Classification of Flame Retardants and Analysis of Their Role Mechanisms

Classification of Flame Retardants and Analysis of Their Role Mechanisms

Abstract: This article classifies flame retardants into four categories: organic flame retardants, inorganic flame retardants, nano-materials flame retardants and composite flame retardants, among which organic flame retardants can be subdivided into halogen-containing organic flame retardants and halogen-free organic flame retardants, halogen-free organic cationic flame retardants can be divided into phosphorus-containing flame retardants, silicone-containing flame retardants and nitrogen-containing flame retardants etc., and the inorganic flame retardants can be divided into aluminum hydroxide flame retardants and magnesium hydroxide flame retardants. Aluminum hydroxide flame retardant and magnesium hydroxide flame retardant, etc., for the different flame retardants and the effect of the differences in the role of the object, its flame retardant mechanism and its advantages and disadvantages of the analysis of the introduction, the conclusion is that the flame retardant applicable to different materials is very different, but different flame retardants can be used in conjunction with each other can play a better role in preventing fires in the future, in addition to the article also on the flame retardants of the In addition, this article also analyzes and predicts the development prospects of flame retardants.

1.1 Introduction

Flame retardants can greatly improve the flame retardant and fire retardant properties of polymer composites, and improve the flame retardant properties of the materials are widely used in transportation, electronic equipment, household and other building materials industry.

Inorganic flame retardants can be divided into additive inorganic flame retardants, thermo-reactive flame retardants and nano-material flame retardants according to the way of adding. Due to the ease of use and better environmental adaptability of additive flame retardants, although they do not enable the material to achieve the function of fully combating the fire, they can still avoid fire accidents, thus giving the people in the fire scene a valuable time to escape.

Reactive flame retardants are stable, long-lasting, and have a low impact on the performance of plastics. The significance of flame retardants in the field of fire safety has been proven. According to the evaluation of the European Commission, the application of fire retardants has led to a 20 percent decrease in the number of people killed in fires in Europe over the past decade.

Inorganic flame retardants usually utilize a number of principles to achieve their flame retardant effect, such as the heat absorption effect, the covering effect, the inhibition of the chain reaction, and the asphyxiating effect of the incombustible gas. Most inorganic flame retardants utilize multiple mechanisms to act jointly to achieve flame retardancy. However, various types of inorganic flame retardants play a role in different mechanisms, and their characteristics are therefore very different.

Inorganic flame retardants can include organic synthetic flame retardants, inorganic flame retardants, nano-materials flame retardants and composite inorganic flame retardants and other four types of inorganic flame retardants, the classification of inorganic flame retardants can also include phosphorus-containing inorganic flame retardants, silicone-containing flame retardants, aluminum hydroxide flame retardant, aluminum hydroxide flame retardant, etc., this paper for the role of the mechanism of the different flame retardants and the advantages and disadvantages of the detailed description.

1.2 Organic flame retardants / Brief description of organic flame retardants and experimental results from Yinsu Company.

Organic synthetic flame retardants, refers to organic synthetic flame retardants can be bromine, nitrogen and red phosphorus and compounds as a typical representative of a variety of inorganic flame retardants.

1. Halogen-containing organic flame retardants

Halogen-containing chemical flame retardants work: polymer auto-ignition process is a thermal oxidation reaction, when the halogen-containing elemental substances in the high heat degradation of halogen molecules, they will react with the hydrogen atoms within the polymer to generate hydrogen halide. Hydrogen halides can combine with free radicals formed during the combustion process and thus have a flame retardant effect on the oxidation reaction. Flame retardants containing bromine in the halogen group elements are effective.

Halogenated elements of flame retardants, in the usual combustion conditions after the dissolution of HX residue can improve the low-temperature dehydration of polymerized materials carbonization and thus generate flame retardant charcoal layer, which greatly reduces the number of low molecular number of cleavage products generated data, thus impeding the smooth progress of the ignition of the chemical reaction. Therefore halogenated flame retardants flame retardant effect is good, the increase is small, the characteristics of the composite material is also less negative impact. Due to the large amount of fuming, there is a strong corrosive nature of the emitted hydrogen halide exhaust, as well as the formation of highly toxic carcinogenic products of polybrominated dibenzo[a]oxo[a]ns and polybrominated dibenzofurans, which seriously jeopardize the healthy metabolism in the human body.

"On July 1, 2006, our country started to implement the "ROHS order to strictly control the application of PBDE and PBB.

2. Halogen-free organic flame retardants

(1) Phosphorus-containing flame retardants

Organic phosphorus as a flame retardant phosphate esters (such as bisphenol A bis (diphenyl) phosphate), phosphorus heterophenanthrene derivatives (DOPO and its derivatives ODOPB, etc.) and polyphosphorus nitrile (hexaphenoxy cyclic triphosphonitrile HPCTP and its hydrogen-substituted derivatives).

It is generally believed that the main flame retardant mechanism of the organophosphorus system is cohesive phase mechanism, that is, phosphorus-containing compounds in the heat of combustion decomposition into phosphoric acid and other non-combustible liquid film, phosphoric acid dehydration to get metaphosphoric acid, polymer with metaphosphoric acid to get the formation of viscous or liquid film of poly(metaphosphoric acid), and wrapped in the harmful substances, and phosphoric acid and poly(metaphosphoric acid) are strong acids, can be dehydrated to deal with the flame-retardant polymers and carbonized to produce a carbon layer, and therefore these liquid and solid membranes. Therefore, these liquid and solid membranes are able to prevent the escape of free radicals and have the effect flame retardant function of isolating indoor air, with a high flame retardant efficiency of up to 4-7 times that of bromide.

The decomposition of APP, PEPA and DOPO is triggered by the breaking of N-O, P-0 and P-II bonds respectively. The addition of phosphorus flame retardants can effectively reduce the release of harmful gases such as CH.O and co P elements are biased during pyrolysis to produce POz, PO4, or complex PO-P-0 structures, which are connected to carbon fragments to form residual carbon structures with P elements as the core. Small amounts of NH3, NO, and N2 products are found in the EP/APP system, which dilute the flammable gas molecules during the pyrolysis reaction to achieve flame retardancy."

(2) Silicon flame retardants

Organosilicon series of fire retardant in the process of its spontaneous combustion will appear earlier in the melt tic state, these organic synthetic silicone fire retardant melt drop products through the pores of the polymer matrix passed to the surface layer of the substrate, thus forming a dense and solid silicon-containing (mainly SiO2) charcoal layer This silicon-containing charcoal layer not only inhibits the combustible dissolution of highly flammable products of the escape, and also has the function of thermal insulation and oxygen barrier, you can Inhibit the thermal decomposition of polymer materials, thus realizing the purpose of high flame retardancy, low smoke and low toxicity.

The inorganic flame retardant STNS can promote PC cross-linking at high temperature, thus effectively improving PC's maister resistance and thermal stability. In addition, the addition of a certain amount of STNS can also significantly improve the hardness of flame-retardant PC, in which when the dose of sTNS reaches seven percent, the impact strength and elongation at break of flame-retardant PC increase by eighty-nine point nine percent and one hundred and eighty-seven point seven percent in that order, whereas its bending and tensile strengths decrease by two point seven percent and zero point seven percent in that order."

(3) Nitrogen-containing flame retardants

The development of nitrogen-based inorganic flame retardants is relatively late, of which melamine and melamine gas derivatives are the more common nitrogen-based inorganic flame retardants. Nitrogen-based flame retardants, in a high heat environment will decompose refractory gases such as N2, NH3 and water vapor, these gases can absorb heat from the polymer matrix and cool the matrix.

At present, the key development direction of this type of inorganic flame retardant is the diazo-based inorganic flame retardant with higher nitrogen content, heat resistance and flame retardancy. The higher the value of LoI theory, the higher the difficult level of combustion grade. When the newly selected nitrogen-containing flame retardants and acrylate UV coatings are blended, the material reliability performance will also be significantly improved, so the LOI value increased from the initial twenty-one to twenty-seven, thus exceeding the flame retardant level. The compatibility with UV coatings is also improved because these nitrogen-containing flame retardants are light-curable and reflective, and the higher the quantity of POP-290, the higher the gel quality. The higher the amount of POP-290, the higher the gel quality, while the higher the amount of POP-290, the lower the reliability: DsC analysis showed that the flame retardant increased the glass transition temperature (Tg) of the UV material.

These results show that the flame retardant effect of UV-curable materials can be achieved by using mixed ammonia-based inorganic flame retardants, which in turn can be used to achieve the effect of flame-retardant modification of light-curable materials."

Comprehensively, organic halogenated flame retardants have better fire retardant performance, and the use of small amounts, not only has a high adhesion, but also high temperature and ultraviolet (UV) performance. It contains halogen phosphate ester type, volatile type is small, colorless and odorless, resistant to degradation. However, this type of flame retardant in the incineration of soot content is larger, and the same release of halogenated sulfur gas there is a strong erosive, so often lead to secondary environmental pollution. And halogenated flame retardants in the fire after incineration can also emit halogenated dibenzodioxin (PBDD) and dibenzofuran, the body's immunity and regeneration system constitutes damage. At present, the organic halogenated flame retardants have been toward the renewable, higher simple, high chemical safety and high chlorine content of the development trend.

1.3 Inorganic flame retardants

Inorganic flame retardant refers to a kind of inorganic compounds added in the synthetic formula, which have good flame retardancy, co-effect flame retardancy and smoke suppression characteristics. Usually divided into aluminum hydroxide, aluminum hydroxide, red phosphorus, ammonium polyphosphate and so on.

(1) Aluminum hydroxide

Aluminum hydroxide flame retardant, referred to as ATH, the main characteristics of the flame retardant: aluminum hydroxide heat decomposition of crystalline water. The reaction is a strong heat-absorbing reaction, when a certain amount of heat inhalation, you can produce the effect of cooling the polymer, while the chemical reaction of the steam generated can also be diluted flammable substances, thereby controlling the spread of the explosion, the production of anti-melting droplets, to promote the charring of the non-volatile, does not produce exudate, etc., high quality and low price, a wide range of sources can be sustained in the polymer medium efficacy, and safety, performance, and high temperature, and the characteristics of a good performance. It does not form harmful chemicals at high temperatures and reduces the rate of smoke generation when the material is ignited.

The specific surface size of ATH has little to do with the flame retardancy of the filler material, which is consistent with the flame retardancy mechanism discussed above. However, the increase of the specific surface layer of ATH also plays an important role in the thermodynamic properties of the filler material, and its tensile ability increases with the increase of the specific surface area of ATH (particle size reduction).

The main factor limiting its use in plastic products and rubber industry at home and abroad at present may be closely related to its specific surface quality, and one of the important ways in which the super-particulation of ATH can enhance the mechanical properties of the filler material."

In the PVC system according to the ATH wt% and 0.1 ratio system, the filler material at the beginning of the oxygen index does not rise quickly, and when the filling dosage of more than forty percent, its oxygen index increases rapidly, which chapter tastes if the ATH alone flame retardant its dosage must reach more than forty wt%, and Shao Changsheng et al. that its aerodynamic properties ester with the increase in the concentration of ATH and a significant decrease in the which also explains that the ATH is mainly an inert filler in wood."

(2) Magnesium hydroxide

Aluminum hydroxide is a new class of filled inorganic flame retardant, through the thermal decomposition of the release of bound water, and adsorption to produce a large amount of latent heat of the phase transition, to reduce the surface temperature of the high synthetic material it is filled in the flame, there is a control of polymer dissolution of the open to the formation of flammable gases in the function of cooling.

Yinsu Company utilizes the refining liquid of light burning powder obtained after removing sulfate, and produces magnesium hydroxide with good flame retardant effect without adding surfactant by taking ammonia of its refining liquid as the main raw material. The effects of ammonia passage rate, reaction temperature and crystal species addition on the production characteristics of magnesium hydroxide were also considered.

The results of the research concluded that, due to the reaction temperature increase, the finished product particle size, but the surface morphology still need to be changed, from irregular shape gradually into an approximate cubic block; due to the speed of ammonia, the performance of the product is also improved, but in the ammonia rate is too large, the dispersion of the product and the particles are also reduced accordingly: due to the increase in the amount of crystalline species added, the size of the magnesium hydroxide continues to improve, but the effect of the change of the surface morphology is not obvious. The effect is not obvious.

Experimental results show that, in the crystal seed addition ratio of three percent (mass fraction), ammonia flow rate of 300m L/min, magnesium precipitation temperature of ninety degrees Celsius, the production of aluminum hydroxide inorganic flame retardant effect is good; product D250 = 1.23 m, specific curvature of 6.3m2 high / g, utilization rate of more than eighty-one point two percent.

In summary, inorganic flame retardants have the following characteristics: less dangerous, so most of the inorganic flame retardants are relatively safe; high thermal safety, non-volatile, non-decomposition, with a long-lasting flame retardant effect, will not form a corrosive substance; relatively inexpensive: and the smoke rate is small, so a lot of inorganic flame retardants are very good demisting agent."

1.4 Nano Flame Retardant

Nano-flame retardant flame retardant mechanism Nano-flame retardant can reduce the flammability of the coated material, prevent the rapid spread of fire, used to increase the limit of the fire-resistant ability of the coated material of a special class of coatings. According to its fire-resistant nature and structural composition, the Jian is a non-expandable fire-resistant coating and a bentonite fire-resistant coating. Non-expansive fire-resistant coatings include two kinds, i.e. explosive fire-resistant coatings and incombustible fire-resistant coatings.

In response to the problems exposed by the above traditional IFR applied to PP system, Yinsu Company, based on the renewable bio-based material phytic acid (PA) and the traditional IFR gas source melamine (MA), used a simple and environmentally friendly hydrothermal synthesis method to obtain melamine phytate (PAMA) supramolecular nano-sheets, and combined with transition metal ions that have a strong catalytic carbonation ability (Mnt, Zn2+, Nf2n), Nf2n). A class of transition metal-doped bio-based flame retardants (PAMA-Mn, PAMA-Zn, PAMA-Ni) with high flame retardant efficiency was produced. Then they were used to replace APP in PPIFR system in large quantities by melt blending method to obtain better flame retardant effect.

After a comparative analysis of the flame retardant effective performance of PP composites before and after the replacement of PAMA-M on the replacement rate of APp in the PPL system for thirty-three wt%, when the total addition of flame retardant for eighteen wt%, the maximum limiting oxygen index (Lo0 maximum value and vertical ignition UL minus ninety-four grade are more than a great value, which is the best performance to the flame retardant effect of the PPMn thirty-three LoL Maximum value of thirty-one point nine percent, and passed the UL-94v-0 rating.

However, the replacement efficiency of APP by PAMA-M E-sheets or PAMA-Ni Nano-sheets can achieve 67 w% or more, provided that the basic flame retardant performance usage conditions (UL94 V-0 rating) are met. In addition, PAMA-M nanosheets not only have excellent dispersibility in PP matrix by themselves, but also both can change the diffusion of APp in PP matrix.

Using the above characterization methods, the study of the flame retardant principles of pPMn33, PPZn33 and PPNi can be obtained as follows: under the joint influence of the transition metal molecular in-situ catalysts and crosslinking carbonization, although the PP material can obtain a high quality carbon layer, due to the gas-phase pyrolysis process there are still part of the soot produced by bicyclic aromatics and polycyclic aromatic hydrocarbons, and so it is not able to be The complete ignition of PPMn33, PPZn33 and PPNi XXXIII has a high LO1 value and can reach UL-94v-0 level.

However, since the catalysts among Zn+ and Ni di+ have a weaker carbon forming effect than Mn di+, the relatively small residual carbon yield of the pP composite prevents it from functioning as a physical barrier for a long period of time in the high continuous heat flow tested by CONE, and the carbon layer may fracture, leading to a large difference in heat release between PPZn33 and PPNi xxxiii."

In conclusion, the application of some of the nanomaterials has the effect of inhibiting combustion, and if they are added as inorganic flame retardants to combustible substances, they can improve the spontaneous combustion characteristics of such combustible substances and turn them into refractory substances. Inorganic flame retardant in the polymer material processing of the main additives a, because as long as the use of nanomaterials to medicinal polymer materials to be flame retardant processing, can be easily explosive high self-interest can be realized.

1.5 Composite Flame Retardant

Composite flame retardant flame retardant mechanism Compound, is a material composed of reinforcing materials and matrix materials combined with each other, so that the advantages of each component can be fully utilized. Therefore, the material will show excellent characteristics that are not found in a single material.

Yinsu company added the flame retardant SNP into the PC material through blending technology and formulated the PC/SNP compound, and then carried out an in-depth study on the ignition efficiency and thermal stability of the compound through the method of Limiting Oxygen Index (LOI), Vertical Combustion (UL-94), Cone Measuring and Temperature Test, Thermogravimetric Analysis Test, etc. The test results showed that the flame retardancy of SNP in PC/SNP compound is very high, and it can be used as the base material of the PC/SNP compound, so as to give full play to the advantages of each component. The test results show that the LOI value of PC/SNP system exceeds the maximum value of 34.5 percent after the addition of SNP less than 0.1 percent and successfully passes the UL-94V-0 class, and the aerodynamic performance of PC substrate is basically unaffected after the addition of SNP less than 0.25 percent.

The increase in SNP reduces the maximum heat release rate and maximum smoke emission rate of PC by 21.1 percent and 25 percent, respectively, resulting in a dual effect of gas-phase and condensed-phase flame retardancy. The increase of SNP advanced the initial dissolution temperature of PC, which was conducive to the formation of a continuous carbon layer.

We also analyzed the thermal decomposition kinetics of the composites using methods such as Flynn-Wal1-Ozawa and Kissinger, and the experimental results showed that SNP could make the activation energy of the thermal decomposition of PC increase greatly, thus improving the thermal stability of the PC matrix.

A study of the apparent morphology of the char layer after LOI testing was carried out using near-infrared spectroscopy and scanning electron microscopy (SEM) techniques, and the results showed that the addition of the flame retardant SNP resulted in a continuous, fluffy char layer of PC/SNP (0.1%) on the surface layer of the system, which consequently resulted in a highly efficient heat and oxygen barrier and hence a flame retardant effect."

In conclusion, the composite flame retardant is produced by a variety of types of flame retardants mixed together, which combines the characteristics of a variety of flame retardants in one, can play a more excellent flame retardant effect, but at the same time, it also has a lot of shortcomings, for example, the production process is relatively complex, there may be some of the disadvantages of the flame retardant.