Preliminary Investigation Of The Failure Behavior Of Scots Pine Wood Coating Under Artificial Accelerated Ageing

Wood coating can undergo degradation when exposed to the UV and visible light, moisture and oxidation condition, and its decorative and Protective function will be destroyed. Therefore, the issues about the failure time, form, degree and mechanism, prevention and detection of wood coating failure have become the concerns of scientists in wood and painting fields. Presently, plenty of researches on wood coating failure have been reported in abroad, but few researches for wood coating failure forms, mechanisms and prevention were investigated in China. Therefore, research on wood coating failure factors, mechanism and behavior has important scientific significance. Aging test of different substrate coating aging samples was tested by ultraviolet irradiation and xenon-arc radiation two artificial accelerated ageing test in this study. Then, the change of physical characteristics, surface features, differences between different substrate(untreated, ACQ preservative treatment, phenolic resin modified treatment and high-heat treatment) and differences among alkyd resin, polyurethane paint and acrylic paint, and feasibility of wood coating failure by near infrared spectroscopy were detected. This study aims to reveal behavior changes in the process of aging, provide scientific basis for failure mechanism of wood coatings and find rapid and effective method for detection of wood coating failure.Combining with the content above, this research results are as follows:1) The size of all samples are changed with the process changes of the irradiation, spray, freezing cycle and wood of heat treatment shows excellent dimensional stability in the whole aging process whether it is ultraviolet or xenon arc lamp artificial accelerated ageing. A less rate of change can be found in the condition of xenon arc lamp artificial accelerated ageing. Coating color and glossiness of wood which was coated by alkyd resin, is changed with the extension of irradiate time until the seventh cycle, which may be indicated that the failure of coating accelerated at the seventh cycle.2) Compared to the failure behavior among different treated substrates, it can be foumd that heat-treated and phenolic resin treated samples show excellent dimensional stability. Consistent with that of untreated wood, the color difference of the other treated samples gradually increased and it remained stable since the seventh cycle. The change extent of glossness of treated samples were less than that of untreated samples, which indicated that the treatment may influence the change of glossness on the sample surface.3) After the comparison among the different type coatings, it can be found that the dimensional stability of samples coated by alkyd resin exhibit better than the others, which indicated that has the advantages of waterproof property. However, serious changes in color and glossiness can be found in the samples coated by alkyd resin.4) After the study about the feasibilty of the detection of wood coating failure, it can be indicated that the near infrared spectroscopy technology has the potential to predict wood coating in different ageing stages and detect coating failure. Discriminant model about the types of recycle established by NIR spectroscopy data does well. Correction of correlation coefficient were higher than 0.9, and calibration standard deviation is less than 0.15. The accuracy using near infrared spectroscopy to predict unknown circulation type samples is above 80% and even reach 100% after freezing stage.5) According to the regular visual observation of the surface of samples at different ageing time in the UV irradiation artificial accelerated ageing, it could be conclued that ageing-resistant performance of coated samples are better than that of uncoated samples. As for the coated samples, the color of samples surface gradually become grey and dark in the process of ageing, and the glossness is progressively lower. In the early stage of ageing, samples surface do not appear blistering, peeling, and chalking, and cracking. As further extension of aging, sample surface become more and more deterioration, and the failure phenomenon begin to appear.