Self-healing Material

Abstract

A glass fiber-reinforced polymer composite includes a polymer matrix, a plurality of glass fibers embedded within the polymer matrix, a first hollow glass fiber containing a resin embedded within the polymer matrix, a second hollow glass fiber containing a catalyst suitable for curing the resin embedded within the polymer matrix. When damage occurs to such a composite, the glass fibers containing the resin and the catalyst are ruptured, resulting in their mixing together so that the resin is cured for repairing the ruptured location.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Ser. No. 61/648,306, which is hereby incorporated by reference herein.

BACKGROUND INFORMATION

[0002] Composite materials are ideal for structural applications where high strength-to-weight and stiffness-to-weight ratios are important. Weight sensitive applications, such as construction, aircraft, and space vehicles, are primary consumers of composites, especially fiber-reinforced polymer matrix composites. However, their use is limited due to the difficulty in damage detection and repair, as well as lack of extended fatigue and impact resistance. One way to protect material degradation is through the incorporation of a self-healing ability.

[0003] To date, there has been significant research in self-healing polymeric materials, and numerous studies, specifically in fiber-reinforced polymers. Polymer composites have been attractive candidates to introduce the autonomic healing concept into modern day engineering materials. A breakthrough in the study of self-healing materials was reported in 2001 by a research group at University of Illinois (see S. R. White et al., "Autonomic healing of polymer composites," Nature 409, pp. 794-797 (2001), which is hereby incorporated by reference herein). White et al. first introduced the incorporation of microcapsules containing a polymer precursor into the matrix material of a non-fiber-reinforced polymer composite for self-healing purposes. The polymer precursor was contained in microcapsules and embedded into the matrix. The matrix contained a randomly dispersed catalyst that was supposed to react with the precursor flowing through any crack formed due to damage and initiate polymerization. The polymer was then supposed to bond the crack face closed. The investigators overcame several challenges in developing microcapsules that were weak enough to be ruptured by a crack but strong enough not to break during manufacture of the composite system. The researchers showed that it was possible to recover up to 75% of the maximum tensile strength of the virgin composites. Successful work was done by Prof Bond's group. The use of functional repair components stored in hollow glass fibers ("HGF") placed with glass fiber/epoxy and carbon fiber/epoxy laminates can effectively mitigate damage occurrence and restore mechanical strength (see R. S. Trask, G. J. Williams and I. P. Bond, "Bioinspired self-healing of advanced composite structures using hollow glass fibres," J. R. Soc. Interface 4, pp. 363-371 (2007), which is hereby incorporated by reference herein). If successful incorporation of the self-healing material into the fiber-reinforced composites ("FRP") can be achieved, the benefit is quite obvious. Those composites can serve longer with better performance. Self-healing materials embedded in the FRP composite or laminate showed considerable restoration of mechanical properties such as flexural strength, compressive strength, impact resistance, and a highly efficient recovery of matrix strength (see G. Williams, R. S. Trask and I. P. Bond, "Self-healing sandwich panels: Restoration of compressive strength after impact," Composites Science and Technology 68, pp. 3171-3177 (2008) G. Williams, R. S. Trask and I. P. Bond, "A self-healing carbon fiber-reinforced polymer for aerospace application," Composites 38(6), pp. 1525-1532 (2007), which are hereby incorporated by reference herein).

[0004] Even though several methods have been suggested in autonomic healing materials, the concept of repair by bleeding of enclosed functional agents has garnered wide attention by the scientific community. The concept of bleeding is also being considered for commercial purposes in the aerospace industry. Achievements in the field of self-healing polymers and polymer composites are far from satisfactory. Working out the solutions would certainly push polymer sciences and engineering forward.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1A illustrates a hollow glass fiber.

[0006] FIG. 1B illustrates a hollow glass fiber filled with a self-healing agent.

[0007] FIG. 1C illustrates a hollow glass fiber filled with as catalyst.

[0008] FIG. 2 illustrates an embodiment configured in accordance with the present invention.

[0009] FIG. 3 illustrates a testing procedure performed on an embodiment of the present invention.

[0010] FIG. 4 illustrates another testing procedure performed on an embodiment of the present invention.

[0011] FIG. 5 shows digital images of GFRP specimens produced in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

[0012] The inventors discovered that a vinyl ester resin and a methyl ethyl ketone peroxide ("MEKP") catalyst can serve well as a self-healing material system for FRP composites due, at least in part, to the following advantages:

[0013] 1. The vinyl ester can be cured at room temperature when contacted or mixed with a MEKP catalyst.

[0014] 2. The viscosity of both the vinyl ester resin and the MEKP catalyst is very low (<2,000 centipoises), which allows hollow glass fibers or microcapsules to be easily filled with each.

[0015] It was found that the vinyl ester resin/MEKP catalyst self-healing system can increase the service life of the panel and recover performance soon after initial damage.

[0016] According to aspects of the present invention, an example is hereinafter described,

[0017] Part I. Base materials

[0018] 1. Self-Healing Agent:

[0019] A vinyl ester resin (e.g., product designation Derakane 411-350) was commercially obtained from Ashland, Inc. The MEKP catalyst was commercially obtained from Crompton Corporation. Other resin systems, such as polyester and an appropriate catalyst may be used instead.

[0020] 2. Hollow Glass Fiber:

[0021] FIG. 1A illustrates a cross-section of a hollow glass fiber 101. Large diameter hollow glass fibers were commercially obtained from Sutter Instrument. The hollow glass fibers may be approximately 4 inches long with an inner diameter ("1D") of approximately 860 microns and an outer diameter ("OD") of approximately 1500 microns, which yields a hollowness fraction of approximately 33%. Other hollow glass fibers with different dimensions or microcapsulates may be filled with self-healing agents instead.

[0022] 3. Silicone Sealant:

[0023] Silicone sealant (e.g., commercially obtained from Master Bond, Inc.) may be used to seal the hollow glass fibers.

[0024] 4. Fiberglass Fabric:

[0025] Product designation Hybon 2006 used to fabricate glass fiber-reinforced polymer ("GFRP") panels was commercially obtained from PPG Industries. Other types of fibers, such as carbon fibers and synthetic fibers, may be used instead.

[0026] 5. Polyester Matrix:

[0027] The polyester matrix used to fabricate the GFRP panels was commercially obtained from Hexion (e.g., Hexion's 712 type polyester resin). Other thermosetting resins, such as epoxy, vinyl ester, etc. may be used instead to perform the duty of the polymer matrix. The polymer matrix may be enhanced with other polymers or fillers, such as carbon nanotubes, ceramic particles, graphite or graphene particles, etc.

[0028] Part 2. Fabricating GFRP Panels

[0029] 1. Filling Hollow Glass Fibers with Self Healing Agent:

[0030] Referring to FIGS. 1B-1C, the hollow glass fibers 101 were first sealed at one end with silicone sealant 102. They were then immersed into the vinyl ester liquid in a vacuum chamber to allow the vinyl ester 203 (i.e., self-healing agent or resin) to be drawn into the hollow glass fibers 101. Then the other ends of the hollow glass fibers were also sealed with silicone sealant 102. The same process was also utilized to fill separate hollow glass fibers 101 with the MEKP catalyst 204.

[0031] 2. Fabricating the GFRP Panels with Self-Healing Agent:

[0032] 12''.times.12''.times.1/2'' GFRP panels were made based on two formulations. Formulation 1 had a loading of 2.5% self-healing agent/catalyst compared to the total polyester matrix in the GFRP panels. Formulation 2 had a loading of 5% self-healing agent/catalyst compared to the total polyester matrix in the GFRP panels. Five panels of each formulation were fabricated, Each panel contained 22 layers of e-glass fiber fabric. For each panel, the hollow glass fibers filled with self-healing agent were placed between the fourth and fifth, and eighteenth and nineteenth layers of the e-glass fiber fabric.

[0033] FIG. 2 illustrates an example of a GFRP panel 200 configured in accordance with embodiments of the present invention. GFRP panel 200 is shown in a cross-section view of a GFRP composite integrated with hollow glass fibers filled with self-healing agent 203 and catalyst 204. Others of glass fibers 201 typically used to make such composites are also shown embedded within the polymer (resin) matrix 201 of the GFRP composite. When damage occurs to such a panel, the glass fibers containing the self-healing agent and the catalyst are ruptured, resulting in their mixing together so that the agent is cued for repairing the ruptured location.

[0034] Part 3. Ballistic Testing of the GFRP Panels with Self-Healing Agent

[0035] The GFRP panels were made by a hot pressing process. The polyester resin mixed with MEKP catalyst (1.5%) was poured onto each layer of the e-glass fiber fabric and put together to form a laminated structure. It was pressed at a temperature of approximately 250.degree. F. degree for approximately 30 minutes and cooled down to room temperature. They were then made ready for V50 ballistic testing.

[0036] FIG. 3 shows a sketch of a typical panel and the planner placement of each shot for V50 ballistic testing. V50 tests were performed with a 0.30 caliber FSP. V50 ballistic testing is the velocity at which 50 percent of the shots go through and 50 percent are stopped by an armor. U.S. military standard MIL-STD-662F V50 Ballistic Test defines a commonly used procedure for this measurement.

[0037] Test Protocol

[0038] 1. First Round of Shots: For each set, there were 3 shots per panel (15 total shots per set). All of these were used to establish a V50 test result (referred to as V50-A). The locations of these shots were near the dots marked "X" in FIG. 3.

[0039] 2. Second Round of Shots: Within approximately 1 hour of the first round of shots, two panels were shot 3 more times and one panel was shot 2 more times near (approximately 1'' from) the original shots (this was done for both sets of panels). The purpose was to test the ballistic performance of the panels before the vinyl ester cured. Those 8 secondary shots were referred to as V50-B. Note, only 8 total shots were used for this test, as the remaining 7 shots were used in the third round of V50 testing (described hereinafter).

[0040] 3. Third Round of Shots: After approximately 1 week of the first round of shots (V50-A), the remaining 7 shots were made near (approximately 1'' from) the remaining original shots. The purpose was to allow the vinyl ester to be fully cured. Those 7 shots were used for another V50 test (referred to as V50-C) Thus all initial shots had a neighboring shot approximately 1'' from the original. Each parcel had 6 shots 3 original and 3 for either V50-B or V50-C testing.

[0041] Table 1 shows the V50 ballistic testing, results of the self-healing GFRP panels. The configuration for placement of hollow glass fibers (HGF) is shown below the table, where GF=glass fiber fabric.

TABLE-US-00001 TABLE 1 Loading of self- healing agent % (V50-A) (V50-B) (V50-C) 2.5 1585 1540 1614 5 1621 1544 1607

[0042] Placement of HGF:

GF/GF/GF/GF/HGF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/GF/HGF/GF/GF/GF/GF

[0043] In summary:

[0044] 1. V50-A is higher than V50-B. It was expected that after the first ballistic shot, the panel would be weakened;

[0045] 2. V50-C is higher than V50-B and very close to the V50-A, which means that the self-healing agent/catalyst effectively heals the damaged area of the panels after the first ballistic shot.

[0046] Another example now described showed that the mechanical properties of the GFRP composites can be recovered if the self-healing agent is embedded in the matrix. This example investigated the mechanical behavior before and after the self-healing agent is cured after impact testing. Compression strength after impact for the GFRP panels integrated with self-healing agents was performed. The dimension of the specimens for compression strength after impact testing is shown in FIG. 4 (based on ASTM D7136 and ASTM D7137 testing). The panel thickness was approximately 0.2 inches, with 4 plies of the e-glass fiber fabric utilized. The self-healing layer will be placed in the middle of the specimens Polyester resin (Hexion's 712 type polyester resin) and e-glass fiber (PPG's Hybon 2006 direct draw roving, 24 oz) were used as base GFRP panel matrix materials for experimentation. Vinyl ester was used as the self-healing agent and MEKP as catalyst. The GFRP specimens were fabricated by being integrated with self-healing agent based on 2.5 wt. % loading of the self-healing agent to resin matrix. The hollow glass fibers filled with self-healing agent and catalyst are placed in between the second and third plies of the e-glass fiber fabric. For comparison, also prepared were control GFRP panels for experimentation. FIG. 5 shows GFRP specimens used in the experimentation.

[0047] Fabricated were 4 GFRP samples. Each of the samples contained 12 GFRP specimens. For the samples with self-healing agent, 6 specimens of each sample were tested with impact. Then the compression strength after impact was performed within an hour. The remaining 6 specimens of each sample were performed with compression strength after impact a week after the impact testing. The average data was given after each testing. For comparison and determining the self-healing efficiency, the compression strength of the GFRP specimens (with no self-healing agent) without impact was also tested.

[0048] When the impact was performed, the hollow glass fibers were broken and the self-healing agent and the catalyst were expelled from the fibers to react with each other. The self-healing agent would barely react with the catalyst within the first hour. However, the reaction would be completed in a week.

[0049] A fully instrumented low velocity impact (Instron) machine was used to perform the impact at energy of 30 J.

[0050] The compression strength of the samples was the following:

[0051] GFRP samples without self-healing agent: [0052] Compression strength (before impact): 50.0 MPa [0053] Compression strength after impact: 38.3 MPa

[0054] GFRP samples with 2.5% self-healing agent: [0055] Compression strength 1 hour after impact: 35.2 MPa [0056] Compression strength 1 week after impact: 48.1 MPa It can be seen that the compression strength observed one week after impact (48.1 MPa) is significantly better than those tested within an hour after impact (35.2 MPa), showing that the self-healing agent plays an important role in healing the GFRP panels after damage. The self-healing efficiency in this case is 96% and it almost recovers to the compression strength of the undamaged GFRP (50.0 MPa), which is almost fully recovered. Optimizing the loading of the self-healing agent may improve the self-healing efficiency.

Claims

1. A glass fiber-reinforced polymer composite comprising: a polymer matrix; a plurality of glass fibers embedded within the polymer matrix; a first hollow glass fiber embedded within the polymer matrix, the first hollow glass fiber containing a resin; and a second hollow glass fiber embedded within the polymer matrix, the second hollow glass fiber containing a catalyst suitable for curing the resin.

2. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the resin comprises a vinyl ester.

3. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the resin comprises polyester.

4. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the catalyst comprises methyl ethyl ketone peroxide.

5. The glass fiber-reinforced polymer composite as recited in claim 2, wherein the vinyl ester has a viscosity lower than 2,000 centipoises at room temperature.

6. The glass fiber-reinforced polymer composite as recited in claim 3, wherein the polyester has a viscosity lower than 2,000 centipoises at room temperature.

7. The glass fiber-reinforced polymer composite as recited in claim 4, wherein the methyl ethyl ketone peroxide has a viscosity lower than 2,000 centipoises at mom temperature.

8. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the polymer matrix comprises a thermosetting resin.

9. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the polymer matrix is selected from the group consisting of polyester, vinyl ester, and epoxy.

10. The glass fiber-reinforced polymer composite as recited in claim 1, wherein the polymer matrix is a thermosetting resin reinforced with a filler.

11. The glass fiber-reinforced polymer composite as recited in claim 10, wherein the filler comprises carbon nanotubes.

12. The glass fiber-reinforced polymer composite as recited in claim 10, wherein the filler comprises ceramic particles.

13. The glass fiber-reinforced polymer composite as recited in claim 10, wherein the filler comprises graphite particles.

14. The glass fiber-reinforced polymer composite as recited in claim 10, wherein the filler comprises graphene particles.