Thiokol processing

R. A. McKay,M Study of Selected Parameters in S olid Propellant Processing,]et Propulsion Lab, Pasadena, Calif., Aug. 1986 J. L. Brown and co-workers. Manufacturing Technologyfor SolidPropellantIngredients/Preparation Reclamation, Morton Thiokol, Inc., Brigham City, Utah, Apt. 1985 W. P. Sampson, Eow Cost Continuous Processing of Solid Rocket Propellant, Al-TR-90-008, Astronautics Laboiatoiy/TSTR, Edwards AEB, Oct. 1990. 

During the 1930s gradual improvements in the product and processing overcame some of the drawbacks of this material. Nonetheless, the apphcations were limited and Thiokol Corp. stmggled to remain solvent. The first year Thiokol reported a profit was in 1941, 13 years after its foundation. This was realized when the U.S. Air Force discovered that the aUphatic polysulftdes were usehil as a fuel-resistant sealant for aircraft tanks and hoses. Polysulftdes also began to be used as sealants for boat hulls and decks. 

The most recent report available on di- -octylphthalate lists three commercial producers Vista Chemical Company, Houston, Texas Aristech Chemical Corporation, Neville Island, Pennsylvania and Teknor Apex Company, Hebronville, Massachusetts and Brownsville, Texas (EPA 1993a). Additional reported producers include Eastman Kodak Company, Rochester, New York (USITC 1994) Tenneco Chemical, Inc., Chestertown, Maryland (EPA 1987a) Alfa Products, Morton Thiokol, Inc., Danvers, Massachusetts Primachem, Inc., Englewood Cliffs, New Jersey and GCA Chemical Corp., Stamford, Connecticut (HSDB 1995). Table 4-1 lists the U.S. facilities that manufacture or process di-w-octylphthalate. 

American scientists at LLNL have studied all aspects of scaling-up followed by optimization of parameters and it appears that TATB would be manufactured by them in future by following the TMHI route. However, a new method proposed by the UK scientists is still at the laboratory scale in UK. According to a recent report in the literature, ATK Thiokol, Inc, USA has performed considerable route development for an alternate TATB process starting with phloroglucinol via Scheme 2.1. 

Picatinny Arsenal, in association with ATK Thiokol and others, are in the process of developing PAX Series of explosive formulations and also a series of IM melt-cast explosives. They claim that the TM-ness is accomplished by dispensing with TNT completely and using dinitroanisole (2,4-dinitroanisole, DNAN) which is a yellow crystalline substance at room temperature [218, 230] and has a m.p. of... 

Various organic dihalides are employed in a reaction with sodium polysulfide to produce organic polysulfides (Thiokols). Ethylene dichloride, from the direct chlorination of ethylene, dichloroethyl formal, and /3,0 -dichlorodiethyl ether are the principal dihalides that have been employed in the process (44). These elastomeric polymers have been commercially available for a number of years, and many applications have been developed for them. They have excellent oil resistance and one of their principal uses has been in hose and tank linings in which that property is required. 

Fig. 9.49 The evolution of the interfacial area of a viscous Thiokol rubber in a 26.6-cm parallel-disk mixing chamber with a. — 0.5, with the number of turns. The rubber filled up half the chamber with one-quarter cream color (at the channel block at the left side) and one-quarter black. The numbers on the figure indicate the number of turns from 1/4 to 10. [Reprinted by permission from B. David and Z. Tadmor, Laminar Mixing in Co-rotating Disk Processors, Int. Polym. Process., 3, 38-47 (1988).]...

Because of its high sulfur content of 84%, Thiokol A has the greatest solvent resistance, but it is very difficult to process and has a strong, unpleasant odor. Thiokol ST does not have these disadvantages, but aromatic ketones and esters swell the polymer more than Thiokol A. Thiokol FA has properties intermediate to those of types A and ST. 

Both Thiokol A and FA require peptization (e.g., in the presence of MBT or DPG) to enable easy processing. 

The next major project for the Industrial Testing Laboratory was an attempt to improve the process of making ethylene glycol from ethylene via the hydrolysis of ethylene chlorohydrin. In his attempt to produce this "anti-freeze" by hydrolysis of ethylene dichloride with sodium polysulfide, "Doc" Patrick obtained a gummy gunk which he named "Thiokol" based on the greek word theion (sulfur) and kommi (gum). 

As mentioned in the previous section the end-groups may be either hydroxyl or thiol (mercaptan) and as a result somewhat different vulcanization processes are used. The older elastomers, such as Thiokol FA, are considered to have hydroxyl end-groups and these are coupled by the use of a zinc compound. The actual mechanism is not clear but since zinc hydroxide, zinc borate and zinc stearate as well as the normally used zinc oxide are all effective it has been suggested (Fettes et al., 1954) that an ionic mechanism may be involved. 

The early commercial synthetic rubbers created were the polysulphide rubbers now known as Thiokols these rubbers had good oil resistance, unlike natural rubber, but with a very serious drawback which prevented their widespread acceptance, namely their smell. Processing of these materials in factory-size batches proved to be very obnoxious. Acrylonitrile-butadiene copol3nners (nitrile rubbers) were developed by Bayer and were to find eventually worldwide acceptance in many applications requiring oil resistance. In the mid 1930s polychloroprene rubbers became a commercial proposition after early experimental work at Du Pont. These rubbers, intermediate in properties between nitrile and natural rubber, soon found wide acceptance. 

Oxygen in the air, whether in combination with light or not, is capable of causing cross-linking of certain elastomers (dienic polymers and copolymers with residual double-bonds). Similarly, the polysulfur type adhesives ( thiokols ) are vulcanized by oxygen. However, in both cases, the processes cannot be controlled and no optimization is possible. The situation is different with the particular acrylic formulations made up of the cyanoacrylate adhesives and the anaerobic adhesives. 

Poly sulfides were first discovered and patented in about 1927 by J.C. Patrick by accident in attempting to develop antifreeze. The polymer was called Thiokol A, a condensation reaction of ethylene dichloride and sodium tetrasulfide, for which manufacturing began in 1929 [1]. This elastomer was quite difficult to process due to its variability and thermoplastic nature, leading to the discontinuation of manufacture after improved grades were developed. 

Zinc oxide is the major vulcanization agent required for Thiokol FA however, the particular grade is important as certain impurities may affect the cure rate and final properties. A French process zinc oxide, such as Midwest AZO 66L or equivalent, is recommended. Other oxides such as lead oxide or dioxide, cadmium oxide, and zinc hydroxide may also be used with varying rates of cure and physical properties. The amount of zinc oxide over or under 10 phr is not critical and will not affect the rate of vulcanization. Note that the MBTS and DPG are peptizing agents, not accelerators. 

---