Mechanoresponsive Healing Polymers

Materials and Coatings
Mechanoresponsive Healing Polymers (LAR-TOPS-132)
Polymer strands utilizing mechanically responsive chemical groups to induce self-healing
Overview
NASA Langley Research Center is developing an innovative self-healing resin that automatically reacts to mechanical stimuli. Current structural materials are not self-healing, making it necessary to depend on complicated and potentially destructive repair methods and long down times. Unlike other proposed self-healing materials that use microencapsulated healing agents, this technology utilizes viscoelastic properties from inherent structure properties. The resulting technology is a self-healing material with rapid rates of healing and a wide range of use temperatures.

The Technology
The method chemically introduces mechanically sensitive chemical groups into the structure of a resin. By introducing mechanoresponsive functional groups to a polymer, it is possible to induce self-healing through the transformation of such chemical groups to where mechanical properties of a structure are almost completely restored. The forces imparted by a damage event can therefore be used to enable healing or repair of the structure.
Prototype space exploration habitat susceptible to micrometeoroid damage 
Illustration of mechanoresponsive healing response within fractions of seconds after a damage event.
Benefits
  • Healing capability at elevated temperatures
  • Fast healing rates (less than 100 microseconds)
  • Healing without the need of foreign inserts or fillers (via structural chemistry)

Applications
  • Aircraft
  • Rotocraft
  • Spacecraft
Technology Details

Materials and Coatings
LAR-TOPS-132
LAR-18368-1
Similar Results
NASA inflatable space habitat
Puncture-healing Engineered Polymer Blends
Puncture healing melt blends were developed by melt blending self-healing polymers with non self-healing polymeric materials. The self-healing polymeric materials consisted of Surlyn&#174 8940, Affinity&#8482 EG 8200 G, and poly(butadiene)-graft-poly(methyl acrylate-co-acrylonitrile) or Barex&#174 210 IN. The non-self-healing polymeric materials consisted of poly(ether ether ketone) (PEEK), LaRC phenyl ethynyl terminated imide 330 (LaRC PETI 330), and Raptor Resins Bismaleimide-1 (BMI-1). Puncture healing blends were also prepared with chopped glass and chopped carbon fibers. The overall goal was to develop a product with superior properties relative to either of the starting materials. The melt blends were prepared in varying compositions to optimize desired properties of the resulting matrix. Ballistic testing was conducted to determine the self-healing characteristics of several developmental polymers subjected to micrometeoroid type damage.
Prototype space exploration habitat susceptible to micrometeoroid damage
Multi-layered Self-healing Material System for Impact Mitigation
This innovation utilizes a tri-layered structure, comprised of solid plastic front and back layers sandwiching a viscous, reactive liquid middle layer. Combined, this system provides rapid self-healing following high velocity ballistic penetrations. Self-healing in the front and back layers occurs when the puncture event creates a melt state in the polymer materials and the materials melt elasticity snaps back and closes the hole. The viscous middle layer augments the self-healing properties of the other layers by flowing into the gap created by a ballistic puncture and concurrently solidifying due to the presence of oxygen. Thus, this innovation has two tiers of self-healing: a puncture-healing mechanism triggered by the projectile and a second mechanism triggered by the presence of oxygen.
24 hour time lapse photos of puncture evaluation in a self healing laminate system
Self-Healing Low-Melt Polyimides
There are multiple space-related systems that can benefit from high performance, thin film, self-healing/sealing systems. Space vehicles and related ground support equipment can contain miles of wire, much of which is buried inside structures making it very difficult to access for inspection and repair. Space-based inflatable structures, solar panels, and astronauts performing extra-vehicular activities are subject to being struck by micrometeoroids and orbital debris. Self-healing or sealing layers on inflatables, solar panels and spacesuits would increase the safety and survivability of astronauts as well as the survivability and functionality of inflatables and solar panels. Self-healing insulation on wiring would greatly improve the reliability and safety of systems containing such wiring and reduce inspection and repair time over the lifetime of those systems. This technology combines the use of a self-sealing low melt, high performance polyimide film that exhibits the ability, when cut, for separated edges to slowly flow back together and seal itself, with the options of a laminate system and the inclusion of healant microcapsules that, when broken, release healant which can then additionally assist in the healing process. Combinations of the healing approaches can be enabling to the healing process proceeding at a much greater rate and dual mode healing approach can also allow for healing of a larger area.
Concept composite aircraft
Healable Carbon Fiber Reinforced Composites
A composite fabrication process cycle was developed from composite precursor materials developed at LaRC to fabricate composite laminates. The precursor material is a pre-impregnated unidirectional carbon fiber preform, or prepreg. In the pre-pregging process, the high strength, structural reinforcing carbon fiber is wetted by a solution containing a self-healing polymer. The resulting material is of aerospace quality and exhibits a significant decrease of internal damage following impacts tests (using ASTM D 7137 standard).
Self-Healing Wire Insulation
Self-Healing Wire Insulation
Insulation is necessary on electrical wires in order to protect electrical systems from shorting. In high voltage systems such shorting can lead to sparking and fires. Many lives have been lost due to electrical wire insulation failure. Many man hours are also expended in the repair and inspection of electrical wiring in order to attempt to prevent wire failure. Wire insulation with a built in "self-healing" capability would greatly improve the safety of systems containing electrical wiring. Such insulation would require far less inspection and repair time over the lifetime of the system. Polyimides such as Kapton are an integral part of high performance electrical wire insulation. Traditional polyimides are very inert to solvents and do not melt. A new set of polyimides, developed for use as films for the manual repair of high performance electrical wire insulation, have a low melting point and can be dissolved in special solvents. These properties can be taken advantage of in self-healing polyimide films. Microcapsules containing a solvent soluble polyimide are prepared using industry standard inter-facial or in situ polymerization techniques. These capsules are then incorporated into a low melt polyimide film for use as either a primary electrical wire insulation or as one of several layers of a composite wire insulation. The low melt polyimide film substrate in which the microcapsules are incorporated has good solubility with the solvent used to dissolve the polyimide which makes up the fluid inside the microcapsule. Such a capsule filled insulation, when cut or otherwise damaged, will result in the release of the capsule contents into the cut or damage area. The solvent then dissolves a small amount of the surrounding polyimide insulation but will also begin the process of evaporation. The combination of these two processes allows for excellent intermingling of the healant and the surrounding substrate, resulting in a repair with superior bonding and physical properties.
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