A Day in the Life of a Plastic Bag

A Day in the Life of a Plastic Bag

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Plastic first appeared on the scene in 1862, at the Great International Exhibit in London. This coincided with Abraham Lincoln’s declaration of war against the Confederacy, a loose coalition of Southern states.

Plastic’s inventor was named Alexander Parks, and his version of this almost ubiquitous substance was a cellulosic compound made from nitrocellulose and camphor that he called xylonite, or parkesine. Park’s original intention was to make a substitute for horn.

Before Parks could perfect his discovery, the Hyatt brothers took it over and produced the world’s first celluloid, or synthetic plastic – a word that came into common usage in the early 1900s with Leo H. Baekeland, who invented Bakelite (a hard plastic made from coal tar that formed the outer shell of such items as telephones, cameras and pipe stems).

It wasn’t until after World War I (in 1918), and the increasing availability of petroleum and natural gas (both more easily handled than coal tar), that plastic manufacture really took off.

Without going into the chemistry of plastics, suffice to say that plastic bags are made from one of three basic kinds of ethelene, a hydrocarbon naturally occurring in coal gas, crude oil and natural gas. They are:

  • Low-density polyethylene (LDPE), dry cleaner’s bags
  • High-density polyethylene (HDPE), or the typical grocery bag
  • Linear low-density polyethylene (LLDPE), which makes shiny and relatively sturdy bags from upscale retail clothiers and the like (Macy’s, Herberger’s, etc.)

Besides thicknesses, or grades of plastic, plastic bags can be differentiated by adding pigment to the crystals, which are melted at around 360 degrees to make a liquid “soup” which is extruded from a specialized machine into the desired thickness and strength.

The first dimension, thickness, is measured using a micrometer. Manufacturers determine if a bag will be 30, 45, 50 or even 100 microns, depending on the retail venue it is slated to serve. This is often converted into “mils”, a unit of measurement representing one-thousandth of an inch. Finally, common usage turns this thickness into “gauges,” a descriptive measure that is also used to calibrate the thickness or strength of wire fencing. For example, the grocery bag is typically one-gauge, or one mil. Fifty gauge would be a relatively thick plastic bag, but manufacturing also takes into consideration the tensile strength of the plastic, so not all 50-gauge bags are equal.

The fluid is extruded from a round canister via a blower, just like a soap bubble, only continuously. The bubble runs through cooling rollers. The farther it gets from the extruder, the more closely it resembled the plastics we are used to seeing. Ultimately, this circle of plastic runs through another high-speed machine which layers and cuts it to the exact specifications of the current job. The job of keeping the plastic flowing is physically hard, but perhaps the most difficult part is avoiding “losing the bubble” (thank you, Polar Plastics). When that happens, all the machinery has to be shut down until the operator can reacquire the bubble.

In the heyday of the plastic bag, say 1970 through 2004, Western nations like the United States and Great Britain accumulated such a burden of plastic, primarily in the form of bags, that a gigantic gyre (also known as a vortex or whirlpool) in the Pacific Ocean has earned the unfortunate name of The Great Pacific Garbage Patch.

This, which was once cited as being as large as the state of Texas, is actually a rather loosely distributed assortment of an inestimable number of plastic bags and other debris which, according to the National Oceanic and Atmospheric Administration, or NOAA, covers 7 to 9 million square miles.

Nor is the North Pacific Gyre the only gyre. The others are the South Pacific Gyre, the North and South Atlantic Gyres, and the Indian Ocean Gyre, all of which have an overabundance of plastic debris largely from bags.

Some more disheartening statistics from various environmental groups include the fact that:

  • The Pacific Gyre has been estimated at one and one-half times the size of the U.S.
  • The Pacific Gyre contains almost 100 pounds of trash per pound of plankton, the latter being the ocean’s biggest foodstock
  • Plastic makes up nine-tenths of all the trash floating in the oceans of the world
  • Of the 300 pounds of plastic manufactured each year, one-tenth ends up in oceans, where 70 percent sinks but continues to wreak havoc at the bottom of the ocean, because plastic does not break down, ever
  • Each year, more than a million sea birds and 100,000 marine creatures, whether mammalian, amphibian and reptilian (i.e., sea turtles), die as a result of ingesting, or becoming tangled in, plastic bags, water bottles and the like.

There is an old joke that God may have invented humans because He wanted styrofoam (i.e., rigid plastic). If you have ever seen the Garbage Patch firsthand, you probably aren’t laughing.


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