Bisphenol A polycarbonate blends: Mechanical properties, morphology, and aging behavior

Bisphenol A polycarbonate (PC) may be modified by incorporating various elastomer containing polymers to improve a number of deficiencies in mechanical properties. Three component blends of PC containing a methacrylated-butadiene-styrene (MBS) impact modifier, and a number of brittle polymers like polystyrene (PS), styrene/acrylonitrile (SAN) copolymers, and poly(methyl methacrylate) (PMMA), were prepared and investigated. The component miscibility or interfacial energy of each pair and other physical characteristics were considered in choosing polymers for ternary blends. Extrusion melt blending was used to prepare the compositions used in this investigation. Blends prepared by a two-step mixing sequence usually exhibited better properties than those prepared by mixing all components simultaneously. A surface energy analysis has been developed for predicting the locus of the MBS particles in the two phase matrix. This scheme combined with knowledge of pair miscibility proved to be a successful prediction method. It was predicted that MBS particles may often be trapped at the PC-BP interface by surface forces, and numerous experiments confirmed this prediction. Significant toughening of PC blends with PMMA and SAN, but not with PS, was obtained by the addition of the MBS impact modifier.; The effects of physical aging due to thermal treatment of binary MBS modified PC blends below the glass transition temperature of PC were also studied. Changes in properties are related to changes in elastomer content, free volume, post-yield stress drop, fracture morphology, discoloration, enthalpy relaxation, glass transition temperature, intrinsic viscosity, and rubber dynamic mechanical behavior. The results show that in addition to physical aging, blend properties are also significantly affected by chemical changes in the impact modifier that occur during this thermal history. The degradation mechanisms reduced the effectiveness of the modifiers for toughening and also cause molecular weight degradation of the PC matrix. Blends containing 10% methacrylated-butadiene-styrene (MBS) core-shell impact modifiers give the maximum extension of time to embrittlement at 135{dollar}spcirc{dollar}C in air. More thermally stable modifiers will be the key for further extending the ductile mode of failure of physically aged PC blends.