The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters: An in Situ NMR Investigation
TL;DR: In this paper, the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied. But, only few works have reported the side reactions induced by it.
Abstract: Due to the poor solubility of aromatic polyesters in common organic solvents, trifluoroacetic acid is usually used as a co-solvent to increase their solubility for characterizations. However, only few works have reported the side reactions induced by it. We present here the application of in situ 1H-NMR techniques to explore its effect on the hydroxyl end-groups, which are usually used for the molecular weight determination of polyesters by end-group estimation method. Using bis(2-hydroxyethyl) terephthalate (BHET) as model compound, 1H quantitative NMR results show the peak integration of hydroxyethyl end-groups decreased with time via a pseudo-first-order kinetics in d-trifluoroacetic acid/d-chloroform mixture solvent (1:10, V:V). This is due to the esterification of hydroxyethyl groups with trifluoroacetic acid, revealed by the 1H-13C gradient-enhanced heteronuclear multiple bond correlation (gHMBC) spectrum. The mixtures of dimethyl terephthalate and BHET with different molar ratio were used to represent poly(ethylene terephthalate) (PET) with different degree of polymerization, and the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied. Our results show that if a relative error of 5% is allowed, the NMR measurements must be finished within 1.3 h of solution preparation at 25 °C in the mixture solvent. The results were confirmed in PET sample, while in poly(ethylene adipate), the obtained esterifaction constant is faster that those in aromatic system. The results can be applied to other polymer systems with alcohol functionalized groups, and used as a guideline for the characterization of polyesters and polyethers by end-group estimation method.
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TL;DR: In this article , the authors reported the valorization of poly(ethylene terephthalate) (PET) plastic wastes to produce nanofibrous adsorptive membranes for their applications in oil removal.
Abstract: The accumulation of plastic wastes has become a global environmental issue, because of their ever-growing production, slow degradation, and potential environmental hazards. Consequently, reducing their presence in the environment by upcycling has sparked tremendous research interest. Herein, we report the valorization of poly(ethylene terephthalate) (PET) plastic wastes to produce nanofibrous adsorptive membranes for their applications in oil removal. In this study, plastic wastes derived from PET bottles were dissolved in trifluoroacetic acid (TFA) or a TFA/dichloromethane (DCM) binary solvent system and then electrospun into nanofibrous recycled PET (rPET) membranes. The nanofiber morphology was tuned by adjusting the polymer concentration. The nanofibers produced via electrospinning from TFA solutions were more uniform than those produced using TFA/DCM. The influence of acid-mediated recycling on the PET structure was explored via thermogravimetric and X-ray photoelectron spectroscopy analyses. A dynamic mechanical analysis showed that the membranes exhibited high flexibility with effective Young’s moduli. The sorption capacities of the nanofibrous PET membranes for crude oil, diesel, gasoline, and pump oil were 22.9 ± 2, 19.6 ± 1.8, 11.1 ± 1, and 19.3 ± 1.6 g g–1, respectively. The membrane could be recycled by squeezing and reused five times for oil removal while maintaining an sorption capacity of >75%. After the sorption tests, an apparent increase in the fiber diameter was observed due to the oil uptake into the fiber matrix. The present study provides a sustainable solution to plastic and oil pollution management, minimizing the production of new carbon-based materials and lowering carbon emissions. This work aligns with the United Nations’ Sustainable Development Goals, specifically, Goal #12 on responsible consumption and production and #14 on life below water.
16 citations
TL;DR: In this article, a cascade polycondensation-coupling ring-opening polymerization (PROP) strategy was proposed for the rapid synthesis of poly(ethylene 2,5-furandicarboxylate)-block-poly(tetramethylene oxide) multiblock copolymers (mBCPs), via the vacuum melt polymerization of cyclic oligo(methylene 2.5-fricarboxylic acid)s (COEFs) with PTMO diols.
8 citations
TL;DR: In this paper, a cascade polycondensation-coupling ring-opening polymerization (PROP) was proposed for the direct preparation of green copolyesters with versatile functionalities.
4 citations
TL;DR: In this paper , the effect of OEG segmental length on properties of cyclic oligo(ethylene glycol) (OEG) segments has been investigated in a cascade polycondensation-coupling ring-opening polymerization method to obtain high molecular weight POEGTs.
4 citations
TL;DR: In this paper , a new process based on SSM technique of polyesters from batch into a continuous process is reported. Butylene terephthalate (PBT) and 1,12-dodecanediol (DDO) are used as model compounds.
3 citations
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TL;DR: This review covers the current methods and challenges for the mechanical recycling of the five main packaging plastics: poly(ethylene terephthalate), polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) through the lens of a circular economy.
Abstract: The current global plastics economy is highly linear, with the exceptional performance and low carbon footprint of polymeric materials at odds with dramatic increases in plastic waste. Transitioning to a circular economy that retains plastic in its highest value condition is essential to reduce environmental impacts, promoting reduction, reuse, and recycling. Mechanical recycling is an essential tool in an environmentally and economically sustainable economy of plastics, but current mechanical recycling processes are limited by cost, degradation of mechanical properties, and inconsistent quality products. This review covers the current methods and challenges for the mechanical recycling of the five main packaging plastics: poly(ethylene terephthalate), polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) through the lens of a circular economy. Their reprocessing induced degradation mechanisms are introduced and strategies to improve their recycling are discussed. Additionally, this review briefly examines approaches to improve polymer blending in mixed plastic waste streams and applications of lower quality recyclate.
385 citations
30 Sep 2004
TL;DR: An overview of the family of polyester polymers is given in this paper, which comprises an important group of plastics that span the range of commodity polymers to engineering resins.
Abstract: Provides an overview of the family of polyester polymers which comprise an important group of plastics that span the range of commodity polymers to engineering resins. It describes the preparation, properties and applications of polyesters. Readers will also find details on polyester-based elastomers, biodegradable aliphatic polyester, liquid crystal polyesters and unsaturated polyesters for glass-reinforced composites. • Presents an overview of the most recent developments. • Explores synthesis, catalysts, processes, properties and applications. • Looks at emerging polyester materials as well as existing ones. • Written by foremost experts from both academia and industry, ensuring that both fundamentals and practical applications are covered.
381 citations
TL;DR: Although Staudinger realized makromolekules had enormous potential, he likely did not anticipate the consequences of their universal adoption as mentioned in this paper, with 6.3 billion metric tons of plastic waste now cont...
Abstract: Although Staudinger realized makromolekules had enormous potential, he likely did not anticipate the consequences of their universal adoption. With 6.3 billion metric tons of plastic waste now cont...
124 citations
TL;DR: In this article, conditions for polymerizing ethylene terephthalate cyclic oligomers (ETCs) with the catalyst antimony trioxide were investigated with the ultimate goal in mind of using ETCs to produce high-performance poly(ethylene terephate) (PET) composites.
Abstract: Conditions for polymerizing ethylene terephthalate cyclic oligomers (ETCs) with the catalyst antimony trioxide were investigated with the ultimate goal in mind of using ETCs to produce high-performance poly(ethylene terephthalate) (PET) composites. The ETCs used were prepared both by a direct synthesis method and by cyclodepolymerization (CDP) in dilute solution. ETCs prepared exhibited a distribution of oligomeric species displaying a broad melting range, the uppermost end of which lies at 290 °C. In the case of ETCs prepared by CDP, purified ETCs (p-ETCs) were prepared by eliminating remaining impurities including linear oligomers and cyclic oligomers containing the diethylene glycol (DEG) unit using dichloromethane and tetrahydrofuran. A homogeneous mixture of ETCs prepared by the direct synthesis method or p-ETCs with antimony trioxide was successfully polymerized to high molecular weight (MW) PET (Mn ≥ 25 000) at 293 °C within 15 min. The lower the contents of remaining impurities, the higher the MW ...
72 citations
TL;DR: In this article, the molecular weight evaluation of poly(ethylene terephthalate) (PET) from different sources was accomplished by using three different techniques: solution intrinsic viscosity, intrinsic visco-ness from melt flow index (MFI), and size exclusion chromatography (SEC).
66 citations