Publication: Separation of pigment from recycled hdpe using limonene and characterization of the recovered polymer
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Date
2025-08-06
Authors
Munirah binti Abd Rahman
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Abstract
High-density polyethylene (HDPE) is one of the world’s most widely used plastics. However, colored HDPE has become a challenge to recycle due to the presence of pigments. This research aims to develop a bio-based solvent recycling process for pigment removal. Purple-colored recycled HDPE was dissolved in D- limonene, environmentally friendly solvent at 130oC then precipitated with ethanol. Activated Carbon (AC) was introduced into dissolution to increase pigment adsorption. Two experimental series were conducted. Series 1 varied the volume of limonene concentration (g/mL) (50 mL, 60 mL, 70 mL, 80 mL and 90 mLand used 30 minutes of stirring times. Series 2 varied AC contact time (30,60 and 90 minutes) while using fixed 70 mL limonene concentration. In both series, the characterization of the recovered AC confirmed pigment adsorption based on visual color changes and weight gain. Characterization of HDPE precipitate using FTIR showed no changes in the main peaks of HDPE, indicating that the structure of polymer remained intact. FTIR confirmed that the CH2 stretching and bending bands remained unchanged, indicate the absence of polymer degradation. Differential Scanning Calorimetry (DSC) also showed consistent thermal behavior across all samples. Series 1 shows that moderate volume of limonene concentration (70 mL) is sufficient for effective pigment removal, whereas Series 2 indicated that 30 minutes of AC contact time is enough for adsorption. The findings suggest that using a low-solvent and short-contact-time approach provides an effective and sustainable method for pigment removal without compromising the integrity of the polymer.