Dynamic mechanical characterization of mechanosorptive effects in wood and paper

• Published in: European journal of wood and wood products Vol. 54; no. 4; pp. 263 - 271
• Main Authors: EBRAHIMZADEH, P. R, KUBAT, J, MCQUEEN, D. H
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01.07.1996
• Subjects: Applied sciences; Exact sciences and technology; Paper, paperboard, non wovens; Polymer industry, paints, wood; Properties and testing; Wood; Wood. Paper. Non wovens; Sorption; Wood; Dynamic mechanical properties; Paper; Softwood; Experimental study; Veneers; Physicochemical properties
• ISSN: 0018-3768; 1436-736X; 1436-736X
• DOI: 10.1007/s001070050179

Dynamic mechanical studies in dual cantilever and tensile stretching mode of Scots pine veneer, birch veneer and paper under stepwise humidity changes between 5% and 85% relative humidity are reported. The loss tangent (tan delta) shows a transient peak every time the relative humidity of the surrounding atmosphere is changed. In the bending mode a clamping arrangement that is freely movable in the longitudinal direction gives more distinct damping peaks than does a static fixture. There is a close relationship between the rate of sorption/desorption and the shape of the tan delta peak. In response to reduction of the rate of humidity change the damping transients slowly disappear. They also diminish in strength as the temperature is raised toward 60 degrees C. Their strengths increase as the measuring frequency is lowered toward 0.01 Hz. Also, when the samples are highly compressed or prestressed with static loads the peak heights are greatly reduced. The tans peaks become less distinct and eventually disappear when the amplitude of the vibration increases. Long time testing results in significant changes in the shapes of the tan delta versus time data. A working hypothesis is that these phenomena are closely related to molecular diffusion of water through the sample material. Simple estimates show that the relaxation time for a diffusion related process should be of the order of a minute.