Impedance measurements to monitor the water content
of the films during a sterilisation cycle show that, without
a heat treatment prior to sterilisation, crystallisation of the
PET can lead to a situation of heavy over saturation. This
water will be expelled to any nearby surface, which can be
the metal/coating interface. Crystallisation will also cause a
mechanical tension due to shrinkage of the polymer, which is
lower than the deformation stresses that are present without
heat treatment.