Thermal Degradation Reaction Mechanism Research Articles

Investigation of kinetic and thermodynamic parameters approaches to non-isothermal pyrolysis of mustard stalk using model-free and master plots methods

Present work based on thermogravimetric analysis (TGA) to decipher in detail the pyrolysis of mustard stalk (MS) for investigating its potential for bioenergy feedstock at three heating rates (5, 10, and 20 °C/min). The thermal degradation behaviors of MS were carried out at three heating rates (5, 10, and 20 °C/min). The kinetic and thermodynamic parameters were examined using model-free isoconversional Flynn- Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) model. The obtained activation energy for pyrolysis of MS using FWO and KAS to be 132.47 and 130.62 kJ/mol. Kissinger method was used to compute pre-exponential factor found to be in the range of 105 to 1016 s−1 at different heating rates. The average ΔH was 127.70, and 125.8 kJ/mol and ΔG is 127.74 and 127.87 kJ/mol from FWO and KAS respectively, all ΔH positive indicated endothermic nature. The Coats-Redfern approach was used to estimate the thermal degradation reaction mechanism, which revealed that the diffusion model was best suited to reflect the degradation process involving both exothermic and endothermic reactions. The analysis can help augment the experimental studies, and physicochemical characterization revealed its fuel characteristic since MS is sustainable and promising biomass for alternative processes in terms of waste management strategies.

Mechanism Identification and Kinetics Analysis of Thermal Degradation for Carbon Fiber/Epoxy Resin.

For carbon fiber epoxy resin used in aerostructure, thermal degradation mechanism and kinetics play an important role in the evaluation of thermal response and combustion characteristics. However, the thermal decomposition process and mechanism are difficult to unify strictly due to the complexity of the components from different suppliers. In the present study, a product of carbon fiber epoxy resin made by AVIC (Aviation Industry Corporation of China) composite corporation is examined to identify its thermal degradation mechanism and pyrolysis products by measurements, including simultaneous thermal analysis, Fourier transform infrared spectroscopy and mass spectrometry, establish the kinetic model by Kissinger/Friedman/Ozawa/Coats-Redfern methods. The results show thermal degradation occurs in three steps under the inert atmosphere, but in four steps under air atmosphere, respectively. The first two steps in both environments are almost the same, including drying, carbon dioxide escape and decomposition of the epoxy resin. In the third step of inert atmosphere, phenol is formed, methane decreases, carbon monoxide basically disappears and carbon dioxide production increases. However, in air, thermal oxidation of the carbonaceous residues and intermolecular carbonization are observed. Furthermore, thermal degradation reaction mechanism submits to the F4 model. These results provide fundamental and comprehensive support for the application of carbon fiber epoxy resin in aircraft industry.

Bioenergy Potential of Salix alba Assessed Through Kinetics and Thermodynamic Analyses

Reutilizing the shavings of willow wood (Salix alba), a waste biomass from cricket bat manufacturing units of Kashmir (India) through pyrolysis, would prove to be a promising way for bioenergy production. The thermal degradation of this waste biomass was carried out under inert atmosphere using thermogravimetric analysis (TGA), at three different heating rates of 10, 25, and 50 K min−1. The kinetic and thermodynamic analyses were performed using isoconversional models of Kissenger-Akahira-Sunrose (KAS) and Ozawa-Flynn-Wall (OFW). The heating value of the willow wood shavings was found to be 18.03 MJ kg−1. The values of activation energy were found to be in the range of around 41.5 to 167.8 kJ mol−1 through conversion points of 0.2 to 0.8. The average value of change in Gibbs free energy were calculated to be of the order of 183.2 and 182 kJ mol−1 using KAS and OFW models, respectively. The thermal degradation reaction mechanism was predicted using Coats-Redfern method which showed that the one-dimensional diffusion model and first-order kinetic reaction model were best suited to represent the degradation process involving both exothermic and endothermic reactions. The thermodynamic parameters including pre-exponential factor, changes in enthalpy, and entropy reflect an enormous potential of the Salix alba shavings as low-cost waste biomass for bioenergy production.

Theoretical studies on thermal degradation reaction mechanism of model compound of bisphenol A polycarbonate

Density functional theory methods (DFT) M062X have been used to investigate the thermal degradation processes of model compound of bisphenol A polycarbonate (MPC) and to identify the optimal reaction paths in the thermal decomposition of bisphenol A polycarbonate (PC). The bond dissociation energies of main bonds in MPC were calculated, and it is found that the weakest bond in MPC is the single bond between the methylic carbon and carbon atom and the second weakest bond in MPC is the single bond between oxygen atom and the carbonyl carbon. On the basis of computational results of kinetic parameters, a mechanism is proposed where the hydrolysis (or alcoholysis) reaction is the main degradation pathways for the formation of the evolved products, and the homolytic cleavage and rearrangement reactions are the competitive reaction pathways in the thermal degradation of PC. The proposed mechanism is consistent with experimental observations of CO2, bisphenol A and 1,1-bis(4-hydroxyphenyl)-ethane as the main degradation products, together with a small amount of CO, alkyl phenol and diphenyl carbonate.

Coumarin-based random copolymer

In this article, coumarin-based random copolymer which can be utilized for atom transfer radical polymerization was investigated both theoretically and experimentally. The thermal degradation mechanism and the activation energies ( Ea) were obtained by means of the Coats–Redfern (CR), Tang, and Flynn–Wall–Ozawa (FWO) methods. The thermal degradation reaction mechanism for random copolymer obeyed the phase boundary model (contracting volume, R3) of solid-state mechanism. The thermodynamic properties in the range from 100 K to 500 K have been obtained. The calculated HOMO–LUMO energy gap and electronic properties, such as chemical hardness ( η), electron affinity ( A), chemical potential ( μ0), global softness ( ζ), electronegativity ( χ), global electrophilicity ( ω), and dipole moment ( μ), were investigated and discussed. The molecular electrostatic potential analysis of the random copolymer was also computed.

Sonication-assisted synthesis of polystyrene (PS)/organoclay nanocomposites: influence of clay content

This article presents the synthesis of a series of polystyrene (PS)/organoclay nanocomposite films consisting of different contents of clay (1–7 wt%) by sonication-coupled solvent-blending technique. The prepared PS nanocomposite films were characterized using various techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and thermal gravimetric analysis (TGA). The XRD and TEM results revealed the formation of exfoliated nanocomposites at lower loading of organoclay (<5 wt%). The presence of various functional groups in the organoclay and PS/organoclay nanocomposite was verified by FTIR spectra. The thermal stability of PS nanocomposites was significantly improved as compared to pristine PS, which is evident from TGA analysis. When 10% mass loss was chosen as a point of reference, the thermal degradation temperature of PS nanocomposite holding 7 wt% of organoclay was found to be 30 °C more over pristine PS. The thermal kinetic parameters such as activation energy (Ea), pre-exponential factor (A), and the order of reaction (n) were determined by employing the Coats–Redfern model. Thermal degradation reaction mechanism of PS nanocomposites was also investigated.

Nonisothermal Degradation Kinetics and Life Prediction of the Pendent Phenyl-Containing Polyarylate

ABSTRACTThe nonisothermal degradation kinetics of a pendent phenyl-containing polyarylate (PAR-P)were studied using different kinetic models, including the Kissinger method, Flynn–Wall–Ozawa (FWO) method, and Coats–Redfern (CR) method. The “three kinetic factors” of degradation, namely, activation energy (E), pre-exponential factor (A), and the reaction mechanism function (f(α)) were determined by these methods. Moreover, the lifetime equations of PAR-P were deduced, and its lifetime was predicted. The Kissinger method could be used to describe the nonisothermal degradation of PAR-P, and the results indicated that PAR-P could be degraded more easily in air than in nitrogen. The FWO method was expected to give more reliable values of the activation energy (209.71 kJ·mol−1 in nitrogen and 176.22 kJ·mol−1 in air) due to not having to introduce the reaction mechanism function during the calculation. According to the results of the CR method, the thermal degradation reaction mechanism was probably the R1 model in nitrogen, while it was likely to be the F2 model in air. The long-term and short-term use temperatures of PAR-P in air were 260°C and 300°C, respectively. The lifetime of PAR-P in nitrogen was much longer than that in air at low temperature, but had little difference when the use temperature exceeded 260°C. Although the lifetime of PAR-P obtained from the present work was unrealistic due to probable contributions from other unconsidered factors and being determined by a single factor method, it still could play a guiding role for designing the structure and determining the use conditions of the material.

Thermal degradation reaction mechanism of xylose: A DFT study

The thermal degradation reaction mechanism of xylose as hemicellulose model compound was investigated by using density functional theory methods M062X with the 6-31++G(d,p) basis set. Eight possible pyrolytic reaction pathways were proposed and the standard kinetic and thermodynamic parameters in all reaction pathways were calculated at different temperatures. In reaction pathway (1), xylose is first transformed into acyclic containing-carbonyl isomer, and then the isomer further decomposes through four possible pyrolysis pathways (1-1)–(1-4). Pathways (2) and (3) depict an immediate ring-opening process through the simultaneous breaking of C–O and C–C bonds. Pathways (4)–(7) describe the pyrolysis processes of various anhydro-xyloses through a direct ring-opening process. Pathway (8) gives the evolutionary process of pyranones. The calculation results show that reaction pathways (1), (2) and (5) are the major reaction channels and reaction pathways (3), (4), and (6)–(8) are the competitive reaction channels in pyrolysis of xylose. The major products of xylose pyrolysis are low molecular products such as 2-furaldehyde, glycolaldehyde, acetaldehyde, methylglyoxal and acetone, and the main competitive products are formaldehyde, formic acid, acetic acid, CO2, CH4, acetol, pyranone, and so on.

Preparation, optimization and thermal characterization of a novel conductive thermoset nanocomposite containing polythiophene nanoparticles using dynamic thermal analysis

Polythiophene nanoparticles as a conductive filler was prepared with average diameter of 20–35 nm and its molecular structure was confirmed by the FT-IR, TEM, XRD and UV–vis analysis. A new conductive epoxy nanocomposite was synthesized by curing of diglycidyl ether of bisphenol A/4,4′-(4,4′ Isopropylidenediphenoxy) bis (Phthalic Anhydride) involving various percentages of polythiophene nanoparticles. DSC and DMTA studies revealed that low percentage of the polythiophene nanoparticles, i.e. 1%, results in improved crosslink density as evidenced by increasing in the glass transition temperature. The addition of polythiophene nanoparticles into the epoxy matrix resulted in a significant increment in the electrical conductivity, mechanical properties, thermal stability and activation energy of thermal degradation. The advanced isoconversional method is utilized to describe the curing behavior and thermal degradation process of the neat epoxy and epoxy nanocomposite. We have utilized the Coats–Redfern and Criado methods to find the solid state thermal degradation reaction mechanism. For the nanocomposite, the mechanism was recognized to be two-dimensional diffusion (D 2) reaction and it changes to a nucleation and growth (A 4) for pure epoxy system.

Thermal Degradation of Bisphenol A Type Novolac Epoxy Resin Cured with 4,4′-Diaminodiphenyl Sulfone

The curing reaction of bisphenol A type novolac epoxy resin (bis-ANER) with 4,4′-diaminodiphenyl sulfone (DDS) was investigated with Fourier-transform infrared (FTIR) spectroscopy. It was found that the obvious structure changes involve the disappearance of epoxide groups and increase of hydroxyls. Thermal degradation of the bis-ANER/DDS network was studied with thermogravimetry in both dynamic air and nitrogen atmospheres. The degradation takes place in two steps in air but in only one step in nitrogen. FTIR measurement was carried out to identify the changes in the structure during the degradation at different steps. In addition, the thermal degradation reaction mechanism of bis-ANER/DDS with the Coats-Redfern method showed that the kinetic model function of the thermal degradation obeys the Avrami-Erofeev model equation, that is, g(α) = [−ln(1 − α)]2/3.

Investigation of thermal behavior of poly(2-hydroxyethyl methacrylate-co-itaconic acid) networks

The thermal behavior of poly(2-hydroxyethyl methacrylate) [PHEMA] homopolymer and poly(2-hydroxyethyl methacrylate-co-itaconic acid) [P(HEMA/IA)] copolymeric networks synthesized using a radiation-induced polymerization technique was investigated by differential scanning calorimetry, thermogravimetric analysis, and Fourier transform infrared spectroscopy. The glass-transition temperature (Tg) of the PHEMA homopolymer was found to be 87°C. On the other hand, the Tg of the P(HEMA/IA) networks increased from 88°C to 117°C with an increasing amount of IA in the network system. The thermal degradation reaction mechanism of the P(HEMA/IA) networks was determined to be different from the PHEMA homopolymer, as confirmed by thermogravimetric analysis. It was observed that the initial thermal degradation temperature of these copolymeric networks increased from 271°C to 300°C with IA content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1602–1607, 2007

Thermal behavior of poly(2-hydroxyethyl methacrylate-maleic acid) networks

Poly(2-hydroxyethyl methacrylate-maleic acid) [P(HEMA/MA)] networks were prepared by radiation-induced polymerization of 2-hydroxyethyl methacrylate and maleic acid in aqueous solution. The thermal properties of the P(HEMA/MA) networks were investigated with differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The thermal behavior of these networks was also compared with PHEMA homopolymer. The glass transition temperature ( T g) of PHEMA homopolymer was found as 87 °C. On the other hand, T g of the P(HEMA/MA) networks decreased from 118 °C to 113 °C with increasing amount of MA in the network. It was observed that the initial thermal degradation temperature of P(HEMA/MA) networks did not change much with the MA content. However, the thermal degradation reaction mechanism of these copolymeric networks was different from PHEMA homopolymer.