Materials Included In Kit

Additional Materials Required

Safety Precautions

Glycerin and acetic acid are skin and eye irritants. Gloves and goggles should be worn at all times while handling these chemicals. Follow all other standard laboratory safety guidelines.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The plastic product may be disposed of in the solid waste disposal according to Flinn Suggested Disposal Method #26a.

Teacher Tips

• This lab can be run a number of different ways. For example, different student groups can be asked to synthesize the potato plastic using slightly different amounts of glycerin (keeping the amount of starch constant throughout the groups) to observe the effects on the properties of the plastic. Another option is to ask each group to synthesize a batch of plastic without adding any glycerin to the reaction mixture.
• It may take up to 2 days for the potato plastic to dry out completely. To speed up the process, a hair drier can be used.

Answers to Questions

1. What might you do to change the properties of the plastic?

   The reaction mixture contains four components: potato starch, acetic acid, glycerin and water. The water is used to solubilize, or dissolve, the potato starch. The acetic acid helps dissolve the starch. Glycerin is a plasticizer which breaks down the polymer chains in potato starch. To increase the plasticity of the potato starch, the amount of glycerin can be increased. If too much plasticizer is added the potato starch will not be able to assume the structure and properties of a polymer ( i.e. the glycerin will depolymerize the mixture).

2. Predict whether the addition of less glycerin would cause the plastic to be more flexible or less flexible? Explain.

   The addition of less glycerin to the reaction mixture makes the plastic harder and less flexible. This is the case because the glycerin serves to break down the amylopectin polymer chains to make the end product more bendable. Glycerin is a plasticizer, in other words.

3. Potato plastic, or plastic made from potato starch, is often called bioplastic and is considered “green” from an environmental perspective. Explain.

   Most plastics are obtained from by-products of petroleum refining and natural gas processing, such as ethylene (CH₂=CH₂), propylene (CH₃CH—CH₂) and styrene (C₆H₅CH—CH₂). Manufacturing plastics consumes nonrenewable resources and requires large investments of energy. Disposing of plastics is also an environmental concern, because most plastics are non-biodegradable. In contrast, plastic derived from potato starch is biodegradable under natural conditions to give innocuous decomposition products. Potato starch is a polymer made up of long chains of glucose molecules (monomers) joined together to form two distinct polymer chains, amylose and amylopectin.

Introduction

Plastic is so much a part of our lives that we often take it for granted. Our cell phones, cars, houses, computers, clothing, sports equipment and food items like bottled water are just a handful of retail items based on plastic. This experiment will teach you how to make plastic from potato starch using a simple, “one-pot” process. You will also learn to alter its properties such as flexibility and hardness by chemical means.

Concepts

• Polymers
• Green chemistry
• Materials chemistry
• Chemical synthesis
• Renewable feedstocks

Background

Materials chemistry is the study of how a chemical’s structure relates to its properties. One application of materials chemistry is the design of plastics to be either brittle or flexible depending on the end use. Plastics are polymers. A polymer is a substance that is made up of many units. The units, or monomers, are small molecules that usually contain less than ten atoms in a row. Carbon and hydrogen are the most common atoms in monomers, but oxygen, nitrogen, chlorine, silicon, fluorine and sulfur may also be present. Polymers can be best visualized as numerous beads (monomers) linked together (or polymerized) on a string to make a chain with at least 100 repeating units. Each bead or monomer is polymerized to the next to form thousands of atoms in a row.

The properties of a polymer can be controlled by carefully varying the types and amounts of starting materials. For example, manufacturers constantly introduce various fillers and additives into polymers to expand product possibilities. Polymers may also have different end units, branches or variations in sequences that lead to various types of materials.

Most plastics are obtained from by-products of petroleum refining and natural gas processing, such as ethylene (CH₂=CH₂), propylene (CH₃CH—CH₂) and styrene (C₆H₅CH—CH₂). Manufacturing plastics consumes nonrenewable resources and requires large investments of energy. Disposing of plastics is also an environmental concern, because most plastics are non-biodegradable. It has been estimated that it would take more than five years for a discarded plastic milk jug to decompose when exposed to environmental conditions. In contrast, plastic derived from potato starch is biodegradable under natural conditions to give innocuous decomposition products. Potato starch is a polymer made up of long chains of glucose molecules (monomers) joined together to form two distinct polymer chains, amylose and amylopectin (see Figure 1). The amylopectin is plasticized, or broken down, until it assumes the properties of plastic, by reaction with glycerin. This experiment demonstrates that the synthesis of plastic can be a straightforward process, and that simple changes to the reaction mixture (such as altering the amounts of reactants by small degrees) can have profound effects on the properties of the end material. These types of simple manipulations are commonly carried out in the development and production of commercial plastics, albeit on a larger scale.

Materials

Safety Precautions

Glycerin and acetic acid are skin and eye irritants. Gloves and goggles should be worn at all times while handling these chemicals. Follow all other standard laboratory safety guidelines.

Procedure

1. Weigh about 20 g of potato starch and place in a medium-sized beaker.
2. Add approximately 120 mL of water with stirring.
3. Add about 10 mL of 10% acetic acid solution to the mixture with stirring.
4. Add approximately 10 mL of glycerin with stirring.
5. Add food coloring if desired.
6. Heat the mixture to near boiling and keep at a simmer for approximately 5 minutes. Stir the mixture continuously until it becomes thick and transparent.
7. Pour the viscous mixture onto a non-stick surface such as a baking pan or non-stick paper, or into a non-stick mold.
8. Allow the mixture to dry for 1–3 days.

Student Worksheet PDF

14103_Student1.pdf