Rubbers carbon-black content measurement

Techniques based on TG analysis have made it possible to readily and accurately measure the carbon-black content in commercial polymer formulations, such as in rubbers, at levels as far apart as 0.1% and 30%. The typical procedure is shown in Fig. 2.15 (sensitivity of the TG scan is 100 wt.% full scale) for a polyethylene masterbatch formulation, which was initially heated in N2 at a rate of 160°C/min. to about 550°C. Pyrolytic decomposition to gaseous products resulted in a 75% weight loss. After changing to O2 atmosphere the carbon-black is then oxidised [151]. The precision of the determination in the PE/CB masterbatch formulation is about 0.05 to 0.1% carbon (absolute). The TG method is fast, le. 6 min at 160°C/min, as compared to 2 h for ASTM D 1063 [266] without TG, thus providing substantial time savings. The compositional analysis (polymer and CB content) of LDPE has been reported [85] Affolter et al [155] have determined the content of carbon-black in polyolefins (2-3% CB) by TG following ISO 9924-1 and have noticed an inhomogeneous distribution in commercial... 

H and 2H NMR have been used in styrene-butadiene rubber (SBR) with and without carbon-black fillers to estimate the values of some network parameters, namely the average network chain length N. The values obtained from both approaches were checked to make sure that they were consistent with each other and with the results of other methods [71, 72, 73]. To this purpose, a series of samples with various filler contents and/or crosslink densities were swollen with deuterated benzene. The slopes P=A/ X2-X 1) obtained on deuterated benzene in uniaxially stretched samples were measured. The slopes increase significantly with the filler content, which suggests that filler particles act as effective junction points [72, 73]. 

Elastomeric or rubber-like materials are typically difficult to use with transmission-based techniques however, dependent on the ingredients, they are ideal for ATR-based measurements. Most elastomers conform well with the IRE surface, providing good intimate contact. Elastomers with a high filler content, and in particular with dispersed carbon black, will cause problems because of the absorption characteristics of the carbon. In such cases, either ATR with a high refractive index IRE (such as germanium) or a photoacoustic measurement may be employed. In the event that such an approach is not available, then a destructive method such as pyrolysis can be used (see Section 5). 

Incorporation of carbon black (CB) increased the viscosity of the mixture while the smaller the CB particles the higher the Mooney viscosity value measured. This is related to the enhanced bound rubber content which followed the increase of the surface area of CB as the particle size was decreasing for the same filler content. 

The advantage of the Py-GC-MS method over other methods for measuring styrene content of SBR copolymer is its relatively easy use for analysis of clear polymers as well as polymers containing process oils, fillers, and carbon black, and even cured rubbers. Moreover, the percent bound styrene obtained by this technique is not affected by changes of copolymer microstructure. Results of this work clearly show that the percentage of styrene obtained by this technique correlates very well with the results obtained by other methods. 

As conductive particles, carbon black particles prepared from acetylene black were used, its size was measured approximately 420 A and as the elastomeric polymer, in view of its durability and chemical stability, silicone rubber was applied. The silicone rubber had a density of 1.20 g/cm3, a specific heat of 0.35 cal/g °c, and a resistivity of 9xl0l l-cm. For the elastomeric conductive specimen, the carbon black particles were dispersed into silicone rubber by the rolling process. The particle contents were selected to be 5 wt%, 12 wt%, 20 wt%, and 40 wt%. The specimens were cured under heating, and its size was measured 10 mm (width)... 

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