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Recycling and Disposal of Waste Plastics
Published in Manas Chanda, Plastics Technology Handbook, 2017
Hydrolysis and methanolysis of PET regenerates the starting monomers. Thus, terephthalic acid (TPA) along with ethylene glycol (EG) are obtained by hydrolysis, while methanolysis yields EG and dimethyl terephthalate (DMT) among other products. Stopping short of complete depolymerization, glycolysis degrades long polymer chains (with typical repeat sequences of 150 units) into short-chain oligomers (repeat sequences of 2–10 units) having hydroethyl end groups.
Technical Implementation of Melt Crystallization
Published in Gerard F. Arkenbout, Melt Crystallization Technology, 2021
Dimethylterephthalate (DMT) is, like terephthalic acid, a basic material for polyesters and is manufactured by oxidation of para-xylene followed by an esterification of the acid groups with methanol. The purity requirements for DMT as a basic material for polymerization are high (>99.99%). Figure 14.5 shows a standard procedure to purify DMT by crystallization from methanol (Nienoord, 1989).
Investigating how the dye colour is impacted when chemically separating polyester-cotton blends
Published in The Journal of The Textile Institute, 2023
Lucas Rosson, Xungai Wang, Nolene Byrne
To further assess the suitability of the recovered polyester for recycling the sample was analysed for changes in chemical bond structure using Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). The FTIR spectra in Figure 3(a) revealed the chemical similarities of the recovered polyester and the 100% polyester fabric. For reference, Figure 3(b) displays spectra for 100% cotton, 100% polyester, and the 80/20 polycotton samples. Analysis into regions where degradation products of polyester would likely occur revealed no signs of chemical degradation caused by thermal, mechanical, hydrolytic, or chemical processing. Thermomechanical degradation of polyester leads to the absorption band at 2962 cm−1 becoming larger due to symmetric and asymmetric stretch vibrations of CH2, and increased absorption intensity at 3548 cm−1 is brought about by the promotion of –OH terminated products (Badia et al., 2012). An increase in intensity of C-H rocking and C-H bending at the 899 and 846 cm−1, as well as 1471 and 1446 cm−1 can be caused by increased crystallinity through thermomechanical processing (Badia et al., 2012). None of these thermomechanical changes were observed in the recovered polyester sample. Hydrolysis of polyester can result in the emergence of two peaks between 2800 and 3000 cm−1 and a reduced intensity of the carbonyl group around 1710–1720 cm−1 (Lindström, 2018). The recovered polyester here shows no such changes at those wavenumbers. Degradation of polyester by sulfuric acid results in the products terephthalic acid (TPA) and ethylene glycol (EG) (Yoshioka et al., 1994), however new peaks in the FTIR spectra in the regions for these products were not seen in the recovered polyester. A study that degraded PET using DMSO showed products of dimethyl terephthalate (DMT) and EG with the DMT being characterised by a peak at 3421 cm−1 (Sharma et al., 2013). No such peak was observed in the recovered polyester here. The use of ionic liquid has also been studied for PET degradation, with the main degradation product representing a shift in the carbonyl peak from 1720 to 1688 cm−1 (Wang et al., 2009), however a strong carbonyl peak can be seen in both the 100% polyester sample and the recovered polyester sample here at approximately 1718 cm−1. The ionic liquid degradation product also showed a strong peak at 1285 cm−1 that was designated to breaks in the ester group during the degradation process (Wang et al., 2009), but this peak was not seen here.