Moisture Content Effect on Tensile Properties of Individual Douglas-Fir Latewood Tracheids
Keywords:<i>Pseudotsuga menziesii</i>, tension tests, fiber strength, stress-strain curve
AbstractA testing system was developed to determine tensile properties of single wood fibers under precisely controlled relative humidity conditions. Individual delignified Douglas-fir summer-wood tracheids were tested axially in tension at moisture contents of 0, 6, 12, 18% and in a water-soaked condition. Load-elongation curves were predominantly linear to failure and curve shape was unaffected by moisture content, implying that stresses in tracheids were borne primarily by a structural framework with a high degree of crystallinity. Moisture content significantly affected tracheid tensile properties. Tracheids tested wet exhibited the lowest strength and elasticity. The overall relationship between strength properties and moisture was curvilinear with maxima in tensile strength and modulus of elasticity at about 12 and 6% moisture content, respectively. Tensile strengths obtained were higher than published values for other cellulosic fibers. Maximum internal stresses on the cellulosic framework of tracheids were considered to approach those theoretically calculated for cellulose chain seission, suggesting highly crystalline microfibrils containing an extended-chain crystal lattice structure.
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