Departments : Integrating Science in Your Classroom :
Paper or Plastic?
By John Cowens
Bring meaning to your celebration of Earth Day this month with these environmentally conscious experiments
Online Extra: For an activity on the mass and volume of paper vs. plastic bags click here
Sure, plastic bags take up less space, but could they actually be not as bad for the environment as we once thought?
I dread going to the grocery store. Not because I buy over $100 worth of groceries, but because of the incredible number of plastic or paper bags I take home. As an incentive to conserve on plastic or paper, some stores offer two cents per paper bag if you bring them back and reuse them. In some grocery stores, plastic bag collection bins are located near the exit. Although the signs on the bins usually say "plastic recycling," the bags are usually deposited in landfills. When the cashier asks, "Would you prefer paper or plastic bags?," the smart, environmentally aware consumer chooses the material that will do the least damage to the environment. So, which is best, paper or plastic?
The production of paper
Paper comes from many types of trees. Huge fossil-fueled-powered machines such as logging trucks or helicopters are used to remove the logs from the forest floor. Once the trees are harvested, they are dried for three years before the bark is stripped. The wood is chipped into one-inch squares and cooked under intense heat and pressure until turned into a "stew." This goopy-looking substance is digested with limestone and sulphurous acid until it becomes pulp. This pulp is washed thoroughly with thousands of gallons of clean water and then bleached. Coloring is added to more water and is combined to a ratio of one part pulp to 400 parts water to make paper. This mixture is dumped into a web of wires that separates the water from pulp, which is then rolled into paper. Don't forget to include all the chemicals, electricity and fossil fuels used in shipment of this raw material and in the production needed to make paper bags. It takes about four times as much energy to manufacture a paper bag than it does a plastic bag.
Paper breakdown
Paper can be thrown away or recycled. If it ends up in the landfill, it will eventually break down. However, if paper is recycled it goes through a process of returning to pulp by the use of chemicals such as sodium hydroxide, hydrogen peroxide and sodium silicate. As the pulp fibers spread out, cleaning and screening processes are used to remove contaminants. Then, the pulp is submerged in lots of clean water and heated to remove the old ink particles. Afterwards, recycling centers treat the water to remove contaminants by the use of screens and mechanical cleaners. Some paper recyclers include a process that separates and cleans water, ink, pigments and small particles of waste. These waste materials can be used to make fertilizers, bricks and other useful products instead of going to landfills.
Take advantage of paper grocery bags. They can hold up to four times the volume of a thin plastic bag. They can be used for trash-can liners or craft projects. These bags can be filled with yard waste and tossed into compost piles.
The production of plastic
Producing plastic also requires huge machinery, lots of fuel and large amounts of energy. As you know, plastic comes from petroleum, which is located deep in the earth. A hole is drilled and oil is either piped or trucked to refining facilities where fuels and plastics are produced.
Electricity is the main source of energy needed to make plastic bags (not to mention the fuel-burning heavy machinery required to acquire the oil). Electric energy needed in the actual production and manufacturing of plastic bags usually comes from coal-burning power plants. About 50% of generated electricity comes from burning old rubber tires, which essentially comes from plastic!
Recycling plastic
If plastic bags end up in landfills, they will stay intact for thousands of years since they do not compost. On the other hand, if plastic is recycled it can be re-melted and reformed. Remelting sterilizes the plastic, which can be made into hospital products. Plastic can be recycled many times before it finally becomes brittle. Nevertheless, this almost worthless plastic can still be made into a useful product such as a doormat, which lasts for many years. Unfortunately, not all plastic bags can be recycled. Instead, they can be bundled and sent to the landfill for lack of another alternative. Some plastics, however, can be burned to produce electricity. Although burning plastic doesn't produce the sulphur emissions that coal does, it can still create dioxins if ink and additives are burned with the plastic. The ash itself is toxic and must be disposed properly at a special toxic waste dumps.
Is plastic a good thing?
Scientists say that plastic makes up only 18% of waste by volume and 7% by weight. If we didn't use plastic, our landfill weight of waste would increase 150%, packaging would weigh 300% more and energy consumed by industry would increase by 100%. Plastic does have additional benefits. By adding plastic to cars our fuel economy has doubled. Furthermore, adding plastic to aircraft saves an average of 10,000 gallons per plane.
Still confused on which bag to use? Time will tell whether paper or plastic grocery bags are better for the environment. The lesson we must learn is to reuse paper and plastic bags frequently. Better yet, bring your own durable cloth bags with you to the grocery store.
Mass and space of plastic vs. paper bags
The lesson below gives students the opportunity to compare the mass of paper and plastic bags and the amount of space they occupy. A few days before starting this activity, have students bring to class a variety of paper and plastic bags that are used in grocery stores. Then, point out that according to the Environmental Protection Agency, the United States has 3,091 active landfills and over 10,000 old municipal landfills. Last year, Americans generated almost 400 million tons of trash and more than half was carted off to landfills. As a result, almost 100 landfills across the country had to be closed since they were crammed to the brim. By the year 2055, it is estimated that 2,216 landfills will reach capacity and shut down.
Materials:
- plastic grocery bags
- paper grocery bags
- shoeboxes (one per group)
Procedures:
- Divide students into groups of four or five.
- Have each group safely cram plastic bags into a shoebox and close the lid. Be careful not to split the shoe box!
- Ask one student in the group to record the number of plastic bags that fill the box.
- Empty the shoebox. Repeat step #2 and #3, but cram paper bags into the shoebox.
Students quickly discover that a paper grocery bag weighs more than a plastic grocery bag while holding them in each hand. How many plastic bags equals the weight of one paper bag?
Materials:
- plastic grocery bags
- standard-size paper grocery bags
- string
- dowel rod (or meter stick)
- two paper clips
Procedures:
- Unbend the two paper clips and shape them into "S" shape hooks. Secure them to each end of the dowel rod.
- Find the balancing point of the dowel rod by placing it on your fingertip. You can then secure a 12" (30 cm) string at this point.
- Using one of the "S" hooks, ask students to hang a paper bag on one end of the dowel rod.
- Using the other "S" hook, hang one plastic bag on the opposite end of the dowel rod.
- Grab the string (located at the center of balance) and suspend the balance system. Does the weight of one paper bag equal the weight of one plastic bag?
- Add more plastic bags to the hook until a perfect balance is established. So, how many plastic bags does it take to equal the weight of one paper bag?
Answer: the weight of 10 plastic grocery bags is equal to one standard-size paper bag. Have fun!
Online Extra: For an activity on the mass and volume of paper vs. plastic bags click here
John Cowens teaches sixth grade at Fleming Middle School in Grants Pass, OR.
April 2007, Vol.37, No.7
