THE INFLUENCE OF MAGNESIUM-HYDROXIDE MORPHOLOGY ON THE CRYSTALLINITY AND PROPERTIES OF FILLED POLYPROPYLENE

Two magnesium hydroxide fillers of different morphology, but almost id entical surface area, were incorporated into polypropylene to assess t heir nucleation properties. The platelet filler was found to reside pa rallel to the flow direction, whereas the pseudospherical filler resid ed isotropically within the matrix. The plate plane (001) of magnesium hydroxide was found to be responsible for causing nucleation, the pol ypropylene b axis growing parallel to the melt flow direction. Vinyl s ilane modification reduced this effect. Filler loading level was found to be influential in governing crystallization initiation, growth, an d final crystallinity levels. Law filler loadings produced fast crysta llization rates but low crystallinity contents, whereas high filler co ntents produced the opposite effects. Mechanical properties were found to be influenced by matrix morphology; however, filler content became the major factor at loading levels of 40% and above. (C) 1998 John Wi ley & Sons, Inc.