Why must we choose aluminum hydroxide as a flame retardant?
What are flame retardants
Flame retardant is a special additive used to improve the combustion performance of flammable and flammable materials. It can make the material flame retardant, self-extinguishing, and smoke-eliminating, and can effectively improve the safe use performance of the material. Flame retardants can generally be divided into two categories: organic flame retardants and inorganic flame retardants. Organic flame retardants have outstanding flame retardant effects and wide application range, and have been widely used. But its shortcomings are equally prominent: it is corrosive, produces smoke when burned, and is accompanied by the production of toxic gases.
Inorganic flame retardants have relatively good thermal stability, do not produce corrosive gases and toxic gases, and have less impact on the environment. Compared with organic flame retardants, inorganic flame retardants are more in line with environmental protection and fire safety requirements. Inorganic flame retardants have also been the focus of research in recent years and have huge market potential.
Inorganic flame retardants include aluminum hydroxide, magnesium hydroxide, magnesium oxide, antimony trioxide, sodium tetraborate, etc. Among them, aluminum hydroxide is the most widely used inorganic flame retardant. It has flame retardant, smoke elimination, and filling properties. Function, especially surface-modified ultrafine aluminum hydroxide, can also improve the mechanical properties of the material.
Advantages of aluminum hydroxide flame retardant
Although brominated flame retardants among organic flame retardants have the advantages of high flame retardant efficiency, low addition amount, and wide application range, in order to comply with the development trend of high flame retardancy, low smoke, and harmlessness in the flame retardant market, inorganic flame retardants The development and utilization of flame retardants has gradually received more support.
Ultrafine aluminum hydroxide has stable physical and chemical properties at room temperature, does not produce secondary pollution when burned, has high whiteness and excellent chromaticity indicators. And nano-aluminum hydroxide can not only improve the limited oxygen index of flame-retardant polymers and increase flame-retardant properties, but also help improve the surface finish and mechanical and electrical properties of polymer products, and enhance their resistance to leakage, arc resistance and wear resistance. ability. In addition, the combined use of aluminum hydroxide and other flame retardants has an ideal effect, and it is an inorganic flame retardant with broad prospects.
Flame retardant mechanism of aluminum hydroxide
The flame retardant mechanism of aluminum hydroxide is relatively complex and consists of the following synergistic mechanisms:
1) The reaction is endothermic
As we mentioned above, aluminum hydroxide reacts with heat to form aluminum oxide and water. This reaction is an endothermic reaction, and the reaction formula is:
During this process, it not only absorbs heat and delays the burning of the polymer, but the water vapor released by the reaction also dilutes the combustible gas and oxygen, and also participates in the condensed phase reaction.
2) Dilution effect
In addition to the water vapor mentioned in 1) that can dilute flammable gases and oxygen, the aluminum hydroxide also plays a filling role, resulting in a reduction in the polymer per unit volume, and the filled aluminum hydroxide plays a diluting role.
3) Covering effect
The aluminum oxide produced by the reaction, together with other carbides, forms a flame retardant barrier that inhibits the spread of flames.
4) Carbonization
Flame retardants produce strongly dehydrating substances under combustion conditions, carbonizing plastics and making it less likely to produce flammable volatiles, thus preventing the spread of flames.
In addition to the water vapor mentioned in 1) that can dilute flammable gases and oxygen, the aluminum hydroxide also plays a filling role, resulting in a reduction in the polymer per unit volume, and the filled aluminum hydroxide plays a diluting role.
3) Covering effect
The aluminum oxide produced by the reaction, together with other carbides, forms a flame retardant barrier that inhibits the spread of flames.
4) Carbonization
Flame retardants produce strongly dehydrating substances under combustion conditions, carbonizing plastics and making it less likely to produce flammable volatiles, thus preventing the spread of flames.
Requirements for aluminum hydroxide in different industries
Excellent performance makes aluminum hydroxide perform well in many industries. But when it is used in different industries, it often has different requirements for quality.
EVA foam material
EVA foam material refers to a foam insulation material made of EVA and low-density polyethylene as raw materials, adding other additives and then molded foaming or injection foaming. Because it is relatively good for the environment, it is widely used indoors and in public places, so it has high requirements for flame retardant performance.
The flame retardant system of EVA foam materials generally uses a single aluminum hydroxide, with an added amount of about 60%. Due to the large amount of addition, there are strict requirements for its stability, stable pH, and the product must not have a trace of impurities. This makes the production process of aluminum hydroxide very strict and the price is higher than other nano-level products.
Silicone rubber products
The special aluminum hydroxide flame retardant for silicone needs to add a variety of silane surface treatments to screen out coarse particles and remove impurities so that the powder can be combined with the silicone rubber as well as possible without affecting the mechanical properties. It also serves as both flame retardant and filling. effect. In addition, aluminum hydroxide can be used alone or in combination with nitrogen-phosphorus flame retardants. The specific proportion needs to be added according to the formula.
Ink coating
Ink and paint are both important printing materials. The former is mainly used in the printing industry, and the latter has both protective and decorative functions. There is no obvious boundary between the two. The requirements for aluminum hydroxide flame retardants are basically the same, that is, they need to have low oil absorption, no impurities, high whiteness, and no precipitation.
TPU
The Chinese name of TPU is thermoplastic polyurethane elastomer. It has excellent high tension, high pull force, strength and aging resistance. It is a mature environmentally friendly material. The aluminum hydroxide added to TPU/TPE materials must first have a particle size below 2.0 microns and a uniform particle size distribution, which can better integrate with other materials and improve the material’s wear resistance and tear resistance.
Secondly, it is necessary to perform surface activation treatment on aluminum hydroxide so that aluminum hydroxide can form a good link with other substances. At the same time, it also enhances the processing fluidity of aluminum hydroxide so that aluminum hydroxide can be more evenly distributed into the material. Produce good flame retardant effect.
