Preparation of Secondary Raw Material for Polymer Compositions Based on Polystyrene Waste and Investigation of Its Structural and Thermal Properties

This article reports the preparation of secondary raw material from expanded polystyrene (EPS) waste and a comparative assessment of its structural and thermal characteristics. The waste was sorted, cleaned, shredded, and processed by dissolution in ethyl acetate followed by precipitation with ethanol. The original PS-0 sample and the recovered polystyrene PS-2 were examined using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Processing 10.0 g of dry EPS yielded 9.3–9.5 g of dry polystyrene, corresponding to a product yield of 93–95%. Both samples showed characteristic absorption bands associated with aromatic and aliphatic C–H bonds, aromatic-ring C=C vibrations, and out-of-plane deformation of aromatic C–H bonds. The glass-transition temperatures were 100.4 °C for PS-0 and 101.2 °C for PS-2. The temperatures corresponding to 5% and 10% mass loss and the maximum decomposition rate were higher for PS-2 than for PS-0. Taken together, the results indicate that the principal structural features of polystyrene and similar thermal characteristics were retained after dissolution–precipitation processing. The recovered material can therefore be considered as a secondary feedstock for further development of polymer compositions.