Phase morphology, fracture toughness and failure mechanisms in super-toughened PLA/PB-g-SAN/PMMA ternary blends: A quantitative analysis of crack resistance

The effect of poly(methyl methacrylate) (PMMA) content on the fracture resistance, failure mechanisms and micromechanical deformation of poly(lactic acid) (PLA)/polybutadiene-g-poly(styrene-co-acrylonitrile) (PB-g-SAN) blend was studied. The fracture toughness of samples was characterized by the essential work of fracture (EWF) method. The specific EWF (we) linearly increased with PMMA content up to 30 wt%, indicating improved fracture toughness of ternary blends with PMMA content. The specific plastic work (βwp) increased at first with PMMA content up to 15 wt% and then decreased at higher loadings of PMMA. The energy dissipated during yielding (we,y) and subsequent tearing (we,t) stages was determined by the energy partitioning approach. Both we,y and we,t components monotonically increased with PMMA content in ternary blends, suggesting enhanced material resistance against crack initiation and subsequent crack propagation. Fracture behavior and toughening mechanisms were studied. Suitable interfacial adhesion, cavitation of rubber particles and irreversible plastic growth of micro-voids caused massive shear yielding of matrix material in the super-toughened blends.