Scrape your elbow in a tough-fought tennis match and you expect your body to heal itself. But damage your racket diving for the tie-breaking serve and you're stuck with the wreckage. Perhaps not in the future, though, if new self-healing plastics live up to expectations. Aside from sports equipment, potential applications include hard-to-repair devices such as spacecraft parts and medical implants.
Plastics are made into just about everything, but we chuck our plastic ware in landfills whenever it breaks, cracks, peels, or fails in some other manner. So a team of researchers led by mechanical engineer Scott White of the University of Illinois, Urbana-Champaign, set out to see if they could give plastic composites--materials composed of two or more components that are typically used for the most demanding applications--a bit more longevity.
The researchers hit upon a two-part solution. They started by mixing a plastic-generating catalyst along with reinforcing fibers into a soft epoxy resin. They stirred in tiny capsules filled with dicyclopentadiene (DCPD), a liquid plastic precursor. After hardening the epoxy around the fibers into a stiff plastic, the researchers mechanically stressed the material. As tiny cracks opened up in the material, this ruptured the capsules and allowed DCPD to flow into the voids. When the precursor encountered the catalyst, a chain reaction turned the fluid into a solid. And as the team reports in the 15 February issue of Nature, the healed plastics recovered up to 75% of their toughness.
"The approach should prove especially useful where it is not possible, or practical, to repair the material once it has been put to use," writes University of Delaware chemical engineer Richard Wool in a commentary in Nature. Prime candidates for such treatment, he adds, are components of vehicles used in deep-space exploration, satellites, rocket motors, and prosthetic organs.