Determinations Santonox

The oxidation is followed by reaction of the ferrous iron produced, with 2, 2 -dipyridyl to form a coloured complex, the intensity of which is proportional to the concentration of antioxidant present. The procedure has been applied to various phenolic and amine type antioxidants, namely, Succanox 18, BHT, lonol (2,6-di-tert-butyl-p-cresol), and Nonox Cl (N-N-di- 3-napthyl-p-phenylenediamine). A typical application of the procedure is given next, namely to the determination of down to 0.01% of Santonox R in PE. As the Metcalfe and Tomlinson [5] procedure determines Santonox R only in its reduced form, it does not include any Santonox R which may be present in the oxidised form in the original polymer, for example produced by atmospheric oxidation of the additive during polymer processing at elevated temperatures. Total reduced plus oxidised Santonox R can be determined by UV spectroscopic procedures. 

Quantitative procedures are described next for determining Santonox R (4,4 -thio-bis-6- er -butyl-w-cresol), and the UV stabiliser Cyasorb UV 531 (2-hydroxy-4-w-octoxybenzophenone) in PE, in amounts down to 20 ppm in polymer with an accuracy of 20% of the determined amount. 

The following compoimds are known to interfere in the procedure for determining Santonox R. The described method may indeed, be used to determine these substances in polyethylene. 

Applications Shake-flask extraction nowadays finds only limited application in polymer/additive analysis. Carlson et al. [108] used this technique to extract antioxidants from rubber vulcanisates for identification purposes (NMR, IR, MS). Wrist-action shaking at room temperature was also used as the sample preparation step for the UV and IR determination of Ionol CP, Santonox R and oleamide extracted from pelletised polyethylene using different solvents [78]. BHT could be extracted in 98 % yield from powdered PP by shaking at room temperature for 30 min with carbon disulfide. 

Various additives in PE (Santonox, Nonox DPPD, Neozone A, Ionol and Agerite White) were determined by conventional TLC [507]. Other additives in PE, studied by means of TLC, were Tinuvin P 120/326/327/770, Cyasorb UV531, Anti UV P (2-hydroxy-4-n-octyloxybenzophenone), Irganox 1076, Sanduvor EPU, AO-4 and Dastib 242/263 [508], TLC has also been used in the analysis of additives in polyurethanes [509,510] as well as of slip additives (ethoxylated amines and amides) in HDPE extracts... 

Fig. 2 Residual antioxidant content (%) of Santonox R in PE determined by HPLC (extraction by MAE), plotted versus the corresponding OIT values, for samples aged in oxygen-free water at 90 °C. owned by the first author [46]...

Spell and Eddy [58] have described IR spectroscopic procedures for the determination of up to 500 ppm of various additives in PE pellets following solvent extraction of additives at room temperature. They showed that lonol (2,6-di- -butyl-p-cresol) and Santonox R... 

Straightforward UV spectroscopy is liable to be in error because of interference by other highly absorbing impurities that may be present in the sample [59-62], Interference by such impurities in direct UV spectroscopy has been overcome or minimised by selective solvent extraction or by chromatography [60], However, within prescribed limits UV spectroscopy is of use and, as an example, procedures are described next for the determination of lonol (2,6-di- e -butyl-p-cresol) and of Santonox R (4,4"-thio-bis-6-terUbutyl-m-cresol) in polyolefins [63-66],... 

Certain additives, e,g, calcium stearate and thiodipropionate, do not interfere in the determination. Other phenolic antioxidants, e,g, lonox 330, Topanol CA and Santonox R, do interfere. 

Campbell and Wise [2] applied column chromatography to the determination of known phenolic antioxidants in polyethylene (PE). This method is applicable to the analysis of mixtures of Santowhite powder (4, 4"-butylidene-bis-(6- er -butyl-w-cresol) with BHT (2,6-di-ter -butyl-p-cresol) and mixtures of Santonox R (4, 4 -thio-bis-(6-fert-butyl-m-... 

Elution with chloroform removes BHT only as the first fraction. Continued elution of the column with solutions of 10% water in methanol removes Santowhite powder or Santonox R as a separate pure fraction, free from BHT. Additives can then be determined in the respective extracts after they have been diluted to a standard volume with solvent by ultraviolet (UV) spectroscopy. 

HPLC of polymer extracts has been used to determine dilauryl dithiopropionate, Irganox 1076 and distearyl-dithiopropionate in polyolefins [18], amine antioxidants and antiozonates in rubbers [16], Irganox 1076, Irganox 1010 and BHT in PE [19] and miscellaneous antioxidants, light stabilisers in polyolefins [20,21] and Santonox R, Ethanox 736, CAO-5, Irganox 1035, Irganox 259 and Topanol [22] in polyolefins and also the determination of antioxidants and accelerators in vulcanised rubber formulations [23-25]. 

Crompton [59] has described a simple direct thin-layer method for the determination of UV 531 ultraviolet stabiliser in hot toluene extracts of HDPE. Interference was encountered from a number of additives, namely, dilauryl thiodipropionate, lonox 330, lonol CP, Topanol CA, Santonox R and Polygard. 

Spell and Eddy [3] described infrared (IR) spectroscopic procedures for the determination of up to 500 ppm of various additives in polyethylene (PE) pellets following solvent extraction of the additives at room temperature. They showed lonol (2,6-di-ter -butyl-p-cresol) and Santonox R (4,4 -thio-bis(6-ter -butyl- /-cresol)) are extracted quantitatively from PE pellets by carbon disulfide in 2-3 hours and by isooctane in 50-75 hours. The carbon disulfide extract is suitable for scanning in the IR region between 7.8 and 9.3 (xm, while the isooctane extract is suitable for scanning in the UV region between 250 and 350 nm. 

Aromatic amines and phenols are among the few classes of compounds in which a large proportion of them exhibit useful fluorescence. Parker and Barnes [21] found that in solvent extracts of rubbers the strong absorption by pine tar and other constituents masks the absorption spectra of phenylnaphthylamines, whereas the fluorescence spectra of these amines are sufficiently unaffected for them to be determined directly in the unmodified extract by the fluorescence method. In a later paper Parker [22] discussed the possibility of using phosphorescence techniques for determining phenylnaphthylamines. Drushel and Sommers [7] have discussed the determination of Age Rite D (polymeric dihydroxy quinone) and phenyl-2-naphthylamine in polymer films by fluorescence methods and Santonox R and phenyl-2-naphthylamine by phosphorescence methods. 

Excess ferric ions react with Santonox R but not with the oxidation products to produce ferrous ions which can then be determined by the spectrophotometric 2,2 -dipyridyl method, giving an estimate of the unoxidised Santonox R content of the extract ... 

A good example of an application of the van t Hoff calorimetric purity method is the determination of purity of 4,4 -thiobis(3-methyl-6-rm-butylphenol), a commercial antioxidant, with the trade name Santonox R and a molecular mass of 358g/mol. This type of phenolic antioxidant is used to prolong the life of polyolefins exposed to oxygen. Two comparative melting scans of different lots of Santonox R revealed a startling difference in melting behavior as shown in Fig. 2.11 (Bair 1997). 

An early report on the direct determination of stabilisers in pressed polymer films by UV spectrophotometry is due to Drushel et al [13]. The determination of a variety of additives (Santonox R, lonol, lonox 330, CAO-5, CAO-6, DPPD, Polygard, Topanol) in the 0.002-1.0% range in ten mils thick... 

In a very early report of direct determination of stabilisers in polymers by luminescence techniques by Drushel et al. [13] the fluorescence of EPR/Age Rite D (trimethyldihydroquinoline) and of EPR/Santonox R were examined. Lack of interference by other polymer additives and polymerisation catalyst residues was emphasised. Age Rite D concentrations can be measured directly in pressed EPR films (<0.01 cm thickness) by fluorescence at levels below 0.1-0.2 wt.% in order to prevent concentration quenching. In the fluorescence emission spectra of Irgafos 168 the fluorescence quantum yield of the phosphate is much greater than that of the phosphite [516]. This difference enables quantification of the phosphate concentration. Although direct quantitative determination of UV stabilisers in extruded polyolefins by means of fluorescence spectroscopy (ex, 370 nm em, 390-550 nm) has been described [517], this is certainly not a universally applicable technique (being additive and matrix dependent). The effects of additives (AOs and cross-linking agent by-products) on electroluminescence... 

Since the determination of inhibitors in polymers by Drushel et al. [13] little information has been added to the literature on the quantitative aspects of the direct examination of polymer films by phosphorescence spectroscopy. These authors examined phosphorescence (at liquid-nitrogen temperature) of thin EPR films containing Santonox R (2,2 -di-methyl-5,5 -di-r -butyl-4,4 -dihydroxydiphenyl sulfide) and V-phenyl-2-naphthyl-amine (PBN). The rather intense phosphorescence of PBN may be used to advantage when other additives interfere in the UV absorption method. As to quantitative phosphorescence analysis, several factors, e.g. film thickness, concentration quenching, and background absorption, etc., affect the linearity of the analytical working curves and precision of the measurements [13]. The reliability of a correlation between stabiliser concentration in the film and phosphorescence intensity at 77 K is also influenced by the degree of crystallinity [544]. 

Unsaturated copolymers were analyzed for the unsaturated comonomer by Kemp Bromine No. (in QKI3) after correcting for the Bromine No, of the antioxidant (Santonox, 125 and phenyl B-naphthyl amine, 143), Chlorine-containing comonomers were determined by a chlorine analysis. The composition of the TMO-EO copolymers was determined by C and H analysis. The PO content of the TMO-PO-AGE terpolymer was determined by infrared analysis. 

In Method 9 is described a quantitative thin-layer procedure for determining a single additive, namely Santonox R (4,4 -thio-bis-6-tert-butyl-m-cresol) in polyethylene. 

METHOD 3 - DETERMINATION OF SANTONOX R PHENOLIC ANTIOXIDANT IN POLYETHYLENE. 2,2 -DIPYRIDYL SPECTROPHOTO-METRIC METHOD. ... 

A method for the determination of various types of antioxidants in polyethylene as exemplified by the determination of Santonox R phenolic antioxidant, (Note 1). 

N = Weight (g) of Santonox R in 10 cm polyethylene extract obtained by referring determined optical density to the calibration graph. 

Down to 0.01% Santonox in polymer can be determined by this procedure with an accuracy of 5%. 

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