Dual Microcapsules Research Articles

High‐performance self‐healing epoxy by microencapsulated epoxy‐amine chemistry II: Performance of the system

AbstractThe self‐healing epoxy based on microencapsulated epoxy‐amine chemistry is a system with great potential for practical applications. Herein, microcapsules respectively containing epoxy and polyetheramine were fabricated using a microencapsulation technique via integrating electrospraying and interfacial polymerization (ES‐IP) and self‐healing epoxy based on the dual microcapsules were systematically investigated regarding the microcapsule dispersion, healing performance, failure mode, and mechanical properties. Microcapsules with different sizes were conveniently prepared by adjusting the injection rate. The microcapsules, regardless of the size, can be well dispersed in the epoxy matrix. The effects of the microcapsule size and concentration on the healing performance were studied. While full healing can be obtained for microcapsule >100 μm, high healing efficiency of about 90% and 70% can be achieved for microcapsules in 50 ~ 100 μm and ~ 50 μm, respectively. The healing performance decreases with the decreased microcapsule concentration. However, healing efficiency >70% can still be obtained when 5.0 wt% microcapsule of 50 ~ 100 μm were adopted. Mixed failure modes including adhesive failure, cohesive failure, and matrix failure, were observed, due to the good performance of the selected healant system. While the incorporated microcapsules, especially the small ones, evidently toughens the matrix, they deteriorate the tensile properties of the formulated self‐healing material.

Dual Microcapsules Encapsulating Liquid Diamine and Isocyanate for Application in Self-Healing Coatings

Dual microcapsule systems, especially those based on the polyurea matrix, have emerged as pivotal components driving innovation in self-healing materials, thanks to the intrinsic properties of polyurea, primarily diamine and diisocyanate, rendering it an optimal choice for enhancing self-healing coatings. However, the encapsulation of polyurea components is fraught with substantial technical hurdles. Addressing these challenges, a novel methodology has been devised, leveraging n-heptane as a solvent in the liquid diamine emulsion process to facilitate the synthesis of diamine microcapsules. These microcapsules exhibit a uniform spherical morphology and a robust shell structure, with an encapsulated core material ratio reaching 39.69%. Analogously, the encapsulation process for diisocyanate has been refined, achieving a core material percentage of 10.05 wt. %. The integration of this bifunctional microcapsule system into diverse polymeric matrices, including epoxy resins and polyurethanes, has been demonstrated to significantly enhance the self-healing efficacy of the resultant coatings. Empirical validation through a series of tests, encompassing scratch, abrasion, and saltwater immersion assays, has revealed self-healing efficiencies of 21.8% and 33.3%, respectively. These results indicate significant improvements in the durability and self-repair capability of coatings, marking a notable advancement in self-healing materials with promising potential for tailored applications in automotive, aerospace, and construction industries.

Synthesis of innovative epoxy resin and polyamine hardener microcapsules and their age monitoring by confocal Raman imaging

AbstractWe present an innovative breakthrough encompassing synthesis, characterization, and age monitoring of epoxy resin and polyamine hardener microcapsules to form a dual‐component system for self‐healing anticorrosion coatings. The epoxy resin microcapsules (ER‐MC) are fabricated through oil–water emulsion and in situ polymerization, with poly (urea‐formaldehyde‐melamine) as shell material and a mixture of epoxy resin and n‐butyl glycidyl ether as core material. Modified aliphatic fast reactive polyamine hardener is microencapsulated with polymethylmethacrylate as shell using double emulsion and solvent evaporation method (PAH‐MC). Characterization includes optical microscopy, scanning electron microscopy, and particle size analyzer utilizing laser diffraction. The resulting microcapsules exhibited spherical shape with smooth surface devoid of porosity. Fourier transform infrared spectroscopy‐attenuated total reflection is utilized to confirm encapsulation by identifying the chemical structures of both microcapsule constituents. The thermogravimetric analysis further confirms the core content of microcapsules obtained from solvent extraction. ER‐MC contains approximately 66 wt %, while PAH‐MC stands 40 wt %, both showcasing remarkable thermal stability below 200°C. A ten‐month storage period fails to diminish the presence of the healing agents encapsulated within the polymeric walls, which is revealed by Raman spectroscopy utilizing 2D compositional mapping. This research demonstrates the viability of creating dual microcapsules and exemplify their potential for developing self‐healing coatings with dual‐component film‐forming healing agents.

Damping behaviour and self-healing performance evaluation of microcapsules reinforced epoxy composites by impulse excitation technique

Micro cracks developed in the composite structures can be repaired autonomously by incorporating microcapsules-based self-healing approach into the composites. In the current study, in order to employ self-healing composites in different structural applications, damping behaviour and self-healing performance of the composites were evaluated. CY230 epoxy and HY951 hardener were chosen as two different self-healing agents and encapsulated in polymethylmethacrylate (PMMA) shell material. Dual microcapsules reinforced carbon fibre epoxy composites were fabricated by employing 15wt% of microcapsules at 1:1 weight ratio and 0.5:0.5 weight fractions of matrix reinforcement. Influence of microcapsules addition and induced damages on the damping behaviour and self-healing performance of the pure epoxy and pure carbon fibre reinforced polymer (CFRP) composites were investigated by impulse excitation technique (IET). It was noticed that with the addition of respective optimized 7.5 wt%, 15 wt% microcapsules to pure epoxy and pure CFRP, damping factor of both the composites increased whereas elastic modulus decreased. Compared to capsules reinforced virgin composites, damping factor of damaged composites was higher in both types of composites. Self-healing efficiency of capsules reinforced pure epoxy and carbon fibre epoxy composites were calculated based on the recovery in stiffness of the composites and noticed respective healing efficiencies of 72.05% and 53.72% at optimized healing conditions and microcapsules concentration.

Dual microcapsules based epoxy/polyethyleneimine autonomous self‐healing system for photo‐curable coating

Self‐healing coatings were fabricated by adding two different epoxy and polyethyleneimine microcapsules to epoxy‐polyester acrylate resin. The first capsule contained polyethyleneimine and the second capsule contained a commercial epoxy resin. Polyethyleneimine (PEI) microcapsules were prepared by filling PEI into hollow poly(melamine‐urea‐formaldehyde) (PMUF)‐shelled polymeric microcapsules. Epoxy microcapsules were prepared by coating with a poly(urea‐formaldehyde) (PUF)‐shelled material using in‐situ polymerization. Using thermogravimetric analysis (TGA), the healing agent contents of the microcapsules for epoxy and PEI were determined to be 55% and 49%, respectively. Moreover, using a zeta‐sizer, the mean sizes of the microcapsules for epoxy/PUF and PEI/PMUF were determined to be 185 nm and 377 nm, respectively. Both capsule types were added to the epoxy‐polyester acrylate‐based photo‐curable coating formulation in the amount of 2% by weight. The coating formulation was applied to plexiglass surface, then cured with UV light and artificial scratches were made on the coating surface. At the end of day two, the SEM images revealed that coating successfully self‐healed the scratch.

The flexural properties of self healing fiber reinforced polymer composites

Fiber reinforced polymer composites have a complex damage prediction and repair mechanism. Such complexities made the researchers to implement new techniques like self healing. Amendments in the existing material can modify its properties. So, it is necessary to study the change in property due to inclusion of self healing in fiber reinforced composite materials. This work aims to investigate the self recovery response of composites prepared by reinforcing glass fibers and carbon fibers in epoxy matrix. The healing was achieved by inclusion of dual microcapsules made of epoxy and hardener encased in separate capsules. To investigate the recovery activity of the composite laminate, a 5mm diameter indentation was produced at the centre of specimen and the healing was monitored by measuring the diameter of indentation after 12 hrs and 24 hrs. To notice the influence of micro-inclusions on flexural strength, flexural test was conducted on neat, indented and healed specimens. It was observed that inclusion of microcapsules did not majorly alter flexural strength of glass fiber reinforced and carbon fiber reinforced polymer composites. Results also indicated complete healing of both carbon fiber reinforced polymer and glass fiber reinforced polymer composite specimens with healing efficiency of 103.4% and 101.8% respectively.

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.

Microencapsulation of oil soluble polyaspartic acid ester and isophorone diisocyanate and their application in self‐healing anticorrosive epoxy resin

ABSTRACTIsocyanate and amine solution are microencapsulated, respectively, via in situ polymerization to realize the self‐healing function in epoxy matrix. First, the isophorone diisocyanate (IPDI) microcapsules prepared with different core/shell ratios, emulsifier dosages and emulsification rates are characterized by field emission scanning electron microscope (FE‐SEM). They exhibit integral spherical shape when the core/shell ratio is 3:1 and emulsifier concentration is 2.52 wt %, and the diameter of IPDI microcapsules ranged from 2.66 μm to 11.25 μm is manufactured by adjusting emulsification rate over the range of 3000–9000 rpm. Besides, during the microencapsulation of polyaspartic acid ester (PAE), urea, tung oil, as well as aqueous isocyanate are proposed to improve the stability of PAE emulsion. SEM and FTIR results reveal that aqueous isocyanate can react with partial PAE and form polyurea (PU) layer to take protection effectively. Further, IPDI‐PAE dual microcapsules are incorporated into epoxy coatings, the self‐healing and anticorrosion performance of coatings with various amounts of microcapsules are investigated systematically. It was found that the degree of repair and anticorrosion are increased with increasing microcapsules loading, and the appropriate amount of microcapsules addition is 15 wt %, which corresponding to 93% repair efficiency. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48478.

Skin-Inspired, Fully Autonomous Self-Warning and Self-Repairing Polymeric Material under Damaging Events

Polymers are susceptible to small damage which is difficult to detect and repair and may lead to catastrophic failure if left unattended at the early stage. How to autonomously warn and repair the damage simultaneously is a promising yet challenging task, owing to the difficulty in integrating different functional elements for packaging and lack of suitable vehicles to carry a multirole trigger with high reactivity. Herein, inspired by human skin in the damage-healing process, we report a genuinely fully autonomous smart material that is capable of warning of and healing damage via simply incorporating dual microcapsules containing polyamine as a multirole trigger and epoxy monomer dyed with a pH indicator, respectively. Both microscopic “subcutaneous” damage and macroscopic surface damage can be warned of by a conspicuous red color, not only rapidly upon occurrence but also permanently after being repaired. Accompanied with the comprehensive warning, the smart material shows high healing performance upon...

Novel dual-functional coating with underwater self-healing and anti-protein-fouling properties by combining two kinds of microcapsules and a zwitterionic copolymer

Antibiofouling and repairing of the micro-cracked coating on the surface of the facilities in underwater environment are two great challenges in marine industries. This paper prepared a dual-functional coating with underwater self-healing and anti-protein-fouling properties by combining two kinds of microcapsules and a zwitterionic copolymer. First, epoxy resin microcapsules and underwater epoxy hardener microcapsules were prepared. Epoxy resin microcapsules with a poly(urea-formaldehyde) shell and the entrapped mixture of epoxy resin and n-butyl glycidyl ether showed homogeneous spherical morphology with encapsulation ratio of 90.42%. Underwater epoxy hardener microcapsules with a polymethyl methacrylate shell and the entrapped underwater epoxy hardener showed cellular spherical morphology with encapsulation ratio of 78.67%. Both of the microcapsules exhibited pretty thermal stability and acid, alkali and salt resistance. Then, two types of microcapsules were mixed with amine cured epoxy coating system to cast film on steel piece, and subsequently a zwitterionic polymer, ploy(sulfobetaine methacrylate-co-glycidyl methacrylate)(PSG) solution was casted on the surface of the un-cured epoxy coating. Therefore, a dual-functional coating with underwater self-healing and antibiofouling functions was obtained. The self-healing anticorrosion function attributed to the dual microcapsules and the anti-protein-fouling performance provided by PSG layer had been certificated. The facile combination of underwater self-healing and anti-protein-fouling functions may provide a new protection strategy for marine and other underwater facilities.

Effect of epoxy resin and hardener containing microcapsules on healing efficiency of epoxy adhesive based metal joints

Dual component microcapsules of epoxy resin and polyamine hardener with polymethyl methacrylate (PMMA) shell were synthesized using a water-oil-water emulsion solvent evaporation method. The high concentration of sodium dodecyl sulfate (SDS) was used to reduce the thickness of shell wall of dual component microcapsules. The dual microcapsules of 1:1 weight ratio were introduced in the epoxy adhesive to study the healing effect. The morphology, chemical structure and thermal characteristics of the microcapsules were characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), respectively. The insertion of dual component microcapsules in epoxy matrix reduced the lap shear strength of adhesive joints, which may be attributed to the generation of stress concentration cites because of micron sized capsules. However, the extension and absorbed failure energy of adhesive joints under uniaxial loading increased with the increase of concentration of dual microcapsules. The viscoelastic nature of the dual microcapsules may be responsible for this enhancement. Significant enhancement in the healing efficiency (90.93%) of the joints was achieved for 10 wt% of dual microcapsules. The crack pinning and crack blunting mechanisms at the vicinity of the crack path adjacent to the microcapsules were found responsible for significant enhancement in the healing efficiency of the adhesive joints.

Study of factors related to performance improvement of self-healing epoxy based on dual encapsulated healant

Our earlier work developed epoxy based self-healing composites with embedded dual microcapsules, which contain unreacted epoxy as the polymerizable component and mercaptan and tertiary amine catalyst as the hardener, respectively. Self-healing was allowed to proceed rapidly, offering attractive repair effectiveness. To give full play to the healing agent, influences of a series of factors on healing chemistry of the composites were studied in this paper. It was found that strong alkality of the catalyst, high activity of mercaptan, and low viscosity of the encapsulated epoxy prepolymer ensured high healing efficiency and rate of healing. In addition, matching of the microcapsules' sizes and fractions was critical for keeping stoichiometric ratio of the components at the damage areas, as required by the mechanism of the healing reaction (i.e. addition polymerization). Homogeneous dispersion of the capsules under proper stirring speed led to timely contacts between the healant fluids flowing out of the fractured capsules. Larger microcapsules favored filling of the cracks in terms of larger amount of the released healing agent, while smaller ones facilitated mixing and interdiffusion of the ingredients. The results provided key data for optimizing the self-healing system.

4532123 Dual microcapsules and process for their preparation: David L Gardner assigned to Battelle Development Corporation

4532123 Dual microcapsules and process for their preparation: David L Gardner assigned to Battelle Development Corporation

4532123 Dual microcapsules and process for their preparation

4532123 Dual microcapsules and process for their preparation