PURIFICATION OF RECYCLED TEREPHTHALIC ACID AND SYNTHESIS OF POLYETHYLENE TEREPHTHALATE

Plastic waste pollution presents one of the major environmental challenges in the 21. Century. Post-consumer textile waste is especially problematic since it is very hard to recycle mechanically due to the high content of various impurities. Therefore routes for chemical recycling needs to be developed. Depolymerization of polyethylene terephthalate (PET) usually yields terephthalic acid (TA) containing impurities that can negatively influence polymerization; thus purification of TA is an essential step in the chemical recycling of PET. In the present study, the purification method for recycled TA (rTA) was developed. Purification method involves dissolving rTA in sodium hydroxide solution, activated charcoal treatment, precipitation and recrystallization in dimethylacetamide (DMAC). The purity of rTA and purified rTA (prTA) was assessed by determining optical density at 340 nm (OD₃₄₀) of TA solution using UV-VIS spectroscopy. After the purification the OD₃₄₀ decreased from 17.764 to 0.170, indicating significant improvement in purity of TA. PET from both rTA and prTA was synthesized in a custom-made 2.5 L stainless steel reactor and characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). PET synthesized from rTA exhibited a low melting point (235 °C), indicating low molecular weight. FT-IR analysis revealed that unreacted TA was still present in the polymer. PET synthesized from prTA exhibited a significantly higher melting point (253 °C), indicating higher molecular weight compared to PET synthesized from rTA.