Microstructural investigation of UV-laser irradiated pine (Pinus silvestris L.)

Abstract

Different surfaces of pre-sanded pine (Pinus silvestris L.), namely radial surfaces, tangential surfaces and cross sections, have been subjected to microstructure examination. UV-laser irradiation with a wavelength of 248 nm and an energy of 350 mJ is used to enhance the microstructure exposure. It has been shown that UV-laser irradiation is a useful and practical method for revealing microstructural details. This is more pronounced on the cross section. Sanding with emery paper finer than 800 mesh can reveal microstructure on the radial surface equivalent to that revealed by UV-laser irradiation. On the radial and tangential surfaces, more earlywood is extracted after UV-laser irradiation, resulting in an uneven surface. Some features such as loose fibres and a rack-gearing-like structure on the radial and tangential surfaces, as well as a loss of radially oriented cell walls on the cross section are observed as a result of the UV-laser treatment. The rack-gearing structure is composed mainly of a sawtooth-like pattern. The length of the sawtooth is in most cases approximately 9 and 19 μm.