Influence of coloration on initial material properties and on thermooxidative ageing of a polyoxymethylene copolymer

Polyoxymethylene (POM) is a semicrystalline thermoplast of white natural colour. To meet the demands in other colours the material has to be coloured. Thus, the aim of the present study was to elaborate the influence of coloration both on the initial material properties and on the thermooxidative degradation behaviour of a POM-copolymer (POM-C). POM material with two different stabilising systems was used. A master batch on a POM substrate was added in a mass fraction of 3% to commercial distributed POM material to obtain the desired coloration. The tested specimens were injection moulded loudspeaker grills. Material properties were investigated on non-coloured and coloured samples before and after artificial ageing. The tests carried out were colour measurement, MVR (melt volume rate), mechanical testing (perforation resistance), DSC (differential scanning calorimetry) and TGA/MS (thermogravimetric analysis coupled with massspectrometry). Artificial ageing was realised by means of an oven storage at 140 C for a duration up to 8 weeks to investigate the thermooxidative induced changes in the degradation behaviour. Test results showed first that the addition of a colorant had an influence on the initial properties and second that the degradation behaviour of the aged specimens depended not only on the presence of the colorant but also on the stabilising system of the material