Q. Li, J. S. Church, M. Naebe, B. L. Fox

Carbon nanotube (CNT) deposition onto carbon fibre resulting in hybrid surface structures with various morphologies were successfully carried out using electrospray technique. In terms of tensile testing and Weibull analysis this process did not degrade fibre mechanical properties. When incorporated into composites, the interfacial shear strength (IFSS), as measured by single fibre fragmentation testing, increased by up to 124%. Experimental work was carried out to develop a deeper understanding of the interfacial reinforcing mechanism. Contact angle measurements demonstrated that the CNT deposition resulted in good wettability by the resin. Significant increases in roughness, friction and surface area were also found after CNT deposition, especially for the sample prepared using the parameter of 20 kV/10 cm at 100 °C. Surface energy analysis revealed that an increase in the dispersive surface energy due to the CNTs likely contributed to the improvement of interaction between fibre and matrix. Fractographic analysis revealed that the length of fibre pull-out and the size of cracks between the fibre and matrix were markedly decreased in the hybrid CNT surface structure, indicating that the stress transfer and interfacial shear strength have been improved. Finally, the potential for further improvement in interfacial composite properties by this approach was assessed.

Q. Li, J. S. Church, M. Naebe, B. L. Fox

By electrospraying solvent dispersed carbon nanotubes (CNTs) with a binder onto carbon fibre (CF), hybrid structures, with an end aim to improve interfacial bonding in composites, were formed. The electrospray parameters controlling the modification of the CNT morphologies were studied. High-speed camera observations found applied voltage was critical for determining spray mode development. Electric field simulations revealed a concentrated electric field region around each fibre. Both voltage and distance played an important role in determining the CNT morphology by mediating anchoring strength and electric field force. The forming mechanism investigation of different surface morphologies suggested that binder with appropriate wetness gives freedom to the CNTs, allowing them to orientate radially from the CF surface. Linear density (LD) measurements and thermogravimetric analysis revealed that a 10 min coating increased the LD of a single CF filament by up to 31.7% while a 1 h treatment increased fibre bundle mass by 1%.

J. Y. Cai, J. McDonnell, C. Brackley, L. O'Brien, J. S. Church, K. Millington, S. Smith, N. Phair-Sorensen

This paper reports on a significant advancement in carbon fiber precursor research. We have successfully applied reversible addition-fragmentation chain transfer (RAFT) technology to polyacrylonitrile (PAN) based carbon fiber precursor synthesis, and developed new PAN precursor polymers with a high molecular weight (M_n > 300 K), while still maintaining a low polydispersity index (PDI) (< 1.2). This desirable molecular profile has not been attainable until now. The paper also reports on the very first comparative study carried out for assessing the properties and performance of such a high molecular weight, low PDI precursor and its resultant carbon fiber against the conventional controls. In this comparative study, a control precursor polymer with a closely matching molecular weight and comonomer content was prepared by conventional free radical polymerization. Both of the RAFT mediated PAN (RAFT PAN) and control PAN precursor polymers were processed into precursor fibers and carbon fibers under identical conditions. The structures and properties of these fibers were characterized and evaluated. The results of this preliminary study have demonstrated a signifcant improvement in the rheological property of RAFT PAN polymer, and significant improvement in the mechanical properties of the precursor fiber and carbon fiber derived from the RAFT PAN precursor polymer.

K. Badii, J. S. Church, G. Golkarnarenji, M. Naebe, H. Khayyam

The production of carbon fiber, particularly the oxidation/stabilization step, is a complex process. In the present study, a non-linear mathematical model has been developed for the prediction of density of polyacrylonitrile (PAN) and oxidized PAN fiber (OPF), as a key physical property for various applications, such as energy and material optimization, modeling, and design of the stabilization process. The model is based on the available functional groups in PAN and OPF. Expected functional groups, including -C≡N,-C=N, -CH₂, -C=C, and -C=O, were identified and quantified through the full deconvolution analysis of Fourier transform infrared attenuated total reflectance (FT-IR ATR) spectra obtained from fibers. These functional groups form the basis of three stabilization rendering parameters, representing the cyclization, dehydrogenation and oxidation reactions that occur during PAN stabilization, and are used as the independent variables of the non-linear predictive model. The k-fold cross validation approach, with k = 10, has been employed to find the coefficients of the model. This model estimates the density of PAN and OPF independent of operational parameters and can be expanded to all operational parameters. Statistical analysis revealed good agreement between the governing model and experiments. The maximum relative error was less than 1% for the present model.

D. Yu, J. Y. Cai, J. S. Church, L. Wang

This paper introduces a novel chemical treatment for achieving sustained shrink-resist performance on natural keratin fibers. The new treatment involves the controlled reduction of keratin in the cuticle regionof the fiber, and the application of a water soluble diacrylate, namely glycerol 1,3-diglycerolate diacrylate (GDA), on the reduced keratin substrate. The acrylate groups of the GDA react with cysteine residues in the reduced keratin through thiol-ene click reactions at room temperature, leading to GDA grafting and the formation of GDA crosslinks in the keratin structure. The modified substrates were characterized by infrared spectroscopy and scanning electron microscopy, and assessed for its shrink-resistance and wet burst strength. This chemical modification has shown to alter the fiber surface morphology and hydrophilicity, resulting in substantially improved shrink-resistance with good fiber strength Retention.Possible shrink-resistance mechanisms were also discussed.

T. D. Rapson, T. D. Sutherland, J. S. Church, H. E. Trueman, H. Dacres, S. C. Trowell

To achieve the sophisticated chemistry required for life, nature uses metal containing proteins (metalloproteins). However, despite intensive research efforts, very few of these metalloproteins have been exploited for biotechnological applications. One major limiting factor is the poor stability of these proteins when they are removed from their cellular environment. To produce stable metalloproteins, we have developed an engineering strategy that uses structural proteins which can be fabricated into a number of different solid-state materials. Here we demonstrate that a recombinant silk protein (AmelF3 − Apis mellifera Fibroin 3) binds heme and other metal macrocycles in a manner reminiscent of naturally occurring metalloproteins, whereby an amino acid coordinates directly to the metal center. Our strategy affords design at four different levels: the metal center, the organic macrocycle, the protein scaffold, and the material format structure. The solid-state metalloproteins produced remained functional when stored at room temperature for over one year.

A. J. Poole, J. S. Church

The industrial utilisation of feather keratin as a biopolymer has proven difficult due to the lack of a viable extraction technique and the poor mechanical properties of the regenerated products. Here, pure keratin films were produced from chicken feathers using sodium sulphide as sole extraction reagent in a scheme that allows films to be formed without residual chemicals. In a comparison to other films, those produced using Na₂S extraction were found to be superior to other regenerated protein films and were similar to un-oriented commercial polymers. However, there was considerable variation in tensile properties between twenty repetitions of extracting and casting films which was attributed to variations in chain entanglement caused by the drying conditions. Chemical and physical treatments including crosslinking, dehydration and addition of nano-particles were investigated as means to enhance these properties. Significant increases were achieved by soaking films in isopropyl alcohol or weak acid (13 to 50 % increases) or by formaldehyde or glutaraldehyde crosslinking (24 to 40 % increases). The wide range of values across the pure keratin films indicates that the best route to further strength improvement maybe from optimising self-assembly via controlling drying conditions, rather than from chemical treatment.

M. G. Huson, J. S. Church, L. K. Hillbrick, A. L. Woodhead, M. Sridhar, A. M. L. Van De Meene

A focused ion beam has been used to mill both individual carbon fibres as well as fibres in an epoxy composite, with a view to preparing flat surfaces for nano-indentation. The milled surfaces have been assessed for damage using scanning probe microscopy nano-indentation and Raman micro-probe analysis, revealing that FIB milling damages the carbon fibre surface and covers surrounding areas with debris of disordered carbon. The debris is detected as far as 100 μm from the milling site. The energy of milling as well as the orientation of the beam was varied and shown to have an effect when assessed by Raman spectroscopy.