Dispersion of Pigments in Rubber¹: I—Microscopical Studies of Agglomeration and Flocculation

Dispersion of Pigments in Rubber—II

“…When rubber was heated with carbon black alone, there was a considerable flocculation of the pigment even though no sulfur was present due to an increased mobility of the rubber. The resin crystals had a great adsorptive tendency towards the carbon-black particles and frequently acted as nuclei for aggregates, as was shown in a previous paper (10). The formation of crystals from the free sulfur was considerably inhibited by the carbon-black particles, this probably being partly due to their adsorptive capacity toward sulfur and partly because they fill up the rubber matrix forming a close network, which prevents the formation of large sulfur crystals in the rubber.…”

“…From a dispersion point of view the presence of the small rhombic crystals is advisable. The large sulfur particles when melting usually produce an aggregation of adherent carbon-black particles as has been shown in a previous paper (10). After the heating is discontinued, a crystallization of free sulfur takes place at different lengths of time, depending on the compounding ingredients used.…”

“…The particle size of the pigment as dispersed in rubber is not necessarily the same as individual or primary particle size. In a previous paper (10) it has been shown that it is possible to distinguish between different types of black from the degree of pigmentation of a mixture of rubber and carbon black, containing 0.5 per cent of pigment. This method, however, gives an indication of the dispersability of the black but not of the ultimate particle size.…”

Glass-like Signatures in the Dynamic Rheology of Particle-Filled Polymers

“…At that time, carbon black flocculation was already presumed to mainly occur during the initial phase of vulcanization before the onset of crosslinking when the mobility of the rubber is at its highest. Evidence of the influence of carbon black morphology on the tendency of the filler to flocculate on heating the rubber was also reported . Almost a century after these pioneering studies, a unified understanding of the physics driving filler flocculation in rubber is still to be proposed and remains a topic of high interest for the rubber scientific community.…”