Thermogravimetric Analyzer for Measuring Moisture and Volatiles in Polymer Materials

The thermogravimetric analyzer measures the mass change of polymer materials during heating to determine their moisture and volatile content. During testing, the sample is heated at a controlled rate in a regulated atmosphere. Moisture and volatiles evaporate or decompose at lower temperature ranges (e.g., 50–150°C), leading to a reduction in mass. The content percentage can be calculated from the thermogravimetric curve. Factors such as sample preparation, heating rate, and atmospheric conditions must be carefully considered in this method, which is widely applied in quality control and process optimization for materials like plastics and rubber.

Introduction

Thermogravimetric analyzer is a technical means to study the thermal stability and composition of materials by measuring the change of sample mass with temperature or time. In the field of polymer materials, moisture and volatile content directly affect processing performance, mechanical properties, and long-term durability. Accurate determination of these components is important for material development, quality control, and process optimization.

Principle overview

Thermogravimetric analysis is based on the heating of a sample in a controlled atmosphere resulting in mass loss due to water evaporation or volatile decomposition. The curve of the relationship between mass change and temperature or time is called the thermogravimetric curve, and its differential curve can identify the weightless step. For polymer materials, the weight loss of moisture and volatiles usually occurs in a relatively low temperature range, and different weight loss stages can be separated by program temperature raising.

The basic relationship can be expressed as: Δm = m₀ - m_t, where Δm is the mass loss, m₀is the initial mass, m_tis the mass at time t. Moisture or volatile content is often calculated as a percentage of mass: w = (Δm/m₀) × 100%。

Test methodology

Instrument calibration, including temperature and quality calibration, is required prior to testing. Sample preparation should be representative, usually crushed or cut into uniform pieces, with a mass of between 5 and 20 mg. The test conditions need to be set according to the material properties, and common parameters include heating rate, atmosphere type and flow rate, temperature range, etc. Moisture and volatile determination mostly uses a temperature range from room temperature to about 150°C, maintaining a constant temperature to ensure adequate removal.

Rate of warming	Usually 5-20°C/min
Atmosphere	Nitrogen or dry air
Sample quality	10±5 mg is recommended
Temperature range	Room temperature to 150°C constant temperature

Influencing factors

Test results are influenced by a variety of factors. Excessive heating rate may lead to incomplete volatile removal or thermal lag. Atmosphere flow rate affects the removal efficiency of volatile products. The particle size and bulk density of the sample may affect heat transfer and diffusion. Instrument sensitivity and baseline stability can also introduce bias. Conditional optimization and repeated testing are required to ensure data reliability.

Data parsing

The weightless step can be identified from the thermogravimetric curve, corresponding to the loss of moisture and volatiles. Curve differentiation allows for more accurate determination of the start and end temperatures. It is necessary to pay attention to the possible low boiling point additives or residual solvents in polymer materials, and their volatilization temperature may overlap with moisture, which needs to be distinguished by material formulation or auxiliary methods.

Weightlessness interval	It is common at 50-150°C
Moisture characteristics	Broad and weightless
Volatile characteristics	It may be weightless for multiple steps
Data repeatability	Three parallel tests are recommended

Application examples

In plastics, rubber, coatings, and composites, this method is used to monitor the moisture content of raw materials, evaluate the drying process effect, and control product quality. For example, some engineering plastics with too high a water content may cause bubbles to form in processing; Too many volatiles in rubber may affect the vulcanization properties. Through regular testing, the material specification can be correlated with the process parameters.

Notes:

The test requires preparing samples in a dry environment to avoid interference from ambient humidity. For materials that are prone to oxidation, inert atmosphere protection is required. The instrument should be regularly maintained to ensure that the furnace is clean and the sensor is sensitive. The interpretation of the results should be combined with the known information of the material, and if necessary, it should be verified with moisture measurement methods such as the Karl Fischer method.

References

1. Application of thermal analysis technology in polymer materials, Journal of Materials Testing, 2020.
2. Standard method for thermogravimetric analysis of polymers, international standard ISO 11358.
3. Effect of Moisture on Polymer Processing, Polymer Science and Engineering, 2019.
4. Thermogravimetric Analyzer Operation and Calibration Guide, Instrument Technical Manual, 2021.