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

The partial impregnation textile preform consisting of chopped-strand, long glass fiber and nonwoven polypropylene (PP) has been prepared by needle-pu nching to improve fiber-matrix distribution before processing. These uncons olidated textile preforms were then preheated and hot-pressed for consolida tion and formation. A multichannel recorder was used to determine the compl etion 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 a nd optical microscopy, along with mechanical analysis. The increasing needl e density up to 400 st/cm(2) has increased the flexural modulus, but the im pact strength decreased. The optimal needle density contained proper flexur al and impact properties is 50-100 st/cm(2), consistent with the observatio ns from scanning electron microscopy and optical microscopy. A similar phen omenon is also observed by using nonwoven maleic-anhydride-modified polypro pylene (mPP) instead of unmodified PP. However, the effect of needle punchi ng on flexural and impact properties is not significant in mPP, which is pr obably due to better adhesion between glass fiber and mPP matrix. (C) 1999 John Wiley & Sons, Inc.