Efficient method for recycling poly(ethylene terephthalate) to poly(butylene terephthalate) using transesterification reaction

A method of recycling postconsumer poly(ethylene terephthalate (PET) using transesterification was studied. Shredded flakes of postconsumer PET waste were transesterified with higher diols, such as 1,4‐butanediol, 1,4‐cyclohexane dimethanol, and 1,6‐hexanediol, to yield copolyesters in the presence of Ti(iPrO)₄ and Sb₂O₃ as catalysts. The extent of the formation of undesirable tetrahydrofuran side products was dependent on the molar ratio of PET to1,4‐butanediol and the time of reflux during transesterification. Quantitative insertion of the butylene moiety into PET could be achieved under appropriate reaction conditions. The mechanical properties of PBT obtained by a transesterification reaction of PET with 1,4‐butanediol were comparable to those of virgin PBT (obtained by direct reaction of dimethyl terephathalate with 1,4‐butanediol). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3720–3729, 2004     

Combustion‐thermal‐sprayed recycled poly(ethylene terephthalate)

Thermal‐sprayed polymer coatings have been used as protection against corrosion and wear. In this study, poly(ethylene terephthalate) (PET) powder, which was obtained from postconsumer beverage bottles, was deposited on 1020 steel by low‐velocity flame‐spray technology. The chemical and structural changes in PET due to the thermal‐spray processing were investigated with Fourier transform infrared spectroscopy and X‐ray diffraction. Changes in tribological behavior were examined by pin‐on‐disk testing and three‐dimensional profilometry. The results show that coatings had the same functional groups as the PET beverage bottles. However, the degree of crystallinity was modified. These changes were rationalized in terms of possible structural modifications of the PET polymer. The study showed evidence that the pin‐on‐disk wear developed by an abrasion process through a ploughing mechanism, although a fatigue mechanism could not be disregarded. A low friction coefficient between PET and steel was confirmed. In the as‐sprayed condition, the PET coatings showed higher friction, likely because of a higher coarse debris production rate during the pin‐on‐disk testing. Heat treating the as‐sprayed coating to increase the amorphous PET content improved the sliding behavior by increasing wear resistance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3159–3166, 2004     

Synthesis and characterization of terephthalamides from poly(ethylene terephthalate) waste

Poly(ethylene terephthalate) (PET) waste flakes (blow‐molded‐grade industrial waste) were degraded with aqueous methylamine and ammonia at room temperature in the presence and absence of quaternary ammonium salt as a catalyst for various times. The catalyst reduced the time required for the degradation of the PET waste. The degraded products were analyzed with IR, nuclear magnetic resonance, mass spectrometry, and differential thermal analysis and were characterized as N,N′‐dimethylterephthalamide and terephthalamide in the case of methylamine and ammonia, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1515–1528, 2005     

Nonisothermal crystallization of reprocessed poly(ethylene terephthalate)

Poly(ethylene terephthalate) was submitted to five reprocessing cycles by extrusion. The materials were analyzed with oligomer and after oligomer extraction. The nonisothermal crystallization of the five samples was investigated by differential scanning calorimetry. Samples with oligomer content and carboxylic end group concentrations between 44 and 98 eqw × 10⁶ g presented a nonlinear correlation with the crystallization temperature. After the oligomer extraction of the polymer, this correlation is linear. The nonisothermal crystallization results were analyzed using the Ozawa model. The polymers containing oligomers obey the Ozawa model for the first reprocessing cycle. After oligomer extraction, the polymers obey the Ozawa model from the first to the third reprocessing cycle. In both cases, the exponential n values are close to 2.0. For the other cycles, deviations from this model occur. The activation energy was calculated using the Kissinger and Varma models. The values obtained for the five reprocessed samples were inversely proportional to the molar mass when analyzed by both models. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 525–531, 2004     

Depolymerization of poly(ethylene terephthalate) waste

Poly(ethylene terephthalate) waste was depolymerized with ethylene glycol in the presence of different catalysts, two conventional metal catalysts (zinc acetate and lead acetate) and two alkalies (sodium carbonate and sodium bicarbonate). The resulting monomer bis(2‐hydroxy ethylene terephthalate) was characterized by thin layer chromatography, melting point, IR spectroscopy, differential scanning calorimetry, and elemental analysis. The results show that the qualitative and quantitative yields of the monomer obtained with alkalies as catalysts were most comparable with the conventional heavy metal catalysts, thus providing a further advantage for the recycling of polyester waste for the cause of environmental pollution abatement. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1765–1770, 2002     

Spinning fibers from poly(ethylene terephthalate) bottle‐grade waste

Poly(ethylene terephthalate) bottle‐grade (BG) waste was converted into spinnable chips and spun on a laboratory‐scale melt‐spinning apparatus into filaments. Virgin fiber‐grade (FG) polyester chips were blended with BG waste during melt spinning so that the influence of blending on the fiber properties could be studied. Subsequently, the scaling‐up of the process was carried out in a polyester recycling plant so that staple fibers could be obtained. In this part of the study, the spinning of blends of BG waste and FG waste was carried out. The BG waste was found to be superior feed stock for melt processing. Fibers with unique properties were obtained from the BG waste. Staple fibers obtained by the blending of FG and BG waste showed properties different from those of fibers spun from BG waste alone. This study also showed that using blends of BG and FG waste could improve the melt processing and staple‐fiber properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3536–3545, 2003     

Modification of poly(ethylene terephthalate) by combination of reactive extrusion and followed solid‐state polycondensation for melt foaming

A combination of reactive extrusion and followed solid‐state polycondensation (SSP) was applied to modify the virgin fiber grade poly(ethylene terephthalate) (v‐PET) and recycled bottle‐grade PET (r‐PET) for melt foaming. Pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) were chosen as the modifiers for the reactive extrusion performed in a twin‐screw extruder. For comparison, commercially available chain extender ADR JONCRYL ADR‐4370‐S was also used. The characterizations of the intrinsic viscosity, i.e., [η], and rheological properties whose changes were correlated to the long chain branches introduced in the molecular structure were performed on the modified PET to evaluate their chain extension extent. The results revealed that the [η] of 1.37 dL/g was obtained for PMDA modified v‐PET while that of 1.15 dL/g for TGIC modified r‐PET. Such difference was attributed to the different reactivity of the two chain extenders with the two types of PET. Increases in shear viscosity and storage modulus, and the high pronounced shear thinning behavior were also observed in the modified PET. Finally, the foamability of the certain modified PET was verified by the batch melt foaming experiments. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42708.     

Influence of the reactive processing of recycled poly(ethylene terephthalate)/poly(ethylene‐co‐glycidyl methacrylate) blends

The effect of the amount of reactive additive and screw speed during extrusion on the morphological characteristics and mechanical performance of recycled poly(ethylene terephthalate)(RPET) was investigated. With an increase in the ethylene–glycidyl methacrylate copolymer (E–GMA) additive content, a gradual increase in the Izod impact strength of the RPET/E–GMA blends was initially recorded. Subsequent increases in the E–GMA content to above 13.5 wt % led to a drastic enhancement in the toughness of the blends. Meanwhile, the density of the blends decreased with increasing amount of the additive E–GMA. The toughness and density of the blends were found to be dependent on the screw rotation speed during the extrusion. In addition, ductile and microporous structures were observed on the Izod impact fracture surfaces. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Analysing metals in bottle‐grade poly(ethylene terephthalate) by X‐ray fluorescence spectrometry

After a rigorous cleaning process, recycled food‐grade poly(ethylene terephthalate) (PET), can be mixed with virgin PET resin in different concentrations and used for packaging of soft drinks. Therefore, it is important to have an experimental method to distinguish the presence of recycled polymer in a batch and to check its “true quality.” One of the issues to be verified is the presence of inorganic contaminants due to the recycling process. X‐ray fluorescence technique is one alternative for this kind of analysis. The results obtained in this work show that bottle‐grade PET samples (PET‐btg) are made either via direct esterification or by a transesterification process. Samples that were subjected to thermo‐mechanical processings (superclean® processing, PET‐btg blends processed in our laboratory and soft drink PET packaging) present Fe Kα emission lines with higher intensities than those presented by virgin bottle‐grade PET. After applying principal component analysis, it can be concluded that Fe is an intrinsic contaminant after the recycling process, furnishing a way to indicate class separations of PET‐btg. A calibration and validation partial least squares model was constructed to predict the weight percent of post‐consumption bottle‐grade PET in commercial PET samples. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of water‐extended polyester based on recycled poly(ethylene terephthalate)

An unsaturated polyester resin was prepared that was based on the reaction of oligomers obtained from the depolymerization of poly(ethylene terephthalate) waste products, with both maleic anhydride and sebacic acid. The structure of the produced polyester was compared with that prepared from the reaction of dimethyl terephthalate with both maleic anhydride and sebacic acid with IR and NMR spectroscopy. Water‐extended polyester resins were prepared from these two polyesters through curing with styrene in the presence of various amounts of water with benzoyl peroxide as an initiator. The mechanical properties of the prepared water‐extended polyesters, as well as scanning electron microscopy, were investigated. The use of water‐extended polyesters based on recycled poly(ethylene terephthalate) waste for the preparation of decorative art objects and statues was investigated. Therefore, three pharaonic statues representing Tutankhamen, Nefertiti, and a black head of a cat were prepared. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3693–3699, 2003     

Properties of poly(butylene terephthalate) chain‐extended by epoxycyclohexyl polyhedral oligomeric silsesquioxane

Epoxycyclohexyl polyhedral oligomeric silsesquioxane (epoxy–POSS) was used to prepare a chain‐extended poly(butylene terephthalate) (PBT) with a twin‐screw extruder. The effect of epoxy–POSS on the melt flow index, mechanical properties, rheological behavior, and thermal properties of chain‐extended PBT was investigated. PBT had an intrinsic viscosity of 1.1 dL/g and a carboxy1 content of 21.6 equiv/10⁶ g, but the PBT chain‐extended with 2 wt % epoxy–POSS had an intrinsic viscosity of 1.7 dL/g and a carboxy1 content lower than 7 equiv/10⁶ g. After the addition of epoxy–POSS, the melt flow index of PBT dramatically decreased, the elongation at break increased greatly, the tensile strength increased slightly, and the thermal stability was also improved. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Depolymerization of poly(ethylene terephthalate) with catalyst under microwave radiation

Grain poly(ethylene terephthalate) (PET) was depolymerized in pure water in the presence of different catalysts. The product quantity of bis(2-hydroxy ethylene) terephthalate (BHET) and glycol obtained was different from the one without catalysts; especially, using zinc acetate as catalyst, the product obtained was in its pure form with sufficiently high yields. Meanwhile, the depolymerization rate nearly reached to 100%. The purified product was characterized by IR spectroscopy. The depolymerization process of PET reported here was economically viable for the high yields of BHET and glycol. Among all the catalysts used in the reaction, zinc acetate was testified as the most effective one, and the optimal dosage of zinc acetate was 0.4% of the feedstock PET. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ageing of poly(ethylene terephthalate) and poly(ethylene naphthalate) under moderately accelerated conditions

PEN is thought to have increased thermal and hydrolytic resistance in comparison to PET. However, due to a lack of research, few studies have been published on the degradation of PEN. In our research, we report on the extent of degradation in PET and PEN after ageing under contrasting environments (dry nitrogen, dry air, wet nitrogen, and wet air) at temperatures between 140°C and 190°C. A combination of analysis techniques were employed in order to characterize and track the physical and chemical changes in the aged polyester samples, enabling the effects of temperature, water, and oxygen to be mapped onto the resultant property changes of PET and PEN. The extent of degradation has been shown to differ between both polymers and the dominant degradation mechanism in PET was shown to differ with ageing temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Recycling of waste poly(ethylene terephthalate) into flame‐retardant rigid polyurethane foams

Waste poly(ethylene terephthalate) (PET) textiles were effectively chemical recycling into flame‐retardant rigid polyurethane foams (PUFs). The PET textile wastes were glycolytically depolymerized to bis(2‐hydroxyethyl) terephthalate (BHET) by excess ethylene glycol as depolymerizing agent and zinc acetate dihydrate as catalyst. The PUFs were produced from BHET and polymeric methane diphenyl diisocyanate. The structures of BHET and PUFs were identified by FTIR spectra. The limiting oxygen index (LOI) of the PUFs (≥23.27%) was higher than that of common PUFs (16–18%), because the aromatic substituent in the depolymerized products improved the flame retardance. To improve the LOI of the PUFs, dimethyl methylphosphonate doped PUFs (DMMP‐PUFs) were produced. The LOI of DMMP‐PUFs was approached to 27.69% with the increasing of the doped DMMP. The influences of the flame retardant on the foams density, porosity, and compression properties were studied. Furthermore, the influences of foaming agent, catalyst, and flame retardant on the flame retardation were also investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40857.     

Acrylonitrile–butadiene rubber functionalization for the toughening modification of recycled poly(ethylene terephthalate)

The incorporation of functionalized acrylonitrile–butadiene rubber (NBR) into recycled poly(ethylene terephthalate) (PET) was introduced as an effective route for modifying the properties of PET and as a new method for PET recycling as well. To achieve modified NBR, glycidyl methacrylate (GMA) was grafted onto NBR with optimized reactive mixing, in which the highest grafting degree and lowest gel content were generated. PET/NBR blends with and without GMA functionalization were produced by melt mixing, and the mechanical properties, dynamic mechanical thermal properties, and phase morphologies of the systems were determined and compared. We found that low amounts of peroxide initiator (dicumyl peroxide) and high levels of the GMA monomer in the presence of the styrene comonomer led to the maximum grafting degree and suppressed the competing rubber crosslinking and GMA homopolymerization reactions. The blend compatibility with PET determined from dynamic mechanical thermal analysis spectra and scanning electron microscopy images was greatly improved when the NBR‐grafted GMA was used instead of the neat NBR in the blend recipes. As a result, the rubber phase dispersed in the PET matrix more finely, and the impact strength of the blend advanced very significantly. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40483.     

1‐Allyl‐3‐methylimidazolium halometallate ionic liquids as efficient catalysts for the glycolysis of poly(ethylene terephthalate)

Series of 1‐allyl‐3‐methylimidazolium halometallate ionic liquids (ILs) were synthesized and used to degrade poly(ethylene terephthalate) (PET) as catalysts in the solvent of ethylene glycol. One important feature of these new IL catalysts is that most of them, especially [amim][CoCl₃] and [amim][ZnCl₃], exhibit higher catalytic activity under mild reaction condition, compared to the traditional catalysts [e.g., Zn(Ac)₂], the conventional IL catalysts (e.g., [bmim]Cl), Fe‐containing magnetic IL catalysts (e.g., [bmim][FeCl₄]), and metallic acetate IL catalysts (e.g., [Deim][Zn(OAc)₃]). For example, using [amim][ZnCl₃] as catalyst, the conversion of PET and the selectivity of bis(hydroxyethyl) terephthalate (BHET) reach up to 100% and 80.1%, respectively, under atmospheric pressure at 175°C for only 1.25 h. Another important feature is that BHET can be easily separated from the catalyst and has a high purity. Finally, based on the experimental phenomena, in ‐situ infrared spectra, and experimental results, the possible mechanism of degradation with synthesized IL is proposed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Expanding the application field of post‐consumer poly(ethylene terephthalate) through structural modification by reactive blending

With the aim of up‐grading the material properties of post‐consumer PET, making them suitable for extrusion of thermoformable thick sheets, a series of polyepoxy chain extenders have been comparatively evaluated as melt viscosity modifiers for a toughened compatibilized blend containing up to 80 wt % of bottle‐grade post‐consumer recycled poly(ethylene terephtalate) (r‐PET). Combinations of a commercial modifier with pentaerythritol were also successfully employed to cause simultaneous hyperbranching and controlled chain scission, thereby modifying the melt rheology of the material without excessively increasing the molecular weight, as highlighted by common technological melt viscosity measurements such as online torque and off‐line melt flow rate (MFR). Since the high melt fluidity of PET plays a critical role on its flame resistance, the combined effect of chain extenders and halogen‐free phosphorated additives on the fire resistance of the modified toughened blends was also investigated. Preliminary results indicate that the chemical reactions among polymer and additives must be taken into careful account to prevent unfavorable effects on the ultimate melt rheology and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40881.     

Preparation and characterization of high‐molecular‐weight poly(l‐lactic acid) by chain‐extending reaction with phosphites

Poly(l ‐lactic acid) (PLLA) of high molecular weight was prepared by a chain‐extending reaction in a microcompounder. Phosphites were used as chain extenders to increase the molecular weight of the PLLA prepolymer, which was prepared by the bulk polycondensation of l‐lactic acid. The effects of the amount of phosphite, the temperature, and the screw speed on the torque of the PLLA melt were studied. Under the optimal conditions, the molecular weight of PLLA increased from 62,100 to 126,000 g/mol. The chemical structure and crystallinity of PLLA were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR and ¹³C‐NMR, differential scanning calorimetry, and X‐ray diffraction. The mechanical properties of PLLA were measured. The results indicate that triphenyl phosphite (TPPi) was an effective chain extender for PLLA. The role of the TPPi in chain extending is suggested to be an esterification‐promotion agent. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Mechanical,thermal, and structural characterization of poly(ethylene terephthalate) and poly(butylene terephthalate) blend systems by the addition of postconsumer poly(ethylene terephthalate)

The focus of this study was mainly on the use of scrap poly(ethylene terephthalate) (PET) in poly(butylene terephthalate)‐rich blend systems. A good combination of tensile and impact properties was observed in the newly formed blend system with scrap PET. The morphology depicted controlled and well‐dispersed phases. The thorough mixing of the constituents was observed in the thermal study. For this innovative blend system, an attempt to correlate the mechanical, thermal, structural, morphological properties and the chemistry of the blend system seemed to be technoeconomical. This study contributed to the recycling of waste material. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of poly(ethylene isophthalate‐co‐ethylene terephthalate) copolyesters

Poly(ethylene isophthalate‐co‐ethylene terephthalate) (PEIPET) copolymers of various compositions and molecular weights were synthesized by melt polycondensation and characterized in terms of chemical structure and thermal and rheological properties. At room temperature, all copolymers were amorphous and thermally stable up to about 400°C. The main effect of copolymerization was a monotonic increase of glass transition temperature (T_g) as the content of ethylene terephthalate units increased. The Fox equation accurately describes the T_g–composition data. The presence of ethylene terephthalate units was found to influence rheological behavior in the melt, with the Newtonian viscosity increasing as the content of ethylene terephthalate units increased. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 186–193, 2004