Standard method
The peel strength of hot melt adhesives is one of the key indicators for evaluating their bonding properties, reflecting the resistance of the adhesive when subjected to peel forces. Electronic tensile machines are commonly used to measure this parameter due to their high precision, repeatability, and easy data processing. Based on relevant domestic and foreign standards and practices, this method aims to provide a set of systematic and standardized testing processes, suitable for hot melt adhesive samples in various industrial fields such as packaging, textile, and wood processing.
Test Principle:
This method uses a 180° peel test mode. The hot melt adhesive is applied to a substrate of the specified size and bonded to another substrate of the same or different to form a specimen. The unbonded end of the specimen is clamped in the upper and lower grippers of the electronic tensioning machine and peeled at a constant speed. The electronic tensile machine records the change of force value during the peeling process in real time, and obtains the peel strength of the hot melt adhesive by calculating the average or characteristic value of the peel force curve, which is usually expressed as the force divided by the bonding width (such as N/mm or kN/m).
Equipment & Materials
The core equipment is an electronic tensile machine, which needs to meet the following basic requirements: the force value range should cover the expected peeling force; The displacement resolution is sufficient; It is equipped with a data acquisition system that can automatically record force-displacement curves. The fixture should be able to hold the specimen firmly and prevent slipping. In addition, it is necessary to prepare the substrate (such as metal sheet, plastic sheet, fabric, etc.), gluing device, pressing device (for preparing specimens), cutting knives, and temperature and humidity control environment (if required by the standard).
Sample preparation
Specimen preparation is fundamental to ensure the accuracy of test results. First, select the substrate according to the relevant product standards or protocols and clean its surface. The hot melt adhesive is melted at a specified temperature to evenly apply the amount of coating to the bonded area of a substrate. The second substrate is quickly aligned and covered and pressed under specified pressure, temperature, and time conditions to form a standard-sized bonded specimen (typically 125mm long and 25mm wide). The specimen should be conditioned for sufficient time in a standard test environment.
Test steps
The formal test is carried out in the following steps:
1. Separate the unbonded end of the specimen after state adjustment and load it into the upper and lower clamps of the electronic tensioning machine to ensure that the axis of the specimen is consistent with the tension direction, and the peeling angle is 180°.
2. Set parameters in the test software: select the peel test mode, set the tensile speed (commonly 100 mm/min or 300 mm/min, according to the standard), and enter the necessary information such as the specimen width.
3. Start the test, the electronic tension machine will automatically separate the fixture, and draw the peeling force-displacement curve in real time.
4. Stop the test when the peeling length reaches the specified value (usually not less than 100mm) or when the specimen is completely separated.
5. Repeat the test for at least five valid specimens.
Data processing
From the recorded peel force-displacement curve, the outliers of the initial and end sections are removed, and the average value of the peel force is calculated within the stable peel section. Peel strength σ calculated according to the following formula:
σ = F / b
where the σ is the peel strength (unit: N/mm or kN/m); F is the average peeling force (unit: N); b is the bonding width of the specimen (unit: mm or m). The calculation is expressed as an arithmetic mean of all valid specimen results, with standard deviation or coefficient of variation reported if necessary.
Notes:
Test results are influenced by a variety of factors and need to be strictly controlled to ensure comparability:
| Substrate surface properties | Cleanliness, roughness, material |
| Gluing process | Melting temperature, coating volume, opening time |
| Pressing conditions | Pressure, temperature, duration |
| Test environment | Temperature and humidity and their stability |
| Device parameters | Peel speed, fixture alignment, data sampling rate |
The above conditions, specimen descriptions, individual results and final averages, and any deviations from standard methods should be documented in detail in the test report.
Scope of application
This method is suitable for evaluating the adhesion properties of hot melt adhesives under the combination of soft-soft and soft-hard materials. For adhesives with very high or low peel strength, the appropriate range of sensors is required. This method mainly reflects the quasi-static peel performance, and other test methods need to be combined for the evaluation of dynamic impact or long-term durability.
References
GB/T 2792-2014 Test method for peel strength of adhesives
ASTM D903-98(2017) Standard Test Method for Peel or Stripping Strength of Adhesive Bonds
ISO 8510-2:2006 Adhesives — Peel test for a flexible-bonded-to-rigid test specimen assembly — Part 2: 180° peel