Network Scission Processes in Peroxide Cured Methylvinyl Silicone Rubber

1967 ◽  
Vol 40 (2) ◽  
pp. 629-634
Author(s):  
D. K. Thomas
Keyword(s):  
Silicone Rubber ◽  
Elevated Temperatures ◽  
Main Chain ◽  
Methyl Groups ◽  
Chain Polymer ◽  
Filled Rubber ◽  
Oxidative Reactions ◽  
Silica Filler ◽  
Silicone Rubbers ◽  
Hydrolysis Of

Abstract In what appeared to be a complex system it transpires that network scission in methylvinyl silicone rubbers at temperatures below 250° C is due largely to hydrolytic reactions in the main chain polymer. At temperatures of 250° C and above there are indications that a significant amount of scission arises from oxidative reactions in the crosslinks, and that this reaction is catalyzed by acidic residues in the rubber. There is no indication that acidic byproducts of the vulcanization reaction catalyze the hydrolysis of siloxane bonds in the polymer. In conventional heat aging tests in which the rubber remains in an unstrained condition the effects of hydrolysis will only be observed if the concentration of water in the system is allowed to rise. Under these circumstances softening will occur because of a shift in the position of equilibrium in the reaction ∼Si—O—Si—O∼ + H2O→∼Si—OH+ HO—Si—O∼ On aging the material in a well ventilated situation the effects of hydrolysis are not seen and the silicone rubber becomes brittle after long exposure at high temperature. This embrittlement must result from additional crosslinking caused by oxidative reactions in the methyl groups of the main chain polymer. When the rubber is used in compression or tension, hydrolytic scission will affect performance, and in applications of this sort it is important to dry the rubber before use and prevent access of moisture to the component during use. With filled rubber the silica filler is a further source of moisture and drying needs to be carried out at elevated temperatures immediately before use. In order to improve the confined heat aging performance of silicone rubber an alternative filler to fine silica is needed which does not have the same affinity for water. It may be, however, that ability to reinforce silicone rubber and affinity for water are inseparable.

Solution and Diffusion in Silicone Rubber. II. Influence of Fillers

1963 ◽  
Vol 36 (3) ◽  
pp. 651-659 ◽  
Author(s):  
R. M. Barrer ◽  
J. A. Barrie ◽  
N. K. Raman
Keyword(s):  
Silicone Rubber ◽  
Porous Silica ◽  
Reference Models ◽  
Silica Filler ◽  
High Area ◽  
Silicone Rubbers ◽  
And Diffusion

Abstract An investigation has been made of the effect of a high area silica filler upon the solubility and diffusion of some C4 and C5 paraffins in silicone rubbers. The membranes studied contained by weight 0, 10, 20, 30 and 40 parts of filler per 100 parts of polymer. The solubilities have been discussed in terms of two reference models: the first in which silica and rubber phases act independently as sorbents; and the second in which the filler is regarded as completely wetted by polymer and is thus a non-sorbent. Diffusion and permeation have also been considered in terms of the models, assuming with the first model an immobile sorbed layer on the porous silica. It has been found that, although some aspects of the behavior can be explained, the results are not fully in agreement with either model, and that the behavior of the heterogenous membrane is complex.

Silicone Rubber, Its Development and Technological Progress

1988 ◽  
Vol 61 (3) ◽  
pp. 470-502 ◽  
Author(s):  
Keith E. Polmanteer
Keyword(s):  
Silicone Rubber ◽  
Technological Progress ◽  
Main Chain ◽  
Backbone Flexibility ◽  
Commercial Development ◽  
Silicone Polymers ◽  
Chronological Sequence ◽  
Group Rotation ◽  
Molecular Forces ◽  
Silicone Rubbers

Abstract This paper has described silicone rubber, its first commercial development in 1944, and its technological progress since then. Pioneering research on silicon opened the door to the development of silicone polymers and silicone rubber. The substitution of two methyl groups on silicon was present in the first examples of silicone rubber and still is the predominant organic group in commercial silicone rubber today. Silicone rubbers have filled a need in the marketplace because of their combination of unusual properties not found in other rubbers. The alternating inorganic main-chain atoms of silicon and oxygen, and the two pendant organic groups, primarily methyl, provide strong chain bonds, backbone flexibility, ease of side-group rotation, and low “inter” and “intra” molecular forces. This molecular makeup and properties thereof are primarily responsible for the observed performance of silicone rubbers. Many significant advances in silicone rubber have been discussed in chronological sequence to trace its history from 1944 to 1987.

Filler material in medical-grade silicones

1984 ◽  
Vol 42 ◽  
pp. 392-393
Author(s):  
R. T. Greer
Keyword(s):  
Silicone Rubber ◽  
Fumed Silica ◽  
Phase Distribution ◽  
Flame Temperature ◽  
Submicroscopic Structure ◽  
Wet Process ◽  
Silicone Rubbers ◽  
Hydrolysis Of ◽  
Degree Of Reinforcement ◽  
Medical Grade

Medical-grade silicone rubber is a widely utilized biomaterial. As is the case for most rubbers, fillers are used to give additional strength to the polymer. The nature of the filler is of interest in the development, fabrication and improvement of medical devices where blood and tissue compatibility may be altered by submicroscopic structure and phase distribution. The medical-grade silicone rubbers are of two types, heat-vulcanizing and room-temperature-vulcanizing (RTV).The filler used in heat-vulcanizing types is fumed silica of a small particle size of the order of 0.03 µm and smaller (0.007 µm; 0.012 µm; Cab-0-Sil®, Cabot Corp., Boston, MA 02110). It is made by a vapor phase process (hydrolysis of silicone tetrachloride at 1100° C ), producing a colloidal amorphous silica (SiO2). It is generally classified as a fumed silica due to its production at a high flame temperature. Fume-process silicas give the highest degree of reinforcement of silicone rubber compared with finely divided silicas made by a wet process (aerogels), or with diatomaceous earth.

Ultrasonic Devulcanization of Precipitated Silica-Filled Silicone Rubber

2001 ◽  
Vol 74 (2) ◽  
pp. 303-316 ◽  
Author(s):  
Sang E. Shim ◽  
A. I. Isayev
Keyword(s):  
Mechanical Properties ◽  
Silicone Rubber ◽  
Crosslink Density ◽  
Performance Characteristics ◽  
Processing Conditions ◽  
Precipitated Silica ◽  
Filled Rubber ◽  
Filled Rubbers ◽  
Silicone Rubbers ◽  
Considerable Enhancement

Abstract This investigation involves the recycling of precipitated silica-filled silicone rubber using a continuous ultrasonic reactor. The processing conditions utilized in devulcanization of the filled systems were similar to those in our previous work on unfilled systems. Significant differences were observed in devulcanization of unfilled and filled systems. A decrease in gel fraction and crosslink density was sufficient for devulcanized silica-filled silicone rubber to be reprocessed and revulcanized. The cure behavior of silicone rubber and the mechanical properties of virgin, and revulcanized rubber were measured. Results showed that unfilled silicone rubbers gave no change in vulcanizate mechanical properties after revulcanization. However, in the filled rubbers there was a decrease in the mechanical properties of revulcanizates. In order to achieve an improvement in the properties, devulcanized filled rubbers were blended with virgin filled rubber in various proportions. The obtained results indicated a considerable enhancement of the performance characteristics of these blend vulcanizates.

scholarly journals The Hsp60 Protein of Helicobacter Pylori Exhibits Chaperone and ATPase Activities at Elevated Temperatures

BioChem ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 19-25
Author(s):  
Jose A. Mendoza ◽  
Julian L. Ignacio ◽  
Christopher M. Buckley
Keyword(s):  
Helicobacter Pylori ◽  
Heat Stress ◽  
Molecular Chaperone ◽  
Elevated Temperatures ◽  
Citrate Synthase ◽  
Gastric Epithelium ◽  
Acidic Conditions ◽  
H Pylori ◽  
Induced Aggregation ◽  
Hydrolysis Of

The heat-shock protein, Hsp60, is one of the most abundant proteins in Helicobacter pylori. Given its sequence homology to the Escherichia coli Hsp60 or GroEL, Hsp60 from H. pylori would be expected to function as a molecular chaperone in this organism. H. pylori is a type of bacteria that grows on the gastric epithelium, where the pH can fluctuate between neutral and 4.5, and the intracellular pH can be as low as 5.0. We previously showed that Hsp60 functions as a chaperone under acidic conditions. However, no reports have been made on the ability of Hsp60 to function as a molecular chaperone under other stressful conditions, such as heat stress or elevated temperatures. We report here that Hsp60 could suppress the heat-induced aggregation of the enzymes rhodanese, malate dehydrogenase, citrate synthase, and lactate dehydrogenase. Moreover, Hsp60 was found to have a potassium and magnesium-dependent ATPase activity that was stimulated at elevated temperatures. Although, Hsp60 was found to bind GTP, the hydrolysis of this nucleotide could not be observed. Our results show that Hsp60 from H. pylori can function as a molecular chaperone under conditions of heat stress.

scholarly journals Investigation of Hydrothermally Stressed Silicone Rubber/Silica Micro and Nanocomposite for the Coating High Voltage Insulation Applications

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3567
Author(s):  
Faiza Faiza ◽  
Abraiz Khattak ◽  
Safi Ullah Butt ◽  
Kashif Imran ◽  
Abasin Ulasyar ◽  
...  
Keyword(s):  
Silicone Rubber ◽  
Structural Changes ◽  
Polymer Chains ◽  
Hydrothermal Conditions ◽  
Silica Filler ◽  
Before And After ◽  
Aging Conditions ◽  
The Stability ◽  
Micro Silica ◽  
Applied Stresses

Silicone rubber is a promising insulating material that has been performing well for different insulating and dielectric applications. However, in outdoor applications, environmental stresses cause structural and surface degradations that diminish its insulating properties. This effect of degradation can be reduced with the addition of a suitable filler to the polymer chains. For the investigation of structural changes and hydrophobicity four different systems were fabricated, including neat silicone rubber, a micro composite (with 15% micro-silica filler), and nanocomposites (with 2.5% and 5% nanosilica filler) by subjecting them to various hydrothermal conditions. In general, remarkable results were obtained by the addition of fillers. However, nanocomposites showed the best resistance against the applied stresses. In comparison to neat silicone rubber, the stability of the structure and hydrophobic behavior was better for micro-silica, which was further enhanced in the case of nanocomposites. The inclusion of 5% nanosilica showed the best results before and after applying aging conditions.

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