Vulcanization of Elastomers. 14. Role of the Oxide in Vulcanization with Compounds of the Thiuram Series. I

1958 ◽  
Vol 31 (3) ◽  
pp. 539-547
Author(s):  
Walter Scheele ◽  
Horst-Eckart Toussaint ◽  
Peter Stange
Keyword(s):  
Zinc Oxide ◽  
Linear Functions ◽  
Practical Significance ◽  
Molar Ratio ◽  
Oxide Content ◽  
Velocity Constant ◽  
Mixing Ratios ◽  
Oxide Addition ◽  
Kinetics Of

Abstract The present paper is concerned with the influence of TETD concentration and of zinc oxide content upon the kinetics of the vulcanization of natural rubber and Perbunan 2818 with TETD. The following results were obtained for vulcanization at 120° C. 1. The velocity constants of TETD decrease and ZnDEDC formation are linear functions of the zinc oxide content at constant TETD concentrations. 2. If TETD and zinc oxide are present in constant molar mixing ratios, then the velocity constant of TETD decrease is independent of the amount of the mixture while that of ZnDEDC formation rises linearly with zinc oxide addition. 3. The velocity constant of TETD decrease diminishes with increasing TETD concentration when the zinc oxide content of the mixture is held constant. Under these conditions the velocity constant of ZnDEDC formation remains unchanged. 4. Everything shows that the velocity constant of ZnDEDC formation depends only on the zinc oxide content of the mixture while that of TETD decrease is dependent on the molar ratio of zinc oxide and TETD. 5. The relationships found are expressed mathematically, and the practical significance of the relationships is pointed out.

Vulcanization of Elastomers. 18. Vulcanization of Natural Rubber with Sulfur in the Presence of Mercaptobenzothiazole. III

1958 ◽  
Vol 31 (3) ◽  
pp. 548-558 ◽  
Author(s):  
Otto Lorenz ◽  
Elisabeth Echte
Keyword(s):  
Zinc Oxide ◽  
Natural Rubber ◽  
Zinc Stearate ◽  
Oxide Content ◽  
Square Root ◽  
Initial Concentration ◽  
Velocity Constant ◽  
Equilibrium Swelling ◽  
Kinetics Of ◽  
Limiting Value

Abstract The present work is concerned with the influence of the concentration of sulfur and the zinc oxide content on the kinetics of the vulcanization of natural rubber with sulfur in the presence of mercaptobenzothiazole, zinc stearate and zinc oxide. The following results were obtained. 1. The velocity constant of the sulfur decrease, kSI, is inversely proportional to the initial concentration of sulfur. 2. The velocity constant of the change with time of the reciprocal equilibrium swelling, kQI, is inversely proportional to the square root of the initial concentration of sulfur. 3. The limiting value of the reciprocal equilibrium swelling, 1/Q∞ (degree of crosslinking), at constant stearate content, is proportional to the square root of the initial concentration of sulfur. 4. The amount of accelerator consumed during vulcanization increases with increase in the initial amount of sulfur. The decrease in the accelerator is a first order reaction having approximately the same rate as the decrease of sulfur. 5. The velocity constants of the sulfur decrease and the change with time of the reciprocal equilibrium swelling are practically independent of the amount of zinc oxide. Other situations exist, of course, for compounds without zinc oxide. 6. Empirical equations were derived to express the dependence of the constants kSI, kQI and 1/Q∞ on the composition of the mixture.

Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 1. Effects of Mediator Concentration

Holzforschung ◽  
2000 ◽  
Vol 54 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Mikhail Yu. Balakshin ◽  
Chen-Loung Chen ◽  
Josef S. Gratzl ◽  
Adrianna G. Kirkman ◽  
Harald Jakob
Keyword(s):  
Kinetic Studies ◽  
Veratryl Alcohol ◽  
Alcohol Oxidation ◽  
Order Rate Constant ◽  
Molar Ratio ◽  
Active Centers ◽  
First Order ◽  
System Part ◽  
Kinetics Of

Summary Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction follows a pseudo-first order reaction law. The first order rate constant (κ) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle. The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing with the original substrate for active centers of the laccase. This results in inhibition of veratryl alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized mediator.

The Vulcanization of Elastomers. VII. The Vulcanization of Natural Rubber with Thiuram Disulfides. Part IV

1957 ◽  
Vol 30 (1) ◽  
pp. 69-76 ◽  
Author(s):  
Walter Scheele ◽  
Peter Stange
Keyword(s):  
Zinc Oxide ◽  
Natural Rubber ◽  
Constant Temperature ◽  
Rate Constants ◽  
Experimental Error ◽  
Oxide Content ◽  
Oxide Crystals ◽  
Kinetics Of ◽  
Limiting Value

Abstract The present paper deals with the kinetics of the thiuram vulcanization at varying thiuram disulfide concentrations as well as with the influence of the zinc oxide content upon vulcanization at constant temperature (120° C). It was found : 1. The limiting value of dithiocarbamate formation of 66 mole per cent relative to the amount of thiuram disulfide used is—within wide limits—independent of the initial thiuram disulfide concentration. 2. At constant thiuram disulfide concentration the limiting value of dithiocarbamate formation is unchanged when the zinc oxide content is successively increased. 3. Changing the zinc oxide content while the thiuram disulfide concentration is kept constant exerts an influence on the kinetics of the decrease of thiuram as well as on the increase of dithiocarbamate. The rate constants of both reactions increase. 4. It is concluded from these results that in all probability vulcanization is initiated on the surface of the zinc oxide crystals. 5. Even in stocks containing as much as 40 g. zinc oxide per hundred g. of compounds, the limiting value of dithiocarbamate formation remains unchanged. This was verified by the analysis of vulcanizates after extremely long cure times. The average limiting value of two experiments after 24 hours of cure was 65 mole per cent which corresponds to a two-thirds reaction within the experimental error.

STRUCTURAL COMPONENTS OF THE PRIVATE MEDICAL SECTOR ACTIVATION MECHANISM

Economical ◽  
2019 ◽  
Vol 2 (2(21)) ◽  
pp. 170-177
Author(s):  
Anzhela Bairak ◽  
Keyword(s):  
Health Care ◽  
Health Care System ◽  
Activation Mechanism ◽  
Practical Significance ◽  
Structural Components ◽  
Medical Sector ◽  
Analysis And Synthesis ◽  
Private Medicine ◽  
Care System

The article examines the problems of private medicine in the health care system of the country. The aim of the article is to determine the structural components of the mechanism of activation of the private medical sector as a reserve for the provision of quality and affordable medical services and a driver for the development of the medical industry. The descriptive-analytical method, methods of analysis and synthesis, comparison, statistical, analysis and scientific generalization were used in the paper. The study substantiates the strengthening of the role of the private medical sector in the health care management system. The key problems of the domestic private medical sector and the restraining factors of its development are identified. It is concluded that it is necessary to develop a mechanism to promote the development of private medicine through a policy of active change in the health care system. The directions of activation of the private medical sector as a target reference point in the process of determining the structural elements of the organizational and economic mechanism are outlined. The structural detail of the mechanism of activation of the private medical sector for optimization of the health care system is offered. The practical significance of the obtained results is that the results of the research presented in the article are a practical basis for the development and improvement of mechanisms of public administration in the field of health care.

Thermodynamic and Kinetic Investigation of the Solvent Effect on the Oxidation of [Co(en)2SCH2COO]+ with S2O82- In Water-Methanol and Water-tert-Butyl Alcohol Mixtures

1993 ◽  
Vol 58 (5) ◽  
pp. 1001-1006 ◽  
Author(s):  
Oľga Vollárová ◽  
Ján Benko
Keyword(s):  
Transfer Functions ◽  
Activation Parameters ◽  
Butyl Alcohol ◽  
Oxidation Of Co ◽  
Kinetics Of Oxidation ◽  
Tert Butyl ◽  
Tert Butyl Alcohol ◽  
Alcohol Mixtures ◽  
Kinetics Of

The kinetics of oxidation of [Co(en)2SCH2COO]+ with S2O82- was studied in water-methanol and water-tert-butyl alcohol mixtures. Changes in the reaction activation parameters ∆H≠ and ∆S≠ with varying concentration of the co-solvent depend on the kind of the latter, which points to a significant role of salvation effects. The solvation effect on the reaction is discussed based on a comparison of the transfer functions ∆Ht0, ∆St0 and ∆Gt0 for the initial and transition states with the changes in the activation parameters accompanying changes in the CO-solvent concentration. The transfer enthalpies of the reactant were obtained from calorimetric measurements.

scholarly journals Hydrothermally Assisted Fabrication of TiO2-Fe3O4 Composite Materials and Their Antibacterial Activity

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4715
Author(s):  
Adam Kubiak ◽  
Marta Kubacka ◽  
Elżbieta Gabała ◽  
Anna Dobrowolska ◽  
Karol Synoradzki ◽  
...  
Keyword(s):  
Antibacterial Activity ◽  
Composite Materials ◽  
Bet Surface Area ◽  
Molar Ratio ◽  
Oxide Content ◽  
Gram Positive ◽  
Gram Negative ◽  
Transmission Electron ◽  
Xrd Patterns ◽  
Oxide Composites

The TiO2-Fe3O4 composite materials were fabricated via the hydrothermal-assisted technique. It was determined how the molar ratio of TiO2 to Fe3O4 influences the crystalline structure and morphology of the synthesized composite materials. The effect of the molar ratio of components on the antibacterial activity was also analyzed. On the basis of XRD patterns for the obtained titanium(IV) oxide-iron(II, III) oxide composites, the two separate crystalline forms—anatase and magnetite —were observed. Transmission electron microscopy revealed particles of cubic and tetragonal shape for TiO2 and spherical for Fe3O4. The results of low-temperature nitrogen sorption analysis indicated that an increase in the iron(II, III) oxide content leads to a decrease in the BET surface area. Moreover, the superparamagnetic properties of titanium(IV) oxide-iron(II, III) oxide composites should be noted. An important aim of the work was to determine the antibacterial activity of selected TiO2-Fe3O4 materials. For this purpose, two representative strains of bacteria, the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, were used. The titanium(IV) oxide-iron(II, III) oxide composites demonstrated a large zone of growth inhibition for both Gram-positive and Gram-negative bacteria. Moreover, it was found that the analyzed materials can be reused as antibacterial agents in three consecutive cycles with good results.

scholarly journals Association between perinatal factors, genetic susceptibility to obesity and age at adiposity rebound in children of the EDEN mother–child cohort

2021 ◽  
Author(s):  
Aminata Hallimat Cissé ◽  
Sandrine Lioret ◽  
Blandine de Lauzon-Guillain ◽  
Anne Forhan ◽  
Ken K. Ong ◽  
...  
Keyword(s):  
Weight Gain ◽  
Genetic Susceptibility ◽  
Gestational Weight Gain ◽  
Gestational Age ◽  
Obesity Risk ◽  
Perinatal Factors ◽  
Gestational Weight ◽  
Adiposity Rebound ◽  
Kinetics Of

Abstract Background Early adiposity rebound (AR) has been associated with increased risk of overweight or obesity in adulthood. However, little is known about early predictors of age at AR. We aimed to study the role of perinatal factors and genetic susceptibility to obesity in the kinetics of AR. Methods Body mass index (BMI) curves were modelled by using mixed-effects cubic models, and age at AR was estimated for 1415 children of the EDEN mother–child cohort study. A combined obesity risk-allele score was calculated from genotypes for 27 variants identified by genome-wide association studies of adult BMI. Perinatal factors of interest were maternal age at delivery, parental education, parental BMI, gestational weight gain, maternal smoking during pregnancy, and newborn characteristics (sex, prematurity, and birth weight). We used a hierarchical level approach with multivariable linear regression model to investigate the association between these factors, obesity risk-allele score, and age at AR. Results A higher genetic susceptibility to obesity score was associated with an earlier age at AR. At the most distal level of the hierarchical model, maternal and paternal educational levels were positively associated with age at AR. Children born to parents with higher BMI were more likely to exhibit earlier age at AR. In addition, higher gestational weight gain was related to earlier age at AR. For children born small for gestational age, the average age at AR was 88 [±39] days lower than for children born appropriate for gestational age and 91 [±56] days lower than for children born large for gestational age. Conclusion The timing of AR seems to be an early childhood manifestation of the genetic susceptibility to adult obesity. We further identified low birth weight and gestational weight gain as novel predictors of early AR, highlighting the role of the intrauterine environment in the kinetics of adiposity.

Sign in / Sign up

Export Citation Format

Share Document