Effects of Crystallinity and Molecular Weight on the Melting Behavior and Cell Morphology of Expanded Polypropylene in Bead Foam Manufacturing

The preparation of expended polypropylene (EPP) by a bead foam processing is of great significance for their potential applications, but the development of a facile method adopting the actual manufacturing process remains a great challenge. In this study, a new bead foam processing based on the actual manufacturing process was successfully developed to produce high quality EPP. Suitable processing conditions as well as the effect of the precursor sample properties associated with expanded polypropylene (EPP) manufactured by the bead foam process were investigated. The elongational viscosity was firstly measured using polypropylene (PP) samples with different crystallinities and molecular weights in order to investigate the relevant foaming temperatures. The crystallinity and molecular weight of each sample were controlled by the addition of comonomer, and the melting behavior and cell morphology of the foamed specimens were analyzed utilizing a pilot-scale foaming experiment. Based on our results and observations, a plausible mechanism for formation of high quality EPP was proposed. This work offers a new method for fabricating EPP with a high quality by the bead foam processing. It also provides important information about how the morphology and cell numbers of EPP may be finely controlled by the processing conditions.