In order to make a significant long-term impact on reducing resource use and disposal, it is not only important that plastic lumber include recycled content, but also that the lumber product itself be recyclable at the end of its life. Otherwise the material will still eventually end up in an incinerator or landfill. Plastics use overall is increasing, while plastics recycling fails to keep pace with that growth.
Plastic lumber could help close that gap – or it could just provide greenwash incentive for more plastic manufacturing and use. Plastic lumber is currently largely made from first-use applications that are not environmentally sound, like packaging made from virgin plastic.
Unless plastic lumber is itself truly, efficiently recyclable and thus can become part of a closed-loop system of plastic products being indefinitely recycled, a growing plastic lumber market could actually increase plastics production and waste volumes. Some manufacturers claim that their plastic lumber products (including wood-plastic composite lumber) are recyclable.
These claims cannot be easily tested at this time. Although most manufacturers claim that there are few technical barriers to recycling their product, the same could be said for most plastics in use today, or bottles or cans or paper, most of which goes unrecycled in the United States for the lack of infrastructure and the public policy to support it. Even if original manufacturers are able to recycle their products once they come out of service, experience shows that in the absence of legislation or a well-developed infrastructure, this is unlikely to happen.
While plastic lumber has been in use for the last 15 years, it is a durable product and little of it has yet to come out of service. Therefore, there is not enough experience with plastic lumber to determine whether or not it will be feasible to recycle after its service life. A number of plastic lumber manufacturers take back scraps from construction or installation and recycle this material back into their product lines. Some companies producing all-HDPE plastic lumber are even selling scraps to third-party recyclers. However, this is far different than recycling the product once it has reached the end of its service life.
Many lumber manufacturers blend wood fiber with plastics. While this may reduce the use of non-renewable plastics, there are several environmental disadvantages to this formula. As with other composites, the record of plastics recycling to date shows that “contaminating” the polyethylene with another material is likely to limit long-term recycling options. The decision to inextricably combine a biodegradable material with a synthetic material also appears to violate a fundamental principle of sustainable design, which is to segregate synthetic from biological materials.
Furthermore, it is unknown whether or not a plastic lumber product containing biodegradable materials can be technically recycled after 10 or more years of exposure to the elements.