The solution crystallization kinetics and crystal dissolution behavior of three grades of poly (ethylene terephthalate) in N-methyl-2-pyrrolidinone were studied using turbidimetric and calorimetric methods. The influence of concentration on the equilibrium dissolution temperature was described using Flory's melting point-composition relationship. The effect of the solvent alkyl group was also investigated. N-Methyl-2-pyrrolidinone was found to be a better solvent than N-ethyl-2-pyrrolidinone or N-cyclohexyl-2-pyrrolidinone for poly (ethylene terephthalate) . From the calorimetric experiments, it was determined that two crystallization processes (primary and secondary crystallization) were responsible for the total crystallinity. The primary process dominated the early stages of the crystallization process and accounted for the majority of the final crystallinity for lower polymer concentrations. Based on coherent secondary nucleation theory, the effect of the crystallization temperature on the primary crystallization rate constant was quantified in terms of a temperature coefficient. This temperature coefficient was found to be relatively insensitive to P E T concentration, P E T structural impurities, and solvent alkyl group. 0 1993 John Wiley & Sons. Inc.
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The solid-waste dilemma faced by many municipalities today as well as the economic value inherent to polymers has spurred research into the separation and reuse of postconsumer plastics. Common methods for separating mixed plastics include air classification, hydrocycloning, flotation-sedimentation, depolymerization-purification-repolymerization, and selective dissolution. Of these, only selective dissolution is capable of removing bound impurities from the plastic as well as differentiating plastics based on the chemical properties of the individual polymers without breaking down the polymer molecule. Therefore, selective dissolution processes should yield high-purity polymers that retain the economic value added by the initial polymerization reaction and can replace virgin resins in high-grade applications. Unfortunately, the higher purity * To whom correspondence should be addressed.