Discussion
Students should be able to see a difference in the two films that are made. The one without the glycerin is much more brittle. Because acetic acid is added to break down the amylopectin, the straight chains of the amylose can line up together. This makes the film crystalline, causing it to be brittle. When glycerin is added to the mixture, the film is more flexible. Plasticizers work by embedding themselves between the chains of polymers, increasing the spacing and free volume between chains, which prevents close packing of the polymer chains. This decreases the glass transition temperature of the polymer and results in a lower degree of crystallinity in the film. Due to this, the film is softer and more flexible.