When polymers undergo stress hardening, their crystallinities and densities are affected. Polypropylene was the material tested in this experiment. It was put under various levels of strain by using a tensile tester. Each sample was pulled to a predetermined strain, allowed to relax for a period of time, and measured for crystallinity using the Differential Scanning Calorimeter (DSC). Stress-hardened and original samples were used to compare the change in crystallinity. The density of each sample was also determined using the Density Gradient Column.
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