A Thermodynamical Framework Incorporating the Effect of the Thermal History on the Solidification of Molten Polymers
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If a polymer melt is quenched sufficiently quickly, the polymer solidifies to a predominantly glassy state. On the other hand, if the rate of cooling is slow, a polymer melt solidifies to a predominantly semi-crystalline state. The rate of crystallization is enhanced in the presence of deformation in the melt, which is termed as flow-induced crystallization, and even under quiescent conditions, the thermal history significantly affects the temperature at which the crystallization is initiated. Thus, there is a competition between quenching that tends to suppress the crystallization process and deformation of the melt that enhances the same. The thermo-mechanical history undergone by the melt determines whether a polymer melt solidifies predominantly to a glass or a crystalline state or a mixture of the two. This chapter discusses deformation history effects in the framework developed by Rao and Raja Gopal to study the problem of solidification of polymer melts within a unified setting. When the cooling rate is sufficiently slow, the crystallization kinetics described by Nakamura type kinetics is insufficient to describe the crystallization as the slower "secondary" crystallization related to the lamellar thickening becomes important. Thus, secondary crystallization effects are also included and a general model is developed within a thermodynamic setting. The melt is modeled as a viscoelastic liquid and the crystalline solid, which comes into being over an interval of time associated with an evolving set of natural configurations, is modeled as a one-parameter family of orthotropic elastic solids. The amorphous glassy solid is modeled as an isotropic viscoelastic solid. 2007 Elsevier Ltd All rights reserved.
