17. Apr 2014
Biopolymer plays sacrificial role in innovative self-healing composite system
Delamination in composites is a long-standing problem, and one which has up until now been a significant factor limiting more widespread use of these materials. A small, internal crack can quickly develop into irreversible damage. However, researchers in the Beckman Institute’s Autonomous Materials Systems (AMS) Group at the University of Illinois, USA, have now developed a new self-healing system, which they say allows fiber-composite materials to heal autonomously.
“This is the first demonstration of repeated healing in a fiber-reinforced composite system,” said Scott White, aerospace engineering professor and co-corresponding author. “Self-healing has been done before in polymers with different techniques and networks, but they couldn’t be translated to fiber-reinforced composites. The missing link was the development of the vascularization technique.”
“Additionally, creating the vasculature integrates seamlessly with typical manufacturing processes of polymer composites, making it a strong candidate for commercial use,” said Nancy Sottos, materials science and engineering professor and co-corresponding author.
The vessel system is made up of two different microchannel networks, each containing one of the two liquid healing agents (an epoxy resin and hardener). In order for the healing agents to combine effectively after being released within the crack, the vessels overlap to further promote mixing of the liquids.
“When a fracture occurs, this ruptures the separate networks of healing agents, automatically releasing them into the crack plane—akin to a bleeding cut,” said Jason Patrick, a Ph.D. candidate in civil engineering and lead author “As they come into contact with one another in situ, or within the material, they polymerize to essentially form a structural glue in the damage zone. We tested this over multiple cycles and all cracks healed successfully at nearly 100 percent efficiency.”
Fiber-composite laminates are constructed by weaving and stacking multiple layers of reinforcing fabric, which are then co-infused with a binding polymer resin. Using that same process, the researchers stitched in a sort of fishing line, made from a bio-friendly polymer and called “sacrificial fiber,” within the composite. Once the composite was fabricated, the entire system was heated to melt and evaporate the sacrificial fibers, leaving behind hollow microchannels, which became the vasculature for the self-healing system.(KL)
3D microvascular networks for self-healing composites: Researchers were able to achieve more effective self-healing with the herringbone vascular network (top) over a parallel design (bottom), evidenced by the increased mixing (orange-yellow) of individual healing agents (red and green) across a fracture surface. Credit: Jason Patrick