Comprehensive studies on the foaming behavior of polypropylene: from microcellular plastics to nanocellular foams

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Most commercially available "lightweight" foams are made of commodity plastics, among which polypropylene (PP) is a highly attractive material for foaming as it is inexpensive, easy to process, thermally stable, and mechanically strong. However, the low melt strength of PP presents severe challenges in foaming. Significant advances have been made to enhance the melt strength of PP to produce microcellular foams, but little research has been conducted so far on the foaming under processing conditions that involve a wide range of combinations of nucleating agents and blowing agents. More limited knowledge is available on bubble nucleation in the presence of polymer microstructure (i.e., crystals) during the foaming process. This proposal outlines a comprehensive, systematic study on the foaming behavior of PP-based materials. Unique aspects of the proposed research are: (i) injection of chemical and physical blowing agents as well as their blends to explore the effects of type, loading, and their synergy on foaming; (ii) exploration of various types, sizes, and loadings of mineral nucleating agents and comparison between the performance of mineral and non-mineral type nucleating agents; (iii) visualization of cell nucleation and polymer crystallization during continuous foaming processes to understand the interaction between bubble and crystal nucleation. Canadian plastics product manufacturing industry in 2016 valued at $25.3 billion. Foaming is an effective way to decrease the cost, weight, and environmental impact of plastic products by reducing the amount of raw materials used to make them. Improved fundamental understanding on the foaming process and rigorous studies on various processing conditions thus have tremendous potential to positively impact the rational design of polymeric foaming processes and are expected to provide substantial environmental benefits to Canada. Finally, a good number of highly qualified personnel will be trained during the course of this project. It is greatly anticipated that these trained professionals will eventually bring their proficiency to the Canadian plastic and foam engineering community as well as to academia.