Self-healing Epoxy Research Articles

Triple Roles of Thermoplastic Polyurethane in Toughening, Accelerating and Enhancing Self-healing Performance of Thermo-reversible Epoxy Resins

Cracks in polymers can be healed by endowing materials with self-healing performance. Cracks in epoxy resins containing thermo-reversible Diels–Alder bonds (EP-DA) can be self-healed via different heat treatments. However, EP-DA exhibits the disadvantages of brittleness and poor impact resistance yet as that existed in the common epoxy resins, and which limits the application of thermo-reversible self-healing epoxy resins. Herein, thermoplastic polyurethane (TPU) was introduced into EP-DA for the purpose of reducing the brittleness and improving the impact resistance of EP-DA. Meanwhile, it was expected that the self-healing performance of EP-DA could not be affected evidently. Results showed that the impact resistance of EP-DA had been improved greatly as expected upon TPU modification. More importantly, instead of affecting the self-healing performance of EP-DA, the self-healing speed of EP-DA was accelerated evidently by the incorporation of TPU. On the other hand, the healing efficiency of EP-DA was also enhanced markedly. In fact, TPU-modified EP-DA was repaired by dual actions of thermo-reversible DA reaction and thermal movement of thermoplastic polymer chains. In addition, TPU-modified EP-DA could also be healed for many damage-repair cycles. Therefore, thermoplastic polyurethane played a triple role as toughening, accelerating and enhancing self-healing performance of thermo-reversible epoxy resins. Thermoplastic polyurethane (TPU) was introduced into thermo-reversible self-healing epoxy resins (EP-DA) successfully. As a result, the brittleness was reduced and the impact resistance of EP-DA was improved greatly. What’s more, instead of affecting the self-healing performance of EP-DA, the self-healing speed of EP-DA was accelerated evidently while the self-healing efficiency of EP-DA was enhanced markedly. Therefore, TPU played a triple role as toughening, accelerating and enhancing self-healing performance of thermo-reversible epoxy resins.

Solvent effects on structural changes in self-healing epoxy composites

Nowadays, there is a very high importance of composite research and variety of their applications in the modern world. In that sense, we researched hollow glass capillaries filled with dissolved Grubbs catalyst (GC) and dicyclopentadiene (DCPD) were incorporated into a fiber-reinforced epoxy with the aim of improving the flow of healing agents to the crack site. The morphological investigation of the crack site was performed using field emission scanning electron microscopy (FESEM), showing the difference between the samples depending on the used solvent. The software analysis of sample photographs has been performed by calculating the fractured/healed surface area of the samples, revealing that approximately 20% of the volume was affected by the impact. Fourier transform infrared spectroscopy (FTIR) revealed that poly (dicyclopentadiene) (PDCPD) formed at the healed interface. However, the FTIR investigation of catalyst stability in different solvents showed structural changes in GC and partial deactivation. The mechanical tests of the samples showed that a recovery of 60% after 24 h at room temperature could be achieved through the use of a solvent and very low concentration of GC. The performed research results are a good base to develop the model for predicting the processes and morphology, with the goal to design the final mechanical and in the future, thermal, properties in advance. This opens a new direction for future research in the field of composite healing.

Electrosprayed PMMA microcapsules containing green soybean oil-based acrylated epoxy and a thiol: a novel resin for smart self-healing coatings

For the first time, the binary components of a self-healing epoxy system was developed comprising of a green acrylated epoxy resin and its thiol-based curing agent encapsulated in a poly (methyl methacrylate) (PMMA) shell by electrospraying technique. The field emission scanning electron microscopy images revealed that the two microcapsules formed were almost spherical with rough and irregular surfaces. The average diameter of microcapsules ranged from 1.165 to 1.418 μm for the two microcapsules. FTIR spectra and thermal analysis were used to investigate the encapsulation of acrylated epoxy resin and thiol curing agent in PMMA as well as the kinetics of crosslinking reaction between the two components. Based on FTIR spectra, the thiol curing agent was involved in the crosslinking reaction with the epoxy group (810 cm−1) and the C = C segment (1634 and 1613 cm−1) of acrylated epoxy resin. The DSC results indicated an exothermic peak (at 65 °C) proving that this system is efficient in self-healing epoxy resins for coating applications. Furthermore, the ability of epoxy coatings to protect the scratched coating substrate from corrosion media (the healing performance) without microcapsule, with dual microcapsules, single healing agent-containing microcapsule and single curing agent-containing microcapsule were also evaluated using potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS). The results were in line with the potentiodynamic polarization and the EIS. The highest self-healing efficiency (78%) was obtained for binary capsule concentration of 1%, indicating presence of sufficient amount of material to heal the cracks.

A novel shape memory-assisted and thermo-induced self-healing boron nitride/epoxy composites based on Diels–Alder reaction

Hexagonal boron nitride (hBN), as one of the two-dimensional (2D) materials, possesses many excellent properties like others. Herein, we report a novel self-healing epoxy filled with hBN. High compatibility between hBN and the epoxy matrix was obtained by the modification of hBN with silane coupling agent (Mi-Si). At the meantime, excellent self-healing behavior was achieved by retro Diels–Alder (r-DA) reaction between the maleimide functional group in the modified hBN (m-hBN-OH) and the added furfurylamine. Besides, the inadequate curing of epoxy led to the glass transition temperature (Tg), which is also seemed as the transition temperature for the shape memory of the epoxy, below the r-DA reaction temperature, and endowed the system with the shape memory-assisted self-healing properties. The m-hBN-OH was characterized by Fourier transform infrared spectra, nuclear magnetic resonance (1H-NMR) spectra, X-ray diffraction experiments, X-ray photoelectron spectroscopy measurements and so on. The new m-hBN-OH modifier was prepared with the optimized Mi-Si/hBN-OH weight ratio of 3.0, which could both improve the thermal property and achieve better thermal conductivity. This designed m-hBN-OH/epoxy could actually show ideal self-healing properties due to the shape memory-assisted self-healing effect. The thermal conductivity of the neat epoxy resin and the m-hBN-OH/epoxy was 0.2156 W m−1 K−1 and 0.4358 W m−1 K−1, respectively. As a novel material with efficient thermal conductivity, hBN made great contribution to the thermally induced shape memory and self-healing property. Systematic researches reveal that the composites are promising as long durable thermal interface materials, anti-scratch materials and so on.

Fabrication of β-cyclodextrin modified halloysite nanocapsules for controlled release of corrosion inhibitors in self-healing epoxy coatings

An effective pH-responsive halloysite with β-cyclodextrin shell was demonstrated to control the release of the inhibitor trapped in the halloysite channel. The effect of solution pH variation on the release behavior of nanocapsules was taken into account. The trapping mechanism by the β-CD molecules was investigated by quantum chemistry calculations. Commercial epoxy coating doped with various concentrations of benzotriazole-loaded containers showed a self-healing effect after 42 h of immersion in 0.5 M NaCl solution of the released benzotriazole. The EIS results confirmed the beneficial effect of the exact concentration of the benzotriazole-loaded container on the barrier properties of the epoxy coating, as distinct from increasing the impedance modulus.

Synthesis and Self-Healing Mechanism of Self-Healing Epoxy Microcapsule Materials

Self-healing epoxy resin microcapsules are prepared by interfacial polymerization, in which the core materials are epoxy resin, the wall materials are constructed with triethylenetetramine and the epoxy resin. The orthogonal experimental L9(34) are designed to investigate the influence of emulsifier dosage, hardener dosage, curing temperature and hardener adding rate on the core content and storage life of epoxy resin microcapsule. Scanning electron microscope is used to characterize surface topography and distribution. Fourier transform infrared spectroscopy is used to study reaction mechanism of the microcapsule wall materials, respectively. The results indicate that when the dosage of emulsifier is 1.2%, the dosage of hardener is 1.2%, the hardener droplets adding rate is 1.2 g/h and the curing temperature is 50°C, the prepared microcapsules with a high level of core content are spherical in shape with good surface compactness and dispersibility. Future research may focus on improving microcapsule storage stability and the obstacles encountered in practical applications.

Preparation and Characterization of Electrosprayed Nanocapsules Containing Coconut-Oil-Based Alkyd Resin for the Fabrication of Self-Healing Epoxy Coatings

In the present study, the preparation of nanocapsules using the coaxial electrospraying method was investigated. Poly(styrene-co-acrylonitrile) (SAN) was used as a shell material and coconut-oil-based alkyd resin (CAR) as a core. Chemical structure, thermal stability, and morphology of nanocapsules were characterized by Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and field emission scanning electron microscopy (FE-SEM), respectively. In addition, the formation of the core–shell structure was approved by transmission electron microscopy (TEM) and FE-SEM micrographs of the fractured nanocapsules. Furthermore, differential scanning calorimetry tests (DSC) were carried out to investigate the reactivity of released healing agents from the nanocapsules. The prepared nanocapsules were then incorporated into the epoxy resins and applied on the surfaces of the steel panels. The effect of capsule incorporation on the properties of the coating was evaluated. The self-healing performance of the coatings in the salty and acidic media was also assessed. The FTIR results revealed the presence of both shell and core in the prepared nanocapsules and proved that no reaction occurred between them. The morphological studies confirmed that the electrosprayed nanocapsules’ mean diameter was 708 ± 252 nm with an average shell thickness of 82 nm. The TGA test demonstrated the thermal stability of nanocapsules to be up to 270 °C while the DSC results reveal a successful reaction between CAR and epoxy resin, especially in the acidic media. The electrochemical impedance spectroscopy (EIS) test results demonstrate that the best self-healing performance was achieved for the 2 and 1 wt.% nanocapsules incorporation in the NaCl, and HCl solution, respectively.

A self-healing superamphiphobic coating for efficient corrosion protection of magnesium alloy

Magnesium alloys have many excellent properties, but the poor corrosion resistance seriously hinders their widespread applications. Here, we report a self-healing superamphiphobic coating for efficient corrosion protection of magnesium alloy by the combination of a compact self-healing epoxy resin (SHEP) coating and a porous superamphiphobic coating. The coating shows (i) excellent superamphiphobicity with high contact angle, low sliding angle and robust impact/bounce behavior, (ii) excellent anti-corrosion performance as demonstrated by the potentiodynamic polarization curves and electrochemical impedance spectroscopy, and (iii) excellent self-healing performance as proved by the scanning electron microscopy and electrochemical impedance spectroscopy. This is owing to synergistic effect of the bi-layer structure. Furthermore, the healed coating retained excellent anti-corrosion performance according to the immersion test and neutral salt spray test. This is because the SHEP layer can effectively drive repair of microstructure of the superamphiphobic layer, and then recover of superamphiphobicity. Therefore, the contact area and contact time of corrosive solutions with the pristine and healed coatings are limited, which efficiently prevents diffusion of corrosive substances such as water, chloride ions and oxygen. The self-healing superamphiphobic coating may find applications in protection of various metal alloys.

Multi-Functional Cardanol Triazine Schiff Base Polyimine Additives for Self-Healing and Super-Hydrophobic Epoxy of Steel Coating

The designing of multifunctional materials in system-level efficiency is one of the main targets and a hot topic for the application of novel green or bio-based materials and structures. In this work, the chemical structure of bio-based cardanol that was derived from cashew oil was modified through a reaction with a bishydrazino-s-triazine derivative followed by condensation polymerization or reaction with terephthaldehyde to obtain a Schiff base polymer. The chemical structures of the modified cardanol-bishydrazino-s-triazine-based monomer and the Schiff base polymer were confirmed from FTIR and NMR spectroscopy analyses. The modified cardanol bishydrazino-s-triazine monomer and polymer were added with different weight ratios during the curing of the epoxy/polyamine hardener to improve the thermal, mechanical, and anti-corrosion characteristics of the epoxy coating of a steel substrate. The data elucidated that the presence of a cardanol bishydrazino-s-triazine monomer and polymer improves the thermal, mechanical, adhesion, and anti-corrosion characteristics of epoxy coatings after exposure for more than 1500 h. The presence of a cardanol- bishydrazino-s-triazine polymer more than 3 wt.% during the curing of epoxy networks produces superhydrophobic and self-healing epoxy coatings. The modification of the epoxy coating with the cardanol bishydrazino-s-triazine polymer improves the seawater contact angle by more than 150° and the adhesion strength of the epoxy coating with the steel surface.

Exploitation of natural gum exudates as green fillers in self-healing corrosion-resistant epoxy coatings

Recently, interest in developing green polymer coatings which provide self-healing and corrosion protection functions using bio-based renewable materials has significantly increased. In this study, microcapsules containing biopolymers from cashew gum and gum Arabic have been prepared by interfacial polymerization. The prepared microcapsules were individually and combinatorially embedded into epoxy coatings and the resulting composite coatings were then applied on Q235 steel substrates. The performance of the composite coatings was evaluated by immersing both scribed and unscribed coatings in simulated seawater. Surface analytical (SEM), physico-chemical (FTIR, XRD, XPS), and electrochemical impedance spectroscopy (EIS) techniques were used to investigate self-healing and corrosion resistance effectiveness of the polymer composite coatings. The obtained results revealed that cashew gum and gum Arabic could heal the scribed coating surface and subsequently suppressed corrosion reaction, without the aid of any catalyst or co-reactant. The performance was observed to be higher when the two gum exudates were combined. Thus, cashew gum and gum Arabic have demonstrated that they possess properties required for potential utilization in the formulation of marine anticorrosion and self-healing epoxy coatings.

Microencapsulation of ethylenediamine and its application in binary self-healing system using dual-microcapsule

Microencapsulation of healing agents has been applied to realize the self-healing function of polymeric composites. In practice, however, microencapsulation of a liquid amine is very complicated because it is soluble in water and most organic solvents. In this paper, we report a new approach to preparing amine microcapsules that constitute a dual-microcapsule epoxy-amine self-healing system for epoxy composites. Ethylenediamine (EDA)-containing microcapsule with epoxy-EDA shell was successfully synthesized via interfacial polymerization in a water-in-oil emulsion. There were three key factors to solve the problem of microencapsulated a liquid amine, including preparation of epoxy-EDA shell prepolymer, a small amount of deionized water into core material, and polydimethylsiloxane as the continuous phase. A series of methods including Fourier transform infrared, differential scanning calorimetry, optical microscope, and scanning electron microscope were carried out to prove that microcapsules were suitable for preparing self-healing composites. Healing efficiency of self-healing epoxy achieved to 80.4% with 12 wt% epoxy-containing microcapsules and 8 wt% EDA-containing microcapsules. In general, this work provides a novel preparation method of liquid amine microcapsules. This novel and effective self-healing system may be useful for the development of epoxy-based structural composites for various applications.

Synthesis and characterization of TiO2/acrylic acid-co-2-acrylamido-2-methyl propane sulfonic acid nanogel composite and investigation its self-healing performance in the epoxy coatings

In the present study, the surface of titanium dioxide (TiO2) nanoparticles was modified with superabsorbent gel based on acrylic acid (AA) and 2-acrylamido-2-methyl propane sulfonic acid (AMPS) via in-situ polymerization using 3-(triethoxysilyl) propyl methacrylate (MPS) as a silane coupling agent. The synthesized TiO2 nanogel composite was then incorporated into a commercial epoxy resin in different weight percent (1, 2, and 4) to prepare an effective self-healing epoxy coating. The chemical structure and surface morphology of the prepared nanogel composite were evaluated by Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Field Emission Scanning Electron Microscopy (FESEM). Furthermore, to calculate the weight ratio of the inorganic to organic materials, the ash content test was employed. The effectiveness of the TiO2 nanogel composite as the self-healing material in the epoxy resin was assessed in 3.5 wt.% NaCl solution by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS).

Optimized synthesis of isocyanate microcapsules for self-healing application in epoxy composites

Microcapsules containing isophorone diisocyanate were fabricated in oil-in-water emulsion. The emulsification effect of different emulsifiers during the capsule synthesis was systematically investigated by optical microscope. Three kinds of shell materials were discussed to obtain the high core content, smooth-surfaced, and robust capsule by scanning electronic microscope and Fourier transform infrared spectroscopy. Self-healing performance of corresponding self-healing epoxy composites was fully evaluated by accelerated corrosion test and mechanical test. The results demonstrated that high core content and smooth-surfaced capsules with dense composite shell could be synthesized in polyvinyl alcohol emulsion, and the core content of the optimized capsules was determined as 71.3–84.6 wt% at the capsule size from 35 µm to 154 µm. In addition, the optimized capsules had good processing properties and the corresponding self-healing epoxy composites exhibited excellent core release and self-healing performance.

Design Strategy for Self-Healing Epoxy Coatings

Self-healing strategies including intrinsic and extrinsic self-healing are commonly used for polymeric materials to restore their appearance and properties upon damage. Unlike intrinsic self-healing tactics where recovery is based on reversible chemical or physical bonds, extrinsic self-healing approaches rely on a secondary phase to acquire the self-healing functionality. Understanding the impacts of the secondary phase on both healing performance and matrix properties is important for rational system design. In this work, self-healing coating systems were prepared by blending a bio-based epoxy from diglycidyl ether of diphenolate esters (DGEDP) with thermoplastic polyurethane (TPU) prepolymers. Such systems exhibit polymerization induced phase separation morphology that controls coating mechanical and healing properties. Structure–property analysis indicates that the degree of phase separation is controlled by tuning the TPU prepolymer molecular weight. Increasing the TPU prepolymer molecular weight results in a highly phase separated morphology that is preferable for mechanical performances but undesirable for healing functionality. In this case, diffusion of TPU prepolymers during healing is restricted by the epoxy network rigidity and chain entanglement. Low molecular weight TPU prepolymers tend to phase mix with the epoxy matrix during curing, resulting in the formation of a flexible epoxy network that benefits TPU flow while decreasing Tg and mechanical properties. This work describes a rational strategy to develop self-healing coatings with controlled morphology to extend their functions and tailor their properties for specific applications.

Development of self-contained microcapsules for optimised catalyst position in self-healing materials

Self-contained microcapsules for use in self-healing epoxy resin are successfully synthesized by suspension polymerization process. The microencapsulation of an epoxy resin using Polymethylmethacrylate (PMMA) as a shell material and the location of scandium triflate (Sc(OTf)3) as the catalyst into microcapsules shell during the microencapsulation processes is presented (PMMA/Sc(OTf)3-walled microcapsules). Spherical microcapsules of 80 μm in diameter with a liquid core content of 30 wt% (determined by HPLC) are produced. Catalyst location on microcapsules are assessed qualitatively by SEM-EADS and quantitatively by TGA showing high yields (⁓70 wt%). The evaluation of the healing efficiency was assessed in terms of fracture toughness recovery. PMMA/Sc(OTf)3-walled microcapsules showed an increased healing efficiency than that of conventional PMMA-walled capsule. The healing efficiency of the PMMA-walled capsules was 46.7 and 55.1% when the system healed at 80 and 120 °C, respectively. However, in the case of PMMA/Sc(OTf)3-walled microcapsules healing efficiency increased to 57.5 and 79.1% for the same healing temperatures.

Rational assembly of mussel-inspired polydopamine (PDA)-Zn (II) complex nanospheres on graphene oxide framework tailored for robust self-healing anti-corrosion coatings application

Abstract There are increasing demands for self-healing anti-corrosion coatings with high efficiency and durability in various industrial applications. Recently, eumelanin polymers especially polydopamine (PDA)-based nanostructures have been served as a mussel-inspired strategy to provide such requirements due to the intrinsic adhesive nature of amines and catechols along with its film-forming ability. Nevertheless, direct embedment of hydrophilic PDA nanoparticles into polymer coatings could eventually trigger corrosion as a consequence of the osmotic pressure exerted beneath the coating. In the present work, we have adopted a rational design for constructing robust self-healing epoxy composites via a tailor-made procedure including oxidative polymerization of dopamine over the graphene oxide (GO) framework and subsequent loading of Zn (II) corrosion inhibitor. The triple-function of GO as a template for polymerization of dopamine; simultaneously being a nanoreservoir for storage of corrosion inhibitors and eventually as an impermeable barrier is very crucial. Curiously, the as-prepared GO-PDA and GO-PDA-Zn nanocomposites exhibit different ion-capturing/releasing properties derived from opposite charges developed on them. This property not only declines the permeation of aggressive species into the coating matrix but also facilitates the release of divalent zinc ions or PDA through an on-demand manner when local corrosion initiates at the damaged zone. The propensity of PDA to anchor ferrous or ferric ions generated from anodic reactions in one hand and Zn (II) to form zinc hydroxide compounds at cathodic sites, on the other hand, endows the GO-PDA-Zn nanocomposite with high efficiency in reducing the corrosion current as measured by polarization and EIS analyses. More importantly, the outstanding self-healing function of GO-PDA/EP and GO-PDA-Zn/EP composite coatings was proved with impedance measurements on scratched coatings immersed in saline solution.

Facile strategy toward the development of a self-healing coating by electrospray method

A self-healing anti-corrosion epoxy coating was prepared by the incorporation of dual capsule healing system. Microcapsules were prepared through the facile electrospray method by using Poly(styrene-co-acrylonitrile) polymer as shell material. Polyetheramine and Methylene diphenyl diisocyanate (MDI) based isocyanate prepolymer were utilized as core materials because of their high reactivity and low sensitivity in forming polyurea polymers. Scanning electron microscopy (sem) images confirmed the spherical morphology of the prepared microcapsules with average diameters of 0.93 ± 0.55 μm and 1.21 ± 0.68 μm for the encapsulated polyetheramine and isocyanate microcapsules, respectively. Moreover, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) results confirmed the successful encapsulation of both core materials with a high encapsulation yield (71% and 68% for Polyetheramine and MDI based isocyanate respectively). Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization technique were used to assess the effects of utilizing the aforementioned system on the intrinsic anti-corrosion barrier property (on pristine samples ) and the self-healing efficiency (after cross scratching) of the resulting smart coatings. The corrosion assessment results confirmed the self-healing performance of the incorporated capsules along with a high healing efficiency (85%) for the optimum microcapsule content.

Preparation and Properties of Self-Healing and Self-Lubricating Epoxy Coatings with Polyurethane Microcapsules Containing Bifunctional Linseed Oil.

An organic coating is commonly used to protect metal from corrosion, but it is prone to failure due to microcracks generated by internal stress and external mechanical action. The self-healing and self-lubricating achieved in the coating is novel, which allows an extension of life by providing resistance to damage and repair after damage. In this study, a new approach to microencapsulating bifunctional linseed oil with polyurethane shell by interfacial polymerization. Moreover, the self-healing and self-lubricating coatings with different concentrations of microcapsules were developed. The well-dispersed microcapsules showed a regular spherical morphology with an average diameter of ~64.9 μm and a core content of 74.0 wt.%. The results of the salt spray test demonstrated that coatings containing microcapsules still possess anticorrosion, which is improved with the increase of microcapsules content, after being scratched. The results of electrochemical impedance spectroscopy showed a |Z|f=0.01Hz value of 104 Ω·cm2 for pure epoxy coating after being immersed for 3 days, whereas the coating with 20 wt.% microcapsules was the highest, 1010 Ω·cm2. The results of friction wear showed that the tribological performance of the coating was enhanced greatly as microcapsule concentration reached 10 wt.% or more, which showed a 86.8% or more reduction in the friction coefficient compared to the pure epoxy coating. These results indicated that the coatings containing microcapsules exhibited excellent self-healing and self-lubricating properties, which are positively correlated with microcapsules content.

Self-Healing Epoxy Coating Modified by Double-Walled Microcapsules Based Polyurea for Metallic Protection

The effectiveness of preploymer and 1,6-Hexamethylene diamine encapsulated by double-walled microcapsules based polyurea (PUA) was explored for healing the cracks generated in epoxy coatings. Double-walled microcapsules were systhesized by interfacial polymerization at the interface between the prepolymer droplets and the 1,6-Hexamethylene diamine droplets to form the polyurea shell. The effect of synthetic stirring speed on the morphology of the microcapsules was observed by scanning electronmicroscopy (SEM) and optical microscopy (OM). The chemical structure as well as the thermal properties and the core content were characterized by Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analyzer (TGA) respectively. Electrochemical impedance spectroscopy (EIS) studies of the artificial scratched area showed that the coating containing 2wt% and 5wt% microcapsules could effectively prevent further corrosion of the coating with high corrosion resistance efficiencies of 61.61% and 45.99% after immersing for 144h in seawater.

Self-healing epoxy nanocomposite coatings based on dual-encapsulation of nano-carbon hollow spheres with film-forming resin and curing agent

The ability of an active protective organic coating to restore its protection functionality in case of a coating defect is of pivotal importance to ensure durable performance under demanding corrosive conditions. In this paper, a self-healing epoxy system is fabricated by separate encapsulation of epoxy and polyamine in carbon hollow spheres (CHSs) and the autonomous healing performance of the system applied on mild steel is investigated. CHSs were synthesized via a silica templating method using carbonization of polysaccharide shells formed on the surface of silica templates. Consequently, epoxy and polyamine were loaded in separate capsules by dispersion of CHSs into the dilute solutions of epoxy/acetone and polyamine/acetone respectively, under vacuum conditions. The synthesized CHSs were characterized before and after the silica removal using field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The CHSs loaded with the film forming agents were assessed using thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. Furthermore, the protective and self-healing properties of the coatings fabricated were studied using electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) and salt spray testing. The results showed that scribe defects in epoxy coatings with 10 wt % epoxy and polyamine capsules were healed effectively upon efficient release and subsequent recombination of the epoxy and polyamine agents reforming a protective layer at the damaged region.