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

大多数商业上可用的“轻质”泡沫是由商品塑料制成的，其中聚丙烯（PP）是一种非常有吸引力的发泡材料，因为它价格低廉，易于加工，热稳定，机械强度高。然而，PP的低熔体强度给发泡带来了严峻的挑战。在提高PP的熔体强度以制备微孔泡沫方面已经取得了重大进展，但在成核剂和发泡剂广泛组合的加工条件下的发泡研究目前还很少。在发泡过程中，在聚合物微观结构（即晶体）存在的情况下，气泡成核的知识更为有限。本文对pp基材料的发泡行为进行了全面、系统的研究。建议研究的独特之处是：(i)化学和物理发泡剂及其混合物的注射，以探索类型，负载和它们的协同作用对泡沫的影响；（ii）探索矿物成核剂的各种类型、大小和装载量，并比较矿物型和非矿物型成核剂的性能；（iii）连续发泡过程中细胞成核和聚合物结晶的可视化，了解气泡和结晶成核之间的相互作用。2016年加拿大塑料制品制造业产值为253亿美元。发泡是降低塑料产品成本、重量和环境影响的有效方法，因为它减少了制造塑料产品的原材料用量。因此，提高对发泡工艺的基本认识和对各种加工条件的严格研究，对聚合物发泡工艺的合理设计产生了巨大的积极影响，并有望为加拿大提供实质性的环境效益。最后，在这个项目的过程中，将培养出一批高素质的人才。这些经过培训的专业人员最终将把他们的专业知识带到加拿大塑料和泡沫工程社区以及学术界。

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.