Nylon has excellent properties and is widely used. Unmodified nylon has low flame retardancy, vertical combustion can only reach UL94V-2 level, oxygen index is about 24%, it will drip during combustion, it is a flammable material, and it is very easy to use in the process. Yes. catch fire. Therefore, reformed nylon flame retardants have become a common concern and research topic in today's academic and industrial circles. Next, Silver Plastic introduces the knowledge about nylon flame retardants. At present, the Flame Retardant modification of nylon materials is usually divided into halogen-containing flame retardant modification and Halogen-Free Flame Retardant modification.
One. Halogen-containing flame retardant systems
The most widely used abroad is brominated styrene polymer, which has excellent thermal stability and is being processed because it can be melt-mixed with nylon. The fluidity of the medium is good. In addition, the flame-retardant nylon prepared by using it also has excellent electrical, physical and mechanical properties. The limitations of this flame retardant are its low light stability and incompatibility with nylon. It is also more expensive than decabromodiphenyl ether, which is widely used in China. Another flame retardant that has been used in nylon for many years is flammable. It is a chlorine-containing flame retardant with high efficiency and electrical properties, but thermal stability. Due to this limitation, it is only suitable for nylon flame retardant systems with low processing temperatures.
The most widely used flame retardant in China is decabromodiphenyl ether. Due to its high bromine content, nylon has a high flame retardant efficiency and is the most economical flame retardant. However, since it is a filled flame retardant, it has a large detrimental effect on the flowability of processing and the physical and mechanical properties of the product. It also has poor thermal and light stability.
The new flame retardant is decabromodiphenoxy ethylene oxide. It has the same bromine content and higher flame retardant efficiency as decabromodiphenyl ether and does not contain DPO like brominated styrene polymers. question. It also has excellent thermal and light stability. The limitation is that it is the same filler-type flame retardant as decabromodiphenyl ether, which has poor compatibility with polymers, resulting in poor processing fluidity and physical and mechanical properties of the product. In addition, the cost increase is significant compared to decabromodiphenyl ether. To date, most flame retardant products related to nylon are based on halogen-containing compounds. The smoke, toxic and corrosive gases generated during the flame retardant process cause secondary hazards to production, use and the environment. This flame retardant plays an important role in the field of flame retardants due to the international debate over the DPO issue and other reasons, but one can replace this flame retardant, which is a halogen-free challenge.
Two. Halogen Free Flame Retardant System
1. Phosphorus flame retardant
Phosphorescent flame retardants suitable for nylon mainly include red phosphorus flame retardants and Ammonium Polyphosphate (APP).
(1) Red phosphorus
The advantage of red phosphorus is that it is high in available phosphorus and produces more phosphoric acid during combustion than other phosphorus-containing compounds. To achieve the same flame retardant grade, the amount of red phosphorus added is less than other flame retardants, so nylon can better maintain its own mechanical properties. However, the main disadvantages of red phosphorus as a flame retardant are its red color, flammability, and reaction with water to form highly toxic phosphines (phosphines). Usually only used with nylon 6. Regular red phosphorus microencapsulation or masterbatches can avoid its drawbacks.
(2) Ammonium polyphosphate (APP)
Polyphosphoric acid (APP) participates in the thermal decomposition process of nylon by lowering the decomposition temperature of nylon and changing the composition of the final gas phase product (which is also a polymer) The formation of a honeycomb carbonized coating on the substrate prevents heat and substances from being trapped at the two-phase interface movement, and played a role in protecting the substrate. Because carbon flows easily, the substrate beneath the carbon layer is exposed, increasing the risk of burning. Inorganic additives such as talc, MnO2, ZnCO3, CaCO3, Fe2O3, FeO and Al(OH)3 can enhance the flame retardant effect.
Adding the above additives (1.5%-3.0%) to nylon 6 with 20% APP can increase the LOI value to 35%-47% and reach the V0 level.
2. Nitrogen-based flame retardant
Nitrogen-based flame retardants are low toxicity, non-corrosive, heat and UV stable, flame retardant effective and inexpensive. The disadvantage is that flame retardant plastics are difficult to process and have poor dispersion on the substrate. Nitrogen-based flame retardants suitable for nylon mainly include MCA (Melamine Cyanurate) and MPP (melamine polyphosphate). The flame retardant mechanism is a physical flame retardant "sublimation endothermic" method, and the flame retardant "sublimation endothermic" reduces the surface temperature of the polymer material and blocks air to make it a flame retardant. realize. One aspect is the direct carbonization and expansion mechanism of flame retardants and nylon in the condensed phase.
Good flame retardancy, but poor thermal stability, easy to absorb moisture, resulting in poor electrical properties in humid environments.
Three. Principles of flame retardant selection
The production process of flame retardant nylon and the selection of flame retardants mainly consider the efficiency of flame retardants, product performance and toxicity, such as the grade requirements of product flame retardants. Requirements for mechanical properties, surface properties, processing properties and coloring properties of materials. It is important to determine the type and amount of flame retardant, choice of additives, and process conditions, depending on the requirements of the application.
The following principles must be followed
①Excellent flame retardant effect, low dosage, good compatibility with nylon;
②It does not decompose at high decomposition temperature and nylon processing temperature;
③Excellent durability,
④ It has little effect on the mechanical and electrical properties of the material, and there is almost no corrosion to the equipment;
⑤Non-toxic, harmless, pollution-free and cheap.
Four. Future research direction of flame retardant nylon
Future flame retardant nylon materials must have the following properties.
①The material does not contain halogen and has low toxicity. Environmental requirements are an important focus for future materials and their use is increasing day by day as the use of halogen-free flame retardants has become a common trend.
②Research on composite flame retardant system. The flame retardancy of flame retardant nylon materials cannot be achieved by adding flame retardants, and it is necessary to combine various flame retardant systems to produce synergistic effects and achieve excellent flame retardant effects. Therefore, it is one of the important directions of future research and development to solve the problem of halogen-free flame retardant nylon by enhancing the synergistic effect of flame retardants, and to develop a new type of flame retardant with excellent performance.
③Various functions. Today, most flame retardant systems achieve the flame retardant properties of nylon materials while reducing mechanical and other electrical properties. Therefore, the successful development of the multifunctional flame retardant system will be a new direction for the development of flame retardant nylon materials in the future.
Novista Group supplies equivalent of FP-2100JC, FP-2200S, FP-2500S, Exolit OP1230, OP930, OP1312, OP1314 to global market.
