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Wednesday, May 25, 2011

Thiokol Adhesive

Thiokol is the trade name and commonly used name for a range of poly sulphide rubbers, are little used by themselves as adhesive although they are widely used as mastics. The are frequently incorporated in adhesive composition, for instant those based on epoxy resins, to impart flexibility.

There are two broad types of poly-sulphide polymer;

  • High molecular weight rubbers and
  • Low molecular weight liquids produced from these by a process of depolymerization
The liquid polysulphides have a certain usefulness as adhesives since they can be converted into solids by oxidative substances such as lead peroxide or dioxide, and show fair adhesive to a variety of materials, including some metals.

The hardening reaction may be exotermic, and in order to obtain a satisfactory pot like the addition of a retarding agent such as stearic acid is often necessary; such as adhesives has been recommended for bonding new concrete to old. The bond strength is not high but it can be substantially improved by adding say 5% of an epoxy resin (a hardener is not necessary if the epoxied molecule contains alcoholic hydroxyl group), or small amounts of a phenolic resin, again containing hydroxyl groups such as the methylol groups present in a resol.

Such thiokol adhesives have outstanding resistance to vibration, low temperature, and aromatic fuel, and therefore they have created interest in connection with integral fuel tanks in aircraft.