ISO 2556 Gas transmission rate GTR test of films and thin sheets

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ISO 2556 Gas Transmission Rate Tester | Manometric Method GTR Test Machine | UnitedTest

UnitedTest manufactures precision ISO 2556 compliant gas transmission rate testers for accurate barrier performance testing of thin plastic films and sheets across packaging and plastic material laboratories.

ISO 2556 Plastics — Determination of the gas transmission rate of films and thin sheets under atmospheric pressure — Manometric method is a globally recognized standard that adopts a professional mercury-based manometric differential-pressure test principle. This method accurately measures the Gas Transmission Rate (GTR) of thin plastic films and thin sheets, with a precise measurable testing range from 1 to 20000 cm³/(m²·d·atm).

Operating under fixed upstream atmospheric gas pressure, the test equipment utilizes a mercury capillary manometer to detect and calculate pressure increases within the evacuated low-pressure chamber, delivering reliable and repeatable gas barrier test data for plastic material quality control and performance validation.

Test Principle

The plastic specimen forms a complete gas-tight partition separating two isolated chambers.

Chamber 1 (upstream): Flushed continuously with test gas held at constant ambient atmospheric pressure throughout the entire test.

Chamber 2 (downstream): Fully evacuated to near-zero vacuum and hermetically sealed before data recording.

Driven by the 1 atm pressure difference across the specimen, test gas diffuses through the plastic film into Chamber 2, raising the internal pressure of the sealed low-pressure cavity.

Rising pressure displaces mercury in the calibrated capillary tube; mercury height readings (h) are logged against elapsed time (t).

The initial non-linear adsorption phase of gas into the polymer matrix is discarded; only the steady-state linear slope dh/dt is used to calculate GTR via the standard formula.

Specific Test Methods

This standard contains only one test approach (no alternative GC method unlike ISO 15105-1). It is a classic differential-pressure manometric technique relying on mercury liquid column to record pressure accumulation from permeated gas. Two distinct hardware setups are permitted for the same core testing logic:

Apparatus with mercury overflow: Mercury maintains zero reference level via continuous overflow; calculation correction coefficient c=1 (no mathematical adjustment needed).

Apparatus without mercury overflow: Mercury level drifts in the U-tube; a geometric correction factor c must be calculated and applied to all GTR computations.

ISO 2556 Gas transmission rate GTR test of films and thin sheets

Test Specimen Requirements

Size: Minimum ~80 mm diameter to fully cover the cell gasket joint and prevent bypass gas leakage.

Quantity: At least three identical specimens for each material batch (mandatory).

Test Equipment of ISO 2556 Gas transmission rate GTR test of films and thin sheets

Recommend UnitedTest Gas Permeability Tester - Gas Permeation Analyzer;

Two-part split chamber

Upper Chamber 1 (high-pressure side): Cylindrical cavity with gas inlet/outlet ports to continuously supply test gas at atmospheric pressure.

Lower Chamber 2 (low-pressure side): Polished flat test plate with two cavity options:

Option A: 20 mm central cavity with perforated disc (requires filter paper support for thin films).

Option B: 60 mm cavity filled with flat glass/bronze sintered disc (no filter paper required).

Cell effective permeation diameter: 100–120 mm; rubber circular gasket for airtight sealing; mechanical clamping device to compress the specimen seal.

Optional metal packing block: Reduces Chamber 2 volume to amplify mercury displacement for ultra-low barrier films.

Manometric Mercury Measurement Assembly

Calibrated vertical capillary tube: 1.5–2 mm inner diameter, 200–400 mm length, scale graduated to 0.5 mm (0.1 mm precision required for low GTR <100 cm³/m²·d·atm).

U-tube mercury reservoir assembly: Closed arm + vacuum stopcock connection to vacuum pump; two reservoir mounting styles for overflow / non-overflow setups.

Mercury liquid as pressure sensing medium.

Auxiliary Supporting Hardware

Vacuum pump: Achieve residual pressure ≤13 Pa (0.1 mmHg) in Chamber 2; pressure gauge with accuracy ≥6 Pa (0.05 mmHg).

Mercury barometer: Record real-time ambient atmospheric pressure during testing.

Precision thermometer (readable to 0.5 °C) inside constant-temperature enclosure (temperature controlled ±2 °C).

Drying column (optional): Remove moisture from test gas (omit only with written agreement between parties).

Vacuum grease, analytical filter paper, test gas supply (air, O₂, CO₂, N₂ etc.).

Standard Test Parameters

Pressure Conditions

Upstream Chamber 1: Constant atmospheric pressure (~1 atm).

Initial downstream vacuum: ≤13 Pa (0.1 mmHg).

Barometric pressure H (ambient atmospheric pressure) recorded via mercury barometer at test completion.

Gas Specifications

Test gas: Air, oxygen, nitrogen, carbon dioxide or other pure single gas; humidity controlled via drying column or documented as tested.

Measurement Precision Rules

Mercury height reading: Nearest 0.25 mm general; 0.1 mm required for low permeability films (<100 cm³/m²·d·atm).

Time recording: Nearest minute for low GTR; nearest 5 seconds for high GTR materials.

Key Test Stipulations

Leakage verification: If low-side pressure rises after full evacuation, re-clamp the specimen and re-evacuate to eliminate air leakage.

Steady-state requirement: Testing continues until permeation signal forms a linear stable curve (pressure sensor) or repeated GC readings show consistent permeated gas volume.

Blank correction (GC method): Conduct blank sampling to deduct background residual gas volume (Vb) from measured permeated gas (Vs).

Precision limitation: The standard states no interlaboratory precision data available at release; precision clauses will be added in future revisions.

Step-by-Step Standard Test Procedures of ISO 2556 Gas transmission rate GTR test for films and thin sheets

1, Prepare mercury reservoir and fill capillary/U-tube to zero reference mark matching apparatus overflow style.

2, Place filter paper (for cavity type A) onto the lower test plate.

3, Apply thin uniform vacuum grease only to cell joint surfaces (avoid contact with filter paper/specimen).

4, Mount disc-shaped specimen, fit rubber gasket, attach upper cell half and clamp evenly to achieve full airtight seal.

5, Connect test gas supply with drying column and slowly purge Chamber 1 continuously for the full test duration.

6, Activate vacuum pump to evacuate Chamber 2 until pressure drops below 27 Pa (0.2 mmHg), then close vacuum stopcock.

7, Tilt apparatus to align mercury to capillary zero scale, set cell upright vertically.

8, Log mercury height h at regular time intervals t until steady linear mercury rise is confirmed over 5–6 readings.

9, Terminate test, drain mercury back to reservoir, shut gas supply, disassemble cell and clean test plate.

10, Measure and record ambient barometric pressure H with mercury barometer.

11, Calculate correction coefficient c (if non-overflow setup), extract steady-state slope dh/dt and compute final GTR using the standard formula.

Industrial Application Fields

ISO 2556 testing is widely applied for low-to-medium barrier thin plastic films and sheets:

Flexible food packaging: Snack films, fresh produce wrapping, laminated food bags to measure oxygen/CO₂ permeation and control shelf life.

Conventional plastic packaging materials: PE, PP, PVC single-layer films, coated thin barrier films.

Agricultural plastics: Thin greenhouse cover films, silage wrap sheets.

Cosmetic & consumer packaging: Thin plastic lidding films for creams, lotions, volatile essential oil containers.

Laboratory & academic material research: Characterize gas permeation of novel polymer films, coated substrates and biodegradable plastic sheets.

General quality control for plastic film manufacturers for routine batch barrier screening.

Related Test Standard:

ISO 15105-1	Plastics - Film and sheeting - Determination of gas-transmission rate - Part 1: Differential-pressure methods
ISO 15105-2	Part 2 – Equal-pressure method. adopting carrier gas equal-pressure principle instead of differential vacuum; complementary testing route for gas permeability measurement.
GB/T 1038.1	Plastics—Film and sheeting—Determination of gas-transmission rate—Part 1:Differential-pressure methods
ISO 2556	Plastics - Determination of the gas transmission rate of films and thin sheets under atmospheric pressure - Manometric method
ASTM D1434	Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and Sheeting
JIS K 7126-1	Plastics -- Film and sheeting -- Determination of gas-transmission rate -- Part 1: Differential-pressure method
DIN 53380-1	Testing of plastics - Determination of gas transmissions rate - Part 1: Volumetrical method for testing of plastic films
ISO 2782-1	Rubber, vulcanized or thermoplastic — Determination of permeability to gases — Part 1: Differential-pressure methods

Keywords: Gas Permeator, UnitedTest ISO 2556 tester, ISO 2556 gas transmission rate tester, manometric method GTR test machine, plastic film gas barrier tester, atmospheric pressure manometric gas transmission test for plastic films, mercury capillary manometer GTR testing equipment, 1–20000 cm³/(m²·d·atm) plastic sheet gas permeability tester, differential pressure gas barrier test machine for thin plastic films, ISO 2556 plastic packaging gas transmission rate analyzer

Gas Permeability Tester is a multi-functional lab instrument dedicated to gas barrier performance testing, gas transmission rate (GTR). Conform to ISO 15105-1, ISO 2556, ASTM D1434, Widely adopted as standard QC testing equipment for flexible packaging, plastic manufacturing and new energy sectors.

Adopts advanced electrochemical coulometric detection method for accurate, time-efficient oxygen transmission rate analysis for medium and high barrier packaging materials. Conform with ISO 15105-2, ASTM D3985. Key testing indicators Oxygen Transmission Rate (OTR), oxygen volume passing through.

Q1: What is ISO 2556, and what test principle does it adopt?

A1: ISO 2556 originates from ISO 2556:1974, published as European standard EN ISO 2556:2000 and British standard BS EN ISO 2556:2001. It specifies a mercury manometric differential-pressure method to measure Gas Transmission Rate (GTR) of thin plastic films and sheets. The core principle: a specimen separates two chambers; the upstream chamber holds test gas at atmospheric pressure, the downstream chamber is fully evacuated and sealed. Permeated gas raises downstream pressure, which is quantified via mercury column height changes to calculate GTR. Its measurable GTR range is 1–20000 cm³/(m²·d·atm).

Q2: What materials can ISO 2556 test? What materials are excluded?

A2: Applicable: Single-layer thin plastic films, thin sheets, lightweight laminated packaging films, coated thin polymer substrates (PE, PP, PVC, biodegradable thin films).

Excluded: Thick rigid plastic slabs, open-cell plastic foams, metal foils, glass sheets, multi-layer high-barrier complex films (better tested via ISO 15105-1 GC method).

Q3: Does ISO 2556 offer multiple test methods like ISO 15105-1?

A3: No. ISO 2556 only has one normative mercury manometric method, with two hardware variants (overflow mercury setup / non-overflow mercury setup). It has no electronic pressure sensor or gas chromatography options.

Q4: Why must we discard the initial non-linear permeation curve data and only use steady-state linear slope dh/dt?

A4: In the early test stage, gas molecules are absorbed into the polymer matrix, causing unstable, accelerating permeation rates. Only after steady state (5–6 consecutive equal time intervals show constant mercury height rise) does gas diffusion achieve equilibrium through the film, ensuring accurate GTR calculation.

Q5: How many test specimens are required for one material batch per ISO 2556?

A5: A minimum of three identical disc-shaped specimens must be tested, which is mandatory for valid average results.

Q6: What size and surface quality requirements apply to specimens?

A6: Specimens are circular discs, minimum ~80 mm diameter to fully cover the cell gasket and avoid gas bypass leakage. Samples must be free of pinholes, creases, thin spots, scratches and uneven thickness; thickness uniformity directly impacts result reliability.

Q7: Do hygroscopic plastic films need pre-conditioning before testing?

A7: Yes. Hygroscopic specimens must be conditioned under standard atmospheres defined in ISO/R 291 for sufficient equilibrium time to eliminate moisture interference. Non-hygroscopic plastics may skip conditioning.

Q8: What two types of mercury manometer setups are allowed under ISO 2556? What is their core difference?

A8: Overflow mercury apparatus: Mercury automatically maintains zero reference level; correction coefficient c=1, no extra mathematical correction needed for calculations.

Non-overflow mercury apparatus: Mercury level drifts in the U-tube during testing; a geometric correction factor c = 1 + a/u must be calculated and applied to all GTR formulas.

Q9: What vacuum performance must the vacuum pump meet for ISO 2556 testing?

A9: The vacuum pump must evacuate the downstream chamber to ≤13 Pa (0.1 mmHg), with a pressure gauge accurate to at least 6 Pa (0.05 mmHg).

Q10: What support materials are used inside the test cell? When do we need filter paper vs sintered disc?

A10: Two cavity designs for the lower test plate:

20 mm small central cavity: Requires analytical filter paper to support thin flexible films;

60 mm large cavity: Uses flat glass/bronze sintered disc, no filter paper required.

Both materials support the specimen while allowing gas to pass through freely.

Q11: What is the function of the optional metal packing block inside Chamber 2?

A11: It reduces the fixed volume of the downstream low-pressure chamber. For ultra-low barrier films with very slow gas permeation, a smaller chamber volume amplifies mercury column displacement, making height readings easier and more accurate.

Q12: What are the key differences between ISO 2556 and ISO 15105-1?

A12: Instrumentation: ISO 2556 relies on toxic mercury liquid manometers; ISO 15105-1 uses mercury-free electronic pressure sensors and gas chromatographs for safer lab operation.

Gas compatibility: ISO 2556 only tests single pure gases and cannot separate mixed gas components; Annex B of ISO 15105-1 uses GC to measure independent permeation rates of each gas in mixtures.

Age & status: ISO 2556 original standard withdrawn, legacy European regional standard; ISO 15105-1:2007 is the current global active international standard.

Measurement range & precision: ISO 15105-1 covers a wider barrier range with higher automation and accuracy, while ISO 2556 is low-cost manual testing for simple single-layer thin films.

Q13: When should labs choose ISO 2556 instead of ISO 15105-1?

A13: Select ISO 2556 only for legacy compliance requirements (old European product specifications referencing BS EN ISO 2556), low-budget routine screening of simple single-layer thin films, or historical material performance comparison with decades-old ISO 2556 test archives. For new product development, mixed gas testing, high-barrier multi-layer films, and modern lab safety rules, ISO 15105-1 is recommended.

Q14: What precision rules apply to mercury height and time readings?

A14: Mercury height: General samples read to nearest 0.25 mm; low-permeability films (GTR <100 cm³/m²·d·atm) require readings precise to 0.1 mm (cathetometer/magnifying glass needed).

Time recording: Nearest 1 minute for low GTR materials; nearest 5 seconds for high GTR materials.

Q15: What blank leak test is required before formal testing, and why?

A15: Replace the plastic specimen with impermeable metal foil and run a full test procedure. If mercury height shifts significantly during the blank test, the cell has air leakage (faulty gasket, loose clamping, incomplete vacuum grease sealing) and must be re-sealed before testing samples.

Q16: Why is ISO 2556 testing important for plastic film materials?

A16: Standardized barrier performance benchmarking: GTR data quantifies oxygen, CO₂ and air penetration, enabling manufacturers to grade raw film materials and optimize polymer formulations.

Shelf-life prediction for packaged goods: Excessive oxygen permeation triggers food oxidation, flavour loss and cosmetic ingredient degradation; ISO 2556 results guide packaging design to extend product stability.

Low-cost quality control: Mercury manometric equipment has lower upfront investment than automated GC/electronic sensor instruments, suitable for high-volume factory batch screening.

Historical cross-lab data compatibility: As a long-standing European differential-pressure standard, it aligns with legacy product technical files and old certification specifications from UK/EU packaging markets.

Support thin-film process optimization: Test data helps adjust film thickness, crystallinity and surface coating to reduce gas transmission without excessive material cost increases.

Q17: Mercury column height rises rapidly after evacuating Chamber 2, before test gas is introduced. What is the root cause?

A17: System air leakage exists. Check damaged rubber gaskets, uneven vacuum grease coating, wrinkled specimens, or loose cell clamping. Re-seal the cell and repeat the blank metal foil leak test until mercury remains stable.

Q18: Mercury readings show inconsistent, unstable slopes even after long testing time. What causes this?

A18: Multiple possible factors: 1) Temperature fluctuation exceeding ±2 °C inside the test enclosure; 2) Insufficient specimen conditioning (hygroscopic films retaining moisture); 3) Vibration disturbing the vertical capillary tube; 4) Poor vacuum seal causing slow background air ingress.

Q19: Can I skip the correction coefficient c calculation for non-overflow mercury equipment?

A19: No. Non-overflow setups have shifting U-tube mercury reference levels during testing; omitting the correction factor will generate large systematic errors in final GTR values. Overflow apparatus only uses c=1 with no correction required.

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