Effect of the liquid-liquid phase separation on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) and paraffin wax blend

Abstract

The effect of liquid-liquid phase-separation (LLPS) on the crystallization behavior and mechanical properties of poly(ethylene-ran-vinyl acetate) (EVA) with various amounts of vinyl acetate and paraffin wax blend was investigated. The blend of EVA-H (9.5% vinyl acetate) and the wax became homogeneous at temperatures greater than its upper critical solution temperature (UCST) (98 degrees C), and an LLPS was observed between UCST and the melting point of 88 degrees C for EVA-H in the blend. The existence of the LLPS is attributed to the relatively large amount of the hydrophilic component of vinyl acetate in EVA, although the molecular weight of the wax was just 560. However, LLPS did not occur for the EVA/wax blend when the content of vinyl acetate in EVA was less than 3%. This behavior was explained by using the Flory-Huggins lattice model with an effective interaction parameter. The degree of crystallinity of EVA-H in the EVA-H/wax blend, judged from a melting endothermic peak in differential scanning calorimeter (DSC) thermograms obtained during heating runs, decreased with increasing duration time in the LLPS region. The flexural modulus of the EVA/wax blend became maximum at certain blend composition (about 30 similar to 40 wt % EVA depending upon the amount of vinyl acetate). This behavior can be explained by the fact that this blend composition has the largest relative degree of crystallinity of EVA measured by DSC and wide-angle X-ray scattering method. We found that the flexural modulus of the binder itself is directly related to that of a feedstock consisting of larger amounts of metal powder and the binder, which can help someone to develop a suitable binder system for a powder injection molding process. (C) 1999 John Wiley & Sons, Inc.