The Distribution of Combined Sulfur in Vulcanized Rubber and Its Bearing on the Sulfide Linkage Theory of Vulcanization

1939 ◽  
Vol 12 (2) ◽  
pp. 191-199
Author(s):  
I. Williams
Keyword(s):  
Physical Properties ◽  
Direct Evidence ◽  
Cross Linking ◽  
Direct Relation ◽  
Vulcanized Rubber ◽  
Free Sulfur

Abstract No direct evidence exists to support the sulfide linkage theory of vulcanization, which assumes that cross-linking of the molecules with sulfur would retain the elasticity and decrease the plasticity of the rubber. The following facts do not favor the sulfide linkage theory of vulcanization : (1) Vulcanized rubber can be peptized under conditions which do not appear to rupture a sulfide linkage. (2) No direct relation exists between the physical properties of vulcanized rubber and the amount of combined sulfur. (3) No direct relation exists between the ease of peptization and the physical properties of the vulcanizate. (4) Combined sulfur appears to assist the solvation of rubber. Rubber vulcanized with thiuram disulfides in the absence of free sulfur has poor physical properties but peptizes with difficulty. An increase in combined sulfur without a corresponding improvement in physical properties assists solvation. (5) Rubber having the best physical properties is also the most heterogeneous with respect to sulfur. The sulfide linkage theory would suggest that an even distribution of sulfur would produce the best physical properties. (6) Fractions of peptized vulcanizates, on evaporation of their solutions, leave insoluble vulcanized films, which shows that linkage by means of primary forces is unnecessary for producing the vulcanized condition.

Investigations of the Reversion of Vulcanized Rubber under Heat

1952 ◽  
Vol 25 (2) ◽  
pp. 241-250 ◽  
Author(s):  
Uma Shankar
Keyword(s):  
Free Energy ◽  
Hydrogen Sulfide ◽  
Methyl Iodide ◽  
Energy Of Activation ◽  
Cross Linking ◽  
Molar Free Energy ◽  
Vulcanized Rubber ◽  
Free Energy Of Activation ◽  
Equilibrium Swelling ◽  
Free Sulfur

Abstract (1) During reversion of a vulcanizate, the breakdown of cross-linkages, including those of polysulfides, predominates over any simultaneous reformation of cross-linkages. (2) The reverting modulus falls exponentially with time. (3) The calculated molar free energy of activation is 33.3 ± 1.7 kcal., irrespective of the temperature or the atmosphere of cure or the composition of the mix, and is sufficient to rupture an —S—S— bond. (4) The degree of cross-linking, estimated from the equilibrium swelling measurements in benzene, falls during reversion. (5) The exclusion of oxygen during curing does not prevent reversion if the temperature is high enough to supply the energy needed to break up the cross-linkages. (6) During reversion in nitrogen, hydrogen sulfide is freely evolved, and the C/H ratio rises above the value for C5H8. (7) Evidence for the formation and breakdown of polysulfides during reversion is provided by an increase in free sulfur and a decrease in combined sulfur during a given cure, and the methyl iodide reaction of the reverted vulcanizates.

The Formation and Structure of Vulcanizates

1949 ◽  
Vol 22 (1) ◽  
pp. 96-104
Author(s):  
J. Bardwell ◽  
C. A. Winkler
Keyword(s):  
Mechanical Properties ◽  
Molecular Weight ◽  
Physical Properties ◽  
Network Structure ◽  
Weight Distribution ◽  
Elastic Behavior ◽  
Cross Linking ◽  
Structural Factors ◽  
Experimental Proof ◽  
Vulcanized Rubber

Abstract The characteristic mechanical properties of vulcanized rubber are believed to result from a network structure made up of chainlike molecules bonded together by occasional cross-linkages. In relating the physical properties of the vulcanizate to the structure of the network, it is therefore necessary to consider the concentration of cross-linkages and the molecular-weight distribution of the rubber molecules before cross-linking. Various theories have been proposed for the dependence of elastic properties on these structural factors, but experimental proof of the suggested relations has been meager, largely because of the complexities met with in, vulcanization reactions. In the present investigation some of these difficulties have been overcome, and the quantitative relations between the elastic behavior of GR-S and its network structure have thereby been revealed.

scholarly journals A new role for bicarbonate in mucus formation

2010 ◽  
Vol 299 (4) ◽  
pp. L542-L549 ◽  
Author(s):  
Eric Y. T. Chen ◽  
Ning Yang ◽  
Paul M. Quinton ◽  
Wei-Chun Chin
Keyword(s):  
Cystic Fibrosis ◽  
Physical Properties ◽  
Direct Evidence ◽  
Hereditary Disease ◽  
Cross Linking ◽  
Swelling Kinetics ◽  
Direct Measurements ◽  
The Impact ◽  
First Time ◽  
Airway Cells

The impact of small anions on the physical properties of gel-forming mucin has been almost overlooked relative to that of cations. Recently, based on the coincident abnormalities in HCO3− secretion and abnormal mucus formed in the hereditary disease cystic fibrosis (CF), HCO3− was hypothesized to be critical in the formation of normal mucus by virtue of its ability to sequester Ca2+ from condensed mucins being discharged from cells. However, direct evidence of the impact of HCO3− on mucus properties is lacking. Herein, we demonstrate for the first time that mucin diffusivity (∼1/viscosity) increases as a function of [HCO3−]. Direct measurements of exocytosed mucin-swelling kinetics from airway cells showed that mucin diffusivity increases by ∼300% with 20 mM extracellular HCO3− concentration. Supporting data indicate that HCO3− reduces free Ca2+ concentration and decreases the amount of Ca2+ that remains associated with mucins. The results demonstrate that HCO3− enhances mucin swelling and hydration by reducing Ca2+ cross-linking in mucins, thereby decreasing its viscosity and likely increasing its transportability. In addition, HCO3− can function as a Ca2+ chelator like EGTA to disperse mucin aggregates. This study indicates that poor HCO3− availability in CF may explain why secreted mucus remains aggregated and more viscous in affected organs. These insights bear on not only the fundamental pathogenesis in CF, but also on the process of gel mucus formation and release in general.

Effect of Plasticizer and Cross-Linking Agent on the Physical Properties of Protein Films

2005 ◽  
Vol 10 (1) ◽  
pp. 88-91 ◽  
Author(s):  
Myoung-Suk Lee ◽  
Se-Hee Lee ◽  
Yu-Hyun Ma ◽  
Sang-Kyu Park ◽  
Dong-Ho Bae ◽  
...  
Keyword(s):  
Physical Properties ◽  
Cross Linking ◽  
Protein Films

Optimize Mixing Process Parameters of Synchronous Rotor Mixer Based on Orthogonal Method

2012 ◽  
Vol 501 ◽  
pp. 442-447
Author(s):  
Ping Fu ◽  
Feng Bao Bai ◽  
Chuan Sheng Wang ◽  
Shan Hu Li
Keyword(s):  
Physical Properties ◽  
Process Parameters ◽  
Fill Factor ◽  
Cooling Water ◽  
Mixing Process ◽  
Rotor Speed ◽  
Orthogonal Method ◽  
Cooling Water Temperature ◽  
Vulcanized Rubber ◽  
The Relationship

In this paper adopting the orthogonal method, self-developed compound formulation had tested, and the relationship between the physical properties of vulcanized rubber and rectangular synchronous rotor mixer parameters had researched. The results showed that when the fill factor was 0.6, the rotor speed was 70r/min, cooling water temperature was 45 °C, pressure on the top bolt was 0.8Mpa, the physical properties of the vulcanized rubber was best.

scholarly journals Reserch on cross-linking densities and fundamental physical properties of rubber.

1993 ◽  
Vol 66 (2) ◽  
pp. 117-123 ◽  
Author(s):  
Hideo NAKAUCHI ◽  
Sakae INOUE ◽  
Kazuo NAITO
Keyword(s):  
Physical Properties ◽  
Cross Linking ◽  
Fundamental Physical

Effects of boric acid addition and sintering temperature on the thermal conductivity of perlitebased insulation materials

2020 ◽  
Vol 62 (4) ◽  
pp. 408-412
Author(s):  
Yuksel Palaci
Keyword(s):  
Thermal Conductivity ◽  
Physical Properties ◽  
Boric Acid ◽  
Thermal Insulation ◽  
Sintering Temperature ◽  
Direct Relation ◽  
Insulation Materials ◽  
Acid Addition ◽  
Composition Characteristics

Abstract In this study, the variation of thermal conductivity and density of 15 wt.-% boric acid - 85 wt.-% sepiolite, 30 wt.-% boric acid - 30 wt.-% sepiolite - 40 wt.-% perlite, 30 wt.-% boric acid - 30 wt.-% cordierite - 40 wt.-% perlite and 30 wt.-% boric acid - 30 wt.-% alumina - 40 wt.-% perlite compositions at 700 °C and 900 °C sintering temperatures were investigated. The results show that increasing the amount of boric acid and decreasing the sintering temperature lead to an improvement in thermal insulation properties. There is a direct relation between the thermal conductivity and density of the specimens. Both physical properties change with a change in the sintering temperature and the composition characteristics. Minimum thermal conductivity has been observed in a specimen consisting of 30 wt.-% boric acid - 30 wt.-% alumina - 40 wt.-% perlite.

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