Isoconversional Technique Research Articles

Investigation of the Thermokinetic and Thermodynamic Parameters of Biodiesel and Associated Oil from Palm Kernel Oil During Thermal Degradation

ABSTRACT This study investigates the kinetic and thermodynamic parameters of the thermal degradation of biodiesel produced from low-grade palm kernel oil. In this work, biodiesel was produced through a two-step transesterification from a palm kernel oil having a free fatty acid content of 5.7%. The first step uses 25% methanol (wt% of palm kernel oil) and 1% sulfuric acid (wt% of palm kernel oil) to reduce the free fatty acids content to 0.3% within 30 min reaction time. In the second step, a methanol-to-oil molar ratio of 6:1 and 0.6% (wt% of palm kernel oil) of KOH yielded a palm kernel oil conversion of 96.96% after 30 min reaction time. The palm kernel biodiesel was analyzed using Fourier Transform Infrared spectroscopy, gas Chromatography tandem mass spectrometry, nuclear magnetic resonance spectroscopy (1H and13C), and thermogravimetric analysis. The thermal stability of palm kernel biodiesel was assessed through the kinetic and thermodynamic parameters of biodiesel thermal decomposition using isoconversional techniques. The Flynn-Wall-Ozawa, Kissinger-Akariha-Sunose, and Starink models were used to evaluate the kinetic parameters, while the Coats and Redfern technique was used to forecast the most probable mechanism of the palm kernel biodiesel thermal degradation. The average activation energies of 108.60 kJ mol−1, 107.75 kJ mol−1 and 95.77 kJ mol−1 using the Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink methods, respectively. FWO method best described palm kernel oil and biodiesel decomposition, with the highest R2 values of 0.94 for the oil and 0.93 for biodiesel The results obtained from the thermodynamic study (ΔH = 218.48 kJ.mol−1, ΔG = 200.05 kJ.mol−1 and ΔS = 27.10 J.mol−1.K−1) revealed that the biodiesel thermal degradation was an endothermic, non-spontaneous process governed by a three-dimensional diffusion reaction mechanism.

Structural Characteristics and Improved Thermal Stability of HDPE/Calcium Pimelate Nanocomposites

In the present research work, calcium pimelate (CaPim) was synthesized and investigated as an additive for high-density polyethylene (HDPE). HDPE/CaPim nanocomposites were prepared by melt-mixing, with CaPim content ranging from 0.1% to 1%, affording white homogeneous materials. The chemical structure of the nanocomposites and the incorporation of CaPim was confirmed by infrared spectroscopy. The surficial morphology and the additive distribution were examined by scanning electron microscopy. Differential scanning calorimetry and X-ray diffraction measurements showed that the thermal transitions and crystal structure of HDPE are not affected by the incorporation of CaPim, while the mechanical properties are retained overall. This study focuses on the thermal degradation of HDPE nanocomposites, investigating the degradation mechanism and kinetic parameters through various analytical methods. Isoconversional techniques, including the Friedman method, Vyazovkin analysis, and Ozawa Flynn Wall analysis, were employed to calculate activation energies (Eα). The degradation mechanism and kinetic triplet were determined based on a multivariate non-linear regression method (model-fitting). Finally, the presence of a CaPim additive was shown to increase the Eα of thermal degradation, consistent with the calculated dependence of Eα on the degree of conversion and the improved thermal stability of the HDPE matrix.

Understanding the pyrolysis kinetics, thermodynamic, and environmental sustainability parameters of Sesamum indicum crop residue

In this work, the physiochemical characteristics, thermodynamics, and sustainability of the pyrolysis of Sesamum indicum biomass were assessed. The pyrolysis kinetics of sesame agro-residues performed using isoconversional techniques such as Kissinger, KAS, and OFW methods showed activation energies of 192, 120, and 123 kJ mol−1, respectively. The impact of the pyrolysis temperature (550, 650, 750 °C) on the generation of biochar, bio-oil, and gas is also studied; the exergy efficiency increased from 82.7 at 550 °C to 87.3% at 750 °C with an increase in the temperature. Sesame biochar’s Van Krevalan diagram showed how its fuel-like characteristics also grew with rising temperatures. The input and output parameters showed a high agreement in the mass, energy, and exergy balance closures. However, it was shown that the overall energy efficiency was greater at 750 °C (71.2%) compared to 55.5% and 69.8% at 550 °C and 650 °C, respectively. Sustainability analysis showed that lower temperatures had a smaller impact on the environment.

Synthesis, Spectral Characterization, Thermal Investigation, Computational Studies, Molecular Docking, and In Vitro Biological Activities of a New Schiff Base Derived from 2-Chloro Benzaldehyde and 3,3'-Dimethyl-[1,1'-biphenyl]-4,4'-diamine.

The current research involves the synthesis of a new Schiff base through the reaction between 2-chlorobenzaldehyde and 3,3'-dimethyl-[1,1'-biphenyl]-4,4'-diamine by using a natural acid catalyst and a synthesized compound physicochemically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, 1H- and 13C-nuclear magnetic resonance, and liquid chromatography-mass spectrometry. Thermal studies were conducted using thermogravimetric, differential thermal analysis, and differential thermogravimetric curves. These curves were obtained in an inert nitrogen environment from ambient temperature to 1263 K using heating rates of 10, 15, and 20 K·min-1. Using thermocurve data, model-free isoconversional techniques such as Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Friedman are used to determine kinetic parameters. These parameters include activation energy, phonon frequency factor, activation enthalpy, activation entropy, and Gibb's free energy change. All of the results have been thoroughly investigated. The molecule's anti-inflammatory and antidiabetic properties were also examined. To learn more about the potential of the Schiff base and how successfully it can suppress the amylase enzyme, a molecular docking experiment was also conducted. For in silico research, the Swiss Absorption, Distribution, Metabolism, Excretion, and Toxicity algorithms were used to calculate the theoretical pharmacokinetic properties, oral bioavailability, toxic effects, and biological activities of the synthesized molecule. Moreover, the cytotoxicity tests against a human lung cancer cell line (A549) using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay demonstrated that the synthesized Schiff base exhibited significant anticancer properties.

Mechanistic investigation of pyrolysis kinetics of water hyacinth for biofuel employing isoconversional method

The current study employs non-isothermal thermogravimetric analysis to analyze the thermal degradation behavior of water hyacinth (WH), with the primary goal of determining the kinetic triplet. The pyrolysis of water hyacinth achieved approximately 80% thermal degradation during three phases of breakdown at temperatures ranging from 30 to 900 °C. The activation energy of feedstock breakdown was calculated using four different model-free approaches i.e., Flynn-Wall- Ozawa (FWO), Starink, Friedman, and Kissinger- Akahira-Sunose (KAS), with mean values ranging from 251.33 to 298.48 kJ/mol inside the conversion band of 0.15–0.75. The Master plot results depicted that for conversion (α) ≤ 0.5, the biomass degradation followed a two-dimensional process of diffusion. For α ≥ 0.5, the response, however, is adequately described by growth processes and nucleation. The values of excitation energy estimated using isoconversional techniques were also utilized to determine various thermodynamic parameters. From the thermodynamic study, the mean value of ΔH was 293.66 kJ/mol, suggesting that the generation of activated complex is simpler since the potential energy barrier is lower. A high ΔS value indicates increased reactivity and less time required to synthesize the activated compound. In conclusion, the characterization and kinetic analyses of biomass reveal their potential as pyrolysis feedstock.

A novel pseudo-multicomponent isoconversional approach for the estimation of kinetic and thermodynamic parameters of potato stalk thermal degradation

This study examined the thermal degradation kinetics of potato stalk (PS) using a unique isoconversional technique. The kinetic analysis was assessed based on mathematical deconvolution approach with model-free method. The thermogravimetric analyzer (TGA) was used for the non-isothermal pyrolysis of PS at different heating rates. The Gaussian function was then used to extract three pseudo-components (PC) from the TGA findings. The average activation energy value for PS (125.99, 122.79, and 122.85 kJ/mol), PC1 (106.78, 103.83, and 103.92 kJ/mol), PC2 (120.26, 116.31, and 116.55 kJ/mol), and PC3 (373.12, 379.40, and 378.93 kJ/mol) based on OFW, KAS, and VZN model respectively. Furthermore, an artificial neural network (ANN) was used to forecast the thermal degradation data. The findings demonstrated a significant correlation between real and anticipated values. The kinetic and thermodynamic results, along with ANN are critical for constructing pyrolysis reactors that might use waste biomass as a potential feedstock for bioenergy production.

Thermal degradation behaviour and chemical kinetic characteristics of biomass pyrolysis using TG/DTG/DTA techniques

The goal of the current study is to investigate the thermal degradation of palm fronds (PF), olive leaves (OL), and wheat straw (WS) through pyrolysis and calculate their kinetic data using TG-DTG and DTA approaches. The kinetic parameters were assessed using isoconversional techniques like the Ozawa-Flynn-Wall (OFW) and Kissinger–Akahira–Sunose (KAS) methods, as well as model-fitting techniques like the integral method, which employs various diffusion and reaction order models. Using kinetics data models, typical parameters for pyrolysis and thermodynamics were estimated. For PF, OL, and WS, the values of activation energy (E) from the integral method ranged between 8.82 and 167.13, 23.06 and 149.20, and 11.01 and 156.27, respectively, for diffusion models. On the other hand, the values of (E) ranged between 22.3 and 117.49, 51.69 and 92.88, and 23.48 and 125.97, respectively, for reaction-order models. The average activation energies (E) calculated by using PF, OL, and WS samples are 91.9, 69.1, and 65.2, respectively, for the OFW method and 87.5, 101.8, and 63.4, respectively, for the KAS method. The results demonstrated that the integral method provided values of (E) that were almost identical to those produced by the KAS and OFW methods. In the same range of (α), results showed that reaction order models yielded greater frequency factor values than diffusion models, demonstrating how simpler and quicker pyrolysis is. The values of (ΔGav\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Delta \\mathrm{G}}_{av}$$\\end{document}) demonstrated the acceptability of these materials for pyrolysis, and for the OFW and KAS techniques, the sequence of the degradation process was OL > WS > PF. The calculated (ΔGav\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\Delta \\mathrm{G}}_{av}$$\\end{document}) showed that more heat energies are required for OL, PF, and WS to dissociate the reagent bonds, which agrees with the (E) values derived from the OFW model.Graphical

Thermogravimetric analysis of pyrolysis of Delonix regia biomass in the presence of zeolite, mixed metal oxides and carbon supported noble metal catalysts

Renewable energy from biomass waste shall become an effective alternative to faster-depleting fossil fuels and pyrolysis is a suitable approach to produce renewable energy from biomass. Further, kinetics parameters are essential in designing reactors for pyrolysis and this work provides kinetics of catalytic pyrolysis (CP) of Delonix regia (DR) biomass. In addition to this significance, the novelty of this work includes the utilization of catalysts of three different kinds such as zeolite (Na–Y), mixed metal oxides (TiO2+ZnO), and supported noble metal (Pt/C) catalysts at varying loads of 30–10 wt %. All experiments were performed in a micro pyrolyzer (thermogravimetry analyzer) under non-isothermal conditions at five heating rates (5, 10, 20, 35, and 55 °C min−1) in a temperature range of 25–1000 °C. To estimate kinetic factors (KF) and thermodynamic parameters (TP), five iso-conversional techniques such as Differential Friedman (DFM), Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), Starink (STK), and Distributed Activation Energy (DAE) were employed. KAS technique yielded the lowest mean activation energy, Eα (181.29 kJ mol−1), and frequency factor, ko (2.10 E+16 s−1) factors by use of Na–Y zeolite of load 10 wt % whereas the corresponding change in enthalpy is 177 kJ mol−1, change in Gibbs free energy is 178 kJ mol−1, and change in entropy is −9.58 E−04 kJ mol−1 K−1. Criado's master plots confirmed the reaction pathway as: second order (F2), power-law (P4), contraction area (R2), zero order (F0), contraction volume (R3), and fourth order (F4) for 20 °C min−1 from DFM technique for CP of DR by using Na–Y zeolite catalyst of load 10 wt %.

Cyanate Ester Polymerization: Overview of Mechanistic and Kinetic Aspects

AbstractThis article reviews both time‐honored and most recent studies of the mechanisms and kinetics of cyanate esters polymerization. Different types of processes, including catalytic, non‐catalytic, bulk, solution, and nanoconfined ones are covered. The mechanistic and empirical models suitable for describing the kinetic and diffusion regimes of polymerization are discussed at length. Recent advances in methodology of the analysis of multistep polymerization reactions by means of model‐fitting and isoconversional techniques are considered as applied to cyanate esters. The importance of the calorimetric measurements in polymerization studies is emphasized.

A novel approach for determination of nucleation rates and interfacial energy of metallic magnesium nanoclusters at high temperature using non-isothermal TGA models

The exploration of temperature-dependent nucleation is required to appraise the extent of kinetic and thermodynamic barriers associated with the origin of subatomic size nuclei, which controls the nucleation rate. The precise computation of nucleation rate, thermodynamic parameters, and interfacial surface energy for ultra-small nanoclusters (0.5–2 nm) is still absent in the high-temperature range. Here, apparent activation energy (Ea), thermodynamic parameters (ΔG, ΔH, and ΔS), and pre-exponential kinetic factor were estimated by utmost accurate Vyazovkin advanced, and KAS isoconversional techniques for calculation of nucleation rate and interfacial energy for ultra-small magnesium nanoclusters (∼0.8 ± 0.24 nm), in the temperature range from 555 to 780 K. The master plots propounded the existence of third order random nucleation in magnesium metal matrix over a specified conversion. Based on the above findings, four mathematical models are proposed to compute nucleation rate and interfacial energy in magnesium clusters over respective temperatures and conversions. These models are beneficial for predicting the nucleation rate and interfacial energy over a high range of temperature and specific conversion.

Effect of Phenolic Resin and Nano-Calcium Carbonate Particles on the Curing Kinetic of Epoxy Composites

The research described here studied the curing kinetics of pure epoxy (EP), epoxy/phenolic resin (EP/PH) and epoxy/nano-CaCO3 particles (EP/NPs) composites by isothermal differential scanning calorimetry (DSC). A model free technique (isoconversional technique) was used to study the curing reaction kinetics and the results showed that the activation energies (Ea) of the pure EP, EP/PH, and EP/NPs composites remained constant at different conversions. The research showed a decrease of Ea for the EP/NPs system, while there was a small increase of Ea for the EP/PH. This can be attributed to the acceleration effect of the nano-CaCO3 for the EP/NPs system and the low reactivity of PH for the EP/PH system.

Microwave co-pyrolysis of kitchen food waste and rice straw for waste reduction and sustainable biohydrogen production: Thermo-kinetic analysis and evolved gas analysis

Physico-chemical characteristics of kitchen food waste (KFW) and rice straw (RS) were explored to determine the optimum feedstock ratio for biohydrogen production. An in-depth investigation on the thermogravimetric degradation was conducted at heating rates of 10, 20, and 30 ℃/min. Friedman, Kissinger-Akahira-Sunose, and Flynn-Wall-Ozawa iso-conversional techniques were applied to investigate the kinetic properties of different mass ratios of the feedstocks. The average apparent activation energy (Ea) increased for all co-pyrolysis blends, reaching a maximum for 75KFW blend samples (138.6911 kJ/mol for Friedman, 136.9028 kJ/mol for KAS, and 146.5558 kJ/mol for FWO). The relatively small difference between ΔH and Ea indicated the production feasibility of the reactions. A microwave reactor was used to investigate product yields for different blend proportions. Gas chromatography analysis showed that co-pyrolysis improved production of biohydrogen, with 25KFW attaining a maximum yield of 43.02%. Overall, this study reflects the viability of scaled-up KFW and RS co-pyrolysis as a waste management alternative and an effective and sustainable source of biohydrogen.

Kinetic modelling for pyrolytic conversion of dedicated short rotation woody crop with predictions for isothermal, non-isothermal and stepwise heating regimes

Sesbania sesban, a promising short rotation woody crop, was first evaluated in order to assess its physicochemical attributes as a feedstock material in biochar manufacturing. Additionally, thermogravimetric analysis (TGA), performed at 0.5, 1, 4 and 8 °C.min−1, was utilised to conduct thermal analysis, with the results being used to analyse the feedstock's kinetic behaviour during thermal degradation in an inert environment. For the first time, advanced kinetics and technology solutions (AKTS) software was used to analyse the kinetic parameters of sesbania pyrolysis and make kinetic predictions under various thermal conditions. The apparent activation energy (Ea) was determined using Friedman's differential iso-conversional model, which is the primary kinetic modelling method utilised. Other traditional models, such as the integral Flynn-Wall-Ozawa (FWO) and ASTM-E698 methods, were employed for comparison purposes. The activation energy of 124.53 kJ.mol−1 was obtained using the ASTM-E698 technique, while the Ea value for the FWO method ranged from 50 to 200 kJ.mol−1. As it accurately reflects the dynamic nature of lignocellulosic biomass degradation, the differential iso-conversional technique is the most reliable and precise approach, with Ea values ranging from 20 to 205 kJ.mol−1. Predictions under isothermal, step-based and non-isothermal conditions were then constructed using the results computed through the differential iso-conversional model. This information can be used to improve production throughput in a variety of reactors. Additionally, the derived kinetic parameters can be used for process modelling.

Study on Combustion Characteristics and Thermodynamic Parameters of Thermal Degradation of Guinea Grass (Megathyrsus maximus) in N2-Pyrolytic and Oxidative Atmospheres

This study provides an extensive investigation on the kinetics, combustion characteristics, and thermodynamic parameters of the thermal degradation of guinea grass (Megathyrsus maximus) in N2-pyrolytic and oxidative atmospheres. A model-fitting technique and three different iso-conversional techniques were used to investigate the kinetics of the thermal process, after which an analysis of the combustion characteristics and thermodynamic parameters was undertaken. Prior to this, experiments on the physico-chemical characterization, thermogravimetric, and spectroscopic analyses were carried out to provide insight into the compositional structure of the guinea grass. The volatile matter, fixed carbon, and total lignin contents by mass were 73.0%, 16.1%, and 21.5%, respectively, while the higher heating value was 15.46 MJ/kg. The cellulose crystallinity index, determined by XRD, was 0.43. The conversion of the GG in air proceeded at a relatively much higher rate as the maximum mass-loss rate peak in a 20 K/min read was −23.1 and −12.3%/min for the oxidative and the pyrolytic, respectively. The kinetics investigation revealed three distinctive stages of decomposition with their corresponding values of activation energy. The average values of activation energy (FWO) at the latter stages of decomposition in the pyrolytic processes (165 kJ/mol) were higher than those in the oxidative processes (125 kJ/mol)—an indication of the distinctive phenomenon at this stage of the reaction. The Coats–Redfern kinetic model revealed that chemical reactions and diffusional models played a predominant role in the thermal decomposition process of the GG. This study showed that the thermodynamic parameters varied with the conversion ratio, and the combustion performance increased with the heating rates. The use of GG as an energy feedstock is recommended based on the findings from this work.

Thermal-stability and microstructure comparison between recycled M2M and conventionally produced sintered neodymium-iron-boron magnets

Abstract Sintered magnets based on neodymium, iron and boron (Nd-Fe-B) are at the core of many modern technologies. While they exhibit high energy products of more than 400 kJm−3 at room temperature, they suffer from a low Curie temperature and thermal stability when compared to other types of permanent-magnet materials. Usually, to improve the coercivity and thermal stability, heavy rare earth elements (HREE) are added during the manufacturing process. However, alternative production routes are being considered in order to decrease the dependence from rare earth mining operations. The magnet-to-magnet (M2M®) processing technique is one of them that used harvested EOL magnets as feedstock rather than refined and reduced RE-ore from mines. In this study, the thermal stability of a M2M® recycled magnet versus conventional magnets of the same energy grade were analyzed. Differential scanning calorimetry (DSC) was used to measure the Curie temperatures of all the magnets. The DSC signal was analyzed using isoconversional techniques to estimate the activation energies of the micromagnetic phenomena associated with the thermal demagnetization. It was found that the recycled magnet, while presenting a level of oxygen and carbon contamination similar to the virgin magnets, has overall better or comparable thermal stability and coercivity. The measured difference in Curie-temperature between the magnets is only of a few kelvins, which is consistent with the temperature fluctuations associated with micromagnetic phenomena at the grain boundaries. A complementary microstructural characterization using scanning electron microscopy (SEM) has been undertaken to support the comparison.

Kinetics of Solid-Gas Reactions and Their Application to Carbonate Looping Systems

Reaction kinetics is an important field of study in chemical engineering to translate laboratory-scale studies to large-scale reactor conditions. The procedures used to determine kinetic parameters (activation energy, pre-exponential factor and the reaction model) include model-fitting, model-free and generalized methods, which have been extensively used in published literature to model solid-gas reactions. A comprehensive review of kinetic analysis methods will be presented using the example of carbonate looping, an important process applied to thermochemical energy storage and carbon capture technologies. The kinetic parameters obtained by different methods for both the calcination and carbonation reactions are compared. The experimental conditions, material properties and the kinetic method are found to strongly influence the kinetic parameters and recommendations are provided for the analysis of both reactions. Of the methods, isoconversional techniques are encouraged to arrive at non-mechanistic parameters for calcination, while for carbonation, material characterization is recommended before choosing a specific kinetic analysis method.

Slow and rapid thermal decomposition characteristics of enhanced blast explosives for burning in fuel-rich, oxygen-rich conditions

The thermal decomposition of metalized polymer-bonded explosives (PBXs) with the addition of ammonium perchlorate (AP) was characterized using slow and fast cook-off simulations, differential scanning calorimetry (DSC), and an isoconversional technique. PBXs #1, #2, and #3 contain 95% cyclotetramethylene-tetranitramine (HMX) with binder; 66% HMX and 25% aluminum with binder; and 25% cyclotrimethylene-trinitramine (RDX), 35% aluminum (Al), 25% AP, and binder, respectively. The roles of Al and AP during thermal decomposition, distinct from the shock-to-detonation transition, were confirmed, indicating that Al does not contribute to the exothermic ignition process due to its higher reaction temperature compared to HMX; instead, Al leads to a higher explosion time and temperature for PBX #2 compared to PBX #1. We extracted the kinetic scheme of PBXs based on the isoconversional technique. In the slow cook-off test for PBX #3, a thermal runaway occurred at the RDX reaction temperature, which is lower than the AP reaction temperature, indicating that AP has a negligible effect. In the fast cook-off test, however, the reactions of RDX and AP occurred simultaneously due to the higher heating rate, demonstrating the influence of AP on the explosion time and temperature.

Determination of thermokinetic parameters and thermodynamic functions from thermoforming of LiMnPO4

This article presents the determination of thermokinetic parameters and thermodynamic functions from the thermoforming of LiMnPO4. In our previous paper, a couple of thermoreaction processes, e.g., co-elimination and polycondensation of thermokinetics and thermodynamics, were incompletely determined. The co-elimination process is considered as dehydration and a deammoniation process in this paper. Evidently, an alternative technique was applied for calculating the extent of conversion values using the ratio of the peak area of the deconvoluted DTG peak after applying the Fraser–Suzuki deconvolution. An iterative equation of the integral isoconversional technique was used to estimate the reliable activation energy Eα. Each separated peak, including dehydration, deammoniation, and polycondensation, was obviously evaluated as a single kinetic process with its own kinetic parameters. In order to choose reliable mechanisms, the y(α) master plots or the plots between the experiment and the model were compared. The plots thus obtained showed that the dehydration, deammoniation, and polycondensation processes were found to be 3/2-order chemical reaction (F3/2), 2-order chemical reaction (F2), and nucleation (P3/2) mechanisms, respectively. The pre-exponential factor values were obtained from Eα, and the reaction mechanisms were found to be 3.78 × 1012, 7.05 × 1012, and 1.96 × 1013 s−1, respectively. The evaluated thermodynamic data of the activated complexes showed that the thermal reaction required thermal energy to complete the reaction.

Investigation of radical polymerization kinetics of poly(ethylene glycol) methacrylate hydrogels via DSC and mechanistic or isoconversional models

Monomers composed of a polymerizable methacrylate moiety connected to a short poly(ethylene) glycol (PEG) chain are versatile building-blocks for the preparation of “smart” biorelevant materials. Hydrogels based on these PEG methacrylates are a very important class of biomaterials with several applications. The radical polymerization kinetics of two such oligomers, namely poly(ethylene glycol) methacrylate (PEGMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) was investigated. Experimental polymerization rate and monomer conversion data were measured using DSC operating under non-isothermal conditions, at several constant heating rates, or isothermal, at different constant reaction temperatures. Isoconversional techniques were employed to estimate the variation of the polymerization effective activation energy as a function of the extent of reaction. It was found that isothermal and non-isothermal experiments results in similar trends of the activation energy, whereas by comparison of differential to integral isoconversional methods it was postulated that in non-isothermal polymerization experiments integral methods should not be used. From comparison of the two oligomers employed in the polymerization experiments, it was clear that the presence of the terminal hydroxyl group in PEGMA compared to the methoxy group in PEGMEMA leads to different conversion time profiles and activation energies. In particular, monomer–monomer association through hydroxyl groups results in initially lower activation energy of PEGMA. As polymerization proceeds, the existence of aggregated hydroxyl structures (···OH···OH···OH···) in the PEGMA macromolecular chains result in higher activation energies and a more abrupt increase in the conversion time curve.

Thermo-kinetic analysis of Ni–Al intermetallic phase formation in powder system

Thermo-kinetic analysis was carried out to determine the kinetics of Ni–Al intermetallic phase formation from powder mixture of Ni and Al. The kinetic data were generated using dynamic temperature program at 5, 10, 15, 20 K min−1 in a differential scanning calorimeter. The phase formation was studied with the help of both qualitative and quantitative powder X-ray diffraction using Rietveld refinement. The activation energy for the reaction was calculated from model-free isoconversional technique employing both differential (Friedman’s method) and integral (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose method) methods. The result shows that formation of NiAl from elemental powders is multi-step in nature involving $$\hbox {Ni}_2\hbox {Al}_3$$ as a major intermediate. The appropriate kinetic model for the reaction was evaluated by means of Malek’s method (model selection technique). Sestak Breggren (auto-catalytic model) was found to be in good agreement with the experimental data. The corresponding kinetic parameters and rate expression were determined for the reaction system involving solid–solid reaction between Ni and Al in the powder form.