Towards the development of accelerated methods for assessing the durability of wood plastic composites

While wood plastic composites have gained an increasingly large share of the market for decks and other outdoor structures, there are many questions about the long-term potential for biodeterioration of these materials. While the plastic does appear to retard moisture uptake, thereby slowing the rate of degradation, a number of laboratory and field studies have found that fungal attack can occur. One approach to addressing this issue is to alter the WPC by either adding biocides or altering structure to retard fungal attack; however, assessing the durability of these new materials poses a challenge because of the lack of standard methods for accelerating the decay. In this study, we explored the use of agar, soil, vermiculite, and liquid media for accelerating the decay rates of pine and maple based WPCs under laboratory conditions. Agar and soil proved to be the most effective substrates, although the agar systems were far easier to prepare, but the degree of fungal attack was a function of moisture uptake. Thicker samples, which tended to absorb moisture more slowly, tended to have sharply lower weight losses. Maple WPCs tended to be more susceptible to fungal attack than those made with pine, suggesting mat altering the wood source could be one simple method for enhancing durability without supplemental biocides. Copyright � 2007 by ASTM International