Polymer Shrink Film Lab Experiment

Polymers have many unique properties that make them ideally suited for everyday products and applications. One of these applications is heat activated shrink film. Shrink film is commonly used for packaging and temporarily insulating windows. Shrink film contains cross links between its polymer chains that are stretched when the film is manufactured. The application of heat allows the polymer chains to move and the cross links between the polymer chains to contract causing the film to shrink. This lab experiment investigates the shrinkage of polymer film that is commonly used to insulate windows. The experiment is performed in an Introduction to Materials class for freshman mechanical engineering technology students. Students first measure the change in length of strips of the film when the film is free from constraints to determine the maximum possible change in length. Then they put the film in a frame and measure the forces generated by the film as it shrinks. The results of the experiment are that the students are able to observe the macroscopic effects of the nanoscale cross links between the polymer molecules in the window film. This experiment provided an opportunity to investigate a unique aspect of the properties of polymers beyond the typical material properties such as tensile strength, elongation and stiffness.