Determination of Polymer Additives

H. J. Goites, B. M. Bell, G. D. Pfeiffer and J. D. Graham, Multidimensional chromatography using on-line coupled microcolumn size exclusion cliromatography-capillary gas chromatography-mass spectrometry for determination of polymer additives , J. Microcolumn Sep. 1 278-288. (1989)... 

Kawamura, Y. Watanabe, Z. Sayama, K. Takeda, Y. Yamada, T. Simultaneous determination of polymer additives in polyethylene by GC/MS. Shokuhin Eiseigaku Zasshi 1997, 38, 307-318. 

There are many publications showing the applications of SFE to the determination of polymer additives. Antioxidants such as Irganox 2246, BHT and others, as well as UV stabilizers such as Tinuvin P, have been effectively extracted with supercritical CO2. Extraction conditions varied from 15 to 25 MPa at 60°C and with a total time of 30 min [1], If microwaves are applied to extract these compounds, a mixture of sol-... 

HPLC is widely used in the chemical and plastics industries. Applications in the chemical industry are quite similar to those for testing pharmaceutical ingredients. They include assay and purity testing of synthetic chemicals such as raw materials, precursors, monomers, surfactants, detergents, and dyes.27,28 In the plastics industry, GPC is used for polymer characterization in product research and quality control. RPC is used in the determination of polymer additives. 

Analytical determination of polymer additives is sometimes complicated, as evaporation of volatile fractions and degradation can occur simultaneously. Py-GC/MS has shown the potential to separate and finally identify volatiles in liquid polymers or oils, which are usually charged with additives. The onset temperature of thermal degradation of a liquid polymer and the characteristics of the pyrolysis at higher temperatures can be assessed by studying the volatiles produced. However, this approach requires that the true thermal degradation products be identified and not just any components that are simply evaporated from the sample. An innovative method, called the temperature-sequence GC method, was proposed. 

Identification and eventual determination of polymer additives is an important issue in many fields, mainly in the area of packaging materials where additive migration from food contact materials may have potential toxic effects in humans.In biomedical applications, plasticizers present in the polymer [e.g., Di(2-ethylhexyl) phthalate (DEHP) in PVC] will readily leach into the liquids passing through it, particularly for lipid-containing fluids, e.g., blood. There is a great concern about the toxicity of DEHP, especially for risk groups such as... 

There are several techniques that can be used for the determination of polymer additives after extraction ... 

Lutzen and co-workers [28] describe an in-line monitoring, UV method for the determination of polymer additives such as thermal and UV stabilisers and antioxidants in polymers. 

Some other applications of polarography to the determination of polymer additives and catalyst remnants are reviewed in Table 2.14. 

Determination of polymer additives (or other low molecular weight, non-polymeric substances) in polymers, as discussed next... 

Dionex Corporation, in an application note on its series 600-D SFC, describe a method for the determination of polymer additives. The possibilities of SFC for determining polymer additives have been recently demonstrated [90-101]. The low elution temperature and high resolution of capillary fluid chromatography makes this technique very attractive. Other advantages are that a FID can be used and that interfacing with spectroscopic detectors is somewhat easier than with HPLC. Quantitation in capillary SFC has been found to be more difficult than in HPLC and capillary gas chromatography, however, because of lack of precision in injection [97]. 

The application of derivative spectroscopy to the determination of polymer additives has also been reported, cfr. also Table 6.37. A typical case is that of the phenolic antioxidants 2,6-di-/ert-butyl-4-methylphenol (AO-4K) and 4-substituted 2,6-xylenol (Chemantox AO-49), which exhibit virtually identical UV spectra [130]. However, the antioxidants can be distinguished in alkaline medium due to a bathochromic phenol-phenolate shift. The use of derivative spectroscopy reduces light scattering and matrix interferences when extracts from PP samples are measured. The use of derivative spectroscopy eliminates those interference phenomena which cause inaccuracies when evaluating direct absorption spectra. Shlyapnikov et al. [147] have used derivative ( = 2) UV spectrophotometry to determine antioxidants (in 0.2-2.0% concentrations) extracted fi om 0.02-0.1 g PE samples by distillation in vacuo at different temperatures with an accuracy of 1-2%. Pump et al. [146] used UV derivative spectroscopy for the quantitative determination of phenolic AOs in LDPE and Talsky et al. [148] determined the polymer/bound azo-content in PC (Fig. 6.4) by means of derivative UV/VIS. 

Column. As mentioned above, columns can be either packed or capillary. The majority of the early work in SFC was performed with conventional HPLC columns, 25 cm or 10 cm x 4.6 mm i.d. and packed with either 5 pm silica or bonded silicas (Cig, CN or diol). However, narrower-bore columns (2-0.5 mm) with 3 pm packing materials are now being considered. Most packed-column SFC uses carbon dioxide plus a polar modifier such as methanol, acetonitrile, tetrahydrofuran, 1,4-dioxan, methylene chloride or formic acid, typically in the range of 1-20%. Separations are usually effected in the normal-phase mode. This technology has been used successfully in the determination of polymer additives, where good quantitative data can be obtained. More efficient separations can, however, be obtained by the use of... 

Juvet et showed that characteristic reaction products occur during photolytic degradation and polymer additives may on this basis be identified without separation from the polymer samples. The excellent reproducibility reported for photolytic degradation of liquid samples indicated the possibility of quantitative determination of polymer additives (Method 102). They developed equations to predict the shape of calibration curves expected for both trace level additives and those present at higher concentration. Photolytic degradation has been shown to yield simple and more reproducible decomposition patterns due to greater control of input energy and the more predictable manner in which compounds decompose photolytically. 

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