Physicochemical characterization of Polystyrene/Polypropylene oil blends as a waste-derived binder for sustainable emulsion paint production

Abstract

The accumulation of polystyrene (PS) and polypropylene (PP) plastic waste presents a growing environmental challenge, particularly in regions with limited recycling infrastructure. This study investigated the conversion of waste PS and PP into pyrolysis oils for use as an alternative binder in emulsion paint formulation. Waste PS and PP were separately collected, washed, shredded, and pyrolyzed using a mini-pyrolysis plant, and the resulting oils were blended at ratios of 90:10, 80:20, 70:30, 60:40, and 50:50 (PS:PP). The physicochemical properties of the pure oils and their blends, including viscosity, density, pH, refractive index, turbidity, pour point, and dispersibility, were determined, and the chemical structures were confirmed by Fourier-transform infrared (FTIR) spectroscopy. Blending markedly improved the rheological and optical properties of the oils relative to the pure components, with viscosity rising from 4.21 cP (PS) and 3.01 cP (PP) to 18.00–36.00 cP across the blends. The 80:20 (PS:PP) blend displayed the most balanced profile, with the lowest turbidity (22.30 NTU), a refractive index of 1.5917, a density of 0.8978 g/cm³, and a pour point of −13°C, and its FTIR spectrum confirmed the coexistence of aromatic (PS-derived) and aliphatic (PP-derived) hydrocarbon structures. These findings demonstrate that pyrolysis oils derived from waste PS and PP, particularly at the 80:20 blend ratio, constitute a viable, environmentally sustainable alternative to petroleum-based binders in emulsion paint production.