In-situ Polymerization Modification And Packaging Properties Of Millimeter-scale Water-bearing Capsule Wall Materials

Encapsulation technology has the advantages of changing the physical and chemical properties of the active ingredients of the core material,controlling the release of core material and protecting it from the environment.Nowadays,it has been widely used in biomedicine,agriculture,computer,food processing,cosmetics and other fields.Millimeter-scale hollow alginate calcium(Ca-SA)water-bearing capsules has the advantages of simple preparation method,simple operation and uniform and controllable capsule size.Because of its special core shell structure,it has important application value in some specific fields,such as biomedicine,food processing,flavor encapsulation,cosmetics,and tobacco and so on.However,because the semi-permeable envelope of Ca-SA capsule cannot completely prevent the evaporation of water in the internal phase of capsule,the capsule is easy to lose water and collapse in the non-aqueous environment,shortening the service life of the capsule.Therefore,How to suppress the volatilization of water inside the Ca-SA capsules and increase its pot life and storage period is a key issue that needs to be solved urgently.Based on this,millimeter-scale hollow Ca-SA water-bearing capsules with good monodispersion,uniform particle size and good sphericity were prepared by reverse dropping method.The surface modification and packaging of Ca-SA capsules were carried out by in-situ polymerization using polydopamine(PDA),inorganic nanomaterial MWNTs and ethyl cyanoacrylate(ECA).Modified capsules coated with one or more resistivity water layer were prepared.The main research work is as follows:The millimeter-scale hollow Ca-SA water-bearing capsules were prepared by the reverse dropping method,and the PDA was coated on the surface of the capsule by in-situ polymerization to prepare PDA@Ca-SA capsules.The reactivity of DA in different conditions was determined by UV-Vis spectrophotometer.The results show that increasing the concentration of DA,adding strong oxidant SP and choosing alkaline buffer system can improve the reactivity of DA in solution and accelerate the rate of DA polymerization to form PDA.The effects of DA concentration,pH value of the reaction system and the type of oxidant on the morphology,diameter,membrane thickness,sphericity and weight loss rate of the modified capsules were investigated.The results showed that during the reaction,DA was oxidized to form PDA nanoparticles coated on the surface of the capsules,and a uniform PDA coating was formed on the surface of the capsules.In the alkaline buffer,using SP oxidant,the modified capsule prepared with DA concentration of 2 g/L has good monodispersity and sphericity,and the water retention performance is the best.Compared with the unmodified capsule,the time of water evaporation was nearly twice longer.Using the special properties of inorganic nanomaterial MWNTs and the strong adhesion of PDA,the surface modification and modification of Ca-SA capsules were carried out by insitu polymerization.The modified capsules of MWNTs-PDA@Ca-SA were successfully prepared.The effects of concentration and reaction time of MWNTs on capsule appearance,size,sphericity and weight loss rate were investigated.The results showed that during the reaction,DA was oxidized to form PDA nanoparticles attached to the surface of the capsule to form a dense and uniform PDA coating.At the same time,the dispersed inorganic nanomaterial MWNTs in the adsorption solution were coated on the surface of the capsules.Then a uniform inorganic coating was formed on the surface of the capsule,which further delayed the loss of phase water in the capsule.When the concentration of MWNTs was 0.6 g/L or 1.0 g/L,the modified capsule had the best water retention effect.The Ca-SA water-bearing capsules were surface-modified by ECA using in-situ polymerization method,and a PECA polymer was coated on the surface of the capsule to reduce the evaporation rate of the capsule core solution.In this study,the suitable solvents were screened first.The effects of different solvent systems,ECA solutions and reaction time on the appearance,size,sphericity and weight loss rate of modified capsules were investigated.The results show that the suitable solvents satisfy three conditions:(1)the solvents are insoluble in water;(2)the solvents can dissolve ECA solution;(3)the solvents will not destroy the structure of Ca-SA capsules.In the aromatic organic solvent containing benzene ring,the modified capsules prepared with toluene and ethylbenzene as solvent,the dosage of ECA solution is 6 mL and reaction time is 60 min had the better sphericity and the best water retention performance.The weight loss rate in 1 h was 16.1% and 35.5% respectively,while the uncoated capsules were completely lost after 1 h.In the chlorinated alkane organic solvent system,modified capsules with good sphericity can be prepared in dichloromethane,chloroform and carbon tetrachloride.When the dosage of ECA solution is 6 mL and reaction time is 60 minutes,the modified capsule prepared in the carbon tetrachloride solvent system has the best water retention performance,the weight loss rate in 1 h is only 11.83%,which greatly increases its pot life and storage period of the capsule in the non-aqueous environment.