Thermal Degradation Mechanism Research Articles

Thermal and Dynamic Mechanical Behaviours of CCTO/ENR-25 Composite

A study on polymer-ceramic composite, CaCu3Ti4O12 (CCTO) embedded in epoxidised natural rubber (ENR-25) were successfully fabricated through mixing method using an internal mixer and two-roll mill followed by hot-pressed via compression moulding for a potential electronic device such as a flexible capacitor. CCTO powders were successfully synthesised through a solid-state reaction and calcined at 900 °C for 12 hours. The ENR-25 was blended with 0, 20, 40, 60, 80, 100, and 120 phr (part per hundreds of rubber) of CCTO powders. Thermal stability and degradation are crucial properties for the composite based polymer. Therefore, thermogravimetric and differential scanning calorimetry (TGA/DSC) used to find out the thermal reaction and degradation mechanism of CCTO/ENR-25 composites. Besides, dynamic mechanical analysis (DMA) also used to investigate glass transition temperature (Tg) and storage modulus. TGA/DSC showed a two-step degradation mechanism with increasing thermal stability over increasing filler content of CCTO and only showed a major endothermic reaction. However, for DMA there is no significant difference in Tg value between each composite but showed high storage modulus up to 4398 MPa for 120 phr. High storage modulus indicates the high stiffness of the composite. In conclusion, the addition of filler content will show high thermal stability, storage modulus, and stiffness of CCTO/ENR-25 composites.

Different thermal degradation mechanisms: Role of aluminum in Ni-rich layered cathode materials

Abstract Despite increasing demands for higher energy density cathode materials, they can be bigger threats unless thermal stability is guaranteed. Herein, the thermal stability of LixNi0.835Co0.15Al0.015O2 (NCA83) and LixNi0.8Co0.15Al0.05O2 (NCA80) is compared by using in-situ transmission electron microscopy. Analysis demonstrates that NCA83 and NCA80 degrade thermally by distinct mechanisms. Al prevents the transition to CoO2-type O1 phase by suppressing O-slab gliding by residual Li. At 67% SOC, in the sub-surface area, thermal degradation of NCA80 is mainly due to reduction of Ni, whereas thermal degradation of NCA83 is a result of concurrent reduction of Ni and Co. The difference indicates that NCA83 has both earlier transition to the rock-salt structure and poorer thermal stability than NCA80. This study presents a protocol to properly evaluate new high energy density cathode materials, and provides important insights into the thermal degradation mechanism of Ni-based layered oxides.

Exploiting Distinct Thermal Response Properties for Power Semiconductor Module Health Monitoring

This article develops the techniques for actively tracking response shifts, induced by thermal–mechanical degradation over components lifetimes’, in spatiotemporal thermal response dynamics. The methodology considers both boundary (e.g., cooling) and internal (e.g., voiding) sources of degradation, and it is considered in the context of power semiconductor devices and packages, including power modules. This article quantifies the transient thermal response sensitivity to degradation using electrothermal impedances viewed with key frequency response function (FRF) metrics over wide dynamic ranges. A developed sensitivity analysis is applied using models and experimental evaluation to relate temperature sensing spatial location, harmonic content of semiconductor device losses, and source of degradation in terms of normalized FRFs that are rapidly interpreted. Complementary loss model parameter sensitivity analysis reveals the advantages in tracking variation in thermal FRF phase delay, rather than amplitude. Finally, to complement pure-FRF approaches for sensing degradation, which use nonparametric data, a method for directly estimating degradation-sensitive physical parameters, in real time, is developed. Experiments demonstrate the automatic estimation of a thermal resistance parameter.

Investigation of thermal degradation and decomposition of both pristine and damaged carbon/epoxy samples with thermal history

Although the investigation of thermal damage in composite materials has increased, the short-term thermal degradation and decomposition mechanisms in a non-oxidative environment have not been well established, as the reported thermal damage results were heavily influenced by the analyses of delicately collected volatiles and the presence of oxygen. The aim of this study, using scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetry, along with kinetics, was to develop a post-mortem solid residual-based microscopic characterising methodology for thermal damage in carbon/epoxy composites induced by simulated lightning strikes. Fibre tufting, resin sublimation and discolouration were found to represent the severity of damage in three damage zones. Whilst fibre tufting was caused not by thermal sublimation but by returning shock waves, resin sublimation and discolouration were dominated by Joule heating. The carbon concentration in the damaged zones was found to radially decrease outwards and vice versa with oxygen. Decomposition started from epoxy dehydration, accompanied by discolouration and formation of water and carbonyl, and released chemical compounds like 2-propenal, acetylene and carbonyl-containing aromatic ether. The successful identification of these unique heating-formed functional groups provided the confirmation of the proposed methodology.

Thermal Degradation Processes of Aromatic Poly(Ether Sulfone) Random Copolymers Bearing Pendant Carboxyl Groups.

Thermal degradation processes of poly(ether sulfone) random copolymers having different molar amount of diphenolic acid (DPA) units were studied by direct-pyrolysis/mass spectrometry, stepwise pyrolysis-gas chromatography/mass spectrometry and thermogravimetric techniques. Results highlighted that thermal degradation processes occur in the temperature range from 370 to 650 °C, yielding a char residue of 32–35 wt%, which decreases as the mol% of DPA units rises. The pyrolysis/mass spectra data allowed us to identify the thermal decomposition products and to deduce the possible thermal degradation mechanisms. Thermal degradation data suggest that the decarboxylation process of the pendant acid moiety mainly occurs in the initial step of the pyrolysis of the copolymers studied. Successively, the scission of the generated isobutyl groups occurs in the temperature range between 420 and 480 °C. Known processes involving the main chain random scission of the diphenyl sulfone and diphenyl ether groups were also observed.

The thermal degradation mechanism and kinetic analysis of hydrogenated bisphenol-A polycarbonate

Hydrogenated bisphenol-A polycarbonate (PHBPA) was successfully synthesized from dimethyl carbonate (DMC) and hydrogenated bisphenol-A (HBPA) by the method of two-step polycondensation. The chemical structure and the molecular weight of PHBPA was identified by 1H-NMR spectra and gel permeation chromatography (GPC), respectively. In order to analyze the thermal degradation mechanism of PHBPA, a non-isothermal pyrolysis process was conducted and the violate products were detected using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS). There were some reactions occurred during the pyrolysis including decarboxylation, disproportionation of the C–H transfer and β–H transfer, and the Fries rearrangement. In addition, the well-known Flynne–Walle–Ozawa (FWO) and Coats–Redfern kinetic analysis methods were used to calculate the values of activation energy and pre-exponential factors. Furthermore, isothermal pyrolysis experiments were performed and revealed that the reaction of decarboxylation occurred at 225 °C. This decarboxylation suggests that the molecular chain of PHBPA does not easily grow to a high-molecular-weight polymer.

Kinetics and mechanism of thermal degradation of aldehyde tanned leather

The thermal degradation of hides before and after tanning with formaldehyde and glutaraldehyde were studied using thermogravimetric analyzer (TGA) and TGA coupled with Fourier transform infrared spectrometry (TGA-FTIR). TG-FTIR analysis indicated that the pyrolysis products of both untanned hides and tanned leathers are mainly CO2, NH3, and CO contained organic components with some HNCO, CH4 and H2O. Compared to that of untanned hides, the peak intensity of evolved NH3 from formaldehyde tanned one is enhanced, while the evolved temperature decreases from 220 °C to 200 °C. The evolution of CO contained organic components is increased due to the introduction of carbonyl groups after formaldehyde tanning. However, for the glutaraldehyde-tanned leather, the evolution peak intensity of CO contained organic components decreases with more CO2 yield, suggesting that the carbonyl groups introduced by glutaraldehyde-tanning is mainly changed to CO2 rather than CO contained organic components. The kinetic analysis of thermal degradation process of the hides and tanned leathers are also investigated by using the methods of Flynn-Wall-Ozawa, Friedman and Criado. Results indicated that the thermal degradation process can be described by the three-dimensional diffusion model (D3) at the conversion below 0.5. Whereas, at the conversion above 0.5, this process turns to comply random nucleation model (F3).

Characterizing the thermal degradation mechanism of two bisphosphoramidates by TGA, DSC, mass spectrometry and first-principle theoretical protocols

The present investigation describes a combined experimental-theoretical strategy to assess the thermal resistance features of two symmetric bisphosphoramidates, tetraphenyl ethane-1,2-diylbis (phosphoramidate) 1 and tetraphenyl propane-1,3-diylbis (phosphoramidate) 5. Therefore, their structural reluctance to thermal decomposition through differential scan calorimetric (DSC) and thermogravimetric (TGA) experiments was evaluated. Then, their molecular degradation path was followed by analysing recorded data from mass spectrometry measurements performed at different temperature conditions. Their corresponding thermal degradation mechanism was then established by searching plausible transition states interconnecting the intermediaries found in our mass spectrometry records using a quantum theoretical protocol based on Coupled-Cluster calculations.Through this strategy, key intermediaries of the two bisphosphoramidates studied during their molecular degradation mechanism were identified, although compound 5 displayed the highest resistance to heat decomposition.

Determination of the mechanism of polymer thermolysis at low temperatures using spin trap electron spin resonance

The thermolysis of polyethylene oxide (PEO) was investigated using the spin trap electron spin resonance technique. Based on the analysis of the formed carbon-center radicals, the PEO thermolysis was initiated at the heating temperature of 60 °C and accelerated from the temperature of 120 °C. Radical production depended on the heating temperature. Observations in this study show that there are two different reaction pathways: below 120 °C, the degradation of PEO was mainly initiated by hydroperoxide (ROOH) species, which may be produced by a high temperature manufacturing process; above 120 °C, the bond in the polymer molecule began to dissociate, leading to decomposition. A comprehensive thermal degradation mechanism of PEO is proposed based on experimental results. The findings from this study are applicable to various polymers produced using a high temperature manufacturing process.

Thermal behavior study and degradation mechanism by TG/MS/FTIR technique of some poly(aryl ether ether ketone)s

This study assesses the thermal and thermo-oxidative stability of some aromatic poly(aryl ether ether ketone)s as well as the degradation mechanism by the TG/MS/FTIR technique (simultaneous mass spectrometry and Fourier transform infrared spectroscopy of off-gases from thermogravimetric analyzer), in two working atmospheres, air and helium. This type of polymers is used in many applications in the electronic, automotive and aerospatial fields. The polymers were synthesized by polycondensation reaction of 4,4′-difluorobenzophenone with several bisphenols, such as 9,9-bis(4-hydroxyphenyl)fluorene, 4,4′-cyclohexylidenebisphenol, 2-(bis[4-hydroxyphenyl]methyl)benzoic acid (phenolphthalin) and 2,5-bis(4-hydroxyphenyl)-1,3,4-oxadiazole. They were characterized by FTIR and 1H NMR spectroscopy, solubility, inherent viscosity and thermogravimetric analysis. Moreover, the main products of polymer thermal decomposition were determined in air and in inert atmosphere (helium). The degradation mechanism of the analyzed samples is influenced by their structure and working atmosphere. Molecular dynamics simulation was also used to evaluate thermal stability of the polymers.

Synthesis and characterization of easily degradable acrylate-epoxy resin with superior dielectric properties and high transmittance

Thermally degradable thermoset acrylate-epoxy resins with thermal cleavable groups had been prepared by a series of acrylate-epoxy pre-polymers which was cured with 4-methyl hexahydrophthalic anhydride (MHHPA). The acrylate-epoxy pre-polymers were synthesized via the radical polymerization of 3, 4-epoxycyclohexylmethyl methacrylate (EMA) with butyl methacrylate (BMA), tert-butyl methacrylate (TBMA), tert-butyl acrylate (TBA) and butyl acrylate (BA), respectively. The chemical structure of pre-polymers was characterized in detail. The thermal degradation mechanism and thermal properties, mechanical properties as well as dielectric properties of the acrylate-epoxy resins were systematically investigated. Results showed that t-butyl group and methyl group had a positive influence on the main thermal degradation process. TBMA-E/M presented lower degradation temperature (The initial degradation temperature is ~214 °C) and dielectric constant (~3.19 at 106 Hz) among these thermosets. Besides, all samples possessed similar high transmittance in the visible range. Therefore, acrylate-epoxy resins had a promising application and degraded at a desirable temperature.

Synthesis of aliphatic–aromatic polyamide carbonized system with phosphoramide structure and study on its thermal degradation mechanism and flame retardancy in polypropylene system

Synthesis of aliphatic–aromatic polyamide carbonized system with phosphoramide structure and study on its thermal degradation mechanism and flame retardancy in polypropylene system

First-Principles Investigation of the Thermal Degradation Mechanisms of Methylammonium Lead Triiodide Perovskite

The poor stability of organometallic halide perovskites, especially CH3NH3PbI3 (MAPbI3), in high-temperature environments is one of the challenges retarding its wider applicability. A better understanding of how MAPbI3 perovskite degrades thermally will allow us to develop strategies to improve its “intrinsic” stability. In this study, we employed first-principles density functional theory to obtain detailed thermal degradation energy landscapes for MAPbI3. We focused on studying two reaction pathways: P1, for proton abstraction from methylammonium (MA) to iodine, and P2, for substitution (SN2) of an iodide anion (I–, as nucleophile) at the carbon atom of MA to yield iodomethane (CH3I) and ammonia (NH3). Our calculations provided kinetic data, allowing us to assess the “intrinsic” (in)stability of MAPbI3 under heat stress and to make sense of the seemingly contradictory experimental results. The I– species is more reactive for reaction P1 but not for P2. The energy of the reaction along pathway P1 increases monotonically with respect to proton abstraction. The reaction along pathway P2 is a two-step process, with a CH3–I–Pb–X intermediate formed in the crystal in conjunction with the release of NH3 gas. Our results suggest that the method of preparation (e.g., iodine-deficient conditions) and the morphology (e.g., improved crystallinity) of MAPbI3 could both influence its thermal stability.

Evaluation of mechanical, optical and thermal properties of PVA nanocomposites embedded with Fe2O3 nanofillers and the investigation of their thermal decomposition characteristics under non-isothermal heating condition

Magnetic Fe2O3 nanopowder was synthesized and characterized by various analytical techniques. The PVA/Fe2O3 nanocomposites were prepared by solution casting method to investigate the effect of nanofillers on their physicochemical properties. The analytical tools such as FTIR, UV–visible spectra and XRD were used to analyze the structure of Fe2O3 nanopowder and PVA/Fe2O3 nanocomposites. The uniform distribution of the Fe2O3 nanofillers on the PVA matrix was inspected using SEM. The particle size of the crystalline Fe2O3 nanofillers was observed to be less than 30 nm from the TEM micrographs. The optical characteristics of the prepared samples were investigated by analyzing their UV–visible spectra. The bandgap of PVA nanocomposites was lower than for pure PVA due to the dispersed Fe2O3 nanofillers in the PVA matrix. The thermal properties of pristine PVA and PVA/Fe2O3 nanocomposites were investigated by TGA. The PVA/Fe2O3 nanocomposite systems exhibited the improved thermal stability. The thermal degradation mechanism of PVA/Fe2O3 nanocomposite system was inspected in depth at five different heating rates under non-isothermal conditions. The electrical and mechanical properties of PVA were enhanced remarkably while increasing the % weight loading of nanopowder.

Effect of atmospheric oxygen on the kinetic parameters of thermal degradation of pine branch particles

Thermal degradation of forest combustibles plays an important role in the ignition and spread of wildland fires. Atmospheric oxygen affects thermal degradation mechanisms. In this paper, the thermal degradation behavior of pine branch (PB) particles of Pinus Sylvestris is investigated by using a thermogravimetric analyzer under inert and oxidative atmospheres. Results indicate that the thermal degradation process of PB particles in nitrogen differs from that in oxidative atmospheres, except for the initial stage from room temperature to 250 °C. Comparison between DTG and DSC curves under atmospheres with oxygen concentrations 5%–21% indicates that thermal degradation is promoted by increasing atmospheric oxygen. A unified scheme composed of four first-order reactions is used for kinetic analysis by simulating TG data with heating rates of 10, 15, 20, and 25 °C/min simultaneously. Kinetic parameters and reaction rate coefficients have been calculated based on multi-heating rate data, by the combined use of Genetic algorithm (GA) and nonlinear fitting algorithm. It is shown that the unified scheme is capable of capturing the characteristics of thermal degradation reactions under all heating rates and oxygen concentrations. It is found that the activation energies of four reactions first increase with oxygen concentration increasing from 0% to 15%, and then remain constant with oxygen concentration increasing from 15% to 21% except for reaction 2. The reaction rate coefficients of reactions 1, 3 and 4 obviously increase with oxygen concentration, while that of reaction 2 does not depend on oxygen concentration.

Study on thermal degradation mechanism of heat-resistant epoxy resin modified with carboranes

To generate a novel heat-resistant phenolic epoxy resin, carborane containing curing agent (1,7-bis(aminophenylene)meta-carborane) was synthesized and applied to cure the resin. The generated carborane-containing phenolic epoxy resin showed better thermal stability and thermal oxidative stability than carborane free phenolic epoxy resin. And the Lap Shear Strength of bonding samples showed the improved bonding performances. The thermal degradation mechanism of carborane-epoxy resin was investigated and the results showed that the carborane of samples was gradually oxidized to B2O3 at high temperatures, which covered at the surface of the adhesives to maintain the thermal resistance at high temperature.

Comprehensive kinetic study of thermal degradation of polyvinylchloride (PVC)

The plastic waste accumulation has been increasing and a solution other than landfilling is required. Due to the high cost of recycling, thermal treatment could be an option. However, the existence of polyvinyl chloride (PVC) would release hydrochloric acid which would cause emission problems as well as damage to the reactor systems. The thermal degradation of PVC has been studied over the years. However, the mechanism of the PVC thermal degradation is not fully developed. Specifically, the mechanism of the PVC thermal degradation at medium temperatures, which is more practical for industries, is still lacking. A degradation temperature of 300 °C was used to study the dehydrochlorination behavior of PVC. A rather comprehensive mechanism with four consecutive reactions has been developed based on the micro-pyrolysis experiments and has been validated and proved by predicting the mass loss, chlorine content, heat content and elemental composition with high precision experimental data in different reactors with/without heat transfer coupling.

Flexible Composite Materials — Between Inorganic Fibers and Organic Polymers

In order to develop a flexible composite material that could play a good cushion role for high temperature ceramic membrane cleaning, we herein report a flexible composite material which could achieve effective buffering to relieve the stress generated by rigid contact and play a certain sealing effect. The coating method is applied to fabricate the composite material, which can be produced by multi-layer superposition using high silica fiber fabric and waterborne polyurethane. The results show that waterborne polyurethane (WPU) as a binder coating plays a key role in improving the strength by six times compared to raw materials and maintaining the elasticity of materials. Meanwhile, the thermal degradation mechanism of the composites calcined at different temperatures (700–1200 °C) in air atmosphere is investigated. The as-made composite materials still have good flexibility, and the tensile strength is about 2.4 MPa after calcination at 1000 °C for 80 h. This provides a method to prepare flexible cushion composite materials for ceramic membrane filtration.

Zinc oxide nanoparticles prepared by thermal decomposition of zinc benzenepolycarboxylato precursors: Photoluminescent, photocatalytic and antimicrobial properties

Zinc oxide (ZnO) nanoparticles were obtained by thermal decomposition of one-dimensional zinc?benzenepolycarboxylato complexes as single- -source precursors at 450 ?C in an air atmosphere. The mechanism and kinetics of thermal degradation of zinc?benzenepolycarboxylato complexes were analyzed under non-isothermal conditions in an air atmosphere. The results of X-ray powder diffraction and field emission scanning electron microscopy revealed hexagonal wurtzite structure of ZnO with an average crystallite size in the range of 39?47 nm and similar morphology. The band gap and the specific surface area of ZnO nanoparticles were determined using UV?Vis diffuse reflectance spectroscopy and the Brunauer, Emmett and Teller method, respectively. The photoluminescent, photocatalytic and antimicrobial properties of the ZnO nanoparticles were also examined. The best photocatalytic activity in the degradation of C. I. Reactive Orange 16 dye was observed for the ZnO powder where the crystallites form the smallest agglomerates. All ZnO nanoparticles showed excellent inhibitory effect against Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Escherichia coli.

Polyethylene high-pressure pyrolysis: Better product distribution and process mechanism analysis

Pyrolysis is currently an effective way to recycle plastics. High-pressure conditions can change the pyrolysis product component distribution, but the microscopic mechanism has not been well elucidated. To explore the relationship of product distribution versus pressure and explain the microscopic mechanism of polyethylene high-pressure pyrolysis, experiments under a large initial pressure range from 1 bar to 51 bar at initial temperatures of 330–380 °C were carried out in an autoclave. In the process of polyethylene high-pressure pyrolysis, the temperature within the reactor exceeded the set temperature by 100 °C at a rate of 150 °C/min. The thermal runaway phenomenon was caused by the polymerization of concentrated olefins in liquid form, which was initiated by hydrocarbon radicals. As the pressure increased, the reaction peak temperature was risen and more small molecules were produced. Under an initial temperature of 340 °C and high-pressure conditions, polyethylene was completely converted into liquid and gas products. The experimental results also revealed that high-pressure conditions led to the production of aromatic compounds and isoparaffins, as well as more cycloalkanes and fewer olefins in the liquid product, making the product characteristics closer to the fuel standard. Finally, this paper proposes the radical microscopic mechanisms of polyethylene thermal degradation under atmospheric-pressure and high-pressure conditions.