Wood-Plastic composite instead of HDPE
Polyethylene (HdPe and LdPe)
High-density polyethylene plastic (HDPE), frequently used to make milk and water jugs and shampoo containers, is one of the most highly recycled plastics. In 2001, the recycling level for high-density polyethylene (HDPE) milk and water bottles was 28.4%. An average 300-pound picnic table made from recycled HDPE utilizes between 1,890 and 2,700 milk jugs. Low-density polyethylene (LDPE) is used to package cream cheese, butter, spreads, and other dairy products. In addition, many plastic bags are made from LDPE.
Like all fossil-fuel-based plastics, polyethylene manufacturing is an energy-intensive process that utilizes numerous toxic and hazardous materials. Emissions of polyethylene manufacturing facilities include a wide range of persistent, bioaccumulative, and toxic outputs. However, both HDPE and LDPE lack additional toxic inputs associated with the two other plastics used in plastic lumber, polystyrene, and PVC. This in turn results in fewer toxic hazards throughout the full production cycle, as well as during routine use and at the end of the product’s service life. Fewer additives and a more uniform composition also help account for the relatively high recycling rate of HDPE. These properties also suggest that recycled polyethylene products intrinsically have high recycling potential.
To convert low-value wood resources into high-value products, researchers at the Forest Products Laboratory (FPL) are combining wood fiber with thermoplastic resin, resulting in wood plastic composites (WPCs). To optimize composite performance, researchers are exploring material options, investigating processing effects, and improving engineering performance and durability.
Thermoplastic resins, such as polypropylene, polyethylene, polystyrene, and polyvinyl chloride, soften when heated and harden when cooled. This property allows other materials, such as wood, to be mixed with the plastic to form a composite product. The resulting WPCs can be easily processed into various shapes and can be recycled.
WPCs are typically made using 30% to 60% wood filler or reinforcements. Most composites research at FPL has used wood flour as a filler in plastics. Wood flour is made commercially by grinding postindustrial material, such as planer shavings, chips, and sawdust, into a fine, flour-like consistency. Wood fiber, although more difficult to process than wood flour, can lead to superior composite properties and act more as a reinforcement than as a filler. Wood fiber is available from both virgin and recycled sources. Recycled sources include pallets, demolition lumber, and old newsprint. Wood from small-diameter trees and underutilized species can also be used.