Polymers identification

Identification of the chemical nature of a plastics sample is a problem facing processors and users of 

Infrared spectroscopy is a major tool for polymer and rubber identification [11,12]. Infrared analysis usually suffices for identification of the plastic material provided absence of complications by interferences from heavy loadings of additives, such as pigments or fillers. As additives can impede the unambiguous assignment of a plastic, it is frequently necessary to separate the plastic from the additives. For example, heavily plasticised PVC may contain up to 60% of a plasticiser, which needs to be removed prior to attempted identification of the polymer. Also an ester plasticiser contained in a nitrile rubber may obscure identification of the polymer. Because typical rubber compounds only contain some 50% polymer direct FUR analysis rarely provides a definitive answer. It is usually necessary first 

Rapid identification of plastics by spectroscopic and x-ray methods were reviewed [17]. Several books are available [2,11]. 

Applications Rapid industrial polymer identification systems have been developed to sort plastic components in cars, plastics used in the building and construction industry and plastic films. In recycling of plastics 

Identification and sorting of plastics in waste materials were reviewed [19,31]. Garbassi [32] has stressed the important role played by polymer analysis and characterisation in plastics recycling. 

Polymer identification starts with a series of preliminary tests. In contrast to low molecular weight organic compounds, which are frequently satisfactorily identified simply by their melting or boiling point, molecular weight and elementary composition, precise identification of polymers is difficult by the presence of copolymers, the statistical character of the composition, macromolecular properties and, by potential polymeric-analogous reactions. Exact classification of polymers is not usually possible from a few preliminary tests. Further physical data must be measured and specific reactions must be carried out in order to make a reliable classification. The efficiency of physical methods such as IR spectroscopy and NMR spectroscopy as well as pyrolysis gas chromatography makes them particularly important. 

Behavior in an open flame can easily be observed by holding about 0.1. .. 0.2g of sample with a suitable implement in the outer edge of a small Bunsen flame. 

To test behavior during dry heating, about O.lg of the sample is carefully heated in a 60 mm long glow tube with a diameter of 6 mm over a small flame. If heating is too vigorous, the characteristic phenomena can no longer be observed. 

Depolymerization is a special case of thermal degradation. It can be observed particularly in polymers based on a, a -disubstituted monomers. In these, degradation is a reversal of the synthesis process. It is a chain reaction during which the monomers are regenerated by an unzipping mechanism. This is due to the low polymerization enthalpy of these polymers. For the thermal fission of polymers with secondary and tertiary C-atoms, higher energies are required. In these cases elimination reactions occur. This can be seen very clearly in PVC and PVAC. 

Depolymerization is in functional correlation with the molecular weight distribution and with the type of terminal groups which are formed in chain initiation and chain termination. 

Infrared spectroscopy can be applied to V. the characterization of polymeric materials at various levels of sophistication. As most commonly used, it is a rapid and easy method for the qualitative identification of major components through the use of group frequencies and distinctive patterns in the fingerprint region of the spectrum. Let s look at a couple of examples. 

When we look at the spectrum of a-PMMA we find bands that are associated with aliphatic CHj and CF groups in the CH stretching and fingerprint regions, but the dominant feature is the presence of the carbonyl stretching vibration at about 1720 

Source K. J. Saunders, Organic Polymer Chemistry, Chapman and Hall (1976).  

Paul Hogan and Robert Banks (Source ConocoPhillips). 

FIGURE 7-22 Infrared spectra in the C-H stretching region (Redrawn from the original spectrum reported by J. J. Fox and A. E. Martin Proc R. Soc, London, A, 175,208 (1940)). 

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Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

Polymer identification 30 2.5 Class-specific polymer/additive analysis. 47... 

Lussier [71] has given an overview of Uniroyal Chemical s approach to the analysis of compounded elastomers (Scheme 2.2). Uncured compounds are first extracted with ethanol to remove oils for subsequent analysis, whereas cured compounds are best extracted with ETA (ethanol/toluene azeotrope). Uncured compounds are then dissolved in a low-boiling solvent (chloroform, toluene), and filler and CB are removed by filtration. When the compound is cured, extended treatment in o-dichlorobenzene (ODCB) (b.p. 180 °C) will usually suffice to dissolve enough polymer to allow its separation from filler and CB via hot filtration. Polymer identification was based on IR spectroscopy (key role), CB analysis followed ASTM D 297, filler analysis (after direct ashing at 550-600 °C in air) by means of IR, AAS and XRD. Antioxidant analysis proceeded by IR examination of the nonpolymer ethanol or ETA organic extracts. For unknown AO systems (preparative) TLC was used with IR, NMR or MS identification. Alternatively GC-MS was applied directly to the preparative TLC eluent. 

It is quite clear from Schemes 2.1-2.5 that in rubbers polymer identification and additive analysis are highly interlinked. This is at variance to procedures used in polymer/additive analysis. The methods for qualitative and quantitative analysis of the composition of rubber products are detailed in ASTM D 297 Rubber Products-Chemical Analysis [39]. 

Environment Polymer identification additive risk assessments... 

Qian, K. Killinger, W.E. Casey, M. Nicol, G.R. Rapid Polymer Identification by In-Source Direct Pyrolysis Mass Spectrometry and Library Searching Techniques. Anal. Chem. 1996, 68, 1019-1027. 

Spencer LM, Heskins M, Guillet JE (1976) Studies on the biodegradability of photode-graded polymers identification of bacterial types. In Sharpley JM, Kaplan AM (eds) Proc 3rd Int Biodegrad Symp. Appbed Science, London, p 753... 

Elastomeric components and compositions in BR/SBR and NR/BR/SBR blends have been studied by 13C solid-state NMR. The MAS spectra are of sufficient quality for polymer identification of the carbon black filled vulcanisates in most cases [51]. 

Fiber analysis Polymer identification and testing (chemistry)... 

One can also use solution and solid state NMR spectroscopy in a similar manner to identify polymers (there are plenty of examples coming up shortly). But we do not want to give the impression that the identification of polymers, and especially copolymers, is as easy as we have implied in the simple infrared example shown in Figure 7-21. There are many subtleties and many industrial scientists have made a career specializing in polymer identification. However, this is enough for our purposes here and we now move on to the characterization of polymer microstructure. 

The intention of the author was to provide information on pyrolysis for a wide range of readers, including chemists working in the field of synthetic polymers as well as for those applying pyrolysis coupled with specific analytical instrumentation as an analytical tool. Some theoretical background for the understanding of polymer structure using analytical pyrolysis is also discussed. The book is mainly intended to be useful for practical applications of analytical pyrolysis in polymer identification and characterization. 

Polymer chemistry is an important branch of science, and polymer analysis and characterization is a common subject in scientific literature. Analytical pyrolysis is one of many tools used particularly for polymer identification and for the evaluation of polymer thermal properties. Before a more in-depth discussion on analytical pyrolysis and its application to polymer science, some basic concepts regarding the chemistry of synthetic polymers will be briefly discussed. 

The characterization of polymer chemical composition is important in numerous practical applications. The polymer identification can be done using various techniques. One of them is the chemical method, which involves reagents that are able to react with the polymer. Oxidation, for example using periodic acid or lead tetraacetate, can be applied to polymers containing 1,2 diol groups, ozonolysis can be applied to polymers containing double bonds, hydrolysis can be applied to esters and amides [4]. 

More frequently than chemical techniques, the spectroscopic methods of analysis are used for the determination of polymer chemical composition. Among these techniques the use of infrared (IR) absorption spectra as fingerprints for polymer identification is probably the most common. The IR absorption is produced tjy the transition of the molecules from one vibrational quantum state into another, and most polymers generate characteristic spectra. Large databases containing polymer spectra (typically obtained using Fourier transform infra-red spectroscopy or FTIR) are available, and modern instruments have efficient search routines for polymer identification based on matching an unknown spectrum with those from the library. For specific polymers, the IR spectra can reveal even some subtle composition characteristics such as interactions between polymer molecules in polymeric blends. 

Raman spectroscopy, which measures the vibrational satellites generated when the polymer is irradiated with an intense monochromatic light such as a laser, also can be used for polymer identification. Since IR absorption of the polymer is difficult to study in water solutions because of the strong IR absorption of water, Raman spectroscopy is particularly useful for the study of polymer water solutions. 

Analytical pyrolysis can be coupled with different analytical techniques for providing information on polymers. Among analytical pyrolysis techniques, Py-GC and Py-GC/MS are probably the most common. The pyrolysis process typically generates a very complex mixture of molecules. For this reason, a chromatographic technique is very important for the separation of pyrolysate components. The fingerprint generated by Py-GC can be used for polymer identification. However, the detection associated with compound identification provided by GC/MS is invaluable in many applications. The exceptional sensitivity and identification capability of mass spectrometric analysis make Py-GC/MS technique the most important analytical pyrolysis technique. 

From the composition of pyrolysate, it is usually possible to determine the nature of the polymer or copolymer that generated the pyrolysate. This capability is discussed for many particular cases in Part 2 of this book. However, polymer identification is not the only application used for analytical pyrolysis. Depending on the purpose of the analysis, the minor components in the pyrolysate can be important or not. For example, when the only goal of the analysis is the polymer identification, the main peaks in the pyrogram are the only ones that need to be identified. For other purposes, such as for the search of potentially harmful compounds, a more detailed analysis is required. 

These cumulative spectra provide information for polymer identification and can generate some structural hints. The search can be done on the special library or on regular mass spectra libraries (e.g. NIST 2002 or Wiley 7). For the cumulative spectrum of polyethylene pyrolysate, the regular mass spectra library indicates a long chain alkene and for poly(ethylene glycol) indicates bis(2-ethoxyethyl) ether, pointing to the dominant structure in the pyrolysate. However, the use of cumulative spectra is very limited in practice. 

An important aspect of the use of analytical pyrolysis is its capability to provide complementary information to other analytical techniques used for polymer characterization. One such technique is IR analysis of polymers. Although IR spectra can be used as fingerprints for polymer identification, the success of this technique can be questionable when the polymer is not pure or is in a mixture with other compounds. The IR spectra are particularly difficult to use when a polymer is present only at a low level in a particular material and cannot be easily separated. The use of Py-GC/MS allows identification of polymers even in low concentration in specific mixtures because it couples pyrolysis with a chromatographic technique. On the other hand, some polymers generate by pyrolysis a low proportion of easily identifiable molecules, producing mainly char and small uncharacteristic molecules such as HF, H2O, CO2, etc. In these cases, IR is the technique of choice. Since for an unknown sample each technique can be misleading, the use of both types of information is always beneficial. 

Analytical pyrolysis has a number of characteristics that can make it a very powerful tool in the study of polymers and composite materials. The technique usually requires little sample and can be set with very low limits of detection for a number of analytes. For Py-GC/MS the identification capability of volatile pyrolysate components is exceptionally good. A range of information can be obtained using this technique, including results for polymer identification, polymer structure, thermal properties of polymers, identification of polymer additives, and for the generation of potentially harmful small molecules from polymer decomposition. In most cases of analysis of a polymer or composite material, the technique does not require any sample preparation, not even solubilization of the sample, which may be a difficult task for the type of materials analyzed. The analysis can be easily automated and does not require expensive instrumentation (beyond the cost of the instrument used for pyrolysate analysis). 

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