A new approach to visualizing the carbon black/natural rubber interaction layer in carbon black-filled natural rubber vulcanizates and to elucidating the dependence of mechanical properties on quantitative parameters

The viscoelastic behavior of carbon black (CB)-filled natural rubber (NR) vulcanizates is explained for the first time by applying a two-phase mixing law, excluding the CB phase, to the volume fraction of the CB/NR interaction layer (CNIL). For CB loadings of 20 phr or less, the CNIL of local CB aggregates induces the reinforcement effect of a series mechanical model of the mixing law. In contrast, for CB loadings of 30 phr or more, the CNIL that forms the CB network (CBN) generates the reinforcement effect of a parallel mechanical model of the mixing law. Therefore, the model of the mixing law presumably changes from a series mechanical model before CBN formation to a parallel one after the network forms. Additionally, employing this fraction, a transition caused by CBN formation was investigated.