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 SILICONE RUBBER

Silicone rubber is an elastomer composed of Silicone. They are thermosetting polymers. The elastomer does not possess a Carbon backbone like in other organic rubbers. The rubbers are chemically polysiloxane of the general formula.

Where R is methyl, phenyl, vinyl or trifluroprofyl

Manufacturing methods of Silicone rubber

02 techniques have been used to manufacture Silicone rubbers

  1. Hydrolysis of the appropriate dichlorosilanes to form cyclic tetrasiloxanes
  2. Conversion of cyclotetracysiloxanes to long-chain siloxanes, in the presence of the suitable catalyst
Silicone rubbers are available in the market in the form of solid or liquid.The solid form molecular weight is high and composed of long polymer chains. The solid Silicone rubbers are processed by the conventional method of the industry and the liquid form is vulcanizing at room temperature.The liquid Silicone rubber is composed of shorter chains, therefore the molecular weight is low. Liquid Silicone rubber has better flow properties. To process liquid form you need specially designed injection mold and extruder machinery. The cure cycle of liquid silicone rubber is shorter, compare with solid form and the process may be fully automated. 

PROPERTIES OF SILICONE RUBBERS
  • Silicone rubber can be used for wide temperature range applications such as 100°C to 350°C
  • These rubbers have outstanding resistance to heat, oxidation, oils, and various types of chemicals. The reason for such resistance is due to the Silicone rubber has a Si-O bond in its structure
  • Like other organic rubbers, Silicone rubber is not subjected to Ozone degradation
  • Electrical insulation
  • Abrasion resistance
Since Silicone rubber is a thermosetting polymer, the mixed compound must be subjected to a shaping process prior to the formation of cross-links. The shaping can be done by, using techniques such as casting, extrusion, or molding. The selection of forming process is determined by the viscosity of the compound mix. 

Curing of Silicone Rubbers

Silicone rubbers only can be cured with organic peroxides. These peroxides are two types.

  1. Diacyl Peroxides   ROC.O.COR
        Example: Benzoyl Peroxide

    2. Dialkyl or Diarylalkyi Peroxides   R-OO-R

        Example: Ditertiary butyl Peroxides
                         Dicumyl Peroxides
The typical dosage of each type used in rubber mix formulation is 3-5phr

Applications of Silicone Rubbers

Silicone rubber exhibits modest physical properties at room temperature but has the ability to maintain strength and resilience properties at elevated temperatures where other elastomers fail. The operating temperature range of the rubber is between 100°C to 350°C and has outstanding resistance to heat, oxidation, oils, and chemicals. 

Applications
  • Aerospace industry
  • Automotive industry
  • Electrical
  • Medicine




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