Wood-plastic composites (WPCs) have slower moisture sorption than solid wood, but over time moisture can impact the strength, stiffness, and decay of the composite. These changes will become increasingly important if WPCs are used in more challenging environments such as in ground-contact applications. There are several options for mitigating the moisture sorption of WPCs. A coupling agent can be added to potentially improve the wetting and dispersion of the wood flour and improve its adhesion with the plastic matrix. In previous investigations, the use of a coupling agent has been shown to further slow, though not stop, moisture intrusion in WPCs. Alternatively, the wood flour can be chemically modified to make the wood itself more hydrophobic and, therefore, reduce the driving force for moisture intrusion rather than just slow it.
While the effects of such approaches to moisture reduction have been investigated somewhat in the laboratory setting, field exposure is ultimately needed to verify the overall long-term durability of such WPCs, which includes the potentially synergistic effects of exposure to sunlight, moisture, wind, temperature fluctuations, freeze/thaw, wet/dry cycling, termites, mold and decay fungi. WPCs containing either a coupling agent or chemically modified wood flour were fabricated. These modified WPCs and a control were installed both above-ground and in-ground in Saucier, Mississippi and Madison, Wisconsin and observations (e.g., appearance, thickness swell, and fungal attack) were recorded over a 12 year time period. Results will be discussed, as well as correlation between laboratory and field measurements.
Ibach, Rebecca E.; Clemons, Craig M. 2017. Long term durability of wood-plastic composites made with chemically modified wood. In: Advancements in fiber-polymer composites conference proceedings. 16-18 May 2017. Madison, WI: 1-17 pp.