Effect of coagent in reactive surface treatment for calcium carbonate filler in polypropylene

Calcium carbonate as a filler for polypropylene has been modified with a reactive coupling system comprising acrylic acid (AA) and dicumyl peroxide (DCP), to promote coupling through grafting at the surface of the filler during melt compounding, in conjunction with trimethylolpropane trimethacrylate coagent (TMP) to limit degradation. The main effects and interactions between these three additives have been assessed via their influence upon selected characterisation data. Inferences from the data analyses suggested that there were competing reactions involving AA and TMP initiated by DCP, with AA predominantly grafting directly to the polypropylene when DCP and TMP levels were low, probably owing to the greater reactivity of AA in comparison with TMP. Only when DCP and TMP concentrations were high did TMP have a pronounced effect upon the system.