Robust, Double-Walled Microcapsules for Self-Healing Polymeric Materials

Abstract

Double-walled polyurethane/poly(urea-formaldehyde) microcapsules (PU/UF) are prepared for use in self-healing materials. This modified encapsulation procedure combines two chemistries to form more robust capsule shell walls in a single operation. Robust capsules are formed by this procedure as long as the aromatic polyisocyanate prepolymer is soluble in the core liquid and the core liquid is compatible with isocyanates. Compared to a standard UF encapsulation, the modified procedure results in capsules with an increase in shell wall thickness from 200 to 675 nm as a function of the amount of PU added to the core liquid. Thermal stability of PU/UF microcapsules prepared with varying amounts of PU is compared to UF microcapsules. Mechanical properties of the PU/UF microcapsules are assessed from single-capsule compression testing.

Autonomic healing of PMMA via microencapsulated solvent

“…Double shell wall poly(urethane)/urea-formaldehyde (PU/UF) microcapsules filled with a core solution of 10 wt% PMMA (average M w z 350 kDa; SigmaeAldrich) dissolved in the solvent anisole (SigmaeAldrich) were prepared using a single batch process adapted from Caruso et al [6]. All materials were used as received.…”

“…The solvent anisole was chosen as the healing agent because its solubility parameter is closest to that of PMMA. The PU prepolymer (4 g) was first dissolved in 60 mL of the core solution (10 wt% PMMA, 90 wt% anisole) and then added to the mixing vessel, which contained double the amount of UF reaction components prescribed by Caruso [6]. A stir rate of 500 revolutions per minute (rpm) was maintained throughout the reaction.…”

Robust synthesis of epoxy resin-filled microcapsules for application to self-healing materials

“…In this approach, the released DCPD comes into contact with the catalyst and undergoes ring-opening metathesis polymerization (ROMP); in this work, poly(urea-formaldehyde) microcapsules containing the DCPD were prepared using in-situ polymerisation in an oil-in-water emulsion [8]. Using this methodology, chemistries including Dicyclopentadiene (DCPD)/ethylidene-norbornene (ENB) [9], organic solvents [10,11], epoxy resins [12] and their cross-linkers such as amines [13,14], thiols [15] and glycidyl methacrylate (GMA) [16] were successfully encapsulated. Typical capsule shell materials include urea-formaldehyde (UF), melamine-ureaformaldehyde (UMF) and melamine-formaldehyde (MF) which have proved promising for sequestration of various reactive ingredients [4][5][17][18].…”

Polyurethanes as self-healing materials

“…IPDI was successfully imprisoned in PUR shell via interfacial polymerization. Following studies yielded variations of the system, like double walled PUR/poly(urea-formaldehyde) microcapsules with improved mechanical strength and thermal stability (up to 180 o C) 10 . Another solutions were poly(urea-urethane) nanoparticles synthesized by self-assembled neutralization emulsification 11 and PUR microcapsules filled with water-borne PUR paint 12 .…”