Hydrolytic Depolymerization of Polyethylene Terephthalate by Reactive Extrusion

Abstract

Continuous hydrolytic depolymerization of polyethylene terephthalate (PET) resin at high temperature and pressure was carried out in a co-rotating twin screw extruder. In this novel process, hydrolysis is achieved by injection of saturated steam at high pressure. Optimum conditions occur at relatively low screw speeds and water/PET ratios. Hydrolysis extent was measured using carboxyl end group titration, and by determination of molecular weights using NMR and GPC analysis. Low molecular weight products are obtained at low residence times in the extruder, suggesting high depolymerization rates. This is supported by the results of a simple kinetic model.

ATR-IR spectroscopy of superheated water and in situ study of the hydrothermal decomposition of poly(ethylene terephthalate)

“…A broader goal of this study is to facilitate the use of superheated or near-critical water for polymer recycling and waste minimisation. There is a recent report 3 on the elegant work of combining hydrolytic depolymerization of PET with reactive extrusion. The PET degradation can be carried continuously in a co-rotating twin-screw extruder, 3 and thus the information obtained in situ would help to optimise such a process.…”

“…In other recent work on continuous hydrolytic degradation of PET the extent of hydrolysis was also measured by carboxyl end group titration. 3 The strong bands at ca. 685 and 780 cm À1 have been observed in the product of PET degradation and have been assigned to the combination bands of the terephthalic acid as in the work of Tellez et al 24 The band at 940 cm À1 corresponds to the r(C-H) mode while bands in the region 1280-1250 cm À1 are due to d(COH) + n(CO) and b(CCH) + n(C=C), in agreement with ref.…”

“…This allows one to use near-critical water to convert used polymeric materials into useful chemicals. Recent reports [3][4][5][6][7] of decomposition of polymers into monomers, in particular polyethylene terephthalate (PET) 3,[8][9][10][11][12] subjected to near-critical or supercritical water, have demonstrated that there is a need for fundamental understanding of this phenomenon though in situ analysis.…”

A New Strategy for Recycling and Preparation of Poly(l-lactic acid): Hydrolysis in the Melt

“…However, the hydrolysis of crystallizable aliphatic polyesters including optically active PLLA in the melt has not been investigated so far. Such treatment in high-temperature and high-pressure water (hydrothermal treatment) has been utilized to decompose a variety of polymers including an aromatic and optically inactive polyester, poly(ethylene telephthalate) (PET). − After the purification, the obtained l -lactic acid can be readily polymerized to high-molecular-weight (HMW) PLLA by a direct condensation procedure as proposed by Ajioka et al However, the hydrolysis of optically active PLLA in the melt may cause racemization and decomposition of the formed lactic acids due to the high temperature. On the other hand, a new procedure by the use of a lipase was proposed by Matsumura et al for one of the biodegradable polyesters, poly(ε-caprolactone) (PCL), in which HMW PCL was enzymatically hydrolyzed to its oligomer by the presence of water and then the oligomer was polymerized to HMW PCL under restricted water concentration.…”