Correlating processing induced orientation with tensile properties for mass polymerized acrylonitrile butadiene styrene test specimens†

Abstract

In this research, we deal with the link between tensile properties and processing-related morphology variations for mass polymerized acrylonitrile butadiene styrene (mABS). The orientation of multi-core polybutadiene (PB) particles, which are intrinsic to mABS, is investigated regarding flow, shear and cooling changes during sample production. The effect of a different sample size and annealing on the tensile responses has been verified by considering ISO 527 1A and 1BA dog bone samples. For the thin 1BA bars, multiple injection velocities and cooling rates during injection molding have been tested to obtain a more pure correlation between morphology and tensile properties. To perform comparable tensile measurements using both types of dog bone samples, a testing method has been designed for which a relation is included between the sample gauge length and cross head velocity, enabling the comparison of elastic deformation for ISO 527 1A and 1BA mABS samples. Regarding the mABS part morphology, injection molded parts display a skin-shear-core gradient morphology with respect to the PB-particle size and orientation. Annealing of both types of injection molded samples successfully removes most flow-induced orientation of the rubber particles but also results in a change in PB morphology by dissolving a small fraction of the rubber into the SAN matrix, forming PB-nanoparticles. These small particles promote shear bands upon craze-based deformation and therefore positively contribute to the sample toughness. High flow-induced orientation within mABS parts causes a significantly increased tensile stiffness, strength and toughness along the flow direction. Irrespective of the PB orientation, tensile bars with a large surface roughness experience early failure, due to premature craze and crack initiation at the sample surface.