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Commentary: Not all plastic's carbon footprints are equal

Recycled PP and HDPE reduce carbon emissions more than recycled PET.

Let’s cut to the chase—plastic waste management may be on everyone’s mind, but disparate initiatives are falling woefully short. In 2010, between 5 million and 13 million metric tons of plastic waste entered the ocean from developing countries with insufficient solid waste infrastructure and high-income countries with very high waste generation. That was 12 years ago and, rather than improving, the situation is getting worse.

According to a report by Science Advances, in 2016, the U.S. generated the largest amount of plastic waste of any country in the world at 42 million metric tons. Between 0.14 and 0.41 metric tons of this waste were dumped illegally in the United States, and 0.15 to 0.99 million metric tons were inadequately managed in countries that imported materials originally collected in the United States for recycling.

The report goes on to show that the amount of plastic waste generated in the United States and estimated to enter the coastal environment in 2016 was up to five times larger than that estimated for 2010.

Waste’s role in the climate race

The direct impact of waste mismanagement sits at the heart of climate change. Because materials are discarded and replaced by new materials, more than 1.3 billion metric tons of CO2 emissions are generated annually. Increased recycling rates and increased use of recycled content can save more than half the CO2 produced by landfilling this waste.

In fact, it has been estimated that by significantly improving waste collection, sorting and recycling, we can reduce CO2 emissions by between 2.1 billion to 2.8 billion metric tons per year compared with business as usual.

CO2 emissions vary from plastic to plastic

While the above is a clear reminder that everything we put into production should be designed to be recycled or reused, we also need to take into account that not all recycled plastics have an equal carbon footprint. This little-known fact potentially has a huge impact on the way we should view recycling.

Take polypropylene (PP). This is a versatile polymer used in many products we use daily, from delicatessen tubs and beverage caps to yogurt cups and trays for meat, fish and fruits. In fact, PP accounts for around 20 percent of the world’s plastic.

According to The Recycling Partnership’s 2020 State of Curbside Recycling report, PP is not broken out as a separate polymer in the United States. To date, it largely has been collected in curbside programs and sorted in material recovery facilities (MRFs). Many MRFs have specific polymer sorting capacity focused on polyethylene terephthalate (PET) and high-density polyethylene (HDPE) because these polymers are in higher demand in the market. They also are more readily recognized mainly as bottles and are presumably available in higher quantities than PP (pots, tubs and trays) in the household stream.

Yet this same report suggests that as much as 17 pounds of PP could be available per year from a single-family household. This would place PP at a higher generation rate than natural and colored HDPE, with total annual PP tonnage generated by single-family households in the U.S. estimated at 827,000 tons.

Despite this data, a serious lack of infrastructure to collect and recycle PP in the United States means this valuable material is on the verge of being removed from use across the 50 states. The hard facts are that collection and recycling rates for all plastics in the United States are dropping—PET is down from 30 percent a few years ago to 27 percent as of 20210. Ironically, recyclers are running short on materials.

In the case of PP, which is barely being recovered, it is a significant missed opportunity. Recovering PP could offer increased economic benefit and jobs, as well as reduce climate impacts, with the latter being one of the most pressing reasons to readdress PP.

Analyzing plastics’ carbon footprints

A recent life cycle assessment by Plastics Europe, Brussels, that compares the carbon footprint of a range of different recycled plastics shows that recycled HDPE (such as milk bottles) and recycled PP (such as most of our pots, tubs and trays that contain our food) have a 25 percent lower carbon footprint than recycled PET.  What this tells us is that 30 percent recycled-content PP or HDPE plastic has the same carbon footprint as 73 percent recycled-content PET.

Image courtesy of Nextek

As such, this study clearly demonstrates that recycled PP or HDPE is more environmentally beneficial than recycled PET, and neither polymer should be ignored. This finding should play a fundamental role in reshaping the way we manage different polymers, given that all our future decisions relating to plastics and recycling should be driven by CO2 emissions.

Pros and cons of PP

PP plays a valuable role in protecting and storing food. It is most often used for single-serve containers, such as soup pots, ice cream tubs and takeaway food containers. On top of being one of the U.D. Food and Drug Administration (FDA) approved food-contact materials, it is microwave safe and nonvolatile, which means it will not react with any type of food it stores whether it's acidic, basic or liquid.

The downside is that, until recently, we have been unable to produce food-grade recycled polypropylene (FGrPP), which has meant all PP food packaging is only made from virgin plastics.

These complexities are not unique to the United States but a large, global challenge that has, in part, been driven by a focus on recycling PET drink bottles. 

The wide use of the pots, tubs and trays that are placed in the recycling boxes yet not generally recovered for specific recycling has not been widely mentioned. PP is rarely used to make bottles and is missing from the recycling stream. Additionally, the complications of recycling PP for reuse in food-grade packaging have traditionally limited the economics of recycling.

Breaking through the challenges

The good news is that we now have cutting-edge technologies to specifically sort and decontaminate PP to food-grade quality. It has taken nine years of extensive research to reach this point, however Nextloopp, a multiparticipant project developed by London-based Nextek Ltd., is well-underway to creating postconsumer FGrPP, which should be on the market within 18 months.

Two key components of this project address the historical barriers to recycling PP. The first is PolyPrism, commercially proven marker technology to separate food-grade PP from the rest. The second is PPristine, a decontamination technology to ensure compliance with food-grade standards in the USA as well as in the U.K. and the EU.

As we get closer to closing the loop on FGrPP, we now have an unparalleled opportunity to redress the balance and boost recycling of a polymer that not only has a relatively reduced carbon footprint but that also plays a vital role in reducing food waste, yet another key factor in our race against global warming.

Pivoting our view of “waste”

Minimizing our waste will only occur once we actively start unlocking the value in the materials we still consider as part of the “waste” stream. Realistically, we can’t eliminate plastic from the supply chain and, even if we did, that wouldn’t solve the world’s climate crisis. Quite the contrary.

According to a waste reduction model, if all of the 37.4 million tons of single-family recyclables were put back to productive use instead of lost to disposal, it would reduce U.S. greenhouse gas emissions by 96 million metric tons of carbon dioxide equivalent. It would also conserve an annual energy equivalent of 154 million barrels of oil and achieve the equivalent of taking more than 20 million cars off the U.S. highways, not to mention generate an estimated 370.000 full-time-equivalent jobs.

What we need to do is efficiently close the loop on each different polymer. We need to expand our success story with PET to all polymers and stop taking a "one solution for all" approach that sees us sweeping millions of tons of plastic resources into our oceans and also removing a polymer from food packaging that could help to reduce food loss and waste globally. 

In 2004, Edward Kosior founded U.K.-based Nextek Ltd. to provide consultancy services to assist in the strategic approaches to sustainable packaging, waste reduction and minimal life cycle impact. He is Nextek’s managing director and is involved with many industry associations, universities and research organizations. He can be contacted at edkosior@nextek.org.