Novel observations on kinetics of nonisothermal crystallization in fly ash filled isotactic-polypropylene composites

A study on nonisothermal crystallization kinetics in fly ash (FA) filled isotactic-polypropylene (PP) composites has revealed some interesting phenomena. Composites made by injection moulding of PP with 0, 20, 45, and 60 wt % of FA were nonisothermally studied using differential scanning calorimetry at cooling rates 10°C, 15°C, and 20°C per min from a melt temperature of 200°C cooled to -30 °C. Whilst neat PP showed a mono modal a crystalline phase- only structure, presence of FA led to bimodal thermographs revealing partial transcrystallisation of a into b, to maximum 14%. The onset and peak crystallization temperatures of all samples decreased by ∼ 3°C with each 5°C/min increase in cooling rate. Parameters such as crystal growth rate, dimensions, and activation energy were determined using a series of established models. The Avrami graphs showed that contrary to the published data, there are two sets of straight lines (a) with a lower slope at low cooling rate and (b) with a distinctly higher slope for high cooling rate. Activation energy of the materials reached a maximum at 45% FA.