Thermal Degradation Mechanism Research Articles

Effect ofCaSt2/ESOthermal stabilizers on the preparation, thermal stability, and thermal stability mechanism of self‐made vinylidene chloride‐methyl acrylate copolymer resin film

AbstractThe effects of heat stabilizer systems on the thermal stability and processability of self‐made vinylidene chloride‐methyl acrylate copolymer (PVDC‐MA) film were investigated via accelerated aging test, Congo red test, FTIR, DMA, and TG‐FTIR. These results displayed that CaSt2/ESO performed excellently in synergistic inhibition of PVDC‐MA thermal degradation. Especially, when the mass ratio of CaSt2/ESO was 1.5:1.5, the static thermal stability time of PVDC‐MA was increased from 14.5 to 46.5 min. The kinetic calculation results also verified this point. Compared with pure PVDC‐MA, the average apparent activation energy (Ēa) of thermal degradation reaction of PVDC‐MA stabilized by CaSt2/ESO enhanced from 144.1 to 169.7 kJ mol−1(α0 ≤ 0.1), indicating that the thermal stability of PVDC‐MA in the initial thermal degradation stage was dramatically improved by CaSt2/ESO. Moreover, the mechanism of the effect of CaSt2/ESO on PVDC‐MA in the initial thermal degradation stage was further explored by the generalized master plot methods. The kinetic analysis result suggested that under the synergistic effect of CaSt2/ESO, the mechanism model followed by the degradation of PVDC‐MA changed essentially (the three‐dimensional diffusion thermal degradation mechanism transformed into two‐dimensional diffusion).

Modeling and experiments of the thermal degradation behavior of PMMA during laser transmission welding process

Reducing thermal degradation of plastics during laser transmission welding (LTW) process is the key to obtain high-quality weld seam. In this study, a thermal degradation prediction model is proposed. First, using polymethyl methacrylate (PMMA) as an exemplary material, the weld seams are prepared at different process parameters, including the laser power, welding velocity and carbon black (CB) content. Full characterization of the prepared weld seams was performed through shear tests, scanning electronic images, and ultra-depth-of-field microscope. The results reveal that thermal degradation occurs with bubbles at the interface and decreases the shear strength of the weld seam. Second, the thermal history model during LTW is simulated through a 3-D transient heat transfer finite element method (FEM), where the highest temperature is extracted to aid in comprehension of thermal degradation mechanism. Third, a thermal degradation prediction model is proposed based on the thermal history model and thermal degradation kinetic model which is solved by the thermogravimetric analysis (TGA). The results from the proposed prediction model is consistent with the occurrence of the initial thermal degradation and the trend of shear strength of the weld seam. Therefore, this study might present a potential way to optimize the processing window by effectively suppressing the appearance of thermal degradation.

Synthesis and pyrolysis mechanism of phenolphthalein poly(aryl ether sulfone) containing isopropyl groups

A novel phenolphthalein poly(aryl ether sulfone) polymer containing isopropyl groups (iPrPESC) has been successfully synthesized by SN2 aromatic nucleophilic polycondensation reaction. The pyrolysis mechanism and behavior of iPrPESC were investigated by thermogravimetry coupled with Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis combined with gas chromatography/mass spectrometry (Py-GC/MS). TG-FTIR and Py-GC/MS were used to identify the thermal decomposition products and to determine the possible thermal degradation mechanism. The main mechanism for iPrPESC was one-stage pyrolysis involving main-chain random scission, and the major products of SO2 and phenol were released from the sulfone and ether groups in iPrPESC. The thermal degradation activation energy of iPrPESC was calculated to be 151 ± 4 and 139 ± 4 kJ mol−1 by the Flynn–Wall–Ozawa and Kissinger methods, respectively, which were much lower than that of phenolphthalein poly(aryl ether sulfone). Furthermore, introduction of isopropyl groups on the main chain can significantly reduce the char yield.

Melt-state degradation mechanism of poly (ether ketone ketone): the role of branching on crystallization and rheological behavior

In the melt-state, poly (ether ketone ketone) (PEKK) undergoes structural changes to the polymer backbone due to its high melting temperature. In this work, the thermal degradation mechanism of PEKK in the melt-state in air is identified using a combination of molecular dynamics (MD) simulations, X-ray photoelectron spectroscopy (XPS), and rheology. Ether linkages in the PEKK backbone are shown to have the lowest bond dissociation energies and preferentially undergo chain scission compared to ketone linkages. Upon chain scission, the formed radical species undergo hydrogen abstraction, chain transfer, and a coupling reaction, resulting in altered viscoelastic properties. Dynamic rheological behavior of PEKK thermally aged in the melt-state display viscoelastic characteristics of long-chain branched polymers. Results indicate that the PEKK rheological properties are highly dependent on time in the melt-state as well as angular frequency. Increased exposure times in the melt-state result in increased complex viscosity and a reduction in the degree and rate of crystallization. Thermal history has a significant impact on thermomechanical properties in the melt-state and during crystallization.

A Thermic Effect on Degradation Kinetics of Sugar Cane Bagasse Polypropylene Composites

In this study, thermal degradation mechanisms and the kinetics of PP (Polypropylene) composites containing alkali and saline treated SC (Sugar cane bagasse) have been evaluated using a non-isothermal thermogravimetric analysis under consistent nitrogen atmosphere. The study indicates dynamics of kinetics that need to be considered should the composites be applied in high temperature applications. NaOH treated composites revealed a reduced fiber size compared to the other composites. The presence of SC generally reduced the functional group intensities of FTIR peaks, however some peaks re-emerged after the treatments. The composites indicated higher thermal stability and char content than the pristine polymer. In fact, NaOH treated composite is more thermally stable, while the saline is the least stable of the rest. Well known reliable degradation kinetics methods were employed in order to unpack thermal degradation behavior and possible metaphors. Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) thermal degradation kinetic models are in agreement that the presence of both SC and those in the PP matrix that have been treated lead to increased activation energy values with the competing reactions in the degradation process. Nonetheless, the linear relation is not absolutely perfect and the competing reactions seem complex at lower temperatures as there are overlying inconsistencies in activation energies. Interestingly, bagasse indicated some effect on the mechanism that included the hindering of free radicals that emanated from the first cleavage of PP.

Properties, kinetics and pyrolysis products distribution of oxidative torrefied camellia shell in different oxygen concentration

Bio-energy would become an important energy supply in the future, but the inherent defects of biomass limit its energy utilization. Torrefaction could improve the energy performance for biomass, and oxidative torrefaction is more practical to reduce the energy consumption and improve the efficiency. In present work, the properties, kinetics and pyrolytic products distribution of oxidative torrefied camellia shell (CS) have been investigated with the oxygen concentration of 0–8% in torrefaction atmosphere. The results show that oxidative torrefaction would alter the cellulose crystals from Iα to Iβ of CS and improve their hydrophobicity, and their surface functional groups have also undergone major changes. Based on the Flynn-Wall-Ozawa method and Distributed Activation Energy Model, torrefaction causes the pyrolysis activation energy to increase first and then decrease. According to the evaluated by Criado method, order of reaction and random nucleation have been identified as the most likely mechanism for thermal degradation of torrefied CS. In addition, Oxidative torrefaction would improve the phenols compounds in pyrolytic products. The present work may provide a reference for the energy utilization of CS.

Fire-exposed stones in constructions: Residual strength, performance loss and damage mode shift due to mineralogical transformation and micro-cracking

The heritage restoration and the design of modern stone masonry structures bear in mind the material response to fire, the residual strength and post-fire resilience. In this attempt, the decomposition of fire-exposed natural and engineered stones and their mineralogical transformations are reported. The fire-induced petrographic change is further correlated to rise in shrinkage and porosity, and loss of mechanical properties, such as strength, toughness and stiffness. Stones of different nature (limestone, sandstone, quartzite, polymer/quartz-based engineered stone) are selected to trigger various thermal degradation mechanisms. Also, the stones were sorted considering their sustainability profile since all stones, except the artificial ones, were collected from local quarries and linked to the regional heritage and architecture. An integrated inspection methodology is designed that implements non-destructive monitoring on mechanical tests. A novel proof-loading concept is introduced at which the residual performance is assessed exclusively based on ultrasound pulse velocity (UPV) and early acoustic emission (AE) data. The damage mechanisms that dominate fracture and the shift of failure from strong brittle to weak pseudo-ductile with an early transition from crack initiation to propagation are determined based on AE features analysis.

Ferrocene based ionic liquid: synthesis, structure, transport properties and mechanism of thermal degradation

Doping with transition metals is a promising way to expand the industrial applications of ionic liquids (ILs). This study reports the synthesis, structure and physicochemical properties of a novel butyl-dimethyl-(ferrocenylmethyl)ammonium bis(trifluoromethanesulfonyl)imide ([BDFA][NTf2]) IL. The thermo-gravimetric analysis combined with mass spectrometry of evolved gases demonstrated the high thermal stability of [BDFA][NTf2] up to 500 K. The thermal degradation of [BDFA][NTf2] at higher temperatures is a multi-step process accompanied by the cation destruction through the Hofmann elimination reaction and the subsequent transformations, such as fragmentation of the products of thermal degradation of the [NTf2]-anion and the direct interaction between these products. The glass transition and melting temperatures of [BDFA][NTf2] measured by the differential scanning calorimetry are 229 and 320 K, respectively. The electrical conductivities and densities of binary mixtures of [BDFA][NTf2] with acetonitrile (AN) were measured in the temperature range of 293 – 348 K at atmospheric pressure. The isobaric thermal expansion coefficients were calculated from the experimental data. The conductivity – temperature dependences were analyzed using the Arrhenius and Vogel-Fulcher-Tammann equations. The activation energy of ion transport and limiting conductivity increased with the IL mole fraction in AN.

Polystyrene/polyolefin elastomer/halloysite nanotubes blend nanocomposites: Morphology‐thermal degradation kinetics relationship

AbstractPolystyrene/polyolefin elastomer (PS/POE) (90/10 and 80/20 wt/wt) blends containing 1, 3, and 5 phr halloysite nanotubes (HNTs) in the presence and absence of a compatibilizer (polypropylene‐graft‐maleic anhydride) were prepared using the melt‐mixing technique. Scanning electron microscopic studies confirmed a matrix‐droplet morphology. Energy dispersive spectroscopy (EDS) mapping indicated that the blends containing 5 phr HNTs possessed aggregates, while no agglomeration was observed after incorporating 5 phr compatibilizer. Thermal stability and thermal degradation kinetics were investigated using thermogravimetry analysis (TGA). The results demonstrated that the PS/POE blend (90/10) containing 5 phr HNTs and compatibilizer (90/10/5/5) has the best thermal stability. Different methods such as Friedman, Flynn‐Ozawa‐Wall, and Kissinger‐Akahira‐Sunose were applied to calculate the degradation activation energy. The 90/10/5/5 nanocomposite exhibited the highest degradation activation energy, indicating that this sample is more difficult to degrade thermally than other samples. A correlation was obtained between the activation energy and the intensity of the TGA‐fourier‐transform infrared spectroscopy (TGA/FTIR) peaks of the evolved products. The Criado method was used to determine the changes in the thermal degradation mechanism of the samples.

Combustion Inhibition Ability of Piperazine Phosphoramide Derivatives and Titanium Carbide on Epoxy Resin

ABSTRACT Herein, piperazine phosphoramide derivatives (PPDO) and titanium carbide modified by hexadecyl trimethyl ammonium bromide (c-Ti3C2) were blended with epoxy resin (EP) to fabricate EP/c-Ti3C2/PPDO nanocomposites. According to thermogravimetric analyzer (TGA) results and pyrolysis kinetic analysis, EP/c-Ti3C2/PPDO nanocomposites can improve the thermal stability and the activation energy of EP. Furthermore, thermal degradation mechanism of EP and its nanocomposites with conversion between 0.55 and 0.99 conforms to the F3 model. With 1 wt% c-Ti3C2 and 3 wt% PPDO incorporated, the LOI value of EP/c-Ti3C2-1/PPDO-3 can reach up to 32% while achieves V-0 rating in the UL-94 test. Based on the cone calorimeter results, the peak heat release rate of EP/c-Ti3C2-1/PPDO-3 reduced by 40.1%. More continuous and dense phosphorus-rich char residues were produced for EP/c-Ti3C2-1/PPDO-3 nanocomposites, which can act as a physical barrier to hinder the heat transfer, protect the underlying polymers from further decomposition and isolate the diffusion of combustible gases. The synergistic effect between c-Ti3C2 and PPDO in catalytic carbonization obviously accounts for the improved flame retardant performance. This work provides an insight into the flame retardant mechanism and the thermal degradation mechanism of c-Ti3C2 and PPDO on EP, showing a promising application potential of c-Ti3C2 and PPDO in enhancing the thermal stability and flame retardancy of EP.

Spin trapping analysis of the thermal degradation of polypropylene

The thermal degradation mechanism of poly(propylene) (PP) fabric from room temperature to 220 °C was analyzed using the electron spin resonance (ESR) spin-trapping technique. This method was adopted to prolong the lifetime of the short-lived radical intermediates generated by thermal degradation with the object of inspecting their molecular structure. A spin-trapping reagent, 2,4,6-tri‑tert-butylnitrosobenzene (TTBNB), was impregnated into the PP fabric using supercritical CO2 (scCO2) treatment in the presence of a co-solvent. The impregnation efficiency and effect were evaluated using proton nuclear magnetic resonance (1H NMR) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM). ESR analysis showed that the degradation of PP is initiated from the tertiary carbon positions via two pathways: homolysis to generate ·CH3 and −CH2−·CH−CH2− radicals, and hydrogen abstraction to generate −CH2−·C(CH3)−CH2− radicals. These radicals are also attacked by oxygen to form hydroperoxides, which then decompose to form the alkoxy radicals −CH2−CH(O·)−CH2− and −CH2−C(CH3)(O·)−CH2−. These radicals are involved in the subsequent β-scission reactions that produce primary and secondary carbon radicals. Alkoxy radicals also take part in the β-scission reactions involving the main chain carbon radicals, which have a hydroxyl group in the β-position, and in hydrogen abstraction from a five-membered ring at temperatures higher than the melting-point to produce an α‑hydroxyl carbon radical, ·CH(OH)−. These inferred processes involved in the thermal degradation of PP fabric were supported by other methods of analysis, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA).

Embedded Target Filler and Natural Fibres as Interface Agents in Controlling the Stretchability of New Starch and PVOH-Based Materials for Rethinked Sustainable Packaging.

A structuring solution converting starch into a multiphase polymeric material was obtained through a melt compounding sequence, which can be irreversibly shaped by thermoforming into rethinked, sustainable packaging, based on the physical modification of starch with polyvinyl alcohol (PVOH), target fillers, (CaCO3 and wood flour), and a good plasticizer compatible with the polar components. Polymeric material can be thermoformed if it can be stretched without breaking in the positive temperature range, have functional properties required by the application, and keep its shape and properties after stretching for more than six months. The properties of the selected quaternary starch-based compound, fulfil the requirements for a thermoformable polymeric material due to the chemical compatibility between the components and the compounding in a selected procedure and optimal conditions wich ensure a comfortable miscibility. Most likely, the obtained miscibility can be explained only by the arrangement of the wood flour at the interface, where it acts as compatibilizer with a main role in structuring the new starch-based materials. The compatibilizer role of the wood flour was proved for the quaternary selected blend by the changing of the thermal degradation mechanism, from one with two stages for binary and tertiary blends, to one consisting of a single stage: decreasing till elimination of morphological defects, the reproducibility of the mechanical properties, stretching without breaking, and dimensional stability after stretching. Future studies will aim to achieve rethinked packaging for applications that require higher strength properties.

Modeling the Formation of Degradation Compounds during Thermal Degradation of MEA

A kinetic model has been developed to predict thermal degradation of aqueous solutions of monoethanolamine (MEA) in carbon capture. The model focusses on both the degradation rate of the amine and the formation rates of selected degradation products as a function of time, temperature, and loading. Experimental literature data on thermal degradation of MEA were used to develop, fit, and evaluate the model. The model was found to have an average relative deviation of 17.5%, most of which was caused by uncertainty in experimental data. The degradation model was also compared to a cyclic degradation campaign. The concentration of 1-(2-hydroxyethyl)-2-imidazolidinone (HEIA), one of the more stable thermal degradation products, is well-predicted with the thermal degradation model. However, the results also indicate that oxidative and thermal degradation mechanisms interact and that this interaction influences the concentration of several thermal degradation products.

Investigation on thermal degradation mechanism of poly(phenylene sulfide)

Thermal degradation occurs inevitably during the practical processing of poly(phenylene sulfide) (PPS) due to its low thermal stability, leading to the deterioration of processability and performance of PPS products. In this study, the structural evolution of PPS during thermal degradation in nitrogen (N2) and oxygen (O2) atmospheres are investigated systematically via X-ray photoelectron spectra (XPS), fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC) and dynamic rheology. A rheological measurement is proposed to distinguish the multi-stage degradation behaviors of PPS efficiently. It is found that the thermal degradation mechanism of PPS differs considerably in N2 and O2 atmospheres. Chain scission is predominant when PPS is heated in N2, while CS and CC crosslinking structures can only be initiated at extremely high temperature. On the contrary, oxidation of PPS is accelerated seriously in the presence of O2. Chain extension and branching reactions are activated even at low processing temperature of PPS, and substantial COC crosslinking structures are created which leads to the sharp increase of melt viscosity. Furthermore, the change of crystallization behaviors after thermal treatments of PPS are also studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The crystalline kinetics of PPS changes significantly during melt processing, which further corroborates the thermal degradation mechanism of PPS.

Thermal Degradation Kinetics Analysis of Ethylene-Propylene Copolymer and EP-1-Hexene Terpolymer.

LLDPE is a less crystalline polymer with vast industrial and domestic applications. It is imperative to understand the synthesis, processing conditions, and thermal degradation mechanism of the co- as well as terpolymers. This paper reports the in-situ synthesis and thermal degradation studies of the ethylene-propylene copolymer and ethylene-propylene-1-hexene terpolymer and its nanocomposite with ZnAL LDH sheets. The 1-hexene dosing during the in-situ process influenced the product yield and immensely affected the thermal stability of the resultant polymer. One milliliter 1-hexene in-situ addition increased the product yield by 170 percent, while the temperature at 10 percent weight loss in TGA was dropped by about 60 °C. While only 0.3 weight percent ZnAL LDH addition in the terpolymer improved the thermal stability by 10 °C. A master plot technique and combined kinetics analysis (CKA) were deployed to access the thermal degradation mechanism of the synthesized polymers.

In-depth study on diffusion of oxygen vacancies in Li(NixCoyMnz)O2 cathode materials under thermal induction

It is generally believed that an increase in Ni content will severely reduce the lattice structure stability of the cathode material, causing it to release more oxygen during thermal induction. However, the thermal degradation mechanism at the microscopic level remains unclear, which hinders the safety design of cathodes. In this work, we focus on the secondary particles of different Li(NixCoyMnz)O2 cathodes, report the formation and condensation of oxygen vacancies on the surface in detail, and quantitatively analyze the oxygen vacancy concentration distribution inside the particles after thermal failure. The results reveal that the increase of Ni content promotes the oxygen vacancies to diffuse deeply from the surface of the secondary particles to the bulk under thermal induction, resulting in an increase of oxygen vacancy concentration in the bulk of the secondary particles and the release of more oxygen. When the Ni content x in Li(NixCoyMnz)O2 increases to 0.8, both the surface layer and bulk exhibit high oxygen vacancy concentrations, leading to an overall failure of the secondary particles. Furthermore, we suggest that the formation and evolution of intergranular cracks inside the secondary particles depend on the oxygen vacancy concentration gradient. Our work provides a new idea for future research on the thermal stability of cathode and the thermal safety design of Ni-rich cathode materials.

Thermal stability and non‐isothermal kinetics of poly(ethyl cyanoacrylate) nanofibers

AbstractA thermogravimetric study of poly(ethyl cyanoacrylate) nanofibers was carried out at five heating rates with a linear increase in the temperature in a nitrogen atmosphere. The data provided by the thermogravimetric study were used to evaluate the kinetics of the degradation process using three isoconversional methods. Considering that the kinetic parameters of the process depend on the reaction mechanism, various approaches were applied in order to determine the most probable mechanism function. In this respect, the mechanism of thermal degradation of poly(ethyl cyanoacrylate) is a phase boundary reaction with cylindrical symmetry (F0.5 function) as demonstrated by the z(α) master plots method, iso‐temperature method and isoconversional method. On their basis, the values of the kinetic triplet (Ea, A and the shape of the most appropriate f(α) function) of the process were obtained, and subsequently the thermodynamic functions of the activated complex formation were calculated. The thermal stability of the polymer was predicted according to the integral procedure decomposition temperature. © 2022 Society of Chemical Industry.

Characterizing and Improving the Thermal Stability of Organic Photovoltaics Based on Halogen-Rich Non-Fullerene Acceptors.

The thermal stability of inverted, halogen-rich non-fullerene acceptor (NFA)-based organic photovoltaics with MoOx as the hole transporting layer is studied at temperatures up to 80 °C. Over time, the power conversion efficiency shows a "check-mark" shaped thermal aging pattern, featuring an early decrease, followed by a long-term recovery. A high Cl concentration at the bulk heterojunction (BHJ)/MoOx interface in the thermally aged device is found using energy dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy shows that the MoOx is chlorinated after thermal aging. With bulk quantum efficiency analysis, we propose an explanation to the check-mark shaped pattern. Inserting a thin C70 layer between the BHJ and MoOx suppresses the thermal degradation mechanisms, resulting in three orders of magnitude increase in device lifetime at 80 °C.

Study on the atomic scale of thermal and thermo-oxidative degradation of polylactic acid via reactive molecular dynamics simulation

The reactive force field molecular dynamics (ReaxFF-MD) simulations were performed on polylactic acid (PLA) for the first time to understand its thermal and thermo-oxidative degradation mechanisms. The main degradation products of PLA observed in actual experiments were well reproduced by ReaxFF-MD simulations. The results showed that the initial thermal degradation pathway for the PLA was the homolytic cleavage of CO bond next to the ester group, followed by CO bond breaking in the ester group and CC bond cleavage. Carbon monoxide, carbon dioxide and acetaldehyde were the major volatile products generated following the thermal degradation after being initiated by the homolytic scission. In thermo-oxidative degradation simulation, the alkyl peroxide and hydroperoxide were formed, which degraded into alkoxyl and hydroxyl radicals, resulting in the increase of the lower carbon fraction (C1–4). This study would provide meaningful theoretical guidance for the mechanisms of thermal and thermo-oxidative degradation of PLA.

Stability of polyphenols in food processing.

In recent years, polyphenols have attracted considerable attention due to their diverse potential health-beneficial effects on humans. Polyphenols are widely distributed in natural plants, and therefore play an important role in human food. Thermal processing, irradiation, fermentation, high pressure, microwave, and drying are several popular food processing methods. However, polyphenols are instable in food processing, which easily degrade and react with other components because of their polyhydroxy characteristic. Traditional and advanced technologies have been used to characterize the stability of polyphenols. The main influence factors of stability of polyphenols such as pH, temperature, light, oxygen, enzymes, metal ions, as well as macromolecules, are summarized. Besides, thermal processing greatly promoted the degradation of polyphenols. Thermal degradation mechanisms and products of some polyphenols, such as quercetin and rutin, have been intensively demonstrated. Nevertheless, the structural changes of polyphenols caused by food processing, may lead to different bioactivities from the obtained results based on unprocessed polyphenols. Therefore, to maximize the beneficial effects of polyphenols ingested by human from processed food, the stability of polyphenols in food processing must be thoroughly investigated to assess their real bioactivities. In addition, some available technologies for improving the stability of polyphenols in food processing have been proposed.