As a thermoplastic adhesive, the properties of hot melt adhesives are significantly affected by temperature. In the high temperature environment, the movement of polymer molecular chain segments intensifies, the material may soften, and the cohesive strength decreases. At low temperatures, the activity of molecular chains decreases, and the material may become brittle and tough. Therefore, a comprehensive evaluation of the tensile properties of a hot melt adhesive over the expected operating temperature range is crucial for predicting its bond reliability and durability under real-world operating conditions. The tensile testing machine provides an accurate means for quantifying the mechanical response of hot melt adhesives by simulating the tensile process under different temperature conditions.
Test Principle:
At the heart of the evaluation is the use of a tensile testing machine equipped with a temperature-controlled chamber to place a standardized hot melt adhesive specimen in a set high and low temperature environment to stretch at a constant speed until failure. The test mainly measures its tensile strength, elongation at break, and stress-strain curve. These data directly reflect the material's bearing capacity, deformation capacity, and toughness at different temperatures. Relevant technical standards at home and abroad provide unified sample preparation, test conditions and result calculation methods for testing, ensuring data comparability and repeatability.
Test parameters
To ensure the accuracy and representativeness of the evaluation results, a series of test parameters must be strictly controlled and recorded. The following table lists the core test conditions and parameters.
| Temperature range | Determined according to the product specification or application environment, such as -40°C, 23°C, 80°C. |
| Specimen shape | Typically dumbbell type (e.g. ISO 527-2 1BA type) or bonded lap shear specimens. |
| Stretch speed | Typical speeds are 50 mm/min to 500 mm/min, to be noted in the report. |
| Environmental equilibrium time | The specimen needs to be kept at the test temperature for a sufficient amount of time to ensure a uniform overall temperature. |
| Data collection | At least record the maximum force, breaking force, corresponding displacement, and complete stress-strain curve. |
Performance indicator analysis
The data obtained through the tensile test can be used to calculate the core performance indicators. The formula for calculating tensile strength (σ) is: σ = Fmax / A, where Fmaxis the maximum tensile force, and A is the original cross-sectional area of the specimen. The formula for calculating elongation at break (ε) is: ε = (L - L0) / L0 × 100%, where L is the length of the gauge at breakage, L0It is the original gauge. It is important to analyze the trend of these indicators at high and low temperatures: tensile strength usually decreases at high temperature, while elongation at break may increase; At low temperature, on the contrary, the strength may increase but the elongation decreases sharply, showing the characteristics of brittle fracture. The area surrounded by the stress-strain curve qualitatively assesses the toughness of a material at different temperatures.
Notes:
There are several points to pay attention to in the actual test. First, the uniformity of sample preparation is the basis for reliable data, and it is necessary to ensure that the thickness of the adhesive layer is consistent and there are no bubbles. Secondly, the temperature uniformity and stability of the temperature control chamber must be verified to avoid local temperature deviations of the sample. During the low-temperature test, care should be taken to prevent frosting on the surface of the specimen or fixture from affecting the test. When testing at high temperatures, it is necessary to consider the creep effect that may occur of the material and choose the appropriate tensile speed. The fixture should be cleaned after each test to prevent residual compound from affecting the accuracy of subsequent tests.
Conclusion
It is an effective and necessary method for material characterization to evaluate the tensile properties of hot melt adhesives at high and low temperatures. It systematically reveals the complex effects of temperature on the mechanical behavior of hot melt adhesives, providing critical data support for product formulation development, quality control, and application selection. By strictly following standard methods, controlling test conditions, and interpreting data accordingly, engineers can more accurately predict the performance of hot melt adhesives in real-world complex temperature environments, thereby improving the reliability and safety of the final bonded product.
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.