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

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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.