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Use of confocal profilometry to quantify erosion of wood and screen chemicals for their ability to photostabilize wood Liu, Chunling


Optical confocal profilometry is a new technology for characterizing the surfaces of materials. In this thesis, I hypothesize that confocal profilometry will be able to more accurately measure the erosion of wood during weathering than optical microscopy. Confocal profilometry may be able to screen photoprotective chemicals, and in this thesis I use confocal profilometry to test the hypothesis that PF resin can photostabilize wood. Confocal profilometry was used to measure the erosion of untreated western red cedar wood exposed to natural and artificial weathering. The erosion of western red cedar specimens increased with time. Specimens exposed in a xenon-arc weatherometer eroded significantly faster than specimens exposed in a QUV weatherometer. The profilometer was able to measure the erosion of specimens exposed for only 100 h in a xenon-arc weatherometer. There was a positive correlation between the size of the area of wood exposed to weathering and the erosion of wood during artificial and natural weathering. The erosion rate was about 2-20 times faster during artificial weathering compared to natural weathering. Profilometry was able to discern differences in the erosion of untreated specimens and specimens treated with PF resin. However, profilometry was not able to detect differences in erosion of specimens treated with different PF resin formulations. In contrast, the thin strip technique, which measured weight and tensile strength losses of treated wood veneers exposed to weathering, was able to discern differences between formulations. I conclude from measurements on western red cedar that confocal profilometry is a more accurate and less labor-intensive way of measuring the erosion of wood during weathering than optical microscopy. The exposure time required to produce erosion that can be measured using the profilometer is much less than that needed when using an optical microscope. But specimens need to be flat, free of checks and have eroded areas that are distinct from unweathered areas. Low molecular weight PF resin shows great promise as a treatment for photostabilizing wood.

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