microencapsulation techniques

Finishing using Microcapsules

It is the process by which individual particles or droplets of solid or liquid material (the core) are surrounded or coated with a continuous film of polymeric material (the shell) to produce capsules in the micrometer to millimetre range, known as microcapsules.

Microcapsules - Definition

Depends mainly on the core material and the deposition process of the shell.

Mononuclear (core-shell) microcapsules contain the shell around the core.

Polynuclear capsules have many cores enclosed within the shell.

Matrix encapsulation in which the core material is distributed homogeneously into the shell material.

In addition, microcapsules can also be mononuclear with multiple shells, or they may form clusters of microcapsules.

Microcapsules - Morphology

Coating materials for the Shell- properties requirements

•Stabilization of core material.

•Inert toward active ingredients.

•Controlled release under specific conditions.

•Film-forming, pliable, tasteless, stable.

•Non-hygroscopic, no high viscosity, economical.

•Soluble in an aqueous media or solvent, or melting

•The coating can be flexible, brittle, hard, thin etc.

Microcapsules – Coating

Coating materials:

•Gums: Gum arabic, sodium alginate, carageenan.

•Carbohydrates: Starch, dextran, sucrose

•Celluloses: Carboxymethylcellulose, methycellulose.

•Lipids: Bees wax, stearicacid, phospholipids.

•Proteins: Gelatin, albumin.

Microcapsules – Coating

1- microorganism and enzyme immobilization:

- Enzymes have been encapsulated in cheeses to accelerate ripening and flavor development.

- The enzymes are protected from low pH and high ionic strength in the cheese.

• The encapsulation of microorganisms has been used to improve stability of starter cultures

2- Protection against UV, heat, oxidation, acids, bases (e.g.colorants and vitamins).

e.g. Vitamin A / monosodium glutamate, appearance (white) protection (water, T, ligth)

3- Improved shelf life due to preventing degradative reactions (dehydration, oxidation).

4- Masking of taste or odours.

Microcapsules - Benefits

5- Improved processing, texture and less wastage of ingredients.• Control of hygroscopy• enhance flowability and dispersibility• dust free powder• enhance solubility

6- Handling liquids as solids

7- Delivering Nutritious foods for children which provides them with much needed vitamins and minerals during the growing age. Microencapsulation could deliver the much needed ingredients in children friendly and tasty way.

8- Enhance visual aspect and marketing concept.

9- Carbonless copy paper - A coating of microencapsulated colorless ink is applied to the top sheet of paper, and a developer is applied to the subsequent sheet. When pressure is applied by writing, the capsules break and the ink reacts with the developer to produce the dark color of the copy.


10- Textile industry makes use of microencapsulated materials to enhance the properties of finished goods. One application increasingly utilized is the incorporation of microencapsulated phase change materials (PCMs).

Phase change materials absorb and release heat in response to changes in environmental temperatures. When temperatures rise, the phase change material melts, absorbing excess heat, and feels cool. Conversely, as temperatures fall, the PCM releases heat as it solidifies, and feels warm.

This property of microencapsulated phase change materials can be harnessed to increase the comfort level for users of sports equipment, clothing, building materials, etc.


11- Pesticides are encapsulated to be released over time, allowing farmers to apply the pesticides less amounts than requiring very highly concentrated and toxic initial applications followed by repeated applications to combat the loss of efficacy due to leaching, evaporation, and degradation.

12- Ingredients in foods are encapsulated for several reasons

• Most flavorings are volatile; therefore encapsulation ofthese components extends the shelf-life of these products

• Some ingredients are encapsulated to mask taste, such as nutrients added to fortify a product without compromising the product's intended taste.

• Alternatively, flavors are sometimes encapsulated to last longer, as in chewing gum.


13- Controlled and targetted release of active ingredients.

• Many varieties of both oral and injected pharmaceuticalformulations are microencapsulated to release over longer periodsof time or at certain locations in the body.

• Aspirin, for example, can cause peptic ulcers and bleeding if dosesare introduced all at once. Therefore aspirin tablets are oftenproduced by compressing quantities of microcapsules that willgradually release the aspirin through their shells, decreasing risk ofstomach damage.

14- Microencapsulation allows mixing of incompatible compounds.


. Microcapsules - Technologies

Microcapsules - Processes with their relative particle size ranges

Physico - Chemical Processes Physico - mechanical Processes

Coacervation (2 - 1200 um) Spray-drying (5 - 5000 um)

Polymer-polymer incompatibility

(0.5-1000 um)

Fluidized- bed technology (20-

1500 um)

Solvent evaporation (0.5-1000

um)Pan coating (600 - 5000 um)

Encapsulation by supercritical fluid Spinning disc (5 - 1500 um)

Encapsulation by Polyelectrolyte multilayer (0.02-20 um)

Co-extrusion (250-2500

um)

Hydrogel microsphere Chemical Processes

Phase Inversion (0.5—5.0 um) Interfacial polymerization (0.5-

1000 um)

Hot Melt (1—1000 um) In situ polymerization (0.5-

1100 um)

Microcapsules - Technologies

Coacervation Polymer-polymer incompatibility (phase separation)

Solvent Evaporation

Rapid Expansion of Supercritical Fluids Hydrogel microspheres


Spray-Drying & spray-congealing


Fluidized-Bed Technology


Pan coating


Co-Extrusion


Spinning Disk


Applications in TextilesIn microencapsulation in general the number of commercial applications in the textile industry continues to grow.

Microencapsulation processes as a means of imparting finishes and properties on textiles for

• Developed textiles with new properties.• New innovations and applications in Medical and Technical Textiles.• Application in the area of cost-effectiveness required.• Application where the technologies are not sufficient or not possible in

imparting some finishes.• Increasing the durability of finishes.

Few Textile applications more interested in the area of

• Durable fragrances to textiles • Skin softeners and other potential applications include, • Insect repellents, • Dyes, • Vitamins, • Antimicrobials, • Phase change materials and in • Specific medical applications, antibiotics, hormones and other drugs.

Applications in Textiles – Phase Change Material

The Technology was utilised in the early 1980s by the US - NASA with the aim of managing the thermal barrier properties of garments, in particular for use in space suits.

They encapsulated phase-change materials (PCMs) (e.g. nonadecane) with the hope of reducing the impact of extreme variations in temperature encountered by astronauts during their missions in space.

The potential was recognised where they can applied.

Outlast has exploited the technology in textile fibres and fabric coatings and PCM capsules are now applied to all manner of materials.

Applications in

Outdoor wear - (vests, thermals, snowsuits and trousers) and

In-house - {blankets, duvets, mattresses and pillowcases).

As well as being designed to combat cold, textiles containing PCMs also helps to combat overheating, so overall the effect can be described as thermoregulation.

The microcapsules have walls less than 1 nm thick and are typically 20-40 nm in diameter, with a PCM loading of 80-85%.

The small capsule size provides a relatively large surface area for heat transfer. Thus the rate at which the PCM reacts to an external temperature changes is very rapid.

Accordis - UK, developed the technology of in-fibre incorporation of the Outlast microcapsules, loading the fibre with 5-10% of microcapsules.

The process utilises late injection technology that was also used to produce the antimicrobial fibre.

In this way the PCM is permanently locked within the fibre; there is no change necessary in subsequent fibre processing (spinning, knitting, dyeing, etc.) and the fibre exhibits its normal properties of drape, softness and strength.

Applications in Textiles – Phase Change Material

Applications in Textiles – Fragrance Finishes

Fragrances to textiles has been carried out for many years in the form of fabric conditioners in the wash and during tumble-dry ing; all are designed to impart a fresh aroma to the textile.

But the effect is relatively short-lived.

Numerous attempts have been made at adding fragrances directly to fibre and fabrics but all fail to survive one or two wash cycles.

Only through microencapsulation are fra grances able to remain on a garment during a significant part of its lifetime.

Microencapsulation of essential oil flavours has led to many novelty applications, particularly for children's garments, but it has also allowed exposure at home and in the work place to the beneficial effects.

The majority of the work has been in microencapsulated 'scratch and sniff T-shirts and in women's hosiery. The nature of the microcap sules is claimed that the durability can be (typically 8-20 cycles), depending on the active agent encapsulated, and the hosiery up to ten washes. The capsules also survive drying in conventional tumble-dryers.

Initial Applications:

Drawer liners, paper hand kerchiefs, gift wrapping, stationary, greeting cards, advertising brochures, books, cartons and labels.

Now, the basic technology of encapsulating fragrances in gelatin or synthetic capsules, which protects the contents from evaporation, oxidization and contamination.

The capsules range in size from 1 to 20 nm.

The technology allows a textile manufacturer to add a fragrance, vitamin, moisturizer or even an insect repellent to all types of textile substrates.

Depending on application weights and the wash cycle used, up to 30 washes can be achieved without complete loss of fragrance. In practice, the smaller the capsules the greater the covering of the product and the longer the fragrance will last, as it takes longer for the capsules to be ruptured by physical pressure. Larger capsules release more fragrance when ruptured.


The aqueous disper sions of encapsulates, which can be applied by pad, exhaustion or hydroextraction techniques to a wide variety of textile substrates.

Durability to washing and handle (or feel) may be further im proved by incorporating suitable formaldehyde-free binders and softeners.

Microcapsules using melamine-formaldehyde systems containing fra grant oil, When attached to cotton these capsules were able to survive over 15 wash cycles.

Microcapsules containing perfumes or cosmetic moisturisers that can be padded, coated or sprayed onto a textile and held in place using an acrylic or polyurethane binder.

Paper-like products have been produced con taining microencapsulated essential oils such as lavender, sage and rosemary for odour control applications in shoe liners and insoles.


For screen-printed application the encapsulates are simply mixed with water-based, solvent-free inks or binders.

The capsule printing must be the last pass under a screen to avoid damage to the walls by further screens.

Once printed, the fabric is then cured as with standard textile inks to achieve a good bond to the fibres.

Usually a softener is also required, as unsoftened fabric containing microcapsules can sometimes appear to be stiffened.

The capsules are colourless and can be applied over coloured fabric or printed patterns without any adverse visible effects.

The fragrant effect can last for a year and a half. Gloves and socks are also available that have fragrance-release properties and some antibacterial effects, which the manufacturers claim to last for up to 25 wash cycles.


Applications in Textiles – Colour Changing Poly chromic and thermo chromic microcapsules

Colour-changing technology has been generally applied to novelty application such as stress testers, forehead thermometers and battery testers.

New applications are now beginning to be seen in textiles, such as product labelling, and medical and security applications.

In addition there is continued interest in novelty textiles for purposes such as swimwear and T-shirts.

Two major types of colour-changing systems:

Thermochromatic: Alter colour in response to temperature, and

Photochromatic : Alter colour in response to UV light.

Both forms of colour-change material are produced in an encapsulated form as microencapsulation helps to protect these sensitive chemicals from the exter nal environment.

Today, manufacturers are able to make dyes that change colour at specific temperatures for a given application.

e.g. colour changes can be initiated from the heat generated in response to human contact.

Physiochemical and chemical processes such as Coacervation and interfacial polymerization have been used to microencapsulate photochromic and thermochromic systems.

To obtain satisfactory shelf life and durability on textiles, interfacial polymerization techniques are nearly always adopted, which is the same techniques used to produce textile fibres and films such as polyester, nylon and polyurethane.

The most widely used system for microencapsulation of thermochromic and photochromic inks involves urea or melamine-formaldehyde systems.

Applications in Textiles – Colour Changing Poly chromic and thermo chromic microcapsules

Applications in Textiles – Flame Retardant

Fire retardants have been applied to many textile products.

But in certain cases they can affect the overall handle, reducing softness and adversely affecting drape.

Microencapsulation has been used to overcome these problems for example in fabrics used in military applications such as tentage.

Others have incorporated the microencapsulated fire retardants during spinning of a polyester fibre for blending with cotton.

In high added value textiles, and in branded and designer goods there is great pressure to protect from illegal copying within the market place.

Microencapsulation can be used to help with this problem by offering a covert yet dis tinctive marking system.

This system for combating textile counterfeiting utilizes microcapsules containing a colour former or an activator applied to, for example, a thread or a label.

The microcapsules adhere to the tex tile and, depending on the type of chemical within the capsules can be detected at a later date to check authenticity.

Detection may be achieved directly using UV light or more likely by using a solvent to break open the capsules, releasing the contents and allowing a colour to develop.

Applications in Textiles – Counterfeiting

In recent years liposomes have been examined as a way of delivering dyes to textiles in a cost- effective and environmentally sensitive way. The liposomes used (for example, commercially available PC liposomes from Transtechnics SL) were cost-effective, and no specific equipment or skills were required to handle them within the dye house.

The results were excellent with pure wool and wool blends, and as the temperature of dyeing could be reduced there was less fibre damage.

In their studies dye bath exhaustion was shown to greater than 90% at the low temperature (80 °C) used resulting in significant saving in energy costs. The impact of the dyeing process on the environment was also much reduced with chemi cal oxygen demand (COD) being reduced by about 1000 units.

Applications in Textiles – Liposomes

Applications in Textiles – General

Encapsulated glycerol stearate and silk protein moisturizers for application on bandages and support hosiery. The material maintains comfort and skin quality through extensive medical treatment where textiles are in direct contact with the skin.

Polypropylene nonwoven material for application as a cleaning/wiping cloth containing microencapsulated octane, tung oil and paraffin oil as cleaning solvents. The cloths feel good in the hand and have very good cleaning properties.

The application of insecticides to textiles to combat dust mites and insects such a mosquitoes, etc.,Microencapsulation has been considered as a mechanism of retaining the effect for significant periods without exposing the user to excessive dosages of hazardous chemicals. The use of alternative insecticidal compounds such as those found in many essential oils and other plant extracts has made the production of longlasting acaricide bed sheets possible.

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