Antimony Trioxide FLAME RETARDANT (FR) THEORY

Antimony oxide by itself is not a fire retardant, and the halogens by themselves, mainly bromine and chlorine, are
weak fire retardants. However, when they are combined they become synergistic and are the most effective and
most widely used flame retardant system for plastics. Usually three to four parts of halogenated flame retardants
are used to one part of antimony oxide on a weight basis. Using more than the 4:1 ratio offers little additional
protection. The stoichiometric ratio of chlorine to antimony in antimony trichloride is 3:1. Formulations in different
applications will depend on thermal stability, cost, tinting strength, change in physical properties, smoke
considerations, streaking, blend ability, and the flame retardant specification.

Two mechanisms exist in the synergistic system. First is the “free radical capture” process that takes place in the
vapor phase. On combustion at a temperature of over 600o F, the halogen forms hydrochloric or hydrobromic acid
that reacts with the antimony oxide to form antimony trichloride, antimony oxychloride, antimony tribromide, or
antimony oxybromide. The flame retarding action takes place in the vapor stage above the burning material. It is
thought that “free radicals” propagate the flame. But, the antimony trihalides or antimony oxyhalides act as “free
radical traps” and take up free radicals. They inhibit ignition and pyrolysis in the solid, liquid, and vapor phases.



A second process occurs in a solid phase and is the “char process”. The antimony oxide promotes the formation
of “char” (essentially carbon) on the substrate which reduces volatile gas formation. The barrier between the
substrate and the vapor phase reduces the available oxygen to the underlying substrate. The barrier effect is
obtained by almost any inert additive. In plastics there is a cross linking with antimony to produce a more stable
thermoset polymer. Additionally in the solid phase, the formation of SbCl3 and SbOCl acts as a dehydrating
agent that increases charring. Sometimes phosphorous compounds (TCP), magnesium oxide, alumina trihydrate,
molybdic oxide, zinc borate, or zinc oxide are used in combination or in place of antimony oxide to reduce costs,
to increase char formation, or to reduce smoke. However, the substitution of the other retardants greatly reduces
the flame retraces normally rendered by antimony oxide. Testing of the amounts of the halogen and antimony
oxide in each formulation is necessary to optimize the flame retardance and lower costs. Alumina trihydrate is
not synergistic with halogenated flame retardants. It functions as a flame retardant by the release of its water of
hydration and cannot be used in high temperature processes. Zinc borate, molybdic oxide, zinc oxide, and
magnesium oxide can be used in conjunction with antimony oxide to augment char formation and decrease
smoke. Replacement of the antimony oxide to meet a smoke requirement compromises the flame retardance.



A relationship exists between particle size and tinting strength. If the particles are very fine (less than 300
nanometers) they are below the visual range and there is no tint strength. However, within the visual range, the
smaller the particle size the higher the tint strength. Or conversely, the larger the particle size, the lower the tint
strength.



Sam Xu
Sales Engineer

DONGGUAN JIEFU FLAME-RETARDED MATERIALS CO.,LTD
Address: jiefu industrial park shuiping industrail district dalang town dongguan GD,P.R.C
Zip: 528770
Tel: 0086-755-83474911
FAX: 0086-755-83474980
Mobile:13929211059
Contact me: xubiao_1996@hotmail.com samjiefu@gmail.com

Jiefu Chemical industry LTD . (Our imports and exports company )

Chinese antimony market



DONGGUAN JIEFU FLAME-RETARDED MATERIALS CO.,LTD