The Effect of Processing Parameters on Barrier Properties of Polymers

The intent of this work was to learn if polyethylene could be made with predictable water transfer rates by control of the microstructure. A series of films were formed from three different polyethylenes with a range crystallinities using melt pressing, a controlled cooling rate, and subsequent heat treatments. The samples were tested on a novel device called the polymer characterization device that measures the water transfer flux as a function of temperature. The samples’ morphology was examined using differential gradient column, differential scanning calorimetry, Fourier transform infrared microscopy, wide-angle X-ray diffractions, small-angle X-ray scattering, and small angle light scattering, and scanning electron microscopy. When the water transfer flux was expressed as the frost point of a dry carrier gas the results showed a remarkable sensitivity that allows for analysis of subtle distinction in rates due to changes in morphology. Analysis showed that the water transfer flux is a function of the polymer, conditions of the samples preparation from the melt, and any subsequent heat treatment. Another interesting finding was that the time for the sample to reach a steady state water transfer flux is a function of morphology. A free volume model was developed to that simulates the response of the polymer as a function of morphology, presence of water, and thermal cycling. The conclusion of this work is that the water transfer flux is a function of the specific polymer, the initial formation conditions, and later heat treatments and with this knowledge the polymer could be made with a specific water transfer flux.