Thermal Degradation Process Research Articles

Field-deployable measurement technique for absolute acoustic nonlinearity parameter values

Over the past two decades, several researchers have demonstrated that changes in the acoustic nonlinearity parameter β can be related to changes in material properties due to mechanical and/or thermal degradation processes. Generally, a piezoelectric sensor-based detection method is used to measure changes in β values because it is operationally simpler than the complex capacitive detection method. However, this method is limited to measuring only relative changes in β values; whereas, the absolute β values of components in service often need to be measured in the field to quantify the degradation level. Accordingly, a novel field-deployable method for measuring absolute β values was developed in this study. Nonlinear ultrasonic experiments were conducted using capacitive detection, conventional piezoelectric sensor-based detection, and proposed detection methods, and the results were compared. The β values of a copper single-crystal sample measured using the new and the capacitive detection methods were 2.49 and 2.1, respectively, and those obtained using the conventional piezoelectric sensor-based detection method ranged between 90 and 130. The test results confirm that the proposed field-deployable measurement method produces more consistent absolute β values without involving the complexity of the capacitive detection method.

Comparative study of the reaction kinetics of three residual biomasses

Kinetic analysis for the combustion of three agro-industrial biomass residues (coconut husk, corn husk, and rice husk) was carried out in order to provide information for the generation of energy from them. The analysis was performed using the results of the data obtained by thermogravimetric analysis (TGA) at three heating rates (10, 20, and 30 K/min). The biomass residues were characterized in terms of proximate analysis, elemental analysis, calorific value, lignin content, α-cellulose content, hemicellulose content, and holocellulose content. The biomass fuels were thermally degraded in an oxidative atmosphere. The results showed that the biomass thermal degradation process is comprised of the combustion of hemicellulose, cellulose, and lignin. The kinetic parameters of the distributed activation energy model indicated that the activation energy distribution for the pseudocomponents follows lignin, cellulose, and hemicellulose in descending order. The activation energy values for each set of reactions are similar between the heating rates, which suggests that it is independent of the heating rate between 10 K/min and 30 K/min. For all the biomass samples, the increased heating rate resulted in the overlap of the hemicellulose and cellulose degradation events.

Destruction of polymers under the action of laser radiation

Laser ablation is one of the main mechanisms of polymers destruction under the action of laser radiation. In this paper, the basic information on laser ablation of polymers is presented. Under the action of laser radiation on the polymer, processes of thermal, thermo-oxidative, and mechanical degradation occur simultaneously, resulting in the evaporation of macromolecules fragments (up to oligomers), and in some cases, separation of polymer particles and filler by a gas or plasma jet is observed. In addition, a substance ablation is accompanied by a large number of concomitant effects: vapor condensation and liquid phase dispersion.

Structural comparisons of pyrodextrins during thermal degradation process: The role of hydrochloric acid

Hydrochloric acid (HCl) is widely used to prepare pyrodextrins, especially the water-soluble pyrodextrin. In this study, the structural difference between pyrodextrins as affected by HCl is compared by characterizing the molecular size, chain-length distributions (CLDs), crystallinity, and solubility. It is found that: 1) dry heating of starch granules without HCl mainly degrades long-amylose chains while slightly affects amylopectin branches; 2) the presence of HCl during dry heating decreases the degree of polymerization (DP) range of amylose chains upon degradation from DP ~ 833–1267 to DP ~ 206–432, suggesting that the presence of HCl accelerates the breakdown of long-amylose chains; 3) both pyroconversion processes have slight effects on A-(DP ~ 6–12) and B1- chains (DP ~ 12–24), which might explain the retained granular and crystalline structure during the process. This study could improve the understanding of the role of HCl in affecting the structure and property during pyroconversion of native starch.

Removal and generation of microplastics in wastewater treatment plants: A review

Wastewater treatment plants (WWTPs) are the primary recipients of microplastics (MPs), prior to their discharge into natural waterbodies. The aim of this article is to summarize the generation process of MPs and the efficiency of their removal by treatment technologies currently adopted by WWTPs, as well as the influence of sludge treatment on the fragmentation of MPs. WWTPs mainly remove MPs by means of adhesion, sedimentation, and filtration. The average removal efficiency of MPs is less than 90% and is affected by the choice of wastewater treatment process and the properties of MPs (such as the size, density and morphology). The secretion of biological enzymes by microbes and the metabolites of biofilm may promote the hydrolysis of microbial carrier materials, resulting in the release of endogenous MPs under shear force. Furthermore, during wastewater pumping, disinfection and sludge thermal hydrolysis treatment, MPs may form sub-micron-scale secondary MPs through mechanical, ultraviolet, ozone and thermal degradation processes. Processes such as thermal drying of sludge and lime stabilization have been found to lead to the fragmentation of MPs increase the specific surface area and number of MPs, leading to an increase in the potential ecological threat posed by MPs in sludge. Currently, the level of MP pollution throughout the environment is continually increasing. This review will help improve wastewater and sludge treatment processes, effectively reducing the risk of MPs entering the natural water bodies and soil through WWTPs.

Study of thermal properties of antioxidant lipoamide and its composites with colloid silica

Lipoamide (LM), amide of α-lipoic acid, is a very powerful antioxidant. However, information on its physicochemical properties, in particular on its thermal behavior, is very limited. In the present work, a DSC study of LM showed that heating above the melting point led to formation of a mixture of polymeric and crystalline forms of LM. In order to increase thermal stability of the drug, LM was encapsulated in colloid silica with various surface chemistry. It was found that encapsulation of LM in unmodified and organomodified silica materials slowed down the process of thermal degradation of the drug. The effect of silica matrix modification on the thermal degradation was revealed. It was shown that the interactions in the drug-silica composites play an important role in thermal stabilization of LM. The indicated thermal behavior of LM and α-lipoic acid in free form and in the synthesized composites was compared.

A new dynamic model of thermal degradation of polymer binary mixes submitted through pyrolysis

This paper shows the validation process of a dynamic model proposed to represent the one-step thermal degradation reaction of individual components in polymer mixtures. It is complicated to model the process of thermal degradation of polymer mixtures inside pyrolysis reactors. Inside the MPW reactor, the distribution of polymeric components in the mixture is shuffled. It occurs high-temperature gradients, and it is difficult to achieve a uniform heat transfer. All these factors make it complicated to predict at all times in the process and each point of the material inside reactor the degradation reactions and the specific presence of hydrocarbon of interest. It is made a comparison between real data provided by TGA of binary mixes of plastic and the result of simulated thermal degradation obtained using a differential equation of the model for thermal degradation of the same plastics. The polymer used in this study were Expanded Polystyrene (EPS) and Low-Density Polyethylene (HDPE). The results of the simulation using the dynamic model proposed were compared to the thermograms of the five samples submitted to TGA tests. The simulation results showed a reasonable degree of approximation with a mean square error of less than 5%. Those results well approximate the loss of mass of the real samples submitted to TGA tests in all the temperature range of the process. Consequently, it is not necessary to segment the process into sub-ranges to look for parameters in each one of them.

Organic salt versus salt cocrystal: thermal behavior, structural and photoluminescence investigations

Two new multicomponent crystal forms based on 4-nitrobenzoic acid-diethanolamine system, 1:1 molecular salt and 1:1:1 salt cocrystal were synthesized in the same conditions but different solvents and analyzed by complementary experimental techniques such as single-crystal X-ray diffraction, infrared absorption spectroscopy, thermogravimetric and kinetic analyses. The compounds differ from each other by the inclusion of 4-nitrobenzoic acid molecule in salt cocrystal and by the way of packaging of the components in crystals, as well as by the mode of connecting of organic cations with anions. Thermogravimetric analysis and kinetic study complete the structural study of the new obtained multicomponent crystals, providing additional information on their thermal stability and degradation process. The packing and inter-/intramolecular differences justify the melting points and enthalpy of fusions for the compounds studied. A good correlation of the activation energy values obtained by four different isothermal and non-isothermal isoconversional methods was observed. In both cases, the additional acid molecule in salt cocrystal decreases the activation energy values compared to salt, which can be related to a slower thermal degradation. Comparative investigation on photoluminescence properties was also discussed.

Effect of isopropanolysis on the structure variation and pyrolysis behaviors of Wucaiwan lignite

Alkanolysis has become an effective approach for lignite extraction due to high organic oxygen content in lignite. To better understand the effect of isopropanolysis on the chemical structure and thermal degradation process of lignite, Wucaiwan lignite (WL) and isopropanolyed residue (RI) were systematically analyzed using four multiple direct tools, including Fourier transform infrared spectrometer (FTIRS), X-ray photoelectron spectrometer (XRPES), Thermogravimetric analysis (TGA), and Pyrolysis-gas chromatography/mass spectrometry (PGC/MS). Combining with the analysis of FTIRS and XRPES, much oxygen-containing species were extracted from WL during isopropanolysis process (IP), and RI has higher carbon content than WL. Kinetic parameters such as activation energy (Ea) and pre-exponential factor (A) were determined by using two model-free methods of Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO). Average Ea for WL pyrolysis was 235.4 and 235.7 kJ mol−1, respectively, obtained by KAS and FWO methods, were lower than that of RI (354.4 and 351.3 kJ mol−1). Besides, based on the obtained kinetics data, thermodynamic analysis was established to evaluate the pyrolysis complexity of WL and RI. PGC/MS results showed that the main volatile products (VPs) of RI fast pyrolysis (FP) were arenes and alkanes while formation of oxygenated compounds reduced, further confirming the extraction of oxygen-containing species from IP of WL. It is noteworthy that isopropanolysis pretreatment of WL can influence its chemical structure and thermal degradation process.

Kinetics of thermal oxidative degradation of poly (vinyl chloride) containing Ca and Sn at low temperature

Calcium metal soap and polyol (dipentaerythritol) additives are replacing or partially replacing organotin in poly(vinyl chloride) (PVC) heat stabilizers due to their low cost, nontoxicity and safety. Therefore, investigating the low-temperature thermal oxidative degradation of stabilized plasticized PVC from the source is essential for recycling. This work uses isothermal thermogravimetry to investigate the thermal degradation process and isothermal discoloration of PVC/calcium metal soap/dipentaerythritol/organotin soft products with excellent heat resistance at 453–503 K and under air atmosphere. The chemical kinetics method is used to fit a single equation model of mass loss and time during the thermal oxidation degradation of PVC, and the kinetic equation obtained is: −ln(1 − α) = 3.83 × 103exp (−6834.4/T)t. When the temperature is 453–503 K, the calculation results are basically consistent with the experimental data and are independent of the heating rate and temperature changes. In addition, the isothermal discoloration of different PVC materials was tested under air atmosphere at 468 K. The results show that when the test material is PVC/calcium metal soap/dipentaerythritol/organotin, the heat aging time to become completely blackened is longer than that of the blank sample, which indicates a strong interaction occurs between Sn, Ca and dipentaerythritol complexes and PVC molecules, inhibiting the release of hydrogen chloride. At the same time, in order to recover PVC and prevent it from carbonization, if the temperature is set to 486 K, the thermal oxidation degradation time of PVC should be less than 130 min.

Eriobotrya japonica Lindl. Kernels: Kinetics of Thermal Degradation under Inert Atmosphere Using Model-Free and Fitting Methods

A kinetic study of the pyrolysis process of raw Eriobotrya japonica Lindl. Kernels (RLK) was investigated using a thermogravimetric analyzer. The weight loss was measured in a nitrogen atmosphere. The samples were heated over a range of temperature from 298 K to 873 K with four different heating rates of 5, 10, 15, 20 K min-1. Mass loss (TGA) and derivative mass loss (DTG) measurements indicate that the increase in heating rate has no noticeable effect on the thermal degradation of the RLK. The results obtained from the thermal decomposition process indicate that there are three main stages such as dehydration, active, and passive pyrolysis. TGA curves indicate that active pyrolysis of RLK is between 160 and 450 °C. In this interval, a shoulder followed by a peak exists on the DTG plots. The shoulder corresponds to the decomposition of hemicelluloses, the first peak to that of cellulose. Lignin decomposes through all temperature range. The kinetic parameters such as activation energy and pre-exponential factor were obtained for two degradation steps by isoconversional model-free methods proposed by FWO, KAS, Kissinger, Tang, MKN, and FR, with degradation mode being: f(α)=(1-α)n with n = 1 for FR and g(α)=-Ln(1- α) for the other methods. The activation energy and pre-exponential factor obtained by the Kissinger method are 173 kJ/mol and 1.9×1016 min-1. While for free model methods, the average kinetic parameters calculated are 172-248 kJ.mol-1 and 5,30×1020 for integral methods (FWO, KAS, Tang and MKN) and 190-271 kJ.mol-1 and 1.77×1022 min-1 for differential Fr method. The activation energy decreases in the final stages of the process. The energy required for hemicellulose degradation is lower than that of cellulose. The most probable reaction functions have thus been determined for these two stages by Coats-Redfern and Criado method, leading to greatly improved calculation performance over the entire conversion range. The reaction, second-order F2, describes the pyrolysis reaction models of RLK. With the Arrhenius parameters obtained from the fitting model of CR, we attempt to reconstruct the temperature-dependent mass conversion curves and have resulted in generally acceptable results. Based on the Arrhenius parameter values obtained by Kissinger equation, the changes in entropy, enthalpy and Gibbs free energy, and lifetime predictions have been estimated concerning the thermal degradation processes of RLK.

Fire Retardancy and Thermal Degradation Kinetics of Epoxy Composites Containing Polyaminopropylphenylsilsesquioxane

Polyaminopropylphenylsilsesquioxane (PA) was proved to be an effective fire retardant for epoxy resin (EP) by cone calorimeter measurements, since a significant peak heat release rate (PHRR) reduction of 42% was achieved from the EP/PA fire retardant epoxy (FREP) system relative to the pure EP. The thermal degradation behavior was investigated by thermogravimetric analysis (TGA) and the fire-retardant mechanism of the FREP system was studied by kinetics analysis methods, including the Kissinger method and the Flynn-Wall-Ozawa method. The calculated results of the Kissinger method showed that the activation energy of the FREP was slightly lower than that of pure EP. The Flynn-Wall-Ozawa method further revealed that the addition of the fire retardant PA increased the activation energies of FREP thermal degradation in the final stage, which illustrated that PA promoted the thermal degradation of EP in the early and middle stages and subsequently, stabilized the char residues and improved the fire retardancy of FREP in the thermal degradation process.

Synthesis and thermal characterization of some hardeners for epoxy resins based on castor oil and cyclic anhydrides

Castor oil, a triglyceride ester of ricinoleic acid containing up to 2.7 hydroxyl groups per molecule, was converted with three cyclic anhydrides into esters with carboxyl in their structures. The obtained products have potential as crosslinking agents for epoxy resins. The chemical structures, thermal properties, degradation mechanisms and gaseous composition obtained during thermal decomposition of the products in nitrogen atmosphere (up to 600 °C) were assessed with the aid of thermogravimetric (TG), Fourier transform infrared (FT-IR) and mass spectroscopy (MS) analyses. The kinetic parameters (pre-exponential factor and activation energy) were evaluated from the data recorded at three heating rates, in a first instance by using the isoconversional method of Friedman (FR). Based on the curve shapes of activation energy versus conversion degree it can be concluded that the thermal degradation processes take place through multi-step kinetics. The most probable thermal decomposition mechanism was obtained by using the multivariate linear regression (MLR) method included in “Thermokinetics-3″ software and is described by a process that takes place in three steps. The main evolved gases during thermal degradation were identified from the FT-IR and MS spectra. The gaseous mixture contained water, carbon dioxide, some saturated and unsaturated hydrocarbons moieties, aromatic compounds and carboxylic derivatives.

Low-Temperature Carbonized Elastomer-Based Composites Filled with Silicon Carbide.

Thermally stable composites obtained by the low-temperature carbonization of an elastomeric matrix filled with hard dispersed silicon carbide particles were obtained and investigated. Evolution of the microstructure and of mechanical and thermal characteristics of composites during thermal degradation and carbonization processes in a wide range of filling from 0 to 450 parts per hundred rubber was studied. For highly filled composites, the compressive strength values were found to be more than 200 MPa; Young’s modulus was more than 15 GPa. The thermal conductivity coefficient of composites was up to 1.6 W/(m·K), and this magnitude varied slightly in the temperature range of 25–300 °C. Coupled with the high thermal stability of the composites, the observed properties make it possible to consider using such composites as strained friction units instead of reinforced polymers.

Molecular dynamics simulation of thermal degradation of silicone grease using reactive force field

AbstractSilicone grease, consisting of polydimethylsiloxane (PDMS) chains and silica, has been widely used in electrical power systems; this causes thermal aging of silicone grease at high temperatures. In this study, the thermal degradation process of silicone grease was analyzed at different temperatures using reactive force field (ReaxFF). The effects of different factors, such as silica surface chemistry and oxygen content, on the final products have been studied. The results showed that the final products can be divided into two main categories: small gaseous molecules and large‐molecule products. The number of gaseous hydrocarbon products and their unsaturation increased with increasing temperature. The large‐molecule products were consisted of silica and surrounding PDMS chains, which were broken and reorganized during the thermal degradation process. The time interval required for the formation of the large‐molecule products is larger when silica with a modified surface is used. The addition of oxygen during thermal degradation provided a new decomposition route. The O/Si ratio in the residue of silica grease increased while the C/Si ratio decreased with the increasing oxygen content. A new method for the generation of SiO2 residues in a sufficient oxygen environment was proposed based on the reactions between oxygen and Si–CH3.

Calculation of foundation platforms on degraded permafrost bases

In connection with degradation of permafrost soils, the issue of designing and building foundations is acutely raised, taking into account the possible thawing of the soil at the base of structures. A spatial foundation platform is less sensitive to deformations of the foundation soil due to the integral work of the structure, compared to other foundations. For this and a number of other reasons, the use of the platform is promising. As the main structural material in spatial foundation platforms, it is advisable to use engineering wood, because of its advantages in comparison with reinforced concrete and metal. The article presents some results of calculations of the foundation platform of the folded type. The COMSOL Multiphysics software package simulates the process of thermal degradation of the soil under the foundation platform caused by an increase in air temperature. As a result, the soil warming zone was established, which is necessary for the design of the foundation platform taking into account changing boundary conditions. Preliminary conclusions are made about the influence of the degradation of the frozen base on the stress-strain state and the structure of the foundation platform of the folded type.

Effects of MgCl2 and Mg(NO3)2 loading on catalytic pyrolysis of sawdust for bio-oil and MgO-impregnated biochar production

For high-quality utilization of biomass resources, co-production of bio-oil and MgO-impregnated biochar from catalytic pyrolysis of Mg-loaded biomass samples is a prospective approach. In this study, the effects of MgCl2 and Mg(NO3)2 loading on catalytic pyrolysis of sawdust for production of high value-added bio-oil and biochar, as well as the catalytic pyrolysis process mechanism were explored. The thermal degradation process behavior and the pyrolysis products of non-condensable gas, bio-oil and biochar were obtained by thermogravimetric analyzer (TGA) and lab-scale fixed-bed reactor system. The product properties were analyzed and characterized by gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), N2 adsorption-desorption, X-rays diffraction (XRD) and transmission electron microscopy (TEM). The obtained results indicated that the loading of Mg salts favored the thermal degradation process of catalytic pyrolysis due to the weakened hydrogen-bonding networks and disrupted the crystalline structures. The enhanced cross-linking and repolymerization reactions of pyrolysis intermediates by the catalytic effect of Mg resulted in the increased non-condensable gas and biochar yields and the decrease of bio-oil yield. The loading of Mg salts also resulted in the decreased CO yield and increased CO2 yield. The relative contents of ketones and furans increased, and the relative contents of phenols and sugars decreased for Mg-loaded SD samples in bio-oil. In addition, the Mg salts loading also favored the formation of developed pore structure and uniformly dispersed MgO nanoparticles in obtained biochar. In general, catalytic pyrolysis of MgCl2-loaded or Mg(NO3)2-loaded sawdust is a feasible method to obtain high value-added bio-oil and MgO-impregnated biochar products.

The Effect of Thermal Degradation Processes on the Physical-Mechanical and Rheological Properties of Polyketone

The effect of polyketone thermal processing duration on the rheological properties of the melts and the physical and mechanical characteristics of the samples, obtained by injection and compression molding methods, is studied.

A DFT Study on the Cyclization-Mechanism during Process of Thermal Vacuum Degradation for Poly(dimethylsiloxanes)

A DFT investigation was performed on the cyclization mechanism during the process of thermal degradation in vacuum for trimethylsilyl-terminated polydimethylsiloxane, methylsiloxane-α,ω-diol and methylsiloxane-1-ol. The formation of an intramolecular, four-centre cyclic transition state results from the flexibility of a main chain and the ability to rearrange siloxane bonds. The energy barrier of the reaction depends mostly on the four-centre cyclic structure, independent of molecular weight, the position of nucleophilic attacking, and products. The replacement of trimethylsilyl by hydroxyl leads to a great decrease of activation energy of degradation reaction, because the energy barrier of the Si-O bond interchange is much higher than that of hydrogen abstraction. The large cyclosiloxane tend to higher degree of cyclization degradation than linear siloxane with the same number Si atoms. From energetic viewpoint, cyclosiloxane products of various sizes have almost equal chance to form. Due to the continuous degradation of large ring, the D3 accounts for the predominating proportion, and steadily decreasing amounts of D4 and D5.

Characterisation of pyrolysis kinetics and detailed gas species formations of engineering polymers via reactive molecular dynamics (ReaxFF)

One of the major limiting factors in fire modelling involving solid pyrolysis of polymer materials is the fundamental understanding of thermal degradation process from solid fuel to gas volatiles. This also brings along other challenges such as the characterisation of the parent combustion fuel in the gas-phase chemical reaction process. To bridge the knowledge gap, this article proposes a methodology applying molecular dynamics (MD) simulation as a tool to characterise the thermal degradation process of polymer composites, especially the emission of volatile and toxic gas species. The method was applied to three common engineering polymers: i) high-density polyethene (HDPE), ii) polymethyl methacrylate (PMMA), and iii) high-impact polystyrene (HIPS). Based on the modelling results, the chemical distribution of the fully-decomposed chemical compounds was realised for the selected polymers. The chemical composition and charring kinetics were validated against thermogravimetry data via experimental measurement. Numerical simulations demonstrated good agreement with the thermogravimetric analysis experiments. It was found that all HDPE, PMMA, and HIPS formed fuel gas with alkane group (i.e. mainly C1-C3) that acted as the combustible source. Furthermore, the composition of char formations for the selective polymers can be predicted by the MD simulation through analysing the accumulation of pure carbon chain compounds. In this study, MD simulation identified the detailed decomposition process from solid to gas phases, which could further act as the precursors of combustible fuel gases in combustion models, and significantly enhance the reliability of toxic gas, charring, and smoke particulate predictions.