Effect of sepiolite on nonisothermal crystallization kinetics of polypropylene

The purpose of this paper is to study the nonisothermal crystallization kinetics of polypropylene (PP)/Sepiolite nanocomposites in the absence/presence of compatibilizer [maleic anhydride-grafted polypropylene (PP-g-MA)] using differential scanning calorimetry. Crystallization exotherms were recorded at four different cooling rates, i.e., 5, 10, 15, and 20 °C/min. Crystallization parameters were analyzed using Ozawa, Avrami, Jeziorny, and Liu’s models. Nucleation ability of Sepiolite was evaluated by employing Dobreva and Gutzowa models. The activation energy of nonisothermal crystallization kinetics process was estimated using three isokinetic models (Augis–Bennet, Kissinger, and Takhore). DSC cooling scans of PP and PP/Sepiolite nanocomposites showed that the crystallization onset temperature, T0, and peak exotherm temperature, Tp, increased in the presence of Sepiolite. However, Tp decreased with the increasing amount of PP-g-MA in PP/Sepiolite nanocomposites. The values of F(T), KA and half-time to crystallization (t1/2) showed that the rate of crystallization of PP was faster in the presence of Sepiolite at a given cooling rate. The t1/2 values also decreased slightly for compatibilized PP/Sepiolite nanocomposites. The values of exponent ‘n’ determined using Avrami analysis indicated that nonisothermal kinetic crystallization corresponded to three-dimensional growth with heterogeneous nucleation in all the samples. Sepiolite shows its better nucleating effect in the presence of PP-g-MA as investigated by Dobreva and Gutzowa method. The increase in ΔE values of PP/Sepiolite nanocomposites is proportional to the Sepiolite content which is in the range of 33–38 % in case of PPS-5 and 44–47 % in case of PPS-10 as compared to PP calculated using three different models while decreasing on adding compatibilizer. Incorporation of Sepiolite in the presence of compatibilizer, PP-g-MA, in the optimized ratio results in accelerating the overall nonisothermal crystallization process of PP/Sepiolite nanocomposites.