Recycled Plastic Lumber
- Common Uses
- Economic Considerations
- Government Procurement
- Research and Development
What Is Recycled Plastic Lumber?
Recycled plastic lumber (RPL) is a wood-like product made from recovered plastic or recovered plastic mixed with other materials, which can be used as a substitute for concrete, wood, and metals.
Can RPL Be Substituted for Wood?
At the present time, RPL has only been used in a few structural applications. However, it is an excellent material for decking, landscaping, and recreational equipment.
Common Uses of RPL
- Agricultural. Vine stakes, ranch fences, gates, animal stalls.
- Civil Engineering. Retaining walls, sound barriers, car stops, walkways, railings.
- Gardening. Fences, flower pots, compost bins.
- Industrial. Flooring, pallets, truck flooring.
- Recreational. Park benches, picnic tables, playground equipment, informational kiosks, wetlands walkways, decking, park bridges, flower bed borders.
- Transportation. Noise barriers, sign posts, guard rail offset blocks, car stops, speed bumps.
- Marine Engineering. Piers, pilings, seawalls, and bulkheads, boat docks.
- Other. Roofing shingles or "cedar shakes."
Types of RPL
High Density Polyethylene (HDPE) RPL
This type of RPL consists of up to 95 percent of HDPE (The same material used to make plastic milk jugs).
- Advantages. Available in many colors. Well suited for decking and landscape applications.
- Disadvantages. Much lower stiffness than wood. Also, material sorting increases labor costs. This cost can be reduced by using automated sorting technology instead of hand sorting.
Commingled RPL is made from mixed recovered thermoplastic (plastic that can be remelted and remolded). Primarily consisting of 80-90 percent polyethylene (PE).
- Advantages. Lowest cost because sorting is reduced or eliminated. Also well suited for decking and landscape applications.
- Disadvantages. Only earth tone colors available in addition to having a stiffness much lower than wood.
Wood-filled RPL is made of plastic mixed with sawdust or other recycled fiber, usually a mix of 50 percent polyethylene (primarily low-density polyethylene or LDPE) and 50 percent sawdust or other recycled fiber.
- Advantages. Fewest voids, best traction, best paintability, greater surface roughness.
- Disadvantages. Can absorb moisture, may have poor impact strength under low temperatures, may not be completely insect resistant, may become discolored in outdoor applications, may contain metal contaminants, much lower stiffness and strength than wood, can degrade, poor flexibility.
Fiber-reinforced RPL consists of plastic mixed with chopped or continuous strands of glass fiber.
- Advantages. Stiffer than other plastic lumber. Well suited for support structures.
- Disadvantages. Less flexible than other plastic lumber, and may irritate skin.
Other Combinations of Materials
Many other combinations of materials are possible, each with different properties, costs and applications. They should be investigated individually to determine the best product for its intended use. Some other formulations include:
- Glass-reinforced plastic lumber.
- Rubber-plastic lumber.
- Mixed plastics and peanut shells.
- Coextruded steel liner (e.g., metal pipe).
- Coextruded steel reinforcing rods.
- Multiple laminations of oriented HDPE.
- Reinforced concrete fill.
- Cross linking of PE molecules by thermoset processes
Advantages of RPL Over Wood
RPL is clean, nontoxic, and nonporous, and lasts longer than wood. In addition, all types except wood-filled RPL have the following advantages over wood:
- Moisture and chemical resistant.
- Graffiti resistant.
- Splinter free, does not crack.
- Does not need sealants or preservatives.
- Colored throughout, does not need paint.
- Impervious to insects.
- Flexible, can be curved and shaped.
- Maintenance free.
- Does not absorb bacteria.
Benefits of RPL to the Community
- Saves money for local governments and other purchasers by lowering long-term maintenance costs.
- Creates additional business opportunities.
- Diverts plastic waste from landfills.
- Reduces wood waste, especially treated wood waste.
- Helps local governments meet their goal of reducing landfill disposal by 50 percent by the year 2000.
RPL currently has a higher purchase price (initial cost) than virgin wood, but usually lasts longer than wood. When maintenance, replacement, and life cycle costs (materials + installation + disposal) are included in the analysis, RPL products can cost less than wood if the structure is designed properly. Also, plastic lumber is recyclable at the end of its useful life.
Purchase prices of RPL are expected to decrease as technology improves and demand increases. Wood prices are expected to continue to increase.
The costs of manufacturing RPL depend partly on:
- Sorting technology.
- Production capacity/rate.
- Quality of recycled resins (feedstock).
- Quality of the additives that improve RPL's properties. (Additives can account for as much as half of the total raw material cost.)
- Quality of the manufacturing process.
The Resource Conservation and Recovery Act mandates a federal "buy recycled" program that requires the United States Environmental Protection Agency (U.S. EPA) to designate products made of recovered material as suitable for purchase by federal agencies. As a result of this mandate, U.S. EPA prepares an annually updated set of comprehensive procurement guidelines and a Recovered Material Advisory Notice that recommends the practical recycled-content level of the materials.
Although California has not developed any procurement guidelines for recycled products, several local agencies have purchased RPL. Some of the California government purchasers include:
- National Parks Service, Golden Gate NRA: Cavalry stables.
- East Bay Regional Park District: Sign and trail posts.
- City of Sacramento, Boating: Boat bumpers.
- U.C. Davis, Student Housing: Dormitory exterior benches.
- Santa Cruz Port District: Decking and piles.
- San Mateo County Harbor District: Railing at the top of a bulkhead wall.
- City of Berkeley Marina: Signs and mooring rails on the floating docks.
- Don Pedro Recreation Agency: Railing.
Plastic Recycling http://www.calrecycle.ca.gov/Plastics/