Hydrolysis Of PET Research Articles

A kinetic study of the depolymerisation of poly(ethylene terephthalate) by phase transfer catalysed alkaline hydrolysis

AbstractBACKGROUND: Chemical or tertiary recycling of waste polymers including PET, poly(ethylene terephthalate), leads to the formation of raw starting monomers by different depolymerisation routes. This work was focused on the identification of the catalytic behaviour, if any, of a series of quaternary phosphonium and ammonium salts as phase transfer catalysts for the alkaline hydrolysis of PET, and on the determination of the kinetics of the phase transfer catalysed process.RESULTS: Among the salts examined tributylhexadecylphosphonium bromide was found to be the most effective catalyst. The proposed kinetic model accounted for the uncatalysed and catalysed reactions and predicted a linear correlation for the reaction rate with the concentration of the quaternary salt. The notable increase in the phase transfer catalysed reaction rate was related mainly to the greater value of the pre‐exponential factor while the value of the activation energy was hardly modified by the presence of the quaternary phosphonium salt, thereby suggesting a similar mechanism for the alkaline hydrolysis with or without phase transfer catalyst.CONCLUSIONS: The use of selected phosphonium quaternary salts exhibited a remarkably positive effect on the experimental conditions under which the depolymerisation of poly(ethylene terephthalate) by alkaline hydrolysis can be carried out, especially in terms of low operating temperature. Kinetic correlations provided a reliable mathematical reaction model for this recycling process, which is in agreement with the principles of sustainable development. Copyright © 2008 Society of Chemical Industry

Enzymatic surface hydrolysis of PET enhances bonding in PVC coating

The effect of polyesterase preparations from Thermomyces lanuginosus and Beauveria brongniartii on the hydrophilicity of PET materials was assessed. As a result of polyesterase treatment the hydrophilicity of PET fabrics was increased by up to 8 cm in terms of rising height with increases in surface tension from 6.2 mNm (heat-inactivated control samples) to above 8 mNm. Both enzymes were able to increase the amount of hydroxyl groups on PET from 90 to a maximum of 182 mmol kg−1, while only the B. brongniartii polyesterase released significant amounts of terephthalic acid from PET. Enzymatic surface hydrolysis of PET increased the bonding strength in PVC coating to 13.40 daN 5cm−1 using 0.5% adhesive compared to 11.5 daN 5cm−1 obtained without enzyme pretreatment and 6% of adhesive.

Next issue (March 2007): Textile biotechnology

AbstractEdited by Prof. Cavaco‐Paolo (Lisbon, Portugal).Highlight articles:– Catalases for cleaner bleaching– Natural retting agents– Decolorization of reactive azo dyes– Wax removal for accelerated cotton scouring– Enzymatic cotton scouring products– Photochemical immobilization on polyethylene– Nitrilases for the surface modification of acrylic fibers– PET hydrolysis by Fusarium esterases– PVA‐degrading enzymes in cotton fabric desizing... and much more: Read the next issue of BTJ!

Low temperature solid‐state extrusion of recycled poly(ethylene terephthalate) bottle scraps

AbstractThe processing of poly(ethylene terephthalate) (PET) involves thermal and hydrolytic degradation of the polymer chain, which reduces not only the intrinsic viscosity and molecular weight, but also the mechanical properties of recycled materials. A novel PET/bisphenol A polycarbonate/styrene–ethylene–butylene–styrene alloy based on recycled PET scraps is prepared by low temperature solid‐state extrusion. Hydrolysis and thermal degradation of PET can be greatly reduced by low temperature solid‐state extrusion because the extrusion temperature is between the glass‐transition temperature and cold‐crystallization temperature of PET. Modification of recycled PET by low temperature solid‐state extrusion is an interesting method; it not only provides an easy method to recycle PET scraps by blend processing, but it can also form novel structures such as orientation, crystallization, and networks in the alloy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2692–2699, 2006

Surface modification of poly(ethylene terephthalate) via hydrolysis and layer-by-layer assembly of chitosan and chondroitin sulfate to construct cytocompatible layer for human endothelial cells

Surface modification of poly(ethylene terephthalate) (PET) film was performed by surface hydrolysis and layer-by-layer (LBL) assembly followed a mechanism of electrostatic adsorption of oppositely charged polymers, exemplified with chitosan and chondroitin sulfate (CS). Hydrolysis of PET in concentrated alkaline solution produced a carboxyl-enriched surface. The changes of weight loss and surface chemistry, morphology and wettability were monitored and verified by UV–vis spectroscopy, atomic force microscopy (AFM) and water contact angle. Assembly of positively charged chitosan and negatively charged CS was then conducted in a LBL manner to create multilayers on the hydrolyzed PET film. The process of layer growth and oscillation of surface wettability were monitored by UV–vis spectroscopy and water contact angle measurement, respectively. In vitro cell culture revealed that the adherence of endothelial cells was significantly enhanced on the biomacromolecules-modified PET film with preserved endothelial cell function, in particular on those assembled with larger number of chitosan/CS layers. However, with regard to cell proliferation and viability properties after cultured for 4 days, minor difference was determined between the modified and the unmodified PET films.

Hydrolytic Depolymerization of Poly(Ethylene Terephthalate) Waste at High Temperature Under Autogenous Pressure

The hydrolytic depolymerization reaction of poly(ethylene terephthalate) (PET) waste in neutral water was carried out in an autoclave at 225, 240, 255, and 270°C under autogenous pressure. Particle size, agitator speed, charge ratio, and reaction time required for PET hydrolysis were optimized. Products of the reaction were terephthalic acid (TPA) and ethylene glycol (EG) that were analyzed and confirmed. Yields of TPA and EG were almost equal to PET conversion. Analysis of PET waste sample was also studied. Two different kinetic models for PET hydrolysis were fitted with our own experimental data. Moreover, a noncatalytic PET hydrolysis was studied to understand the effect of autocatalyzed action during reaction. Thermodynamics was undertaken to calculate the Gibbs free energy, and enthalpy and entropy of reaction. Furthermore, the effect of temperature on the rate constant was examined by Arrhenius plot to evaluate the activation energy, and Arrhenius constant for PET hydrolysis.

Microkinetics and Mass Transfer Study of Treatment of Aqueous and Alcoholic Potassium Hydroxide on Poly (Ethylene Terephthalate) Waste

The depolymerization reactions of poly (ethylene terephthalate) (PET) waste with aqueous as well as alcoholic (methanolic and ethanolic) solutions of potassium hydroxide was studied in a batch reactor at atmospheric pressure and at various temperatures (35–98°C) for different time periods (0.5–60 min). Methanolic alkaline solution was shown to have a greater reaction effect compared to that of aqueous as well as ethanolic solutions. The products of the reaction were found to be ethylene glycol (EG) and dipotasium terephthalate salt (K2-TPA) in liquid phase. The K2-TPA was converted into terephthalic acid (TPA) by using HCl. The EG, TPA, and PET wastes were analyzed and confirmed. Acid value as well as carboxyl-group concentrations of TPA significantly increases with reaction time. Kinetic analysis was undertaken. A microkinetic-mass transport model was developed, and simulated data was compared with experimental data. The model showed good agreement with the experimental data. The model prediction was undertaken by using our own laboratory data. The mass transport was described by using a classical diffusion equation according to Fick's law and a modified Wilke-Chang diffusion model. Diffusion coefficient and mass transfer coefficient were calculated at different temperatures as a function of operation time to understand the process phenomena. Thermodynamics was undertaken. Activation energy for methanolic KOH hydrolysis of PET, calculated from an Arrhenius plot, was 24 kJ/mol, and the Arrhenius constant was recorded as 76,326 L/min/cm2.

Surface‐initiated polymerization from poly(ethylene terephthalate)

AbstractThe free‐radical polymerization of styrene initiated from a functionalized poly(ethylene terephthalate) (PET) surface yielded a tethered polymer layer. The anchoring of the initiator species on the PET surface was performed from surface‐reactive groups easily generated by an alkaline hydrolysis of PET. After each surface modification, PET films were characterized by X‐ray photoelectron spectroscopy, measurements of water contact angles, and time‐of‐flight secondary‐ion mass spectrometry. The influence of the polymerization duration, the grafted initiator density, and the grafting mode on the efficiency of the surface‐initiated polymerization of styrene was investigated. In some cases, the tethering of the polystyrene layer on PET could be a reversible process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1347–1359, 2003

Chemical Recycling, Kinetics, and Thermodynamics of Hydrolysis of Poly(Ethylene Terephthalate) (PET) Waste in Sulfuric Acid in Presence of Phosphoric Acid

Poly(ethylene terephthalate) (PET) powder was depolymerized at atmos‐ pheric pressure in sulfuric acid in presence of 2.5 N phosphoric acid at 88–140°C. Particle sizes ranging from 50 to 512.5 µm and reaction time 30–200 min required for PET hydrolysis were optimized. Terephthalic acid (TPA) and ethylene glycol (EG) were produced by acid‐catalyzed heterogeneous PET hydrolysis. To avoid the carbonization/oxidation of EG and to reduce corrosion, reaction was undertaken below 150°C using less concentration of sulfuric acid at a lower reaction time. To enhance reaction rate, 2.5 N phosphoric acid was introduced during reaction. Ethylene glycol was recovered during hydrolysis by salting‐out technique. Terephthalic acid was separated out by using NaOH solution and then being acidified. Subsequently, TPA and EG were analyzed qualitatively and quantitatively. Yields of TPA and EG were almost equal to PET conversion. A modified shrinking‐core model based on obtained acid value of TPA explained depolymerization in sulfuric acid (in presence of phosphoric acid). Effective surface area is proportional to the degree of hydrolyzed PET (X), affected by formation and growth of pore and crack on PET powder. Hydrolysis rates as well as apparent rate constant are inversely proportional to particle size. Thermodynamics are also undertaken to determine activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy, and entropy. Dependence of rate constant on reaction temperature was correlated by the Arrhenius plot, which shows an activation energy of 56.8 kJ mol−1 and a Arrhenius constant of 530.3 L min−1 cm−2.

Kinetic and thermodynamic studies of depolymerisation of poly(ethylene terephthalate) by saponification reaction

AbstractDepolymerisation reaction of polyester waste was carried out by a saponification reaction. Yields of depolymerised products were up to 85% for a 2.5‐h reaction time. Products obtained were characterized by chemical as well as instrumental analysis such as mp (sublimation), acid value and FTIR spectra. The valued obtained for terephthalic acid (TPA) agreed with those for the pure substance. Chemical kinetics of this reaction shows that it is a first‐order reaction with respect to poly(ethylene terephthalate) (PET) concentration with a velocity constant of the order of 10−2 min−1. In the light of the Yashioka modified shrinking core model, a simultaneous fragmentation and depolymerisation model was proposed for the kinetics of hydrolysis of PET. The modified model is based on change in acid value of the product obtained, which is directly related to the change in surface area of particle. The energy of activation and the Arrhenius constant (frequency factor) obtained by Arrhenius plot were 59.71 kJ g−1 and 8.325 × 106 min−1 respectively.© 2002 Society of Chemical Industry

Recycling of postconsumer poly(ethylene terephthalate) and high‐density polyethylene by compatibilized blending

AbstractTwo ways of recovering the properties of the scrap plastics poly(ethylene terephthalate) (PET) and high‐density polyethylene (HDPE) were analyzed: (1) blending incompletely segregated polymers with a compatibilizer and (2) blending nonsegregated polymers with a small amount (2 pph) of another compatibilizer. The advancement of the compatibilization reaction in a twin‐screw extruder depended on the residence time and intensity of mixing according to melt viscosity measurements and scanning electron microscopy observations. The acceptable mechanical properties for systems with different PET contents were obtained in blends compatibilized with ethylene–glycidyl methacrylate (EGMA) and styrene–ethylene–butylene–styrene grafted with maleic anhydride. For a blend with 75% PET and 25% HDPE, the optimum content of EGMA was determined to be about 4 pph, and a film was produced with this composition. Admixtures present in recycled HDPE migrated to PET during blending and accelerated the hydrolysis of PET. As a result of migration, differences in the mechanical properties of the blends were observed, depending on the brand of recycled HDPE used. EGMA was also successfully used for the improvement of mechanical properties of a nonsegregated mixture based on PET. Tensile properties of two compatibilized PET‐rich and HDPE‐rich commingled scraps indicated the possibility of using these blends for film extrusion, with potential applications in the packaging of technical products. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1473–1485, 2002

Kinetics of Hydrolysis of Poly(ethylene terephthalate) Powder in Sulfuric Acid by a Modified Shrinking-Core Model

Poly(ethylene terephthalate) (PET) powder from waste bottles was degradated at atmospheric pressure in 3−9 M sulfuric acid below 150−190 °C for 12 h to clarify the mechanism for a feedstock recycle process. Terephthalic acid (TPA) and ethylene glycol (EG) were produced by the acid-catalyzed heterogeneous hydrolysis of PET in sulfuric acid. The TPA yield agreed with the degree of hydrolysis of PET, but the EG yield decreased with increasing sulfuric acid concentration because of carbonization of EG. The kinetics of hydrolysis of PET in sulfuric acid could be explained by a modified shrinking-core model for the chemical reaction control, in which the effective surface area is proportional to the degree of hydrolyzed PET, x, affected by formation and growth of pore and crack on PET powder. The apparent rate constant was proportional to the reciprocal of the particle size and the activity of sulfuric acid, and the activation energy was 88.7 kJ/mol.

A review on the potential biodegradability of poly(ethylene terephthalate)

This paper reviews the state of the art in the field of the hydrolytic degradation of poly(ethylene terephthalate) (PET) under bio-environmental conditions. Most of the papers published so far on this subject have been focused on the hydrolysis of PET at high temperatures. Although some authors claim to enhance the biodegradation properties of this aromatic polyester by copolymerization with readily hydrolysable aliphatic polyesters, no clear and satisfying conclusions can yet be formulated. Poly(ethylene terephthalate-co-lactic acid), poly(ethylene terephthalate-co-ethylene glycol), and poly(ethylene terephthalate-co-e-caprolactone) block and random copolymers are the modifications mainly investigated for biodegradable applications. The hydrodegradability and biodegradability of PET, PET copolymers and PET blends are detailed in this review. A total of 89 references including 16 patents are cited. © 1999 Society of Chemical Industry

Hydrolysis of poly(ethylene terephtalate). A steric exclusion chromatography study

The hydrolysis of PET ( M w 27 kg mol −1) in boiling water has been studied by steric exclusion chromatography. It appears that both the average molar mass and the polydispersity index decrease in a pseudohyperbolic way and tend towards asymptotic values, respectively M n ∞ →2 kg mol −1 and I ∞→1.50. This behaviour indicates that hydrolysis is homogeneous at dimension scales higher than Lc (lamellae thickness). Hydrolysis occurs in the amorphous phase and at chain folds at the crystal surface, whereas crystals are unaffected due to their impermeability to water. The chain length decreases to tend, thus, towards L c . Embrittlement is expected to occur when the entanglement network is destroyed in the amorphous phase. Since the corresponding critical chain length L e and the initial chain length L 0 are such as L e and L 0>> L c , it can be considered that in the conversion range of practical interest (e. g. before embrittlement). PET hydrolysis, despite its above quoted peculiarities, can be considered as a random chain scission process in kinetic studies.

Chemical Surface Modification of Poly(ethylene terephthalate)

Reactions of semicrystalline poly(ethylene terephthalate) (PET) film with ester-selective reagents at the film−solution interface can be controlled to produce modified film samples containing a thin (less than ∼ 40 A) surface layer of the reagent-induced functionality. Hydrolysis of PET yields a surface mixture of alcohol and carboxylic acid groups. Reduction with lithium aluminum hydride and transesterification with ethylene glycol (glycolysis) both produce surfaces with alcohol functionality (PET−OHR and PET−OHG, respectively). Each of these modification reactions involves chain cleavage and can lead to significant sample degradation (reactive dissolution); for each modification reaction, conditions were optimized to maximize conversion and minimize degradation. The reactivity of surface alcohols (PET−OH) was assessed for samples prepared by both reduction and glycolysis, and a comparative analysis was made: the presence of benzylic alcohols in reduced samples and their absence in glycolyzed samples as...

Kinetics of Hydrolytic Depolymerization of Melt Poly(ethylene terephthalate)

The hydrolytic depolymerization of poly(ethylene terephthalate) (PET) was carried out in a stirred batch reactor at 235, 250, and 265 °C above its melting point and under autogenous pressure. The solid products which were mainly composed of terephthalic acid were analyzed by potentiometric titration and elemental analysis. The liquid products which were mainly composed of ethylene glycol and a small amount of its dimer were analyzed by gas chromatrography. A kinetic model consisting of forward and backward reactions for the PET hydrolysis fitted well with the experimental data. Moreover, an autocatalytic mechanism was suggested, which indicates that some of the hydrolytic depolymerization of PET was catalyzed by the carboxyl groups produced during the reaction. The dependence of the rate constant on the reaction temperature was correlated by the Arrhenius plot giving the activation energy of 123 kJ/mol for the PET hydrolysis.

Kinetics of Hydrolysis of PET Powder in Nitric Acid by a Modified Shrinking-Core Model

Poly(ethylene terephthalate) (PET) powder from waste bottles was degraded at atmospheric pressure in 7−13 M nitric acid at 70−100 °C for 72 h, to clarify the mechanism of a feed stock recycling process. Terephthalic acid (TPA) and ethylene glycol (EG) were produced by the acid-catalyzed heterogeneous hydrolysis of PET in nitric acid, and the resulting EG was simultaneously oxidized to oxalic acid. The kinetics of the hydrolysis of PET in nitric acid could be explained by a modified shrinking core model of chemical reaction control, in which the effective surface area is proportional to the degree of unreacted PET, (1 − X), affected by the deposition of the product TPA. The apparent rate constant was inversely proportional to particle size and to the concentration of the nitric acid. The activation energy of the reaction was 101.3 kJ/mol.

Degradation of waste poly(ethylene terephthalate) in a steam atmosphere to recover terephthalic acid and to minimize carbonaceous residue

Poly(ethylene terephthalate) (PET) waste was successfully decomposed in a steam atmosphere, yielding an amount of terephthalic acid predicted from the chemical formula of PET. It was found that steam accelerated the hydrolysis of PET, yielding terephthalic acid and oxygen-containing compounds such as aldehyde and ester with less than 1% carbonaceous residue. The amount of carbonaceous residue decreased with an increase in the fraction of steam in the carrier gas and was about 16% in nitrogen steam and below 1% in steam. The amount of terephthalic acid predicted from the chemical formula of PET (about 87%) was recovered at about 723 K in a carrier gas containing 70% steam and 30% nitrogen. Kinetic equations are proposed by considering both the hydrolysis and thermal pyrolysis of PET.

Hydrolysis of waste PET by sulfuric acid at 150°C for a chemical recycling

Hydrolysis of waste PET by sulfuric acid at 150°C for a chemical recycling

Size Exclusion Chromatography of Poly(Ethylene Terephthalate) Using o-Chlorophenol

Abstract Ortho-chlorophenol (OCP) has previously been reported as one component in mixed solvent systems for the size exclusion chromatography of poly (ethyiene terephthalate) (PET)1,2, In order to avoid the problems involved in maintaining mixed solvents, a technique has been developed to analyze PET in OCP alone. The system has been calibrated using narrow polystyrene and broad PET standards. Problems addressed include the high viscosity and high refractive index of OCP, solvent purity, sample preparation, and sample degradation. The system has been used to investigate the hydrolysis and degradation of PET during extrusion processes.