Browsing by Author "Halley, PJ"

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    A fundamental study on photo-oxidative degradation of linear low density polyethylene films at embrittlement
    (Elsevier, 2012-05-25) Hsu, YC; Weir, MP; Truss, RW; Garvey, CJ; Nicholson, TM; Halley, PJ
    Film embrittlement criteria were determined for photo-oxidative degradation of linear low density polyethylene (LLDPE) films by using a range of characterisation techniques: tensile, high-temperature GPC, MAS-NMR, FTIR-ATR, WAXS and SAXS. The key embrittlement criteria was the loss of 95% elongation at break and the reduction in interlamellar distance, reduced down to approximately 30–50 Å, as a result of recrystallisation of mobile short chain fragments produced from chain scission reaction. Interlamellar thinning correlated well with the changes in double yield points seen in the tensile data, where the absence of the second yield point signified that the tie molecules at the lamellar interface underwent chain scission and could no longer transfer the tensile stress to reach c-axis slip of the lamellar crystals. This was also supported by a reduction in amorphous–lamellar interfacial width with ageing time, extracted from SAXS data using the linear correlation function. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.
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    Impact of controlled particle size nanofillers on the mechanical properties of segmented polyurethane nanocomposites
    (Inderscience, 2007-08-06) Finnigan, B; Casey, P; Cookson, DJ; Halley, PJ; Jack, KS; Truss, RW; Martin, DJ
    The impact of average layered silicate particle size on the mechanical properties of thermoplastic polyurethane (TPU) nanocomposites has been investigated. At fixed addition levels (3 wt% organosilicate), an increase in average particle size resulted in an increase in stiffness. Negligible stiffening was observed for the smallest particles (30 nm) due to reduced long-range intercalation and molecular confinement, as well as ineffective stress transfer from matrix to filler. At low strain (<= 100%), an increase in filler particle size was associated with an increase in the rate of stress relaxation, tensile hysteresis, and permanent set. At high strain (1200%), two coexisting relaxation processes were observed. The rate of the slower (long-term) relaxation process, which is believed to primarily involve the hard segment rich structures, decreased on addition of particles with an average diameter of 200 nm or less. At high strain the tensile hysteresis was less sensitive to particle size, however the addition of particles with an average size of 200 nm or more caused a significant increase in permanent set. This was attributed to slippage of temporary bonds at the polymer-filler interface, and to the formation of voids at the sites of unaligned tactoids. Relative to the host TPU, the addition of particles with an average size of 30 nm caused a reduction in permanent set. This is a significant result because the addition of fillers to elastomers has long been associated with an increase in hysteresis and permanent set. At high strain, well dispersed and aligned layered silicates with relatively small interparticle distances and favourable surface interactions are capable of imparting a resistance to molecular slippage throughout the TPU matrix. © 2007, Inderscience Enterprises Ltd.
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    Nanocomposite bone cements for orthopaedic applications
    (Elsevier, 2010-06-06) Dunne, N; Ormsby, R; McNally, T; Mitchell, CA; Martin, DJ; Halley, PJ; Nicholson, T; Schiller, T; Gahan, LR; Musumeci, AW; Smith, SV
    Poly methylmethacrylate (PMMA) is the principal component of orthopaedic bone cement. However, it is susceptible to fatigue-related cracking or impact-induced failure. We have previously reported that adding MWCNTs (Multi Walled Carbon Nanotubes)(0.1wt.%) significantly improved the mechanical performance of PMMA-based bone cements and reduced the thermal necrosiscaused by the exothermic curing reaction of the cement [1].However, the effect of MWCNTs of various loading (wt.%) and functionality has yet to be considered. Recently there have been increased efforts to determine the effects of nanosized materials in vivo, with a particular emphasis on tracking their movement. Attachment of radioactive metal ions to MWCNTs via a bi-functional caged ligand would potentially allow for labelling and tracking. The objective of this study was to investigate the effect of MWCNT loading and functionality on mechanical, thermal and rheological properties of PMMA cements. In addition a method for radiolabelling MWCNTs has also been investigated Unfunctionalised, carboxyl (–COOH) functionalised and amine(–NH2) functionalised MWCNTs (Nanocyl S.A., Belgium) at varied wt% loadings (0.1, 0.25, 0.5, and 1.0) were incorporated into ColacrylB866 (Lucite International Ltd., UK) bone cement. Static mechanical properties were measured in accordance with ISO 5833:2002 [2].The plane strain fracture toughness was determined using Chevron-Notch Short Rod method [3]. The fatigue properties of the cements were determined in tension – tension with a lower stress of 0.3 MPa and an upper stress of 22.0 MPa being applied at a frequency of2 Hz [4]. Rheology was used to determine the time at which the onset of cure (tons) occurred and the critical gelation time (gel-time). Radioactive labelling of –COOH functionalised MWCNTs with gamma emitting 57Co (T1/2= 270 days) was completed using a bi-functional cage ligand (MeAMN3S3sar).Incorporating MWCNTs (≤0.25wt%) into cement significantly (p-value<0.001) improved the static and dynamic mechanical properties. However greater loadings of MWCNTs did not provide any further improvements and in some cases resulted in significant(p-value<0.001) reductions in mechanical properties. The extent of this effect was dictated by MWCNT functionality and the wt% used. Improvements were attributed to the MWCNTs arresting crack propagation. The exothermic polymerisation reaction for the PMMA cement was significantly reduced when thermally conductive MWCNTs were added. This was supported by the rheological characterisation as adding MWCNTs significantly altered tons and gel-time. The potential to radioactively label MWCNTs was successfully demonstrated, and further work will be conducted to assess the biological implications by tracking the radiolabelled MWCNTs under in vivo conditions. © 2006 Elsevier Ltd.