Non-isothermal Kinetic Analysis Research Articles

Nonisothermal Kinetic Analysis and AC Conductivity for Polyvinyl Chloride (PVC)/Zinc Oxide (ZnO) Nanocomposite

The behavior of polyvinyl chlorine (PVC)/zinc oxide (ZnO) nanoparticles was investigated. To improve the dispersion and distribution of zinc nanoparticles within the host polymer (PVC), they were treated with water before being added to the polymer. The nanocomposite samples were prepared by casting method using different weight ratios of ZnO nanoparticles. The prepared nanocomposite samples were characterized by thermogravimetric analysis (TGA). Both thermal stability and kinetic analysis of the prepared samples were investigated. The ZnO nanoparticles lower the activation energy and decrease the thermal stability of PVC. Kissinger, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose models were used in the nonisothermal kinetic analysis of PVC/ZnO nanocomposite samples. The thermal stability behavior due to the addition of zinc oxide nanoparticles was explained and correlated with the behavior of the kinetic parameters of the samples. The AC conductivity as function of frequency and temperature was also investigated. The addition of ZnO nanoparticle increases the AC conductivity, and the temperature-independent region decreased by increasing temperature. Both S and A coefficients were predicted using the Jonscher power law and OriginLab software. The trends of S and A coefficients were discussed based on the glass transition of the host polymer.

The curing kinetics and mechanical properties of epoxy resin composites reinforced by PEEK microparticles

In this paper, a polyether-ether-ketone (PEEK)/epoxy composite was prepared by using PEEK microparticles as the reinforcement. The nonisothermal differential scanning calorimetry (DSC) test was used to evaluate the curing reaction of PEEK/epoxy resin system. The curing kinetics of this system were examined utilizing nonisothermal kinetic analyses (Kissinger and Ozawa), isoconversional methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose) and an autocatalytic reaction model. During these analyses, the kinetic parameters and models were obtained, the curing behavior of PEEK/epoxy resin system under dynamic conditions was predicted. The results show that isoconversional methods can adequately interpret the curing behavior of PEEK/epoxy resin system and that the theoretical DSC curves calculated by the autocatalytic reaction model are in good agreement with experimental data. Furthermore, the tensile elongation at break, tensile strength, flexural strength, compression strength and compression modulus increased by 81.6%, 33.66%, 36.53%, 10.98% and 15.14%, respectively, when PEEK microparticles were added in epoxy resin composites.

Synthesis and Structural Characterization of Sequential Structure and Crystallization Properties for Hydrophilic Modified Polyester.

The hydrophilic copolyester polyethylene terephthalate (PET) (ENCDP-X) was successfully synthesized by chemical modification consisting of copolymerization and blending and the comonomers, including sodium isophthalate-5-sulfonate (SIPE), polyethylene glycol (PEG), 2,2-dimethyl-1,3-propanediol (NPG) and matting agent TiO2 with different content. Moreover, the structural characterization of sequential structure, crystallization and thermal properties were studied. The results showed that the comonomers were successfully embedded in the copolyester, the actual molar ratio in the copolyester was consistent with the relative feed ratio and the degree of randomness was calculated to be 0.99, showing that the random copolymers synthesized during the melt polycondensation process and the chemical structure was roughly consistent with the expected molecular chain sequence structure. The thermal parameters of the modified copolyester, containing the glass transition temperature (Tg), melting point (Tm), crystallinity (Xc) and thermal degradation temperature, were decreased, and the cold crystallization temperature (Tc) was increased. In addition, with the increasing of the TiO2 content, it improves the thermal performance of the copolyester and it is beneficial to processing and application. The above conclusion is further verified by non-isothermal kinetic analysis. In addition, the copolyester exhibited the better hydrophilicity than pure PET.

Isoconversional nonisothermal kinetic analysis of municipal solid waste, refuse‐derived fuel, and coal

AbstractThe thermal characteristics and kinetic behavior of various solid wastes, including refuse‐derived fuel (RDF) and municipal solid waste (MSW), were investigated as a potential renewable energy source, in comparison with low‐rank coal. The experimental data were obtained in nonisothermal conditions through TGA analysis at specific heating rates. In addition to thermal characteristics of solid fuels, four isoconversional (model‐free) kinetic methods: a: Kissinger‐Akahira‐Sunose (KAS), b: Flynn‐Wall‐Ozawa (FWO), c: Friedman, and d: Vyazovkin were applied to calculate activation energies. In case of solid wastes, it is possible to say that the trend of activation energies of all isoconversional methods remains almost same in the selected region of conversion (0.1‐0.6 and 0.7‐0.9). Whereas in case of coal, Friedman model exhibits lower and inconsistent values of activation energy than others selected isoconversional methods. The experimental and modeling results revealed that that solid wastes (RDF and MSW) can be promising alternative energy sources to encounter energy crisis and uncontrolled waste disposal issues.

Thermal Degradation of Nafion in the Presence of Nanostructured Materials: Thermally Expanded Graphite, Carbon Black, and Platinum

Thermal degradation in air of Nafion proton-conducting polymer in composites containing nanostructured carbon materials [carbon black of Vulcan XC-72 grade and a graphene-like material (thermally expanded graphite)] and platinum nanoparticles was studied by nonisothermal kinetic analysis. The effect of the contact of Nafion with one or another material of the composite on the degradation kinetics was examined. The activation energy of Nafion desulfonation was calculated in relation to the component composition. The temperature dependence of the polymer lifetime for materials of different component compositions was evaluated. The materials were characterized by scanning and transmission electron microscopy and by differential thermal analysis. The presence of carbon materials enhances the heat resistance of Nafion and narrows the temperature interval of its degradation. The presence of various forms of carbon material (carbon black, thermally expanded graphite) and of platinum nanoparticles influences the Nafion desulfonation and its kinetic characteristics differently. The mechanism of thermal stabilization of Nafion in the presence of carbon materials was suggested.

Kinetic Modeling of Pyrolysis and Combustion of High-Density Polyethylene-Based Polymer Mixtures

In this study, the pyrolysis and combustion of a binary mixture of most waste polymers (HDPE and PC) were investigated using MCC measurements at different heating rates of 0.25, 0.5, 1, 1.5 K/s. The non-isothermal kinetic analysis of mixture was conducted for equally mass fraction ratio of 50% HDPE and 50% PC, as well as for individual polymers. The activation energy was calculated by the isoconversional methods (Friedman, Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa). The estimated activation energy on the conversion equals to 0.1-0.95. The Friedman method being more sensitive, as is shown by the variation of decomposition of PC and the first stage for a blend of HDPE/PC. As the equations used in FWO and KAS methods are derived assuming constant activation energy, which produces systematic errors in the estimation of Ea, so they have the same profile but FWO always is higher than KAS.

Characterization of PVC/MWCNTs Nanocomposite: Solvent Blend

Abstract Polyvinyl Vinyl Chloride (PVC) multiwall carbon nanotubes (MWCNTs) nanocomposite flexible films were prepared using the solvent blend technique. Chloroform (CHCl3) and tetrahydrofuran ((CH2)4O) were used as solvents for MWCNTs and PVC, respectively. The effect of the solvents’ blend on electrical, optical and thermal properties of PVC/MWCNTs were investigated. The results of the Raman spectrum showed that all the characteristic bands of PVC polymer have a slight shift due to addition of MWCNTs. Electrical results showed that the nanocomposite samples with chloroform volume ratios of 10% and 25% had nearly the same conductivity. This is attributed to the formation of the MWCNTs network, which assisted in electrical conductivity. The I-V hysteresis curve decreases as the temperature increases and as it approaches the glass transition temperature. The non-isothermal kinetics analysis for PVC and PVC/MWCNTs were investigated by Thermogravimetry Analysis (TGA) using the model-free kinetic method. The non-isothermal measurements were carried out at five heating rates of 5 to 40∘C/min. The results show that the main decomposition process has constant apparent activation energies for all samples. The use of the bi-solvent method has improved the dispersion of untreated MWCNTs, and this has been reflected on the stability of both electrical and thermal properties.

Nucleation effect of aliphatic polycarbonate in its blends with poly(ethylene terephthalate)

Aliphatic polycarbonate (PDCM) was synthesized from dimethyl carbonate and 1,4-cyclohexanedimethanol via melting polymerization in this study. The molecular weight of PDCM was determined by gel permeation chromatography (GPC) to be ca. 49,900. The crystallization behavior and crystallinity of polyethylene terephthalate (PET) were significantly modified by adding 0.3–5.0 wt% PDCM, which was confirmed by differential scanning calorimetry (DSC), photomicrography with a heating stage and SAXS analysis. In nonisothermal crystallization kinetics analysis, the reciprocal of half-time crystallization (i.e., G parameter) for the 1.0 wt% PDCM/PET blends is 3.5 times greater than that of pristine PET at a cooling rate of 10 °C/min. Observation via polarized optical microscopy showed that the spherulites size of PET was condensed by PDCM. In addition, the fold surface energy (σe) decreased with the presence of PDCM. According to the results of dynamic mechanical analysis (DMA) examination, the mechanical strength of 1.0 wt% PDCM/PET thin film was enhanced as the transparency still maintained above 85%, which illustrated the transparent thin film has better thermal stability and has high potential to be used such as in the electronic appliances.

Kinetics of partially depolymerized lignin as co-curing agent for epoxy resin

Lignin, which is crosslinked by ether and carbon‑carbon linkages, is a highly branched polymer consisting of phenyl propane units. And owing to the abundant phenolic hydroxyl groups and its structural heterogeneous characteristics, lignosulfonate, considered as a renewable aromatic macropolymer, can be used as co-curing agent in EP thermoset systems. In this study, kinetics of lignosulfonate (LS) and partially depolymerized lignosulfonate (DLS) as co-curing agents for applications to EP thermoset were discussed with the differential scanning calorimetry (DSC) measurement. The activation energy (Ea) and dynamic modeling of curing reaction were obtained by the methods of non-isothermal kinetic analysis reported by Kissinger and Ozawa. The glass transition temperature (Tg) was determined by DSC and mechanical properties of epoxy resins were carried out using the Universal Testing Machine. The LS dropped the exothermic peak temperature and Ea of curing reaction of EP thermoset. Those of DLS were more active than the higher molecular weight lignosulfonate. The EP thermoset cured with DLS (EP-DLS) exhibited much higher reactivity, and the curing reaction could be occurred at lower temperature. The Tg of EP-DLS has risen by 10 °C compared with the case without lignosulfonate. The tensile strength, elongation at break and impact strength of EP-DLS rose by 28.7%, 52.5% and 53.5%, respectively, than those of the epoxy resin cured with LS (EP-LS).Molecular weight of lignosulfonate could be an important factor of the curing reaction of EP thermoset. The high performance EP thermoset could be obtained by partially depolymerized lignin as co-curing agents.

Synergistic effects of catalytic co-pyrolysis of macroalgae with waste plastics

This study unveiled the synergistic effects of catalytic co-pyrolysis of the macroalgae (Enteromorpha prolifera) and waste plastics (HDPE) for enhanced biofuels production. Results revealed that catalytic co-pyrolysis of macroalgae (seaweeds) and waste plastics lowered greatly the high contents of the acids, oxygenates and nitrogen-containing compounds in the seaweed bio-oils, while the aromatics and light hydrocarbons contents of the bio-oils were significantly increased, owing to blending of seaweeds with co-feeding element of high hydrogen content. Results also unveiled that the existence of the co-pyrolysis synergy inhibited catalytic coking and reduced solid residues’ formation. Also, the addition of HZSM-5 catalyst further improved the reaction activity, yields and selectivity of aliphatic hydrocarbons than aromatics, and reduced the activation energy without changing the reaction mechanisms. This significant reduction in activation energy can be easily observed in the results of non-isothermal kinetic analyses performed using the TGA data via five different methods: Friedman, FWO, Vyazovkin, KAS and DAEM methods, as a single kinetics-evaluation model lacks the flexibility to account for different types of materials without further modifications to reaction scheme. The FTIR-spectra of the catalytic co-pyrolysis oils were consistent with the results of the GC/MS analysis of the oils from catalytic-co-pyrolysis.

Non-isothermal reduction kinetics of roasted high alumina iron ore pellets

Non-isothermal reduction of roasted Guangxi high alumina iron ore pellets with CO and H2 was conducted with NETZSCH STA 409C/CD. Non-isothermal kinetics analysis was carried out and kinetics data were obtained. Compared with the possible common mechanisms function in solid state reaction about the correlation coefficient(r), the optimal equations for CO reduction and H2 reduction were determined. Furthermore, the Arrhenius plots for CO and H2 reduction were clarified when the kinetic mechanism functions were determined. The results show that the activation energy values of CO and H2 reduction are 295.82 kJ ∙ mol−1, and 185.42 kJ ∙ mol−1, respectively. Obviously, when the temperature is higher than 1357 K, the level of the reaction rate constant of H2 reduction higher than that of CO reduction increases sharply, that is the capacity of H2 reduction is better than that of CO reduction in certain conditions.

Preparation, characterization and kinetic evaluation of struvite in various carboxylic acids

In this study, struvite crystallization was investigated using different carboxylic acid media—propionic, tartaric, and trimesic acid. The struvite was synthesized as a result of the reaction between magnesium chloride hexahydrate and ammonium dihydrogen phosphate. In the first part.of the study, the crystals prepared with and without additives were characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. XRD results showed that the struvite prepared in pure media comprised crystals with the normal orthorhombic structure. SEM images confirmed that the struvite underwent morphological changes when prepared in carboxylic acid media. FTIR analysis indicated that the carboxylic acids affected the functional groups of the struvite. Zeta potential measurements showed that struvite crystals have a −13.2 ± 1.8 mV zeta potential value, and that the surface of the crystals in trimesic acid media became more positive than that created in pure media with an increase in value to −2.3 ± 0.9 mV. In the second part of the study, the thermal decomposition of the struvite crystals was investigated in detail. The thermal data were used to calculate the activation energy that corresponded to struvite dehydration prepared with and without additives using a nonisothermal kinetic analysis based on the Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Starink, and Tang models. The mean activation energy calculated for struvite crystallization in pure media was between 56.06 and 52.13 kJ/mol, depending on the kinetic method used.

A Modified Model for Kinetic Analysis of Petroleum Coke

In this study, a nonisothermal kinetics analysis of petcoke was performed at heating rates of 10, 15, and 20°C/min using thermal gravimetric analysis (TGA). The behaviour of petcoke at different gasification stages (dewatering, volatilization, char burning, and burnout) was studied. The effect of heating rate on the activation energy of petcoke gasification was also investigated. The activation energy of petcoke was estimated using different kinetic models that include volume reaction model (VRM), shrinking core model (SCM), random pore model (RPM), Coats and Redfern model (CRM), and normal distribution function (NDF). The NDF model was modified in this study. It was found that the experimental data were best fitted with the modified normal distribution function (MNDF) and SCM. The results also showed that activation energy decreases as heating rate increases, leading to reduction in gasification completion time.

Kinetic analysis of the formation of high-temperature phases in an illite-based ceramic body using thermodilatometry

A non-isothermal kinetic analysis of the sintering process of an illitic clay is studied by thermodilatometry. For this study, illitic clay with over 80 mass% of illite content, originated in the Fuzerradvany location in northeastern Hungary, is used as basic material. The measurements are performed using a push-rod dilatometer on compact samples with heating rates from 1 to 10 °C min−1 in dynamic N2 atmosphere. The Kissinger method is used for the parameterization of the process. The results show that the reaction sintering runs in several overlapping steps. The determined values of the apparent activation energy of the first step and second step are EA = (625 ± 18) kJ mol−1 and EA = (575 ± 14) kJ mol−1, respectively. The results also show that both reactions could be characterized by the thickening of long cylinders (needles) or growth of needles and plates of finite long dimensions.

Non-isothermal kinetic analysis of high temperature oxidation of Ti–6Al–4V alloy

In this study, non-isothermal kinetic analysis of high temperature oxidation of Ti–6Al–4V alloy by thermogravimetric analysis (TGA) at heating rates of 10, 15, and 20 °C/min up to 1550 °C in air atmosphere was studied. The results revealed that the formed oxide layer consists of several different parts; an inner part of TiO2, an outer part of TiVO4, and an intermediate part of Al2O3. Also, the thickness of oxide layer increased by an increase in the maximum heating temperature, while its density decreased by formation of the pores and cracks in higher maximum temperature due to the mismatch between the thermal expansion coefficient of the oxide layer and the substrate. This mismatch led to formation of large stresses in the oxide layer at high temperatures (≥1000 °C) and thereby isolation of the oxide layer during cooling. The microhardness profiles shift to higher microhardness values by an increase in the maximum temperature due to the increasing of oxygen solubility in the substrate. On the other hand, the kinetic results performed by isoconversional Starink, KAS, FWO, Tang, and Friedman methods in combination with the invariant kinetic parameters (IKP) method and fitting model estimated the activation energy (E) and pre-exponential factor (lnA) of the oxidation process equal to 205–235 kJ/mol and 12-13 min−1, respectively. Furthermore, it was approved that this reaction is controlled by a diffusion control model (D1 model).

Non-isothermal kinetic analysis of the combustion of argan shell biomass

Abstract Argan shell is one of the main by-products during argan oil production. It is considered as an attractive, cheap and renewable biomass source for sustainable energy utilization. The present paper reports on combustion characteristics of argan shell in order to evaluate their potential for thermochemical conversion. Combustion studies using thermogravimetry (TG) are performed at four different heating rates of 5, 10, 15 and 20 °C·min−1. Kinetic parameters under non-isothermal condition are calculated using FWO (Flynn-Wall-Ozawa method) and KAS (Kissinger-Akahira-Sunose) model free methods. From the results obtained, it was revealed that when the conversion level (α) fluctuates between 0.1 and 0.55, the average activation energy were 154 and 145 KJ/mol for FWO and KAS methods, respectively. Then, it decreases drastically with α ≥ 0.6, reflecting the kinetic complexity of the combustion process characterized by a faster reaction caused by the intense devolatilization stage. Overall, the results highlight the potential use of argan shell as a biomass product for thermal conversion through combustion.

Barium calcium titanate solid solution: Non-isothermal kinetic analysis of Ca2+ incorporation into BaTiO3

This paper investigates the non-isothermal kinetic analysis of Ca2+ incorporation into BaTiO3 in Ba0.85Ca0.15TiO3 (BCT15) lead-free ferroelectric material, prepared via the solid-state reaction method, using differential scanning calorimetry (DSC) technique at multiple heating rates. The X-ray diffraction technique (XRD) has demonstrated the formation of pure cubic BaTiO3 phase when the BCT15 precursors were calcined at 1000 °C. Incorporation kinetics was analyzed by Freidman, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) isoconversional methods. The results indicate that the incorporation process was carried out through a single-step. The kinetic parameters were determined through the combined kinetic analysis method. It was established that the incorporation mechanism follow perfectly the Avrami-Erofeev (A3) kinetic model. The values of activation energy (Ea) and preexponential factor (A) were found to be 388 kJ/mol and 4.1 × 1017 min−1, respectively. The obtained kinetic parameters are critical to better understand and optimize the incorporation process for BCT15 preparation with suitable and promising properties.

Comparative Thermogravimetric Assessment on the Combustion of Coal, Microalgae Biomass and Their Blend

In this work, thermogravimetric analysis (TGA), differential thermogravimetry (DTG), and differential scanning calorimetric (DSC) were used to assess the combustion of microalgae biomass, a bituminous coal, and their blend. Furthermore, different correlations were tested for estimating the high heating value of microalgae biomass and coal, with both materials possessing similar values. TGA evidenced differences between the combustion of the studied fuels, but no relevant interaction occurred during their co-combustion, as shown by the DTG and DSC curves. These curves also indicated that the combustion of the blend mostly resembled that of coal in terms of weight loss and heat release. Moreover, non-isothermal kinetic analysis revealed that the apparent activation energies corresponding to the combustion of the blend and coal were quite close. Overall, the obtained results indicated that co-combustion with coal might be a feasible waste to energy management option for the valorization of microalgae biomass resulting from wastewater treatment.

Kinetic analysis of sinter-crystallization of mullite and cristobalite from kaolinite

A non-isothermal kinetic analysis of high-temperature processes occurring during thermal treatment of kaolinite is performed by the thermodilatometric analysis. The measurements are carried out using the horizontal push-rod dilatometer on compact samples with heating rates from 1 to 10 °C min–1 in dynamic N2 atmosphere. For the parameterization of thermodynamically stable phases such as mullite and cristobalite, the Kissinger method is used. The obtained value of apparent activation energy for sinter-crystallization of mullite is (726 ± 9) kJ mol–1 and the thickening of long mullite needles is determined as a mechanism of this process. The results also show that the apparent activation energy for sinter-crystallization of cristobalite is (565 ± 38) kJ mol–1.

Determining the quasi-real-time change in the glass transition temperature of a thermoset resin under cure using fast scanning calorimetry

A fast scanning calorimetric method to obtain the time and temperature dependence of the glass transition temperature (Tg) under a chemical reaction was reported. The cross-linking reaction of an epoxy-amine system is perfectly suppressed by an ultrafast temperature scan. By inserting the quenching and fast heating measurements in an isothermal or non-isothermal process, the quasi-real-time change in Tg during cure can also be obtained from a single piece of neat resin. In addition, the relation between Tg and conversion is obtained in a full range of conversion by combining with the conventional analysis of isothermal or non-isothermal reaction kinetics using differential scanning calorimetry or temperature modulated differential scanning calorimetry.