Synthesis of flame retardant organic polymer and f

2022-10-20
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Overview and Prospect of organic polymer flame retardant and flame retardant polymer composites

polymer materials, whether plastic, rubber, or fiber, generally have a low oxygen index and belong to flammable materials. When burning, they produce a large amount of smoke and toxic gases, poisoning and even death, which has become a social problem of increasing concern. On the one hand, polymer materials provide human beings with rich and colorful material conditions, on the other hand, they also hide a lot of fire hazards. Therefore, many countries have done a lot of work on the development, production, application, testing of polymer flame retardants and the establishment and improvement of flame retardant regulations, which also provides a broad market and legal guarantee for the development of flame retardants

the so-called flame retardant actually refers to reaching a specific standard of a certain specification or a certain test method. The "flame retardant" or "flame retardant" of plastics is generally only for small fires, which can still burn in large fires. However, foamed plastics with good flame retardancy will self extinguish in case of a small fire, which is not easy to cause a fire; In the new environmental protection law and emission standard implemented in 2015, the risk of fire spread and irritating toxic smoke can be reduced due to the reduction of combustion performance. Therefore, to some extent, to improve the flame retardancy of plastics is to make plastics only produce carbonization without ignition or flame, or although carbonization, ignition and flame, the combustion is difficult to expand, that is, the time of delayed combustion (flame) and residual ember (flameless combustion) is short

necessity of flame retardant materials: the time for evacuating people and rescuing property after a fire is 15 times that of non flame retardant samples; The mass loss rate of the material during combustion, and the flame-retardant sample is less than 1/2 of that of the non flame-retardant sample; The heat release rate of the material during combustion, the flame-retardant sample is only 1/4 of that of the non flame retardant sample; The amount of toxic gas generated by the combustion of the material, and the flame-retardant sample is only 1/3 of the non flame-retardant sample; There is little difference in the amount of smoke generated during combustion between flame-retardant samples and non flame-retardant samples

1 flame retardant mechanism

in principle, the combustion process is a rapid oxidation reaction between combustibles and oxidants. When the concentration and temperature of combustibles are high enough, combustion can be caused

the combustion of polymers can be divided into two processes: thermal degradation and combustion, involving a series of links, such as heat transfer process, thermal degradation of condensed phase, diffusion of decomposition products in solid phase and gas phase, and chain combustion reaction formed by mixing with air. Therefore, the key to improve the flame retardant performance is to inhibit degradation and oxidation, reduce the generation of combustibles, and block the transfer of heat. For example, the flame retardant performance of materials can be improved by vaporization to take away heat, cooling to reduce the temperature of condensed phase and other methods [1]

The flame retardant mechanism of polymer is a very complex physical and chemical process. It is generally believed that the flame retardant behavior of flame retardants on polymers is mainly achieved through cooling, dilution, formation of insulation layer and termination of free radical chain reaction, of which the first three are physical pathways and the latter is chemical process

can also be divided into vapor phase flame retardant mechanism, condensed phase flame retardant mechanism, interrupted heat exchange flame retardant mechanism, etc

2 combustion performance of polymer materials

all kinds of plastics have different flame retardant properties, and the quality of flammability is generally expressed and divided by oxygen index (OI). Those with an oxygen index below 22 belong to flammable materials and have no flame retardancy; Between 22 and 27, it is a non combustible material, that is, it has self extinguishing property, and PVC belongs to this category; Those above 27 are highly flame retardant materials, as shown in Table 1 [2]: Table 1 flame retardant properties of polymer materials

3 flame retardant ways and methods

in order to improve the flame retardancy of polymer materials, materials containing flame retardant elements must be introduced. There are two main ways: first, organic compounds containing chlorine, bromine, phosphorus, antimony and other elements are added in the form of additives to produce additive or reactive flame retardant materials; Second, the above flame retardant elements are directly introduced into the molecular chain to obtain structural flame retardant materials. It can also be blended with polymers with good flame retardancy to produce flame retardant alloys, and inorganic heat conducting materials can be added

flame retardants are chemicals added to materials during or after production to reduce the flammability of materials. They are usually used in electronic equipment, furniture and building materials. Once there is a fire, the flame retardant can reduce the spread speed of the fire, so as to provide sufficient escape time

3.1 add small molecule flame retardants

add flame retardants to change the thermal degradation mode of polymers to reduce the combustible products generated by the thermal cracking of polymers; Adopt external flame retardant coating. To isolate oxygen from the polymer surface; Use internal barriers to prevent the escape of combustible gases; The inert gas is released to dilute the combustibles produced by the thermal cracking of polymers and disperse the heat at the front of the flame

adding flame retardant is an effective method, which has the characteristics of convenient use, simple manufacturing process, good flame retardant effect and is widely used. The mechanical properties of additive flame retardant materials will decline in varying degrees, and the flame retardant will migrate gradually with the passage of time

3.1.1 mix with organic small molecule flame retardants

organic small molecule flame retardants, such as halogen flame retardant systems, organic phosphorus, nitrogen, silicon flame retardant systems, etc

the advantage of adding organic small molecule flame retardant is that the amount of flame retardant is small and the flame retardant effect is not bad. For example, if the polymer contains more than 5% phosphorus, it has flame retardant effect. Most organic phosphorus flame retardants are liquid and have plasticizing and lubricating effects at the same time. However, it has high volatility, high smoke emission, poor hydrolytic stability and thermal stability, and the flame retardant is expensive, so the flame retardant cost of this method is high

3.1.2 reaction with inorganic small molecule flame retardants

inorganic small molecule flame retardants mainly include metal hydroxide, borate, organosilicon oxide. And red phosphorus flame retardant, molybdenum trioxide, antimony trioxide, ammonium sulfate, Zn Compound [3], kaolin flame retardant micro powder [4], intumescent flame retardant, etc

in addition, Weil et al. Found that when K2CO3 is used in ABS resin, it can improve the thermal aging resistance of ABS resin, resulting in basic catalytic oxidation on the surface and crosslinking of unsaturated rubber. CaCO3 can also be added to ABS resin as an inorganic filler. Although it does not participate in the reaction itself, it is considered to change the reaction kinetics of ABS thermal degradation, so that a carbon layer is formed on the surface of the resin [5]

the cost of this flame retardant method is low, but the flame retardant needs to be doubled to have obvious effect. At the same time, the processability, formability, mechanical properties and electrical properties of the polymer are significantly reduced by high addition. Some smoke suppressants need to add inorganic small molecules, but the amount is also large

3.1.3 synergistic effect of inorganic small molecules and halogen system

some inorganic substances do not have flame retardancy or have little flame retardancy effect, but their synergistic effect with some substances does have good flame retardancy effect. For example, when antimony flame retardants and halogen flame retardants are used together, they can produce good synergistic effect and improve the flame retardancy of materials

the experiment found that it was difficult to find the flame retardant effect of ABS if antimony trioxide was added alone up to 20% without halogen. If halogen and antimony trioxide are added to ABS pellets at the same time, the flame retardant effect of ABS will take a qualitative leap

3.2 structural flame retardant

structural flame retardant treatment method through modifying the structure of the polymer, the flame retardant elements are combined into the molecular chain in the form of chemical bonds, so as to improve the carbonization tendency of the material and reduce its flammability, so as to meet the requirements of fire prevention and flame retardance. The products prepared by this method can overcome the uneven distribution of flame retardants in the additive method and the shortcomings of low flame retardant stability. It is a more effective flame retardant treatment method. While for structural flame retardant materials, flame retardants have non migration

polymers with flame retardancy usually have other excellent properties, such as strength, dimensional stability, chemical resistance and wear resistance, but these materials are usually more expensive than those without flame retardancy. However, these resins are needed to show their talents in applications requiring high performance and high flame retardancy. These polymers mainly include polyether ether ketone (PEEK), polyether imide (PEI), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyether sulfone (PES), polyvinylidene fluoride (PVDF) and liquid crystal polymer (LCP). Other polymers such as PVC and modified polyphenylene oxide (PPO) have certain flame retardancy, but a certain amount of additives need to be added to enhance this performance

Zhang Liying et al. [6] synthesized a structural flame retardant grafted polymer polyether polyol by grafting polyether polyol. It does not contain halogen and phosphorus. The polyurethane foam prepared with it can not only meet the flame retardancy of polyurethane foam, but also improve the mechanical properties of the material, and has a very low smoke emission. Feng Wei et al. [7] prepared flame retardant resin through the polycondensation of phosphoric acid, trimethylolpropane and epichlorohydrin, and then also prepared soft polyurethane foam with good performance and oxygen index of 26%

only aromatic polyamide fibers can be mass produced and applied in high-performance and high-quality heat-resistant and refractory protective fabrics [8]. Due to its high thermal stability of the chemical structure containing benzene ring, the loss of thermal weight loss, thermal shrinkage and thermal strength of the fiber are very small. It is not easy to produce smoke when exposed to the flame, and only carbonization is generated on the surface. It is a very good heat-resistant fiber material

the flame retardancy of foam made of ordinary polyester polyols is low, and the oxygen index is only about 17. The flame retardancy of foam can be improved by using aromatic polyester polyols. Xing Yihui and others chose a formula system based on aromatic polyester polyols and supplemented by flame retardant polyether polyols, so that the oxygen index of the foam can reach 25 without additive flame retardants, and the brittleness of the foam is small [9, 10]

Feng Wei et al. [11] synthesized a new flame retardant polyether polyol containing triazine ring and cyclic phosphate structure with azoxyamine, formaldehyde, phosphorus oxychloride and ethylene oxide as the main raw materials. This flame-retardant polyether polyol and TDI are made by one-step foaming process. The formula and properties of the flame-retardant polyurethane foam with molecular structure are tested and studied. The maximum limiting oxygen index is 29.3, the tensile strength is 0.56mpa, the elongation is 158%, and the density is 35kg/m2. This soft foam plastic avoids the disadvantages of poor stability and uneven distribution of flame retardants of the additive flame-retardant soft foam plastic, and the foaming process is simple and the equipment investment is small, Easy to operate and manage

Zhang Tiancai [12] in view of the fact that the phenolic core and methylene in the molecular structure of phenolic resin are sensitive to thermal oxygen, which is easy to cause the degradation of phenolic resin, starting from the concept of molecular design, it blocks the strong polar phenolic light group with B-O bond and Si-O bond with high heat resistance, passivates the benzene ring, changes the connection mode of methylene, and improves the heat resistance and stability of the molecular structure; At the same time, the cured phenolic resin matrix forms a three-way cross-linked structure centered on boron, which has high oxidation resistance [13]

Xia Yanzhi [14] studied the structure, thermal properties, combustion properties and charring properties of the synthesized phosphorus copolymer flame retardant polyethylene terephthalate (PET) chips by using NMR, SEM, DSC, dta/tga, LOI and other test methods. The results showed that the polymerization of flame retardant with EG and TPA widened the thermal degradation temperature of PET chips, and had good flame retardancy (loi>28) and charring properties

the introduction of a-methylstyrene or N-phenylmaleimide can improve the heat resistance of ABS resin. Under the condition of not reducing other performances of ABS, add ABS

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