Effects of temperature profiles through preform thickness on the properties of reheat-blown PET containers

Abstract

Nonuniform temperature distributions through preform sidewalls have been studied in relation to their effects on the orientation and functional properties of reheat-and-blown PET containers. Each temperature profile, through the preform thickness, was computed from processing conditions by solving the energy equation with radiation as the heating source. The computed temperature profile was verified by measuring the inside and outside preform surface temperatures using infrared thermocouples. Bottles were then blow molded with various temperature profiles and measurements were carried out on samples cut from the sidewalls. Thickness distributions and axial ratios were determined as were changes in mechanical, optical, and barrier properties. It was found that optical anisotropy through bottle wall thickness was minimal when the inside preform surface was at a higher temperature than the outside surface. Densities of the bottle sidewalls were found to be higher for bottles blow molded at higher average temperatures and there were small increases in density for bottles blown with the preform inside surface at a higher temperature than the outside surface. Haze measurements showed that, to obtain optically clear containers, bottles with an inside hoop ratio of 5.25 should be blown with an inside surface temperature of at least 100°C. © 1998 John Wiley & Sons, Inc. Adv Polym Techn 17: 237–249, 1998