Activation Energy Of Degradation Research Articles

Co/Fe and Co/Al layered double oxides ozone catalyst for the deep degradation of aniline: Preparation, characterization and kinetic model.

In this work, Co/Fe and Co/Al layered double oxides (Co/Fe-LDO and Co/Al- LDO)ozone catalysts were obtained from Co/Fe and Co/Al layered double hydroxides intermediates (Co/Fe-LDH and Co/Al-LDH). Firstly, the optimal preparation parameters of the two intermediates were determined, then the morphology and mineralogy microstructure of the derived Co/Fe-LDO and Co/Al- LDO ozone catalysts were systematically studied. Finally, the reaction kinetics of the two ozone catalysts for the deep degradation of aniline wastewater in catalysts/ozone systems were established. The results showed that the optimal preparation conditions were set as pH12, temperature 60°C, cobalt‑iron ratio 3:1 for Co/Fe-LDH intermediate, and pH12, temperature 70°C, cobalt‑aluminum ratio 3:1 for Co/Al-LDH intermediate. During calcination treatment, the dehydration and recrystallization effect impelled LDH intermediate to form LDO catalyst. The derived ozone catalysts Co/Fe-LDO and Co/Al-LDO possess layered structure, and Co species was mainly based on Co3O4 as the main mineral phase of the two ozone catalysts. The addition of catalyst can realize the deep ozonation catalysis of aniline wastewater. The kinetic models established on the aniline oxidized by ozone or catalyst/ozone systems were both fitted the first-order reactions, and the reaction activation energy for CODCr and TOC degradation were significantly reduced in catalyst/ozone system.

Compressive stress-thermo oxidative ageing behaviour and mechanism of EPDM rubber gaskets for sealing resilience assessment

EPDM rubber gaskets, as a water-proof sealing material installed in the tunnel segment joints, were subjected to compressive stress-thermo oxidative ageing at different temperature and compressive stress levels. It was found that compared with thermo-oxidative ageing, compressive stress-thermo oxidative ageing of EPDM samples was more aggressive due to the destructive effect of compressive stress: the molecular structure was oxidized to form oxygenated species such as carbonyl groups, while high compressive stress level resulted in the degradation of EPDM with lower degradation activation energy (Ea), and the breakage of CB network structure and phase separation. Meanwhile, the crosslinking reaction dominated over the chain scission reaction especially at high temperature during the whole ageing process, leading to the increase of crosslinking density of EPDM samples. With increasing ageing temperature and compressive stress, the ageing degree of EPDM rubber was much severe, and compressive stress promoted the degradation of samples, resulting in the decrease of glass transition temperature (Tg) and increase of free volume at high stress levels, while thermo-oxidative ageing promoted the crosslinking reaction of samples, leading to the higher Tg and lower free volume at high ageing temperature. As a result, the surface of EPDM rubber became much rough and interfacial debonding occurred between CB and EPDM matrix, while the mechanical and durable sealing resilience performance were deteriorated during stress-thermal ageing.

Kinetic study of the multistep thermo‐oxidative degradation of thermosetting siloxane‐containing polyimide and unmodified polyimide

AbstractIn this study, the thermo‐oxidative degradation kinetics of thermosetting siloxane‐containing polyimide (SPI) and unmodified polyimide (PI) were comparatively studied to reveal effect of siloxane on the thermo‐oxidative stability, and to understand how they behave under elevated temperature. Results of thermogravimetirc analysis complemented by structural and morphological observations indicate two individual processes compose thermo‐oxidative degradation of SPI and PI. Therefore, different kinetic triplets are employed to describe the two processes. It is found that the degradation activation energy (E) of the first process for SPI is lower than that for PI, while in the second process, the E value of SPI goes beyond that of PI. The difference of structural changes between SPI and PI during thermo‐oxidative degradation offers rational explanation. The oxidation of siloxane in the first process results in weight loss of SPI at relatively lower temperature, while the formed silica‐type structures retard the second degradation process, making SPI exhibited a slower degradation rate than PI. In addition, the two constituent processes for thermo‐oxidative degradation of SPI and PI obey the Avrami‐Erofeev models. Based on the obtained kinetic parameters, simulations of thermo‐oxidative degradation for both SPI and PI were successfully realized, which gives a precise mathematical description of their degradation behaviors.

Thermal Degradation of p‐Hydroxybenzoic Acid in Macadamia Nut Oil, Olive Oil, and Corn Oil

Abstractp‐Hydroxybenzoic acid (PHBA) plays a significant role in sustaining the oxidative stability of macadamia nut oil (MNO). However, PHBA undergoes thermal decarboxylation and loses its bioactive antioxidant properties. In this study, we determine PHBA degradation kinetics in oils at various heating temperatures, which provides fundamental understanding of PHBA thermal degradation in oils and oil quality changes during high‐temperature processing. PHBA degradation kinetics in MNO, olive oil, and corn oil were evaluated at temperatures typical for cooking and frying. PBHA headspace concentration was measured using selected ion flow tube mass spectrometry. PHBA decarboxylation followed a zero‐order reaction, where degradation could be affected by factors such as the type of oil matrix having different FA compositions, antioxidants, and component interactions. PHBA degradation activation energies (E a) showed that PHBA was more stable against thermal decarboxylation in MNO (85 kJ mol–1) than in olive oil (40 kJ mol−1) or corn oil (22 kJ mol−1). The higher enthalpy () of decarboxylation in MNO (82 kJ mol−1) indicates that PHBA is more inhibited from decomposition than olive oil (37 kJ mol−1) or corn oil (19 kJ mol−1). Moreover, the negative entropy values () of PHBA degradation from MNO (−192 J mol−1 K−1), olive oil (−277 J mol−1 K−1), and corn oil (−325 J mol−1 K−1) indicates that these oils impart some inhibitory properties against PHBA thermal decarboxylation.

Effect of tensile action on retrogradation of thermoplastic cassava starch/nanosilica composite

Thermoplastic cassava starch (TPS)/nanosilica (SiO2) composite was prepared by melt mixing, and the effect of tensile action (stress) on the structures and properties of TPS/SiO2 composite during the retrogradation stages was investigated. Differential scanning calorimetry (DSC) analysis indicated that the retrogradation enthalpy of TPS/SiO2 composite with the tensile action was higher than that of the composite without the tensile action after short retrogradation time. Thermogravimetric analysis (TG) displayed that the decomposition temperature and activation energy of thermal degradation of the composite under the tensile action were higher than those of composites without the tensile action. The contact angle and tensile strength of TPS/SiO2 composite with the tension action became larger after the tension stress was applied during the short retrogradation time. From the Fourier transform infrared (FTIR) spectroscopy results, the stretching vibration of the hydroxyl group enhanced with the increase in retrogradation time. According to the polarized light microscopy (PLM) analysis, the composite samples showed Maltese cross-pattern, and it became blurred after the tensile stress was exerted on the samples. With the increase in retrogradation time, the inter-planner spacing decreased and crystal size of TPS/SiO2 composite increased. The tensile action could weaken the A-type and promote the formation of the V-type crystalline structure. The scanning electron microscopy (SEM) results showed that the fracture surface of composite sample without the tensile action was smooth, and the granular structure of starch could not be clearly seen, however, the fracture surface of composite under the tensile action was rough, and the granular structure of starch was clear.

Replication and surface properties of micro injection molded PLA/MWCNT nanocomposites

Multi-walled carbon nanotube (MWCNT) reinforced polylactide (PLA) nanocomposites were injected molded into a mold with micro needle patterns. In order to alleviate the hesitation effect caused by an increased melt viscositgy of PLA/CNT nanocomposites, the effects of the injection speed and holding pressure on the replication property were investigated. The effects of MWCNTs on the crystallization, thermal behavior, replication properties, replication and surface properties of micro injection molded PLA/CNT nanocomposites were investigated. An analysis of crystallinity and thermal behavior indicated that the MWCNTs promoted the unique α’ to α crystal transition of PLA, leading to an enhancement of surface modulus and hardness, as measured using a nanoindentation technique. The specific interaction between PLA and MWCNTs was characterized using an equilibrium melting point depression technique. Furthermore, the MWCNTs increased the activation energy for thermal degradation of PLA due to the physical barrier effect. The improved replication quality of the microfeatures in the PLA/MWCNT nanocomposites has been achieved by elevating injection speed and holding pressure, which enhances the polymer filling ability within the micro cavity. A replication ratio greater than 96% for the micro injection molded PLA/CNT nanocomposites were achieved at holding pressure of 100 MPa and injection speed of 120 mm/s. This study shows that processing conditions significantly influence the replication and surface properties of micro injection molded PLA/CNT nanocomposites.

Thermal degradation kinetics of functional polysiloxane with pendent γ-chloropropyl groups

A kind of functional polysiloxane containing pendent γ-chloropropyl groups, α, ω-trimethylsiloxy-poly(methylchloropropyl)siloxane (PMCPS), was synthesized. Its thermal stability and thermal degradation kinetics were studied through thermogravimetric analysis (TGA) in nitrogen atmosphere. The effect of the introduced γ-chloropropyl units on the thermal degradation behavior of PMCPS was discussed. The TGA revealed that PMCPS exhibited three degradation stages in the temperature range of 30–800 °C. The depolymerization of the main chain of polysiloxane was accelerated by introducing the γ-chloropropyl groups. Two isoconversional methods, the Friedman and the modified Kissinger–Akahira–Sunose (KAS) by Starink, were chosen to investigate the thermal degradation kinetics of PMCPS. The average activation energies of the thermal degradation of PMCPS obtained from the two methods were compared and found to be in good agreement with each other.

Relationship between stress relaxation behavior and thermal stability of natural rubber vulcanizates

Abstract It is well-recognized that different sulphur curing systems have greatly influenced to the final properties of the rubber vulcanizates. In this study, the properties of vulcanizates with conventional vulcanization (CV) and efficiency vulcanization (EV) systems were correlated in the aspect of stress relaxation and thermal stability. The stress relaxation behaviour and thermal stability were studied with the temperature scanning stress relaxation (TSSR) and with thermogravimatric analysis (TGA) techniques, respectively. Thermo-oxidative degradation of rubber chains in the CV system was greater than the EV system, leading to easier stress relaxation and poorer aging resistance of the CV system. Also, thermal stability of the rubber crosslinked with CV system was poorer than that with the EV system as corroborated by the activation energy of degradation. TSSR result correlated well with TGA result, and both revealed type of crosslinkages governed the thermo-oxidative degradation and thermal stability of vulcanizates.

Thermal degradation in edible oils by surface enhanced Raman spectroscopy calibrated with iodine values

We present a facile surface enhanced Raman scattering (SERS) based methodology to study the thermal degradation of edible oils using a special gold sputtered SERS tattoo. The methodology is calibrated with Iodine values, which is an industrial standard. This analytical study aims to compare the safety of 7 edible oils rich in monounsaturated (MU), polyunsaturated (PU), and saturated (S) fatty acids (FA) against high temperature re-cooking as done in most restaurants, and street food joints. The changes in the SERS signal intensity (I) ratio of the saturated (@1440 cm-1), and unsaturated (@ 1265 cm−1) FA, I1265/I1440, was studied as a function of heating time, and temperature (T), around the ‘smoke point’. The SERS marker for thermal degradation, I1265/I1440, measuring the normalized unsaturated FA content in the oils decreased consistently, and significantly for the PUFA, and MUFA oils when heated above the ‘smoke point’, following the changes in the industrial standard ‘Iodine value’. Olive (MUFA), and Coconut (SFA) oil showed marginal, and no decrease, respectively, of the SERS marker over the temperature range studied. Based on the SERS marker, a parameter ζ, -the decrease of (I1265/I1440) value of the heated oil with respect to the as-purchased value, is defined that can compare the degradation of the edible oils under different thermal stressing. The Arrhenius fit of the SERS marker yielded similar activation energy of the thermal degradation to that obtained independently from Iodine value, and demonstrates the correctness of the presented methodology.

Effects of Winding Vibration on the Mechanical-Thermal Aging Properties of Insulating Paper

The oil-paper insulation in power transformer is under a complicated environment, and there is little research on the combined effects of winding vibration-generated mechanical stress and thermal stress on the aging of insulating paper. To investigate the effects of combined mechanical-thermal stress on the aging properties of insulating paper, this paper carried out accelerated aging test using the as-designed mechanical-thermal stress combined aging oven in the aging environment at the temperature of 130 °C, and the mechanical stress intensities of 1 MPa, 1.5 MPa and 2 MPa. Besides, the degree of polymerization (DP), tensile strength, infrared spectroscopy, and scanning electron microscope (SEM) tests were performed on the aging paper samples. The test results suggested that, the combined mechanical-thermal aging might be regarded as thermal aging with lower degradation activation energy; the DP and tensile strength of insulating paper markedly declined during the mechanical-thermal aging process. At the same time, mechanical stress promoted the destruction of glycosidic bond, intramolecular and intermolecular hydrogen bonds, and increased the insulating paper cracks and holes. Typically, the above factors accelerated the aging of insulating paper. Finally, an improved degradation rate equation for insulating paper with consideration of mechanical stress was put forward.

Hydrogen-induced degradation: Explaining the mechanism behind light- and elevated temperature-induced degradation in n- and p-type silicon

Light- and elevated temperature-induced degradation (LeTID) has been extensively studied on p-type silicon materials with increasing evidence suggesting the involvement of hydrogen. Recent findings of the identical phenomenon in n-type silicon wafers have further opened up new areas of understanding into the inherent behavior and root cause of the defect. In this work, we compare LeTID observed in both p- and n-type silicon wafers under both dark and illuminated annealing conditions, highlighting previously unobserved similarities in defect formation and recovery kinetics. We report thermal activation energies of the LeTID-related degradation and recovery in n-type silicon to be 0.76 ± 0.02 eV and 0.97 ± 0.01 eV without illumination, respectively, and 0.70 ± 0.05 eV and 0.83 ± 0.15 eV under illumination (0.02 kWm−2), respectively. Furthermore, we present additional experimentation demonstrating the thermal and illumination dependency of surface-related degradation (SRD) in n-type silicon. We report an extracted activation energy of this SRD of 0.38 ± 0.10 eV. Through modelling of the hydrogen charge state fractions, we speculate that the behavior of LeTID both in the dark and under illumination may be explained by the migration of and interactions between charged hydrogen species and dopant atoms within the diffused layers and the silicon bulk.

Correlation between the cross-linking and degradation activation energy of cotton fabric treated with chitosan kinetic study by ‘model-free’ multiple heating rate methods

The different concentrations of chitosan were applied on cotton fabrics using glutaraldehyde as a cross-linking agent. The fabric samples were thermally analysed from ambient temperature to 700 °C at four different linear heating rates, i.e. 2.5, 5, 10 and 20 °C min−1 in a flowing nitrogen medium. Non-isothermal ‘model-free’ multiple heating rate methods like Friedman and Kissinger–Akahira–Sunose have been employed for the determination of degradation activation energy of the samples. The degradation mechanism based on activation energy calculation at different conversions has been proposed and compared with the extent of cross-linking. Also the method of universal master plots has been employed on isothermal data and worked on different models and their optimizations. This research work tries to achieve a correlation between activation energy and extent of cross-linking with the increase in chitosan concentration to the fabric.

Thermal properties and degradation of enantiomeric copolyesteramides poly(lactic acid-co-alanine)s

Thermal properties and degradation of enantiomeric random copolyesteramides poly(l-lactic acid-co-l-alanine) [P(LLA-LAL)] and poly(d-lactic acid-co-d-alanine) [P(DLA-DAL)] copolymers with wide alanine unit content ranges from 0 to 21 and 22 mol% were investigated by differential scanning calorimetry and themogravimetry. The total enthalpy of cold crystallization enthalpy and melting enthalpy as an indicator of crystallinity decreased with a decrease in lactic acid unit content or an increase in alanine unit content. Equilibrium melting temperature values of α-form homo-crystallites for the unblended samples decreased with an increase in alanine unit content (157.3–179.6 °C) and those of δ-form homo-crystallites for the unblended L100 and D100 (190.7 and 185.1 °C) were much higher than the reported values (both 172.8 °C, Polymer 2017, 9, 625). Thermal stability was enhanced by enantiomeric polymer blending, although thermal degradation was accelerated by incorporated alanine units. The activation energy for thermal degradation (ΔEtd) of the blend samples decreased with an increase in alanine unit content, whereas that of the unblended samples showed complicated dependence on alanine unit content and became maximum at alanine unit contents of 21 and 22 mol%. The blend samples had higher ΔEtd values comparted to those of the unblended samples, except for the alanine unit contents of 21 and 22 mol%. The reason for the high ΔEtd values of the unblended samples compared with that of the blend sample at the alanine unit contents of 21 and 22 mol% is discussed.

Synthesis and Characterization of High Heat Resistant Hydroxyl Silicone Oil with Boron and Sulfoxide in Backbone

High heat resistant hydroxyl silicone oil with boron and sulfoxide in backbone (HSOBS) was synthesized by copolymerizing of hydroxyl polyborosiloxane oil (HPBSO) with thionyl chloride (SOCl2). The molecular structure of HSOBS was confirmed by Fourier-transform infrared spectroscopies (FT-IR) and nuclear magnetic resonance (1H-, 11B- and 29Si-NMR) spectroscopies. The thermogravimetric analysis (TGA) results showed that incorporation of sulfoxide group in backbone obviously improved the heat resistant of HSOBS. The temperature at 5% mass loss (T5) and maximum decomposition rate (Tmax) of HSOBS-1 were 490 °C and 590 °C, respectively. The thermal degradation activation energy (Ea) was systematically studied by the Flynn-Wall-Ozawa method, and the Ea of HSOBS was higher than that of HPBSO.

Carborane-Containing Aromatic Polyimide Films with Ultrahigh Thermo-Oxidative Stability.

Carborane-containing aromatic polyimide (CPI) films with ultrahigh thermo-oxidative stability at 700 °C have been prepared by casting poly(amic acid) (PAA) resin solution on a glass surface, followed by thermal imidization at elevated temperatures. The PAA solution was prepared by copolymerization of an aromatic dianhydride and an aromatic diamine mixture, including carborane-containing aromatic diamine in an aprotic solvent. The CPI films showed excellent thermo-oxidative stability at 700 °C due to the multilayered protection layers formed on the film surface by thermal conversion of the carborane group into boron oxides. The boron oxide layer enhanced the degradation activation energy and suppressed the direct contact of inner polymer materials with oxygen molecules in a high-temperature environment, acting as a “self-healing” skin layer on the polyimide materials. The CPI-50 film was still flexible and maintained 50% retention of mechanical strength even after thermo-oxidative aging at 700 °C/5 min. The mechanism of thermo-oxidative degradation was proposed.

A new pseudo-partition coefficient based on a weather-adjusted multicomponent model for mushroom uptake of pesticides from soil

In this study, a weather-based multicomponent model was developed based on the unique biostructures and metabolic processes of mushrooms to evaluate their uptake of pesticides from soils, and the effects of temperature and relative humidity on the bioaccumulation of pesticides in mushrooms was comprehensively quantified. Additionally, a new pseudo-partition coefficient between mushrooms and soils was introduced to assess the impacts of different physiochemical properties on the pesticide uptake process. The results indicate that, in general, the pseudo-partition coefficient increases as the relative humidity increases for both the air and soil according to Fick’s law of gas diffusion and the spatial competition of molecules, respectively. Meanwhile, the effect of temperature on the pesticide bioaccumulation process is more complex. For most pesticides (e.g., atrazine), the pseudo-partition coefficient that was computed from the transpiration component had a maximum value at a specific temperature due to the temperature dependency of the transpiration and biodegradation processes. For some pesticides (e.g., ethoprophos), the pseudo-partition coefficient of the air-deposition component had a maximum value at a certain temperature that was caused by the ratio of the soil–air internal transfer energy and degradation activation energy of the pesticide. It was also concluded that for relatively low-volatility pesticides, transpiration dominated the bioaccumulation process; this was mainly determined from the pesticide water solubility. For nonbiodegradable pesticides (e.g., lindane), the computed coefficient values were relatively low due to their insolubility in water, which inhibits bioaccumulation in mushrooms and is one of the main reasons for their long-term persistence in soils.

Thermal Degradation of Polystyrene under Extreme Nanoconfinement.

Extreme nanoconfinement has been shown to significantly affect the properties of materials. Here we demonstrate that extreme nanoconfinement can significantly improve the thermal stability of polystyrene (PS) and reduce its flammability. Capillary rise infiltration (CaRI) is used to infiltrate PS into films of randomly packed silica nanoparticles (NPs) to produce highly confined states. We demonstrate that as the NP size is decreased, increasing the degree of confinement, the isothermal degradation time is dramatically increased, by up to a factor of 30 at 543 K for PS confined in ∼3 nm pores. The activation energy of PS degradation is also increased, by 50 kJ/mol in the most confined state (∼3 nm pores). We demonstrate that the degradation proceeds through the film surface and from the center of large holes toward NP surfaces, indirect evidence that the process is diffusion limited. The surface-driven process dramatically reduces char formation even in large NP packings that show no significant changes in their dynamics and glass transition temperature (Tg) compared to the bulk.

Removal of perchlorate from wastewater through adsorption and reductive degradation using Ni-Fe bimetallic nanoparticles supported on modified activated carbon: A simple strategy to degrade persistent pollutants

In the present study, nickel and iron (Ni/Fe) bimetallic nanoparticles (Ni-Fe NPs) were produced in the presence of activated carbon (AC) to prepare supported Ni/Fe bimetallic nanoparticles (Ni-Fe NPs/AC). The NPs were modified using cetylpyridinium chloride and used for the simultaneous adsorption and degradation of perchlorate. Synthesized Ni-Fe NPs/AC was characterized using FE-SEM, EDS, and XRD. The influential factors in the removal of perchlorate by Ni-Fe NPs/AC were optimized based on experimental design. According to the results, adsorption and degradation efficiencies were 96.98% and 78.81%, respectively, which could be achieved to the efficiency of nearly 100% by increasing the process time to 110 minutes. Reaction kinetics complied with the pseudo-first-order characteristics. Moreover, the rate constant of adsorption and degradation were estimated at 0.0848 and 0.0199 min-1 at 303 K, and the activation energy for adsorption and degradation was 42.39 and 12.47 kJ/mol, respectively. The proposed method could effectively remove perchlorate from well water and industrial wastewater. Therefore, Ni-Fe NPs/AC could be an effective nanomaterial for the complete degradation of perchlorate. This novel method could also remove persistent organic and inorganic pollutants and promote the industrial application of bimetallic NPs in environmental remediation.

Kinetic, thermal, structural and degradation studies on the effect of meta-substituted aromatic-aliphatic polyesters built through ring-opening polymerisation

Here we synthesise and characterise novel aromatic-aliphatic polyesters based on poly(2-(2-hydroxyethoxy)benzoate) (P2HEB). The polyesters were a product of the ring-opening polymerisation of their respective substituted benzodioxepinones catalysed by an aluminium salen catalyst. The electronic effects of the substituents on the polymerisation and thermal behaviour were investigated. The polymerisation and depolymerisation kinetics showed faster rates for electron withdrawing groups with selective depolymerisation back to their cyclic monomers in 10 min at 110 °C. The thermal characterisation showed varying glass transition temperatures from 29.7 °C to 60.7 °C with electron withdrawing groups exhibiting higher values. An increase in the melting temperatures and the thermal degradation activation energies of the polyesters were also observed. The crystal structures of the polyesters corresponded to semi-crystalline polyesters. The polymerisation and thermal behaviour of these novel aromatic-aliphatic polyesters can be tuned through manipulation of the meta-positioned R group, thus expanding the scope of catalytically degradable, functionalized aromatic-aliphatic polyesters that are accessible through ring-opening polymerisation.

High methoxyl pectin extracts from Hylocereus polyrhizus's peels: Extraction kinetics and thermodynamic studies

The effect of physicochemical treatment on pectin yield, degree of esterification, along with the kinetics and thermodynamics characteristics was investigated in the present study. Several extraction parameters were observed to have impacted the yield and degree of esterification significantly, and the best extraction condition was as follows: agitation rate of 250 rpm, temperature of 70 °C, extraction time of 120 min, pH 2, and liquid to solid ratio of 10 v/w which has resulted in 28.20% of pectin yield, with DE (degree of esterification) of 57.00%. A theoretical model which describes the extractability, dissolution and degradation rate of pectin to predict the maximal yield at the maximal time was established to study the extraction kinetics of pectin from HPP. The kinetic analysis from Panchev's model shows the extraction rate was found highest at LSR 10 with ymax 30.85%. The calculated activation energy for pectin dissolution and degradation was found to be 4.532 kJ/mol and 28.054 kJ/mol, respectively. The thermodynamic study has suggested that the process was endothermic, spontaneous and reversible. These results suggest that the physical and chemical treatment applied could be an efficient technique for the extraction of pectin from Hylocereus polyrhizus peels.