Synergistic inhibitory action of P- and Si-containing precursors in sol-gel coatings on the thermal degradation of polyamide 6

In this study, a combination of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide-modified vinyl trialkoxysilane (DOPO-VTS) and tetraethoxysilane (TEOS) was used as a sol-gel finishing for the preparation of polyamide 6 (PA6) fibres with increased thermo-oxidative stability, retarded combustion performance and anti-dripping properties. Both DOPO-VTS and TEOS alone or in mixture were applied to the PA6 fabric at three different concentrations using a pad-dry-cure method. The presence of the coating on the PA6 fabric was confirmed by scanning electron microscopy and Fourier transform infrared spectroscopy. A thermal analyses of the coated samples revealed that the coatings affected PA6 decomposition at lower temperatures, favoured char formation and reduced the total heat release. Vertical flame spread test showed that, at higher precursor concentrations in the coating, the carbonized char completely stopped the melt dripping of the polymer. This phenomenon was attributed to the coating's reinforcement of the fibre structure, which reduced its dripping capacity. TEOS and DOPO-VTS clearly acted synergistically in the condensed phase.