According to the combustion mechanism of PP, starting from the key points of the PP combustion chain, additive flame retardants can achieve the purpose of flame retardancy by controlling one or more of the combustion elements. Therefore, the flame retardant mechanism has gas phase flame retardancy. mechanism, solidified phase flame retardant mechanism, endothermic flame retardant mechanism, etc. Sometimes a flame retardant process has more than one flame retardant mechanism.
Highly practical flame retardant mechanism andflame retardant Agentsare of the following types:
（1）Gas phase flame retardant mechanism The typical gas phase flame retardant is to interrupt the chain reaction. From the termination of the PP combustion chain reaction, the generation of flammable gas can be reduced, thereby achieving the purpose of flame retardancy. If the halogen flame retardant decomposes at a relatively high temperature, HX is released. HX captures the free radicals generated during the combustion of PP and interrupts the combustion chain reaction. Some flame retardants release inert gases, diluting the concentration of flammable substances and oxygen concentration, reducing them below the ignition limit. Halogen flame retardants using a gas-phase flame retardant mechanism are one of the most produced flame retardants in the world. The small amount of halogen flame retardants added to PP and the significant flame retardant effect make them occupy an important position in the flame retardant field. However, the halogen flame retardant system will produce a large amount of toxic smoke when burning, causing secondary pollution. Especially when a fire occurs, the toxic smoke can be fatal to humans and animals. In recent years, with the improvement of environmental protection requirements, the use of halogen flame retardants in PP has been increasingly restricted, and halogen flame retardants will gradually fade out of the field of PP flame retardants.
（2）Endothermic Flame retardant mechanism Endothermic flame retardant means that the flame retardant absorbs the heat generated by the thermal decomposition of PP combustion and reduces the system temperature, so that the heat generated is not enough to maintain PP cracking or gas combustion. Such as aluminum hydroxide and boric acid inorganic flame retardants. Aluminum hydroxide and boric acid-based inorganic flame retardants that adopt the endothermic flame retardant theory have the advantages of being non-toxic, good thermal stability, and smoke suppression. The disadvantages are large addition amounts, lack of affinity with PP, dispersion, and phase resistance. The capacitance is poor and the mechanical properties of the material are reduced. Ultra-fine and surface treatment of inorganic flame retardant particles can enhance the interfacial bonding force with PP. The quantum size effect and surface effect of ultrafine particles are used to enhance the interface with PP, improve compatibility, and achieve the purpose of reducing dosage and improving flame retardant efficiency. The finer the flame retardant particles, the smaller the dosage and smoke generation, and the more significant the flame retardant effect. Therefore, ultrafine particle size is the main development direction of inorganic flame retardants in the future.
(3)Solidized phase The flame retardant mechanism is solid phase flame retardancy, that is, the flame retardant forms a flame retardant carbon layer or glassy melt coating on the surface of PP, which reduces the generation of flammable gases, thus achieving the purpose of flame retardancy. Phosphorus and Intumescent Flame Retardants (IFR) are mainly responsible for this flame retardant mechanism. Fuqiang flame retardant uses phosphorus and intumescent flame retardant (IFR) with this flame retardant mechanism, which can form a layer of expanded porous homogeneous carbon layer or glassy melt coating on the surface of the material to provide heat insulation and insulation. It achieves the purpose of flame retardancy through the functions of oxygen, smoke suppression and droplet prevention. The disadvantages of phosphorus-based and intumescent flame retardants are generally poor water resistance and poor thermal stability. However, due to less smoke during combustion, the gas released is harmless and the generated carbon layer and coating can effectively prevent polymer droplets. It is suitable for PP flame retardant. Therefore, the new IFR, which overcomes its shortcomings and continuously improves its comprehensive performance, has very broad development prospects and has always been a hot topic of research.
atDuring the research and use of PP flame retardants, it was discovered that any current flame retardant has its own shortcomings. The composite flame retardant system can reduce the dosage of a single flame retardant. It is composed of traditional flame retardants. The synergistic flame retardant system combines their respective excellent properties. It has good flame retardant effect and low cost. It can be both flame retardant and smoke suppressor. It also has some other special functions, and its prospects are still very broad. Using new technologies and new processes to correct the shortcomings of existing PP flame retardants and improve the flame retardants is a practical and effective method for developing new flame retardants at this stage. Some emerging flame retardants under the existing flame retardant mechanism have also achieved good comprehensive effects in flame retardant PP and have certain development prospects, such as nano-inorganic flame retardants, layered clay, and nanocarbon tubes. Become the front-end product for the development of PP flame retardant materials.
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