Thermo-oxidative Decomposition Research Articles

Study of Thermooxidation of Oil Shale Samples and Basics of Processes for Utilization of Oil Shale Ashes

A circular economy becomes an object of actual discussions as a real alternative to the existing linear economy system. The problem is actually in Estonia also, first of all in the sector of heat and power production which based mainly on the combustion of local solid fossil fuel—Estonian oil shale (OS) resulting in the formation of ~5–6 million tons of OS ashes annually. The thermooxidative decomposition of OS samples from different deposits and estimation of the possibilities of utilization of OS ashes formed at both—pulverized firing (PF) and circulating fluidized bed combustion (CFBC) of Estonian OS were studied. The thermal analysis combined with evolved gas analysis (EGA) methods like Fourier transform infrared (FTIR) and mass-spectroscopy (MS) was exploited. It was established that the differences in the thermal behaviour of different OS samples are caused by the differences in the chemical matrix of organic matter, chemical and mineralogical composition of the inorganic part of OS, and morphology of samples. It was also found that moderate grinding of OS ashes with simultaneous moderate water treatment notably improved the SO2 binding efficiency of cyclone ash, and that the strength and leachability characteristics of granulated OS ashes strongly depend on the post-granulation treatment conditions allowing to increase the soil neutralizing ability of the granulated products. This overview was based on our investigations carried out during the last fifteen years.

One-step fabrication of transparent superhydrophobic surface

A self-cleaning, transparent superhydrophobic silica-based surface with water contact angle (CA)/sliding angle (SA) 168°/2° was fabricated by simple one-step thermal oxidation of silicone grease. Microstructural studies (FESEM/TEM) confirmed the presence of a sponge-like pore structure of amorphous silica nanoparticle having a diameter of around 20 ± 2.2 nm. EDS analysis confirms the presence of C, Si, and O in coated substrates. Also, phase and thermal studies (XRD, FTIR, and TG-DSC) analysis showed the thermo-oxidative decomposition of silicone grease results in superhydrophobic –H2C-Si-O-Si-CH2- network structure at 400 °C followed by thermally stable superhydrophilic HO-Si-O-Si-OH network structure at 500 °C. The coated surface showed excellent stability towards corrosive liquids (1 M NaCl, NaOH, HCl aqueous solution, and hot water) and exposed temperature up to 400 °C. The maximum visible light transparency of the superhydrophobic glass was 92.4% compared to the uncoated glass (93.3%). Thus, making transparent superhydrophobic surfaces by a simple and straightforward process can be potentially used in self-cleaning glasses for various engineering applications.

Kinetic study of the thermo-oxidative decomposition of metformin by isoconversional and theoretical methods

The drug metformin is the most prescribed drug to treat type II diabetes and has been recently reported to have anticancer activities. Because of its wide use, its potential risk on the environment is extremely concerning. In this study, the mechanism and the thermodynamics of the thermo-oxidative decomposition of the metformin were investigated as part of a new solution for the pharmaceutical contamination of water bodies. Thermogravimetry and mass spectrometry were used to demonstrate the metformin thermo-oxidative decomposition under air in the temperature range 25–800 °C. The isoconversional methods of Kissinger-Akahira Sunose (KAS) and Friedman (FR) were implemented to deduce the trends of effective activation energies. As expected, the effective activation energy (Eα) of the reaction was dependent on the reaction temperature, suggesting multi-step reactions. The Eα ranged from 100 to 145 kJ/mol and 200–300 kJ/mol for the KAS and FR methods, respectively. The kinetic triplet, Aα, ΔS‡, and ΔG‡ were also determined by finding the appropriate reaction model. Theoretical calculations were implemented to propose a full reaction mechanism. The oxidation of metformin was investigated with both molecular O2(t) and atomic O(t) oxygen. The experimental results were then explained under the light of the computational data to explain the variation of Eα with temperature, and the competition between the O2(t)/O(t) species.

Exploration of flame retardant efficacy of cellulosic fabric using in-situ synthesized zinc borate particles

In the present context, synthesized zinc borate was demonstrated as a thermal resistant agent by applying it by in-situ method on the cotton fabric wherein zinc borate was synthesized from zinc nitrate and borax. Particle formation and its morphology were confirmed by particle size analyzer, and scanning electron microscopy analysis, respectively. It has been observed that zinc borate-cotton registered the high oxygen index value of 30% against 18% oxygen index of the control cotton fabric. Furthermore, zinc borate treated cotton fabric showed a black colour char and a char length of 25 mm. The extent of heat generated from the treated cotton fabric was also found to be 75% less compared to the untreated cotton fabric. A thermo-oxidative decomposition experiment was performed by thermo-gravimetry analyzer and reported in detail. It was found that the treated fabric recorded more than 40% weight retention at a higher temperature. The surface morphology of the charred mass was also examined to fortify the dehydration mechanism of the treated sample.

Synthesis and thermo-oxidative degradation of acyclic polyimides

For the first time, film-forming aromatic acyclic polyimides were obtained as a result of in situ rearrangement or as a result of heat treatment of polycarboxyimidates by the Mumm-Hess mechanism. Intermediate polycarboxyimidates were prepared using the acid-catalyzed reaction of dicarboxylic acids and dinitriles in ionic liquids. The probable mechanism and the corresponding kinetic parameters of thermooxidative decomposition of acyclic polyimides were determined using NetzschThermokinetics 3 – multidimensional nonlinear regression software.

Thermo-oxidative decomposition of multi-walled carbon nanotubes: Kinetics and thermodynamics

Multi-walled carbon nanotubes (MWCNTs) are familiar well owing to their capability of finding wide-reaching applications based on their fascinating properties. Kinetics of thermally activated processes in MWCNTs can help in understanding and controlling those processes which might eventually lead to develop materials with optimized efficiencies. Even though, inadequate information on the kinetics of thermal decomposition of WMCNTs has been reported in the literature, and its thermodynamics is yet to be addressed. In this regard, the present study deals with a detailed kinetic investigation on the thermo-oxidative decomposition of MWCNTs by employing advanced kinetic approaches. Kinetic analysis of MWCNTs decomposition reveals that although the kinetic triplets remain comparable, reaction model under isothermal condition is not the same as under non-isothermal conditions. It alters from contracting cylinder (non-isothermal) to random nucleation followed by isotropic growth of particles (isothermal). Thermodynamics of MWCNTs thermal decomposition points out that the process is non-spontaneous with enhanced endothermicity. In addition, the structure of activated complex is found to be relatively more organized in comparison with the reactant. An account of the interpretations of the obtained kinetic and thermodynamic parameters is also given and discussed in this study.

Thermo-Oxidative Decomposition Behaviors of Different Sources of n-C7 Asphaltenes under High-Pressure Conditions

Effects of pressure on thermo-oxidative decomposition of different sources of n-C7 asphaltenes were investigated at high pressure using a thermogravimetric analyzer under an air atmosphere. The n-C...

Термическая стабильность полиуретанового покрытия, полученного с использованием дифенилолпропана

Thermal stability of polyurethane varnish coating prepared by using diphenylolpropane, polyetherpolyol and polyisocyanate with an equimolar ratio of isocyanate and hydroxyl groups was assessed in the air. The polyurethane weight loss thermogram shows three temperature regions: I – (217-275)°С, II – (275-380)°С, and III – above 380°С. For interpreting thermogram of the polyurethane under study the model substances simulating the urethane groups of a polymer were synthesized. The substance containing the urethane group formed by phenolic hydroxyl of diphenylolpropane was shown to demonstrate relatively low thermal stability and gets broken down into isocyanate and bisphenol. Decomposition of the substance containing the urethane group formed by alcoholic hydroxyl occurs at the higher temperature. The data obtained allow interpreting the occurrence of thermal decomposition step I in TGA curve by structural changes in the blocks formed by diphenylolpropane and polyisocyanate being the least stable when exposed to elevated temperatures. The next step can be attributed to decomposition of more thermostable urethane groups formed by functional groups of oligooxypropylenetriol and polyisocyanate. Transition to the step III accompanied by severe sample weight loss due to decomposition of urethane groups is explained by thermal oxidation of oligoether units of polymer. Based on the data obtained the conclusion was made that the presence of urethane groups formed by phenolic hydroxyl of diphenylolpropane in polymer structure results in the decreased thermooxidative decomposition onset temperature of polymer. At the same time, a deceleration of thermooxidative processes due to the stabilizing effect of diphenylolpropane released at the beginning of thermal decomposition of polyurethane is observed in a high-temperature region. The proposed polyurethane coating is inferior to commercial counterparts in thermal decomposition onset temperature but superior to them in the temperature corresponding to a 50% polymer weight loss.

Thermo-Oxidative Decomposition of Lovage (Levisticum officinale) and Davana (Artemisia pallens) Essential Oils under Simulated Tobacco Heating Product Conditions

Summary The thermo-oxidative decomposition of lovage (Levisticum officinale) and davana (Artemisia pallens) essential oils has been studied by pyrolysis-gas chromatography/mass spectrometry in 9% oxygen and 91% nitrogen atmosphere at 300 °C to simulate low-temperature tobacco heating conditions. Both lovage and davana oils contain numerous chemical substances; the main components of both oils are various oxygen-containing compounds. Isobenzofuranones are the most important constituents of lovage oil, and their relative intensity changed significantly during oxidative pyrolysis. (Z)-ligustilide underwent two kinds of decomposition reactions: an aromatization reaction resulting in the formation of butylidenephthalide and the scission of the lactone ring with the elimination of carbon dioxide or carbon monoxide. Davanone is the main component of davana oil, which did not decompose considerably during low-temperature oxidative pyrolysis. However, the relative yield of the second most intensive component, bicyclogermacrene, reduced markedly due to bond rearrangement reactions. Davana ether underwent oxidation reactions leading to the formation of various furanic compounds. The changes in the composition of both essential oils could be interpreted in terms of bond splitting, intramolecular rearrangement mechanisms and oxidation reactions of several constituents during low-temperature oxidative pyrolysis. The applied thermo-oxidative method was found to be suitable to study the stability of the essential oils and monitor the decomposition products under simulated tobacco heating conditions. In spite of the complicated composition of the essential oils, no evidence for interaction between the oil components was found. [Beitr. Tabakforsch. Int. 29 (2020) 27–43]

Flameless burning of wood: parameters of macrokinetics of pyrolysis and thermo-oxidative decomposition

Introduction. Many materials are subject to flameless, smoldering combustion: coal, cotton, peat, carbonizing ­polymers, etc. The fire hazard of smoldering burning of organic materials is that low-calorie ignition sources are sufficient to initiate the combustion process, the process is hidden, making it difficult to detect, and can spontaneously turn into a fiery one. Purpose and objectives. The purpose of this work was to determine the macrokinetics of pyrolysis and thermo­oxidative decomposition of wood of different types of conifers and deciduous species by thermal analysis. Methods. Samples were investigated by thermal analysis in an inert and air environment. For this, we used the automated modular system Du Pont-9900, including the TGA-951 thermobalance, and the DSK-910 diffe­rential scanning calorimeter. Results. It was found that the pyrolysis of the main components of wood (hemicellulose and cellulose) proceeds according to the nucleation and growth mechanism of nuclei according to the case law R ( n = 1) with activa­tion energies close in order of magnitude for different species (98–136 kJ/mol for hemicelluloses and 203–233 kJ/mol for cellulose). At the stages of thermooxidative decomposition of wood components and heterogeneous oxidation of the carbonized product, diffusion of the D3 (D4) type in spherical geometry becomes the mechanism controlling the process. The effective activation energy of the decomposition of hemicelluloses is reduced to 90.9–95.8 kJ/mol, and of cellulose to 138.3–160.9 kJ/mol. The reaction of heterogeneous oxidation of carbonized products makes a significant contribution to the flameless, smoldering combustion of the material. It is diffusion-controlled and is characterized by high values of activation energy (up to 285 kJ/mol). Conclusion. The results of the work make it possible to evaluate the macrokinetic parameters of pyrolysis and thermooxidative decomposition of wood of different species during flameless combustion. The obtained data can be used as the main parameters for modeling the heterogeneous combustion of wood of different species in buildings.

Novel nanocomposite based on EVA/PHBV/[60]Fullerene with improved thermal properties

A novel nanocomposite was prepared from ethylene-co-vinyl acetate copolymer (EVA) and poly-3-hydroxy butyrate-co-valerate (PHBV) in combination with small amounts of [60]Fullerene (C60). The thermal degradation as well as the incorporation effect of C60 on the thermo-oxidative decomposition of EVA/PHBV/C60 nanocomposites was investigated using thermogravimetric analysis (TGA). In order to assess the level of stabilization of nanocomposites, the oxidation induction time test was also determined. The obtained results indicated that the dispersion of C60 even at low loading (0.3, 0.5 and 0.7 wt.%) exerts a significant increase on the thermal stability properties of nanocomposite. The oxidation induction time values of nanocomposites were remarkably increased with the increase of C60 amounts. Surprisingly, the oxidation induction time of EVA/PHBV/C60 (0.3 wt.%) is 1643 s higher than that of unfilled EVA/PHBV blend.The flammability properties investigated in pyrolysis combustion flow calorimetry (PCFC) showed that the addition of C60 could prolong the time to peak of Heat Release Rate (pHRR) of around 30 °C compared to EVA/PHBV blend. It was demonstrated that C60 is inhibitor of the thermal and thermo-oxidative degradation of EVA/PHBV blend.

The Effect of Heat Treatment Regimes of Polyphenylene Sulfides on their Thermal Properties

Thermal and thermo-oxidative degradation, as well as crosslinking and "curing" processes of polyphenylene sulfide, depending on the heat treatment regimes, have been studied using gas chromatography. The effect of sorbed water in the polymer on the processes of thermal and thermo-oxidative decomposition of polyphenylene sulfide is shown and the optimal modes of drying the samples are established.

Kinetics and evolved gas analysis of the thermo-oxidative decomposition for neat PPS fiber and nano Ti–SiO2 modified PPS fiber

Using isoconversional methods and model-fitting methods, the non-isothermal thermo-oxidative decomposition kinetics of the nano Ti–SiO2 modified PPS fiber (AO-PPS) and neat PPS fiber are investigated. Decomposition processes of both PPS fibers can be differentiated into two stages with totally different mechanisms. Using the Málek method combined with residual sum of squares, the most probable mechanism model of the first stage is derived, which belongs to the deceleration α-t curve and the integral form is g(α) = (1-α)−1-1. Thermo-oxidative decomposition processes of the second stage are the aggregation of many complicated reactions, which cannot be expressed through the simple, single kinetic mechanism. Evolved gas analysis of both PPS fibers gives an insight of the mechanism of the thermo-oxidative decomposition processes. The main reactions of the first stage involve the breaking of the phenyl-S bonds and the cross-linking of remaining molecules. The multiple complex reactions in the second stage verify the kinetic analysis of the mechanisms.

Facile Room-Temperature Preparation of Flexible Polyurethane Foams from Carbon Dioxide Based Poly(ether carbonate) Polyols with a Reduced Generation of Acetaldehyde.

Carbon dioxide (CO2) is becoming more attractive as a renewable feedstock for chemical synthesis. In this study, CO2 was incorporated into poly(ether carbonate) (PEC) polyols by using a double-metal-cyanide catalyst. By adjusting the CO2 pressure, the content of propylene carbonate units in the PEC polyols was controlled, indicating successful and semiquantitative incorporation of CO2 into the PEC polyols. Polyurethane foams (PUFs) with different propylene carbonate content were easily prepared at room temperature by employing the PEC polyols due to their adequate viscosity under ambient conditions. The firmness of the PUFs increased as the amount of propylene carbonate units increased due to the rigidity of the carbonate linkage, representing predictable mechanical properties. Interestingly, reduced generation of volatile organic compounds (VOCs) from the PUFs, namely acetaldehyde, was observed with a high content of propylene carbonate units at 120 °C, indicating good stability of the carbonate units against thermo-oxidative decomposition. This study demonstrates the importance of CO2 as an environmental-friendly and renewable resource that can provide not only industrially important but also problem-solving products in terms of processability and low generation of VOCs.

Thermal and thermo-oxidative degradation kinetics and characteristics of poly (lactic acid) and its composites

Thermal degradation behavior and kinetics of starch/PLA composites in an inert and oxygen atmosphere were investigated by TG and TG-FTIR techniques. It is shown that the thermal degradation process can be divided into three stages, and a significant difference between thermal and thermo-oxidative degradation is the third stage in which the residual chars are further cracked for the thermo-oxidative degradation. The activation energy was calculated using the iso-conversional Flynn-Wall-Ozawa (FWO) method. The lower activation energy for thermo-oxidative degradation indicated that oxygen had an accelerated effect on thermal degradation. The variation of activation energy indicated that the decomposition of all the samples was a complex process that included at least two different mechanisms. Evolution of the evolved gaseous products with temperature was studied to understand the thermal and thermo-oxidative decomposition comprehensively. According to the TG-FTIR analysis, the gaseous products mainly contained lactide, cyclic oligomers, aldehydes, CO2, CO, and H2O.

Thermo-oxidative decomposition of lime, bergamot and cardamom essential oils

The thermal decomposition of three essential oils has been studied at 300 °C, using a 9% oxygen in nitrogen atmosphere, to mimic the thermal environment of flavours under low-temperature tobacco heating conditions. The starting compositions of the lime, bergamot and cardamom oils were determined by gas chromatography/mass spectrometry (GC/MS). The thermo-oxidative decomposition was evaluated by applying on-line pyrolysis-GC/MS. The main constituents of the oils studied were cyclic and linear monoterpenoids; however, the relative intensities of these components were characteristically different between oils. Lime oil was dominated by monoterpene hydrocarbons, while the other citrus oil, bergamot oil contained in addition a significant number of esters and alcohols. Oxygen-containing monoterpenoids were the dominant constituents of cardamom oil. The relative proportion of the constituents of all three essential oil samples significantly altered during oxidative pyrolysis at 300 °C. The strained rings of bicyclic monoterpenes (pinenes, sabinene, and thujene) underwent scission, resulting in the formation of monocyclic monoterpenes (limonene etc.). Both linear and cyclic terpene acetates decomposed via elimination of acetic acid, so linalyl acetate produced myrcene and ocimene, while terpinyl acetate formed mostly limonene and terpinolene. The relative intensities of linalool and eucalyptol were reduced during pyrolysis, which can be explained by dehydration reactions resulting in the formation of myrcene and ocimene, or limonene and terpinolene, respectively. The chemical reactions that occurred were explained by bond splitting and intramolecular rearrangement mechanisms, with oxygen playing a role in the initiation processes.

Thermal behavior of collagen crosslinked with tannic acid under microwave heating

With the aim at assessment of thermal stabilities of collagen crosslinked with tannic acid under microwave, some thermo-analysis methods have been employed to analyze the properties of the crosslinked product. Meanwhile, for getting some information about the non-thermal effect of microwave on the process, microwave heating with simultaneous cooling (MHSC) method was adopted and compared with water bath heating. The thermal decomposition of the collagen material was characterized by the mass-loss ratio with thermo-gravimetry/derivative thermo-gravimetry curves recorded in nitrogen flow. The crosslinked collagen under MHSC exhibited a higher peak temperature and a lower degree of thermo-oxidative decomposition. The thermal denaturation of the material was determined by the differential scanning calorimetry (DSC) analysis in nitrogen flow. DSC curves showed that microwave gave a higher denaturation temperature and enthalpy, which increased about 3.9 °C and 73.0 J g−1, respectively. The hydrothermal stability of the product was evaluated using the method of micro hot table in glycerol–water condition. The results showed that the shrinkage temperature increased about 3.5 °C under MHSC. In result, microwave gave a higher thermal and hydrothermal stability of the crosslinked collagen, which could be attributed to a stronger bonding of the collagen with tannic acid as a result of microwave non-thermal effect. The results presented here may lay a foundation for the application of microwave in vegetable tanning.

Characterization of the complexing agents’ influence on bioscouring cotton fabrics by FT-IR and TG/DTG/DTA analysis

The nature of the complexing agents used in the bioscouring process of cotton fabrics aiming to eliminate the non-cellulosic compounds (pectin, waxes, etc.) and to improve the hydrophilic and wetting properties influences the thermal behaviour and the FT-IR spectra of the textile materials. In this paper, we study the influence of the experimental conditions and complexing agent nature (sodium citrate or disodium EDTA salt) on the pectin elimination in bioscouring treatment of cotton fabric by FT-IR and TG/DTG/DTA analysis. The changes from FT-IR spectra of the specific bands (absorbance intensity at 2916, 2852, 1732 and 1640/1642 cm−1) were evaluated. The thermal behaviour of the investigated samples’ fabric by using TG/DTG/DTA analysis was studied at 30–600 °C temperature range, in air atmosphere. All samples showed three mass-loss steps due to the elimination of humidity, decomposition of the non-cellulosic and cellulosic components (main degradation stage of the samples) and thermo-oxidative decomposition of the formed degradation products. The Tonset values corresponding to the main decomposition step, the mass-loss values (%Δm) and the % residual mass (at 600 °C) were influenced by the complexing agent nature as well as the concentration and the action time of the commercial enzyme product. In addition, the calcium content of some samples treated with and without ultrasound was determined using atomic absorption spectroscopy method (AAS) in order to correlate the results with TG/DTG/DTA analysis. The obtained results have shown that the synergistic action of experimental conditions (enzyme concentration, pH, enzyme product action time, ultrasound) and the presence of sodium citrate as a biodegradable complexing agent led to the elimination of a higher amount of pectin from the cotton samples than that eliminated when using EDTA.

Mechanical, Thermal and Fire Retardant Characteristics of NR/PP/ATH Thermoplastic Vulcanizates

Blends of natural rubber (NR) and polypropylene (PP) were melt-mixed with phenolic resin crosslinking agent to obtain thermoplastic vulcanizates (TPVs). The blend composition of NR and PP was at 60/40 %wt. Alumina trihydrate (ATH) was incorporated into the blends to improve the flame retardancy, and the effect of ATH incorporation at different levels (20 - 120 PHP, part per hundred polymers) on blend morphology, ATH dispersion, mechanical properties, thermal resistance and flame retardancy was investigated. Analyses by transmission electron microscopy (TEM) and energy dispersive X-ray-scanning electron microscopy (EDX-SEM) revealed the dispersed phase-like morphology of 60/40 NR/PP TPVs. The presence of ATH in the TPVs did not have much influence on morphology of 60/40 NR/PP blends. Increasing ATH content decreased the dispersion level of ATH, which caused a decrease of tensile strength and elongation at break. Furthermore, an addition of ATH into the NR/PP blends resulted in lower elastic recovery, but slight increase of hardness. It was also found that the ATH suppressed the intensity of mass loss rate of NR and PP, resulting slower thermo-oxidative decomposition process of the blend materials. Limiting oxygen index (LOI) and UL94-V rate were enhanced with more incorporated ATH content. According to the results present in this study, the addition level of ATH for development of flame retardant NR/PP blend-based TPVs with acceptable elastomeric properties was recommended at 100 PHP.

Thermo-oxidative decomposition behavior of starch-g-poly(citronellyl methacrylate) and starch-g-poly(citronellyl acrylate) copolymers

The paper describes the studies on the thermo-oxidative decomposition behavior of two types of starch graft copolymers: starch-g-poly(citronellyl acrylate) copolymers with the grafting percent (%G): 21.3% ± 0.5, 35.8% ± 0.6 and 59.8% ± 0.3 and starch-g-poly(citronellyl methacrylate) copolymers with %G: 21.3% ± 0.4, 37.0% ± 0.2 and 51.8% ± 0.3 prepared applying the “grafting from” method. The decomposition course of copolymers by using the TG/DTG/DSC/FTIR analysis was evaluated. As it was found, the course of TG/DTG/DSC curves was independent on the %G but it was directly dependent on the type of analyzed copolymer. It resulted in completely different decomposition course of starch-g-poly(citronellyl acrylate) copolymers under the presence of oxidative conditions as compared to starch-g-poly(citronellyl methacrylate) copolymers. Thanks to applying the FTIR analysis of the gaseous products emitted under the heating of the studied materials, the detailed decomposition course of copolymers was evaluated.