Method for preparing stiffened capsules

Abstract

The present invention relates to a method for preparing capsules comprising a liquid core, a stiffened intermediate envelope and a gelled external envelope, comprising a step of forming a multi-component liquid drop, a gelification step and a stiffening step. The present invention also relates to a method for preparing capsules comprising a liquid core and a stiffened envelope, comprising a step of forming a multi-component liquid drop, a gelification step, a stiffening step and a depolymerizing step.

Claims

1. A method for preparing capsules, each capsule comprising a liquid core and a stiffened intermediate envelope totally encapsulating at its periphery the liquid core, said method comprising the following steps of: (A) forming a multi-component liquid drop comprising: (1) a liquid core, (2) a liquid intermediate envelope formed with an intermediate composition comprising at least one first reagent R1, totally encapsulating at its periphery the liquid core, and (3) a liquid external envelope formed with an external aqueous composition, different from the intermediate composition, said composition comprising at least one polyelectrolyte different from the first reagent R1 and at least one surfactant, totally encapsulating at its periphery the intermediate envelope, (B) gelling by immersion of said multi-component liquid drop in a gelling solution containing a reagent able to gel the polyelectrolyte of the liquid external envelope, in order to obtain a gelled capsule comprising a gelled external envelope, (C) stiffening the first reagent R1 of the liquid intermediate envelope of the gelled capsule comprising a gelled external envelope obtained in (B), in order to obtain a gelled and stiffened capsule comprising a stiffened intermediate envelope, and (D) recovering said gelled and stiffened capsules.

2. The method according to claim 1, wherein the polyelectrolyte of the external composition is selected from polyelectrolytes which react to multivalent ions.

3. The method according to claim 2, wherein the polyelectrolyte is a sodium alginate.

4. The method according to claim 1, wherein the stiffening step is carried out by coacervation of the first reagent R1 of the liquid intermediate envelope.

5. The method according to claim 4, wherein the stiffening step is carried out by coacervation of the first reagent R1 caused by a variation of the temperature, of the pH, or by electromagnetic radiation.

6. The method according to claim 4, wherein the stiffening step is carried out by coacervation of the first reagent R1 with a multivalent cation.

7. The method according to claim 4, wherein the stiffening step is carried out by coacervation of the first reagent R1 with a second reagent R2, different from the first reagent R1.

8. The method according to claim 7, wherein the first reagent R1 is a hydrophilic anionic polymer and the second reagent R2 is a hydrophilic cationic polymer.

9. The method according to claim 7, wherein the first reagent R1 is a hydrophilic cationic polymer and the second reagent R2 is a hydrophilic anionic polymer.

10. The method according to claim 7, wherein the first reagent is a lipophilic cationic polymer and the second reagent R2 is a hydrophilic anionic polymer.

11. The method according to claim 4, wherein the first reagent R1 is in the form of latex of polymers.

12. The method according to claim 1, further comprising after the stiffening step, a step for depolymerizing the polyelectrolytes in the gelled state of the gelled external envelope, in order to remove the gelled external envelope.

Description

(1) The invention will be better understood upon reading the following, only given as an example, and made with reference to the appended drawings, wherein:

(2) FIG. 1 is a large scale view, in a section along a middle vertical plane of a gelled and stiffened capsule according to the invention; and

(3) FIG. 2 is a large scale view, in a section along a middle vertical plane of a stiffened capsule according to the invention.

(4) A capsule 10 according to the invention comprises a liquid core 20, a stiffened intermediate envelope 30 and a gelled external envelope 40.

(5) A capsule 50 according to the invention comprises a liquid core 20 and a stiffened envelope 60 encapsulating the whole of the outer surface area of the liquid core.

EXAMPLES

Experimental Device

(6) The methods for preparing capsules is based on concentric co-extrusion of compositions via a three envelope device for forming multi-component drops.

(7) A first composition (C1) circulating in a first compartment of a triple envelope forms the first flow.

(8) A second composition (C2) circulating in a second compartment of the triple envelope forms the second flow.

(9) A third composition (C3) circulating in a third compartment of the triple envelope forms the third flow.

(10) Formation of Gelled and Stiffened Capsules

(11) At the exit of the triple case, a multi-component drop is then formed, the first flow forming the liquid core, the second flow forming the liquid intermediate envelope and the third flow forming the liquid external envelope of the multi-component drop.

(12) The size of the liquid core, the thickness of the intermediate envelope and of the external envelope of the form of the capsules are controlled by using several independent pusher syringes, adjusting the injection flow rates of the different compositions C1, C2 and C3.

(13) The flow rate Q1 of composition C1 is adjusted to 10 ml/h.

(14) The flow rate Q2 of the composition C2 is adjusted to 1 ml/h.

(15) The flow rate Q3 of the composition C3 is adjusted to 1 ml/h and may be reduced down to 0.01 ml/h.

(16) Each multi-component drop detaches itself from the triple envelope and falls in a volume of air, before being immersed in a gelling solution of calcium lactate concentrated to 1M.

(17) Once the external envelope is gelled, the formed gelled capsules are rinsed in a rinsing solution based on water, and are then immersed in a stiffening bath.

(18) Formation of Stiffened Capsules

(19) The thereby formed gelled and stiffened capsules are then immersed in a depolarization solution of citrate concentrated to 10%.

(20) Once the external envelope is depolymerized and removed, the obtained stiffened capsules are rinsed in a rinsing solution based on water and stored in a storage solution based on water.

Example 1

(21) The composition C1 is an aqueous solution of an amaranth dye at 1 mM.

(22) The composition C2 is an aqueous dispersion of natural latex (chemical name cis-1,4-polyisoprene, from the family of dienes, an example of commercial natural latex: natural rubber grade TSR, SRM, SIR, STR, SVR, ADS, RSS, Crepes, DPNR, from Astlett Rubber Inc.) diluted down to a mass fraction of particles of polymers from 20% to 40% based on the total mass of the natural latex dispersion, also comprising 1% by mass of a surfactant of the ionic or non-ionic type depending on the grade.

(23) In this example, the mass fraction of particles of polymers is set to 30% (the latex dispersion is titrated by gravimetry after washing by centrifugation) and the SDS (sodium dodecylsulfate) surfactant is used.

(24) The composition C3 is an aqueous solution having a mass percentage of sodium alginate of 2.0% and a mass percentage of SDS of 0.1%.

(25) The obtained capsules, with a standard diameter of a few mm, are maintained in the gelling solution of calcium ions for one minute and are then rinsed with distilled water. They are then stored in an isotonic solution with the internal solution. Dual coacervation is thereby obtained by permeation of the calcium ions through the gelled alginate envelope. The capsules may then be incubated for 10 minutes in a 10% citrate solution in order to dissolve the outer membrane of hydrogel alginate. Capsules are thereby obtained having an outer envelope of stiffened natural latex.

Example 2

(26) Example 2 is made under the same conditions as Example 1, except that the composition C2 further comprises carbon black CB: carbon black. To do this, a CB solution is prepared (from the carbon black N234 from CABOT Corporation) in the presence of 2% SDS surfactant, the mass fraction of particles of polymers being always comprised between 20% and 40% based on the total mass of the natural latex dispersion, the CB fraction being comprised from 1% to 15%.

(27) For this example, the mass fraction of particles of polymers is set to 30% and the CB mass fraction to 5% based on total mass of the composition C2.

(28) After gelling of the alginate envelope, the capsules are incubated in distilled water for about 20 minutes. The surfactant diffuses towards the outside of the capsules through the alginate envelope and causes coacervation of the mixed natural latex/CB mixture, giving rise to a stiffened envelope of reinforced rubber.

Example 3

(29) Example 3 is made under the same conditions as Example 1, except that the composition C2 further comprises colloidal silica with an average diameter of 100 nm (Aerosil from Degussa, Ludox from Sigma), according to a mass fraction from 1% to 15% based on the total mass of the composition C2.

(30) For this example, the mass fraction of particles of polymers is set to 30% and the mass fraction of colloidal silica to 5% based on a total mass of the composition C2.

(31) Capsules are thereby obtained including a stiffened envelope of reinforced rubber.

(32) The capsules prepared according to the invention are easy to form, they have a resistant envelope of small thickness which gives the possibility of ensuring efficient disintegration of the capsule when the liquid contained in the capsule has to be released.