Gas permeation of polymer blends. IV. Poly(vinyl chloride) (PVC)/acrylonitrile–butadiene–styrene (ABS) terpolymer

The transport behavior of He, O₂, N₂, and CO₂ in membranes of poly(vinyl chloride) (PVC)/acrylonitrile–butadiene–styrene (ABS) blends has been studied at 25°C. The blends were further characterized by dynamic mechanical measurements, differential thermal analysis (DTA), density measurements, and x-ray diffraction. The equilibrium sorption of CO₂ and N₂ was measured directly at atmospheric pressure using an electromicrobalance and compared with sorption values obtained as P/D ratios from permeation measurements. The rates of permeation (P) and diffusion (D) increase with increasing ABS content in the blends. The P and D values are not additive, and only slight indications of phase inversion in the blends are observed at 5–10 wt-% ABS in the blends. Experimental densities of the blends are higher than calculated densities assuming volume additivity. The data are interpreted to mean that the PVC/ABS blends form a two-phase system composed of a soft polybutadiene (rubber) phase and a rigid PVC/styrene–acrylonitrile copolymer (SAN) phase of mutually compatible components. DTA and dynamic mechanical measurements also show a two-phase system. Sorption values of CO₂ and N₂ by equilibrium sorption measurements increase with increasing ABS content in the blends without the large fluctuations which have been observed for the sorption values obtained from the time lag method. Comparison of the two types of sorption values (from direct measurements and from P/D ratios) show larger deviations for CO₂ than for N₂. This suggests that the time lag method is not valid for permeants with polar character in heterogeneous two-phase systems where chemical immobilizing effect on the permeant molecules occurs.