1,721,037 research outputs found
Surface modifications of natural fibers and synthesis of inorganic nanoparticles for tailoring of the interphase and the flame retardancy of green composites
Full text linkThis thesis wants to show some applications which exploit sol-gel methodologies and its advantages to solve industrial and technological problems inherent the use of polymer based bio-composites. These composites can show severe limitations due to the easy flammability of the polymer matrix; this behavior can significantly restrict the application fields of these materials, especially when the possibility of the use of the composites is strictly related to specific regulatory fire tests that have to be passed, hence ensuring public safety (e.g., in the aerospace industry). Additional limitations descend from the mechanical properties of the above mentioned bio-composites, which may be due to a low interfacial adhesion between the filler (e.g., natural fibers) and the polymer matrix. Sol-gel methodologies can improve the fire behavior and the mechanical properties of bio-composites through the in-situ synthesis of ceramic domains in the polymer network and the tailoring of the interphase between filler and matrix.
The main results obtained can be summarized as follow:
- In this thesis, hemp fabrics have been modified with a new, inexpensive, simple and eco-friendly waterglass treatment, hence improving their fire behavior when utilized as reinforcing agent fillers in epoxy-based composites. A silica-based coating, able to protect the fabrics from heat sources, has been obtained. Moreover, when properly treated with the above-mentioned waterglass solution, hemp fabric easily gives silica-based coated fibers of diameters from tens of microns to tens of nanometers with the aid of a low power mixer. The silica-based coated fibers can be easily functionalized with a coupling agent and then dispersed in epoxy resin. Micrographs of the composites show a tendency to give web-like structure formed by fibrils and microfibrils continuously interconnected, from which particularly good mechanical properties may be expected to descend.
- In this thesis, new hybrid silica/epoxy composites cured with a cycloaliphatic amine have been prepared by using an in-situ sol–gel process. The experimental results suggest that the new hybrid structures consist of very fine silica nanoparticles, homogeneously dispersed in an epoxy/silica hybrid network. The presence of the silica domains in the hybrid organic–inorganic networks prevents melt dripping phenomena in vertical flame spread tests. In addition, as assessed by forced-combustion tests, the inorganic domains act as a thermal protective layer, hence improving the heat and smoke-related parameters. Finally, the efficiency of the protective ceramic layer decreases after the non-isothermal post curing treatment carried out on the hybrid systems. The above-mentioned in-situ sol-gel process. has been modified by adding two phosphorous based flame retardants and eventually melamine just before the addition of the hardener. The use of the two phosphorous-based flame retardants allow to achieve self-extinguishing capacity for the studied epoxy system with only 2 wt. % of P-loading. Additionally, the presence of only 2% silica guarantees the absence of dripping phenomena during the burning of the epoxy resin. The formation of an intumescent char is observed when the two flame retardants are used in combination with melamine, hence a remarkable increase of the post-combustion residues is recorded. The flame retardancy of the epoxy composites has been improved by adding very low amount of phosphorous and silica.
As a future prospective, the above sol-gel functionalized hemp fibers may be used as reinforcement in in-situ silica/polymer bio-composites added with green phosphorous-based flame retardants. This may allow to combine excellent performances in terms of fire behavior with improved mechanical properties
Recyclable flame-retardant epoxy thermosets and composites: chemical concepts and future prespectives
No full textThe presence of cross-linked networks, flame retardants, or other functional molecules makes the recycling of nonhalogenated flame retardant (NHFR) epoxy thermosets (ETs) very challenging. The use of fire-safe epoxy-based materials in a variety of applications has increased in the past few decades, together with the demand for their recycling. To address this issue, next-generation thermosets with inherent fire resistance and recyclability are being designed. Recyclable epoxy materials containing covalent adaptable networks are paving the way to energy-efficient and more sustainable recycling technologies, where recyclability is considered during material design and fabrication. Recent developments in the reuse and recycling of NHFR ETs are presented here. In addition to fire-safe applications, recovery strategies and challenges for the polymeric matrix and valuable fibers from fiber-reinforced polymer composites are described
Thermal decomposition of flame retardant polymers
No full textMost of polymeric materials exhibit high flammability, owing to their chemical composition and thermal stability. During their combustion, polymer-based products release smoke, melt drips, heat, and toxic species, which cause image damage to human life, natural environment, and materials surrounding them. The decomposition pathway of polymers strongly depends on their chemical structure, which may collapse generating large amounts of flammable volatiles and some residues. Over the years, the use of different flame retardant systems (e.g., functional additives, nanotechnology) and strategies (e.g., intumescence, plasma treatment) have been used to improve the fire performances of polymers and to fulfil requirements of the industry, without compromising other properties. Such flame retardant additives may have a strong influence on the thermal decomposition of polymers. Accelerated decomposition, and altering of pathways of decomposition to form char or flammable and nonflammable volatiles are some outcomes of such interactions. This chapter briefly outlines the characteristics related to the decomposition behavior of most common polymeric materials, with a special focus on their flame retardation and potential usage on the market
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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