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Bai S.,Polymer and Composite Engineering PaCE Group | Ho K.K.C.,Polymer and Composite Engineering PaCE Group | Knox G.,Gates Corporation | Bismarck A.,Polymer and Composite Engineering PaCE Group | Bismarck A.,University of Vienna
Composite Interfaces | Year: 2013

A continuous atmospheric plasma (AP) polymerisation method was developed, using an acrylonitrile precursor, to enhance the adhesion of carbon fibres to an elastomeric resorcinol formaldehyde latex (RFL) matrix. Different processing speeds, corresponding to different residence times in the afterglow zone of the plasma jet, and precursor dosing rates were explored to optimise the treatment. X-ray photoelectron spectroscopy showed that carbon fibres were successfully functionalised in this process. The higher hydrophilicity and better adhesion to RFL was mainly attributed to the introduction of polar amide and hydroxyl groups introduced onto carbon fibre surfaces. Single fibre tensile tests confirmed that AP treatment did not affect the bulk mechanical properties of carbon fibres. The adhesion behaviour between carbon fibres and RFL was characterised by single fibre fragmentation tests. The interfacial shear strength, as measure of practical adhesion, increased by 30% for the fibres exposed longest to the plasma. The plasma-treated carbon fibres were aged in ambient atmosphere for up to three months to determine the effect of storage on the adhesion between the fibres and RFL. After ageing, an 11% reduction of interfacial shear strength was observed. © 2013 Taylor and Francis.

De Luca F.,Polymer and Composite Engineering PaCE Group | Menzel R.,Imperial College London | Menzel R.,University of Leeds | Blaker J.J.,Polymer and Composite Engineering PaCE Group | And 5 more authors.
ACS Applied Materials and Interfaces | Year: 2015

The bricks and mortar in the classic structure of nacre have characteristic geometry, aspect ratios and relative proportions; these key parameters can be retained while scaling down the absolute length scale by more than 1 order of magnitude. The results shed light on fundamental scaling behavior and provide new opportunities for high performance, yet ductile, lightweight nanocomposites. Reproducing the toughening mechanisms of nacre at smaller length scales allows a greater volume of interface per unit volume while simultaneously increasing the intrinsic properties of the inorganic constituents. Layer-by-layer (LbL) assembly of poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte and well-defined [Mg2Al(OH)6]CO3.nH2O layered double hydroxide (LDH) platelets produces a dense, oriented, high inorganic content (∼90 wt %) nanostructure resembling natural nacre, but at a shorter length scale. The smaller building blocks enable the (self-) assembly of a higher quality nanostructure than conventional mimics, leading to improved mechanical properties, matching those of natural nacre, while allowing for substantial plastic deformation. Both strain hardening and crack deflection mechanisms were observed in situ by scanning electron microscopy (SEM) during nanoindentation. The best properties emerge from an ordered nanostructure, generated using regular platelets, with narrow size dispersion. © 2015 American Chemical Society.

Ikem V.O.,Polymer and Composite Engineering PaCE Group | Menner A.,Polymer and Composite Engineering PaCE Group | Bismarck A.,Polymer and Composite Engineering PaCE Group
Soft Matter | Year: 2011

Highly interconnected macroporous polymers can be produced by the polymerization of high internal phase emulsions (HIPEs) with a dispersed phase exceeding 74 vol%. Until recently, it was thought that poly(merized)HIPEs with a maximum reported gas permeability of 0.46 D could only be produced by the polymerization of surfactant stabilized HIPE templates. However, highly permeable macroporous polymers with a gas permeability of up to 2.6 D were successfully prepared by adding small amounts of a non-ionic surfactant to pre-made Pickering emulsion templates; poor mechanical properties (crush strengths of ≤2.2 MPa) however limit the applicability of these materials. The mechanical properties were improved by altering the composition of the emulsion template. This involved using the flexible crosslinker polyethylene glycol dimethacrylate (PEGDMA), alongside other organic additives like divinylbenzene (DVB) and squalene in the organic phase. We also increased the material density by using medium internal phase emulsion (MIPE) templates and increased the surfactant concentration added to the pre-made Pickering-MIPEs. The resulting materials were characterized in terms of pore structure, gas permeability and mechanical performance. SEM images revealed pores of up to 1700 μm in diameter and interconnecting pore throats of up to 100 μm in diameter. The highest gas permeability and crush strength achieved were 0.92 ± 0.09 D and 5.6 ± 0.1 MPa, respectively, for a macroporous polymer synthesized from a Pickering-MIPE containing 50:40:10 (by volume) styrene, PEGDMA and DVB respectively, in the organic phase, to which 10 vol% Hypermer 2296 was added. © 2011 The Royal Society of Chemistry.

Blaker J.J.,Polymer and Composite Engineering PaCE Group | Lee K.-Y.,Polymer and Composite Engineering PaCE Group | Bismarck A.,Polymer and Composite Engineering PaCE Group
Journal of Biobased Materials and Bioenergy | Year: 2011

Recent interest in the utilisation of greener materials has reinitiated the interest in natural fibres and/or fibrils as reinforcement for polymers. However, such bio-based composites often exhibit properties that fall short of expectations due to (i) inadequate processing conditions, resulting in filler agglomeration and poor filler dispersion within the matrix, (ii) variations in natural fibre properties, often due to geographical and seasonal variability, (iii) anisotropy of the natural fibres themselves, (iv) high linear coefficient of thermal expansion for natural fibres and (v) the incompatibility between typically hydrophilic natural fibres and hydrophobic polymer matrices resulting in poor interfacial adhesion between the phases. Chemical modification of natural fibres is often performed to enhance the fibre-matrix interface. A new type of modification, which involves depositing a coating of nanosized cellulose onto natural fibres or dispersing nano-sized cellulose in natural fibre reinforced composites, has been shown to improve the fibre-matrix interface and the overall mechanical performances of such composites, which we term hierarchical (nano)composites. Such composites are also known as multiscale, nanoengineered or nanostructured composites. This paper reviews the current progress of green hierarchical (nano)composites made entirely from renewable materials. As a backdrop, here we look at how nature organises structures across different length scales. We discuss techniques to achieve percolated nanofiller networks within the matrix, at low-medium loading fractions (typically 6-10 vol.%) and processing routes to achieve high loading fractions, then focus on those used to produce truly hierarchical structures in terms of their processing and resultant properties. By creating hierarchical structures within bio-based composite materials we expect to match and improve upon non-renewable polymers. Copyright © 2011 American Scientific Publishers All rights reserved.

Blaker J.J.,University of Manchester | Lee K.-Y.,University College London | Walters M.,Polymer and Composite Engineering PaCE Group | Drouet M.,Polymer and Composite Engineering PaCE Group | And 2 more authors.
Reactive and Functional Polymers | Year: 2014

In an effort to enhance the properties of polylactide (PLA), we have developed melt-spinning techniques to produce both PLA/nanocellulose composite fibres, and a method akin to layered filament winding followed by compression moulding to produce self-reinforced PLA/nanocellulose composites. Poly(L-lactide) (PLLA) fibres were filled with 2 wt.% neat and modified bacterial cellulose (BC) in an effort to improve the tensile properties over neat PLA fibres. BC increased the viscosity of the polymer melt and reduced the draw-ratio of the fibres, resulting in increased fibre diameters. Nonetheless, strain induced chain orientation due to melt spinning led to PLLA fibres with enhanced tensile modulus (6 GPa) and strength (127 MPa), over monolithic PLLA, previously measured at 1.3 GPa and 61 MPa, respectively. The presence of BC also enhanced the nucleation and growth of crystals in PLA. We further produced PLA fibres with 7 wt.% cellulose nanocrystals (CNCs), which is higher than the percolation threshold (equivalent to 6 vol.%). These fibres were spun in multiple, alternating controlled layers onto spools, and subsequently compression moulded to produce unidirectional self-reinforced PLA composites consisting of 60 vol.% PLLA fibres reinforced with 7 wt.% CNC in a matrix of amorphous PDLLA, which itself contained 7 wt.% of CNC. We observed improvements in viscoelastic properties of up to 175% in terms of storage moduli in bending. Furthermore, strains to failure for PLLA fibre reinforced PDLLA were recorded at 17%. © 2014 Elsevier B.V. All rights reserved.

Kot E.,Imperial College London | Kot E.,Polymer and Composite Engineering PaCE Group | Shirshova N.,Polymer and Composite Engineering PaCE Group | Bismarck A.,Polymer and Composite Engineering PaCE Group | And 2 more authors.
RSC Advances | Year: 2014

In order to develop inks suitable for roll-to-roll printing processes, which can be cured into in situ electrolyte filled high porosity macroporous polymer membranes, non-aqueous high internal phase emulsions (HIPEs) were prepared. The external phase of the formulated HIPEs consisted of lauryl methacrylate (LMA) and 1,14-tetradecanediol dimethacrylate (TDDMA) while a solution of bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) in a mixture of ethylene (EC) and propylene carbonate (PC) served as the internal phase. The stability of these non-aqueous HIPEs was strongly affected by the surfactant and the LiTFSI concentration in the internal phase. HIPE templates could only be polymerised when the LiTFSI concentration varied between 0.06 and 0.8 mol l -1. Electrochemical, thermal properties as well as morphology of the resulting polyHIPEs are discussed with respect to HIPE composition. The ionic conductivity of the resulting polyHIPEs was measured to be in the range from 4.18 to 8.64 mS cm-1. © 2014 The Royal Society of Chemistry.

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