1,721,129 research outputs found
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)
Innovative Solutions To Enhance The Flame Retardancy Properties Of Natural And Synthetic Fabrics: Sol-Gel, Dual-Cure Processes And Layer By Layer Assembly
No full textNowadays, nanotechnology has a real and great potential in the textile industry, considering that conventional methods used to give different properties to fabric textiles often do not lead to permanent effects against wearing or laundering; in such scenario, the use of nanotechnology has been proved to give high durability for fabrics, improve the performance of fibres and create unprecedented functions [1]. The idea is to develop a new method based on the introduction of nanoparticles during the finishing step. Multilayered thin films made of nano size layers, with total thickness ranging from submicron to a few millimetres, can be prepared with a new technique called layer-by-layer (LbL). Now, the technique can be tailored to multimaterial assembly of several compounds without special chemical modifications, thus enabling the production of multilayer films. Furthermore, the technique is very easy and applicable to different field applications, such as textile sector. It consists in an alternate immersion or more simply in alternate spraying of the substrate with an oppositely charged polyelectrolyte solutions, thus creating a structure of positively and negatively charged layers piled up on the substrate surface. On the other hand, the nano-sized particles have been synthesized by sol-gel process, which involves inorganic precursors (organo-silicates, -titanates-aluminates, etc.) that undergo several reactions resulting in the formation of a three-dimensional molecular network. The sol-gel process is conducted at a low temperature which also enables the incorporation of organic compounds into the inorganic structure without decomposition.
[1] J. Alongi, F. Carosio, R.A. Horrocks, G. Malucelli. Flame Retardant Textiles: State of the Art, Environmental Issues and Innovative Solutions, Rapra, In press
Layer by Layer Assembly: A Current Emerging Technique for Conferring Flame Retardancy
No full textLayer by Layer (LbL) assembly consists in a step-by-step film build-up based on electrostatic interactions; it was introduced in 1991 for polyanion/polycation couples in order to obtain the so-called polyelectrolyte multilayers [1], and subsequently extended to inorganic nanoparticles [2] exploiting different interactions (e.g. covalent bonds, hydrogen bonds, etc.) beside the electrostatic one. The LbL assembly through electrostatic interactions simply requires the alternate immersion of the substrate into an oppositely charged polyelectrolyte (usually water-based) solution (or dispersion). Thus, an assembly of positively and negatively charged layers piled up on the substrate surface is obtained, exploiting a total surface charge reversal after each immersion step. LbL was first described in 1966 [3] and has been rediscovered and optimized decades later [4, 5]. Very recently, such approach proved to be extremely advantageous when exploited for the flame retardancy of foams [6, 7], thin and thick films [8-10], fibres and fabrics [11-13]. More specifically, different types of architectures have been deposited on fabrics: namely, i) inorganic LbL coatings; ii) hybrid organic-inorganic or intumescent LbL coatings; and iii) char-former/enhancer LbL coatings. The main results collected in the literature will be described in the present work, with particular attention to the possible industrial exploitations. Indeed, although dipping has been widely investigated as deposition technique, surprising results have been obtained employing spray, as well. A deep overview of all these results will be presented.
References
1. Decher G, Hong JD. Buildup of ultrathin multilayer films by a self-assembly process, 1 consecutive adsorption of anionic and cationic bipolar amphiphiles on charged surfaces. Makromol Chem, Macromol Symp 1991;46(1):321-327.
2. Tang Z, Kotov NA, Magonov S, Ozturk B. Nanostructured artificial nacre. Nature Mater 2003;2(6):413-418.
3. Decher G. In: Decher G, Schlenoff JB, editors. Multilayer thin films, sequential assembly of nanocomposite materials. Weinheim (Germany): Wiley VCH, 2003. p. 1.
4. Decher G, Schlenoff J, editors. Multilayer thin films, sequential assembly of nanocomposite materials. Weinheim (Germany): Wiley VCH, 2002.
5. Decher G. In: Decher G, Schlenoff JB, editors. Multilayer thin films, sequential assembly of nanocomposite materials. Weinheim (Germany): Wiley VCH, 2003. p. 1.
6. Laufer G, Kirklan C, Cain AA, Grunlan JC. Clay−chitosan nanobrick walls: completely renewable gas barrier and flame-retardant nanocoatings. ACS Appl Mater Interfaces 2012;4(3):1643-1649.
7. Kim YS, Davis R, Cain AA, Grunlan JC. Development of layer-by-layer assembled carbon nanofiber-filled coatings to reduce polyurethane foam flammability. Polymer 2011;52(13):2847-2855.
8. Apaydin K, Laachachi A, Ball V, Jimenez M, Bourbigot S, Toniazzo, Ruch D. Polyallylamine–montmorillonite as super flame retardant coating assemblies by layer-by layer deposition on polyamide. Polym Degrad Stab 2013;98(2):627-634.
9. Laachachi A, Ball V, Apaydin K, Toniazzo V, Ruch D. Diffusion of polyphosphates into (poly(allylamine)-montmorillonite) multilayer films: flame retardant-intumescent films with improved oxygen barrier. Langmuir 2011;27(22):13879-13887.
10. Carosio F, Di Blasio A, Alongi J, Malucelli G. Layer by Layer nanoarchitectures for the surface protection of polycarbonate. Eur Polym J 2013;49(2):397-404.
11. Carosio F, Alongi J, Frache A, Malucelli G, Camino G. In: Morgan AB, Nelson GL, Wilkie CA, editor. Fire and polymers VI: new advances in flame retardant chemistry and science. Washington DC (USA): ACS Symposium Series 1118, 2012. Chapter 22.
12. Alongi J, Carosio F, Malucelli G. Current emerging techniques to impart flame retardancy to fabrics, Polymer Degradation and Stability, In press.
13. Alongi J, Carosio F, Horrocks AR, Malucelli G, editors. Update on Flame Retardant textiles: State of the art, Environmental Issues and Innovative Solutions. Shawbury, Shrewsbury, Shropshire (UK): Smithers RAPRA Publishing, 2013, ISBN: 978-1-90903-017-6
La Polimerizzazione Frontale. Una Nuova Tecnica Per L’ottenimento Di Materiali Polimerici
No full textThermal stability, flame retardancy and abrasion resistance of cotton and cotton-linen blends treated by sol-gel silica coatings containing alumina micro- or nano-particles
No full textSol-gel processes have been carried out to deposit silica coatings "doped" with alumina micro- or nanoparticles on cotton and cotton-linen fabrics in order to enhance their thermal stability, flame retardancy and mechanical properties (namely, abrasion resistance). The joint effect between silica and alumina particles (regardless of their size) has proven to enhance the thermal stability in air, and consequently to affect the flame retardancy of the treated fabrics, as assessed by thermogravimetry, flammability and cone calorimetry tests. Furthermore, the presence of traces of alumina particles has turned out to be responsible of a remarkable increase of the abrasion resistance of the fabric
Cotton fabrics treated with novel oxidic phases acting as effective smoke suppressants
No full textSol-gel processes have been applied to cotton fabrics in order to coat the fibres with a silica film, able to improve their thermo-oxidative resistance and their combustion behaviour under the irradiative heat flow of a cone calorimeter. To this aim, tetramethoxysilane, inorganic precursor of the silica phase, has been employed alone or coupled with species having either smoke suppressant features (namely, zinc oxide, zinc acetate dihydrate and zinc borate) or well known flame retardant properties (like ammonium pentaborate octahydrate, boron phosphate, ammonium polyphosphate and 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide). In addition, the use of barium sulphate, which is a smoke suppressant and, at the same time, a flame retardant, has been investigated. Cone calorimetry turned out to be a suitable technique for assessing the flammability and smoke production of the treated fabrics (particularly when referring to total smoke release, smoke production rate and CO and CO 2 yields). The composition and morphology of the deposited coatings, assessed by scanning electron microscopy, have been found to influence their combustion behaviour, as well as their thermal and thermo-oxidative stability evaluated by thermogravimetric analysis in nitrogen and air, respectively
Cotton flame retardancy: state of the art and future perspectives
No full textAs clearly reported in the scientific literature, the history of cotton flame retardancy is very old: this is easily attributable to the chemical and physical properties of this fibre that made it predominant during the 20th century; at present, it is only exceeded in volume by polyester. As a consequence, the huge number of papers published in the scientific literature so far covers an extended period and, sometimes, it could be easy to forget some of the knowledge already developed in the past and to focus the attention on the recent highlights only. Therefore, the present work is aimed to review the most significant scientific and technological results about the flame retardancy of cotton, merging the past experience and the current efforts, trying also to foresee a possible scenario for the next future. After a historical excursus on the achievements up to 2010, the review will summarize the recent developments reached in the so-called “era of nanotechnology” for cotton, as a consequence of the setup of new approaches like nanoparticle adsorption, Layer by Layer assembly and sol–gel processes. Finally, a possible alternative development route indicated by the potential exploitation of bio-macromolecules as green flame retardant systems will be briefly discussed
An up-to-date combination of different analytical techniques for better understanding the thermal degradation and combustion behaviour of textiles
No full textThe present work aims to review the analytical techniques commonly used for the thermal and combustion characterization of flame retarded textiles, also taking into account the recent development of new instrumentations. More specifically, the use and abuse of standard characterizations like thermogravimetry and thermogravimetry coupled with infrared spectroscopy will be referred and compared to pyrolysis-combustion flow calorimetry, thermogravimetry at high heating rates and flash pyrolysis. The collected results from these latter techniques can be somehow correlated with those coming from (horizontal or vertical) flame spread, LOI and cone calorimetry tests: this has been clearly assessed when bio-macromolecules have been used as flame retardants for cotton. Hence, the proposed approach can be applied for investigating a new flame retardant system, provide an exhaustive characterization of its thermal and fire performances
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