Exterior Decay of Wood-Plastic Composite Boards: Characterization and Magnetic Resonance Imaging
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Forest Products Journal
Magnetic resonance imaging (MRI) was used to evaluate free water content and distribution in wood-plastic composite (WPC) materials decayed during exterior exposure near Hilo, Hawaii. Two segments of the same board blend were selected from 6 commercial decking boards that had fungal fruiting bodies. One of the two board segments was exposed in sun, the other in shadow. Whole board segments were imaged using a clinical MRI unit, and cross-section segments were inspected using scanning electron microscopy (SEM). Samples were cut from the cross section of the board to determine material density as an indicator of the degree of decay advancement. Presence of water detected by MRI was correlated to progression of decay in the WPC board segments and to water distribution measured before decay was observed. Both board segments showed a significant amount of decay, where SEM images showed the presence of fungal hyphae inside the boards, particularly the segment exposed in shadow. MRI showed that the expected pattern of free water distribution—a moisture gradient from greatest on the outside of the board to least inside—was not evident in the decayed board evaluated in this study. On the contrary, a reverse moisture gradient was observed in some areas where there appeared to be a relatively high concentration of free water in the center of the board. This could be explained by moisture transfer of fungal mycelia into the core of the board and the generation of water as decay fungi metabolize wood.
Keywordsmagnetic resonance imaging MRI scanning electron microscopy SEM woodplastic composites WPC moisture decay fungi density
Ibach, Rebecca; Sun, Grace; Gnatowski, Marek; Glaeser, Jessie; Leung, Mathew; Haight, John. 2016. Exterior decay of wood-plastic composite boards: characterization and magnetic resonance imaging. Forest Products Journal. 66(1/2): 4-17. https://doi.org/10.13073/FPJ-D-15-00011.