Universal material testing machine for testing the tensile strength of hot melt adhesive.

Overview

As a common bonding material, the tensile strength of hot melt adhesive is a key index for evaluating its mechanical properties and reliability. The universal material testing machine can accurately determine the strength and deformation behavior of hot melt adhesive under stress by simulating tensile loads, providing data support for material research and development, quality control and application selection. The test follows a number of common standards both domestically and internationally, ensuring comparability and repeatability of results.

Test Principle:

The test is based on the basic principles of material mechanics, applying axial tensile force to a standardized hot melt adhesive specimen until it breaks. By recording the load-displacement curve, parameters such as tensile strength, elongation at break, and elastic modulus can be calculated. Key reference standards include ISO 527 (Determination of Tensile Properties of Plastics) and ASTM D638 (Standard Test Methods for Tensile Properties of Plastics), which specify specimen shape, test speed, and environmental conditions.

Sample preparation

Specimens are usually prepared in dumbbell type to ensure that fractures occur in parallel segments. Hot melt adhesives are melted and molded under controlled conditions (e.g., specific temperatures and humidity) before being fully cured. The specimen size should strictly comply with the standard, such as the length, width and thickness of the parallel segments should be consistent to reduce measurement deviation. Prepared specimens should be conditioned in a standard laboratory environment for at least 24 hours prior to testing.

Parameter settings

The universal material testing machine needs to be equipped with appropriate load cells (the range is selected according to the estimated strength) and pneumatic or mechanical fixtures to ensure a secure grip and avoid specimen slippage. Key parameter settings include:

• Test speed: usually set to 50 mm/min to 500 mm/min, according to material properties and standard requirements;

• Initial clamping distance: determined according to the specimen gauge, the common value is 50 mm or 100 mm;

• Data acquisition frequency: No less than 50 Hz is recommended to accurately capture the breaking point.

Before the test, the load and displacement should be calibrated, and the ambient temperature should be maintained at 23±2°C and the relative humidity should be 50±10%.

Testing process

1. The specimen is symmetrically clamped in the upper and lower fixtures to ensure axial alignment;

2. set the test speed, initial gauge and other parameters, and clear the displacement and load;

3. Start the testing machine and continuously apply tensile load until the specimen breaks;

4. record the maximum load, fracture displacement and complete load-displacement curve;

5. The fracture specimen was taken out, the fracture morphology was observed and recorded.

Analysis of results

The formula for calculating tensile strength (σ) is:

σ = F_max / A

where F_maxis the maximum load (unit: N), and A is the original cross-sectional area of the specimen (unit: mm²).

The formula for calculating elongation at break (ε) is:

ε = (L - L₀) / L₀ × 100%

where L is the gauge length at the time of fracture, L₀is the original gauge length.

Typical hot melt adhesive tensile performance ranges are examples of:

The results should be combined with the load-displacement curve morphology to evaluate the toughness, brittleness or yield characteristics of the material. After multiple tests (usually no less than 5 valid specimens), the average value was taken, and the standard deviation was calculated to evaluate the data dispersion.

Notes:

Test results are influenced by a variety of factors, including:

• Sample preparation quality: bubbles, impurities or uneven curing will lead to low strength;

• Test speed: higher speed may increase the measured strength and decrease elongation;

• Clamping conditions: Excessive clamping may cause stress concentration and lead to premature fracture;

• Ambient temperature and humidity: Rising temperature usually reduces the strength of the hot melt adhesive and increases its plasticity.

Calibrate equipment regularly during operation, check for fixture wear, and ensure batch consistency of specimens. For abnormal fractures (e.g., breaks near the fixture), the data should be considered invalid and retested.

Application significance

The tensile strength of hot melt adhesive is measured by the universal material testing machine, which can systematically evaluate its bearing capacity and deformation characteristics, and guide formula optimization, process improvement and application scenario adaptation. This method has the characteristics of standardized operation and reliable data, and is a widely used method in material research and industrial testing. Testers should have a deep understanding of the standard requirements and strictly control the test conditions to obtain reference value mechanical performance data.

References

ISO 527-1:2019, Plastics — Determination of tensile properties — Part 1: General principles.

ASTM D638-14, Standard Test Method for Tensile Properties of Plastics.

GB/T 1040.1-2018, Determination of tensile properties of plastics - Part 1: General provisions.

Review of Performance Test Methods for Hot Melt Adhesives, Polymer Materials Science and Engineering, 2020.