How To Make EPDM Halogen-free Flame Retardant？YINSU Flame Retardant Give You The Answer!

How To Make EPDM Halogen-free Flame Retardant？ YINSU Flame Retardant Give You The Answer!

Ethylene propylene diene rubber (EPDM) is a copolymer of ethylene, propylene and non-conjugated diene, EPDM molecular main chain for the saturated structure, only a small number of unsaturated groups of the molecular side chain, the molecular structure of the EPDM has excellent resistance to aging, ozone, corrosion, electrical insulation and other properties are widely used in construction, automotive parts, cables and wires and other fields. 

However, EPDM is a hydrocarbon material, oxygen index is only about 19, very easy to burn, and the amount of smoke is larger when burning, these are restrictions on its application. In order to solve the problem of flammability, it is necessary to add flame retardants in EPDM. The traditional flame retardant method is to add a higher flame retardant efficiency in EPDM halogen / antimony flame retardant system, this type of flame retardant additive is small, the mechanical properties of the material and the processing performance of the impact is small, but in the combustion of a large amount of smoke will be generated as well as toxic, corrosive hydrogen halide gas, resulting in secondary pollution, a lot of regulations issued on the restriction of the use of halogenated flame retardants.

At present, the research direction of EPDM flame retardant at home and abroad is shifting from traditional halogen flame retardants to halogen-free and environmentally friendly flame retardants. This paper summarizes and analyzes the current status of domestic and foreign research on EPDM halogen-free flame retardants, and also looks forward to the development direction of EPDM halogen-free flame retardant research.

Inorganic Metal Compound Flame Retardants

Commonly used inorganic metal compound flame retardants are calcium aluminum, calcium carbonate, zinc borate, Al(OH)3, Mg(OH) 2, etc. Among them, Al(OH) 3 flame retardant accounts for more than 80% of the dosage of inorganic metal compound flame retardant, which has the advantages of good stability, non-volatility, corrosive and low price, etc. The flame retardant mechanism of Al(OH) 3 is as follows: Al(OH) 3 can be used as a filler to The mechanism of flame retardant of Al(OH)3 is as follows: Al(OH)3 can be used as a filler to reduce the concentration of combustible polymer materials, and decompose and dehydrate by heat at high temperature, and the water vapor formed by dewatering can dilute the concentration of oxygen and combustible gases and take away a part of the heat to inhibit the rise of temperature of the rubber; at the same time, the metal oxide covering on the surface of the rubber after the dehydration of Al(OH)3 can prevent the rubber from continuing to burn, and thus play the role of flame retardant.

However, this kind of flame retardant has the disadvantages of low flame retardant efficiency, poor compatibility with rubber, etc., and it needs to be added in a higher amount in order to obtain moderate flame retardant properties, and the addition of too much will definitely affect the mechanical properties and processing performance of the substrate. Usually used to improve the flame retardant properties of inorganic hydroxides are: surface modification treatment, the use of smaller particle size micron or nano-scale hydroxide, and other flame retardants synergistically blended with the use of high filler aluminum hydroxide to prepare halogen-free flame retardant EPDM rubber.

It was found that the tensile strength of EPDM was 5.3 MPa when filled with 160 parts of aluminum hydroxide; the tensile strength of EPDM was increased to 5.9 MPa and the oxygen index was decreased from 30 to 29 after surface modification of aluminum hydroxide with vinyltriethoxysilane; the tensile strength of EPDM was increased to 9.1 MPa and the oxygen index was decreased from 30 to 29 after the aluminum hydroxide was mechanically crushed to make it smaller in particle size, and the tensile strength was increased to 7.9 MPa. 9.1 MPa, oxygen index increased from 26.5 to 29.0; aluminum hydroxide and other flame retardants such as magnesium hydroxide, antimony trioxide, zinc borate and so on, and found that the single use of aluminum hydroxide high filler EPDM high oxygen index.

YINSU's R&D team studied the effect of different amounts of aluminum hydroxide and magnesium hydroxide on the flame retardant properties of EPDM by using a cone calorimeter to determine the rate of heat release during the combustion process of EPDM and analyzing the morphology of the combustion products. The results show that: EPDM with high filler hydroxide is suitable for the preparation of low-smoke halogen-free flame retardant rubber; the flame retardant synergists red phosphorus and zinc borate can effectively promote the formation of charcoal and enhance the flame retardant properties of the material, but increase the total smoke emission when the material burns; the addition of an appropriate amount of carbon black can help to enhance the flame retardant properties of the rubber, but the filling of paraffinic oil is not conducive to the flame retardant, and the phenomenon of combustion-assisting phenomenon is more prominent.

Silicon flame retardants

Silicon flame retardants can be categorized into inorganic silicon flame retardants and organosilicon flame retardants according to their structure. Inorganic silicone flame retardants are mainly used to form a SiO2 cover layer on the surface of the substrate during combustion, which plays the role of heat insulation and shielding, but their flame retardant efficiency is not high, and they are generally not used individually. Organosilicon flame retardant is an environmentally friendly halogen-free flame retardant developed in recent years, mainly silicone oil, silicone resin, silicone rubber, organosilanol amide and caged sesquisiloxane, etc., which has the advantages of high efficiency, low smoke, anti-dripping and so on. Caged sesquisiloxane is a new type of organic-inorganic hybrid material with an inorganic skeleton composed of Si, O and covered by organic substituents, which has excellent thermal stability, flame retardancy and dielectric properties, and thus has good application prospects.

YINSU's R&D team made a composite material by using self-synthesized caged octaphenyl sesquicarbosiloxane (OPS) with EPDM and vulcanizing agent, and measured the mechanical properties, oxygen index, UL-94 flame retardancy and thermal stability of the composite material. The results showed that the addition of 20 OPS doubled the tensile strength of EPDM, increased the initial thermal decomposition temperature by 19°C, increased the oxygen index by 18.5%, and reduced the heat release rate by 18.3%.

YINSU's R&D team used octamethyl oligosilsesquioxane (OMPOSS) and ExolitOP950 (phosphate ester compound) as flame retardants and compounded them with recycled PET to explore their synergistic flame retardant effects. the addition of OP950 and OMPOSS promoted the formation of a charcoal layer during the combustion process and effectively inhibited melt dripping, and when the mass ratio of OP950 to OMPOSS was 9:1, it increased the tensile strength of EPDM by 18.5% and reduced the heat release rate by 18.5%. When the mass ratio of OP950 and OMPOSS is 9:1, the oxygen index of the composite system is high, the heat release rate is reduced to low, and the expanded char layer is uniform and dense after combustion, so the synergistic effect is more obvious.

Intumescent flame retardant

Intumescent flame retardant is an important material for the preparation of halogen-free environmentally friendly flame retardant rubber. Intumescent flame retardant is a composite flame retardant with carbon, nitrogen and phosphorus as the core components, which usually consists of 3 parts: carbon source (carbonizer), acid source (dehydrating agent) and gas source (intumescent agent). Intumescent flame retardants mainly include ammonium polyphosphate, melamine, tetracosanol and so on. Rubber with intumescent flame retardant will form a uniform carbon foam layer on the surface when burning, and this carbon layer can play the role of heat insulation, oxygen barrier, smoke suppression, and can better prevent combustion. Intumescent flame retardants have the advantages of better flame retardant effect, low smoke, low toxicity, no corrosive gases, low cost, etc., and thus are widely used in polymer flame retardancy.

YINSU's R&D team prepared flame-retardant EPDM materials using a composite intumescent flame retardant NP430. The results show that the intumescent flame retardant NP430 has a good flame retardant effect on EPDM, and the synergistic flame retardant effect is good when the acid source ethylene vinyl acetate copolymer (EVA) and the carbon source high styrene (HS) resin are used in parallel; when the ratio of EPDM/EVA/HS is 80 ∶ 8.6 ∶ 11.4, and the dosage of the flame retardant NP430 is 90, the ultimate oxygen index can reach 47.6%, and the flame retardant NP430 can be applied to EPDM, which is a good flame retardant. However, filling inorganic fillers such as carbon black, silica, calcium carbonate, expandable graphite, etc. will lead to the escape of combustion gases, which is seriously unfavorable to the expansion process, and will lead to the failure of intumescent flame retardants.

YINSU's R&D team prepared flame-retardant EPDM materials by synthesizing a new type of intumescent flame retardant, PDP, which combines three intumescent active components in one organic molecule. The results show that when PDP is added in an amount of 60 parts, the limiting oxygen index of EPDM reaches 30, and the UL-94 test result is FV-0 grade. Mechanical test results showed that increasing the content of PDP can improve the flame retardant properties of EPDM, but will damage its mechanical properties.

Phosphorus flame retardants

Phosphorus flame retardants can be divided into two categories: inorganic phosphorus flame retardants and organic phosphorus flame retardants.

Inorganic phosphorus flame retardants mainly include red phosphorus, ammonium phosphate and ammonium polyphosphate, etc. They have the advantages of good stability, non-volatile, non-halogenated, etc. However, they also have the shortcomings of low flame retardant efficiency and moisture absorption, and the red phosphorus also has the problem of coloring, which affects the color of the products.

YINSU's R&D team prepared EPDM rubber using red phosphorus as a flame retardant. The results showed that the oxygen index of EPDM rubber was saturated when the addition amount of red phosphorus was 9 parts; red phosphorus and Mg(OH)2 played a sum-retardant effect in EPDM rubber, and SiO2 had an inhibitory effect on the flame retardant effect of red phosphorus in EPDM rubber. Organic phosphorus flame retardants include phosphate ester, phosphite, phosphonate, organic phosphorus salts, phosphorus oxide, alkyl phosphorous acid, phosphorus heterocyclic compounds and polymer phosphorus (phosphonic) acid esters.

Organic phosphorus flame retardants mainly through the condensed phase flame retardant mechanism to play the role of flame retardant. When combustion occurs, organophosphorus flame retardants will decompose at high temperatures to generate phosphoric acid and non-combustible gases, phosphoric acid decomposes into metaphosphoric acid at high temperatures, and metaphosphoric acid can be polymerized into poly(metaphosphoric acid). Among them, metaphosphoric acid is a viscous material, can form a layer of phosphoric acid - metaphosphoric acid - poly metaphosphoric acid film, the boiling point of the film up to 300 ℃. This film covers the surface of the rubber, which can play the effect of isolating the air and preventing the free radicals from escaping; poly(metaphosphoric acid) is a strong acid, which can make the polymer dehydrate and carbonize, and form a charcoal layer on the surface of the rubber, which can further isolate the air and improve the flame retardant effect. Compared with halogen flame retardants, phosphorus flame retardants in the material to give good flame retardant properties at the same time, but also has a small amount of smoke, is not easy to form toxic gases and corrosive gases and other advantages, and will not affect the mechanical properties of the substrate and processing performance. Organic phosphorus flame retardants are considered to be one of the varieties that may replace halogen flame retardants.

At present, the phosphorus flame retardant applied to polymer flame retardant reports more, but applied to flame retardant rubber material reports are less seen, it is mainly used as a synergistic flame retardant, which is commonly used is phosphorus - nitrogen synergistic flame retardant.

Phosphorus-nitrogen synergistic flame retardant system

Phosphorus-nitrogen synergistic flame retardant system has the advantages of phosphorus flame retardant and nitrogen flame retardant. By adding nitrogen into the phosphorus flame retardant, it can improve the thermal stability and reduce the amount of smoke, and at the same time, it can reduce the amount of flame retardant. Due to the synergistic and synergistic effect between phosphorus and nitrogen flame retardant elements, the phosphorus - nitrogen synergistic flame retardant system has become a hot spot in the research of halogen-free flame retardant materials in recent years, and is regarded as one of the directions for the development of halogen-free flame retardant in the future.

We prepared halogen-free flame-retardant EPDM rubber materials by using melamine cyanurate and diethylaluminum hypophosphite as compound flame retardants and aluminum hypophosphite as synergist. It was shown that when the dosage of melamine cyanurate was 76 parts, the dosage of diethylaluminum hypophosphite was 14 parts, and the dosage of aluminum hypophosphite was 10 parts, the vertical combustion level of EPDM was up to FV-0, the oxygen index was 30, and the EPDM had good processing and mechanical properties.

We introduced the charcoal-forming catalyst heteropolyacid (HPA) and the flame retardant modifier CR, and the results showed that the glass-fiber-reinforced nylon 6 could achieve UL-941.6 mm V-0 level of flame retardancy and good mechanical properties with the addition of 2% of HPA and 2% of CR to the flame retardant system.

Research Outlook

EPDM is a kind of important synthetic rubber, and its usage is only second to SBR and cis-butadiene rubber, becoming the third largest synthetic rubber in the world. Meanwhile, with the development of economy and the enhancement of people's awareness of environmental protection, new type of halogen-free, environmentally friendly and efficient flame retardants will gradually replace the traditional halogen flame retardants.