'Cold extrusion' process recycles mixed plastics.

Unsorted and uncleaned mixtures of waste plastics with up to 25% paper, metal, or glass may seem like junk, but they're prime feedstock for a proprietary ambient-temperature recycling process developed by Innovative Recycling Corp. (IRC), a recycler in Albuquerque, N.M. With this process, IRC hopes to exploit the vast majority of post-consumer and post-industrial plastics waste generated in the U.S. annually that is not currently recycled.

Film, purgings, or parts composed of LDPE, LLDPE, HDPE, PS foam, nylon, PET, ABS, PVC, polycarbonate, and even rubber are processed together with special chemical, mixing, and die technology in a process that uses temperatures no higher than 100 F to yield a uniform plastic lumber-type product. Typical feedstock materials used by IRC include polyester blinds, credit-card regrind, packaging materials, tv frames, plastic strapping, and plastic drum scrap.

IRC's Albuquerque plant produces 6 tons of product a day and IRC intends to double its capacity this year. Last November, IRC started up its first large-scale manufacturing facility in Bradley, Ill. It can process 90 tons of commingled waste a day, says Gary Estepp, IRC founder and CEO. The facility, called I-Rock Bradley LLC, is a joint venture between IRC and MTAE (Means To An End) Inc., Bloomington, Ill., a venture-capital firm. The site currently processes 21 tons a day in one 8-hr shift but plans to scale up to three shifts producing 90 tons a day later this year. I-Rock Bradley turns the recycled product into pallets, parking stops, landscaping timbers, and railroad ties.

IRC's technology is not offered for license, but the firm hopes to open additional plants through joint ventures around the country.

THE MIX ADDS VALUE

Although recyclers frequently engage in labor-intensive and costly material-separation steps to get value from commingled waste, IRC's process actually depends on a mix of materials to obtain desirable end-use properties. "We need to see at least six different materials in the mix," says Estepp. IRC products show compressive strength up to 5000 psi, tensile strength up to 2200 psi, negligible thermal creep at up to 200 F, no outgassing, and uv stability to 2000 hr of accelerated weathering.

Granulation is the first step in the process. At I-Rock Bradley, one grinder is devoted to film waste, while a second grinder chops everything else to granules of 1/4-in. or smaller. "We are not looking for uniform pieces, we just need to reduce the size of the material," Estepp says. Ground material is transported pneumatically to five outdoor silos, which together hold 4.5 days worth of material. I-Rock draws resin into its process from at least two silos to ensure a sufficiently varied mix.

The material enters a twin-screw mixer/extruder - a counter-rotating, non-intermeshing unit from Welding Engineers, Inc., Blue Bell, Pa. - where small amounts of two proprietary, nonhazardous chemical formulations are introduced. The first formulation is a proprietary liquid that softens the resins in the mix. The second, added farther down the barrel, consists of a proprietary resin and chemicals. It acts as a compatibilizer. The chemicals are said to bind the different resins together to form a new hybrid material. The chemical additives become part of the hybrid material thus eliminating off-gases.

The special chemicals are also said to ensure good flow characteristics without the need to add heat to the process. "We want to stay below the temperature of outgassing, which is 200 F," Estepp says. Hence, only ambient temperature and frictional heat are used in the process, which typically operates at 60-100 F. Estepp also says the chemical additives improve the properties. "The commingled product has flexibility but with poor thermal expansion characteristics. Our chemicals add thermal expansion as well as compressive strength and heat resistance."

The unusual twin-screw machine features one screw that's longer than the other. The machine is modified with thinner barrel walls in the mixing section because no pressure is needed there. The two-stage mixing set-up involves a 15:1 L/D initial section where the two chemical additions are made, followed by a 30:1 L/D section that completes mixing and devolatilization, if necessary. One screw is extended to function as a 15:1 L/D single-screw discharge section. The product is extruded through a die into a water trough for cooling.

Since the product has a typical density of 62 pcf, it floats in water. By varying the amount of the chemical formulations, together with the use of a proprietary "adjustable" screw design, I-Rock is able to reduce the density of the product to as little as 32 pcf.