Synthesis and characterization of chitosan/urea-formaldehyde shell microcapsules containing dicyclopentadiene

Preparation and Characterization of Microencapsulated Ethylenediamine with Epoxy Resin for Self-healing Composites

Healing agent microcapsules have been used to realize self-healing for polymeric composites. In this work a novel kind of microcapsules encapsulating ethylenediamine (EDA) with epoxy resin as shell material were prepared by interfacial polymerization technology. The oil phase was epoxy resin prepolymer and carbon tetrachloride, and the water phase was EDA and deionized water. Under the action of emulsifier, a stable water-in-oil emulsion was formed. Then the emulsion was added to dimethyl silicone oil, stirred and dispersed, to prepare microcapsules. In addition, the factors affecting the preparation of microcapsules were studied. In this study, Fourier transform infrared(FTIR) was carried out to demonstrate the chemical structure of ethylenediamine microcapsules. Optical microscope(OM) and scanning electron microscope(SEM) were used to observe the morphology of microcapsules. Thermogravimetric analysis and differential scanning calorimetry were done to investigate the thermal properties of microcapsules. Permeability experiment and isothermal aging test were executed to verify the environment resistance of microcapsules. Results showed that EDA was successfully coated in epoxy resin and the microcapsule size was in the range of 50~630 μm. The synthesized microcapsules were thermally stable below 75 °C and perfect permeability resistance to ethanol solvent.

Influence of synthetic conditions on the performance of melamine–phenol–formaldehyde resin microcapsules

Melamine (M), phenol (P) and formaldehyde (F) were used as raw materials to synthesize a melamine–phenol–formaldehyde resin (MPF) which was used as shell material to prepare a self-healing microcapsule with E-51 epoxy resin as the core, via in situ polymerization. Fourier transform infrared spectroscopy, environmental scanning electron microscopy and laser particle size analysis were used to characterize the surface morphology, structure and properties of the microcapsule. The influence of the reaction conditions on the properties of the microcapsule was investigated by orthogonal testing. The mass ratio between the MPF shell and the epoxy resin core was found to be 1.2:1.0, optimum pH for shell formation was found to be 3, the emulsification speed was 800 r/min, the acidification speed was 400 r/min and the acidification temperature was 60°C. Under these conditions, the prepared microcapsules are regular and spherical with a smooth, dense surface and uniform particle size with a normal distribution. The microcapsules remained well dispersed and did not aggregate. The orthogonal test revealed that the average particle size and yield of the microcapsules are mainly determined by the core/shell mass ratio, whereas the reaction temperature had a greater impact on the core content of the microcapsules. Although the best microcapsule samples showed poor anti-permeability in ethanol, they exhibited good thermal, isothermal and storage stabilities. This indicates that they may be stored at a constant temperature.

Effect of 3D-Printed Microvascular Network Design on the Self-Healing Behavior of Cross-Linked Polymers

This article describes the manufacturing procedure and the characterization of self-healing polymers based on embedded microvascular networks. The samples were realized by resin casting into water-soluble PVA molds, fabricated via 3D printing. This technology allowed us to exploit the 3D printers' ability to produce complex structures with high resolution for the creation of independent microchannels networks. The two reacting components of a two-part resin could be stored separately within the microstructure. The materials' self-healing ability resulted from their reaction when severe damage caused the healing liquids to leak out, wetting the sample cross section and diffusing one into the other. The mechanical properties of healed samples were investigated by means of uniaxial tensile tests and compared to those of undamaged samples. The effect of microchannel density and different network designs on self-healing efficiency was determined. The different microstructures used were characterized using computerized X-ray microtomography. The versatility of the fabrication technique presented in this work allows conversion of any water-resistant resin into a fully functional self-healing polymeric composite.

Thermally induced release from polymeric microparticles with liquid core: the mechanism

Herein we demonstrate how the volatility of a liquid can be manipulated by enclosing microdroplets of the liquid into thin polymeric shells. In this way, composite core-shell microparticles consisting of 80 wt% of a liquid core material and 20 wt% of a polymer can be made 150 °C more stable than the individual core component. The thermal stability of the composite microparticles is found to be determined by the boiling point of the core material and the average particle size, while the role of the particle shell thickness is much less relevant. Two mechanisms responsible for the release of the core material from the microparticles at elevated temperatures were resolved: (1) thermally induced degradation of the shell and (2) diffusion of the core material through the polymeric shell boosted by the increased inner pressure.

Conductive microcapsules for self-healing electric circuits

Well dispersed conductive microcapsules can be processed directly with inorganic-based Ag paste and perform high restoration efficiency for as-cast electrical circuits.

Structural analysis of chitosan hydrogels containing polymeric nanocapsules

The incorporation of different concentrations of polymeric nanocapsule suspensions into chitosan hydrogels is proposed, in order to study the structure of a formulation with the properties of great tissue adhesion and controlled release of the nanoencapsulated drugs, represented here by capsaicinoids. The gels presented acceptable acid pH values and the nanoparticles were visually observed in the system. A transition from the micrometer to the nanometer scales suggested that the nanocapsules are initially agglomerated in the hydrogel. A sedimentation tendency of the nanocapsules in the system was observed and only physical interaction between the chitosan chains and polymeric nanocapsules was verified. The hydrogels, despite the presence of nanocapsules, presented shear-thinning properties and an elastic behavior under low and high frequencies, showing a very structured gel network. The observed variation in the elasticity of the hydrogels may arise from a decrease in the number of interactions and degree of entanglement between the chitosan chains, caused by the presence of nanoparticles.