Bronwyn L. Fox

Tailoring the fibre-to-matrix interface using click chemistry on carbon fibre surfaces

A convenient and effective strategy to control the surface chemistry of carbon fibres is presented, comprising electro-chemical reduction of aryl diazonium salts onto the surface, followed by ‘click chemistry’ to tether the desired surface characteristic of choice. The power of this approach was demonstrated by engineering a small-molecule interface between carbon fibre and an epoxy matrix improving interfacial shear strength by up to 220%, relative to unmodified control fibres. The techniques used in this work do not impede the fibre performance in tensile strength or Youngs modulus. This work provides a platform upon which any carbon fibre-to-resin interface can be easily and rapidly designed and implemented.

Rapid surface functionalization of carbon fibres using microwave irradiation in an ionic liquid

The modification of carbon fibre surfaces has been achieved using a novel combination of low power microwave irradiation (20 W) in both an ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and an organic solvent (1,2-dichlorobenzene). The use of the ionic liquid was superior to the organic solvent in this application, resulting in a higher density of surface grafted material. As a consequence, carbon fibres treated in the ionic liquid displayed improved interfacial adhesion in the composite material (+28% relative to untreated fibres) compared to those treated in organic solvent (+18%). The methodology presented herein can be easily scaled up to industrially relevant quantities and represent a drastic reduction in both reaction time (30 min from 24 h) and energy consumption, compared to previously reported procedures. This work opens the door to potential energy and time saving strategies which can be applied to carbon fibre manufacture for high performance carbon fibre reinforced composites.

Using ionic liquids to reduce energy consumption for carbon fibre production

Carbon fibre composites are lightweight, high performance materials with outstanding mechanical properties. However, the use of carbon fibre is limited to high-end applications largely due to their high manufacturing cost. A significant portion of the cost results from the energy input required to convert the precursor into carbon fibre. Stabilization is the first critical step whereby the fibre undergoes a series of thermal treatments creating a stabilized fibre ready for carbonization. In this study, we demonstrate the use of ionic liquids as polyacrylonitrile fibre impregnation agents, resulting in substantially lower fibre stabilization temperatures and thus significant energy savings. The use of infrared, calorimetric, and thermogravimetric studies indicated that the beneficial effect of ionic liquids is due to higher stabilization chemical reaction rates.

The effect of thermally induced chemical transformations on the structure and properties of carbon fibre precursors

The transformation of functional groups and development of radial structural heterogeneity during the thermal stabilization of polyacrylonitrile (PAN) precursor fibres were quantitatively defined for the first time using high resolution spectroscopic imaging techniques. The infrared imaging of isothermally treated fibre cross-sections reveals the radial distribution of specific functional groups (CN, CN, CH2, CH and CO) that forms the ladder polymer structure, the most critical stage in the precursor stabilization process. Apparently, it was found that the cyclization reaction of PAN polymer chains occurred at a faster rate in the core of the fibre during heating where it further selectively promoted the dehydrogenation reaction. On the other hand, the conversion of sp3 to sp2 hybridized carbon atoms was found to be higher around the skin layer compared to the core of the fibres, thus providing evidence for different cross-linking mechanisms in these regions. The simultaneous occurrence of a higher extent of cyclization and dehydrogenation reactions due to the excess heat developed in the core and a delay of oxygen diffusion in to the core of the fibres played a critical role in the polymer chain cross-linking in the skin and core regions that further led to the evolution of radial heterogeneity in the fibres. It was also found that the mechanical properties were built upon the structural transformations and the variation in the modulus across the fibre cross-section further confirmed the reaction mechanism.

A facile method to fabricate carbon nanostructures via the self-assembly of polyacrylonitrile/poly(methyl methacrylate-b-polyacrylonitrile) AB/B′ type block copolymer/homopolymer blends

The self-assembly and high temperature behavior of AB/B′ type block copolymer/homopolymer blends containing polyacrylonitrile (PAN) polymers were studied for the first time. Here, microphase separated nanostructures were formed in the poly(methyl methacrylate-b-polyacrylonitrile) (PMMAN) block copolymer and their blends with homopolymer PAN at various blend ratios. Additionally, these nanostructures were transformed into porous carbon nanostructures by sacrificing PMMA blocks via pyrolysis. Spherical and worm like morphologies were observed in both TEM and AFM images at different compositions. The thermal and phase behavior examinations showed good compatibility between the blend components in all studied compositions. The PAN homopolymer (B′) with a comparatively higher molecular weight than the corresponding block (B) of the block copolymer is expected to exhibit ‘dry brush’ behavior in this AB/B′ type system. This study provides a basic understanding of the miscibility and phase separation in the PMMAN/PAN system, which is important in the nanostructure formation of bulk PAN based materials with the help of block copolymers to develop advanced functional materials.

Graphene based room temperature flexible nanocomposites from permanently cross-linked networks

Graphene based room temperature flexible nanocomposites were prepared using epoxy thermosets for the first time. Flexible behavior was induced into the epoxy thermosets by introducing charge transfer complexes between functional groups within cross linked epoxy and room temperature ionic liquid ions. The graphene nanoplatelets were found to be highly dispersed in the epoxy matrix due to ionic liquid cation–π interactions. It was observed that incorporation of small amounts of graphene into the epoxy matrix significantly enhanced the mechanical properties of the epoxy. In particular, a 0.6 wt% addition increased the tensile strength and Young’s modulus by 125% and 21% respectively. The electrical resistance of nanocomposites was found to be increased with graphene loading indicating the level of self-organization between the ILs and the graphene sheets in the matrix of the composite. The graphene nanocomposites were flexible and behave like ductile thermoplastics at room temperature. This study demonstrates the use of ionic liquid as a compatible agent to induce flexibility in inherently brittle thermoset materials and improve the dispersion of graphene to create high performance nanocomposite materials.

Mechanical, Thermal, and Morphological Behavior of Silicone Rubber during Accelerated Aging

ABSTRACT An accelerated aging study on silicone rubber exploring the effects of exposure to a functional oil (polyalkylene glycol) at elevated temperature (195°C) is reported in this paper. Variations in mechanical (tensile, tear, hardness) and thermal (conductivity, specific heat capacity) properties were monitored versus aging time while permanent deformation of the rubber was evaluated through creep and recovery measurements. Morphology and surface chemistry of the aged rubber were also investigated through scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy, respectively. Aging had a significant impact on the mechanical properties with the ultimate tensile strength and elongation at break decreasing from 7.4 MPa and 2250% in unaged samples to 1.5 MPa and 760% in 6-week aged samples, respectively. The tear strength and hardness exhibited an initial increase during the early stages of aging, followed by a decreasing trend. In contrast, the thermal properties did not change significantly and FTIR did not detect any changes in the surface chemistry of the rubber with aging. SEM however, provided evidence of an increase in brittle behavior from the morphology of the fractured surfaces. GRAPHICAL ABSTRACT

Smarte Kunststoff-Bauteile für Automotive Innovation und Industrie 4.0

Kurzfassung Labs Network Industrie 4.0 e. V. (LNI) ist ein Partner der Plattform Industrie 4.0. Der vorwettbewerbliche und gemeinnützige Verein dient kleinen und mittelständischen Unternehmen (KMU) als Dialog-, Kompetenz- und Experimentierplattform. Über Testfelder können Unternehmen Industrie-4.0-Anwendungen risikolos probieren. In einem Anwendungsfall testen Forscher aus Australien und Deutschland nun gemeinsam den Einsatz von Faserverbundwerkstoffen in der Automobilindustrie. Das Projekt wird im Forschungscampus ARENA2036 umgesetzt.