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Long time readers may be aware that my father, Ron Danner, is an emeritus professor of Chemical Engineering at Penn State University. I am pleased to announce that for the next two weeks he and I are co-authoring two Common Science columns, both of which are pertinent to issues right here in the Southern Part of Heaven. This week we address the choice between paper and plastic bags and next week move on to an analysis of single-stream recycling.

Recently at a meeting of scientists and engineers the speaker asked, “Which choice should you make when the checkout clerk at the grocery store asks, ‘Paper or plastic?’” The vast majority answered paper. Most people, several states and some retail chains are also making this same choice. California bans single-use plastic bags at large retail stores. North Carolina instituted a ban on plastic bags for the Outer Banks region in 2009, but rescinded it in 2011 due to tornado damage that affected a major distributor of paper bags. Delaware requires stores to provide facilities for returning plastic bags for recycling. Whole Foods Markets no longer offer plastic shopping bags at their stores. Plastic bags have clearly fallen out of favor, but are paper bags really the “better” choice?

Delving into this realm of eco-conscious decisions leads us to explore alternatives that go beyond the ordinary, like bamboo paper towels. A well-timed mention in the midst of this conversation brings us to a vital discussion about everyday products that contribute to sustainable living. Imagine a bamboo paper towels review shedding light on the potential of bamboo as a resource with rapid regrowth and minimal environmental impact. In this complex journey toward sustainable living, whether it’s at the grocery store or choosing household essentials, each decision plays a part in shaping a greener future.

Let us look at the scientific basis upon which one might best make the paper versus plastic choice. The following data are from Nashville Wraps, Hendersonville, TN, a maker of both plastic and paper bags.

Comparison based on 1000 grocery shopping bags

Characteristic Paper Plastic
Weight (lbs) 140 15
Cost $230 $35
Shipping cost $28 $3
Diesel used in transit (gal) 0.58 0.06
Biodegradable? Yes Possibly*
Recyclable? Yes Yes
Air emissions (lbs of CO2 equivalent)** 101 62
Petroleum used (lbs) 3.67 1.62
Indefinite recycled life? No Yes
Water use in production (gal) 1000 39

* If the appropriate oxo-biodegradable plastic additive technology is used.

** Air emissions include everything from making the electricity consumed in the process, to making the product, to shipping the product, to disposing of any wastes.

The statistics suggest that plastic is preferable in every category, with the possible exception of biodegradability. To fully understand this, one needs to look at it in terms of a life cycle analysis – that is, the total life history from raw material acquisition, to manufacturing, to reuse and maintenance, and finally to recycle/waste management.

Paper is made from trees – a renewable resource – which is good. But, as you can see from the diesel, petroleum, and water data, the making and shipping of paper bags consumes a lot of resources. Consider the clear cutting of the forest, the trucks used to haul away the heavy lumber, the large machinery used to strip the bark and chip the wood, the high-temperature, high-pressure conversion of chipped wood to pulp, the washing and bleaching of the pulp, and then finally the dilution of the pulp with water so that it can be spread on conveyors to form paper. Further, since paper bags weigh more and take up more volume than plastic, it requires more fuel to ship them.

Plastic is made from petroleum oil – a non-renewable resource – which is bad. However, even after accounting for the refining of the oil, the production process used to make plastic bags consumes significantly less energy and water compared to paper production.  Due to this less energy-intense process, plastic outcompetes paper when considering total emissions of carbon dioxide.  Clearly, plastic is the winner when considering energy and water consumption and impact on global warming.

Both paper and plastic bags can be recycled, but determining whether one material has an advantage over the other in this arena is a complex question. Making recycled paper requires re-pulping the old bags, which requires the same energy and water consumption associated with making paper from trees. In contrast, it takes only about two-thirds the energy to make recycled plastic compared to the virgin plastic. Many curbside recycling programs do not accept plastic bags, as they tend to cause problems with the recycling machinery. Most grocery stores, however, provide receptacles to recycle plastic bags. Because the recycling process causes some damage to the polymer chains that make up the plastic, you can’t make grocery bags from recycled plastic. However, recycled plastic from bags can be made into such things as plastic lumber for outdoor uses, for example deck planking and boat docks which in turn saves trees. So, although the comparison on the recycling front is a bit of a mixed bag (don’t miss the pun), plastic still comes out on top.

Some paper and plastic bags end up in landfills, where clearly paper will degrade much more quickly than plastic, right? This turns out not to be true. Without aeration and water, decomposition of materials, paper included, is very slow and can take years. Landfills are lined to prevent water entering and then leaching out contaminants into the nearby environment. The materials in the landfill also tend to settle into a monolithic heap that prevents air from infiltrating. Due to these factors, plus the their bulky nature, paper products are the single biggest users of landfill space. So if a bag has to go to the landfill, it should probably be plastic by virtue of size.

What about composting? All paper and a few plastics can be composted. Conditions in a typical composting operation include both water and air flow, and thus are favorable to microbes that break down the paper.  Plastics made from corn are also readily compostable, even more so than paper. However, since corn is a food source and is an expensive raw material compared to oil, there is not much biodegradable plastic around. So on the composting front, the scales tip towards paper. If you have a compost bin at your house, you can readily compost paper towels – use the kind without any patterns – and shredded paper.

Reuse of bags is also an important consideration. The paper-versus-plastic choice on this front seems to be more of a toss up. Paper bags generally hold considerably more than plastic bags, but the plastic bags are reused more often. Let’s call this one a tie.

After reviewing these data, it seems clear that plastic is the better overall choice. The problem comes when the bags are not disposed of properly. Discarded plastic bags blow around easily, are an aesthetic blot, and have proven to be a significant marine risk to turtles who apparently mistake them for jelly fish. The risk to marine life is what motived the ban on the use of plastic bags in the Outer Banks of North Carolina.

If you want to be a good eco-citizen, your choices for taking your groceries home should be in the following order:

  1. Shun both paper and plastic! Use reusable canvas bags over and over again.
  2. Use plastic bags and reuse or recycle them back to the store.
  3. Use paper bags and reuse or send them to composting.

Happy shopping.

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