PE has excellent processability, electrical insulation, mechanical properties and high and low temperature resistance, and is widely used in construction, electrical, medical and other industries, but its LOI value is only about 17.4%, which is flammable, limiting its application range. Improving the flame retardancy of PE is also a hot spot in research, and the commonly used flame retardants for PE include halogens, phosphorus and nitrogen, aluminum/magnesium inorganic flame retardants, etc., but magnesium hydroxide is favored for its low cost and environmental friendliness.
Three kinds of magnesium hydroxide with different particle sizes were used as flame retardants, mixed with PE to make composite materials, and their mechanical properties, electrical properties, thermal stability and flame retardant properties were studied. The results show that the flame retardancy and thermal stability of PE can be significantly improved, and the comprehensive performance of the composite is the best when the particle size of magnesium hydroxide is 3.1 μm, and its tensile strength is 16.1 MPa, elongation at break is 400%, LOI value is 22.3%, peak heat release rate (PHRR) is 270kW/m2, and volume resistivity is 5.2×1013 Ω·m.
The magnesium hydroxide was modified by melamine formaldehyde resin, and the composite materials were prepared by melting and blending with PE, and the composites were studied. The results show that compared with the simple magnesium hydroxide flame retardant and the composite made of PE, the LOI value of the composite made of modified magnesium hydroxide is increased by 11%, the smoke suppression effect is more obvious, and the tensile strength and elongation at break are increased to 12.71MPa and 45.07%, respectively.
Magnesium hydroxide is modified with a composite modifier and applied to high-density polyethylene (HDPE). The results show that the flame retardant properties of the prepared composites are significantly improved, and the tensile properties are not significantly reduced compared with pure HDPE.
Magnesium hydroxide and graphene were used as composite flame retardants and PE to prepare composite materials. The results showed that compared with magnesium hydroxide alone, the flame retardant had a higher flame retardant effect on PE, and the LOI value increased by 6.4%. Although magnesium hydroxide, as a green and environmentally friendly, excellent flame retardant effect and low cost flame retardant material, can be widely used in the plastics industry, because magnesium hydroxide is an additive flame retardant, a large amount of fuel retardant needs to be added to meet the high flame retardant requirements. Moreover, magnesium hydroxide has strong polarity, strong hydrophilicity, is not easy to disperse in polymers, and is easy to agglomerate, which will lead to poor compatibility with plastics, and the strength of the prepared composite plastics decreases, and the processability and fluidity deteriorate, which limits its large-scale application in the plastics industry.
Therefore, the future research directions of magnesium hydroxide flame retardants include:
(1) Ultra-detailed research. The ultra-fine magnesium hydroxide as a flame retardant does not reduce the mechanical properties of plastics, and can also enhance the rigid particles, while the increase in its surface area will further enhance the flame retardant properties.
(2) Surface modification research. The surface modification of magnesium hydroxide is carried out with a suitable surface modifier to improve its dispersibility, reduce the occurrence of agglomeration, and stabilize the mechanical properties of plastics.
(3) Research on composite flame retardants. Other flame retardants suitable for magnesium hydroxide were developed to reduce the amount of magnesium hydroxide added while improving the flame retardant effect and reducing the impact on the mechanical properties of plastics.
(4) Microencapsulation technology. Magnesium hydroxide is embedded or sealed in polymer materials to form microcapsule flame retardant, which aims to improve the compatibility of magnesium hydroxide and improve the flame retardant and mechanical properties of composite materials.