The mechanical behaviour of ZnO nano-particle modified styrene acrylonitrile copolymers

Abstract Two amorphous SAN copolymers with acrylonitrile contents of 24% and 34% have been modified by the incorporation of ZnO nano-particles at volume fractions of up to 2.00%. For the SAN with 24% acrylonitrile content, three types of nano-particles were added. The first two were cylindrical (nano-rods) and the third were spherical. For the SAN with 34% acrylonitrile content, just one of the cylindrical nano-particle types were used. The dispersion of the nano-particles was assessed using atomic force microscopy and agglomeration was observed for the higher volume fractions. Young’s modulus and fracture toughness values were measured for each system as a function of volume fraction. The smaller nano-rods were found to be the most effective for both stiffening and toughening the polymers and the spherical particles were found not to contribute to stiffness due to poor particle–matrix adhesion. At room temperature the maximum toughening contributions for all particles occurred at volume fractions of about 0.1%, above which a reduction was observed. At 80 °C the toughening contributions continued to rise slowly past 0.1% volume fraction. The toughening is consistent with the notion that the particles debond from the matrix and then plastic hole growth around the detached particles is initiated. The peak toughening observed at 0.1% volume fractions are the result of agglomeration occurring at higher volume fractions.