Plasticisers polymer identification

Most polymers can be analysed as received, as pellets, powders, films, fibres, in solution, or even as whole articles such as mouldings. Fine fibres can present some difficulties if a Raman microscope is not available. Raman spectroscopy has found applications in the identification of polymers in which additives obscure the polymer peaks in the IR spectrum. Reclaimed polymer is more prone to fluorescence than virgin material, causing problems for Raman analysis [394], Laser-Raman spectroscopy often allows polymer identification (e.g. in recycled material) only in conjunction with IR spectroscopy. Raman spectroscopy has been used to examine weathered PVC plasticised with DOP, DOA and BBP for dehydrochlorination [395], Laser-Raman spectroscopy has also been proposed as a suitable method for precise detection of ageing deterioration of vinyl chloride resins containing plasticisers and fillers used as electrical wire and cable coatings [396]. 

More recently, the same author [41] has described polymer analysis (polymer microstructure, copolymer composition, molecular weight distribution, functional groups, fractionation) together with polymer/additive analysis (separation of polymer and additives, identification of additives, volatiles and catalyst residues) the monograph provides a single source of information on polymer/additive analysis techniques up to 1980. Crompton described practical analytical methods for the determination of classes of additives (by functionality antioxidants, stabilisers, antiozonants, plasticisers, pigments, flame retardants, accelerators, etc.). Mitchell... 

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... 

Cyclic oligomers of PA6 can be separated by PC [385,386] also PET and linear PET oligomers were separated by this technique [387]. Similarly, PC has been used for the determination of PEGs, but was limited by its insensitivity and low repeatability [388]. PC was also used in the determination of Cd, Pb and Zn salts of fatty acids [389]. ATR-IR has been used to identify the plasticisers DEHP and TEHTM separated by PC [390]. Although this combined method is inferior in sensitivity and resolution to modem hyphenated separation systems it is simple, cheap and suitable for routine analysis of components like polymer additives. However, the applicability of ATR-IR for in situ identification of components separated by PC is severely restricted by background interference. 

Applications Conventional TLC was the most successful separation technique in the 1960s and early 1970s for identification of components in plastics. Amos [409] has published a comprehensive review on the use of TLC for various additive types (antioxidants, stabilisers, plasticisers, curing agents, antistatic agents, peroxides) in polymers and rubber vulcanisates (1973 status). More recently, Freitag [429] has reviewed TLC applications in additive analysis. TLC has been extensively applied to the determination of additives in polymer extracts [444,445]. 

APCI-MS/MS is not only useful in the analysis of polymers, such as cellulose acetate, but is also of great value in the identification of copolymer substrates, and the various polymer additives such as antioxidants, stabilisers, and plasticisers. 

Applications Identification of polymer additives by TLC-IR is labour intensive and comprises extraction, concentration of extracts, component separation by TLC on silica, drying, removal of spots, preparation of KBr pellets and IR analysis. The method was illustrated with natural rubber formulations, where N-cyclohexyl-2-benzothiazyl sulfenamide, IPPD and 6PPD antioxidants, and a naphthenic plasticiser were readily quantified [765]. An overview of polymer/additive type compounds analysed by transfer TLC-FTIR is given in Table 7.80. 

Applications The general applications of XRD comprise routine phase identification, quantitative analysis, compositional studies of crystalline solid compounds, texture and residual stress analysis, high-and low-temperature studies, low-angle analysis, films, etc. Single-crystal X-ray diffraction has been used for detailed structural analysis of many pure polymer additives (antioxidants, flame retardants, plasticisers, fillers, pigments and dyes, etc.) and for conformational analysis. A variety of analytical techniques are used to identify and classify different crystal polymorphs, notably XRD, microscopy, DSC, FTIR and NIRS. A comprehensive review of the analytical techniques employed for the analysis of polymorphs has been compiled [324]. The Rietveld method has been used to model a mineral-filled PPS compound [325]. 

Fichtner and Giese [16] include plasticisers in their brief review of the application of LC-MS methodology to the identification of extractables from polymer materials. 

Griddle [43] has described a column chromatographic procedure for the identification and semi-quantitative determination of plasticisers in PVC. In this procedure the plasticiser is first Soxhlet extracted from 1 to 2 gram of PVC sample using anhydrous diethyl ether. Ether is then evaporated from the extract and residual traces of PVC precipitated by the addition of 2 ml of absolute ethanol. Following filtration of any polymer, the ethanol is finally evaporated off to provide a PVC free plasticiser extract. 

On the other hand, GC, because of the physical separation it effects, furnishes both a qualitative and a quantitative analysis of polymer-plasticiser mixtures with almost the same ease as the analysis of plasticisers alone, and this is discussed further in Chapter 5.1. It suffices to submit the sample, prepared as for the pyrolysis of plastics, to a controlled pyrolysis in order to disengage the vaporised plasticisers. The polymer is partially degraded, but its pyrolysis products were in all the cases studied by Guiochon and Hennicker [82] much lighter than the plasticisers and in no way prevented their separation and identification. Figure 4.18 shows the separation obtained of four plasticisers (a) dibutyl succinate, (b) tributyl phosphate, (c) dimethyl sebacate and (d) diethyl phthalate and the pyrolysis products of polyvinyl chloride. The latter are eluted during the first minute of operation. 

The analysis of plastics comprises the identification of the monomers which participate in polymer formation and of products of degradation reactions [49] and also the detection of plastic additives like plasticisers, stabilisers and catalysts. Any simple alcohols, aldehydes, ketones or fatty acids occurring amongst these may be detected with the TLC procedures described elsewhere in the relevant chapters of this book. 

IR spectroscopy may be used for detection of plasticisers in soft PVC cables [75], but does not distinguish clearly between the many possible di-alkylphthalates. With the advent of difference spectroscopy, identification of a plasticiser in a polymer no longer requires isolation of the additive. Identification can readily be made without separation if the polymer is known and a plasticiser-free spectrum is available. This was illustrated for di-2-ethylhexylsebacate in an acrylonitrile-butadiene copolymer [76]. IR can sometimes quantify plasticisers in solid plastic compositions without the need for extraction or dissolution steps. FTIR difference spectroscopy has also been used for quantitative analysis. Another example of difference spectroscopy is the case of two plastic films which differed in printability [77]. Difference mid-IR spectra of the surfaces of the two films in the 1600-1300 cm region revealed a stearate (and eventually a free acid, at 1720 cm ). Surface properties of... 

Other reported NIRS applications are the determination of micro-additives in PP pellets [260], of additive levels in masterbatches or shipments, of plasticisers in PVC, of moisture content in polyalky-lene glycol ethers [292], of rest monomer in polymers (e.g. PPO) [278], On-line monitoring of the moisture and lubricant levels on polyacetate fibre film using NIR reflectance measurement was reported [293], NIRS allows rapid identification of polymer dispersions and an accurate water content determination ( 0.2%). The method replaces the tedious gravimetric determination of the non-volatile solid content of dispersions according to DIN 53189. 

Some more specific polymer chemistry applications for TG-FTIR are solvent and water retention, curing and vulcanisation reactions, isothermal ageing, product stability, identification of base polymer type and additives (plasticisers, mould lubricants, blowing agents, antioxidants, flame retardants, processing aids, etc.) and safety concerns (processing, product safety, product liability, fire hazards) [357]. A wide variety of polymers and elastomers has been studied by TG-FTIR [353,358,359]. The potential applications of an integrated TG-FTIR system were discussed by various authors [346,357]. 

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