A comparative study on the artificial UV and natural ageing of beeswax and Chinese wax and influence of wax finishing on the ageing of Chinese Ash (Fraxinus mandshurica) wood surfaces

Abstract

This study investigated and compared the behaviour of two types of natural waxes, beeswax and Chinese wax, by means of two different ageing tests: an artificial accelerated ageing test using UV light and a simulated natural ageing test (indoors conditions) based on the action of natural, window-filtered light. The same tests were employed to evaluate the influence of wax finishing on the ageing behaviour of Chinese Ash (Fraxinus mandshurica) wood surfaces. Ageing effects were evaluated by direct and microscopic observation, colour measurements in the CIELab system and FTIR investigations. The results yielded by both accelerated UV ageing (72 h) and simulated indoors natural ageing (6 months) indicate that the waxes under analysis here are materials with a good ageing resistance. FTIR investigation revealed only minor chemical changes following ageing, more evident with beeswax than with Chinese wax. Finishing Chinese Ash wood surfaces with the two types of waxes influenced their ageing behaviour in terms of colour and surface chemistry changes. For both UV and natural ageing the maximum colour differences occurred for the samples finished with Chinese wax. The colour differences ΔE after 72 h accelerated UV ageing were in all the cases higher than those occurring after 6 months of indoors simulated natural ageing. Acceleration indexes for UV exposure compared to exposure to natural window-filtered sunlight, of about 40X-60X, were calculated. Both UV accelerated ageing and natural simulated ageing resulted in significant surface chemistry changes for the unfinished Chinese ash wood samples, consisting mostly in lignin degradation and formation of carbonyl containing chromophores. FTIR investigation of wax finish wood samples revealed only very minor chemical changes of the top wax layers, although chemical changes occurring beneath the coating layer on the wood surface are highly probable. Overall, the experiments presented in this paper indicate that Chinese wax seems slightly more resistant to ageing than beeswax.