Rubbers, deformulation

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Scheme 2.6 Rubber deformulation. After Coz and Baranwal [80]. Reproduced by permission of Rubber World Magazine (Lippincott)...

Deformulation of vulcanised rubbers and rubber compounds at Dunlop (1988) is given in Scheme 2.3. Schnecko and Angerer [72] have reviewed the effectiveness of NMR, MS, TG and DSC for the analysis of rubber and rubber compounds containing curing agents, fillers, accelerators and other additives. PyGC has been widely used for the analysis of elastomers, e.g. in the determination of the vulcanisation mode (peroxide or sulfur) of natural rubbers. 

Scheme 2.3 Dunlop s deformulation of vulcanised rubbers. After Schnecko and Angerer [72]. Reproduced by permission of Hiithig GmbH...

Applications A limited number of papers refer to the use of AAS in relation to polymer/additive deformulation. Elemental analysis of polymers and rubbers by AAS may be carried out after dissolution in an organic solvent (Table 8.21), after oxidative wet digestion (Table 8.12), after dry ashing (Table 8.22) or directly in the solid state (Table 8.23). 

If additional information pertaining to the rubber composition were sought, FTIR analysis of the pyrolysis products would have been performed. Even more detailed analysis can be obtained by gas chromatography (GC) separation of the multiple pyrolysis products followed by mass spectrometric (MS) detection. The gas chromatography-mass spectrometry (GC-MS) method is well suited to deformulation and contaminant analysis. 

Although it would be interesting to study s-NMR for rubber vulcanisates, this nucleus has such low abundance and sensitivity that it is now not possible. On the other hand, P s-NMR is of more interest because of the sensitivity of the nucleus and lack of polymeric matrix interference the spectra can usually be acquired in a relatively short time. The main applications in polymer/additive deformulation are found in the analysis of phosphorous containing additives such as secondary antioxidants (e.g. Irgafos 168 and Sandostab P-EPQ), flame retardants and transesterification suppressants, as well as in quantitative determinations. P s-NMR is an efficient tool for the stmctural analysis of insoluble polyphosphates and melamine phosphates. 

A number of elemental, spectroscopic, chromatographic and thermal techniques are described for the analysis of rubber compounds and products. This review aims to provide an introduction to the techniques and methods that are used to carry out quality control work on mbbers, to investigate the failure of rubber products and to deformulate rubber compounds. 379 refs. 

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