Though WPC’s can divert recyclable wood and plastic from the landfill and into durable building applications, additional environmental benefit could be obtained if the composites themselves are recycled at the end of their useful life. The thermoplastic nature of the waste materials used in WPCs facilitates makes this possible (Boeglin 1997). However, there are a number of challenges that may impede recycling.
“Useful service life” varies depending on product and the perception of the user. For example, some studies suggest that the normal US. decking material (i.e., the deck surface, not the deck substructure) is replaced in about 8-1 4 years because of non-durability related reasons (Smith 2001). The most often given reason was that the checking and splitting of the deck surface due to cyclic wetting and drying and poor maintenance caused significant enough aesthetic degrade that the user was no longer satisfied with its appearance and wanted to replace it. Another prime reason was related to remodeling or a change in the deck use-pattern or design resulting in deck-surface replacement.
If recycling of the base polymer used in WPC results in WPC products having less UV- or biological- resistance or reduced structural capacities when compared to virgin polymer-based WPC, then user acceptance will lessen. Some of the primary advantages of WPC’s over treated-wood decking are its reduced maintenance and the fact that it does not check and split resulting in reduced aesthetic- appeal. Manufacturers of Recycled WPC must keep these issues in mind when further developing their WPC products or when modifying their processing procedures. This will become an even greater issue as WPC’s enter markets requiring even greater durability.
Youngquist et al. examined the effect of virgin versus recycled raw materials on the properties of WPCs. There was virtually no difference in the performance values of test panels on either mechanical or physical property tests when virgin and recycled polyethylene terepthalate were compared, or when hemlock fiber was compared with demolition wood fiber (Youngquist 1993). Further, demolition wood fiber performed as well as panels made from virgin hemlock fiber and compression molded WPC’s containing recycled high density polyethylene from milk bottles were equivalent to WPC’s containing virgin high density polyethylene. They found that using fiber from old newspapers as reinforcing agent provided measurable property advantages over wood flour, which is currently the most commonly used filler in commercial composites. Also, these recycled newsprint WPC systems could themselves be recycled (re-extruded and injection molded) numerous times with little or no apparent loss in mechanical properties.