Methanol desorption in poly(methyl methacrylate) with stress distributions
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Fuqian Yang Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506, USA
Chi Wei Liu, Kuo-Chen Ho, and Sanboh Leea) Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan (Received 15 May 2014; accepted 29 July 2014)
Understanding solvent transport in polymers is of practical importance for the applications of polymers in the fields of food packaging, biomedical bandages, materials engineering, etc. We studied one-side desorption in poly(methyl methacrylate) (PMMA). Experimental results showed that methanol desorption in PMMA depended on temperature and the initial distribution of concentration. The diffusion coefficient in PMMA and the evaporation rate of methanol across the PMMA surface followed the Arrhenius relation. The activation energies for the diffusion and the evaporation of methanol are 18.3, 42.6 and 8.6, 18.3 kJ/mol for the specimens with the ratio of initial mass to the equilibrium saturated absorbed mass, Mi /M∞ , being 14.6% and 35.3%, respectively. The partial molal volume increased with the increase of the desorption temperature for Mi /M∞ 5 14.6%, while it had an opposite trend for M i /M∞ 5 35.5%. The chemical stresses developed in PMMA during the desorption were also studied.
I. INTRODUCTION 1
Alfrey et al. proposed that the transport behavior of solvents in polymers can be categorized as Case I, Case II and anomalous transport. The Case I transport is dominated by Fickian diffusion and the Case II transport is controlled by stress relaxation of polymer chains. Anomalous transport occurs when the effect of solvent penetration is comparable to the effect of stress relaxation. Chen and Edin2 studied the Case I diffusion of bisphenol-A in polycarbonate. Crank3 solved various diffusion problems for different geometries and boundary conditions. Thomas and Windle4 attributed the Case II transport to the advancement of a sharp interface at a constant velocity, which separates an inner glassy core from an outer swollen layer. Friedman and Rossi5 identified the transition surface between the glassy state and the rubber state for the Case II kinetics. Hui and Wu 6,7 studied the transient swelling and the steady-state front motion in the Case II transport. Kwei et al.8 were the first group to propose an equation for describing the anomalous transport of solvent in a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.232 2162
J. Mater. Res., Vol. 29, No. 18, Sep 28, 2014
http://journals.cambridge.org
Downloaded: 13 Mar 2015
polymers. Their solution was only valid for semiinfinite materials. Harmon et al.9,10 modified Kwei’s equation and applied it to specimens of finite sizes; they also solved and extended the transport kinetics to various solvent–polymer systems.11–14 All the above studies had been concentrated on the mass uptake in polymeric materials where the glassy core and the outer rubber-state material are separated by a sharp interface. Understanding the desorption
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