Aromatic Polyester Polyols from Polyethylene Terephthalate Wastes Bottles, Films, Fibres

2 Aromatic Polyester Polyols from Polyethylene Terephthalate Wastes (Bottles, Films, Fibres) [12-24] 

PET wastes, proved to be an excellent raw material for low cost aromatic polyester polyols. By transesterification with DEG and (or) propylene glycol or dipropyleneglycol (DPG), liquid, low viscosity and low functionality aromatic polyester polyols were obtained. Due to the low cost, DEG is the preferred glycol for transesterification (reaction 16.3) [4, 6-8, 12]. 

Of course the product of the transesterification reaction is much more complex, being a mixture of superior oligomers and free diethyleneglycol together with the main product and the mixed ester terephthalate of ethyleneglycol and DEG. 

The reaction between PET and DEG takes place at higher temperatures, around 200-230 °C, without catalysts or better still in the presence of the usual catalysts for polyester synthesis (lead, manganese, tin, titanium or zinc compounds). In the situation of transesterification without catalyst, the catalyst existing in PET wastes acts as the catalyst for glycolysis, but the reaction needs longer times. The time for liquefaction of PET with DEG varies from 6-14 hours [2, 4]. 

The process of PET glycolysis with DEG has several disadvantages the reaction products are viscous liquids with a tendency to solidification or even to be solid at room temperature, the reproducibility of the characteristics of the resulting polyester polyols are difficult to realise (poor consistency) and the products of transesterification are not compatible with the blowing agents (pentanes or hydrofluorocarbons) [4, 6]. 

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