Abstract
Biaxial extensional flows are a commonly encountered phics. and yet poorly understood deformation. The reason for this is that controlled pure biaxial flows are difficult to produce for rheological measurements. In this study, the optical properties of blown polymer films, the product of a major process with biaxial flows, are related to the mechanical properties of the alms and a novel lubricated squeezing rheometer for generating pure biaxial elongation is constructed and tested in constant strain rate and constant stress tests. Specifically, poly(ethylene) films are used in the optical testing and two molecular weights of poly(isobutylene) are tested in the lubricated squeezing rheometer. Our results on the optical properties of blown poly(ethylene) films demonstrate that the machine and transverse direction tear strengths are strongly related to the film birefringence. These correlations held over a range of precessing conditions. The correlations for pure poly(ethylene) films did not describe the film sample produced from a poly(ethylene) blend. Comparison of the shear rheology to the biaxial rheology of the poly(isobutylene) samples shows that Trouton's rule is followed in constant strain rate testing and followed, but not as closely, in constant stress testing. Comparison of the strain developing in the steady state region to theoretical predictions for the cases of perfect slip and no slip revealed similar results as the comparison to shear rheology. The consent strain rate data follow the prediction for pure slip, indicating that the lubricated plates are performing well. The consent stress data fell in the region between the pure slip and no slip predictions. Since we know that the lubrication is sufficient, the problem with the constant stress tests are concluded to be mechanical in nature.
Maxey, Jason E (1998). Extensional rheology of polymers and optical properties of blown polymer films. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1998 -THESIS -M39.