Effect of compatibilizer on fatigue failure initiation of immiscible PC/PS polymer blends.

Abstract

The existence of a correlation between interfacial adhesion, i.e. compatibilizer, and fatigue failure initiation was investigated in immiscible polycarbonate (PC)/polystyrene (PS) blends. The fatigue failure initiation phase was studied by the transmission electron microscope (TEM), and the role of the compatibilizer was characterized according to five different failure initiation modes resulting from different levels of interfacial adhesion. The knowledge elucidating how fatigue properties of immiscible polymer blends are improved by the addition of a third polymer, i.e. compatibilizer, that is miscible with both of the primary components, is requisite to understanding fatigue failure mechanisms of polymer blends. The role of interfacial adhesion, i.e. compatibilizer, in fatigue failure initiation of immiscible polymer blends is reported for the first time in this research. First, it was found that the addition of a PC-PS graft copolymer, i.e. compatibilizer, improved static mechanical properties and fatigue performance of immiscible PC/PS blends. The systems with compatibilizer exhibited longer fatigue lifetimes and longer incubation time to craze initiation than those of systems without compatibilizer. Distinct discontinuous crack growth (DCG) bands were also observed on the fracture surfaces of the systems with compatibilizer. To determine and analyze criteria of fatigue failure initiation modes found by TEM, Finite Element Method (FEM) analysis was conducted using the degree of interfacial adhesion as a variable. The increase in incubation time to craze initiation resulted from the change in failure initiation mechanism when using the PC-PS graft copolymer as a compatibilizer. It was found that the compatibilizer changed the fatigue fracture initiation modes from adhesive fracture to cohesive fracture. It was suggested that molecular chain disentanglement mechanism played an important role in inducing fatigue failure initiation in the PC/PS blends and the adhesive fracture initiation modes enhanced this chain disentanglement process. The TEM method proved to be very successful in elucidating the structural changes during fatigue failure initiation.