Single-use plastics — a bad wrap?

Single-use plastic packaging won’t win any popularity contests these days: One survey of 28 countries found that 3 out of 4 people agree that plastic bags, straws and water bottles should be banned. A bipartisan bill introduced by members of both the U.S. Senate and House has put forth the Break Free From Plastic Pollution Act, which if passed would be our country’s first nationwide law to phase out what are considered to be unneeded single-use plastic products.

But things are always more complicated than they seem. For example, a shrink-wrapped cucumber lasts up to 15 days whereas 5 to 7 days is all you get without the plastic packaging. Food is less likely to be damaged during shipping if it’s packaged. The upshot is that single-use plastic packaging, for all its drawbacks, leads to less food loss due to damage, as well as less spoilage, safer food, more choice, and less expensive produce.

Electric vehicles pose a similar dichotomy. If you switch to an EV in an area primarily powered by coal-fired plants, it actually may be worse for the environment than a gasoline-powered vehicle. The same would be true if EVs lead to more people choosing to take air transportation, discouraged from driving because traveling long distances by EV takes so much longer due to charging at each stop and cold weather saps as much as 40 percent of the power to run the heater.

Many people don’t know these things because most life cycle assessments do not account for these alternatives and downstream effects, which often turn the tables on what appear to be straightforward carbon footprint comparisons.

Plastics account for around 1.2 gigatons of greenhouse gas (GHG) emissions, out of a world total of approximately 50 gigatons. That means about 2 percent of GHG comes from plastic. Contrast that with the fact that food waste, which estimates peg at perhaps one-third of all the food intended for people in the U.S. alone, amounts to some 8 percent of GHG — 4 times the emissions of all plastics. So, if getting rid of single-use plastics leads to more food waste, these bans will make climate change occur even faster.

What are the alternatives? Paper is one, but it’s been long known that paper packaging can be worse for the environment, as it takes a lot more paper to do the same job as plastic. So, more energy is expended making the paper material, and it takes more energy to transport it. Yet many consider it “greener” to choose paper bags over plastic bags.

Reusable containers also have their issues, depending on how many times you can reuse the material and what the material is. As the reusable material is heavier and you have to wash it, in some cases you can never make up the difference in emissions due to the extra material and heat and water used in washing. Even in cases in which you can, it takes more than 200 uses of a polypropylene container to make it a better choice than a single-use Styrofoam™ container. A ceramic coffee mug needs to be used more than 120 times to have a better outcome than a single-use Styrofoam cup. That’s a lot of coffee!

Then there is multi-use, polypropylene-based tableware, which is never better than paper-based single-use packaging. One life cycle assessment study of quick service restaurants in Europe showed that these multi-use systems generate more than 2.5 times the CO2 emissions and use 3.6 times the amount of freshwater (for washing and sanitizing) than paper-based, single-use systems.

In nearly every case, lightweight disposable plastic, such as Styrofoam and plastic film, is the best single-use choice over paper and other materials, due to it being much lighter than anything else. That conclusion doesn’t even account for other issues like water usage: In desert environments, reusables exacerbate water use due to washing, which may turn out to be a much bigger issue, locally.

This is why I’ve been researching green materials and their processing for some time with an understanding of complexity and tradeoffs. For example, I lead a team that develops materials based on cellulose, the primary structural component of plant cell walls. Paper, derived from cellulose fibers in wood, is biodegradable, recyclable and compostable. In the U.S., trees are farmed, and old-growth forests are not used. This practice is very efficient, using marginal land like the red clay soil in the South and fewer resources. It also provides a living habitat for nature.

However, paper produces more GHG than plastic in packaging, due to more material being needed in a paper package, which also requires transporting twice the weight of material as plastic. Paper also provides little functional food preservation unless it’s coated with plastic, which reduces its recyclability and compostability.

My team has developed green cellulose nanomaterial (CN)-based layers and associated manufacturing processes to help preserve foods. CN consists of very small whiskers and thread-like fibers extracted from woody biomass like trees. Being cellulose, they are biodegradable and nontoxic. Their nano size also confers on them special properties, such as being stronger and stiffer than Kevlar®.

Cellulose nanomaterial (CN)-coated molded pulp tray (center) and CN-coated molded pulp tray with bioplastic “lidding” film (right) compared with uncoated molded pulp tray (left). The two trays with CN coating are renewable, compostable, and mostly recyclable, and they can extend the shelf life of blueberries and raspberries. (Purdue University photo/Jingxuan Zhang)

One project we’re pursuing calls for applying CN films and coatings to flexible films to prevent oxygen and C02 transport. Oxygen causes oils to become rancid in nuts, chips and other foods, and makes tomato ketchup turn brown. Putting CN onto flexible film allows better use of biodegradable materials such as cellophane, or industrially compostable films like polylactic acid (PLA), which is derived from plant sources. These CN barrier films are even better than industrially-used fully synthetic materials.

We’re also investigating how to make green functional paper packages. This effort involves using CN-based functional layers on molded pulp containers to reduce weight and provide preservation capabilities. Molded pulp is the material used in egg cartons, and sometimes found in food service trays. It is super-cheap, recyclable, compostable and biodegradable. But the material lacks preservative ability and grease resistance, and it’s heavy because it has to be thick to provide the needed mechanical properties. Our CN-coated molded pulp strengthens and stiffens the material, which could lower the weight, and we’ve shown that it could double the room-temperature shelf life of some foods.

These and other advances piggyback on the latest evidence-based analyses of total life cycle carbon emissions to promote the most informed decisions around plastics and sustainability.

Jeffrey P. Youngblood, PhD

Professor

School of Materials Engineering

Environmental and Ecological Engineering (by courtesy)

College of Engineering

Purdue University

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