1,720,957 research outputs found
Cyclodextrin nanosponges and phosphorus compounds as flame retardants for ethylene vinyl acetate copolymer
No full textInfluence of nanoparticles on the morphology, thermal stability and air permeability of electrospun polylactic-acid fibres
Full text linkPolylactic-acid (PLA) and PLA-clay fibres have been produced from solution of 1,1,1,3,3,3-hexafluoro-2-propanol by electrospinning. Nanoclays having different aspect ratio, namely a montmorillonite and a sepiolite, have been added and dispersed within the polymer matrix in order to enhance the thermal stability and air permeability of PLA. The influence of the polymer molecular weight, the solution viscosity and conductivity on the morphology of the fibres has been investigated. Electron microscopy has shown that fibre diameter and the presence of beads defects in the fibres depend on the type of clay added to the polymer matrix. The thermal stability in nitrogen and in air has been drastically enhanced for the presence of the clays as compared with neat polymer. Finally, permeability tests performed on the electrospun condensed fibres pointed out that PLA-clay fibres exhibit a lower permeability to air (up to 90%) with respect to neat PLA fibres
Novel flame retardants containing cyclodextrin nanosponges and phosphorus compounds to enhance EVA combustion properties
No full textA novel flame retardant intumescent system, aimed to improve the fire stability of ethylene vinyl acetate copolymer (EVA), has been prepared by melt blending of the copolymer and a complex of cyclodextrin nanosponge-phosphorus compounds. As compared to traditional systems, this complex, stable in processing conditions, has the advantage that nanosponges act as both carbon sources and foam forming agents while the phosphorus compounds are able to directly generate phosphoric acid in situ. In this context, cyclodextrin nanosponges undergo dehydration in presence of the acid source, generating water vapour and char, and thus protecting the copolymer against combustion. Different acid sources have been investigated in order to reach the optimum interaction with the nanosponges. Raman measurements and thermogravimetric analyses have shown that the cavities of nanosponges entrapped the phosphorus derivatives forming stable complexes at the temperature of EVA processing. Different amounts of these complexes (5, 10 and 15 wt.%) have been added to EVA via melt blending and their flame retardancy properties measured by UL94 test and cone calorimetry. Strongly modified burning kinetics, as compared to the behaviour of the neat copolymer, have been found by UL94 test: V2 classification has been achieved for every formulation regardless of the type and the amount of complex used. EVA combustion behaviour by cone calorimetry has also been significantly affected: the heat release rate decreased dramatically down to ca. 20% in the presence of these new additives
Role of β-cyclodextrin nanosponges on polypropylene photo-oxidation
No full textThe interactions between β-cyclodextrin nanosponges and two different UV stabilizers (namely, 2-hydroxy-4(octyloxy)-benzophenone and triphenyl phosphite) in the photooxidation of polypropylene exposed to UV light have been investigated. A significant decrease of the oxidation induction time (OIT) has been observed in presence of β-cyclodextrin nanosponges. On the contrary, the combination of the above nanosponges with 2-hydroxy-4(octyloxy)-benzophenone turned out to be very efficient and advantageous since a remarkable increase of OIT has been registered, namely a threefold increase of polypropylene OIT. This result has indicated a possible synergistic effect between the two species due to the occurring of some chemical or physical interactions, verified by comparing the experimental results and data calculated on the basis of simple additivity rule. Some hypotheses on the interaction mechanism between the two species have been given. Conversely, no effect has been found for the triphenyl phosphite-nanosponge pair
Cyclodextrin nanosponges as novel green flame retardants for PP, LLDPE and PA6
No full textNovel green flame retardant systems based on a complex of cyclodextrin nanosponges and phosphorus derivatives (namely, triethylphosphate and ammonium polyphosphate) have been prepared. The above additives have been subsequently melt compounded with polypropylene, linear low density polyethylene or polyamide 6 in order to improve the thermal stability of the latter polymers and their flame retardancy properties (assessed by combustion and flammability tests). The role of cyclodextrin nanosponges both as a carbon source and a foaming agent in such intumescent formulations has been demonstrated: indeed, the phosphorus derivatives are embedded and protected by the nanosponge architectures and thus are able to generate phosphoric acid directly in situ at high temperatures. As a consequence, cyclodextrin nanosponges dehydrate in presence of this acid source, giving rise to water vapour, favouring char formation and thus significantly enhancing the polymer resistance toward combustion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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