Modeling and optimization of the parameters affecting the in-situ microencapsulation process for producing epoxy-based self-healing anti-corrosion coatings (original) (raw)
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Advanced Materials Letters, 2016
Novel self-repairing Urea-Phenol-Formaldehyde (UPF) microcapsules containing linseed oil were prepared via in-situ polymerization in an oil-in-water emulsion. The main purpose of encapsulation is to control the release of linseed oil, when external conditions such as mechanical stress or energy cause microcapsules to break. These controlled release mechanisms of linseed oil make them suitable for application in self-healing coatings. Chemical structure analyses of microcapsules were studied by Fourier transform infrared spectroscopy (FTIR), optical microscopy and scanning electron microscopy for their structural & morphological illustrations. Controllable particle sizes were determined under optical microscope and as well using particle size analyzer. To determine the healing efficiency, the microcapsules, were incorporated in the epoxy coatings in varying proportions. The effects of the same on anti-corrosion performance was carried out in 5% NaCl aqueous solution (ASTM B117) and Decreasing trend of pencil hardness, scratch hardness, Impact resistance with the increase in concentration of microcapsules was observed. Chemical resistance could also be attributed to the presence of aromatic structures in epoxy which impart chemical stability. Secondary hydroxyl moiety in epoxy chain forms hydrogen bonding with the metal substrate that would contribute to good adhesive forces. Epoxy coatings incorporated with microcapsules showed better corrosion resistance than neat epoxy coating, where neat epoxy coating showed rust and spreading of rust observed on tested panel. Mechanical properties decreased on incorporating microcapsules into epoxy matrix, hence development of mechanical properties without effecting the corrosion properties shall be studied further.
Progress in Organic Coatings, 2015
Core-shell microcapsules of urea-resorcinol-formaldehyde shell and linseed oil (LO) core material as paint additives for self-healing coatings were prepared. The capsules contained LO either with or without Co-octoate as drier material and/or octadecylamine (ODA) as corrosion inhibitor. The microcapsules embedded in a commercial paint were applied on sandblasted mild steel sheets. After scratching the coated surface, the inhibition efficiency of core-shell microcapsule-containing coat, dipped into corrosive media, was followed visually and evaluated numerically by electrochemical impedance spectroscopy (EIS). In separate experiments, to optimize for the self-healing process, the composition of the core material, the effect of the drier and/or the inhibitor ODA on drying process of LO films were monitored by infrared spectroscopy. Pure LO needed 6-7 days to dry completely. The drying period could be shortened (to 5 h) via application of a dryer, but the addition of the corrosion inhibitor alone increased significantly the time needed for solifidicaiton. To minimize the drying period we have found the proper combination of the ODA and the dryer of the LO. The EIS measurements, in accordance with the drying tests, resulted in the next order of selfhealing ability: LO<LO (+ODA) <LO (+Co-octoate) <LO (+ODA+Co-octoate) .
Preparation and Property Investigation of Epoxy/Amine Micro/Nanocapsule Based Self-healing Coatings
International Polymer Processing, No. 5, 2018
Autonomous self-healing was achieved by synthesizing epoxy coatings which contain dual micro/nanocapsules; epoxy and amine. Epoxy micro/nanocapsules were prepared by an in situ polymerization process and amine microcapsules were fabricated by vacuum infiltration of diethylenetriamine into nanoporous hollow glass microspheres. Both types of capsules were embedded into epoxy matrix. When cracks were created and started to grow in the coating, the micro/nano-capsules near the crack were ruptured and released their contents. As a result of curing reaction between released curing agents (epoxy and amine), healing of the cracked sites was completed. In this work, some properties of epoxy/amine micro/nanocapsule based self-healing coatings such as morphology of micro/nanocapsule and coating, healing and corrosion properties were studied. Also thermal stability and adhesion properties of this kind of coating were evaluated comprehensively. It was found out that optimum mass ratio of epoxy/amine capsules ratio is 1 : 1 and the highest healing efficiency was achieved for a total micro/nanocapsule concentration of 15 wt.%. Regarding thermal and adhesion behavior of coatings, it was observed that adding micro/nano-capsules to epoxy matrix did not change these properties significantly which means self-healing characteristics were achievable without deteriorating other properties.
6th International Conference on Materials Engineering & Metallurgy, (iMat 2017), 2017
In the present study, the preparation of microencapsulated epoxy and it's curing agent and evaluation of this two-component repair system for producing self-healing epoxy coating, with the objective of improving healing efficiency is reported. Epoxy contained microcapsules were prepared by in situ polymerization of urea–formaldehyde resin to form shell over epoxy resin droplets. Chemically and thermally stable nano-porous containers have been synthesized to store DETA as a reactive agent for self-healing epoxy based coatings. The optimal process parameters for synthesizing the micro/nano capsules were selected. The microcapsules were incorporated into the paint formulations just before application. The filled epoxy coatings were prepared by uniformly mixing of the microcapsules together with the mixture of EPON 828 and DETA. When cracks were initiated or propagated in the coating, the neighbor microencapsulated epoxy and DETA would be damaged and released. As a result, repair of the cracked sites is completed through curing of the released epoxy. Micro/nano capsules and final coatings were characterized. All the obtained results show that the prepared self-healing coatings could be suitable for using in different applications.
Polymer Science, Series B, Vol. 59, No. 3, 1–11, 2017
–In the field of coatings, extensive laboratory research has been conducted in the last decade. In the present work, effectiveness of epoxy resin filled micro/nanocapsules was investigated for future using in healing of cracks generated in coatings. Micro/nanocapsules were prepared by in situ polymerization of urea– formaldehyde resin to form shell over epoxy resin droplets. The optimal process parameters for synthesizing the micro/nanocapsules were selected. The as-synthesized capsules were studied by various characterizations techniques, including scanning electron microscope (SEM), particle size analyzer (PSA), Fourier transform-infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicate that micro/nanocapsules containing epoxy resins can be synthesized successfully. The rough outer surface of microcapsule is composed of agglomerated urea–formaldehyde nanoparticles. They basically exhibit good storage stability at room temperature, and they are chemically stable before the heating temperature is up to approximately 250°C.
Progress in Organic Coatings, 2020
In this research, polyurea-formaldehyde-based microcapsules loaded with linseed oil were synthesized by means of in-situ polymerization in an oil-in-water emulsion. The surface of the microcapsules was treated with 3aminopropyltrimethoxy silane (APS) using sol-gel procedure at pH 7.5. SEM and optical microscopy were used to characterize untreated and APS-treated microcapsules. The mechanical properties of epoxy-based nanocomposite coatings comprising different combinations of APS-treated microcapsules and nanoclay particles were evaluated by means of tensile strength measurements. The standard salt spray test, Electrochemical Impedance Spectroscopy (EIS) and SEM were utilized to study the corrosion resistance and healing performance of the samples in the presence of nanoclay. The results revealed improvement in tensile strength properties and anti-corrosion resistance by the simultaneous use of APS-treated microcapsules and nanoclay. This was attributed to the enhanced interactions between the polymer coating and the microcapsule shell and the barrier properties of intercalated nanoclay platelets. The natural salt spray test EIS results revealed enchasing corrosion resistance of the coating samples containing APS-treated microcapsule in comparison with neat epoxy samples during 7 days exposure to the conditions of the tests. The sample containing APS-treated microcapsules and nonoclay particles showed the best performance along with all samples. APS-treated microcapsules were more likely to rupture during the scratching, leading to better corrosion resistance and self-healing properties.
Applied sciences, 2020
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.
Progress in Organic Coatings, 2017
Linseed oil filled urea-formaldehyde microcapsules with various sizes were prepared via in-situ polymerization. To understand the healing performance of linseed oil as a healing agent and the progression of corrosion processes beneath the healed area, long term corrosion performance of scratched epoxy-based coating samples containing microcapsules was evaluated using Electrochemical Impedance Spectroscopy (EIS) as well as salt spray testing over a period of 6-days. EIS results were fitted to various equivalent circuit models and a modified model for the justification of the observed corrosion behavior was proposed. It was found that the addition of microcapsules enhances the corrosion resistance of the scratched samples, the extent of which depends on the microcapsule size and loading. At a given loading, corrosion resistance increased with increasing microcapsule size, however, the effect of microcapsule size was more significant than that of loading. Moreover, with increased exposure time to the salt solution, the corrosion behavior of scratched coated samples shifted from uniform corrosion to crevice corrosion. EIS results showed that although linseed-oil can significantly improve the corrosion performance of the damaged coating in short term however it rapidly decreases with time and hence this should be taken into account in designing of microcapsule's core composition.
International Journal of Industrial Chemistry, 2013
Background This paper describes the microencapsulation of linseed oil along with drier and corrosion inhibitor in polyurethane coating. Results Linseed oil along with drier and corrosion inhibitor was encapsulated in phenol formaldehyde microcapsules successfully by in situ polymerization process. These microcapsules were characterized by Fourier transform-infrared and nuclear magnetic resonance spectroscopies, and their surface morphology was studied by scanning electron microscopy. The particle size of the prepared microcapsules was estimated by optical microscopy and confirmed using a particle size analyzer. The self-healing properties as well as anticorrosive performance of encapsulated microcapsules were studied in polyurethane coating. Corrosion protection of coatings with microcapsules containing linseed oil, corrosion inhibitor, and drier was compared with pristine coating free from microcapsules. Conclusions The cracks in the paint film could be successfully repaired by the...
Electrochimica Acta, 2014
The self-healing ability of water based epoxy coatings modified with nanocapsules loaded with 2-Mercaptobenzothiazole (MBT) and applied on AA5083 and galvanneal substrates was investigated by electrochemical techniques and salt spray corrosion tests. The electrochemical impedance results show that the presence of nanocapsules does not affect the barrier properties of the coatings and evidence a decrease of the corrosion activity in the presence of inhibitor-loaded nanocapsules. Localised electrochemical impedance spectroscopy (LEIS) and the scanning vibrating electrode technique (SVET) revealed that the corrosion process over artificial defects exposed to NaCl electrolytes was healed in the presence of the nanocapsules loaded with corrosion inhibitor. The coated galvanneal samples show corrosion attack when exposed to the salt spray test, but the AA5083 samples did not show signs of corrosion activity over 1000 h of exposure. All the as prepared samples revealed good adhesion behaviour. However, after immersion delamination across defects was more intense for the galvanneal samples. The results highlight that addition of nanocapsules in water based epoxy coatings is a promising strategy towards the development of self-healing water based epoxy coatings.