Designing for Recyclability: Sorting Out the Issues with Plastics Recycling

Thursday, 02 Mar 2023

In his article below, Brian Schmatz, who heads our team in the US, provides interesting insights into how plastics are sorted at recycling facilities and why a better understanding of the underlying sorting technology is crucial on our path towards a circular economy.

“ Make sure to tell your friends Recycling is Real ”

An interesting farewell to receive on my way out of the largest and most advanced recycling center in the United States.

SIMS Municipal Recycling, where all of NYC’s mixed glass, metal and plastic waste is processed, is about as real as recycling gets. Trucks and barges from across the 5 boroughs stream in and out of their facility in Brooklyn, unloading about 1,000 tons of mixed recyclable waste per day into their assembly line sortation process – where a series of screens, magnets, optical sorters, and human operators work to separate glass, metal, and plastic.

Recycling Facilities like SIMS, commonly known as a Materials Recovery Facility or MRF, play a vital role in our post-consumer recycling infrastructure: Sorting.

The quality and value of recycled materials is correlated with how well it has been sorted out from dissimilar materials. An aluminum can manufacturer can’t make a product with a pile of waste that is 50% aluminum and 50% other stuff. They want a pile of waste that is as 100% aluminum. The same logic holds for all recyclables, and it is much more complex than glass, metal, and plastic. There are ferrous and non-ferrous metals and dozens of plastic types; all which need to be individually separated. MRFs enable us to throw all these materials into one or two bins so they may be sold as alternatives to virgin materials. Without sortation, there is no post-consumer recycling.

Sims recycling new york trinamiX Sims recycling new york trinamiX

The Recycling Dilemma

Over 300 MRFs across the United States are sorting and selling post-consumer waste, but a shadow of doubt exists over the recycling industry. “I’ve heard none of the recycling is actually going anywhere” is something a friend declared to me over lunch about a week before my visit to SIMS. She’s not alone in this opinion. A recent Mason-Dixon poll shows that while recycling is viewed positively by 85% of respondents, nearly two-thirds (65%) are either unsure (21%) of what happens to their materials, or don’t believe (44%) that the materials are being recycled.

And while I can unequivocally say that Recycling is Real (!), how well it’s working is a fair question. The latest EPA Municipal Solid Waste study had the US Recycling Rate at 32.1% of total waste generated. This is largely driven by paper/cardboard recycling (68%) and metals (34%) while glass (25%) and plastics (9%) are lagging. Multiple factors contribute to these low recycling rates:

Recycling Challenges Sortation Recycling Challenges Sortation

While each of these warrants a lengthy discussion, I would like to focus on Sortation Challenges. Since trinamiX NIR Spectroscopy Solutions is used for Plastic Identification and Sorting, I’ve been closely involved with the challenges of waste sortation. Prior to this work I had no idea that common items like bottle caps and utensils were falling through the cracks, black food trays and shampoo bottles were going unseen, and plastic mailing envelopes were being incorrectly sorted as paper.

Even at an advanced MRF like SIMS, the challenge of sortation is regularly on display. “At the end of almost every shift, you can see plastic bags stuck on the screens and VHS tape flailing in the rotating separator wheels” says Kara Napolitano, Outreach and Education Coordinator at Sims Municipal Recycling. As Kara shows me around their Brooklyn MRF, she notes the blue colored material seen throughout the process. These are the bags the city instructs residents to use as a containment and collection solution. They are not recyclable. They can get clogged up in the sortation system. In a way, they are symbolic of the compromises being made throughout our recycling infrastructure to get the job done.

Design for Recyclability

Seeing these issues firsthand has made transparent the disconnect across the recycling chain – packaging just isn’t produced to be easily recycled. On the positive side, stakeholders are beginning to coalesce on this topic. The US Plastic Pact, a consortium founded by The Recycling Partnership and World Wildlife Fund, recently published a Problematic and Unnecessary Materials List as part of their effort to make 100% of plastic packaging reusable, recyclable, or compostable by 2025. This list echoes the messaging of the Association of Plastics Recyclers (APR), who have been promoting easier to recycle packaging for over a decade through their APR Design® Guide. Both are advocating for packaging to be designed for recyclability; or designed in a way so that it can be realistically recycled through our current infrastructure.

To explain what I mean by realistic, I want to come back to the black food trays and shampoo bottles that are going unseen. These packages are typically made of materials like Polyethylene (PP) or Polypropylene (PP) that can be effectively reused and have well-established end markets. They are theoretically recyclable. But they are made with colorants that render them invisible to the optical sorters used within a MRF, and therefore end up in a landfill. They are not realistically recyclable.

The culprit in black and other darkly colored plastics is Carbon Black, a pigment widely used in plastics, makeup, and paint for its quintessential “Piano Black” look. Unfortunately, this pigment completely obscures the vision of Near-Infrared (NIR) optical sorters used in MRFs. These sorters work a lot like our eyes; but where we can see the difference between blue and red, they can see the difference between PET and Polyethylene. The issue arises because Carbon Black dominates the signal seen in NIR, much like the color black can dominate a signal seen by our eyes. Look at the 2 images below:

To our eyes, the image on the right is more difficult to read because the dark writing is masked by the surrounding color. A similar principle in NIR vision leads to the Plastic Type being masked by the surrounding Carbon Black. This is why on a technical level, black plastics are not realistically recyclable through our current infrastructure.

But hope is not lost for your favorite shampoo bottle! Last year I had the opportunity to work on the question “How can package designers know if plastic is too dark for sorting?” Together with a group of stakeholders in the APR, we developed a method to test for Sort Potential in dark plastics and set a PASS/FAIL threshold. As shown in the images below, packaging designers can now use a handheld NIR device like our trinamiX Mobile Spectroscopy Solutions to simulate how a package will respond to industrial optical sorters within MRFs.

trinamiX NIR detection dye based black vs carbon black trinamiX NIR detection dye based black vs carbon black

In the example above, colorant modifications from a Carbon Black pigmented plastic (left) to a dye-based black plastic (right) leads to a much higher likelihood that the part will be successfully identified, sorted and recycled. Instead of ending the use of dark colors in branding, this quick test allows package designers to tweak their formulations so they can retain design freedom around dark colors while also assuring sortability, and therefore realistic recyclability.

With the support of APR guidance, more and more brands are making investments into packaging that is designed for recyclability. Unilever has reformulated its black shampoo bottles to be optically sortable, P&G is replacing non-recyclable flexible film packaging with cardboard packaging in it’s Gillette and Venus razors, and Kraft Heinz has swapped their silicone ketchup cap valves for polyethylene (PE) valves that make the cap sortable and recyclable. The work above on black plastics was done in collaboration with multiple large brands, and trinamiX is currently leading a group of stakeholders to develop a method to test the Sort Potential of labels and shrink sleeves, which can also obscure the vision of optical sorters. The industry is generally open to these changes so long as realistic alternatives can be identified.

Recycling is Real

Despite the challenges outlined above (and there are many, many more), recycling still works. It is a messy, imperfect marvel of engineering that is constantly reacting to an increasingly complex waste stream. But it can and needs to work better. We can start by making our waste stream less complex. Brands and producers have a responsibility to design packaging and products for realistic recycling, and consumers have a responsibility to recycle those materials correctly when available.

“Recycling is Real” is something SIMS and other recyclers need to promote because consumer support and faith in the system is critical to its success. I’ve focused on designing for recyclability from an industrial sortation perspective, but equally important is designing to encourage recycling. “Culturally, we presume the responsibility lies on the consumer when it comes to disposal, but so often they aren't instructed how to do so properly and the act of recycling is ineffective”, says Michelle Mattar, who leads the creative brand building house Practice and Waste Not, an open-source database of sustainable packaging materials. “A cultural shift is desperately needed to place that responsibility on the businesses producing these goods: all packaging design should clearly instruct how to properly dispose and detach components of products for waste streams. Until that becomes a mainstream idea, it makes sense that so many of us feel that we leave our recycling up to hope.”

The work Michelle leads with the Practice team exemplifies how packaging can provide end of life transparency and promote recyclability through engaging design. Shown below, this toast bag engages customers to learn about the material and the proper way to dispose of it. Packaging is designed to communicate effectively, so using that space to convey proper recycling instructions is a natural fit.

Recycling Packaging NIR Detection Recycling Packaging NIR Detection

We still have a long way to go, but I hope I’ve done some work convincing readers that recycling is real. Because believing it’s not real doesn’t make the problem it addresses any less real. Material producers, brands, and package designers need to design products for recyclability and to encourage proper recycling so the system can run smoothly. But we also need people using the system for it to work. So please, tell your friends Recycling is Real.

If you want to learn more about our Mobile NIR Spectroscopy Solution, make sure to drop by our booth at the Plastics Recycling Conference from March 6-8 in National Harbor, Maryland.

Or click here for more information.

Contact the author

Brian Schmatz, PhD
Brian Schmatz, PhD