Flammability Characteristics and Performance of Halogen-Free Flame-Retarded Polyoxymethylene Based on Phosphorus-Nitrogen Synergistic Effects

The flammability characteristics and thermal stability of a novel halogen-free flame-retardant compounding system based on polyoxymethylene (POM) were studied, and a very effective flame retarding formulation for POM was developed from a combination of ammonium polyphosphate (APP), melamine cyanurate (MC), novolak, and dipentaerythritol. The decomposition behavior of POM compounds was evaluated by thermogravimetric analysis. The compound shows optimal flame retardancy with a limiting oxygen index of 52.8 and flammability rating of UL94 V-0, when 27 wt % APP, 9 wt % MC, 4 wt % novolak, and 4 wt % dipentaerythritol are simultaneously incorporated into POM. The presence of novolak and dipentaerythritol as char-forming agents results in a dense and compact multicellular char residue for the test bar after combustion, while Fourier transform infrared spectra confirm a characteristic phosphorous- and carbon-rich char resulting from the APP/MC formulation. The pyrolysis gas chromatography/mass spectrometry analysis indicates that highly flammable formaldehyde gas, the main pyrolysis product of POM, is annihilated by amide derivatives produced by the pyrolysis of MC, imparting better flame retardancy. The comprehensive flame-retardant mechanisms based on phosphorus nitrogen synergism promote the high flame retardancy of POM to reach the nonflammability of V-0 rating. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 611-622, 2010