Experiment 18-Physical Science Plastics Identification Experiment Plastics are an integral part of our society. They are used for just about anything. They are made up of long changes of carbon based material obtained primarily from petroleum and coal. Plastics are polymers made from monomers as shown to the right for polyethylene. The monomer for polyethylene is CH 2 =CH, for PVC is CH 2 =CHCl, for PP is CH 2 =CHCH 3, for PS is CH 2 =CH C 6 H 5, and for Teflon or polytetrafluoroethylene is CF 2 =CF. There are basically three types of plastics. Thermosets are hard and have a very tight-meshed, branched molecular structure. Curing proceeds during shaping, after which it is no longer possible to shape the material by heating. Further shaping may then only be performed by machining. Thermosets are used, for example, to make light switches. While elastomers also have a crosslinked structure, they have a looser mesh than thermosets, giving rise to a degree of elasticity. Once shaped, elastomers also cannot be reshaped by heating. Elastomers are used, for example, to produce automobile tires. Thermoplastics have a linear or branched molecular structure which determines their strength and thermal behavior; they are flexible at ordinary temperatures. At approx. 120-180 C, thermoplastics become a pasty/liquid mass. The service temperature range for thermoplastics is considerably lower than that for thermosets. The thermoplastics polyethylene (PE), polyvinyl chloride (PVC) and polystyrene (PS) are used, for example, in packaging applications. (For history of plastics see: http://www.glencoe.com/sec/science/cgibin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link=http://www.americanplastic scouncil.org/benefits/about_plastics/history.html http://www.glencoe.com/sec/science/cgibin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link=http://www.teachingplastics.org/hands_on_plastics/intro_to_plastics/students.html)
106 Experiment 18-Physical Science Plastics Identification We will be looking at mostly thermoplastics, which are used in packaging. There are six basic types of plastics used in packaging. Using the Society of Plastic Industries, Inc. (SPI) numbering system they are: (1) PET-Polyethylene Teraphthalate- Milk, water, detergent & oil bottles, toys, containers used outside, surfboards, paint brushes, parts and plastic bags. (2) HDPE-High Density Polyethylene- Milk, water, detergent & oil bottles, toys, containers used outside, traffic cones, parts and plastic bags. (3) PVC-Polyvinyl Chloride- Food wrap, vegetable oil bottles, floor mats, hoses, pipes, blister packages or automotive parts. (4) LDPE-Low Density Polyethylene- Many plastic bags. Shrink wrap, grocery bags, garment bags or containers and parts. (5) PP-Polypropylene- Refrigerated containers, some bags, most bottle tops, some carpets, paint buckets, video cassette containers, some food wrap, yogurt containers, syrup bottles and diapers. (6) PS-Polystyrene- Throwaway utensils, meat packing, styrofoam cups, food service trays, license plate holders, trash cans and protective packing. (7) Other-layered or mixed plastics The type of plastic is stamped generally on the bottom of the container in a triangular frame. Either the number or the abbreviation (PET, P VC, etc.) are stamped in or near the triangle. The triangle and the coding system were designed to help in recycling plastics. Plastics destined for recycle need to be sorted by number or type, cleaned and stripped of all labeling. (For explanation of numbering system see: http://www.glencoe.com/sec/science/cgibin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link =http://www.dec.state.ny.us/website/dshm/redrecy/plastic.htm ) (For more information on recycling plastics see: http://www.glencoe.com/sec/science/cgibin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link=http ://www.mines.edu/stu_life/organ/earth/plasticfl.html http://www.glencoe.com/sec/science/cgibin/splitwindow.cgi?top=http://www.glencoe.com/sec/science/top2.html&link=http ://www.ci.redding.ca.us/solwaste/r_plastics.htm)
Experiment 18-Physical Science Plastics Identification 107 Experiment Materials: Students collect examples of the 6 plastics, copper wire and burner, isopropyl alcohol, acetone, cooking oil, burner and matches, 6 large test tubes, crucible tongs, scissors, balance, small 10 ml graduated cylinder Hypothesis: Can you determine the identity of an unknown plastic? The six main kinds of plastics may be identified through an analysis scheme that separates each one based on chemical and physical properties of density, reaction in a flame, reaction with acetone and reaction when heated. You should collect samples of the 6 types of plastics prior to the experiment. The instructor may have some unknown samples as well. Refer to the diagram flow chart and the following detailed instructions. Density Test 1. Cut small pieces of each plastic and place them in water, alcohol, or oil. Make sure they do not float due to surface tension. Try to make them sink. Be sure to dislodge any adhering air bubbles. Record if they float or sink and compare to flow chart. 2. Cut several or a long narrow strip of each plastic. Weigh it dry. Measure the volume of a graduated cylinder half to ¾ filled with water. Place the plastic sample(s) in the cylinder completely submerged in water and measure the total volume. Subtract to get the volume of the plastic. Divide the mass by the volume to get the density. Compare to the following chart for identification: Substance Density Table Density water 1.00 (1) PET 1.38-1.39 (2) HDPE 0.95-0.97 (3) PVC 1.16-1.35 (4) LDPE 0.92-0.94 (5) PP 0.90-0.91 (6) PS 1.05-1.07
108 Experiment 18-Physical Science Plastics Identification Flame Test 1. Heat up a copper wire and melt a portion of the plastic on the end of it. 2. Using the copper wire, place the plastic in a flame and observe and record the color. Use the flow chart to help identify the plastic. Acetone Test 1. Place a piece of the plastic in a small test tube of acetone. 2. Observe and record if it dissolves or not and use the flow chart to help identify the plastic. Heat Test 1. Using tongs hold a piece of the plastic high over a flame or a hot plate and observe how readily it melts. 2. Do not put the plastic directly in the flame or heat the sample too high. Do not allow melted plastic to drop onto a hot plate or burner. 3. Compare samples to see which one is more readily melted.
Experiment 18-Physical Science Plastics Identification 109
110 Experiment 18-Physical Science Plastics Identification
Experiment 18-Physical Science Plastics Identification 111 Experiment 18-Plastics ID Lab Report Name: Section: Date: Sample Source Observations from Flow Chart Type of Plastic Unknown Number or Letter: Observations when identifying the unknown: Type of Plastic:
112 Experiment 18-Physical Science Plastics Identification Questions 1. Your boat is sinking about two miles off shore and you are not a good swimmer. You notice six large solid plastic blocks labeled 1, 2, 3, 4, 5, 6. Which two should you grab and why? 2. You wish too make a plastic handle for a cooking pan out of recycled plastic. Which plastic should you avoid? 3. You decide to jazz up your bathroom cabinet by transferring the fingernail polish remover into a more stylish container. The next day you open the cabinet door to find a messy blob. What as the plastic used in this stylish bottle? What is the active ingredient in the fingernail polish? 4. From what you observed, tell the approximate density of the isopropyl alcohol solution and explain. 5. Why is it important to dislodge any adhering bubbles in the density tests? 6. Sometimes plastic containers are made from two polymers and not just one. What would happen to the water density test if LDPE and PP were mixed? If Pet and HDPE were mixed?