There are two main methods for instrumental analysis of plastics:
I. Infrared Spectroscopy – Instrumental Analysis Method for Plastics
Infrared spectroscopy is used to detect organic compounds. When light emitted by an infrared spectrometer shines on the surface of the object being tested, the organic compound absorbs the emitted infrared light, producing an infrared spectrum. Since each organic compound has its own specific infrared absorption spectrum, infrared spectroscopy is a powerful tool for qualitative analysis. Infrared spectroscopy can also be used for quantitative analysis, based on the Lambert-Beer law. Examples include analyzing and identifying the types of plastics, determining their chain structure, studying orientation effects during plastic processing, and investigating reactions. Quantitative analysis using infrared spectroscopy is widely used in polymer research, such as determining the content of additives or impurities in samples, determining the composition of copolymers or blends, analyzing polymer grafting and crosslinking degrees, and measuring the consumption of raw materials and the formation rate of products during polymer reactions.
Infrared spectroscopy is an ideal method for identifying polymers due to its simplicity and highly characteristic spectra. It can also be used to distinguish between different types of plastic films.
II. Gas Chromatography – Instrumental Analysis Method for Plastics
Gas chromatography (GC) is a chromatographic method that uses gas as the mobile phase. It is a powerful tool for analyzing and measuring low-boiling-point organic compounds and permanent gases. GC has high sensitivity when detecting the content of different additives in plastic products. Commonly used detectors include electron capture detectors (ECD) and flame ionization detectors (FID). However, both of these detectors are susceptible to contamination by organic matter, resulting in significant variations in sensitivity. This necessitates rigorous sample pretreatment.
