Mechanical behavior related to the phase morphology of PC/SAN polymer blends

The phase morphology of intensively melt mixed and injection moulded bisphenol‐A polycarbonate (PC)/styrene‐acrylonitrile copolymer (SAN) blends changes on annealing above the glass‐transition temperature ( T g ) of both components. For the selected PC and SAN resins, the phase morphology of the 60/40 PC/SAN blend changes from a fine dispersion of the PC phase in a SAN matrix to a coarse co‐continuous phase network, whereas a co‐continuous 70/30 PC/SAN blend changes to a dispersion of SAN domains in a PC matrix. The effect of the blend morphology on dynamic mechanical properties and ambient tensile stress‐strain properties have been studied thoroughly. An increase of the storage modulus between T g (SAN) and T g (PC) is observed with increasing coarsening of the phase structure until a continuous PC matrix is formed. The coarsening of the phase structure of the blends gives rise to a transition from ductile to brittle fracture. The loss in ductility is related to a decrease in relative amount of interface and a transition in the type of dispersion.