Recycled Plastic Lumber
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.
In general, the RPL manufacturing process includes the following steps:
- Material Preparation. Sort and clean (optional), then grind the recovered plastic material into small flakes.
- Extrusion. Homogenize and rapidly melt the flakes using heat and pressure inside a rotating screw (extruder).
- Forming. Discharge or force the molten mixture into a mold, cool the mold in a water bath, and eject the finished product.
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 re-melted 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 paint-ability, 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
RPL is clean, nontoxic, nonporous, and lasts longer than wood. In addition, all types except wood-filled RPL have the following benefits:
- 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.
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.
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.
- Commodity Prices
1340 N. Jefferson Street
Anaheim, CA 92807
104 East Turner Road
Lodi, CA 95240
Urban Design Furniture
PO Box 77806
Corona, CA 92877
- Plastic Lumber Trade Association (PLTA) -- Uniting diverse plastic lumber producers and other industry-related plastic lumber producers to promote the engineering, art and science, marketing and procurement of recycled plastic lumber and other recycled plastic lumber products.
- American Chemistry Council -- Plastics -- The Plastics Division of the American Chemistry Council (ACC) represents leading manufacturers of plastic resins.
- SPI -- The Plastics Industry Trade Association -- SPI delivers advocacy, market research, industry promotion, and the fostering of business relationships and zero waste strategies.
- Society of Plastics Engineers -- The objective of the Society is to promote the scientific and engineering knowledge relating to plastics.
- ASTM International Section D20.20 -- Subcommittee D20.20 on Plastic Lumber.
Plastic Recycling http://www.calrecycle.ca.gov/Plastics/