Polysulfone composites were prepared by solution casting, using various types of treated carbon nanotubes (CNTs) at loadings of up to 5 wt%. The CNT types tested were: as‐received, acid treated, OCA surfactant, OCA functionalized and Poly(methyl methacrylate) functionalized nanotubes prepared using both as‐received and acid treated CNT. The treatment types investigated were selected based upon their solubility parameters and on the results of previous studies. The treated CNTs, CNT/solvent dispersions and the final composite samples were characterised using Fourier Transform Infrared Spectroscopy (FTIR), thermal analysis, Transmission Electron Microscopy (TEM), Ultraviolet‐Visible (UV‐vis) spectroscopy, optical microscopy, electrical conductivity and tensile testing. It was observed that the all the treatments studied improved the stability of CNT in the solvent. Of the CNT types studied, composites containing OCA functionalised CNT displayed the lowest percolation threshold (3 wt%) and highest mechanical performance. While the use of Hildebrand solubility parameters is useful in indentifying promising CNT treatments, their use can not fully predict CNT dispersion behaviour and composite performance. It is also critical to consider the influence of any treatments on CNT length and residual solvent levels. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
The solution method was used to create polysulfone/carbon nanotubes composites. The effect of three solvents (NMP, DMF, and THF), treatments (nitric acid and ethanol) and surfactants (ODA and OCA) on CNT/ solvent stability was investigated. NMP and DMF resulted in improved stability compared to THF, and all CNT treatments improved stability. Four composites were produced with CNT loadings of 0-5 wt%: as-received CNT and nitric acid treated in THF, as-received CNT and OCA surfactant CNT in NMP. Optical, TEM, and electrical percolation measurements confirmed the role of CNT/solvent stability on the final composite dispersion. Tensile testing and thermal analysis confirmed the presence of residual solvent in all samples.
The fabrication of conductive composite microneedle (MN) patches modified with palladium clusters for the electrocatalytic detection of peroxide is described. Micro molding techniques are utilized in which carbon nanoparticles are bound within a polystyrene matrix resulting in the production of a 10x10 array of needles of length 700 micron. Electrochemical anodization of the carbon particles increases the interfacial carboxyl group population which facilitates the capture of Pd2+ ions. Their subsequent electroreduction yields a catalytic interface with a high sensitivity towards the electroreduction of peroxide (-0.3 V : 49.7+/-2.8 A mM-1 cm-2 ;-0.5 V: 102.1+/-2.32 A mM-1 cm-2). The microneedle sensing system and the various modification stages has been characterized using mechanical testing (fracture testing), cyclic voltammetry and high resolution x-ray photoelectron spectroscopy.
Through-thickness stitching, in the form of tufting, has been shown to be a potentially successful method of improving resistance to delamination. Tufting is a single-sided stitching technique that involves the insertion of a yarn through a fabric, in the z-direction. However, further research into the development of a tailored tufting yarn could yield a greater improvement in the mechanical properties of the overall composite. Unlike other published works which rely on commercially available materials, for this study four thermoplastic yarns were produced from polyetheretherketone, polysulfone, polyethersulfone and polyphenylsulfone. Their ability to be tufted into a composite was examined along with their influence on the overall mechanical properties of the composite.
A problem for wind turbine operators is decreasing prices for wind-generated electricity. Many turbines are approaching their rated 20-year lives. A more economically viable and sustainable solution that reduces Levelized Cost of Energy (LCOE) and avoids expensive turbine replacement is retrofitting new spar caps blades. A new cost model assesses the feasibility of retrofitting 35 to 75 m turbines with GFRP (glass fiber reinforced polymer composite) and longer length CFRP (carbon fiber reinforced composite) spar caps. Spar cap cost scales with features such as mass, volume fraction and complexity. Organizational learning is a cost factor. Material and direct labor increase as proportions of total cost while tooling, capital, utilities, and indirect labor decrease. There is good agreement between a manufacturer and the model. Twenty-year turbines were compared with retrofitted spar caps over 25 years for LCOE. Same length GFRP and longer length CFRP spar cap retrofits decrease LCOE. Longer length CFRP spar caps decrease LCOE compared with GFRP retrofits over 25 years. CFRP material cost impacts CFRP retrofit feasibility. Retrofitted turbines must meet engineering, operational performance, and planning requirements criteria. Software algorithms may improve human learning and enable automatic updates from varying design and cost inputs, thereby increasing cost prediction accuracy.
Sewing has attracted a great deal of attention as a method to improve the delamination performance of carbon fibre laminate composites. A critical factor in the commercial exploitation of the technology is the development of a suitable sewing yarn, with other researchers looking at a variety of commercial fibres such as Kevlar. It would appear from the literature that fundamental research into what properties a suitable yarn should have has not been carried out. In this work, a commercial fibre designed for sewing applications was sourced from Toho Tenax (Germany) and used as a control. Unlike in published works, rather than relying on yarns which could be purchased commercially, selection criteria were drawn up and promising polymers identified and then extruded as a yarn. Based on the selection criteria, thermoplastic yarns were extruded using polysulfone, polyethersulfone, polyphenylsulfone and polyetheretherketone. It was found that despite the fact that the commercial fibre had much better mechanical properties as a straight fibre, when it was knotted or looped (to try and simulate the effects of sewing), there was a dramatic decrease in the mechanical properties (the ultimate tensile strength dropped by 88% due to a single knot). There was no significant change in the mechanical properties of the thermoplastic yarns. As a result, it is concluded the thermoplastic fibres created could potentially be better suited for sewing applications compared to commercial fibres such as Kevlar and further work is planned to sew the yarns and test the delamination performance.
Large composite structures manufactured out-of-autoclave require the assembly and bonding of multiple parts. A one-shot cure manufacturing method is demonstrated using powder epoxy. Lap shear plates were manufactured from powder epoxy and glass fiber-reinforced plastic with four different bonding cases were assessed: secondary bonding using standard adhesive film, secondary bonding using powder epoxy, co-curing, and co-curing plus a novel Z-pinning method. This work investigates the lap shear strength of the four cases in accordance with ISO 4587:2003. Damage mechanisms and fracture behavior were explored using digital image correlation (DIC) and scanning electron microscopy (SEM), respectively. VTFA400 adhesive had a load at break 24.8% lower than secondary bonding using powder epoxy. Co-curing increased the load at break by 7.8% compared to powder epoxy secondary bonding, with the co-cured and pinned joint resulting in a 45.4% increase. In the co-cured and co-cured plus pinned cases, DIC indicated premature failure due to resin spew. SEM indicated shear failure of resin areas and a large amount of fiber pullout in both these cases, with pinning delaying fracture phenomena resulting in increased lap joint strength. This highlights the potential of powder epoxy for the co-curing of large composite structures out-of-autoclave.
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