Isothermal crystallization of novel polypropylene/polyaniline-grafted-short glass fiber (Pan-g-SGF) composites

Isothermal crystallization kinetics of composites of isotactic-polypropylene (iPP) reinforced with polyaniline-grafted short glass fibers (PAn-g-SGF) were studied by differential scanning calorimetry (DSC). The concentration of PAn-g-SGF ranged from 10 to 30 wt%. Furthermore, a composite of iPP blended with 5% polypropylene-grafted maleic anhydride and 30 wt% PAn-g-SGF was also studied. DSC showed that the crystallization temperature of iPP, T_c, was significantly increased by the microfiller. Isothermal crystallization results showed that the kinetics of neat iPP is well described by the Avrami model, with half-time crystallization τ_1/2 in the range of 3 to 22 mins. Regarding the composites, τ_1/2 was five times faster than neat iPP. Furthermore, the kinetics of crystallization was described by the Avrami model only at temperatures not too close to the respective crystallization temperature T_c. That is, the PAn-g-SGF microfiller acted as nucleating agent was significantly accelerating the rate of crystallization of the composites. The rate of crystallization was even faster than when using only bare glass fibers. Hot-stage polarized optical microscopy showed transcrystallinity induced by PAn-g-SGF; that is, crystallization in the composites starts first on the surface of the microfillers and then spreads out into the polymer matrix. This might explain the extremely fast rate of crystallization kinetics observed in the composites.