Polyolefins, analysis Extraction

Applications Dissolution/reprecipitation is claimed to be the most widespread approach to polymer/additive analysis [603], but recent round-robins cast some doubt on this statement. Dissolution appears to be practised much less than LSEs. However, in cases where exhaustive extraction is difficult, e.g. for polyolefins containing high-MW (polymeric) additives, a dissolution/precipitation method is preferred. 

Oligomeric hindered amine light stabilisers, such as Tinuvin 622 and Chimassorb 944, resist satisfactory analysis by conventional HPLC and have required direct UV spectroscopic analysis of a polyolefin extract [596], PyGC of an extract [618,648], or SEC of an extract [649]. Freitag et al. [616] determined Tinuvin 622 in LDPE, HDPE and PP by saponification of the polymer dissolution in hot toluene via addition of an... 

GC is extensively used to determine phenolic and amine antioxidants, UV light absorbers, stabilisers and organic peroxide residues, in particular in polyolefins, polystyrene and rubbers (cf. Table 61 of Crompton [158]). Ostromow [159] has described the quantitative determination of stabilisers and AOs in acetone or methanol extracts of rubbers and elastomers by means of GC. The method is restricted to analytes which volatilise between 160 °C and 300 °C without decomposition. A selection of 47 reports on GC analysis of AOs in elastomers (period 1959-1982) has been published... 

In SEC analysis of additive extracts from polymers, the effect of the extraction solvent on the mobile phase is less critical than in HPLC analysis. The extraction solvents typically employed generally do not interfere with the SEC mobile phases. Moreover, the same solvents are often used both as extraction solvent and as mobile phase. Therefore, there is no need to evaporate the extract to dryness prior to analysis and then to redissolve it in a suitable solvent. Typical extraction procedures often produce extracts that generally contain a small amount of wax. Frequently, removal of such oligomers from an extract is necessary, e.g. by means of precipitation, centrifuging, precolumn filtration or protection (use of a reversed-phase guard column). In SEC separations the presence of polyolefin wax does not usually disturb provided that the MW of the wax is higher than that of the analysed compounds. 

Applications Multidimensional SEC techniques can profitably be applied to soluble polymer/additive systems, e.g. PPO, PS, PC - thus excluding polyolefins. A fully automated on-line sample cleanup system based on SEC-HRGC for the analysis of additives in polymers has been described, as illustrated for PS/(200-400ppm Tin-uvin 120/327/770, Irgafos 168, Cyasorb UV531) [982], In this process, the high-MW fractions are separated from the low molecular masses. SEC is often used as a sample cleanup for on-line analysis of additives in food extracts these analyses are usually carried out as on-line LVI-SEC-GC-FPD. 

B. Marcato and M. Vianello, Microwave-assisted extraction by fast sample preparation for the systematic analysis of additives in polyolefines by high-performance hquid chromatography. J. Chromatogr.A 869 (2000) 285-300. 

The analysis of antioxidants is based on their non-volatile nature, their modest molecular weight and the fact that they absorb light due to their chro-mophore groups. In works concerning the separation of additives from polyolefins the main difficulty is generally to achieve the extraction and recovery in a reasonable time. Differences in shape, size or thickness of a polymer film or the presence of other additives may significantly affect the result of the extraction and analysis of the antioxidant content in a polymer. Consequently, method development has to be performed to find standardized methods. 

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. 

UV stabilisers can be determined by direct analysis of polyolefins and polyvinyl chloride (PVC) (i.e., without solvent extraction) using the Perkin Elmer model LS-50 luminescence spectrometer (L255-0105) fitted with a front surface accessory. The relation between fluorescence emission and stabiliser content was found to be linear over the range obtained for both natural and extruded polymer samples [23]. 

Yu and co-workers [59] discussed liquid chromatographic interfaces for bench-top single quadruple LC-MS. The two most popular interfaces are particle beam and atmospheric pressure ionisation types. The system was applied to the analysis of additives in PP. Dilts [60] used a photodiode array detector coupled with particle beam LC-MS to characterise the degradation of Isonox 129, Irganox 1010, Ii anox 1076, andirgafos 168 in polyolefins. Sidwell [61] examined extractables from plastic and rubber components of medical products by LC-MS and GC-MS. 

XPS analysis is an adequate technique to characterize the siuface ehemical composition of cotton fibres. The present study clearly shows that the raw fibers, whatever their origin and maturity, are totally covered by waxes and other non-eellulosic materials and exhibit surface properties eloser to those of polyolefin polymers (or high molecular weight alkanes) than those of eellulose. It appears also that a standard treatment of extraction by means of hot ethanol for 6 hrs is not able to remove all the waxes initially present on the fiber surfaces. These results are in good agreement with previous ones concerning the mechanisms of adsorption of gas probe molecules onto such raw and extracted fiber siufaces... 

---