Abstract
A range of experimental copolymeric poly(acrylonitrile) filament tows containing dispersed phyllosilicate or montmorillonite clays have been extruded from commercial fibre-grade polymer (as a commercial dope) and from in-situ-clay-containing, suspension copolymerised polymers dissolved in sodium thiocyanate solution. The filaments show evidence of nanocomposite structures because of their excellent tensile properties and enhanced initial Young’s moduli. In the never-dried condition, they have been shown to be able to absorb the flame retardant ammonium polyphosphate (APP) at levels which appear to be dependent on clay type and concentration to yield high levels of flame retardancy with limiting oxygen index values in excess of 40 vol% being achieved. The clays present, which have different functionalities, have been shown to contribute to a flame retardant effect in addition to that conferred by the APP present and this has been quantified in terms of respective LOI contribution. This effect appears to be greater for the unfunctionalised Cloisite Na+ clay with APP levels in the fibre equivalent to a phosphorus level, PF = 6%w/w yielding an LOI value of 41.0 vol% with the component arising from the 1% clay presence being 5.0 vol%. However, when the accompanying increased flame retardant absorption caused by each clay present is used to calculate an expected LOI value contribution, the actual LOI increases conferred by each clay become less and are significant only when fibre phosphorus levels, PF, are in excess of 4% w/w. Char levels appear to be independent of phosphorus concentration for the condition4≥PF≥1%. For PF≥4%, char levels decrease in the region where the additional effects of nanoclay become significant. Finally, while the absorbed APP is not durable, this work has demonstrated that a clay dispersed together with a flame retardant yields an acrylic filament having acceptable tenacity, improved modulus and high levels of flame resistance.