LESSON 4: Corn that Bounces & Stretches
SUBJECT: Science
OBJECTIVE: Students will experiment with different recipes that create different forms of biodegradable plastic made from corn. They will be introduced to polymers, both natural and synthetic, and will gain an understanding of the products which can be made from natural polymers like cornstarch.
MEASUREMENT: Students will know that many of the plastic materials they encounter in their everyday lives can be made from cornstarch, and that they would then be more biodegradable.
BACKGROUND FOR TEACHERS:
Plastics are a major problem in our rapidly filling landfills. Plastics made from petroleum do not decompose quickly. New plastics are being developed that are made from cornstarch-a plastic bag containing 10 percent cornstarch will degrade 10-20 times faster than other plastic bags. Other benefits of biodegradable plastic products include: (from http://www.ohiocorn.org/kids/corny.htm)
- Plastic bottles can be made stronger and lighter when made from 15 percent cornstarch.
- Biodegradable plastics are not expensive.
- Biodegradable plastics can be composted and used as a carbon-rich soil supplement.
It is possible to make plastics from starch because starch is a polymer, a molecule of many individual pieces (monomers) all hooked together. A polymer might be demonstrated as a string of beads or paper clips - individual pieces joined together into one long chain. Polymers behave in interesting ways because of their long chain structure.
Some polymers are natural, and some are synthetic (made by people). Many of the natural polymers (protein, starch, cellulose) have names without "poly" because they were named long before people knew about their repeating nature. Their chemical structures are more complex than synthetic polymers due to the complex metabolic functions the natural polymers play in living organisms.
The following are some examples of synthetic polymers and some of their applications:
- Polyethylene: milk jugs, toys, oil containers, squeeze bottles, plastic bags, shrink wrap
- Polyvinyl Chloride: food wrap, vegetable oil bottles, blister packaging, pipes
- Polystyrene: StyrofoamTM cups, packaging, housewares, toys
STUDENT ACTIVITIES:
1. Ask students to read the story Hugh Buys a Car, then discuss the concept of creating a "vegetable" car from products made from plant-based industrial products.
2. Ask students to list the "plastic" components of a car. Then ask if they think it's possible to make such plastics from corn.
3. Introduce students to the concept of polymers by having them create chains from 6-10 paper clips, beads, or rubber bands. Polymers are long chains of individual molecules. Explain that polymers can be made by man (synthetically) but the chemicals used are often petroleum-based and do not decompose easily. This is in contrast to the natural polymers, like those found in cornstarch. These natural polymers are biodegradable and can be used in combination with, or in substitution for, synthetic polymers.
4. Ask students to study the list of familiar things made from polymers and circle those that they consider plastic. (Plastics are defined as "synthetic or natural materials that may be shaped or molded when soft and then hardened.") (Worksheet 1)
5. Then break students into teams, letting each team make a different kind of "plastic" from cornstarch using the recipes that follow. (For more information on cornstarch see Unit 9, Lesson 3). (Worksheet 2)
6.Point out that these products are very safe and are "biodegradables," even dissolving in water. |
KEY ISSUES
