Kinetic study of vetiver grass powder filled polypropylene composites

Polypropylene composites containing vetiver grass powder as filler are used in Thailand in many applications, i.e. household articles, furniture and office appliances. A widely used method of disposal of these composites after use is through pyrolysis in incinerators, gasification plants, or combustion systems. A knowledge of the pyrolysis kinetics of these composites is useful for the efficient design of these disposal plants. In this paper, the results of an experimental study of the pyrolysis kinetics of polypropylene (PP), vetiver grass, and PP composites containing vetiver grass powder are presented and mathematical models of the kinetics are developed. A thermogravimetric analysis of the PP, vetiver grass and PP composites has been carried out. Mass loss data for the thermal decomposition process have been obtained for PP, vetiver grass and PP composites at four different heating rates of 5, 10, 15 and 20 °C min−1 in a nitrogen atmosphere. The kinetics of the PP decomposition has been modeled by a single-stage reaction describing the degradation of hydrocarbon polymer. The kinetics of the vetiver grass decompositions are modeled with three independent decomposition reactions describing the degradation of hemicellulose, cellulose and lignin. The kinetics of the decompositions of the vetiver grass filled PP composites are modeled by both a three series reaction process and by a process involving three independent reactions. One of the three independent reactions modeled the decomposition of hemicellulose and cellulose, the second modeled the main decomposition of PP and remaining cellulose, and the third modeled the decomposition of lignin and remaining cellulose and PP. Values of the kinetic parameters (activation energy, pre-exponential factor and reaction order) are obtained which give a good fit between the kinetic models and the experimental data.