Epoxy Microcapsules Research Articles

Microcapsulated epoxy resin with nanosilica‐urea formaldehyde composite shell

ABSTRACTIn this study, the epoxy microcapsules with the nanosilica (0, 1, 2, and 3 wt %)—urea formaldehyde composite shell were synthesized and then characterized by optical microscope (OM), field emission scanning electron microscope (FESEM), Fourier‐transform infrared spectroscopy (FT‐IR), and thermogravimetric analysis. According to the OM analysis, the without nanosilica microcapsules had the semitransparent structures and equal size distributions. Also, the formation of the microcapsule clusters and rupturing microcapsules in the sample containing 3 wt % nanosilica were observed by OM method. The FESEM analysis showed that without nanosilica, microcapsules had a smooth surface, whereas by increasing the percentage of nanosilica up to 2 wt %, the surface roughness was enhanced. It was also observed that on the surface of the microcapsules without nanosilica, two size ranges of the submicrocapsules with the average diameters of 1.12 μm and 208 nm were formed. By adding 1 wt % nanosilica, three size ranges of submicrocapsules were formed, with the average size of 2.63 μm, 824 and 179 nm. The interesting phenomena in the microcapsules containing 2 and 3 wt % nanosilica were the packing submicrocapsules with the polymeric shell and the formation of the microcapsule clusters, respectively. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48580.

Preparation and Self-Repairing Properties of Urea Formaldehyde-Coated Epoxy Resin Microcapsules

Urea formaldehyde resin-coated epoxy resin microcapsules were prepared by two-step in situ polymerization. The effects of five factors on the yield, coverage rate, repair rate, and morphology of the microcapsules were investigated by five factors and four levels of orthogonal test. These five factors were the mass ratio of the core to the wall material (Wcore:Wwall), the mass ratio of the emulsifier to the core material (Wemulsifier:Wcore), stirring rate, deposition time, and mass ratio of the emulsifier solution to the core material (Wemulsifier solution:Wcore). The ideal technological level of microcapsule synthesis was determined. According to the results of the range and variance of yield, coverage rate, and repair rate, the comprehensive properties of microcapsules became ideal. At this time, the Wcore:Wwall was 0.8 : 1, Wemulsifier:Wcore was 1 : 100, stirring rate was 600 r/min, deposition time was 32 h, and Wemulsifier solution:Wcore was 8 : 1. When the concentration of microcapsules in the epoxy resin was 10.0%, the self-repair rate was the best and the repair rate was 114.77%. This study is expected to provide a reference value for the preparation of a microcapsule self-healing technology and lay a foundation for the subsequent development of self-healing materials.

Preparation and Characterization of Urea Formaldehyde @ Epoxy Resin Microcapsule on Waterborne Wood Coatings

Urea formaldehyde @ epoxy resin microcapsules were prepared by two steps in situ polymerization, and the morphology and composition of microcapsules with different mass ratios of core to wall material were examined by scanning electron microscopy (SEM) and infrared (IR) spectroscopy. The microcapsules were added to the waterborne wood coatings to explore the effect of microcapsules on the properties of coatings and their self-repairing characteristics, and the gloss, hardness, adhesion, and impact resistance of the waterborne wood coatings were investigated. The results showed that when the concentration of microcapsule was 10.0% and the mass ratio of core to wall material was 0.83:1, the waterborne wood coatings had a good comprehensive performance and less negative impact. In the scratch test, the waterborne wood coatings with a concentration of 10.0% microcapsule had good repair ability. The possibility of applying the self-repairing technology of microcapsule to waterborne wood coatings was discussed through the preparation and performance characterization of self-repairing coatings and the results can become a guideline for the engineering application of waterborne wood coatings.

Synthesis and reaction mechanism of self-healing epoxy microcapsules

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 (TETA) and the epoxy resin. The orthogonal experiments 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 and static dynamic wide angle laser light scattering instrument synchronization are used to characterize surface topography, particle size and distribution. Fourier transform infrared spectroscopy and thermo-gravimetric analyzer are used to study reaction mechanism of the microcapsule wall materials and thermal stability of the microcapsules, 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 microcapsules prepared are spherical in shape with good surface compactness, dispersibility and thermal stability and the capsule core content is 82.3% and the average particle size is 275.3 μm. However, this type of epoxy resin microcapsule has relatively poor chemical stability. The core content decreases by 2.0% after 12 d storedat room temperature. After epoxy resin composite doped with 2.0% mass fraction of 200~300 μm microcapsules is damaged by the tensile testing machine, their repair rate is 67.04%.

Preparation Process of Epoxy Resin Microcapsules for Self - healing Coatings

The self-healing microcapsules were prepared by in-situ polymerization with urea formaldehyde resin and epoxy resin E-5l as the wall material and core material separately in this paper. The effects of the amount of epoxy resin, sodium dodecyl benzene sulfonate (SDBS), ammonium chloride, resorcinol and the stirring rate on the particle size of microcapsules were discussed. The microcapsules were added into the epoxy resin composite coating for corrosion resistance evaluation. The results showed that when the ratio of epoxy resin to urea was 24%, the amount of SDBS was 8%, the amount of ammonium chloride was 5.6%, the content of resorcinol was 10.4% and the stirring speed was 450 rpm, the average particle size of the capsules was 55.7 μm. When the addition number of microcapsules was 2% in the coating, the corrosion resistance was best with its service life prolonged by about 4 times.

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.

Microencapsulation of reactive amine by interfacially engineered epoxy microcapsules for smart applications

The most common approach for incorporation of extrinsic self-healing functionality relies on introducing healant-loaded micro-containers in the polymeric formulation. In this context, a healing system based on encapsulated epoxy resin and amine hardener appears to be one of the most economically viable solutions, in view of the chemical as well as mechanical compatibility with the matrix. Encapsulation of epoxy resins has been extensively studied while the high reactivity of the amine hardener renders its encapsulation rather difficult and has been attempted with only modest success. The purpose of the present work is to adopt an interfacial polymerization approach for the preparation of epoxy microcapsules encapsulating a reactive amine hardener (triethylene tetramine). The effects of experimental parameters, including reaction temperature, stirring speed and epoxy/amine concentration ratio on the microcapsule formation were investigated. A polymeric surfactant was used to stabilize the suspension to modulate the particle size distribution of the resultant microcapsules. The highest encapsulation efficiencies were obtained when the reaction medium was maintained at 70 °C under stirring (600 rpm) at epoxy/amine ratio of 10/3.2. The microcapsule dimensions and core content could be tailored, following this encapsulation approach of interfacial polymerisation. Under optimal conditions, spherical microcapsules with 100% yield and 12% core content were obtained.

Mesoporous silica as amine immobiliser for endowing healing functionality to epoxy resin

Abstract Feasibility of physical entrapment approach towards the immobilisation of amine hardener in mesoporous silica has been demonstrated for potential applications in the perspective of self-healing. A representative mesoporous silica (SBA-15) was synthesised using polymer-templated technique and employed as a substrate for immobilizing triethylene tetramine, a conventional epoxy hardener. Polymeric composites containing microencapsulated epoxy microcapsules and amine loaded SBA-15 were prepared by room temperature curing. The autocatalytic nature associated with the curing of epoxy remained unaltered due to introduction of either SBA-15 or epoxy loaded microcapsules, as confirmed by calorimetric studies. Healing efficiency, as quantified in terms of the ratio of impact strength before and after healing, was found to increase proportionally with increasing loading of healing additives in the formulation, with complete healing (100%) being exhibited at 20% microcapsule loading.

Pickering emulsion-based fabrication of epoxy and amine microcapsules for dual core self-healing coating

Facile and efficient encapsulation of epoxy and tetraethylenepentamine (TEPA) in polyurea (PU) microcapsules are accomplished with Pickering emulsion templates by one-step, interfacial polymerization. The formation of microcapsule is deftly achieved by lightly shaking Pickering emulsions. The whole process is time andenergy saving hardly with any waste and residual. Epoxy microcapsules keep the spherical shape with core content of more than 90 wt%. Amine microcapsules shrink a little for evaporation of water and the conserved TEPA after air-dried is 82.1 wt%. The shell walls of two microcapsules are about 1 μm. With the protection of PU shells, both microcapsules exhibit excellent thermal resistance. Furthermore, self-healing function of epoxy and amine microcapsules is measured by incorporating microcapsules into epoxy coating, and tested by brine-submersion corrosion-accelerating experiment. The dual core self-healing coatings demonstrate excellent self-repairing performance with the crack of embedded microcapsules and reaction between epoxy and amine. The core materials can outflow from microcapsules and form isolations for metal substrate from corrosion hazard, therefore, make for good self-repairing and preserving function of the self-healing coating.

Assessment of microcapsule—catalyst particles healing system in high performance fibre reinforced polymer composite

Autonomous self-healing in carbon fibre reinforced polymer (CFRP) is demonstrated using epoxy resin filled microcapsules and a solid-state catalyst. Microcapsules filled with oligomeric epoxy resin (20–450 μm) and particles of Sc(OTf)3 are embedded in an interleave region of a unidirectional CFRP laminate and tested under mode I loading. Double cantilever beam (DCB) test specimens containing variable concentrations of microcapsules and catalyst were prepared, tested and compared to those healed by manual injection with corresponding healing resin formulation. The healing efficiency was evaluated by comparing the maximum peak load recorded on load–displacement curves for pristine and healed specimens. A 44% maximum recovery was observed for specimens containing 10 wt% of solid phase catalyst and 11 wt% of epoxy microcapsules. However, a significant (80%) decrease in initial strain energy release rate (GIC) was observed for specimens with the embedded healing chemistries.

Optimization of Processing Conditions and Properties of Epoxy Microcapsule

A series of microcapsules were prepared by interfacial polymerization method using epoxy and urea formaldehyde resin as core material and shell material, individually. The effects of processing conditions on the properties of epoxy microcapsules were systematically investigated based on w(Core), average diameter and decomposition temperature of microcapsules through the method of orthographic factorial design and the most optimum processing conditions were included. The results indicated that core/shell mass ratio was the most important factor on w(Core), average diameter and decomposition temperature of microcapsules. The optimum processing conditions were concluded: 1:1 for the core/shell mass ratio, 300 rpm for agitation rate and 0.8% DBS as emulsifier. The microcapsules prepare in the optimum processing conditions were well encapsuled and presented thin shell and smooth surface. Moreover, the addition of 10% microcapsules can improve the mechanical properties of epoxy matrix greatly.

Preparation and properties of bisphenol A epoxy resin microcapsules coated with melamine–formaldehyde resin

Microcapsules containing epoxy resins have potential applications, such as in adhesive, electronic packaging, and self-healing polymeric composites. A series of microcapsules were prepared by in situ polymerization with poly(melamine–formaldehyde) as the shell materials and a mixture of diglycidyl ether of bisphenol A and epoxy diluent as the core substances. Morphology, chemical structure, mean particle size, and thermal properties of the microcapsules were studied by means of optical microscope, Fourier transform infrared spectroscopy, laser particle size analyzer, and microcomputer differential thermal balance, respectively. Effects of kind of epoxy diluent, surfactant type, emulsifier concentration, and emulsifying rate on the physical properties of microcapsules were investigated. Results indicate that the formation of microcapsules is affected by the epoxy diluent type and surfactant type. The highest core content of the resultant microcapsules is about 88 wt% and average diameters of the capsules range from 67 to 201 μm, which can be adjusted by changing the emulsifier concentration and emulsifying rate. Thermo gravimetric analysis indicated that the prepared microcapsules experienced excellent stability up to 235 °C.

Development of self-healing polymers via amine–epoxy chemistry: II. Systematic evaluation of self-healing performance

Part I of this study (H Zhang and J Yang 2014 Smart Mater. Struct. 23 065003) reported the preparation and characterization of epoxy microcapsules (EP-capsules) and amine loaded hollow glass bubbles (AM-HGBs), and the modeling of a two-part self-healing system. In part II, the self-healing performance of this material system is systematically investigated. Various factors including the ratio, the total concentration and the size of the two carriers are studied as well as the healing temperature and the post heat treatment process. The best healing performance is obtained at a ratio of 1:3 of EP-capsules to AM-HGBs. It is observed that a higher concentration of larger carriers, together with a higher healing temperature, enables better healing behavior. Healing efficiency of up to 93% is obtained in these systems. In addition, post heat treatment decreases the healing efficiency due to stoichiometric mismatch of healing agents caused by leakage of amine in the HGBs at elevated temperature.

High Performance Self-Healing Epoxy/Polyamide Protective Coating Containing Epoxy Microcapsules and Polyaniline Nanofibers for Mild Carbon Steel

Epoxy microcapsules and polyaniline nanofibers are incorporated into epoxy/polyamide coatings to enhance the protective and self-healing performance of the coatings for mild carbon steel. Epoxy microcapsules are prepared through the well-known interfacial polymerization process. Sodium chloride (NaCl, 12 wt %) solution is used as the model corrosion media. Protective and self-healing performance of the coatings is characterized by the electrochemical impedance spectroscopy (EIS) technique, scanning electron microscope (SEM) image analysis, and X-ray photoelectron spectroscopy characterization. The results demonstrate that the coatings containing epoxy microcapsules and polyaniline nanofibers have almost no deterioration in the 100-day testing period under the condition of being immersed in 12 wt % NaCl solutions at room temperature. The excellent protective performance and self-healing behavior are ascribed to the controlling release of epoxy which is encapsulated and the passive property of PANI nanofibe...

Preparation of epoxy microcapsule based self-healing coatings and their behavior

In this paper, epoxy microcapsules were prepared by interfacial polymerization of epoxy resin droplets with ethylenediamine (EDA), and the capsules were characterized by scanning electron microscope (SEM). Then, the coatings containing epoxy microcapsules were applied on carbon steels, and their behavior and self-healing effect were investigated by electrochemical impedance spectroscopy (EIS) technique and SEM observation. The experimental results demonstrate that the artificial scratches were successfully healed in about 4-h after made. Furthermore, coating prepared from 20wt.% epoxy microcapsules shows the best performance among all the prepared coatings.

Self-healing thermoset using encapsulated epoxy-amine healing chemistry

Self-healing was achieved with a dual-microcapsule epoxy-amine chemistry in thermoset epoxy. One capsule contained a modified aliphatic polyamine (EPIKURE 3274) while the second capsule contained a diluted epoxy monomer (EPON 815C). Amine microcapsules were prepared by vacuum infiltration of EPIKURE 3274 into hollow polymeric microcapsules. Epoxy microcapsules were prepared by an in situ polymerization method. Both types of capsules were incorporated into an epoxy matrix (EPON 828:DETA) and recovery of mode-I fracture toughness was measured using tapered-double-cantilever-beam (TDCB) specimens. The optimal mass ratio of amine: epoxy capsules was 4: 6 and an average healing efficiency of 91% was achieved with 7 wt% amine capsules and 10.5 wt% epoxy capsules. Long-term stability of the healing system was demonstrated for six months at ambient conditions. Thermal stability was investigated by post curing samples at 121 °C and assessing healing performance.

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%.

Microspheres and microcapsules: A survey of manufacturing techniques. Part 1: Suspension cross‐linking

AbstractA methodological survey of preparation of microspheres and microcapsules by suspension cross‐linking is presented. Thus, basic features of suspension cross‐linking, i.e., the formation of small droplets of a polymer solution (or melt) in an immiscible liquid followed by hardening of these droplets by covalent cross‐linking, are discussed. Typical microspherical and microcapsular products manufactured by suspension cross‐linking of naturally occurring and preformed synthetic polymers, including agarose and cellulose beads, albumin microspheres and microcapsules, polystyrene beads and epoxy resin microcapsules, are described. Manufacturing parameters controlling microsphere/microcapsule characteristics are also briefly outlined.