Innovation in action

Recycled resin does not necessarily have to go into a new consumer part to be considered a circular economy superstar.

Clean Harbors, a major provider of environmental and industrial services across North America, takes high-density polyethylene (HDPE) containers used mostly for lubricants and solvents that previously were shredded and landfilled and recycles and injection molds them into containers it needs to incinerate toxic chemicals.

Using these recycled pails means Clean Harbors no longer purchases new pails and containers to fill with toxic chemicals that go into a 2,370 F incinerator.

Before the in-house recycling project, Clean Harbors bought an estimated 2.5 million pounds of blow-molded 30-gallon drums and 5-gallon injection-molded pails per year manufactured with virgin resin. The containers were used only to incinerate toxic materials.

Finding the right partners

To make this complex project successful, Clean Harbors worked with Austria-based Starlinger & Co. GmbH to turn the containers it collected from its customers into a uniform-sized material; Calframax Technologies Inc., which was later acquired by Ontario-based SyBridge Technologies, to build industrial pail molds; and Ontario-based Husky Technologies for a special three-nozzle hot-runner system and a highly modified injection molding machine.

Clean Harbors, which had no injection molding experience, also had to train its staff to mold the pails and containers.

“This is one of the most satisfying projects I have been a part of,” says Andrew Kerley, senior packaging engineer at Clean Harbors. “Taking a waste material, which in most cases was costing the company to discard, and repurposing it to replace the raw material cost of new containers is Clean Harbors’ innovation in action. All the while we are reducing our environmental impact.”

Kerley declined to say how much Clean Harbors spent to buy the Starlinger recoStar recycling system, Husky injection molding machines and SyBridge Technologies molds and to hire two additional employees, but he says the company expects to recoup its investment in less than three years.

Clean Harbors, a publicly traded company headquartered in Norwell, Massachusetts, has more than 400 service locations in North America, including more than 50 hazardous waste management facilities in the U.S., Canada, Mexico and Puerto Rico. Safety-Kleen is a well-known subsidiary.

The new recycling and molding operation is at the company's El Dorado, Arkansas, facility, which specializes in high-temperature incineration of regulated waste materials, like industrial and laboratory chemicals, manufacturing byproducts, medical waste, fertilizers and other solid and liquid materials that are hazardous to the environment and public health.

Success despite a rocky start

The project started in October 2018, and nine months later, the collected material was tested on the Starlinger recoStar recycling system. Two months later, a proof of concept was completed at SyBridge in Ontario, but the COVID-19 pandemic delayed the project before it was finally completed in August 2022.

The company collects and processes HDPE from many of its customers, and the material stream is far from homo-geneous. It has a melt flow index (MFI) of less than 1, and the high viscosity made blow molding impractical and injection molding very difficult.

An early challenge was to convince the machinery suppliers that the contaminated pails collected from customers could be used for this application. The material finally was tested and pelletized on the Starlinger system.

Once the recycled resin was converted to a uniform size, it was sent to the SyBridge facility in Windsor, Ontario, where industrial pail molds were designed and built.

The initial test used an existing 5-gallon pail mold on a 500-ton Husky injection molding machine. Given the resin’s high viscosity, it was very difficult to fill the mold more than halfway up the sidewall. Mold modifications eventually overcame this problem, but the test machine setup had limited temperature and pressure options.

However, SyBridge and Husky technicians were able to use data from the test to design a workable molding system.

Up for the challenge

Clean Harbors commissioned SyBridge to design molds for 5- and 22-gallon containers and lids that could be molded with fractional melt HDPE. At the same time, Husky built a specialized three-nozzle hot-runner system for the 22-gallon containers, and a 1,200-ton Husky molding machine was configured for high-torque, high-injection pressure and equipped with a wear-resistant screw for the low-MFI HDPE.

The 22-gallon container’s shot size is 11 pounds, which necessitated 1,200 tons of clamping force. The same machine also produces the 5-gallon pail and both lids. Husky designed the press with a 135-millimeter screw and a 115-millimeter screw, which makes the molding machine shorter than one with a single larger screw.

The three smaller molds can be filled using only the 115-millimeter screw, which reduces energy consumption and improves shot control. A crane was installed over the machine to facilitate quick mold changes, and because the Clean Harbors facility has low ceilings, Husky built the press with a tie-bar pulling option.

Today, the HDPE containers are collected at Clean Harbors sites across the country and shredded before being shipped to the Arkansas facility. They then are granulated, cleaned and fed into a pelletizer.

The repelletized resin is put directly into the molding machine. Because of variations in the recycled HDPE, operators must make regular checks on the melt index and fine-tune the molding machine when needed.

The 5-gallon pails and lids are being molded with 100 percent recycled resin. The 22-gallon container currently is using 70 percent recycled material, and Clean Harbors is working to get that to 100 percent, Kerley says.

Equipment suppliers primarily trained the staff to operate the recycling system and injection molding machine.

“We have developed a team of 16 employees to support this new process,” says Rico White, the company’s facility operations supervisor. “Prior experience with injection molding was limited to myself and one other. This process is different and challenging, but everyone has invested the energy needed to operate successfully.”

The recycling and molding operation runs 24 hours per day, six days per week, with the seventh day for change-over and maintenance.

“The program has been successful, and we are looking to expand the operation,” Kerley says.

The author is editor of Plastics Machinery & Manufacturing and can be reached at rshinn@endeavorb2b.com.