Ternary composites of polypropylene/elastomer/calcium carbonate: effect of functionalized components on phase structure and mechanical properties

Abstract

Investigated ternary composites assume two phase structures: (i) ethylene-propylene elastomer (EPR) and filler are dispersed separately in polypropylene (PP) matrix; (ii) EPR encapsulates filler particles, thus forming a low-modulus interlayer between the filler and PP. Formation of these phase structures is promoted by acid-base interactions when functionalized PP or functionalized EPR is added. PP functionalized with maleic anhydride or acrylic acid enhances the interfacial adhesion between matrix and filler, which prevents dewetting of filler particles and thus accounts for higher yield stress and alteration in failure mechanism. Alternatively, the addition of 5 to 20 vol% of an analogously functionalized EPR results in extensive filler encapsulation, i.e. formation of core-shell particles. The functionalized elastomers have lower molecular mobility manifested in smaller dissipative capacity and higher glass transition temperature. Thus, it seems advisable to combine functionalized species with a standard EPR to ensure good interfacial adhesion and high molecular mobility of the interlayer. Simple model calculations indicate that virtually complete encapsulation of filler can be achieved. Composites with core-shell particles have lower yield stress and higher impact strength than composites with functionalized matrix. These two mechanical properties were found to be inversely proportional in all series of tested composites. However, core-shell particles are apparently less effective impact modifiers than elastomer inclusions, presumably because of improper size (predestined by the size of filler cores) and/or shell modulus.