Aluminum hydroxide is a filler inorganic flame retardant, in order to achieve better flame retardant effect, the filling amount needs 40%, even up to 60%, but the high filling amount not only seriously affects the mechanical properties of the product, but also makes the extrusion and processing properties worse. Therefore, in order to make aluminum hydroxide powder can be widely used in flame retardant materials such as polyolefin, surface modification must be carried out.
(1) silane coupling agent
There are more than one hundred kinds of silane coupling agents. According to the structure of R functional groups in the molecules, silane coupling agents are divided into α-functional group, β-functional group and γ-functional group silane coupling agent.
γ-functional group silane coupling agent is the most stable, which is used for thermoplastic and thermosetting filler aluminum hydroxide modification treatment, improve the strength of products is very significant. The stability of α-functional group silane coupling agent is between β and γ. In addition to enhancing the mechanical properties of products, α-functional group silane coupling agent can also improve the electrical properties and moisture-proof properties of products. The modified aluminum hydroxide products treated by α-functional group silane coupling agent are suitable for application in the wire and cable industry.
(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) High fatty acids and salts
Advanced fatty acids and their salts are the earliest used mineral surface modifiers, the main commonly used are stearic acid and stearate. 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 that can react with the surface functional groups of aluminum hydroxide. The treatment of superfine aluminum hydroxide powder with high fatty acid and its salt can improve the affinity between aluminum hydroxide powder and polymer molecules, and improve the mechanical properties and processing properties of the products.
(4) unsaturated organic acids
Unsaturated organic acids with one or more unsaturated double bonds and one or more hydroxyl groups. The carbon atom number of unsaturated organic acid modifiers is generally less than 10. Common unsaturated organic acids are: acrylic acid, methacrylic acid, cinnamic acid and so on. Generally speaking, the stronger the acid, the easier it is to form an ionic bond, so acrylic acid and methacrylic acid are used. Various organic acids can be used alone or mixed to treat mineral aluminum hydroxide powder containing alkali metal ions with good effect.
(5) Organic silicon
Polymer silicone, also known as silicone oil, is a kind of polymer with silicon oxygen bond chain (Si-O-Si) as the skeleton and silicon atoms connected to organic groups. Commonly used are hydrogen containing polymethylsiloxane, hydroxyl end polydimethylsiloxane and so on.
(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 has just reached saturation infiltration, and it is used to characterize the amount of resin needed when a certain amount of Al (OH) 3 powder has just reached saturation infiltration.
The detection method is as follows: the ultrafine aluminum hydroxide powder is weighed about 10g dry sample, placed in a beaker, dripped with castor oil with burette, and gently blended with a glass rod to make castor oil and sample infiltrated evenly into a pellet. The amount of castor oil adsorbed per 100g of aluminum hydroxide is calculated as the oil absorption rate of ultra-fine aluminum hydroxide powder.
After surface modification of aluminum hydroxide powder, the oil absorption rate will be changed to some extent. For example, the oil absorption rate of ultra-fine aluminum hydroxide powder modified by silane coupling agent will decrease by about 10%.
(2) SEM test
The morphology of the ultrafine aluminum hydroxide powder before and after modification was detected by scanning electron microscope equipment. The dispersion of the modified powder in the matrix was better than that of the unmodified product.
(3) FTIR test
The groups on the surface of the product were analyzed by FT-IR spectroscopy. For example, the content of vinyl-VI and -Si can be measured by infrared spectrum in the alumina hydroxide powder modified by methyl vinyl silane wet surface method.
(4) Determination of product performance
The cable indexes such as oxygen index, tensile strength and elongation at break were tested by modified and unmodified ultra-fine aluminum hydroxide powders. By comparison, it was found that the flame retardancy and mechanical properties of the modified products were improved.
(5) Activation index
Activation index is an index to evaluate the effect of surface modification by measuring the percentage of alumina hydroxide floating on the water surface after modification. Due to the different types of surface modifiers and treatment methods of ultra-fine alumina hydroxide powder, some of the modified powder float on the water surface, and some will sink.
Such as sodium stearate, titanate wet modified, hydrophobic silane dry modified ultrafine aluminum hydroxide powder, can be used to evaluate the modification effect of activation index; However, the ultra-fine aluminum hydroxide powder modified by hydrophilic silane dry method and silane wet method will sink in the water. Activation index cannot be used to evaluate the modification effect. The accurate evaluation method is infrared spectrum test.