1,721,152 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)
Il DNA, non solo la macromolecola della vita, ma anche il giusto equilibrio chimico tra fosforo, azoto e carbonio per avere un eccellente ritardante di fiamma
No full textIl DNA è la molecola che contiene il patrimonio genetico di ciascun essere vivente e rappresenta quella specifica “impronta digitale” che caratterizza ogni essere umano. La sua struttura chimica, alquanto complessa, insieme agli elementi che la costituiscono (carbonio, idrogeno, ossigeno, fosforo e azoto) sono essenziali per la vita.... ma non solo, rappresentano anche la “RICETTA PERFETTA” per preparare un efficace ritardante di fiamma.
Una delle scoperte più all’avanguardia riguarda proprio l’uso del DNA come ritardante di fiamma per tessuti di cotone. L’utilizzo di questa molecola come rivestimento superficiale per fibre di cotone lo rende completamente ignifugo a un flusso di calore di 35kW/m2 (circa 500°C) condizione a cui tutti i comuni tessuti, prendono fuoco, sviluppando un vigoroso incendio. Allo stesso tempo, quando una fiamma di metano, tipo quella della cucina, è avvicinata al cotone, se trattato con il DNA brucia solo per qualche secondo e poi si spegne completamente
Green Flame Retardants
No full textIn the last decade, several studies involving the researchers from academics and industry have been specifically focused on seeking environmental-friendly flame -retardants (FRs) that exhibit a remarkable “green” character and ensure fire performances comparable to those achieved by the conventional FR compounds.
Recently, we have started to assess the effectiveness of different biomacromolecules (whey proteins, caseins, hydrophobins, and deoxyribonucleic acid – DNA) to be a valuable unusual green alternative to the conventional compounds [1, 2]. These new “odd” FRs have proven to be efficient for both fabrics (cotton, polyester and blends of them) as well as for polymeric films (ethylene-vinyl-acetate copolymer - EVA -, polypropylene - PP -, acrylonitrile-butadiene styrene - ABS -, polyester - PET - and polyamide 6 - PA6). Simple water-based procedures such as impregnation or Layer-by-Layer assembly have been successfully employed for depositing efficient fireproof coatings. Here, the collected results will be thoroughly described and presented.
References
1. Malucelli, G, Bosco F, Alongi J, Carosio F, Di Blasio A, Mollea C, Cuttica F, Casale A. Biomacromolecules as novel green flame retardant systems for textiles: an overview. RSC Adv. 2014 ;4:46024-46039.
2. Alongi J, Malucelli G. Cotton flame retardancy: state of the art and future perspectives. RSC Adv. 2015;5:24239-24263.
3. Alongi J, Di Blasio A, Cuttica F, Carosio F, Malucelli G. Bulk or surface treatments of ethylene vinyl acetate copolymers with DNA: investigation on the flame retardant properties. Eur. Polym. J. 2014;51:112-119.
4. Alongi J, Cuttica F, Carosio F. DNA coatings from by-products: a panacea for the flame retardancy of EVA, PP, ABS, PET and PA6? ACS Sustainable Chemsitry and Engineering, 2016;4:3544–3551
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
Flame retardancy of flexible polyurethane foams: traditional approaches versus layer-bylayer assemblies
No full textThis chapter provides an overview of the flame retardancy of flexible polyurethane foams. In particular, the different chemical structures of polyurethanes are discussed, underlining the most relevant aspects related to thermal decomposition and combustion. A brief description of the toxicity of the combustion gases is provided. The traditional strategies developed in the past are presented and commented upon, highlighting the main results achieved. Subsequently, layer by layer is discussed as new emerging approach for conferring flame-retardant properties to open-cell polyurethane foam. The principles of this technique and its practical applications in flame retardancy are presented, providing a complete overview of the results achieved so far. Finally, there is a discussion on the future perspectives and unmatched needs, and a comparison between old and new approaches
Investigation on flame retardancy of poly(ethylene terephthalate) by combination of an organo-modified sepiolite and Zn phosphinate for plastics and textiles
No full textZn phosphinate, organo-modified sepiolite and poly(ethylene terephthalate) (PET) have been melt blended to develop a new flame retardant system for PET plastics and textiles. The combination of Zn phosphinate and sepiolite have been exploited in order to enhance the flame retardancy of PET for both plastics and textiles. The thermal stability of PET blends evaluated by thermogravimetric analysis and differential scanning calorimetry results remarkably affected by the loaded fillers. The combustion tests by cone calorimetry reveal a relevant decrease of combustion rate and a high increase of fire performance index for both plastics and textiles due to the presence of this novel flame retardant mixture. Analogously, limiting oxygen index has been found increased in a remarkable way
Intumescence: Tradition versus novelty. A comprehensive review
No full textThe objective of current research on intumescent formulations is on consolidated approaches for conferring flame retardancy properties to polymers and polymer blends. Numerous academic and industrial efforts have been carried out in the last fifteen years, by revisiting the traditional concept of intumescence on the basis of the new chemical synthesis or novel nano-technological developments. The main concepts of intumescence are reviewed in this report, highlighting the novelties as well as the most significant results achieved in the flame retardancy of polymeric materials in the last 10-15 years. Although the basic aspects of intumescence such as the chemical components, thermal and rheological aspects are well-known, the modeling and simulation of these systems are completely new and never reviewed. Analogously, the traditional chemical compositions will be compared with the novel systems, most of them based on the nanotechnology and synergistic aspects. Thus, the results collected up-to-now by using these new intumescent formulations will be dealt with the different polymer families. The use of current intumescent coatings for metals, steel, wood and plastics as well as the application of novel intumescent coatings deposited on fabrics, films and foams through layer-by-layer assembly are reviewed. Although the latter technique is not new, its use to confer flame retardancy properties to polymers is a recent development
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
Synthesis and characterization of layered materials obtained by insertion of dendritic macromolecules for nanocomposite preparation
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