Surface modification of rice husk-based carbon-silica dual-phase filler by ethanol-assisted milling and its reinforcing on natural rubber

Silica carbon black (SiCB) was used as a natural carbon-silica dual-phase filler (CSDPF) containing both biochar and silica, which was obtained by pyrolysis of rice husks. The reinforcing performances of SiCB were limited by the large particle size and poor surface activity. In this work, the size and distribution of the SiCB particles were modified by ethanol-assisted milling (S/E), and increase in oxygen-containing groups enhanced the surface activity of SiCB and promoted the grafting of silane coupling agent (Si69). The filler-rubber interfacial interactions were enhanced when the Si69-grafted SiCB (S/E-X, X means the amount of Si69) was used as filler for natural rubber (NR). Compared with the SiCB-filled NR (SiCB/NR), the S/E-3-filled NR (S/E-3/NR) showed 44%, 19%, and 27% improvement in the tensile strength, tear strength, and stress at 300% strain, respectively, and the reinforcing properties have reached the level of commercial carbon black (N774). This study provides a novel way for surface modification of CSDPF and improves the application of rice husk-based materials in rubber composites.