Failure mechanisms in blends of linear low-density polyethylene and polystyrene

Mechanical models that explicitly consider microdeformation and failure mechanisms were developed for the high-strain tensile properties of uncompatibilized blends of linear low-density polyethylene (LLDPE) and polystyrene (PS). A decrease in ultimate tensile properties with increasing PS content resulted in a ductile-to-quasi-brittle transition. By scanning electron microscopy, it was determined that the irreversible microdeformation mechanisms that controlled the high-strain properties of these blends were interfacial debonding and void growth around particles of the dispersed PS phase. The void morphology was characterised by two parameters: the debonding angle (theta), and the local extension ratio of the void (lambda). The yield-stress calculation was based on a modification of the effective-cross-section approach to incorporate the debonding angle; the true fracture stress was determined by considering the further reduction in effective cross section during void growth with, additionally, the strain-hardening characteristics of the LLDPE matrix. Because the true fracture stress decreased more rapidly than the yield stress with increasing PS fraction, a ductile-to-quasi-brittle transition was observed.