Controllable crystal growth of Mg(OH)2 hexagonal flakes and their surface modification using graft polymerization

Abstract

Mg(OH)2 crystals with excellent flame retardance in the application of polymer materials are always in demand. Herein, regular and well-dispersed Mg(OH)2 hexagonal flakes were hydrothermally prepared with the existence of polyethylene glycol (PEG) and then modified by surface grafting-polymerization of methyl methacrylate (MMA) monomers. The results showed that the morphology and dispersity of Mg(OH)2 relied on the precise control of the reaction parameters including hydrothermal conditions, the molecular weight and additive amount of PEG. PEG with a molecular weight of 8000 exhibited an enhanced directing role due to its more appropriate length of molecular chains and intensive interaction with the formed Mg(OH)2 crystallites. The molecular chains of PEG-8000 can be preferentially adsorbed onto the (001) and (101) planes of Mg(OH)2 crystallites and sub-micro hexagonal flakes with low-polarity were consequently assembled. The optimal conditions for preparing Mg(OH)2 hexagonal flakes with higher crystallinity and more regular morphology were determined to be hydrothermal treatment at 120 °C for 12 h with 3 wt% PEG-8000. The dimension and decomposition temperature of the end products were 400 ~ 500 nm and 388 °C, respectively. The surface graft-modified Mg(OH)2 hexagonal flakes exhibited high hydrophobicity with a water contact angle of 148°, indicating an excellent compatibility with polymers.