Thermogravimetric analyzer for measuring the thermal weight loss of PVC cables

With the continuous expansion of the application field of cable materials, the requirements for their thermal performance are also increasing. The development and quality monitoring of various new cable materials, from ordinary polyvinyl chloride (PVC) to high-performance cross-linked polyethylene, ethylene propylene diene monomer rubber, etc., cannot be separated from the support of thermogravimetric analysis technology. Thermogravimetric analysis technology, with its high sensitivity and quantitative ability, has become an important tool for analyzing the thermal behavior of polymer materials such as cable insulation layers and sheaths. The stability of cable materials is directly related to the safety and reliability of power transmission. In high-temperature environments, the thermal decomposition of materials may lead to a decrease in insulation performance and even cause fire accidents. Therefore, accurately evaluating the thermal weight loss characteristics of cable materials is of great significance.

1、 Experimental operation process

PVC, as a traditional cable sheath material, is representative. This experiment mainly observed the thermal decomposition behavior of cables through thermogravimetric analysis technology by testing PVC.

1. Experimental equipment:DZ-TGA201 Thermogravimetric Analyzer

2. Sample preparation: Use frozen grinding or accurate cutting to obtain small pieces of sample weighing approximately 10-20mg. A small sample size can easily lead to weak signals, while a large sample size may cause uneven heat transfer and insufficient pyrolysis. For multi-layer protected cables, layer by layer stripping tests are required to distinguish the material characteristics of each layer and avoid cross interference.

3. Experimental setup: Set the temperature range according to the material type. Conventional insulation materials use room temperature to 700 ℃, while high-temperature resistant materials can be extended to 1000 ℃; The heating rate is usually selected between 5-20 ℃/min. If the rate is too fast, it can lead to thermal hysteresis effect, while if it is too slow, it can reduce testing efficiency. Our PVC material is more suitable at a rate of 10 this time.

4. Atmosphere selection: A nitrogen atmosphere with a flow rate of 50ml/min is used to simulate thermal cracking behavior in an inert environment, while air or oxygen is used to evaluate the thermal oxidation properties. PVC testing experiments are usually conducted under nitrogen protection.

5. Experimental graph analysis:

Figure 1

PVC, as a traditional cable sheath material, exhibits a typical two-stage characteristic of thermal weight loss (Figure 1)

Stage 1 (room temperature - around 430 ° C): The weight loss rate of the experimental sample is about 21%, corresponding to the reaction of hydrogen hydride (HCI), with a decomposition temperature of around 300 ° C. A peak of di appears at around 320 degrees through the DTG curve. If used in conjunction with an infrared spectrometer, the released HCI gas can be detected by an infrared device as a characteristic absorption peak. This stage is also the reason for the yellowing and brittleness of the material due to the formation of conjugated sparse tight chain segments.

The second stage (around 430-700 °); The weight loss rate is about 77%, which is the further cracking of conjugated double bond segments, generating a large amount of small molecule products such as CO2 and methane, reaching the maximum weight loss rate at around 520 ° C. The use of TG-IR technology can analyze the infrared spectra of decomposition products, achieving more accurate identification of material composition. Zui has a residual amount of about 1%.

2、 TG-IR Combined Technology - In Situ Identification of Decomposition Products

For cable materials containing complex components or fillers, TG-IR combination can break through the limitations of single quality monitoring. For example, multi-layer rubber cable sheaths cannot be directly characterized by infrared spectroscopy due to the presence of a large amount of carbon black. Through TG-IR combination, it was found that the three-stage weight loss corresponds to different products: 15 minutes (200 ℃) release of CH ₂ groups (additive volatilization), 24 minutes (500 ℃) generation of methane and ethylene (main chain cracking), and 29 minutes (600 ℃) detection of CO ₂ (oxidation end product), successfully identifying the substrate as chloroprene rubber.

3、 Experimental conclusion

Thermogravimetric analyzer, with its accurate quality monitoring capability, has become a core tool for evaluating the thermal stability of cable materials. By analyzing the characteristic parameters of TG/DTG curves, the decomposition stages, heat resistance rating, and degradation mechanism of typical cable materials such as PVC, EVA, ETFE can be divided. The combined technology of TG-IR and TG-MS has further expanded the testing depth, enabling in-situ identification of decomposition products and trace components, providing molecular level evidence for formula optimization and failure traceability.