Synergistic effect of ammonium polyphosphate and layered double hydroxide on flame retardant properties of poly(vinyl alcohol)

A novel flame retardant system of poly(vinyl alcohol) (PVA) is prepared via using ammonium polyphosphate (APP) and layered double hydroxide (LDH). The flammability of PVA composites containing APP-based LDH at a 15 wt.% global percentage showed that the flame retardancy of all PVA/APP/LDH samples increase with the increase of LDH concentration in the range of 0.1-1.0 wt.%, and reach a LOI value of up to 33 and UL-94 V-0 rating for most composites. Thermo-gravimetric analysis reveals that PVA/APP/LDH samples show higher initial decomposition temperature in comparison with PVA/APP composite. The morphology and structures of residues generated during LOI test were investigated by scanning electronic microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to analyze the composition of the residue formed after thermo-oxidation to support a fundamental analysis for the mechanism of char formation. The test of mechanical properties demonstrated that LDH can enhance tensile strength, Young's modulus and elongation at break of PVA/APP composites.