Micro-capsule preparation methods commonly used CS

Micro-capsule preparation methods commonly used CS

1, in situ polymerization

36% of the concentration of the solution of 488.5g and 240g urea formaldehyde mixture, triethanolamine adjust pH = 8, and heated to 70, the reaction heat by viscous liquid 1h, then diluted with 1000ml of water to form a stable urea - formaldehyde pre- polymer solution.

Add to the above-mentioned oil-soluble flavors to urea - formaldehyde prepolymer solution, and fully dispersed into very fine granular mixing. Adjust pH by adding hydrochloric acid in the 1-5 range, the formation of condensation in the solid acid catalyst is not easy penetration of the micro-capsules.

Control the solution pH value is important, when the solution pH values above 4, the formation of microcapsules not strong enough to easily penetrate; and when the pH is below 1.5, the acidity is too strong, too fast wall formation, quality difficult to control. To get below 2.5μm in diameter, small capsule, acid pH adjustment is slower, such as 3 times within 1h sour, at the same time with high-speed mixing. In alkaline conditions, the same can be obtained urea - formaldehyde prepolymer system into the microcapsules, pH control in the 7.5-11 range, the reaction time was 15min-3h, the temperature control in 50-80. High temperature, reaction time can be shortened.

When the condensation reaction of 1h, the appropriate temperature to 60-90, is conducive to the formation of microcapsule wall integrity, but note that the temperature does not exceed the flavor and the boiling point of the prepolymer. The general response time control in 1-3h, proved that the reaction time extended to 6h, and no significant improvement over results.

With urea - formaldehyde prepolymer for polymerization of the microcapsule has a remarkable resilience and resistance to penetration. This method obtained a method for making microcapsules are other good unparalleled tightness. The disadvantage is the smell of formaldehyde is difficult to clean, all except the overall flavor will be affected. Rarely used for the production of microencapsulated flavor.

2, the tiny hole - coagulation bath

The aqueous solution of sodium alginate drops with a dropper or syringe into the calcium chloride solution, the droplet surface will be solidified forming a capsule, which is one of the most simple tiny hole - coagulation bath operation. Dropper or syringe is a tiny hole device, the calcium chloride solution is a coagulation bath. Tiny hole - coagulation bath is generally made of polymer materials soluble flavor coating, and curing in the coagulation bath to form microcapsules.

Sodium alginate with 1.6%, 3.5% polyvinyl alcohol, 0.5% gelatin, 5% glycerol solution as microcapsule wall material, the concentration of coagulation bath of calcium chloride with 15% aqueous solution. Device with a tiny hole in calcium alginate coating flavor infusion of coagulation bath, in the droplet surface layer of dense, has a smooth surface, flexible, but not water-soluble calcium alginate film.

With tiny hole - coagulation bath can be the essence of the process of film coating materials and wall material separate from the curing process is conducive to control the size of the microcapsules, the wall thickness of the membrane.

3, complex coagulation

Coacervation method characterized by the use of two oppositely charged water-soluble polymer electrolyte membrane made of material, when the two colloidal solution when mixed with each other and in the charge arising out of or film material produced from the solution condensed condensed phase. The typical composite coagulation technology is gelatin - gum arabic coagulation.

Specific operating conditions were: 10% gelatin solution to maintain the temperature at 40, pH = 7, the oil add flavor in stirring to get a the flavor into the desired particle size dispersed oil in water dispersion. Continue to maintain the temperature at 40, stirring and adding an equal amount of 10% aqueous solution of gum arabic mixture, stirring dropping 10% acetic acid solution until the pH value of 4.0, mixed system, then gradually increase the sol viscosity and become opaque. Resulting in the original oil-water two-phase system into a condensed phase in the oily flavor and the formation of coated gathered around. When the condensed phase is formed, so that the mixture of natural cooling system to leave the water bath to room temperature, then cooled to ice bath so that the system 10 to maintain 1h, and then curing. The suspension system cooling to 0-5, and add 10% NaOH, the solution into the alkaline pH = 9-11 by adding 36% formaldehyde solution, mixing 10 - and 30-minute increase in the rate of once, heating to 50 the condensed phase to complete solidification, filtration, drying, that are fragrance microcapsules.

4, a simple condensation method

Coated with polyvinyl alcohol to form a semipermeable fragrance microcapsules oily flavor mixing process can be dispersed in polyvinyl alcohol solution to form colloidal dispersion emulsion system. In this emulsion system by adding carboxymethyl cellulose solution, since CMC more hydrophilic than PVA, polyvinyl alcohol molecules to be destroyed and the formation of hydration film of water-insoluble gel, and Essential oil droplet condensation film. When added to the solution of carboxymethyl cellulose and polyvinyl alcohol mass ratio of 40: (4-6) range, have uniform size, particle size, membrane wall of moderate-intensity micro-capsules. To increase the film's mechanical strength, curing agent can be IGRS aldehydes hardened, the amount of formaldehyde to 3% of membrane weight is appropriate. Cured over the membrane wall is too close, can not release fragrance. In order to obtain small particle size, uniform microcapsules, polyvinyl alcohol solution as in the formation of fragrance dispersion system, the addition of 0.6% of the total mass of total system flavor emulsifier. Emulsifier can be used with a variety of different flavors and flavor compatibility. Wall membrane curing polyvinyl alcohol solution by adding a small amount of inorganic salts, can decrease the viscosity, so that the wall of polyethylene film for curing more.

It is said that in this way a variety of fragrance microcapsule prepared, for textiles, cotton and wool fabric in the good adhesion of the microcapsules on the fabric Fragrance time of up to one year. Small gap due to surface chemical fiber fabrics, adhesive micro-capsules of small, low-affinity, fragrant time in about six months. After repeated washing can still maintain a certain fragrance.

The disadvantage of this method with the "in situ polymerization," just like the smell of formaldehyde is difficult to completely eliminate the influence flavor.

5, molecular embedding

Cyclodextrins as starch, as can be stored for years without deterioration. Molecular embedding is β-cyclodextrin microcapsules material for is a formation at the molecular level, the micro-capsules, the preparation is used widely in recent years, a physical method of micro-capsules.

Molecular shape from the CD look like an inner space to the top of the cone, has been described as the shape of a donut. Strong rigid ring, the middle of a hollow cave. CD of the hollow cave, and the role of a lipophilic hydrophobic matching effects of the volume of space, and with the appropriate size, shape and hydrophobicity of the molecule through non-covalent interactions to form a stable inclusion complex. Spices, pigments and vitamins and other elements appropriate molecular size can form inclusion complexes with cyclodextrin. Response to the formation of inclusion generally only when in the presence of water. When the water soluble cyclodextrin, cyclodextrin cavity part of the ring center was occupied water molecules, when adding external non-polar molecules (flavor), due to the hydrophobic cavity more exotic and non-polar molecules, The water molecules were soon replaced foreign molecules to form more stable inclusion complex precipitated from aqueous solution. That the formation of fragrance microcapsules.

Specific processes are as follows, cyclodextrin: water = 1:1 mix, stirring even after adding fragrance dried crushed.

Cyclodextrin complexation with the formation of microcapsules, the advantages of low moisture absorption, 85% relative humidity in the environment, its water absorption of less than 14%, so this is not easy to absorb moisture microencapsulated powder agglomeration of long-term preservation. CD itself is a natural product, with non-toxic, biodegradable advantages. Has been widely used in flavors such as oil-based microcapsule heart sac.

6, spray drying

Spray drying is the state of a solid solution droplets sprayed into the hot air, when the water evaporated, the solid dispersed in droplets are almost dry and assembly Jibei spherical powder. This is an industrial flavor microcapsules are prepared commonly used method.

Spray drying is divided into two steps, first selected wall dissolved in the water, the choice of gelatin, gum Arabic, carboxymethyl cellulose sodium (CMC-Na), sodium alginate, xanthan gum, sucrose, denatured milk protein, modified starch, maltose, etc. for wall, then add liquid flavor mix, so that a uniform emulsion material sent Spray Dryer in the state; in spray dryer, you can use a variety of techniques to milk turbid liquid atomization, and then contacts with the 180-200 hot air, rapid-drying of materials. Abrupt evaporation of water to carrier material in essence form a thin film around the droplets bead, this layer of thin film embedded in the beads to make the water droplets to penetrate and evaporate. On the other hand, large molecules will be retained flavor compound, its concentration is increasing. Finally, in the drying machine for 30 seconds after the removal of a relatively small carrier phase.