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The Composition C family is a family of related US-specified plastic explosives consisting primarily of RDX. All can be moulded by hand for use in demolition work and packed by hand into shaped charge devices. Variants have different proportions and plasticisers and include composition C-2, composition C-3, and composition C-4.
The term composition is used for any explosive material compounded from several ingredients. In particular, in the 1940s the format "Composition <letter>" was used for various compositions of the (relatively) novel explosive RDX, such as Composition B and other variants.
The original material was developed by the British during World War II, and standardised as Composition C when introduced to US service. This material consisted of 88.3% RDX and a mineral oil-based plasticiser and phlegmatiser. It suffered from a relatively limited range of serviceable temperatures, and was replaced by Composition C-2 around 1943.
Composition C-2 contained a slightly smaller proportion of RDX, but used an explosive plasticiser, which contained tetryl, nitrocellulose and a mixture of nitroaromatics produced during the manufacture of TNT (containing trinitrotoluene, dinitrotoluene and mononitrotoluene), and a trace of solvent. While Composition C-2 had a much wider serviceable temperature range than Composition C, it could not be stored at elevated temperatures. Consequently it was replaced around 1944 by Composition C-3.
Composition C-3 was very similar to Composition C-2, but removed the solvent and varied the exact proportions of plasticisers to improve high temperature storage. It is a yellow, putty-like material. It remained a service item through the Korean War, but had marginal plasticity at the very low temperatures encountered in Korean winters, and was significantly toxic, including by vapour and skin absorption. The velocity of detonation is about 7600 m/s (25,000 feet per second.)
Composition C-3 consists: 77%–85% cyclonite (RDX) and 15%–23% gel made out of liquid nitro compounds (e.g. liquid DNT and small amount of NT) and nitrocellulose or butyl phthalate and nitrocellulose.
One of the first reported and tested Composition of C-3 was very similar to earlier Composition C-2 and contained: 77% of RDX, 3% of tetryl, 4% of TNT, 1% of NC, 5% of NT, and 10% of DNT.  The last two compounds (they are very poor explosives) are oily liquids and plasticize the mixture. The most important later innovation of C-3 there was introduced non-explosives plasticizer butyl phthalate instead of this mixture of nitro compounds. In such way the toxicity of C-3 was reduced, the concentration of RDX was increased, it improved safety of usage and storage. it also opened way to start study on applying new non-explosive and low toxic plasticizer (esters dicarboxylic acid) and binder (branched polymers).
Research on a replacement for C-3 was begun prior to 1950, but the new material, new generation of Composition C (number four, C-4), did not begin pilot production until 1956.
The Composition C-3 was improved and designed as well-known Composition C-4.
Since 1960 the mixture of C-4 has contained:
- 90.0–91.0% of cyclonite (RDX explosives)
- ~2.1% of polyisobutylene (short chain)
- ~1.6% of motor oil
- ~5.3% of di-(2-ethylhexyl)sebacate (sometimes it was replaced partly by similar compounds: dioctyl sebacate or dioctyl adipate)
- less than 0.6% of water
- (small amount of marker or odorizing taggant)
It is less volatile than C-3 and has less tendency to harden at low temperature. It has a density 1.48–1.60g/ml, does not become hard even at -55°C (-70°F), and does not excude at +77°C (170°F). C4 has a detonation velocity of 8,092 m/s (26,550 ft/s) at high density and velocity of 7,550 m/s (24,770 ft/s) at low density 1.48g/ml. It is so successful that it remains in army service up to current time without any significant changes.
- Composition B
- Composition H6
- Composition C4
- RE factor
- Plasticizers for energetic materials
- Polymer-bonded explosive
- Rudolf Meyer, Josef Köhler, Axel Homburg. Explosives. Wiley-VCH. p. 63.
- OARDEC (2005-11-23). "Unclassified Summary of Evidence for Administrative Review Board in the case of Nashir, Sa id Salih Sa id". United States Department of Defense. pp. 7–9. Retrieved 2008-12-07. "The detainee was trained to use the Kalashnikov rifle, rocket propelled grenades, hand grenades , land mines, Composition-3 (C-3) and Composition-4 (C-4) explosives."
- Urbanski Tadeusz (1985) . Chemistry and Technology of Explosives. Volumes I–IV (second ed.). Oxford: Pergamon.
- GlobalSecurity.org. "Explosives - Compositions". "Composition-3 (C-3) and Composition-4 (C-4) explosives, Semtex."