Surfactants in PTFE dispersions

1 Separation and identification of nonionic and anionic surfactants. This procedure is based on that described previously [2]. The polymer is precipitated by adding 5 g of the dispersion drop wise to 50 ml of stirred ethanol in a 250 ml beaker, warming the mixture if necessary to coagulate the polymer. The polymer is removed by filtration, and the solvent is collected in a beaker and evaporated to dryness to yield the total surfactant present. This 

To separate these two types, about 20 ml of diethyl ether (dried over anhydrous sodium sulphate) are added to the surfactant extract and allowed to stand for 1 h with occasional swirling, to dissolve any nonionic material. The ether is decanted through a filter paper into a glass basin. The residue in the beaker, if any, is washed twice more with dry ether and the total washings are evaporated to dryness, yielding nonionic surfactant. The ether-insoluble residue is treated with 10 ml of cold water, which is decanted through a filter paper into a glass basin and evaporated to dryness to yield anionic surfactant. 

The IR spectrum of each of these fractions is recorded and compared with reference spectra as found in ref. 23, where useful aids to interpretation precede each section. If confirmation of the IR findings or more detailed information is required then NMR spectroscopy is used. 

3 The determination of an alkylphenol ethoxylate by UV spectroscopy. This can be carried out on the same test solution as used for the determination of anionic surfactant. The spectrum is recorded in a 10 mm pathlength cell against water over the region 350-230 nm, and the absorbance, due to the alkylphenol chromophore, is measured at the maximum which occurs at about 

275 nm with a baseline drawn tangentially between 295 and 245 nm. Calibration is carried out by using a reference sample of the alkylphenol ethoxylate present, and should cover the approximate range 0-40 mg per 100 ml. Anionic surfactants such as sodium alkyl sulphates and sodium alkyl sulphonates do not interfere, but sodium alkyl benzenesulphonates, which absorb in the region 250-275 nm, do. 

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