Plasticisers Soxhlet

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

As to artefacts, various plasticisers (DEP, DBP, DIBP, DHP) have been found as a constituent of paper Soxhlet thimbles [124]. 

Soxtherm can be used for a variety of substrates, such as plasticisers, and additives in plastics and rubber, fibre and textile coatings, colorants on textiles, fat in food, oils and lubricants, fertiliser coatings, etc. Specific reports are scarce. EPA method 3541 has adopted automated Soxhlet extraction [151]. 

Some typical applications in SFE of polymer/additive analysis are illustrated below. Hunt et al. [333] found that supercritical extraction of DIOP and Topanol CA from ground PVC increased with temperature up to 90 °C at 45 MPa, then levelled off, presumably as solubility became the limiting factor. The extraction of DOP and DBP plasticisers from PVC by scC02 at 52 MPa increased from 50 to 80 °C, when extraction was almost complete in 25 min [336]. At 70 °C the amount extracted increased from 79 to 95 % for pressures from 22 to 60 MPa. SFE has the potential to shorten extraction times for traces (<20ppm) of additives (DBP and DOP) in flexible PVC formulations with similar or even better extraction efficiencies compared with traditional LSE techniques [384]. Marin et al. [336] have used off-line SFE-GC to determine the detection limits for DBP and DOP in flexible PVC. The method developed was compared with Soxhlet liquid extraction. At such low additive concentrations a maximum efficiency in the extractive process and an adequate separative system are needed to avoid interferences with other components that are present at high concentrations in the PVC formulations, such as DINP. Results obtained... 

Applications Most plasticisers can be removed almost quantitatively from PVC by Soxhlet extraction or direct refluxing with diethyl ether for several hours. With the dissolution (THF)/reprecipitation (n-hexane) method, PVC compounds can be isolated. However, reliable results are also obtained by using a short cut in which a PVC compound (0.3g) is dissolved in THF (lOg), insoluble material is allowed to settle and then the THF solution including PVC is injected on to the GC column [12]. Although direct gas chromatographic analysis... 

Single solvent (Soxhlet) Polyvinyl chloride (PVC) Diethyl ether Plasticisers... 

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. 

Tetrahydrofuran extracts of the PVC were mixed with methyl alcohol to reprecipitate the polymer or diethyl ether Soxhlet extractions of PVC were applied to a Merck fluorescent silica Gel G plate which was developed with ethyl acetate-isooctane (15 85 v/v) or methylene chloride or diethyl ether - petroleum ether (40-60). After development the plate was sprayed with 2% ethanolic resorcinol, then 4 N sulfuric acid. The plates were then heated to 135 °G and sprayed with 25% sodium hydroxide to locate the plasticisers. 

In this scheme the sample is dissolved in THF and centrifuged at 20 000 rpm to isolate inorganic materials and polymeric impact modifiers together. The polymer is precipitated from the THF centrifugate with ethanol and isolated by filtration. The THF-ethanol filtrate is evaporated to dryness to yield the soluble organic additives. This yields a total of three fractions to examine. When a polymeric plasticiser is either known to be present or found to be present in the THF-ethanol-soluble fraction, then the isolated polymer is Soxhlet extracted with hot ethanol to remove residual non-extracted plasticiser. All fractions are examined by IR spectroscopy and use is made of reference spectra. 

As shown in Table 2.4 this procedure will quantitatively extract monomeric plasticisers such as DOP, but for polymeries such as PPA (polypropylene adipate) only 94% was found to be extracted and therefore the dried polymer is Soxhlet extracted with ethanol for 18 h to remove the rest. The validation was carried out by weighing the plasticiser and filler into a 600 ml beaker together with sufficient blank PVC to give a total of 2 g, dissolving in 40 ml of THF and proceeding as described. 

Mention has already been made in Section 4 of the isolation of plasticisers from a plastic matrix by solvent extraction. Careful choice of solvent is required to ensure that the polymer itself doesn t undergo dissolution and that the plasticiser is selectively isolated. A solvent which has been found to be useful for polymers such as PVC is methanol. The extraction is carried out under Soxhlet conditions with the weight of extract being obtained from the weight gain of the conditioned solvent reservoir flask once the solvent has been dried off at 105 °C. 

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