Thiokol fillers

Elemental sulfur is altered by chemical, allotropic, or me-chanical means. Of the chemical modifiers the Thiokol family of additives are some of the most effective modifiers available. By control of the time-temperature history of sulfur in the liquid and solid phases, it is possible to control the allotropic modification of sulfur and its mechanical properties. Mechanical modification of sulfur with non-chemically reactive filler materials such as aggregates and fibers yields materials with properties different from those of the parent materials. 

Thiokols are amorphous polymers which do not crystallize when stretched and hence reinforcing fillers, such as carbon black, must be added to obtain relatively high tensile strengths. Thiokol may be... 

The low temperature properties are largely determined by the position of the Tg. The copolymers such as Thiokol FA do not crystallize whilst the homopolymers such as Thiokol ST show little tendency to crystallize in the presence of curing agents, reinforcing fillers and other additives commonly incorporated into commercial... 

Stearic acid has a double function in Thiokol compounds. The first benefit is as in internal lubricant to improve null release and also to aid in releasing from the mold after vulcanization. Note that 0.5 phr is normal for most compounds however, if good tack and ply to ply adhesion is needed, such as for rollers, the level may be reduced to 0.25 phr. The second function of the stearic acid is to aid in the dispersion of fillers and to activate the cure system for a tighter state of cure. 

Thiokol ST Filler Stearic acid Zinc peroxide Calcium hydroxide Results 100.0 As shown 1.0 5.0 1.0 Hardness, Modulus, Tensile Strength, Elongation,... 

Poor or logy cures may be caused by contamination of the compound with foreign accelerators, acidic materials such as clay in a dip, curatives on the surface of wrapping tapes, and so on. Always be sure that processing equipment is clean and free of any previously handled compounds and new or only tapes reserved for Thiokol compounds be used. Avoid acidic compounding materials such as clays or other low pH fillers or process aids. 

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. 

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