Inverse Pickering Emulsion Polymerization Using Starch-based Micro/Nanoparticles As The Stabilizer

In traditional emulsions,small-molecule surfactants are used to reduce the interfacial tension between two immiscible liquids and maintain the stability of emulsions.However,molecular surfactants have a number of drawbacks,including high toxicity,high pollution,and difficulty in recovery.When solid particles are used in place of surfactant molecules to stabilize the emulsion,such an emulsion is referred to as a Pickering emulsion,in which the solid particles irreversibly locate at the interface between two phases,forming a rigid shell around the droplets and preventing coagulation.Consequently,the particulate emulsifiers can provide superior stability than conventional surfactant molecules.Moreover,because surfactants are not used in Pickering emulsions,new application prospects are opened up for emulsion,such as drug delivery and fabrication of new functional materials.In this paper,the amphipathic starch-based particles were prepared by copreciptation process using amphipathic groups modified starch ester.Those starch-based particles could adsorb on the interface of oil and water phases to stabilize a w/o Pickering emulsion.Inverse Pickering emulsion polymerization of verisous water-soluble monomer,including N-isopropylacrylamide(NIPAM),acrylamide(AM),acrylic acid(AA)and methacryl oxyethyl trimethyl ammonium chloride(DMC)were carried out to prepare composite particles or water-soluble polymer for drug delivery and flocculation.Finally,the full process of experiment was discussed in detail.There were four parts in this study.1.To improve the hydrophilcity of starch,amphiphilic groups,tosylate and palmitoyl groups,were introduced in acidified corn starch,and the starch-based nanoparticles(SNPs)were prepared by a nanoprecipitation process.The results showed that SNPs could stabilize the water-ethyl acetate emulsion when the degrees of substitution of tosylate and palmitoyl groups and were 0.32 and 1.48.It has been proved that the oil-water volume ratio and SNPs concentration could affect the stability and type of emulsion and the size of emulsion droplets by a large number of experiments.The PNIPAM/SNPs composite particles synthesized by inverse Pickering emulsion polymerization of NIPAM exhibited typical raspberry-like morphology,and presented apparent temperature sensitivity.The polymer particles are promising in the food and pharmaceutical fields.2.Butyl glycidyl ether(BGE)and palmitoyl chloride(PA)were used to improve the emulsifying efficiency of starch.The optimum degree of substitution(DS)of BGE and PA of SNPs for stabilizing the pickering emulsion were 0.65 and 1.42.The size of SNPs prepared by a nanoprecipitation process was about 80 nm.The SNPs could adsorb at the interface of oil and water phases easily for their nanosize,and the emulsions were very stable for slightly aggregation of SNPs.The stable emulsion could be obtained even at a very low concentration of SNPs,0.125 wt%.The emulsion polymerization of was carried out with the oil-water volume ratio of 5:5 and the SNPs concentration of 0.25 wt%.Millimeter-sized hydrogel beads were obtained after polymerization.The pH-responsive and drug release properties of beads were studied.Moreover,the polymerization process and potential formation mechanism of hydrogel beads were investigated in detail.3.Water-soluble P(AM-co-AA)was prepared by inverse Pickering emulsion polymerization stabilized by SNPs without crosslinker.The effects of reaction time,temperature,initiator,monomer content and the mass ratio of AM and AA on resultant polymer molecular weight were studied and the best experiment formula for the polymerization was determinated by setting a series of experiments.Finally,the resultant polymer as flocculants was used to remove cationic dye in wastewater and the application of polymer prepared by inverse Pickering emulsion polymerization was developed in flocculation.4.Generally,solvent evaporation will break the stabilization of emulsion in polymerization process.In order to avoid solvent evaporation,the liquid paraffin with high boiling point and high viscosity was selected as an oil phase to preparation the inverse Pickering emulsion.The stable inverse Pickering emulsion was used for copolymerization of AM and DMC.The different initiator systems were used in the Pickering emulsion polymerizations,and the appropriate one was verified by investigating the morphology and molecular weight of polymers.Moreover,the effects of the mass of initiator,reaction time,temperature,monomer content and the mass ratio of AM and DMC on resultant polymer molecular weight were investigated,and the best formula of polymerization was determinated by simulating bentonite flocculation in wastewater using resultant polymer.