Abstract
A novel reactive intumescent fire retardant hexa-[4-[(2-hydroxy-ethylimino)-methyl]-phenoxyl]-cyclotriphosphazene (HEPCP), containing both cyclotriphosphazene and Schiff base structures, is successfully prepared. The chemical structures of HEPCP and flame-retardant waterborne polyurethane (WPU) (FR-WPU) were characterized via31P, 1H NMR and FT-IR. Thermogravimetric (TG) analysis showed that HEPCP exhibited excellent thermal stability and produced rich char residue under high temperature compared with the control sample. The Schiff base and cyclotriphosphazene had a synergistic effect on the WPU. Limiting oxygen index (LOI) values of up to 26.7% were recorded; the dripping behavior was simultaneously improved and achieved a V-1 rating in the UL-94 test by incorporating 0.5 wt% phosphorus. In contrast to the pure WPU, the peak heat release rate (pHRR) of the FR-WPU/HEPCP5 decreased by 43.8%. The char residues increased from 0.63% to 6.96%, and scanning electron microscopy (SEM) showed a relatively continuous and membranous substance, with few holes. The results of TGA-FIR, Py-GC/MS and SEM indicated that HEPCP displayed a fire-retardant mechanism in the condensed-phase. In addition, the thermomechanical behaviors and the mechanical properties indicated that both mechanical properties and Tgh increased.
Highlights
Waterborne polyurethane (WPU) is largely employed in textile laminating, wood coatings, adhesives and leather nishing due to its high chemical resistance, superior mechanical properties, excellent exibility and remarkable adhesion.[1,2,3,4] the high ammability of polyurethane materials limit their application in everyday use.[5,6,7] To endow WPU with ame retardant properties, various halogen-free ame retardants have been introduced,[8,9,10,11] among them, phosphorus containing ame retardants have attracted much attention
Characterization of HDPCP, HEPCP and FR-WPU 1H NMR, 31P NMR and Fourier transform infrared (FT-IR) were used to characterize the chemical structures of HDPCP and HEPCP, and the results are shown in Fig. 1 and 2
HEPCP, a novel reactive intumescent re retardant constructed with a Schiff base and cyclotriphosphazene structures, was utilized to prepare WPU
Summary
Waterborne polyurethane (WPU) is largely employed in textile laminating, wood coatings, adhesives and leather nishing due to its high chemical resistance, superior mechanical properties, excellent exibility and remarkable adhesion.[1,2,3,4] the high ammability of polyurethane materials limit their application in everyday use.[5,6,7] To endow WPU with ame retardant properties, various halogen-free ame retardants have been introduced,[8,9,10,11] among them, phosphorus containing ame retardants have attracted much attention. The traditional phosphorus-containing ame retardants scavenge the active radicals OHc or Hc in the gas phase, and facilitate dehydration and carbonization in the condensed phase. Phosphorus-containing ame retardants o en decrease the thermal stability of polymers due the low stability of the P–C bond. A common method used to circumvent this issue is to combine phosphorus with nitrogen to prepare intumescent ame retardants (IFRs).[12,13,14,15] Hexachlorocyclotriphosphazene and its derivatives are widely used phosphorus–nitrogen containing ame retardants with high reactivity and excellent re Schiff base, which is known as azomethine or imine, is made from the condensation reactions of ketones or aldehydes with primary. Owing to the excellent rigidity of azomethines, Schiff base compounds have been seen as effective in improving the thermal properties of polymers.[23,24,25] The azomethine group can facilitate the crosslinking of melt to enhance the antidrip properties. The compound was found to promote the formation of an intumescent coating without extra acid sources or synergists, though the total heat release (THR)
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