The anisotropic self-assembly effect of silica hairy nanoparticles: toward sustainable rubber nanocomposites for tire application

With the aim of identifying possible strategies to reduce the environmental impact of tires, we propose the use of advanced rubber materials based on silica hairy nanoparticles (HNPs), which consist of a core of silica surrounded by end-grafted rubber chains. The rationale has been to impart unique surface reactivity to silica NPs, which are usually used as reinforcing fillers, for coupling with noncrosslinked host elastomers as well as for the subsequent ability to employ coupling agents other than conventional sulfur-bridged bis-alkoxy silanes. SiO2 HNPs, which have polybutadiene (PB) chains as polymeric brushes, were prepared with different PB grafting density and embedded in elastomers to produce rubber nanocomposites (NCs) following the standard tire formulation but without the use of silane coupling agents. A deep investigation of the relationship between the mechanical properties of the NC materials and the self-assembly of HNPs was performed, revealing a high degree of structural order and a significant percolative HNPs network. In fact, silica HNPs can construct anisotropic energy dissipation structures that act as additional cross-linking junctions, reducing chain relaxation and consequently enhancing chain deformation. The presence of domains of self-assembled fillers induces a reduction in the mobility of the filler and consequently in the energy consumption due to the deformation of the microstructure of the rubber composite, as well as its breakage and subsequent recovery, which are not completely reversible. The reduction of the energy dissipation is supported by both the low Payne effect and tan delta, both of which are strong predictors of the rolling resistance coefficient that determines vehicle energy consumption and CO2 emissions. For this purpose, the present study supports the use of HNPs as reinforcing fillers for producing more sustainable rubber materials.