Abstract
Alginate microcapsules containing epoxy resin were developed through electrospraying method and embedded into epoxy matrix to produce a capsule-based self-healing composite system. These formaldehyde free alginate/epoxy microcapsules were characterized via light microscope, field emission scanning electron microscope, fourier transform infrared spectroscopy and thermogravimetric analysis. Results showed that epoxy resin was successfully encapsulated within alginate matrix to form porous (multi-core) microcapsules with pore size ranged from 5–100 μm. The microcapsules had an average size of 320 ± 20 μm with decomposition temperature at 220 °C. The loading capacity of these capsules was estimated to be 79%. Under in situ healing test, impact specimens showed healing efficiency as high as 86% and the ability to heal up to 3 times due to the multi-core capsule structure and the high impact energy test that triggered the released of epoxy especially in the second and third healings. TDCB specimens showed one-time healing only with the highest healing efficiency of 76%. The single healing event was attributed by the constant crack propagation rate of TDCB fracture test. For the first time, a cost effective, environmentally benign and sustainable capsule-based self-healing system with multiple healing capabilities and high healing performance was developed.
Highlights
Different microvascular networks have been introduced including hollow glass fibers[7], hollow tube reinforced shape memory polymer[8], conductive microwire/glass microtubes network[9], fugitive wax scaffold[10] and polyacrylonitrile (PAN) nanofibres[11]
Field-emission scanning electron microscope (FESEM) micrographs show that these dried microcapsules have irregular shapes and bumpy surfaces as water from the surrounded calcium alginate matrix evaporated and shrank during the drying process, whereas the multi-core epoxy resin did not, leaving the capsules to have bumpy surface which was the shapes of the encapsulated multi-core epoxy resin
During the cross section study, porous internal structure was observed on the AG/EPX microcapsule after removing the encapsulated epoxy resin by acetone (Fig. 3e,f) and the pore size was found to be in the range of 5–100 μm through FESEM
Summary
Different microvascular networks have been introduced including hollow glass fibers[7], hollow tube reinforced shape memory polymer[8], conductive microwire/glass microtubes network[9], fugitive wax scaffold[10] and polyacrylonitrile (PAN) nanofibres[11]. Studies have shown that formaldehyde may cause cancer and adverse health effects, it has been regulated in the work place for years[20] Synthesis of these formaldehyde containing capsules such as urea-formaldehyd[2], polyurethane/urea-formaldehyde[21] and poly (melamine-formaldehyde)[16] capsules through in situ polymerization process is complicated because temperature and pH alteration are required. Other capsules such as conducting polymer[22] and polystyrene nanocapsules[23] were reported, but they were used for corrosion inhibitor These self-healing microcapsules do not possess the properties as a reinforcement to the whole composite system. Alginate hydrogels are formed by ionic crosslinking with Ca2+ or Ba2+ ions[26,27] which is a simple and cost effective process without temperature and pH alteration
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