woodfiber plastic materials

Several reasons may be involved in making woodfiber plastic materials more abrasive to knives than solid wood. One is the issue of impurities. Since all of these products are made from recycled wood and most of them are made using recycled plastic (mainly HDPE), contamination of these materials cannot be completely prevented. Contamination  wood plastic composite product could explain a part of the difference between, for example, the wear observed with the ChoiceDek (NW after 125 feet of cutting 65.6 µm) and the Fiberon (NW 25.0 µm) material. To our knowledge, ChoiceDek uses post-consumer recycled plastic, whereas Fiberon is made from virgin HDPE. However, this would still leave the difference in wear between, for example, ChoiceDek and Trex (NW 25.4 µm), both of which are made from recycled, post-consumer plastic.

Also, contamination does not explain the differences in wear observed between the woodfiber plastic materials and solid wood. The smallest difference observed between these two materials was with the Fiberon material. Still, Fiberon’s NW was with 25.0 µm more than double the one measured for white pine (NW 10.4 µm) after 125 feet of cutting. One explanation for this phenomenon could be that the pigments used to color the composite material, which are often made from minerals, have a negative effect on knife sharpness. Other reasons such as, for example, cutting speed, knife material composition, or the appropriate rake angle, could also play an important role. The surface roughness of the wood plastic floor materials was lower or similar to the one of the solid wood control sample (white pine). Fiberon had, with Rqs of 139, 90, and 60 µin. across the surface, and lengthwise at the border and in the center, respectively, the smoothest surface of all specimens tested (Table 3).

ChoiceDek, on the other hand, had, with the exception of lengthwise in the center, the roughest surface with Rqs of 308, 153, and 209 µin. across the surface, and lengthwise at the border and in the center. Smartdeck, whose surface roughness in the center was larger than the one for ChoiceDek, had values of 275, 193, and 251 µin. for the same measurement points. In comparison, the control sample's (white pine) values for the same measurements were 188, 99, and 88 µin. This data shows that woodfiber plastic composite surfaces, although rougher than the ones of properly cut solid wood, seem to be rather smooth after cutting. The high roughness values of ChoiceDek are no surprise, given the higher wear that this material causes on the tool.

Besides the size and immersion of the wood particles mixed with the plastic, a potential reason for the rougher surface of the composites could be the moisture content uptake of the woodfibers freshly cut by the knife. Since these fibers are dried below the ambient equilibrium moisture content prior to being encapsulated in the plastic, it would appear that these fibers, when again coming into contact with the environment, would take up moisture and thus swell. This, of course, would lead to a rougher surface. Conclusions There are differences in respect to tool wear and surface roughness between the five different woodfiber plastic products tested. Differences also exist when these materials are compared to solid wood. Knife wear was smallest when cutting the solid wood (white pine) control sample. Of the five wpc products, Fiberon was the one wearing the knife the least, whereas ChoiceDek wore the knife the most. Reasons for these differences could be possible contaminants contained in some of the woodfiber plastic composites and the pigments used for coloring. However, specific analyses of these observations have yet to be conducted.