Thermal Degradation Mechanism Research Articles

A review on Copoly(ether-ester) elastomers: degradation and stabilization

This review focuses on the possible mechanisms of thermal or thermo-oxidative degradation of the copoly(ether-ester) elastomer (COPE) reported in formed literatures. The ester group, apart from the other functional groups, can occur in both hard and soft segments. The lifetime of the COPE is controlled by both oxidation and thermal degradation processes, which mostly proceed independently. The thermal oxidation of ester elastomers may occur during every stage of their life cycles during the synthesis, processing, storage or use of the final goods. The influences of the introduction of various additives on the processes of decomposition and aging of the COPE are compared. The proper choice of stabilizers and anti-oxidants, as well as initial substrates, caused the materials to endow them with excellent properties and high resistance to various environmental conditions.

An Alginate Hybrid Sponge with High Thermal Stability: Its Flame Retardant Properties and Mechanism.

The worldwide applications of polyurethane (PU) and polystyrene (PS) sponge materials have been causing massive non-renewable resource consumption and huge loss of property and life due to its high flammability. Finding a biodegradable and regenerative sponge material with desirable thermal and flame retardant properties remains challenging to date. In this study, bio-based, renewable calcium alginate hybrid sponge materials (CAS) with high thermal stability and flame retardancy were fabricated through a simple, eco-friendly, in situ, chemical-foaming process at room temperature, followed by a facile and economical post-cross-linking method to obtain the organic-inorganic (CaCO3) hybrid materials. The microstructure of CAS showed desirable porous networks with a porosity rate of 70.3%, indicating that a great amount of raw materials can be saved to achieve remarkable cost control. The sponge materials reached a limiting oxygen index (LOI) of 39, which was greatly improved compared with common sponge. Moreover, with only 5% calcium carbonate content, the initial thermal degradation temperature of CAS was increased by 70 °C (from 150 to 220 °C), compared to that of calcium alginate, which met the requirements of high-temperature resistant and nonflammable materials. The thermal degradation mechanism of CAS was supposed based on the experimental data. The combined results suggest promising prospects for the application of CAS in a range of fields and the sponge materials provide an alternative for the commonly used PU and PS sponge materials.

XPS evidence of degradation mechanism in CH3NH3PbI3 hybrid perovskite

In this study, we investigate the photo-/thermal degradation mechanism of hybrid perovskites by using x-ray photoelectron (XPS) valence band (VB) spectra coupling with density functional theory (DFT) calculations. Herein, CH3NH3PbI3 is respectively subjected to irradiation with visible light and annealing at an exposure of 0–1000 h. It is found from XPS survey spectra that, in both cases (irradiation and annealing), a decrease in the I:Pb ratio is observed with aging time, which unambiguously indicates the formation of PbI2 as the product of photo/thermal degradation. The comparison of the XPS VB spectra of irradiated and annealed perovskites with the DFT calculations of CH3NH3PbI3 and PbI2 compounds have showed a systematic decrease in the contribution of I-5p states, which allows us to determine the respective threshold for degradation, which is 500 h for light irradiation and 200 h for annealing. This discrepancy might be due to the fact that the relaxation of thermal excitations of the system is carried out only by the phonons (which are non-radiative physical processes) while the radiative processes occurred during the photoexcitation will elastically or inelastically divert part of the external energy from the system to reduce its impact on perovskite degradation.

Thermal degradation mechanism of a cured acetylene/aldehyde functional benzoxazine with high thermal stability

A cured mono-benzoxazine (PHB-apa) with both acetylene and aldehyde functional groups exhibits excellent heat resistance. The thermal degradation process of this polybenzoxazine was studied in this work. The pyrolysis temperature range and major thermal degradation products were determined by TGA-FTIR analysis. The stepwise-temperature Py-GC/MS was employed to identify the structures and the contents of the pyrolysis products at different temperature stages. Transformation of chemical structures of the polymer bulk during the pyrolysis process was speculated. The results suggest that the concerted reaction of the aldehyde groups and the polymerization of the acetylene groups form special crosslinking structures that can effectively prevent the release of the amines and the phenols.

Investigations on thermostability of carotenoids from tomato peels in oils using a kinetic approach

Our study focused on the characterization of the extract obtained from tomato peels. The chromatographic profile revealed the presence of lycopene and β-carotene. The in silico tests suggested that the thermal treatment of lycopene molecules pairs at temperatures over 100°C cause the alteration of all-trans conformation into 9,9′cis lycopene, which might decrease its biological activity. Also, the thermal degradation of the total carotenoids, β-carotene, and lycopene was studied in the temperature range 100–145°C and followed a first-order kinetic model, with activation energy of 81.76 ± 6.82 kJ/M, 89.81 ± 8.48 kJ/M, and 79.66 ± 4.03 kJ/M, respectively. The Rancimat analysis indicated that the enriched peanut and cotton oils with extract displayed higher induction time values, thus showing a protection factor of the tomato-derived carotenoids. The present results highlighted the thermostability of carotenoids in vegetable oils and the potential of using tomato peel as a valuable source of biologically active compounds, with antioxidative properties. Practical applications Our study explores the possibilities of reuse the underutilized tomato-derived by-products, rich in biologically active compounds such as lycopene and β-carotene. The results are valuable because the thermal degradation mechanisms of the main biologically active compounds extracted from tomato peels are described by two methods: classical kinetic models and in silico approach. Both methods have highlighted the degradation of lycopene and β-carotene, with an impact on antioxidant activity. The present study provides cumulative information for the selection of industrial processing parameters from the perspective of preservation of bioactives and obtaining the desired quality end products. The extracts have gained also applicative value in our study, being tested for its protective effect on commercial vegetable oils, but also for improving their antioxidant activity and color.

Thermal decomposition of rice husk: a comprehensive artificial intelligence predictive model

This study explored the predictive modelling of the pyrolysis of rice husk to determine the thermal degradation mechanism of rice husk. The study can ensure proper modelling and design of the system, towards optimising the industrial processes. The pyrolysis of rice husk was studied at 10, 15 and 20 °C min−1 heating rates in the presence of nitrogen using thermogravimetric analysis technique between room temperature and 800 °C. The thermal decomposition shows the presence of hemicellulose and some part of cellulose at 225–337 °C, the remaining cellulose and some part of lignin were degraded at 332–380 °C, and lignin was degraded completely at 480 °C. The predictive capability of artificial neural network model was studied using different architecture by varying the number of hidden neurone node, learning algorithm, hidden and output layer transfer functions. The residual mass, initial degradation temperature and thermal degradation rate at the end of the experiment increased with an increase in the heating rate. Levenberg–Marquardt algorithm performed better than scaled conjugate gradient learning algorithm. This result shows that rice husk degradation is best described using nonlinear model rather than linear model. For hidden and output layer transfer functions, ‘log-sigmoid and tan-sigmoid', and ‘tan-sigmoid and tan-sigmoid' transfer functions showed remarkable results based on the coefficient of determination and root mean square error values. The accuracy of the results increases with an increasing number of hidden neurone. This result validates the suitability of an artificial neural network model in predicting the devolatilisation behaviour of biomass.

Synthesis, Thermal Properties and Decomposition Mechanism of Poly(Ethylene Vanillate) Polyester.

Plastics are perceived as modern and versatile materials, but their use is linked to numerous environmental issues as their production is based on finite raw materials (petroleum or natural gas). Additionally, their low biodegradability results in the accumulation of microplastics. As a result, there is extensive interest in the production of new, environmentally friendly, bio-based and biodegradable polymers. In this context, poly(ethylene vanillate) (PEV) has a great potential as a potentially bio-based alternative to poly(ethylene terephthalate); however, it has not yet been extensively studied. In the present work, the preparation of PEV is reported. The enthalpy and the entropy of fusion of the pure crystalline PEV have been estimated for the first time. Additionally, the equilibrium melting temperature has also been calculated. Furthermore, the isothermal and non-isothermal crystallization behavior are reported in detail, and new insights on the thermal stability and degradation mechanism of PEV are given.

Torrefaction, pyrolysis and two-stage thermodegradation of hemicellulose, cellulose and lignin

This study aims to investigate the thermal degradation mechanisms of hemicellulose, cellulose, and lignin using pyrolysis–gas chromatography/mass spectrometry. To characterize the decomposition behaviors, the torrefaction, pyrolysis, and their combination of the three constituents are performed using single-shot and double-shot reactions, with emphasis on the influence of torrefaction upon pyrolysis. The analysis suggests that O-acetyl and pentose units contained in the hemicellulose are thermally degraded into acetic acid and furfural in torrefaction, so acetic acid and furfural contents decrease significantly in the pyrolysis of torrefied hemicellulose. The impact of torrefaction upon cellulose is insignificant, resulting from the high thermal stability of the crystalline structure in the cellulose. When the pyrolysis temperature is higher than 300 °C, the cellulose starts to decompose and form organic volatile products. The products from lignin mild torrefaction at 250 °C are not obvious, except for vanillin. The severe torrefaction at 300 °C has a significant influence on lignin pyrolysis, and the pyrolysis of torrefied lignin results in an increase in aromatic compounds. Overall, the analysis suggests that torrefaction can be applied for biomass pyrolysis to stabilize pyrolysis bio-oil, make its composition more uniform, and separate certain chemicals. Based on the thermal degradation of the three main biomass components from torrefaction, pyrolysis, and their combination analyzed by Py-GC/MS, the obtained findings have provided useful insights into the applications of torrefaction, pyrolysis, and their combination for biofuel production.

Mechanism and effect of thermal degradation on electrolyte ionic diffusivity in Li-ion batteries: A molecular dynamics study

Electrolyte ionic diffusivity significantly affects the power density and useable energy density of a lithium ion battery. During usage, electrolyte can decompose, leading to reduced ionic diffusivity. Understanding the degradation mechanism and its effect on ionic diffusivity is important for both battery design optimization to provide superior performance with a long cycle life and for better battery management during usage to extend the battery life. In this research, the ionic diffusivity of key electrolytes and their degradation, including DMC-LiPF6, EMC-LiPF6 and DEC-LiPF6, are quantitatively predicted with classical and ReaxFF molecular dynamics simulations. The electrolyte solvent structures and reaction pathways are characterized. The effect of temperature, salt concentration and degree of thermal degradation on electrolyte ionic diffusivity are identified. A list of gas-phase, solvent-phase and solid-phase degradation products are categorized. DMC-LiPF6 shows the highest thermal stability, while DEC-LiPF6 shows the lowest thermal stability because of a large amount of –CH3CH2 group in the molecule. PF6- tends to decompose first. The decomposed product of PF5 can further lead to C–O bond breaking in solvent molecules, causing them to decompose into products composed of smaller molecules. Simulations show that the diffusion coefficients of cations and anions decrease with thermal degradation. The mechanism is found to be related to the clustering of Li+, R-O- and (R–OCO2)-, which impedes ion diffusion in the electrolyte. This paper provides a quantitative understanding of electrolyte thermal degradation, revealing the underlying mechanisms and effects on electrolyte properties at the atomistic level by a systematic comparative study for the first time. The approach will provide valuable guidance to the development of lithium ion batteries.

Mechanism investigation of thermal degradation of CO2-based poly(cyclohexene carbonate caprolactone)

The thermal degradation behaviors and mechanisms of CO2-based poly(cyclohexene carbonate caprolactone)s (PCHCCLs) were deeply studied taking advantage of thermogravimetric analysis/Fourier transform infrared spectrometry (TG/FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) techniques. The experimental results indicate that the decomposition temperatures of PCHCCLs increase with the increasing contents of polycaprolactone (PCL) segments. Backbiting reaction was found to be the dominant degradation pathway for PCHCCLs, and a complicated random rupture process was also observed at higher pyrolysis temperature.

Kinetics and mechanism of thermal degradation of vegetable-tanned leather fiber

Thermal degradation of vegetable-tanned leather fiber (VLF) was investigated by thermogravimetric analysis aiming to know the exact kinetics and degradation mechanism. The thermogravimetric (TG) and differential thermogravimetric (DTG) curves showed that decomposition of the VLF occurs mainly in the range of 150–600 °C, and the latter exhibits asymmetrical peak with a pronounced shoulder. The decomposition process was first analyzed by deconvolution of the experimental DTG curves, followed by reconstruction of the weight loss profiles of two individual processes. Several common isoconversional approaches were applied to calculate the activation energy over a wide range of conversion for the sample, including modified Kissinger-Akahira-Sunose (MKAS), Friedman, and Flynn-Wall-Ozawa. The average activation energy of vegetable-tanned leather fiber was found to be 241.9 kJ mol− 1 by MKAS method. The activation energy values obtained for the pseudocomponents representing highly-crosslinked and low-crosslinked collagen in VLF were given as 190.6 and 124.8 kJ mol− 1, respectively. Generalized master plots results suggested that the reaction mechanism for highly-crosslinked collagen follows the random nucleation and growth process at conversion values lower than 0.5. When the conversion is higher than 0.5, the mechanism tends to random scission model. For low-crosslinked collagen, the degradation is mainly governed by random nucleation and nuclei growth. The gaseous products of VLF thermal degradation were analyzed with an online-coupled TG-Fourier transform infrared spectroscopy system.Graphical abstract

Influence of the Chemical Nature and Structural Characteristics of Nanofillers on the Mechanism of Polyethylene Pyrolysis

The influence of different types of nanofillers on the mechanism of polyethylene thermal degradation is studied. The composition of the products of pyrolysis of composite material was evaluated using gas chromatography–mass spectrometry (GC–MS). It has been found that incorporating carbon nanofillers (carbon nanotubes, graphite nanoplates, and reduced graphite oxide) into polyethylene leads to increase in the fraction of heavy hydrocarbons of the pyrolysis products. The varying influence of carbon fillers on the pyrolysis process is explained in terms of the surface defectiveness of the fillers and their specific effect on the segmental mobility of the polyethylene macroradicals within the framework of the previously proposed theory. The use of montmorillonite-layered silicate as a filler leads to a qualitative change in the composition of pyrolysis products, which is caused by the presence of catalytic acid sites and the ionic character of the polyethylene thermal degradation mechanism.

Thermal Degradation of Polysiloxanes Containing Chloropropyl Groups

We synthesized a series of polysiloxanes containing chloropropyl groups, and studied its thermal stability and degradation mechanism through thermogravimetric analysis (TGA) in nitrogen atmosphere. The effect of the introduced chloropropyl units on the thermal degradation behavior of polysiloxanes was discussed. The depolymerization of the main chain of polysiloxane was accelerated by increasing the molar content of chloropropyl groups. The introduction of chloropropyl groups can cause the formation of a cross-linking network in the residue of polysiloxanes at 800 °C and restrain the formation of volatile components.

Thermal Stability and Early Degradation Mechanisms of High‐Density Polyethylene, Polyamide 6 (Nylon 6), and Polyethylene Terephthalate

The thermal stability and degradation mechanisms of three semicrystalline polymers (polyethylene terephthalate [PET], high‐density polyethylene [HDPE], and polyamide 6 [nylon 6]) were studied. Thermogravimetric traces were acquired first at heating rates of 1°C/min and 10°C/min, and it was determined that the heating rate significantly affected the thermal decay curves of the three polymers. The results allowed the selection of specific temperatures at which to carry out heating and cooling cycles from room temperature to the molten state. The thermal behaviors of HDPE, nylon 6, and PET each had particular characteristics. HDPE showed the highest thermal resistance, whereas nylon 6 displayed the lowest. PET had the lowest activation energy for degradation, 93.5 kJ/mol, and retained 14 wt% after thermal recycling with no influence of molecular weight. Thermal cycling also revealed gradual morphological changes in HDPE, nylon 6, and PET, and their crystals changed from regular to branched spherulites with variations in the nucleation patterns. Fourier‐transform infrared spectroscopy measurements allowed us to explain the early stages of degradation for each polymer. POLYM. ENG. SCI., 59:2016–2023, 2019. © 2019 Society of Plastics Engineers

Thermal destruction of the components of high-sulfur vacuum residues

The problem of processing vacuum residues is relevant due to the enhancement of heavy crude oil recovery. The processing of fuel oil and vacuum residues is complicated due to the high content of resins and asphaltenes present in them. In order to develop new approaches to the processing of vacuum residues, it is necessary to comprehend the mechanisms of thermal degradation of high-molecular-weight oil components. Three samples of high-sulfur vacuum residues are cracked at a temperature of 500 °C and with a various process duration. The characteristic changes in the material and fractional composition of the products of the vacuum residue cracking depending on the process conditions are shown. It is found that the ratio of light to medium distillates in the composition of the products depends on the duration of cracking.

Self-Limiting Processes in the Flame-Based Fabrication of Superhydrophobic Surfaces from Silicones.

Outdoor applications of superhydrophobic coatings require synthetic approaches that allow their simple, fast, scalable, and environmentally benign deployment on large, heterogeneous surfaces and their rapid regeneration in situ. We recently showed that the thermal degradation of silicones by flames fulfills these characteristics by spontaneously structuring silicone surfaces into a hierarchical, textured structure that provides wear-resistant, healable superhydrophobicity. This paper elucidates how flame processing-a simple, rapid, and out-of-equilibrium process-can be so counterintuitively reliable and robust in producing such a complex structure. A comprehensive study of the effect of the processing speed and flame temperature on the chemical and physical properties of the coatings yielded three surprising results. (i) Three thermal degradation mechanisms drive the surface texturing: depolymerization (in the O2-rich conditions of the surface), decomposition (in the O2-poor conditions found a few micrometers from the surface), and pyrolysis at excessive temperatures. (ii) The operational condition is delimited by the onset of the depolymerization at low temperatures and the onset of pyrolysis at high temperatures. (iii) The remarkably wide operational conditions and robustness of this approach result from self-limiting growth and oxidation of the silicone particles that are responsible for the surface texturing and in the extent of their deposition. As a result of this analysis we show that superhydrophobic surfaces can be produced or regenerated with this approach at a speed of 15 cm s-1 (i.e., the length of an airport runway in ∼4.5 h).

Thermal Behavior Analysis of Two Synthesized Flavor Precursors of N‐alkylpyrrole Derivatives

To expand the library of pyrrole‐containing flavor precursors, two new flavor precursors—methyl N‐benzyl‐2‐methyl‐5‐formylpyrrole‐3‐carboxylate (NBMF) and methyl N‐butyl‐2‐methyl‐5‐formylpyrrole‐3‐carboxylate (NUMF)—were synthesized by cyclization, oxidation, and alkylation reactions. Thermogravimetry (TG), differential scanning calorimeter, and pyrolysis–gas chromatography/mass spectrometry were utilized to analyze the thermal degradation behavior and thermal degradation products of NBMF and NUMF. The TG‐DTG curve indicated that the maximum mass loss rates of NBMF and NUMF appear at 310 and 268°C, respectively. The largest peaks of NBMF and NUMF showed by the differential scanning calorimeter curve were 315 and 274°C, respectively. Pyrolysis–gas chromatography/mass spectrometry detected small molecule fragrance compounds appeared during thermal degradation, such as 2‐methylpyrrole, 1‐methylpyrrole‐2‐carboxylic acid methyl ester, limonene, and methyl formate. Finally, the thermal degradation mechanism of NBMF and NUMF was discussed, which provided a theoretical basis for their application in tobacco flavoring additives.

Insights into Pyrolysis of Nano-Polystyrene Particles: Thermochemical Behaviors and Kinetics Analysis

The thermal degradation kinetics of nano-polystyrene particles with diameters of 60, 90, 160, and 225 nm were investigated in nitrogen atmosphere using thermogravimetric analysis (TGA). Various kinetic models were employed to determine the thermal degradation mechanism and kinetics. Nano-polystyrene particles have relatively lower thermal stability when compared to micro-polystyrene. Both differential thermo-gravimetric (DTG) data and apparent activation energies indicate that the thermal degradation of nano-polystyrene particles at 60 nm is a two-step reaction process where the second step plays a dominant role, while nano-polystyrene particles with diameter greater than 60 nm exhibit single-step degradation. Similar to most micro/macro polystyrene particles, DTG peaks of nano-polystyrene particles shift towards higher temperatures with increasing heating rates. Thermal degradation of nano-polystyrene particles under nitrogen atmosphere follows the first-order reaction model. However, the apparent activation energies increase (162-181 kJ·mol−1) with the increase of particle sizes (60-225 nm). This study could provide some insights into pyrolysis of nano-polystyrene particles and a safer process of manufacturing, storage and handling of nano-polystyrene particles.

THE EFFECT OF THIN DIELECTRIC LAYERS AT SILICON ON INTERCONNECTION HEATING DYNAMICS AT THERMAL SHOCKS

The relevance of the study is due to the fact that in the conditions of development of micro-and nanoelectronics, it is necessary to pay attention to resistive switching systems, which are the basis in the structures of these areas of electronics. The work deals with the investigation of the role of thin dielectric layers of silicon oxide and nitride on interconnection heating dynamics at monocrystalline silicon plates. The leading method to the study of this problem is the method of experiment, which allows identifying the features of the influence of the dielectric sublayer on the thermal regimes of multilayer systems. It is shown that passage of current pulses (amplitude up to 6x1010 A/m² and duration up to 600 μs) leads to thermal damage of interconnections right up to breaking the electric circuit. The character of destruction strongly depends on the quality of deposition of dielectric and metal films as well as on the state of the dielectric-metal interface. It was found that the oscillograms of the inclusion, taken during the passage of a current pulse, clearly reflect the change in the dimensional (h2) and thermal (λ2) parameters of the dielectric sublayers; considered the thermal degradation mechanisms of the aluminum metallization systems with thin dielectric sublayers related to its melting; it was found that formation of melted zones is related to local reduction of film cross-section and consequently to the appearance of a melted zone that coagulates into drops in the course of current pulse passing and promotes breaking the electric circuit. The proposed method can be applied to assess the thermal properties of thin films of dielectrics.

RAFT mediated miniemulsion copolymerization of ethylene and BMA and their non-isothermal model-free kinetic analysis

Miniemulsion copolymerization of ethylene and butyl methacrylate (BMA) was carried out at 60 °C using 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid as the reversible addition fragmentation chain transfer (RAFT) agent, sodium dodecyl sulphate as emulsifier and potassium per sulphate as free radical initiator under extremely low ethylene feed pressure of 5–20 bar. In the absence of a co-stabilizer, very stable emulsion was obtained, wherein the RAFT agent acted both as the chain transfer agent and as the co-stabilizer. FT-IR as well as NMR analysis established the formation of poly(ethylene-co-BMA) copolymer nanoparticles. The SEM analysis was used to study the morphological behaviour of poly(ethylene-co-BMA) copolymer nanoparticles. DLS analysis confirmed that the particle diameter Zavg of copolymer nanoparticles is in the range 100–140 nm and confirmed miniemulsion polymerization. In order to establish the stability of copolymers against thermal degradation, the kinetics and mechanism of thermal degradation of copolymers were investigated by thermogravimetric analysis. Thermogravimertic analysis established that thermal decomposition of poly(ethylene-co-BMA) copolymer nanoparticles occurred in the range 250–450 °C. This range is lower than the decomposition temperature of neat polyethylene (350–580 °C). Kinetic parameters were determined according to the model-free approaches of Friedman and Flynn–Wall–Ozawa. The multivariate nonlinear regression analysis was performed to determine the kinetic model and the corresponding kinetic triplets.