 blends agree well with calculated values, assuming volume additivity of the two components, while those of PVC/EVA‐65 blends are higher than the calculated densities. These results are interpreted as due to denser packing of polymer molecules and increased PVC‐EVA interaction at higher VAc content and with higher milling temperature, indicating better compatibility between the blend components. The x‐ray diffraction data give no evidence of crystallinity. Sharp increases in P and D values at about 7.5% EVA (by weight) are found for PVC/EVA‐45 blends (in agreement with our previous work) but not for PVC/EVA‐65 blends. This is interpreted as due to a phase inversion at increasing EVA content in the former blends but not in the latter blends. The dynamic mechanical measurements show that the PVC/EVA‐65 blends milled at 160°C behave largely as semicompatible systems with maximum interaction between the two polymers at compositions of about 50/50 by weight.