Thermal Degradation Process Research Articles

Multi-step polymer degradation kinetics using activation energy-dependent cataluminescence

The multi-step thermal degradation processes of polyoxymethylene were distinguished using rate constants and activation energies through cataluminescence dynamic curves.

Synthesis and Study of Thermal Degradation Process of 2,4-Dihydroxyacetophenone-Guanidine-Formaldehyde Copolymer

The resin DAPGF-III, in a molar ratio of 3: 1: 5 was made by heating in the presence of 2M hydrochloric acid for 5h by polycondensation of Guanidine hydrochloride and 2,4-Dihydroxyacetophenone in the presence of formaldehyde. The preliminary structure of the copolymer was evaluated by spectral methods such as elemental analysis, 1H-NMR, FTIR and UV-Visible techniques. The molecular weight of the copolymer was determined by non-aqueous conductivity titration performed by using alcoholic KOH. TGA analysis of the synthesized copolymer is carried out by non-isothermal thermogravimetric analysis, where the sample is exposed to continuous temperature rise at a heating rate of 20°C / min in an air atmosphere and is used to study the rate, decomposition and thermal stability analysis of newly synthesized copolymer at which it was executed. Thermal parameters such as apparent entropy (ΔS), frequency factor (A), change in free energy (ΔG), and rate of reaction were determined according to the methods of Freeman Carroll (FC) and Sharp Wentworth (SW). The activation energy measured by the FC method was confirmed by the SW method.

Kinetic model and parameters optimization for Tangkou bituminous coal by the bi-Gaussian function and Shuffled Complex Evolution

In this paper, deconvolution procedure coupled with Shuffled Complex Evolution (SCE) algorithm was employed to fit the thermogravimetric curve for Tangkou bituminous coal in nitrogen atmosphere. The kinetic model and parameter optimization of detailed stages of coal pyrolysis were studied to simplify and characterize the thermal degradation process with complex behavior. The reaction rate curve of Tangkou bituminous coal was separated into three stages: primary pyrolysis, secondary depolymerization and secondary repolymerization. Based on the deconvolution results of bi-Gaussian function, the kinetic parameters were determined by Friedman and Coats-Redfern methods. The results showed that the reaction order model was responsible for each individual stage. Then, SCE algorithm was employed to optimize the obtained parameters to get more accurate results. The optimization results showed that the experimental curves can be well characterized by the parameters obtained by the deconvolution procedure and SCE algorithm. Eventually, the accuracy and applicability of the reaction model and optimization parameters of Tangkou bituminous coal were verified by blind prediction of the experimental curve at an extra heating rate. Good fitting indicated that the three-stage reaction model has great potential in describing and predicting the pyrolysis behavior of Tangkou bituminous coal.

Facile synthesis of bio-based latent curing agent and its high-Tg epoxy network

Developing latent curing agents from bioresources are of great significance to the sustainable development of epoxy resins. In this work, a bio-based latent curing agent--phytate salt PAIM--was prepared by a simple salt-forming reaction between imidazole and naturally occurring phytic acid, and was mixed with commercial bisphenol A epoxy to obtain one-component epoxy system. The system exhibited excellent storage stability at storage temperature and high curing reactivity at curing temperature. Since phytic acid possesses twelve hydroxyl groups that can react with epoxy groups, the cross-link density of the resin can be increased, as a result, Tg of the cured one-component epoxy reached up to 205 °C. Thermal stability and degradation process of the cured epoxy were investigated by thermal gravimetry-infrared analysis. Due to the introduction of phytic acid, residual carbon of resins increased and the gas release rate decreased. This latent curing agent with facile synthesis, environmental protection and biomass origin is in line with the current development trend and has great industrial application value.

On the thermogravimetric analysis of polymers: Polyethylene oxide powder and nanofibers

AbstractThermogravimetric analysis of polyethylene oxide (powder and nanofibers obtained by force spinning water or chloroform solutions of polyethylene oxide) was studied using different theoretical models such as Friedman and Flynn‐Wall‐Ozawa. A semiempirical approach for estimating the “sigmoid activation energy” from the thermal degradation was suggested and confirmed by the experimental data on PEO powder and nanofibers' mats. The equation allowed for calculating a “sigmoid activation energy” from a single thermogram using a single heating rate without requiring any model for the actual complex set of chemical reactions involved in the thermal degradation process. For PEO (powder and nanofibers obtained from water solutions), the “sigmoid activation energy” increased as the heating rate was increased. The sigmoid activation energy for PEO mats obtained from chloroform solutions exhibited a small decrease as the heating rate was increased. Thermograms' derivatives were fitted to determine the coordinates of the inflection points. The “sigmoid activation energy” was compared to the activation energy determined from the Flynn‐Wall‐Ozawa model. Similarities between the thermal degradation of polyethylene oxide powder and of the nanofibers obtained from water solutions were discussed. Significant differences between the sigmoid activation energies of the mats obtained from water and chloroform solutions were reported.

Kinetic Analysis of Pyrolysis and Thermo-Oxidative Decomposition of Tennis String Nylon Wastes.

Thermal degradation of nylon-6 tennis string nylon wastes in inert nitrogen and air atmospheres was investigated by means of multiple heating-rate thermogravimetric analyses. The results obtained under the heating rates of 5–20 K/min are compared in terms of degradation feature and specific temperature for two atmospheres. Using nonisothermal data, kinetic analysis was thoroughly conducted using various isoconversional model-free methods, including Starink, Madhusudanan–Krishnan–Ninan, Tang, Coats–Redfern, and Flynn–Wall–Ozawa methods. With these kinetic analysis methods, the activation energy over the entire degradation process was successfully calculated. By means of the model-fitting master-plots method, the first-order chemical reaction model was determined to be the most appropriate mechanism function for describing pyrolysis and oxidative thermal degradation of nylon-6 waste. Using kinetic parameters, satisfactory matching against experimental data resulted using the Coats–Redfern method for both cases. Furthermore, thermodynamic parameters such as changes in entropy, enthalpy, and Gibbs free energy during thermal degradation processes were evaluated.

Biodiesel Production Using Residual Vegetable Oil and Activated by Geopolymer Matrixes with Magnetic Particles

The cooking oil, when reused in frying, undergoes a thermal degradation process that changes its physical and chemical characteristics. After repeated use of the oil, it becomes viscous and increasingly dark, it has high acidity and unpleasant odor, being inconvenient to use for new fried food because it gives unpleasant odor and taste to food and also harmful chemical characteristics to health. When these residues become unusable usually they are dumped into the sewage system and have a negative environmental impact, for example, in rainwater and sanitary sewage systems the oil mixes with the organic matter and obstructs grease boxes and pipes. Therefore, the recycling of residual vegetable oil is necessary and very useful, because it transforms the oil for other applications, for example, in this work the use of porous geopolymer with magnetic particles in the concentrations of 1%, 2%, and 3% were studied for act on the activation of the biodiesel reaction from the used cooking oil. The geopolymers with and without magnetic particles were studied using Fourrier Transform Infrared (FT-IR) and X-Ray Diffraction (XRD). The density, the kinematic viscosity, and yield of the biodiesel formation reaction were investigated. The results, calculated using analysis of variance (ANOVA) with a 95% confidence limit, indicate that all the biodiesel samples analyzed are in accordance with the kinematic viscosity value established by the Agência Nacional do Petróleo, Gás Natural e Biocombustíveis (ANP) but only samples with 0% and 1% magnetic particles have density according to the stipulated parameters.

Hybrid Proton-Exchange Membrane Based on Perfluorosulfonated Polymers and Resorcinol-Formaldehyde Hydrogel.

Organic resorcinol–formaldehyde (RF) hydrogels were introduced into a hybrid cation-exchange membrane in order to enhance its following properties: water uptake, thermal stability, and ionic conductivity. This study was aimed to investigate the modifications induced by the RF organic clusters that form a uniform distributed network within the perflourosulfonated acid (PFSA) matrix. RF concentration was controlled by resorcinol and formaldehyde impregnation time using water or ethanol solvents. The specific morphological and structural properties were characterized by atomic force microscopy, UV–Vis, and Fourier transform infrared spectroscopy. Thermo-gravimetric analysis was employed to study the thermal stability and degradation processes of the composite membranes. Proton conductivity, as a function of relative humidity (RH) at 80 °C, was measured using in-plane four-point characterization technique. Compared to the pristine membrane, the PFSA–RF hybrid membranes showed improved thermal stability at up to 46 °C and higher ionic conductivity for low RF content, especially at low relative humidity, when using ethanol-based solvents. Single fuel cell testing on RF-based membrane–electrode assembly revealed impeccable fuel crossover and power performance at 80 °C and 40% relative humidity, delivering a 76% increase in power density compared to a reference assembled with a pristine membrane and the same catalyst loadings.

Development of a novel microbiological method for detection of gamma irradiated spices

Spices are food additives that are used in many different areas of food technology. Most of the spices contain essential oils sensitive to thermal degradation processes. Therefore, an alternate method of decontamination, other than thermal, should be used so that the microbial safety of the spices is ensured. This study was focused on the evaluation of the effect of ionizing radiation, known as radurization, on microbiological safety in samples of red pepper, black pepper, and stinging nettle, from North Macedonia. Samples were irradiated by 60Co γ-rays. The possibility for development of a novel, shortened microbiological method was investigated. The conventional agar plate method was used, as a standard microbiological method, in order to evaluate the effect of irradiation on the microbiological safety of the food. The red pepper and the stinging nettle did not show any microbial growth when inoculated on both growth media, after being irradiated. Additionally, the photostimulated luminescence and thermoluminescence method were used as physical methods. By comparing the two glow curves for the glow ratio, the obtained values are greater than 0.1, which confirms that the samples have been irradiated.

Exploration of Thermal Degradation Kinetics of Epoxy Resin Composites

The thermal degradation process of epoxy resin/intumescent flame retardant/flake graphite/hexagonal boron nitride (EP/IFR/FGP/h-BN) was analyzed by thermogravimetry. The effects of binary nano flake graphite/hexagonal boron nitride as synergistic flame retardant on the thermal stability. Flynn wall Ozawa method was used to calculate the activation energy of thermal degradation kinetics of EP/IFR/FGP/h-BN. The mechanism functions of the EP/IFR/FGP/h-BN in different reaction stages were determined according to Malek method, and the thermal degradation mechanism of EP/IFR/FGP/h-BN was obtained. The binary nanoFGP/h-BN is helpful to improve the thermal stability of EP.

Assessing the thermal and fungal behavior of eco-friendly epoxy thermosets derived from vegetable oils for wood protective coatings

The paper deals with the study of the obtaining, characterization and thermal and fungal behavior of a green thermoset based on epoxidized soybean oil (ESO), castor oil maleic anhydride adduct (COMA) and methyl nadic anhydride (MNA). By varying the MNA/COMA crosslinking agent ratio, resins with different degree of stiffness can be obtained suitable for green thermosets coatings. Differential scanning calorimetry (DSC) and a simultaneous TG/FT-IR/MS coupling were used to establish the crosslinking behavior, evolved gases analysis and thermal decomposition mechanisms associated with their corresponding kinetic parameters. The non–isothermal global kinetic parameters values (activation energy and pre–exponential factor) were calculated with the aid of the Friedman and Flynn–Wall–Ozawa isoconversional methods. The curves shape of the variation of activation energy versus conversion degree and first derivative (DTG) curves shapes suggest that the thermal degradation processes occurred in multi-step kinetics. Using a multivariate linear regression method the most probable thermal decomposition and crosslinking kinetic models were established. A good concordance between experimental and simulated data was obtained, confirming the correct description of the thermal mechanisms. The main identified gaseous fragments were water, carbon dioxide, saturated and unsaturated hydrocarbons and carboxylic derivatives. The decay resistance against two wood decaying strains, P. chrysogenum and A. brasiliensis was also evaluated.

Replacement of volatile styrene by flame retardant crosslinking diluents in unsaturated polyester resins

<p indent="0mm">The flammability of unsaturated polyester resins (UPR) and the volatility of their toxic styrene diluents pose serious safety risks. In this paper, three non-volatile flame retardant diluents (PBHA, POHA and PSHA) containing different phosphorus structures were synthesized, which can completely replace styrene and provide excellent flame retardant performance for UPR. Their structures were characterized by FTIR and NMR (¹H, ³¹P). The potential of synthesized reactive diluents as substitutes in UPR and their glass fabric reinforced composites was assessed through volatility, processability, curing kinetics and gel contents. Meanwhile, by comparing the effects of different phosphorous structures, PBHA diluent can bring best flame retardant efficiency. UP/PBHA reached V0 in UL-94 and 28% of LOI. The PHRR and THR of UP/PBHA were decreased by 64.06% and 61.54% compared with neat UP/St. For glass fabric/UPR composites, GF/UP/PBHA also reached V0 rating, and LOI was as high as 38%. Meanwhile, through the study of thermal stability, thermal degradation and combustion process, it was found that PBHA mainly worked in gas phase to capture H<x content-type="symbol">×</x> and HO<x content-type="symbol">×</x>, supplemented by promoting formation of dense carbon layer in condensed phase to isolate oxygen and thermal radiation.

EFFECTS OF TEMPERATURE IN DEGRADATION KINETICS OF ANTHOCYANIN FROM JAMUN FRUIT (Eugenia jambolana) USING THE ARRHENIUS, EYRING AND BALL MODELS

Anthocyanins are flavonoids found in fruits and vegetables, ranging from red to violet and blue, which are shown to be a potential substitute for artificial colors, especially in food. Due to its thermal instability, this work had as objective to establish the kinetic and thermodynamic parameters that describe the thermal degradation of the anthocyanins from jamun fruit between 50 and 80 ° C using the Arrhenius, Eyring and Ball models. The thermal degradation process of the anthocyanins followed a model of first-order kinetics and the three models correlated the temperature to the degradative process coefficients of determination between 0.939 and 0.960. The activation energy was 93.383 kJ mol -1 and, thermodynamically, the values of ΔH, ΔS and ΔG did not differ when using the Arrhenius or Eyring approaches, allowing, according to both, to characterize the degradation reaction as endothermic, non-spontaneous and with the transition state with less structural freedom than the regents. According to the Ball model, the temperature range z was 27.03°C.

Pyrolysis of peanut shell: Kinetic analysis and optimization of thermal degradation process

Thermal degradation kinetics of peanut shell (PS) biomass has been investigated at the heating rates of 10, 15, and 20 °C/min using thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) analyses techniques in the temperature range of ambient to 800 °C. The iso-conversional methods of Flynn-Ozawa-Wall (FOW), Kissinger-Akahira-Sunose (KAS), Starink, Tang, Vyazovkin, and Vyazovkin AIC have yielded activation energy Eα,varying from 186 to 226.97 kJ/mol. Effects of heating rate, temperature and nitrogen gas flow rate on the bio-char and bio-oil yields have been investigated using a fixed bed batch pyrolyser. The Box-Behenken design (BBD) of response surface methodology (RSM) has been used to optimize the process parameters. The average values of bio-oil and bio-char yields at the optimum conditions have been found to be 43.24 and 28.25 %, respectively. The product bio-oil is highly acidic and has the higher heating value (HHV) of 26.49 MJ/kg and the bio-char is rich in micronutrients.

Multi-dimensional Analysis and Correlation Mechanism of Thermal Degradation Characteristics of XLPE Insulation for Extra High Voltage Submarine Cable

This paper focuses on the multi-dimensional performance analysis including the oxidation performance, crystal morphology, thermal properties, mechanical properties and dielectric behavior of the thermally aged extra high voltage XLPE submarine cable insulation. Results show that the antioxidation and thermal oxidative aging of XLPE insulation are coexisting and competing during the thermal degradation process. In the early stage of thermal degradation, the antioxidation of XLPE insulation is dominant resulting in the decline of the spacing between spherulites. In the later stage of thermal degradation, thermally oxidative aging of XLPE insulation is dominant, which leads to the damage of the crystalline morphology and the rapid generation of aging products. It is indicated that the mechanical strength of the XLPE insulation is mainly determined by its internal crystalline morphology, while the dielectric properties of the XLPE insulation are governed by the crystalline morphology, aging products and micro interface. With the thermal aging time extended, the breakdown strength of XLPE insulation first increases and then decreases, which is determined by its amorphous region and aging products.

Thermal Degradation Behavior of Epoxy Resin Containing Modified Carbon Nanotubes.

Via the surface-grafting of carbon nanotubes (CNTs) with a silicon-containing flame retardant (PMDA), a novel flame retardant CNTs-PMDA was synthesized. The flame retardancy was tested by cone calorimeter. Compared with pure epoxy resin, the total heat release (THR) and peak heat release rate (PHRR) of epoxy resin containing CNTs-PMDA were significantly reduced, by 44.6% and 24.6%, respectively. Furthermore, thermal degradation behavior of epoxy resin based composite was studied by the thermogravimetric analysis with differences in heating rates. The kinetic parameters of the thermal degradation for epoxy resin composites were evaluated by the Kissinger method and Flynn-Wall-Ozawa method. The results suggested that activation energy values of epoxy resin containing CNTs-PMDA in thermal degradation process were higher than those of pure epoxy resin in the final stage of the thermal degradation process, which was closely related to the final formation of char layer residues. Finally, the results from Dynamic mechanical thermal analysis (DMTA) and Scanning electron microscopy (SEM) measurements exhibited that the functionalization of CNTs with PMDA obviously improved the dispersion of CNTs in the epoxy resin matrix.

Effect of Degradation Time on Carotene Content in Crude Carotene Extract of Carrot for the Formation of its Derivative Aromatic Compounds

Background: The difference in degradation time on the formation of carotene’s derivative aromatic compounds [β-ionone and dihydroactinidiolide (dhA)] due to thermal degradation process of carotenes in crude carotenoid extract of carrot was studied. Methods: β-ionone and dhA formation and that of carotenes degradation during thermal degradation (T=140°C) was observed periodically for 4 h. The constant oxygen supply during degradation was maintained at approx. 7 L/h. Result: The formation of β-ionone and dhA accumulated significantly with increasing duration of the degradation process. The maximum formation of β-ionone and dhA could be estimated with the pattern of carotenes degradation. After 4 h of degradation, more than 80% carotene has degraded. It can be concluded that the degradation process of crude carotene extract from carrots at temperature of 140°C will result in a maximum carotene degradation process when the degradation process is carried out for 5 h.

Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere

In order to utilize woody biomass effectively for bioenergy and chemical feedstocks, the comparative thermal degradation behaviors and kinetic mechanisms of typical hardwood (beech wood) and softwood (camphorwood) were studied at various heating rates in air. The Kissinger-Akahira-Sunose approach combined with the Coats-Redfern approach was employed to estimate the kinetic triplet. Softwood degradation began and ended at lower temperatures than hardwood. Compared with softwood, the maximal reaction rate of hardwood was greater and occurred in the higher temperature region. Two decomposition regions were determined by the variation of activation energy, and the dividing point was α = 0.6 and α = 0.65 for hardwood and softwood, respectively. Moreover, the average activation energy of hardwood was larger than that of softwood during the whole decomposition process. The thermal degradation process occurring in region 1 was dominated by the Avrami-Erofeev and 3D diffusion models for hardwood and softwood, respectively. Furthermore, the kinetic modeling results showed good consistency between the experimental and simulated curves under 5, 15, 20, and 40 K/min. It is noted that the thermogravimetric experimental profile under 20 K/min was not used for estimating the kinetic triplet. Besides, the combustion performance of hardwood is superior to softwood under the same external conditions (heating rate and atmosphere).

Smoldering suppression and synergistic effect of alginate fiber‐based composite paper by flame‐retardant lyocell fiber

AbstractThe application of traditional cellulosic paper is limited because of its flammability, so it is necessary to explore new materials that can be used in the field of flame‐retardant paper. Based on the synergistic effect between fibers, flame‐retardant lyocell (FRL) and calcium alginate (FRL/Ca‐Alg) composite paper is prepared by a simple but efficient method. The thermal degradation process of the composite paper is analyzed by thermogravimetric (TG) and TG analysis coupled with Fourier transform infrared, the flame retardancy of the composite paper is analyzed by vertical flammability (VF) tests, limiting oxygen index test and cone calorimetry test, and the morphology of the residue after VF tests is observed by scanning electron microscopy. It is found that, the Ca‐Alg releases a large amount of CO2 before ignited, which delayed the ignited time of the composite paper; FRL reduces the effective combustion heat of composite paper during combustion, and the compact char formed by FRL effectively inhibits the smoldering of Ca‐Alg in the end stage of combustion. Based on these, the synergistic flame‐retardant effect of composite paper is proposed.

The Effect of Heat Treatment on the Structure of Zeolite A.

Knowledge about the thermal properties of zeolites is extremely important due to their potential application in the chemical industry. In this work, the thermal stability and the dehydration process of zeolite A were investigated by in situ high temperature Fourier transform infrared spectroscopy. The progress of thermal decomposition that zeolite A underwent during the controlled temperature increase in the range of 25–600 °C was determined by the DRIFT spectroscopic method. Infrared spectra are presented and discussed for this compound on the basis of the crystal structure. Based on the courses of the obtained DRIFT spectra, it was found that, during heating, water was gradually removed from the structure of the material, followed by dehydration and formation of hydrogen bonds. It was established that the process of thermal degradation began as early as 550 °C. The analysis of the obtained results of structural tests can be repeated on other materials from the zeolite group and complements the research work on the thermal analysis of these materials.