Construction Of Stable Pickering Emulsion Based On Rosin Derivatives And Its Properties

Emulsions stabilized with solid particles as stabilizers instead of surfactants are called Pickering emulsions.In recent years,organic particle-stabilized Pickering emulsions obtained from renewable sources have attracted considerable attention.However,how to develop different types of green and stable Pickering emulsions by facile methods has always been a major challenge.The rosin derivative maleopimaric acid（MPA）has three carboxylic acid groups and can be used to stabilize Pickering emulsions.The wettability of MPA can be changed by adjusting the p H value,thereby obtaining different types of colloidal Pickering emulsions,such as oil-in-water（O/W）,water-in-oil（W/O）,double emulsions,and multiple emulsions.In this thesis,a natural rosin-based solid stabilizer with adjustable wettability is provided,and on this basis,the Pickering emulsion synergistically stabilized by MPA,inorganic nanoparticles and metal ions is studied.The research contents are as follows:1.Separate MPA particle stabilized Pickering emulsion.MPA readily forms O/W Pickering emulsions in the ionic state（p H 2.4-5.4）,while W/O Pickering emulsions form at p H 1.4.Complex Pickering emulsions,such as double or multiple emulsions,appeared during the transition from O/W to W/O as the p H decreased from 5.4 to 1.4.The effects of MPA concentration and oil-water ratio on Pickering emulsion stability,emulsion type and droplet size were mainly studied.The stability of Pickering emulsions under high temperature,freeze-thaw and centrifugation conditions was evaluated.The results show that the formed colloidal Pickering emulsion has good external stimuli and mechanical stability,and can withstand high temperature（70°C）,freeze-thaw treatment and high centrifugal force.The stability mechanism of Pickering emulsions was explained by the measurement of surface and interfacial tension and the characterization of microstructure.Its excellent stability is due to the network structure formed by the self-assembly of MPA with stable interfacial film and heterogeneous ionization degree.2.Pickering emulsion co-stabilized by nano-Al₂O₃ and MPA.The positively charged nano-Al₂O₃ and the negatively charged MPA attract each other in water.When nano-Al₂O₃was added to MPA,the hydrophilic Al₂O₃ adsorbed on the MPA particles led to the increase in the hydrophilicity of the MPA particles,so that the W/O Pickering emulsion could be transformed into an O/W Pickering emulsion（p H=1）.When p H=6,MPA and nano-Al₂O₃have strong hydrophilicity at the same time and cannot form stable emulsions respectively,but the mixed system of the two can form stable W/O Pickering emulsions.This is because MPA and nano-Al₂O₃ can form stable emulsions.It forms a highly hydrophobic complex in aqueous solution.In addition,the effects of MPA concentration and oil phase volume fraction on the appearance and particle size of the emulsion were studied.It was found that the particle size of Pickering emulsion gradually decreased with the increase of MPA concentration.However,increasing the oil phase volume fraction would cause the particle size to increase.Finally,the stabilization mechanism of the stabilized Pickering emulsion was studied using Zeta potential,adsorption rate of particles at the oil-water interface,contact angle and surface/interfacial tension,the armor-like particle layer adsorbed on the oil-water interface and the network structure formed between the particle layers This is why the emulsion droplets remain stable.3.Pickering emulsion co-stabilized by Cu²⁺and MPA.Based on the above research,this chapter further studies the stable Pickering emulsion after metal ions complexed with MPA,and selects Cu²⁺to provide a certain antibacterial property for Pickering emulsion and broaden its application range.Cu²⁺has a strong complexing effect with the carboxyl group in MPA,and the complexed Cu²⁺will not be oxidized and can remain stable for a long time.First,the binding of Cu²⁺to MPA was characterized by XPS and EPS,and the results showed that Cu²⁺was successfully complexed.Then SEM and TEM were used to characterize the microstructure of the complexes,and it was found that MPA still maintained a porous network structure after complexation.Then,the effects of Cu²⁺concentration and oil-water ratio on the stability of Pickering emulsion and the type of emulsion were mainly studied.The stabilization mechanism of the stabilized Pickering emulsions was investigated using microstructure characterization,rheological behavior,contact angle and surface/interfacial tension.It is found that the complexation of MPA with Cu²⁺still has the characteristics of rapid formation of stable interfacial film and self-assembly to form a network structure.The antibacterial effect of MPA complexed with Cu²⁺was measured by Staphylococcus aureus and Escherichia coli.The results showed that the complex has strong bactericidal activity,and the bactericidal activity came from Cu²⁺.This research broadens the application scenarios of Pickering emulsions,such as pesticides,antibacterial paints,environmental protection and new materials.