Immersion Peel Test Steps: Complete Procedure, Standards, and Applications

The immersion peel test is a standardized adhesion evaluation method used to measure the interlayer bond strength of laminated films, coated materials, and bonded assemblies after exposure to a liquid medium. By comparing peel strength before and after immersion in water, acid, alkali, electrolyte, or oil, manufacturers can assess durability and long-term reliability of flexible packaging, battery materials, footwear, and industrial laminates. This article explains the complete immersion peel test procedure, covering sample preparation, conditioning, immersion treatment, peel measurement, data processing, and applicable standards such as ASTM D1876, ASTM D903, ISO 8510, and GB/T 8808.

Technical Overview

The immersion peel test, also known as a soak peel test or wet peel test, determines the resistance of a bonded or laminated interface to separation after the specimen has been soaked in a defined liquid medium. The test is widely used to evaluate whether adhesives, tie-layer resins, coatings, or heat-sealed structures can maintain sufficient bond strength when exposed to water, food simulants, chemicals, battery electrolytes, or oils during service.

The basic principle is straightforward: identical specimens are tested in two conditions. One group is peeled in the dry state to establish a baseline peel strength, while a second group is fully immersed in a specified liquid at a controlled temperature for a defined duration, then peeled under identical machine settings. The ratio of the wet (post-immersion) peel strength to the dry peel strength, expressed as a percentage, is the peel strength retention rate, which serves as the key indicator of environmental durability.

Depending on the material and the applicable specification, the peel configuration may be a T-peel, a 180-degree peel, or a 90-degree peel, performed on a universal testing machine. Commonly referenced standards include ASTM D1876 (T-peel test for flexible adherends), ASTM D903 (180-degree peel or stripping strength), ISO 8510-1 and ISO 8510-2 (peel tests for flexible-to-rigid and flexible-to-flexible bonded assemblies), ASTM D3167 (floating roller peel), GB/T 8808 (peel force of flexible laminated films), GB/T 2790 and GB/T 2791 (180-degree and T-peel strength of adhesive bonds), and JIS Z 0238 for flexible packaging evaluation. Many manufacturers also submit samples to accredited third-party laboratories for conformance testing against these standards.

Testing Samples

Flexible Packaging Laminates

Multilayer films such as PET/AL/PE, BOPP/CPP, PA/PE, and paper/aluminum/foil structures used for food pouches, retort packaging, and pharmaceutical sachets are typical candidates. These structures are frequently tested after immersion in food simulants such as acetic acid solutions, vegetable oil, or ethanol/water mixtures to verify that the lamination bond survives contact with acidic, oily, or aqueous contents.

Lithium Battery Materials

Aluminum-plastic laminate films used in pouch cells are tested for peel strength between the aluminum foil and the polymer layers after immersion in electrolyte, which reveals whether the laminate can withstand long-term electrolyte exposure. Ceramic-coated separators and electrode coatings on copper or aluminum current collectors are also evaluated to confirm coating adhesion after soaking in electrolyte or water.

Bonded and Coated Assemblies

Footwear outsole-to-upper bonds, automotive interior laminates, protective films, pressure-sensitive tapes, wire and cable insulation sheaths, and industrial coated fabrics are tested after immersion in water, salt solution, detergent, or process chemicals to assess hydrolysis and chemical resistance of the bond line.

Testing Items

The immersion peel test program typically includes the following measurable parameters:

• Dry peel strength: the baseline bond strength measured before any liquid exposure, reported in N/15 mm, N/25 mm, N/mm, or kN/m.
• Wet or post-immersion peel strength: the bond strength measured after the specified immersion period in the selected medium.
• Peel strength retention rate: the ratio of wet peel strength to dry peel strength, expressed as a percentage.
• Failure mode classification: identification of adhesive failure at an interface, cohesive failure within a layer or adhesive, or substrate tear in which the material breaks before peeling.
• Optional supplementary items: peel strength after combined immersion plus heat aging, immersion plus flexing, or immersion at elevated temperature for accelerated aging studies.

Testing Methods

The complete procedure consists of six controlled stages. Exact parameters vary by product specification and standard, so the applicable test plan should always be confirmed before testing.

Step 1: Specimen Preparation

• Cut specimens from representative production material at the specified width, typically 15.0 mm or 25.0 mm with a tolerance of ±0.1 mm, and a length of at least 150 mm to 200 mm.
• Prepare a minimum of five valid specimens for each condition (dry and immersed), and record the machine direction or transverse direction of each specimen.
• Separate an unbonded tab of approximately 30 mm to 50 mm at one end of the specimen using a knife, heat wire, or solvent-assisted technique, taking care not to damage the layers to be peeled.
• Avoid stretching, creasing, or contaminating the peel interface, as fingerprints, dust, and edge damage will distort the measured peel force.

Step 2: Conditioning

• Condition all specimens in a standard laboratory atmosphere of 23 ± 2 °C and 50 ± 5 % relative humidity for at least 40 hours before testing, following ISO 291 or ASTM D618 as applicable.
• Condition any liquid medium to the specified immersion temperature before submerging the specimens.

Step 3: Immersion Treatment

• Select the immersion medium according to the product specification, for example distilled water, 3 % to 4 % acetic acid, sodium carbonate or sodium hydroxide solution, ethanol/water mixture, vegetable oil, battery electrolyte, or salt solution.
• Set the immersion temperature, commonly 23 ± 2 °C for room-temperature evaluation, or an elevated temperature such as 40 °C or 60 °C for accelerated conditioning.
• Set the immersion duration, commonly 24 hours, 48 hours, 72 hours, or 7 days depending on the end-use requirement.
• Fully submerge the specimens in the medium with the peel interface exposed to the liquid, keeping specimens separated and preventing contact with the container walls where practical.

Step 4: Post-Immersion Handling

• Remove the specimens from the medium and gently blot surface liquid with a lint-free cloth without stressing the bond line.
• Perform the peel test within the time window defined by the specification, for example within 10 minutes or 1 hour of removal, since drying can artificially change the measured value.
• Visually inspect and record any delamination, blistering, whitening, swelling, or corrosion observed after immersion, as these observations support the interpretation of the peel data.

Step 5: Peel Strength Measurement

• Mount the specimen in a universal testing machine fitted with a load cell of suitable capacity and accuracy of ±1 % or better.
• Select the peel configuration and crosshead speed specified by the standard: common settings include 200 mm/min to 300 mm/min for flexible laminated films per GB/T 8808, and configurations per ASTM D1876 for T-peel, ASTM D903 for 180-degree peel, or ASTM D3167 for floating roller peel.
• Clamp the separated tab ends in the grips so that the peel front propagates along the intended interface without twisting the specimen.
• Run the test until at least 100 mm of peel length has been traversed, ensuring the recorded curve contains a stable plateau region.
• Repeat the measurement for every valid specimen in both the dry and immersed groups.

Step 6: Data Processing and Reporting

• Calculate the average peel force from the stable region of the force-displacement curve, excluding the initial peel-in segment and any obvious atypical peaks or troughs as permitted by the standard.
• Divide the average peel force by the specimen width to obtain peel strength, reported in N/15 mm, N/25 mm, N/mm, or kN/m as required.
• Compute the peel strength retention rate: retention (%) = (average wet peel strength / average dry peel strength) × 100.
• Classify the failure mode for each specimen as adhesive interface failure, cohesive failure, or substrate tear; specimens that tear before peeling are recorded as material break with the peel value noted as greater than the tear value.
• Compile the test report with the standard referenced, specimen dimensions and orientation, immersion medium, temperature, duration, test speed, individual and average peel values, standard deviation, retention rate, and failure mode descriptions, together with representative force-displacement curves.

Applications

The immersion peel test supports quality control and material qualification across many industries:

• Food and pharmaceutical flexible packaging: verification of lamination integrity for retort pouches, liquid packaging, and sachets exposed to acidic, oily, or aqueous contents.
• Lithium-ion battery manufacturing: qualification of aluminum-plastic laminate films, ceramic-coated separators, and electrode coatings against electrolyte attack over the cell lifetime.
• Footwear industry: assessment of sole bonding durability against water, sweat, and hydrolysis during wear.
• Automotive sector: evaluation of interior laminates, trim attachments, and cable jacket adhesion after exposure to water, detergent, and humidity.
• Electronics and wire and cable: confirmation of insulation and sheath adhesion after water immersion for long-term reliability.
• Research and development: screening of adhesives, tie resins, surface treatments, and coating formulations for wet-environment performance, frequently carried out in accredited third-party laboratories for independent verification.

FAQ

What is the difference between a dry peel test and an immersion peel test?

A dry peel test measures bond strength under standard laboratory conditions, while an immersion peel test measures bond strength after the specimen has been soaked in a specified liquid for a defined time and temperature. The immersion result shows how moisture or chemical exposure weakens the interface, and the retention rate quantifies that degradation.

Which immersion media are most commonly used?

Distilled water is the most common medium for general durability studies. Food-simulant liquids such as acetic acid, ethanol/water mixtures, and vegetable oil are used for packaging, while battery electrolyte is used for cell materials. Salt solutions, detergents, and process chemicals are selected according to the intended service environment.

What sample dimensions are required?

Typical specimens are 15 mm or 25 mm wide with a tolerance of ±0.1 mm, and at least 150 mm to 200 mm long, with a pre-separated tab of 30 mm to 50 mm for gripping. A minimum of five valid specimens per condition is recommended for statistical reliability, although the governing standard takes precedence.

What peel strength retention rate is considered acceptable?

Acceptance criteria depend entirely on the product specification. Many internal specifications for battery laminates and high-performance packaging require retention above 70 % or 80 % after the defined immersion period, and some critical applications require a minimum absolute wet peel value as well. Always verify the pass/fail threshold with the applicable standard or customer specification.

Which standards govern the immersion peel test?

No single standard covers every case, so the test is usually built by combining a peel method such as ASTM D1876, ASTM D903, ASTM D3167, ISO 8510-1, ISO 8510-2, GB/T 8808, GB/T 2790, GB/T 2791, or JIS Z 0238 with an immersion conditioning procedure defined by the product specification or end-user requirement.

How are specimens handled if the material tears instead of peeling?

If a layer tears before the interface separates, the result is reported as a material break or substrate tear, and the peel strength is recorded as greater than the force at which the tear occurred. This outcome generally indicates that the bond strength exceeds the tensile strength of the weakest layer, which is usually a favorable result for adhesion quality.