Controllable Preparation,Wall Modification And Performance Of Millimeter-scale Ca-alginate-based Capsules

Encapsulation technology has the advantages of controlling the release of core material,protecting the core material from environmental influences,and properly shielding the odor of the core material.Nowadays,it has been widely used in biological medicine,food and agriculture,construction chemicals and other industrial fields.It has a great influence on the mechanical properties,degradability and permeability of the capsule to choose the wall materials of capsule,so how to choose the wall materials has a key significant on the performance of the capsule.Sodium alginate?SA?,a naturally polymer material obtained from brown algae,has excellent biocompatibility and degradability.It is one of the preferred materials for capsule wall materials.At present,the study of Ca-SA?Ca-alginate?microcapsules as a carrier for controlled release is extensively reported in the field of biomedicine.However,microcapsules is difficult to meet the requirements of large doses and long-term sustained release.Therefore,it is of great practical significance to prepare millimeter-scale capsules.In this paper,Ca-alginate as the main wall material was used to systematically conduct theoretical and theoretical studies on the preparation and processing of millimeter-scaleCa-SA-based capsules,the structure and modification of the capsule wall,and the quantitative relationship between capsule morphology and properties.In this thesis,we firstly studied the operation conditions of capsules.We obtained the millimeter-scaleCa-SA capsules by dropping the sodium carboxymethylcellulose?CMC?/SA solution into Ca²⁺solution.The effects of sodium alginate concentration,calcium chloride concentration,velocity ratio of core and wall solution and gelation time on capsules morphology,diameter,mechanical property and slow release property were investigated systematically.The results showed that capsules having good roundness and ultrathin membranes were successfully prepared by adjusting the technological parameters.The capsules diameter were gradually decreasing with the sodium alginate concentration increasing,while capsules diameter increase with the increasing of calcium chloride concentration and velocity ratio of core and wall solution.The velocity ratio of core and wall solution had significant effect on capsules diameter.The capsules diameter could be controllably adjusted in3.0 mm-4.0 mm.The crush strength of capsules could be enhanced by increasing of membrane thickness and cross-link degree.The release process of B4BD in capsules presented a good fit to first-order release kinetic equation.To improve crush strength of the capsules and meet practical applications,we prepared the capsules by dropping CaCl₂/CMC solution into SA solution and investigated the influence of viscosity of alginate and CaCl₂/CMC solutions on size and shape of Ca-SA capsules.The results showed that the prepared Ca-SA capsules are highly monodisperse,and the average diameter of capsules are about 3.8 mm-4.8mm.As a recommendation,uniform and spherical capsules could be formed when the viscosity of SA solution was 16.2-72.0 mPa·s,the viscosity of CaCl₂/CMC solution was 168.5-917.5 mPa·s,CaCl₂ concentration was 10 g/L,dropping height was 10 cm and dropping velocity was 0.5 mL/min in this study.The capsules was very easy to lost water with its good diffusibility when it was storedinnon-aqueous environment.It could be improved by two methods.One way was to improve the crosslinking density of capsules membraneby adding a second cross-linking agent into the core solution.We prepared the chitosan?CS?/Ca-SA capsules by dropping the CaCl₂/CS solution into SA solution successfully.The structure of the capsules membrane was analyzed by FTIR.The effects of SA concentration and CS concentration on size,shape and weight loss rate of capsules were investigated.The results showed that SA not only reacted with Ca²⁺but also CS.The capsules diameter could be controllably adjusted in 4.2 mm-5.2 mm.Uniform and spherical capsules could be formed when the SA concentration was<0.75 wt.%and the CS concentration were?29?1.25 wt.%.Compared to Ca-SA capsules,the weight loss rate of CS/Ca-SA capsules decreased significantly from 96.17%to 39.34%when the test time was 24 h.The other was to attach barrier materials around the capsules membrane.The polydopamine?PDA?/Ca-SA capsules was obtained via in-situ polymerization of Ca-SA capsules and dopamine hydrochloride.The effect of dopamine hydrochloride concentration and the pH of reaction system on size,shape and weight loss rate of capsules were investigated.The results showed that there were PDA nano-particles on the surface of capsules,the diameter of capsules increased at first,then decreased and its shape didn't change.There were more PDA nano-particles around the capsules membrane when increased the dopamine hydrochloride concentration.Compared to Ca-alginate capsules,the weight loss rate of PDA/Ca-SA capsules decreased significantly from 93.02%to 29.57%when the test time was 24 h.The results showed that capsules with different morphology and properties could be prepared by adjusting preparation process.The water loss and service life of capsules at non-aqueous environment could be improved by the modification of capsules.The millimeter-scale Ca-SA-based capsules have good application prospect in the field of food,medicine,health and textile etc.