The Drying-induced Capsulation Phenomenon Of Cyclopentanone In Water Pickering Emulsion Stabilized By Alkali Lignin Particles And Its Application

Alkali lignin is derived from pulping and papermaking waste liquid,with abundant output and low price.The molecule contains functional groups such as methoxy,phenolic hydroxyl,alcoholic hydroxyl,carboxyl,benzene ring,etc.,so it has anti-photolysis performance and certain surface activity.And it is suitable for the preparation of microcapsules.Using alkali lignin to prepare Pickering emulsion and further preparing microcapsules can not only overcome the limitation of poor water solubility of alkali lignin,but also make it become a part of the capsule shell with excellent anti-photolysis performance.We have found in our experiments that the Pickering emulsion prepared by alkali lignin particles and cyclopentanone can form lignin microcapsules after drying.However,there is no research and application report on this aspect.In this paper,the effect of physicochemical properties of four solid particles on the formation of microcapsules after emulsion drying were discussed,and the mechanism of microcapsule formation after drying of cyclopentanone in water Pickering emulsion which stabilized by lignin particles was revealed.The effects of emulsion components and process conditions on the formation of alkali lignin microcapsules were investigated.The alkali lignin microcapsules produced by Pickering emulsion drying were further applied to encapsulate easily photolytic pesticide avermectin(AVM),and their application performance were studied.In order to solve the problem of poor encapsulation performance of the emulsion after heat storage,alkali lignin / silica composite microcapsules were prepared by using Pickering emulsion as template.The main findings of this paper are as follows:(1)Four kinds of particles with different physicochemical properties(alkali lignin,silica,titanium dioxide,chitosan)emulsified cyclopentanone respectively to form oil-in-water Pickering emulsion.It was found that the emulsion stabilized by alkali lignin particles could form microcapsules with size of 1?2 ?m and shell thickness of 130 nm after drying.According to the good solubility of alkali lignin in cyclopentanone,the alkali lignin was dissolved in cyclopentane as oil phase and four kinds of particles emulsified oil phase to form Pickering emulsion,the emulsion condition and the formation of microcapsule after emulsion drying were further studied.The emulsions stabilized by silica and alkali lignin particles could form microcapsules after drying,and the shell of microcapsules was composed of alkali lignin.Based on these,the mechanism of microcapsule formation after emulsion drying was proposed: in the Pickering emulsion system,alkali lignin particles are adsorbed on the cyclopentanone/water interface to form a stable emulsion.While the alkali lignin particles at oil-water interface are partially dissolved in cyclopentanone,and the undissolved particles act as templates.During the process of emulsion drying,along with the volatilization of the oil phase the dissolved alkali lignin precipitates to the interface of the emulsion droplets and microcapsules thus form.(2)The influence of the polarity of the oil phase and the hydrophobicity of the alkali lignin on the formation of microcapsule after emulsion drying was studied,by mixing n-butanol with ethyl acetate as oil phase and changing the hydrophilicity or hydrophobicity of alkali lignin particles.It was found that,when the volume ratio of n-butanol to ethyl acetate was 1:9,the emulsion could form microcapsules after drying.Besides,enhancing the hydrophilicity of alkali lignin particles was not conducive to the formation of microcapsule after emulsion drying.It showed that the polarity of oil phase should match the hydrophilicity of lignin particles.That is to say,only when the oil phase has good solubility for alkali lignin,and the three-phase contact angle of lignin particles/oil phase/water turns out to be about 90°,emulsion can be dried to form microcapsules.Under the conditions which the oil-water ratio is 5:5?1:9,the pH of the water phase is about 4?6,and the concentration of alkali lignin particles is greater than 0.1wt%,lignin microcapsules with good morphology can be obtained after drying of emulsion that forms by hand shaking,homogenizing or ultrasonic treatment.(3)The cyclopentanone in water Pickering emulsion stabilized by alkali lignin particles was tested for dilution and storage stability.The results showed that the emulsion had better stability after dilution and cold storage,and could form microcapsules after emulsion drying.After heat storage the stability of emulsion became poor,and could not form microcapsules after emulsion drying.When Pickering emulsion was used to encapsulate AVM,the synergistic crystallization of AVM could enhance the heat storage stability and the effect of microencapsulation.The encapsulation efficiency of the alkaline lignin microcapsules formed by drying of Pickering emulsion for AVM was 90.8%,and the drug loading was 47.5%.The release rate of AVM in the microcapsule was only 4.1% after 120 h in the sustained-release medium.With the increase of pH value of sustained-release medium,the sustained-release rate of AVM in microcapsules also increased.The remaining rate of AVM in the microcapsules was39.7% after 60 h of anti-photolysis experiment.It showed that the alkali lignin microcapsule has a good protection on photosensitive pesticides.(4)The cyclopentanone in water Pickering emulsion stabilized by alkali lignin particles could not form microcapsules after heat storage.In order to solve this problem,a silica layer was a layer of silica was synthesized on the inner shell of the emulsion by using Pickering emulsion as template,ethyl orthosilicate(TEOS)was hydrolyzed and condensed in the emulsion.And the alkali lignin / silica composite microcapsules could be formed by drying emulsion.The optimal preparation conditions for the silica capsule shell were: pH value was3.5,the ratio of cyclopentanone to TEOS was 9:1,and stirring was performed at 800 rpm for 4h.The alkali lignin / silica composite microcapsules have a thicker shell is 330 nm,and it was200 nm thicker than alkali lignin microcapsules.