Evaluation of proposed test methods to determine decay resistance of natural fiber plastic compounds

Methodologies for assessing the decay susceptibility of natural fiber plastic composite extrusions were evaluated. The susceptibility to fungal decay of five natural fibers (hemp, flax, rice husks, softwood and hardwood flour) in a malt extract agar medium was assessed based on weight loss of the isolated flour. The weight and compressive strength changes of a rice husk/high-density polyethylene composite were measured after 16 weeks of exposure in a soil block test as suggested by a proposed technical guide for evaluation report preparation. Composite samples along with control blocks of spruce (Picea glauca), western red cedar (Thuja plicata), and red maple (Acer rubrum) were exposed to several species of fungi including agricultural, brown-rot, and white-rot fungi. All of the types of flour were degraded by brown- and white-rot fungi with weight losses between 6.2 percent and 66 percent, whereas the agricultural fungi caused decay of the non-wood fibers only, with weight losses up to 35 percent. Weight losses up to 11 percent of the fiber component of a natural fiber plastic composite were measured after 16 weeks of fungal decay exposure. However, the compressive strength of the composite did not change and no correlation was found between the weight loss and this property.

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