Effect of temperature on removal torque of discontinuous-thread plastic closures

摘要

This experiment is a follow-up to an earlier study, which examined the effect of time on torque loss for two discontinuous-thread plastic bottle/closure combinations. (For a complete description, see TEST Engineering & Management, October/November 2004, pages 18-19.) Both experiments utilized the same sample bottles and torque meter, and followed the same procedure for cap application and removal, as well as torque measurement. In the preliminary experiment, caps were left in place for time intervals ranging from 15 minutes to four days, and specimens were exposed only to ambient temperature conditions. Three main results were found in the earlier experiment. First, the observed rate of torque loss over time was similar for both high-density polyethylene (HOPE) and polypropylene (PP) caps. Second, all samples reached a steady state of torque loss after approximately 72 hours. Finally, the percent torque loss (%R) was higher for PP caps (～56 percent) than for HDPE caps (～40 percent). Data gathered from the preliminary experiment created a better understanding of the samples being tested, and also helped with the design of the follow-up experiment.