In this lecture, we will revisit the definition of thermoplastics as well as thermosets, sometimes referred to as heat set and we'll talk about what makes a polymer recyclable. We have two major categories of synthetic polymers. We have our thermoplastics and our thermal sets or heat sets. The thermoplastics are generally going to be either amorphous or semi-crystalline. Our thermosets are going to be lightly cross-linked elastomers, where we actually introduce either some sulfur or carbon between the change to connect them. Well, we can have our heavily cross-linked 3D thermal sets. They can also be referred to as linear in reference to the amorphous. You can also think of it like a bowl of spaghettis where we change the slide over top of one another. Semi-crystalline polymer. Due to the processing, they're going to have regions of semi crystallinity that are going to be connected by these chains. We have semi crystalline and amorphous regions. They can also be referred to as branched, meaning we have some side chains and makes it more difficult for the change to slide across or top of one another hence, their strength goes up. For our elastomers. If we recall, elastomers have super elasticity. We're going to put some cross-linking between the chains. It reduces the elasticity, but it increases the strength and then finally we have our networks, which refers to our 3D thermosets. Thermoplastics are typically semi-crystalline and amorphous. The nice thing about them, they are thermal plastics. If we recall, thermoplastic are likely the ice. They can be reversibly melted and solidified, hits their ideal for recycling. Typically you heat them up. They soften, you shape them cooling down below the glass transition temperature. They become rigid again, useful and that refers to our polyethylene, polypropylene, polystyrene. Thermosets, on the other hand, and elastomers, once you heat them to introduce the 3D cross-linking, they are no longer recyclable. If you cool them down, they are not going to change, and if we think of this, like the egg. Once you hit the egg up, it doesn't go back. If you cool it down, it doesn't go back to the liquid state. Here we take elastomer, do some cross-linking, sulfur carbon black oxygen. Heated up to enable the cross-linking. However, cooling it down, it doesn't go back to the original thing. You can think of your all of your elastomers. Now I'll thermal set heavily cross-linked such that we have a 3D network like the Bakelite epoxies. Once you heat them into shape, they're done. These items are not ideal for recycling. However they are ideal for repurposing. These materials you want to find another purpose for them, whether for the case of the automobile tires. If you can chop them up, put an epoxy with it. Now you have fluorine for outdoor playgrounds. Let's take a moment for inquiry. We've seen this exercise before. We'll just walk through it quickly. If you call we have our, let's start from the polystyrene. That's an easy one. PVC, another easy one. The low density polyethylene. High density polyethylene that's the milk jug and then we have our pete and finally, we have the polypropylene. Again, remember, we want to have an idea of or at least an example of the various polymers under our hat. With this lecture, we had a understanding of the difference between thermosets and thermoplastics or the heat set, as well as what makes a polymer recyclable and when do we have to make the decision for our polymer to be repurpose. Thank you.
