A powerful combination

Polywood LLC is a leading manufacturer of outdoor furniture produced from recycled high-density polyethylene (HDPE) plastic. Through innovations in chemistry, Polywood has created a plastic lumber that has the look of real wood but with the strength and lasting durability of plastic. Since manufacturing its first classic Adirondack chair, the company has expanded its product offerings to include additional styles of Adirondack chairs, as well as dining sets, lounges, deep seating, benches and swings.

In addition to manufacturing outdoor furniture, Polywood also is an efficient plastics recycler. At its production center in Syracuse, Indiana, it operates one of the world’s most modern HDPE recycling plants, which is equipped with machinery supplied by Germany-based Lindner WashTech, with a U.S. branch, Lindner reSource America LLC, in Tucker, Georgia.

At the heart of the plant is a combination of shredding and washing components specifically customized for this application by Lindner Recyclingtech GmbH, which is based in Austria. The company is represented in the U.S. by Lindner America LLC, Raleigh, North Carolina.

The Polywood production center’s feedstock is postconsumer HDPE plastic, primarily in the form of empty but unwashed nonreturnable milk containers. The equipment from Lindner converts these containers into flakes, which are well-suited for the company’s recycling process in terms of purity, residual moisture and particle size.

Sustainable and efficient

Chad Rassi, process engineer at Polywood, says, “We had the fortune of planning our recycling plant from scratch. The key aspect here was to ensure a high level of sustainability through the particularly efficient use of water, heating and energy power, as well as low-maintenance operation, maintenance-friendly design and a high nominal throughput in long-term operation. We wanted to achieve outstanding cost-efficiency so as to make the recycling of plastics a success for us both technically and economically.”

Lindner reSource America received an offer from Polywood to tailor a complete washing line, including all supply lines, for the recycling of the nonreturnable milk bottles.

“We finally accepted this offer because Lindner had really got to grips with our project and familiarized itself so intensively with our work that it was able to come up with the best possible solution at every stage,” Rassi says. “The company’s regular presence on the site, the expertise of its representatives and the personal trust we built up with them was just as convincing for us as the excellent reputation of this manufacturer’s products.”

Made to measure

In the first step of the Lindner system, a Micromat Plus 2000 single-shaft shredder is filled by a chain conveyor. This shredder is designed to ensure low energy consumption and high efficiency, the manufacturer says. Different drive systems, rotors and blades can be combined to maximize productivity for the material to be shredded. The point blade rotor (with a length of 78 inches and a diameter of 22 inches) is equipped with 104 2.6-inch-by-2.6-inch blades that are indexable four times and designed to ensure precise cutting and high throughput, even with abrasive material.

The shredder’s large inspection and maintenance flap allows adjustment and replacement of the blades and counterblades, cleaning of the hopper or removal of impurities.

Because of the special characteristics of postconsumer milk jugs, Lindner can customize the line using new washing components. The washing equipment combination of the Floater and Twister, a highly efficient friction washer from Lindner washTech that detaches any paper label residue and other contamination from the plastic, is the right solution for this specific material.

To achieve Polywood’s requested flake size, material is size reduced using a specially designed wet grinder. A jet of water is directed onto the rotor so that the friction arising during the grinding process can be used to detach remaining dirt particles. The amount of water can be regulated to ensure uniform and controlled material discharge. The particle size is ideal for the next cleaning stage in the Graviter, where heavier plastics, such as polyethylene terephthalate (PET), acrylonitrile butadiene styrene (ABS) or polyvinyl chloride (PVC), are removed.

This is followed by drying of the cleaned material in a Lindner Loop Dryer with a rotor diameter of 48 inches, a rotor length of 78 inches and a 120-horsepower motor before the fines are separated in an air wash system. The material can be transferred directly to octabins / Big Bags or to a storage silo before entering the recycling line.

Experience brings success

Tomas Kepka, vice president of Lindner reSource America LLC, says he optimized the washing unit in cooperation with Polywood and Lindner washTech.

He says, “Two important factors provided us with the basis that enabled us to comply with Polywood’s requirements quickly and completely. Firstly, the Lindner systems have a modular structure. This enables us to meet a wide variety of different demands simply through the clever combination of standard and new components. Secondly, we benefit from our long-lasting cooperation with main suppliers of plastics recycling machineries. As a result, we are very familiar with their demands made on the input material for their recycling process. From this experience, we know without extensive preliminary trials how we must configure our systems to provide them with a clean, shredded and dried material optimized for these machines.”

Rassi says of the system, “In the meantime, we know that our decision to accept the offer from Lindner was absolutely correct. The complete system began operating September 2016 after a six-month lead time. Water and energy consumption are even lower than expected, and the performance and end product are outstanding.”

Lindner reSource America LLC, Tucker, Georgia, supplied this article. More information is available from the company’s Vice President Tomas Kepka at tomas.kepka@l-rt.com.