Study on the properties of magnesium hydroxide in flame retardant ABS

ABS is widely used in mechanical, electrical appliances, meters, transportation industries, but ABS is flammable and will release toxic gas and smoke during combustion. Considering the safety of residential, electrical appliances, pipelines, automobiles, office supplies..., it is very important to develop flame retardant ABS material.

Among the flame retardant for ABS, magnesium hydroxide is a fast-developed additive flame retardant. Magnesium hydroxide is low smoke and toxic-free, it can neutralize toxic acid gas released during combustion. In addition, magnesium hydroxide can absorb soot particles to achieve a smoke suppression function.

Magnesium hydroxide is an inorganic polymer with many -OH groups on its surface, easily agglomerate into 10~100micron secondary particles, and has a large specific surface area. When used in composite material, it shows poor dispersion and compatibility, so we use a surfactant to modify magnesium hydroxide. And generally, it requires high loading amount (above 50%) in order to achieve better flame retardant performance, which will affect the mechanical property of composite material. So we use another flame retardant to synergy with magnesium hydroxide to decrease the adding amount and improve the flame retardant performance of ABS material.

This passage mainly introduced the properties of the magnesium hydroxide-red phosphorus synergy system in flame retardant ABS.

1.?Experiment

1.1?Raw material

ABS750, magnesium hydroxide (particle size less than 5 microns), Micro-encapsulated Red Phosphorus, surfactant.

1.2?Equipment and instrument

10L high-speed mixer, twin-screw extruder, tableting machine.

1.3?Sample preparation

Weighing the ABS, flame retardant, and other agents, mixing 5~6 minutes in a high-speed mixer, then cooling the material, add all the mixture into twin screw extruder, mixing and melting, then extrude and pelleting. The temperature of all cylinders are 175℃, 190℃, 210℃, 220℃, 210℃, 210℃, 200℃, screw speed 40~60 r/min. Then prepare a 2mm thick flame retardant ABS sample on the tableting machine under 200℃, and made it into a width 12mm sample for the combustion test.

2.?Results and discussion

2.1?Surface modification of magnesium hydroxide

Magnesium hydroxide is a strongly polar hydrophilic compound, that has poor compatibility with ABS. Doing surface treatment could improve the compatibility, and dispersion of magnesium hydroxide. The study chooses 100hr ABS, 50phr magnesium hydroxide, and 4phr surface treatment agent, to see the influence of three different surface treatment agents on the flame retardant property.

From table 1, we can see that agent C has better flame retardant performance, so the following test is based on using agent C. To enhance the coating efficiency, the drying process is applied, which disperse surfactant into dispersion agent in the mass proportion of 1:3, then do the coating to magnesium hydroxide.

2.2?Flame retardant performance of magnesium hydroxide

We choose 100phr ABS, 4phr surface treatment agent C, to study the effect of magnesium hydroxide loading amount on flame retardant performance. The result shows in Table 2, and we can see from table 2, the more magnesium hydroxide, the better flame retardant. And when the loading amount reaches 60phr, the composite material can reach the V-0 level, but at the same time, the processing performance decrease rapidly, the screw meshing is difficult, and there is abnormal sound, the toughness of the product became worse.

2.3 Magnesium hydroxide and red phosphorus synergy flame retardant performance

When adding oxygen-containing flame retardant to red phosphorus?and ABS flame retardant system, it can achieve better flame retardant performance. And Mg(OH)2 can meet this requirement, so the synergy of Mg(OH)2 and red phosphorus can generate better flame retardant performance.

100phr ABS, 35phr synergy flame retardant, and 4phr surface treatment agent C is chosen to study the effect of different proportion of red phosphorus-Mg(OH)2 on flame retardant performance. The result shows in Table 3, and we can see that when the mass ratio of red phosphorus is 18% in 35phr synergy flame retardant, the flame retardant performance is the best.

100phr ABS, 25phr synergy flame retardant, 4phr surface treatment agent C are chosen to study the effect of different proportions of red phosphorus-Mg(OH)2 on flame retardant performance. The result seen in Table 4, we can see that along with the decreased amount of synergy flame retardant, the content of red phosphorus decrease, and the flame retardant performance is better when the mass ratio of red phosphorus is 14%.

100phr ABS, 20phr synergy flame retardant, 4phr surface treatment agent C are chosen to study the effect of different proportion of red phosphorus-Mg(OH)2 on flame retardant performance. The result see Table 5, we can see that in 20phr synergy flame retardant formula, the flame retardant performance is better when the mass ratio of red phosphorus is 18%.

Based on the above test result, the formula can reach V-0 level when the synergy flame retardant is 20~25phr, and the mass ratio of red phosphorus is 14~18phr, and it also decreases the effect on toughness of the material and improve the process performance of flame retardant ABS.?

3. Conclusion

(1)?Using modified Mg(OH)2 and red phosphorus synergy flame retardant can develop flame retardant ABS, and it can reach V-o level when adding 25phr synergy flame retardant.

(2)?Red phosphorus can synergy with Mg(OH)2, adding a small amount of red phosphorus can greatly decrease the loading amount of Mg(OH)2.