Polymer Engineering Faculty Research


Modeling of Crystallization, Birefringence and Anisotropic Shrinkage in Injection Molding of Thermoplastics

Document Type


Publication Date

Fall 2004


A novel approach for the numerical simulation of the development of crystallinity, frozen-in birefringence and anisotropic shrinkage in moldings of thermoplastics is proposed. The approach is based on the calculation of elastic recovery and crystalline and amorphous orientation functions frozen when the flow-induced crystallization occurs. To model crystallization, the flow effect on the equilibrium melting temperature elevation due to the entropy reduction between the oriented and unoriented melts is incorporated. To find frozen-in elastic recovery during crystallization and entropy change, a non-linear viscoelastic constitutive equation is used. The crystalline and amorphous contributions to the overall birefringence were obtained from the crystalline orientation function and the flow birefringence, respectively. To calculate anisotropic shrinkage, the PVT equation of state and the dependence of the thermal expansion and compressibility on the frozen-in orientation function are used. The skin layer thickness, crystallinity, birefringence profiles and anisotropic shrinkage were predicted and compared with those measured in moldings obtained at various packing pressures, packing times, melt temperatures, mold temperatures and injection speeds.



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