Eco-Friendly Thermoplastic Composites Produced from Waste Polystyrene and Lignin Particles

Abstract

The world's population growth motivated humanity to more economical and ecologically friendly composites in the manufacturing of industrial products. For this purpose, this study aimed to produce new value-added composite materials by using waste polystyrene (w-PS) and two types of lignin, including deep eutectic solvent lignin (DES-lig) and commercial lignin (T-lig). Firstly, w-PS was melted with commercial-type acetone, and the lignin particles were added to the melted w-PS at 1%, 2%, and 4%. The w-PS/lignin blends were stirred with a mechanical mixer at 500 rpm for 15 min. The obtained blends were kept in the oven in hot air to remove acetone from the blends. The characterization of the samples was conducted with physical and mechanical tests, the morphological characterization with scanning electron microscopy (SEM), structural analysis with fourier transform infrared spectroscopy (FTIR) and x-ray diffraction spectroscopy, and thermogravimetric analysis (TGA). Although both lignin types were found to increase the water uptake amount of the samples by 1-4%, the increase did not cause any significant change in the thickness swelling of the blends. However, lignin caused the samples to foam and reduced their density by 2-36%. In general, adding lignin improved some mechanical properties, especially flexural strength (6-33%), and improved the thermal stability of the samples. This study investigated the interactions of lignin and polystyrene, which are considered as waste materials; the obtained results exhibited to be used w-PS/lignin blends as a more environmentally friendly composite.