Identification Analysis of Plastic Materials

Plastic products are manufactured using a variety of processing techniques and materials. It is practically impossible to identify a plastic material or product by a visual inspection or a simple mechanical test. There are many reasons that necessitate the identification of plastics. One of the most common reasons is the need to identify plastic materials used in competitive products. Defective products returned from the field are quite often put through rigorous identification analysis. Sometimes it is necessary to identify a finished product at a later date in order to verify the material used during its manufacture. The custom compounders of reprocessed materials may also need to identify already processed material purchased from different sources. Quite often, processors find substantial quantities of plastic material, hot stamp foils, and decals in the warehouse without any labels to identify the particular type. A little knowledge of the identification process can save time and money. 

On a rare occasion, the buyers of molded parts may choose to verify the material specified in the product by performing a simple identification analysis. The development of new material is another reason for such analysis. 

There are two ways plastic materials can be identified. The first technique is simple, quick, and inexpensive. It requires very few tools and little knowledge of plastic materials. The second approach is to perform a systematic chemical or thermal analysis. The latter technique is very complex, time-consuming, and expensive. The results can only be interpreted by a person well-versed in polymer chemistry. Plastic materials are often copolymerized, blended, and modified with filler or compounded with different additives such as flame retardants, blowing agents. 

Handbook of Plastics Testing and Failure Analysis, Third Edition, by Vishu Shah Copyright 2007 by John Wiley Sons, Inc. 

The results of the simple identification technique can be further confirmed by the following tests  

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As discussed in introduction section of this chapter, a complete and positive identification analysis of plastics materials is very complex and time-consuming task. 

Analysis of realistic aspects of fabrication and performance of plastic materials involves the combination of complex geometrical, material and physical factors. The identification of the material mechanisms responsible for a specific phenomenon requires the development of relatively complex numerical models which accommodate the critical factors. Once the model is in place, it is possible to simulate different material mechanisms and verify their predictions through a comparison with experimental results. 

The ehallenge in this analysis lies in the efficient extraction and analysis of the complex matrices in which PBDEs are found. The compounds are used in a variety of plastic materials found in consumer products, and samples are prepared typically using either Soxhlet extraction or microwave digestion, followed by few or no clean-up steps. MS/MS can be used to isolate M + and [M-2Br] + isotopic cluster ions for accurate identification and quantitation. Three stages of the MS/ MS analysis of a PBDE are shown in Eigure 15.43. Eigure 15.44 shows a TIC of the common PBDE isomers that are tested for under the RoHS regulations these common PBDE isomers are listed in Table 15.2. Excellent quantitative results... 

Infrared spectroscopy is a recognized standard method of analysis for characterization and identification, and for the measurement of composition of a wide range of materials. The infrared spectrum is a unique physical property of a molecular species, and the spectral information obtained can be correlated directly to the chemical structure of the material, and the underlying composition in the case of admixtures. Infrared spectroscopy is also one of the most widely utilized analytical methods for the identification and characterization of plastics and polymers. The first sections of this chapter have focused on the specific attributes of the technique as they relate to the analysis of polymeric materials. In this final section, the focus is on the more general and fundamental aspects of infrared measurements, and the methods used for the handling of plastics and polymers. 

Despite the success of these techniques with other spectroscopic data, very little has been published on their use with Raman data. The aforementioned work on postconsumer plastic identification by Allen et al. [43] utilized KNN for their analysis, although they present little of the actual classification results. Similarly, Krizova et al. [54] simply state that the SIMCA analysis of Norway spruce needles resulted in similar results to PCA and cluster analysis studies. More detail was given by Daniel et al. [52] when comparing KNN and ANN for analysis of exposive materials. 

DSC is thus a quick and reliable method of analysis, not only in material development, but primarily in the areas of quality assurance, raw material control and failure analysis. DSC is used for identification of incoming plastic materials e.g. HDPE/PA6 and LDPE/EVAL/PA6 composite film. DSC can not only identify the major components of polymers, but can also detect minor components such as adhesives, if these have a melting behaviour which differs from that of the polymers. Quality control of packaging film without sample preparation is based on the measurement of the solid/liquid phase transition of melting by means of DSC. Sass [175] has given various examples of quality assurance and defect analysis of plastics by DSC. There is increased demand for sensitivity and capability because of the growing complexity of materials. 

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... 

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. 

Si element ATR-FTIR spectroscopy was used to analyze this residue, and its spectrum, along with the closest library matches, are shown in Figure 41. The absorbance of this residue is low as a consequence of the thin layer present on the plate. This makes matching the sample spectrum with a reference spectrum somewhat difficult. The closest matches extracted from the library interrogated are to ester-based plasticizer materials, which is consistent with a phthalate-plasticized PVC. A more specific identification could have been made with further testing such as subjecting the residue to GC-MS analysis, but the information suggested by the ATR-FTIR analysis was, in this case sufficient. 

Liquid oral preparations are usually contained in PET or PETG containers. PETG has a different polymeric composition than PET as discussed under Types of Packaging Materials. Physical characteristics are listed in the USP and 21 C.F.R. specifies their composition. Identification of PET and PETG shows that these plastics are distinct and distinguishable from one another by IR spectrum, but the two compounds are similar as evaluated by thermal analysis.f " This type of plastic should be tested for colorant extraction as previously discussed. " ... 

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]. 

This handbook s primary aim is to provide the tools to help a bench chemist to obtain a more complete listing of additives present in a particular matrix. The techniques that we have been using successfully are described in this book to help the analyst to correctly identify the complex nature of the materials that have been added to the plastic. We provide information on analyzing polymers through thermal desorption, and the use of GC with a mass selective detector (MSD). Many compounds break apart either during extraction or analysis, so identification by key fragments, and typical moieties for the final compound is critical. The use of the GC/MS system allows the analyst to characterize a compound based on the utilization of these fragments or moieties. 

The (C)RM has to fulfil a defined task. Therefore, the material must be accurately chosen. The selection of the material itself is easy when pure substances for calibration or identification purposes are considered. For artificial materials such as manufactured products e.g. steel, alloys, plastics, ceramics etc., the manufacturing process may be the defining tool. Where natural matrix materials are concerned, the selection of the (C)RM passes through a careful study of the objective of the method to be validated. A method for contaminated soil analysis has to cover soils of various origin, the CRM(s) to validate... 

Determination of the residual antioxidant content in polymers by HPLC and MAE is one way to determine the amoimt needed for reasonable stabilization of a material, and also to compare different antioxidants and their individual efficiencies. During ageing and oxidation of PE, carboxyhc acids, dicarboxylic acids, alcohols, ketones, aldehydes, n-alkanes and 1-alkenes are formed [86-89]. The carboxyhc acids are formed as a result of various reactions of alkoxy or peroxy radicals [90]. The oxidation of polyolefins is generally monitored by various analytical techniques. GC-MS analysis in combination with a selective extraction method is used to determine degradation products in plastics. ETIR enables the increase in carbonyls on a polymer chain, from carboxylic acids, dicarboxyhc acids, aldehydes, and ketones, to be monitored. It is regarded as one of the most definite spectroscopic methods for the quantification and identification of oxidation in materials, and it is used to quantify the oxidation of polymers [91-95]. Mechanical testing is a way to determine properties such as strength, stiffness and strain at break of polymeric materials. 

Mr. Mldklff continues, "When a sample from a suspected arson is examined by gas chromatography, additional peaks from materials present at the scene, as for example, plastics, in the sample may be observed. These additional peaks make difficult pattern recognition, normally relied upon for detectlon/ldentlfIcation of flammable liquids in the debris. Similar problems may be encountered in the analysis of samples from a bomb scene where chemicals in soil or debris from the bomb crater complicate the detection and identification of explosive components. 

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