Polypropylene Foaming in a Reactive Process

Abstract

Long-chain branches are incorporated into the molecular backbone of a polypropylene (PP) in a foaming process. The branching of PP occurs by radical reactions of dicumyl peroxide and a tri-functional monomer, trimethylol propane trimethacrylate. Use of peroxide without tri-functional monomer results in scission of PP molecular chains and significant reduction in melt viscosity. The increase in melt viscosity in conjunction with the flow ability of the modified PP indicates that the polymer has a branched structure. Melting temperature of PP remains unchanged with branching reactions implying that reactions occur mainly in amorphous regions of PP. The improvement in melt strength and strain-hardening of the modified PP is examined by a batch foaming process. The foaming process conditions are optimized for the level of blowing agent, time and temperature of process, and talc content as nucleating agent. The formation of closed and evenly distributed cells in the foam structure verifies improvement in the rheological behavior of modified PP resulting from the presence of long branches in the molecular structure.