Chemical Plastic

July 21, 2010

Paper or plastic bags?

Filed under: Chemical Related Story — Administrator @ 7:12 am

It’s an old question, and still in debate, when it is time to check out when we are doing grocery shopping: paper bag or plastic bag? It seems like it should be an easy choice, but there’s an incredible number of details and inputs hidden in each bag. From durability and reusability to life cycle costs, there’s a lot more to each bag than meet the eye. Let’s figure it out behind each bags.
   Paper is made from trees. The logging industry is huge, and the process to get that paper bag to the grocery store is long, sordid and exacts a heavy toll on the planet. First, the trees are found, marked and felled in a process that all too often involves clear-cutting, resulting in massive habitat destruction and long-term ecological damage.

Once the trees are collected, they must dry at least three years before they can be used. More machinery is used to strip the bark, which is then chipped into one-inch squares and cooked under tremendous heat and pressure. This wood stew is then “digested,” with a chemical mixture of limestone and acid, and after several hours of cooking, what was once wood becomes pulp. It takes approximately three tons of wood chips to make one ton of pulp.

The pulp is then washed and bleached; both stages require thousands of gallons of clean water. Coloring is added to more water, and is then combined in a ratio of 1 part pulp to 400 parts water, to make paper. The pulp/water mixture is dumped into a web of bronze wires, and the water showers through, leaving the pulp, which, in turn, is rolled into paper.

Unlike paper bags, plastic bags are typically made from oil, a non-renewable resource. Plastics are a by-product of the oil-refining process, accounting for about four percent of oil production around the globe. The biggest energy input is from the plastic bag creation process is electricity, which, in this country, comes from coal-burning power plants at least half of the time; the process requires enough juice to heat the oil up to 750 degrees Fahrenheit, where it can be separated into its various components and molded into polymers. Plastic bags most often come from one of the five types of polymers — polyethylene — in its low-density form (LDPE), which is also known as #4 plastic.

l        A look at the facts and numbers
Further insight into the implications of using and recycling each kind of bag can be gained from looking at overall energy, emissions, and other life cycle-related costs of production and recycling. According to a life cycle analysis by Franklin Associates, Ltd, plastic bags create fewer airborne emissions and require less energy during the life cycle of both types of bags per 10,000 equivalent uses — plastic creates 9.1 cubic pounds of solid waste vs. 45.8 cubic pounds for paper; plastic creates 17.9 pounds of atmospheric emissions vs. 64.2 pounds for paper; plastic creates 1.8 pounds of waterborne waste vs. 31.2 pounds for paper.

Paper bags can hold more stuff per bag — anywhere from 50 percent to 400 percent more, depending on how they’re packed, since they hold more volume and are sturdier. The numbers here assume that each paper bag holds 50 percent more than each plastic bag, meaning that it takes one and half plastic bags to equal a paper bag — it’s not a one-to-one comparison, even though plastic still comes out ahead.

It’s important to note that all of the above numbers assume that none of the bags are recycled, which adds a lot of negative impacts for both the paper and plastic bags; the numbers decrease in size (and the relative impacts decrease) as more bags are recycled. Interestingly, the numbers for paper bag recycling get better faster — the more that are recycled, the lower their overall environmental impact — but, because plastic bags use much less to begin with, they still ends up creating less solid and waterborne waste and airborne emissions.

l        Paper and plastic bags’ required energy inputs
From the same analysis, we learn that plastic also has lower energy requirements — these numbers are expressed in millions of British thermal units (Btus) per 10,000 bags, again at 1.5 plastic bags for every one paper bag. Plastic bags require 9.7 million Btus, vs. 16.3 for paper bags at zero percent recycling; even at 100% recycling rates, plastic bags still require less — 7.0 to paper’s 9.1. What does that mean to me and you? Plastic bags just take less energy to create, which is significant because so much of our energy comes from dirty sources like coal and petroleum.

Both paper and plastic bags require lots and lots of resources and energy, and proper recycling requires due diligence from both consumer and municipal waste collector or private recycling company, so there are a lot of variables that can lead to low recycling rates.

Ultimately, neither paper nor plastic bags are the best choice; we think choosing reusable canvas bags instead is the way to go. From an energy standpoint, according to this Australian study, canvas bags are 14 times better than plastic bags and 39 times better than paper bags, assuming that canvas bags get a good workout and are used 500 times during their life cycle.

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