Abstract
We demonstrate for the first time the direct stereolithographic 3D printing of an extrinsically self-healing composite, comprised of commercial photocurable resin modified with anisole and PMMA-filled microcapsules. The composites demonstrate solvent-welding based autonomous self-healing to afford 87% recovery of the initial critical toughness. This work illustrates the potential of stereolithographic printing to fabricate self-healing composites with user-defined structures, avoiding the need for extensive rheological optimization of printing inks, like in direct-write 3D printing. Importantly, this work also demonstrates the inclusion of microcapsules into 3D printing resins to incorporate additional functionality into printed composites, which could be adapted for applications beyond self-healing materials.
Highlights
The lifetimes of composite materials are typically limited by fatigue or other material failure mechanisms due to damage encountered during service
We demonstrate a technique of combining UV-curable resin embedded with solvent-containing microcapsules in conjunction with stereolithographic (SL) 3D printing (3DP) to construct user-defined 3D structures, whereby a laser (405 nm) spatioselectively polymerizes/crosslinks the resins according to a computer aided design
The high boiling point and immiscibility of anisole with water allows it to be encapsulated using in situ polymerization of urea-formaldehyde in an oil-in-water emulsion[21]
Summary
We demonstrate a technique of combining UV-curable resin embedded with solvent-containing microcapsules in conjunction with stereolithographic (SL) 3DP to construct user-defined 3D structures, whereby a laser (405 nm) spatioselectively polymerizes/crosslinks the resins according to a computer aided design. Thermogravimetric analysis (TGA) of anisole/PMMA-filled urea-formaldehyde microcapsules showed a sudden rupture of the capsules at approximately 260 °C Repeating this experiment twice more, we again observed this phenomenon each time. TGA of microcapsules in cured resin mixtures did not show a similar rupture event, presumably as the presence of the resin matrix prevented explosion of microcapsules (Fig. S7) To investigate their self-healing properties, mode 1 fracture testing was performed on tapered double cantilever beam (TDCB) test samples comprising of these mixtures (Fig. S8), which were generated using a molding technique. Both the tail and hackle markings increase the surface area of the crack plane, and the energy absorbed by the composite during crack growth, thereby increasing the resulting fracture toughness This fracture toughening mechanism as a result of incorporation of urea-formaldehyde capsules is supported in the literature for a number of materials including epoxy resins[29] and thermoplastics such as PMMA22. This promising approach has widespread applications that can be modified to incorporate alternative functionalities to 3D printed materials, such as for hollow glass sphere containing light-weight composites[31], or for flame retardant composite materials; we will investigate such alternative applications in future work
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