scholarly journals Empirical Kinetic Modelling and Mechanisms of Quercetin Thermal Degradation in Aqueous Model Systems: Effect of pH and Addition of Antioxidants

2021 ◽  
Vol 11 (6) ◽  
pp. 2579
Author(s):  
Abdessamie Kellil ◽  
Spyros Grigorakis ◽  
Sofia Loupassaki ◽  
Dimitris P. Makris
Keyword(s):  
Thermal Degradation ◽  
Empirical Model ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Kinetic Modelling ◽  
Degradation Mechanism ◽  
Antioxidant Properties ◽  
Biological Significance ◽  
Model Systems ◽  
Molar Ratio

Quercetin (Qt) is a natural flavonoid of high biological significance, and it occurs in a wide variety of plant foods. Although its oxidation by various means has been extensively studied, its behavior with regard to thermal treatments remains a challenge. The study described herein aimed at investigating Qt thermal decomposition, by proposing an empirical sigmoidal model for tracing degradation kinetics. This model was employed to examine the effect of addition of antioxidants on Qt thermal degradation, including ascorbic acid, L-cysteine, and sulfite. Furthermore, degradation pathways were proposed by performing liquid chromatography-tandem mass spectrometry analyses. Upon addition of any antioxidant used, the sigmoidal course of Qt thermal degradation was pronounced, evidencing the validity of the empirical model used in the study of similar cases. The antioxidants retarded Qt degradation in a manner that appeared to depend on Qt/antioxidant molar ratio. No major differentiation in the degradation mechanism was observed in response to the addition of various antioxidants, and in all cases protocatechuic acid and phloroglucinol carboxylic acid were typical degradation products identified. Furthermore, in all cases tested the solutions resulted after thermal treatment possessed inferior antioxidant properties compared to the initial Qt solutions, and this demonstrated the detrimental effects of heating on Qt. The empirical model proposed could be of assistance in interpreting the degradation behavior of other polyphenols, but its validity merits further investigation.

Bis(isomaleimide) and diphenol blends: Non-isothermal degradation kinetics and TG-FTIR studies

2018 ◽  
Vol 51 (7-8) ◽  
pp. 644-668
Author(s):  
V Sarannya ◽  
S Shamim Rishwana ◽  
R Mahalakshmy ◽  
A Mahendran ◽  
CT Vijayakumar
Keyword(s):  
Thermal Stability ◽  
Thermal Degradation ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Thermal Polymerization ◽  
Molar Ratio ◽  
Exponential Factor ◽  
Ftir Studies ◽  
D Values ◽  
Thermal Stability Of

Blends of 4,4′-bisisomaleimidodiphenyl methane (VS) with structurally different diphenols are made in 1:1 molar ratio and thermally polymerized. Thermogravimetric studies of the cured materials show that the thermal stability, the degradation pattern and the char yield are much dependent on the structure of the diphenol that is used for blending. The decreased thermal stability of materials from the blends is attributed to decreased cross links owing to the opening of the isomaleimide rings by diphenols during thermal polymerization. The materials with trimethylphenylindane and tetramethylspirobiindane units exhibit char residue of 21% at 800°C. This is due to the thermal stability of the indane and spirobiindane moieties present in the diphenol molecules. The apparent activation energy for thermal degradation ( Ea-D) and pre-exponential factor (ln A) are derived. The Friedman, corrected Flynn–Wall–Ozawa, corrected Kissinger–Akahira–Sunose and advanced Vyazovkin methods are used to calculate the Ea-D values for various reaction extents ( αs). The Ea-D values of poly(4,4′-bisisomaleimido-diphenyl methane) vary from 168 to 226 kJ mol−1. A slight decrease in Ea-D is noted for the initial α levels and increases constantly up to α = 0.3–0.75 and then the Ea-D values decrease with increasing α values. The highest values of Ea-D and ln A are observed for the polymer derived from the blend of VS with tetramethylspirobiindane diphenol. The volatile products obtained during the thermal degradation of these polymers are analysed using thermogravimetry–Fourier transform infrared (TG-FTIR) spectroscopy. The TG-FTIR studies showed the compounds carbon monoxide, carbon dioxide and aromatic amines are the major degradation products from the polymerized blends.

Thermal degradation kinetics of Opuntia Ficus Indica flour and talc-filled poly (lactic acid) hybrid biocomposites by TGA analysis

2021 ◽  
pp. 002199832110082
Author(s):  
Azzeddine Gharsallah ◽  
Abdelheq Layachi ◽  
Ali Louaer ◽  
Hamid Satha
Keyword(s):  
Thermal Stability ◽  
Lactic Acid ◽  
Thermal Degradation ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Melt Processing ◽  
Thermal Degradation Kinetics ◽  
Poly Lactic Acid ◽  
Opuntia Ficus Indica ◽  
Model Free

This paper reports the effect of lignocellulosic flour and talc powder on the thermal degradation behavior of poly (lactic acid) (PLA) by thermogravimetric analysis (TGA). Lignocellulosic flour was obtained by grinding Opuntia Ficus Indica cladodes. PLA/talc/ Opuntia Ficus Indica flour (OFI-F) biocomposites were prepared by melt processing and characterized using Wide-angle X-ray scattering (WAXS) and Scanning Electron Microscope (SEM). The thermal degradation of neat PLA and its biocomposites can be identified quantitatively by solid-state kinetics models. Thermal degradation results on biocomposites compared to neat PLA show that talc particles at 10 wt % into the PLA matrix have a minor impact on the thermal stability of biocomposites. Loading OFI-F and Talc/OFI-F mixture into the PLA matrix results in a decrease in the maximum degradation temperature, which means that the biocomposites have lower thermal stability. The activation energies (Ea) calculated by the Flynn Wall Ozawa (FWO) and Kissinger Akahira Sunose (KAS) model-free approaches and by model-fitting (Kissinger method and Coats-Redfern method) are in good agreement with one another. In addition, in this work, the degradation mechanism of biocomposites is proposed using Coats-Redfern and Criado methods.

scholarly journals Electrochemical degradation of diclofenac by boron doped diamond anode: degradation mechanism, pathways and influencing factors

2021 ◽  
Author(s):  
Huimin Qiu ◽  
Pingping Fan ◽  
Xueying Li ◽  
Guangli Hou
Keyword(s):  
Influencing Factors ◽  
Wastewater Treatment Plants ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Electrochemical Process ◽  
Sodium Sulphate ◽  
Boron Doped Diamond ◽  
Quenching Effect ◽  
Boron Doped

Abstract Nonsteroidal anti-inflammatory drugs (NAIDS) have been widely detected in wastewater and surface water, which indicates the removal of NAIDS by wastewater treatment plants was not efficiency. Electrochemical advanced oxidation technology is considered to be an effective process. This study presents an investigation of the kinetics, mechanism and influencing factors of Diclofenac (DCF) degradation by an electrochemical process with the boron doped diamond anodes. Relative operating parameters and water quality parameters are examined. It appears that the degradation follows the pseudo-first-order degradation kinetics. DCF degradation was accelerated with the increase of pH from 6 to 10. The degradation was promoted by the addition of electrolyte concentrations and current density. HA and HCO3− significantly inhibited the degradation, whereas Cl− accelerated it. According to the inhibition tests, hydroxyl radicals (•OH) and sulfate radicals (SO4•–) contributed 76.5% and 6.5%, respectively, to the degradation. Sodium sulphate remains a more effective electrolyte, compared to sodium nitrate and sodium phosphate, suggesting the quenching effect of nitrate and phosphate on •OH. Major DCF transformation products were identified. According to the degradation products detected by liquid chromatography-mass spectrometry, hydroxylation and decarboxylation are the main pathways to DCF degradation; meanwhile, dechlorination, chlorination and nitro substitution are also included.

scholarly journals “Thermal Peroxidation” of Dietary Pentapeptides Yields N-Terminal 1,2-Dicarbonyls

2021 ◽  
Vol 8 ◽  
Author(s):  
Maria Bikaki ◽  
Nikolai Kuhnert
Keyword(s):  
Lipid Peroxidation ◽  
Reaction Mechanism ◽  
Thermal Degradation ◽  
Primary Amine ◽  
Elevated Temperatures ◽  
Degradation Products ◽  
Degradation Mechanism ◽  
Reaction Products ◽  
Unsaturated Lipids

In this contribution we investigate the thermal degradation of dietary-relevant pentapeptides. Most unsaturated lipids degrade by the well-known peroxidation mechanism. Here we show a degradation mechanism of peptides analogous to lipid peroxidation, forming a series of novel degradation products with possible toxicological relevance. At elevated temperatures above 180°C, pentapeptides with an N-terminal phenylalanine moiety react via a debenzylation to form 1,2-dicabonyl compounds, replacing the N-terminal primary amine. We propose a radical-based reaction mechanism that leads via a common peroxoaminal intermediate to two distinct types of reaction products with a terminal α-1,2 diamide or an α-amide-aldehyde functionality.

scholarly journals Photoassisted Degradation of a Herbicide Derivative, Dinoseb, in Aqueous Suspension of Titania

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Niyaz A. Mir ◽  
Malik M. Haque ◽  
Abuzar Khan ◽  
Mohd. Muneer ◽  
Colin Boxall
Keyword(s):  
Uv Light ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Aqueous Suspension ◽  
Electron Acceptors ◽  
Potassium Persulphate ◽  
First Order Kinetics ◽  
Degradation Rates ◽  
Degussa P25

The titanium dioxide (TiO2) photoassisted degradation of herbicide dinoseb has been examined in aqueous suspensions under UV light irradiation. The degradation kinetics were studied under various conditions such as substrate concentration, type of catalyst, catalyst dosage, pH, and light intensity as well as in presence of electron acceptors such as hydrogen peroxide, potassium bromate, and potassium persulphate under continuous air purging, and the degradation rates were found to be strongly influenced by these parameters. The Degussa P25 was found to be more efficient photocatalyst as compared to other photocatalysts tested. Dinoseb was found to degrade efficiently in acidic pH and all the electron acceptors studied enhanced the degradation rate. The results manifested that the photocatalysis of dinoseb followed pseudo-first-order kinetics. A qualitative study of the degradation products generated during the process was performed by GC-MS, and a degradation mechanism was proposed.

scholarly journals THERMAL DECOMPOSITION OF WOOD FIBERS: THERMAL SIMULATION USING THE F-TEST STATISTICAL TOOL

2021 ◽  
Vol 55 (3-4) ◽  
pp. 231-241
Author(s):  
HEITOR L. ORNAGHI JR. ◽  
FELIPE GUSTAVO ORNAGHI ◽  
ROBERTA MOTTA NEVES ◽  
DANIEL MAGALHÃES DE OLIVEIRA ◽  
MATHEUS POLETTO
Keyword(s):  
Thermal Degradation ◽  
Fossil Fuels ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Low Cost ◽  
Eucalyptus Grandis ◽  
Theoretical Data ◽  
Wood Fibers ◽  
F Test ◽  
Statistical Tool

"Wood biomass is an alternative for fossil fuels to produce bioenergy, due to its low cost, renewability and environmental friendliness. In order to use biomass as an energy source, understanding its thermal degradation behavior is highly recommended. This work focuses on the thermal degradation of wood fibers belonging to different species (Pinus elliotti (PIE), Eucalyptus grandis (EUG) and Mezilaurus itauba (ITA)), commonly used by the Brazilian lumber industry. The prediction of their degradation kinetics and overall thermal behavior was performed based on the most common theoretical data using the F-test statistical tool. The most probable degradation mechanism was found to be autocatalytic for all the wood fibers tested, with three different degradation steps. The results obtained were in accordance with the findings recently reported in the literature using other fitting methods. It was found that cellulose is the major contributor to Arrhenius parameters, while hemicelluloses – to reaction order."

The influence of pH on the molecular degradation mechanism of PLGA

MRS Advances ◽  
2018 ◽  
Vol 3 (63) ◽  
pp. 3883-3889 ◽  
Author(s):  
Rainhard Machatschek ◽  
Burkhard Schulz ◽  
Andreas Lendlein
Keyword(s):  
Degradation Products ◽  
Bulk Material ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Controlled Drug Release ◽  
Interfacial Rheology ◽  
Alkaline Conditions ◽  
A Chain ◽  
The Impact ◽  
Kinetics Of

ABSTRACTPoly[(rac-lactide)-co-glycolide] (PLGA) is used in medicine to provide mechanical support for healing tissue or as matrix for controlled drug release. The properties of this copolymer depend on the evolution of the molecular weight of the material during degradation, which is determined by the kinetics of the cleavage of hydrolysable bonds. The generally accepted description of the degradation of PLGA is a random fragmentation that is autocatalyzed by the accumulation of acidic fragments inside the bulk material. Since mechanistic studies with lactide oligomers have concluded a chain-end scission mechanism and monolayer degradation experiments with polylactide found no accelerated degradation at lower pH, we hypothesize that the impact of acidic fragments on the molecular degradation kinetics of PLGA is overestimated. By means of the Langmuir monolayer degradation technique, the molecular degradation kinetics of PLGA at different pH could be determined. Protons did not catalyze the degradation of PLGA. The molecular mechanism at neutral pH and low pH is a combination of random and chainend-cut events, while the degradation under strongly alkaline conditions is determined by rapid chainend cuts. We suggest that the degradation of bulk PLGA is not catalyzed by the acidic degradation products. Instead, increased concentration of small fragments leads to accelerated mass loss via fast chain-end cut events. In the future, we aim to substantiate the proposed molecular degradation mechanism of PLGA with interfacial rheology.

scholarly journals Mechanism and Kinetic Analysis of Degradation of Atrazine by US/PMS

2019 ◽  
Vol 16 (10) ◽  
pp. 1781 ◽  
Author(s):  
Yixin Lu ◽  
Wenlai Xu ◽  
Haisong Nie ◽  
Ying Zhang ◽  
Na Deng ◽  
...  
Keyword(s):  
Kinetic Analysis ◽  
Degradation Rate ◽  
Degradation Products ◽  
Degradation Kinetics ◽  
Degradation Mechanism ◽  
Reaction System ◽  
Mechanism Analysis ◽  
Product Analysis ◽  
Suppression Effect ◽  
Degradation Effect

The degradation effect, degradation mechanism, oxidation kinetics, and degradation products of Atrazine (ATZ) by Ultrasound/Peroxymonosulfate (US/PMS) in phosphate buffer (PB) under different conditions were studied. It turned out that the degradation rate of US/PMS to ATZ was 45.85% when the temperature of the reaction system, concentration of PMS, concentration of ATZ, ultrasonic intensity, and reaction time were 20 °C, 200 μmol/L, 1.25 μmol/L, 0.88 W/mL, and 60 min, respectively. Mechanism analysis showed that PB alone had no degradation effect on ATZ while PMS alone had extremely weak degradation effect on ATZ. HO• and SO4−• coexist in the US/PMS system, and the degradation of ATZ at pH7 is dominated by free radical degradation. Inorganic anion experiments revealed that Cl−, HCO3−, and NO3− showed inhibitory effects on the degradation of ATZ by US/PMS, with Cl− contributing the strongest inhibitory effect while NO3− showed the weakest suppression effect. According to the kinetic analysis, the degradation kinetics of ATZ by US/PMS was in line with the quasi-first-order reaction kinetics. ETA with concentration of 1 mmol/L reduced the degradation rate of ATZ by US/PMS to 10.91%. Product analysis indicated that the degradation of ATZ by US/PMS was mainly achieved by dealkylation, dichlorination, and hydroxylation, but the triazine ring was not degraded. A total of 10 kinds of ATZ degradation intermediates were found in this experiment.

scholarly journals New experimental diagnostics in combustion of forest fuels: microscale appreciation for a macroscale approach

2018 ◽  
Vol 18 (7) ◽  
pp. 1957-1968
Author(s):  
Dominique Cancellieri ◽  
Valérie Leroy-Cancellieri ◽  
Xavier Silvani ◽  
Frédéric Morandini
Keyword(s):  
Thermal Degradation ◽  
Mass Loss ◽  
Large Scale ◽  
Kinetic Modelling ◽  
Degradation Mechanism ◽  
Morphological Characteristics ◽  
Field Scale ◽  
New Device ◽  
Forest Fuels ◽  
Experimental Diagnostics

Abstract. In modelling the wildfire behaviour, good knowledge of the mechanisms and the kinetic parameters controlling the thermal decomposition of forest fuel is of great importance. The kinetic modelling is based on the mass-loss rate, which defines the mass-source term of combustible gases that supply the flames and influences the propagation of wildland fires. In this work, we investigated the thermal degradation of three different fuels using a multi-scale approach. Lab-scale experimental diagnostics such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), use of the cone calorimeter (CC) or Fire Propagation Apparatus (FPA) led to valuable results for modelling the thermal degradation of vegetal fuels and allowed several upgrades of pyrolysis models. However, this work remains beyond large-scale conditions of a wildland or forest fire. In an effort to elaborate on the kinetic models under realistic natural fire conditions, a mass-loss device specifically designed for the field scale has been developed. The paper presents primary results gained using this new device, during large-scale experiments of controlled fires. The mass-loss records obtained on a field scale highlight the influence of the chemical composition and the structure of plants. Indeed, two species with similar chemical and morphological characteristics exhibit similar mass-loss rates, whereas the third presents different thermal behaviour. The experimental data collected at a field scale led to a new insight about thermal degradation processes of natural fuel when compared to the kinetic laws established in TGA. These new results provide a global description of the kinetics of degradation of Mediterranean forest fuels. The results led to a proposed thermal degradation mechanism that has also been validated on a larger scale.

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