The conversion of post-consumer polyethylene terephthalate (PET) into a thermosetting polyester resin

By Raheem A. B. and Uyigue L.

ABSTRACT
This paper covers the research carried out by the authors on the conversion of post-consumer polyethylene terephthalate (PET) into a thermosetting polyester resin. Glycolysis and hydrolysis-glycolysis were chemical recycling techniques used in the depolymerisation of PET wastes to reprocess able monomers and oligomers. The experiment was performed on PET sourced from soft drink bottles. The flakes were glycolysed using Diethylene glycol and Polyethylene terephthalate of various w/w ratios at various temperatures and reaction times, with potassium acetate (1% w/w of the total raw materials) as catalyst. For hydrolysis-glycolysis method, Diethylene glycol/ water/ polyethylene terephthalate w/w ratio at various operating temperatures and residence times were used. The w/w ratios were carefully chosen to know the trend of the yield increment at specific operating conditions. Also, water was used as hydrolysis medium in the case of hydrolysis-glycolysis to avert equipment corrosion and pollution, and is very cheap. The products obtained were purified using methanol and sun dried. From physical and chemical properties analyzed (density, refractive index, viscosity, melting point, freezing point, boiling point, acidity number, hydroxyl number and molecular weight) and a Fourier transform infrared test conducted, it was found that the glycolysed products consisted mainly of the monomers “Bis (hydroxyethylene) terephthalate (BHET)?, and oligomers because of the excess Diethylene glycol used that resulted in two hydroxyl end-groups, that is, mixtures of oligoesters diols were formed. It can be used to re-synthesis ethylene terephthalate or co-polymers. Recycling of PET does not only serve as a partial solution to the solid-waste problem, but serve as a source of raw material to some industries and also contribute to the conservation of raw petrochemical products and energy which is of high importance due to high cost of energy in the World of today.

Keywords: Depolymerization, glycolysis, hydrolysis, recycling.

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