Modification Of Rice Husk Based Silica-carbon Composites By Ethanol-assisted Milling Method And Their Rubber Reinforcing Properties

Rubber is an important industrial material that has a wide range of applications due to its excellent properties.Carbon black and white carbon black(silica)are the two traditional reinforcing fillers in the rubber industry,but they are non-renewable materials.With the increase of environmental pressure,it is urgent to find an alternative renewable material.Rice husk ash(RHA)is the main product of renewable biomass rice husks pyrolysis.Silica carbon black(SiCB,silica to carbon mass ratio of 43:57)and white rice husk ash(WRHA,silica content>90 wt%)can be obtained by controlling the pyrolysis conditions,which have the potential to replace carbon black and silica as reinforcing filler.However,the insufficient particle size and surface activity of RHA lead to poor dispersion in the rubber matrix,and it is difficult to form a strong interaction with the rubber matrix.Therefore,in order to improve the application value of RHA in the rubber industry,it is necessary to modify the surface of RHA to improve its reinforcing performance.In this paper,rice husk based silica-carbon composites(SiCB and WRHA)were used as reinforcing fillers for rubber.The surface of SiCB and WRHA were treated by ethanol-assisted milling to promote the grafting reaction of bis[?-(triethoxysilyl)propyl]-tetrasulfide(Si69),modified SiCB and WRHA were prepared to improve the compatibility between filler and rubber matrix.The effects of ethanol-assisted milling on the physicochemical properties of SiCB and WRHA and the grafting of Si69 were investigated,and the mechanical properties of the modified SiCB and WRHA filler vulcanizates were tested.The results are as follows:1.The biochar surface of SiCB was modified by ethanol-assisted milling to improve its surface activity.It was found that ethanol-assisted milling not only produced smaller and uniform SiCB particles,but also increased oxygen-containing groups on the surface of biochar.The oxygen-containing groups promoted the grafting reaction of Si69 on the surface of SiCB.Si69 acted as a molecular bridge between SiCB and natural rubber,improving the compatibility between SiCB and natural rubber,thus improving the mechanical properties of SiCB filled vulcanizates.Si69-grafted SiCB(S/E-3)filled natural rubber S/E-3/NR has the optimal mechanical properties.Compared with SiCB filled natural rubber SiCB/NR,the tensile strength,tear strength,and stress at 300% strain of S/E-3/NR increased from16.17 MPa,37.80 k N/m,and 3.05 MPa to 23.36 MPa,45.05 k N/m,and 3.86 MPa,respectively.The tensile strength and tear strength of S/E-3/NR were higher than that of the commercial carbon black(N774)filled natural rubber N774/NR,indicating that the reinforcing effect was similar to that of N774.2.Surface hydroxylated WRHA was obtained using the method of ethanol-assisted milling,and the generated hydroxyl groups promoted the graft modification of Si69.The surface of the modified WRHA changed from hydrophilicity to hydrophobicity,which improved the compatibility with the hydrophobic rubber matrix,thereby enhancing the ability to reinforce natural rubber/butadiene rubber.Compared with WRHA filled natural rubber/butadiene rubber WRHA/NR/BR,the tensile strength,tear strength,and stress at 300% strain of modified WRHA(W/E-3)filled natural rubber/butadiene rubber W/E-3/NR/BR increased from 1.84 MPa,13.37 k N/m,and 1.56 MPa to 7.75 MPa,34.71 k N/m,and3.03 MPa,respectively.In addition,the tensile strength and tear strength of W/E-3/NR/BR were higher than that of N774 filled natural rubber/butadiene rubber N774/NR/BR,indicating that W/E-3 has the potential to replace N774 as a reinforcing filler in the rubber industry.3.Ethanol-assisted milling was not only to modify the biochar surface of SiCB,but also promoted the grafting modification of Si69 on the surface of WRHA.The interaction between the filler and the rubber matrix was enhanced by the modified SiCB and WRHA,and the mechanical properties have reached the reinforcing effect of N774.Therefore,the modified rice husk based silica-carbon composites by ethanol-assisted milling method can be used to replace the commercial carbon black,which is important for the effective utilization of RHA and the sustainable development of the rubber industry.