Equibiaxial extensional flow of polymer melts via lubricated squeezing flow. I. Experimental analysis
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The technique of lubricated squeezing flow is evaluated using experiments in both constant strain rate and constant stress flows of two low-density polyethylene melts. Experimental parameters that include the lubricant viscosity and sample aspect ratio are systematically varied to examine their effect on the viability of the technique in the linear viscoelastic regime by comparing measured quantities to those predicted by finite linear viscoelastic theory. An evaluation is also made by comparing viscosities measured using the lubricated squeezing flow technique and Meissner's rotating clamp (MAD) rheometer in the non-linear regime. In both cases, deviations between the expected and measured viscosities were observed, indicating that the technique is not applicable to large strains for constant strain rate and constant stress flows. It is suggested that this limit is the result of lubricant thinning.
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