Effect of needle density on the mechanical properties of fiber-reinforced polypropylene composites

Abstract

The partial impregnation textile preform consisting of chopped-strand, long glass fiber and nonwoven polypropylene (PP) has been prepared by needle-punching to improve fiber–matrix distribution before processing. These unconsolidated textile preforms were then preheated and hot-pressed for consolidation and formation. A multichannel recorder was used to determine the completion of impregnation on multilayer glass fiber-reinforced PP, which could significantly reduce the required consolidation time. The effect of needle density on their impregnation has studied by scanning electron microscopy and optical microscopy, along with mechanical analysis. The increasing needle density up to 400 st/cm2 has increased the flexural modulus, but the impact strength decreased. The optimal needle density contained proper flexural and impact properties is 50–100 st/cm2, consistent with the observations from scanning electron microscopy and optical microscopy. A similar phenomenon is also observed by using nonwoven maleic-anhydride-modified polypropylene (mPP) instead of unmodified PP. However, the effect of needle punching on flexural and impact properties is not significant in mPP, which is probably due to better adhesion between glass fiber and mPP matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2169–2176, 1999