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The effect of fines on oriented strandboard bending properties Cafferata, Alicia

Abstract

The presence of fines in oriented strandboard (OSB) can influence the profitability of a mill. Because the disposal of fines can be costly, mill managers may be compelled to incorporate them into the final product. However, the presence of fines in the product diminishes certain technical attributes such as the bending properties. The objective of this study was to assess the effect of the proportion and location of fines on the modulus of elasticity (MOE) and modulus of rupture (MOR) of oriented strandboard. The research program employed a 91 cm by 91 cm (3 ft by 3 ft) electrically heated laboratory press to produce OSB in two phases: alternating layers of strands and fines (a "homogeneous" distribution); and, fines in the core only (sandwich construction with multiple layers of strands adjacent to one another and only one layer of fines). In both cases, the strands were oriented parallel to one another and the parallel orientation was confirmed using an imaging system (SAM-Weyerhaeuser). The homogeneous distribution results showed that for a constant density: • MOE decreased in linear fashion with an increase in fines as confirmed with literature data; • MOR decreased linearly with increased fines; • The mechanical properties are amenable to modeling using the Rule of Mixtures. The sandwich construction results showed that for a constant density: • MOE (in the plank orientation) did not decrease in a linear fashion with an increase in fines; • MOE/MOR (in the joist orientation) decreased linearly with an increase in fines; • The joist properties are amenable to modeling using the Rule of Mixtures; • The plank MOE can be modeled using simple beam bending theory; • The MOR (plank orientation) cannot be modeled using either Rule of Mixtures or simple beam bending theory • Failure mode in the plank orientation can be predicted (for these specific conditions); i.e., boards between 10 to 45% fines typically fail in shear • The end use of the panel (i.e. as a joist or as a plank) affects the degree to which fines affect the bending properties This work suggests that it may be possible to increase the use of fines in sheathing products while maintaining individual mill strength requirements if the fines are limited to the middle of the panel. The effect of fines on the pressing cycle and the effect of adding fines to the center of the panel on other strength properties such as the nail holding or the shear strength properties are beyond the scope of this work and have yet to be explored.

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