Improving the Technical Characteristics of Untreated and Heat-Treated Ayous Wood against Accelerating Ageing by Testing Two Application Modalities of an Innovative Polyurethane Coating for Outdoor Uses

Abstract

This paper presents the results of tests of a new mono-component polyurethane coating for wood with the aim of evaluating its effect on Ayous (Triplochiton scleroxylon K. Schum), which is a wood species used in Europe for various applications, especially outdoors, after being heat treated. The coating was tested on both untreated and thermally treated samples, as the latter procedure is commonly used in the wood industry to modify the material’s characteristics. Moreover, two kinds of coating application were tested: coatings applied via brushing and coatings applied via spraying; in this test, we also verified the most suitable and effective modality. Samples were investigated using the following techniques: colour measurement, roughness mapping, contact angle measurement, surface micro-hardness and the wearing test; these techniques were applied before and after a period of artificial ageing under simulated solar irradiation. Upon synthesizing the main results, we identified the following results: (i) the polyurethane coating reduced the colour variation as a result of artificial aging of the untreated Ayous wood; in contrast, heat-treated wood underwent large colour changes; (ii) the coating acted effectively as a hydrophobic agent on the surface of the wood in each case examined, though even a short aging time altered the initial wettability characteristics; and (iii) the application of the coating caused a decrease in the roughness of both untreated and heat-treated surfaces, though this trend was much more evident in the case of the spray modality of application; however, aging always induced an increase in roughness, which was mainly observed in uncoated wood samples.

Discoloration and Surface Changes in Spruce Wood after Accelerated Aging

“…Wood degradation caused by the effects of various environmental factors is a very intricate and effort-demanding issue that needs a comprehensive approach. For a long time, the research on wood resistance against aging has been oriented on the variability of wood surface structure and properties, on degradation causal agents, on possibilities of how to avoid the degradation, and on the study of a range of factors supposed to influence the aging of wood surfaces [7][8][9][10][11][12][13][14][15]. The results of several works dealing with this problem have been summarized in [1,2].…”

“…This is mainly typical for coniferous wood species displaying differences in density between their early wood and late wood. Changes in wood structure are accompanied by changes in other surface properties [11,15,[26][27][28].…”