Study of the phase morphology and toughness in poly (vinyl chloride)/acrylonitrile–styrene-acrylic/styrene–butadiene–styrene ternary blends influenced by interfacial/surface tension

The effect of interfacial interaction on the phase morphology and toughness of poly (vinyl chloride) (PVC)/acrylonitrile–styrene-acrylic (ASA) terpolymer/styrene–butadiene–styrene (SBS) block copolymer ternary blends has been investigated. Water and diiodomethane liquids were used for static contact angle measurements to get surface tension and calculate interfacial tension. A dispersed phase morphology of ASA and SBS in the PVC matrix was predicted by the spreading coefficient theory, which was calculated through interfacial tensions between different polymer pairs. Extraction experiment and scanning electron microscopy were combined to verify this morphology. When the volume fraction of SBS was small, SBS was dispersed in the matrix as droplets and the strong PVC/styrene–acrylonitrile interfacial interaction made up for the poor interfacial adhesion between SBS and PVC. Herein, SBS showed an effective toughening effect on PVC/ASA blends. With the addition of 2.5- and 5-phr SBS, the blends had the highest impact strength of 88.75 kJ/m² at 23 °C and 9.98 kJ/m² at 0 °C, respectively. With the further increase of the SBS content, the diameter of the SBS drops increased largely and the poor interfacial adhesion between SBS and PVC played a leading role, resulting in a sharp decrease in toughness and a sharp ductile–brittle transition.