In situpoly(urea-formaldehyde) microencapsulation of dicyclopentadiene

Abstract

Microencapsulated healing agents that possess adequate strength, long shelf-life and excellent bonding to the host material are required for self-healing materials. Urea-formaldehyde microcapsules containing dicyclopentadiene were prepared by in situ polymerization in an oil-in-water emulsion that meet these requirements for self-healing epoxy. Microcapsules of 10-1000 mm in diameter were produced by appropriate selection of agitation rate in the range of 200-2000 rpm. A linear relation exists between log(mean diameter) and log(agitation rate). Surface morphology and shell wall thickness were investigated by optical and electron microscopy. Microcapsules are composed of a smooth 160-220 nm inner membrane and a rough, porous outer surface of agglomerated urea-formaldehyde nanoparticles. Surface morphology is influenced by pH of the reacting emulsion and interfacial surface area at the corewater interface. High yields (80-90%) of a free flowing powder of spherical microcapsules were produced with a fill content of 83-92 wt% as determined by CHN analysis.

Solvent-Promoted Self-Healing Epoxy Materials

“…16 The autonomic self-healing system requires that solvent be encapsulated and the capsules embedded in the epoxy matrix. Unfortunately, the five highly efficient solvents noted above have yet to be successfully encapsulated using the ureaformaldehyde (UF) in situ polymerization method 19 due to their high degrees of polarity. Reverse-phase encapsulation procedures 26 were attempted for these solvents, but also proved unsuccessful to date.…”

“…Thus, chlorobenzene emerged as a potential solvent for our initial autonomic healing experiments since it was encapsulated previously. 27 Chlorobenzene was encapsulated by the UF in situ polymerization method 19 with average diameters of 160 ( 20 µm. Though a chlorobenzene system does not show the best recovery of fracture peak load ( Figure 1), it serves as an adequate choice for initial demonstration of the solvent-based, autonomic healing concept.…”

“…17 In contrast to these methods, autonomic self-healing materials can repair damage in thermosets through chemical reactions at room-temperature based on ring-opening metathesis polymerization (ROMP). [18][19][20][21][22][23][24] Microcapsules containing dicyclopentadiene (DCPD) and wax-protected Grubbs' catalyst are both embedded in an epoxy matrix, and upon crack propagation through the material, the capsules rupture to release DPCD into the crack plane. Poly(DCPD) is formed in the crack plane resulting from the ROMP reaction of DCPD initiated by Grubbs' catalyst to restore the original structural properties of the polymer matrix.…”

SECM study of steel corrosion under scratched microencapsulated epoxy resin

“…air-oxygen [7]. The most explored self-repairing bulk phases are epoxy [3,4,[8][9][10] and polyester matrices [11]. Selfhealing microcapsules and slow release microspheres in paints studied by several authors [12] showed that microcapsules built in paint lose their core material which fills the scratch line and so the corrosion damage is diminished by an autonomous self-healing mechanism [13].…”

Use of FTIR Analysis to Control the Self-Healing Functionality of Epoxy Resins

“…The challenge facing materials scientists is to assure these systems must be able to stem fatigue damage and preserve their integrity, increase their life span, reduce maintenance costs and provide safety during use. A lot of strategies were formulated up to now in the development of self-healing materials [5,[16][17][18][19][20][21][22][23][24][25][26][27].…”