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The Effect of Functional Nanoclays in Enhancing the Fire Performance of Fibre-forming Polymers

This paper reviews the present interest in the use of functionalised nanoclays as additives for improving tensile properties and fire performance in fibre-forming polymers. However, evidence over the last three years suggests that, when present by themselves, they will not be able to fulfil all the required features of an ideal flame-retardant, such as conferring ignition-resistance, self-extinguishability, and char-forming propensity. By using cast films as models for eventual fibre geometries, recent work in our own laboratories suggests that nanoclays may increase the effectiveness of more conventional normal flame-retardants (FRs) and thus enable lower quantities to be used, an especially important requirement in synthetic-fibre production and processing. In this paper, we also extend earlier work and report the effect of introducing two commercial nanoclays of known chemical structure into films of polyamide 6 and 6.6 in combination with selected phosphorus-containing flame-retardants. By using the limiting-oxygen index as a means of measuring increased flame-retardant properties, it is shown that the addition of low levels (2% w/w) of nanoclay does increase the over-all flame-retardant behaviour of films in the presence of defined concentrations (11–27% w/w) of flame-retardant, thus enabling lower concentrations of the latter to be used. As a means of understanding such synergistic activity and in order to be able to develop more effective combined nanoclay-FR systems, a simple model is proposed.