Thermogravimetric Analysis (TGA) for Determining the Thermal Stability of Polyvinyl Chloride (PVC) Resin

Thermogravimetric Analysis of Resin

Polyvinyl chloride (PVC) resin, as a core variety of general-purpose plastics, is widely used in key areas such as building pipes, electronic and electrical insulation, and packaging materials. Its thermal stability directly determines the feasibility of product processing and its service safety. During high-temperature processing or long-term use, PVC is prone to dehydrochlorination chain degradation, leading to discoloration, embrittlement, and even failure. Therefore, accurately characterizing thermal degradation behavior is a core requirement for formulation optimization and quality control.

Thermogravimetric analysis (TGA) can monitor the quality changes of PVC under programmed temperature rise in real time, providing key parameters such as initial decomposition temperature and maximum degradation rate, providing a scientific basis for PVC resin research and development, stabilizer screening, and quality control in the production process.

I. Experimental Procedure

1. Measuring Instrument: TGA200 Thermogravimetric Analyzer

2. Sample Preparation Procedure: This experiment uses industrial-grade PVC resin as the test object, focusing on the optimization of TGA test conditions and the analysis of thermal degradation behavior.

2.1 Pretreatment: The PVC resin was dried in an 80°C drying oven for 4 hours to remove moisture interference.

2.2 Preparation Method: The sample was pulverized using a grinding machine and sieved to ensure uniform particle size.

2.3 Sample Amount: 10-20 mg of sample was weighed and placed in a ceramic crucible. Too large a sample amount would lead to uneven heat transfer, while too small a amount would result in a weak signal, affecting data accuracy.

3. Software Parameter Settings: Temperature, heating rate, and atmospheric environment were set through the equipment's operating software. Cut-off temperature: 700°C, heating rate: 20°C/min, nitrogen atmosphere throughout.

4. Spectral Analysis:

From the data in the above figure, we can see that the thermal degradation of PVC resin under a nitrogen atmosphere exhibits a typical two-stage characteristic:

1. Dechlorination Stage (200-350℃): Unstable chlorine atoms on the PVC molecular chain initiate a chain reaction, releasing HCl gas and forming a conjugated polyene structure. This stage accounts for approximately 70% of the total mass loss.

2. Main Chain Breaking Stage (300-700℃): The conjugated polyene structure further decomposes into low-molecular-weight hydrocarbon compounds, with the residue ultimately forming carbonaceous residue.

The DTG peak in the first stage (around 300℃) verifies the concentrated occurrence of the dechlorination reaction; coupled with infrared spectroscopy, the characteristic absorption peak of HCl can be detected. The peak broadening in the second stage indicates a more complex carbon chain degradation reaction. Furthermore, from this figure, we can also obtain the initial decomposition temperature of the PVC sample, i.e., Toneset, which is 246.83℃. The peak values ​​of the DTG curve correspond to the maximum degradation rate Tmax for each stage, with the maximum decomposition rate temperature being 303℃.

II. Experimental Conclusions

Thermogravimetric analysis (TGA), as a core technology for evaluating the thermal stability of PVC resin, can quantitatively characterize degradation stages, heat resistance levels, and reaction mechanisms by accurately analyzing the characteristic parameters of the TG-DTG curve. It effectively distinguishes the differences in thermal stability among PVC formulations. Even resins with similar appearances can be identified by the thermogravimetric analyzer through parameters such as initial decomposition temperature and maximum decomposition rate temperature, providing crucial support for production consistency and reliability control. Furthermore, by coupling TGA with infrared spectroscopy or mass spectrometry, the chemical mechanisms of PVC degradation can be further revealed, providing a microscopic basis for stabilizer molecule design.