Pyrolysis–Gas Chromatography/Mass Spectrometry of Polymeric Materials

The following sections are included:

• Preface to the Second Edition
• About the Author
• Acknowledgments for the Second Edition
• Contents

The word pyrolysis, translated from the original Greek pyros = fire and lyso = decomposition, means a chemical transformation of a sample when heated at a temperature higher than ambient in an inert atmosphere in the absence of oxygen [1]. Pyrolysis can be divided into two types, applied pyrolysis and analytical pyrolysis [2]. Applied pyrolysis is concerned with the production of chemicals. When performed on a large scale, pyrolysis is involved in industrial processes as the manufacture of coke from coal and the conversion of biomass into biofuels. In contrast, analytical pyrolysis is a laboratory procedure in which small amounts of organic materials undergo thermal treatment. The pyrolysis itself is just a process that allows the transformation of the sample into other compounds. The pyrolytic process is carried out in a pyrolysis unit (pyrolyzer) interfaced with the analytical instrumentation.

Figure 2.1 illustrates a schematic diagram of a pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) measuring system with the direct connections of an oven pyrolyzer together with the temperature and pressure controller, a gas chromatograph (GC) equipped with a capillary separation column, and detection device using a quadrupole mass spectrometer (MS)…

Starting at the University of Cologne (Germany) in the 1960s, Hummel and co-workers studied the process of thermal decomposition of polymers in detail using Py–GC/MS and Py–GC/FTIR [9, 10]. In general, decomposition proceeds through radical formation, which, due to the high reactivity of radicals, initiates numerous consecutive and parallel reactions. The authors summarized the main pathways of polymer decomposition in four categories:

• retropolymerization from the end of the polymer chain, predominantly forming monomers (e.g. poly(methyl methacrylate) (PMMA), poly (α-methylstyrene));
• statistical chain scission followed by:
  • retropolymerization from radical bearing chain ends (e.g. poly-isobutylene (PIB), polystyrene (PS));
  • radical transfer and disproportionation (e.g. polyethylene (PE), isotactic polypropylene (PP)); and
  • stabilization of fragments by cyclization (e.g. polydimethylsiloxane (PDMS)).
• splitting side chain leaving groups (e.g. poly(vinyl chloride) (PVC), polyacrylonitrile, polyacrylates)); and
• intramolecular condensation reactions with loss of smaller molecules (e.g. phenol-epoxide resins)

Since the beginning of the 20th century a rapid development has taken place in the field of macromolecular chemistry, the end of which has not yet been foreseen. Polymeric commodities and specialty products are widely used in modern life. Today, there is a large number of plastics on the market which are compounded according to the application. All of these products are complex mixtures where compositions of both, the actual polymers and the additives, have been carefully fine-tuned to obtain the desired properties [47]. Additives include antioxidants, chemical stabilizers, bio-stabilizers, light-stabilizers, crosslinkers, lubricants, processing aids, impact modifiers, fillers, fire retardants, antistatic agents, optical brighteners, chemical propellants, and plasticizers. Additives can improve or modify the mechanical properties (fillers and reinforcements), modify the color and appearance (pigments and dyestuffs), give resistance to heat degradation (antioxidants and stabilizers), provide resistance to light degradation (UV stabilizers), improve the flame resistance (flame retardants), improve the performance (antistatic or conductive additives, plasticizers, blowing agents, lubricants, mold release agents, surfactants, and preservatives), and improve the processing characteristics (recycling additives) of polymers or copolymers [48–50]. Due to the large number of substances involved, the chemical identification of a plastic becomes a complex task. Detailed information of the chemical structure, molecular weight (MW) and the levels of the additives in the polymer is crucial for understanding and improving the properties of a product. It is for this reason that the development of analytical tools for such analyses has received a great deal of attention. The most important compositional parameters of polymeric materials are the composition of the polymer phase on the one hand, and of the additive package on the other hand [47]. Even for the simplest polymeric systems a full characterization is not trivial. Several distributions will generally be present in the polymer, i.e. distributions of chain length, degree of branching, end-groups, etc. For mixtures of homopolymers or for copolymers this is even more complex. Particularly difficult, but at the same time also highly relevant, is the determination of copolymer composition as a function of MW [47]…

Biomass is a complex material, mainly composed of cellulose, hemicelluloses, and lignin, in addition to extractives (tannins, fatty acids, resins) and inorganic salts. This renewable raw material is of great potential. It can be used for energy generation and for production of high-value chemicals. Biomass resources that can be used for energy production cover a wide range of materials such as forestry residues, energy crops, organic wastes, agricultural residues, etc. [144, 145]. The chemical structure and major organic components in biomass are extremely important in biomass pyrolysis processes. Knowledge of the pyrolysis characteristics of the three main components is the basis, and thus essentially important for a better understanding of biomass thermal chemical conversion. Fast pyrolysis, which is known as a promising process to convert pretreated biomass to bio-oil, is affected by the biomass types and reaction conditions. It is an effective method to convert biomass into high-value gaseous, liquid, and solid fuels. Because this biomass fast pyrolysis is an endothermic process and therefore requires an external energy input, considerable attention has been paid to reducing the energy consumption during the pyrolysis process [146].

The following sections are included:

• Reactive Pyrolysis
  • Thermally assisted hydrolysis and methylation
  • Silylation
  • On-line ultraviolet irradiation pyrolysis–GC/MS (UV/Py–GC/MS)
• Analytical Pyrolysis–Two-Dimensional Gas Chromatography/Mass Spectrometry (Py–GC × GC/MS)
• Pyrolysis–Gas Chromatography–Time-of-Flight Mass Spectrometry (Py–GC-TOF-MS)
  • Time-of-Flight Mass Spectrometry (TOF-MS)
  • Pyrolysis–GC × GC/HRTOF-MS
• Pyrolysis–Mass Spectrometry (Py–MS)
  • Analytical conditions
  • Portable pyrolysis–mass spectrometer

The applications of the analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) range from research and development of new materials, quality control, characterization and competitor product evaluation, medicine, biology and biotechnology, geology, airspace, environmental analysis to forensic purposes or conservation and restoration of cultural heritage. These applications cover analysis and identification of polymers/ copolymers and additives in components of automobiles, tires, packaging materials, textile fibres, coatings, adhesives, half-finished products for electronics, paints or varnishes, lacquers, leather, paper or wood products, food, pharmaceuticals, surfactants, and fragrances. In this chapter selected application examples of pyrolysis–GC/MS are described, which originate from the participation of the author (P. K.) in various research projects.

The following sections are included:

• Background Information
• Introduction to Analytical Pyrolysis–Gas Chromatography/Mass Spectrometry (Py–GC/MS)
• Apparatus in Analytical Pyrolysis
• Application of Analytical Pyrolysis–GC/MS
• Handout for the Instructor
• Handout for the Students
  • Materials
  • Equipment
  • Experimental procedure
  • Directions for students
• Results
• Report Form

Analytical Py–GC/MS has proved to be a valuable hyphenated technique for the analysis and identification of synthetic organic polymeric materials, their additives, and for the analysis of biopolymers. This technique allows the direct analysis of very small sample amounts (5–200 μg) without the need for time-consuming sample preparation or after a simple sample derivatization. Py–GC/MS can be applied to research and development of new materials, quality control, characterization and competitor product evaluation, medicine, biology, biotechnology, geology, airspace, and environmental analysis for forensic purposes or conservation and restoration of cultural heritage. These applications cover analysis and identification of polymers/copolymers and additives in components of automobiles, tires, packaging materials, textile fibres, coatings, adhesives, half-finished products for electronics, paints, varnishes, lacquers, leather, paper, wood products, food, pharmaceuticals, surfactants, and fragrances. Pyrolysis–GC/ MS allows the confirmation of the source of a failed product, the identification of contaminants causing failure, the competitive analysis, as well as overcoming a problem in product development or quality control. The obtained analytical results are then used for troubleshooting and remedial action of the technological process…

The following sections are included:

• References
• Appendix A
• Appendix B
• Appendix C
• Appendix D
• Index