Smoke density reducers

It is well known that freshly formed oxides have high surface areas and in addition, can be cata-lytically active,52 thereby promoting both carbon deposition and subsequent oxidation processes.53 The reduced combustion rate arising from the effects of the fire-retardant filler also contributes to lowering the rate of smoke evolution and, by improving oxygen to fuel ratios, further limits levels of smoke density.1... 

The flammability properties of an intumescent fire retardant PP formulation with added MH has been investigated.65 The results show that the intumescent flame-retardant ammonium polyphosphate-filled PP has superior flammability properties but gives higher CO and smoke evolution. The addition of MH was found to reduce smoke density and CO emissions, in addition to giving superior fire resistance. PP filled with ammonium polyphosphate, pentaerythritol, and melamine has given improved flammability performance, without reducing its mechanical properties. 

The increasing demand for FR PVC-U applications has prompted work in this area. The use of functional fillers can cause a dramatic deterioration of physical properties at the addition levels necessary to achieve the requirements of flame retardancy and smoke emission. An evaluation has shown zinc hydroxystannate to give the best overall FR and SS characteristics without adversely influencing important physical properties (129). The addition of low levels of zinc borate and/or ATH was noted to improve flame retardancy and reduce smoke density in a PVC-U formulation (265). 

Outstanding property low temperature flexibihty, oxidative stability, reduced smoke density ... 

It is also a good smoke suppressant. The addition of 9% to polystyrene reduces the maximum smoke density in the NBS Smoke Chamber from 2556 to 375. In a test on an EPDM compound, a mixture of 75% magnesium hydroxide and 25% ATH produced significantly less smoke than ATH alone in Smouldering Mode NIST (ASTM 2843) smoke chamber testing. 

Smoke opacity is another increasingly important characteristic measured by optical density. Fire-retardant additives can be halogenated or halogen-free, which reduces the corrosivity, toxicity and pollution risks. 

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