Additives in a capsule
Microencapsulation is not a new technology. Its application to lubricants, however, has never been attempted before. Currently, additives are blended with base oils to be used as lubricants. A research team from George Washington University (GWU) located in the U.S. capital is looking at a completely different delivery system for additives that may solve some of the problems that the current system faces.
Lubricants are compounded with many additives to meet the ever-increasing demands in performance and emission standards. With so many additives in the lubricants (sometimes 15-18% by weight), the additive molecules interact with each other, forming micelles or chemical clusters in oil solution, said Stephen Hsu, team leader. Oftentimes, some of the additive molecules get tied up with others and may not be available for their intended use, so that formulators will add extra additives to compensate for this, he said. New additive chemistry that is invented has to avoid being entangled with existing additive molecules, he said. Microencapsulation could help solve this problem and could help isolate some chemistry to be able to function, Hsu explained.
“It’s the same chemistry. But now you can reduce waste… and safeguard synergistic additive combinations, hence reducing cost, and [have a] far better delivery system,” said Hsu, a professor of Engineering and Applied Science at GWU, who gave a presentation at the Annual Meeting of the Society of Tribologists and Lubrication Engineers (STLE) in Dallas, Texas, U.S.A. last week.
Time release is another nice feature of microcapsules, allowing additives to be replenished over time. So even though there is no new chemistry, the delivery method of the additive to the lubricated system will change. Hsu, a well-known tribologist, likens it to changing the interface.
“It has become very difficult to add some small amount of new additive to change the lubricant performance anymore” in the current lubricant formulations, Hsu explained, because the complex chemical soup formed by the additives in the lubricant has become so big and complex that it is difficult to add any new molecules.
Friction modifiers, for example, are known to degrade as a function of time, gradually losing their friction modification ability. Microcapsules have the potential to replenish additional friction modifiers to prolong the effectiveness of the additive, hence increase fuel economy. Capsules have to be tough and strong to endure the high temperature, high shear environment of the lubrication system. According to Hsu, several additives can be put into a single capsule, forming a mini-package to reinforce the lubricant when the capsules break, releasing the protected additives.
In the current system, there is not enough control on how much additive remains as a function of time, he said. Microencapsulation can hopefully help to deliver the additive at the right place and at the right time.
Hsu suggested that microencapsulation technology can provide high performance, long drain oils at a lower cost. The capsules can be released by various triggering mechanisms built into the polymer chemistry and will break up when the acidity becomes high, or under some pre-specified temperatures.
While this technology is currently in the testing phase and not yet commercialized, it is an exciting development that could potentially open up a new avenue to deliver additives to the lubrication system.