The self-assembly of sepiolite and silica fillers for advanced rubber materials: The role of collaborative filler network

Composite materials based on hybrid filler systems can be a promising approach to produce advanced rubber nanocomposites (NCs). Recently, the positive effect of the combined use of silica and sepiolite on NCs mechanical properties has been reported, compared to those of compounds reinforced with the same amount of the only silica filler. In this context, the present work aims at studying the possible synergistic self-assembly of nanosilica and sepiolite in the generation of a cooperative hybrid filler network in rubber-based NCs, in connection with material performance for tires application. In detail, the influence of the introduction of a secondary anisotropic filler in conjunction with isotropic nanosilica on their dispersion and interaction with the rubber matrix has been comprehensively investigated, in order to define the best formulation ensuring low rolling resistance and significant fuel saving. NCs, containing simultaneously silica and sepiolite, either pristine (Sep) or chemically modified (mSep) by an acid treatment, were prepared by combining latex compounding technique (LCT) and melt blending. Rheological and dynamic-mechanical analyses highlighted that the use of a double white filler, constituted by particles with different aspect ratio, affords a good balance between efficient reinforcement and low Payne effect. Tansmission electron microscope (TEM) analysis evidenced the formation, within the rubber matrix, of cooperative superstructures due to the self-assembly of sepiolite and silica nanoparticles containing occluded rubber, when the secondary filler is mSep. The peculiar characteristics of mSep, characterized by fibers shorter than Sep and higher surface silanol bonding sites, bring about significant interactions between mSep and silica, which promote self-assembly of the two fillers in a collaborative hybrid network, improving dynamic-mechanical performances. These results, even if related to sepiolite/silica NCs, demonstrate the effective role of the collaborative filler network, based on the hybrid double fillers, able to lend enhanced properties to rubber materials.

Automated summary

Composite materials based on hybrid filler systems, such as silica and sepiolite, have shown promising results in improving the mechanical properties of rubber nanocomposites. This study focused on the synergistic self-assembly of nanosilica and sepiolite in rubber-based nanocomposites, particularly for tire applications. The use of a double white filler, consisting of particles with different aspect ratios, was found to provide a good balance between efficient reinforcement and low rolling resistance. Transmission electron microscope analysis confirmed the formation of cooperative superstructures within the rubber matrix when chemically modified sepiolite was used as the secondary filler, leading to improved dynamic-mechanical performance.