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Chemical crosslink densities of gum and carbon black-filled natural rubber (NR) and styrene-butadiene rubber (SBR) were estimated by using a newly developed rheometer. The rheometer is the Rubber Process Analyzer (RPA 2000) which is designed specifically to measure dynamic properties such as shear storage modulus G′ and shear loss modulus G″ in cured and uncured rubber. It was found that the differences between the G′ values of dicumyl peroxide-cured NR and those of uncured samples yielded estimates of the crosslink densities which were nearly the same as the values inferred by chemical analysis. For TMTD-cured SBR, the same procedure yielded estimates of chemical crosslinks very close to those estimated by a tensile stress-strain method and by NMR. In addition, accelerated sulfur-cured natural rubber was also investigated. The agreement between the crosslink densities of these stocks determined from G′ values and from a solvent-swelling method was very good.

A new dynamic mechanical rheological tester called the RPA 2000 rubber process analyzer by Monsanto can analyze rubber masterbatches as well as rubber compounds before, during and after cure. It requires no special sample preparation, is easy to operate, and can apply a wide range of dynamic test conditions to a rubber sample, including very high strains. This paper discusses the use of this new instrument as a processability tester in predicting the effects of variations in filler and oil types and loadings on rubber compound behavior.

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Abstract:In the last two decades, thermoplastic vulcanizates (TPVs) and other thermoplastic Elastomers (TPEs) have significantly increased their usage in the rubber industry. New concerns regarding variability in processing characteristics and product performance have emerged and new methods to effectively and quickly predict these differences among different lots or different grades of TPEs have been developed using the Advanced Polymer Analyzer with parallel plate dies. Also this paper explores the advantages of different sample preparation techniques.