Preparation Of Modified Silica/Carbon Composites Derived From Rice Husks And Its Effects On Properties Of The Natural Rubber Composites

Natural rubber?NR?is an important macromolecule elastic material due to its excellent properties,which is widely used in various fields,especially in the tire industry.Carbon black and silica are the two most commonly used reinforcing fillers in rubber because they can significantly improve the mechanical properties of rubber.However,both carbon black and silica are non-renewable resources with high production costs and high energy consumption.In recent years,with the continuous increase of environmental pressure and the improvement of sustainable development requirements,people have reduced the use of petroleum materials,began to use a large amount of renewable biomass materials,and modified biomass fillers,hoping to replace the traditional reinforcing fillers.Here,silica/carbon composites?SiCB?from rice husks were used as reinforcing fillers for natural rubber.By wet milling,natural rubber latex?NRL?was grafted onto the surface of SiCB treated by different methods including untreated,3-?Trimethoxysilyl?propyl methacrylate?KH570?pretreatment and co-pretreatment of nitric acid and KH570.The modified SiCB was prepared to improve its compatibility with natural rubber.The effects of different pre-treatments and NRL content on the grafting efficiency was investigated,and the mechanical properties of NR/SiCB vulcanizates were tested.The results are as follows:1.The pure SiCB,SiCB treated with KH570 and SiCB treated with nitric acid and KH570 were grafted with NRL?10 wt%of SiCB?,respectively.SiCB_PR10,SiCB_SIR10and SiCB_MR10 were obtained.SiCB_MR10 showed the highest grafting efficiency,and the NRL layer was the most uniform on the surface of the particles.The NR/SiCB vulcanizates were prepared by direct compounding of SiCB particles and NR.The NR/SiCB_MR10 vulcanizate exhibits the best mechanical properties and wear resistance,which presented optimal properties:its tensile strength,300%modulus and elongation at break were 21.55 MPa,4.73 MPa and 1166.61%,respectively.The tear strength reaches 44.38 kN m^-1.Akron abrasion is 0.837 cm³,showing good wear resistance.2.After pretreatment with nitric acid and coupling agent,SiCB was grafted with NRL of different content,and the grafted samples were added into NR as reinforcing fillers to obtain the corresponding vulcanizates.When the grafted NRL is 10%of the mass of SiCB,the obtained sample SiCB_MR10 had the best coating effect,forming a thin and uniform NRL film.It also had the strongest reinforcing effect on natural rubber,and the tensile strength,300%modulus,tear strength and abrasion resistance all reached the optimum;When the NRL content was less than 10%,the SiCB cannot be completely coated by NRL.Therefore,the NRL can not be effectively used as a compatibilizer when the SiCB was filled into rubber,resulting in poor compatibility;When the NRL content exceeded 10 wt%of SiCB,the excess NRL formed the autopolymer,resulting in uneven dispersion of the SiCB in rubber matrix.According to the experimental data,the optimum conditions for the modification can be determined:SiCB was pretreated with nitric acid and KH570,and then grafted with NRL.The proper content of NRL was about 10%of the mass of the treated SiCB.3.For comparison,pure SiCB_P and commercial carbon black?N774?were filled in NR to prepare vulcanizates NR/SiCB_P and NR/N774,respectively.For NR/SiCB_P,its tensile strength,300%modulus and tear strength were 13.38 MPa,3.72 MPa and38.29 kN m^-1,respectively,which were far from the performance difference of NR/N774.The tensile strength,300%modulus and tear strength of NR/SiCB_MR10were 61%,27%and 16%higher than those of NR/SiCB_P,respectively,and the reinforcing effect was similar to that of carbon black?N774?.4.Pure SiCB has poor surface activity and few functional groups.The carbonyl group and hydroxyl group on the surface of SiCB increased greatly by nitric acid oxidation treatment.Then KH570 was grafted onto the surface of SiCB by the condensation reaction between the surface hydroxyl group and silane coupling agent.The terminal C=C group of KH570 and the C=C of NRL underwent radical polymerization to form a stable inorganic-silane-organic network,so NRL can be effectively grafted onto the surface of SiCB.The effectively grafted NRL acted as a compatibilizer between the filler and the matrix,which made effective stress transfer between NR and filler,so the mechanical properties of vulcanizate had been greatly improved.In this paper,modified silica/carbon composites derived from rice husks were prepared and filled in NR,and the reinforcing effect was similar to that of traditional carbon black?N774?.Therefore,as a biomass filler in the rubber industry,the modified SiCB can be used to replace carbon black for economic and ecological reasons.The SiCB exhibits unlimited potential in a variety of engineering applications.