Determination of Plasticisers in Extractants

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. 

Plasticiser/oil in rubber is usually determined by solvent extraction (ISO 1407) and FTIR identification [57] TGA can usually provide good quantifications of plasticiser contents. Antidegradants in rubber compounds may be determined by HS-GC-MS for volatile species (e.g. BHT, IPPD), but usually solvent extraction is required, followed by GC-MS, HPLC, UV or DP-MS analysis. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out. The determination of antioxidants in rubbers by means of HPLC and TLC has been reviewed [58], The TLC technique for antidegradants in rubbers is described in ASTM D 3156 and ISO 4645.2 (1984). Direct probe EIMS was also used to analyse antioxidants (hindered phenols and aromatic amines) in rubber extracts [59]. ISO 11089 (1997) deals with the determination of /V-phenyl-/9-naphthylamine and poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ) as well as other generic types of antiozonants such as IV-alkyl-AL-phenyl-p-phenylenediamines (e.g. IPPD and 6PPD) and A-aryl-AL-aryl-p-phenylenediamines (e.g. DPPD), by means of HPLC. 

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]. 

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). 

PVAc has been determined according to equation Tg = 18.4 - 6.77C + 0.2197C (plasticiser content C in % validity range 0-12.5% correlation coefficient 0.9986) [85]. Whereas further chlorinating (PVCC) increases Tg from approximately 86°C towards 100°C, it can be lowered to almost any value by addition of plasticisers (-40° to +90°C), as indeed is true also for PVAc. When the additive concentration in a resin exceeds a few weight percent, it is often possible to assay the additive calorimetri-cally without extracting it. If the additive is incompatible with the resin, it can be detected in a separate crystalline or glassy phase by either its Tm or Tg and measured quantitatively from A7/f determinations at Tin or Acp measurements at Tg. When an additive is soluble in a polymer, its concentration can be estimated from shifts in Tm or Tg of the resin. Once a master curve of Tg V5. plasticiser concentration has been prepared for a particular PVC composition, it can be used to determine the amount of plasticiser in an unknown formulation of the particular plasticiser, e.g. PVC/DIDP (cfr. Fig. 2.1) [27]. For PVC/DOP a linear relationship from zero to 45 wt.% plasticiser has been reported [86]. DSC was also used in miscibility studies of erucamide and PA 12 [87]. 

In extraction from a polymer/additive solid matrix the rate-determining step in the extraction process is governed by the interaction of the solvent of sufficient dissolution power with the matrix and the removal of the analyte (cf. Section 3.4.1.3). There appears to exist a direct relationship between degree of swelling and efficiency of extraction. The amount of C02 absorbed depends on temperature, pressure and the polymer concerned. Crystalline polymers are-not surprisingly-plasticised less... 

On-line SFE-GC finds use especially in petroleum-related applications [54], but has also been applied to polymer additives [47,55]. PBT polymers were extracted at 200 bar and 55 °C for the determination of carbonic acid diphenyl esters and other volatiles, using on-line SFE-GC-MS [47]. Extraction of entrained volatiles is a quality test for some polymers. SFE-GC-FTIR-MS has been employed to reveal the cause of odour of a smelly hose (a plasticiser) [56]. SFE-GC can also profitably be used for the determination of residual solvents in polymers such as benzene, toluene and o-xylene [57]. Oligomers of PE (up to 1000 Da) were determined by GC after supercritical fluid extraction [58]. 

Polymer extracts are frequently examined using GC-MS. Pierre and van Bree [257] have identified nonylphenol from the antioxidant TNPP, a hindered bisphenol antioxidant, the plasticiser DOP, and two peroxide catalyst residues (cumol and 2-phenyl-2-propanol) from an ABS terpolymer extract. Tetramethylsuccino-dinitrile (TMSDN) has been determined quantitatively using specific-ion GC-MS in extracts of polymers prepared using azobisisobutyronitrile TMSDN is highly volatile. Peroxides (e.g. benzoyl or lauroylperoxide) produce acids as residues which may be detected by MS by methylation of the evaporated extract prior to GC-MS examination [258]. GC-MS techniques are... 

TG-MS is an ideal technique for identifying residual volatiles in polymers. The detection of residual volatiles (and of other impurities) can often yield clues as to manufacturing processes. In many cases, such as in the determination of highly volatile materials, of residual solvents or plasticisers, use of TG-MS is requested. Specifically, there are reports on the entrapment of curing volatiles in bismaleimide laminates [145] and elastomers [48], on the detection of a curing agent (dicumylperoxide) in EPDM rubbers and of bromine flame retardants in electronic waste [50], of plasticisers such as bambuterol hydrochloride [142] or TPP and diethylterephthalate in cellulose acetate [143], on solvent extraction and formaldehyde loss in phenolic resins [164], and on the evolution of toxic compounds from PVC and polyurethane foams [146]. 

---