Tag: polymers

Making a Non-Stick Frying Pan the Old Fashioned Way: Creating Polymers at Home

"Seasoning" a cast iron frying pan creates a non-stick coating. (Image by Evan-Amos via Wikipedia).

Back in the day, if you wanted a non-stick cooking skillet, your best option was to do it yourself by seasoning a cast metal pan. Sheryl Canter has an excellent post describing the science behind the “seasoning” process. The key is to bake on a little bit of oil to create a strong cross-linked polymer surface. This is a nice tie into our discussion of polymers and polymerization in the middle school science class; although I’m not sure how many of my students have actually seen a cast iron pan, or even know what cast iron is.

Normal polymers are long molecules made up of smaller molecules linked together, much like a paperclip chain.
Cross-linked polymers are created when the long chained polymers are linked together by cross-links. It makes for a much sturdier molecule.

To season, you coat the pan with a thin layer of oil and bake it for a while (without anything in it). Baking releases free radicals from the metal that react with the oil to create a cross-linked polymer that’s really hard to break down or wear out, and prevent food from sticking to the pan. Different, cross linked polymers are used in car tires for their durability, but probably not for their lack of stickiness.

Apparently, linseed oil is the best seasoning agent, but it might be a bit hard to find.

Most non-stick, artificial surfaces, are also made of polymers of hydrocarbons, silicon oxides and other interesting chemicals.

Making a cross-linked polymer with borax and polyvinyl alcohol.

In the lab, you can make your own cross-linked polymer “slime” by adding a solution of borax (sodium tetraborate) to a solution of polyvinyl alcohol (1:1 ratio of concentrations) (Practical Chemistry, 2008).

The result is a satisfying goo.

Cross-linked polymer "slime".

Exothermic Reaction: Epoxy

A little stick of epoxy from the hardware store can be used to demonstrate exothermic reactions, and, if you’re interested, some organic chemistry.

You should be able to find all sorts of epoxies in the store, but the easiest to work with are the little cylindrical sticks that you have to massage with your fingers to mix the resin and hardener. As they combine, you can feel the epoxy getting warmer. The plumber’s epoxy warmed quite nicely.

You can also feel it get softer and easier to work, more malleable, so it could also be a good demonstration of plasticity. Especially since, as the chemical reaction occurs, the material hardens till, after a few minutes, it can’t be worked at all.

Epoxies are used a lot as adhesives and protective coatings, because they are extremely strong when they harden and can be quite sticky.

Image adpated from Wikipedia (resin molecule produced by Cacycle).

Their chemistry is fascinating. Epoxies work by mixing a resin and a hardener. The resin’s molecules have epoxide rings at either end, while the hardener’s molecules also have reactive ends. So when you mix them, they create long chained molecules called copolymers: polymers are long chains of a single molecule (the base molecule is called a monomer); copolymers are long chains with two base molecules instead of one.

The resulting network will not dissolve in any solvents, and resists all but the strongest chemical reagents. The plurality of OH groups provides hydrogen bonding, useful for adhesion to polar surfaces like glass, wood, etc.

–Robello (accessed 2011): Epoxy Polymers