The synergists of halogen-free flame retardants mainly consist of nitrogen-based, phosphorus-based compounds and metal hydroxides, and also include nitrogen-phosphorus expansion systems, graphite expansion systems, etc. The compounds of this type of system do not volatilize or produce corrosive gases when burning, and are thus called pollution-free flame retardants, which conforms to the development trend of flame retardants. The following is a detailed introduction to halogen-free flame retardant synergists:
Nitrogen-based flame retardant synergist
Nitrogen-based flame retardant synergists are mainly additive types, with commonly used ones including melamine and melamine-cyanuric acid (MCA), etc. When nitrogen-based flame retardants are used alone, their flame retardant effect is not good. However, when combined with phosphorus-containing flame retardants to form an intumescent flame retardant system, the flame retardant effect is significantly improved. For example, Melapur®200/70 produced by BASF is a special halogen-free flame retardant of melamine polyphosphate type with high molecular weight, high purity, linear chain structure and stabilized end sealing treatment (referred to as “high molecular weight m-MPP”), which has excellent thermal stability. It is particularly suitable for halogen-free flame retardant modification of light or colored glass fiber reinforced nylon polyamide, PET, PBT, etc.
Phosphorus-based flame retardant synergist
Phosphorus-based flame retardants play an important role in halogen-free flame retardants, and their flame retardant mechanisms are mainly condensed phase flame retardancy and gas phase flame retardancy. Phosphorus-based flame retardants can effectively lower the temperature around the combustion area. The water vapor or some inert gases produced can also dilute the surrounding combustion-supporting and toxic gases. The generated phosphoric acid and metaphosphoric acid can adhere to the surface of the material, playing a barrier role, and can also serve as an acid source to promote carbonization. Active free radicals can also block the combustion chain reaction in the gas phase, thereby preventing combustion.
Metal hydroxide synergist
Metal hydroxide synergistic agents such as aluminium hydroxide (ATH) and magnesium hydroxide (Mg(OH)2), etc., have the advantages of good stability, low toxicity or non-toxicity, no volatilization during storage, not easy to precipitate from plastics, abundant raw material sources, and low prices. They also have the dual functions of flame retardancy and filling. They mainly lower the temperature around the burning object by absorbing a large amount of heat during the combustion process, while generating water vapor. Meanwhile, the products produced adhere to the surface of the material to play an isolation role, thereby achieving a flame-retardant effect. For instance, magnesium hydroxide, as a rare earth flame retardant synergist, has a remarkable flame retardant effect when applied in the plastic industry. It can also enhance the thermal stability of materials, reduce the release of toxic gases, and improve the mechanical properties of plastics.
Synergist for the nitrogen-phosphorus expansion system
The nitrogen-phosphorus expansion system synergist is a kind of composite flame retardant, mainly composed of acid source, gas source and carbon source. When this material burns, it will produce a thick layer of carbon foam under the influence of three sources, thereby blocking heat and oxygen and achieving the effect of suppressing smoke and preventing dripping. This flame retardant expands when heated, and thus is called an intumescent flame retardant.
Synergistic agent for graphite expansion system
Graphite expansion system synergistic agent is a new type of halogen-free flame retardant. It is produced by acidifying natural graphite with concentrated sulfuric acid, washing it with water, filtering it, drying it, and then expanding it at 900-1000℃. Expandable graphite mainly plays the following roles in the flame retardant process: forming a tough carbon layer on the surface of the polymer, separating the combustible material from the heat source; It absorbs a large amount of heat during the expansion process and reduces the temperature of the system. During the expansion process, the acid radical ions in the interlayer are released, promoting dehydration and carbonization, and can combine with the free radicals produced by combustion to interrupt the chain reaction. When graphite is used in combination with phosphorus compounds and metal oxides, it can produce a synergistic effect. Adding a small amount can achieve the purpose of flame retardancy.
The role of synergists
Synergists play a role in coordinating physical properties and enhancing flame retardant effects in halogen-free flame retardant systems. Through the research on the compounding synergy mechanism, the synergist can significantly reduce the dosage of the main flame retardant, while optimizing the physical properties, making the flame-retardant materials more in line with the actual needs. For instance, rare earth elements have a synergistic effect with magnesium hydroxide. Rare earth elements can promote the decomposition of magnesium hydroxide, absorb heat in advance, and enhance the flame retardant efficiency. Meanwhile, rare earth elements can also react with the free radicals produced during combustion, interrupting the combustion chain reaction and further enhancing the flame-retardant effect of plastics.
