Effect of the Viscosity Ratio, Composition and Enhancement of Interface on Melt Rheology and Concomitant Morphology of Model Polyalloy

Abstract

In continuation of the systematic study on melt flow dependence of the phase structure (morphology) in a model*, "incompatible" polyalloy, several complemen tary and 1:1 compositions were investigated for two LDPE/PS systems with the LDPE/PS/SEP (=2/1/5 phr) polyalloy as the reference. The system was intended to repre sent the effect of the higher viscosity ratio (group I polyalloy in which SPE block copo lymer is used as the compatibilizer—as in the model polyalloy), and the effect of chemical bonding at the interface (group II polyalloy prepared from commercial grades of LDPE and PS in an industrial mixer) upon the morphology of the polyalloys. The latter was stud ied using quantitative SEM on solvent etched and/or stained (PS matrix polyalloys) samples of "bulk," i.e., as removed from a mixer, and the capillary-extruded specimens. The mean (minor phase) domain size increases in the following order: II < reference < I polyalloy; for the mixing energy intake the ordering is reversed. The energy of mixing ap pears to be a function of the interfacial tension and the viscosity ratio. The rubberlike pat tern of the (shear) viscosity and elasticity (normal stress difference) functions is most pro nounced for the II polyalloy; the composition of melt viscoelasticity synergism at a standard shear-stress level appears to depend on the interface "strength." A preliminary evaluation of the domains' fibrillation in I and the "reference" polyalloys, the latter in the extrusion blown film form, indicates similarity with structures observed in the synthetic paper. Selected mechanical properties measured on molded and extruded samples in the dynamic and steady-tensile modes were compared with the Kerner-Faucher model predic tion for the composition dependence; results will be published in a forthcoming paper.