DEGRADATION PRODUCT PATTERN AND MORPHOLOGY CHANGES AS MEANS TO DIFFERENTIATE ABIOTICALLY AND BIOTICALLY AGED DEGRADABLE POLYETHYLENE

Degradation product patterns and morphology changes are demonstrated t o be means by which to differentiate between physical/chemical (abioti c) and biological (biotic) ageing of degradable polymers. Comparison i s made between low-density polyethylene (LDPE), LDPE + 7.7% starch and LDPE + 20% (starch + pro-oxidant). Pro-oxidized samples were subjecte d to aqueous sterile and aqueous biotic (Arthrobacter paraffineus) env ironments at ambient temperatures for 15 months, and thermo-oxidation at 95 degrees C in water. Carboxylic acids were identified in the abio tically degraded samples in contrast to the biotic environment, where assimilation of lower molecular weight products, especially carboxylic acids, had taken place as determined by gas chromatography and gas ch romatography-mass spectrometry. Several hydrocarbons (C-C) were also p resent in these samples. This is in agreement with the proposed biodeg radation mechanism of LDPE. The morphology changes, as monitored by X- ray diffraction (XRD) and scanning electron microscopy, were different in the two environments. A decrease in lamellar thickness (l) was dem onstrated for biotically degraded LDPE + 20% (starch + pro-oxidant), w hile the corresponding abiotically aged samples showed a constant or i ncreased value of l. The crystallinity (XRD-w(c)) for samples aged at ambient temperature showed that prolonged exposure to A. paraffineus r esulted in decreasing value of w(c). In the accelerated environment, h owever, a constant increase in XRD-wc was monitored. The principal dif ference between abiotic and biotic degradation of polymers is that mic ro-organisms use polymers to gain energy. This is manifested as differ ent degradation product patterns (reflecting degradation mechanisms) a nd a decreasing value of crystallinity and lamellar thickness with tim e. The abiotic degradation breaks bonds and releases degradation produ cts, leaving the remaining polymer rearranged with a higher degree of order.