Thermophysical Properties of Polymer Composites Based on Secondary Polypropylene Filled with Chalk

One of the most common ways to create polymer composites based on polypropylene is to fill it with chalk, which allows one to improve the appearance of the resulting plastic products and their performance properties. The thermoplasticity of the resulting polymer composites determines the possibility of involving retired polymer materials in reprocessing, which requires studying the laws of the influence of heating on the thermophysical properties of the polymer phase. The regularities of changes in the thermophysical parameters of polymer composites based on secondary polypropylene in the process of filling it with a chalk additive have been studied. It is shown that processing of primary polypropylene by injection molding leads to a decrease in the thermal stability of the resulting secondary polymer material without changing the melting and crystallization points of the polymer phase, but it is accompanied by a decrease in the melting enthalpy (by 9–11%) and the degree of crystallinity of the polymer (by 5.6–6.5%). Filling secondary polypropylene with chalk additionally reduces the temperature of the beginning of decomposition of the composite, while the temperature corresponding to the maximum rate of thermo-oxidative destruction is shifted by 18–25°С to the lower temperature region. The introduction of 2 wt parts chalk into polypropylene reduces the melting point by 3.6°С and increases the crystallization point of the polymer phase by 1.3°С. Filling of secondary polypropylene with a chalk additive in the amount of 5–10 wt parts reduces the degree of crystallinity of the polymer, which can lead to changes in the physical and mechanical properties of plastic products.