Impacts of filler covalent and non-covalent modification on the network structure and mechanical properties of carbon-silica dual phase filler/natural rubber

The carbon-silica dual phase filler (CSDPF) was modified by bis (3-triethoxy-silylpropyl) tetrasulphane (Si69) and 1-allyl-3-methyl-imidazolium chloride (AMI), respectively. The natural rubber (NR) vulcanizates filled with modified CSDPF were fabricated through mechanical mixing followed by a high-temperature cure process. The impacts of filler surface modification on the curing characters, crosslinked junctions, network structure, and mechanical properties of NR vulcanizates were investigated. The results showed that the Si69 interacted with CSDPF through covalent bond, while the interaction between AMI and CSDPF was hydrogen bond. Both modifications increased the cure rate of CSDPF/NR compounds as well as the crosslinked degree, compared with those of pristine CSDPF/NR compound. The modifications improved the dispersion of CSDPF in NR matrix. The covalent modification by Si69 caused a limited movement of NR chains in the CSDPF surface, which contributed to a greater tensile modulus of Si69-modified CSDPF/NR. However, the higher content of mono-sulfidic crosslink and the poorer content of strain-induced crystallization in the NR matrix led to a slight increase of tensile strength and tear strength of Si69-modified CSDPF/NR, compared with those of CSDPF/NR. The tensile modulus of AMI-modified CSDPF/NR had a lower value due to a faster polymer chain motion on the CSDPF surface. However, the tensile and tear strength of AMI-modified CSDPF/NR increased significantly because of the increase of mono-sulfidic crosslink, strain-induced crystallization, and the existed hydrogen bond between CSDPF and NR.