Magnesium Hydroxide Uses and Synergies

By: Dr. Ed Weil

Research Professor, Polytechnic Institute of NYU (off-campus)
IP Fellow, University of Akron Research Foundation
Adjunct Professor., SUNY Stony Brook (off-campus)
Consultant in flame retardancy; U.S. patent agent

In applications above the water-loss range of ATH (i.e., around 200°C), MDH can be used where ATH cannot. They both work by water release (heat sink and fuel dilution) and leave a barrier. Combinations of ATH and MDH often show a better-than-additive effect. In chlorinated polymers with antimony trioxide, magnesium hydroxide generally provides not only enhanced flame retardancy but lower smoke.

A recent patent shows improved flame retardant performance of MDH in an ethylene elastomer by use of a maleic polyethylene graft compatibilizer.

The flame retardant performance of MDH can be synergized by zinc borate (Marshall Additive Technologies CT ZB800). In general, zinc borate is useful as a synergist with MDH at about a 1:10 to 1:5 weight ratio. At a 5:1 ratio of MDH to ZB, a total loading of 64% gives a V0 rating and LOI of 39 in EVA. This lower loading permits the use of a higher molecular weight EVA with adequate processing rheology.

Calcium borate on a silicate carrier such as wollastonite has been marketed as an effective synergist for MDH in polyethylene-ethylene vinyl acetate.

[from E. Weil and S. Levchik, Flame Retardants for Plastics and Textiles: Practical Applications (Hanser, 2016)]

Next post we will look into Huntite-Hydromagnesite.