What Is The Flame Retardant Mechanism And Development Trend Of Red Phosphorus Flame Retardant?

What Is The Flame Retardant Mechanism And Development Trend Of Red Phosphorus Flame Retardant?

In the practical application of plastic production, for the shape and structure of particularly complex plastic products, it is often difficult to once injection molding, need to use a variety of connection technology to connect the injection molded parts. As an efficient way to connect plastic products, ultrasonic welding technology can shorten the product production time and improve production efficiency.

In the work of flame retardant modification of polymer materials, we often hear people say white phosphorus, yellow phosphorus, red phosphorus, as can be seen from their names, is a different color of phosphorus. However, white phosphorus and yellow phosphorus refer to one kind of substance, and yellow phosphorus is a yellow waxy solid formed by partial oxidation of white phosphorus, while chemically speaking, white phosphorus and red phosphorus belong to isotopes, just like diamond and graphite, which belong to different monomers of the same element. Next, we talk about the structural properties, flame retardant properties, flame retardant mechanism and development trend of red phosphorus.

Structural Properties And Flame Retardant Characteristics Of Phosphorus Flame Retardants

1. Structural properties of red phosphorus flame retardants

Chemically speaking, the structure determines the properties. Since red phosphorus and white phosphorus have very different structures, their properties are not the same. Red phosphorus is stable in air, while white phosphorus ignites spontaneously in air; red phosphorus is basically non-toxic, while white phosphorus is highly toxic; red phosphorus can be used as flame retardant, while white phosphorus can be used as incendiary bomb. Structural composition, white phosphorus is composed of P4 molecules, the phosphorus atoms in the molecule for the orthotetrahedral structure, red phosphorus is also composed of P4 molecules, but the bonds of its constituent molecules have a break and polymerization to form a macromolecular structure, so it can be said that red phosphorus is an inorganic macromolecular substance. Its molecular formula can be written as (P4)n (n indicates the degree of polymerization). Note: White phosphorus heated in isolation from air produces red phosphorus.

Red phosphorus (RP), or red phosphorus, has the appearance of a red to deep purplish-red powder, insoluble in water, dilute acids and many organic solvents, but slightly soluble in anhydrous ethanol, phosphorus tribromide and aqueous sodium hydroxide. When red phosphorus is heated to 200℃ in air, it ignites to generate P2O5, besides, red phosphorus can also burn when heated in chlorine gas. As the phosphorus element in red phosphorus is in the low valence state (zero valence), when it is mixed with KClO3, KMnO4, peroxide and other strong oxidizers, it may explode if the conditions are suitable.

2. Flame retardant properties of red phosphorus flame retardants

Red phosphorus flame retardant is the highest phosphorus content of phosphorus flame retardant flame retardant, in the fight against fire achievements, and its types are also complicated and miscellaneous, according to the functional components can be divided into halogenated flame retardants, phosphorus flame retardants and other flame retardants, phosphorus flame retardant, its application is very wide, the status of the halogenated flame retardant, and with the accusation of people who do not know the truth of the halogenated flame retardants and questioning and halogen monopoly of the company's With the accusation and questioning of halogenated flame retardants by unknown people and the price increase of various halogenated monopoly companies, phosphorus system is more and more favored. Red phosphorus, as a member of phosphorus-based flame retardants, has a higher flame retardant efficiency than other phosphorus-based flame retardants because it contains only the flame retardant element phosphorus, and this is true even when the amount of flame retardant is very low. In some cases, the flame retardant efficiency of red phosphorus is even slightly better than that of halogenated flame retardants.

In addition, it has been reported that no phosphorus-based flame retardant can match red phosphorus for PET (polyethylene terephthalate). For the substrate, the added flame retardant is, after all, a foreign substance, and if the two sides are poorly coordinated, it is easy to damage the excellent performance of the substrate itself. While red phosphorus, add a small amount to achieve the required flame retardant properties, so the original excellence of the flame retardant substrate is easier to maintain. In addition, red phosphorus has a high melting point and poor solubility, which is beneficial to the maintenance of certain physical properties of polymers compared with other flame retardants. Finally, red phosphorus smoke is small, low toxicity, wider application, can be used alone, can also be shared with other flame retardants, can be widely used in flame retardant polyolefin, polystyrene, polyester, polyurethane, nylon, polycarbonate, polyformaldehyde, epoxy resins, rubber, textiles and so on.

Problems Of Red Phosphorus Flame Retardant

As the saying goes, “there is no such thing as gold, there is no such thing as perfect”, as a flame retardant red phosphorus, there are also many shortcomings, mainly in the following six aspects:

1. Substrate corrosion

Red phosphorus can be used as a desiccant, has strong water absorption, after absorbing water to generate H3PO2, H3PO3, H3PO4 and other substances, at this time, red phosphorus due to the viscosity increase and loss of mobility, the phosphoric acid produced by the absorption of water belongs to the more absorbent substances, so that the last into dilute sludge-like substances. Therefore, when the red phosphorus added to polymer materials, with the passage of time, the red phosphorus in the surface layer of the material will be oxidized due to moisture absorption and corrosion of the surface of the product, and then lose the luster and some of the original properties, more seriously, this corrosion will slowly expand to the inner layer of the material.

2. Difficulty of compatibility

Inorganic and organic are always difficult to be compatible, as the inorganic red phosphorus and organic resin compatibility is naturally not good, not only difficult to disperse, but also precipitation will occur, so that the viscosity of the resin rises, which brings a lot of inconvenience to the resin's subsequent processing and use (casting, impregnation, extrusion, etc.), and in serious cases, it will lead to a decline in the performance of the material.

3. Pollution of the environment

The nature of the material is stable, generally relative (on the philosophical level, stability is relative, instability is absolute), therefore, when the red phosphorus long-term contact with the air, a slow chemical reaction will occur in the generation of phosphorus-containing oxygen acid at the same time, but also will release a highly toxic PH3 gas, which will pollute the environment. PH3 gas, the other flavors, the author has not been informed of what the reason for the generation of the red phosphorus flame retardant anyway In any case, the smell of thermoplastic elastomers flame retardant with red phosphorus is bigger than that of bromine flame retardant and phosphorus-nitrogen flame retardant.

4. Application Limitations

Due to the hygroscopicity and instability of red phosphorus, when it is added to plastic products, it will affect the physical properties of the products, especially on the leakage of weak components and the insulation of high-voltage components, thus limiting the application of red phosphorus in the field of electrical components of flame retardant.

5. Flame explosion

Although red phosphorus can be used as a flame retardant, it is flammable itself, especially when red phosphorus is impacted, it is more likely to be ignited, so the dry red phosphorus dust has the danger of combustion and explosion, and it is also classified as a dangerous chemical in China.

6. Coloring substrate

Compared with other white flame retardant substances, the deep purple-red color of red phosphorus is easy to color the flame retardant products, which makes it difficult to control the color of the products produced or increases the cost of color mixing.

Flame Retardant Principle Of Red Phosphorus Flame Retardant

Monomers of phosphorus are flammable, but in the resin, red phosphorus and other phosphorus-containing additives are not purely oxidizing, the phosphorus-containing additives are mainly in the condensed phase, and the flame retardant mechanism is as follows

1. Formation and heat reduction effects

The formation of phosphoric acid or polyphosphoric acid with as a dehydrating agent, the formation of high-viscosity molten glassy and dense carbonized layer on the surface of the combustibles, the generation of carbon reduces the heat conduction from the flame to the condensed phase.

2. Heat absorption by phosphoric acid and chemical changes

Phosphoric acid absorbs heat because it prevents the oxidation of CO to CO2 and reduces the heating process.

The following changes occur: phosphorus flame retardant → phosphoric acid bi → phosphoric acid → poly metaphosphoric acid, poly metaphosphoric acid is a non-volatile stable compounds, with strong dehydration, in the polymer surface mixture isolated from the air, out of the water absorbs a large amount of heat, so that the thermal decomposition of polymer surface flame retardant releases volatile phosphide, the mass spectrometry shows that the concentration of the stored hydrogen atoms is greatly reduced, suggesting that the red phosphorus decomposition of the PO-, HPO- radicals, capturing the H-, HO- radicals generated during combustion of macromolecules, i.e., PO- + H- = HPO.

3. Protective layer and synergistic flame retardant mechanism

A thin glassy or liquid protective layer is formed on the condensed phase, thus reducing oxygen diffusion and heat and mass transfer between the gas phase and the solid phase, inhibiting the carbon oxidation process, and reducing the thermal decomposition of phosphorus-containing flame retardants.

The flame retardant mechanism of each phosphorus-based flame retardant is a combination of these three, producing a synergistic flame retardant effect exactly which mechanism is dominated by the structure of the flame retardant and combustibles.

4. Microencapsulated red phosphorus flame retardant mechanism

Microencapsulated red phosphorus flame retardant mechanism: in the polymer to add coated red phosphorus flame retardant mechanism has the following aspects, that is, in the combustion, the formation of phosphoric acid derivatives, play the role of heat adsorbent, hindering the combustion of further occurrences; retention of free radicals, improve thermal stability; react with oxygen to form phosphorus oxygencapsulation, and continue to react with the polymer, resulting in the production of crosslinked structure, to get the phosphorus-oxygen crosslinking of carbonized layer; and the environmental reaction with oxygen to generate oxygen-containing phosphorus; and the environment React with oxygen in the environment to generate oxygenated phosphate, this oxygenated phosphate has strong hygroscopicity, can reduce the surface temperature of the burning polymer, while promoting the surface humidity of the polymer, and at the same time promote the surface carbonization of the polymer.

The flame retardant mechanism of red phosphorus is usually considered to be in the condensed phase, adding red phosphorus flame retardant polymer combustion, red phosphorus is first oxidized and generated phosphoric acid, and then phosphoric acid and further dehydration to generate metaphosphoric acid and poly(metaphosphoric acid), which forms a layer of non-combustible liquid on the polymer surface; at the same time, due to the metaphosphoric acid and poly(metaphosphoric acid) of the strong dehydrating effect, prompting the surface of the polymer material dewatering charring, the formation of a dense layer of charring layer. At the same time, due to the strong dehydrating effect of metaphosphoric acid and poly(metaphosphoric acid), the surface of the polymer material is dehydrated and carbonized, forming a dense carbonized layer. On the one hand, the liquid film and carbonized layer provide heat and oxygen insulation, and at the same time effectively prevent the diffusion of flammable gases generated by polymer decomposition at high temperatures, thus inhibiting the combustion of the material and achieving the purpose of flame retardancy. Compared with other additive phosphorus flame retardants, red phosphorus has high phosphorus content. Therefore, in order to achieve the same level of flame retardancy, the amount of red phosphorus added is less than other flame retardants, and the polymer with its flame retardant has better physical and mechanical properties.

Red phosphorus flame retardant thermoplastic rubber TPV and thermoplastic elastomer TPE-S, can reach 1.6mm UL94 V0 level, and mechanical properties are beyond the use of bromine flame retardant flame retardant elastomer.

The development Trend Of Red Phosphorus Flame Retardant

1. Coating technology

At present, there are some preliminary researches on the coating technology of microencapsulated red phosphorus, but they are not systematic and in-depth enough. Therefore, it is necessary to conduct more systematic and in-depth researches on the selection and modification of coating capsule material, capsule core treatment, coating method, coating method, coating conditions, coating process, coating results and effects (e.g., film structure, film thickness, particle size and particle size distribution, whiteness, agglomeration and compatibility with the substrate), etc., so as to obtain better flame retardancy. In order to obtain better flame retardant properties.

2. Smoke suppression and elimination

Microencapsulated red phosphorus flame retardant has smoke suppression and smoke effect, but still need to further improve its smoke suppression and smoke performance, the most effective way may be to find a suitable smoke suppressant or substrate and its effective compounding.

3. Multifunctionalization

Plasticizer is the largest consumption of a plastic additive, one of the future direction of the development of microencapsulated red phosphorus flame retardant should be through the capsule material coated with modification (methods can be grafting, copolymerization, surface reprocessing, etc.), in order to both plasticizing and flame retardant function In addition, it can be made to both heat stabilization and flame retardant function, etc., development of multifunctionality of the microencapsulated red phosphorus flame retardant products, so as to reduce the amount of plastic additives materials, optimize the structure of additives In order to reduce the amount of plastic additives in the material, optimize the structure of the additives, and enhance the mechanical properties of the material.

4. Combination flame retardant synergy

Research on the effective compounding relationship between various flame retardants and red phosphorus flame retardants, and make it microencapsulated, in order to enhance the flame retardant effect, reduce the amount of flame retardant, improve the mechanical properties of the material, and then more effective to achieve the purpose of flame retardant, which is also one of the important trends of the development of the flame retardant industry at home and abroad.

The article mainly discusses the red phosphorus flame retardant, including its properties, advantages, disadvantages, and flame retardant mechanism. YINSU Flame Retardant produces various series of red phosphorus flame retardants such as FRP-950, FRP-301, FRP-750, etc. Their red phosphorus flame retardant PG-50 combines red phosphorus powder and synergist, presenting high phosphorus content, excellent flame retardant performance, and user-friendly features. It has high efficiency, requires low addition amount, is cost-effective, and has wide application versatility in epoxy resin, coatings, electrical appliances, etc. Moreover, the microencapsulated red phosphorus flame retardant FRP-950 and FRP-8050 overcome some disadvantages of ordinary red phosphorus, showing good compatibility and other properties, which is conducive to better play its flame retardant role in different materials.