Characterization of a maleic anhydride-modified polypropylene as an adhesion promoter for glass fiber composites

Isothermal and nonisothermal crystallizations of isotactic polypropylene (i PP), maleic anhydride (MAH)-grafted PP, and MAH-modified IPP were studied b y differential scanning calorimetry (DSC), to evaluate the influence of a s mall amount of MAH-grafted PP in iPP on its crystallization behavior. Isoth ermal crystallization was followed in the temperature range from 391 K to 4 03 K, and the rate constant and Avrami exponents were determined. Nonisothe rmal crystallization was carried out at different cooling rates (1-20 K/min ). It was found that the crystallization kinetics of IPP was significantly altered by modification with the MAH-grafted polymer. A decreased equilibri um melting temperature, as well as decreased surface energy of folding and critical dimensions of a growing nucleus, was determined for the MAH-modifi ed iPP, indicating faster growth of lamellae and a higher rate of crystalli zation. The improved nucleation ability of the modified polymer was shown t o cause a shift in the crystallization peak temperature towards higher valu es (from 393.7 K to 399.6 K, at a cooling rate of 1 K/min), resulting in cr ystal structures less disposed to recrystallization. Model composites of iP P and MAH-modified iPP with grass fibers were also analysed. The apparent s hear strength of single-fiber model composites with MAH-modified iPP was dr astically increased compared with homo-iPP.