Investigating the structure-property relationships of a high-temperature epoxy matrix for structural and thermal applications

  • Samuel Swan

    Student thesis: Doctoral ThesisDoctor of Philosophy


    This project explores the network formation and structure-property relations of some high
    temperature epoxy resins cured with aromatic diamines. A highly aromatic dimeric
    naphthalene epoxy resin monomer, bis(2,7 glycidyl ether naphthalenediol) methane (NNE), is
    cured with 4,4’-diaminodiphenyl sulfone (DDS) to produce a network that exhibits rapid
    gelation, vitrification, and an ultimate glass transition temperature approaching 350°C. An
    array of thermal, spectral, rheological, and thermo-mechanical analysis techniques are used to
    comparatively assess the formation of the NNE-DDS network to a commercial high-Tg epoxy
    resin comprised of 4,4’-tetraglycidyldiaminodiphenyl methane (TGDDM) and DDS. The
    difference between the glycidyl ether (NNE) resin and glycidyl amine (TGDDM) resin through
    cure was explored. It was determined that the NNE resin showed primarily epoxy-amine
    addition and no signs of etherification or side reactions which was, in contrast to TGDDM,
    attributed to the absence of tertiary amine within the epoxy backbone. The time-temperaturetransformation
    (TTT) diagrams of the resins are constructed to explain the processing and
    formation of the glass transition temperature and show competition between devitrification (Tg)
    and the ultimate glass transition temperature of NNE.
    The structure-property relations of the NNE and TGDDM networks are explored via thermal
    analysis and mechanical testing of the cured resins and their carbon fibre composites. It is
    shown that the structure of the NNE monomer and limited mobility produces a network with
    high free volume and poor equilibrium packing density. The rapid vitrification at low degree
    of conversion prevents a high degree of cure and the network becomes topologically
    constrained. That in turn results in higher moisture ingress, lower strength and modulus, but
    achieves better thermal stability than TGDDM at temperatures above 200°C. Further ageing of
    the resins and composites at 250°C for 504hr indicate some benefit for high temperature, short
    duration thermal performance of NNE compared to TGDDM. That is attributed to the limited
    mobility of the matrix after cure and the effects of the tertiary amine contained in TGDDM
    providing more pathways to degradation.
    The NNE resin, whilst possessing superior thermal performance, is difficult to process and
    exhibits poor mechanical performance compared to TGDDM. An approach to modify the
    network for improved strength and stiffness combined with reduced viscosity was taken at the
    molecular level. A monofunctional reactive epoxy diluent, partially reacted substructures
    (PRS), a molecular fortifier (MFN), and pure naphthalene were synthesised and cured with
    NNE in percentages ranging from 5-20 mol% or wt%. This survey showed an antiplasticising
    effect where strength reduced, and modulus increased significantly. Further, the
    monofunctional epoxy and naphthalene, when added at 10 mol % and 10 wt%, respectively,
    reduced the melt viscosity and increased the processing window to values in the range of
    conventional resin transfer moulding parameters. Carbon fibre composites of the modified
    resins at 10% loading showed the neat resin properties transferred to improvements in the
    composite flexural modulus with minimal impact on strength and interlaminar shear.
    Finally, the toughening of a multi-functional epoxy resin was achieved by use of core-shell
    rubber (CSR) particle toughening. The improvement to room temperature fracture toughness
    of nearly 40% of the neat resin at 20 wt% particle addition was then used to create a carbon
    fibre composite. The composite mode I fracture toughness was evaluated by means of in situ
    acoustic emission (AE) spectroscopy and scanning electron microscopy (SEM) imaging of the
    fracture surface. A nearly two-fold increase in G1C was shown. AE spectroscopy indicated that
    toughening by CSR contributed to high frequencies of interply-, fibre bridging-, and fibredominated
    failure events than the unmodified composite where the frequencies of events
    showed lower energy matrix-dominated failure.
    This project investigates the capabilities of a high temperature naphthalene-based epoxy-amine
    resin formulations and routes to achieve simultaneous improvements to thermal resistance and
    stability, mechanical performance, and fracture toughness for structural composite
    Date of Award16 Aug 2022
    Original languageEnglish
    Awarding Institution
    • Coventry University
    • Deakin University
    SupervisorJames Griffin (Supervisor) & Bekim Gashi (Supervisor)


    • structural and thermal applications
    • NNE-DDS
    • TGDDM
    • TTT
    • thermal performance
    • epoxy
    • core-shell rubber

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