Preparation And Properties Of Surface Organic Modified LDHs/Bitumen Composites

Bitumen and styrene-butadiene-styrene block copolymer(SBS)modified bitumen have been widely used in road construction because of their outstanding road performance.However,like other organics,bitumen and SBS are vulnerable to aging when exposed to ultraviolet(UV)light,heat,oxygen,which leads to the degradation of the physical and rheological properties of bituminous pavement and results in the shortening of the service life of pavement.Therefore,the improvement of the ageing resistance of bitumen and SBS modified bitumen is particularly important for the prolongation of the service life of bituminous pavement.Due to the excellent physical reflection to UV light,oxygen and heat,layered double hydroxides(LDHs)have been applied to improve the ageing resistance of bitumen and SBS modified bitumen in recent years,but LDHs(strongly hydrophilic inorganic nonmetal powders)have difficulty in dispersing uniformly in the hydrophobic,which severely affects the sufficient utilization of the ageing resistance of LDHs.In order to obtain the outstanding anti-aging performance and storage stability of LDHs modified bitumen and LDHs/SBS composite modified bitumen,silane coupling agents have been used to surface modify LDHs to improve the dispersibility and stability of LDHs in bitumen.Moreover,surface organic LDHs and SBS composite is prepared by mechanical blending to improve the dispersibility and stability of LDHs in SBS modified bitumen.Three kinds of different long-chain silane coupling agents with different functional groups: Vinyl Triethoxy Silane(TEVS),γ-Aminopropyltriethoxy Silane(KH550),γ-(2,3-Epoxypropoxy)propyltrimethoxy Silane(KH560)are used to prepare surface organic modified LDHs,the preparation of surface organic modified LDHs/SBS composite is through mechanical blending.The composition and structure of surface organic modified LDHs and LDHs/SBS composite were characterized and analysed by fourier transform infrared(FTIR)spectroscopy,X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),scanning electron microscopy(SEM).Then,surface organic LDHs modfied bitumen and LDHs/SBS composite modifed biutimen were preapred by melt blending,the effect of surface organic LDHs and LDHs/SBS composite on the compatibility,physical and rheological properties of bitumen before and after ageingwas thoroughly investigated.Thin-Layer Chromatography with Flame Ionization Detection(TLC-FID),FTIR,Atomic Force Microscopy(AFM)were applied to study the chemical composition and structure,microstructure of surface organic LDHs and LDHs/SBS composite modified bitumen,which was explored to the action mechanism on the improvement of anti-ultraviolet aging of bitumen.Based on the experimental results,the following conclusions can be made:(1)FTIR、XPS show that,three kinds of silane coupling agents have been grafted onto the surface of LDHs through chemical bonds,the resukt of XRD and SEM show that silane coupling agents surface organic modification has no effects on the crystal structure of LDHs and the aggregation state of LDHs have been reduced.Contact angle and SEM tests shows that the surface hydrophilicity of LDHs has been reduced after surface organic modification.Ultraviolet and visible spectrophotometry indicates that the UV absorption ability of surface organic LDHs has been improved,and the physical reflection to UV light of LDHs has been enhanced to some extent after surface organic modification.(2)Surface organic modified LDHs did not exhibit obvious settlement during the thermal storage,which had excellent compatibility in bitumen.The compatibility of surface organic modified LDHs in bitumen depended on the chemistry structure of silane coupling agents: the longer the molecualr chain and the smaller the polarity of silane coupling agents,the better compatibility of surface organic modified LDHs in bitumen.(3)Compared with LDHs,surface organic LDHs have improved the anti-thermal oxidative aging and anti-UV aging of bitumen,the better the compatibility of surface organic LDHs in bitumen,the more obvious promotion on anti-the thermal ageing and anti-UV ageing of bitumen,the order of the improvenent effect of surface organic LDHs on the ageing resistance of bitumen was: KH560 surface organic LDHs(KH560-LDHs)> TEVS surface organic LDHs(TEVS-LDHs)> KH550 surface organic LDHs(KH550-LDHs).The result of FTIR shows that the addition of surface organic LDHs in bitumen reduced significantly the generation of oxygen containing functional groups during the ageing,FTC-FID indicates that surface orgainc modified LDHs inhibited the changing of colloidal structure of bitumen from sol-gel structure to gel structure,weakened the association of dispersion phase in bitumen,prevented theconversion single phase of bitumen after UV ageing.(4)SEM implies that surface organic modification improves the dispersibility of LDHs in SBS.FTIR and XPS show that that the interaction mechanism between surface organic LDHs and SBS was different: the connect between TEVS-LDHs or KH550-LDHs and SBS was through chemical bonds,as for KH560-LDHs was through chain entanglement.(5)The compatibility of SBS and LDHs in bitumen have been enhanced after the recombination between surface organic LDHs and SBS,surface organic LDHs/SBS composite reduced the the separation of LDHs and SBS in bitumen,improved the stability network structure of SBS in bitumen.The addition of surface organic LDHs/SBS composite improved the low-temperature flexibility and high-temperature anti-deforming of bitumen.(6)The tests of physical and rheological property before and after ageing show that the anti-thermal oxidative aging and anti-UV aging of bitumen have been enhanced.FTIR indicates that the addition of surface organic LDHs in SBS modified bitumen reduced significantly the generation of oxygen containing functional groups and the decrease of carbon-carbon double bond.AFM indicates that the addition of surface organic LDHs/SBS composite effectively restrained the conversion of bitumen from sol-gel structure(two-phase structure)to Sol-gel structure(single phase),improved the UV ageing resistance of bitumen.