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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)
Green DNA-based flame retardant coatings assembled through Layer by Layer
No full textFor the first time, DNA and chitosan are employed using the Layer by Layer technique in order to build green coatings exhibiting efficient flame retardant properties. DNA by its chemical structure can be considered as an intrinsically intumescent compound, since it contains precursor of phosphoricpolyphosphoric acid, a polyhydric char source (deoxyribose) and the nitrogen-containing bases that may release ammonia, acting as a blowing agent. When combined with chitosan, DNA layers promote the char formation of the former, by releasing phosphoric and polyphosphoric acid. Such bioarchitectures show an exponential growth as assessed by infrared spectroscopy and scanning electron microscopy. Very interestingly, these LbL assemblies are capable of i) reaching the selfextinguishment of cotton during horizontal flammability tests, ii) increasing the limit oxygen index up to 24% and iii) reducing the heat release rate by 40% during cone calorimetry test
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
Addition reactions on co-ordinated olefinic ligands. Part 8. Platinum(II) complexes of 1,1-dimethylallene and their reaction with amines. Molecular structure of the zwitterionic derivative dichloro-[1-(NN-diethylammoniomethyl)-2-methylprop-1-enyl](triphenylphosphine) platinum(II)
No full textSome new platinum(II) complexes of 1,1-dimethylallene (dma) of general formula cis-[PtCl2(dma)L] (L = PPh3, AsPh3, H2NC6H4Me-p, or SMe2O) have been prepared. They react with aliphatic and aromatic amines to give zwitterionic alkenyl derivatives of the type cis-[PtCl2(Me2C=CCH2NR1R 2R3)L], which on treatment with hydrogen chloride afford the ammonium salts [NR1R2R3(CH2CH=CMe2)]Cl. The structure of the alkenyl complexes has been confirmed by X-ray diffraction analysis in the case of the title complex. Crystals are triclinic, space group P1, with Z = 4 in a unit cell of dimensions a = 11.130(3), b = 18.887(5), c = 14.370(5) Å, α = 108.8(3), β = 90.1(2), γ = 95.1(2)°. The structure has been solved by Patterson and Fourier methods and refined by block-diagonal least-squares to R = 0.10 for 3 630 observed reflections. The σ-bonded alkenyl group is perpendicular to the metal co-ordination plane. A short intramolecular contact between the nitrogen and a chlorine atom suggest the existence of a hydrogen bond
Interferon-inducible genes, TNF-related apoptosis-inducing ligand (TRAIL) and interferon inducible protein 27 (IFI27) are negatively regulated in leiomyomas: implications for a role of the interferon pathway in leiomyoma development
No full textUterine leiomyomas are the most common tumors in the human female pelvis and the leading indication for pelvic surgery. Lack of understanding of the molecular pathogenesis of leiomyoma has put severe limitations on the availability of alternative treatments. Using an oligonucleotide micro-array-based hybridisation analysis we observed a group of genes with a broad range of functional activity differentially expressed in smooth muscle cells (SMC) derived from leiomyomas when compared to matched myometrial cells. Among them, two IFNα inducible genes, TRAIL and IFI27, were underexpressed in leiomyoma vs. myometrial cells. Expression levels of TRAIL and IFI27 were also measured in myometrial and leiomyoma cells by real-time quantitative PCR in basal condition and after IFNα stimulation. In both cell types, the transcription of the two genes resulted induced by IFNα but the IFI27 transcription stimulation was weaker in leiomyoma than myometrial cells whereas the TRAIL transcription stimulation resulted stronger in leiomyoma respect myometrial cells. Based on this finding and on previous observations we have hypothesized that a reduced response to IFNα stimulation might be involved in leiomyoma formation and growth
Serum concentrations of the adipocyte-derived hormone leptin are similar in women with and without endometriosis
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