The Design of Packaging Materials

Additional packaging may be provided to prolong shelf life. Food items are often packaged to maintain freshness and prevent the loss of moisture. In other cases, the opposite result is desired Atmospheric moisture is tiie enemy and must be excluded by a suitable protective barrier. This arises in the packaging of moisture-sensitive items such as electronic components. Both instances require a barrier with low water permeability. 

Consider the case of a moisture-sensitive item that must be kept in an atmosphere of less than 10% relative humidity. This means that the partial pressure of moisture in the air cannot exceed 10% of the saturation vapor pressure. To protect the item against accidental excursions of the humidity of the surrounding air, it is proposed to package it in an appropriate material. Inspection of Table 3.6 shows that high-density polyethylene has a suitably low permeability to water vapor. We now stipulate that the thickness of the packaging material should be sufficient to protect the item against the accidental exposure to 95% humidity air of 1-h duration. 

Combining Equations 3.12a and 3.12b and introducing the molar conversion factor then yield 

We set temperature at 25dC, area-to-volume ratio A/y at 2, and the initial interior humidity at zero. Using a permeability of 9 x 10 cm STP cm/cm s Pa listed in Table 3.6 we obtain 

This thickness of less than 0.1 mm is not imduly large. In fact, we could extend the exposure time to 10 h without exceeding acceptable thickness limits. 

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The design of packaging materials for conservation of fresh fruits and vegetables, which means good specific permeation and selectivity properties in order to maintain a modified/controlled atmosphere ... 

The design of packaging materials must avoid printing errors and possible mix-ups during the packaging operations, and confusion during distribution and use, in particular ... 

Figure 8.5 Diagrammatic flow chart of factors influencing the design of packaging materials.

Sterilization by exposure to ethylene oxide is bounded by at least four variables gas concemratton, time of exposure, temperature, and humidity. It is also affected by product design, packaging design, and the composition of packaging materials. The shape, size, and materials of construction of individual sterilizers, the location of gas entry ports, and the presence or absence of forced circulation may all influence sterility assurance. There is no theory to describe these interactions. Validation and routine control of ethylene oxide sterilization processes boils down finally to the integration of all of these variables by reference to biological monitors. 

Suitable test programmes need to be adopted in the development of packaging materials to ensure fitness for purpose. In terms of adhesive bonding, the peel test is common but can suffer many in-house variants, causing some confusion. The use of adhesive design techniques such as finite-element analysis has not been exploited within the packaging industry, a difficulty being the thin nature of most substrates that make interpretation difficult. 

Storage conditions are the most important factors determining the applicahon and utiUty of packaging materials. Biopolymers are of special origin, so their behavior has to be taken into account during the design of packaging products. 

Great care is needed in the design of autoclaves and sterilization cycles because of the requirement for the presence of moisture. The autoclave must be loaded to allow complete steam penetration to occur in all parts of the load before timing of the sterilization cycle commences. The time required for complete penetration, the so-called heat-up time, varies with different autoclave constmction and different types of loads and packaging materials. The time may not exceed specific limits in order to guarantee reproducibility and, for porous loads, saturated steam. The volume of each container has a considerable effect on the heatup time whenever fluids are sterilized. Thermocouples led into the chamber through a special connector are often employed to determine heatup times and peak temperatures. The pressure is refleved at the end of each sterilization cycle. Either vented containers must be used or... 

A great choice is available in product design and packaging material because sterilization depends on radiation penetration, which is relatively independent of the chemical composition of the packaging and product material. 

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