Plastics Cleaning Equipment by Mark Henricks

The number of North American businesses involved in recycling post-consumer plastics has tripled in the last few years to more than 1,800, according to the Association of Postconsumer Plastic Recyclers. That’s good news for plastic cleaning systems vendors.

The trend today is toward larger, higher-capacity systems, according to Curt Cozart, sales agent for Sorema in Montclair, New Jersey. “Ten years ago, a one ton per hour system was typical. Now a typical plant would be a three ton per hour system.”

Sorema emphasizes use of automation to reduce the number of human operators required to run its systems, Cozart says. In another move to cut cost of operation, the company also seeks to reduce use of water for cleaning and electricity for running the machines. “We don’t have as many people and we’re managing our water and electricity very well,” Cozart says.

Sorema’s plastic washing systems tend to be heavily customized, based on the nature of the recycling stream. The most popular recycling materials today are PET bottles and HDPE bottles, with plastic film in the form of grocery bags and stretch film also coming on strong.

“With PET you have to be in the low parts per million of total contamination because it’s going to make a bottle or something of very high quality,” Cozart says. “And it’s clear so they don’t want black spots.” Because PET bottle labels are applied with hot melt glue, cleaners employ a hot chemical solution to dissolve the glue.

HDPE streams don’t have to be quite so clean. “You don’t have the clarity issues,” Cozart says. “Your glue is also water-based in most cases and your labels are paper. So it’s a little easier to clean.” Another difference is that, unlike PET which is heavier than water, HDPE floats in water.

With grocery bag cleaning systems, the issue is handling the plastic film material. “It just doesn’t flow very well, particularly when it’s wet,” Cozart says. Also, because film is much thinner than bottle plastic, the cleaners must wash far greater surface area per pound of output. “The system really needs to be designed to handle those types of things.”

Because of the differences in the way common plastics must be handled, Cozart says most equipment sold today is for systems designed to handle one type of plastic. “Each one of the polymers and each one of the shapes has something special to it,” he says. “So the lines are very specialized. There aren’t any general-purpose lines any more. We had them 20 years ago, but those lines pretty much have become specialty lines.”

At Polymer Recovery Systems in Eau Claire, Wisconsin, President John Ayres says the company’s Float/Sink Tank is one of its most popular products today. The Float/Sink Tank is used to separate plastic regrind from other materials in the stream. Ground materials are deposited in the tank that contains a water solution with a specific gravity that can be altered to suit the situation. Materials heavier than the solution sink to a sloping bottom and are removed.

Many Float/Sink Tank customers are industrial users recycling shop scrap. “A lot of times people will have a plastic that floats in water and, if it’s floor sweepings or whatever, they can run it through this and it will separate the dirt from the plastic,” Ayres says.

Polymer Recovery’s PlastiCycler is a complete system that incorporates an air classifier, washer, de-waterer and dryer for shredded plastic, as well as a secondary air classifier for use after the plastic is granulated. The washer/dryer portion employs a series of rotating drums where material is sprayed with hot water. Contaminants are removed through the combination of heated water and rubbing against other particles in the drums, and washed out through screens.

After de-watering in another set of drums, air heated by gas or electricity is blown through to complete the drying.

The PlastiCycler is more likely to be used in post-consumer applications. “That’s where a more thorough washing is necessary, where you may have residue like food residue or glue or labels,” Ayres says. “This provides a more aggressive washing and cleaning of the materials.”

The air classifiers are important components of the cleaning process, Ayres says. In these, material is deposited on a column of air which carries lighter materials up and out of the system while heavier materials fall through. The PlastiCycler capacity is normally one ton per hour, put Ayres says they are studying increasing the capacity. “We see some market applications where people are calling for higher throughput,” he says.

In Ipswich, Massachusetts, EREMA North America takes a different approach to removing contaminants from plastic grocery bags. CEO Tim Hanrahan says the company’s recycling system directs a constant flow of melted plastic through a pair of disks, each of which has up to one million tiny, laser-drilled holes. Laser filters with different-sized holes can separate particles of varying sizes.

The laser filter doesn’t clean well enough for applications where there are more stubborn contaminants than are typically found in grocery bags. “If you have really bad stuff, you need a washing system. But if you have stuff you can be selective about, they may get away with this laser filter,” says Ayres.

Most of the more than one billion pounds of PET bottles collected in North America for recycling annually, are shipped to other countries for recycling. However, vendors of plastic washing systems see good, long- term domestic demand as long as high oil prices make virgin plastic more expensive.