Typical application rubber analysis

The aim of rubber analysis is to quantitatively determine the main constituents of technical elastomer systems. Basically, it is possible to distinguish between the following main components  

Volatile substances such as moisture, plasticisers and other additives. The actual elastomers involved. 

Besides the quantitative information obtained from the mass loss steps, qualitative results can also be obtained from the DTG curve. For example, the measured peak temperatures are characteristic of certain types of elastomers some examples are summarised in Table 12.3. 

Other methods can also be used including lowering the temperature before switching to the oxidising atmosphere. 

Please also refer to Chapter 6 for additional discussion of the analysis of rubber com-povmds. 

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Typical applications at Polysar included the quantification of residual solvents and monomers in finished rubber products (e.g. styrene in SBR), quality control of feedstocks such as benzene or ethyl benzene as impurities in styrene monomer, and the analysis of samples collected from environmental monitoring programs. 

Valuable reviews and books of structural analysis of elastomers have been published by several authors [1-6]. Some of these reviews provide excellent explanation on the basic theory of sequence distribution of copolymer and NMR techniques applicable to elastomers. Typical high-resolution 3H- and 13C-NMR spectra of various vulcanisates and raw rubbers are depicted in a book written by Kelm [6]. The assignments and references shown for each rubber are very useful for structural studies of elastomers. In view of recent progress in the hardware and software of NMR, this chapter describes some of the more recent applications of high-resolution NMR to the structural characterisation of elastomers, after a brief description on the fundamental structural features of elastomers. 

In Chapter 18, we described solvent extraction and solid-phase extraction sample preparation methods, which are applicable to GC analyses as well as others. A convenient way of sampling volatile samples for GC analysis is the technique of head-space analysis. A sample in a sealed vial is equilibrated at a fixed temperature, for example, for 10 min, and the vapor in equilibrium above the sample is sampled and injected into the gas chromatograph. A typical 20-mL glass vial is capped with a silicone rubber septum lined with polytetrafluoroethylene (PTFE). A syringe needle can be inserted to withdraw a 1-mL portion. Or the pressurized vapor is allowed to expand into a 1-mL sample loop at atmospheric pressure, and then an auxiliary carrier gas carries the loop contents to the GC loop injector. Volatile compounds in solid or liquid samples can be determined at parts per million or less. Pharmaceutical tablets can be dissolved in a water-sodium sulfate solution... 

In view of the wide application of Py—GC in industry and research, the development of techniques and equipment for automatic analysis by this method is of great practical interest. An automatic Py—GC system was developed by Coulter and Thompson [69] for Curie-type cells with a filament for specific application in the tyre industry. A typical analysis involves the identification and determination of polymers in a tyre material sample. The material of a tyre is essentially a mixture of polymers, most often natural rubber (polyisoprene), synthetic polyisoprene, polybutadiene and butadiene-styrene copolymer. A tube is normally made of a material based on butyl rubber and a copolymer of isobutylene with small amounts of isoprene. In addition to the above ingredients, the material contains another ten to twelve, such as sulphur, zinc oxide, carbon black, mineral oil, pine pitch, resins, antioxidants, accelerators and stearic acid. In analysing very small samples of the tyre material, the chemist must usually answer the following question on the basis of which polymers is the tyre made and what is their ratio The problem is not made easier by the fact that cured rubber is not soluble in any solvent. 

Some typical important industrial applications of coulometry include the continuous monitoring of mercaptan concentration in the materials used in rubber manufacture. The sample continuously reacts with bromine, which is reduced to bromide. A third electrode measures the potential of B12 vs. Br and, based on the measurement, automatically regulates the coulometric generation of the bromine. Coulometry is used in commercial instruments for the continuous analysis and process control of the production of chlorinated hydrocarbons. The chlorinated hydrocarbons are passed through a hot furnace, which converts the organic chloride to HCl. The latter is dissolved in water and the Cl titrated with Ag" ". The Ag" " is generated by coulometry from a sUver electrode, Ag°. It is necessary for the sample flow rate to be constant at all times. Integration of the coulometric current needed to oxidize the silver to silver ion results in a measurement of the Cl concentration. 

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