Urea-formaldehyde Microcapsules Research Articles

Cerium nitrate microcapsules for coating application: characterization and corrosion study

Microcapsules show great potential in metal anticorrosive coating in recent years. In the following paper, first, urea-formaldehyde (UF) microcapsules containing cerium nitrate were synthesized under different parameter conditions. Three different quantities of the microcapsules were introduced to the epoxy coatings and applied on the AZ31B substrate to meet the increasing demands for anticorrosive coatings. An analysis of the scanning electron microscopy surface morphology of UF microcapsules synthesized by nine different parameter conditions shows that the ratio of formaldehyde to urea is 1.5:1, and 2 wt.% of emulsifier, 25 wt.% of cerium nitrate, and 150 r/min of rotation speed are the best choice for the synthesis of microcapsules, resulting in spherical particles with an average particle size of about 25 μm. The characteristics of microcapsules were studied by optical microscope, Fourier transform infrared, and thermogravimetric analysis. The result of electrochemical impedance spectroscopy indicated that the 2 wt.% microcapsule content in the defective coating shows better corrosion protection performance than neat epoxy coating and cerium nitrate inhibitor coating.

Evaluation of self-healing in reactive powder concrete with urea–formaldehyde/epoxy microcapsules

The use of microcapsules as preservative vessels for healing materials has led to a great revolution in the repair of materials. Microcapsules have been used in medicine, agriculture, metallurgy and mechanics. In civil engineering applications, microcapsules are usually used for the self-healing of concrete, asphalt and cementitious materials. Concrete and cement are widely used in civil engineering and are the predominant construction materials worldwide. The objective of this study was to design and produce urea–formaldehyde microcapsules for the recovery of reactive powder concrete (RPC). It was found that RPC specimens with and without microcapsules exhibited different behaviours. All of the RPC specimens containing microcapsules were found to have lower strengths than specimens without microcapsules. The smallest reductions in compressive strength were observed in specimens with a microcapsule content of 4–6% by weight of cement. The healing ratio of compressive strength increased with an increase in the weight percentage of microcapsules. Scanning electron microscopy and energy-dispersive spectroscopy were used to observe the process of crack healing, and the results showed that the cracks were filled with healing products.

Unraveling the detrimental effect of polymeric microcapsules on the corrosion performance of epoxy resin coatings

Organic micro- or nanocapsules are widely used as reservoirs to carry sealing agents or corrosion inhibitors to achieve the self-healing functionality of coatings. To understand the impact of the capsules' incorporation on the barrier properties of organic coatings, composite epoxy resin coatings containing different concentrations (e.g., 5 wt%, 10 wt% and 20 wt%) of urea-formaldehyde (PUF) microcapsules were deposited on the top of Q235 carbon steel. The features of PUF microcapsules and composite coatings were characterized, and the corrosion behaviors of the coating-protected carbon steel were investigated in NaCl solution. The results showed that the spherical PUF microcapsules (∼40 μm) with 290 nm thick shell and hexyl acetate core are synthesized through in situ polymerization. The prepared microcapsules can uniformly distribute within the epoxy resin coatings, which in turn deteriorates the corrosion resistance of the microcapsules-containing composite coatings (MCECs). Lower volume (5 wt%) microcapsules incorporation caused a slight reduction in the corrosion resistance (Rc) and effective capacitance (Ceff) from 4.39 × 107 Ω·cm−2 and 6.50 × 10−5 mF·cm−2 to 8.72 × 106 Ω·cm−2 and 5.63 × 10−5 mF·cm−2, respectively. For higher volume (10 wt% and 20 wt%) groups, the Rc further decreases to 7.47 × 105 Ω·cm−2 and 1.45 × 105 Ω·cm−2, whereas the Ceff increases to 5.63 × 10−5 mF·cm−2 and 5.63 × 10−5 mF·cm−2, respectively. The failure mechanism of the MCECs can be ascribed to the rupture of the PUF microcapsules during the curing process and/or immersion in NaCl electrolyte, which suggested the mechanical strength and chemical stability of the capsules should be carefully determined to avoid their negative impact on the barrier property of polymeric coatings.

Feasibility of micro-organisms in soil bioremediation and dust control

Detrimental impacts of dust caused by mine tailings have yielded to several studies on the efficiency of different soil stabilizers. Bacterial stabilization has been recognized as a reality within recent decades, where bacteria could get adhesion to the grains and stabilize the soil particles. However, these bacteria are prone to be destroyed while exposed to the normal environmental conditions. In this study, the effects of microcapsules containing two types of bacterial freeze-dried spores (B.Subtilis Natto LMG 19457 and B.ESH) have been investigated on the mine tailing stability in terms of two parts. The first part of the study is dedicated to the fabrication of microcapsules within the two bacteria and identification of the characteristics of these microcapsules to set the time of microcapsules break and release in the soil. The urea-formaldehyde microcapsules containing tung oil were synthesized using microencapsulation method and at the following, the bacterial spores of B.Subtilis Natto LMG 19457 and B.ESH which had the high durability and the capability to grow in the silicon oil, were added to the microcapsules. The microcapsules effect on MT specimens and the viability of encapsulated spores were determined. The characteristics of the capsules were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric thermal analysis (TGA). In the second part, wind tunnel tests were conducted to study the effects of microorganism stabilizers on mine tailings. The results indicated that the dust erosion reduced from 16% - using water as a stabilizer- to the 0.2% while using microcapsules containing B.Subtilis Natto LMG 19457 and 0.8% while using microcapsules containing ESH. The results showed the high efficiency of microcapsules containing bacteria in stabilizing the MTs. This phenomenon was proved by SEM imaging in which the voids were bounded significantly while using the bacteria.

Road Performance and Self-Healing Property of Bituminous Mixture Containing Urea-Formaldehyde Microcapsules.

Urea-formaldehyde (UF) is a common shell material for self-healing microcapsules; however, the influence of urea-formaldehyde microcapsules (UFMs) on the road performance of bituminous mixtures and the sensitivity of their healing abilities remains unclear. In this paper, UFMs were prepared via in situ polymerization (ISP), followed by an investigation into the road performance of UFM self-healing bituminous mixtures through various tests, including wheel tracking, immersed Marshall, freeze-thaw splitting, low-temperature bending, and three-point bending fatigue tests. Subsequently, the impact of the damage degree, healing duration, and temperature on the self-healing property was discussed. The results indicated that incorporating 3 wt% UFMs into bitumen significantly improved the high-temperature stability and fatigue resistance of the bituminous mixture; for example, its dynamic stability and fatigue life could be increased by about 16.5% and 10%, respectively. However, it diminished the thermal crack resistance, as evidenced by decreases in bending tensile strength and strain by 3.7% and 10.1%, respectively. And it did not markedly improve the moisture susceptibility. Additionally, the maximum improvement observed in the healing rate was about 9%. Furthermore, the healing duration and temperature positively influenced the bituminous mixture's self-healing, whereas the degree of damage exerted a negative impact, with a relatively significant effect.

Micro-Pocket Embedded Carbon Capsulated Cement with Urea-Formaldehyde Microcapsules for Enhanced Performance in Construction Cement

Abstract: The innovative integration of Micro-Pocket Embedded Carbon Capsulated Cement (MPECCC) with UreaFormaldehyde Microcapsules (UFMCs) marks a paradigm shift in construction material engineering. This research endeavors to explore the synergistic effects of combining carbon encapsulation within micro-pockets and the controlled release mechanisms offered by urea-formaldehyde microcapsules. The resulting material, herein referred to as MPECCC with UFMCs, presents a novel approach to address critical challenges in the construction industry, such as enhanced durability, improved mechanical properties, and innovative functionalities.

Corrosion sensing and self-healing composite coatings on magnesium alloy AZ31 enabled by stimuli-responsive microcapsules loaded with phenolphthalein and epoxy resin

Polymer coatings inevitably suffer from micro-damage during film formation and the in-service period, leading to interfacial corrosion of the metal substrate and even catastrophic accidents. Constructing a coating system that integrates early corrosion sensing and efficient damage self-healing capabilities is highly pursued yet difficult to achieve in practice. This work reports a strategy for designing smart anticorrosion coating with autonomous corrosion-detecting and in-situ self-healing functions. The dual-functional composeite coating was designed on magnesium (Mg) alloy AZ31, via embedding urea-formaldehyde microcapsules loaded with phenolphthalein (PhPh)/epoxy resin. By immersing the scribed samples in a 3.5 wt% NaCl solution, the interfacial corrosion reaction at coating damage can be timely sensed and visualized by the apparent pink color in just 7 min. The local alkaline environment produced by Mg corrosion, initiates the chromogenic reaction of PhPh and indicates interfacial corrosion. Meanwhile, the released epoxy resin, as a healing agent can effectively fill the coating defects and thus prevent the intrusion of corrosive medium. Electrochemical impedance spectroscopy shows that the long-term corrosion resistance of the coating was significantly improved after introducing synthesized microcapsules. After 115 d of immersion, the low-frequency impedance of the composite coating with 3 wt% of microcapsules (PUM3) is above 1010 Ω·cm2, whereas the pure polyurea coating (PUA) has dropped to 109 Ω·cm2.This feasible and effective design concept of microcapsule-based intelligent anticorrosive coating provides a new idea for developing environmentally adaptive protective materials with corrosion sensing and self-healing functions.

Multilayered LDH/Microcapsule Smart Epoxy Coating for Corrosion Protection.

A multilayered smart epoxy coating for corrosion prevention of carbon steel was developed and characterized. Toward this direction, as a first step, zinc-aluminum nitrate-layered double hydroxide (Zn/Al LDH) was synthesized using the hydrothermal crystallization technique and then loaded with dodecylamine (DOD), which was used as an inhibitor (pH-sensitive). Similarly, the synthesis of the urea-formaldehyde microcapsules (UFMCs) has been carried out using the in-situ polymerization method, and then the microcapsules (LAUFCs) were encapsulated with linalyl acetate (LA) as a self-healing agent. Finally, the loaded Zn/Al LDH (3 wt %) and modified LAUFCs (5 wt %) were reinforced into an epoxy matrix to develop a double-layer coating (DL-EP). For an exact comparison, pre-layer epoxy coatings comprising 3 wt % of the loaded Zn/Al LDH (referred to as LDH-EP), top-layer epoxy coatings comprising 5 wt % linalyl acetate urea-formaldehyde microcapsules (referred to as UFMLA COAT), and a blank epoxy coating (reference coating) were also developed. The developed epoxy coatings were characterized using various techniques such as XRD, XPS, BET, TGA, FTIR, EIS, etc. Electrochemical tests performed on the synthesized coatings indicate that the DL-EP demonstrates improved self-healing properties compared to LDH-EP and UFMLA COAT.

Development and characterization of self-healing microcapsules, and optimization of production parameters for microcapsule diameter and core content

PurposeThis study produced epoxy-filled urea-formaldehyde (UF) microcapsules (MCs) and T-403 amine MCs using the in situ technique. The Taguchi method was used to determine the effects of the control factors (temperature, stirring speed, core-shell ratio and surfactant concentration) affecting MCs’ core diameter and core content and optimizing their optimum levels with a single criterion. Optimum control factor levels, which simultaneously provide maximum core diameter and core content of MCs, were determined by the PROMETHEE-GAIA multi-criteria optimization method. In addition, the optimized MC yield was analyzed by thermal camera images and compression test.Design/methodology/approachMicrocracks in materials used for aerospace vehicles and automotive parts cause serious problems, so research on self-healing in materials science becomes critical. The damages caused by micro-cracks need to heal themselves quickly. The study has three aims: (1) production of self-healing MCs, mechanical and chemical characterization of produced MCs, (2) single-criteria and multi-criteria optimization of parameters providing maximum MC core diameter and core content, (3) investigation of self-healing property of produced MCs and evaluation. Firstly, MCs were produced to achieve these goals.FindingsThe optimized micro cures are buried in the epoxy matrix at different concentrations. Thermal camera images after damage indicate the presence of healing. An epoxy-amine MC consisting of a 10% by weight filled aluminum sandwich panel was prepared and subjected to a quasi-static compression test. It was determined that there is a strong bond between the UF shell and the epoxy resin.Originality/valueThe optimization of production factors has been realized to produce the most efficient MCs that heal using less expensive and more accessible methods.

Corrosion-sensing and self-healing dual-function coating based on 1,10-phenanthroline loaded urea formaldehyde microcapsules for carbon steel protection

In this work, a smart coating with corrosion-sensing and self-healing dual functions was developed on carbon steel by incorporating the urea formaldehyde (UF) microcapsules loaded with 1,10-phenanthroline (Phen) molecules. Phen as both the corrosion-sensing indicator and corrosion inhibitor was encapsulated into the UF microcapsules via the oil-water (O/W) emulsion in-situ polymerization method. When the coating was damaged, the Phen molecules released from UF/Phen microcapsules would react with the Fe2+ ions generated from the active anodic corrosion site of the carbon steel substrate, and displayed a prominent red color chelate compound for corrosion-sensing application. During the neutral salt spray test, the corrosion evolution underneath the damaged coating can be rapidly detected within 15 min. Besides, the corrosion activity near the coating scratch can be effectively inhibited due to the adsorption of released Phen on the exposed substrate surface. After 72 h of immersion in 3.5 wt% NaCl solution, the low frequency impedance modulus of the scratched coating containing 10 wt% UF/Phen microcapsules was almost 7 times that of the scratched blank coating. The smart coating can not only achieve timely corrosion sensing, but also suppress the corrosion activity, which is of great importance for practical corrosion protection applications.

Anti-corrosion performance and mechanical properties of epoxy coatings containing microcapsules filled with linseed oil and modified ceria nanoparticles

In this study, the anti-corrosion and mechanical properties of epoxy coatings containing microcapsules filled with linseed oil and neat and modified ceria nanoparticles were evaluated. To this end, first, the surface of ceria nanoparticles was modified with Cerium (III) nitrate hexahydrate using different methods and then the corrosion resistance of linseed oil containing 1 wt% of nanoparticles was studied by electrochemical impedance spectroscopy (EIS). To evaluate the protection mechanism of cerium nanoparticles, the corrosion performance of linseed oil containing calcium carbonate and Zirconia nanoparticles was also studied. In the next step, urea-formaldehyde microcapsule containing linseed oil and 1 wt% nano-ceria modified from the previous step, was synthesized via in situ polymerization in an oil-in-water emulsion. The results of EIS Test showed that the addition of ceria nanoparticles to the microcapsule’s core content improves the anti-corrosion performance of the epoxy coatings containing microcapsules due to increased barrier properties as well as through inhibition mechanism. The mechanical properties of the coating samples decreased up to 35% by the addition of microcapsules due to disruption of the structural integrity of the resin matrix. However, the DMTA test revealed that the glass transition temperature of the samples did not change significantly by adding microcapsules to the coating samples.

Anti–corrosion and self-healing coatings with polyaniline/epoxy copolymer–urea–formaldehyde microcapsules for rusty steel sheets

Polyaniline (PANI)/Epoxy copolymer as a core material was synthesized via a chemical oxidation method. Various analytical techniques, including scanning electron microscope, Fourier transform infrared spectroscopy, energy dispersive spectroscopy, thermogravimetry, and electrochemical impedance spectroscopy, were used to characterize the morphology, compositions, and self-healing and anticorrosion properties of the prepared microcapsules and coatings. The prepared PANI/Epoxy copolymer showed the best electrochemical corrosion resistance when the ratio of PANI to epoxy was 0.05: 1 (wt.:wt.). For the mass fraction of the core (PANI/Epoxy copolymer) of 60.84 ± 0.06 wt%, the mean particle diameter of the prepared microcapsules was 4.20 ± 0.92 μm. The coatings with 15 wt% microcapsules possessed excellent self-healing performance and corrosion resistance. The low-frequency impedance modulus at 0.01 Hz of scratched coatings immersed in the NaCl solution for 24 h was 5.27 × 106 Ω·cm2. Scratched self-repairing coating samples were able to resist corrosion for 384 h; thus, the microcapsules can be used to significantly extend the service life of the coatings. Microcapsule-containing PANI/Epoxy copolymers are expected to find use in anticorrosion coating systems, where the coatings could be applied directly on rusty steel surfaces.

Self-healing coatings based on poly(urea-formaldehyde) microcapsules

Self-healing coatings based on poly(urea-formaldehyde) microcapsules

Multilevel Self-Healing Characteristics of Smart Polymeric Composite Coatings.

Smart polymeric composite coatings demonstrating multilevel self-healing characteristics were developed and characterized. The pH-responsive smart carriers were synthesized by loading halloysite nanotubes (HNTs) with the benzotriazole corrosion inhibitor (BTA) using the vacuum cycling method, referred to as (BTA-loaded HNTs). Similarly, mechanically triggered melamine urea-formaldehyde microcapsules encapsulated with the boiled linseed oil-self-healing agent (LO) denoted as (MUFMCs) having an average size of a ∼120 μm diameter with a wall thickness of ∼1.84 μm were synthesized by the in situ polymerization technique. The newly designed double-layered smart polymeric composite coatings (DLPCs) were developed by mixing 3 wt % BTA-loaded HNTs with epoxy and applying it on the clean steel substrate to form a primer layer. After its complete curing, a top layer of epoxy containing 5 wt % of MUFMCs was deposited on it. For an exact comparison, single-layer polymeric composite coatings (SLPCs) containing 3 wt % BTA-loaded HNTs were also developed. The Fourier transform infrared radiation spectra of MUFMCs and BTA-loaded HNTs indicate the existence of all desired functional groups, confirming the presence of loaded chemical species such as LO and BTA into the smart carriers. Thermogravimetric analysis (TGA) indicates that ∼18% BTA is successfully loaded into HNTs. Quantitative UV-spectroscopic analysis indicates a pH-responsive release of BTA from BTA-loaded HNTs, which is time-dependent, attaining its maximum value of ∼ 90% in an acidic medium after 30 h. Electrochemical impedance spectroscopy analysis conducted in 3.5 wt % NaCl solution at room temperature for different immersion times reveals that SLPC exhibits the maximum charge-transfer resistance (Rct) of 55.47 GΩ cm2 after the 7th day of immersion, and then, a declining trend is observed, reaching 26.6 GΩ cm2 after the 9th day. However, in the case of DLPC, the Rct values show a continuous increment, attaining a maximum value of 82.11 GΩ cm2 after the 9th day of immersion. The improved performance of DLPC can be ascribed to the efficient triggering of the individual carriers in the isolated matrices, resulting in the release of LO and BTA to form individual protective films at the damaged area due to the oxidative polymerization process and triazoles' ability of passive film formation on the substrate, respectively. The tempting self-healing properties of DLPCs justify their decent role for long-term corrosion protection in many industrial applications.

Double-layered Polymeric Nanocomposite Coatings for Corrosion Inhibition

The proposed work is focused on the multi-level corrosion inhibition performance of the double-layered polymeric nanocomposite coatings (DLNCs). For this purpose, Melamine urea-formaldehyde microcapsules encapsulated with linseed oil were synthesized by in situ polymerization technique. A vacuum cycling method was used to load the benzotriazole (BTA) into halloysite nanotubes (HNTs). Furthermore, 3wt.% of loaded HNTs was mixed with epoxy and applied on the clean steel substrate with 150 µm thickness to form the pre-layer. A top layer of epoxy reinforced with 5wt% of MUFMCs was coated on the cured primer layer of BTA loaded HNTs/epoxy with the same thickness and cured for 24 hours resulting in the development of DLNCs. For comparison, single layer epoxy coatings modified with HNTs loaded with BTA and plain epoxy coatings (without any reinforcement) having ⁓300 µm thickness were also developed. Later, the structural, morphological, thermal, and electrochemical analyses of the developed DLNCs were studied. Electrochemical Impedance Spectroscopy (EIS) tests in 3.5 wt.% NaCl solution at room temperature which confirms that DLNCs exhibit superior corrosion resistant properties as compared to single-layer coatings. This improvement can be ascribed to the efficient triggering of the individual carriers in the isolated matrix which in turn increases the overall corrosion efficiency. The promising corrosion inhibition performance of DLNCs makes them attractive for many industrial applications.

Self-healing epoxy coating synthesis by embedment of metal 2-methyl imidazole and acetylacetonate complexes with microcapsules

The restoration of mechanical properties is desired for creating the self-healing coatings with no corrosion capabilities. The encapsulation of epoxy resins is limited by various factors in urea and melamine formaldehyde microcapsules. An improved method was developed, where epoxy resin was encapsulated by individual wrapping of poly(melamine-formaldehyde) and poly(urea-formaldehyde) shell around emulsified epoxy droplets via oil-in-water emulsion polymerization method. The synthesized materials were characterized analytically. The curing of the epoxy was achieved by adding the [Ni/Co(2-MI)6].2NO3 as a latent hardener and iron acetylacetonate [Fe(acac)3] as a latent accelerator. Isothermal and non-isothermal differential scanning calorimetric analysis revealed lower curing temperature (Tonset = 116 °C) and lower activation energies (Ea ≈ 69–75 kJ/mol). The addition of microcapsules and complexes did not adversely alter the flexural strength and flexural modulus of the epoxy coatings. The adhesion strength of neat coating decreased from 6310.8 ± 31 to 4720.9 ± 60 kPa and percent healing increased from 50.83 to 67.45% in the presence of acetylacetonate complex at 10 wt% of microcapsules.

Synthesis of Urea-Formaldehyde Microcapsule Containing Fluororesin and Its Effect on Performances of Waterborne Coatings on Wood Surface.

In order to self-repair the cracks of waterborne coatings on Basswood at room temperature, with fluororesin and waterborne coatings embedded in the shell structure of urea formaldehyde (UF) resin, the microcapsules were fabricated via in-situ polymerization, and the effect of microcapsules on the chroma, gloss, mechanics and repair effect for waterborne coatings on wood was discussed. The results indicated that the coating effect was the most significant when the ratio value of the core materials to the shell material of microcapsules in mass was 0.75, and the agglomeration of particles was the least and the surface was the smoothest when the content of microcapsules was 1.0%. It was negative between the gloss of the film and microcapsule content. The ratio value of the core materials to the shell material in mass and the amount of microcapsules had great influence on the film hardness and adhesion, but had little effect on the impact resistance. When the ratio value of the core materials to the shell material of microcapsules in mass was 0.65 and the addition amount was 4.0–10.0%, the aging resistance of the film was improved most significantly. When the ratio value of the core materials to the shell material of microcapsules in mass was 0.65 and the addition amount was 7.0%, the overall properties of topcoat film on Basswood board was the most significant. It is for the application of fluororesin microcapsules possessing self-repairing effect in waterborne coating on Basswood board that a technical groundwork is provided by this study.

Self-Healing Performance of Smart Polymeric Coatings Modified with Tung Oil and Linalyl Acetate.

This work focuses on the synthesis and characterization of polymeric smart self-healing coatings. A comparison of structural, thermal, and self-healing properties of two different polymeric coatings comprising distinct self-healing agents (tung oil and linalyl acetate) is studied to elucidate the role of self-healing agents in corrosion protection. Towards this direction, urea-formaldehyde microcapsules (UFMCs) loaded with tung oil (TMMCs) and linalyl acetate (LMMCs) were synthesized using the in-situ polymerization method. The synthesis of both LMMCs and TMMCs under identical experimental conditions (900 rpm, 55 °C) has resulted in a similar average particle size range (63–125 µm). The polymeric smart self-healing coatings were developed by reinforcing a polymeric matrix separately with a fixed amount of LMMCs (3 wt.% and 5 wt.%), and TMMCs (3 wt.% and 5 wt.%) referred to as LMCOATs and TMCOATs, respectively. The development of smart coatings (LMCOATs and TMCOATs) contributes to achieving decent thermal stability up to 450 °C. Electrochemical impedance spectroscopy (EIS) analysis indicates that the corrosion resistance of smart coatings increases with increasing concentration of the microcapsules (TMMCs, LMMCs) in the epoxy matrix reaching ~1 GΩ. As a comparison, LMCOATs containing 5 wt.% LMMCs demonstrate the best stability in the barrier properties than other developed coatings and can be considered for many potential applications.

Concurrent recovery of mechanical and electrical properties in nanomodified capsule-based self-healing epoxies

We propose a novel self-healing capsule based polymer system for the concurrent recovery of electro-mechanical properties and demonstrate for the first time the successful monitoring of the damage and healing process with a real time monitoring of the change of the electrical resistance. Urea-formaldehyde (UF) microcapsules containing an epoxy resin modified with multi-walled carbon nanotubes (MWCNTs) were prepared via in-situ emulsification polymerization. MWCNTs were beneficial to mechanical performance, which was even enhanced, in contrast to typical systems where the inclusion of the healing agent deteriorates performance. The capsule shell morphology and mean diameter were characterized via Scanning Electron Microscopy (SEM) and optical microscopy, while thermogravimetric analysis confirmed a high thermal stability of about 222 °C. Fracture toughness tests and impedance spectroscopy were employed to assess healing. The MWCNT microcapsule enhanced epoxy exhibited an impressive 22% improvement compared to the virgin system followed by a self-healing efficiency of 80% in mechanical and 95% in electrical properties.

Laboratory assessment of early-age durability benefits of a self-healing system to cementitious composites

Shrinkage of cement composites (paste, mortar, grout, or concrete) due to moisture loss during the curing period is a challenge for their durability. In this laboratory study, urea-formaldehyde (UF) microcapsules and polyvinyl alcohol (PVA) microfibres were utilized as a self-healing system to improve the early-age durability of cement mortars by mitigating their total shrinkage during the curing period. Experimental results revealed that the admixed UF microcapsules/PVA microfibres together could mitigate 25% of the total shrinkage during the curing period of 35 days. In addition, this self-healing system could reduce the gas permeability of the mortars by over 75%. The UF microcapsules and PVA microfibres could interfere with the formation of some crystalline hydration products and modify the microstructure of hydrated cement mortar, resulting in slight reductions in the compressive strength (less than 12%) and at some dosages significantly reduced the chloride migration coefficient of the mortars (i.e., 1% 1100+PVA, 2% 700, and 1% 1100). The UF microcapsules mainly affected the pores with a radius between 10 nm and 1000 nm, whereas the PVA microfibers mainly affected the larger pores at the interfacial transition zone.