- Email: [email protected]
Self-repairing hollow-fiber polymer composites
Self-repairing hollow-fiber polymer composites
17
Harikrishnan Pulikkalparambil1, M.R. Sanjay1, Suchart Siengchin1, Anish Khan2, Mohammad Jawaid3 and Catalin Iulian Pruncu4,5 1 Department of Mechanical and Process Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand, 2Center of Excellence for Advanced Materials Research (CEAMR), Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia, 3Department of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia (UPM), Serdang, Malaysia, 4Department of Mechanical Engineering, Imperial College London, London, United Kingdom, 5Department of Mechanical Engineering, School of Engineering, University of Birmingham, London, United Kingdom
17.1
Introduction
The concept of using self-repairing hollow fibers in polymer composites was a major breakthrough leading to many revolutionary findings in the field of smart self-healing materials [1 3]. The first reports on self-healing in thermoplastics and cross-linked systems were in 1969, 1979, and 1981 [4 6]. Since then, many polymer composites with excellent self-healing capabilities have been developed [7]. Several self-healing approaches for self-healing materials have been developed to date and there is expected to be huge demand in the fields of construction, electronics, and aviation [8,9]. The first studies reported on self-healing polymer composites were based on self-repairing hollow glass fibers (HGFs) [10,11]. The advantages of self-healing polymer composites include a reduction in the cost of maintenance and improved lifespan [12]. Several matrix materials such as polyester, polyimide, polyurethane, silicone rubber, and epoxy resins have been considered for developing self-healing composites. This is due to their low density, excellent chemical inertness, low cost, and versatility in fabrication methods. In addition, such materials exhibit better adhesion of substrates [13]. There are several key parameters in determining polymers as healing agents for self-healing applications. Some of these parameters include viscosity, gelling time, enthalpy of reaction, cross-linking temperature, stoichiometric ratio of hardeners, etc. [14]. In the past, most researchers were focused on self-healing materials based on microencapsulation of healing agents in polymeric containers. Urea formaldehyde and melamine formaldehyde are commonly used polymeric microcapsules along with catalyst/hardener dispersed in matrix [15,16]. However, polymeric Self-Healing Composite Materials. DOI: https://doi.org/10.1016/B978-0-12-817354-1.00017-X © 2020 Elsevier Inc. All rights reserved.
314
Self-Healing Composite Materials
microcapsules may adversely affect the mechanical property and may have limited healing capabilities. Furthermore, the polymeric microcapsules left in the polymer matrix after one-time healing may deteriorate the mechanical performance of the composites. Also, such a technique follows interfacial polymerization at the interface of healing agents and monomer solutions to produce microcapsules. This may not be suitable for very highly reactive healing agents for encapsulation due to their possible interaction with the polymerization process [17,18]. Thus, an alternate method to encapsulate healing agents that provides structural integrity as well as functional ability to the composites is preferred. HGFs are an excellent alternative for microcapsules because of their mechanical stability and thermal properties. Also, hollow fibers are able to store more healing agents without compromising the reinforcement and are easily integrated into the matrix with less restriction of the activation method and healing chemistry of healing agents [19,20]. Recently, fibers such as HGFs, halloysite nanotubes (HNTs), titanium dioxide nanotubes (TNTs), and polymeric fibers have gained a great deal of acceptance in designing the selfrepairing composites for structural applications. When damage is triggered by an external stimulus, the fiber breaks, this allows the healing agents to flow into the crack site, and it undergoes polymerization in the presence of a hardener or catalyst present at the crack site. In the following sections, self-repair polymer composites encapsulated with HGFs, hollow nanofibers, and hollow polymeric fibers are discussed.
17.2
Self-repairing techniques
17.2.1 Hollow glass fibers Among several hollow fibers, the self-healing composites made up of HGFs are widely used due to their (1) ability to retain mechanical properties, and (2) cost effectiveness [20,21]. However, the efficiency of such hollow fiber composites depends on several parameters such as (1) the viscosity of the healing agent, (2) the diameter of the hollow tube, and (3) the interfacial adhesion between the fiber and the matrix, etc. [22]. Dry et al. introduced the self-repairing concept by the release of chemicals stored in the hollow glass tubes for repairing of cracks to prevent corrosion in cement matrices [23 26]. Later, Dry et al. [26] reported two-part epoxy adhesive encapsulated HGFs to visualize the release of healing agents. This was one of the initial works carried out to develop self-healing polymer composites. Glass pipette tubes with c. 4 inches length and 100 µL volume were used as containers to encapsulate a cyanoacrylate-based adhesive healing agent. The encapsulation of healing agent was carried out by the vacuum method. Impact and bend tests of epoxy samples containing HGF with and without healing agents were used to demonstrate the retention of structural properties after the healing process. The impact test and bend test show the possibility of healing agents to demonstrate repairing, crack reopening resistance, and extending of crack propagation delay. However, specific concerns such as matrix material, fiber distribution, sample
Self-repairing hollow-fiber polymer composites
315
thickness, impact energy, and processing quality were not considered. Later Motuku et al.[17] developed passive-smart polymer composites (PSPCs) that help to repair damage caused by low-velocity impact. The authors compared epoxy resin encapsulated within glass capillary tubes such as borosilicate glass microcapillary pipettes, flint glass pasteur pipettes, copper tubing, and aluminum tubing. The selfhealing composite panels were prepared by placing encapsulated hollow fibers halfway between the top half and bottom half of the laminates while a resin injection was carried out by vacuum-assisted resin transfer molding (VARTM). The lowvelocity impact response in borosilicate glass, copper tubings, microcapillary pipettes, and flint glass pasteur pipette composites is poor due to the matrix cracking, fiber breakage, and delamination, etc. However, the insertion of glass tubing with healing agents exhibited a much improved impact response. This is because the lower energy impact may not damage the aluminum or copper tubings to release the healing chemicals. On the other hand, microcapillary pipettes were considered as containers. In conclusion, the authors reported the number and spatial distance of the fibers, thickness, and the impact energy played a vital role in the efficiency of self-healing in polymer composites. However, Dry and Motuku et al. demonstrated the reduced use of hollow glass capillary tubes to repair crack sites, and fiber thickness was still a major concern. The thickness of fibers to develop self-healing composites has to be controlled in order to avoid failures (the optimum thickness of glass fibers is ,15 µm), as thick glass fibers could lead to weak spots in composite materials that may further promote delamination or composite damages. In order to avoid such weak spots in composite materials, Bleay et al. [27] demonstrated the potential of self-healing HGF/epoxy reinforced composites with comparatively smaller diameters (internal diameter of 5 µm and outer diameter c. 15 µm). The laminates with c. B6.5 mm thickness were prepared by laying up unidirectional prepreg material. Twenty-four-ply, 300 mm 3 600 mm composite panels of [(0 , 90 )12]s and other [(0 , 45 , 90 )6]s ply layup arrangements were compared. The vacuum-assisted capillary strategy for filling as shown in Fig. 17.1 was carried out to encapsulate healing agents. The epoxy resin was entrapped in one fiber direction with hardener in the other direction. Both epoxy and hardener are mixed with acetone prior to encapsulation to reduce viscosity and improve the flow of healing agents into the damage site and to effect a cure. The self-repairing hybrid epoxy composites with HGF and E-glass fiber containers were investigated by Bond et al. [28 32]. The robustness of the self-repairing process was performed, before and after healing of specimens, by conducting flexural strength. The quasistatic indentation that replicated impact damage was manually produced on the composite specimens and the damage recovery was detected by a four-point bending experiment. Pang and Bond [29] used an ultraviolet (UV) fluorescent dye along with epoxy resin (MY750 Ciba-Geigy 1 30%/vol. acetone) to trigger self-healing by a UV lamp. They used samples made of 0 /90 hand layup (HLU) process to prepare composites with 0 HGF filled with epoxy resin and 90 HGF filled with hardener. A conventional HGF fabric with borosilicate inner layer and inner diameter of 60 µm and 50% hollowness was used to hold the healing agents. Once the crack is triggered, it requires c. 24 h to complete the resin cross-linking
316
Self-Healing Composite Materials
Figure 17.1 The vacuum-assisted capillary strategy for filling in order to encapsulate healing agents inside hollow glass fibers [27].
process. The four-point bending tests performed on the composites show that unfilled composites had 25% less bending strength than filled ones. This is because the unfilled composites undergo cracks during bending forces. On the other hand, the crack propagation of filled HGFs is restricted by the healing agents. Fig. 17.2 shows the ultraviolet mapping technique (UMVT) and ultrasonic C-scan image of impact specimens to visualize the self-healing process. Kling et al. [19] studied the damage detection and self-repair of thin HGFs (inner diameter of 5 6 µm and outer diameter of 10 12 µm) in epoxy composites. Here, HGFs filled with polyester (Polimal 1058) healing agent and its initiator were used to study the self-healing process. An indicator liquid (UV fluorescent dye) mixed with epoxy resin was used to visualize the healing process. The composites containing fluorescent dye-filled HGFs exhibited better damage detection under UV illumination. To study the healing process, the samples prepared by HLU and VARTM methods were damaged by a falling weight impact-testing machine. The damaged samples were left to heal at 60 C and 23 C for 12 and 120 h, respectively. The samples containing polyester healing agents were able to generate a 20% improvement in the bending properties compared to reference specimens without a healing agent. This is due to the incompressibility of the liquid healing agents inside the hollow fibers, and friction between the liquid polyester resin and the fiber inner wall. Zainuddin et al. [33] reported a novel self-healing technique to recover lowvelocity impact properties of E-glass/epoxy composites and they found a good improvement during multiple impacts. The authors used a smart encapsulation strategy as shown in Fig. 17.3 for the preparation of impact specimens. One end of the HGFs was immersed in a curing agent (unsaturated polyester resin) and initiator (cobalt octate) at room temperature, then a suction force was applied to the other
Self-repairing hollow-fiber polymer composites
317
Figure 17.2 UVMT images of (A) front face of impact specimen, (B) back face of impact specimen, and (C) ultrasonic C-scan image of impact specimen [29].
Figure 17.3 The process of HGF encapsulation and preparation of e-glass/epoxy composite [33].
end. Similarly, the encapsulation of MEKP in the HGF was conducted. Later, both ends of the HGFs were closed by a commercially available adhesive to avoid leakage. A vacuum-assisted resin infusion molding (VARIM) process was used for the preparation of composites. Table 17.1 shows the impact tests conducted on control epoxy samples, plain composites, and self-healing agent (SHA)-filled composites. The composites recorded an increase of 53.6% on the peak load after the second impact for composites containing SHA-filled HGF compared to control epoxy composites. The improved peak load during the second impact was attributed to curing
318
Self-Healing Composite Materials
Table 17.1 Low-velocity impact tests of control, plain, and self-healing agent-filled composites [33].
Control—first impact Control—second impact Plain HGF—first impact Plain HGF—second impact SHA-filled HGFs— first impact SHA-filled HGFs— second impact
Total energy (J)
Energy to maximum load (J)
Absorbed energy (J)
Peak load (kN)
55.8 6 1.6 50.9 6 1.4
39.9 6 2 24.6 6 1.4
15.9 6 2 26.3 6 4
9.7 6 0.1 7 6 0.9
54.6 6 2.1
47.3 6 1
7.3 6 1
11.2 6 0.2
55.7 6 1.3
43.5 6 1.3
12.2 6 2
10 6 0.2
54 6 1.5
47 6 2.8
761
12.3 6 0.8
54 6 1.6
45.8 6 0.8
8.2 6 2
10.6 6 0.4
of unsaturated polyester resin in crack sites that may regain the strength of composites. It is worth mentioning that once the crack healing occurs, the healed location in the composites may be left without fillers [34,35].
17.2.2 Hollow nanofibers In a recent study, Bekas et al. [35] modified epoxy healing agents with multiwalled carbon nanotubes (MWCNTs) encapsulated in glass fibers. Here, interlaminar fracture toughness, dynamic viscosity, etc., was evaluated to understand the effect of CNT loading in the healing agent. It was found that the healing efficiency of the composite increased from 120% to 192% in comparison with neat epoxy. However, the addition of CNTs in the healing agent increased the viscosity tremendously. However, the viscosity can be controlled by the addition of solvent ethyl phenylacetate (EPA). The increased healing efficiency is due to the presence of MWCNTs in crack sites that may hinder the crack initiation/propagation after the healing process. Also, the presence of CNTs in the crack site provides a nanoreinforcement effect during fracture toughness studies. Lanzara et al. [36] proposed a molecular dynamic simulation study of a singlewalled carbon nanotube to examine the feasibility of CNTs as novel nanocontainers for self-healing of composites. Fig. 17.4 provides the self-healing concept using the carbon nanotube reservoirs. The advantage of using carbon nanotube-based composites for self-healing is driven by their ability to generate strength to the composites prior to healing [37]. Once the composite is susceptible to damage, an organic healing agent is released to contact the catalyst deposited in the matrix to undergo cross-linking and heal the cracks. However, the efficiency of containing healing agents in the CNT capsules depends on the (1) nanotube diameter, (2) nanotube
Self-repairing hollow-fiber polymer composites
319
Figure 17.4 Self-healing concept using carbon nanotubes as nanoreservoirs for healing agents [36].
length, (3) nanotube orientation in the matrix, (4) nanotube dispersion, (5) nanotube loading density, (6) type of matrix, and (7) healing agents [37]. Fig. 17.5 presents a schematic diagram of a healing agent encapsulated in HNTs and curing agent immobilized in mesoporous silica. The encapsulation of a healing agent in a HNT is simple, as they are produced by a vacuum infiltration method. First the nanotubes are kept under repeated vacuum pressure to replace the air inside the tubes with healing agents. Vijayan et al. investigated the self-healing performance of dual-container self-healing systems with a HNT and/or TNT with an epoxy healing agent (Epon 826) and mesoporous silica containing diethylene triamine (Epikure 3223) curing agent [38,39]. The vacuum infiltration process was used for encapsulation of healing agents inside the nanotubes. The nanotube is encapsulated by mixing with epoxy and then applying a repeated vacuum to replace the air inside the inner lumen of the nanotubes with epoxy. An amine curing agent is immobilized onto the pores of the mesoporous silica by shaking for 24 h. Further, Vijayan et al. [40] compared the healing efficiency of the HNT with two different tube diameters (TNT 1 1.5 nm and TNT 2 10 nm) in order to understand the effect of tube volume. The nanotubes together with stoichiometric amounts of diethylene triamine curing agent immobilized in silica were mixed with epoxy resin and curing agent followed by sonication. The percentage of recovery of healing was found to be 31, 64, and 105% for EP/HNT, EP/TNT1, and EP/TNT2 coatings, respectively.
17.2.3 Hollow polymeric fibers Zhu et al. [41] reported the use of polypropylene (PP) tubes as reservoirs for an epoxy/mercaptan healing agent. The PP tubes (Paradigm Optics, Inc.) with an outer tube diameter of 250 mm and inner tube diameter of 200 mm were selected as a potential reservoir due to several advantages, including: (1) easy filling of large tubes followed by thermal stretching to make them smaller; (2) compartmented version of PP tubing can produce repeated healing; (3) surface modifications generated to achieve good compatibility; (4) its flexibility allows knitting of fibers into mats;
320
Self-Healing Composite Materials
Figure 17.5 Schematic representation of the halloysite nanotube encapsulation and mesoporous silica immobilization [38].
and (5) inertness of the fibers toward healing agents. Fig. 17.6 show a schematic representation of thermal stretching for easy filling, compartmented structure, knitting, and surface modifications. A foaming agent along with the encapsulated healing agent can greatly influence the self-healing ability. The foaming agent can generate a self-pressurized gas due to the thermal decomposition resulting in the formation of pressure inside the container. This may result in a sudden discharge of healing agent to flow much faster and wider into the damaged site, as a result a higher self-healing performance is produced. Another way to produce hollow polymer fibers for self-healing is by using the electrospun fibers with healing liquids encapsulated within the fibers during the electrospinning process. This is carried out using a triaxial electrospinning process. In an interesting work, Zajani et al. [42] used a one-step triaxial electrospinning process as shown in Fig. 17.7 to produce hollow fibers capable of storing healing
Self-repairing hollow-fiber polymer composites
321
Figure 17.6 Thermoplastic tubing forming a microvascular self-healing composite: (A) the healing fluid encapsulated inside a thicker tube, (B) thermal thinning of a tube, (C) a compartmented structure made of a tube to hold healing agents, (D) surface modification of a tube, and (E) knitted thermoplastic fiber with glass fiber [41].
Healing agent
Middle layer solution Outer layer solution Tri axial healing fiber PAAm PMMA Epoxy
High-voltage supply
Collector
Figure 17.7 A triaxial electrospinning set-up used to prepare the healing agent-encapsulated hollow PMMA/PAAm fibers [42].
agents. Here, a XB 3458 hardener and acetone diluted Araldite LY 564 epoxy resin was separately encapsulated inside an electrospun polymer fiber. The healing agent-encapsulated electrospun fibers were spun using polymethyl methacrylate (PMMA) and polyacrylamide (PAAm) polymers as outer and middle cores, respectively. The outer PMMA core is responsible for better compatibility with the matrix by forming a semi-interpenetrating (semi-IPN) network. On the other hand, the middle PAAm core helps to protect the healing agent by reducing the interaction of healing agents with the outer core as well as the matrix due to its lower affinity. This can increase the efficiency and lifetime of healing agents.
322
Self-Healing Composite Materials
Figure 17.8 Some SEM images showing (A and B) the PMMA/PAAm hollow fiberreinforced composite and (C and D) epoxy/hardener encapsulated PMMA/PAAm healing fiber-reinforced composite [42].
SEM images of PMMA/PAAm hollow fiber-reinforced composite are shown in Fig. 17.8A and B and an epoxy/hardener encapsulated PMMA/PAAm healing fiber-reinforced composite is depicted in Fig. 17.8C and D showing interfacial delamination and crack repairing in the presence of PMMA/PAAm/(epoxy, hardener) healing fibers. Kim et al. [15] studied the self-healing of polyethersulfone (PES) films using methylene diphenyl diisocyanate (MDI) prepolymer encapsulated in fluorinated ethylene propylene (FEP) capillary tubes. Fig. 17.9 shows a schematic diagram of (1) the encapsulation process using a microfluidic device, and (2) fabrication of selfhealing membrane on PET fabric support followed by PES casting and phase inversion apparatus. In this work, the mechanism of self-healing is the water-induced phase separation of healing agents to produce an increase in the viscosity, followed by a further phase separation reaction to form an expanded polyurethane/polyurea matrix that heals the damaged area. The advantage of using FEP tubes unlike other capsule systems are (1) water penetration in FEP tubes is inhibited to avoid deactivation of healing agent, (2) improved physical strength of the tubes, and (3) the use of more reactive liquids as healing agents.
Self-repairing hollow-fiber polymer composites
323
Healing agent
(A)
Outlet Syringe pump
PTFE tube
Epoxy glue 400 µm
250 µm
Slide glass
FEP capillary tube
Glass capillary tube (B)
(i) Membrane area marking Membrane area
PET support
90 µm
(ii) Installation of capillary tube Membrane area Core-filled FEP capillary tube
PET support
(iv) Phase inversion process
(iii) Membrane casting
Water bath Core-filled Membrane FEP capillary tube
Membrane Core-filled casting solution FEP capillary tube
PET support
Figure 17.9 Schematic diagram that presents (A) the encapsulation of healing agents located inside the core of an FEP capillary tube using a microfluidic device, (B) fabrication of selfhealing membrane (i, ii), casting of PES solution (iii), phase inversion process using water bath (iv) [15].
17.3
Conclusion
The recent developments in self-repairing hollow fiber composites have been discussed in this chapter. Self-repair has broadened the application areas of polymeric materials and enabled improvement in the life of materials. The works dedicated to encapsulated self-repairing composite fibers require classification based on the fiber
324
Self-Healing Composite Materials
types used. In the early stage most work was carried out in conjunction with glass fibers. Recently, the possibilities of employing self-repairing material with the aid of polymeric fibers and hollow nanofibers (HNT, TiO2, and CNT) have been explored. Therefore, these areas still need more expertise to achieve better results. However, great improvements in the number of research works dedicated to healing mechanisms on the composites have been made, yet multiple self-repairing hollow fibers are still a major challenge.
Acknowledgment This research was partly supported by the King Mongkut’s University of Technology North Bangkok through the PhD and PostDoc Program (Grant No. KMUTNB-61-PHD-001, KMUTNB-61-Post-001, and KMUTNB-62-KNOW-001).
References [1] Wang S, Liu N, Su J, Li L, Long F, Zou Z, et al. Highly stretchable and self-healable supercapacitor with reduced graphene oxide based fiber springs. ACS Nano 2017;11:2066 74. [2] Tee BC, Wang C, Allen R, Bao Z. An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications. Nature Nanotechnol 2012;7:825 32. [3] Benight SJ, Wang C, Tok JBH, Bao Z. Stretchable and self-healing polymers and devices for electronic skin. Progr Polym Sci 2013;38:1961 77. [4] Malinskii YM, Prokopenko VV, Ivanova NA, Kargin VA. Investigation of self-healing of cracks in polymers. Mekhanika Polim 1969;2:271 5. [5] Wool RP. Crack healing in semicrystalline polymers, block copolymers and filled elastomers. Adhes Adsorp Polym 1979;12A:341 62. [6] Wool RP, O’Connor KM. A theory of crack healing in polymers. J. Appl. Phys. 1981;52:5953 63. [7] Tittelboom KV, Belie ND. Self-healing in cementitious materials—a review. Materials 2013;6:2182 217. [8] Guimard NK, Oehlenschlaeger KK, Zhou J, Hilf S, Schmidt FG, Barner-Kowollik C. Current trends in the field of self-healing materials, macromolecular chemistry and physics. Macromol Chem Phys 2012;213:131 43. [9] Zhong N, Post W. Self-repair of structural and functional composites with intrinsically self-healing polymer matrices: a review. Compos. : A 2015;69:226 39. [10] Carlson JA, English JM, Coe DJ. A flexible, self-healing sensor skin. Smart Mater. Struct. 2006;15:N129 35. [11] Mishra DK, Yu J, Leung CKY. Self-sensing and self-healing ‘smart’ cement-based materials a review of the state of the art, conference: sixth international conference on durability of concrete structures; 2018. [12] Escobar MM, Vago S, Va´zquez A. Self-healing mortars based on hollow glass tubes and epoxy amine systems. Composites: Part B 2013;55:203 7.
Self-repairing hollow-fiber polymer composites
325
[13] White SR, Sottos NR, Geubelle PH, Moore JS, Kessler MR, Sriram SR, et al. Autonomic healing of polymer composites. Nature 2001;409:794 7. [14] Brown EN, Sottos NR, White SR. Fracture testing of a self-healing polymer composite. Exp Mech 2002;42:372 9. [15] Kim SR, Getachew BA, Kim JH. Toward microvascular network-embedded self-healing membranes. J Membr Sci 2017;531:94 102. [16] Cohades A, Branfoot C, Rae S, Bond I, Michaud V. Progress in self-healing fiber-reinforced polymer composites. Adv Mater Interfaces 2018;1800177. [17] Motuku M, Vaidya UK, Janowski GM. Parametric studies on self-repairing approaches for resin infused composites subjected to low velocity impact. Smart Mater Struct 1999;8:623. [18] Pulikkalparambil H, Siengchin S, Parameswaranpillai J. Corrosion protective selfhealing epoxy resin coatings based on inhibitor and polymeric healing agents encapsulated in organic and inorganic micro and nanocontainers. Nano-Struct Nano-Obj 2018;16:381 95. [19] Kling S, Cziga´ny T. Damage detection and self-repair in hollow glass fiber fabricreinforced epoxy composites via fiber filling. Compos Sci Technol 2014;99:82 8. [20] Scheiner M, Dickens TJ, Okoli O. Progress towards self-healing polymers for composite structural applications. Polymer 2016;83:260 82. [21] Dry CM. Advances in cementitious materials conf. Gaithersburg, MD: American Ceramic Society; 1990. p. 729 67. [22] Dry CM. Recent advances in adaptive and sensory materials and their applications conf. Blacksburg, VA: Technomic Publishing Co; 1992. p. 207 23. [23] Dry CM. In: Knowles GJ, editor. ADPA/AIAA/ASME/SPIE conf. on active materials and adaptive structures. Alexandria, VA: IOP Publishing; 1992. p. 191 3. [24] Dry CM. In: Erdogan F, Hartranft RJ, editors. Fracture mechanics: 25th volume ASTM STP 1220. Philadelphia, PA: Society for the Advancement of Materials and Process Engineering; 1994. p. 268 81. [25] Dry CM. Matrix cracking repair and filling using active and passive modes for smart timed release of chemicals from fibers into cement matrices. Smart Mater Struct 1994;3:118 23. [26] Dry CM. Procedures developed for self-repair of polymer matrix composite materials. Compos Struct 1996;35:263 9. [27] Bleay SM, Loader CB, Hawyes VJ, Humberstone L, Curtis PT. A smart repair system for polymer matrix composites. Compos: Part A 2001;32:1767. [28] Pang JWC, Bond IP. ‘Bleeding composites’ damage detection and self-repair using a biomimetic approach. Compos Part A Appl Sci Manuf 2005;36:183 8. [29] Pang JWC, Bond IP. A hollow fibre reinforced polymer composite encompassing selfhealing and enhanced damage visibility. Compos Sci Technol 2005;65:1791 9. [30] Pang JWC, Bond IP. Biomimetic self-healing of advanced composite structures using hollow glass fibres. Smart Mater Struct 2006;15:704 10. [31] Williams G, Trask RS, Bond IP. A self-healing carbon fibre reinforced polymer for aerospace applications. Compos Part A Appl S 2007;38:1525 32. [32] Trask RS, Williams GJ, Bond IP. Bioinspired self-healing of advanced composite structures using hollow glass fibres. J R Soc Interface 2007;4:363 71. [33] Zainuddin S, Arefin T, Fahim A, Hosur MV, Tyson JD, Kumar A, et al. Recovery and improvement in low-velocity impact properties of e-glass/epoxy composites through novel self-healing technique. Compos Struct 2014;108:277 86.
326
Self-Healing Composite Materials
[34] Mittal G, Rhee KY, Miskovic-stankovic V, Hui D. Reinforcements in multi-scale polymer composites: Processing, properties, and applications. Compos Part B 2018;138:122 39. [35] Bekas DG, Baltzis D, Paipetis AS. Nano-reinforced polymeric healing agents for vascular self-repairing composites. Mater Design 2017;116:538 44. [36] Lanzara G, Yoon Y, Liu H, Peng S, Lee W-I. Carbon nanotube reservoirs for selfhealing materials. Nanotechnology 2009;20:335704. [37] Syrett JA, Becer CR, Haddleton DM. Self-healing and self-mendable polymers. Polym Chem 2010;1:978 87. [38] Vijayan PP, Al-Maadeed MASA. TiO2 nanotubes and mesoporous silica as containers in self-healing epoxy coatings. Sci Rep 2016;6:38812. [39] Vijayan PP, El-Gawady YMH, Al-Maadeed MASA. Halloysite nanotube as multifunctional component in epoxy protective coating. Ind Eng Chem Res 2016;55:11186 92. [40] Vijayan PP, El-Gawady YMH, Al-Maadeed MASA. A comparative study on long term stability of self-healing epoxy coating with different inorganic nanotubes as healing agent reservoirs. eXPRESS Polym Lett 2017;11:863 72. [41] Zhu Y, Ye XJ, Rong MZ, Zhang MQ. Self-healing glass fiber/epoxy composites with polypropylene tubes containing self-pressurized epoxy and mercaptan healing agents. Compos Sci Technol 2016;135:146 52. [42] Zanjani JSM, Okan BS, Yilmaz C, Menceloglu Y, Yildiz M. Monitoring the interface and bulk self-healing capability of tri-axial electrospun fibers in glass fiber reinforced epoxy composites. Composites: Part A 2017;99:221 32.
17
Harikrishnan Pulikkalparambil1, M.R. Sanjay1, Suchart Siengchin1, Anish Khan2, Mohammad Jawaid3 and Catalin Iulian Pruncu4,5 1 Department of Mechanical and Process Engineering, The Sirindhorn International Thai-German Graduate School of Engineering (TGGS), King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand, 2Center of Excellence for Advanced Materials Research (CEAMR), Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia, 3Department of Biocomposite Technology, Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia (UPM), Serdang, Malaysia, 4Department of Mechanical Engineering, Imperial College London, London, United Kingdom, 5Department of Mechanical Engineering, School of Engineering, University of Birmingham, London, United Kingdom
17.1
Introduction
The concept of using self-repairing hollow fibers in polymer composites was a major breakthrough leading to many revolutionary findings in the field of smart self-healing materials [1 3]. The first reports on self-healing in thermoplastics and cross-linked systems were in 1969, 1979, and 1981 [4 6]. Since then, many polymer composites with excellent self-healing capabilities have been developed [7]. Several self-healing approaches for self-healing materials have been developed to date and there is expected to be huge demand in the fields of construction, electronics, and aviation [8,9]. The first studies reported on self-healing polymer composites were based on self-repairing hollow glass fibers (HGFs) [10,11]. The advantages of self-healing polymer composites include a reduction in the cost of maintenance and improved lifespan [12]. Several matrix materials such as polyester, polyimide, polyurethane, silicone rubber, and epoxy resins have been considered for developing self-healing composites. This is due to their low density, excellent chemical inertness, low cost, and versatility in fabrication methods. In addition, such materials exhibit better adhesion of substrates [13]. There are several key parameters in determining polymers as healing agents for self-healing applications. Some of these parameters include viscosity, gelling time, enthalpy of reaction, cross-linking temperature, stoichiometric ratio of hardeners, etc. [14]. In the past, most researchers were focused on self-healing materials based on microencapsulation of healing agents in polymeric containers. Urea formaldehyde and melamine formaldehyde are commonly used polymeric microcapsules along with catalyst/hardener dispersed in matrix [15,16]. However, polymeric Self-Healing Composite Materials. DOI: https://doi.org/10.1016/B978-0-12-817354-1.00017-X © 2020 Elsevier Inc. All rights reserved.
314
Self-Healing Composite Materials
microcapsules may adversely affect the mechanical property and may have limited healing capabilities. Furthermore, the polymeric microcapsules left in the polymer matrix after one-time healing may deteriorate the mechanical performance of the composites. Also, such a technique follows interfacial polymerization at the interface of healing agents and monomer solutions to produce microcapsules. This may not be suitable for very highly reactive healing agents for encapsulation due to their possible interaction with the polymerization process [17,18]. Thus, an alternate method to encapsulate healing agents that provides structural integrity as well as functional ability to the composites is preferred. HGFs are an excellent alternative for microcapsules because of their mechanical stability and thermal properties. Also, hollow fibers are able to store more healing agents without compromising the reinforcement and are easily integrated into the matrix with less restriction of the activation method and healing chemistry of healing agents [19,20]. Recently, fibers such as HGFs, halloysite nanotubes (HNTs), titanium dioxide nanotubes (TNTs), and polymeric fibers have gained a great deal of acceptance in designing the selfrepairing composites for structural applications. When damage is triggered by an external stimulus, the fiber breaks, this allows the healing agents to flow into the crack site, and it undergoes polymerization in the presence of a hardener or catalyst present at the crack site. In the following sections, self-repair polymer composites encapsulated with HGFs, hollow nanofibers, and hollow polymeric fibers are discussed.
17.2
Self-repairing techniques
17.2.1 Hollow glass fibers Among several hollow fibers, the self-healing composites made up of HGFs are widely used due to their (1) ability to retain mechanical properties, and (2) cost effectiveness [20,21]. However, the efficiency of such hollow fiber composites depends on several parameters such as (1) the viscosity of the healing agent, (2) the diameter of the hollow tube, and (3) the interfacial adhesion between the fiber and the matrix, etc. [22]. Dry et al. introduced the self-repairing concept by the release of chemicals stored in the hollow glass tubes for repairing of cracks to prevent corrosion in cement matrices [23 26]. Later, Dry et al. [26] reported two-part epoxy adhesive encapsulated HGFs to visualize the release of healing agents. This was one of the initial works carried out to develop self-healing polymer composites. Glass pipette tubes with c. 4 inches length and 100 µL volume were used as containers to encapsulate a cyanoacrylate-based adhesive healing agent. The encapsulation of healing agent was carried out by the vacuum method. Impact and bend tests of epoxy samples containing HGF with and without healing agents were used to demonstrate the retention of structural properties after the healing process. The impact test and bend test show the possibility of healing agents to demonstrate repairing, crack reopening resistance, and extending of crack propagation delay. However, specific concerns such as matrix material, fiber distribution, sample
Self-repairing hollow-fiber polymer composites
315
thickness, impact energy, and processing quality were not considered. Later Motuku et al.[17] developed passive-smart polymer composites (PSPCs) that help to repair damage caused by low-velocity impact. The authors compared epoxy resin encapsulated within glass capillary tubes such as borosilicate glass microcapillary pipettes, flint glass pasteur pipettes, copper tubing, and aluminum tubing. The selfhealing composite panels were prepared by placing encapsulated hollow fibers halfway between the top half and bottom half of the laminates while a resin injection was carried out by vacuum-assisted resin transfer molding (VARTM). The lowvelocity impact response in borosilicate glass, copper tubings, microcapillary pipettes, and flint glass pasteur pipette composites is poor due to the matrix cracking, fiber breakage, and delamination, etc. However, the insertion of glass tubing with healing agents exhibited a much improved impact response. This is because the lower energy impact may not damage the aluminum or copper tubings to release the healing chemicals. On the other hand, microcapillary pipettes were considered as containers. In conclusion, the authors reported the number and spatial distance of the fibers, thickness, and the impact energy played a vital role in the efficiency of self-healing in polymer composites. However, Dry and Motuku et al. demonstrated the reduced use of hollow glass capillary tubes to repair crack sites, and fiber thickness was still a major concern. The thickness of fibers to develop self-healing composites has to be controlled in order to avoid failures (the optimum thickness of glass fibers is ,15 µm), as thick glass fibers could lead to weak spots in composite materials that may further promote delamination or composite damages. In order to avoid such weak spots in composite materials, Bleay et al. [27] demonstrated the potential of self-healing HGF/epoxy reinforced composites with comparatively smaller diameters (internal diameter of 5 µm and outer diameter c. 15 µm). The laminates with c. B6.5 mm thickness were prepared by laying up unidirectional prepreg material. Twenty-four-ply, 300 mm 3 600 mm composite panels of [(0 , 90 )12]s and other [(0 , 45 , 90 )6]s ply layup arrangements were compared. The vacuum-assisted capillary strategy for filling as shown in Fig. 17.1 was carried out to encapsulate healing agents. The epoxy resin was entrapped in one fiber direction with hardener in the other direction. Both epoxy and hardener are mixed with acetone prior to encapsulation to reduce viscosity and improve the flow of healing agents into the damage site and to effect a cure. The self-repairing hybrid epoxy composites with HGF and E-glass fiber containers were investigated by Bond et al. [28 32]. The robustness of the self-repairing process was performed, before and after healing of specimens, by conducting flexural strength. The quasistatic indentation that replicated impact damage was manually produced on the composite specimens and the damage recovery was detected by a four-point bending experiment. Pang and Bond [29] used an ultraviolet (UV) fluorescent dye along with epoxy resin (MY750 Ciba-Geigy 1 30%/vol. acetone) to trigger self-healing by a UV lamp. They used samples made of 0 /90 hand layup (HLU) process to prepare composites with 0 HGF filled with epoxy resin and 90 HGF filled with hardener. A conventional HGF fabric with borosilicate inner layer and inner diameter of 60 µm and 50% hollowness was used to hold the healing agents. Once the crack is triggered, it requires c. 24 h to complete the resin cross-linking
316
Self-Healing Composite Materials
Figure 17.1 The vacuum-assisted capillary strategy for filling in order to encapsulate healing agents inside hollow glass fibers [27].
process. The four-point bending tests performed on the composites show that unfilled composites had 25% less bending strength than filled ones. This is because the unfilled composites undergo cracks during bending forces. On the other hand, the crack propagation of filled HGFs is restricted by the healing agents. Fig. 17.2 shows the ultraviolet mapping technique (UMVT) and ultrasonic C-scan image of impact specimens to visualize the self-healing process. Kling et al. [19] studied the damage detection and self-repair of thin HGFs (inner diameter of 5 6 µm and outer diameter of 10 12 µm) in epoxy composites. Here, HGFs filled with polyester (Polimal 1058) healing agent and its initiator were used to study the self-healing process. An indicator liquid (UV fluorescent dye) mixed with epoxy resin was used to visualize the healing process. The composites containing fluorescent dye-filled HGFs exhibited better damage detection under UV illumination. To study the healing process, the samples prepared by HLU and VARTM methods were damaged by a falling weight impact-testing machine. The damaged samples were left to heal at 60 C and 23 C for 12 and 120 h, respectively. The samples containing polyester healing agents were able to generate a 20% improvement in the bending properties compared to reference specimens without a healing agent. This is due to the incompressibility of the liquid healing agents inside the hollow fibers, and friction between the liquid polyester resin and the fiber inner wall. Zainuddin et al. [33] reported a novel self-healing technique to recover lowvelocity impact properties of E-glass/epoxy composites and they found a good improvement during multiple impacts. The authors used a smart encapsulation strategy as shown in Fig. 17.3 for the preparation of impact specimens. One end of the HGFs was immersed in a curing agent (unsaturated polyester resin) and initiator (cobalt octate) at room temperature, then a suction force was applied to the other
Self-repairing hollow-fiber polymer composites
317
Figure 17.2 UVMT images of (A) front face of impact specimen, (B) back face of impact specimen, and (C) ultrasonic C-scan image of impact specimen [29].
Figure 17.3 The process of HGF encapsulation and preparation of e-glass/epoxy composite [33].
end. Similarly, the encapsulation of MEKP in the HGF was conducted. Later, both ends of the HGFs were closed by a commercially available adhesive to avoid leakage. A vacuum-assisted resin infusion molding (VARIM) process was used for the preparation of composites. Table 17.1 shows the impact tests conducted on control epoxy samples, plain composites, and self-healing agent (SHA)-filled composites. The composites recorded an increase of 53.6% on the peak load after the second impact for composites containing SHA-filled HGF compared to control epoxy composites. The improved peak load during the second impact was attributed to curing
318
Self-Healing Composite Materials
Table 17.1 Low-velocity impact tests of control, plain, and self-healing agent-filled composites [33].
Control—first impact Control—second impact Plain HGF—first impact Plain HGF—second impact SHA-filled HGFs— first impact SHA-filled HGFs— second impact
Total energy (J)
Energy to maximum load (J)
Absorbed energy (J)
Peak load (kN)
55.8 6 1.6 50.9 6 1.4
39.9 6 2 24.6 6 1.4
15.9 6 2 26.3 6 4
9.7 6 0.1 7 6 0.9
54.6 6 2.1
47.3 6 1
7.3 6 1
11.2 6 0.2
55.7 6 1.3
43.5 6 1.3
12.2 6 2
10 6 0.2
54 6 1.5
47 6 2.8
761
12.3 6 0.8
54 6 1.6
45.8 6 0.8
8.2 6 2
10.6 6 0.4
of unsaturated polyester resin in crack sites that may regain the strength of composites. It is worth mentioning that once the crack healing occurs, the healed location in the composites may be left without fillers [34,35].
17.2.2 Hollow nanofibers In a recent study, Bekas et al. [35] modified epoxy healing agents with multiwalled carbon nanotubes (MWCNTs) encapsulated in glass fibers. Here, interlaminar fracture toughness, dynamic viscosity, etc., was evaluated to understand the effect of CNT loading in the healing agent. It was found that the healing efficiency of the composite increased from 120% to 192% in comparison with neat epoxy. However, the addition of CNTs in the healing agent increased the viscosity tremendously. However, the viscosity can be controlled by the addition of solvent ethyl phenylacetate (EPA). The increased healing efficiency is due to the presence of MWCNTs in crack sites that may hinder the crack initiation/propagation after the healing process. Also, the presence of CNTs in the crack site provides a nanoreinforcement effect during fracture toughness studies. Lanzara et al. [36] proposed a molecular dynamic simulation study of a singlewalled carbon nanotube to examine the feasibility of CNTs as novel nanocontainers for self-healing of composites. Fig. 17.4 provides the self-healing concept using the carbon nanotube reservoirs. The advantage of using carbon nanotube-based composites for self-healing is driven by their ability to generate strength to the composites prior to healing [37]. Once the composite is susceptible to damage, an organic healing agent is released to contact the catalyst deposited in the matrix to undergo cross-linking and heal the cracks. However, the efficiency of containing healing agents in the CNT capsules depends on the (1) nanotube diameter, (2) nanotube
Self-repairing hollow-fiber polymer composites
319
Figure 17.4 Self-healing concept using carbon nanotubes as nanoreservoirs for healing agents [36].
length, (3) nanotube orientation in the matrix, (4) nanotube dispersion, (5) nanotube loading density, (6) type of matrix, and (7) healing agents [37]. Fig. 17.5 presents a schematic diagram of a healing agent encapsulated in HNTs and curing agent immobilized in mesoporous silica. The encapsulation of a healing agent in a HNT is simple, as they are produced by a vacuum infiltration method. First the nanotubes are kept under repeated vacuum pressure to replace the air inside the tubes with healing agents. Vijayan et al. investigated the self-healing performance of dual-container self-healing systems with a HNT and/or TNT with an epoxy healing agent (Epon 826) and mesoporous silica containing diethylene triamine (Epikure 3223) curing agent [38,39]. The vacuum infiltration process was used for encapsulation of healing agents inside the nanotubes. The nanotube is encapsulated by mixing with epoxy and then applying a repeated vacuum to replace the air inside the inner lumen of the nanotubes with epoxy. An amine curing agent is immobilized onto the pores of the mesoporous silica by shaking for 24 h. Further, Vijayan et al. [40] compared the healing efficiency of the HNT with two different tube diameters (TNT 1 1.5 nm and TNT 2 10 nm) in order to understand the effect of tube volume. The nanotubes together with stoichiometric amounts of diethylene triamine curing agent immobilized in silica were mixed with epoxy resin and curing agent followed by sonication. The percentage of recovery of healing was found to be 31, 64, and 105% for EP/HNT, EP/TNT1, and EP/TNT2 coatings, respectively.
17.2.3 Hollow polymeric fibers Zhu et al. [41] reported the use of polypropylene (PP) tubes as reservoirs for an epoxy/mercaptan healing agent. The PP tubes (Paradigm Optics, Inc.) with an outer tube diameter of 250 mm and inner tube diameter of 200 mm were selected as a potential reservoir due to several advantages, including: (1) easy filling of large tubes followed by thermal stretching to make them smaller; (2) compartmented version of PP tubing can produce repeated healing; (3) surface modifications generated to achieve good compatibility; (4) its flexibility allows knitting of fibers into mats;
320
Self-Healing Composite Materials
Figure 17.5 Schematic representation of the halloysite nanotube encapsulation and mesoporous silica immobilization [38].
and (5) inertness of the fibers toward healing agents. Fig. 17.6 show a schematic representation of thermal stretching for easy filling, compartmented structure, knitting, and surface modifications. A foaming agent along with the encapsulated healing agent can greatly influence the self-healing ability. The foaming agent can generate a self-pressurized gas due to the thermal decomposition resulting in the formation of pressure inside the container. This may result in a sudden discharge of healing agent to flow much faster and wider into the damaged site, as a result a higher self-healing performance is produced. Another way to produce hollow polymer fibers for self-healing is by using the electrospun fibers with healing liquids encapsulated within the fibers during the electrospinning process. This is carried out using a triaxial electrospinning process. In an interesting work, Zajani et al. [42] used a one-step triaxial electrospinning process as shown in Fig. 17.7 to produce hollow fibers capable of storing healing
Self-repairing hollow-fiber polymer composites
321
Figure 17.6 Thermoplastic tubing forming a microvascular self-healing composite: (A) the healing fluid encapsulated inside a thicker tube, (B) thermal thinning of a tube, (C) a compartmented structure made of a tube to hold healing agents, (D) surface modification of a tube, and (E) knitted thermoplastic fiber with glass fiber [41].
Healing agent
Middle layer solution Outer layer solution Tri axial healing fiber PAAm PMMA Epoxy
High-voltage supply
Collector
Figure 17.7 A triaxial electrospinning set-up used to prepare the healing agent-encapsulated hollow PMMA/PAAm fibers [42].
agents. Here, a XB 3458 hardener and acetone diluted Araldite LY 564 epoxy resin was separately encapsulated inside an electrospun polymer fiber. The healing agent-encapsulated electrospun fibers were spun using polymethyl methacrylate (PMMA) and polyacrylamide (PAAm) polymers as outer and middle cores, respectively. The outer PMMA core is responsible for better compatibility with the matrix by forming a semi-interpenetrating (semi-IPN) network. On the other hand, the middle PAAm core helps to protect the healing agent by reducing the interaction of healing agents with the outer core as well as the matrix due to its lower affinity. This can increase the efficiency and lifetime of healing agents.
322
Self-Healing Composite Materials
Figure 17.8 Some SEM images showing (A and B) the PMMA/PAAm hollow fiberreinforced composite and (C and D) epoxy/hardener encapsulated PMMA/PAAm healing fiber-reinforced composite [42].
SEM images of PMMA/PAAm hollow fiber-reinforced composite are shown in Fig. 17.8A and B and an epoxy/hardener encapsulated PMMA/PAAm healing fiber-reinforced composite is depicted in Fig. 17.8C and D showing interfacial delamination and crack repairing in the presence of PMMA/PAAm/(epoxy, hardener) healing fibers. Kim et al. [15] studied the self-healing of polyethersulfone (PES) films using methylene diphenyl diisocyanate (MDI) prepolymer encapsulated in fluorinated ethylene propylene (FEP) capillary tubes. Fig. 17.9 shows a schematic diagram of (1) the encapsulation process using a microfluidic device, and (2) fabrication of selfhealing membrane on PET fabric support followed by PES casting and phase inversion apparatus. In this work, the mechanism of self-healing is the water-induced phase separation of healing agents to produce an increase in the viscosity, followed by a further phase separation reaction to form an expanded polyurethane/polyurea matrix that heals the damaged area. The advantage of using FEP tubes unlike other capsule systems are (1) water penetration in FEP tubes is inhibited to avoid deactivation of healing agent, (2) improved physical strength of the tubes, and (3) the use of more reactive liquids as healing agents.
Self-repairing hollow-fiber polymer composites
323
Healing agent
(A)
Outlet Syringe pump
PTFE tube
Epoxy glue 400 µm
250 µm
Slide glass
FEP capillary tube
Glass capillary tube (B)
(i) Membrane area marking Membrane area
PET support
90 µm
(ii) Installation of capillary tube Membrane area Core-filled FEP capillary tube
PET support
(iv) Phase inversion process
(iii) Membrane casting
Water bath Core-filled Membrane FEP capillary tube
Membrane Core-filled casting solution FEP capillary tube
PET support
Figure 17.9 Schematic diagram that presents (A) the encapsulation of healing agents located inside the core of an FEP capillary tube using a microfluidic device, (B) fabrication of selfhealing membrane (i, ii), casting of PES solution (iii), phase inversion process using water bath (iv) [15].
17.3
Conclusion
The recent developments in self-repairing hollow fiber composites have been discussed in this chapter. Self-repair has broadened the application areas of polymeric materials and enabled improvement in the life of materials. The works dedicated to encapsulated self-repairing composite fibers require classification based on the fiber
324
Self-Healing Composite Materials
types used. In the early stage most work was carried out in conjunction with glass fibers. Recently, the possibilities of employing self-repairing material with the aid of polymeric fibers and hollow nanofibers (HNT, TiO2, and CNT) have been explored. Therefore, these areas still need more expertise to achieve better results. However, great improvements in the number of research works dedicated to healing mechanisms on the composites have been made, yet multiple self-repairing hollow fibers are still a major challenge.
Acknowledgment This research was partly supported by the King Mongkut’s University of Technology North Bangkok through the PhD and PostDoc Program (Grant No. KMUTNB-61-PHD-001, KMUTNB-61-Post-001, and KMUTNB-62-KNOW-001).
References [1] Wang S, Liu N, Su J, Li L, Long F, Zou Z, et al. Highly stretchable and self-healable supercapacitor with reduced graphene oxide based fiber springs. ACS Nano 2017;11:2066 74. [2] Tee BC, Wang C, Allen R, Bao Z. An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications. Nature Nanotechnol 2012;7:825 32. [3] Benight SJ, Wang C, Tok JBH, Bao Z. Stretchable and self-healing polymers and devices for electronic skin. Progr Polym Sci 2013;38:1961 77. [4] Malinskii YM, Prokopenko VV, Ivanova NA, Kargin VA. Investigation of self-healing of cracks in polymers. Mekhanika Polim 1969;2:271 5. [5] Wool RP. Crack healing in semicrystalline polymers, block copolymers and filled elastomers. Adhes Adsorp Polym 1979;12A:341 62. [6] Wool RP, O’Connor KM. A theory of crack healing in polymers. J. Appl. Phys. 1981;52:5953 63. [7] Tittelboom KV, Belie ND. Self-healing in cementitious materials—a review. Materials 2013;6:2182 217. [8] Guimard NK, Oehlenschlaeger KK, Zhou J, Hilf S, Schmidt FG, Barner-Kowollik C. Current trends in the field of self-healing materials, macromolecular chemistry and physics. Macromol Chem Phys 2012;213:131 43. [9] Zhong N, Post W. Self-repair of structural and functional composites with intrinsically self-healing polymer matrices: a review. Compos. : A 2015;69:226 39. [10] Carlson JA, English JM, Coe DJ. A flexible, self-healing sensor skin. Smart Mater. Struct. 2006;15:N129 35. [11] Mishra DK, Yu J, Leung CKY. Self-sensing and self-healing ‘smart’ cement-based materials a review of the state of the art, conference: sixth international conference on durability of concrete structures; 2018. [12] Escobar MM, Vago S, Va´zquez A. Self-healing mortars based on hollow glass tubes and epoxy amine systems. Composites: Part B 2013;55:203 7.
Self-repairing hollow-fiber polymer composites
325
[13] White SR, Sottos NR, Geubelle PH, Moore JS, Kessler MR, Sriram SR, et al. Autonomic healing of polymer composites. Nature 2001;409:794 7. [14] Brown EN, Sottos NR, White SR. Fracture testing of a self-healing polymer composite. Exp Mech 2002;42:372 9. [15] Kim SR, Getachew BA, Kim JH. Toward microvascular network-embedded self-healing membranes. J Membr Sci 2017;531:94 102. [16] Cohades A, Branfoot C, Rae S, Bond I, Michaud V. Progress in self-healing fiber-reinforced polymer composites. Adv Mater Interfaces 2018;1800177. [17] Motuku M, Vaidya UK, Janowski GM. Parametric studies on self-repairing approaches for resin infused composites subjected to low velocity impact. Smart Mater Struct 1999;8:623. [18] Pulikkalparambil H, Siengchin S, Parameswaranpillai J. Corrosion protective selfhealing epoxy resin coatings based on inhibitor and polymeric healing agents encapsulated in organic and inorganic micro and nanocontainers. Nano-Struct Nano-Obj 2018;16:381 95. [19] Kling S, Cziga´ny T. Damage detection and self-repair in hollow glass fiber fabricreinforced epoxy composites via fiber filling. Compos Sci Technol 2014;99:82 8. [20] Scheiner M, Dickens TJ, Okoli O. Progress towards self-healing polymers for composite structural applications. Polymer 2016;83:260 82. [21] Dry CM. Advances in cementitious materials conf. Gaithersburg, MD: American Ceramic Society; 1990. p. 729 67. [22] Dry CM. Recent advances in adaptive and sensory materials and their applications conf. Blacksburg, VA: Technomic Publishing Co; 1992. p. 207 23. [23] Dry CM. In: Knowles GJ, editor. ADPA/AIAA/ASME/SPIE conf. on active materials and adaptive structures. Alexandria, VA: IOP Publishing; 1992. p. 191 3. [24] Dry CM. In: Erdogan F, Hartranft RJ, editors. Fracture mechanics: 25th volume ASTM STP 1220. Philadelphia, PA: Society for the Advancement of Materials and Process Engineering; 1994. p. 268 81. [25] Dry CM. Matrix cracking repair and filling using active and passive modes for smart timed release of chemicals from fibers into cement matrices. Smart Mater Struct 1994;3:118 23. [26] Dry CM. Procedures developed for self-repair of polymer matrix composite materials. Compos Struct 1996;35:263 9. [27] Bleay SM, Loader CB, Hawyes VJ, Humberstone L, Curtis PT. A smart repair system for polymer matrix composites. Compos: Part A 2001;32:1767. [28] Pang JWC, Bond IP. ‘Bleeding composites’ damage detection and self-repair using a biomimetic approach. Compos Part A Appl Sci Manuf 2005;36:183 8. [29] Pang JWC, Bond IP. A hollow fibre reinforced polymer composite encompassing selfhealing and enhanced damage visibility. Compos Sci Technol 2005;65:1791 9. [30] Pang JWC, Bond IP. Biomimetic self-healing of advanced composite structures using hollow glass fibres. Smart Mater Struct 2006;15:704 10. [31] Williams G, Trask RS, Bond IP. A self-healing carbon fibre reinforced polymer for aerospace applications. Compos Part A Appl S 2007;38:1525 32. [32] Trask RS, Williams GJ, Bond IP. Bioinspired self-healing of advanced composite structures using hollow glass fibres. J R Soc Interface 2007;4:363 71. [33] Zainuddin S, Arefin T, Fahim A, Hosur MV, Tyson JD, Kumar A, et al. Recovery and improvement in low-velocity impact properties of e-glass/epoxy composites through novel self-healing technique. Compos Struct 2014;108:277 86.
326
Self-Healing Composite Materials
[34] Mittal G, Rhee KY, Miskovic-stankovic V, Hui D. Reinforcements in multi-scale polymer composites: Processing, properties, and applications. Compos Part B 2018;138:122 39. [35] Bekas DG, Baltzis D, Paipetis AS. Nano-reinforced polymeric healing agents for vascular self-repairing composites. Mater Design 2017;116:538 44. [36] Lanzara G, Yoon Y, Liu H, Peng S, Lee W-I. Carbon nanotube reservoirs for selfhealing materials. Nanotechnology 2009;20:335704. [37] Syrett JA, Becer CR, Haddleton DM. Self-healing and self-mendable polymers. Polym Chem 2010;1:978 87. [38] Vijayan PP, Al-Maadeed MASA. TiO2 nanotubes and mesoporous silica as containers in self-healing epoxy coatings. Sci Rep 2016;6:38812. [39] Vijayan PP, El-Gawady YMH, Al-Maadeed MASA. Halloysite nanotube as multifunctional component in epoxy protective coating. Ind Eng Chem Res 2016;55:11186 92. [40] Vijayan PP, El-Gawady YMH, Al-Maadeed MASA. A comparative study on long term stability of self-healing epoxy coating with different inorganic nanotubes as healing agent reservoirs. eXPRESS Polym Lett 2017;11:863 72. [41] Zhu Y, Ye XJ, Rong MZ, Zhang MQ. Self-healing glass fiber/epoxy composites with polypropylene tubes containing self-pressurized epoxy and mercaptan healing agents. Compos Sci Technol 2016;135:146 52. [42] Zanjani JSM, Okan BS, Yilmaz C, Menceloglu Y, Yildiz M. Monitoring the interface and bulk self-healing capability of tri-axial electrospun fibers in glass fiber reinforced epoxy composites. Composites: Part A 2017;99:221 32.