Identification of Common Plastics

Williams, R. S., Brooks, A. T, Williams, S. L., and Hinrichs, R. L. (1998). Guide to the identification of common clear plastic films. Society for the Preservation of Natural History Collections (SPNHC) Newsletter, 3, Pall 1998, 1. ... 

When all the components have been identified from the pyrogram of a polymer, the composition of the decomposition products can be determined, and moreover, useful conclusions about the structure and constitution of the original polymer can be drawn. In most cases, however, the chromatograms are quite complicated and only the most common components (if any) can be identified by comparison with known compounds or by the pyrolysis of well-defined polymers. These pyrograms are however still very informative as fingerprints suitable for the comparison and identification of the plastics. The component identification reaches near-perfection by cou-... 

The use of IR spectroscopy for the identification of plasticisers was discussed in Section 2.4. Separation by SEC is often required to confirm the use of polymeric plasticisers. Most of the common plasticisers for plastic materials can be detected and analysed either by GC-MS or LC-MS. Complex plasticisers such as epoxidised soya bean oil can be fully characterised by LC-MS using chromatography in hexane/propionitrile with detection by positive ion APCI. 

The uses of IR spectra in identification, classification and mechanistic studies have been well documented. Tests for the identification of plastics utilized in Naval ordnance weaponry are discussed in Ref 21. Correlations between polymeric structure and ablative properties using IR spectroscopy have been obtained by monitoring changes in functional group absorption,properties.(Ref 12). The application of IR spectroscopy to the detection of more than 40 of the most common constituents of primers, tracers, igniters, incendiaries,... 

Analytical pyrolysis is used frequently in practice for qualitative identification and for obtaining quantitative or semiquantitative information on samples containing polymers, either synthetic or natural. However, most of this work remains unreported in peer reviewed literature but is rather common in industrial laboratories. Since the objects made from plastic or elastomers are typically insoluble or not easily analyzed by other techniques, analytical pyrolysis is very successful in this type of analysis [11]. The very small amount of material necessary for pyrolysis also allows in many cases performance of the analysis without the destruction of the object to be investigated. Qualitative and quantitative work includes applications for the identification of unknown samples and also for quality control purposes, evaluation of starting materials, evaluation of finished products, reverse engineering and competitor s product analysis, etc. [1]. Among other applications, Py-GC/MS can be used to quantitatively differentiate between natural and synthetic organic materials [12]. 

The emphasis of this work is on the analysis of plastic additives through gas chromatography/mass spectrometry (GC/MS). GC/MS systems are a common analytical tool in quality control and analytical service laboratories and electron impact (El) mass spectra are recognized as reliable data for the identification of organic compounds. Traditional methods have employed a flame ionization detector (FID) with identifications based solely on GC retention time data. These methods lack the specificity necessary to distinguish between components attributable to the sample matrix or the additive(s). 

Plasticizers, often phthalic acid and dialkylphthalates, are common contaminants, especially in small-scale work, and are very diffficult to avoid as they are common additives m polymerization processes used in the manufacture of plastic vessels and tubing that may be used during an extraction. An example of this was the identification of a compound widely used as a light stabilizer in plastics, Tinuvin 770 (Scheme 3), as a potent L-type calcium channel blocker... 

It has already been mentioned that a large number of components are used for the construction of wood-based furniture. In addition to the compounds described earlier, a large spectrum of volatile organics can be found in emission studies (Salthammer, 1997b). The main sources for formaldehyde (which is not considered here), phenol and acetic acid are substrates such as particle board and MDF. BHT is a common antioxidant. Volatile plasticizers include dimethyl phthalate (DMP), dibutyl phthalate (DBP), as well as esters of adipic acid and sebacic acid. Further important compound groups are amines, siloxanes, carboxylic acids and naphthalenes. The identification of special substances does not only require suitable analytical equipment. Both experience and detailed knowledge of the chemical composition of furniture are also necessary. 

Polyethylene and polypropylene are the polyolefins most commonly used as plastics. Polybutene-1 and poly-4-methylpentene-l are less common. Also important are certain copolymers of ethylene and also polyisobutylene, which is used for gaskets. The simplest method of identification of these materials is by infrared spectroscopy (see Section 8.2). However, some information can also be obtained from the melting range (see also Section 3.3.3) ... 

These fibres have few surface features and a circular cross-section - see Fig. 13.12(a) and (b). However, these features cannot be used as the sole basis for identification. In common with other man-made fibres, such characteristics may be influenced by the temperature of extrusion, the viscosity of the spinning solution or pressure exerted by processing equipment, depending upon the degree of plasticity in different stages of production. Fine marks and striations may therefore be visible on the surface of all such fibres. ... 

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