Packaging materials, permeability

Packaging material permeability, P = 15.0 cm mil/m d atm Shelf life expected 6 months (180 days) Area of the package 400 in ... 

Vacuum packaging. Fresh, chilled beef and other low pH meat has been successfully vacuum packed since the 1960s due to control of hygiene, storage temperature and packaging material permeability to... 

Numerous variations and other appHcations are common for flexible packaging materials, eg, oxygen-permeable wraps for fresh red meat and produce shrinkable, low oxygen permeabiHty bags for meat and rigid tray closures. 

During the 1970s there was considerable interest for a time in copolymers with a high acrylonitrile content for use as barrier resins, i.e. packaging materials with low permeability to gases. Problems associated with free acrylonitrile have, however, led to the virtual disappearance of these materials from the market. 

Compared with more common plastics used as packaging materials, the compound does have some disadvantages, such as a high water vapour permeability and limited heat resistance, losing dimensional stability at about 70°C. It is also substantially more expensive than the high-tonnage polyolefins. Last but not least its biodegradability means that it must be used in applications that will have completed their function within a few months of the manufacture of the polymer compound. 

Among the commonly used flexible packaging materials, aluminum foil probably provides the most complete permeation barrier while paper is the most permeable. Although aluminum foil provides a barrier to moisture, gas, grease, and light, it usually needs protection from the contents of the package and from the environment since it is a soft metal and subject to chemical attack. 

Moyssiadi T, Badeka A, Kondyli E, Vakirtzi T, Savvaidis I and Kontominas M G (2004), Effect of light transmittance and oxygen permeability of various packaging materials on keeping quality of low fat pasteurized milk chemical and sensorial aspects , International Dairy Journal, 14, 429 -36. 

The WVTR through the container is determined by the container wall thickness, the permeability of the material and the difference between the external and internal relative humidity environments. Waterman et al. [99] determined the theoretical rate of water permeation through a standard 60-cc bottle when stored at 40°C/75% RH. This equated to an uptake of 1 mg of water per day. They commented that even if the product had been packed under low water vapour conditions the relative humidity conditions within the container would be equate to 50% RH within 1 day. The WVTRs (see Table 2.8) for some common packaging materials were reported by Waterman et al. [99]. 

Subramaniam, 1988]. Hydrochlorination, usually carried out at about 10°C, proceeds by electrophilic addition to give the Markownikoff product with chlorine on the tertiary carbon (Eq. 9-33) [Golub and Heller, 1964 Tran and Prud homme, 1977]. Some cyclization of the intermediate carbocation (XXVI) also takes place (Sec. 9-7). The product, referred to as rubber hydrochloride, has low permeability to water vapor and is resistant to many aqueous solutions (hut not bases or oxidizing acids). Applications include packaging film laminates with metal foils, paper, and cellulose films, although it has been largely replaced by cheaper packaging materials such as polyethylene. 

Table 10 Oxygen Permeability (Transmission Rate) for Packaging Materials...

Baner, A. L. The estimation of partition coefficients, solubility coefficients and permeability coefficients for organic molecules in polymers using group contribution methods. New Developments in the Chemistry of Packaging Materials. ACS Symposium Dallas 1998. ACS Symposium Series, ACS Washington D.C. 1999. 

In practice it must not be forgotten that P values give an order of magnitude estimation for the selection of suitable packaging materials and thus allow a closer calculation of the total package permeability with the help of the flux J ... 

Q is the sum of the permeabilities for individual packaging materials and wall thickness of different packaging components. Using the corresponding P and d values for every component i, the corresponding flux J is calculated using Equation (9-1) and multiplied by the component s surface Aj. The partial pressure difference Ap is treated as a constant. The total permeability of a package developed in this way must nevertheless be checked experimentally due to the above mentioned uncertainties (see next Section). 

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