Non-Halogen Flame Retardants for Polyolefins
Gandara Amarasinghe, Christopher Preston, Robert Shanks, Jefferson Hopewell
CRC for Polymers
Australia
Keywords: flame-retardant, polyolefin, halogen-free
Halogenated organic compounds have been found to be effective flame retardants for many polymers including polyolefins. Decabromodiphenyl ether is a typical example of a successful flame retardant, particularly when it is combined with antimony oxide. Halogenated organic compounds are of concern in the environment, and in a fire they release toxic and corrosive products. There is increasing interest in development of halogen-free flame retardants.
Flame retardant can function by several mechanisms: removal of heat or oxygen from combustible materials, absorption or restriction of flammable gases from joining the fire, coupling with active radicals that propagate the fire, prevention of the polymer from flowing after it has melted. Examples of halogen-free flame retardant are hindered amine light stabilisers and other antioxidants that react with radicals, glass forming borates such as boric acid and zinc borate, finely divided powders such as antimony oxide, char forming substances such as ammonium polyphosphate, particularly in combination with nitrogen containing compounds such as melamine and urea. Polyolefins have no natural flame retardant capacity and in a fire melt and drip, evolve flammable gases, and leave no carbonaceous residue. Combinations of flame retardants have been found to be useful for polyolefins.
The flame retardant effectiveness of additives in polyolefins has been measured using limited oxygen index (LOI), thermogravimetry in the presence of air compared with nitrogen atmosphere and cone calorimetry. Critical values for the test results are required for application of polyolefins in various applications. These critical performance indicators can be met with halogen-free flame retardants. The results obtained for flammability testing are interpreted in terms of the mechanisms of flame propagation and retardation.