Regenerating plastic grows back after damage
Self-healing plastics have been around for about a decade, but they have never been able to heal damage much larger than the width of a human hair.
Now, a team from the University of Illinois has developed a system that not only repairs minor cracks in plastic, but also regenerates to heal large holes.
"We have demonstrated repair of a non-living, synthetic materials system in a way that is reminiscent of repair-by-regrowth as seen in some living systems," said Professor Scott White, who led the research.
The regenerating capabilities build on the team's previous work in developing vascular materials.
Using specially formulated fibres that disintegrate, they were able to create materials with networks of capillaries inspired by biological circulatory systems.
"Vascular delivery lets us deliver a large volume of healing agents – which, in turn, enables restoration of large damage zones," said Sottos, a professor of materials science and engineering. "The vascular approach also enables multiple restorations if the material is damaged more than once."
For the regenerating materials, two adjoining, parallel capillaries are filled with regenerative chemicals that flow out when damage occurs.
The two liquids mix to form a gel, which spans the gap caused by damage, filling in cracks and holes. Then the gel hardens into a polymer, restoring the plastic's mechanical strength.
"We have to battle a lot of extrinsic factors for regeneration, including gravity," said White. "The reactive liquids we use form a gel fairly quickly, so that as it's released it starts to harden immediately. If it didn't, the liquids would just pour out of the damaged area and you'd essentially bleed out. Because it forms a gel, it supports and retains the fluids. Since it's not a structural material yet, we can continue the regrowth process by pumping more fluid into the hole."
The team demonstrated their regenerating system on the two biggest classes of commercial plastics: thermoplastics and thermosets.
They found they could tune the chemical reactions to control the speed of the gel formation or the speed of the hardening, depending on the kind of damage.
Looking ahead, they now plan to optimise the regenerative chemical systems for different types of materials.
"For the first time, we've shown that you can regenerate lost material in a structural polymer. That's the kicker here," White concluded, "Prior to this work, if you cut off a piece of material, it's gone. Now we've shown that the material can actually regrow."
