Introduction to Plastic Lumber

While Recycled Plastic Lumber as a building material is still a very new material relative to the long history of natural lumber, recycled plastic lumber has been in manufactured since the early 1980s.  It is differentiated by the materials used in it's construction, and can be either 100%  plastic, or a composite of plastic and other materials.

100% Plastic lumber is usually made from relatively clean recovered plastics such as post-consumer high density polyethylene (HDPE), but linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) and Polypropylene (PP) can be used as well.  More rarely PVC is also used. These plastic feed stocks are derived from such raw materials as post-consumer milk jugs, soda bottles, grocery bags, plastic wrap, bubble rap, detergent bottles, and water bottles, and other used plastic commodities.

When Composite plastic lumber is manufactured, which is plastic mixed with fiber materials (saw dust, rice hulls other misc. fibers), the fiber material is prepared by grinding and drying it,  then blending the fiber with plastic. A typical mixture is 50/50. It is recommended that this blend be compounded by processing through an extruder to achieve an optimum mix and to thoroughly dry it. The compounding extruder feeds into a pelletizer which produces uniform pellets. The colorant can be added either prior to the compounding or at the hopper when the plastic lumber board is made.

Both recycled plastic lumber and recycled fiber/ plastic composite lumber are either molded by use of flow molding or continuously extruded by use into standard lumber forms.