Data di Pubblicazione:
2015
Citazione:
Fire protection of films, fabrics and foams achieved through surface nano-structuring / J. Alongi, A. Di Blasio, F. Carosio, F. Cuttica, G. Malucelli. ((Intervento presentato al 15. convegno European Meeting on Fire Retardancy and protection of Materials tenutosi a Berlin nel 2015.
Abstract:
Generally 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 e
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Keywords:
Flame retardancy; combustion; polymeric materials; polymers
Elenco autori:
J. Alongi, A. Di Blasio, F. Carosio, F. Cuttica, G. Malucelli
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