PLASTICS: A COMMON OCCURENCE

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Mary Boyd
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1 PLASTICS: A COMMON OCCURENCE Introduction Plastics are very common in our society today. They are used extensively for food storage and in this area alone, generate tons of waste for landfills. If one evaluates the amount of household garbage generated, it could easily be seen plastic and paper combined accounts for around 70% of the waste. Plastics can be recycled for use. This cuts down appreciably on the amount of waste that needs to be buried in the landfills. To make recycling more efficient, a code was established and stamped on the bottom of most containers to identify the composition of the plastic. Although more than 60,000 types of plastic are manufactured, there are only six plastics that are commonly identified by this code. These six make up about 70% of the plastics used today. The code is a triangle composed of arrows with a number in the center of the triangle. It usually appears on the bottom of the container. Number Name of Plastic Abbreviation 1 Polyethylene terephthalate PET 2 High density polyethylene HDPE 3 Polyvinyl chloride PVC 4 Low density polyethylene LDPE 5 Polypropylene PP 6 Polystryene PS 7 Others/mixtures Most plastics used today are identified by this triangle but their identity can also be predicted based on their use or appearance. Most soft drink containers are made of polyethylene terephthalate. Most opaque translucent containers such as milk containers are high density polyethylene,

2 Today the properties of the six common plastics will be identified. Four tests will be run on each of the six and observations will be made to help distinguish between them. Using these observations, a flow chart will be made which will then be used to identify unknown plastics samples. A sample data sheet is included at the end to aid with observations. Do not feel limited though by this sheet. The more detailed the observations, the easier it will be to construct and use the flow chart. Tests 1. Density test 2. Melt test 3. Ignition test 4. Copper wire test Safety Notes: 1. Burn all samples in your individual fume hoods, as the burning process will generate unpleasant and toxic vapors. 2. Care should be taken when melting plastics to avoid burns due to contact with the hot liquid. Procedure I. Density Perform the following procedure on a sample of each of the six common plastics. 1. Gather three test tubes. Label and half fill each test tube with one of the following: 1:1 95% ethanol: water (Density is 0.94 g/cm 3 ) Water (Density is 1.00 g/cm 3 ) 10% NaCl (Density is 1.08 g/cm 3 ) 2. In each test tube place a narrow strip of the plastic sample. Be sure the sample size is small enough so it does not touch the sides of the test tube. 3. Using a stirring rod, push each plastic sample under the surface of the liquid. Observe whether the sample floats, sinks, or suspends in the liquid. Record observations. 4. Interpret observations. If the sample floats, the density of the plastic is less than that of the liquid. If the sample suspends in the liquid, the density is the same as the liquid. If the sample sinks, the density is greater than the liquid s density. 5. Once all six plastic types are tested, rank the plastics in order of their density, from the least to the greatest.

3 II. Melt Test Perform the following procedure on a sample of each of the six common plastics. 1. Place a sample of the plastic in a metal spatula. 2. Slowly heat the sample over a Bunsen burner in the small hood provided at each workstation. Do not heat too quickly. The goal is to melt the sample, not char or ignite it. 3. Record observations of the sample once it has melted and again after it cools. Look at both the appearance and flexibility. III. Ignition Test Using the samples from the melt test, perform the following procedure on a sample of each of the six common plastics. Be sure the test is performed in the fume hood. 1. Fill a beaker with water and have available for use. Once samples ignite and observations are made, the burning samples will be placed in the beaker to extinguish the flame. 2. Using tongs or forceps, place a piece of the melted plastic directly into the burner flame and observe. Things to consider: Look at the color of the flame and its characteristics, the color and amount of smoke or vapor generated and did the sample continue to burn once it was removed from the flame? 3. Hold a piece of wet litmus paper in the vapors. Does the color indicate acidic, or basic properties? Red indicates acidic nature, blue indicates basic nature. 4. Extinguish the plastic by putting the sample in the beaker of water prepared in step 1 of this section. IV. Copper Wire Test Perform the following procedure on a sample of each of the six common plastics.. Be sure the test is performed in the fume hood. 1. Obtain a copper wire with a cork attached to one end. The cork will serve as a handle to hold the wire. 2. Heat the free end of the copper wire in the flame until there is no evidence of a green color in the flame. 3. Melt a sample of the plastic in a metal spatula as before and then dip the hot wire into the melted sample so a bit of the sample adheres to the wire. 4. Place the wire with sample back into the flame and observe the color of the flame as the sample ignites. As the plastic ignites a slight luminous flash should be evident. 5. If the temporary flash of flame is green in color, chlorine is present. Using the results of these four tests, devise a separation scheme (flow chart) that could identify an unknown plastic sample using these test results. The goal is to use the minimum number of tests possible to identify an unknown plastic. Once

4 Unknown #2 #1 Unknown Home Sample #2 #1 Sample Home PS PP LDPE PVC HDPE PET Plastic 0.94g/cm3 Ethanol:Water 1:1 Observation In 1.00g/cm3 Water 1.08g/cm3 NaCl 10% your scheme is complete, test it on the samples brought from home. If necessary the separation scheme can be fine-tuned. Now using your separation scheme, test and identify the unknown samples supplied by your TA. Postlab Questions 1. Outline the procedure used to separate the six plastics. 2. Suppose you decide to add two more plastics to your separation scheme, polymethylmethacrylate (density g/cm 3 ) and poly-4-methyl-1- pentene (density 0.83 g/cm 3 ). Where would they fit in your separation procedure? 3. Polyethylene terephthalate (PET) is the most valuable of the waste plastics. Suggest a method to separate it from the other five waste plastics. 4. Why is it preferred to identify and separate the six plastics during the recycling process rather than just mixing them together? 5. Waste plastics consist mostly of hydrocarbons. Could they be used as a fuel source? Using your data from this experiment, would this be feasible? Would some be preferred over others? Explain and defend your opinion. PLASTICS DATA SHEET

5 I. Density results Observation In 1:1 Ethanol:Water Water 10% NaCl Plastic 0.94g/cm3 1.00g/cm3 1.08g/cm3 PET HDPE PVC LDPE PP PS Home Sample #1 Home Sample #2 Unknown #1 Unknown #2 Summary of density results < 0.94g/cm3 <1.00g/cm3 <1.08g/cm3 >1.08g/cm3 Ranking of density results (lowest) (highest) II, III, IV Melt Test, Ignition Test, Copper Wire Test

6 Plastic Melt Test Ignition Test Copper Wire Test PET HDPE PVC LDPE PP PS Home Sample #1 Home Sample #2 Unknown #1 Unknown #2 Identification of Unknown Samples Home sample #1: Identity Source Home sample #2: Identity Source Unknown 1 number Identity Unknown 2 number Identity

Physical Properties of Polymers

Physical Properties of Polymers Objective: The objective of this experiment is to test and compare the physical properties of thermoplastic polymers. Review of Scientific Principles: Plastics are long