SOP: Determination of Bursting Strength (Mullen Test)

GIFSQ — Global Institute for Food Safety & Quality

Principle

Bursting strength is the hydrostatic pressure required to rupture the material: pressure is applied at an increasing rate through a rubber diaphragm to a circular area 1.2 inch in diameter. The material under test is initially flat and held rigidly at the circumference but free to bulge as the pressure rises. The test is simple and rapid, and is important in material selection for bags and in determining the durability of paper.

Apparatus required

• Bursting tester (commonly the Mullen tester) having:
• (i) clamps that firmly and uniformly secure the test specimen without slippage;
• (ii) a rubber diaphragm of pure gum rubber, 0.034 ± 0.002 inch in thickness;
• (iii) a pressure gauge with scale graduations at intervals of 0.2, 0.5 and 1.0 for gauges having ranges up to 30, 50 and 300 units respectively (the middle range and unit wording are garbled in the printed text);
• (iv) a hydraulic pressure system that forces liquid (usually glycerine) into the pressure chamber under the diaphragm at a rate of 95 ml per minute.
• A pneumatic burst tester may be used instead for individual papers, films and laminates, since it gives more accurate values: air under pressure bursts the horizontally clamped specimen. The instrument generally carries two scales — one up to 3.5 kg/cm² with 0.05 kg/cm² readings, and the other up to 11.0 kg/cm² with 0.2 kg/cm² readings.

Procedure — Bursting strength

Cut the specimens 2.5 × 2.5 inch and condition them

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Make a preliminary test to determine the required gauge capacity; to avoid overloading and possible damage to the gauge, use a high-capacity gauge for the preliminary test

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Clamp the specimen securely and apply the pressure until the specimen ruptures; record the maximum pressure registered by the gauge

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Watch the specimen carefully — if any slippage is observed, discard the reading

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Make at least five tests on each side of the paper; do not test papers containing water marks, creases, imperfections or any visible damage

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After each test, return the indicator needle to zero

Results

• Report the maximum, minimum and arithmetic mean of the values to three significant figures.
• The Mullen burst strength is reported in “points bursting strength,” which is the hydraulic pressure indicated on the gauge; to avoid confusion, the hydrostatic pressure used is referred to as “points bursting strength.”
• The bursting strength of individual papers, films and laminates is considerably lower. Note: the printed sentence ends here and is truncated; no comparator is given in the source.

References

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

Annual Book of ASTM Standards, 1972, Part 1, ASTM D: 774-67 (Reapproved 1971) — cited in the book.