Flame retardancy properties of nanoparticle-based fabrics

Different approaches have been employed to prepare nanoparticle-based fabrics in order to verify the flame retardant properties of the different materials. TOP-DOWN as impregnation and Layer by Layer assembly and BOTTOM-UP approaches as sol-gel processes have been investigated and developed to distribute several nanoparticle types on the textile surface. Electron microscopy has been used to check the obtained morphologies and the flame retardancy properties have been measured by cone calorimetry and vertical tests. Text Nowadays, 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 which the use of nanotechnology has been proved to give high durability for fabrics, improve the performance of fibers and create unprecedented functions, all these improvements obtained thank to the nano-sized of these fillers conferring both a large surface area-to-volume ratio and a high surface energy, obtaining a higher clay compatibility for fabrics and leading to an increase in durability of the final product [1]. The production of textile fabrics resistant to fire with high performances required for the human life is the main objective of this work. 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 millimeters, can be prepared with a new technique called layer-by-layer (LbL). A practical method for LbL assembly, first described by Iler in 1966[2], was developed in the early 1990s by the group of Decher[3]. Now, the technique can be tailored to multimaterial assembly of several compounds without special chemical modifications, thus enabling the production of multilayer films whose complex functionality gives access for example either to tailoring of surface interactions to improve physical and chemical properties or to fabrication of surface based devices.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. Due to the fact that during multilayer building-up there is an electrostatic attraction between each layer the resulting interactions are very strong. Moreover it’s important to underline that the process is independent of the substrate size and topology. This approach may allow the fabrication of products that are normally difficult or impossible to produce by conventional/traditional techniques. Experimental, results & discussion TOP-DOWN method consists in the immersion of the fabrics into an aqueous stable dispersion of nanoparticles followed by its final fixation using a thermal treatment. The textile material put in contact with the dispersion of nanoparticles absorbs them and, because of the formation of bindings according to fiber typology and nanoparticles, prevents any release. LbL approach consists in the use of positively and negatively charged silica nanoparticles of different size and functionalization to realize the suspensions, Textile fabrics were alternately immersed into the positive and negative suspensions to let nanoparticles adsorption onto the surface; after each immersion step fabrics were washed with deionized water to remove the nanoparticles in excess. Morphology and distribution of the coating were assessed by scanning electron microscope (SEM). 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 in conjunction with acidic or basic catalysts resulting in the formation of a three-dimensional molecular network following a BOTTOM-UP approach. The sol-gel process is conducted at a low temperature which also enables the incorporation of organic compounds into the inorganic structure without decomposition. The subsequent aging/drying step results in the production of powders, xerogels, aerogels, fibres, or coatings [4-5]. Furthermore, plasma technology was applied in this work in order to improve the performances of textile fabrics obtained by both sol-gel process and simply immersion of textile fabric in a nanoparticle dispersion. In fact, preliminary results demonstrated that plasma treatment is able to modify the surface properties of textiles giving a major number of activate sites. In this way, the following step of immersion into nanoparticle dispersion resulted more efficient: the flame retardancy properties of textiles previously treated by plasma are improved as compared to neat textiles. In order to measure the flame retardant properties of loaded textiles, vertical flame tests and cone calorimetry are used. References [1] Wong, Y. W. H.; Yuen, C. W. M.; Leung, M. Y. S.; Ku, S. K. A.; Lam, H. L. I., Selected Applications of Nanotechnology in Textiles. AUTEX Research Journal 2006, 6, (1), 1-8. [2] Iler, R. K., Multilayers of Colloidal Particles, J. Colloid Interface Sci. 1966, 21, 569 [3] Decher, G., Hong, J.-D., Buildup of Ultrathin Multilayer Films by a Self-Assembly Process: I. Consecutive Adsorption of Anionic and Cationic Bipolar Amphiphiles, Makromol. Chem., Macromol. Symp. 1991, 46, 321. [4] Brinker, C. J.; Scherer, G. W., Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing. Academic Press: San Diego, 1990. [5] Wright, J. D.; Sommerdijk, N. A. J. M., Sol-Gel Materials: Chemistry and Application. Gordon and Breach Science Publisher: Amsterdan, 2001.