Aspirin and adhesive. Rivets and floor cleaners. Uranium fuel and food flavoring. What do all such widely divergent products have in common? Answer: They have all been improved and made more practical by a little-known but rapidly spreading process called microencapsulation.
By breaking up substances into tiny particles or droplets, and encapsulating each one in a protective coating of its own, scientists have turned volatile liquids into docile, easily handled solids. They have extended the effectiveness of drugs and insecticides, learned to mask unpleasant smells and tastes and to help preserve pleasant ones. By removing or rupturing the protective coating suddenly, or by allowing it to be penetrated or dissolved gradually, they have produced startling and useful effects in both industrial processes and commercial products.
Carbonless Paper. Microencapsulation was first used by the National Cash Register Co. in 1954 as a means of producing carbonless copying paper. One sheet of paper was coated on the back with a layer of microscopic capsules containing one chemical; the copy sheet was coated on the front with another chemical. When the two pieces were inserted in a typewriter or Teletype machine, the force of the keys hitting the top sheet broke the capsules, releasing the chemicals they contained. While the typewriter ribbon supplied ink for letters on the top sheet, the combined chemicals made an inklike copy of the letter on the bottom sheet.
The carbonless paper quickly caught on, and now brings N.C.R. more than $25 million a year. But N.C.R. scientists saw no reason to settle for that one payoff from encapsulation. They, and researchers for other companies, have been busy working out countless other applications. Among the most familiar: "timed release" decongestants such as Contac, and a newly introduced aspirin called Measurin.
Timed-release decongestant medicines contain hundreds of small but visible pellets of gelatin-or wax-coated drugs in a single dose. The period required for each pellet to dissolve in the digestive system and release its drug varies from almost no time at all to as long as twelve hours, depending on the thickness of the coating. Measurin tablets contain some 6,000 microscopic particles of aspirin, each coated with a semipermeable plastic. Gastric fluids flow through the plastic walls and dissolve the aspirin—which flows out of the capsule at a controlled rate for a continuous eight-hour period.
Solid Gasoline. The varied uses of the encapsulation process seem limited only by the human imagination. Microcapsules of water have been incorporated in cigarette filters. Before a smoker lights up he pinches his cigarette, thus breaking the capsules and moistening the filter. Dry floor-scouring pads containing capsules of cleaning and polishing fluid are also being marketed. Aircraft companies are using rivets coated with microcapsules containing primer. When the rivet is forced into place, the capsules break, allowing the primer to flow over both the rivet and the adjoining metal to protect them from corrosion. Manufacturers are testing encapsulated flavors and fragrances in food mixes to increase their shelf life, and nuclear-reactor fuel is being encapsulated to increase its efficiency.