Application of Thermogravimetric-Fourier Transform Infrared (TG-FTIR) Coupling Technology in the Study of PP Pyrolysis
Tianjin Port East Technology Co., Ltd. Applied Analysis Department
Abstract
PP (polypropylene) is non-toxic and odorless, with low density. Its strength, stiffness, hardness, and heat resistance are all superior to those of low-density polyethylene, and it can be used at temperatures around 100°C. It possesses good dielectric properties and high-frequency insulation, and is not affected by humidity; however, it becomes brittle at low temperatures, is not wear-resistant, and is prone to aging. It is suitable for manufacturing general mechanical parts, corrosion-resistant parts, and insulating parts. Common organic solvents such as acids and alkalis have virtually no effect on it, making it suitable for tableware. Since PP remains in a high-temperature molten state during processing and molding, studying its thermal degradation mechanism is of considerable importance.
1. Experimental Methods
1.1 Samples and Instruments
PP (Polypropylene, granules, manufactured by Borealis, industrial grade)
FTIR-850
Heated gas cell and transfer line accessories
TG 209 F1 (Netzer, Germany)
1.2 Experimental Procedure Setup
1.2.1 TGA Settings
High-purity nitrogen gas at a flow rate of 30 ml/min
The thermal gravimetric analysis begins at 40°C (held for 1 minute), then rapidly increases to 180°C at a heating rate of 60°C/min, followed by a rise to 600°C at a rate of 20°C/min.
1.2.2 Temperature Settings for the Heated Gas Chamber and Conveyor Line
The temperature at the transmission line interface is 200°C
The conveyor belt temperature is 210°C
The temperature of the heated gas chamber is 210°C
1.2.3 FTIR-850 Setup
Resolution: 4 cm⁻¹; measurement range: 4000–400 cm⁻¹.
1.3 Experimental Methods
After venting for 30 minutes, enable continuous data acquisition in the FTIR-850 software with a 1-minute interval and select “Wait for trigger.”
Place a single PP pellet into the sample crucible and run the TGA and FTIR analyses according to the experimental procedure set out in Section 1.2.
2. Experimental Results and Discussion
Figure 1. TG curve and its first derivative curve
As shown in Figure 1, the thermal decomposition of PP in a N₂ atmosphere exhibits only one weight loss interval, with the temperature range for weight loss primarily occurring between 390 and 500°C. The DTG curve shows only one weight loss peak, and the thermal degradation rate reaches its maximum at approximately 470°C (18 min), indicating that the thermal degradation of PP occurs in a single step. FTIR can be used to study the gases generated during this thermal decomposition process.
Figure 2: FTIR spectrum of the gaseous products from the thermal degradation of PP at 18 min
At 18 min, the peak at 2965 cm⁻¹ reached its maximum, which is fully consistent with the DTG curve. As shown in Figure 2, a strong absorption peak appears near 2965 cm⁻¹, indicating the presence of CH₃⁻ (2963 cm⁻¹, 2879 cm⁻¹) and -CH₂⁻ (2928 cm⁻¹). An absorption peak characteristic of alkenes appears at 890 cm⁻¹; these two regions represent mixtures of various alkanes and alkenes, confirming the random chain-breaking degradation mechanism of PP.
As can be seen from the above results, the combined TG-FTIR technique is a useful tool for studying the thermal degradation behavior or mechanisms of polymers.