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”泡沫塑料都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，因为它价格便宜，易于加工，热稳定，机械强度高。然而，PP的低熔体强度对发泡提出了严峻的挑战。在提高PP熔体强度以生产微孔泡沫塑料方面已经取得了重大进展，但到目前为止，关于在涉及成核剂和发泡剂的广泛组合的加工条件下发泡的研究还很少。关于在发泡过程中存在聚合物微结构(即晶体)的情况下的气泡成核，可获得的知识更有限。该提案概述了对PP材料发泡行为的全面、系统的研究。拟议研究的独特方面是：(1)注射化学发泡剂和物理发泡剂及其混合物，以探索类型、用量及其协同作用对发泡的影响；(2)探索各种矿物成核剂的类型、大小和用量，并比较矿物和非矿物类型成核剂的性能；(3)连续发泡过程中的泡孔成核和聚合物结晶可视化，以了解气泡和晶体成核之间的相互作用。加拿大塑料产品制造业2016年的估值为253亿美元。发泡是通过减少制造塑料产品所使用的原材料数量来降低塑料产品的成本、重量和对环境影响的有效方法。因此，提高对发泡工艺的基本了解和对各种工艺条件的严格研究具有积极影响聚合物发泡工艺的合理设计的巨大潜力，并有望为加拿大带来巨大的环境效益。最后，在这个项目过程中，将培训一大批高素质的人员。人们非常期待这些训练有素的专业人员最终将他们的专业知识带给加拿大的塑料和泡沫工程界以及学术界。

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.