Stabilization Of Pickering Emulsion Based On Particle Size Fractionation And Physical Modification Of Kaolinite

Pickering emulsion,as an environment-friendly emulsion,has the advantages of long stabilization period and good thermal stability.It has wide application prospects in the fields of food,cosmetics,petroleum and pharmaceutical preparation.Kaolinite has received extensive attention as a Pickering emulsion stabilizer due to its typical layered structure.The physicochemical characteristics of kaolinite particles have an important influence on the stability of Pickering emulsion.This paper studies the settlement of kaolinite by sedimentation,calcination and mechanical ball milling modification to obtain specific Pickering particles,and as an emulsifier to stabilize the paraffin oil / water emulsion system.The modified kaolinite was characterized by laser particle size analyzer,Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),contact angle measuring instrument,Thermal analysis(TG-DSC),Specific Surface Area Analyzer(BET)and field emission scanning electron microscopy(SEM).The emulsion stability and stability mechanism were studied by emulsion static treatment,viscosity and microstructure observation.The following conclusions were obtained:(1)The results showed that the matching characteristics between the kaolinite particle size and the droplet size of the emulsion not only affected the interaction between the emulsifier and the surface of the dispersed phase of the emulsion.Moreover,it affects the characteristics of the network structure formed in the continuous phase while changing the viscosity of the Pickering emulsion,which in turn affects the stability of the emulsion.If the kaolinite particle size is too large or too small,it is not conducive to the stability of the emulsion.The optimum effect of kaolinite particle size on emulsion stability is present.When the particle size D90 of kaolinite is 1.42 ?m,the emulsion viscosity is 378 mPa·S,and the droplet size distribution is 59~210 ?m.The emulsifier particles are closely and orderly distributed at the oil-water interface,and the three-dimensional network structure formed by the particles in the continuous phase tends to be firm.After standing at 25?for 30 days,the residual emulsion phase volume fraction was 58.7%,and the emulsion stability was the best.(2)During the calcination temperature of kaolinite from 350? to 950?,the crystal structure is destroyed,the hydroxyl groups are gradually removed,the surface roughness is increased,and the hydrophobicity is increased.The shape of the obtained emulsion droplets is converted from a spherical shape to an aspherical shape and then converted into a spherical droplet.The kaolinite calcined at 950°C forms a synergistic emulsification with the decomposed spinel and amorphous silica.The emulsion droplet size distribution is 40~204 ?m,the emulsion viscosity is 370 mPa·S,and the residual emulsion phase volume fraction is 58.8% after standing for 30 days at 25°C.The emulsion breaking rate is only 2.5% after 60 days.The emulsion stability is significantly higher than that of the uncalcined kaolinite.(3)The destruction of the internal crystal structure of the mechanical ball-milling modified kaolinite particles causes a change in the morphology of the kaolinite particles,which causes a change in surface roughness and wettability,which in turn affects the strength of the interface film forming the emulsion and the stability of the emulsion.When the kaolinite was ball milled for 24 hours,the layered kaolinite dehydrogenated under the action of ball milling mechanical force,the crystal structure was destroyed,and the specific surface area increased.The kaolinite is transformed from a regular hexagonal or pseudo-hexagonal sheet-like layer structure to a circular sheet or a spheroidal particle structure,and the hydrophobicity of the particles increases the three-dimensional contact angle of the kaolinite to 79.6°.The stable emulsion droplet size distribution is 26~175 ?m,the emulsion droplet size is below 90?m,the ratio is up to 90%,the emulsion viscosity is 452 mPa·S,and the formed emulsion remains at 25? for 30 days.The phase volume fraction is 63.0%,and the demulsification rate is 0% after 60 days.The stability of the emulsion is significantly higher than that of the emulsion which is stabilized by the unmilled kaolinite.