6 - Mechanochemistry of natural rubber during processing

Abstract

Formation of filler agglomerate network structure in filled rubber is discussed in terms of mechanochemical cross-linking, which takes place during mixing. Chain scission during mixing occurs mostly in the agglomerate phase, forming bound rubber that binds aggregates to form filler agglomerate through mechanochemical cross-linking. The amount of bound rubber is found proportional to that of chain scission. Chain scission takes place most vigorously during the filler incorporation stage, and so does bound rubber formation. Consequently, aggregates are wrapped with cross-linked bound rubber as soon as they are incorporated. For them to be dispersed, it is difficult to strip off from agglomerate surface by shear force. Filler dispersion proceeds efficiently when agglomerate is continuous, as in the case of rubbers for practical use, which contain large amounts of carbon black. That is, dispersion in an ordinary commercial rubber compound proceeds through elongation. Elongation causes drawing and thus thinning the agglomerates. Incorporated aggregates stay in the layer of the polymer where they are incorporated. It is deduced that agglomerate network indicates the portions of the polymer which experienced surface where aggregates are incorporated. The agglomerate and the filler-free polymer phases thus become inevitably continuous.