Activation Energy Of Degradation Reaction Research Articles

Interpretation of the formation of unstable halogen-containing disinfection by-products based on the differential absorbance spectroscopy approach

Concentrations of several toxic disinfection by-products (DBP), notably haloacetonitriles (e.g., trichloroacetonitrile, TCAN) and haloketones (e.g., di- and trichloropropanone, DCPN and TCPN, respectively) are affected by chlorination conditions and the inherent instability of these DBPs. In this study, effects of temperature, chlorine dose and reaction time on the formation of TCAN, DCPN and TCPN were interpreted using the approach of differential absorbance spectroscopy. Experimental data obtained for a wide range of water quality conditions demonstrate that in some cases the concentrations of some of the unstable DBPs increased rather than decreased at low temperatures and realistically long contact times. Despite the presence of pronounced changes of the kinetics of generation and degradation of these DBPs at varying temperatures and chlorine doses, their concentrations were strongly correlated with the concurrent changes of spectroscopic properties of DOM quantified via differential absorbance measurements at 272 nm (ΔA272). The maximum values of TCAN, DCPN and TCPN concentrations observed for the chlorination of eight different surface waters occur at the relative decreases of absorbance at 272 nm (defined as RΔA272) values of ca. 0.32 (±0.03), 0.24 (±0.05), and 0.42 (±0.03), respectively. The activation energies of degradation reactions of unstable DBPs were examined and the results indicate that TCAN and TCPN are caused by their hydrolysis with OH− while the degradation of DCPN is mainly caused by halogenation reaction with HOCl. These results in this study may be important for controlling the formation of unstable DBPs and further optimization of drinking water treatment.

A DFT Study on the Cyclization-Mechanism during Process of Thermal Vacuum Degradation for Poly(dimethylsiloxanes)

A DFT investigation was performed on the cyclization mechanism during the process of thermal degradation in vacuum for trimethylsilyl-terminated polydimethylsiloxane, methylsiloxane-α,ω-diol and methylsiloxane-1-ol. The formation of an intramolecular, four-centre cyclic transition state results from the flexibility of a main chain and the ability to rearrange siloxane bonds. The energy barrier of the reaction depends mostly on the four-centre cyclic structure, independent of molecular weight, the position of nucleophilic attacking, and products. The replacement of trimethylsilyl by hydroxyl leads to a great decrease of activation energy of degradation reaction, because the energy barrier of the Si-O bond interchange is much higher than that of hydrogen abstraction. The large cyclosiloxane tend to higher degree of cyclization degradation than linear siloxane with the same number Si atoms. From energetic viewpoint, cyclosiloxane products of various sizes have almost equal chance to form. Due to the continuous degradation of large ring, the D3 accounts for the predominating proportion, and steadily decreasing amounts of D4 and D5.

Degradation of Ethylene Diaminetetra Acetic Acid With Ferrous Ions Using Fenton’s Reagent in Absence of Light

Accumulation of deposit corrosion products inside secondary side of steam generator can lead to serious issue for pressurized water reactor in operation.One way to avoid accumulation of these deposits is to perform chemical cleaning which removes certain amount of deposits but this kind of operation generates high amount of liquid waste which contains process chemicals and metal ions in complex state. Oxidation of complexes will render radioactive ions in free state enabling us for further treatment to innocuous level and condition. In waste treatment there are various treatment technologies (advance oxidation process, ozone, hydrogen peroxide, electrochemical oxidation, supercritical water oxidation, electro flocculation etc to remove the accumulated deposit.).In decontamination process removal of the deposits was carried out using EDTA. which complexes the metal ions but it generates secondary waste with EDTA. We have made an attempt to degrade ethylene diaminetetra acetic acid (with ferrousions) using Fenton’s reagent in absence of light. This will free the radioactive ion for further treatment. We have studied different volume of hydrogen peroxide (H2O2) and different concentration of ethylene diamine tetra acetic acid (EDTA). Study was also done to find the effect of pH and temp on the degradation of EDTA. In the range of concentration of ethylene diamine tetra acetic acid 400ppm to 22500 ppm % degradation was found to change from 57 to 98% in 180 min. The pH was found to change from 4.0 to 8.2. The temperature was found to change from 298K to 328K. The rate constant of the degradation reaction was found to be in the range 10-4 to 10-3 in temperature range 298K to 328K. Activation energy for degradation reaction was found to be 33-88 KJ/mol.

Reliability and diffusion-controlled through thickness oxidation of optical materials in LED-based products

In this study the temperature-induced oxidation reaction in bisphenol A polycarbonate (BPA-PC), leading to discoloration of the polymer used in solid state lighting applications, is studied. BPA-PC plates used as optical material in LED-based products suffer from yellowing and discoloration during service, resulting in a gradual deterioration of optical performance of the product. Discoloration reaction is greatly influenced by the temperature-induced oxidation of the polymer. In this study BPA-PC plates are aged at elevated temperature of 100–140°C for a period up to 3000h, aiming for accelerated oxidation of the plates. Diffusion of oxygen through the aged sample is studied up to 40μm. A significant oxygen uptake is observed up to 20μm. Activation energy of oxygen diffusion is measured to be 0.25eV, which is close to activation energy of degradation reaction, reported in our previous works.

Study on lanthanum-pentaerythritol alkoxide as a thermal stabilizer for rigid polyvinyl chloride

Lanthanum-pentaerythritol (La-PE) alkoxide, a polyol-based metal alkoxide, had been synthesized and used as a thermal stabilizer for polyvinylchloride (PVC). Thermogravimetric (TG), differential thermal analysis (DTG), mass spectrum (MS), and Fourier transform infrared (FTIR) spectroscopy were used to confirm the synthesis reaction. The thermal stability of rigid PVC stabilized with La-PE was tested by means of the Congo Red test, conductivity test, thermal aging test, thermal gravimetric analysis (TGA), and UV-visible (UV-vis) spectroscopy. The results showed that addition of La-PE could significantly prolong static stability time of PVC and increase the apparent activation energy for degradation reaction. The oven aging test showed that La-PE could improve the initial color of PVC. Moreover, addition of La-PE could significantly reduce the concentrations of the conjugated double bonds of PVC and reduce weight loss. The possible thermal stability mechanism had also been discussed. Besides having good ability to neutralize hydrochloric acid (HCl), La-PE could substitute or inactivate the labile chlorine atoms in the PVC chains. J. VINYL ADDIT. TECHNOL., 2015. © 2015 Society of Plastics Engineers

Dynamic mechanical analysis and thermal properties of LLDPE/EVA/modified silica nanocomposites

The effect of hexamethylene disilazane modified nanosilica on the dynamic mechanical analysis (DMA), crystallization, melting and thermal degradation behavior of linear low density polyethylene/ethylene vinyl acetate copolymer (LLDPE/EVA) blends are explored.Detailed DMA analysis is carried out in order to investigate the reinforcing behavior of nanosilica adopting Kerner–Nielson model. Oxidative degradation and thermal stabilities of samples are also studied by the thermogravimetery analysis. The high content of nanosilica particles results in significant shift of degradation temperature to higher temperatures in the oxygen atmosphere. This behavior might be attributed to the barrier properties of nanoparticles against oxygen and gaseous degradation products. However, incorporation of modified nanosilica into LLDPE/EVA blend is decreased the onset of degradation temperature of the unfilled system. In nitrogen atmosphere, no changes are observed in the thermal degradation range and only a reduction is documented in the onset of degradation temperature. Considering important role of onset of degradation temperature, activation energy of starting of degradation temperature is calculated utilizing Kissinger-Ozawa model in both oxygen and nitrogen atmospheres. Results showed that activation energy of degradation reaction is decreased by ∼ 20 kJ/mol. This decrease is owing to the release of modifiers from the nanoparticles.

Thermal behavior of some organic/inorganic composites based on epoxy resin and calcium carbonate obtained from conch shell of Rapana thomasiana

Thermal behavior of some diglycidyl ether of bisphenol A/p-aminobenzoic acid systems with calcium carbonate as a filler were studied. The kinetics parameters of the curing reactions were estimated using the variable peak exotherm method of Kissinger and Ozawa. The most probable kinetic model and the kinetic parameters of the degradation process were also estimated. The energies of crosslinking reactions are situated in the range of 46–57kJmol−1 for the first exotherm and between 68 and 72kJmol−1 for the second exotherm. The cured resins have a good thermal stability and the activation energies of degradation reactions are situated in the range of 178–218kJmol−1.

Kinetics of Curing and Thermal Degradation of POSS Epoxy Resin/DDS System

Polyhedral oligomeric silsesquioxanes epoxy resin (POSSER) was prepared from 3-glycidypropyl-trimethoxysilane (GTMS) and tetramethylammonium hydroxide (TMAH) by hydrolytic condensation. POSSER was characterized using Fourier-transformed infrared spectroscopy (FTIR), 1H-NMR, and liquid chromagraphy/mass spectrometry (LC/MS). The epoxy value of POSSER is 0.50 mol/100 g. The LC/MS analysis indicated that T10 is the majority and contain some amount of T8, besides, a trace T9 also exists. The curing kinetics of POSSER with 4,4′-diaminodipheny sulfone (DDS) as a curing agent was investigated by means of differential scanning calorimetry (DSC). The curing reaction order n is 0.8841 and the activation energy Ea is 61.06 kJ/mol from dynamic DSC analysis. Thermal stability and kinetics of thermal degradation were also studied by thermal gravimetric analysis (TGA). TGA results indicated that the temperature of POSSE/DDS system 5% weight loss is approximately 377.0°C, which is higher by 12.6°C than that of pure POSSER, and the primary degradation reaction (300–465°C) followed first order kinetics; the activation energy of degradation reaction is 75.81 kJ/mol.

Synthesis, Characterization, and Properties of Multifunctional Epoxy Maleimide Resins

Summary: Novel multifunctional formaldehyde resins bearing diaminodiphenylmethane groups are synthesized by the polymerization of a mixture of diaminodiphenylmethane (DDM), o-cresol (o-Cz), and cyclohexanone (CHx) with formaldehyde (FA) (at a molar ratio of monomers/formaldehyde, 1/1), in the presence of acid catalyst (HCl). The obtained resins are epoxidated with a large excess of epichlorohydrin and transformed into multifunctional epoxy resins. The multifunctional epoxy maleimide resins are obtained by reaction of the epoxy resins with carboxy phenyl maleimide in the presence of triethylamine as a catalyst. The resultant resins are characterized by IR and NMR spectroscopy, elemental, and thermal analysis. The curing and thermal behavior of these epoxy maleimide resin/DDM systems are investigated using differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques. The activation energies of the curing reactions are situated in the range of 53–90 kJ · mol−1. The cured products have good thermal properties, and activation energies of degradation reactions have values between 42–74 kJ · mol−1. The curing reaction of multifunctional epoxy maleimide resins with DDM.

Formaldehyde Resins Bearing Diaminodiphenylmethane Groups: Synthesis, Characterization and Properties

AbstractSummary: Novel formaldehyde resins bearing diaminodiphenylmethane groups were synthesized by the polymerization of a mixture of diaminodiphenylmethane (DDM), cyclohexanone (CHx) and o‐cresol (o‐Cz) with formaldehyde (FA) in the presence of an acid catalyst (HCl). The resins obtained were characterized by spectral, elemental and thermal analysis and used as a hardener for epoxy resins. The curing and temperature behavior of these epoxy resin/formaldehyde systems were investigated using differential scanning calorimetry and thermogravimetry techniques. The resins had good thermal stability and the activation energies of degradation reactions had values between 70–98 kJ · mol−1.The curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.magnified imageThe curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.

Thermal stability of epoxy-silica hybrid materials by thermogravimetric analysis

The thermal degradation behavior and thermal stability of epoxy-silica nanocomposites were studied with thermogravimetric analysis (TGA). Detailed and precise factors on the thermal stability based on the initial decomposition temperature (IDT), temperature of maximum rate of weight loss ( T max), integral procedure decomposition temperature (IPDT), decomposition temperature range, and activation energy ( E a) of the decomposition reactions were studied. Introduction of nanoscale silica into epoxy resins certainly improved their thermal stability and reduced their weight loss rates, and the improvement can be further enhanced with using a phosphorous compound as the curing agent. The activation energies of the thermal degradation reactions of the nanocomposites were calculated from various methods, and the results from the Ozawa method provided reliable data. It was shown that the presence of nanoscale silica leveled up the values of the activation energies of the degradation reactions, and phosphorus group depressed the values of E a.