Conception
Bottle design considerations
Any major project begins with a design phase; designing a single serving water bottle is no different. Careful thought goes into how the bottle will be used, the size, the shape, the color and texture, the label, the closure, and other visible marketable features of the bottle. Most design considerations, however, seem to be about marketing the product. Unfortunately, the ultimate end of life scenario for the single serving water bottle does not seem to be given very much consideration these days. 1 The book Paper or Plastic makes a good case for the need to consider the ultimate destination of the product when the first design considerations are being made.
A polyethylene terephthalate bottle is typically made from several layers of plastics. Each layer serves a different function in the performance of the bottle. For example, the inside of the bottle, the part that is in contact with the liquid contained in the bottle, will typically be made from virgin PET, or PET that is made fresh for this purpose as opposed to being recycled. The central sections of the bottle may or may not be made from virgin PET and the label is frequently made from something other than PET like paper or poly vinyl chloride (PVC) film. Then, there is the consideration of the cap. The cap may be made from PET, but it will frequently also contain some sort of lining, frequently PVC, to keep water from seeping out if the bottle is turned upside down or laid on its side. This diversity of material going into a single bottle has a number of advantages, but it also causes a number of problems. Clearly the materials decisions serve a purpose, which is carefully considered, but the eventual impact of those design decisions do not seem to be given as careful a consideration. For example, when multiple types of plastic are combined in a single product, it becomes very difficult and sometimes impossible to recycle the product at the end of its life. Even if the different types of plastic are not fused together, separating the types of plastic can become an expensive undertaking. When plastics are not fully separated before they are recycled, the resulting product will not have the intended properties because of the contaminants introduced when the plastics were not properly separated. New products made from the recycled plastic materials will have unintended properties caused by the contaminants, which can cause product failure, such as the plastic cracking or being too soft, or safety problems from unintended leaching of contaminants into the new container's contents. The later issue is why most PET food containers are required to have a layer of virgin plastic in contact with the food.
A number of countries, particularly in Europe have passed legislation to encourage or require that the end of life of the product be considered at its beginning. Paper or Plastic goes into quite a bit of detail about some of these considerations. These end of life considerations will be the focus of our class discussions. A large focus of my teaching in this class, beyond the delivery of content, is to encourage my students to think about the consequences of their actions. The curriculum includes a segment about the human impact on the world around us, and the topic of the effects of design choices on the environment will fit into this part of the curriculum very nicely. I intend to have the students answer the question of why are end of life issues important considerations in the design phase of a product. The answers will likely come in the form of a persuasive writing assignment, which happens to fit into the English curriculum, and is also an important part of science, particularly when it comes to policy decisions.
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