Invariant Kinetic Parameters Method Research Articles

Thermal Degradation Kinetics of Completely Biodegradable and Biobased PLA/PHB Blends

In this article, the influence of blend ratio of plasticized poly(lactic acid)/poly(3-hydroxybutyrate) (PLA/PHB) and chitin nanoparticles (ChNP) nanocomposites on the thermal stability and degradation kinetics has been investigated using thermogravimetric analysis under nitrogen atmosphere at four different heating rates (i.e., 5, 15, 30, and 50°C/min). The derivative thermogravimetric curves have indicated single-step and two-step degradation processes for individual polymers and polymer blends, respectively. It suggests immiscibility or partial miscibility between the polymers. The degradation kinetic parameters were studied over the 30 – 500°C temperature range by using the Kissinger-Akahira-Sunose (KAS) and Vyazovkin isoconversional methods under non-isothermal conditions. The average values of the effective activation energies of the deconvoluted PHB and PLA peaks in the PLA:PHB 70:30 (B73) blends were higher than those of the pure polymers, while in the PLA:PHB 60:40 (B64) blends were lower, which was attributed to the different morphology of the blends. Furthermore, the effective activation energy of the nanocomposites diminished due to the catalyzing effect of the chitin nanoparticles. By means of the invariant kinetic parameters (IKP) method, it was possible to evaluate the preexponential factor and the activation energy of the blends without any assumptions concerning kinetic model. The invariant activation energies calculated were in accordance with the ones estimated by the isoconversional methods. Finally, Avrami-Erofeev function was determined as the most probable kinetic mechanism of the systems studied by applying the Sestak-Berggren equation.

STUDY OF THERMAL DECOMPOSITION OF THE COPOLYMER BASED ON POLYETHYLENE GLYCOL FUMARATE WITH METHACRYLIC ACID

Thermal performance of copolymer based on polyethylene glycol fumarate and methacrylic acid in a dynamic mode, in an inert nitrogen environment are considered in the present work. Kinetic evaluation of thermal decomposition process was conducted using three different data processing methods (Friedman, Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose). Utilizing a mixed-method approach kinetic triplets Eа, A, g(a) were received. The received kinetic parameters were used to calculate the thermodynamic characteristics of Gibbs energy (∆G), enthalpy (∆H) and entropy of activation (∆S). Copolymer thermal gravimetric analysis (TGA) and differential thermogravimetric analysis (DTA) curves were studied under nitrogen environment using a heating rate of 2,5, 5, 10 or 20°C/min. The method of Invariant Kinetic Parameters was used to identify the reaction model and pre-exponential factor. The main phase of copolymer decomposition was set, which occurred within a narrow temperature interval and is evidenced by the spike on the differential curve. Values for 13 reaction models were received. Utilised methods resulted in a proper energy activation alignment within 223-229 kJ mol-1. Design and experimental data provided close values. TGA and DTA curve analysis has shown a sufficient thermal stability of these copolymers under the nitrogen environment.

Kinetic parameters of thermal destruction of the copolymer of polyethylene glycol fumarate with acrylic acid in inert medium

Thermal decomposition of the copolymer of polyethylene glycol fumarate with acrylic acid (p-EGF:AA) of two different compositions synthesized earlier was studied in the present work. TG and DTG curves prove that decomposition takes place in several stages. According to thermogravimetric curves it has been found out that for the copolymer with higher content of acrylic acid the decomposition of the copolymer’s sample is started at higher temperatures. It has been shown the shift of the temperature of decomposition’s start to the higher area with the increase of heating rate which is necessary for the detorsion of macromolecular coil. Experimental data processed using graphical methods of Kissinger–Akahira–Sunose and Friedman allowed us to calculate the activation energy of the thermal decomposition process. It has been established that the copolymer with the composition of 21.03:78.97 mass.% has lower meaning of activation energy than the one with the composition of 68.96:31.04 mass.%. As a result of calculation one can see that the meanings found out using these methods depend slightly on conversion. Using Achar-Brindley-Sharp method and the method of invariant kinetic parameters the kinetic triplet of the decomposition process has been found which was used to build the calculated curve. The dependences of g(α) on α using these parameters showed a satisfactory agreement of calculated curves with the experimental ones. One can conclude that the decomposition process of the copolymer of polyethylene glycol fumarate with acrylic acid is well described with of D3 (three-dimensional diffusion) model.

Chloramphenicol loaded polylactide melt electrospun scaffolds for biomedical applications

Melt electrospinning of polylactide (PLA) loaded with chloramphenicol (CAM) has been performed and characteristics of fibers, physical properties of scaffolds, CAM release behavior, antibacterial properties and biocompatibility have been evaluated. The interest of CAM loaded samples is nowadays enhanced for biomedical applications since this antibiotic has been demonstrated to be efficient for the treatment of cancer. Melt electrospinning has been selected as an ideal preparation process because it avoids the use of toxic solvents which are harmful to the environment and could be problematic for biomedical applications. The electrospinning process rendered fibers with a relatively large diameter (between 20 μm and 40 μm depending on the load) and minimum polymer degradation. Characteristics of melt electrospun scaffolds were also compared with those prepared by solution electrospinning. Differences consisted in a more sustained release and a higher biocompatibility for the melt processed samples. Bactericide effect was evaluated as an evidence of the maintenance of the CAM bioactivity after melt processing at high temperature and the slower release caused by the relatively high diameter of the constitutive fibers. Since pure CAM showed thermal degradation at temperatures relatively close to the PLA melting temperature, a complete analysis of the degradation process of pure CAM as well as of PLA samples loaded with CAM was performed. The Invariant Kinetic Parameters method allowed determining an initial decomposition step that followed an autoaccelatory Avrami model, and then an autocatalytic decomposition reaction took place for conversions higher than 50%. Dispersion in the PLA matrix enhances the thermal stability of the antibiotic, with an onset temperature of degradation that was higher by 16 °C in the melt-electrospun fibers than in the liquid state of pure CAM.

Non-isothermal kinetic analysis of the oxidation of Al–50Mg powder mixture

In this research, non-isothermal kinetic analysis of the oxidation process of Al–50Mg (wt%) powder mixture was performed by employing differential scanning calorimetry and thermogravimetry analysis techniques. The research findings revealed that oxidation of this powder mixture was completed at lower temperatures compared to that of pure aluminum powder; and furthermore, it enjoyed a higher thermal efficiency than that of pure magnesium powder. Oxidation of this mixture powder led to the formation of magnesium oxide (MgO) and spinel phase (MgAl2O4) during the first and second oxidation steps, respectively. Moreover, to calculate the activation energy (E) over a wide range of degree of conversion (α), two isoconversional methods, including Starink and Friedman methods were used. Activation energies decreased as the reaction progressed at both stages, indicating that these stages were multi-step reactions. Furthermore, the invariant kinetic parameter method and fitting model were used to determine the empirical kinetic triplets (i.e. E, pre-exponential factor (A) and reaction model (g(α))). The obtained results showed that the first stage was controlled by the second order Avrami-Erofeev mechanism (A2), two-dimensional phase boundary reaction (R2), and two-dimensional diffusion (D2) models at heating rates of 5, 10, and 30 °C/min. The second stage was controlled by the third order Avrami-Erofeev mechanism (A3) and A2 at heating rates of 5 and 10 °C/min, while for a heating rate of 30 °C/min, the mechanism of reaction changes from A3 to A2.

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).

Different approaches to the kinetic analysis of thermal degradation of poly(ethylene oxide)

Kinetic analysis of the non-isothermal degradation of poly(ethylene oxide) has been performed using isoconversional model-free methods, model-fitting methods, invariant kinetic parameters method and Netzsch Thermokinetics software in order to establish whether different kinetic approaches yield consistent kinetic parameters. It has been shown that these approaches yield consistent kinetic parameters and can be combined in such a way as to enhance the reliability and quality of each other and consequently the overall kinetic analysis. The most probable kinetic parameters for the non-isothermal degradation of poly(ethylene oxide) have been determined. These kinetic parameters have been used for prediction of isothermal kinetics of poly(ethylene oxide), and their potential for reliable prediction has been noticed.

Non-isothermal kinetic analysis of nano-crystallization process in (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy

In this work, non-isothermal kinetic analysis of the crystallization process was performed on a (Fe41Co7Cr15Mo14Y2C15)94B6 amorphous alloy heated by DSC at various heating rates (5, 10, and 20°C/min) up to 1200°C. The research findings revealed that three crystalline phases including Fe23 (B, C) 6, Fe3Mo3C, and Mo3Co3C were formed during the crystallization process; furthermore, the presence of nano-crystalline grains was confirmed by FE-SEM. Two isoconversional methods including Starink, and Friedman (FR) were used to determine the variation of activation energy with a (Eα). Moreover, the invariant kinetic parameters (IKP) method and free model were used to calculate the empirical kinetic triplets (E, A, and g(α)). The best reaction models, chosen by fitting methods to describe the mechanism of four crystallization steps were A2, A3/2, A2, and A4, respectively.

Thermokinetic study of CODA azoic liquid crystal and thin films deposition by matrix-assisted pulsed laser evaporation

Azoic dyes are compounds of interest from the point of view of their potential applications, such as the use of liquid crystals in optoelectronic and organic electroluminescent devices, or may be employed as template matrices for producing high-aspect ratio inorganic nanomaterials. Herein, 4-[(4-chlorobenzyl)oxy]-3,4′-dichloroazobenzene azoic dye, known as CODA, is selected as a choice compound among such materials due to its liquid crystalline properties and may be further used as nanostructured material in various applications. Thermokinetic study of CODA azoic dye thermal decomposition in air flow atmosphere was performed by employing thermogravimetric data; the kinetic parameters of the two decomposition steps were obtained under non-isothermal linear regimes, by means of multi-heating rates methods. Differential and integral “model-free” kinetic methods like Friedmann, Kissinger–Akahira–Sunose and Ortega, the invariant kinetic parameters method and the Perez-Maqueda et al. criterion (by Coats–Redfern and differential equations) were used. The kinetic study reveals very different behaviour related to the two decomposition steps of CODA, with complex processes composed of more than one kinetic mechanism for each of those, as indicated also by the Gotor et al. master plot method. Modern devices incorporating such materials tend to use them as thin films due to their specific properties; the CODA thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG laser working at the wavelength of 266 nm. The preservation of the CODA compound after the transfer on the substrates was confirmed by Fourier transform infrared spectroscopy, while the morphology and topography of the deposited materials and of the thin film surfaces were investigated by atomic force microscopy and optical microscopy.

The Degradation Kinetics of EVA‐Clay Nanocomposites

SummaryThe influence of organoclay content on the thermal degradation kinetics of EVA‐clay nanocomposites was studied using thermal gravimetric analysis (TGA) coupled with Fourier transfer infrared (FTIR) spectroscopy. The mass ratio of vinyl acetate (VA) to ethylene (E) was varied between 9:91 and 28:72 and the clay loading between 2.5 and 7.5 wt%. Samples were heated under an inert atmosphere up to 700°C, at which point all organic components were volatized. The mass loss curves revealed two‐stage mass‐loss events; the first due to scission of the acetate functional group and the second due to the break‐down of the carbon backbone. The presence of organoclay in the polymer resulted in initiation of the mass‐loss events at lower temperatures. This was more pronounced for the first mass‐loss event. Kinetic analysis of the mass‐loss events was conducted using the method of invariant kinetic parameters (MIKP). These showed that the latter mass loss curve was more likely to fit a diffusion based kinetic model when nano‐clay was present possibly indicating the influence of a char layer on the degradation processes. The effects of the presence of nanoclay on the kinetic parameters of the mass‐loss events are reported.

Kinetic analysis of the non-isothermal degradation of high-density polyethylene filled with multi-wall carbon nanotubes

The thermal stability and non-isothermal degradation kinetics of high-density polyethylene (HDPE)/multi-wall carbon nanotube (MWNT) nanocomposites were studied by thermogravimetric and derivative thermogravimetric analyses using multiple heating rates (5, 10, 15, 20 °C min−1) under nitrogen gas atmosphere. A series of HDPE/MWNT composites of various vol% concentration of nanotubes were fabricated using melt mixing process. The morphology and nanostructure of prepared nanocomposites was examined by field emission scanning electron microscopy (FESEM). The kinetic parameters were evaluated using multiple heating rate-based four different “model-free” methods (viz., Kissinger, Friedman, Flynn–Wall–Ozawa, and Kissinger–Akhaira–Sunose) and single heating rate-based one “model-fitting” method (Tang approach), and 18 kinetic model equations were used. FESEM images confirmed that the dispersion and distribution of the MWNTs in the HDPE polymer matrix was homogeneous. The kinetic parameters [E a, A, n, and k (Arrhenius constant at 600 °C)] for all the samples studied were calculated. The highest values of E a, A, and n were found for the composites filled with 0.25 vol% MWNTs. For various vol% concentrations of HDPE/MWNT nanocomposites, the dependence of the apparent activation energy (E a) on fractional conversion (α) showed two-stage decomposition process, within the conversion window (0.05 ≤ α ≤ 0.95). Invariant kinetic parameter method (IKP) has been employed for all investigated nanocomposite system. A linear dependence between ln(A i) and E a,i was observed, making use of so-called compensation effect. Using IKP method, the values of the artificial isokinetic temperature “T iso” and artificial isokinetic rate constant “k iso” have been also estimated for all heating rates and found increases with increase in the heating rate (β). In addition, the dependence of lnA α on α was evaluated, and it was found that the lnA α revealed the same dependence on α as the apparent activation energies (E a) versus α plot shown. In order to estimate the kinetic degradation mechanism(s) of investigated system, Criado method was employed. The thermal decomposition kinetics of HDPE/MWNT composites were found to be best described by kinetic equations of n th order (AnFn and Dn mechanisms) to be more precise A1F1 → D1 → D2 kinetic models.

Synthesis and thermal kinetic study of phosphoric acid, P, P′-1, 4-phenylene P, P, P′, P′-tetraphenyl ester

A phosphorous flame retardant of phosphoric acid, P, P′-1, 4-phenylene P, P, P′, P′-tetraphenyl ester (PAPTE) was synthesized by diphenyl chlorophosphate and hydroquinone. The structural features of PAPTE were investigated with mass spectrometry, infrared spectroscopy, X-ray powder diffraction and nuclear magnetic resonance methods. The thermal behavior of PAPTE was carried out with thermogravimetric (TG) analysis instruments. The kinetic parameters, including the activation energy and pre-exponential factor of the decomposition process for the title compound, were calculated through the Friedman method, the Kissinger–Akahira–Sunose method and the Flynn–Wall–Ozawa method, while the thermal decomposition mechanism was also studied with the invariant kinetic parameters (IKP) method based on a set of TG data obtained at different heating rates. It was shown that the activation energies calculated for the decomposition reaction by different methods were found to be consistent with the conversion functions calculated by means of the IKP method which depend on a set of kinetic methods.

Green chemical incorporation of silicon into polyoxoanions of molybdenum: characterization, thermal kinetics study and their photocatalytic water splitting activity

Cetylpyridinium silicomolybdate (CSM) nanorods were successfully synthesized by applying green chemistry principles using sodium molybdate and a structure directing cationic surfactant, cetyl pyridinium chloride (CPC) at room temperature. The composition and morphology of the nanorods were established by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and inductively coupled plasma atomic emission spectroscopic (ICP-AES) techniques. The thermal decomposition kinetics of CSM nanorods were investigated by a non-isothermal thermogravimetric analyzer at various heating rates. The thermal decomposition of CSM occurred in two stages. The activation energies of the first and second stages of thermal decomposition for all heating rates have been estimated using the iso-conventional methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) and the results are found to be in good agreement with each other. The invariant kinetic parameter (IKP) method and master plot method were also used to evaluate the kinetic parameters and mechanism for the thermal decomposition of CSM. The photocatalytic water oxidation mechanism using the CSM catalyst in the presence of platinum (Pt) co-catalyst enhances the H2 evolution and was found to be 1.946 mmol g−1 h−1.

Characterization, non-isothermal decomposition kinetics and photocatalytic water splitting of green chemically synthesized polyoxoanions of molybdenum containing phosphorus as hetero atom

In here, the green synthesis and thermal characterization of a novel polyoxoanions of molybdenum containing phosphorus as hetero atom are reported. The composition and morphology of the nanorods were established by fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and inductively coupled plasma atomic emission spectroscopic (ICP-AES) techniques. Thermal properties of the nanoparticles were investigated by non-isothermal analysis under nitrogen atmosphere. The values activation energy of each stage of thermal decomposition for all heating rates was calculated by Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunnose (KAS) methods. Invariant kinetic parameter (IKP) method and master plot method were also used to evaluate the kinetic parameters and mechanism for the thermal decomposition of cetylpyridinium phosphomolybdate (CPM). Photocatalytic water oxidation mechanism using CPM catalyst in the presence of platinum (Pt) co-catalyst enhances the H2 evolution and was found to be 1.514mmol/g/h.

Non-isothermal kinetic analysis on the phase transformations of Fe–Co–V alloy

In this study, occurrence of different phase transformations was investigated in a FeCo-7wt% V alloy upon heating to 1200°C by the dilatometry method at different heating rates (5, 10, and 15°Cmin−1). It was found that four phase transformations (including B2-type atomic ordering in α phase, first stage of polymorphic transformation (α→αr+γ), ordering to disordering, and second stage of polymorphic transformation (αr→γ) occur in this alloy up to 1200°C. Two isoconversional methods, as Starink and Friedman, were used to determine variation of the activation energy with temperature, E(T). Moreover, the empirical kinetic triplets (E, A, and g(α)) were calculated by the invariant kinetic parameters (IKP) method and fitting model.

The kinetic analysis of non-isothermal carisoprodol reaction in nitrogen atmosphere using the invariant kinetic parameters method

The non-isothermal kinetic parameters corresponding to the thermal decomposition of carisoprodol under nitrogen atmosphere was investigated at four different heating rates 5, 10, 15 and 20 °C/min. The activation energy was determined using three linear isoconversional methods, Friedman, Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose. Results showed good agreement with each other. Invariant kinetic parameters (IKP) method was applied in the conversion range of 0.2 ≤ α ≤ 0.8 for the determination of the kinetic triplet. E inv = 95.81 kJ/mol, A inv = 2.275×10 7 1/min and the decomposition mechanism corresponds to nucleation and growth, following the Avrami-Erofeev model, A1.5, as the kinetic model. The Perez-Maqueda et al. criterion associated with the independence of activation parameters on the heating rate (by means of Coats-Redfern and Flynn-Wall equation) confirmed the model.

Green synthesis of novel polyoxoanions of tungsten containing phosphorus as a heteroatom: characterization, non-isothermal decomposition kinetics and photocatalytic activity

Synthesis of cetylpyridinium phosphotungstate (CPW) nanospheres was carried out by using sodium tungstate and a structure directing cationic surfactant, cetyl pyridinium chloride (CPC), at room temperature by applying green chemistry principles. The composition and morphology of the nanospheres were established by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and inductively coupled plasma atomic emission spectroscopic (ICP-AES) techniques. Thermal properties of the nanoparticles were investigated by non-isothermal analysis under a nitrogen atmosphere at four different heating rates 10, 15, 20 and 25 °C min−1. The thermal decomposition of CPW occurred in two stages. The activation energy values at each stage of thermal decomposition for all heating rates were calculated by Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunnose (KAS) methods. The invariant kinetic parameter (IKP) method and the master plot method were also used to evaluate the kinetic parameters and mechanism for the thermal decomposition of CPW. The photocatalytic water oxidation mechanism using a CPW catalyst in the presence of a platinum (Pt) co-catalyst enhances the H2 evolution, which was found to be 2.0 mmol g−1 h−1.

Kinetic analysis of nicotine desorption from silicon dioxide under non-isothermal conditions

Abstract The non-isothermal kinetics of nicotine desorption from precipitated silicon dioxide was investigated. The non-isothermal thermogravimetric curves of nicotine desorption at different heating rates (β = 5, 10 and 20 K/min) were recorded. The kinetics model of non-isothermal kinetics of nicotine desorption was determined by using the model-fitting and master-plot methods. It was found that non-isothermal nicotine desorption can mathematically describe by the theoretical kinetics model of phase – boundary controlled reaction (contracting volume, i.e., three dimensional shape) – R3. By applying the method of Kissinger and method of invariant kinetic parameters the values of kinetic parameters were determined. It was established that both applied method give almost identical kinetic parameters regardless their theoretical limitations. The dependence of activation energy on the degree of nicotine desorption was determined using the KAS method. It was found that the value of activation energy is independent on the degree of nicotine desorption. The effect of heating mode on the kinetic of nicotine desorption was analyzed. It was established that the type of heating mode (isothermal and non-isothermal) does not influence the mechanism of the formation of the activation complex nor the kinetics model of desorption. The increase in the values of kinetic parameters obtained for non-isothermal heating in comparison to the isothermal ones are explained with the Larson's model of selective transfer of energy.

Non-isothermal kinetics of phase transformations in magnetron sputtered alumina films with metastable structure

The paper reports on non-isothermal kinetics of transformation processes in magnetron sputtered alumina thin films with an amorphous and γ-phase structure leading ultimately to the formation of the thermodynamically stable α-Al2O3 phase. Phase transformation sequences in the alumina films were investigated using differential scanning calorimetry (DSC) at four different heating rates (10, 20, 30, 40°C/min). Three isoconversional methods (Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO) and Friedman (FR) method) as well as the invariant kinetic parameters (IKP) method were used to determine the activation energies for transformation processes. Moreover, the pre-exponential factors were determined using the IKP method. The kinetic models of the transformation processes were determined using the Málek method. It was found that the as-deposited structure of alumina films affects kinetics of the transformation processes. The film with the amorphous as-deposited structure heated at 40°C/min transforms to the crystalline γ phase at a temperature of ∼930°C (Ea,IKP=463±10kJ/mol) and subsequently to the crystalline α phase at a temperature of ∼1200°C (Ea,IKP=589±10kJ/mol). The film with the crystalline γ-phase structure heated at 40°C/min is thermally stable up to ∼1100°C and transforms to the crystalline α phase (Ea,IKP=511±16kJ/mol) at a temperature of ∼1195°C. The empirical two-parameter Šesták–Berggren kinetic model was found to be the most adequate one to describe all transformation processes in magnetron sputtered alumina films.

ChemInform Abstract: Comprehensive Method Based on Model Free Method and IKP Method for Evaluating Kinetic Parameters of Solid State Reactions

AbstractReview: 77 refs.