Abstract
In this paper the relative influence of the stretch ratio in machine direction (MD) and transverse direction (TD) on the permeability of tubular polyethylene terephthalate (PET) films was studied. The biorientation process was realized on a laboratory scale by means of a double-bubble tubular film apparatus. In order to evaluate interaction between the stretch ratios in MD and TD on barrier properties, an experimental design to measure the interaction of two independent variables was applied. The study was also performed on annealed PET films. The results have shown that some degree of interaction exists between the stretch ratio in MD and TD. In particular, for annealed PET films, the relative influence of the stretch ratio in MD and TD depends largely on the size of the penetrant gas: the lowest permeability results were obtained using the highest second draw ratio (SDR) values for CO2 and the lowest second blow-up ratio (SBUR) values for N2, respectively. However, it was verified that annealing strongly influences the barrier properties of PET films. Copyright © 2000 John Wiley & Sons, Ltd.
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