Preparation And Performance Of Rice Husk-based Hybrid Filler/rubbers Composites

Rice husk is a readily available,abundant,and renewable biomass resource with a unique lignocellulosic/silica structure.The utilization of rice husk has been paid more and more attention by scientists.However,many utilization methods only focus on using rice husk as the source material of carbon or silicon material,ignoring the unique microstructure of rice husk.In the previous work,we had prepared the biochar/silica hybrid filler silica carbon black（Silica-Carbon Black,SiCB）from rice husk and applied it as a reinforcing filler.SiCB has shown good performance in rubber reinforcement,however,SiCB has the disadvantages of large particle size and low surface activity,which limit SiCB to improve the mechanical properties of rubber.Therefore,it is important to find a suitable method to modify SiCB,overcome the existing shortcomings,enhance the reinforcing performance,and improve the application value of SiCB.When the filled rubber material is subjected to repeated mechanical strain load,stress softening occurs due to the viscoelastic characteristics of the rubber and the inelastic behavior caused by filler,which affects the performance of the material.Therefore,confirming how to evaluate"failure"and finding effective methods to suppress the performance degradation have become the basic works of the design and application of new materials.Therefore,the systematic study on the stress softening of SiCB-filled vulcanized rubber is a theoretical basis for the further application of SiCB.In addition,natural rubber（NR）is an excellent insulating material.The special dual-phase structure SiCB endows it with rich interfaces,and the special structure of rice husk could provide permanent dipole.So,SiCB-filled natural rubber are expected to obtain excellent dielectric properties.Therefore,it is of great value to study the influence of SiCB on the dielectric properties of natural rubber for expanding the application field of SiCB.Based on the above results,we carry out the research work of this paper.Firstly,SiCB was modified by combining ball milling and chemical surface modification,and the mechanical properties and viscoelastic properties of the modified SiCB filled vulcanized rubber were tested.Then,the influence of filler size and crosslinking degree of polymers on the Mullins effect in SiCB-filled rubber composites was systematically investigated by adjusting the crosslinking degree of the matrix via adding maleic anhydride into a rubber matrix and controlling the particle size of the filler via ball milling.Finally,the influence of SiCB’s unique hybrid structure on the dielectric properties of natural rubber also was investigated.The main results were showed as follows:1.The particle size of SiCB was decreased from 25μm to about 10μm by ball milling,the surface activity of milled-SiCB was improved by phenolic formaldehyde resin（PF）melting blending.FTIR results showed that there were active groups belonging to PF in the modified samples.The modified samples were used as filler to prepare NR/BR composites and mechanical properties were tested.The results showed that MS/P-90 sample had the best reinforcing performance and the tensile strength of NR/BR-MS/P-90 reached 8.37 MPa,which was even higher than that of NR/BR-N774（6.67 MPa）,implying the reasonable modification can effectively improve the reinforcing performance of SiCB.2.The energy dissipation during in cyclic loading was used to evaluate the Mullins effect of SiCB filled vulcanized rubber.The energy dissipation can be divided into short-term recoverable part and short-term unrecoverable part,the unrecoverable part can better reflect the degree of Mullins effect.The energy dissipation（D_r）of the filled rubber material during the first loading-reloading process can be approximated as the short-term unrecoverable part.Considering D_r was expected to increase with an increase in W₀,so the ratio of D_r to W₀ was defined as the dissipation factor（?_r）.The value of?_r was used to reflect the stress softening degree of materials:the higher the value of dissipation factor is,the greater the energy dissipation is and the more obvious stress softening is.3.The particle size of SiCB was adjusted by ball milling,and milled SiCB samples with different particle sizes were prepared.NR/BR composites were prepared by filling samples with different particle sizes,and the effect of particle size on the Mullins effect of composites was investigated.The results showed that the dissipation factor had a simple linear relationship with strain:the dissipation factor increases linearly with strain.In addition,when the other conditions were same,the smaller SiCB particle size,the smaller the dissipation factor,the less obvious the Mullins effect.4.A part of natural rubber was grafted with maleic anhydride,and a series of SiCB filled vulcanized rubber materials with different crosslinking densities were prepared.The effect of crosslinking density of vulcanizates on the Mullins effect was studied.The results showed that the dissipation factor has a simple linear relationship with strain:the dissipation factor increases linearly with strain.In addition,when the other conditions were same,the higher the crosslinking density of composites,the smaller the dissipation factor,and the less obvious the Mullins effect.5.The particle size of filler and the crosslinking density of matrix had different effects on the Mullins effect during uniaxial cyclic tensile process.When the conditions were same,the larger particle size,the larger the loss factor and the more obvious the Mullins effect.The higher the crosslinking density,the smaller the loss factor and the less obvious the Mullins effect.It is worth noting that the two factors have different influences on the dissipation factor increased with strain（the slope of?-_mfitting curve）.The filler particle size affects the slope of?-_m fitting curve.However,the crosslinking density affects the?-axis intercept of?-_m fitting curve.In conclusion,the effects of particle size and crosslinking density on the Mullins effect have obvious regularity,so it is feasible to evaluate the Mullins effect based on energy dissipation.6.The physical and chemical properties of SiCB and rice husk ash（RHA,SiO₂content above 98 wt%）were investigated systematically.The results showed that most of the biochar in SiCB was amorphous carbon,but there was also a little graphitization tendency,and Si-O-C bond was observed in XPS.SiCB and RHA were filled into NR respectively,and the effect of filler loading on dielectric properties of NR were investigated.Compared with RHA,SiCB obviously improved the dielectric properties of NR.The dielectric constant at 10² Hz of NR-SiCB-60 composites filled with 60 phr SiCB reached 7.96,which was 2.25 and 2.52 times of NR-RHA-60（3.53）and NR（3.16）,respectively.This showed that the special structure of SiCB can endow excellent dielectric properties to NR.