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Silicon Based

Silicon-based materials are potential flame retardants as they produce protective surface coatings during a fire, caused by a low rate of heat released. Low levels of silicone in certain organic polymer systems have been reported to improve their LOI and UL-94 performance. Some compounded silicone (polydimethylsiloxane-type) contains dry powders with a variety of organic plastics. Particularly in PS, they showed that an additive level, as low as 1 to 3 %, reduces the rate of heat released by 30 to 50%. They reported similar improvements in HIPS, PP, PS-blends, PP and EVA. 

By studying silicone-modified polyurethane, a significant decrease of the rate of release of these materials in comparison with unmodified polyurethanes has been observed. The proposed mechanism is the following one: while burning, formation on material surface of a silicon dioxide layer which can act as a thermal insulator and prevents the feedback of energy to the substrate by re-radiating the external heat flux. 

New silicone derivatives for polycarbonate (PC) and PC/ABS resins offer both good mechanical properties (strength, moulding, …) and high flame retardancy performance (UL-94, 1/16 inch V-0 at 10 phr). Linear and branched chain-type silicone with (hydroxy or methoxy) or without (saturated hydrocarbons) functional reactive groups have been evaluated. The silicone, which has a branch chain structure and which contains aromatic groups in the chain and non-reactive terminal group is very effective. In this case, the silicone is finely dispersed in the PC resin and it may move to the surface during combustion to form a highly flame-retarding barrier on it.