Flame retardant mechanism of polymer materials summary-Iota

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Service > Flame retardant mechanism of polymer materials summary

Flame retardant mechanism of polymer materials summary

The burning of the polymer is a very intense complex thermal oxidation, smoke or have to take hair blazing flame characteristics. When the combustion process is typically in the continuous heating of the external heat source, the first polymer with atmospheric oxygen free-radical chain degradation reactions produce volatile combustible material, the material reaches a certain concentration and temperature will catch fire and burn up, the combustion part of the heat evolved is supplied degradable polymer, further exacerbating their degradation, produce more combustible gas flame in a short time will spread rapidly and cause a fire.
Is a class of flame retardants can prevent or inhibit flame propagation ignite plastic additives. According to its use, and the reaction can be divided into two types add type, addition type flame retardant is incorporated into the plastic during processing of the plastic, used for thermoplastics. Reactive flame retardant in the polymer synthesis process as monomers chemically bonded to the polymer chains, used for thermosetting plastics, some reactive flame retardant may be used as additive flame retardant. According to the chemical structure, can be divided into inorganic and organic flame retardant types, and more in these compounds containing a halogen and phosphorus, some contain antimony, boron, aluminum and other elements.
1. Flame retardant mechanism
The flame retardant material, often by gas flame, and condensed phase flame retardant heat exchange interrupt mechanism to achieve. Inhibit the promotion of the combustion reaction chain radicals play flame retardant functions belong vapor; in the solid phase delay or prevent the polymer from the thermal decomposition of condensed phase flame retardant effect of the case; the polymer combustion section fire caused by heat away, the heat exchange mechanism are interrupted classes retardant. But combustion and flame are very complex process, involving a lot of influence and constraints, the mechanism of a flame retardant system is strictly divided into a certain kind of hard, in fact, a lot of flame retardant system simultaneously in several flame retardant mechanism works.
1.1 vapor retardant mechanism
Vapor retardant system refers to a gas phase combustion interrupt or delay the chain reaction of combustion flame retardant, flame under the following situations belong vapor retardant.
Can produce free radical inhibitor (1) heating or combustion flame retardant material, so that the combustion chain reaction interrupted.
Generating fine particles (2) when the combustion heat or flame retardant material, they can promote free radicals combined with each other to stop the combustion chain reaction.
(3) the release or burn large amounts of heat-retardant materials inert gas or high-density steam, the former can be diluted oxygen and gaseous fuel, and this can reduce the temperature of the gas, resulting in the burning aborted; the latter can be covered on gas , cut it into contact with the air, thus making the combustion suffocation. Volatile, low boiling phosphorus-containing compound, such as trialkyl phosphorous oxide (R3PO), belongs to the gas phase flame retardant. Mass spectral analysis showed that the triphenyl phosphine and triphenylphosphine oxide ester cleavage fragments into free radicals in the flame, such as free radicals and a halide as capturing H · O · radical, thereby to restrain the combustion chain reaction effect.
In the combustion and pyrolysis of red phosphorus, but also the formation of P ·, they and the polymer react with oxygen to generate ester structure. In addition, the expansion flame retardant system may also play a role in the gas phase, in which the amine compounds decompose when heated to produce NH3, H2O and NO, the first two can dilute the concentration of oxygen gas flame zone, which allows the combustion waging The free radical quenching, resulting in chain termination reaction.
1.2 condensed phase flame retardant mechanism
This refers to the delay or interruption in the condensed phase thermal decomposition of the flame retardant material of flame retardant, flame retardant belong to the following situations are condensed phase flame retardant.
(1) flame retardants phase delay or prevent combustible gas can generate heat and radical decomposition cohesion.
(2) flame retardant material heat capacity larger than inorganic filler, heat storage and heat conduction through the material is not easy to achieve the thermal decomposition temperature.
(3) thermal decomposition endothermic flame retardants, flame retardant materials to make the temperature rise slowed or discontinued.
Generation (4) fire-retardant material on the surface of the porous carbon combustion layer that flame, heat, oxygen barrier, but also can prevent the gas into the combustion vapor, causing combustion in order to maintain continued to burn, you must have enough oxygen and combustible gas mixture. If the radicals produced by thermal cracking trapped disappear, will slow down or interrupt combustion. When the flame retardant thermoplastics flame retardant comprising an organic bromide as combustion occurs, the following reactions.
RH → R · + H · chain initiation
HO · + CO = CO2 + H · chain growth (highly exothermic reaction)
H · + O2 = HO · + O · chain branching
O · + HBr = HO · - + Br · chain transfer
HO · + HBr = H2O + Br · chain termination
Having a highly reactive free radical HO · play a key role in the combustion process. When HO · is less reactive Br · replaced terminate radical chain reaction occurs.
1.3 interrupt retardant heat exchange mechanism
This means that part of the heat produced by the combustion of the flame retardant material is taken away, so that the thermal decomposition temperature of the material can not be maintained, and therefore can not be maintained to produce combustible gas, so the combustion self-extinguishing. For example, when the material is exposed to strong heat or flame combustion can melt, and the molten material is easy to drop, and thus most of the heat away, reducing the feedback to the body heat, so that the combustion delay, may eventually terminate combustion. So, flammable meltable materials are usually low, but the dripping of burning droplets can ignite other materials, increased fire risk.
2. retardant effect of a flame retardant
Flame retardant effect in the combustion process is a polymer material can prevent or inhibit its physical or chemical change in speed, specifically, the role is reflected in the following aspects.
(1) an endothermic effect its role is to make the temperature rise in difficulty polymeric material, e.g., borax having 10 molecules of water of crystallization, due to release of water of crystallization to seize 141.8kJ / mol of heat, leaving its endothermic rise in temperature of the material is inhibited, resulting in flame retarding effect. Flame retardant hydrated alumina is the reason for its endothermic heat dewatering effect. In addition, some of the thermoplastic polymer droplet cleavage often generated, because it can be removed leaving the combustion zone heat of reaction can also play a flame-retardant effect.
(2) blocking effect and its role is to generate stable at higher temperatures the cover layer, or decomposed to generate a foam-like substance covering the surface of the polymer material, so that the heat generated by the combustion is difficult to pass the interior material, so that the polymer combustible gas generated by thermal decomposition material is difficult to escape, and the material isolated from the effects of air, thereby inhibiting the cleavage of the material, to achieve the effect of flame retardant. Such as phosphate compounds and fire foam coatings can click here to play a role in the mechanism.
(3) the dilution effect of these substances decompose when heated to produce a large amount of nonflammable gas, flammable gas and oxygen in the air resulting diluted polymer material and reach the combustible concentration range, thereby preventing high polymer pyrophoric material burning. There can be used as diluent gas CO2, NH3, HCl, and H2O and the like. Will be able to produce such nonflammable gas heating amine phosphates, ammonium chloride, carbonate, amine and the like.
(4) Transfer effect its role is to change the mode of thermal decomposition of the polymer material, thereby suppress the generation of the combustible gas. For example, the use of an acid or base to make the dehydration reaction to produce cellulose decomposed into carbon and water, because they do not produce a combustible gas, will not be ignited. Ammonium chloride, ammonium phosphate, phosphoric acid ester, etc. can decomposition of such materials, the catalytic material fused ring carbonization, to achieve the purpose of fire-retardant.
(5) The inhibitory effect (capture free radicals), the main polymer is a free radical chain reaction of combustion, some substances can capture the combustion reaction active intermediate HO ·, H ·, · O ·, HOO ·, etc, inhibit free radical chain reaction, the combustion speed is reduced until the flame is extinguished. Commonly used bromine, chlorine and other organic halogen compounds have this inhibitory effect.
(6) enhancement effect (synergy) Some materials, when used alone has no effect or flame retardant effect is not, you can play a variety of materials with enhanced flame-retardant effect. Antimony trioxide and halogen compounds and use, is the most typical example. As a result, not only can improve the flame retardant efficiency, and also reduce the amount of flame retardant.
Several typical flame retardant mechanism of 3
3.1 halogen flame retardant
Halogen flame retardants include bromine-based flame retardants and chlorine. Halogen flame retardant is currently one of the world's largest production of organic flame retardants. In most of the halogen-based flame retardants are brominated flame. Industrial production of brominated flame retardants can be divided into additive, reaction type and polymer-type three categories, and variety. The domestic market of more than 20 kinds of existing additive brominated flame retardants, more than 10 kinds of polymer type brominated flame retardants, more than 20 kinds of reactive bromine-based flame retardants. Additive flame retardant mainly decaBDE (DBDPO) tetrabromobisphenol A bis (2,3 or two alkyl propyl) ether (TBAB), eight polybrominated diphenyl ethers (OBDPO) etc; reaction type flame retardants mainly tetrabromobisphenol A (TBBPA), 2, 4, 6- tribromophenol and the like; a polymer type flame retardant mainly brominated polystyrene, brominated epoxide, tetrabromobisphenol A carbonate ester oligomer and the like. Brominated flame retardants reason for being popular, mainly because of its high flame retardant efficiency, and affordable. Since the C-Br bond in the lower, most brominated flame retardants decomposition temperature at 200 ℃ -300 ℃, this temperature range is just common polymer decomposition temperature range. Therefore, when the polymer decomposition, brominated flame retardants have begun to decompose, and captures the radical decomposition of polymer materials, thereby delaying or inhibiting the chain reaction of burning and then, while the release of HBr itself is a flame retardant gas, you can cover the surface of the material, play a role in blocking and diluted oxygen concentration. Such exceptions are all flame retardant and antimony (antimony trioxide or antimony pentoxide) compound used to make fire by synergy effect has been significantly improved.
Halogen flame retardant to play a major role in the gas phase. Since hydrogen halide gas halide decomposition, is nonflammable gas, has a dilution effect. It is a larger proportion of the gas film layer covering the surface of the solid polymer materials can be isolated from the air and heat, from the mulch. More importantly, the suppression of hydrogen halide polymer chain reaction of combustion of materials, from the scavenging of free radicals. With bromide, for example, the inhibition of free radical chain reaction mechanism is as follows:
Brominated flame retardants → Br ·
Br · + RH → R · + HBr
HO · + HBr = H2O + Br ·
OH · radical reactions in polymer materials added brominated flame retardants, fire thermal decomposition reaction of free radicals Br ·, it generates polymer materials react with hydrogen bromide, hydrogen bromide and highly active On the one hand makes Br regeneration, on the one hand so that the concentration of OH · radicals reduce the combustion chain reaction is inhibited, slow burning speed, until extinguished.
But when the fire occurred, due to decomposition and combustion of these materials produce a lot of smoke and toxic corrosive gases cause a "second disaster" and the combustion products (halide) has a long atmospheric lifetime, once into the atmosphere is difficult to remove, seriously polluted the atmosphere, destroy the ozone layer. In addition, the combustion and pyrolysis products PBDE flame retardant polymer materials contain toxic polybrominated diphenyl and dioxane (PBDD) and polybrominated dibenzofurans (PBDF). September 1994, the US Environmental Protection Agency evaluation demonstrated that these substances on humans and animals caused by toxic substances.
3.2 flame retardant mechanism of phosphorus and phosphorus compounds
Phosphorus and phosphorus compounds have long been used as a flame retardant, it was too early retardant mechanism, initially found to generate a lot of coke when using phosphorus-containing flame combustion of materials and reduce the flammability of volatile production of substance, thermogravimetric combustion retardant material is greatly reduced, but the smoke density is increased when the combustion retardant material than when no flame retardant. Based on the above facts made some flame retardant mechanism. Phosphorus compounds in different reaction zone from the role played by flame retardant mechanism can be divided into phases and vapor phase flame retardant mechanism cohesion, organophosphorus flame retardants play a role in the condensed phase, the flame retardant mechanism is as follows :
When burning, non-flammable liquid phosphorus compound decomposition film-forming phosphate has a boiling point of up to 300 ℃. Meanwhile, phosphoric further dehydration metaphosphoric acid, metaphosphoric acid and further polymerized to form poly metaphosphoric acid. In this process, not only by the phosphate coating layer covering the effects produced play, and because the resulting polyvinylidene phosphoric acid is a strong acid, is a strong dehydrating agent, dehydration and carbonization of the polymer, changing the mode of the combustion process and the polymer the formation of carbon on the surface to cut off the air, and thus play a stronger flame effect.
Flame retardant phosphorus flame retardant mainly in the early stages of a fire polymer decomposition, because dehydration can promote hair polymer, thereby reducing the amount of polymer produced by thermal decomposition of combustible gas, and the resulting The carbon can cut outside air and heat. Typically, the phosphorus-based flame retardant effect of the oxygen-containing polymer of the best, which is primarily used in the hydroxyl group-containing cellulose, polyurethane, polyester and other polymers. For oxygen-hydrocarbon polymer, the phosphorus-based flame retardant effect is relatively small.
Phosphorus-containing flame retardant is a free radical trapping agent, found by mass spectrometry, any phosphorus-containing compound in the polymer PO · combustion has formed. It can be combined with the flame zone of the hydrogen atoms so as to suppress the flame effect. In addition, the water produced in the phosphorus-based flame retardant process, one can reduce the temperature of the condensed phase, on the other hand can dilute the concentration of combustibles in the gas phase, in order to better play a flame retardant.
3.3 inorganic flame retardant mechanism of
Inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, graphite, borate, oxalate, aluminum, and zinc sulfide-based flame retardant. Aluminum hydroxide and magnesium hydroxide is a flame retardant inorganic main varieties, it has no toxicity and low smoke and so they absorb heat due to thermal decomposition of the burning zone, the temperature of the combustion zone is reduced to below the critical temperature of the combustion burner self-extinguishing : After the decomposition of metal oxides most high melting point, good thermal stability, covering the surface of the solid phase in the burning heat conduction and thermal radiation barrier, which play a role in flame. At the same time generate a lot of water vapor decomposition, can be diluted combustible gases, but also play a flame retardant.
Alumina hydrate has good thermal stability, heated at 300 ℃ 2h may be converted to AlO (OH), does not produce harmful gases upon contact with the flame, and to neutralize released acid gas is pyrolysed polymer, hair smoke less, cheap, etc., so it becomes important species of inorganic flame retardants. Hydrated alumina combined heat released from the chemical water absorbs the heat of combustion, reducing combustion temperature. When play a flame retardant, mainly two crystal water works, in addition, activated alumina dehydration product, some of the polymer can promote the fused ring charring during combustion, thus having a condensed phase flame retardant. This mechanism is known from the use of hydrated alumina as a flame retardant additive amount should be bigger.
Magnesium main varieties of magnesium hydroxide flame retardant, a flame retardant is being developed at home and abroad in recent years, it starts at about 340 ℃ endothermic decomposition reaction of magnesium oxide, the weight loss at 423 ℃ reached its maximum , the decomposition reaction at 490 ℃ terminated. From calorimetry, it appears that the reaction to absorb a lot of heat (44.8KJ / mol), the resulting water also absorbs a lot of heat, reducing the temperature to reach the flame retardant. Thermal stability and smoke suppression capacity than the hydrated alumina magnesium hydroxide good, but because of the large surface polarity of magnesium hydroxide, poor compatibility with an organic substance, it is necessary after surface treatment can be used as effective flame retardants. In addition, its thermal decomposition temperature is high, the decomposition of suitable thermoset materials of relatively high temperature polymer flame retardant.
At high temperature, heat expandable graphite intercalation layer easily degradable, so that the generated gas of the graphite layer spacing
Quickly expanded to several times its original to several hundred times. When expandable graphite is mixed with the polymer, the flame may be
Use under tough carbon layer can be generated in the polymer surface, which play a role in flame.
Borate flame retardants borax, boric acid and zinc borate. At present, the main use of zinc borate. Zinc borate
300 ℃ crystals began to release water, under the action of a halogen compound, to generate a boron halide, zinc halide, inhibit and capture free hydroxyl, preventing combustion chain reaction; while forming a solid phase covering layer, isolated from ambient oxygen, prevent flame continues to burn and has a smoke suppression effect. Zinc borate can be used alone, can also be used with other flame retardant compound. At present, the main products are fine zinc borate, zinc borate heat, anhydrous zinc borate and zinc borate high water.
Aluminum oxalate is a crystalline substance derived aluminum hydroxide, low alkali content. When the polymer contains oxalic acid aluminum combustion, releasing H20, CO and CO2, without generating corrosive gas, aluminum oxalate also reduce cigarette smoke density and speed. Since aluminum oxalate of low alkali content, so when using the flame-retardant wire, cable coating materials, do not affect the electrical properties of the material.
Now developed five kinds of zinc sulfide-based flame retardant, wherein the four kinds used in rigid PVC, another may be used in soft PVC, polyolefins diameter and nylon. Such flame retardants can improve the anti-aging properties of the material, and there is good compatibility and enhance the thermal stability of polyolefins and fiberglass.
3.4 synergistic flame retardant mechanism of mixed use
Halogen-containing flame retardants used in conjunction with the phosphorus can generate significant synergies. For halogen - phosphorus flame retardant synergistic effect has been proposed halogen - phosphorus used in conjunction with each other to promote decomposition and the formation of a stronger than the single use of halogen flame retardant effect - phosphorus compounds and their conversion products PBr3, PBr ·, POBr3 so on. By pyrolysis gas chromatography, differential thermal analysis, differential scanning calorimetry analysis, oxygen index, the researchers observed flame temperature programmed methods such as halogen-phosphorus showed a synergistic effect, halogen - phosphorus flame retardants used in conjunction with decomposition slightly lower temperature than when used alone, and the decomposition is very intense, smoke clouds of chlorine and phosphorus compounds combustion zone formed hydrolyzate can stay a long time in the combustion zone to create a strong vapor barrier.
About P - N interaction mechanism was not perfect, is generally believed by nitride (such as urine, melamine, guanidine, dicyandiamide, methylolmelamine etc.) can promote cellulose phosphate and phosphorylation reactions. Amine phosphates formed more easily occurs as the cellulose ester, the thermal stability of such esters thermal stability than phosphate. Phosphorus - nitrogen flame retardant system can promote the formation of coke and water sugars decompose at lower temperatures, and increased production of coke residue, thereby enhancing the flame retarding effect. Phosphide and nitride formation expandable coke layer at a high temperature, it acts as an oxygen barrier protective insulating layer, a nitrogen-containing compound acts as a blowing agent and a char enhancer. Basic element analysis showed that the residue of nitrogen, phosphorus, oxygen three elements, the thermal stability of the amorphous substance which is formed at the flame temperature, like glass body, as an insulating protective layer of cellulose.
Can not be used alone as a flame retardant antimony trioxide (except halogen-containing polymer), but with a halogen-based flame retardant is greatly enhanced synergistic effect. This is because the presence of halides in the case of antimony trioxide, the relative density of the combustion generated SbCl3, SbBr3 antimony halide such as large, since the polymer covering the surface of the covering effect, and also when the gaseous capture free radicals effect. For example, antimony trioxide and chlorinated flame retardants and use, due to thermal decomposition of hydrogen chloride chloride, hydrogen chloride and antimony trioxide reacts antimony trichloride and chlorine oxide, antimony oxide, antimony thermal decomposition of chlorine continues to generate trichlorosilane antimony.
Hydrated zinc borate and halogenated flame retardants used in conjunction with good synergy. Under combustion conditions, and the cleavage products between them by the interaction, allows almost all elements can exert flame retardant effect. Hydrated zinc borate reaction product with a halogen-based flame retardant and zinc dihalide boron trihalides, they can capture HO · in the gas phase, H ·, in the solid phase to form a glassy insulating layer, heat, oxygen barrier, water generated dilute oxygen combustion zone and take away the heat of reaction, and therefore can play a larger role in flame.
Retardant mechanism 3.5 expansion system
Intumescent flame retardant system main components can be divided into three parts acid source, carbon source, gas source. Acid source is generally heated to an inorganic acid or an inorganic acid generating compound 100 ^ -250 ℃, such as phosphoric acid, sulfuric acid, boric acid, various ammonium salts, phosphates, and borates; carbon (char-forming agent) is forming a base layer of carbonized foam, generally polyhydroxy compound is carbon-rich, such as starch, pentaerythritol and its dimers, trimers and organic resin including a light group; gas source (foam source) or more for an amine amides, such as melamine, dicyandiamide, amine polyphosphate.

Intumescent systems char complicated structure, many factors. Chemical structure and physical properties of the polymer body, the expansion flame retardant composition, conditions (such as temperature and oxygen content) during combustion and pyrolysis, the crosslinking reaction rate, and many other factors have an impact on the expansion of the structure of the char. The protective effect of the thermal expansion of the carbon layer depends not only on the coke yield, char layer height, char layer structure, the thermal stability of the protective char layer, and also depends on the chemical structure of the carbon layer, especially the emergence of a cyclic structure increases the thermal stability resistance, in addition to the chemical bond strength, and the number of crosslinks.
Intumescent systems generally considered flame retardant mechanism for condensed phase flame retardant, amine polyphosphate first thermal decomposition, generate a strong dehydration of the phosphoric acid and pyrophosphoric acid, pentaerythritol ester, and then dehydrated carbonized, and the water vapor formed by the decomposition reaction of melamine Ammonia make charcoal layer expands, eventually forming an extra layer of microporous carbon layer, so isolated from the air and heat transfer, protective polymer body, to fire purposes.
Intumescent flame retardant added to the polymer material, you must have the following properties: good thermal stability, can withstand high temperature polymer processing of more than 200 ℃; thermal degradation due to large amounts of volatile substances to be released, and the formation of residues, and the procedure should not adversely affect the expansion of the foaming process; such flame-retardants have uniform distribution in the polymer, during the combustion of materials can form a layer completely covering the surface of the expanded carbonaceous material; flame retardants must be retardant polymers have good compatibility, adverse effects can occur with polymers and additives, not too much deterioration in the physical and mechanical properties of the material. Intumescent flame retardant than the general non-halogen flame retardants is that no antimony oxide: smoke, less toxic, non-corrosive gases; expansion of flame-generated carbon layer can absorb fire melted polymer to prevent Its dripping spread fire.
3.6 ammonium retardant mechanism
Ammonium poor thermal stability, release ammonia when heated, such as [NH4) 2SO4, which decomposition process is as follows:
[NH4) 2SO4 → NH4HSO4
NH4HSO4 → H2SO4 ten NH3 ↑
Ammonia released difficult nonflammable gas, which dilutes the oxygen in the air; H2SO4 formation plays dehydration charring catalyst. The latter effect is generally considered a major additional experiments show, NH3 also occur following reaction in the fire:
NH3 + O2 → N2 + H2O
And with deep oxidation products, such as N2O4, which can be seen not only physical NH3 retardant effect, but also the chemical flame retardant.
3.7 nanocomposite flame retardant material mechanism
Nanocomposites singled out, although both belong to the complex fire, but the principle little different. Nanocomposite material refers to one or more components to nanometer size or molecular dispersed in another component of the matrix, this study only 10 years of history. Experiments show that the nano material with ultra-fine size exist, so the performance of various types of nanocomposites are greatly improved than the corresponding macro or micro-scale composite materials, wherein the thermal stability and flame retardant properties of the material will be improved greatly.
Some scaly inorganic able fragmentation in the role of the physical and chemical structure of a nano-sized micro-district,
Its lamellar spacing typically a few tenths to a few nanometers, they only allow certain polymer intercalated into the nano
Interlayer space size to form "intercalated nanocomposite", and, an inorganic interlayer will be a large aspect ratio of the polymer formed softened inorganic single sheet, uniformly dispersed in the matrix polymer, the formation of "delamination nanocomposites." The use of a porous or layered inorganic compound properties, preparation of inorganic / polymer nanocomposite, in the process of thermal decomposition and combustion, carbon and inorganic salts may be formed multi-layer structure, heat insulation and prevent the combustible gases to effect, retardant polymers to make. In addition, the use of inorganic / polymer nanocomposites also has anti-corrosion, anti-leakage, wear and weathering effect. Now nanocomposite nylon / clay, PS / clay nanocomposites, PET / clay nanocomposites, PBT / clay nanocomposites, research PP / clay nanocomposites such as nanocomposites made gratifying achievements.
3.8 silicone flame retardants
The silicone compounds as flame retardants research began in the early 1980s. In 1981, Kamber and other published studies on methyl silicone blend of polycarbonate and polyethylene, can improve the flame retardancy. Although silicone flame behind the research and development department and phosphorus flame retardant halogen, however, silicone flame retardants as a new class of non-halogenated flame retardants, with its excellent flame resistance, moldability and environment-friendly and unique style. Silicone flame retardant silicone oil, silicone resin, polysiloxane with functional groups, a polycarbonate siloxane copolymer silicone acrylate composite material and a silicone gel and the like. A silicone compound flame retardant polymer materials, silicone flame will probably migrate to the surface of the material to form a surface layer of silicone polymer concentration gradient materials.
Once burned, it will generate a unique silicone-containing inorganic thermal insulation for a S iO button and a Si-C- bonds, both to prevent the combustion decomposed into material to escape, but also inhibits the polymer material thermal decomposition, reaching a high flame-retardant, low smoke, low harmful purposes. At present, the development and application of silicone flame retardants American DowCorning developed and commercialized "DC RM" series flame retardants: Japan's NEC and GE Toshiba Silicones joint research and development of silicone flame "XC-99-B6645 "; also developed SFR104 American GE silicone resin.
(End)
Supplementary information:
An intumescent flame retardant composition
IFR is mainly composed of three parts: charring agent (carbon source), charring catalyst (acid source), expanders (air). Charring agent for the expansion of the porous carbon layer of carbon source, usually carbon-rich multi-functional groups (eg -OH) material, pentaerythritol (PER) and two acetal, three acetal is commonly charring agent. Charring catalyst is generally releasable inorganic acid compound under heating. Inorganic acids require high boiling point, but not too strong oxidizing. Ammonium polyphosphate (APP) is commonly used charring catalyst. Bulking agent is an inert gas heated release compound, generally ammonium and amides substances, such as urea, melamine, dicyandiamide and derivatives thereof. The criteria for selecting the components as follows:
1) acid source: In order to have a practical, acid source must be able to make the carbonaceous polyol dehydration. Before the fire, we do not want the dehydration reaction, so commonly used acid source is a salt or ester. Acid source acid must be released at a lower temperature, in particular below the decomposition temperature of the polyol. If the organic fraction contribute to carbon, organic phosphide better.
2) carbon source: the number of carbon sources and carbon content and the effectiveness of active hydroxyl groups concerned. Carbon source should be at a lower temperature by itself or matrix decomposition of the catalyst prior to the reaction.
3) gas source: the blowing agent must be at the appropriate temperature decomposed, and release large amounts of gas. Foam should be melted before solidification occurs. Appropriate temperature and system-related. For a particular intumescent flame retardant polymer system, do not need the three components are present simultaneously, the polymer itself can sometimes serve as an element therein. Using the above criteria can predict the effectiveness of most of the system.
2 flame retardant mechanism
When the intumescent flame retardant heat, charring agent in the charring catalyst dehydration into carbon, carbides under the effect of the expansion agent gas decomposition char layer formed fluffy closed pore structure. Once formed, its own non-combustible, and can weaken the heat conduction between the polymer and the heat source, and prevent gas diffusion. Once combustion can not get enough fuel and oxygen combustion
The polymer will be self-extinguishing. This char layer formation through the following steps.
(1) can be released at a lower temperature esterified polyhydric alcohols can be used as a dehydrating agent is an inorganic acid from the acid source.
(2) at a temperature slightly higher than the release of an acid, esterification, and the system can be used as an amine esterification catalyst.
(3) System melted before the esterification or the esterification process.
(4) generated by the reaction of water vapor and non-combustible gases generated by the gas supply system expansion molten foam.
(5) reaction nears completion, the system gelled and cured, the final form of the porous carbon foam layer. On the basis of the above discussion, it seems any of several compounds containing functional groups can be foam, foam albeit to varying degrees, in fact, this is wrong. For foaming, each reaction must occur almost simultaneously, but must be carried out in strict order. Intumescent flame retardant may also have a role in the gas phase, because phosphorus - nitrogen - carbon system when exposed to heat may produce NO and NH3, and they combine to make a radical chain reaction resulting in combustion terminated.
Factors affecting intumescent flame retardant effect
Intumescent flame retardant effect depends char reaction, swelling reactions and carbon layer structure.
3.1 char reaction
Char intumescent flame retardant effect was mainly due to thermal decomposition of the acid source APP phosphate and pyrophosphate strong dehydration, which generate phosphate dehydration and charring agent hydroxyl or amino or deamination reaction. The combustion heat generated by the decomposition of an ester of unsaturated olefins, then the carbon layer multi-molecular cyclization polymerization reaction to form a stable polyaromatic structures unsaturated olefin occurs, instead of the aromatic structure in the branched alkyl group is a small molecule is broken .
Char reaction common APP and PER system in several steps in the process. First, APP long strand phosphorothioate linkages generated when 210 ℃. After dehydration and ammonia, can form the cyclic phosphate. If the temperature continues to rise, by carbonization reaction, phosphate bond is almost completely broken, an unsaturated carbon-rich structures, reactions may have Diels-Aider reaction, making the cyclic olefins, aromatics and thick hydrocarbon structure into the coke structure.
3.2 expansion reaction
Expansion is due to gas migration caused cleavage. Migration rate and viscosity of the melt and the combustion zone related to the amount of gas emitted, by controlling the viscosity of the polymer can influence the degree of crosslinking and thus to adjust the carbon structure. Expansion of the carbon layer shape enclosed chamber will depend on the number and the viscosity of the gas released into the matter when carbon char. Expanders must meet the gas release process and carbonization process match. Decomposition temperature of the foaming source is too low, the gas into carbon before the spill, would not achieve the foaming action; foam decomposition temperature is too high, the gas may be carbon layers from the top or blow away. Urea is not a good match and APP-PER system. Though urea can release 70% of the gas, but its decomposition temperature (150 ~ 230 ℃) and expandable layer (APP- PER) formation temperature (280 ~ 320 ℃) compared to low. Melamine can occur in a range of 250 ~ 380 ℃ reaction, gas evolution, as commonly used bulking agents. In addition, PER PER ether phosphoric acid ester structure and the structure of the carbonization reaction will occur upon heating swelling phenomenon.
3.3 carbon layer structure
Expansion of the system by the carbon polymer incomplete cleavage or oxidation at a lower temperature. The rate of formation of carbon quickly and relates to thermal oxidation. Char formation of complex structures such as barrier decomposition gases and molten polymer through the barrier. Expansion of multiple carbon layers, expansion rate, strength and composition of the carbon layer is an important factor affecting the quality. According to another report, a number of physical properties of the carbon layer, such as penetrating geometric swelling degree of mechanical strength, continuity, the opening and closing of the hole, the more efficient gas and liquid. SEM is displayed after adding inorganic additives, carbon honeycomb structure tends to crack, so that the oxygen index fell. In order to ensure a good flame retardancy, the size of the chamber should be controlled in a certain range. This is because although the air chamber can lower the thermal conductivity, but if the cell size is too large, the air convection can improve the thermal conductivity. Thermal conductivity increases cause thermal degradation accelerate, thereby reducing flame retardant.

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