Closing the loop on bottle caps

Recycler, processor and manufacturer Greenpath Enterprises has partnered with TOMRA Recycling Sorting to install and optimize a plastic flake sorting line designed to identify and separate mixed polyolefin caps from beverage bottles.

Joe Castro (left) and Eric Olsson with the INNOSORT machine.

“We are at the genesis of creating a sorting system for caps similar to what is more common today for the bottle,” said Eric Olsson, area segment manager, plastics for TOMRA Recycling.

Operating for more than 25 years, the vertically integrated Greenpath accepts a wide range of materials, and the inbound flow can be somewhat inconsistent. Greenpath creates value being a one-stop solution by accepting mixed trailer loads with variable supply streams and producing consistent, quality products.

“Developing a mechanical sorting process to close the loop for food-grade cap-to-cap recycling by consistently separating mixed polyolefins by polymer and colour with high purity is a game changer,” said Joe Castro, president of Colton, California-based Greenpath.

Considering only the post-consumer polyolefin materials – low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) – Greenpath accepts film, rigid plastics and bottle caps. Polypropylene and polyethylene (PE) are together the most abundant plastic family on earth, but the market is limited for valuable applications for mixed polyolefins, according to Olsson.

PE and PP have very close density characteristics and are challenging to separate. So, mixed polyolefins are primarily downcycled into more forgiving applications that allow for more contamination.

The quest for cap to cap

A beverage container commonly consists of four parts: the bottle, cap or closure, ring and label. A more mature PET recycling infrastructure has led to brand owners incorporating up to 100% PCR material in their bottles.

As regulations increase the percentage of recycled content by weight, the next logical container component to address is the cap. “Following Greenpath’s approach, the industry can move toward a 100% PCR by weight package using only mechanical sortation,” says Olsson.

During the recycling process, bottles, labels, caps and rings are shredded, and a sink-float process is used to separate the PET bottles from the PE and PP caps. The heavier PET sinks and the lighter polyolefins float and are skimmed off as a secondary byproduct.

Logic may dictate using PET for both bottle and cap to solve the issue, but Olsson explains it’s not that simple. “Different polymers have different strengths and weaknesses, and polyolefins lend themselves especially well to building in the threading on a cap,” he says.

Greenpath has extensive processing capabilities with different lines to sort diverse feedstock and is adept at mechanical, multi-material and batch recycling processes. To close the loop on caps, Greenpath investigated various technologies to sort the mixed polyolefins.  With PE and PP densities being very close to one another, float/sink tanks were not deemed effective, and alternative recycling technologies didn’t offer the desired recovery for both PE and PP resins.

“The yields are low, and you have to consider the expenditure, space and waste generated from the separation process,” said Castro.

Greenpath zeroed in on a mechanical solution using flake sorters and met with TOMRA to discuss a new type of flake sorting technology. One of its design parameters was to extract value from multicomponent plastic waste streams.

“It’s best to pursue a path that introduces the least amount of change to the material and sorts in the most efficient way, and we haven’t begun to reach the ceiling limit for mechanical polyolefin sorting,” Olsson said.

“Sorting technology OEMs are just getting the first processes off the ground to produce materials resulting from the 2025 and 2030 circularity commitments made in the twenty-teens. Flake sorting can get us to 95% or greater purity-by-polymer streams.”

Mechanical sorting flexibility

Greenpath’s purity, yield and throughput goals led them to selecting INNOSORT FLAKE. One appealing feature: the sorter does not require a large footprint, allowing for easier integration.

Designed for flexibility, INNOSORT FLAKE incorporates a unique combination of sensor technologies, including colour cameras capable of identifying 16.8 million colour variations. “A camera is positioned on each side of the chute, so it can see the difference between each side of the flake,” explains Olsson. This helps to identify in-mold labeling that can be a contaminant.

Its Flying Beam lighting system offers material detection by the sorter’s near-infrared (NIR) sensors. Homogeneous light distribution ensures classification of PE and PP materials, as well as other polymers and materials. Integrated into the scanner box for protection against damage, it offers up to 80% energy savings over conventional light sensors.  

Configuration flexibility allows for single or multiple step sorting with the same unit. “We can split the machine into multiple sorting tasks by chute and even split a chute into two different process streams or more,” said Olsson. Castro adds, “TOMRA’s technology allows us to purify at a higher level that opens up the whole circular opportunity with going cap to cap,” he says.

Optimizing for consistency

Both companies have been committed to getting the process right and have paid special attention to sorting optimization. “We wanted a company who would support us on this journey. TOMRA has been very supportive in this project, and it has been more like a partnership,” said Castro.

Optimizing the process means meeting Greenpath’s high purity goals of mono-polymer PE and PP from inconsistent mixed polyolefin feedstock. While there is still some work to be done at the facility, “mechanical viability is there,” confirms Olsson.

The system first sorts by polymer with the INNOSORT FLAKE units and then by colour. “If a customer wants a natural or specific sorted colour such as red, white, blue, orange, or green PE or PP product, we can purify and provide them a sorted colour that meets their specific application using PCR,” says Castro.

TOMRA’s Olsson shows optimism for the accomplishment, its impact on the market and what it means for packaging companies trying to meet recycled content targets. “We’re at the beginning for mixed waste streams of polyolefins going closed loop. It won’t just be a pipe dream for polyolefins anymore.”