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.

Comparison of rheological behavior of branched polypropylene prepared by chemical modification and electron beam irradiation under air and N2

“…Special rheological behaviour of branched polymers makes them suitable for thermo-forming processes. Some researchers have tried to introduce long-chain branches to polypropylene backbone for improving its melt strength (Wang et al, 1996;Graebling, 2002;Frounchi et al, 2007;Krause et al, 2004;Weng et al, 2003;Ye and Zhu, 2003;Graebling et al, 1997;Lagendijk et al, 2001;Lugao et al, 2000Lugao et al, , 2002Lugao et al, , 2003. Because of extreme sensitivity of low-frequency rheological response to molecular structure (Wong and Baker 1997;Dealy and Wissbrun, 1990), the rheological behaviour was used to characterize the branched polypropylene prepared via different methods (Graebling, 2002;Krause et al, 2004;Lagendijk et al, 2001;Tsenoglou and Gotsis, 2001;Romani et al, 2002;Auhl et al, 2004).…”

Desenvolvimento de espumas a partir de misturas poliméricas de polipropileno linear (PP) e polipropileno de alta resistência do fundido (HMSPP)

“…Devido a isso, optou-se pela mistura física, 50% em peso, entre o PP linear e o PP ramificado (HMSPP), pois a adição de apenas 10% de PP ramificado no homopolímero já reduz consideravelmente o endurecimento por deformação 22 . O HMSPP, quando usado em misturas com o PP linear, permite a obtenção controlada de espumas de células abertas e fechadas 22,23,24,25,26,27 .…”