Fundamental study for control of cell nucleation and growth in thermoplastic foaming process

众所周知，在工业泡沫加工设备中，塑料受到显著的剪切和拉伸应力，这些应力会影响泡沫产品的最终细胞密度和形态。目前的塑料发泡可视化和计算机模拟研究是基于静态条件下的发泡，通过解耦各种实验参数的研究提供了有价值的见解，但需要进一步的研究来提高我们对工业塑料发泡过程中的发泡行为的理解。我们建议开发两种新型的间歇发泡可视化系统来捕捉塑料样品的原位发泡过程，一种是在可控的拉伸应力下，另一种是在剪切应力下。此外，还将测量热物理和流变性能，包括聚合物中气体的溶解度和扩散率，PVT行为，以及聚合物/气体溶液的表面张力和粘度；所有这些新数据将作为一个新的计算机模拟系统的输入，该系统将用于模拟在拉伸和剪切应力下的细胞成核和生长行为。应力作用下的泡沫可视化数据将用于验证和改进计算机模拟背后的理论。随后，我们将能够全面了解拉伸和剪切应力对塑料发泡的影响及其与发泡中其他关键因素的关系。由此产生的知识将用于开发模具和模具设计的有效策略，并优化工业塑料发泡设备的加工条件，以控制泡沫质量和定制不同应用的细胞形态。这将有助于我们的加拿大塑料工业生产增值塑料泡沫产品，为他们提供全球市场竞争力，特别是在来自生产成本较低的发展中国家的竞争之后。此外，该项目每年将为17名hqp提供培训，这些hqp将成为加拿大大学研究人员和全球领先塑料行业员工的优秀候选人。

It is known that in industrial foam-processing equipment, plastics are subjected to significant shear and extensional stresses, and these can affect the final cell density and morphology of foam products. While our current plastic foaming visualization and computer simulation studies, which are based on foaming under static conditions, offer valuable insight by decoupling the investigations of various experimental parameters, further studies are needed to improve our understanding of the foaming behavior in industrial plastic foaming processes. We propose to develop two novel batch foaming visualization systems that capture the in situ foaming process of a plastic sample, first, under controlled extensional stress, and second, under shear stress. In addition, thermophysical and rheological properties, including solubility and diffusivity of gas in polymers, and PVT behavior, as well as surface tension and viscosity of polymer/gas solutions, will be measured; all of this new data will serve as inputs to a new computer simulation system that will be developed to model cell nucleation and growth behaviors under extensional and shear stress. The foaming visualization data under stresses will be used to verify and improve the theory behind the computer simulation. Subsequently, we will be able to establish comprehensive knowledge of the effect of extensional and shear stresses on plastic foaming and its relationships to other critical factors in foaming. The resulting knowledge will be used to develop effective strategies for die and mold design and to optimize processing conditions in industrial plastic foaming equipment in order to control the foam quality and tailor the cell morphology for different applications. This will help our Canadian plastics industries to produce value-added plastic foam products, providing them with global market competitiveness especially in the wake of competition from developing countries with lower production costs. Moreover, the project will contribute to the training of 17 HQPs each year who will become excellent candidates as researchers in Canadian universities and employees at leading global plastics industries.