Thermal Oxidative Degradation Research Articles

Monoethanolamine (MEA) Degradation: Influence on the Electrodialysis Treatment of MEA-Absorbent.

The thermal-oxidative degradation of aqueous solutions of carbonized monoethanolamine (MEA, 30% wt., 0.25 mol MEA/mol CO2) was studied for 336 h at 120 °C. Based on the change in the color of the solution and the formation of a precipitate, the occurrence of thermal-oxidative degradation of the MEA solution with the formation of destruction products, including insoluble ones, was confirmed. The electrokinetic activity of the resulting degradation products, including insoluble ones, was studied during the electrodialysis purification of an aged MEA solution. To understand the influence of degradation products on the ion-exchange membrane properties, a package of samples of MK-40 and MA-41 ion-exchange membranes was exposed to a degraded MEA solution for 6 months. A comparison of the efficiency of the electrodialysis treatment of a model absorption solution of MEA before and after long-time contact with degraded MEA showed that the depth of desalination was reduced by 34%, while the magnitude of the current in the ED apparatus was reduced by 25%. For the first time, the regeneration of ion-exchange membranes from MEA degradation products was carried out, which made it possible to restore the depth of desalting in the ED process by 90%.

Effect of Silica Nanofiller on Thermal-Oxidative Degradation of Epoxy Composites Synthesized by the Sol-Gel Method

Effect of Silica Nanofiller on Thermal-Oxidative Degradation of Epoxy Composites Synthesized by the Sol-Gel Method

Degradation of oxo-biodegradable rubber and its impact on ecosystem services

Rubber has become essential in everyday life, but the poor degradation rates of natural rubber products present an environmental challenge. This study focused on the development and characterization of oxo-biodegradable rubber by modifying vulcanized natural rubber (VNR) with pro-degradant additives (PDA) such as iron (III) stearate (VNR-FeSt) and cobalt (II) stearate (VNR-CoSt). No observable degradation of the PDA-incorporated latex films occurred during the preparation processes of the film which include rubber latex coagulant dipping and vulcanization. The addition of PDA also had minimal effects on the mechanical properties of the latex films. While latex VNR without PDA was relatively stable to oxidative degradation at 65 °C for eight weeks, the formation of carbonyl and hydroxyl functional groups in VNR-CoSt and VNR-FeSt indicate that the PDAs facilitated oxidative degradation the rubber. VNR-CoSt and VNR-FeSt showed significantly greater decreases in weight and gel content than neat VNR, with CoSt being most effective for enhancing thermal oxidative degradation. Growth parameter analysis showed that the addition of oxo-biodegradable latex films to the soil had little effect on the nutrient content of spinach, in line with the soil analysis. These data support the promotion of oxo-biodegradable rubbers as a promising sustainable alternative to conventional rubbers, with the potential to aid in rubber waste management in the agriculture sector.

Pyrolysis and Oxidative Thermal Decomposition Investigations of Tennis Ball Rubber Wastes through Kinetic and Thermodynamic Evaluations

Thermal decomposition of tennis ball rubber (TBR) wastes in nitrogen and air has been studied through thermogravimetric analysis. The samples were thermally decomposed from room temperature to 950 K at heating rates of 3 to 20 K/min with a purging flow of 30 cm3/min. The degradation features and specific temperatures for two purging gases are thus compared according to the nonisothermal results. Kinetic analyses of two thermal decomposition processes have been isoconversionally performed using differential or integral methods. The activation energy as a function of mass conversion has been thus obtained over the entire decomposition range, varying from 116.7 to 723.3 kJ/mol for pyrolysis and 98.2 to 383.6 kJ/mol for oxidative thermal decomposition. The iterative Flynn-Wall-Ozawa method combined with the linear compensation effect relationship has been proposed for determining the pre-exponential factor and reaction mechanism function, resulting in chemical order reaction models of f(α) = (1 - α)5.7 and f(α) = (1 - α)5.8 for describing pyrolysis and the oxidative thermal degradation of TBR wastes, respectively. With these kinetic parameters, very satisfactory matching against experimental data has been obtained for both gases. Additionally, the thermodynamic parameters, such as the changes of entropy, enthalpy and Gibbs free energy, over the whole thermal degradation processes have also been evaluated.

Investigating into physical properties of composites of polymer blends and cobalt chloride irradiated by gamma ray for optical devices development

The present work studies the influence of cobalt chloride (CoCl2) and γ-irradiation dose on the optical, thermal properties, and dynamic mechanical analysis (DMA) of different blends of (PVA/PEG /PVP). Different optical parameters were deduced before and after γ-irradiation with different doses (5, 10, and 15 kGy). The optical conductivity (σoptical) values for the prepared blends and composites indicate their importance for optical energy applications, especially after γ-irradiation. Modifying and enhancing the refractive index of γ-irradiated samples enables their use in various optical devices. Linear optical susceptibility (χ(1)) and the third nonlinear susceptibility (χ(3)) increased by decreasing the PVA amount in the blend and composites. Thermogravimetric analysis TGA confirmed that by adding CoCl2 to the hosting blends, the thermal oxidative degradation energy Ea became much higher than unirradiated samples. The DMA results show that the storage modulus was significantly improved after adding CoCl2 and after irradiating the samples by 5 and 10 kGy. Also, all the samples exhibited two relaxation temperatures and were greatly affected by adding the filler.

Key process of the defection of PET buffer layer in XLPE power cable by a case study: Thermo-oxidative degradation

Buffer tape ablation failures in the buffer layer of high voltage XLPE cables have become a common failure mode in cable transmission system. In this work, we aimed to analyze the degradation mechanism and evolution process of the buffer tape, which mainly consists of polyethylene terephthalate (PET) fibers, based on a fault in a 110 kV cable line. First, the gas inside the cable were extracted on site, and the gas components were analyzed using gas chromatography technology. Then the mechanism of the combustion phenomenon caused by thermo-oxidative degradation of PET fibers was proposed. Subsequently, the discharge simulation experiment of the PET buffer tape under different background gas was conducted to study the effect of oxygen on the thermal-oxidative degradation process. The research results show that oxygen plays a key role in the discharge ablation process of the PET buffer tape. Due to the thermal-oxygen degradation process, the O2 concentration in the buffer layer decreases, and the CO and CO2 concentration increases, and at the same time the combustible gases such as hydrogen and methane are generated. The internal pressure of the buffer layer also increases under the influence of the gas partial pressure. The gas components mentioned above are not generated by the discharge under anaerobic conditions. Finally, a method of preventing the ablation defect of the buffer layer of the high-voltage cable according to the thermo-oxidative degradation mechanism of the buffer tape PET material is proposed.

Biocomposite films based on chitosan and cerium oxide nanoparticles with promising regenerative potential

Polymeric nanocomposite materials have great potential in the development of tissue-engineered scaffolds because they affect the structure and properties of polymeric materials and regulate cell proliferation and differentiation. In this work, cerium oxide nanoparticles (CeONPs) were incorporated into a chitosan (CS) film to improve the proliferation of multipotent mesenchymal stem cells (MSCs). The citrate-stabilized CeONPs with a negative ζ-potential (−25.0 mV) were precoated with CS to obtain positively charged particles (+20.3 mV) and to prevent their aggregation in the composite solution. The composite CS–CeONP films were prepared in the salt and basic forms using a dry-cast process. The films obtained in both forms were characterized by a uniform distribution of CeONPs. The incorporation of CeONPs into the salt form of CS increased the stiffness of the CS–CeONP film, while the subsequent conversion of the film to the basic form resulted in a decrease in both the Young's modulus and the yield stress. The redox activity (Ce4+ ⇌ Ce3+) of cerium oxide in the CS–CeONP film was confirmed by thermal oxidative degradation. In vitro culture of MSCs showed that the CS–CeONP film has good biocompatibility, and in vivo experiments demonstrated its substantial regenerative potential.

Dielectric Breakdown Performance of Deashed Polypropylene for HVDC Film Capacitors

The metal ash in polypropylene (PP) significantly weakens the breakdown performance, and the deashing process can reduce the ash content. In this article, a novel deashing solution of metal deactivator (MD)/ethanol (ET) is prepared in an attempt to reduce the ash content and improve the breakdown performance. The film sample is prepared for the breakdown and conductivity performance tests, and the results reveal that the breakdown strength of the deashed sample is increased by 34%, the conductivity is greatly suppressed by 77%, and the discharge energy density is significantly enhanced by 80%. In addition, the total metal ash content of the deashed sample is decreased by 65%, and the defect coefficient after crystallization is reduced by 70%. A stable ring structure is formed between MD and metal ashes, which plays a great role in deashing. Therefore, the metal ash ionization and the catalytic effect on the thermal-oxidative degradation of PP are significantly inhibited, resulting in a great improvement in the breakdown strength. This deashing method provides a feasible reference for the study of high-reliability capacitor films with excellent insulation performance.

Investigation of the effect of thermal-oxidative destruction of pyrocarbon on formation of structure of a binder and residual strength of sand-liquid-glass mixtures

A study of the effect of thermal-oxidative degradation of a carbon-containing additive on the formation of the binder film structure and the residual strength of sand-liquidglass mixtures after various calcination temperatures is presented. Pyrolyzed industrial carbon (pyrocarbon) of P324 grade was used as an additive. The methods of differential thermal and thermogravimetric analyzes were used to study the physical and chemical processes that occur with the investigated carbon-containing material when heated to a temperature characteristic of the heating of the surface layer of the core (molding) mixture in contact with liquid steel. This made it possible to reveal the temperature ranges of the degradation of the carbon-containing additive, which lead to a violation of the integrity of the sodium silicate film and a decrease in the residual strength of the sand-liquid-glass mixture. For a comparative analysis of the structure of silicate binder films and the residual strength of sand-liquid-glass mixtures after calcination at temperatures of 453, 673, 873, and 1073 K (180, 400, 600, and 800 °C), standard cylindrical samples from reference (quartz sand of 1K2O303 grade and liquid glass with a silicate modulus of 2.8, a density of 1490 kg/m3 as a binder) and experimental (with the introduction of pyrolytic carbon in the amount of 2 % (wt.)) mixtures have been prepared. As a result of the study, it was found that the residual strength of the studied sand-liquid-glass mixtures depends on the morphological features of the surface of the silicate binder film, expressed by the presence of carbonaceous formations (soot), pores and crystals of sodium carbonates (stress concentrators in the binder film).

Influence of a Hydride-Forming Multi-Component Alloy on the Carbonization Behavior of Vulcanized Elastomer Composites

In this work, composites based on a hydride-forming fiber of a multi-principal-component (MPC) Ti20Zr20Nb20V20Hf20 alloy, carbosil, dicumylperoxide and nitrile butadiene rubber (NBR) matrix were obtained. The composites were prepared in a three-stage process including the mixing of elastomeric compounds via a rubber mixing mill and low-temperature vulcanization by heat pressing. Using dynamical mechanical analysis (DMA) and differential scanning calorimetry (DSC) the effect of the metallic filler on the process of carbonization of the composite elastomeric matrix was studied. The microstructure and gas separation properties of the resulting composites were also studied. The results showed that the filler content increase in the elastomeric matrix leads to a noticeable and gradual decrease in the activation energy of the carbonization process, reduces the temperature of this process, and accelerates the growth of the elastic modulus during carbonization. It was shown that the finely dispersed fiber of the MPC acts as an activation center for the process of thermal-oxidative degradation in the elastomeric matrix accompanying the onset of carbonization. The gas permeability values were found to be relatively low and no visible correlation with the MPC alloy content in the composite membrane was observed.

Thermal and photo oxidative degradation of natural rubber film in the presence of iron (III) stearate

Thermal and photo oxidative degradation of natural rubber film in the presence of iron (III) stearate

A comprehensive study into the thermo-oxidative degradation of sulfur-based engineering plastics

The use of sulfur-based plastics has led to the accumulation of end-of-life sulfur-based plastic waste that should ideally be recycled. In this study, several technologies were applied to investigate the thermal-oxidative degradation property of sulfur-based plastics (polyphenylene sulfide (PPS), polyether sulfone (PES), and polysulfone (PSU)). Thermogravimetric analysis (TGA) revealed that these plastics undergo major decomposition at 450–650 °C under N2, whereas two-stage weight loss at 450–690 °C was observed in air. X-ray photoelectron spectroscopy (XPS) and in-situ radical monitoring by heated electron spin resonance (heated-ESR) spectroscopy revealed that the samples had altered their chemical structures, and that radicals are involved in samples treated at low temperature (≤ 400 °C). The thermo-oxidative products were analyzed by customized pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). PPS pyrolysis mainly produced sulfur-containing aromatic compounds, with H2O, CO2, and SO2 released during two-stage degradation in air, which suggests that pyrolysis and oxidation occur simultaneously during the first stage. PES pyrolysis generated various oxygen-containing products, whereas the oxidation of PES resulted in a great number of furans and dioxins at the expense of phenolics. Extensive evolution of SO2 was initially observed, irrespective of the degradation atmosphere. PSU pyrolysis produced various aromatics, phenolics, and esters, with SO2 formed as the major sulfur-containing compound, which was released at a lower temperature (∼50 °C) in air compared to N2, confirming that PSU is less thermally stable than PPS and PES in air, as observed by TGA. The thermo-oxidative degradation behavior of sulfur-based plastics was comprehensively characterized by combining conventional techniques (TGA and XPS) with advanced analytical technologies (heated-ESR and customized Py-GC/MS).

Investigating the Thermo-Oxidative Degradation and Operational Limits for Hybrid AlOX–PET Fabrics Created Via Vapor Phase Infiltration (VPI)

In vapor phase infiltration (VPI), vapor phase metalorganic precursors are diffused into polymers and further reacted with water vapor to form hybrid organic-inorganic materials. Hybrid materials created through VPI have shown utility in industrially relevant applications including membranes for chemical separation, photovoltaics, and catalysis. VPI can be conducted at different temperatures, with each processing temperature resulting in different chemical states that alter the properties of the hybrid material. In this project, polyethylene terephthalate (PET) fabrics are infiltrated with a trimethylaluminum (TMA) precursor and co-reacted with water vapor at a range of infiltration temperatures (60-140 ˚C) to create hybrid AlOX - PET fabrics. The purpose of this project is to develop a set of thermal operational limits for these hybrid organic-inorganic materials and translate techniques for thermal characterization from the textile community to the VPI community. Thermo-oxidative degradation for the hybrid fabrics was quantified through changes in degradation temperature and activation energies. Thermogravimetric analysis (TGA) was employed to quantify inorganic loadings (~20 weight percent inorganic), degradation temperatures, and the activation energy for degradation using the Flynn/Wall/Ozawa (FWO) method for decomposition kinetics. Most hybrid fabrics demonstrated lower degradation temperatures than neat PET, except for the fabric infiltrated at 140˚C which had increased degradation temperatures. Activation energies for the first thermal-oxidative degradation event for the 80˚C, 100˚C, and 140˚C fabrics decreased by a range of 62˚C to 84˚C compared to neat PET, while the 120˚C fabric’s activation energy slightly increased by 10˚C. Additionally, a new degradation event occurred for fabrics infiltrated at low temperatures which was explored through FTIR characterization and attributed to structural rearrangements of the inorganic component. Overall, this work demonstrates how VPI process conditions alter both the organic-to-inorganic chemical binding as well as the inorganic cluster structure in these hybrids and how these structural features affect thermophysical operational limits of the material.

Short-term aging characteristics and mechanisms of SBS-modified bio-asphalt binder considering time-dependent effect

• Short-term aging mechanisms of the SBAs considering time-dependent effect. • Effects of aging time on the ageing mechanisms of the SBAs. • Effects of bio-asphalt content on the aging mechanisms of the SBAs. Bio-asphalt has emerged as a reliable material for replacing conventional asphalt in asphalt modification owing to its well social, environmental and economic benefits. However, the short-term aging mechanisms of modified bio-asphalt binders considering time-dependent effect have not been discussed widely in previous studies. In this study, considering the extensive use of SBS-modified bio-asphalt binders, the aging characteristics of an SBS-modified bio-asphalt binder (SBA) based on six different aging times (0 min, 40 min, 65 min, 130 min, 195 min, and 260 min) and four different bio-asphalt contents (0%, 3%, 6%, and 9%) are investigated using the rolling thin film oven test (RTFOT). Bio-asphalt can significantly improve the aging resistance of the SBA, although the improvement effect decreases as the bio-asphalt content increases. Moreover, the short-term aging mechanisms of the SBA considering time-dependent effect are determined based on fluorescence microscope (FM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that the aging of the SBA at early stage is primarily attributed to the disintegration of the SBS cross-linked structure due to the volatilization of light components (e.g., saturates and aromatics) and the thermal-oxidative degradation of styrene-butadiene. With the increase of aging time, aging is primarily caused by the conversion of resins, saturates, and aromatics to asphaltenes due to the oxidation of the polyunsaturated carbon chain and sulfur. Although bio-asphalt can delay the aging, it does not change the evolution process.

A small addition of reduced graphene oxide to protect fluorosilicone rubber from thermal oxidative degradation

AbstractAs an essential elastomer used in edge technologies, fluorosilicone rubber (FSR) suffers serious oxidative aging problem when serving at high temperature. In this study, a small amount of reduced graphene oxide (rGO) was added to FSR, and the resulting rGO/FSR compounds were vulcanized using 2,5‐dimethyl‐2,5‐di(tert‐butyl) peroxyhexane as the vulcanizer. The dispersion of rGO was investigated using scanning electron microscope. The mechanical properties and thermal‐oxidative stability of the rGO/FSR vulcanizates were investigated via thermal aging test at 230°C for 72 h, thermogravimetric analysis (TGA), and isothermal degradation test at 280, 320, and 350°C. The results showed the small addition of rGO (0.5 wt%) significantly improved the thermo‐oxidative stability of FSR. In particular, the FSR incorporating of 0.5 wt% of rGO could maintain more than 85% of tensile strength after aging at 230°C for 72 h. The FSR incorporating of 0.5 wt% of rGO can maintain more than 90% of initial weight after aging at 350°C for 12 h. The experiment of scavenging hydroxyl radical by rGO, and quantum chemistry calculation indicated rGO containing aryloxy radicals can scavenge the initial radicals during thermal degradation of FSR, which might be prime reason for the antioxidant properties of rGO.

Improvement of dielectric properties of polypropylene films for capacitors based on metal-ash suppression

In this paper, polypropylene (PP) composite films modified with the metal deactivator (MD) are prepared in order to suppress the adverse effect of metal ashes on the dielectric properties. The dielectric properties of samples are tested and the results show that the breakdown strength of the composite sample at 25, 55 and 85 °C is significantly enhanced, and the deterioration of the DC conductivity by the electrical field and heat is greatly weakened. The dielectric constant of the composite sample is slightly increased with the relatively low dielectric loss, and the discharge energy density is increased by 68%. Due to the complexation reaction between MD1024 and metal ashes, the catalytic effect of metal ashes on thermal-oxidative degradation is significantly suppressed, and the oxidation induction time (OIT) of the composite film is greatly increased to 40.5 min from 7.7 min of pure PP, which improves the thermal-oxidative stability of the composite sample. This study provides a feasible reference for the development of high-reliability PP films for capacitors.

Superior flame retardancy, antidripping, and thermomechanical properties of polyamide nanocomposites with graphene‐based hybrid flame retardant

AbstractGraphene is considered one of the most prominent halogen‐free multifunctional flame retardants for polymers, and the resultant nanocomposites also display a good balance of properties. However, the biggest concern nowadays is thermal oxidative degradation, which mainly affects the flame retardant (FR) efficiency of graphene. To improve the flame retardancy and thermal oxidative degradation efficiency, graphene was functionalized with a combination of polycyclotriphosphazes and siloxanes via a sol–gel surface modification method, yielding a graphene‐based hybrid FR (PSGO) containing multiple elements (P, N, S, and Si). The PSGO‐containing PA6 composite exhibited significant improvements in the water resistance, thermal, mechanical, and FR properties, as compared with those of 3‐isocyanatopropyltriethoxysilane functionalized graphene oxide (ITS‐GO) and siloxane‐modified polycyclotriphosphazenes (m‐PZS) individually. The peak heat release rate and total heat release values of the PA6 composites with 10 wt% PSGO decreased by 45.7% and 36.9%, respectively, compared to those of pristine PA6. Moreover, it was confirmed that 10 wt% PSGO in the PA6 composite resulting in a V–0 rating in the UL‐94 tests, even after the water immersion test. These attractive properties are attributed to the resistance to thermal‐oxidative degradation of PSGO and the improved interfacial interactions with the polymer matrix. Therefore, this PSGO can be used as a multifunctional modifier to improve the water resistance, thermal, mechanical, and FR properties of polymers.

Study of the toxicity of combustion products of polymer materials using chromatomass spectrometry

Introduction. Carrying out studies of the toxicity of combustion products (HCL50) of polymer materials: epoxy glue grade EK-5T and compound ELPLAST-180 ID according to GOST with the additional use of gas chromatography with mass selective detection. Objective. Experimental study of the toxicity of combustion products (HCL50) of polymer materials in various modes of thermal oxidative degradation: epoxy glue grade EK-5T and compound ELPLAST-180 ID, as well as a survey mass spectrometric analysis of products of thermal oxidative degradation. Material and methods. The studies were carried out in accordance with GOST 12.1.044-89. Equipment: “Toxicity” unit, “Infracar M2.01” gas analyzer, Focus GC chromato-mass-spectrometric instrumental complex with DSQ II mass spectrometer (Thermo Scientific, USA), Nova Medical Stat Profile automatic analyzer of blood gases, electrolytes and oximetry Model CCX (USA). Blood sampling was carried out in capillaries “Stat Profile Critical Care Express Capillary Tube 230 µL with Na Heparin” LOT 107669, CO2 chamber. Results. In the course of studying the products of outgassing of polymer materials using an exposure chamber and a gas chromatomass spectrometer, a significant increase in toxicity (4.8 times) of a mixture of chemicals released from epoxy glue EK-5T during the transition from thermal-oxidative decomposition (smoldering) to flame combustion was established. The toxicity index of the combustion products of the ELPLAST-180 ID compound under the same conditions increases by 1.8 times. A linear dependence of the percentage of lethality of laboratory animals on the integral indicator of the toxicity of combustion products has been established. Limitations. Studies of the toxicity of combustion products were carried out on non-metallic materials: epoxy glue EK-5T, compound ELPLAST-180 ID. These materials are planned to be used in hermetically sealed objects of the Navy. Conclusion. The expediency of using gas chromatography-mass spectrometry for assessing the combined effect of combustion products is shown.

Recent advances on the stability of dietary polyphenols

Recent advances on the stability of dietary polyphenols

Effect of torrefaction on thermal oxidative degradation kinetics of lignite using multi-distributed activation energy model

Torrefaction treatment is a promising method for lignite upgrading. However, its effect on the combustion characteristics has not been fully evaluated. In this study, the combustion characteristics of lignite and its upgrading samples by torrefaction were studied via non-isothermal thermogravimetric analysis. Results show that increasing the torrefication temperature decreases the volatile content while increasing the fixed-carbon in the fuels. The mole ratios of both H/C and O/C in the samples decreases as the torrefaction temperature increases. Torrefaction treatment significantly improves the combustion performance of lignite with a higher reactivity index S, and the optimum torrefaction temperature was determined to be 200 °C. The upgrading lignite by torrefaction at 200 °C has the lowest temperatures of Tf and Tp as well as the maximum corresponding DTG value. Furthermore, the results of three-parallel-DAEM model analysis results show that the activation energies corresponding to the three peaks are 176.1 kJ/mol, 186.5 kJ/mol and 221.7 kJ/mol, respectively, and that increasing torrefaction temperature had no significant effects on activation energies. With the torrefaction temperature increasing, the first standard deviation decreased while the third standard deviation increased.