Metal compounds as catalysts in the intumescent flame retardant system for polyethylene terephthalate fabrics

Abstract

Forming a carbonaceous protective layer during combustion has been proven to be an effective way to improving the flame retardancy of polymers and it has been found that some metal compounds could promote dehydrogenation and aromatization of the degradation products. In this research, several divalent or multivalent metal compounds were added in the intumescent flame retardant (IFR) based on ammonium polyphosphate, pentaerythritol and melamine for polyethylene terephthalate (PET) fabrics. The prepared flame retardant dispersions containing 25 wt% IFR and 1 wt% metal compounds were applied on PET fabrics by the common pad-dry-cure method. None of the treated samples generated any dripping during the vertical burning test, with the highest limiting oxygen index being up to 33.4%. Thermogravimetric analysis showed that the catalytic effect of metal compounds may occur in promoting the formation of char residues. The morphology of char residues of two of the IFR/metal compound-treated PET fabrics, IFR/FeCl3 and IFR/ZnCl2, were smooth and compact, as shown by scanning electron microscopy. Laser Raman spectroscopy of the char residues suggested that a higher graphitization degree was obtained by adding the metal compounds. Real-time Fourier transform infrared spectroscopy showed that metal compounds made more phosphorus available for phosphorylation and char formation. The results of the present study indicate the possibility for enhancing char formation via the catalytic effect of metal compounds to improve the flame retardant and anti-dripping properties of the PET fabrics.