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The effect of ultrastructure and moisture content on mechanical parameters of pine wood (Pinus sylvestris L.) upon tensile stress along the grains

Selected mechanical parameters of earlywood and latewood from Pinus sylvestris subjected to tensile stress were measured as a function of moisture content. Microfibril angles (MFAs) to the longitudinal axis of the cell in the S2 layer of tangent cell walls in the same wood samples were also measured. | Turkish Journal of Agriculture and Forestry http://journals.tubitak.gov.tr/agriculture/ Research Article Turk J Agric For (2014) 38: 413-419 © TÜBİTAK doi:10.3906/tar-1306-81 The effect of ultrastructure and moisture content on mechanical parameters of pine wood (Pinus sylvestris L.) upon tensile stress along the grains Edward ROSZYK* Department of Wood Science, Faculty of Wood Technology, Poznań University of Life Sciences, Poznań, Poland Received: 26.06.2013 Accepted: 27.10.2013 Published Online: 14.03.2014 Printed: 11.04.2014 Abstract: Selected mechanical parameters of earlywood and latewood from Pinus sylvestris subjected to tensile stress were measured as a function of moisture content. Microfibril angles (MFAs) to the longitudinal axis of the cell in the S2 layer of tangent cell walls in the same wood samples were also measured. The tensile strength and modulus of elasticity of earlywood were practically independent of its moisture content, while the same parameters of latewood significantly decreased as its moisture content increased in the hygroscopic range. For earlywood, the strain at break was greater the higher its moisture content. For latewood, no notable effect of moisture content on the strain at break was observed. The influence of moisture content on mechanical parameters measured upon tensile stress was proven to be determined by mean MFA values. This influence was the most pronounced for low MFA values, up to about 13°, while for mean MFAs from 13° to 22° the tensile strength and modulus of elasticity were practically constant and independent of moisture content. Key words: Earlywood, latewood, microfibril angle, moisture content, pine wood, tensile stress 1. Introduction It has been known for a long time that the effect of moisture on mechanical parameters of wood during tensile stress is different for early and latewood. As follows from the studies from the 1960s on pine wood (Pinus taeda L.), an increase in the moisture content from .