Data di Pubblicazione:
2015
Citazione:
Layer by Layer Assembly of fire proofing coatings for textiles, films and foams / J. Alongi, F. Carosio, G. Malucelli. ((Intervento presentato al 7. convegno Asia-Europe Symposium on Processing and Properties of Reinforced Polymers - Cost Flaretex Workshop “Advanced in Flame Retardancy of Polymeric Materials tenutosi a Madrid nel 2015.
Abstract:
This paper presents the recent achievements by our research group on fire retardancy based on surface modification of textiles, films and foams achieved through layer by layer assembly. Such approach will be discussed through selected case studies involving the deposition of coatings with different fire proofing mechanisms (i.e. inorganic thermal shielding barriers or micro-intumescent coatings) [1-3].
Layer by Layer (LbL) assembly is a step by step deposition technique that allows the molecularly-controlled fabrication of surface-confined nanostructured materials. The layer by layer has been discovered by Iler in 1966 and reinvented by the group of Decher in early 90s [4]. It simply consists in an alternate adsorption of chemical species on the selected substrate due to an interaction (e.g. the electrostatic interaction that occurs in between positively and negatively charged species); because of unlimited possibilities of materials choice and deposition parameters it is possible to target a wide range of application fields including flame retardancy. The first papers that showed the potentialities of LbL were focused on the LbL assembly of totally inorganic or hybrid organic-inorganic coatings made, as an example, of oppositely charged silica nanoparticles or polyelectrolytes coupled to zirconium phosphate nanoplatelets [5,6]. The same inorganic architectures can be also assembled by employing spray-assisted LbL depositions; in a direct comparison with dipping, only the horizontal spray allows the assembly of a very homogeneous coating that subsequently leads to the best fire retardant properties [7,8]. Pursuing this research, the technique was extended to other substrates, such as rigid plastics [9, 10], and, mostly important, the coating composition and fire proofing action were directed toward the intumescence field [11-14]. Seeking for an intumescent-like coating capable of protecting both synthetic and natural fabrics, the Layer by Layer has been exploited for building coatings with enhanced char forming ability based on polyacrylic acid and ammonium polyphosphate [12,13]. The deposited coatings were able to protect both cotton and PET fabrics, preventing flame spread in flammability tests and reducing the heat release rate and total heat release when tested by cone calorimetry under different irradiative heat fluxes (namely, 25, 35 and 50 kW/m2). Our research group has recently proposed the use of deoxyribonucleic acid (DNA) coupled with chitosan in order to assembly novel and environmentally sustainable LbL coatings.[15] In particular, the DNA macromolecule has been demonstrated to represent an all in one intumescent system that, when applied to cotton, is capable of extinguishing the flame during horizontal flammability tests, increase cotton LOI values as well as to strongly reduce the combustion rate in cone calorimetry tests. DNA has been also deposited in a 100 μm coating on ethylene vinyl acetate (EVA) copolymers and compared with its bulk addition via melt blending. The collected results have shown that the DNA coating can greatly delay the ignition of the copolymer when tested by cone calorimeter (35 kW/m2 heat flux), increasing the time to ignition by 228s (+380%), while the bulk addition led to an anticipation of combustion. A similar effect has been observed under a heat flux of 50 kW/m2 with an increase of 102s (+625% with respect to pure EVA). [16] As far as foamed materials are concerned, a LbL architecture containing poly(acrylic acid), chitosan, and poly(phosphoric acid) has been recently assembled; the deposited coating was able to adapt to flame or heat exposure and to evolve into thermally stable carbon-based structures capable of a 55% reduction in heat release rate during cone calorimetry tests unde
Tipologia IRIS:
14 - Intervento a convegno non pubblicato
Keywords:
Flame retardancy; combustion; textiles; polymers; Layer by Layer assembly
Elenco autori:
J. Alongi, F. Carosio, G. Malucelli
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