A Sustainable Circular Route for PET LDH Nanocomposites: Catalyst-Driven Polymerization and Depolymerization for a BHET-to-BHET Cycle

The effect of thermal and non-thermal routes on treatment of the Mg–Al layered double hydroxide catalyst dispersed by titania nanoparticles in products distribution arising from poly(ethylene terephthalate) degradation

Simple SummaryExploring new polyethylene terephthalate (PET)-degrading enzymes is essential for improving the efficiency of PET degradation. Bis(2-hydroxyethyl) terephthalate (BHET) is a key intermediate in the enzymatic depolymerization of PET. In this study, we investigated, for the first time, the BHET degradation activity and thermal stability of the esterase Gs. Our results indicate that Gs exhibits excellent BHET degradation activity; however, it lacks thermal stability during BHET hydrolysis. We performed a comparative structural analysis of the key amino acids involved in the catalysis of BHET and p-nitrophenyl butyrate (pNPB) by Gs using molecular docking. Gs not only demonstrates strong BHET degradation activity but also degrades the PET model substrate bis(benzyloxyethyl) terephthalate (3PET) and PET nanoparticles. Moreover, the combination of Gs and the mono-2-hydroxyethyl terephthalate (MHET) hydrolase, MHETase, can completely hydrolyze BHET. Finally, considering the structural similarity between LCC-ICCG and Gs, this study presents a novel approach to expanding the search for efficient biocatalysts for the degradation of PET plastic.The continuous increase in demand for polyethylene terephthalate (PET) has drawn global attention to the significant environmental pollution caused by the degradation of PET plastics. Exploring new PET-degrading enzymes is essential for enhancing the degradation efficiency of PET, and esterases and lipases with plastic degradation capabilities have become a focal point of research. In this study, we utilized the ultra-efficient mutant FASTase of the PET-degrading enzyme IsPETase, derived from Ideonella sakaiensis, as a positive control, based on the similarity in enzyme activity and substrate. We investigated the PET model substrate degradation activities of the esterase Gs and lipase GI, both derived from Bacillus spp., as well as the lipase CAI derived from Pseudomonas spp. The results indicated that Gs exhibited excellent bis(2-hydroxyethyl) terephthalate (BHET) degradation activity; however, Gs demonstrated a lack of thermal stability when hydrolyzing BHET. Molecular docking analyses were conducted to identify the key amino acids involved in the degradation of BHET by Gs from a structural perspective. At the same time, GI and CAI showed no BHET degradation activity. The combination of Gs and the mono-2-hydroxyethyl terephthalate (MHET) hydrolase, MHETase, can completely hydrolyze BHET, and Gs also exhibited degradation activity against the PET model substrate bis(benzyloxyethyl) terephthalate and PET nanoparticles. Given the structural similarity between PET hydrolase LCC-ICCG and Gs, this study provides new enzyme resources for advancing the efficient biological enzymatic degradation of PET plastics.

Characterization of a novel esterase and construction of a Rhodococcus-Burkholderia consortium capable of catabolism bis (2-hydroxyethyl) terephthalate

Effects of layered double hydroxides on poly(vinyl alcohol)/poly(acrylic acid) films for green food packaging applications

Bis(2-hydroxyethyl) terephthalate (BHET) is one of the major products in the process of chemical recycling of waste poly(ethylene terephthalate) (PET). In this study, we synthesized a series of biodegradable aromatic–aliphatic random copolymers, poly(ethylene aliphatate-co-terephthalate), directly from BHET together with aliphatic dicarboxylic acids including succinic acid (SA), adipic acid (AA), sebacic acid (Seb), and dodecanedioic acid (DDDA) via a two-step melt polycondensation reaction. The composition of the copolymers was adjusted precisely to optimize their crystallinity, thermo-mechanical properties, and biodegradation performance. In particular, the aromatic–aliphatic copolymer films exhibited excellent elastic properties, displaying tensile strength <27 MPa and elongation at break near 700%, as well as excellent optical transparency (haze <10%), thereby outperforming the conventional petroleum-derived and biodegradable polymers. The biodegradable aromatic–aliphatic copolymers synthesized based on BHET with excellent transparency, mechanical properties, and biodegradability show remarkable potential for open-loop recycling from PET waste and sustainable packaging applications.

This paper was designed and prepared a new nanoarchitectonics of LDH/polymer composite with specific morphology. For this purpose, CTAB surfactant was used to control the morphology of layered double hydroxide (LDH) and to prepare LDH/polymer nanocomposites (LDH–APS–PEI–DTPA). The polymer was synthesized using diethylenetriaminepentaacetic acid (DTPA), polyethylenimine and used with LDH to form a nanocomposite with high thermal stability. Subsequently, the prepared nanocomposite was identified using FTIR, EDX, TGA, XRD, FESEM, and BET techniques. In addition, the prepared LDH–APS–PEI–DTPA nanocomposite was used as a heterogeneous and recyclable catalyst for the synthesis of imidazole derivatives under green conditions. The results showed that the LDH–APS–PEI–DTPA nanocomposite benefit from suitable morphology, simple preparation, high catalytic activity, and high surface area. Also, the proposed LDH–APS–PEI–DTPA heterogeneous catalyst showed high stability and reusability for five consecutive runs which was consistent with the principles of green chemistry.

Bis(2-hydroxyethyl) terephthalate (BHET) is an important compound produced from poly(ethylene terephthalate) (PET) cleavage. It was selected as the representative substance for the study of PET degradation. A bacterial strain HY1 that could degrade BHET was isolated and identified as Enterobacter sp. The optimal temperature and pH for BHET biodegradation were determined to be 30°C and 8.0, respectively. The half-life of degradation was 70.20 h at an initial BHET concentration of 1,000 mg/L. The results of metabolites' analysis by liquid chromatograph-mass spectrometer revealed that BHET was first converted to mono-(2-hydroxyethyl) terephthalate (MHET) and then to terephthalic acid. Furthermore, an esterase-encoding gene, estB, was cloned from strain HY1, and the expressed enzyme EstB was characterized. The esterase has a molecular mass of approximately 25.13 kDa, with an isoelectric point of 4.68. Its optimal pH and temperature were pH 8.0 and 40°C, respectively. The analysis of the enzymatic products showed that EstB could hydrolyze one ester bond of BHET to MHET. To the best of authors' knowledge, this is the first report on the biodegradation characteristics of BHET by a member of the Enterobacter genus.

Polyethylene terephthalate (PET) bottle is one of the common plastic wastes existed in the municipal solid waste in Malaysia. One alternative to solve the abundant of PET wastes is chemical recycling of the wastes to produce a value added product. This technology not only can decrease the PET wastes in landfill sites but also can produce many useful recycled PET products. Bis(2-hydroxyethyl) terephthalate (BHET) obtained from glycolysis reaction of PET waste was purified using crystallization process. The hot distilled water was added to glycolysis product followed by cooling and filtration to extract BHET in white solid form from the product. The effect of three operating conditions namely crystallization time, crystallization temperatures and amount of distilled water used to the yield of crystallization process were investigated. The purity of crystallization products were analyzed using HPLC and DSC. The optimum conditions of 3 hours crystallization time, 2 °C crystallization temperature and 5:1 mass ratio of distilled water used to glycolize solid gave the highest yield and purity of the crystallization process. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

The waste polyethylene terephthalate (PET) recycling technology using plasma has been studied for reasons of low pollution and high resource yield[1]. The microwave-excited atmospheric pressure plasma jet (ME-APPJ) provides high electron density and abundant active species[2]. For those reasons, the ME-APPJ is suitable for bis(2-hydroxyethyl) terephthalate (BHET) decomposition as a plasma source. The BHET that basic component of PET is a monomer produced by depolymerizing the PET[3]. The boiling point of BHET is about 317 at 1 atm. Also, the gas temperature of ME-APPJ did not exceed 310 revealing that the results are not by the thermal decomposition. In this study, the reaction between ME-APPJ and BHET was analyzed by using optical emission spectroscopy, intensified charge coupled device and Fourier- transform infrared spectroscopy. The gas of double bonded CO and single bonded OH were produced from the BHET during reactions. The electron energy of ME-APPJ was estimated by comparing bonding energy of BHET with CO and OH which were experimentally produced. The electron energy of ME-APPJ is 347 – 467 kJ/mol. The concentration of CO gas was measured by reaction of BHET with ME-APPJ according to input power. In this study, CO gas was obtained from BHET decomposition through the ME-APPJ. These result can be used as basic study for the development of high value-added technology for recycled waste using plasma.

(Mg–Zn)–Al layered double hydroxide as a regenerable catalyst for the catalytic glycolysis of polyethylene terephthalate

Sustainable Green Polymerizations and End-of-Life Treatment of Polymers.

Poly-ethylene terephthalate (PET)/ MgAl or LiAl layered double hydroxides (LDH) nanocomposites were successfully prepared by polycondensation of bis(2-hydroxyethyl) terephthalate (BHET) mixing sulfanilic acid sodium salt hydrate (SAS) modified - LDH or dimethyl 5-sulfoisophthalate (DMSI) - modified LDH. Effects of MgAl or LiAl LDH contents on the crystallization, mechanical properties, thermal stability and barrier properties of the PET/LDH nanocomposites were discussed. The MgAl LDH and LiAl LDH were synthesized by hydrothermal reaction with the different of aspect ratio and AEC (anionic exchange capacity). The modified LDH, synthesized by hydrothermal reaction, can promote the compatibility both of LDH and PET matrix. The d-spacing of modified- LDH by XRD (X-ray diffraction) measurement and corroboration by JCPDS (Joint Committee on Powder Diffraction Standars). Function groups of modified agents intercalated into LDH galleries, were provide by FT-IR (Fouier Transform Infrared) spectrum. Not only interlayer anion of modified LDH, but also contents of modified agents were calculated and analyzed by TGA (Thermogravimetry Analyzer). Both XRD data and TEM (Transmission Electron Microscopy) micrographs of PET/MgAl LDH-SAS nanocomposites indicate the co-existence of island type exfoliated and intercalated morphologies. TEM images provide the island type intercalated morphologies of PET/MgAl LDH-DMSI whereas sea type intercalated and exforliated morphologies of PET/LiAl LDH nanocomposites. The crystallization behaviors and kinetics of PET and PET/LDH nanocomposites were investigated by using DSC (Differential Scanning Calorimetry). Two stages heating/cooling and non-isothermal melt-crystallization results show that the addition LDH into PET induced nucleation in the crystallization that significantly increases crystallization rate. Decreasing of the crystallization rate is PET/LiAl LDH-DMSI > PET/MgAl LDH-SAS > PET/LiAl LDH-SAS > PET/MgAl LDH-SAS. Mechanical properties of PET and PET/LDH nanocomposites were investigated by using DMA (Dynamic Mechanical Analyzer). The result indicate that the best of storage modulus is increased from 1790 Mpa for pristine PET to 3271 Mpa for PET/MgAl LDH-SAS-1.0 wt% nanocomposites. Thermal properties of PET and PET/LDH nanocomposites were investigated using TGA (Thermal Gravimetry Analyzer). The result indicate the best of decomposed temperature is increased from 383 ℃ for pristine PET to 405 ℃ for PET/LiAl LDH-SAS-1.0 wt% and PET/ LiAl LDH-DMSI 1.0 wt% nanocomposites. The UV-visible barrier properties of PET and PET/LDH nanocomposites were measured by UV-visible spectrophotometer. It indicates that the UV light transmittance is decreased from 79.3 % for pristine PET to 39.3 % for PET/LiAl LDH-SAS-1.0 wt% nanocomposites at the wavelength 375 nm. The gas barrier property of PET and PET/LDH nanocomposites were measured by GPA (gas permeability analyzer). The result indicate the best of BIF (Barrier Improvement Factor) is 4.5 (O2), 5.3 (N2) and 8.6 (CO2) for PET/MgAl LDH-SAS-1.0 wt% nanocomposites.

Polyethylene terephthalate was depolymerized by two different chemical recycling techniques i.e. glycolysis and aminolysis. Glycolysis is carried out with Zinc hydroxide and with conventional catalyst i.e. Zinc acetate for the comparable yield of the monomer. Glycolysis is carried out with ethylene glycol whereas aminolysis is done with ethanolamine. Products obtained from both the techniques namely Bis(2-hydroxyethyl) terephthalate (BHET) and Bis(2-hydroxyethyl) terephthalamide (BHETA) have different chemical structure but have hydroxyl functionality at the terminals in both hence can be used as monomer for resin synthesis. The synthesized monomers, resin were characterized by FTIR, 1 HNMR and chemical characterization techniques.Combination of the both products helps to get the structural benefit of both. Synthesis resin is used as binder for the primer synthesis. By varying the pigment type and keeping the pigment volume concentration constant system is studied for anticorrosive properties. Application of conventional polyurethane topcoat helps to improve the anticorrosion performance further. Keywords : Recycling, Bis(2-hydroxyethyl)terephthalate, Bis(2-hydroxyethyl) terephthalamide, Glycolysis, aminolysis Cite this Article Aarti P. More, S. T. Mhaske. Development of Primer as a value added product from waste PET. Journal of Thin Films, Coating Science Technology and Application . 2015; 2(3): 5–16p.

A low-cost process for the depolymerization of polyethylene terephthalate (PET) was investigated in this work by the development of catalysts derived from food wastes for the glycolysis reaction of post-consumable waste of drinking bottles. Bis (2-hydroxyethyl) terephthalate (BHET) is obtained as a product from the glycolysis of polyethylene terephthalate (PET). Calcium oxide (CaO) catalysts derived from shells were used in this reaction. The yield of bis (2-hydroxyethyl) terephthalate (BHET) was obtained and the purity of BHET was confirmed by NMR spectroscopy.

The blends of poly(butylene adipate‐co‐terephthalate) (PBAT), poly(propylene carbonate) (PPC), chain extender (ADR) and layered double hydroxides (LDH) are prepared by different extrusion methods. Effects of LDH and its distribution on rheology, phase morphology, mechanical properties, water vapor barrier properties and food preservation properties are investigated. Results show that when PBAT, PPC, and LDH are mixed directly, LDH is preferentially distributed in the PBAT phase. When LDH are mixed with PPC firstly and then further with PBAT, LDH mostly migrates to the interface of PBAT and PPC. The epoxy groups of ADR react with the terminal groups of the polymers to improve the interfacial compatibility. Adding LDH, the mechanical properties and barrier properties of the materials are improved and by premixing of PPC and LDH, properties of composites are further improved. Compared with PBAT/PPC blends, the tensile strength and elongation at break of PBAT/PPC(LDH‐0.5)/ADR increased by 25.2% and 15.3%, respectively. The banana packaged in PBAT/PPC/LDH films maintains good freshness. It illustrates that PBAT/PPC(LDH)/ADR composites have a good application prospect in the field of barrier and food packaging based on their excellent mechanical, barrier, and preservation properties.