Self-healing Epoxy Composites Research Articles

Multiple phase change-stimulated shape memory and self-healing epoxy composites with thermal regulation function

Form-stable phase change materials (FSPCMs) are widely used for cost-effective thermal management and energy storage applications. However, the strong rigidity of most FSPCMs at low temperatures and the weak resistance of them to damages when the temperature is exceeding their phase transition points have hindered their installations in limited places. Herein, we developed a novel kind of thermal regulation FSPCM possessing multiple phase change-stimulated shape memory and self-healing properties to address these issues. The synthesis of the FSPCMs is based on confining ethylene glycole distearate (EGDS) within the epoxy-based polymer matrix through photo-initiated polymerization. This strategy, on one hand, prevents the leakage of the liquid EGDS in macroscales, and on the other hand, maintains the mobility of the flowing EGDS in micro-scale regions to allow the FSPCM to perform shape deformation and recovery and enable self-repairing effects through solid-liquid phase transitions. Notably, the polymer matrix in the FSPCM consists of pre-grafted crystalline segments of stearic acid (SA) which improve the compatibility between the matrix and EGDS, and impart the FSPCM with multiple phase transitions to realize stepwise control of the shape memory behaviors. The resulting composite FSPCM also demonstrates good thermal regulation performance and high thermal reliability, which can be promisingly engineered into thermal management of integrated circuits and building glazing system with thermal regulation purpose.

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.

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.

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.

A thermally remendable multiwalled carbon nanotube/epoxy composites via Diels-Alder bonding

Mechanically robust and self-healing epoxy composites are highly desired to satisfy the increasing demand of high-performance smart materials. Herein, a dual functionalized epoxy composite (EpF-MWCNT-PA-BM) with self-healing performance based on Diels-Alder chemistry has been investigated. The furfuryl grafted epoxy (EpF) and furfuryl modified MWCNTs (MWCNT-F) are reacted with bifunctional maleimide (BM) and normal anhydride curing agent (PA) to form a covalently bonded and reversibly crosslinked epoxy composite with two types of intermonomer linkage. That is, thermally reversible Diels-alder bonds between the furan groups of both epoxy and MWNCTs with malemide and thermally stable bonds of epoxide and anhydride groups. MWCNTs act as both reinforcer and a healant in the epoxy composite. In this way, the cured epoxy composite possessed not only enhanced mechanical properties but also thermal remendability that enabled elimination of cracks. The latter function took effect as a result of successive retro-DA and DA reactions, which led to crack healing upto 79.82% healing efficiency in a controlled manner through chain reconnection.

Development of self-healing epoxy composites via incorporation of microencapsulated epoxy and mercaptan in poly(methyl methacrylate) shell

Self-healing composites based on epoxy resin containing poly(methyl methacrylate) (PMMA) microcapsules filled with healing agents were prepared. The effect of healing agents microcapsules on mechanical properties and self-healing behavior of epoxy composites were investigated in this work. Epoxy and mercaptan as curing agent were microencapsulated in PMMA shell as two-component healing agent through internal phase separation method, and then, epoxy composites containing 2.5, 5, 7.5 and 10 wt% of healing agent microcapsules were prepared. The fracture toughness and healing efficiency of these composites were measured using a tapered double cantilever beam (TDCB) specimen. The results indicated that about 80% healing efficiency was achieved with 10 wt% PMMA microcapsules at room temperature after 24 h. The tensile strength of the epoxy with 2.5 wt% PMMA microcapsules increased initially and then decreased gradually with increasing microcapsules content up to 10 wt% PMMA microcapsules. DSC results also indicated that this system has good potential for spontaneous self-healing performance at room temperature.

‘Containers’ for self-healing epoxy composites and coating: Trends and advances

The introduction of self-healing functionality into epoxy matrix is an important and challenging topic. Various micro/nano containers loaded self-healing agents are developed and incorporated into epoxy matrix to impart self-healing ability. The current report reviews the major findings in the area of self-healing epoxy composites and coatings with special emphasis on these containers. The preparation and use of polymer micro/nano capsules, polymer fibers, hollow glass fibers/bubbles, inorganic nanotubes, inorganic meso- and nano-porous materials, carbon nanotubes etc. as self-healing con- tainers are outlined. The nature of the container and its response to the external stimulations greatly influence the self-heal- ing performance. The self-healing mechanism associated with each type of container and the role of container parameters on self-healing performance of self-healing epoxy systems are reviewed. Comparison of the efficiency offered by different types of containers is introduced. Finally, the selection of containers to develop cost effective and green self-healing sys- tems are mentioned.

Correction: A facile method for preparation of self-healing epoxy composites: using electrospun nanofibers as microchannels

Correction for ‘A facile method for preparation of self-healing epoxy composites: using electrospun nanofibers as microchannels’ by Vahdat Vahedi et al., J. Mater. Chem. A, 2015, 3, 16005–16012.

A facile method for preparation of self-healing epoxy composites: using electrospun nanofibers as microchannels

Electrospun nanofibrous mats of polyacrylonitrile (PAN) carrying epoxy and amine dual healing solutions were incorporated into an epoxy matrix to impart self-healing functionality.

Preparation and Performance of Self-Healing Epoxy Composites by Microcapsulated Approach

Microencapsulated E-51 epoxy resin healing agent and phthalic anhydride latent curing agent were incorporated into E-44 epoxy matrix to prepare self-healing epoxy composites. When cracks were initiated or propagated in the composites, the microcapsules would be damaged and the healing agent released. As a result, the crack plane was healed through curing reaction of the released epoxy latent curing agent. In the paper, PUF/E-51 microcapsules were prepared by in-situ polymerization. The mechanical properties of the epoxy composites filled with the self-healing system were evaluated. The impact strength and self-healing efficiency of the composites are measured using a Charpy Impact Tester. Both the virgin and healed impact strength depends strongly on the concentration of microcapsules added into the epoxy matrix. Fracture of the neat epoxy is brittle, exhibiting a mirror fracture surface. Addition of PUF/E-51 microcapsules decreases the impact strength and induces a change in the fracture plane morphology to hackle markings. In the case of 8.0 wt% microcapsules and 3.0 wt% latent hardener, the self-healing epoxy exhibited 81.5% recovery of its original fracture toughness.

Self-healing epoxy composites: preparation, characterization and healing performance

Low velocity impact damage is common in fiber reinforced composites, which leads to micro-crack and interfacial debonding, where damage is microscopic and invisible. The concept of self-healing composites can be a way of overcoming this limitation and extending the life expectancy while expanding their usage in structural applications. In the current study, extrinsic self-healing concept was adopted using urea-formaldehyde microcapsules containing room temperature curing epoxy resin system (SC-15) as the healing agent prepared by in situ polymerization. Microcapsules were characterized using Fourier transform infrared spectroscopy (FTIR) for structural analysis. Size and shape of microcapsules were studied using optical microscopy and scanning electron microscopy (SEM). Size of the microcapsules was between 30 and 100μm. Thermal characterization was carried out using thermogravimetric analysis. Microcapsules were thermally stable till 210°C without any significant decomposition. Fiber reinforced composite fabrication was carried out in three different steps. In the first step, epoxy resin was encapsulated in urea-formaldehyde shell material, which was confirmed by FTIR analysis. In the next step, encapsulation of amine hardener was achieved by vacuum infiltration method. These two different microcapsules were added with epoxy at 10:3 ratio and composite fabrication was done with hand layup method. Finally, healing performance was measured in terms of low velocity impact test and thermoscopy analysis. Low velocity impact test with 30J and 45J impact loads confirmed the delamination and micro-crack in composite materials and subsequent healing recovery observed in terms of damaged area reduction and restoration of mechanical properties.

Self-Healing Epoxy Composites – Part I: Curing Kinetics and Heat-Resistant Performance

This paper reports a study of self-healing epoxy composites. The healing agent was a two-component one synthesized in the authors laboratory, which consisted of epoxy-loaded urea-formaldehyde microcapsules as the polymerizable binder and CuBr2(2-MeIm)4 (the complex of CuBr2 and 2-methylimidazole) as the latent hardener. Both the microcapsules and the matching catalyst were pre-embedded and pre-dissolved in the composites matrix cured by 2-ethyl-4-methylimidazole (2E4MIm), respectively. The data of curing kinetics show that the latent hardener CuBr2(2-MeIm)4 is not affected during the curing process of 2 h at 80°C, 2 h at 120°C and 2 h at 140°C, and heat deformation temperature of composites consisting of 2 wt% CuBr2(2-MeIm)4 and 5 wt% mcirocapsules cured at the same curing process is 180.2°C.

Self-Healing Epoxy Composites Based on the Use of Nanoporous Silica Capsules

Self-Healing Epoxy Composites Based on the Use of Nanoporous Silica Capsules

Self-healing epoxy based on cationic chain polymerization

A two-component healing agent consisting of epoxy- and ((C 2H 5) 2O·BF 3)-loaded microcapsules was synthesized and applied to fabricate self-healing epoxy composites. Curing of epoxy healing agent catalyzed by (C 2H 5) 2O·BF 3 belongs to cationic chain polymerization, which is characterized by fast reaction at ambient temperature and low catalyst concentration. The experimental results showed that cracks in the composites containing the above healing system can be quickly re-bonded with satisfied healing efficiency. In the case of 5 wt% epoxy- and 1 wt% (C 2H 5) 2O·BF 3-loaded capsules, for example, a ∼80% recovery of impact strength was detected within 30 min at 20 °C. Because the healing capsules took effect at low content, mechanical properties of the matrix were largely retained. It is believed that the present healing system provides a possible solution to preparation of self-healing polymeric materials with practical applicability.

Self-healing epoxy composites – Preparation and effect of the healant consisting of microencapsulated epoxy and latent curing agent

To provide epoxy based composites with self-healing ability, two-component healing system consisting of urea–formaldehyde microcapsules containing epoxy (30–70 μm in diameter) and CuBr 2(2-MeIm) 4 (the complex of CuBr 2 and 2-methylimidazole) latent hardener was synthesized. When cracks were initiated or propagated in the composites, the neighbor microencapsulated epoxy healing agent would be damaged and released. As the latent hardener is soluble in epoxy, it can be well dispersed in epoxy composites during composites manufacturing, and hence activate the released epoxy wherever it is. As a result, repair of the cracked sites is completed through curing of the released epoxy. The present paper studied the preparation of epoxy microcapsules by amino resins, and the influencing factors as well. On the basis of this work, mechanical properties of the epoxy filled with the healing system were evaluated. It was found that incorporation of the two-component healing system nearly did not change the fracture toughness of the neat epoxy, as indicated by the single-edge notched bending test. In the case of 10 wt% microcapsules and 2 wt% latent hardener, the self-healing epoxy exhibited a 111% recovery of its original fracture toughness. Besides, the preliminary result of double-cantilever beam testing showed that the plain weave glass fabric laminates using the above self-healing epoxy as the matrix received a healing efficiency of 68%.