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Fire protection of films, fabrics and foams achieved through surface nano-structuring
No full textGenerally speaking, polymer combustion is fuelled by pyrolysis products escaping from its surface due to the heat transferred from the flame to the polymer surface and also radiated from the flame itself. The oxygen required for sustaining the flaming combustion diffuses in and from the surrounding air environment. Solid particles escape from the flame as smoke, which is accompanied by gaseous species, some of which can be toxic1, 2. The most significant polymer degradation reactions usually occur in the condensed phase, as they take place mainly within 1mm of the interphase between the flame and polymer, where the temperature raise is high enough. These reactions involve the polymer and any additives (in particular flame retardants) included in the formulations or applied as surface treatments. Experimental studies of this region have been published by Price and co-workers3 and by Marosi and coworkers4. The volatile species formed during combustion escape into the flame zone, whilst heavier species undergo further reactions and may eventually turn into char: this multi-lamellar carbonaceous structure acting as a thermal insulator protects the surrounded polymer.
Therefore, the polymer surface can be considered the critical zone in the polymer combustion scenario because, being the interface between gas and condensed phase, it controls mass and heat transfers which are the processes responsible for flame fuelling. Indeed, the heat reaching the polymer surface is transmitted to the polymer bulk, from which volatile products of thermal degradation diffuse towards the surface and the gas phase, feeding the flame. Thus, the polymer surface plays a key role in polymer ignition and combustion because its chemical and physical characteristics affect the combustible volatiles flux towards the gas phase5.
One of the most valuable fire retardant strategy pursued by bulk addition, proved to be the production or accumulation of a thermally stable surface layer able to act as a barrier to mass and/or heat exchange. Such a layer is built during the early stage of combustion as a consequence of polymer surface layer decomposition, in the presence of different kinds of fire retardants, including inorganic nanoparticles. However, the time required for build-up of the surface barrier is straightforwardly connected to the development of the fire in the early stage, consequently adversely affecting the effectiveness of the protective barrier.
Results and discussion
Here it is shown how the combination of advancements in polymer surface engineering and development of nanotechnologies, supplies an innovative environmentally friendly approach to fire retardance, based on providing polymer material products with a surface barrier, which either reradiates heat and/or slows down heat transmission and volatiles diffusion, without affecting the bulk properties. To this purpose, nanoparticle adsorption6, sol-gel and dual-cure processes7, 8, Layer by Layer assembly8, will be thoroughly described. By building the fire protection onto the original polymer surface, its effectiveness will be larger than in the case of protection created during combustion as usually happens with traditional bulk addition. Numerous examples of the above mentioned approaches applied to films, fabrics and foams will be presented. A glimpse on the use of biomacromolecule-based coatings will be proposed, as well9, 10.
Conclusion
Engineering the polymer surface is shown to provide a potential promising, environmentally-friendly and effective approach to polymer fire retardance, particularly when combined with nanostructurating technologies. Feasibility is demonstrated for textiles, films and foams while present efforts are directed towards composites with possible future extension to thick polymer materials. A major interest in this approach to surface polymer properties is the possibility to simultaneously confer multifunctional features that, besides fire retardance, may involve gas barrier, hydrophobicity, biocide activity, surface electrical conductivity, etc.
Keywords: surface; coatings; Layer by Layer; sol-gel; combustion;
Acknowledgments
The European COST Action “Sustainable flame retardancy for textiles and related materials based on nanoparticles substituting conventional chemicals“, FLARETEX (MP1105) is gratefully acknowledged.
References
1. J. Alongi, F. Carosio, A.R. Horrocks, G. Malucelli G, Update on Flame Retardant textiles: State of the art, Environmental Issues and Innovative Solutions, Shawbury, Shrewsbury, Shropshire (UK): Smithers RAPRA Publishing, 2013.
2. T.R. Hull, “Challenges in fire testing: reaction to fire tests and assessment of fire toxicity” in Advances in Fire Retardant Materials, edited by D. Price and A.R. Horrocks, Cambridge (UK): Woodhead Publishing, 2008, pp. 255-290.
3. D. Price, F. Gao, G.J. Milnes, B. Eling, C.I. Lindsay, T.P. McGrail, Polym. Degrad. Stab. 64, 403-410 (1999).
4. G. Marosi, “Use of Organosilicone Composites as Flame Retardant Additives and Coatings for Polypropylene” in Fire Retardancy of Polymers: New Strategies and Mechanisms, edited by T.R. Hull and B.K. Kandola, Cambridge (UK): The Royal Society of Chemistry, 2009, pp. 49-58.
5. G. Malucelli, F. Carosio, J. Alongi, A. Fina, A., Frache, G. Camino, Mater. Sci. Eng. R 84, 1-20(2014).
6. J. Alongi, J. Tata, F. Carosio, G. Rosace, A. Frache, G. Camino, Polymers 7, 47-68(2015).
7. J. Alongi, F. Carosio, G. Malucelli, Polym. Degrad. Stab. 106, 138-149(2014).
8. J. Alongi, G. Malucelli, J. Mater. Chem. A 22, 21805-21809(2012).
9. G. Malucelli, F. Bosco, J. Alongi, F. Carosio, A. Di Blasio, C. Mollea, F. Cuttica, A Casale, RSC Adv. 4, 46024-46039(2014).
10. J. Alongi, F. Bosco, F. Carosio, A. Di Blasio, G. Malucelli, Mater. Today 17, 152-153(2014)
Thermal And Flame Retardant Properties of Ethylene Vinyl Acetate Copolymers Containing Deoxyribose Nucleic Acid or Ammonium Polyphosphate
No full textThe present study is aimed to compare the effect of the presence of deoxyribose nucleic acid (DNA) or ammonium polyphosphate (APP) in ethylene vinyl acetate (EVA) copolymers, as far as their thermal and flame retardant properties are considered. Indeed, although DNA has been recently discovered as a novel green flame retardant, its performances have not been compared with a conventional flame retardant such as APP yet. With this purpose, EVA compounds containing 10 or 20wt.-% of DNA or APP have been melt-blended and their thermal and flame retardant properties thoroughly investigated. The morphology of the samples has proven to be significantly different, as assessed by Scanning Electron Microscopy (SEM): indeed, APP gave rise to numerous micro-aggregates homogeneously distributed within the polymer matrix; on reverse, DNA was finely dispersed. Both the additives have favoured the char formation, inhibiting the production of volatile species, as assessed by thermogravimetry (TG) and pyrolysis-combustion flow calorimetry (PCFC). The char features of both the additives turned out to be extremely advantageous for strongly modifying the combustion behaviour of EVA, as clearly demonstrated by cone calorimetry test
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
Self-assembled hybrid nanoarchitectures deposited on poly(urethane) foams capable of chemically adapting to extreme heat
No full textIn the present paper the layer by layer (LbL) technique has been adopted for the construction of hybrid organic-inorganic nanoarchitectures capable of adapting to extreme heat or flame exposure and chemically evolving into thermally-stable carbon based structures. More specifically, the LbL technique has been applied to an open cell poly(urethane) (PU) foam in order to increase its thermal and flame stability. Scanning electron microscopy showed that the LbL assembly covered each surface of the PU complex three-dimensional structure without altering its open cell morphology. When exposed to a direct flame, the treated PU foam was capable of stopping combustion within a few seconds after ignition, unlike the untreated foam that burned completely. Under different irradiative heat fluxes (from 35 up to 75 kW m2), the coating demonstrated exceptional performances by reducing the rate of heat release up to 60% with respect to the untreated counterpart. Finally, when subjected to a flame torch penetration (Tflame ≈ 1300 °C), the LbL-coated PU foam was capable of maintaining its three-dimensional structure, thus successfully insulating the unexposed side (T below 100 °C after two flame torch applications) with temperature drops of 800 °C achieved with a specimen thickness of only 10 mm
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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