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Influence of hot water extraction on the physical and mechanical behavior of OSB

Published: Dec 1, 2008

Author(s): , , ,

Abstract:

This study evaluated the influence of hot water extraction on hemicellulose removal, the concomitant change in wood properties, and finally production of oriented strandboard (OSB) from the modified wood. Three red maple (Acer rubrum L.) trees were felled, debarked, and their butt logs used to produce strands of 4-in length with a target thickness of either 0.025 inches,0.035 inches, and 0.045 inches. Two hot water extraction procedures (320 °F, 90 psig) of 45 and 90 minutes duration (plus 50 minutes of preheating) were used, resulting in an average weight loss of 16.4 and 17.2 percent, respectively. Weight loss was significantly influenced by extraction time (p = 0.0011) and tree source (p = 0.0001) while the influence of strand thickness was not statistically significant (p = 0.1026). One OSB panel (17.6 inches by 12.4 inches by 0.5 inches) was manufactured for each of the 27 material combinations (2 extraction conditions and unextracted control, 3 trees, and 3 strand thickness). Panels were blended individually with a resin load of 3.2 percent pMDI resin, no wax, and an average density of 41.8 pcf (test volume basis). Physical and mechanical properties were determined following ASTM D1037–06 A procedures. Water absorption by OSB produced from both extraction treatments was significantly higher than the control for both 2 and 24 hours immersion while the thickness swell of panels from extracted material was slightly improved after 24 hours. The modulus of rupture (MOR) was not statistically significantly different between the control (5,966 psi) and the 45 minutes of extraction time (6,162 psi) panels, while the 90 minutes extraction time was significantly lower (4,093 psi). Internal bond strength in dry conditions from both extraction times (29 and 45 psi) were significantly lower than the control (117 psi), and similar results were obtained in wet condition (35 and 15 psi).

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