Polymeric Self-healing Composites for Longer Lasting Products

This proven, patent-pending material that enables a wide variety of composite products to "self-heal" is available for licensing by or joint development with commercial companies, universities, or government laboratories. Structural polymers are susceptible to cracks that form deep within the structure where detection is difficult, and repair is often impossible. Once these cracks have formed, the product's structural integrity is significantly diminished. Researchers at the University of Illinois at Urbana-Champaign have developed self-healing composite materials to address this microcracking problem. In these materials, the resin matrix typically used in making composite products is infused with monomer-containing microcapsules and a corresponding polymerization catalyst. When a crack forms in the composite, the microcapsules rupture, releasing the monomer. As the monomer contacts the catalyst, polymerization occurs and the crack is "self-healed," requiring no manual intervention. Once healed, the polymer recovers as much as 90% of its original fracture toughness.

Description/Details

In nature, damage to an organism elicits a healing response. University of Illinois researchers have applied this same concept to synthetic material design, creating a self-healing polymer composite.

An additional unique feature of this healing concept is the use of a catalyst that remains active even after triggering polymerization. Therefore, when additional cracking occurs, the catalyst crystals will continue to trigger polymerization, allowing multiple healing events to occur.  

The Chemistry of Self Healing

The University's researchers identified ring-opening metathesis polymerization (ROMP) reaction as the best method to self-heal cracks quickly.

To achieve a ROMP reaction, the microcapsules contain dicyclopentadiene (DCPD) monomer. DCPD offers a long shelf life, low viscosity and volatility, and low shrinkage upon polymerization. When a crack ruptures the microcapsule, the DCPD interacts with a ruthenium-based Grubbs catalyst. This reaction causes the DCPD to polymerize at room temperature, yielding a tough, crosslinked polymer network (Figure 2 attached).

Test Results

This technology has been extensively tested in epoxy and polyester matrix composites, including tapered double-cantilever beam (TDCB) fracture tests, optical and scanning electron microscopy, and infrared spectroscopy. Research is ongoing in optimizing the self-healing process.

  • Confirmation of Self-Healing: Environmental scanning electron microscopy and infrared spectroscopy confirmed that self-healing does occur within test specimens (Figure 3 attached). ESEM images showed that a thin polymer film formed on a fracture surface, and IR spectroscopy showed that this film absorbed radiation similarly to ring-opened DCPD.
  • Healing Efficiency: Fracture toughness tests showed that specimens with self-healed cracks regained between 70% and 90% of the original toughness. Furthermore, this repaired fracture toughness was equivalent to that of a test specimen made only with the DCPD epoxy and no catalyst (Figure 4 attached).
  • Effects of Catalyst on Healing Efficiency: One series of tests showed that the lower the concentration of the Grubbs catalyst, the greater the healing efficiency (Figure 5 attached).

Applications

The uses for these self-healing polymer composites are virtually endless. This technology can be used in nearly any plastic or composite part that is subject to microcracking. Below are just a few examples.

  • Transportation: Cracks in the structure or components of automobiles, airplanes, and spacecraft shorten vehicle life and can compromise passenger safety. This self-healing technology would repair these cracks before they grow to dangerous levels.
  • Sporting Goods: Many consumers are willing to pay top dollar for high-quality fishing equipment, tennis rackets, helmets and other protective gear, boats and surfboards, skis, and other sports equipment. This self-healing technology would improve the quality of these products.
  • Medicine: Once implanted in the body, prosthetics and other medical devices are difficult to monitor and access for repair. This self-healing technology could prevent problems caused by damaged pacemakers, hip and knee replacements, dental materials, and other medical devices.
  • Electronics: Polymer composite circuit boards and electronic components can suffer from mechanical and electrical failures if microcracks progress unabated. This self-healing technology would help to prevent such failures.
  • Paints, Coatings, and Adhesives: Used in a wide variety of products, paints, coatings, and adhesives are subject to scratches, cracks, and deterioration. This self-healing technology would repair this damage, maintaining protection from environmental conditions and/or a longer lasting seal.

Benefits

  • Self-healing: Polymeric and composite materials are subject to weakening due to fatigue cracking. A self-healing composite has the potential to defend against material failure due to fatigue and to greatly improve product safety and reliability and to extend product lifetimes.
  • Improved toughness: Adding the microcapsules to the resin and later initiating the self-healing process increases the toughness of the resin over what it would have been without the microcapsules. Improving the toughness of a previously brittle material makes it more durable and less likely to suffer brittle fracture.

Reference #

TF01013

Patents

6858659
print