1. Material Identification: This primarily involves identifying types such as LLDPE, LDPE, HDPE, PP, PET, and PA bags. The specific plastic material can be determined by observing characteristics such as the bag's transparency and thickness.
2. Combustion Method: A flame is used to ignite the plastic packaging bag. The type of plastic is then identified based on the odor produced during combustion and the nature of the resulting residue. For instance, LLDPE and LDPE emit a burnt, aromatic scent when burned, whereas PP and PET produce no distinct odor.
3. Dissolution Method: A dissolution test is performed using specific corresponding solvents. For example, LLDPE, LDPE, and HDPE are soluble in dichloromethane; PP is soluble in trichloromethane; while PET is insoluble in common organic solvents.
4. Polarizing Microscopy: A polarizing microscope is used to distinguish between different plastics by observing phenomena such as birefringence and refraction. Low-density polyethylenes (such as LLDPE and LDPE) exhibit low birefringence and weak refraction; HDPE demonstrates strong refraction; while PET and PP possess relatively high refractive indices.
5. Density Determination Method: A balance and a volumeter are used to measure the density of various plastics. Typical density ranges are as follows: LLDPE (0.910–0.925 g/cm³), LDPE (0.910–0.940 g/cm³), HDPE (0.941–0.960 g/cm³), PET (1.33–1.39 g/cm³), and PP (0.89–0.91 g/cm³).
6. Infrared Spectroscopy Analysis: Infrared spectroscopy is employed to analyze different plastics. The characteristic infrared absorption peaks for LLDPE and LDPE are similar, with the absorption peaks at 2916 cm⁻¹ and 2848 cm⁻¹ appearing relatively broad and flat; conversely, the absorption peaks for HDPE are sharper; while the overall infrared spectra for PET and PP are comparatively more complex.
7. Chromatographic Analysis. Gas chromatography, liquid chromatography, and two-dimensional liquid chromatography are employed to perform qualitative and quantitative analyses of monomers and additives in finished plastic products, in order to identify the type of plastic and determine the additive content.
