Unsaturated polyester resin via chemical recycling of off‐grade poly(ethylene terephthalate)

Abstract

BACKGROUND: The chemical recycling of poly(ethylene terephthalate) (PET), e.g. bottles and fibre wastes, has been studied for many years. Among several methods proposed for chemical recycling of waste PET, glycolysis makes it possible to employ very low amounts of reactants and lower temperatures and pressures compared with critical methanol and thermal degradation. Furthermore, unlike hydrolysis under acidic or basic conditions, glycolysis does not cause any problems related to corrosion and pollution. RESULTS: PET from off‐grades of industrial manufacture was depolymerized using excess glycol. The effects of the reaction time, volume of glycol and catalyst concentrations on the yield of the glycolysis products were investigated. A reaction time of 3 h, weight ratio (catalyst to PET) of 0.25 wt% and PET to ethylene glycol molar ratio of 1:5 were determined as suitable conditions for depolymerization. Then, the reaction of polyesterification of maleic anhydride (MA) and glycolysed products of PET was successfully performed at 160 and 190 °C for 8 h. CONCLUSION: Differential scanning calorimetry and vapour pressure osmometry results for the product of the glycolysis reactions, under suitable condition, confirmed the structure of the desired product. This sample underwent reaction with MA to produce unsaturated polyester resin (UPR). The results of Fourier transform infrared and NMR spectroscopy confirmed that the UPR had been synthesized successfully. This is the first direct report on the glycolysis reaction of off‐grade products of petrochemical companies in order to regenerate raw materials or other secondary value‐added products. Copyright © 2009 Society of Chemical Industry

Kinetics of catalytic glycolysis of PET wastes with sodium carbonate

“…Further, BHET (and higher oligomers) thus obtained can be used as building blocks to synthesise other polymers with higher economical values such as unsaturated polyesters, polyurethane foams, polyisocyanurate foams, copolyesters, polyurethane coatings, alkyd resins, low-temperature curable resins, or UV curable resins [18][19][20][21][22][23]. These numerous applications, in turn, provide an economical flexibility when using the raw recycled monomer or oligomers for the most profitable option upon demand.…”

“…Glycolysis of PET is most frequently carried out, either under pressure or at atmospheric pressure, using zinc acetate as catalyst [22,[24][25][26][27][28][29][30]. Other metal salts, including metal (Co, Pb and Mn) acetates [25,[31][32][33], metal (Zn, Li, Mg and Fe) chlorides [34] or titanium phosphate [35], have been also investigated.…”

Chemical recycling of poly(ethylene terephthalate). Application to the synthesis of multiblock copolyesters

“…To the best of our knowledge, no one has ever been used BHET as diol for the PET glycolysis. Similarly, several studies have been carried out on the reaction of PET and ethylene glycol for the synthesis of hydroxytelechelic oligomers of PET [34][35][36] which were mainly used for producing unsatured polyester resins [34,35] and very few polycondensations have been carried out by using hydroxytelechelic oligomers of PET with !-caprolactone [37]. Copolyesters with PET and !-caprolactone units are mainly synthesized by polycondensation of dimethyl terephthalate, ethylene glycol and !-caprolactone [38], or by transesterification in copolyester blend [39,40].…”

Optimization of phthalic/maleic anhydride-endcapped PET oligomers using response surface method

“…Glycolysis of PET waste with ethylene glycol (EG) can lead to the production of bis(hydroxyethyl) terephthalate (BHET) monomer and PET oligomers. BHET has been used extensively in the production of polymeric substances, such as unsaturated polyester resins (UPR) , rigid or flexible polyurethanes , and polymer nanocomposites . Vaidya and Nadkarni studied the formation of UPR from PET glycolysis.…”

“…They showed that the glycolysis reaction rate is extremely based on the operating conditions such as reaction time, amounts of catalyst, and glycol/PET molar ratio. In previous works, a simple glycolysis system was set up in the presence of zinc acetate, as an efficient catalyst, and the glycolyzed products of off‐grade PET (OPET) were identified .…”