Thermal-oxidative induced degradation behaviour of polyoxymethylene (POM) copolymer detected by TGA/MS

The influence of reprocessing and thermooxidative ageing on the degradation behaviour of a commercial poly(oxymethylene) (POM) copolymer was studied by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. Five heating rates were used to evaluate activation energies at several degrees of conversion. TGA-measurements were accompanied by simultaneous monitoring of the evolved gases with a mass spectrometer (MS) coupled to the TGA-furnace outlet. The mass spectra showed that the main degradation product was formaldehyde and that in air further formation of water was detectable. In nitrogen atmosphere aged specimens emitted small amounts of carbon dioxide at the beginning of the mass loss. The activation energy for low degrees of conversion (<5%) increased in air and in nitrogen as a function of the conversion. For higher conversions a difference with progressing degradation emerged: in air, activation energies lowered continuously while they remained nearly constant under nitrogen.