SOP: Determination of Water Vapour Permeability by the Cycle Method

GIFSQ — Global Institute for Food Safety & Quality

Principle

The cycle method tests the water vapour permeability of finished packages subjected to extremes of temperature and relative humidity when closed and sealed in the conventional manner. It is intended for shelf-size packages that are shipped in outside containers. The sealed package is cycled between a low-temperature room and a high-temperature, high-humidity chamber, and the weight gain per cycle gives the permeability.

Apparatus required

• Low-temperature room or cabinet at −17.8°C (0°F)
• Test chamber maintained at 37.8°C and 90% RH
• Desiccant (CaCl₂) or the product

Sample preparation

Place the required quantity of desiccant or the product in the package and seal it as in the package method; note the weight of the package. Prepare the desiccant as for the dish method (anhydrous CaCl₂ dried at 200°C, in lumps passing a No. 8 / 2.38 mm sieve and free of fines passing a No. 30 / 595 µm sieve). Use the desiccant, CaCl₂, when the test is made for determining the water vapour permeability of a package for research, control or standard purposes; use the product instead of desiccant when testing the suitability of the package for water vapour resistance with respect to that product.

Procedure — Cycle method

Place the sealed package in the low-temperature room or cabinet at −17.8°C (0°F) for 24 hr

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Immediately thereafter, place the package in the test chamber maintained at 37.8°C and 90% RH for 6 days — this forms one cycle

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Note the weight of the package and return it to the low-temperature (−17.8°C) chamber

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Make successive weighings of the package at the completion of each cycle, which occurs at the conclusion of the high-temperature and humidity storage

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Plot weight gain against time in cycles; continue the operation until a constant rate of gain is indicated by at least three successive points in a straight line — the slope of this portion of the curve gives the water vapour permeability per cycle

Results

• Report the result as grams of water per cycle when the desiccant is used, and as grams of water gained per number of cycles when the product is used; the results are expressed for the package as a unit. Report details as for the package method.
• The method may be applied for (i) evolving materials and constructions for a specific type of package, (ii) comparing the performance of different types of packages, (iii) determining the adequacy of protection for a specific product or application, and (iv) quality control.
• The test may be applied to the package as packed, or after one or more performance tests (such as drum, vibration or shipping tests) have been completed.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Annual Book of ASTM Standards, 1972, Part 15, ASTM D: 1251–68 — cited in the book.