Vulcanization of an Ethylene Propylene Diene Rubber

1968 ◽  
Vol 41 (2) ◽  
pp. 316-329 ◽  
Author(s):  
H. K. Frensdorff
Keyword(s):  
Rate Constants ◽  
Order Reaction ◽  
Double Bonds ◽  
Fast Reaction ◽  
First Order ◽  
Equilibrium Swelling ◽  
Before And After ◽  
Ethylene Propylene Diene Rubber ◽  
Two Stages ◽  
Diene Rubber

Abstract This study concerns the sulfur vulcanization of EPT with dithiocarbamate accelerators. The reactions undergone by the accelerators are equivalent to those found during natural rubber or SBR vulcanization; TMTM and TMTD are almost completely converted to ZDMC. During vulcanization about 50% of the double bonds are saturated, and approximately one crosslink is formed for each two double bonds initially present. Equilibrium swelling measurements before and after mercaptan cleavage were used to determine the concentration of all crosslinks and that of monosulfide ones as functions of vulcanization conditions. Vulcanization kinetic were followed by Monsanto rheometer measurements. The process takes place in two stages: an initial fast reaction representing vulcanization by the primary accelerator, followed by a slower first order reaction due to acceleration by ZDMC. Accelerator, sulfur, and zinc oxide concentrations have little effect on the rate constants which, however, are nearly proportional to polymer unsaturation. The rate constants approximately double with each temperature rise of 10° C.

Vulcanization Kinetics of Natural Rubber Coagulated by Microorganisms with Use of a Vulcameter

2010 ◽  
Vol 160-162 ◽  
pp. 1181-1186 ◽  
Author(s):  
Zhi Feng Wang ◽  
Si Dong Li ◽  
Xiao Dong She
Keyword(s):  
Activation Energy ◽  
Natural Rubber ◽  
Rate Constants ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Second Stage ◽  
End Stage ◽  
Two Stages ◽  
Kinetics Of

Kinetics of vulcanization of natural rubber coagulated by microorganisms (NR-m) was studied with the use of a vulcameter. In the induction period of vulcanization, the time t0 of NR-m is shorter than that of natural rubber coagulated by acid (NR-a), and the rate constant k1/a of NR-m are greater than that of NR-a. Both the curing periods of NR-m and NR-a consist of two stages. The first stage follows first-order reaction. The rate constants k2 of NR-m in the first stage are greater than that of NR-a at the same temperature, and so are the activation energy E2. The second stage (end stage of the curing period) does not follow first-order reaction, and the calculated reaction order n of NR-m is in the range of 0.82-0.85, and that of NR-a is in the range of 0.64-0.72. The rate constants k3 of the second stage for NR -m are greater than that of NR-a at the same temperature, and so is the activation energy E3.

On the Chemical Reactivity of the Phytochrome Chromophore in the Pr and Pfr Form

1985 ◽  
Vol 40 (3-4) ◽  
pp. 215-218 ◽  
Author(s):  
Fritz Thümmler ◽  
Peter Eilfeld ◽  
Wolfhart Rüdiger ◽  
Doo-Khil Moon ◽  
Pill-Soon Song
Keyword(s):  
Reaction Kinetics ◽  
Rate Constants ◽  
Chemical Reactivity ◽  
Order Reaction ◽  
First Order Reaction ◽  
Limiting Factor ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order ◽  
The Difference

The reactivity of the phytochrome chromophore and related tetrapyrroles towards ozone and tetranitromethane was investigated. Both oxidizing reagents cause bleaching of the main absorp­tion band of the pigment. The rate constants for this bleaching were determined under conditions of pseudo first order reaction kinetics. The rate constants for the reaction with ozone are similar for native phytochrome and for freely accessible tetrapyrroles (biliverdin, small chromopeptides from phytochrome) indicating that accessibility is not the limiting factor for the reaction with ozone. Under a variety of conditions, the Pfr chromophore reacts by about 10% faster than the Pr chromophore. This may reflect the true difference in reactivity. The rate constants for the reaction with tetranitromethane are much larger for biliverdin, bilirubin and small chromopeptides from phytochrome than for native phytochrome. The limiting factor for this reaction in native phytochrome therefore is the accessibility of the chromophore by the reagent. Previous conclusions on the difference in exposure of the tetrapyrrole chromophore in Pr and Pfr are confirmed.

scholarly journals Decontamination performance of air filter paper impregnated with zirconium hydroxide on sulfur mustard

2021 ◽  
Vol 267 ◽  
pp. 02063
Author(s):  
Xingqi Huang ◽  
Ting Zhao ◽  
Chunxiao Yan ◽  
Yanren Jin ◽  
Yue Wu ◽  
...  
Keyword(s):  
Filter Paper ◽  
Degradation Rate ◽  
Sulfur Mustard ◽  
Filtration Efficiency ◽  
Zirconium Hydroxide ◽  
Order Reaction ◽  
Reaction Products ◽  
Air Filter ◽  
First Order ◽  
Before And After

Using zirconium hydroxide as a decontaminant, a kind of self-decontaminating air filter paper that can effectively degrade HD was successfully prepared by impregnating. The morphology and filtration efficiency of the filter paper before and after immersing were compared. The filtration efficiency increased linearly and slowly, with the regression equation: η=0.0001L+99.971. The liquid-solid decontamination reaction of HD on zirconium hydroxide powder and self-decontaminating filter paper conformed to the kinetic of quasi-first-order reaction and found that half-lives were 0.4 h and 2.1 h respectively. Good degradation performance for HD was exhibited and the degradation rate reached more than 99 % in 12 hours. Reaction products were analysed by GC-MS, which displayed that HD was decomposed through the substitution of chlorine and the elimination of H on α-C. The ultimate decontamination products were thiodiglycol and 2-hydroxyethyl vinyl sulfide without erosive toxicity.

scholarly journals Kinetics of aflatoxin B1 and G2 adsorption on Ca-clinoptilolite

2000 ◽  
Vol 65 (10) ◽  
pp. 715-723 ◽  
Author(s):  
Aleksandra Dakovic ◽  
Magdalena Tomasevic-Canovic ◽  
Vera Dondur ◽  
Aleksandra Vujakovic ◽  
Predrag Radosevic
Keyword(s):  
Adsorption Process ◽  
Order Reaction ◽  
Active Centers ◽  
Fast Reaction ◽  
First Order ◽  
Ph Values ◽  
Zero Order Reaction ◽  
Rate Method ◽  
Adsorption Rates ◽  
Kinetics Of

The kinetics of aflatoxins B1 and G2 adsorption on Ca-clinoptilolite at pH2 and 7, in aqueous electrolyte at 37?C were studied. For both aflatoxins, the adsorption process begins with a fast reaction whereby most of the toxin is adsorbed in the first few minutes. This fast process is followed by the significantly slower process of aflatoxin bonding at active centers of mineral adsorbent. The initial rate method showed that the fast adsorption process of aflatoxin ?1 and G2, at both pH values is a first order reaction, while the slow adsorption process of these aflatoxins is a zero order reaction. The adsorption indexes and adsorption rates for both examined toxins were pH dependent. In the investigated initial toxins concentration ranges (500-3000 ?g/dm3), high adsorption indexes were achieved (> 80 %).

Kinetics of Methylation of Methyl 5-Deoxy-α/β-D-xylofuranosides

2004 ◽  
Vol 69 (10) ◽  
pp. 1877-1888
Author(s):  
Mária Oščendová ◽  
Jitka Moravcová
Keyword(s):  
Sodium Hydroxide ◽  
Methyl Iodide ◽  
Rate Constants ◽  
Reaction Rate ◽  
Steric Effect ◽  
Order Reaction ◽  
Half Time ◽  
First Order ◽  
Consecutive Reactions ◽  
Kinetics Of

The kinetics of methylation of methyl 5-deoxy-α-D-xylofuranoside (1), methyl 5-deoxy-β-D-xylofuranoside (2) and their partly methylated derivatives with methyl iodide in the presence of sodium hydroxide in acetonitrile was studied. The reaction rate was independent of the base concentration during the first half-time only and the methylation proceeded as a first-order reaction. The rate constants of all side and consecutive reactions were calculated and the influence of both polar and steric effect is discussed. The methylation of 1 was highly regioselective giving almost exclusively 5-deoxy-2-O-methyl-α-D-xylofuranoside.

Direkte Bestimmung der Geschwindigkeitskonstanten des Durchtritts vom kleinen zum großen Hohlraumsystem im Molekularsieb Typ 13 X für Sr-und Ba-Ionen / Direct Determination of the Rate Constants for the Sr- and Ba-exchange Between the Small and Large Channels in LMS 13 X

1975 ◽  
Vol 30 (8) ◽  
pp. 951-954 ◽  
Author(s):  
K. Frohnecke ◽  
H. Fischbach
Keyword(s):  
Ion Exchange ◽  
Rate Constants ◽  
Diffusion Coefficients ◽  
Large Diameter ◽  
Direct Determination ◽  
Order Reaction ◽  
First Order Reaction ◽  
First Order ◽  
Total Exchange

Abstract Direct Determination of the Rate Constants for the Sr-and Ba-exchange Between the Small and Large Channels in LMS 13X The rate constants for the intracristalline Sr-and Ba-exchange between the small and large diameter channels of LMS 13X were measured. For this matter the method of interrupting the ion exchange was modified. It is assumed, that a first order reaction takes place. Using the rate constants and the diffusion coefficients, which were measured by Hoinkis and Levi, the total exchange of Sr 2+ and Ba 2+ could be calculated.

Effects of Carrageenan and Chitosan as Coating Materials on the Thermal Degradation of Microencapsulated Phycocyanin from Spirulina sp.

2019 ◽  
Vol 15 (5-6) ◽  
Author(s):  
H. Hadiyanto ◽  
Marcelinus Christwardana ◽  
Meiny Suzery ◽  
Heri Sutanto ◽  
Ayu Munti Nilamsari ◽  
...  
Keyword(s):  
Antioxidant Activity ◽  
Thermal Degradation ◽  
Rate Constants ◽  
Reaction Rate ◽  
Order Reaction ◽  
Coating Materials ◽  
First Order ◽  
Reaction Rate Constants ◽  
Kinetics Of

AbstractPhycocyanin is a natural substance that can be used as an antioxidant and food colorant. The quality of phycocyanin deteriorates when it is exposed to heat, and such deterioration is evidenced by decreases in its antioxidant activity and color. Encapsulation, which introduces a coating material over a substance of interest, has been applied to prevent changes in substance quality. The objective of the present research is to evaluate the kinetics of thermal degradation of phycocyanin coated with carrageenan or chitosan. Encapsulated phycocyanin samples were exposed to temperatures of 40, 50, or 60 °C for 90 min, and kinetics of the resulting degradation was evaluated to determine changes in sample quality. The results showed that the thermal degradation of encapsulated phycocyanin at 40–60 °C follows first-order reaction kinetics with reaction rate constants (k) of 4.67–9.17 × 10–5 s-1 and 3.83–7.67 × 10–5 s-1 for carrageenan and chitosan, respectively, and that the k of encapsulated phycocyanin is slower than that obtained from samples without the coating materials (control). Encapsulation efficiencies (EE) of 68.66 % and 76.45 %, as well as loading capacities of 45.28 % and 49.16 %, were, respectively, obtained for carrageenan and chitosan.

scholarly journals Photocatalytic degradation of natural organic matter: Kinetic considerations and light intensity dependence

2004 ◽  
Vol 6 (2) ◽  
pp. 73-80 ◽  
Author(s):  
Ceyda Senem Uyguner ◽  
Miray Bekbolet
Keyword(s):  
Humic Acid ◽  
Light Intensity ◽  
Photocatalytic Degradation ◽  
Rate Constants ◽  
Reaction Rates ◽  
Order Reaction ◽  
First Order Reaction ◽  
Pseudo First Order Reaction ◽  
First Order ◽  
Pseudo First Order

The current study was conducted to investigate the photocatalytic degradation kinetics of humic acid at different light intensities using commercialTiO2powders. The pseudo first order kinetic model and Langmuir-Hinshelwood (L-H) rate equation in modified forms were used to compare the photocatalytic activities ofTiO2materials as a function of light intensity. Under constant irradiation conditions, the pseudo first order reaction rates as well as L-H rates were found to be decreasing in the following trend; Degussa P-25, Millennium PC-500 and Millennium PC-100. The pseudo first order rate constants showed the same decreasing trend as the pseudo first order reaction rates while L-H rate constants exhibited a light intensity related change in the ordering of the photocatalysts. At the lowest light intensity, L-H rate constants decreased as follows: Millennium PC-500>Millennium PC-100>Degussa P-25. However, increasing the light intensity changed the order to; Millennium PC-100>Millennium PC-500>Degussa P-25 revealing the significance of the L-H adsorption constant. Under constant irradiation conditions, ionic strength dependent changes in the structure of humic acid did not alter degradation efficiency trend of the photocatalyst specimens and they were ordered such as; Degussa P-25>Millennium PC-500>Hombikat UV-100>Millennium PC-100 > Merck. The results presented in this research also confirmed the effectiveness of Degussa P-25 as a photocatalyst for the degradation of humic acid.

scholarly journals Formation and decomposition of 3-chloropropane-1,2-diol in model systems

2004 ◽  
Vol 22 (SI - Chem. Reactions in Foods V) ◽  
pp. S263-S266 ◽  
Author(s):  
M. Doležal ◽  
P. Calta ◽  
J. Velíšek
Keyword(s):  
Rate Constants ◽  
Maximum Concentration ◽  
Order Reaction ◽  
Model Systems ◽  
Processed Foods ◽  
Surface Layers ◽  
First Order ◽  
Maximum Value ◽  
Thermally Processed ◽  
Added Salt

Model experiments were carried out using mixtures of 3-chloropropane-1,2-diol (3-MCPD), its precursor glycerol, NaCl, water and an emulsifier. The aim of this study was to simulate formation and decomposition of 3-MCPD at the surface layers of thermally processed foods containing naturally present or intentionally added salt. The formed 3-MCPD levels depend on temperature and reach the maximum value at 230°C. One kg of glycerol gives rise to about 50 mg of 3-MCPD, while about 0.6 mg of 3-MCPD arise at 100°C. The rate constants k<sub>1</sub> of 3-MCPD formation from glycerol and constants k<sub>2</sub> of 3-MCPD decomposition were calculated employing the first order reaction kinetics. The rate constants k<sub>2</sub> of 3-MCPD degradation are higher than the respective constants of its formation. Other kinetic parameters (time of maximum concentration) were also calculated and the achieved results were discussed with respect to levels of 3-MCPD in foods.

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