Solvent Effects on Cure in a 2K Polyurethane—Mechanical and Dielectric Studies

Abstract

The effect of change in solvent type on the processes involved in film formation of a 2K polyurethane are investigated using dynamic mechanical thermal analysis [DMTA] and dielectric relaxation [DR] measurements. The film formation and cure reactions for a polyol reacting with an isocyanate for solutions in ethyl acetate, tolene, xylene, and n-butyl acetate solutions and their mixtures are reported. Mechnical studies are used to observe the various stages of film formation and cure using a paper substrate. The fluid initially wets the substrate and film formation accompanies solvent evaporation. The rate of these initial processes correlates well with the vapor pressure of the solvent. The rate of cure of the films however is influenced by the polarity of the solvent system. Analysis of the broad band dielectric relaxation data yields conductivity data, which can be modeled to give kinetic data on the cure process. The rate of cure of this 2K system demonstrates sensitivity to the solvent composition used. The rate constant derived from conductivity data parallel those derived previously from FTIR studies. DMTA and DR measurements indicate that as cure proceeds, the glass transition temperatureT g , increases. Differences are observed in the ambient temperature-cured films, which reflect retained solvent plasticization of the matrix. Post cure aids release of trapped solvent and the final physical properties are essentially independent of the solvent used in the cure process.

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