Stearates, analysis

A typical example is total monomers. 100 sodium stearate, 5 potassium persulfate, 0.3 lauryl mercaptan, 0.4 to 0.7 and water, 200 parts. In this formula, 75 parts of 1,3-butadiene and 25 parts of 4-methyl-2-vinylthiazole give 86% conversion to a tacky rubber-like copolymer in 15 hr at 45°C. The polymer contains 62% benzene-insoluble gel. Sulfur analysis indicates that the polymer contains 21 parts of combined 4-methyl-2-vinylthiazole (312). Butadiene alone in the above reaction normally requires 25 hr to achieve the same conversion, thus illustrating the acceleration due to the presence of 4-methyl-2-vinylthiazole. 

In a typical application of SPE as a clean-up device in polymer/additive analysis Nelissen [157] has examined a PA6 compound with calcium stearate adhered on the surface by means of paraffin oil. 

An analytical solution for molecules with alkaline functionality is acid/base titration. In this technique, the polymer is dissolved, but not precipitated prior to analysis. In this way, the additive, even if polymer-bound, is still in solution and titratable. This principle has also been applied for the determination of 0.01 % stearic acid and sodium stearate in SBR solutions. The polymer was diluted with toluene/absolute ethanol mixed solvent and stearic acid was determined by titration with 0.1 M ethanolic NaOH solution to the m-cresol purple endpoint similarly, sodium stearate was titrated with 0.05 M ethanolic HC1 solution [83]. Also long-chain acid lubricants (e.g. stearic acid) in acrylic polyesters were quantitatively determined by titration of the extract. 

Aromatic amines formed from the reduction of azo colorants in toy products were analysed by means of HPLC-PDA [703], Drews et al. [704] have applied HPLC/ELSD and UV/VIS detection for quantifying SFE and ASE extracts of butyl stearate finish on various commercial yarns. From the calibrated ELSD response the total extract (finish and polyester trimer) is obtained and from the UV/VIS response the trimer only. Representative SFE-ELSD/UV finish analysis data compare satisfactorily to their corresponding SFE gravimetric weight recovery results. GC, HPLC and SEC are also used for characterisation of low-MW compounds (e.g. curing agents, plasticisers, by-products of curing reactions) in epoxy resin adhesives. 

Infrared measurement of additive concentrations is a more complex analysis than initially expected, as some additives may undergo a variety of chemical reactions during processing, as shown by Reeder et al. [128] for the FTIR analysis of phosphites in polyolefins. Some further examples of IR work refer to PVC/metal stearates [129], and PE/Santonox R [68,130]. Klingbeil [131] has examined the decomposition of various organic peroxyesters (TBPB, TBPP, TBPA and TBPO) and a peroxidicarbonate (BOPD) as a function of pressure, temperature and solvent by means of quantitative FTIR using an optical high p, T reaction cell. 

On-line SFE-SFC-ELSD analysis of the textile and fibre finish components, butyl stearate/palmitate/myri-state, was reported [118]. Similarly, Kirschner et al. [119] used on-line SFE-pSFC for fibre finish analysis on-line SFE-SFC was also instrumental in the analysis of the total composite finish on a commercial textile thread [120]. 

On-line SFE-pSFC-FTIR was used to identify extractable components (additives and monomers) from a variety of nylons [392]. SFE-SFC-FID with 100% C02 and methanol-modified scC02 were used to quantitate the amount of residual caprolactam in a PA6/PA6.6 copolymer. Similarly, the more permeable PS showed various additives (Irganox 1076, phosphite AO, stearic acid - ex Zn-stearate - and mineral oil as a melt flow controller) and low-MW linear and cyclic oligomers in relatively mild SCF extraction conditions [392]. Also, antioxidants in PE have been analysed by means of coupling of SFE-SFC with IR detection [121]. Yang [393] has described SFE-SFC-FTIR for the analysis of polar compounds deposited on polymeric matrices, whereas Ikushima et al. [394] monitored the extraction of higher fatty acid esters. Despite the expectations, SFE-SFC-FTIR hyphenation in on-line additive analysis of polymers has not found widespread industrial use. While applications of SFC-FTIR and SFC-MS to the analysis of additives in polymeric matrices are not abundant, these techniques find wide application in the analysis of food and natural product components [395]. 

Haslam et al. [32] reported the determination of Al in polyolefins by AAS. Typical AAS tests on rubber compounds involve several steps. The sample is combusted, and the resulting ash is dissolved in distilled de-ionised water. The solution is then used for AAS [126]. AAS or EDS can also be used for element analysis of filler particles. In order to determine the uniformity of tin compounds in polychloroprene after milling and pressing, Hornsby et al. [127] have ashed various pieces from one composition. After fusion of the residue with sodium peroxide and dissolution in HC1, the Sn content was determined by means of AAS. Typical industrial AAS measurements concern the determination of Ca in Ca stearate, Zn in Zn stearate, Ca- and Zn stearate in PE, Ca and Ti in PE film or Al and V in rubbers. 

XRD can be used for studies of polymorphic transformations in bloom formation. In combination with DTA, XRD has been used to study polymorphic transformations of Ca stearate and Ca stearate monohydrate [338]. Full pattern refinement has been used for quantitative analysis of mixtures of crystalline... 

Crompton [21] has reviewed the use of electrochemical methods in the determination of phenolic and amine antioxidants, organic peroxides, organotin heat stabilisers, metallic stearates and some inorganic anions (such as bromide, iodide and thiocyanate) in the 1950s/1960s (Table 8.75). The electrochemical detector is generally operated in tandem with a universal, nonselective detector, so that a more general sample analysis can be obtained than is possible with the electrochemical detector alone. 

Lubricants are used in tablet preparation and include magnesium stearate, stearic acid and polyethylene glycol. They only comprise at most 1-2% of the tablet bulk so that their potential to interfere is slight, particularly since their chromophores are weak. The fatty acid lubricants can often be observed if analysis of a tablet extract is carried out by GC-FID. Tablet coatings are often based on modified sugar polymers such as hydroxypropylmethylcellulose. These coatings are used at about 3% of the tablet bulk, are water soluble and do not absorb UV light. 

Figure 10 SIMCA analysis of the scans shown in Figure 5. (A) SICMA model for Avicel PH 101, (B) SIMCA model for Lactose, (C) SIMCA model for Mg Stearate and (D) SIMCA model for di-tab. Abbreviation SIMCA, Soft Independent Modelling of Class Analogies.

Figure 7.10 Chemical image analysis of six tablets composed of 80 mg of furosemide (API) mixed with 240mg of the excipient mix (99.7% Avicel PH 102 and 0.33% magnesium stearate). Tablets A-E were created in the laboratory using increasing blending time, tablet F is an example of a commercial product. These PLS score images of the tablets highlight the location of the API component (bright pixels), and show the gross blend-quality differences.

A key factor in the QA program is the performance control of the instrumentation. A number of test compounds have been recommended for checking the performance of a GC/MS instrument for the analysis of scheduled chemicals (34). These include DMMP, DMMP-rf9, trimethylphosphate, 2,6-dimethylphenol, 5-chloro-2-methylaniline, tri-n-butylphosphate, dibenzothiophene, malathion, and methyl stearate. DMMP is a moderately polar compound and is considered to be a good test compound for checking the GC performance. The deuterated form is recommended because it does not give cross-contamination in the analysis of authentic samples. However, because no scheduled chemicals can be brought on-site during an inspection, the use of DMMP-<79 has been replaced by trimethylphosphate for on-site analysis. The correctness of the intensity ratios in the El mass spectra can be verified by means of the test compounds with the different isotopic peaks 5-chloro-2-methylaniline... 

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