One way of classifying polymers is to break them up into two classes. The two classes of polymers are thermoplastic polymers and thermosetting polymers. The basic property that separates a thermoplastic polymer from a thermosetting polymer is the polymer’s response to being heated. When the thermoplastic polymer is heated, it melts, softens, and can be reformed when cooled. When the thermosetting polymer is heated, it hardens and cannot be reformed and stays hard when cooled. We will learn much more about each of these two classes of polymers and the reasons for their defining properties later in our lesson on polymer structures.
Since thermoplastic polymers can be melted and reformed, they are easily recycled. However, their properties do degrade with each reuse. Thermosetting polymers are much more difficult to recycle. Some of them can be ground up and used as filler for other processes, and, on a case-by-case basis, some can be processed to be broken down into their underlying base units which can be reused. Another approach to reducing the amount of plastic that ends up in our landfills is the development of biodegradable plastic. The idea here is that plastic can be made to breakdown (be compostable). In addition, bioplastics often come from renewable raw materials. But this leads to an ethical issue: do you use the available arable land for plastic or food production?
Now, please watch the following video (4:38) on plastics and biodegradable plastics which summarizes some of the issues around plastic recycling and bioplastics as discussed in your e-book and this website.
In the previous video, incineration of waste was discussed. Incineration leads to a huge volume reduction of waste, which results in less waste ending up in the landfill. Waste in the landfill is the least environmentally friendly option. However, incineration typically results in less recycling, which would be a more efficient use of recyclable material than incinerating it. This reduction of recycling due to incineration is considered the major disadvantage of incineration. Although an important concern with incineration is the production of toxins, with proper technology these toxins can be managed. A segment of the video for this week, Making Stuff: Cleaner, discusses burning waste to create electricity. Please watch the following short video (4:40) which discusses burning waste to create electricity as well as the issues regarding incineration discussed above.
Lastly, please watch the following video (5:40) on the recycling of paper, which touches on several themes of this lesson including sustainability, downcycling, and green design principles.