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Plastic wood makes good.

First the process belonged to Hearthbrite Industries in Philadelphia. Then the technology was sold in 1989 to what became Rivenite Corp. And last year, Houston-based Mobil Chemical Co. was shopping for a film recycler, bought Rivenite's assets and technology, and formed a new Composite Products Div. The process in question is a proprietary and supposedly very efficient way to extrude plastic "lumber" from 100% recycled PE stretch film and sawdust from furniture factories and ground-up wood pallets.

Mobil proceeded to move the former Rivenite operation to Tampa, Fla., to better supply "Timbrex" recycled lumber to Disney World and other customers with applications where real wood would rot or be eaten by termites. Earlier this year, Timbrex passed Federal Highway Administration tests for a component of highway guardrails.

Mobil's Timbrex line now runs on a 24-hr, seven-day basis, making about 10 million lb/yr of lumber, Mobil says. Three more plants are planned--the next in the mid-Atlantic region. Mobil also set up a new marketing unit for Timbrex in Norwalk, Conn.

Timbrex wood composites are made by mixing finely ground (30-mesh) sawdust with shredded (not granulated) PE film. Metal contaminants are removed, and the mixture is heated in a custom-built mixer/dryer with a steam jacket in order to remove moisture. In this initial heating stage, the material melts to the consistency of clay. It's then fed into a short-barreled extruder, which pushes it out the die to form 2 x 4 and other lumber profiles. These profiles pass through a water cooling bath and are cut with a traveling saw to 8-, 10- and 12-ft lengths.

The lumber looks and feels more like wood than competing all-plastic lumber, Mobil says, because wood fibers are exposed at the surface. These surface fibers also provide a non-slip surface for docks and walkways, and make the lumber paintable with either oil- or water-based paint. Wood fiber is also said to be a natural uv stabilizer, so the material doesn't need to be colored black like many plastic lumber products for outdoor use. Instead boards are available precolored in tan or dark brown or left natural, which starts out looking like raw wood and then weathers gray just like real wood.

Piling on the Recycle

Another recycler with a proprietary process using unwashed, recycled plastic is also qualifying wood replacement products for "infrastructure" projects--specifically, dock pilings. Hammer's Plastic Recycling Corp., Iowa Falls, Iowa, had 22 pilings installed as a test in the port of Los Angeles last November. The patented pilings have a 4-in. sheath of plastic extruded around used oil-field drilling casings. Pilings of 13 in. diam. are screwed together in sections up to 80 ft long.

Hammer's says 60% of the plastic that is used comes from beverage-bottle basecups, which cost 2-5|cents~/lb delivered. The pilings sell for $30/ft, which puts roughly 70|cents~/lb value on the plastic portion. Hammer's says it has more pilings on order for L.A. and test pilings have been installed in Australia.
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Publication:Plastics Technology
Date:Mar 1, 1993
Previous Article:Where Miles is headed in RIM & engineering thermoplastics.
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