Introduction
A thermogravimetric analyzer is a commonly used instrument to evaluate the thermal stability of a material by measuring the change in sample mass with temperature or time. In the production and application of plastic films, thermal stability is one of the key parameters that determine their processing performance and service life. The purpose of this paper is to explore how to use thermogravimetric analyzers to test the thermal stability of plastic films, and interpret the data according to relevant technical standards to provide reference for material selection and process optimization.
Test Principle:
The basic principle of thermogravimetric analyzers is to continuously record changes in sample quality under programmed temperature control conditions. For plastic films, testing is typically performed in an inert atmosphere (such as nitrogen) or an oxidizing atmosphere (such as air) to simulate different environments. The mass loss curve can reflect the thermal decomposition process of the film, and its characteristic parameters such as the starting decomposition temperature and the maximum decomposition rate temperature can be used to quantify the thermal stability. The relationship between mass change and temperature can be expressed as:
Δm = f(T)
where Δm is the mass change and T is the temperature. Through differential processing, differential thermogravimetric curves can be obtained for identifying the decomposition stage.
Sample preparation
Before testing, the plastic film is cut to the appropriate size, usually in sheets of a few millimeters in diameter, to ensure that the sample is evenly spread in the sample tray. Sample quality is generally controlled between 5 and 20 mg to avoid heat transfer effects. If the film contains volatile components, it needs to be dried at low temperature beforehand.
Test conditions
The test conditions are set according to the film type and application requirements. Common parameters include the rate of rise (e.g., 10°C/min), temperature range (room temperature to 800°C), and atmosphere flow (e.g., 50 mL/min). The rate of rise affects the apparent value of the decomposition temperature, and a lower rate can improve the resolution. The choice of atmosphere depends on the purpose of the test: inert atmospheres are used to evaluate mere thermal decomposition, and oxidizing atmospheres are used to study oxidative degradation behavior.
Data analysis
Several key parameters can be extracted from the thermogravimetric curve, as shown in the following table:
| Characteristic temperature points | Description |
| Initial decomposition temperature | The temperature at which the mass loss reaches a certain threshold (e.g., 5%) |
| Maximum decomposition rate temperature | The temperature corresponding to the peak of the differential curve |
| Residual mass | The percentage of remaining mass after the high temperature segment |
These parameters can be used to compare the thermal stability of different film formulations. For example, a higher starting decomposition temperature generally indicates better thermal stability. In addition, through kinetic analysis, the decomposition activation energy can be estimated to further quantify the heat resistance of the material.
Application examples
Taking polyolefin film as an example, thermogravimetric analysis shows that it mainly decomposes in a single stage in nitrogen, and the initial decomposition temperature is about 300°C. In air, the decomposition temperature may decrease due to oxidation. By comparing the curves before and after treatment of additives (e.g., stabilizers), the effect of the additive on thermal stability can be evaluated. The test data helps optimize the processing temperature window and prevent film degradation during thermoforming.
Notes:
Ensure that the instrument is calibrated accurately, especially on temperature and quality scales. The sample should be representative of the overall material and avoid local inhomogeneity affecting the results. The purity of the atmosphere needs to be controlled to prevent impurities from interfering. In addition, data interpretation needs to be combined with other analytical methods (e.g., differential scanning calorimetry) to obtain more comprehensive thermal performance information.
Epilogue
Thermogravimetric analyzers provide a reliable method for evaluating the thermal stability of plastic films. Through standardized testing and data analysis, it can effectively guide material research and development and process improvement, and improve the applicability of thin film products in high-temperature environments. In the future, with the improvement of standards and technological advancements, this method is expected to play a role in a wider range of fields.
References
1. General principles of thermal analysis technology and compilation of material testing standards.
2. Research on the kinetics of polymer thermal decomposition, Journal of Polymer Science.
3. Plastic film performance test guide, industrial materials manual.