Hebei Meixi Biotechnology said that in the development of flame-retardant magnesium hydroxide, the production capacity of the United States, Japan and other countries has reached 10,000 tons. Since the 80s of the 20th century, a large number of developments have been carried out in this area, and after the mid-80s, it entered the scale of production. In comparison, the gap in our country is about 15 years. What are the problems in this regard, depending on the situation abroad?
1. The amount of magnesium oxide can be as high as 60%, and the physical and mechanical properties of rubber, plastics, wires and cables and other materials may be reduced (especially the changes in mechanical strength such as tensile strength and bending strength). Therefore, how to reduce the amount of magnesium hydroxide and maintain its high flame retardancy and good mechanical properties of flame retardant materials is still a problem that continues to be studied abroad.
2. After adding magnesium hydroxide to the polymer material, after a certain period of time, it absorbs carbon dioxide in the air and makes the material white, especially for colored rubber, plastics, wires and cables. This whitening is called albinism. It not only intuitively affects the appearance of flame retardant materials, but also because part of the magnesium hydroxide becomes basic magnesium carbonate after absorbing carbon dioxide, although it is also flame retardant, but it is not as flame retardant as magnesium hydroxide, and its mechanical properties have also decreased. Therefore, a solution has been developed abroad, that is, adding additives (such as nickel oxides, etc.) to magnesium hydroxide, which can not only inhibit the whitening phenomenon, but also produce a synergistic effect of improving flame retardancy. Changing the shape of magnesium hydroxide can also reduce the occurrence of bleaching, such as globular magnesium hydroxide due to its smaller specific surface area. Our work in this area has not yet been reported.
3. At present, it is generally believed that magnesium hydroxide as a flame retardant must be treated on the surface, but according to the magnesium hydroxide produced by the American company, it is not surface treated, and can be applied in PVC and other thermoplastics. From this point of view, whether flame retardant grade magnesium hydroxide must be surface treated depends on the specific situation of the application.
The surface treatment of magnesium hydroxide is also related to its structure. If it is amorphous, the necessity of magnesium hydroxide surface treatment is even more important. In the case of magnesium hydroxide, which is dominated by crystal structure, the problem of surface treatment is not so prominent. The reason for this is that the former has a large specific surface area and poor compatibility with polymers, while the latter has a small specific surface area and is better than the former in compatibility with polymers.
4. There are 4 kinds of raw materials for the preparation of flame retardant magnesium hydroxide, one is the use of magnesium ore (including magnesite, dolomite and rhododium, etc.), the second is various magnesium salts (including magnesium chloride, magnesium sulfate, etc.), the third is bitter brine after seawater salting, and the fourth is salt lake brine.
Considering the preparation of high-purity and low-cost magnesium hydroxide, Hebei Magnesium Xi Biotechnology said that the bitter brine content of seawater (including underground concentrated seawater) after salt production is much lower than that of magnesium ore and salt lake brine, and the purification process is simple, and it is easy to prepare high-purity magnesium hydroxide (98%), while the purification process of the latter to remove impurities is relatively complex and the cost is higher. If magnesium hydroxide is produced by using magnesium salts with higher purity, high-purity magnesium hydroxide can be prepared, but the cost is high, such as using magnesium salts with lower purity as raw materials to produce magnesium hydroxide, the cost is still high. Therefore, it is more appropriate to use the bitter brine after salt production from seawater (including underground concentrated seawater) as a raw material for the production of magnesium hydroxide.
5. In order to improve the flame retardant performance of magnesium hydroxide, in addition to the surface modification treatment of magnesium hydroxide prepared by the above method with surfactant, it can also be considered from the preparation of various grades of magnesium hydroxide, because the specific surface area of crystalline magnesium hydroxide is small, and the dispersion and compatibility in the polymer are good, which have been studied in the United States, Japan and other countries. In the late 80s and early 90s of the 20th century, Japan developed various forms of magnesium hydroxide, and they believed that the better one was spherical magnesium hydroxide, because its specific surface area was smaller than the first two, it had better dispersion and compatibility in polymers, and had better mechanical properties (such as tensile strength, flexural strength and flexural modulus, etc.). Due to its small specific surface area, the impact of carbon dioxide absorption is relatively small, which can prevent the whitening of flame retardant materials.
At present, there are many studies on various functional and structural materials at home and abroad, and in terms of functional and structural materials of magnesium series, magnesium oxide is more studied, and magnesium hydroxide as a functional and structural material is not much studied, among which the United States, Japan and other countries have studied more. The different crystal forms of magnesium hydroxide described above have the dual effect of better flame retardant and increased mechanical strength (so-called reinforcing agent).
In the method of preparing flaked, fibrous and spherical magnesium hydroxide, Japan uses hydrothermal method, that is, the use of sodium hydroxide and magnesium salt solution to obtain colloidal magnesium hydroxide, and then in an autoclave or reaction kettle, under a certain pressure and temperature, heating for a few hours, you can prepare magnesium hydroxide with different crystal shapes (in fact, directly in the autoclave or reaction kettle to produce crystalline magnesium hydroxide). The specific surface area of crystalline magnesium hydroxide has a large relationship with the pressure, and the greater the pressure, the smaller the specific surface area, which is inversely proportional.
China's development of crystalline flame retardant grade magnesium hydroxide is about 15 years behind Japan, there is no report in this regard, China's coastal magnesium (renewable) is very rich, should make full use of this favorable condition, developed China's independent intellectual property rights of innovative technology.
6. It is reported that some European countries (such as Germany, the Netherlands and other countries) have raised objections or restrictions on the use of polybrominated diphenyl ethers as flame retardants in the past few years. At present, the EU has proposed a ban on three brominated flame retardants, including pentabromodiphenyl ether, octabromodiphenyl ether and decabromodiphenyl ether, and has limited the ban timetable. Although the United States, Japan and other countries have different views, it cannot be denied that PBDEs will produce toxic substances when they are flame retardant. Therefore, how to solve this problem has become the question of whether PBDEs can be used as flame retardants for sustainable development. One solution to this problem is to develop brominated composite flame retardants, which can inhibit the production of toxic substances, so that there is still room for development of flame retardants such as high-efficiency polybrominated diphenyl ethers.
Hebei Meixi Biotechnology said that magnesium hydroxide has a good flame retardant effect, but also non-toxic and has the effect of smoke suppression, added to polybrominated diphenyl ethers under the condition of similar decomposition temperature, it can inhibit the production of toxic substances when polybrominated diphenyl ethers are flame retardant, and does not affect the flame retardant effect of polybrominated diphenyl ethers, and can play a synergistic flame retardant effect. Not only can the above situation be considered in this way, but also from the consideration of not affecting (or not having much impact) on the flame retardant effect and reducing the production cost of flame retardant, the addition of magnesium hydroxide is not limited to the above three, and the variety of brominated flame retardant can be expanded. In this regard, a variety of flame retardants with magnesium and bromine compounds have been studied in foreign countries (such as Japan and other countries), and some people in China have also made preliminary attempts. It should be said that the use of magnesium hydroxide to solve the above problems is an important development direction worthy of research and application prospects.