In the field of materials science and engineering, the hygroscopic properties of resin materials are a key indicator for evaluating their long-term reliability in humid environments. High temperature and high humidity will accelerate the diffusion and adsorption of moisture into the material, which may lead to plasticization, size change, mechanical property degradation or electrical insulation performance of the material. Therefore, the use of damp heat test chambers to simulate harsh environmental conditions and accurately determine the moisture absorption rate of resins is of great practical significance for product development, quality control and life prediction.
Test Principle:
At its core, moisture absorption testing measures the change in the quality of resin specimens before and after exposure to specific high temperature and humidity environments. The basic calculation formula is as follows:
Moisture absorption rate (M) = [(Wt - W0) / W0] × 100%
Among them, W0 Represents the drying quality of the specimen before testing, Wt It represents the mass of the specimen after exposure time t in high temperature and high humidity environment. The test is usually carried out with reference to standard methods such as IEC 60068-2-78 and GB/T 2423.3 on damp heat testing. Before testing, the specimen is thoroughly dried to a constant weight under standard conditions (e.g., temperature 23±2°C, relative humidity 50±5%) to obtain an accurate initial mass W0。
Parameters and controls
To ensure the reliability and repeatability of test results, the moist heat chamber needs to provide a stable and uniform environment. Key parameters include:
| Temperature range | Typically covers 40°C to 95°C, with common test conditions such as 85°C |
| Relative humidity range | Typically covers 20% to 98% RH, with common test conditions such as 85% RH |
| Temperature uniformity | The temperature difference of each point in the working space in the box should be controlled within a small range (e.g., ±0.5°C) |
| Humidity uniformity | The humidity deviation at each point in the working space in the box should be controlled within a small range (e.g., ±2%RH) |
| Temperature fluctuations | The temperature of the control point should change little enough over time |
During the test, the dried specimen is placed in the test chamber and set to the target temperature and humidity (e.g. 85°C/85%RH). Take out the specimen at the preset time point (such as 24h, 48h, 96h, 168h, etc.), quickly wipe the surface condensate, weigh it, and record Wt。 Each weighing operation should be prompt to avoid additional moisture absorption or water loss in the environment.
Data analysis
The moisture absorption rate of resins is influenced by various factors. Factors related to the material itself include the chemical structure, polarity, crystallinity, type and content of the filler, and the thickness of the specimen. The environmental factors are mainly the temperature and relative humidity set by the test chamber. Generally, the higher the temperature, the greater the moisture diffusion coefficient; The higher the relative humidity, the greater the partial pressure of ambient water vapor, both of which promote the hygroscopic process.
When analyzing data, the moisture absorption rate curve over time can be used to evaluate moisture absorption kinetics. The moisture absorption rate increases rapidly at the beginning, then gradually slows down, and may eventually approach saturation equilibrium. By fitting diffusion models such as Fick's second law, parameters such as moisture diffusion coefficient can be calculated, which provides a theoretical basis for material modification.
Notes:
The following points should be paid attention to when conducting testing: the specimen should be representative, and the surface should be clean and free of pollution; The specimens in the box should be placed to ensure the surrounding air circulation and avoid overlapping. The accuracy of the weighing equipment should meet the requirements (at least 0.1mg is recommended); the test report should record in detail the test conditions, specimen information, measurement data and any observed cosmetic changes.
Conclusion
The determination of the moisture absorption rate of resin at high temperature and humidity by using a damp heat test chamber is an effective means to evaluate the moisture resistance of materials. Through standardized testing processes and precise environmental control, repeatable and reliable data can be obtained that are essential for understanding material failure mechanisms, optimizing material formulations, and guiding application design. In practical applications, it is necessary to formulate and interpret test conditions and results based on the specific usage scenarios of materials.
References
International Electrotechnical Commission. Environmental Tests Part 2-78: Tests Test Cab: Steady-State Damp Heat. IEC 60068-2-78.
National Standardization Administration of China. Environmental Test of Electrical and Electronic Products Part 2: Test Method Test Cab: Constant Humidity and Heat Test. GB/T 2423.3.
A review of test methods for moisture absorption of materials. Polymer Materials Science and Engineering.