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Room Temperature Vulcanizing silicones have been designed to serve many purposes.  Over the years the form and function of these materials has evolved.  Here's a basic primer on the basic differences between the grades of RTV and how they work.

RTV-1 SILICONE RUBBER

ELASTOSIL® RTV-1 silicone rubbers are ready-to-use, one-part products of free-flowing to non-sag consistency, which cure under the influence of atmospheric moisture to form a silicone elastomer (RTV-1 = room-temperature vulcanizing, 1 part). Thanks to the outstanding properties of silicones, these products are ideal for many sealing, bonding and coating applications.

Curing commences when the product is exposed to atmospheric moisture, with elimination of by-products. This reaction, also referred to as vulcanization, begins at the surface of the applied layer of silicone rubber and gradually progresses inwards. Depending on the type of crosslinker used, the curing system can be one of three kinds:

RTV-1 Cure System Types

  •  Basic or amine systems: small amounts of an amine are eliminated.
  •  Acidic or acetoxy systems: small amounts of acetic acid are eliminated.
  •  Neutral, i.e. oxime or alkoxy systems: small amounts of an oxime or alcohol are eliminated.

 

RTV-2 SILICONE RUBBER
Condensation-Curing Systems

Condensation-curing WACKER RTV-2 silicone rubbers are composed of a rubber base and a curing agent which contains a tin catalyst. In condensation curing, the polymer chains bond together via a crosslinker and ethanol is released as a by-product. Temperatures exceeding 90 °C before curing is complete result in reversion.

Properties

  •  RTV-2 grades contain an organo-tin catalyst
  •  Volatile alcohol by-product released during curing
  •  At temperatures exceeding 90 °C, reversion sets in
  •  When heating to boost curing rate, temperature must not exceed 80 °C
  •  No inhibition of curing
  •  Weight loss and shrinkage occur during curing (0.2 - 2 % linear shrinkage)
  •  Curing rate can be adjusted to a certain extent by varying the quantity of the curing agent
 

RTV-2 SILICONE RUBBER
Platinum Catalyzed Systems

Platinum-curing WACKER RTV-2 silicone rubbers are composed of two components, designated A and B. In platinum-curing, polymer chains are linked through a hydrosilylation reaction at the vinyl groups by means of the hydrogen-containing curing agent. Some platinum-curing silicone rubbers are available as ready-to-use one-component products. These are cured by heating to high temperatures.

Properties

  •  RTV-2 grades contain an organo-platinum compound as catalyst
  •  No weight loss on curing and very low shrinkage (< 0.1 %)
  •  No by-products released
  •  Curing can be accelerated by heating (e.g. 2 min at 200 °C)
  •  Pot life can be adjusted with platinum
  •  No reversion of curing
  •  Curing can be inhibited by certain substances, e.g. compounds that contain amine, sulfur or tin
  •  One-component materials available

 

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Last modified: December 28, 2010

Elastosil, Semicosil, and Powersil are registered trademarks of Wacker Chemical.