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Degradation kinetics of polymers in solution: Time-dependence of molecular weight distributions. [Quarterly report, January--March 1996]

Description: Polymer degradation occurs when polymer chains are broken under the influence of thermal, mechanical, or chemical energy. Chain-end depolymerization and random- and midpoint-chain scission are mechanisms that have been observed in liquid-phase polymer degradation. Here we develop mathematical models, unified by continuous-mixture kinetics, to show how these different mechanisms affect polymer degradation in solution. Rate expressions for the fragmentation of molecular-weight distributions (MWDs) govern the evolution of the MWDs. The governing integro-differential equations can be solved analytically for realistic conditions. Moment analysis for first-order continuous kinetics shows the temporal behavior of MWDs. Chain-end depolymerization yields monomer product and polymer molecular-weight moments that vary linearly with time. In contrast, random- and midpoint-chain scission models display exponential time behavior. The mathematical results reasonably portray experimental observations for polymer degradation. This approach, based on the time evolution of continuous distributions of chain length or molecular weight, provides a framework for interpreting several types of polymer degradation processes.
Date: February 27, 1996
Creator: McCoy, B.J. & Madras, G.
Partner: UNT Libraries Government Documents Department

Effect of tetralin on the degradation of polymer in solution

Description: The effect of a hydrogen-donor solvent tetralin on thermal degradation of poly(styrene-allyl alcohol) in liquid solution was investigated in a steady-state tubular flow reactor at 1000 psig at various tetralin concentrations, polymer concentrations, and temperatures. The experimental data were interpreted with continuous- mixture kinetics, and rate coefficients determined for the specific and random degradation processes.
Date: December 31, 1995
Creator: Madras, G.; Smith, J.M. & McCoy, B.J.
Partner: UNT Libraries Government Documents Department

Thermal degradation of poly({alpha}-methylstyrene) in solution. [Quarterly report, July--September 1995]

Description: The thermal degradation of poly({alpha}-methylstyrene) in solution was investigated at various temperatures (150-225 C) and polymer concentrations (2.00-20.0 g/L) at 6.8 MPa (1000 psig). The molecular weight distributions (MWDs) of the reacted polymer at these conditions were examined at four different residence times. Experimental data indicated that the polymer degraded to its monomer, {alpha}-methylstyrene. No other degradation products were observed. Continuous-mixture kinetics was used to examine the MWDs and to obtain the rate coefficient for degradation and its activation energy. The rate was first-order in polymer concentration with a rate constant at 225 C of 0.01 min{sup {minus} 1} and an activation energy of 66.5 kJ/mol (16.0 kcal/mol). The maximum conversion observed at 275 C was 1.2%. Hydrogen-donor solvent, tetralin, had no effect on the degradation.
Date: November 11, 1995
Creator: Madras, G.; Smith, J.M. & McCoy, B.J.
Partner: UNT Libraries Government Documents Department

Fundamental kinetics of supercritical coal liquefaction: effect of catalysts and hydrogen-donor solvents. Second quarterly report, 1996

Description: This quarterly report relates our recent progress toward the overall objective of understanding the supercritical fluid extraction of hydrocarbons from coal. Our approach is to simulate coal as a high molecular-weight polymeric material and study the degradation of polymers under various conditions, including temperature, pressure, and solvent. The degradation of such macromolecules is applicable to the decomposition (depolymerization) of the coal network. Another potential application of this research is to the recycling of plastics. Our recent research involved the study of the oxidative degradation of polystyrene in tricholorobenzene using tertbutyl peroxide. A continuous-mixture kinetics model for the rate of polymer degradation and peroxide consumption was developed to describe the temporal behavior of the molecular-weight distributions and its various moments. Based on this work, a research paper entitled `Oxidative Degradation Kinetics of Polystyrene in Solution,` will be submitted to the journal, Chemical Engineering Science.
Date: July 1, 1996
Creator: McCoy, B.J.; Smith, J.M.; Madras, G. & Kodera, Y.
Partner: UNT Libraries Government Documents Department

Effect of tetralin on polymer degradation in solution. [Quarterly report, January--March 1995]

Description: The effect of a hydrogen-donor solvent (tetralin) on the thermal degradation of poly(styrene-allyl alcohol) in solution was investigated in a steady-state tubular flow reactor at 1000 psig (6.8 MPa), at various tetralin concentrations (0--50%), polymer concentrations (1--4 g/L), and temperatures (130--200 C). The molecular weight distributions of the effluent at each condition were examined as a function of residence time by gel permeation chromatography. In the presence of tetralin, the polymer degrades by deploymerization to specific low molecular weight compounds and by random chain scission. No reaction was observed in the solvent 1-butanol in the absence of tetralin. The experimental data were interpreted with a rate expression first-order in polymer concentration based on continuous mixture kinetics, and rate coefficients were determined for the specific and random degradation processes. Activation energies were in the range of 5--10 kcal/mol for specific degradation and 33 kcal/mol for the random degradation process. A plot of rate coefficients versus tetralin concentration indicates a first-order rate at low tetralin concentrations and a zero-order dependence at high tetralin concentrations.
Date: April 26, 1995
Creator: Madras, G.; Smith, J.M. & McCoy, B.J.
Partner: UNT Libraries Government Documents Department