Polymers and Plastics
The benefits of polymers and plastics have been so essential to manufacturing and the marketplace that the makers and the government didn't really address the possible negative side effects. Plastics keep our food fresh; reduce packaging weight, they are also durable and inexpensive to produce. Fresher food means longer lasting food therefore, less money can be spent on food. Packages that are lighter need less fuel to transport them to the marketplace. It is also durable so it can be used in products that are used over time such as: shampoo bottles, Tupperware, building materials, clothing, and car parts. Inexpensive production costs keep product prices down as well.
The U.S. plastics industry has $379 billion in annual sales and employs 850,000 people.1 There are an estimated 21,000 companies manufacturing plastic products or plastics raw materials. Based on all of this information, pose the question (without telling them that you are referring to plastic), "What if I told you there was a product that could keep our food fresh, clothe us, reduce fuel costs, was durable, inexpensive, and versatile? What if this product generated $379 billion dollars for our economy and employed 850,000 people? Would you want to use it?" The polymer/plastics industry is huge and accounts for seventy percent of the synthetic chemical industry in the US.2
Students might brainstorm a list of polymers and plastics by looking around their homes, workplaces, stores, schools, cars, etc. to find things made of plastic such as: pencils, furniture, carpet, cars, packaging, clothes, cosmetics, baby products, lotions, scented candles, dryer sheets, and a vast array of many other items. They will probably not realize all of the things that are considered polymers or plastics. I imagine their lists will be more obvious items. Plastic is everywhere - where does it come from? How do plastics differ?
Polymers are found in nature and are composed of chains of hydrocarbons or monomers which come from natural gas, oil, coal, and plant materials. (It may be useful to discuss the prefixes poly- and mono-). Plastic is made from polymer however synthetic chemicals have been added therefore, all plastic can be considered polymers but polymers are not necessarily plastic. Polymers are natural and always used in the production of plastic but, plastic has additional synthetic chemicals so polymers are not necessarily plastic.
Create a display of polymers and plastics. Ask students to determine which items are polymers v. plastics. Items from nature that are polymers that could be displayed: hair, wool, fur, proteins, silk, tree sap, shellac, amber, and cellulose from trees. Yes, trees are actually used in the production of plastic. Synthetic polymers or plastics can be molded into almost anything (toys, bumpers, clothes, food packaging, bottles, diapers, carpet, furniture, etc.) when synthetic chemicals or plasticizers are added.
Plasticizers are chemical additives such as Di (2-ethylhexyl) phthalate or DEHP, and bisphenol-A or BPA that increase flexibility and make the plastics heat resistant. These chemicals are added to hard plastic like PVC (composed of salt and ethynol) and they act as a spacer between the molecules sometimes creating the "weaker" more flexible version. This concept can be demonstrated with the following analogy: pasta. Uncooked pasta is hard and not flexible (some more than others) but when you add water and heat it becomes pliable. This is a VERY simple analogy. However, imagine if the water and heat were foreign chemicals such as DEHP and BPA and we were unsure if they were safe.
Unfortunately, until recently, these chemicals were not thoroughly tested to determine their impact on our health or the environment. DEHP and BPA are common ingredients in plastics. Infants suck on bottles and toys, wear diapers, and we all consume food and beverages from plastic containers that are made from some of these chemicals. Are they safe?
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