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Title: Self-healing composites via metal triflate catalytic curing agents
Author: Cope, Tim S.
ISNI:       0000 0004 5923 3773
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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This research focuses on the development and implementation of novel self-healing chemistries for fibre reinforced polymer (FRP) composite materials that are cost effective, compatible with the host epoxy-based matrix material, stable to environmental conditions (i.e. air and moisture) and achieve high healing efficiencies after the initial fracture event. The initial 'proof of concept' study involved identifying a suitable catalytic curing agent that was capable of initiating the ring-opening polymerisation (ROP) of epoxides, to restore the fracture toughness of the host epoxy matrix after a fracture event had occurred. The solid-state Lewis acid catalytic curing agent, scandium(III) triflate (Sc(OTf)3), was selected as the healing agent and the healing efficiency was quantitatively evaluated using a tapered double cantilever beam (TDCB) test specimen geometry. To provide an efficient delivery method for the epoxide constituent, microcapsules containing diglycidyl ether bisphenol A (DGEBA) epoxy resin and a non-toxic solvent, ethyl phenylacetate (EPA), were synthesised via an in situ urea-formaldehyde microencapsulation procedure. Autonomous (AUTO) test specimens containing embedded Sc(OTf)3 particles and DGEBAEPA microcapsules, resulted in >80% recovery of the host matrix fracture toughness value. Heating at moderately raised temperatures accelerated the ring-opening polymerisation (ROP) of the epoxy resin. Due to the inherent volume limitations of a microcapsule-based system, a bio-inspired microvascular geometry for self-healing agent delivery was implemented into glass and carbon FRP composites, to facilitate the repair of large internal damage volumes. Thermal cure analysis and mechanical characterisation of the metal triflate-initiated self-healing polymers were also investigated to optimise cure conditions at low temperature and to investigate the influence of reagent loadings on the mechanical properties. Suitable self-healing agents were externally injected into a double cantilever beam (DCB) test specimen geometry via 0.5 mm microvascule channels located on the composite laminate mid-plane, where the healing agent was left to autonomously wet out the exposed fractured crack planes. Initially, pre-mixed and non-mixed self-healing agents were evaluated in glass FRP (GFRP) DCB test specimens and left to cure at moderately raised temperatures, to provide healing efficiency values of >99% for fracture toughness and load, at the point of crack initiation. To assess the transfer of this technology to carbon FRP composites, DCB test specimens were manufactured using out of autoclave (OOA) techniques that contained embedded Sc(OTf)3 catalyst on the composite laminate mid-plane. The catalyst was subsequently exposed during testing via the propagating crack. Fractured specimens were injected with an epoxy-EPA solution to initiate healing and provide a 60% restoration of the initial fracture toughness value after 24 hours at 80 QC. This research, therefore, demonstrates the tailorability of the underpinning chemistry of this self-healing system, across a variety of delivery systems, in epoxy-based polymer composite materials.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available