Thiokol Neoprene

The first synthetic rubbers to be commercially available in United States were Thiokol (1930) and Neoprene (1931). Both of these are still being produced commercially because they have special properties that are not matched by natural rubber. Various types of synthetic rubbers were introduced during (1939-43) World War II. After world war, stereo rubbers have been made using stereo specific catalysts. 

In 1931 Du Pont introduced the first synthetic elastomer, polychloroprene (Neoprene , Duprene ), and Thiokol Corporation introduced a polysulfide rubber called Thiokol . Polychloroprene, although veiy expensive compared to polyisoprene, has superior age resistance and chemical inertness. It is also nonflammable. 

These are based on polymer types. Neoprene, acrylonitrile, silicone rubbers and thiokol rubbers are to be chosen. 

RUBBER (Synthetic). Any of a group of manufactured elastomers that approximate one or more of the properties of natural rubber. Some of these aie sodium polysulfide ( Thiokol ). polychloiopiene (neoprene), butadiene-styrene copolymers (SBR), acrylonitrilebutadiene copolymers (nitril rubber), ethvlenepropylene-diene (EPDM) rubbers, synthetic poly-isoprene ( Coral, Natsyn ), butyl rubber (copolymer of isobutylene and isoprene), polyacrylonitrile ( Hycar ). silicone (polysiloranei. epichlorohy-drin, polyurethane ( Vulkollan ). 

Significant developments in synthetic rubber began at this time. Outstanding were the introduction of polychloroprene (neoprene) by Carothers, and of the oil-resistant polysulfide rubber Thiokol by Patrick. These were soon followed by styrene-butadiene copolymers, nitrile rubber, butyl rubber, and various other types, some of which were rushed into production for the war effort in the early 1940s. The stereospecific catalysts researched by Ziegler and Natta aided this development, including synthesis of true rubber hydrocarbon (polyisoprene). Since 1935 synthetic rubbers have been referred to as elastomers. 

The elastomer must exhibit a low value of Tg. Among polymers that might be regarded as engineering elastomers the following should be mentioned—butadiene-styrene copolymer (GR-S or SBR), butyl, neoprene, EPR (copolymer ethylene-propylene), nitrile, polybutadiene, thiokol, polyiso-prene, silicon, polyurethane, Hypalon, and EPDM. The internal breakdown by consumption is about 75% synthetic versus 25% natural rubber. Within the family of synthetic elastomers a typical breakdown is about 46% SBR, 19% polybutadiene, 9% EPR, 4% neoprene and 3% nitrile. 

Eucolloidal (pol. degree > 500) Natural rubber, synthetic rubbers (neoprene. Buna, Butyl-rubber, Thiokol) Natural cellulose fibres (wood, cotton, flax, hemp) starch pectin. Keratin CO-haemoglobin Serum albumin Haemocyanin ditto, in the highest polymerisation stage Polymerised shellac, damar and copal. Phenol- or urea-formaldehyde between the B-and C-stages... 

The commercial development of Neoprene (polychloroprene) by du Pont followed that of Thiokol by only a few years, and this turned out to be the second synthetic rubber to be developed in the USA, because it was far superior to natural rubber in oxidation and solvent resistance. However, it is not being included in this review, since it is "outperformed" by both Thiokol and nitrile rubber. The latter is actually the most commonly used solvent-resistant rubber today. 

Other Names Neoprenes CR, GR-M Butyl, HR, GR-I ThiokolS PS, GR-P AdipreneS PU... 

While progress was erratic until about the 1930 s, synthetic elastomers were not only born, but expanding technically. It is perhaps notable that the first few products of the synthetic elastomer industry s resurgence then brought forth elastomers which offered environmental resistances vastly superior to natural products. Most notable of these were Thiokol (polysulfides) in 1929, neoprene (polychloroprene) in 1931, Buna N (copolymers of butadiene and acrylonitrile) in 1937, and butyl (copolymer of isobutylene and isoprene) in 1940. Many more were to follow. 

Up to the advent of World War II, practically all of the rubber consumed was of the natural variety, mostly derived from Hevea brasiliensis plantations in the Far East. With the entrance of Japan into the war, both the United States and western Europe were cut off from the main source. At this point one of the most massive organic chemistry research and development efforts in history was launched, which ultimately resulted in the development of synthetic elastomers such as Buna N, Neoprene, Thiokol, and styrene-butadiene. While these were not equivalent to the natural product in some respects, product improvement continued so that by 1970 worldwide synthetic rubber production was 3.8 million metric tons compared to 2.7 million of the natural product. Styrene-butadiene rubber sold for about the same price as natural rubber. Although national defense interest dictated a policy of independence from foreign raw materials, conventional bias-belted tires still required 15% natural rubber for optimum performance. 

Elastomeric vulcanized natural rubber and hard rubber and oil-resistant polyethylene sulfide (Thiokol) and polychloroprene (Duprene, Neoprene) were all available commercially in the 1930s. 

Thiokol FA parts that require good tack for building may need a slight increase in the level of MBTS to 0.5 or 0.6 phr if the compound is calendered, but this would probably be too high for extrusion. The addition of 5 phr of a coumarone indene resin such as Cumar P25 will also improve tack. Blends of Thiokol FA with neoprene are usually tacky enough for most applications. 

Polysulhdes often are blended with other elastomers such as nitrile rubber, NBR, or neoprene, CR, for improved physical properties and factory processing. Traditionally, Thiokol FA is blended with neoprene for improved strength and processing for rollers, at some sacrihce in solvent resistance. Table 11.9 has information on Thiokol FA blends. If minimal loss in chemical resistance is indicated, then a blend with a high ACN nitrile is employed. A cure system that is compatible with both rubbers needs to be used in all cases. The zinc peroxide-cure system is NBR specihc, hence it is important that the recommended one be used or others be tested since many NBRs do not cure with zinc peroxide. Best results are obtained with blends if separate masterbatches are made with the individual polymers, which are then blended in the... 

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