To evaluate how the formulation components affect extrusion prod­uct performance, a fractional factorial design was created for statistical analysis. The fractional design is shown for the Neat and treated straw composite testing in Table 2. As already noted, Degrade1 and Degrade2 represent wheat straw that was inoculated with P. ostreatus and incubated for 6 and 12 wk, respectively. The values in Table 2 are percentages required to make a 2-kg batch for extrusion.

Composite formulations were prepared as follows: The straw samples as received from INEEL were ground to 0.69 mm in a hammer mill and oven dried to 1.1% moisture. The dried straw samples were then blended with various amounts of high-density polyethylene (HDPE), lubricants, and maleated polyethylene blends (MAPE) (see Table 2). The mixed formula­tions were then extruded with a 35-mm Cincinnati Milacron® Model CMT 35 counterrotating conical twin screw extruder (Cincinnati Milacron, Batavia, OH), which produced a 9.525 x 38.1 mm2 solid cross-section. Flex­ural strength, density, and water sorption were measured for the extruded samples according to ASTM Standard Methods (13,14).