Depolymerisation of poly(ethylene terephthalate) fibre wastes using ethylene glycol

Poly(ethylene terephthalate) [PET] fibre wastes from an industrial manufacturer was depolymerised using excess ethylene glycol [EG] in the presence of metal acetate as a transesterification catalyst. The glycolysis reactions were carried out at the boiling point of ethylene glycol under nitrogen atmosphere up to 10 h. Influences of the reaction time, volume of EG, catalysts and their concentrations on the yield of the glycolysis products were investigated. The glycolysis products were analysed for hydroxyl and acid values and identified by different techniques, such as HPLC, ¹H NMR and ¹³C NMR, mass spectra, and DSC. It was found that the glycolysis products consist mainly of bis(hydroxyethyl)terephthalate [BHET] monomer (>75%) which was effectively separated from dimer in quite pure crystalline form.     

Kinetics of poly(ethylene terephthalate) glycolysis by diethylene glycol. Part II: Effect of temperature, catalyst and polymer morphology

The influence of various parameters on the kinetics of poly(ethylene terephthalate) (PET) glycolysis by diethylene glycol (DEG), namely temperature (from 190 to 220 °C), temperature profile, catalysis and PET morphology has been studied.The results showed a strong influence of some experimental conditions (temperature and catalysis) on the mixture evolution during depolymerisation. The temperature study showed a critical temperature between 210 and 220 °C which seems to be the consequence of a better diffusion of DEG in PET, allowing easier reactions in solid phase. The initial morphology of PET scraps does not affect the rates of reactions much, in contrast to the temperature profile which has a great importance: time of PET dissolution at 220 °C is considerably shorter by heating PET and DEG separately at 220 °C before mixing, than by heating a cold mixture of the two reagents to 220 °C.     

Ultrasound assisted alkaline hydrolysis of poly(ethylene terephthalate) in presence of phase transfer catalyst

Alkaline hydrolysis of poly(ethylene terephthalate) (PET) flakes from waste packaged drinking water bottles was carried out with and without influence of ultrasound waves rated 20 kHz frequency and 190 W power. Alkali used for hydrolysis was 10% NaOH (w/w). Tetrabutyl ammonium iodide (TBAI) was used as phase transfer catalyst (PTC) to enhance rate of hydrolysis. The experiment yields terephthalic acid (TA) and ethylene glycol as products of hydrolysis. Minimum time required for ultrasound assisted (UA) reaction and without ultrasound assistance (WUA) reaction to complete was investigated and compared. PTC: PET ratio = 0.03:1 w/w, temperature (90 °C) and NaOH concentration (10% w/w) were kept constant. All reactions were carried out at atmospheric pressure. For UA reaction, time required for 100% conversion of PET was found to be 45 min. For WUA reaction, the time required for 100% conversion of PET was found to be more than 65 min. Yield of TA was found to be >99% on the basis of moles of repeating units of PET fed. Melting point of product was found nearly equal to standard TA. Product TA was confirmed by comparing Fourier-transform infrared spectroscopy (FTIR) spectra of product with that of standard TA. Ratio of PTC to PET was fine-tuned for UA reaction keeping reaction time constant at 45 min.     

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) into the monomer bis(2-hydroxyethyl) terephthalate (BHET)

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) with ethylene glycol (EG) to bis(2-hydroxyethyl) terephthalate (BHET) was investigated for the purpose of developing a PET recycling process. Supercritical glycolysis was carried out at 450 °C and 15.3 MPa while subcritical glycolysis was carried out at 350 °C and 2.49 MPa or at 300 °C and 1.1 MPa. High yields (gt; 90%) of the monomer BHET were obtained in both super- and subcritical cases. For the same PET/EG weight ratio of about 0.06, the optimum reaction time was 30 min for supercritical glycolysis and 75 and 120 min for two cases of subcritical glycolysis. GPC, RP-HPLC, ¹H NMR and ¹³C NMR, and DSC were used to characterize the polymer and reaction products. Supercritical glycolysis will be suitable to a process requiring a high throughput due to its short reaction time.     

Microwave assisted ecofriendly recycling of poly (ethylene terephthalate) bottle waste

Glycolysis of poly (ethylene terephthalate) bottle waste was carried out using microwave energy. A domestic microwave oven of 800 W was used with suitable modification for carrying out the reaction under reflux. The catalysts used for the depolymerization in ethylene glycol (EG) were zinc acetate and some simple laboratory chemicals such as sodium carbonate, sodium bicarbonate and barium hydroxide. Comparison of results was made from the point of view of the yield of bis (2-hydroxyethylene) terephthalate (BHET) and the time taken for depolymerization. It was observed that under identical conditions of catalyst concentration and PET:EG ratio, the yield of BHET was nearly same as that obtained earlier by conventional electric heating. However, the time taken for completion of reaction was reduced drastically from 8 h to 35 min. This has led to substantial saving in energy.     

Kinetics of poly(ethylene terephthalate) glycolysis by diethylene glycol. I. Evolution of liquid and solid phases

The kinetics of uncatalysed glycolysis, at 220 °C, of poly(ethylene terephthalate) (PET) by diethylene glycol (DEG) in high excess has been studied. An experimental device allowing good separation, at reaction temperature, of the solid and liquid phases was set up.The results suggest that PET is initially depolymerized in the slightly swollen solid phase, by glycolysis of the amorphous interlamellar chains. This mechanism continues until a solid phase of highly crystallized polyester is obtained.The internal tensions engendered by this chemical modification cause cracks, delamination and mechanical disintegration of the polymer. The transfer towards the liquid phase is then strongly accelerated and the solvolysis of the depolymerization products continues in the liquid phase, up to equilibrium.     

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.     

Direct usage of products of poly(ethylene terephthalate) glycolysis for manufacturing of glass-fibre-reinforced plastics

The paper reports on the possibility of direct use of some products of poly(ethylene terephthalate) glycolysis, bis(2-hydroxyethyl) terephthalate and ethylene glycol mainly, in the process of glass-fibre-reinforced plastics manufacturing. The addition of toluene diisocyanate as an intermediating agent was an important prerequisite for their incorporation into the resin composition. The composites containing products of poly(ethylene terephthalate) glycolysis up to 15% mass display improved mechanical properties in comparison with the unmodified samples.     

Chemical recycling of poly(ethylene terephthalate) waste using ethanolamine. Sorting of the end products

There is a growing keen interest aimed at recycling post-consumer poly(ethylene terephthalate), PET, wastes for both environmental and economic reasons. In this study ethanolamine (EA) has been investigated for aminolytic degradation of PET waste in the presence of dibutyl tin oxide (DBTO) as a catalyst. The process proceeds at 190 °C and under atmospheric pressure. The yield of white precipitate was subject to spectroscopic measurements (FT-IR, NMR, XRD and MS), to thermal analyses (DSC, DTA and TG) and to chemical testing (elemental analysis and solubility characterization).Based on the data reached from various examinations, the product formed is identified as bis(2-hydroxyethylene) terephthalamide (BHETA) which could be consider a source for differing polyurethanes. These kinds of materials have potential for many applications such as adhesives and coatings.     

Ethylene glycol aluminum as a novel catalyst for the synthesis of poly(ethylene terephthalate)

Ethylene glycol aluminum was prepared efficiently and characterized by FT-IR and NMR.It exhibited higher catalytic activity and had profitable effect than titanium glycolate and ethylene glycol antimony for the synthesis of poly(ethylene terephthalate) (PET).It was only used as polycondensation catalyst because it was sensitive to water.For this catalyst,the degree of esterification of the theoretical amount of water was produced up to 95%at 260℃,while the intrinsic viscosity and content of terminal carboxyl groups of the corresponding PET polyester,polymerized at 280℃,70 Pa for 39 min,was 0.87 dL/g and 23.0μmol/g,respectively. Ethylene glycol aluminum was a promising catalyst for the synthesis of PET polyester.     

High‐pressure DTA of poly(butylene terephthalate), poly(hexamethylene terephthalate), and poly(ethylene terephthalate)

Pressure effect on the melting behavior of poly(butylene terephthalate) (PBT) and poly(hexamethylene terephthalate) (PHT) was studied by high‐pressure DTA (HP‐DTA) up to 320 and 530 MPa, respectively. Cooling rate dependence on the DSC melting curves of the samples cooled from the melt was shown at atmospheric pressure. Stable and metastable samples were prepared by cooling from the melt at low and normal cooling rates, respectively. DTA melting curves for the stable samples showed a single peak, and the peak profile did not change up to high pressure. Phase diagrams for PBT and PHT were newly determined. Fitting curves of melting temperature (T_m) versus pressure expressed by quadratic equation were obtained. Pressure coefficients of T_m at atmospheric pressure, dT_m/dp, of PBT and PHT were 37 and 33 K/100 MPa, respectively. HP‐DTA curves of the metastable PBT showed double melting peaks up to about 70 MPa. In contrast, PHT showed them over the whole pressure region. HP‐DTA of stable poly(ethylene terephthalate) (PET) was also carried out up to 200 MPa, and the phase diagram for PET was determined. dT_m/dp for PET was 49 K/100 MPa. dT_m/dp increased linearly with reciprocal number of ethylene unit. The decrease of dT_m/dp for poly(alkylene terephthalate) with increasing a segmental fraction of an alkyl group in a whole molecule is explained by the increase of entropy of fusion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 262–272, 2000     

Heterogeneous CaO(SrO,BaO)/MCF as highly active and recyclable catalysts for the glycolysis of poly(ethylene terephthalate)

Research on Chemical Intermediates - A new group of basic species, CaO(SrO and BaO), supported on mesocellular siliceous foam (MCF) has been prepared and used for catalyzing glycolysis of...     

Poly(ethylene terephthalate) waste recycling and uses for enhancement of bioremediation of arsenic in groundwater

Various studies on arsenic pollution reveal that high concentrations of arsenic were found in many districts of western Uttar Pradesh, India. There arsenic concentrations were higher than the permissible limit given by the World Health Organization (WHO) and Bureau of Indian Standards (BIS). There is a requirement to bioremediate arsenic due to its harmful effect. On the other hand, Poly(ethylene terephthalate) was being repeatedly used as packaging materials, due to which various environmental issues regarding PET waste disposal have generated. In the present study, PET waste was recycled into various aromatic amides by aminolysis and ammonolysis. These aromatic amides were used as surfactants. Various studies have been carried out for biosorption of heavy metal through Bacillus cereus. The efforts were made to enhance bioremediation of arsenic in different water samples spiked with Bacillus cereus in the presence of synthesized aromatic amides. This study explored the possibility to increase bioremediation of arsenic by bacteria using recycled PET waste. The results of this study indicated that in the presence of aromatic amides the percent biosorption could be enhanced by bacteria up to 20–60%.The other significant approach of this study is recycling of PET waste.     

Analysis of the 1030-cm−1 band of poly(ethylene terephthalate) fibers using polarized raman microscopy

Polarized Raman spectroscopy was used to analyze uniaxially oriented fibers of poly(ethylene terephthalate) (PET) fibers. The second-order and fourth-order Legendre polynomials of the orientation distribution function of the 1030-cm⁻¹ vibrational band were determined to be zero for samples of low-to-moderate orientation. Because this band was assigned to the gauche conformation of the ethylene glycol unit, the orientation of the gauche configuration of ethylene glycol units in PET for PET of low-to-moderate orientation was random. This was consistent with the assumptions used by Ward and coworkers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 47–52, 2004     

Nonisothermal crystallization behavior of exfoliated poly(ethylene terephthalate)‐layered silicate nanocomposites in the presence and absence of organic modifier

Exfoliated poly(ethylene terephthalate) (PET)‐layered silicate nanocomposites (P_etLSNs) excluding (P_etLSN_eom) and including (P_etLSN_iom) organic modifiers were obtained by solution methods with and without solvent‐nonsolvent system, respectively. From wide angle X‐ray diffraction and high resolution transmission electron microscopy, both P_etLSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in P_etLSN_eom was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in P_etLSN_iom. Thus, the effect of the presence and absence of organic modifiers in P_etLSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both P_etLSNs had higher degrees of crystallinity and shorter crystallization half‐times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both P_etLSNs. However, P_etLSN_iom exhibited a lower degree of crystallinity and longer half‐time of crystallization than P_etLSN_eom. Difference of crystallization behavior between P_etLSN_eom and P_etLSN_iom was ascribed to organic modifier in P_etLSN_iom, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 989–999, 2008     

Synthesis of highly pure poly(aryleneethnylene)s using palladium supported on calcium carbonate as an eco‐friendly heterogeneous catalyst

Metal catalyst contamination is a major concern in the preparation of polymeric materials. For conjugate polymers, trace amount of metal catalyst is detrimental to the optoelectronic properties. In this work, a method for synthesizing highly pure fluorescent polymers, poly(aryleneethynylene)s (PAEs), was developed using heterogeneous Pd/CaCO₃ catalytic system. Polymerization between a variety of aryl diethynes and aryl diiodides or dibromides were achieved using a catalytic amount of Pd/CaCO₃, CuI, and PPh₃ at 80 °C in good to excellent yields (79–100%). Resulting polymers possess degree of polymerization ranging from 8 to 50 with polydispersity index of 1.5–3.6. Importantly, PAEs from Pd/CaCO₃ catalytic system contain considerably lower level of Pd and Cu contamination (1.9 and 3.4 ppm, respectively) than those obtained from classical homogeneous catalyst, Pd(PPh₃)₄ and PdCl₂(PPh₃)₂ or heterogeneous catalyst Pd/C. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1556–1563     

Kinetics and mechanistic aspects on electron‐transfer process for permanganate oxidation of poly(ethylene glycol) in aqueous acidic solutions in the presence and absence of Ru(III) catalyst

The kinetics and mechanism of oxidation of poly(ethylene glycol) (PEG) by the permanganate ion as a multiequivalent oxidant in aqueous perchlorate solutions at an ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction kinetics was found to be of complex in nature. The pseudo–first‐order plots showed curves of inverted S‐shape, consisting of two distinct stages throughout the entire course of reaction. The first stage was relatively slow, followed by a fast reaction rate at longer time periods. The first‐order dependence in [MnO₄⁻], fractional first‐order dependence in [H⁺], and fractional first‐order kinetics in the PEG concentration for the first stage have been revealed in the absence of the Ru(III) catalyst. The influence of the Ru(III) catalyst on the oxidation kinetics has been examined. The oxidation was found to be catalyzed by the added Ru(III) catalyst. The First‐order dependence on the catalyst and zero order with respect to the oxidant concentrations have been observed. The kinetic parameters have been evaluated, and a tentative reaction mechanism consistent with the kinetic results is suggested and discussed.     

Online wide‐angle X‐ray diffraction/small‐angle X‐ray scattering measurements for the CO2‐laser‐heated drawing of poly(ethylene terephthalate) fiber

Fiber‐structure‐development in the poly(ethylene terephthalate) fiber drawing process was investigated with online measurements of wide‐angle and small‐angle X‐ray scattering with both a high‐luminance X‐ray source and a CO₂‐laser‐heated drawing system. The intensity profile of the transmitted X‐ray confirmed the location of the neck‐drawing point. The diffraction images had a time resolution of several milliseconds, and this still left much room for improvement. Crystal diffraction appeared in the wide‐angle X‐ray images almost instantaneously about 20 ms after necking, whereas a four‐point small‐angle X‐ray scattering pattern appeared immediately after necking. With the elapse of time after necking, the four‐point scattering pattern changed into a meridional two‐point shape. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1090–1099, 2005