Gas Chromatography in Analysis of Polymers and Rubbers

This chapter gives an overview of gas chromatography (with mass spectrometry) (GC/MS) of polymers and rubbers. Gas Chromatography (GC) analyzes volatile organic compounds, with an upper limit of 350°C, which means that the compounds to be analyzed must be volatile below this temperature. The technique is able to analyze small quantities of material, which means that it is applicable for example to residual monomers, initiators, catalysts, some additives and degradation products of polymers. It is generally not suitable for analysis of organic compounds at high molecular weight or of low volatility. Care must be taken not to analyze reactive species, which may ruin columns or other parts of the equipment. Proper sample preparation is necessary before GC/MS. Sensitive and selective techniques are used to separate and extract low-molecular-weight organic compounds from polymers. The sample preparation–extraction techniques may be grouped into (1) solvent extraction from solid matrices, (2) solvent extraction of organic compounds from aqueous solutions containing polymer (e.g. biomedical implants in physiological buffers) and (3) solvent-free extraction methods. An ideal extraction method is quantitative, selective, rapid and uses little or no solvent. Soxhlet is the old and traditional method for solvent extraction from solid sample matrices. Soxhlet is, however, time-consuming (two or three days is not uncommon), nonselective, uses large volumes of solvents and is often not quantitative. Ultrasonication and microwave-assisted extraction (MAE) are instead much more effective. Ultrasonication works by agitating the solution and producing cavitation in the liquid. The technique is useful for example to extract antioxidants from polyethylene (PE). MAE, extracts (semi)volatiles from solid matrices and has been successfully used to extract additives from polyolefins, aroma and flavor compounds from recycled polymers, and oligomers from poly(ethylene terephthalate) (PET). Solvent extractions from aqueous solutions are liquid–liquid extraction (LLE) and solid-phase extraction (SPE). LLE is rapid, but lacks in selectivity, is labor intensive and uses large volumes of organic solvents. SPE is instead suitable for separating volatile and semivolatile compounds and is a physical extraction process involving liquid and a solid phase (sorbent). Examples of separations are degradation products of PE and hydroxyacids in buffer solutions. Solvent-free extraction methods are headspace gas chromatography (HS/GC), solid-phase microextraction (SPME) and supercritical fluid extraction (SFE). HS/GC determines volatile compounds in liquids and solids. SPME is an inexpensive, rapid and solvent-free technique with applications reported for air samples, water and soil, based on 1-cm long, thin fused silica fiber coated with a polymeric stationary phase mounted in a modified syringe. The stationary phase is available in four different kinds. SFE uses a supercritical fluid to penetrate a material. Applications are antioxidants in polyolefins, aroma vapors absorbed in PE and surface coatings and their raw materials. This article reports applications in synthesis-related compounds in polymers, HS (headspace) analysis of polymers in indoor environments, thermal degradation products of polymers at processing temperatures, environmental degradation products, and additive systems in plastics and coatings.