Probing into why anisotropic nanoclay offers better reinforcement in natural rubber than isotropic nano zinc oxide by determining their interaction with sol and gel fractions

Role of sol–gel interaction with anisotropic nanoclay in raw natural rubber (NR) for offering higher mechanical reinforcement than isotropic nano zinc oxide was reported in this article. Experiments were carried out on four different grades of NR, having equal Mooney viscosity but different gel contents (toluene insoluble fraction), with commercial grades of nanofillers. In raw NR, the green strength was found to be influenced by higher apparent viscosity instead of higher gel content. In unvulcanised nanocomposites, however, the reinforcement was subjected to interaction between the nanofillers and the sol fraction (toluene soluble fraction, major part of the matrix) of NR. The mixing energy was decreased by approximately 2.9% for nanoclay (Cloisite 30B) and 4.4% for nano zinc oxide addition, whereas the gel content has increased upon addition of Cloisite 30B and nano zinc oxide by 12% and 49%, respectively. The ability was found higher with nano zinc oxide due to its isotropic shape and lower overall size than Cloisite 30B. Conversely, higher sol concentration of Cloisite 30B along with higher filler volume fraction offered higher mechanical reinforcement in both high and low gel grades of NR. The fact was established from extensive studies on morphology, filler crystallography, gel content, and viscoelastic responses.