The use of melt rheology and solution viscometry for degradation study of post-consumer poly(ethylene terephthalate): The effects of the contaminants, reprocessing and solid state polymerization

Time‐resolved rheometry and size exclusion chromatography system [advanced polymer chromatography (APC)‐multi‐angle laser light scattering (MALLS)‐refractive index detector (RID)] were employed to investigate post‐polycondensation process of nonstirred high‐viscosity poly(ethylene terephthalate) (PET) of molten film forming by high‐flow inert gas sweeping at atmospheric pressure. In view of chemical reaction kinetics together with mass transfer to adjust reactive parameters, including moisture content of the sample, temperature, concentration of the active groups, residence time, and mass transfer factor, this work aims to distinguish the different reactions in reprocessing of high‐viscosity PET. Results indicated that hydrolysis is observed initially before thermal degradation and polycondensation reactions on remelting process. Promotion of thermal degradation is stronger than polycondensation with the increase in temperature. Fiber‐grade PET exhibits polycondensation as the dominant reaction at 275 °C in a reasonable reaction time, which leads to the increase of average molecular weight and the phenomenon of double distribution proved by APC‐MALLS‐RID system. However, the average molecular weight of industrial yarn‐grade PET is very difficult to improve when the thermal degradation reaction is not effectively inhibited. Importantly, the experimental study of the interfacial mass‐transfer area and mass‐transfer intensification demonstrated that mass transfer is the rate‐determining factor for the overall post‐polycondensation of high‐viscosity melt. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47484.

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“…The value of η 0 is changing in the course of testing time. Thus, the following formulas are used for dynamic processing

η_{r} = \frac{{([], {normalη}_{0})}_{t}}{{([], {normalη}_{0})}_{t = 0}} = \frac{{italicKM}_{t}^{\partial}}{{italicKM}_{0}^{\partial}} = \frac{M_{t}^{\partial}}{M_{0}^{\partial}} = {(\frac{M_{t}}{M_{0}})}^{\partial}

where [η 0 ] t and [η 0 ] t = 0 denote zero‐shear viscosity of samples at different moments and initial zero‐shear viscosity, respectively.…”

Section: Resultsmentioning

confidence: 99%

Continuous post‐polycondensation of high‐viscosity poly(ethylene terephthalate) in the molten state

Wang

Chen

Guang

et al. 2019

J of Applied Polymer Sci

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“…Mechanical recycling, where the waste is ground and washed, followed by extrusion and/or injection molding to generate new products, are the main recycling techniques used for PET residues. The properties of the resulting product, however, are significantly lower than those of virgin PET because weathering of the post-consumed material, grinding and processing (extrusion and/or injection) at high temperatures can induce degradation by a variety of reactions such as chain scission (which lowers molecular weight) as well as other reactions due to the high reactivity and to the variety of chemical groups present in PET 1,4,7 .…”

Section: Introductionmentioning

confidence: 99%

“…PET is degraded by random scission of ester bonds and the rate of thermal degradation is affected by by-products such as acetaldehydes and by stirring conditions of the molten PET 13 . The high temperatures (between 200 and 300 °C) combined with the shear rate required during PET processing exposes the resin to favorable conditions for degradation reactions resulting in changes in properties such as the decrease in intrinsic viscosity and mass 7 .…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Poly(Ethylene Terephthalate) by Torque Rheometry

et al. 2021

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Polymer processing parameters may considerably affect final product characteristic as, if properly chosen, these parameters may lead to products with optimal properties. The aim of this work is to evaluate the rheological characteristics of poly(ethylene terephthalate) (PET) by torque rheometry, as well as to estimate its incipient degradation rate during processing in an internal laboratory mixer. In order to estimate the temperature coefficient of the viscosity (β), and the pseudoplasticity index (n) of PET, two sets of experiments need to be performed. In the first one, the polymer is processed at three different temperatures at a single rotor speed for 10 min, getting temperature coefficient of the viscosity equal to β = 0.053 °C-1. In the second set of experiments, the resin (PET) is processed at a single temperature at six different rotor speeds for the same time interval and the pseudoplasticity index was determined, n = 0.78. From the results obtained, it is possible to indicate the internal mixer as an equipment not only for mixing polymers or composites, but as a tool for determining important rheological variables for predicting degradative processes.

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“…Moreover, most of this waste cannot be recycled because it contains significant amounts of impurities such as inks and metals that interfere with the processing. This recycling technology is specially focused on transparent PET, due to material without pigments has greater value in applications such as the reuse in packaging market [9]. However, the cycle number is finite due to the continuous degeneration of the material [10].…”

Section: Introductionmentioning

confidence: 99%

Rheological modification of recycled poly(ethylene terephthalate): Blending and reactive extrusion

Asensio

Núñez

Guerrero

et al. 2020

Polymer Degradation and Stability

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The use of recycled PET (rPET) in long-term applications, such as composites, may provide an environmentally friendly solution for PET wastes. Main problem to overcome to use rPET in composites is its high viscosity which compromises the impregnation with the fibers during the consolidation process. As it is well known, PET undergoes thermo-mechanical and hydrolytic degradation during its mechanical recycling decreasing its viscosity and causing a loss of mechanical properties. For this reason, this paper takes into consideration a rheological modification during mechanical recycling to achieve the necessary fluidity for composites while maintaining the mechanical properties. Rheological modification was carried out by physical and chemical methods. Physical method was realized through blending with virgin PET (vPET) of low melt viscosity. Chemical method was performed on rPET, vPET and its blends by reactive extrusion. The effect of rheological modifications on the final thermal and mechanical properties was studied. Main results showed that both methods are able to decrease the viscosity without compromising mechanical properties. In addition, the chemical method during the reactive extrusion provided higher Elastic Modulus values.

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The use of melt rheology and solution viscometry for degradation study of post-consumer poly(ethylene terephthalate): The effects of the contaminants, reprocessing and solid state polymerization

Cited by 28 publications

References 27 publications

Continuous post‐polycondensation of high‐viscosity poly(ethylene terephthalate) in the molten state

Continuous post‐polycondensation of high‐viscosity poly(ethylene terephthalate) in the molten state

Characterization of Poly(Ethylene Terephthalate) by Torque Rheometry

Rheological modification of recycled poly(ethylene terephthalate): Blending and reactive extrusion

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