Study On Preparation Of HCNFs/SiO₂ Dual-phase Nanofiller And Its Application In Reinforcing Natural Rubber

In order to fight with the energy and environmental crisis and solve the technical bottleneck problem of how to improve the combination properties such as abrasion resistance,wet-skid resistance and low rolling resistance of traditional tires at the same time,more and more researchers from around the world is stepping up the research and development of new fillers for green tires.Helical carbon nanofibers（HCNFs）have become a promising new type of filler due to its special carbon helical structure,but it is still difficult to make a breakthrough of rubber reinforcement performance for any single carbon-based filler.Therefore,a novel kind of HCNFs/SiO₂ dual-phase nanofiller can be designed specially and then prepared controllably by using the technology of"heat treatment modification in-situ grafting".In this study,it is focused on discussing the influence of synthesis temperature,TEOS dosage,ammonia dosage and other process parameters on the synthesis of HCNFs/SiO₂ and further exploring the preparation mechanism of HCNFs/SiO₂.On this basis,HCNFs/SiO₂ dual-phase nanofiller was used for reinforcing natural rubber（NR）with addition of carbon black N330.The microscopic morphology,macroscopic mechanical properties,dynamic mechanical properties,bound rubber content,swelling index and other characterization analysis of the rubber composites were carried out.At last,the reinforcing mechanism of HCNFs/SiO₂ dual-phase nanofiller was revealed,by comparing the difference of HCNFs/SiO₂,HCNFs and N330 filler system in reinforcing NR.The results from the preparation of HCNFs/SiO₂ dual-phase nanofiller shows that HCNFs/SiO₂ with uniform distribution of silica nanoparticles（about 30⁴0 nm）on the surface of carbon helix was successfully prepared under the condition of synthesis temperature at 80°C,the dosage of TEOS and ammonia at 0.4 mL and 12 mL,respectively.Compared with the acidification modification grafting method and two-step modification grafting method,the heat treatment modification in-situ grafting method has the advantages of controllable synthesis without usage of acid,high preparation efficiency and environmentally-friendly process.Heat treatment modification is the crucial step of in-situ grafting and growing silica nanoparticles,which can effectively make a transformation of HCNFs from amorphous structure to incomplete graphite structure and thus provide a large number ofπbond active growth points for in-situ growth of silica nanoparticles on the surface of HCNFs.By optimizing the parameters of synthesis temperature,the dosage of TEOS and ammonia,the O-H…πabsorption reaction can take place between the hydroxyl in Si（OH）₄ and theπbond in the partially graphitized HCNFs,and then the polycondensation reaction of Si（OH）₄ occurs on the surface of HCNFs,resulting in the in-situ growth of silica nanoparticles.The results from natural rubber reinforced by HCNFs/SiO₂ dual-phase nanofiller shows that the addition of HCNFs/SiO₂ can simultaneously improve the modulus at300%strain,abrasive resistance,tensile strength,elongation at break and wet slip resistance,and reduce rolling resistance of vulcanizates,compared with N330 standard reference sample.This is mainly due to the fact that the complex filler network structures such as carbon black-carbon black,carbon black-HCNFs,carbon black-silica and HCNFs-silica can be formed in HCNFs/SiO₂-NR composite materials,showing the excellent reinforcement efficiency.Here,HCNFs and silica nanoparticles can play the outstanding role in improving rigid reinforcement of carbon filler and wet slip resistance of silica filler through chemical and physical adsorption by virtue of their abundant surface chemical functional groups.Moreover,an extra reinforcing effect can also be obtained by carbon helix and their protruding structure entangling more rubber molecular chains and preventing the premature fracture of vulcanized rubber.