Seeing as Earth Day was yesterday it seems appropriate to learn a bit more about our favorite frenemy (friend/enemy): plastic. More and more consumer products are made of plastic and this means that more and more of our consumer waste is made of plastic. Only very special plastics biodegrade and this causes them to fill our landfills and pollute our oceans, however many of them are easily recyclable. Plastics are polymers, essentially long chain molecules, so they rarely form an ordered structure, like a crystal, they tend to be more like a lot of spaghetti. The way that these molecules, noodles, interact breaks plastics into two major categories: thermoplastics and thermosets.
Thermoplastics are the most common form of plastic. The molecules in these plastics are only weakly bonded to each other by tangling and van der Waals bonds. These can be easily broken and this makes the melting temperature of the polymer pretty low. This makes these plastics easy to recycle because they can be melted and formed into whatever shape desired, used, then melted back down and used over and over.
Thermosets are the other most common form of plastic and these are typically seen as polyurethanes, epoxies, resin and hardener combinations. The molecules in these materials are actually bonded to each other by cross-linking. This raises the melting temperature very high, for most plastics this is above the the point of decomposition so these kinds of plastics burn before they melt. This means that the materials are committed to the shape they solidified in and cannot be turned back to a liquid state and reused making them impossible to economically recycle.
Unfortunately it is usually cheaper to make new plastic than it is to use recycled plastics due to the added coloring and logos printed on bottles and packages. Plastics are also mostly produced from petroleum products, a non-renewable resource. But as technology improves new plastics are coming out that solve some of these problems, for example PLA is becoming more popular and there is a special bacteria that can decompose it. The future of plastics may lie in algae or insect exoskeletons but where ever it is, it’s looking good for the environment!