Retort shock

Equation 2 has the new term "Bw" which corrects for the dependence of oxygen permeability on the thermal-moisture history of the sample, sometimes called the Retort Shock, A and B are constants and w is the concentration of water in the EVOH layer following retort (as calculated from equations published in reference [3J or determined experimentally). 

With an adequate amount of desiccant In the structure, the EVOH Is not prone to Retort Shock and does not suffer from a prolonged lag time In approaching steady state. Oxygen permeation through EVOH barrier/desiccant containers Is controlled by the partition of water between the desiccant and the EVOH. Simply said, the desiccant keeps the EVOH dry. 

Not only is there negligible Retort Shock, but with desiccant containers, a lag time to reestablish oxygen barrier in the EVOH is not detectable. In fact, a very low permeability coefficient of 0.02 is established within seven days of retorting, the minimum time period at which permeability can be measured. The high initial oxygen permeation rate, that is seen immediately after retorting with non-desiccant containers, is never seen with desiccant containers. 

Putting desiccant in a layer of multilayer containers made with the same EVOH polymer results in much less oxygen permeation. The Retort Shock and slow barrier recovery effects do not take place. Moreover, this is true even when the desiccant is separated from the EVOH by a thin polymeric layer so that the EVOH and the desiccant cannot interact chemically. Retorted containers with desiccant behave more like unretorted containers without desiccant oxygen permeation is controlled almost exclusively by the water activity of the EVOH layer. Morphological changes in the EVOH layer after retorting appear to be very small when desiccant is present. We attribute this to rapid transport of excess moisture from the EVOH to the desiccant which results in healing the... 

EVOH experiences retort shock which causes an irreversible decrease in barrier properties. EVOH is commonly used for many packaging applications, including PP and EVOH retortable barrier sheet for thermoformed packaging. [6]... 

Chemical and processing towers, condensers. Furnace parts such as retorts and low stressed parts subject to temperatures up to 800 "C. Type 430 nitric-acid storage tanks, furnace parts, fan scrolls. Type 430F-pump shafts, instrument parts, valve parts Products requiring high yield point and resistance to shock... 

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