The use of surface coated magnesium hydroxide as a flame retardant additive in polymers

Bell, Graeme M. (1996) The use of surface coated magnesium hydroxide as a flame retardant additive in polymers. (MPhil thesis), Kingston University, .


Magnesium hydroxide as a halogen-free inorganic filler has been shown to improve the thermal characteristics of polypropylene systems. The degradation of polypropylene filled with magnesium hydroxide was studied by means of various thermal analysis techniques, with further work involving Pyrolysis - Gas Chromatography. The latter technique showed that magnesium hydroxide interferes with the degradation process by reducing the chain length of residual fragments. Two decomposition steps. were noted in magnesium hydroxide / polypropylene formulations, the first step being associated with the dehydration of the filler and the second step due to polymer degradation. In order to prove or disprove information cited in patents, several coatings were added to the filler in an attempt to reproduce an elevation in dehydration temperature and activation of the coated material. Initially, six coatings were examined. These coatings incorporated such groups as silane, stearate, phosphate and fatty acid. From these tests, it was determined that further investigation of the silane and fatty acid type derivatives were required. Initially, methyltriethoxysilane gave promising results. However, structural variations of this compound proved to be expensive. As a result, trimethyl-trihexyl- and triphenyl- chlorosilanes were tested, with a further increase in effectiveness noted for those coatings with the bulkier side groups. Fatty acid based coatings provide a cost-effective, environmentally friendly product that has comparable effects to those seen by the silane derivatives. The addition of both types of compounds increased the dehydration temperature of magnesium hydroxide (by up to 20°C) whilst also increasing the enthalpy of dehydration (by up to 8.5%).

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