Polyester fibers currently represent more than half of fibers in global use, and the most commonly-used of them is polyethylene terephthalate (PET), which has continued to increase in its production. In addition, with the improvement in the people’s living standard, the use cycle of textiles is getting much shorter, which leads to the production of textile waste, reaching 90% of global fiber production. On the other hand, resource depletion and environmental pollution have become a serious problem, and people have been better aware of the environmental system, which has encouraged positive efforts to recycle textile waste.
There are three main ways to reuse waste textiles, namely, mechanical, physical and chemical methods. In the chemical method, polyester is decomposed into monomers or oligomers before being separated and purified to obtain desired chemical products. This is a complete fiber-fiber cycle technique that can produce new textile fibers from waste textiles. In the 2010s, some countries synthesized PET for textile fibers by applying the chemical method to PET waste plastics to produce clothing such as suits, shirts, etc. Chemical recycling methods of post-consumer PET include glycolysis, hydrolysis and others. In glycolysis, in particular, Bis(2-hydroxyethyl terephthalate) monomer (BHET) and oligomer are obtained by trans-esterification between diol and ester groups of PET.
Since BHET is used as a PET synthetic feedstock, many studies have been carried out on glycolysis of PET. However, previous studies addressed glycolysis of relatively clean PET waste, and little attention has been paid to PET waste fibers containing various impurities such as dyes.
Ri Myong Chol, a researcher at the Faculty of Materials Science and Technology, has investigated the preparation of BHET by glycolysis of PET textile waste under microwave irradiation.
The experimental results show that high purity BHET used as a precursor for PET synthesis can be prepared by pre-decolorization of PET textile and glycolysis of PET before recrystallization of BHET.
When PET textile and PET plastics are glycolyzed under the same reaction conditions, the conversion of PET and the yield of BHET are higher in the fiber than in the plastics. The reason lies in the fact that the depolymerization reaction rate gets faster in the PET fiber because the specific surface area of fiber is much larger than that of plastics and the molecular weight of PET fiber is lighter than that of PET plastics.
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