Study Onquaternary Ammonium Salt/Chitosan Composite Used As Emusifier For Asphalt

Cationic asphalt emulsion is widely used in road construction because of its low construction temperature,low VOC（volatile organic compounds）,low cost and excellent adhesion.The key factor determining the quality of asphalt emulsion is emulsifier.At present,small molecule quaternary ammonium salt emulsifiers are the most widely used and studied,while single small molecule emulsifiers are limited in many aspects.Therefore,this paper explored the combination of chitosan（CTS）and small molecular quaternary ammonium salt emulsifier.The synergistic effect of Chitosan on small molecular quaternary ammonium salt was based on its large molecular weight,many active sites and controllable characteristics.During the experiment,we studied the interaction between them with the help of computer simulation,and combined with the macro experimental results to explore the interaction mechanism of the two.2,3-epoxy propyl dimethyl octadecyl ammonium chloride（2,3-EDOAC）was synthesized from epichlorohydrin and N,N-dimethyl octadecylamine.The structure of the product was characterized by fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance（¹H-NMR）.In addition,it was combined with CTS to form complex 2,3-EDOAC/CTS.Secondly,octadecyl trimethyl ammonium chloride（1831）and CTS were selected to form another complex 1831/CTS.The above two complexes were used to emulsify asphalt respectively,and the effects of complex ratio and p H value on the surface activity of emulsifier were explored.The particle size,Zeta potential,apparent viscosity and stability of the asphalt emulsion were characterized,and the industrial parameters of asphalt emulsions were tested according to the industry regulations.The results showed that 2,3-EDOAC/CTS complex exhibited excellent surface activity.But CMC andγ_cmcwere lower than the corresponding value of single 2,3-EDOAC.At the same time,the complex had good emulsification effect on asphalt,the emulsion was fine and the color was brown.The mass ratio and p H value of the mixture had great influence on the interfacial film strength,particle size and apparent viscosity of the asphalt emulsions.The results of mixing experiments with aggregate showed that the demulsification speed of asphalt emulsion can be controlled with the p H value of the system and the mass ratio of the mixture.For 1831/CTS composite system,the addition of CTS had little effect on the interfacial tension;the ratio of 1831/CTS had almost no effect on the interfacial film strength of asphalt emulsion.The ratio of 1831/CTS had a certain effect on the particle size of emulsion.In this composite system,the most significant role of CTS was to increase the apparent viscosity of the system.The results of mixing experiments with aggregate showed that the breaking speed of asphalt emulsion did not change with changing the total dosage and p H of the complexes.Through quantitative calculation,the configuration optimization and energy calculation of CTS,2,3-EDOAC and their complexes were carried out by using density functional theory（DFT）.The results showed that there were many hydroxyl-hydroxyl and hydroxyl-amino hydrogen bonds in the complexes system of CTS and 2,3-EDOAC.There were Van der Waals effect and cage effect between the interfaces of the two monomers.The combined action of these factors reduced the energy of the complexes system and maintained its stability.