Butadiene rubber, pyrolysis products

The GC results are computed automatically with the aid of a calculator. The natural rubber butadiene-styrene rubber butadiene rubber ratio in the sample material is printed out together with the initial data on pyrolysis product peak retention time, peak area, etc.). This system has been used successfully by Coulter and Thompson [69] for over 2 years in industrial analysis. As a result, the quality of the end product (tyres) was drastically improved. A similar device can be developed using a furnace-type pyrolyser. 

Naturally, the more complex the composition of the substances to be pyrolysed, the more characteristics are needed for identification. For example, in identifying isoprene rubbers (NK, SKN-3, SKIL, Natsyn, Coral, Cariflex IR), the characteristic pyrolysis products are isoprene and dipentene, whereas with butadiene rubbers (SKB, SKD, Budene, Diene NF, Buna CB, Asadene NF, Cariflex BR, Ameripol CB) they are butadiene and vinylcyclohexane. With copolymer rubbers, the number of characteristic products necessary for identification increases to three, viz., butadiene, vinylcyclohexene and styrene are used for butadiene -styrene rubbers (SKS-10, SKS-30, Buna S. Europrene-1500, Solprene) and butadiene, vinylcyclohexene and methylstyrene are used for butadiene-methylstyrene rubbers (SKMS-10, SKMS-30) [139, 140]. Fig. 3.12 [139, 140] shows as an example pyrograms of individual general-purpose rubbers and a four-component mixture of rubbers. The shaded peaks correspond to those components in the pyrolysis products which are used for identification. The ratio of the pyrolysis products changes depending on the composition of the copolymer and the structure of the polymer. 

Pyrolysis coupled with gas chromatography - mass spectroscopy (Py-GC-MS) in an inert atmosphere has been used to study thermal degradation products of styrene-butadiene rubber (SBR). Introduction of samples, using the pyrolysis carrier... 

Mixtures, formulated blends, or copolymers usually provide distinctive pyrolysis fragments that enable qualitative and quantitative analysis of the components to be undertaken, e.g., natural rubber (isoprene, dipentene), butadiene rubber (butadiene, vinylcyclo-hexene), styrene-butadiene rubber (butadiene, vinyl-cyclohexene, styrene). Pyrolyses are performed at a temperature that maximizes the production of a characteristic fragment, perhaps following stepped pyrolysis for unknown samples, and components are quantified by comparison with a calibration graph from pure standards. Different yields of products from mixed homopolymers and from copolymers of similar constitution may be found owing to different thermal stabilities. Appropriate copolymers should thus be used as standards and mass balance should be assessed to allow for nonvolatile additives. The amount of polymer within a matrix (e.g., 0.5%... 

Krishen [42] obtained the products listed in Table 4.10 by pyrolysis of ethylene-butadiene rubber and ethylene-propylene-diene terpolymer. He showed that the 2-methyl-2-butene peak was linear with the natural rubber content of the sample. Styrene-butadiene rubber was determined from the peak area of the 1,3-butadiene peak. The ethylene-propylene-terpolymer content was deducted from the 1-pentane peak area of the pyrolysis products. 

Kodama et al [805] have analysed antioxidants in vulcanised SBR compounds using heat-desorption by means of a double-shot pyrolyser followed by GC-MS analysis. Schulten et al [675] performed TPPy-FIMS experiments using direct introduction. Rubber vulcanisates (BR, NR, SBR) were heated without any pretreatment from 50°C to 750°C in high vacuum with a heating rate of 1.2°C s mass range recorded 50-1500 Da. Figure 2.41 shows the thermogram for some pyrolysis products for BR. The counts (in arbitrary units) for the total ion current, butadiene (m/z 54), butadiene dimer (m/z 108), mercaptobenzothiazole (MBT) (m/z 167),... 

An illustration of the products present in the gas, oil and char fractions resulting from the pyrolysis of a styrene-butadiene rubber (SBR) tyre is presented in the following [2] ... 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

Pyrolysis in an inert atmosphere under precisely controlled conditions (Figure 4) generates duplicable amounts of products, which are separated by capillary GC and provide an estimate of the ratio of polymeric constituents. Natural rubber produces iso-prene and limonene as two of the characteristic products, which distinguish it from polybutadiene (BR), styrene-butadiene co-polymer (SBR), butyl rubber (HR), and some of the other polymers. Quantification involving a mixture of polymers requires calibration curves derived from similar combinations of polymers (Figure 5). Cured and uncured formulations require separate calibrations and the differences in the microstructure of a polymer affect the products obtained on pyrolysis. 

The major degradation product of natural rubber is l-methyl-4-(l-methylethenyl)cyclo hexene. The presence of this compound as the major degradation product along with 2-methyl-1,3-butadiene (monomer) and groups of compounds containing 15 and 20 carbon atoms (three and four monomer units) in the pyrolysate of a rubber is sufficient to identify it as natural rubber. Similarly, the presence of l-chloro-4-(l-chloroethenyl)cyclohexene and 2-chloro-l, 3-butadiene, the cyclic dimer and monomer of poly(chloroprene) rubber, in the pyrolysate of a rubber identify it as poly(chloroprene) rubber. A correlation between the crosslink density and the product ratio of isoprene dimer species to isoprene formed from pyrolysis of natural rubber vulcanisates has been reported 697436 [a.232]. The major products of the isoprene dimer species were l,4-dimethyl-4-vinylcyclohexene and... 

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