Additives to reduce the flammability of polymers

Abstract

Introduction. This review article provides data on additives used to reduce the flammability of polymer compositions. It is shown that not individual substances are used for this purpose, but their mixtures, including flame retardants, synergists, and stabilizers. The principle of operation of flame retardants is that when the appropriate degree of concentration of flame retardants in the material is reached, they do not allow it to burn without the presence of an ignition source. Under the influence of fire on the processed material, various chemical and physical processes occur in it, preventing the flame from flaring up. Main part. The advantages and disadvantages of the main flame retardants currently used, which include antimony compounds, halogen-containing compounds, phosphorus-containing substances, as well as aluminum and magnesium hydroxides, are analyzed. Various mechanisms for slowing down combustion processes when flame retardants are used are considered. It has been shown that bromine-containing flame retardants are much more effective than chlorine-containing ones. They decompose in a narrow temperature range. In addition, plastics containing bromine compounds as flame retardants are easily recycled due to the high thermal stability of such flame retardants. Phosphorus-containing compounds have a plasticizing ability and increase the fire resistance of plastic compounds. The action in the condensed phase is that during the decomposition of the flame retardant, phosphoric acid residues are formed, which act as dehydrating agents, contributing to the formation of carbonized structures. In this case, an aerosol can also be formed, which contributes to the deactivation of radicals due to the wall effect. Of particular interest are compounds containing halogen and phosphorus. The advantages of these compounds are as follows: by splitting off halogen radicals during decomposition, they deactivate active radicals; contribute to the formation of carbonized structures. Metal hydroxides decompose under the influence of high temperatures with the release of water. The decomposition reaction is endothermic, resulting in cooling of the substrate to temperatures below the flash point. The formation of water contributes to the dilution of combustible gases released during decomposition, weakens the effect of oxygen and reduces the rate of combustion. The effectiveness of hydroxides is directly proportional to their content in the polymer. The greatest efficiency is observed when aluminum hydroxide is introduced into oxygencontaining polymers (polyethylene terephthalate, polybutylene terephthalate, polyamide). Magnesium hydroxide is more expensive than aluminum hydroxide, but has a higher heat resistance (up to 300оC). Conclusion. Thus, among the listed flame retardants, aluminum and magnesium hydroxides occupy the first place in terms of the volume of use (more than 40% of the total volume of flame retardants). This is due to their low cost, manufacturability of their application and environmental safety. A well-chosen metal hydroxide system produces a low-cost non-combustible material with little fumes from decomposition. Therefore, the use of metal hydroxides as flame retardants is constantly increasing.

Keywords

• flame retardants
• flammability
• fire resistance
• polymer compositions.