THERMAL AGEING OF CELLULOSE WITH NATURAL AND SYNTHETIC ANTIOXIDANTS UNDER VARIOUS CONDITIONS.

Studies were undertaken of the influence of both the natural stabilizers present in wood (lignin and extractives) and synthetic antioxidants on the thermal ageing of cellulose. Among the synthetic antioxidants, butylated hydroxytoluene, propyl gallate and 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline (ethoxyquin) were examined. In order to study the thermal ageing of cellulose with antioxidants, accelerated ageing tests were carried out under various conditions. The ageing tests were performed at a temperature of 95 °C in an air and nitrogen atmosphere in anhydrous conditions and at 65% relative air humidity. To study the degradation of the cellulose, size exclusion chromatography was used. The results revealed that ethoxyquin was the best synthetic stabilizer. In addition, butylated hydroxytoluene had stabilizing properties and slowed down the depolymerisation of the cellulose. In turn, the behaviour of the propyl gallate under elevated temperature conditions was the most interesting. This antioxidant, relating to the cellulose degradation process, showed inhibitory as well as catalytic properties under specific conditions. In the ageing conditions applied, the smallest decrease was observed in the average molar mass of the cellulose in the wood without extractives. The results indicate that in this case, lignin played a very important role as a hidden antioxidant. In the presence of the lignin, oxidative the cellulose depolymerisation process proceeded more slowly than with the participation of synthetic antioxidants. The extractives, under elevated temperature conditions, did not show stabilizing properties, and furthermore, they accelerated the degradation of the cellulose. [ABSTRACT FROM AUTHOR]