Method of assessing thermoformability of extruded polypropylene sheet

Plastics in sheet form are widely used in the production of thin gauge containers for the food and beverage industry using the thermoforming process. The present paper assesses the thermoformability of polypropylene sheet by hot tensile testing in conjunction with dynamic mechanical thermal analysis (DMTA). Hot tensile testing, in which the stress-strain behaviour of heated extruded sheet under tension is measured, is used in an attempt to simulate the heating and stretching processes involved in thermoforming. The tests yielded useful information on the effect of processing parameters, such as sheet temperature and strain rate, on the behaviour manifested by the polymer during processing. Drawn test specimens produced by tensile elongation were subjected to DMTA with a view to predicting the mechanical response of finished parts over a wide temperature range.