Plastics: Synthetic Polymers

Transcription

1 Date Lab Time Name Objective Plastics: Synthetic Polymers Synthesizing nylon (a polyamide) and silly putty will illustrate the chemical production of plastics. Some physical properties of these polymers will be examined. Background Polymers are large, chain-like molecules made of hundreds or thousands or smaller, repeating molecular units called monomers. Many occur naturally in plants and animals such as cellulose, which is a natural plant polymer made of glucose monomers. Wool and hair are natural animal polymers made of protein monomers. Since the early 1900 s, synthetic polymers or plastics have been produced for a variety of industrial and household uses. One common method for joining molecular units together to produce synthetic polymers is called condensation polymerization. During this chemical reaction, a small molecule such as H 2 O or HCl is eliminated as the larger polymer molecule is formed. In the early pioneering days of polymer research, DuPont successfully synthesized nylon utilizing such techniques. There are different nylon type polymers. The reaction of sebacoyl chloride with 1,6-hexanediamine to form Nylon 6-10 is used in this experiment. Nylon 6-10 is thus a copolymer made by the chemical combination of two different monomers. Each of these monomers is dissolved separately in two immiscible liquids, water and tetrachloroethylene (TCE). When these two solutions are in contact with each other, the monomers can only react at the interface between them. The nylon rope is drawn from this polymer film that forms at the interface. As soon as old polymer film is removed, new film forms immediately behind it. Thus, the reaction results in the continuous creation of polymeric material until at least one of the reactant monomers is completely consumed. Addition polymerization is another method of synthetic polymer production. In this chemical reaction, monomer units of the same molecule link together to form the long-chain polymer molecule without the elimination of any small molecules. Polyethylene (Tupperware, plastic tarpaulins, etc.) and polystyrene (Styrofoam ) are common examples of polymers produced in this fashion. Polystyrene can be molded into either a hard solid or a light foamed shape and is generally cheap to produce. This low cost makes foamed polystyrene economical as a paper substitute for applications such as food and fragile object packaging. However, an increasing number of such products are being banned by states because the low boiling liquid, methylene chloride, used as the foaming agent is thought to be harmful to the earth s ozone layer. Materials needed 100 ml beaker sebacoyl chloride in TCE 350 ml beaker 1,6-hexanediamine in water stirring rod paper cup and wax paper 100 ml graduated cylinder (3) distilled water forceps or tweezers acetone or methanol meter stick Elmer s glue disposable gloves 4% sodium borate safranin 0 (optional) orcein (optional) Plastics: Synthetic Polymers 1

2 Date Lab Time Name Procedure Part I: Nylon 1. CAUTION: Wear disposable plastic gloves while performing this part of the experiment and do not breathe vapors nor let any of the chemicals contact your skin. Carry out the chemical reaction in a fume hood. 2. Fill a 350 ml collection beaker with 200 ml of water and 50 ml of acetone or methanol. This beaker will be used to collect and rinse the nylon that is produced in the reaction. 3. Measure 30 ml of the sebacoyl chloride solution in a graduated cylinder and pour into the 100 ml beaker. 4. Measure 15 ml of the 1,6-hexanediamine solution in a clean graduated cylinder and slowly and carefully pour it on top of the sebacoyl chloride solution already in the 100 ml beaker. Do not stir or agitate the beaker contents. Note your observations on your report sheet. 5. COLOR OPTION: If you wish, you can dye your polymer some interesting colors by adding food coloring to the 100 ml reaction beaker. Only 1 or 2 drops in the top liquid layer is needed. 6. Use tweezers or forceps to reach down through the top liquid layer and carefully grasp the center of the thin interfacial polymer film. Slowly pull the large mass up through the top liquid. Tear off the large nylon mass and continue to bring the thin nylon cord from the center of the beaker. Slowly and steadily (to keep the nylon from getting too thin) feed it into the 350 ml beaker until the top layer of liquid is gone. TIP: Place the end of the cord over the side of the beaker so you can easily find it later. 7. When the polymerization is complete, drain off (into the appropriate collection container) the water/acetone mixture until there is just enough to keep the nylon submerged. Add enough cold water to bring the level back to its original amount. 8. While the cord is still in the 350 ml beaker, grab the free end and place it on the table top. Walk along the table with the beaker while gently pulling the rope out. Once you have completely stretched out your nylon cord, use a meter stick to measure its total length. 9. Record the following observations on the report sheet: a. Describe the color, appearance, texture, shape and tensile strength of your damp nylon rope. b. Spread out your polymer on the bench top in such a way that you can measure its total length with a meter stick. Record your results on the report sheet. c. Test the inertness (non-reactivity) of your polymer with the solvent acetone by placing a peasized polymer wad into about 10 ml of acetone in a 50 ml beaker. Plastics: Synthetic Polymers 2

3 Date Lab Time Name Part II: Silly Putty 1. Wear disposable plastic gloves while performing this part of the experiment. 2. Use a graduated cylinder to measure out 25 ml of water. Pour into a paper cup and mark the water level. Discard the water. 3. Fill the paper cup with glue up to the mark 4. COLOR OPTION: If you would like to create a colored piece of silly putty, place 2-3 drops into your cup at this point. 5. Add 20 ml of water to the cup and stir with stirring rod for several minutes. 6. Add 10 ml of 4% sodium borate and stir with stirring rod for several minutes. 7. Remove polymer from the cup and place on wax paper until the polymer becomes firm and rubbery. 8. Make the following observations on your report sheet: room temperature, the total time for polymer formation & some physical properties. 9. After the silly putty has sufficiently hardened and is no longer sticky, describe the physical properties of the polymer such as hardness, texture, color, and general appearance. 10. Test the inertness of your polymer by placing a few drops of acetone onto a surface of your polymer. Rub the plastic surface with your finger where the acetone has been dropped. Note your observations on the report sheet. Disposal Procedure *** Dispose of all remaining chemicals in the appropriate collection containers. *** The nylon rope can be rolled up and taken home or placed in the appropriate collection container. *** Silly Putty can be taken home or placed in the appropriate collection container *** The rubber gloves, paper cup and wax paper can be placed in the trash. *** Wash and dry all glass containers and stirring rods and return them to their proper location. Plastics: Synthetic Polymers 3

4 Date Lab Time Name Report Sheet Data Analysis Part I: Nylon * Observations upon mixing the monomer solutions: Physical properties of the nylon rope: Color Texture Shape Tensile Strength Total length of rope (show calculations, if necessary): # of breaks feet meters 1 m = ft 1 ft = m * Observations on solubility in acetone: Part II: Silly putty Room temperature: Time required for polymer formation: * Observations during preparation: Physical Properties of the Silly Putty: Hardness Texture Color * Observations on solubility in acetone: Plastics: Synthetic Polymers 4

5 Date Lab Time Name Post-lab questions: 1. What was the purpose of washing the newly formed polymer with an acetone/water solution? 2. List three principle consumer uses for nylon. 3. List several examples of a naturally occurring plant polymers and where they are produced. 4. Why does the price of plastics depend on the price of oil? Plastics: Synthetic Polymers 5

6 Date Lab Time Name Summary/Conclusions: Plastics: Synthetic Polymers 6