The incorporation of carbon nanofibres to enhance the properties of hot compacted self-reinforced single polymer composites

Nanoscale fillers offer the potential for significant enhancement of a range of polymer properties, as they are available in a wide variety of shapes and properties. Carbon nanotubes (CNT) and nanofibres (CNF) have been used extensively in the literature, yet very few analytical studies of the material properties have been reported. Here we use the Cox-Krenchel model to interpret the experimentally measured changes in Young’s modulus from particle aspect ratio reduction during to processing, in addition to the measurement of the mechanical properties of the composite. Hot Compaction, a process developed at the University of Leeds [1], utilises high modulus, highly oriented elements to form thick section, homogeneous sheets without the need to introduce a second phase of different chemical composition. These ‘single polymer’ composites are produced by selective melting on the surface of the oriented elements; on cooling, this molten material re-crystallises to form a matrix phase and bind the oriented elements together. CNF filled polypropylene (PP) tapes have been produced and successfully hot compacted into sheets. The properties of these nanofilled self-reinforced single polymer composites is reported. Of particular interest has been to investigate the introduction of interleaved films, an extension of recent work conducted by two of this papers authors [2] of the same polymer or nanocomposite in order to establish the change in properties when the CNF are incorporated in the drawn tapes, in the interleaved films or both

Pyrolysis activation energy of cellulosic fibres investigated by a method derived from the first order global model

The pyrolysis kinetics of cellulosic fibres, a natural cotton yarn (NCY) and a mercerized cotton yarn (MCY), has been explored with a modified first order global analysis method (FOG), via a series of non-isothermal experiments, using thermogravimetric analysis (TGA). The modified FOG analysis routine was developed to overcome discrepancy in heating rate and the difference between exact results and approximations in integrals. The intrinsic pyrolysis activation energy, with temperature range tending to zero, was found to be independent of heating rate and approximation used, giving average values of 153 ± 2 kJ/mol for NCY and 192 ± 7 kJ/mol for MCY. This proves the applicability of the reported analysis routine under the conducted TGA measurements. The reasons for different values were hypothesized to be the difference in chemical composition and crystalline structure. The findings provide a new approach in the investigation on pyrolysis kinetics of biomass and factors impacting their pyrolytic behaviour

Three methods to measure the dissolution activation energy of cellulosic fibres using time-temperature superposition

Three methods are established to explore the dissolution kinetics of cellulosic fibres in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate ([C2mim][OAc]), based on optical microscopic images of processed dried cellulose and cellulose hydrogels. The dissolution process for different times at various temperatures was analysed using time-temperature superposition, and from this the dissolution was found to follow an Arrhenius behaviour. Three values for the activation energy of dissolution were obtained from three different quantifying methods; these were found to agree, giving an average value of 73 ± 2 kJ/mol. A new method is developed to determine the swelling ratio of different regions of the processed cellulose samples, along with the different water volume fractions contained therein. The findings will be of interest to researchers making all cellulose composites and those studying the dissolution of cellulose by ionic liquids

Predicting the visco-elastic properties of polystyrene/SIS composite blends using simple analytical micromechanics models

This paper is concerned with the prediction of the viscoelastic properties of rubber filled polymer blends. The question asked was as follows. Can the temperature dependent viscoelastic properties of phase separated polymer blends be adequately predicted using only a rational two phase micromechanics based analytical model with no empirical fitting parameters? In particular using only a knowledge of the individual bulk phase properties and the blend microstructure, but without any further detailed polymer physics knowledge such as the presence of an interphase region or any additional nanoscale structures within the separated rubber phase with the properties different from those of the two bulk phases? Blends of a polystyrene matrix and phase separated rubber inclusions (a polystyrene-polyisoprene-polystyrene triblock polymer (SIS)) were manufactured in a range of blend fractions (up to 20 vol % of the triblock co-polymer). Experimental measurements, for the storage modulus G′ and the loss tangent tanδ, of both the individual phases and the blends, were made using dynamic mechanical tests over a range of temperatures from −50 to +70 °C. Numerical predictions, of the same parameters, were first obtained using the generalised self-consistent Christensen and Lo model which uses a simple representative volume element (RVE) of an isolated sphere of the minority rubber component in a surrounding sheath of polystyrene matrix embedded in a homogeneous effective medium. The agreement between the Christensen and Lo model and the experimental measurements, for G′ and tanδ, was found to be excellent for rubber contents up to 10%. For a 20% rubber content, an improved prediction was obtained by altering the RVE to include the observed effect of having a polystyrene central core in a number of the dispersed rubber zones at this rubber fraction, using the Herve and Zaoui generalization of the Christensen and Lo model. Although conjoined (and therefore non-spherical) zones became more prevalent at the highest rubber content, use of the Tandon and Weng model showed that this shape anisotropy would not be expected to affect the viscoelastic properties

Toward In Silico Design of Highly Tunable Liquid Crystal Elastomers

In this work, a two-component acrylate liquid crystal elastomer, with varying composition and templating phase, is synthesized in the laboratory and investigated in parallel using atomistic molecular dynamics simulations. The anisotropic nature of both the mono- and bifunctional acrylates used in this study enables a large tunability in the compositional range while still retaining liquid crystalline properties in the final elastomer. The use of simulations allows important evaluation and comparison of physical properties such as glass transition temperature, nematic to isotropic phase transition temperature, and order parameter. The dependence of physical properties (glass transition, nematic to isotropic transition, order parameter, coefficient of thermal expansion, and mechanical properties) is established as a function of chemical composition, showing a high degree of tunability. Interestingly, the templating phase (nematic or isotropic) is also shown to impact the subsequent elastomer properties, with excellent agreement shown here between experiments and simulations. The in silico approach to polymerization, coupled with excellent comparison with the experimental system, represents a new methodology for the targeted design of liquid crystal elastomers with specific physical properties

Liquid Crystal Elastomers for Biological Applications

The term liquid crystal elastomer (LCE) describes a class of materials that combine the elastic entropy behaviour associated with conventional elastomers with the stimuli responsive properties of anisotropic liquid crystals. LCEs consequently exhibit attributes of both elastomers and liquid crystals, but additionally have unique properties not found in either. Recent developments in LCE synthesis, as well as the understanding of the behaviour of liquid crystal elastomers—namely their mechanical, optical and responsive properties—is of significant relevance to biology and biomedicine. LCEs are abundant in nature, highlighting the potential use of LCEs in biomimetics. Their exceptional tensile properties and biocompatibility have led to research exploring their applications in artificial tissue, biological sensors and cell scaffolds by exploiting their actuation and shock absorption properties. There has also been significant recent interest in using LCEs as a model for morphogenesis. This review provides an overview of some aspects of LCEs which are of relevance in different branches of biology and biomedicine, as well as discussing how recent LCE advances could impact future applications

Intermodal exchange stations in the city of Madrid

The City of Madrid is putting into operation Intermodal Exchange Stations (IESs) to make connections between urban and suburban transportation modes easier for users of public transportation. The purpose of this article is to evaluate the actual effects that the implementation of IESs in the City of Madrid has on the affected stakeholders: users, public transportation operators, infrastructure managers, the government, the abutters and other citizens. We develop a methodology intended to help assess the welfare gains and losses for each stakeholder. Then we apply this methodology to the case study of the Avenida de América IES in the city of Madrid. We found that it is indeed possible to arrive at win–win solutions for the funding of urban transportation infrastructure, as long as the cost-benefit ratio of the project is high enough. Commuters save travel time. Bus companies diminish their costs of operation. The abutters gain in quality of life. The private operator of the infrastructure makes a fair profit. And the government is able to promote these infrastructure facilities without spending more of its scarce budgetary resources

Social richness, socio-technical tension and the virtual commissioning of NHS research

<p>Abstract</p> <p>Background</p> <p>This paper draws on a recent study that evaluated the process of commissioning NHS funded research using virtual committees. Building on an earlier paper that reported our evaluation, here we focus on the effects of asynchronous computer mediated communication (CMC) when used to support group work.</p> <p>Methods</p> <p>To do this the discussion focuses on how CMC affected three key group factors, building relationships, group cohesion and group commitment. The notion of socio-technical tension is elaborated and the paper explores how social richness can act to counter the socially impoverishing and time extending effects of asynchronous CMC.</p> <p>Results</p> <p>We argue that social richness in this context results from the presence of five principal influences. These are: a dynamic range of participant aspirations and personal agendas; participant commitment to and identification with the work and ideals of the group; a rich diversity of social, professional and work-related backgrounds; a website designed to enhance participation and interaction and the mediating effects of an effective chairperson.</p> <p>Conclusion</p> <p>If virtual work groups are to be used by the NHS in the future, then there is a need for more research into the role of social context and its relationship to the effectiveness of newly formed virtual groups. Equally as important are studies that examine the effects of socio-technical interaction on groups undertaking tasks in the real world of work.</p

Evaluation of a 'virtual' approach to commissioning health research

BACKGROUND: The objective of this study was to evaluate the implementation of a 'virtual' (computer-mediated) approach to health research commissioning. This had been introduced experimentally in a DOH programme – the 'Health of Londoners Programme' – in order to assess whether is could enhance the accessibility, transparency and effectiveness of commissioning health research. The study described here was commissioned to evaluate this novel approach, addressing these key questions. METHODS: A naturalistic-experimental approach was combined with principles of action research. The different commissioning groups within the programme were randomly allocated to either the traditional face-to-face mode or the novel 'virtual' mode. Mainly qualitative data were gathered including observation of all (virtual and face-to-face) commissioning meetings; semi-structured interviews with a purposive sample of participants (n = 32/66); structured questionnaires and interviews with lead researchers of early commissioned projects. All members of the commissioning groups were invited to participate in collaborative enquiry groups which participated actively in the analysis process. RESULTS: The virtual process functioned as intended, reaching timely and relatively transparent decisions that participants had confidence in. Despite the potential for greater access using a virtual approach, few differences were found in practice. Key advantages included physical access, a more flexible and extended time period for discussion, reflection and information gathering and a more transparent decision-making process. Key challenges were the reduction of social cues available in a computer-mediated medium that require novel ways of ensuring appropriate dialogue, feedback and interaction. However, in both modes, the process was influenced by a range of factors and was not technology driven. CONCLUSION: There is potential for using computer-mediated communication within the research commissioning process. This may enhance access, effectiveness and transparency of decision-making but further development is needed for this to be fully realised, including attention to process as well as the computer-mediated medium

Reporting bias in medical research - a narrative review

Reporting bias represents a major problem in the assessment of health care interventions. Several prominent cases have been described in the literature, for example, in the reporting of trials of antidepressants, Class I anti-arrhythmic drugs, and selective COX-2 inhibitors. The aim of this narrative review is to gain an overview of reporting bias in the medical literature, focussing on publication bias and selective outcome reporting. We explore whether these types of bias have been shown in areas beyond the well-known cases noted above, in order to gain an impression of how widespread the problem is. For this purpose, we screened relevant articles on reporting bias that had previously been obtained by the German Institute for Quality and Efficiency in Health Care in the context of its health technology assessment reports and other research work, together with the reference lists of these articles