Preparation And Properties Of Lignin Intercalated/grafted LDHs And Their Application In Bitumen Modification

Bituminous materials have been widely used in road construction owing to the excellent road performance.With the ultraviolet light(UV),heat and oxygen,the aging of bitumen would be occurred.Furthermore,the service life of bituminous pavement could be affected.In order to prolong the service life of bituminous road,it is crucial to improve the aging resistance of bitumen.Layered double hydroxyl compound metal hydroxides(LDHs),which has been an excellent physical barrier to ultraviolet ray,could be applied to improve the anti-aging ability of bitumen recently.However,with the strong hydrophilicity,LDHs have poor compatibility with bitumen,and it is hard for them to disperse in bitumen well.Some problems such as the thermal storage and transportation process in the bitumen reduce the effect of LDHs on the improvement of the bituminous aging resistance.Lignin materials have more hydrophobic structure and better compatibility with organic materials.In addition,the unique aromatic ring structure of lignin materials could effectively absorb ultraviolet radiation well.Meanwhile,the hindered phenol structure of lignin materials could effectively capture free radicals generated in the process of thermal and photooxidative aging,so that the thermal and oxidative aging resistance of the materials could be enhanced.The chemical combination of LDHs and lignin could not only improve the compatibility between LDHs and bitumen,but also significantly improve the thermal and photo-oxidative aging resistance of LDHs modified bitumen.In this paper,the lignin and sodium lignin sulfonate(LS)were chosen,through intercalating/grafting methods to modify LDHs.Lignosulfonate intercalated LDHs(LSc-LDHs),lignin grafted LDHs(LG-g-LDHs)and lignosulfonate grafted LDHs(LS-gLDHs)had been prepared.Through infrared spectrometer(FTIR),X-ray diffraction(XRD),UV-vis spectrophotometer(UV-vis)and field emission scanning electron microscope(SEM)of three kinds of lignin intercalating/grafting LDHs had been used to characterize the chemical composition and structure.To adopt the method of melt blending,LS-c-LDHs modified bitumen(LS-c-LMB),lignin grafted LDHs modified bitumen(LG-g-LMB)and lignosulfonate grafted LDHs modified bitumen(LS-g-LMB)have been obtained.Through the high temperature storage stability experiment,three kinds of lignin intercalating/grafting LDHs modified bitumen were studied.Through the compatible stability of using hot oxygen aging and ultraviolet aging test,three kinds of lignin intercalating/grafting LDHs were investigated in the physical properties of bitumen,hot oxygen and oxygen aging resistance,the components and chemical structures of three kinds of lignin intercalating/grafting LDHs modified bitumen was discussed.Finally,by means of viscosity-temperature curve fitting,dynamic shear rheometer(DSR)test and rheological model establishment,the rheological properties of lignin intercalating/grafting LDHs modified bitumen before and after ultraviolet aging,were investigated.The main conclusions are as follows:(1)FTIR and XRD showed that LS-c-LDHs,LG-g-LDHs and LS-g-LDHs were successfully prepared by intercalation/grafting.SEM and contact Angle test showed that through modification of lignin/LS,reunion reduced between LDHs particles significantly,and LDHs hydrophilic raised from 28.25 °to 76.25,91.50 and 92.00 °.UV-vis analysis showed that LDHs modified by intercalation or grafting of lignin materials not only had good UV physical reflection ability,but also had excellent UV chemical absorption ability.(2)LS-c-LDHs,LG-g-LDHs and LS-g-LDHs could be evenly dispersed in the bitumen by introducing the hydrophobic and oil-wet structure of lignin materials,and obviously reduce the segregation in the process of thermal storage,showing excellent compatibility with bitumen compared to LDHs.Segregation in thermal stability test tube and two pieces of the softening point of difference(Δ S)drops from 1.21 to 0.53 ° C.(3)Compared with LDHs,LS-c-LDHs,LG-g-LDHs and LS-g-LDHs enhanced the anti-aging abilities of bitumen.The better the compatibility of lignin intercalating/grafting LDHs in bitumen is,the better the effect of enhancing the aging resistance of bitumen to thermal oxygen and photo-oxygen is,followed by the effect of improving the aging resistance of asphalt: LG-g-LDHs > LS-g-LDHs > LS-c-LDHs.(4)The addition of lignin intercalating/grafting LDHs increases the complex shear modulus of bitumen and reduced the phase Angle,so that the elastic component of bitumen increased while the viscous component decreases.In addition,the temperature of bitumen increased to some extent when the dominant position of its elastic modulus and viscous modulus changed.After UV aging,the complex shear modulus of bitumen increased significantly,the phase angle decreased rapidly,the elastic component of bitumen increased,the viscous component decreased,and the temperature sensitivity decreased significantly.The addition of lignin intercalating/grafting LDHs into bitumen could effectively retard the effect of UV aging on the rheological behaviors.(5)After UV aging,lignin intercalating/grafting LDHs could inhibit the damage and permanent deformation of high temperature rutting resistance.LG-g-LMB had better photo-oxidation resistance than pristine bitumen,LDHs modified bitumen,lignin modified bitumen and LS-c-LMB.(6)According to the rheologic model analysis,the model of lignin intercalating/grafting LDHs modified bitumen is Burgers from 30 to 60 °C and change to Lethersich model from 70 to 80 °C.The rheological parameters variations and deformation arguments amplitudes of LLMB were lowest among PB,LMB and LLMB,which demonstrated that the anti-aging ability of LLMB was the best.