Self-healing properties of epoxy resins with poly(ε-caprolactone) healing agent

Abstract

Abstract:Thermally induced healing through thermoplastic poly(ε-caprolactone) (PCL), dissolved in 12.5, 25, 37.5 and 50 wt.%, respectively, in amine cured epoxy resins (EPs) was studied on compact tension (CT) specimens. Aromatic (hydrogenated diglycidyl ether of bisphenol A-type) and aliphatic (glyceroltriglycidylether) EPs were cured with the same amine (Jeffamine D 230) to receive EPs with different glass transition temperatures (Tg). Tg values of the parent EPs were lower (Tg= 32 o C) and higher (Tg= 90 o C), respectively, than the melt temperature (Tm≈60 o C) of the PCL. The curing-induced phase separation morphology of PCL was studied by light microcopy. Additional information on the phase structure was deduced from dynamic mechanical analysis (DMA). Blending with PCL reduced the Tg of the corresponding EPs. Fully broken CT specimens were repeatedly healed at 80 o C which was close to or higher than the actual Tg of the EP/PCL blend. It was found that the transition of PCL from disperse to continuous phase depends not only on the PCL amount but also on the EP type and its curing. EP/PCL systems with semi interpenetrating network structure (bi-continuous) exhibited markedly higher healing efficiencies compared to those in which PCL was present as disperse phase. The healing efficiency depended also on the temperature difference between the healing temperature and Tg of the EP with respect to Tm of PCL. When Tg>Tm then the related difference should be kept small while for Tg<Tm the temperature difference should be large to support healing. Accordingly, the segmental mobility within the crosslinked EP network is a key parameter for thermal mending, too.

3D printing-assisted interphase engineering of polymer composites: Concept and feasibility

“…Healing occurs via chain entanglement of the PCL molecules above the T m . Not surprisingly, semi-IPN structured EP/PCL outperformed EP variants with dispersed PCL phase with respect to healing [9]. Note that all the above information is related to EP/PCL modified in the bulk.…”

“…The related structure can be termed as quasi (with the nanoweb) or real semi-interpenetrating network (semi-IPN) because the thermoplastic phase is also continuous. It was also reported that thermoplastic PCL may work as a healing agent in EPs [9]. Healing occurs via chain entanglement of the PCL molecules above the T m .…”

Novel Poly(Caprolactone)/Epoxy Blends by Additive Manufacturing

“…PCL finds wide application in biodegradable packaging, in sutures, in adhesives, in non-woven fabrics or for the production of synthetic leather and dressings [32]. One of the most recent applications of PCL is as blending agent in epoxy system for self-healing applications [7,37,38].Self-healing capability, intended as the ability to repair damages and restoring partially or completely the lost properties and functions, has been already demonstrated in many types of polymers [39] including thermoplastics, elastomers, and thermosets [40]. Generally speaking, the self-healing mechanism can be summarized in three principal steps: actuation of self-healing feature, transportation of healing agent or chemicals in the damaged zone, final chemical or physical reparation [41].…”

“…Generally speaking, the self-healing mechanism can be summarized in three principal steps: actuation of self-healing feature, transportation of healing agent or chemicals in the damaged zone, final chemical or physical reparation [41]. Thermoplastic polymers have demonstrated an ability to heal after heating above their melting temperature by molecular re-entanglement processes across the broken surfaces [38]. However, even if their repairing mechanism is quite easy, they were considered less interesting than thermosets when high thermal stability and solvent resistance are required.…”

“…PCL finds wide application in biodegradable packaging, in sutures, in adhesives, in non-woven fabrics or for the production of synthetic leather and dressings [32]. One of the most recent applications of PCL is as blending agent in epoxy system for self-healing applications [7,37,38].…”