Control of the melt strength of polypropylene in rotational foam molding

The rotational molding process can be readily modified to serve as a foam processing technology so that it becomes capable of creating a foam layer or core in the interior of the rotomolded hollow articles. Although polypropylene (PP) is being traditionally considered unfeasible for foaming because of its low melt strength, its advantageous end-use properties over polyethylene (PE) render it into a preferred candidate for replacing PE in rotational foam molding. This study is primarily focused on investigating the effects of concurrently implementing the rotational foam molding technology and PP into the processing of hollow rotomolded articles with a view of reducing their inherent mechanical, insulative, and shock mitigation weaknesses. The effects of varying the processing parameters on the foaming behavior of differently formulated PP-based foamable blends were thoroughly studied through conducting extensive rotational foam molding trials. The preliminary experimental results revealed that it is feasible to successfully process PP foams in rotational foam molding. However, it is crucial to process the PP foams at the lowest processing temperature possible so that the melt strength of PP during foaming can be preserved. The PP melt strength control strategy implemented during the trials included reducing the oven temperature and/or lowering the decomposition temperature of the chemical blowing agent (CBA) by using an activator. Consequently, PP foams with acceptable cell morphologies have been produced.