Glycolysis of poly(ethylene terephthalate) catalyzed by ionic liquids

Poly(ethylene terephthalate) (PET) from an industrial manufacturer was depolymerized by ethylene glycol in the presence of a novel catalyst: ionic liquids. It was found that the purification process of the products in the glycolysis catalyzed by ionic liquids was simpler than that catalyzed by traditional compounds, such as metal acetate. Qualitative analysis showed that the main product in the glycolysis process was the bis(hydroxyethyl) terephthalate (BHET) monomer. Thermal analysis of the glycolysis products was carried out by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and water content in the catalyst on the conversion of PET, selectivity of BHET, and distribution of the products were investigated. Results show that reaction temperature is a critical factor in this process. In addition, a detailed reaction mechanism of the glycolysis of PET was proposed.     

Synthesis and hydrolytic degradation of poly(ethylene succinate) and poly(ethylene terephthalate) copolymers

The conditions of synthesis of statistical poly(ethylene succinate-co-terephthalate) copolymers (2GTS) and high molecular weight poly(ethylene succinate) (PES) with good hydrolytic and optical parameters, designed for the production of biodegradable products and resins, are presented in this article. Copolymers were prepared by melt polycondensation of bis-(β-hydroxyethylene terephthalate) (BHET) and succinic acid (SA) with excess of ethylene glycol (2G) in the presence of a novel titanium/silicate catalyst (C-94) and catalytic grade of germanium dioxide (GeO₂) as cocatalyst. The chemical structure and physical properties of those materials were characterized by ¹H NMR, FT-IR, dynamical-mechanical thermal analyses (DMTA), differential scanning calorimetry (DSC), solution viscosity and spectroscopic methods. The hydrolytic degradation was performed in a water solution with variable pH, also in garden soil and in compost. The highest hydrolytic degradation rate was observed for pH 4 and for compost. Better hydrolytic degradation values in compost medium were observed for copolyester prepared in the presence of GeO₂ as polycondensation cocatalyst. The copolyester with 40 mol% of aliphatic units was chosen for industrial syntheses which were performed in ELANA and subsequently the processing parameters and compatibility with potato starch of this polyester were checked by BIOP Biopolymer Technologies AG.     

Thermal and crystallization characteristics of poly(trimethylene terephthalate)/poly(ethylene naphthalate) blends

Poly(trimethylene terephthalate) (PTT)/poly(ethylene naphthalate) (PEN) blends were miscible in the amorphous state in all of the blend compositions studied, as evidenced by a single, composition-dependent glass transition temperature (T_g) observed for each blend composition. The variation in the T_g value with the blend composition was well predicted by the Gordon-Taylor equation, with the fitting parameter being 0.57. The cold-crystallization peak temperature decreased with increasing PTT content, while the melt-crystallization peak temperature decreased with increasing amount of the minor component. The subsequent melting behavior after both cold- and melt-crystallization exhibited melting point depression, in which the observed melting temperatures decreased with increasing amount of the minor component. During melt-crystallization, both components in the blends crystallized concurrently just to form their own crystals. The blend with 60% w/w of PTT exhibited the lowest total apparent degree of crystallinity.     

Alkyd resins derived from glycolized waste poly(ethylene terephthalate)

In this investigation the production of secondary value-added products, such as alkyd resins, derived from the glycolysis of poly(ethylene terephthalate) (PET) is examined as an effective way for its recycling. PET was taken from common soft-drink bottles and diethylene glycol (DEG) was used for the depolymerization at several initial molar ratios. The oligomers obtained were analyzed according to their average molecular weights. Furthermore, the glycolyzed PET products (oligomers) were reacted with maleic anhydride, phthalic anhydride and propylene glycol to form unsaturated polyester resins. These were subsequently mixed with styrene and cured using the benzoyl peroxide/amine initiator system to carry out the reaction in ambient temperature. The curing characteristics of the resins produced were investigated with respect to the initial molar ratio of DEG/PET as well as the initial initiator concentration. Finally, the mechanical properties (tensile strength and elongation at the break point) of the resins were compared with the conventional general purpose resin and were found to be comparable.     

Colour formation in poly(ethylene terephthalate) during melt processing

The discolouration, that occurs in virgin poly(ethylene terephthalate) - PET during melt processing, was studied using various bulk and surface analytical techniques. Proton nuclear magnetic resonance (¹H NMR) was used to study the bulk chemical changes occurring in the polymer during thermo-oxidative degradation. Chemical derivatisation with trifluoroacetic anhydride (TFAA) was used to label the hydroxyl groups introduced on the polymer surface by thermal oxidation.From the surface analysis studies using photoacoustic Fourier transform infrared spectroscopy (PA/FT-IR), diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) and X-ray photoelectron spectroscopy (XPS) it was evident that colour formation starts initially with the hydroxylation of the terephthalic ring. Further, the formation of additional carbonyl functionalities and conjugated chromophoric systems complete the colour formation process.     

Structure and properties of new polyester elastomers composed of poly(trimethylene terephthalate) and poly(ethylene oxide)

Series of PTT-b-PEO copolymers with different composition of rigid PTT and PEO flexible segments were synthesized from dimethyl terephthalate (DMT), 1,3-propanediol (PDO), poly(ethylene glycol) (PEG, M_n = 1000 g/mol) in a two stage process involving transesterification and polycondensation in the melt. The weight fraction of flexible segments was varied between 20 and 70 wt%. The molecular structure of synthesized copolymers was confirmed by ¹H NMR and ¹³C NMR spectroscopy. The superstructure of these polymers was characterized by DSC, DMTA, WAXS and SAXS measurements. It was observed that domains of three types can exist in PTT-b-PEOT copolymers: semi-crystalline PTT, amorphous PEO rich phase (amorphous PEO/PTT blended phase) and semi-crystalline PEO phase. Semi-crystalline PEO phase was observed only at temperature below 0 °C for sample containing the highest concentration of PEO segment. The phase structure, thermal and mechanical properties are effected by copolymer composition. The copolymers containing 30÷70 wt% of PEO segment posses good thermoplastic elastomers properties with high thermal stability. Hardness and tensile strength rise with increase of PTT content in copolymers.     

Electron beam irradiation effects on poly(ethylene terephthalate)

Changes in poly(ethylene terephthalate) subjected to electron beam irradiation at doses up to 15 MGy and dose rate of 1.65 MGy/h, were investigated by differential scanning calorimetry, molecular weight measurement, X-ray photoelectron spectroscopy, and scanning electron microscopy. Irradiated samples showed a decrease of molecular weight with a minimum at 5 MGy, which is attributed to chain scission of the macromolecules and then an increase at further doses due to branching and some degradation effect. Irradiation in air is not an important factor because the high dose rate of irradiation inhibits oxygen diffusion in the samples.     

Blood compatibility of surface-engineered poly(ethylene terephthalate) via o-carboxymethylchitosan

Poly(ethylene terephthalate) (PET) films were treated by argon plasma following by graft copolymerization with acrylic acid (AAc). The obtained PET-surface grafted PAA (PET-g-PAA) was coupled with chitosan (CS) and o-carboxymethylchitosan (OCMCS) molecules, respectively. Their surface physicochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), water contact angle and streaming potential measurements. The PET-g-PAA surface containing carboxylic acid, CS immobilized PET surface containing amino and OCMCS immobilized PET surface containing both carboxylic acid and amino groups, make the PET surface exhibited a hydrophilic character. The blood compatibility was evaluated by platelet contacting experiments and protein adsorption experiments in vitro. The results demonstrate that the PET surface coupling OCMCS shows much less platelet adhesive and fibrinogen adsorption compared to the other surface modified PET films. The anticoagulation of PET-OCMCS is ascribed to the suitable balance of hydrophobicity/hydrophilicity, surface zeta potential and the low adsorption of protein.     

Study on the pyrolysis of Moroccan oil shale with poly (ethylene terephthalate)

Investigations into the pyrolytic behaviours of oil shale, poly (ethylene terephthalate) (PET) and their mixture have been conducted using a thermogravimetric analyzer. Experiments were carried out dynamically by increasing the temperature from 298 to 1273 K with heating rates of 2 to 100 K/min under a nitrogen atmosphere. Discrepancies between the experimental and calculated TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. The maximum degradation temperature of each component in the mixture was higher than those the individual components; thus an increase in thermal stability was expected. The kinetic processing of thermogravimetric data was carried out using Flynn-Wall-Ozawa (FWO) method.     

Reaction to fire of recycled poly(ethylene terephthalate)/polycarbonate blends

In the present paper, we study the effect of both morphology and compatibilization on the reaction to fire of blends of recycled poly(ethylene terephthalate) (PETr) with recycled polycarbonate (PCr). It is shown that while the flame retardancy of blends containing less than 50% w/w of PCr increases almost linearly with PCr content, blends containing more than 50% w/w of PCr react to fire like pure PCr. This change of reaction to fire correlates with the formation of a continuous PCr phase in the blend.The compatibilization of the blend by a trans-esterification reaction leading to the formation of copolymers at the interface decreases the overall fire performances due to PETr chain breaking as a side effect which results in a strong decrease of blend viscosity and of the temperature at which mass loss begins.     

Elastic behavior of poly(ethylene terephthalate) chains

The Monte Carlo (MC) method based on the rotational-isomeric-state (RIS) model is adopted in studying the elastic behavior of poly(ethylene terephthalate) (PET) chains in this paper. The mean-square end-to-end distance 〈R²〉, the mean-square radius of gyration 〈S²〉, and the ratio of 〈R²〉/〈S²〉 all increase with elongation ratio λ. The interior conformations are also investigated through calculating the a priori probability of rotational state in the process of tensile elongation. The radius of gyration tensor S is introduced here in order to measure the shape of PET chains, and increases with elongation ratio λ, however, some different behaviors are obtained for . Here , and are the eigenvalues of the radius of gyration tensor . The average energy per repeat unit 〈U〉 and the average free energy per repeat unit 〈A〉 are also calculated, and we find that the average energy decreases with elongation ratio λ, however, the average free energy per repeat unit increases with elongation ratio λ. Elastic force f, energy contribution to force f_U, and entropy contribution to force f_S are also investigated. Both elastic force f and entropy contribution to force f_S increases with λ, however, energy contribution to force f_U and the ratio f_U/f decreases with λ. The ratio of f_U/f is less than zero and almost independent of chain length. The results of these microscopic calculations may explain some macroscopic phenomena of rubber elasticity.     

Non-isothermal crystallization kinetics of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends

The glass-transition temperature and non-isothermal crystallization of poly(trimethylene terephthalate)/poly(ethylene 2,6-naphthalate) (PTT/PEN) blends were investigated by using differential scanning calorimeter (DSC). The results suggested that the binary blends showed different crystallization and melting behaviors due to their different component of PTT and PEN. All of the samples exhibited a single glass-transition temperature, indicating that the component PTT and PEN were miscible in amorphous phase. The value of T_g predicted well by Gordon-Taylor equation decreased gradually with increasing of PTT content. The commonly used Avrami equation modified by Jeziorny, Ozawa theory and the method developed by Mo were used, respectively, to fit the primary stage of non-isothermal crystallization. The kinetic parameters suggested that the PTT content improved the crystallization of PEN in the binary blend. The crystallization growth dimension, crystallization rate and the degree of crystallinity of the blends were increased with the increasing content of PTT. The effective activation energy calculated by the advanced iso-conversional method developed by Vyazovkin also concluded that the value of E_a depended not only on the system but also on temperature, that is, the binary blend with more PTT component had higher crystallization ability and the crystallization ability is increased with increasing temperature. The kinetic parameters U^* and K_g were also determined, respectively, by the Hoffman-Lauritzen theory.     

Effect of silica nanoparticles on solid state polymerization of poly(ethylene terephthalate)

In the present study, the effect of silica nanoparticles, on the solid state polycondensation (SSP) kinetics of poly(ethylene terephthalate) (PET) is thoroughly investigated. At silica concentrations less than 1 wt% and reaction temperatures between 200 and 230 °C higher intrinsic viscosity (IV) values were measured, compared to neat PET at all reaction times. However, with 1 wt% of nanosilica (n-SiO₂), the IV increase of the nanocomposites was similar to that of neat PET and a further increase to 5 wt% n-SiO₂ resulted in significantly lower IV values. A simple kinetic model was also employed to predict the time evolution of IV, as well as the carboxyl and hydroxyl content during SSP. The kinetic parameters of the transesterification and esterification reactions were estimated at different temperatures with or without the addition of n-SiO₂. The activation energies of both reactions were determined together with the concentration of inactive end-groups. From the experimental measurements and the theoretical simulation results it was proved that n-SiO₂ in small amounts (less than 1 wt%) enhances both the esterification and transesterification reactions at all studied temperatures acting as a co-catalyst. However, as the amount of nanosilica increases a number of inactive hydroxyl groups were estimated corresponding to participation of these groups in side reactions with the nanosilica particles. These side reactions lead initially to branched PET chains and eventually (5 wt% n-SiO₂ concentration) to crosslinked structures.     

Recycling of waste poly(ethylene terephthalate) with castor oil using microwave heating

The chemical recycling of waste poly(ethylene terephthalate) (PET) using castor oil (CO) as a reagent is reported. CO presents a renewable alternative to petrochemical based reagents, e.g. glycols, and enables also substantial modification of final physico-chemical properties of a received product. Advantageously, microwave irradiation was used to accelerate the depolymerization of PET. A composition of obtained product was strongly influenced by the reaction temperature. When the decomposition of PET was performed at temperature higher than 240 °C, then a significant extent of side products based on PET oligomers and transesterified CO was observed due to dehydration and hydrolysis of CO. Contrary to that, PET decomposition took place at slow rate below 230 °C and the optimal reaction temperature lies in the relatively narrow interval from 230 °C to 240 °C. The product prepared in the optimal temperature range did not contain any high molecular weight PET oligomers. MALDI-TOF mass spectrometry enabled to identify the structures included in the obtained polyol product. The maximum number of six repeating monomeric unit of PET was found in the product, which confirmed practically the complete depolymerization of PET chain and good reactivity of the acylester hydroxyl groups of CO.     

In situ preparation of poly(ethylene terephthalate)-SiO2 nanocomposites

Poly(ethylene terephthalate) (PET)/silica nanocomposites were synthesized by using the in situ polymerization approach. Sol-gel transformation based on the hydrolysis and condensation of tetraethoxysilane (TEOS) is used to prepare the inorganic phase, concurrent with condensation polymerization of terephthalic acid and ethylene glycol to produce the PET matrix. Due to the simultaneous formation of the polymer matrix and the inorganic networks, a macrophase separation is avoided, and the resulting materials have a high degree of homogeneity. The morphology and the crystallization behavior of the composites were examined by scanning electron microcopy (SEM) and differential scanning calorimetry (DSC), respectively.     

Miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) blends by transesterification

The effects of transesterification on the miscibility of poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) were studied. Blends were obtained by solution precipitation at room temperature to avoid transesterification during blend preparation. The physical blends and transesterified products were analyzed by wide-angle x-ray scattering, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy. It was found that the physical blends are immiscible and when the extent of transesterification reaches 50% of the completely randomized state, independent of blend composition, the blends are not crystallizable and show a single glass transition temperature between those of starting polymers. The interchange reactions were significantly influenced by annealing temperature and time but negligibly by blend composition. © 1996 John Wiley & Sons, Inc.     

Graft copolymerization of itaconic acid-methacrylamide comonomers onto poly(ethylene terephthalate) fibers

The graft copolymerization of itaconic acid-methacrylamide (IA-MAAm) comonomers was carried out using benzoyl peroxide as initiator onto poly(ethylene terephthalate) (PET) fibers in an aqueous medium. The grafted fibers were characterized by FTIR, TGA, DSC and SEM analysis. Effect of various parameters on graft yield such as feed composition, feed and initiator concentration, reaction time and temperature were investigated. The graft yield in the presence of MAAm increased because of the synergistic effect of MAAm comonomer. While, the graft yield alone with the IA onto PET fiber was 2.2%, the use of MAAm as a comonomer increased the amount of IA introduced to the PET fiber up to 13.7%. The reactivity ratios for both monomers were determined by using a Fineman-Ross plot. The grafting rate and saturation graft yield was increased upon increasing the temperature between 65 °C and 85 °C. When the temperature increased further than 85 °C, the saturation graft yield decreased. The graft yield has shown an increase up to an initiator concentration of 1.0 × 10⁻² M and slightly decreased. The grafting increased the dyeability with acidic and basic dyes, and moisture absorption capacity but decreased the thermal stability of the fibers.     

A novel halogen-free flame retardant for glass-fiber-reinforced poly(ethylene terephthalate)

In order to prepare halogen-free flame-retardant glass-fiber-reinforced poly(ethylene terephthalate) (FR-GF-PET), a novel flame retardant containing three flame-retardant elements, P, N and S, was synthesized by melt condensation reaction. Its chemical structure was characterized by FT-IR and ¹H NMR spectra. FR-GF-PET was prepared by melt-mixing the flame retardant with GF-PET. The effects of the flame retardant on the flammability and thermally decomposing behaviors of GF-PET were studied via LOI, UL-94 and TGA tests. The results showed that despite a negative effect on the thermal stability of GF-PET, the incorporation of the flame retardant improved the flame retardancy of GF-PET largely. The LOI values of GF-PET increase linearly with the increase of flame retardant content. The GF-PET passed the V-0 rating in UL-94 tests when 15 wt% of the flame retardant was added to GF-PET. An interesting phenomenon was found, that is, with the increase of flame retardant content, the flame retardancy of the system increased but the char yield decreased, which was explained according to the evidences of XPS tests and the kinetics of thermally decomposing reaction.     

Thermal,crystallization, mechanical,and rheological characteristics of poly(trimethylene terephthalate)/poly(ethylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) in the amorphous state were miscible in all of the blend compositions studied, as evidenced by a single, composition‐dependent glass‐transition temperature observed for each blend composition. The variation in the glass‐transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.91. The cold‐crystallization (peak) temperature decreased with an increasing PTT content, whereas the melt‐crystallization (peak) temperature decreased with an increasing amount of the minor component. The subsequent melting behavior after both cold and melt crystallizations exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of the minor component of the blends. During crystallization, the pure components crystallized simultaneously just to form their own crystals. The blend having 50 wt % of PTT showed the lowest apparent degree of crystallinity and the lowest tensile‐strength values. The steady shear viscosity values for the pure components and the blends decreased slightly with an increasing shear rate (within the shear rate range of 0.25–25 s^?1); those of the blends were lower than those of the pure components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 676–686, 2004     

Segmented block copolymers of poly(ethylene glycol) and poly(ethylene terephthalate)

A new series of segmented copolymers were synthesized from poly(ethylene terephthalate) (PET) oligomers and poly(ethylene glycol) (PEG) by a two‐step solution polymerization reaction. PET oligomers were obtained by glycolysis depolymerization. Structural features were defined by infrared and nuclear magnetic resonance (NMR) spectroscopy. The copolymer composition was calculated via ¹H NMR spectroscopy. The content of soft PEG segments was higher than that of hard PET segments. A single glass‐transition temperature was detected for all the synthesized segmented copolymers. This observation was found to be independent of the initial PET‐to‐PEG molar ratio. The molar masses of the copolymers were determined by gel permeation chromatography (GPC). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4448–4457, 2004