Magnesium hydroxide is an inorganic flame retardant filler for polymer matrix composites with good application prospects. Like aluminium hydroxide, magnesium hydroxide flame retardant has the advantages of non-toxicity, low smoke, stable chemical properties and no secondary pollution, because it relies on chemical decomposition to absorb heat and release water when heated. However, compared with halogen-containing organic flame retardants, in order to achieve a considerable flame retardant effect, the filling amount should generally reach more than 50%. Because magnesium hydroxide is inorganic, the compatibility between the surface and the polymer matrix is poor. Such a high filling amount, if it is not treated by surface modification, the mechanical properties of the composite will be reduced after filling into the polymer material. Therefore, it is necessary to modify its surface to improve its compatibility with polymer matrix, so that the mechanical properties of filler materials do not decline, or even improve some of the mechanical properties of materials.
Experiments show that unmodified magnesium hydroxide exists in the form of aggregates in PP. Although the powder itself is very fine, because the surface of the particles is incompatible with the PP matrix, there are obvious boundaries or even voids between the particle aggregates and the PP matrix. The voids formed by the escape of magnesium hydroxide particles during brittle fracture indicate that the unmodified magnesium hydroxide only plays a filling and flame retardant role in PP, but does not bond with PP chemically. The surface modified magnesium hydroxide disperses evenly in PP matrix, and most of the particles disperse in the form of primary particles or small agglomerated particles.