GB/T 7131-2026Plastics - Identification of polymers - Pyrolytic gas chromatography (English PDF)

6.2 Pyrolysis Unit

6.2.1 Hot filament pyrolyzer It is constructed from a spiral tube made of platinum or nickel heating wire. The sample can be placed directly on the spiral heating wire, or it can be placed inside a quartz tube and then... The pyrolysis tube is placed in a spiral tube. The maximum pyrolysis temperature is not lower than 800°C, and the heating temperature accuracy is better than 5°C.

6.2.2 Tubular Furnace Cracker It consists of a quartz tube heated by an external heating wire. The maximum pyrolysis temperature is not lower than 800°C, and the heating temperature accuracy is better than 5°C.

6.2.3 Curie Point Cracker It consists of a Curie-point high-frequency induced heating element. Ferromagnetic materials are used as the heating element; the pyrolysis temperature varies depending on the material of the Curie-point heating foil. Depending on the degree, the highest pyrolysis temperature is not lower than 800°C, and the heating temperature accuracy is better than 5°C.

6.3 Gas Chromatograph

6.3.1 Composition of Gas Chromatograph It consists of a vaporization chamber (inlet), a column oven, a detector, a data processing system, and a column.

6.3.2 Vaporization chamber (sample inlet) Split/non-split vaporization chamber, maximum operating temperature not lower than 350°C, temperature accuracy better than 1°C. Carrier gas pressure adjustable, pressure accuracy not... Greater than

0.1 kPa.

6.3.3 Chromatography column oven It can perform programmed heating, with a heating temperature adjustable from at least 30°C to 350°C, and a temperature control accuracy better than 0.1°C; the heating rate is at least... Adjustable within the range of 1°C/min to 20°C/min.

6.3.4 Detector The flame ionization detector (FID) has a maximum operating temperature of 350°C and a temperature accuracy better than 1°C. Some plastics produce large amounts of permanent gases during pyrolysis. For example, the pyrolysis of polyvinyl chloride produces large amounts of hydrogen chloride, and the pyrolysis of polycarbonate produces large amounts of hydrogen chloride. The reaction produces a large amount of carbon dioxide, and these permanent gases do not respond to FID, therefore they cannot be detected by FID. If you want to detect... For measuring these permanent gases, other detectors such as thermal conductivity detectors (TCDs) are preferable.

6.3.5 Data Processing System It can acquire the detector signal and automatically calculate the retention time and peak area of the chromatographic peak.

6.3.6 Chromatographic Column Capillary column, stationary phase. 100% polydimethylsiloxane, or 5% diphenyl-95% dimethylpolysiloxane, or 5% diphenyl... 1% vinyl (94%) dimethyl polysiloxane can effectively separate the main components in plastic pyrolysis products. A column length of 25m is typically chosen. For nonpolar or weakly polar capillary columns up to 50m in length, a 30m nonpolar or weakly polar capillary column is recommended.

7.1 Sample Pretreatment

7.1.1 If the sample contains a large amount of low-molecular-weight organic additives or low-molecular-weight filler oils, and interferes with the separation and determination of plastic pyrolysis products... Therefore, an appropriate solvent should be used to extract and separate the sample to remove interfering substances. The extraction solvent should not dissolve the plastic.

7.1.2 The extraction method should be selected from Soxhlet extraction or heating and reflux, etc.

7.2 Analysis Conditions

7.2.1 The thermal decomposition temperature is 500°C~700°C, and 600°C is preferred.

7.2.2 If the pyrolysis unit is connected to the gas chromatography vaporization chamber (inlet) via a transfer line, the transfer line temperature should be selected as 250°C~320°C.

7.2.3 The temperature of the gas chromatograph vaporization chamber (injector) shall not be lower than 300°C, and the detector temperature shall not be lower than 300°C. The column temperature shall be programmed. Temperature should be increased gradually, and different temperature programs should be selected according to the column length. When using a 30m weakly polar and nonpolar capillary column, typical... The analytical conditions for the type are shown in Table

1.Specific examples of analytical conditions and corresponding spectra are shown in Appendix A and Appendix B.

7.3 Establishment of Chromatograms for Known Plastic Pyrolysis Products

7.3.1 Power on the instrument and set the pyrolyzer and gas chromatograph according to the analysis conditions (7.2).

7.3.2 Depending on the type of pyrolysis device, take

0.01 mg to

0.1 mg of known plastic and place it in a pyrolysis device-specific sample tube/sample boat/sample cup. Alternatively, the sample can be directly coated onto a heating wire or heating plate and then placed in a pyrolysis apparatus for pyrolysis. The pyrolysis residue after gas chromatography separation is then detected. The product was obtained by chromatographic analysis of the pyrolysis products of the plastic. Note

1.Excessive sample volume can overload the chromatographic column, affecting the separation of pyrolysis products. Excessive pyrolysis products may also cause system contamination. Note

2.During the sampling process, the tools, gloves, glass wool, sample tubes/sample boats/sample cups used may be contaminated. It is recommended to perform a blank test to check for contaminants.

7.3.3 Without adding a sample, run the pyrolysis unit and gas chromatograph to remove the sample pyrolysis products remaining in the system from the experiment in 7.3.2. The high-boiling-point components were removed until the chromatographic baseline was smooth with no residual peaks.

Note. The thermal decomposition of plastics produces high-boiling-point components that may remain in the system and flow out with the next sample analysis, interfering with the decomposition chromatogram.

7.3.4 Repeat

7.3.3 to retest the known plastic until the chromatogram of the pyrolysis products is consistent.

7.3.5 If it is necessary to determine the major pyrolysis products, gas chromatography-mass spectrometry can be used to identify the major pyrolysis products, or comparison with standard samples can be used. The main pyrolysis products were analyzed.

7.3.6 Establish chromatograms of the thermal decomposition products of known plastics. The main characteristic products of plastic thermal decomposition are shown in Appendix A.

7.3.7 Identification of unknown plastics based on chromatograms of pyrolysis products and key characteristic products. Chromatograms of thermal pyrolysis products and corresponding key characteristic products for some plastics. Characteristic products are shown in Appendix B and Appendix C.

7.4 Detection of Unknown Samples Under the same analytical conditions,

0.01 mg to

0.1 mg of sample was placed in a pyrolyzer for pyrolysis, and the pyrolysis products were separated by gas chromatography. The chromatograms of the pyrolysis products of the unknown sample were obtained through detection. Note

1.Excessive sample volume can overload the chromatographic column, affecting the separation of pyrolysis products. Excessive pyrolysis products may also cause system contamination. Note

2.Excessive sample volume can alter the peak shape of the chromatogram of the pyrolysis products, making comparison with known plastic pyrolysis products difficult and affecting the analysis of unknown samples. Identification.

7.5 Identification of Unknown Samples The unknown plastic is identified by comparing its chromatogram with that of known plastics. The comparison method is as follows:

---Identification of unknown plastics based on the distribution characteristics of the chromatograms of the main pyrolysis products, i.e., the relative intensity of the main products;

---Based on the retention time or relative retention time of the main pyrolysis products, the composition of the main products is determined, and the unknown plastic is identified. Note

1.The chromatograms of pyrolysis products may vary depending on the type of pyrolyzer. Note

2.For copolymer plastics and products, the relative strength of the pyrolysis products of the same copolymer plastic will vary due to the different contents of polymer monomers in the copolymer plastic. Note