Ultrafine aluminum hydroxide powder has multiple functions such as flame retardant, smoke elimination and filling, and can produce synergistic flame retardant effect with phosphorus and other substances. It is an important environmental protection flame retardant in the electronics, chemical, cable, plastic, rubber and other industries.
Aluminum hydroxide is a filling type inorganic flame retardant, in order to achieve better flame retardant effect, the filling amount needs to be more than 40% (total amount), some even as high as 60%, but the high filling amount not only seriously affects the mechanical properties of the products, but also makes the extrusion and processing performance worse.
Therefore, in order to make the super-fine aluminum hydroxide powder can be widely used in the flame retardant materials such as polyolefin, has to be aluminum hydroxide powder surface modification, in order to improve the surface physical and chemical properties, enhance the super-fine aluminum hydroxide powder and substrate, the organic polymer or resin compatibility and dispersity in organic substrate, in order to improve the mechanical strength of the material and the comprehensive performance.
1. Surface modifier commonly used for ultrafine aluminum hydroxide
(1) silane coupling agent
There are more than one hundred kinds of silane coupling agents, among which the monolayer – functional group silane coupling agent is the most stable.The stability of the -functional group silane coupling agent is between steel and metal. In addition to enhancing the mechanical properties of the products, the -functional group silane coupling agent can also improve the electrical properties and moisture resistance of the products.
(2) zirconium coupling agent
Class zirconium coupling agent containing zirconium aluminate low relative molecular mass of inorganic polymer in the main chain of the molecule on the complexation of two kinds of organic ligand subunits, a dentate with coupling agent good hydroxyl stability, another dentate to coupling agent good organic reactions, the aluminum hydroxide superfine aluminum hydroxide powder has good modified effects.
(3) higher fatty acids and their salts
In the molecular structure of higher fatty acids and their salts, one end is a long-chain alkyl group, and the other end is a carboxyl group and its metal salt which can react with the surface functional groups of aluminum hydroxide.Treating ultrafine aluminum hydroxide powder with high fatty acid and its salt can improve the affinity between ultrafine aluminum hydroxide powder and polymer molecule, and improve the mechanical and processing properties of the product.
(4) unsaturated organic acids
Common unsaturated organic acids are: acrylic acid, methacrylic acid, cinnamic acid, etc.Generally speaking, the stronger the acid, the easier to form ionic bond, so choose more: acrylic acid and methacrylic acid.
A variety of organic acids can be used alone, can also be mixed use, treatment of alkali metal ions containing mineral ultrafine aluminum hydroxide powder, the effect is better.
(5) organosilicon
Macromolecule organosilicon, also known as silicon oil, is a kind of polymer which is connected with organic group on silicon atom by silicon oxygen bond chain (si-o-si) as skeleton.Commonly used are hydrogen-containing polymethylsiloxane, hydroxyl-terminated polydimethylsiloxane, etc.
2. Surface modification process of ultra-fine aluminum hydroxide
At present, the surface modification methods of ultrafine aluminum hydroxide powder are mainly dry and wet.
(1) dry modification
In this process, the modified ultrafine aluminum hydroxide powder is preheated to a certain temperature, and the modifier is slowly dripped into the high-speed aluminum hydroxide powder, and the product is stopped for packaging after the reaction to a certain time.
The advantages of dry modification are low requirements on equipment and simple operation.The disadvantage is that the labor intensity of workers is large, aluminum hydroxide powder coating rate is low.
(2) wet modification
Wet modification is in the production process of ultrafine aluminum hydroxide powder, the synthesis of aluminum hydroxide slurry after filtering, washing, filter cake beating, in a certain temperature of beating slurry after adding modifier, stirring for a period of time, filtering, drying and beating packaging.
The advantages of wet modification are low labor intensity, no dust pollution, high production efficiency, high aluminum hydroxide powder coating rate, 20-30%, the modification effect is high and stable.Compared with dry modification, wet modification has a longer process and higher requirements on equipment.Due to the advantages of wet modification, it is gradually replacing the dry modification production method.
3. Evaluation method of surface modification effect of ultrafine aluminum hydroxide
(1) oil absorption rate test
Oil absorption rate is mainly used to measure the amount of castor oil needed when a certain amount of Al (OH) 3 powder just reaches saturation infiltration, and it is used to characterize the amount of resin needed when a certain amount of Al (OH) 3 powder just reaches saturation infiltration.
The detection method is as follows: the superfine alumina hydroxide powder is weighed and dried sample is about 10g, placed in a beaker, drop castor oil with burette, and gently mixed with a glass rod to make castor oil and sample evenly infiltrated into a ball.The amount of castor oil adsorbed per 100g of aluminum hydroxide was calculated, that is, the oil absorption rate of ultrafine aluminum hydroxide powder.
After surface modification of aluminum hydroxide powder, the oil absorption rate will change to a certain extent.If the ultrafine aluminum hydroxide powder is modified with silane coupling agent, the oil absorption rate will decrease by about 10%.
(2) SEM test
The morphology of the ultrafine aluminum hydroxide powder before and after modification was detected by electron microscope. The dispersion of the modified powder in the matrix was better than that of the unmodified product.
(3) FTIR test
Fourier infrared spectroscopy (ftir) was used to analyze the groups on the product surface.For example, the content of vinyl – Vi and – Si can be determined by ir spectra of aluminum hydroxide powder with wet surface modification of methyl vinyl silane.
(4) determination of product properties
The modified and unmodified ultrafine aluminum hydroxide powders were used to test the cable indexes such as oxygen index, tensile strength and elongation at break.Through comparison, it can be found that the flame retardant and mechanical properties of the modified products have been improved.
(5) activation index
Activation index is an index to evaluate the surface modification effect by measuring the percentage of the amount of aluminum hydroxide floating on the surface of water to the total amount of aluminum hydroxide after modification.Due to the different types of surface modifiers and different treatment methods of ultrafine aluminum hydroxide powders, some of the modified powders will float on the water surface and some will sink
Such as sodium stearate, titanate wet modification, hydrophobic silane dry modification after the ultrafine aluminum hydroxide powder, the activation index can be used to evaluate the modification effect;However, hydrophilic silane was modified by dry method, and the ultrafine aluminum hydroxide powder modified by silane wet method would sink in water, so the modification effect could not be evaluated by activation index, and the accurate evaluation method was infrared spectroscopy.
Post time: Apr-24-2020