In Situ Observation of Plastic Foaming Under Static Condition, Extensional Flow and Shear Flow

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OCLC: 1019463731

Abstract

Traditional blowing agents (e.g., hydrochlorofluorocarbons) in plastic foaming processes has been phasing out due to environmental regulations. Plastic foaming industry is forced to employ greener alternatives (e.g., carbon dioxide, nitrogen), but their foaming processes are technologically challenging. Moreover, to improve the competitiveness of the foaming industry, it is imperative to develop a new generation of value-added plastic foams with cell structures that can be tailored to different applications. In this context, the objective of this thesis is to achieve a thorough understanding on cell nucleation and growth phenomena that determine cell structures in plastic foaming processes. The core research strategy is to develop innovative visualization systems to capture and study these phenomena. A system with accurate heating and cooling control has been developed to observe and study crystallization-induced foaming behaviors of polymers under static conditions. The cell nucleation and initial growth behavior of polymers blown with different blowing agents (nitrogen, argon and helium, and carbon dioxide-nitrogen mixtures) have also been investigated in great detail. Furthermore, two innovative systems have been developed to simulate the dynamic conditions in industrial foaming processes: one system captures a foaming process under an easily adjustable and uniform extensional strain in a high temperature and pressure environment, while the other achieves the same target, but with shear strain. Using these systems, the extensional and shear effects on bubble nucleation and initial growth processes has been investigated independently in an isolated manner, which has never been achieved previously. The effectiveness of cell nucleating agents has also been evaluated under dynamic conditions, which have led to the identification of new foaming mechanisms based on polymer-chain alignment and generation of microvoids under stress. Knowledge generated from these researches and the wide range of future studies made possible by the visualization systems will be valuable to the development of innovative plastic foaming technologies and foams.

Cited Works (6)

Year	Entry
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1999	Sato Y, Fujiwara K, Takikawa T; Sumarno, Takishima S, Masuoka H. Solubilities and diffusion coefficients of carbon dioxide and nitrogen in polypropylene, high-density polyethylene, and polystyrene under high pressures and temperatures. Fluid Phase Equilib. August 1999;162(1-2):261-276.
2002	Naguib HE, Park CB, Panzer U, Reichelt N. Strategies for achieving ultra low-density polypropylene foams. Polym Eng Sci. July 2002;42(7):1481-1492.
2003	Xu X, Park CB, Xu D, Pop-Iliev R. Effects of die geometry on cell nucleation of PS foams blown with CO₂. Polym Eng Sci. July 2003;43(7):1378-1390.
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Cited By (5)

Year	Entry
2013	Jung PU. Development of Innovative Gas-Assisted Foam Injection Molding Technology [PhD thesis]. University of Toronto; 2013.
2014	Chu RKM. Open-Cell Foaming With Injection Molding [PhD thesis]. University of Toronto; 2014.
2016	Ding W. Development of Polylactic Acid/cellulose Nanofiber Biocomposite Foams [PhD thesis]. University of Toronto; 2016.
2017	Tabatabaei Naeini A. In-Situ Visualization and Quantification of Polymer Crystallization Under Complex Flows During Foam Extrusion Processing [PhD thesis]. University of Toronto; 2017.
2018	Romero Diez S. Crystallization Study of Polymers Under High Pressure Gas / Supercritical Fluid [Master's thesis]. University of Vermont; October 2018.