Fracture behaviour of a self-healing microcapsule-loaded epoxy system

Abstract

Polymer materials often experience micro-cracks during their service. Self-healing polymeric materials have the built-in capability to substantially recover their load transferring ability after damage. This field of self-healing materials is a relatively new one, beginning in the early 1990s, with the majority of the research occurring in the past decade [1,2]. The ring-opening metathesis polymerization of dicyclopentadiene (DCPD) [3,4], addition and ionic polymerization of epoxy [5], condensation polymerization of polysiloxane [6], organic solvents [7] and isocyanates [8], have been reported for automatically repairing cracks in polymers at room temperature.Several researchers [5,[9][10][11] have successfully measured fatigue-crack propagation in epoxy resins. Brown and coworkers [5,9] investigated the effect of embedded urea-formaldehyde (UF) microcapsules on the monotonic fracture properties of a selfhealing epoxy. In addition to providing an efficient mechanism for self-healing, the presence of liquidfilled microcapsules increased the virgin monotonic-fracture toughness of epoxy by up to 127%. The increased toughening was correlated with a change in the fracture plane morphology from mirror-like to hackle markings with subsurface microcracking. The addition of microcapsules to an epoxy matrix significantly increased the resistance to crack growth under dynamic loading conditions. Abstract. The effect of temperature on the fracture behaviour of a microcapsule-loaded epoxy matrix was investigated. Microencapsulated epoxy and mercaptan-derivative healing agents were incorporated into an epoxy matrix to produce a polymer composite capable of self-healing. Maximum fracture loads were measured using the double-torsion method. Thermal aging at 55 and 110°C for 17 hours [hrs] was applied to heal the pre-cracked samples. The addition of microcapsules appeared to increase significantly the load carrying capacity of the epoxy after healing. Once healed, the composites achieved as much as 93-171% of its virgin maximum fracture load at 18, 55 and 110°C. The fracture behavior of the microcapsule-loaded epoxy matrix was influenced by the healing temperature. The high self-healing efficiency may be attributed to the result of the subsurface micro-crack pinning or deviation, and to a stronger microencapsulated epoxy and mercaptanderivative binder than that of the bulk epoxy. The results show that the healing temperature has a significant effect on recovery of load transferring capability after fracture.

Effect of cross-link density and the healing efficiency of self-healing poly(2-hydroxyethyl methacrylate) hydrogel

“…In response, a new and alternative approach, known as "self-healing", has been developed, which was inspired by biological mechanisms (2)(3)(4). These self-healing polymers possess the ability to heal in response to damage using resources inherently available to the system.…”

Solid-state Self-healing Systems: The Diffusion of Healing Agent for Healing Recovery

“…Self-healing polymers possess the ability to heal in response to damage using resources inherently available to the system. To date, self-healing has been demonstrated by three conceptual approaches: capsule-based healing systems (Lee et al 2011), vascular healing systems (Norris et al 2011) and intrinsically healing polymers (Billiet et al 2013;Guohua et al 2012;Julia et al 2013). …”

Self-healing of Poly(2-hydroxyethyl methacrylate) Hydrogel through Molecular Diffusion

“…In recent years there is fast growing interest on a variety of self-healing polymers Maes et al 2012;Murphy & Wudl 2010). Selfhealing mechanism in bulk polymer materials are either based on release of repair agents upon damage (Lee et al 2011) or on the inclusion of latent molecular functionalities in the polymer structure that trigger repair via thermally reversible reactions, hydrogen bonding, ionomeric arrangements, or molecular diffusion and entanglement (Bergman & Wudl. 2008;Billiet et al 2013).…”