Hexagonal magnesium hydroxide flame retardant has the advantages of smoke suppression, green and environmental protection, but due to its low flame retardant efficiency, it often requires a large filling amount when used in polymer substrates, and because magnesium hydroxide is used as an inorganic The powder has the characteristics of hydrophilic and oleophobic, and high polarity, which is not conducive to the interfacial compounding of inorganic/organic materials. A higher filling amount will lead to a significant decrease in the mechanical properties of the polymer composite material added with magnesium hydroxide. In order to improve the compatibility of the inorganic/organic interface between magnesium hydroxide and polymer substrates, Hebei Messi Biology Co., Ltd. selected 3-methacryloxypropyltrimethoxysilane (A-174) to hexagonal Magnesium hydroxide is used for dry modification. This silane coupling agent can be copolymerized with vinyl acetate, acrylic acid or methacrylic acid monomers. It is often used in the wire and cable industry. It can improve the interfacial compatibility of composite materials and improve Anti-static performance of cable material.
Hebei Messi Biology Co., Ltd. has studied the factors affecting the effect of dry process modification of hexagonal magnesium hydroxide, namely the amount of modifier, modification temperature, modification time and stirring speed. Using the single factor experiment method, through the determination of the activation index of the modified powder, the optimal process conditions for the effect of the silane coupling agent A-174 modified magnesium hydroxide were determined, and characterized by SEM, thermogravimetric analysis and infrared spectroscopy. Methods The modification mechanism and modification effect of magnesium hydroxide modified by silane coupling agent A-174 were discussed.
1.1.1 Reagents and instruments
Hexagonal magnesium hydroxide (Hebei Messi Biology Co., Ltd.), 3-methacryloxypropyltrimethoxysilane, dioctyl phthalate DOP, DHG-9140A type electric heating constant temperature blast drying oven, FA2004 Type electronic balance, Y100L2-4 high-speed mixer, DJ-1 timing electric mixer, JSM-5610LV/INCA scanning electron microscope, STA449F3 synchronous thermal analyzer, Nexus Fourier transform infrared spectrometer
1.1.2 Modification method
First, put the magnesium hydroxide powder into a drying oven, and dry it at 120°C for 5 hours to remove the moisture absorbed in the raw material, and then cool the dried magnesium hydroxide to room temperature for later use. Weigh 1kg of dried magnesium hydroxide powder and add it to a high-speed mixer, preheat it to the experimental design temperature at a stirring speed of 1000rpm, when the temperature rises to the specified temperature, increase the stirring speed of the high-speed mixer to a certain set value, and use Add a certain amount of silane coupling agent A-174 to the powder with a medical syringe. After the modification has been carried out for a certain period of time, the heating and stirring are stopped, and the modified powder is taken out and cooled to room temperature. The modification process flow is shown in Figure 2.1, and the modification process conditions are shown in Table 2.1.
Figure 2.1A-174 dry modified magnesium hydroxide process flow chart
Table 2.1A-174 Dry Process Conditions of Modified Magnesium Hydroxide
2.2 Characterization method
1.2.1 Activation index
Take a 200ml beaker, add 100ml of distilled water, weigh about 3g of modified magnesium hydroxide powder and put it in the beaker, use an electric stirrer to stir continuously for 1min, then let it stand for 10min, collect the remaining powder floating on the water surface, and then place it In an oven, dry at 110°C for 4h, cool to room temperature and weigh. The activation index of the sample can be calculated from formula (2-1): A=m1m2×100% formula (2-1)
In the formula: A is the activation index of the sample; m1 is the mass of the powder floating on the water surface; m2 is the total mass of the sample.
The bare magnesium hydroxide powder without surface modification will naturally settle in distilled water, and the activation index is 0%. The surface of magnesium hydroxide modified by silane coupling agent is hydrophobic, the modified powder will float on the water surface, and the activation index A>0%; when the surface of magnesium hydroxide powder is completely covered by the coupling agent, A= 100%. Therefore, the change of activation index value can directly reflect the effect of surface chemical modification to a certain extent.
1.2.2 Oil absorption rate
Weigh about 1g of modified magnesium hydroxide powder and place it on a clean watch glass, slowly add DOP to it with a 25ml burette, and use a glass rod to stir continuously during the dropping process until the powder sample is completely mixed into a Record the volume of DOP consumed, and calculate the oil absorption rate of the sample according to the formula (2-2), the unit is ml/100g.
Q=Vm×100 formula (2-2)
In the formula: Q is the oil absorption rate of the sample; V is the consumed DOP volume; m is the mass of the sample.
Due to the high surface energy of unmodified magnesium hydroxide, agglomeration usually occurs between powders, and the degree of dispersion is low, the gaps between particles are large, and the invalid absorption of DOP is serious. The agglomeration phenomenon of the modified magnesium hydroxide powder is alleviated, the bulk density is increased, and the oil absorption rate will be relatively reduced, which reduces the influence of magnesium hydroxide addition on the comprehensive performance of polymer materials. Therefore, the oil absorption rate is one of the important indicators to control the quality of powder modification.
1.2.3 Scanning Electron Microscope
Scanning electron microscopy can be used to observe the shape, size, particle size distribution and particle dispersion of the sample, which is reliable and intuitive. In this test, a vacuum drying oven was used to dry the powder to be tested, and then the dried powder was dispersed by ultrasonic waves and then stuck to the conductive adhesive. After spraying gold, the shape and size of the powder could be directly observed.
1.2.4 Thermogravimetric analysis
Magnesium hydroxide powder will show different thermal decomposition behavior after surface modification by silane coupling agent, because the difference in the degree of surface organicization will lead to different decomposition behavior of inorganic powder in the process of thermal decomposition. Therefore, through research Its thermogravimetric analysis curve can analyze the organic situation of the powder surface. This experiment was carried out in a nitrogen atmosphere, the temperature range was 30-1050 °C, and the heating rate was 5 °C/min.
1.2.5 Fourier Transform Infrared Spectroscopy
Fourier transform infrared spectroscopy is mainly used to study the mechanism of surface modification. According to the position and shape change of the characteristic absorption peak of the test sample, the effect of various functional groups of the modifier on the surface modification process of magnesium hydroxide is compared and analyzed. Using KBr pellets, the wave number range is 4000~500cm-1.