Heat-cured rubber

Silicone Heat-Cured Rubber. Sihcone elastomers are made by vulcanising high molecular weight (>5 x 10 mol wt) linear polydimethylsiloxane polymer, often called gum. Fillers are used in these formulations to increase strength through reinforcement. Extending fillers and various additives, eg, antioxidants, adhesion promoters, and pigments, can be used to obtain certain properties (59,357,364). 

The spectral dispersion for organosilicones may be considerable for certain families of compounds. This is reflected in the Si chemical shifts of siloxanes, -(SiRR 0) -, an important class of compounds which includes resins, fluids, room-temperature vulcanized and heat-cured rubber consumer products. The first, Si NMR results (5,78) reported on polydimethylsiloxanes showed that individual resonance... 

This article looks at a new line of antimicrobial conqxmnds for heat-cured rubber that helps to solve cleanness problems in conversion sectors for food, medicine and industry and other apphcations prone to the ptolifetafion of microbes. The new Elastoguard antimicrobial elastomers offer effective prevention against bacteria, fungi and yeast in rubber parts, and, at the same time, avoid problems caused in the past by or nic biocides. Processes are discussed along with a ]ications and uses for Elastoguard in matty walks of life. USA... 

HCR heat-cured rubber HMWR high-molecular-weight rubber... 

Cured silicone LIM rubber can be fabricated with physical properties equivalent to heat-cured rubber (500). Shore A hardness can range from 30 to 70, depending on formulations. Typical physical properties include tensile strengths as high as 9.7 MPa (1400 psi), elongations at break of 500-775%, and tear strengths... 

Quality control testing of silicones utilizes a combination of physical and chemical measurements to ensure satisfactory product performance and processi-bility. For example, in addition to the usual physical properties of cured elastomers, the plasticity of heat-cured rubber and the extrusion rate of RTV elastomers under standard conditions are important to the customer. Where the silicone application involves surface activity, a use test is frequently the only reliable indicator of performance. For example, the performance of an antifoaming agent can be tested by measuring the foam reduction when the silicone emulsion is added to an agitated standard detergent solution. The product data sheets and technical bulletins from commercial silicone producers can be consulted for more information. 

With all of the aforementioned variables, hundreds of Pt-curable silicone products are available including heat-cured rubber, liquid injection moldable products and release coatings. There are also many curable products based on chemistry other than platinum condensation cure RTV, peroxide-cured and UV-cured epoxy silicones. With other functional groups and/or molecular weights, even more products are... 

White, sulphur chloride factices for heat-cured rubber goods, treated to remove labile chlorine. 

Originally, vulcanization implied heating natural rubber with sulfur, but the term is now also employed for curing polymers. When sulfur is employed, sulfide and disulfide cross-links form between polymer chains. This provides sufficient rigidity to prevent plastic flow. Plastic flow is a process in which coiled polymers slip past each other under an external deforming force when the force is released, the polymer chains do not completely return to their original positions. 

Kraton Polymers has developed a multiarm SIS (Kraton 1320X [37,46,47,50]) and SBS (Kraton KX-222C, [48,49]) for rapid UV/e-beam cure. Besides heat resistance improvements, plasticizer resistance is also improved in cured rubber-based systems. The dioctyl phthlate plasticizer common in PVC backing films is soluble in the styrenic domains of SBCs. Crosslinking of the mid-block provides cohesion even after plasticizer attack [51]. 

Other transparent cured rubber goods Transparency, safe for food application, weatherability. heat resistance... 

The quantity of heat (J/kg/K) required to raise the temperature of unit mass of the substance through 1 °C. The specific heat of rubber (around 2000) is much higher than that of metals (around 400 for steel) and it is therefore much more expensive to heat rubber than the mould, mandrel or last on which it is cured. 

Overcuring is encountered to some degree in all compounds of any thickness because of the slow conductance of heat through rubber. Earthmover tires may have tire shoulder gauges in excess of 0.3 m (M2 in.). The outside/inside are overcured to effect a satisfactory state-of-cure in the tread rubber. 

The time taken to heat the rubber to curing temperature, and... 

The relative effectiveness of nucleating agents in a polymer can be determined by measuring recrystallization exotherms of samples molded at different temperatures (105). The effect of catalyst concentration and filler content has been determined on unsaturated polyesters by using dynamic thermal techniques (124). Effects of formulation change on the heat of rubber vulcanization can be determined by dsc pressurized cells may be needed to reduce volatilization during the cure process (125). 

Thermal and Chemical Stability. In addition to load-bearing properties, tire reinforcement must be able to resist degradation by chemicals in cured rubber and heat generation. The most critical degradant depends on the material in use. Most thermoplastic reinforcements are either modified direedy or stabilized with additives to offset some, mosdy thermal, degradation (32,33). 

Polyethylene, polypropylene, polyvinyl chloride, polyamide Phenol-formaldehyde-cured rubber styrenated polyester Polyimide (ladder molecules) Polyethylene terephthalate Terylene, cellulose acetate Chloroprene rubber, polyisoprene Heat-resistant polymers... 

Silicone rubbers, such as General Electric RTV, represent a useful type of flexible adhesive. They can be clear or opaque, are fairly inert chemically, and some are usable up to 300°C or above. These silicones are just poured or extruded from a tube, and no heat cure is required since they cure by air drying. The resulting seals are not mechanically strong but will provide protection against water and oil. 

Sheet membrane linings are usually shipped in rolls. Exceptions include plasticized-unplasticized vinyl laminates, specially compounded asphalt and asphalt and rubber compounded sheets, usually shipped flat in cartons or boxes. These are applied to properly prepared surfaces with an adhesive that may be air-cured or heat-cured. At all events, so far as storage is concerned, temperatures above freezing and under 100°F are usually not matters of concern, unless the manufacturer or applicator so advises. Water and dirt, however, damage these materials so they should be stored in a clean storage area, off the ground and under cover. 

---