Tuning of molecular weight and chemical composition of polyols obtained from Poly(ethylene terephthalate) waste recycling through the application of organocatalysts in an upcycling route

Abstract

High molecular weight liquid polyols were produced from complex Poly (ethylene terephthalate) (PET) waste (low molecular weight PET waste, monolayer compounds, and coloured PET bottles) in one-step synthesis using mild reaction conditions. For the first time, a wide range of upcycled polyols were obtained by modulating the reaction conditions to control the chemical composition and molecular weight, in order to revalorize the same PET waste in different polyols.A new versatile, efficient, selective and sustainable chemical recycling method was developed, employing cheap reagents (ethylene carbonate) and basic organocatalysts, under mild reaction conditions (moderate temperatures and atmospheric pressure). Chemically, the polyols showed a singular composition, consisting of three types of repeating units, two coming from PET and one belonging to the ethylene carbonate ring-opening. Depending on the depolymerisation conditions of the PET waste and the catalyst used, the ratio between these moieties varied considerably, giving rise to a wide portfolio of liquid polyols. In addition, the ability of the organocatalyst to introduce the carbonate unit into the polyol chain was analysed as a function of the number of ethylene carbonate units used.As a proof of concept, these new liquid secondary raw materials served as a starting point for the synthesis of polyurethanes under standard conditions. Ultimately, the final objective of this upcycling process will be the application of a wide range of high-quality polyols as soft segments to produce more sustainable and high-performance polyurethanes (flexible foams, coatings, sealants, adhesives, elastomers).