Determination of Plasticiser

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. 

Having quantified the plasticiser present by extraction it is then possible to obtain an identification by the use of transmission IR. There is an excellent database available (399) which enables an identification to be made. Where the plasticisers have distinct IR spectra (e.g., phthalates and sulfonamides) it is possible to detect the presence of a blend of plasticisers. If a quantification of the blend composition is required, though, this is usually easier to achieve by HPLC then IR. 

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For direct determination of plasticisers in PVC the sample was dissolved in THF, and phthalate or phosphate plasticisers were measured from absorbance at 240 and 275 nm or 257, 262 and 268 nm, respectively... 

A fractional reprecipitation procedure involving a solution of the polymer in acetone, followed by reprecipitation with light petroleum can be used to separate additives from acrylics. The acetone - light petroleum extract can be used for the determination of plasticisers and lubricants (Figure 2.2). 

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. 

Turnstall [81] has described a gas chromatographic method for the determination of plasticisers in propellent compositions. This procedure which might also be applicable to polymer extracts involves extracting the sample with dichloromethane and concentration of the extract for analysis on a column (2 m x 3.175 mm) of 5% of Antarox CO-990 on AW-DMCS Chromosorb G (80 to 100 mesh) the column was operated at 185 "C, with nitrogen as carrier gas (25 ml per minute) and flame ionisation detection. The method permitted the measurement of dimethyl phthalate, dimethyl sebacate, triacetin, diacetin, and diethyl phthalate. 

FTIR and pulsed NMR) for quantitative determination of plasticiser content in filled PVC. PAS was also instrumental in detecting the presence of absorbed water and filler modifiers, such as calcium carbonate treated with stearic acid, in aged silicone based sealants [482]. 

Fig. 2.10. Exact determination of plasticiser content (29%) of SBR rubber by means of vacuum TG. Reproduced by permission of Netzsch-Geratebau GmbH, Selb (TG 209 Technical Data Sheet).

Table 6.27. Materials for solvent- and heat-extractive determinations of plasticisers ...

Table 6.28. Normalised methods for the determination of plasticisers from polymeric materials by means of solvent...

ASTM D 3421, Recommended Practice for Extraction and Determination of Plasticiser Mixtures from Vinyl Chloride Plastics, Annual Book of ASTM Standards, ASTM, Philadelphia, PA (1987). 

The validation of an analytical method for the determination of plasticisers (DEHA, DEHP) in PVC has been reported [90], as well as that of the calibration procedure in AAS methods [91], In an original development Van Every el al. [13] have applied infrared principle components/Mahalanobis distance discriminant (PMD) analysis to validate polyolefin (film) products. PMD is a technique designed to classify complex materials into groups or identify unknowns by using n principle components to map data characteristics into an n-space cluster [92]. An unknown material can then be assigned a distance from this cluster based on the number of standard... 

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