Search Results (45)

The recycling of polyethylene terephthalate (PET) is gaining increasing importance, as it enables the conversion of plastic waste into valuable raw materials and contributes to a circular economy. Recent research has primarily focused on optimizing the depolymerization step of PET glycolysis, while downstream processes often overlook what are at least equally critical downstream steps in recovering the monomer bis(2-hydroxyethyl) terephthalate (BHET). The implementation of a water-free PET glycolysis process eliminates challenges related to internal solvent and homogeneous catalyst recycling that commonly occur in conventional processes. This study, therefore, focuses on BHET crystallization and filtration as key downstream unit operations. Two nucleation strategies, gassing and seeding, were investigated and compared with experiments without a nucleation strategy. The aim was to achieve reproducible process control during crystallization and to obtain crystals with good filterability, which can be critical for subsequent steps in the product purification process. Experiments without a nucleation strategy showed poor reproducibility. In contrast, gassing and seeding improved crystallization control, particularly regarding nucleation temperature and relative crystallization yield. However, these strategies also resulted in significantly prolonged filtration times due to differences in filter cake properties. The anisotropic crystals exhibited a broad particle size distribution with a high fraction of fine particles, leading to small and heterogeneous pores in the filter cake. Limited crystal growth was identified as the main cause of the unfavorable filtration behavior. Full article

As the demand for polyethylene terephthalate (PET) continues to rise, significant environmental pollution caused by challenges in PET degradation has garnered global attention. Given the crucial role of esterases in depolymerizing PET into reusable monomers, such enzymes capable of degrading plastics have attracted considerable interest. In this study, we used the previously reported ultra-efficient mutant of the PET-degrading enzyme Ideonella sakaiensis PETase, known as FASTase, as a positive control. We investigated the PET-degrading activity of esterase E4, derived from Altererythrobacter indicus. The results demonstrated that E4 exhibits degradative activity toward the PET substrate bis(2-hydroxyethyl) terephthalate, the PET model substrate bis(benzyloxyethyl) terephthalate, and PET nanoparticles. Notably, E4 retains its degradation activity under high-temperature and high-salt conditions and can enhance the enzymatic activity of FASTase when acting synergistically. Given the low structural and sequence similarity between E4 and IsPETase, our research broadens the scope for screening PET-degrading enzymes. Full article

The rapid growth of polyethylene terephthalate (PET) waste and the limitations of conventional recycling methods for mixed waste streams emphasize the need for chemical recycling routes that deliver high-value monomers in a sustainable, resource-efficient manner. This work explores N-heterocyclic carbenes (NHCs) as organocatalysts for the glycolysis of PET with ethylene glycol to bis(hydroxyethyl)terephthalate (BHET), aiming for milder conditions and higher activity. A systematic catalyst screening links steric and electronic properties (percent buried volume, Tolman electronic parameter) of the NHCs to performance in the glycolysis process, resulting in a catalyst system with high PET conversion (up to 97%) and BHET yield (up to 65%). Mechanistic investigations (experimental and computational) support an anionic activation pathway for glycolysis. To lower the reaction temperature, selective cosolvent systems were explored, albeit with some loss of catalytic activity. Cooperative catalysis combining NHCs with Lewis acids enhances activity, leading to a high conversion (up to 90%) while maintaining lower temperatures than state-of-the-art glycolysis methods. The process was successfully transferred to post-consumer waste streams to validate the practicality. Full article

In recent years, sustainability and the concept of a circular economy have grown in importance within almost all industrial sectors. Especially in the chemical industry, recycling of polymer waste streams has become an important pathway to avoid plastic waste being landfilled or incinerated. Additionally, traditional carbon sources, such as fossil fuels, can be substituted with streams of recycled polymer. For example, polyethylene terephthalate (PET), which is utilized in plastic bottles and textiles, may be recycled via glycolysis. This depolymerization yields the monomer bis(2-hydroxyethyl) terephthalate (BHET). This study focuses on the thermal behavior and stability of BHET, both in pure form as well as in the presence of ethylene glycol (EG), as it results from PET glycolysis. For this, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), high-performance liquid chromatography (HPLC), powder X-ray diffraction (PXRD), and thermogravimetry (TG) were utilized. The results exhibited pure BHET polymerizing to PET at temperatures above 120 °C, while further increasing temperatures increased the reaction kinetics. Additionally, no reaction was observed in BHET/EG mixtures at any temperature investigated, which can be attributed to the presence of EG shifting the equilibrium of the reaction towards the BHET, thus inhibiting polymerization. Based on these results and the determined BHET/EG (solubility) phase diagram, potential purification strategies based on crystallization are proposed. Full article

Growing environmental concern over plastic pollution has increased the need to address the persistence of PET-derived monomers, such as bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA). This work examines the use of excimer radiation lamps combined with hydrogen peroxide (H₂O₂) to enhance advanced oxidation processes (AOPs) for their degradation. This approach stands out for its high selectivity, absence of mercury, and lower production of toxic byproducts. Experimental tests assessed how different operational factors affect pollutant degradation, such as the initial pollutant concentration (50–200 mg/L), the reaction volume (125–500 mL), and the H₂O₂:monomer mass ratio (0:1–6:1 for BHET and 0:1–4:1 for TPA). For BHET, the best results occurred with a 5:1 mass ratio, while TPA degraded optimally with a 3:1 ratio, with a 250 mL reaction volume and a 100 mg/L initial concentration for both compounds. Under these conditions, total degradation of the initial monomers was achieved in around 30 and 80 min for BHET and TPA, respectively, and at the end of the reaction, COD decreased by 46% and 32% relative to their initial values. In both cases, hydrogen peroxide was crucial since UV radiation alone led to much lower degradation efficiency. These results emphasize the need to optimize operational conditions for greater efficiency and establish a starting point for future use of excimer technology in the treatment of wastewater contaminated with PET and its derivatives. Additionally, the degradation data closely matched a pseudo-first-order kinetic model (R² ≈ 1), confirming its reliability for predictive analysis, which is of high importance for the simulation and optimization of the process. Full article

Bacillus licheniformis Mb1, a thermophilic strain isolated from the Yungas rainforest in northwestern Argentina, was analyzed through genomic and experimental approaches to explore its biotechnological potential. Phylogenomic analysis confirmed its close relationship with B. licheniformis reference strains. The genome revealed multiple genes associated with hydrolytic, oxidative, carbohydrate-active, and polyester-degrading activities, indicating a wide enzymatic capacity. Experimental assays demonstrated strong extracellular hydrolytic activities and efficient degradation of bis(2-hydroxyethyl) terephthalate (BHET), a key polyethylene terephthalate (PET) intermediate. In liquid cultures with 3 mg/mL BHET, B. licheniformis Mb1 achieved 99.9% depletion within four days, with transient BHET dimer accumulation and progressive terephthalic acid (TPA) production, reaching 1.17 mg/mL after 15 days. Mono (2-hydroxyethyl) terephthalate (MHET) and vanillic acid were not detected. Complete BHET and dimer degradation suggests the presence of versatile hydrolases acting on short-chain polyester intermediates. Sequence and molecular docking analyses identified a BHETase-like carboxylesterase as the main enzyme candidate, featuring a truncated lidC region that generates a more open catalytic cleft. This structural trait, not previously reported in bacterial BHETases, enables the accommodation of bulkier substrates such as BHET dimer. These findings highlight B. licheniformis Mb1 as a promising biocatalyst for polyester depolymerization and a valuable microbial resource for future enzyme discovery and plastic bioremediation strategies. Full article

A sustainable circular pathway was developed for poly(ethylene terephthalate) (PET) nanocomposites through a catalyst-driven polymerization and depolymerization process. In this study, calcium dodecylbenzene sulfonate with n-butyl alcohol modified ZnAl layered double hydroxides (LDHs) were utilized as bifunctional catalysts to synthesize highly exfoliated PET/LDH nanocomposites via in situ polycondensation of bis(2-hydroxyethyl) terephthalate (BHET). The organic modification of LDHs expanded interlayer spacing, improved interfacial compatibility, and promoted uniform dispersion, leading to enhanced mechanical, thermal, and barrier properties. In the second stage, the pristine LDH catalyst efficiently depolymerized the prepared PET/LDH nanocomposites back into BHET through glycolysis, completing a closed-loop BHET-to-BHET cycle. This integrated strategy demonstrates the reversible catalytic functionality of LDHs in both polymerization and depolymerization, reducing metal contamination and energy demand. The proposed approach represents a sustainable route for designing recyclable high-performance PET nanocomposites aligned with the principles of green chemistry and circular material systems. Full article

Poly(ethylene terephthalate) (PET) is a widely used polymer that accumulates in the environment due to its low degradability, requiring efficient recycling strategies. In this study, CaO filler derived from calcium carbide slag (CS) waste was used for the first time as a catalyst for PET depolymerization. PET/CaO composites were prepared via hot extrusion of PET with the finely dispersed CaO filler. The resulting composite demonstrated consistently higher PET conversion (≥95%) and the yields of dimethyl and dibutyl terephthalates (80 and 84%, respectively). Kinetic studies of glycolysis demonstrated that embedding 1 wt% of CaO in the PET matrix doubled the bis(2-hydroxyethyl) terephthalate (BHET) formation rate relative to an externally added CaO catalyst, which resulted in BHET yields of 84.7% and 41.1% after 40 min. SEM and EDX investigations demonstrated good adhesion between the polymer matrix and the filler. The recovered BHET was successfully re-polymerized to produce recycled PET (r-PET). The maximum rate of weight loss of r-PET samples (at T_max = 438.7–444.7 °C) was comparable to the original materials (at T_max = 455.3–457.7 °C). In fact, the direct incorporation of CaO catalyst derived from waste into the polymer matrix during additive manufacturing enabled the implementation of an efficient and scalable closed-loop recycling strategy. Full article

The accumulation of polyethylene terephthalate (PET) in the environment demands efficient microbial strategies for its degradation. This study evaluates the biodegradation potential of Schizophyllum commune BNT39 toward bis(2-hydroxyethyl) terephthalate (BHET), a major PET intermediate, and PET itself. Clear halos on BHET-agar plates indicated extracellular hydrolytic activity. In liquid culture, thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) analyses revealed a three-phase degradation profile characterized by rapid BHET hydrolysis, transient dimer accumulation, and subsequent conversion to terephthalic acid (TPA). BHET was reduced by approximately 96% within seven days, while TPA accumulation reached 0.8 mg/mL after 30 days of incubation. Although PET degradation was limited, TPA was consistently detected as the principal product, with no BHET or MHET intermediates. To explore strategies for enhancing enzymatic activity, apple-derived cutin, PET, BHET, and polycaprolactone (PCL) were tested as inducers. Cutin markedly stimulated extracellular enzyme production, suggesting activation of cutinase-like enzymes. Overall, S. commune BNT39 demonstrates the ability to transform PET-related substrates, with cutin emerging as a promising natural stimulant to enhance enzymatic depolymerization. Future studies should focus on enzyme purification, activity profiling, and reaction optimization near PET’s glass transition temperature, where the polymer becomes more accessible for enzymatic attack. Full article

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. Full article

Polyethylene terephthalate (PET) is a widely used polymer whose accumulation in the environment poses a significant pollution challenge. This study explores the degradation of bis(2-hydroxyethyl) terephthalate (BHET) and terephthalic acid (TPA)—two monomers commonly produced during PET hydrolysis and widely used as intermediates in PET recycling—through Advanced Oxidation Processes (AOPs) employing KrCl (222 nm) and XeBr (283 nm) excimer lamps in the presence of hydrogen peroxide (H₂O₂). The effects of the H₂O₂/monomer mass ratio, initial monomer concentrations, and reaction volume on degradation efficiency were systematically evaluated. The results demonstrate that excimer lamp technology, particularly KrCl, holds promising potential for the effective degradation of both BHET and TPA, and thus represents a viable strategy for PET waste treatment. Full article

In this study, a poly [ε-caprolactam-co-bis(2-hydroxyethyl) terephthalate] copolymer (P (CL-co-BHET)) was synthesized from para-terephthalic acid (PTA), ethylene glycol (EG), and caprolactam (CL). The crystallization behavior and thermal stability of the copolymer were thoroughly investigated. With the aid of molecular simulation, this study investigated the variation in interchain hydrogen bonding in the copolymer, focusing on the direction and the number of hydrogen bonds. The results revealed a close relationship between the copolymer chain structure, the variation in interchain hydrogen bonding, and the crystallization behavior and thermal stability of the copolymer. The introduction of BHET segments disrupted the regularity of the PA6 backbone and hydrogen bonding, leading to a decrease in the melting point, crystallization temperature, and crystallinity of the copolymer. The thermal stability of the copolymers also decreased, and the crystallization form gradually shifted from the α-crystalline to the γ-crystalline phase. The findings of this study are significant for evaluating the crystallization behavior of polyester amides and for predicting and regulating the properties of polyesteramide polymers. Full article

Polyethylene terephthalate (PET) products are ubiquitous in daily life, offering convenience but posing significant environmental challenges due to their persistence and the difficulty of recycling them. Improper disposal of waste PET contributes to severe pollution and resource loss. Chemical degradation has emerged as one of the most effective methods for recovering and reusing waste PET. This article introduces a catalytic glycolysis strategy for efficient and environmentally sustainable PET recycling using potassium-rich biomass, specifically banana peels. The study demonstrated that K₂O and K₂CO₃, derived from calcined banana peels, significantly catalyze the glycolysis of PET. Under optimal conditions, complete degradation of PET was achieved within 1.5 h at 180 °C, without additional chemical reagents. Product distribution confirmed that high-purity bis(2-hydroxyethyl) terephthalate could be obtained. The interaction between K₂CO₃ and ethylene glycol plays a critical role in determining the competition between glycolysis and alkaline hydrolysis. Furthermore, Density Functional Theory calculations provided valuable insights into the transesterification process during glycolysis. The reaction system also demonstrated excellent compatibility with colored PET products. This study successfully realized the simultaneous recycling of post-consumer PET and banana peels, offering a novel and sustainable approach to waste valorization. Full article

Glycolysis of poly(ethylene terephthalate) (PET) is a prospective way for degradation of PET to its monomer bis(hydroxyethyl) terephthalate (BHET), providing the possibility for a permanent loop recycling. However, most reported glycolysis catalysts are homogeneous, making the catalyst difficult to recover and contaminating the products. Herein, we reported on the Pd-Cu/γ-Al₂O₃ catalyst and applied it in the glycolysis of PET as catalyst. The formed structure gave Pd-Cu/γ-Al₂O₃ a high active surface area, which enabled these micro-particles to work more efficiently. The PET conversion and BHET yield reached 99% and 86%, respectively, in the presence of 5 wt% of Pd-Cu/γ-Al₂O₃ catalyst within 80 min at 160 °C. After the reaction, the catalyst can be quickly separated by filtration, so it can be easily reused without significant loss of reactivity at least five times. Therefore, the Pd-Cu/γ-Al₂O₃ catalyst may contribute to an economically and environmentally improved large-scale recycling of PET fiber waste. Full article

Poly(1,4-butylene succinate) (PBS) is a promising sustainable and biodegradable synthetic polyester. In this study, we synthesized PBS-based copolyesters by incorporating 5–20 mol% of –O₂CC₆H₄CO₂– and –OCH₂CH₂O– units through the polycondensation of succinic acid (SA) with 1,4-butanediol (BD) and bis(2-hydroxyethyl) terephthalate (BHET). Two different catalysts, H₃PO₄ and the conventional catalyst (nBuO)₄Ti, were used comparatively in the synthesis process. The copolyesters produced using the former were treated with M(2-ethylhexanoate)₂ (M = Mg, Zn, Mn) to connect the chains through ionic interactions between M²⁺ ions and either –CH₂OP(O)(OH)O⁻ or (–CH₂O)₂P(O)O⁻ groups. By incorporating BHET units (i.e., –O₂CC₆H₄CO₂– and –OCH₂CH₂O–), the resulting copolyesters exhibited improved ductile properties with enhanced elongation at break, albeit with reduced tensile strength. The copolyesters prepared with H₃PO₄/M(2-ethylhexanoate)₂ displayed a less random distribution of –O₂CC₆H₄CO₂– and –OCH₂CH₂O– units, leading to a faster crystallization rate, higher T_m value, and higher yield strength compared to those prepared with (nBuO)₄Ti using the same amount of BHET. Furthermore, they displayed substantial shear-thinning behavior in their rheological properties due to the presence of long-chain branches of (–CH₂O)₃P=O units. Unfortunately, the copolyesters prepared with H₃PO₄/M(2-ethylhexanoate)₂, and hence containing M²⁺, –CH₂OP(O)(OH)O⁻, (–CH₂O)₂P(O)O⁻ groups, did not exhibit enhanced biodegradability under ambient soil conditions. Full article