Growth of polypropylene crystals in the vicinity of carbon fibers and improvement of their interfacial shear strength

The effect of polypropylene (PP) crystals on the interfacial shear strength between PP and carbon fiber (CF) was investigated using isotactic PP (iPP), which has high tacticity, blended to atactic PP (aPP), with low tacticity, or maleic anhydride-modified PP (MAPP). The interfacial shear strength of iPP/CF is improved by adding MAPP; however, it is decreased after adding aPP. Micro-Raman spectroscopy analysis of the PP matrix around CF reveals that the crystallinity of iPP and iPP/aPP (70/30) is gradually decreased toward the CF surface, whereas that for iPP/MAPP (91/9) is gradually increased. Moreover, the crystallinity of iPP/aPP (70/30) in the vicinity of CF is much smaller than that of iPP, while that for iPP/MAPP (91/9) is larger than that for iPP, although the crystallinity of iPP in the bulk (without CF) is reduced by the presence of MAPP and aPP. The development of PP crystals around CF improves the interfacial shear strength for PP/CF, and maleic anhydride modification of PP chains promotes the growth of PP crystals in the vicinity of the CF surface.