What is the most common method of microencapsulation?
The method that is mostly used for microencapsulation is spray drying. Apart from other methods like freeze drying (using a lyophilization machine), extrusion, coating, and agglomeration, the spray drying method of microencapsulation has its own advantages like more simple operation and lower cost (more of its advantages will be introduced in the following passage). What else should you know about the spray drying microencapsulation?
Spray drying microencapsulation — what should be avoided?
Among the microcapsules prepared by spray drying, the more the proportion of smooth and round microcapsules, the better the fluidity of the product; the dents, shrinkage, cracks, and the core material leakage caused by the micropores on the surface of the microcapsules will all worsen the fluidity of the product. Since the cracks and pores on the surface of the microcapsules will cause the leakage of the core material and make it lose the protective effect of the wall material, the appearance of cracks and pores should be avoided when using a spray dryer machine for microencapsulation.
Spray drying microencapsulation — what is it suitable for?
The spray drying method of microencapsulation is most suitable for lipophilic liquid materials. The stronger the water increase of the core material, the better the embedding effect. Its wall material is easily soluble in water, so the wall material is dissolved immediately after rehydration, and the core material can be released immediately. It is not suitable for sustained release requirements. The spray drying microencapsulation process is very short, only a few seconds, and the production is continuous. The product can be free from constant heat, so it is more suitable for many heat-sensitive materials. Compared with other methods, this method has a wider range of core-wall material ratio. For flavors and spice oleoresins, the core material rate is generally not more than 20%, while the powder oil can reach 70%. However, if the core material rate is too high, the strength of the capsule is weakened, and the product is not resistant to friction or extrusion. When the operation is not good, the more free core material will be distributed on the surface of the capsule.
Spray drying microencapsulation — why use it?
Although there are many methods that can be used for microencapsulation, the most researched and commercialized production application is mainly spray drying microencapsulation. Because this method has many advantages:
(1) The production process is simple, the equipment is easy to obtain, and it is suitable for continuous, automated, and industrialized production, so the production capacity is high and the production cost is low;
(2) There are many types of wall materials that can be used, which is suitable for most materials that need to be wrapped;
(3) The microcapsules can achieve a large amount of embedding;
(4) The product has uniform particles and good solubility;
There are usually 5-30 seconds of heating time when using the spray drying method of microencapsulation, and when the outer layer of water evaporates quickly during the granulation process, the core material temperature can be kept below 100°C. Considering the two, the spray drying microencapsulation can handle many thermally unstable materials though it is carried out at a high temperature.
Spray drying microencapsulation — what are the limits?
However, this method also has its limits.
(1) Too small particles produced (generally less than 100μm) make the product fluidity poor;
(2) When the amount of embedding is large, the embedding rate is not high, and the core material will be adsorbed on the surface of the microcapsule, causing oxidation and volatilization loss;
(3) The drying temperature using the spray drying method of microencapsulation is relatively high, which will inevitably cause the loss of highly volatile substances and the destruction of heat-sensitive substances;
(4)Micropores and gaps will appear on the surface of the microcapsules, and the wall of the capsule has poor compactness, which cannot effectively prevent the entry of oxygen;
(5) The equipment is large, so is the power consumption.