Application Of Lignin Particles In The Preparation Of Pickering Emulsions And Microcapsules

Lignin is a natural amphiphilic polymer material with rich yield,renewable,non-toxic,biocompatibility and anti-oxidation and ultraviolet absorption,but at present the utilization rate is low.The preparation of Pickering emulsion with lignin particles has the advantages of high flexibility,low cost,non-toxic,renewable and so on,which is helpful to the utilization of industrial lignin resource,but there are few systematic studies at present.In this paper,lignin particles with different wettability were prepared by physical and chemical modification,and the effects of physical and chemical properties of lignin particles on the properties of emulsion were investigated.Furthermore,the preparation of microcapsules by interfacial cross-linking with Pickering emulsion stabilized by lignin particles is a new way to solve the problem of low strength of capsule wall in the preparation of lignin microcapsules.It is a novel research method for efficient utilization of lignin.In this study,alkali lignin was used as raw material to prepare different hydrophobic lignin particles by physical and chemical modification.The effects of physical and chemical properties of lignin particles on the properties of emulsion and stable Pickering emulsion were investigated,under the condition of different concentration of lignin,the polarity of oil phase(cyclohexane and n-decanol)and the volume ratio of oil to water,the lignin particles with different hydrophobicity.The Pickering emulsion prepared by lignin particles was used as template and 1,6-dibromohexane or epichlorohydrin was used as cross-linking agent to cross-link the lignin particles at the interface of the emulsion into capsules under acidic conditions to preparation microcapsule(LMC).The main findings are as follows:(1)Six kinds of lignin particles with different wettability were prepared from alkali lignin,amination modified lignin,microwave assisted carboxymethylation-crosslinking modified lignin,lignin mixed with sodium dodecyl sulfate(SDS)in alkaline condition by acid precipitation method.Their hydrophilicity is as follows: HAH-LPs< LAH-LPs< LPs< LCMCM-LPs< HCMC-LPs< LSNP.The surface charge is as follows: HCMCM-LPs> LSNP> LCMCM-LPs> LPs> LAH-LPs> HAH-LPs.When pH= 4,the three-phase contact angle of lignin particles at the interface between decanol and water is generally higher than that at the interface of cyclohexane and water.The wettability of HAH-LPs and HCMCM-LPs at the oil-water interface is the worst and the best,respectively.(2)The emulsion size increased with the increase of oil-water ratio,and the decrease of lignin particles.Increasing the concentration of lignin and reducing the particle size of lignin can improve the emulsification performance.At a certain oil-water ratio,the closer the three-phase contact angle of lignin particles(except LSNP)in the oil-water interface is to 90°,the smaller the particle size of the emulsion is,and the stronger the emulsifying ability of the lignin particle is.When the three-phase contact angle of the oil-water interface is too large,lignin particles can not form stable emulsion.When pH= 4,increasing the surface charge of lignin particles,the stability of the emulsion can be improved.(3)When the oil-water ratio is less than 5:5,six kinds of lignin particles have strong emulsifying ability to cyclohexane with weak polarity,but only the lignin particles with high hydrophilicity and high electric charge can emulsify decanol with stronger polarity.When the oil-water ratio is moderate,the hydrophilicity and electrical conductivity of lignin particles are enhanced,which is not conducive to emulsifying cyclohexane.(4)When using 1,6-dibromohexane as cross-linking agent to prepare lignin microcapsules using cyclohexanone in water Pickering emulsion prepared by lignin particles as template,the optimal reaction conditions were as follows: the concentration of lignin particles in aqueous phase was 2%,the ratio of oil to water is 2:8,the amount of cross-linking agent is 70% of lignin,and the crosslinking temperature is 55 ?.When epichlorohydrin is used as crosslinking agent,the ratio of oil to water is 2:8,the amount of cross-linking agent is 90% of lignin,and the crosslinking temperature is 65 ?.(5)Compared with the wall of microcapsules prepared by crosslinked lignin particles with 1,6-dibromohexane,the wall of microcapsules prepared by crosslinked lignin particles with epichlorohydrin was more loose and thinner,which need higher reaction temperature and more amount of crosslinking agent.Under the same conditions,the encapsulation ability of LMC prepared with 1,6-dibromohexane as cross-linking agent was stronger and the encapsulation effect was better.(6)The entrapment efficiency of AVM@LMC(1,6-dibromohexane)and AVM@LMC(epichlorohydrin)to AVM was 61.2% and 76.4% respectively,and the drug loading was 11.2% and 20.6% respectively.The cumulative release amounts of AVM@LMC(1,6-dibromohexane)and AVM@LMC(epichlorohydrin)were respectively 78.4% and 85.7% after 48 h release in acetone / water sustained release system.And the effective retention rates were respectively 93.7% and 88.9%.