SOP: Determination of Grease Resistance by Transudation Time
GIFSQ — Global Institute for Food Safety & Quality
Principle
Grease resistance of a packaging material is compared by the transudation time: coloured turpentine is applied to sand spread over the test specimen, and the elapsed time in seconds between the addition of the turpentine and the appearance of the first definite red stain on a paper underneath is noted. The test gives an accelerated comparison of the relative rates at which ordinary oils or greases, such as those commonly found in foodstuffs, may be expected to penetrate papers such as uncoated or impregnated grease-proof paper, glassine and vegetable parchment.
Apparatus required
- Tubes: 1 inch (D) × 1 inch (L) with smooth ends
- Pipette: 1.1 ml
- Sand: silica sand passing through a No. 20 sieve and retained on a No. 30 sieve
- Paper: sheets of coated 80 lb paper (used for making books), 25 × 38 inch, 500 basis, cut to a convenient size
Reagents
a. To 100 ml of pure turpentine, add 5 g of anhydrous CaCl₂ and 1 g of oil-soluble red dye (e.g., Sudan IV dye). Store for 10 hr with occasional shaking, filter, and use.
Procedure — Transudation time
Draw the samples according to the sampling procedure; cut 30 numbers of 4-inch square samples and condition them; make an equal number of determinations on each side of the sample
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Place each specimen on a sheet of paper resting on its smooth side; place the tube on the specimen, pour 5 g of sand into the tube, and remove the tube; add 1.1 ml of the coloured turpentine solution to the sand and note the time
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Move the test specimen to different positions on the paper and examine the uncovered area of the paper for any colour stain — every 30 sec in the first 2 min, every 1 min in the next 8 min, and every 3 min thereafter
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As soon as the first stain appears, note the time; record in seconds the time between the application of the coloured turpentine solution and the appearance of the first definite red stain — this time is the transudation time
Report
State the number of specimens tested (15 on each side) and the maximum, minimum and average transudation time in seconds, (i) with the felt side up and (ii) with the wire side up. When the transudation time is more than 1,800 sec, report the result as “1,800+ sec”; if values of “1,800+ sec” are included in the average, add a + sign in front of the average value.
Notes
- This type of test, especially for coated materials and films, is often performed at a specified temperature using the oil or the fat of the product.
- Grease resistance ratings (from the book’s table): below 30 sec = D; 30–120 sec = C; 120–1,800 sec = B; more than 1,800 sec = A.
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: 72-45 (Reapproved 1971) — cited in the book.