Oxygen-barrier resins, effect

Gas-Barrier Properties. The oxygen-barrier properties of PVA at low humidity ate the best of any synthetic resin. However, barrier performance deteriorates above 60% th (Fig. 9). No additives or chemical modifiers are known that can effectively reduce moisture sensitivity. The gas-barrier performance is affected by the degree of hydrolysis and rapidly diminishes as the hydrolysis is decreased below 98%. 

Table II. Effect of Orientation on Oxygen Barrier Characteristics of Semicrystalline Barrier Resins...

The effect of orientation on amorphous barrier resins SELAR PA 3426 and XHTA-50A are shown in Table III. The measured oxygen permeability of 1.4 cc-mil/100 in 24 hr. atm for unoriented extrusion cast SELAR PA 3426 film is reduced by 19% upon uniaxial orientation, while the permeability of biaxially oriented films are 28% lower than that of extrusion cast film. Similarly, the decrease in oxygen permeability with 2X and 2.5X uniaxial orientation in XHTA-50A are 5% and 9% respectively, from the measured value of 3.1 cc-mil/100 in 24 hr. atm for unoriented film. The corresponding reduction in permeability with 2X x 2X biaxial orientation is 12%. 

The effect of orientation on oxygen permeability of the medium and high barrier resins is seen to be dependent upon the morphological nature of the barrier resin prior to orientation. A plot of the oxygen transmission rates as a function of the overall draw ratio (figure 3) illustrates this clearly. While the semicrystalline polymers, VDC copolymer, and aromatic nylon MXD-6, show little change in the permeability with moderate amounts of orientation in the solid state, orientation of the amorphous polymers SELAR PA 3426 and XHTA-50A causes reduction in the permeability by 5-30% in both resins, depending upon the overall level of orientation. 

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