Thiokol/Polysulphide

Most additives that affect mix procedirres are reactive chemicals. To run a chemical reaction successfully in a Banbury internal mixer or other equipment, three variables need to be controlled time, temperature and stoichiometry (the ratio of the reactants). The effect of these variables on the chemical peptising of NR, SBR, polychloroprene (CR) and Thiokol polysulphide are discussed. Other topics include additives to increase viscosity, when to add zinc oxide, filler treatments and bin storage problems. 10 refs. 

Polysulphide rubbers. Ethylene dichloride and excess of sodium tetrasulphide when heated together give a polymeric polysulphide, Thiokol A, with properties resembling those of rubber ... 

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

Early examples of such branched polysulphides, e.g. Thiokol FA, are believed to possess hydroxyl end groups and are coupled by means of zinc compounds such as the oxide, hydroxide, borate and stearate by a mechanism which is not understood. Later elastomers, e.g. Thiokol ST, have been modified by a restricted reductive cleavage (see below) and this generates thiol (mercaptan) end groups. These may be vulcanised by oxidative coupling as illustrated below with lead peroxide ... 

A liquid produced by the addition of chlorine to the ethylene double bond. It is reacted with sodium polysulphide to produce polysulphide polymers, trade name Thiokol. 

According to descriptions published by the Thiokol Chemical Corporation [9] and Gobel [10] liquid thiokol is obtained in the following way ethylene chloro-hydrin is condensed into dichlorodiethylformal (I) which is then treated with sodium polysulphide to form the polymer (II) ... 

A premix is prepared by mixing the fuel binder (i.e. a polysulphide rubber in the case of the Thiokol propellant) with the necessary curing agents, inert additives, and ballistic modifiers in a double-acting paddle mixer. This mixer is equipped... 

Thiokol Chemical Corp Trenton, NJ, Bulletins on Polysulphide rubbers, Urethanes, and Acrylics. 

The properties of polysulphide polymers are summarised in Table 7.2. Cured polysulphide systems possess excellent resistance to most solvents and mild inorganic acids. The solvent resistance depends on the sulphur content of the polymer. Table 7.3 compares the resistance of various liquid polysulphide polymers to a variety of solvents and chemical solutions. However, these data cannot be considered as absolute because the resistance is to some extent dependent on the efficiency of cure. Volume swell values below 40% illustrate excellent resistance. Those between 40% and 90% illustrate fair to good resistance whereas values above 90% may be only fair or even unsatisfactory (Thiokol Chemical Co., 1969). 

Morton Thiokol Corp. (1987) Bioresistance of LP based Polysulphide Sealants, Morton Thiokol Corporation, Coventry. 

Thiokol Chemical Co. (1969) Solvent Resistance of LP Liquid Polysulphide Polymers, bulletin 565 M, May, Thiokol Chemical Corporation, Trenton, NJ. 

Polysulphide rubber, thiol end groups Thiokol LP Thiokol- Morton Polyamides, polychloroprene... 

Wilkinson SM, Beck MH (1993) Allergic contact dermatitis from sealants containing polysulphide polymers (Thiokol ). Contact Dermatitis 29 273-274... 

Rubbers (natural and synthetic) Polyvinyl and cellulose esters Polyhydric alcohol-polybasic acid resins Polysulphide resins (Thiokol A) Polysulphide rubbers Cellophane, polyvinyl alcohol and acetal, and regenerated cellulose 10-0-6 18-0-2 (10-1 3) X 10-1 (10-0-7) X 10-1 (6-3-31) X 10-2 (8-0-0-05) X 10- ... 

The first poly sulphide elastomer was discovered in 1924 by Patrick during an attempt to prepare ethylene glycol by hydrolysis of ethylene dichloride. Commercial production was begun in 1929 by the Thiokol Chemical Corp. (U.S.A.). The current consumption of polysulphide elastomers, compared to that of other elastomers, is very small, use being restricted mainly to special applications involving resistance to oils and solvents. 

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