Drying and oxidative degradation of linseed oil

The drying and oxidative degradation of linseed oil have been investigated through exposition of samples in form of thin films to indoor laboratory conditions, or treated at a constant temperature of 80 degrees C, or with irradiation at wavelengths > 295 mm. Structure and property changes resulted almost independent of the different treatments and were followed by Fourier transform infrared analysis (FTIR), thermogravimetry (TG), differential scanning calorimetry (DSC), insoluble determination and size exclusion chromatography (SEC). The initial phase of drying consists of the autoxidation phenomenon of the unsaturated fatty acid components with the development of extensive cross-linking, together with formation of conjugated unsaturations. The following stage of slow consumption of labile cross-links gives rise to a highly stable network, which contains small amounts of low molecular weight molecules, either formed by fragmentation or still present as unreacted triglycerides. The oxidative degradation of linseed oil consists of the continuation of the hardening process, and only for long periods of artificial ageing, corresponding to years of natural ageing, the oxidation also takes place on the alkylic segments, leading to partial fragmentation of the structure. (C) 1999 Elsevier Science Ltd. All rights reserved.