Megatrends are among the major drivers of innovation. At the top of this list are neo-ecology and mobility. They encounter the ever important issues of industrial applications such as process optimization and economization or conservation of resources, respectively. Microencapsulation has long since become an integral part in handling these issues and is becoming increasingly important in the investment and capital-intensive value chain.
Of course, the targeted release of substances is not "neo" - but it does make an important contribution to ecology and is extremely innovative. A prime example of this is fabric softener with perfume oils that promise a lasting fragrance for up to twelve weeks. Without microencapsulation of the fragrances, 99 % would end up in the sewage system with the rinsing water from the washing machine. Now, the fragrances are only released when the garments have dried again and the capsules are opened by simply rubbing the fibers. The waste water is relieved and the product "fabric softener" gains additional benefits - quite apart from the positive influence on the product image.
Much older than the use of core-shell microcapsules in laundry care is their use in the paper industry. This is also where the roots of this technology are: Already in the 1950s, patent applications were filed that document the first industrial application for the production of non-carbon copy paper.
Since then, the number of patents for microcapsules that permanently protect their contents from environmental influences, such as humidity, oxidation or reaction with other substances, has increased continuously in all industrial sectors to more than 5,000 patents.
From Airbus via BMW to Delphi Technologies or NASA – they have all filed patents on how substances can be released on demand and how reactions can be controlled in a targeted manner.
New innovative approaches for corrosion protection,
touch-dry lubrication or the indication of micro damage have found their way
into practice. The fact that the price-sensitive paper industry or the end
consumer industry use microencapsulation indicates that this elegant process
only appears cost-intensive at first glance, but has interesting economic
aspects when used intelligently. This is particularly true in the light of
recent patent applications for tasks involving new forms of mobility.
Electromobility and microencapsulation
Adhesives are an important enabler in the implementation of electromobility, because modern adhesive technology replaces screws and rivets and permits the necessary weight reduction of electric vehicles by lightweight construction, and thus a longer range for cars. Microencapsulation creates the option of using and storing reactive resin/hardener blends in a single formulation: this provides for greatly simplified adhesive handling and hence potential for process optimization in industrial applications. One-component reaction adhesives can be pre-applied to the components and cured by targeted release of the encapsulated components. External causes for the capsule opening include pressure, shear, heat, high-energy radiation or destruction by pH-dependent, chemically reacting substances.
Thermal energy storage
In addition to lightweight construction, the storage of thermal energy in the traction battery is a factor that provides for a greater range for electric vehicles. The microencapsulation of latent heat storage substances such as paraffins is one of the efficiency-enhancing technologies in electromobility. Waxes or paraffins are easy to encapsulate. Depending on their chain length, they melt from solid to liquid at different temperatures, absorbing heat and releasing it again at temperatures below the melting point. Together with an insulating housing, this ensures smooth operation of the traction battery at low outside temperatures. As part of the Optemus project (a joint project with partners from industry and research), an optimized energy management system is being developed for electric cars. Microencapsulated latent heat storage substances can contribute to an efficiency increase by improving the heat transfer.
In addition to megatrends, increasing safety requirements are also driving innovations in microencapsulation. Self-healing paints, “smart coatings”, became part of the history of microencapsulation applications immediately after the use of microcapsules for non-carbon copy papers and fabric softeners. Reactive monomers are encapsulated with a suitable catalyst and applied homogeneously in a paint layer. If microcracks then occur in this lacquer layer, the microcapsules are opened. Due to the capillary forces they release the reactive substances into the crack, where they cross-link in combination with the catalyst and “heal” the damage at a very early stage.
Microcracks are hardly perceptible, but represent a considerable safety risk for crash helmets or aircraft components, for example. This risk can be avoided by incorporating microcapsules into a crash helmet. If microcracks occur during use, a bad smelling liquid is emitted. This safety feature reveals the often invisible damage and signals the consumer to replace the helmet.
This application can also be transferred to aviation. Instead
of x-raying large components and checking that they are fully functional,
microcapsules can be integrated as the weakest part of the matrix, so to speak.
If the sensitive material experiences invisible damage that causes microcracks,
an odor is emitted. The localization can then be sniffed out by dogs, for
Microencapsulation is a proven technology that is more than 60 years old. Its history is also that of innovative application opportunities:
1950/60: Microencapsulation starts in the paper industry. For the first time, carbon copy paper is produced without a carbon layer. Instead, microcapsules are applied to the paper, which release the encapsulated colouring substance when pressed.
1980: Thread locking with pre-applied, touch-dry adhesive: The screws are coated with the microencapsulated reactive component of an adhesive and the hardener. The capsule is destroyed by the shearing forces during tightening and polymerization is activated. The pre-application and controlled release make the process independent of time and location.
1997: The microcapsule finds a completely new use as a carrier for Phase Change Materials (PCM). Capsules filled with paraffins and waxes are integrated into textiles and building materials and reversibly store and release heat.
2001: The first self-healing coating system with incorporated microcapsules is published. If microcracks occur, the coating is able to close these autonomously by means of targeted cross-linking.
2004: The end consumer benefits from the microencapsulation of fragrances in fabric softeners: These are no longer released into the waste water in high concentrations, but remain much more efficiently on the textile fibers, where they develop their effect through friction.
The accompanying article lists a large number of industries in which
microencapsulation are already being used. Birgit Megges asked Klaus Last, Head
of Technology in the Koehler Innovative Solutions Business Unit at Papierfabrik
August Koehler, questions about the future innovation potential of the
CHEManager: The technology of microencapsulation itself is not new, but can you still report something new?
Klaus Last: After more than 60 years of development, microencapsulation has arrived in a wide variety of industries, thanks to numerous industrial-scale optimizations and greater awareness. But even if the method is not entirely new: Whoever deals with it, can become an innovator again and again, because the system allows a constant growth of know-how. New applications are usually accompanied by modified core materials that continually demand specific solutions. So the ingredients are simple: Terrific is what comes out, when all influences are matched with each other.
Can you name specific innovations?
K. Last: You will find them especially in PCM encapsulation. In
addition to the demand for high heat capacity thanks to the capsule system,
improved heat conductivities are an issue as well. Antibacterial finishing of the microcapsules, improved
adhesion to the fibers they are applied to as well as ecological and economic
requirements for the capsule systems are a long runner. If the tightness of the capsule systems is important,
as is the case with latent heat storage substances, the core material in the
permanent capsules should ensure, depending on the temperature, the phase
change from solid to liquid and back over thousands of cycles without the
capsules being destroyed. A leakage of core material is fatal. Here, the
technology is very advanced. Another interesting issue is the optical properties of
the PCM capsules, which result from the phase change, in different substrates. Another
strong focus is on new opening mechanisms for the capsules, which are not based
on mechanical stress but on other triggers such as pH, UV, temperature or a
laser. The aim here is a sudden release of the core content under gentle
But microencapsulation still seems to be something for enthusiasts. Do you think so, too?
K. Last: In fact, there are perhaps 1,000 colleagues worldwide,
which can be considered true experts. But there are areas where you can no
longer avoid microencapsulation: Screw locking, scented oil encapsulation and
the encapsulation of latent heat storage substances. When it comes to
application-oriented future requirements in the field of microencapsulation,
the Fraunhofer Institutes, especially the Institute for Applied Polymer
Research (IAP), are in the vanguard. In addition, there are many small and few
large providers, some of which are very specialized.
© 2016 Koehler Innovative Solutions