Study and Application of Flame Retardant Properties of Aluminum Hydroxide

In recent years, polymer materials have been widely used in construction, transportation and daily necessities. However, because of their flammability and high smoke output, they have become the direct activators of fire, causing serious harm to people and things, and the resulting fire hazards have become a global concern, so the flame retardancy of these materials has become one of the important issues.

Flame retardants can be divided into two categories: organic and inorganic. Inorganic flame retardants are thermally stable, do not produce corrosive gases, non-volatile, long-lasting effect, non-toxic, inexpensive, the main varieties of aluminum hydroxide (VK-LA50, VK-LA100), magnesium hydroxide (VK-MHT01), red phosphorus, antimony oxide, tin oxide, zinc borate, zirconium hydroxide (VK-RH30) and so on. Among them, aluminum hydroxide (VK-LA50, VK-LA100) has three functions: flame retardant, smoke elimination and filler, is chemically inert, non-toxic, does not produce secondary pollution, and is regarded as a harmless flame retardant at home and abroad. It not only has high whiteness value, but also has excellent chromaticity index, small covering of coloring, which makes the products beautiful and elegant; good dispersion in resin, when adding more, it is not easy to bend and whiten; it can produce synergistic effect of flame retardant with a variety of substances, with good flame retardant effect; it is rich in sources, low price, and its consumption accounts for more than 80% of the inorganic flame retardant in domestic and international markets, accounting for more than 50 % of the total amount of flame retardants. More than 50 % of the total amount of flame retardants.

Properties of aluminum hydroxide (VK-LA50 , VK-LA100):

Aluminium hydroxide (Aluminium hydroxide), chemical formula Al(OH)3, is the hydroxide of aluminum. Aluminum hydroxide is also an amphoteric hydroxide because it reacts with both acids to form salts and water and with strong bases to form salts and water. The chemical formula Al(OH)3, is a hydroxide of aluminum. It is also called aluminum acid (H3AlO3) because of its acidity. However, when it actually reacts with a base, it produces a tetrahydroxy aluminate ([Al(OH)4]-). Therefore, it is usually regarded as meta-alumina monohydrate (HAlO2-H2O), which is classified into industrial grade and pharmaceutical grade according to its use.

Aluminum hydroxide decomposes thermally into Al2O3 and water with the following reaction.

2α2Al2O3-3H2O → Al2O3 + 3H2O.

The data measured in the range of 240-500 ℃ show that the heat absorption of this reaction is 1967.2kJ/kg, and the absorption of such a large amount of heat is the main reason for its flame retardant effect. The dehydration and phase transition of aluminum hydroxide by heat is very complex, according to the differential thermal curve there are three heat absorption peaks can be inferred that the loss of its crystalline water in three stages. The first heat absorption peak at about 230 ℃, equivalent to α2 alumina trihydrate into α2 alumina monohydrate, that is, α2 Al2O3-3H2O → α2 Al2O3-H2O + 2H2O. the second heat absorption peak at about 300 ℃, equivalent to the decomposition of α2 alumina trihydrate into Χ2Al2O3, that is, α2Al2O3-3H2O → Χ2Al2O3 + 3H2O. the third heat absorption peak at about 300 ℃, equivalent to α2Al2O3-3H2O decomposed into Χ2Al2O3, that is, α2Al2O3-3H2O → Χ2Al2O3 + 3H2O. The third heat absorption peak is around 530 ℃, which is equivalent to the decomposition of α2 alumina monohydrate into γ2Al2O3, i.e., α2Al2O3-H2O → γ2Al2O3 + H2O. The temperature at which the dehydration of alumina hydroxide starts and the maximum heat absorption peak are somewhat different due to the size and distribution of the particles of alumina hydroxide, the heating conditions and the content of impurities, so the selection of the alumina hydroxide (VK-LA50, VK-LA50, VK-LA50, VK-LA50, VK-LA50, VK-LA50, VK-LA50) is based on the following results LA50, VK-LA100) as a flame retardant, according to the polymer matrix materials, thermal decomposition temperature and molding processing temperature requirements to choose a good aluminum hydroxide quality indicators.

Flame Retardant Mechanism of Aluminum Hydroxide (VK-LA50 , VK-LA100)

Regarding the flame retardant mechanism of aluminum hydroxide (VK-LA50, VK-LA100), due to the different types of polymers used in conjunction with it, the description of its natural process is not consistent. In the late 1980s and early 1990s, scholars at home and abroad carried out more in-depth discussions on this issue. For example, P. D. Moran added different amounts of ATH flame retardant epoxy resin, respectively, in the N2O - N2 and O2 - N2 gas mixture to determine its nitrous oxide index and oxygen index, the two curves obtained are similar, indicating that the change of oxidizing agent is not sensitive to the flame reaction, flame retardant effect is due to the formation of the cohesive phase of the protective film on the combustion of the inhibition; determination of the heat loss curve (TGA), the heat loss curve (TGA), and the heat loss curve (TGA), and the heat loss curve (TGA), and the heat loss curve (TGA), and the heat loss curve (TGA). The heat loss curve (TGA) of ATH samples was measured, and the change of oxygen index was investigated in PVC system, and it was found that the flame retardant effect of ATH depended on its heat absorption and dehydration effect. It was also found that the degradation of ATH-doped polymer started at 210 ℃, and when the temperature was increased to 300-350 ℃, ATH absorbed a lot of heat and dehydrated, so that the temperature rise of the polymer was slow and the degradation was slowed down, which was the main reason for the flame retardancy of ATH. In addition, it will form Al2O3 protective film on the surface of polymer, which not only blocks the entry of oxygen, but also prevents the escape of flammable gases, and also avoids the formation of soot, which plays a better role of flame retardant smoke suppression.

The general view is that the flame retardant effect of ATH is the result of the synergistic effect of the above mechanisms. Therefore, the flame retardant mechanism of ATH can be summarized as follows.

(1) Heat absorption. Dehydration and heat absorption at 300~350 ℃ to inhibit the temperature rise of the polymer; 

(2) Dilution, ATH filling, so that the concentration of flammable polymers down, ATH dehydration of water vapor released to dilute the concentration of flammable gases and oxygen, can prevent combustion.

(3) Covering effect: ATH dehydration generates a protective film of Al2O3 on the surface of combustible materials, which prevents further combustion by isolating oxygen.

(4) Carbonation. Flame retardant produces strong dehydrating substance under burning condition, which makes the plastic carbonized and not easy to produce combustible volatiles, thus preventing the flame from spreading.

Application of Aluminum Hydroxide (VK-LA50, VK-LA100)

Aluminum hydroxide (VK-LA50 , VK-LA100) flame retardant is one of the halogen-free flame retardants for synthetic materials. It has 3 major functions of flame retardant, smoke elimination and filling, no secondary pollution during combustion, not only good dispersion in polymers, but also easy to produce synergistic effect of flame retardant with other additives, which can be widely used in electricians, wires, cables, daily necessities, building materials, transportation and other plastic and rubber products.