Advanced Isoconversional Method Research Articles

Thermal degradation of polytetrafluoroethylene, modified polytetrafluoroethylene, and their nanocomposites with boron nitride nanobarbs: Lifetime predictions and kinetic analysis

AbstractFlexible polymeric materials including dielectric thermal interface materials (TIMs) used in integrated circuits and other high frequency applications are exposed to extreme thermal and electrical conditions during their service life. Insight into the in‐use thermal stability and material lifetime is valuable to maintaining performance durability and preventing premature failure in actual end use. Herein, the thermal stability of polytetrafluoroethylene (PTFE), modified PTFE and their nanocomposites with recent generation boron nitride nanobarbs (BNNBs) was investigated based on lifetime prediction from thermogravimetric analysis and tensile strength deterioration of heat‐aged samples. Additionally, thermal degradation kinetics and mechanism was investigated using the model‐free advanced isoconversional method based on changing activation energy. The result shows that BNNB extends the lifetime of the PTFE by an order of magnitude. The degradation mechanism proposed from TGA‐MS result is supported by the multistep degradation mechanism identified in the kinetic computation. These results are valuable for predicting materials' in‐use lifetime to avoid premature failure.

Effect of the accelerated aging process on the thermal decomposition of LiAlH4-based composite solid propellants

In the present work, a study was carried out on the effect of the accelerated aging process on the thermal decomposition of two composite solid propellants based on ammonium perchlorate (AP) and hydroxy‑terminated polybutadiene (HTPB). The first one (CP1) was enriched with aluminum (Al) powders, while the second (CP2) contained a mixture of aluminum and lithium alanate (LiAlH4) as a high-energy fuel additive. The thermal properties of the investigated propellant samples were determined using differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. The obtained results clearly demonstrated the effect of the aging process on the thermal degradation of the aged samples compared to the unaged ones, by shifting the temperature peaks of their main decomposition step to lower temperatures with a decrease in their DSC heat release. In addition, the residual unburnt propellant was increased, particularly for the complex metal hydride-based propellant. Kinetic modeling of the main thermal degradation phase, applying two advanced isoconversional methods, revealed a significant decrease in activation energy for the aged samples. Furthermore, the three-dimensional diffusion model involved during the investigated decomposition phase of the unaged samples was changed to a random nucleation model after 60 days of aging time.

Multistep kinetic analysis of additive-enhanced plastic degradation

In the realm of non-isothermal degradation kinetics, the utilization of multi-heating rate data has unveiled a fascinating distributed apparent activation energy (Eα) profile when employing isoconversional methods. The advanced isoconversional method (AIC) emerges as a reliable tool, offering Eα values that evolve as chemical reactions progresses. This phenomenon finds its roots in the complex solid-state degradation of plastics, where long-chain hydrocarbons undergo intricate transformations into smaller components through a web of parallel and sequential reactions under the influence of heat. To comprehensively characterize this multifaceted kinetic process, variable pre-exponential factor (A) values were calculated, considering all available heating rate data, in conjunction with the isoconversional principle. These factors complement the changing Eα values, providing crucial insights into the evolving material transformations throughout the reaction. Remarkably, our investigation revealed that in the initial degradation stage, centered around the breakdown of Brominated Flame Retardant (BFR), the reaction follows a contracting spherical model (R3). Transitioning to the subsequent stage, the polymer material undergoes degradation following the diffusion model D4. The incorporation of the isoconversional principle and Criados' masterplot technique effectively facilitates the precise determination of all three kinetic parameters. The process layout we present holds considerable promise for advancing the understanding and control of complex kinetic phenomena.

Isoconversional analysis of thermally stimulated events on pillared cyanometallates

We report the analysis, by the advanced isoconversional method of Vyazovkin, of the thermal events of pyridine molecule loss and spin crossover occurring in the two-dimensional compounds of molecular formulas: Fe(Pyridine)2[Fe(CN)5NO] and Fe(Pyridine)2[Ni(CN)4]. Experimental thermogravimetric data were used to analyze the thermal evolution of pyridine molecules in both compounds. Calorimetry was used to study the spin crossover in Fe(Pyridine)2[Ni(CN)4], while SQUID magnetometric for Fe(Pyridine)2[Fe(CN)5NO]. The analysis of the effective activation energy of the pyridine loss process suggested that, in both compounds, the thermal evolution of these molecules is highly influenced by the particle size due to the occurrence of a structural transformation of the gate-opening type. The effective activation energy of the latter technique applied to compound Fe(Pyridine)2[Ni(CN)4] showed a behavior very similar to that expected for a solid–solid transition that occurs by the nucleation mechanism. The results obtained shed light on the way towards the application of the studied compounds in sensors and switches devises for molecular detection.

Insight into the kinetics and thermodynamic analyses of co-pyrolysis using advanced isoconversional method and thermogravimetric analysis: A multi-model study of optimization for enhanced fuel properties

Waste management is quite challenging and it has become a major concern across the globe. The most common wastes are in the form of polymers or plastics that are composed of a mixture of various commodity plastics like PE, PP, PVC, HDPE, LDPE, etc. Pyrolysis is found to be a promising technology for managing wastes as well as converting them into valuable hydrocarbons. The present study investigated to discern the synergism in thermal degradation behavior and to identify the interaction between polymer molecules in co-pyrolysis. The advanced isoconversional model was employed for trustworthy estimation of activation energy as the thermal effects on a reaction deviate the temperature of a sample from the set heating value. The results were also compared with the model-free methods to understand the synergism, reactivity, and thermodynamic system with the progress of the conversion. The activation energy was found to be lowest when the polymers were used in a certain proportion and the synergy effect was more significant when PP content was > 40 % in the mixture. The positive synergetic effect could be attributed to the intermolecular hydrogen transfer from a less stable polymer to a free radical de-propagating chain of the other polymer during thermal degradation. The complex governing thermochemical reaction mechanism was determined using the Criado master plot and the analysis revealed that with increasing PP content in a binary mixture the reaction mechanism shifted from R2 to R3. The high regression coefficient value (R2 > 0.99) in the regenerated TGA profiles signified a good agreement between the theoretical and experimental results. While thermodynamic analysis showed that the process was endothermic and non-spontaneous in nature. Moreover, the radical reaction during co-pyrolysis of polymers enhances intermolecular hydrogen transfer resulting in the formation of iso-alkane and iso-alkene along with secondary radicals, which undergo β-scission to form alkenes/dienes and short primary radicals. As a result, the enhanced intermolecular hydrogen transfer phenomenon initiates the co-pyrolysis reaction at a relatively lower activation energy compared to individual polymer molecules.

Pyrolysis and co-pyrolysis of Egyptian olive pomace, sawdust, and their blends: Thermal decomposition, kinetics, synergistic effect, and thermodynamic analysis

The pyrolysis and co-pyrolysis kinetics of two Egyptian olive-pomace (Kroneiki and Shamlali), wood dust, and their blends were investigated by advanced isoconversional model-free methods (Vyazovkin and Senum-Yang) and model-fitting methods (Coats and Redfern integral method) using different integrated reaction mechanisms g(α) through TGA/DTG, and DTA techniques. Master Plot's method was applied to determine the best reaction mechanisms for the pyrolysis of the tested materials. The synergistic effect of co-pyrolysis on kinetics and the role of biomass were examined. The average values of activation energy estimated from VYA and SY kinetic methods, respectively, for KROP, SHOP, FSSD, Blend (1), and Blend (2) were 90.57 and 85.67 kJ/mol, 70.05 and 65.26 kJ/mol, 131.66 and 126.71 kJ/mol, 66.73 and 62.09 kJ/mol, and 113.12 and 108.21 kJ/mol. The co-pyrolysis of KROP, SHOP, and FSSD at a heating rate of 10 °C/min showed the best synergistic pyrolysis performance. The diffusional reaction mechanisms are the most likely reactions to describe the pyrolysis process of the first conversion stage (α = 0.1–0.5), while the reaction mechanism C8 and the reaction order model (F4) are the most likely reactions to describe the second stage (α = 0.5–0.9) pyrolysis process. The higher ΔH and ΔS values for the FSSD and Blend (2) signify that these materials consumed more energy during the pyrolysis process, while the lower ΔH and ΔS values for the KROP, SHOP, and Blend (1) showed the opposite. A blending ratio of 50% KROP, 25% SHOP, and 25% FSSD showed the best performance at a heating rate of 10 °C/min. The obtained kinetics parameters and the solution of the master plots method were validated by solving the Coats and Redfern integral method based on the reaction mechanism function g(α) that showed the best fit in the master plots method.

A Review of Degradation and Life Prediction of Polyethylene

After around 50 years of development, the key substance known as polyethylene has been extremely influential in a variety of industries. This paper investigates how polyethylene materials have been used in the domains of water, packaging, and medicine to advance contemporary society in order to comprehend the physical and chemical alterations that polyethylene undergoes after being subjected to long-term environmental variables (e.g., temperature, light, pressure, microbiological factors, etc.). For the safe operation of polyethylene materials, it has always been of the utmost importance to evaluate polyethylene’s service life effectively. This paper reviews some of the most common literature journals on the influence of environmental factors on the degradation process of polyethylene materials and describes methods for predicting the lifetime of degradable polyethylene materials using accelerated aging tests. The Arrhenius equation, the Ozawa–Flynn–Wall (OFW) method, the Friedman method, the Coats–Redfern method, the Kissinger method and Kissinger–Akahira–Sunose (KAS) method, Augis and Bennett’s method, and Advanced Isoconversional methods are all discussed, as well as the future development of polyethylene.

Validity of isothermal kinetic prediction by advanced isoconversional method

Isothermal prediction based on kinetic parameters from advanced isoconversional method (NLN) has been successfully used in various materials. However, the validity of the method is sometimes suspected because of some depressing predictions. In this paper, we set a single-step solid state reaction and a multi-step solid state reaction to simulate and predict. The effects of set temperature and composition of heating rate group on the isothermal prediction are evaluated. For the single-step reaction, all the relative errors of single-step reaction are less than 10%. Therefore, the method provides accurate enough isothermal predictions at different set temperatures and heating rate groups. As for the multi-step reaction, the accuracy of prediction varies with the set temperature and the composition of heating rate group. The reason for the failure of multi-step reaction prediction is the inconsistency in the concept of isothermal and nonisothermal isoconversional activation energy.

The Kinetics of Formation of Microporous Polytriazine in Diphenyl Sulfone.

This study highlights the value of nonisothermal kinetic methods in selecting temperature conditions for the isothermal preparation of microporous polymeric materials. A dicyanate ester is synthesized and the kinetics of its polymerization in diphenyl sulfone are studied by calorimetry under nonisothermal conditions. The kinetics are analyzed by a model-based approach, using the Kamal model, as well as by a model-free approach, using an advanced isoconversional method. Both approaches correctly predict the time to completion of polymerization at a given temperature. The material prepared independently at the predicted temperature is characterized by electron microscopy and CO2 adsorption measurements and is confirmed to possess a microporous structure with a multimodal distribution of micropores with two major maxima at ~0.5 and 0.8 nm.

Novel adamantane-based dicyanate ester: Synthesis, polymerization kinetics, and thermal properties of resulting polymer

A new adamantane-based dicyanate ester has been synthesized. The kinetics of its thermal polymerization is studied by means of conventional and temperature-modulated differential scanning calorimetry. The kinetics is analyzed comprehensively by a combination of an advanced isoconversional and model-fitting method. Polymerization proceeds via transition from a kinetic- to diffusion-control regime, which becomes operative at the later stages of the process. The kinetically-controlled regime manifests itself as a quasi-one-step auto-catalytic reaction. A contribution of diffusion to the overall kinetic is accounted for by means of the Fournier model. The polymerization product possesses excellent thermal properties (the glass transition temperature of ∼370 °C and 5% mass loss temperature of ∼480 °C), which makes it a promising candidate for application in hot-section components for aerospace and military industry.

Synthesis of macromolecular brush and its thermal degradation studies

The di-1,2-propanediol ester of fumaric acid (Diol) is synthesized and polymerized to yield the macromolecular brush (PDiol). The structure of monomers and their polymer is confirmed by Fourier transform infrared spectroscopy (FTIR) studies. The PDiol material shows the number average molecular weight (Mn ) as 951 g/mol, weight average molecular weight (Mw ) as 4,378 g/mol, and a polydispersity index (PDI) of 4.6. The hydroxyl value for PDiol is 471 (mg KOH/g). The thermal degradation property of the brush is investigated using thermogravimetric analysis (TGA). The cyclic intra and inter loops are formed while annealing at a temperature of around 200 °C. Using the TG curves recorded at different heating rates and by applying advanced isoconversional methods by model-free kinetics, the apparent activation energy for the thermal degradation (Ea-D) at different reaction extents (α) are calculated and discussed. Advanced methods are also used to refine the apparent activation energy data. The Ea-D values for PDiol range from 100 to 155 kJ/mol. For a lifetime of 20,000 h, the 20% degraded PDiol can withstand a temperature of 39 °C.

Graphene oxide and silane-modified graphene oxide/unsaturated polyester resin nanocomposites: A comparative cure kinetic and diffusion study

The curing behavior of pure unsaturated polyester resin (Neat UP), resin containing 0.5 wt% graphene oxide (UPGO) and resin containing 0.5 wt% graphene oxide modified by silane agent (UPMGO) was studied. The kinetic parameters of the systems were calculated using the advanced isoconversional method. The cure index was used to evaluate the curing quality of the systems. The results showed that the functional groups on the surfaces of graphene oxide and modified graphene oxide caused significant changes in the activation energies of different regions of resin curing. The formation of radical traps and stabilization of cobalt complexes by the added particles were other factors affecting the activation energy of the systems. The diffusion phenomenon was investigated in all three systems Neat UP, UPGO and UPMGO. The presence of attraction interactions between particles and alkyd resin chains are among the factors affecting the diffusion region of UPGO and UPMGO systems.

Experimental Analysis of Intrinsic Kinetics and Rate Profiles for Coal Char Conversion under Different Atmospheres

ABSTRACT This study focuses on determining intrinsic kinetic parameters and interpreting and simulating the rate profile. First, reactivity of coal char prepared at different temperatures was analyzed. Results showed that when coal pyrolysis temperature increases, coal char reactivity decreases; however, activation energy for coal char conversion does not always increase. Next, the weight loss process in non-isothermal conversion was discussed, and results illustrated that the weight loss mechanisms differ in each stage. The weight loss at the second stage was slightly influenced by residual volatile matter and gas diffusion, and the activation energy at this stage was close to an intrinsic value. Meanwhile, discussions on the effects of kinetic analysis methods in determining activation energy showed that Friedman and advanced isoconversional methods can obtain a true activation energy profile, whereas the Kissinger–Akahira–Sunose method was unsuitable. The rate profiles of isothermal conversion were then studied. The results demonstrated that occurrence of a maximum was an inherent feature but the “gas change” operation could shift or even cover up the true position of the maximum. Moreover, an increase in particle temperature could intensify the maximum value but slightly shift its position. Finally, an intrinsic reaction model that combines random pore model and the derived intrinsic kinetic parameters properly reproduced the rate profile of isothermal conversion (e.g., maximal conversion deviation was less than 5%).

Cure kinetics of a nadic methyl anhydride cured tertiary epoxy mixture

Cure kinetics of a methyl nadic anhydride cured tertiary epoxy (i.e., Diglycidyl ether of bisphenol A, a tetrafunctional epoxy and a fluorine-containing diepoxy), which is potential matrix for a polyimide fiber reinforced composites, were studied using dynamic and isothermal differential scanning calorimeter scans. Results showed that addition of the tetrafunctional epoxy and fluorine-containing diepoxy has negligible effects on the underlying cure mechanisms. Variation of glass transition temperature with extent of cure can be fitted using DiBenedetto equation. The Kamal model coupled with an empirical diffusion factor can adequately model the isothermal cure data. The Kamal model can model the reaction data well before vitrification. However, after vitrification, obvious deviation from Kamal model was observed, which have to be corrected using a diffusion factor. The apparent activation energy obtained from the Kamal model using isothermal data, agrees with that from the advanced isoconversional method, which utilizes the dynamic cure data.

Nanoconfined gelation in systems based on stearic and 12-hydroxystearic acids: A calorimetric study

This study applies differential scanning calorimetry (DSC) to probe the effect of nanoconfinement on gelation of mineral oil (MO), soybean oil (SO), ethylene glycol (EG), polyethylene glycol (PEG), and polypropylene glycol (PPG) by low molecular weight gelators, stearic and 12-hydroxystearic acids. Nanoconfinement is accomplished by embedding the gels into silica nanopores. In agreement with our previous work on high molecular weight polymeric gelators, nanoconfinement invariably causes a decrease in the heat of gelation. The effect is linked to restricted molecular mobility, which hampers integration of the gelator molecules into the network as well as spatially limits its growth. A new effect discovered in this work is a decrease in the gelation temperature of the nanoconfined MO and SO systems. By combining an advanced isoconversional method with the Turnbull-Fisher nucleation model it has been possible to link this effect to deceleration of gelation that originates from an increase in the nucleation energy barrier. It has been proposed that whether nanoconfinement causes a decrease or an increase in the gelation temperature can depend on polarity of liquid. The proposal is upheld by measurements on the systems involving polar liquids (EG, PEG, PPG) that have demonstrated an increase in the gelation temperature under nanoconfinement.

Non-isothermal decomposition kinetics of lipids recovered from oleaginous microbial biomass (C. vulgaris and L. starkeyi): reaction mechanism and TGA-MS analysis

Oleaginous microorganisms and the thermal decomposition of their recovered lipids are new attractive research fields for the sustainable production of biofuels from actual biomass. In this work, the thermal decomposition of lipids from C. vulgaris and from L. starkeyi was investigated using a thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) under non-isothermal conditions. Thermal decomposition was examined using the one-step reaction model. Integral, differential, and advanced isoconversional methods were implemented to analyze the conversion-dependent activation energy. The Friedman method resulted in an accurate and reliable estimation of the kinetic parameters. The activation energy showed a strong dependence on conversion from 123.5 to 246 kJ mol-1 for lipids from C. vulgaris and from 80.3 to 299.9 kJ mol-1 for lipids from L. starkeyi. The generalized master plot approach evidenced that the thermal decomposition of lipids from C. vulgaris proceeds via three-dimensional diffusion (D3—Jander’s equation). Also, the kinetic analysis indicated that Valensi’s equation (D2), controlled by a two-dimensional diffusion model, is the most likely mechanism for the thermal decomposition of lipids from L. starkeyi. The rate parameters were evaluated via a kinetic compensation plot. Ion temperature evolution was investigated by TGA-MS revealing many of the functional groups evolved in the range of 350–500 °C as C1–C7 aliphatic hydrocarbons, aromatic hydrocarbons, aldehydes, carboxylic acids, and furan derivatives. All these aspects favor the lipid biosynthesis from microbial biomass to potential lipid-based building blocks.

Thermal stability, degradation kinetic and electrical properties studies of decorated graphene oxide with CeO2 nanoparticles-reinforced epoxy coatings

We synthesized decorated graphene oxide with CeO2 nanoparticles (CeO2-GO) hybridusing silane coupling agents, then we dispersed them in the epoxy resin after optimizing it at a weight fraction %1 using differential scanning calorimetry (DSC). The structural and morphological characterization was evaluated using Fourier Transform Infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and X-ray diffraction. The thermal stability of CeO2-GO/Epoxy (CGE) and neat epoxy (NE) were studied by TGA analyses and showed that the CGE system has a good thermal stability and higher char yield comparing to the NE system. The degradation kinetic parameters for CGE matrix were computed by the Vyazovkin’s advanced isoconversional method. The master plots as model fitting was used to estimate the thermal decomposition mechanism, and the results show a good agreement between the experimental data and the F1 theoretical model. We have used electrical impedance spectroscopy (EIS) to evaluate electrical resistance of the CGE system at different percent of (CeO2-GO) nanoparticle. This research highlights that the (CeO2-GO) nanoparticleis a promising candidate for fabrication of anticorrosive coatings.

Lifetime Prediction Methods for Degradable Polymeric Materials-A Short Review.

The determination of the secure working life of polymeric materials is essential for their successful application in the packaging, medicine, engineering and consumer goods industries. An understanding of the chemical and physical changes in the structure of different polymers when exposed to long-term external factors (e.g., heat, ozone, oxygen, UV radiation, light radiation, chemical substances, water vapour) has provided a model for examining their ultimate lifetime by not only stabilization of the polymer, but also accelerating the degradation reactions. This paper presents an overview of the latest accounts on the impact of the most common environmental factors on the degradation processes of polymeric materials, and some examples of shelf life of rubber products are given. Additionally, the methods of lifetime prediction of degradable polymers using accelerated ageing tests and methods for extrapolation of data from induced thermal degradation are described: the Arrhenius model, time–temperature superposition (TTSP), the Williams–Landel–Ferry (WLF) model and 5 isoconversional approaches: Friedman’s, Ozawa–Flynn–Wall (OFW), the OFW method corrected by N. Sbirrazzuoli et al., the Kissinger–Akahira–Sunose (KAS) algorithm, and the advanced isoconversional method by S. Vyazovkin. Examples of applications in recent years are given.

Pyrolysis characters and fire behavior of bus ceiling materials

The pyrolysis characters and fire behavior of ceiling materials have a great impact on the fire retardant of the whole bus because the fire might spread along the ceiling. This study investigated the pyrolysis characters of five plastic ceiling components with TG tests at four heating rates, and then, the kinetic parameters were calculated with Kissinger method, Friedman method and an advanced isoconversional Vyazovkin method. The obtained kinetic parameters were also validated by reconstruction of conversion curves. Finally, the flammability of each component from three ceiling materials was estimated using PCFC, and the fire behavior of three ceiling materials was investigated with cone calorimeter at different heat fluxes. Results show the pyrolysis characters of surface material could explain the early stage fire behavior of ceiling materials. The ignition and fire resistance were also highly dependent on the properties of surface materials. A transition between limited and more fierce combustion occurs at some heat flux for three ceiling materials. This property was related to the composition and structure of ceilings. Below this transition heat flux level, only the surface layer of ceiling was ignited and the fire load was limited. Above this level, the underlying layer was involved in combustion and leads to a sharply increased heat release. These results suggest that the flame retardant of surface material was important to promote fire retardant of the whole ceiling. Moreover, the obtained parameters can be used for predicting fire propagation in bus ceiling.

Interpretation and Physical Meaning of Kinetic Parameters Obtained from Isoconversional Kinetic Analysis of Polymers.

Several successful examples—where physically sounded kinetic information was obtained from thermoanalytical data in different application fields, such as polymerization of thermosetting resins, biobased polymers and nanocomposites, crystallization and glass transition of semi-crystalline polymers and their nanocomposites—are here presented and discussed. It is explained how the kinetic parameters obtained from advanced isoconversional methods can be interpreted in terms of reaction mechanisms or changes in the rate-limiting step of the overall process, in the case of complex chemical reactions or complex physical transitions, and how these parameters can be used to extract model-fitting parameters.