Passaro, Jessica (2021) DEVELOPMENT OF INNOVATIVE ELECTROSPUN COMPOSITES VIA SOL-GEL PROCESS. [Tesi di dottorato]

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Everything is made of something. Material science represents a branch of the natural sciences that becomes crucial in a world dominated by the importance of the choosing of suitable material. New materials are required for a wide variety of applications, which have to be extremely specialized and at the same time sustainable and economically affordable. High technology materials are required in every technological field, ranging from opto-electronics or bio-materials for medical application to adsorbent materials, and they must be designed or invented with great care. In this scenario the use of hybrid materials opens new routes to the production of innovative materials, whose properties can be tailored depending on the demands for the different applications. Their properties, in fact, can be chosen so as to obtain the best performances of the organic materials and the inherent stability of the inorganic ones. In particular, when the two phases are structured on a micro- and nanometer scale, the result can be considered as a new material with desired properties and a structure that can diverge from those of the starting components, so called: “composite material”. In the last decades, the use of composite hybrid materials has appeared crucial in many fields of application (e.g. building engineering, naval engineering, aerospace, high tech industries etc.); therefore there has been a intensive increase of interest in the chemical procedures needed for their fabrication. The sol–gel synthesis route has been extensively exploited since the 1970s, in combination with polymer synthesis methodologies, to produce not only inorganic materials (glassy or ceramic) but also hybrid organic/inorganic (O/I) composites in the form of aerogels, monoliths, coatings, fibers, and particles. The strategy takes advantage of the fact that almost all the important oxides MOn (where M is a metal or semimetal and n is not necessarily an integer), as well as many mixed oxides, have been prepared by the sol–gel process through reactions occurring at low temperatures starting from precursors that are commercially available at high purity. Sol–gel synthesis also allows the easy production of particles at the nanoscale, where materials properties change. Moreover, the sol–gel process has been extensively employed as the most important route in tailoring textile surfaces and in forming new hybrid inorganic–organic materials. This is because this process can modify the chemical nature of material surfaces and introduce ceramic phases into composites through chemistry. Very mild reaction conditions and low reaction temperatures are particularly useful for incorporating inorganic filler into organic materials or organic materials into inorganic matrices. The aim of this PhD project was to show the use of sol-gel chemistry in the development of innovative electrospun composites materials for relevant industrial applications. In this work the sol-gel methodology has applied to solve some technological problems inherent to the use electropsun polymer composites for industrial and environmental applications. The electrospun fibers have become very interesting topic for the researchers due to their applications ground, and they have been used in various research fields such as industrial, biomedical, electrical & electronics, environmental and energy resources due to their advanced properties and high potentials applications. However, these electrospun mats can show some limitations. For example, low resistance to organic solvents and thermal instability (i.e. shrinkage) of the fiber; or easy flammability of the polymer matrix that can significantly restrict the application fields of these materials. This latter issue, is of particular importance especially in the aerospace industry where the introduction of new material is dictated by specific regulation. In fact, often fire tests have to be passed by the new material, in order to guarantee public safety and be compatible with the aerospace application. Sol-gel methodologies can improve the fire behavior, the resistance to organic solvents and thermal stability of electrospun polymer composites through the use of sol-gel particles added into polymer solution. Therefore, this PhD thesis covered the series of experiments related to electrospun composites for aerospace and environmental applications. For this purpose, the incorporation of sol-gel nanoparticles with a biocompatible polymer to the formation of blended micro and nanofibers was started. The novelty of this work relies on the use of a biocompatible polymer namely poly (vinyl pyrrolidone) (PVP), which has a great interest in recent years. The successful fabrication of novel electrospun fibers using high content of silica sol-gel nanoparticles incorporated in PVP for aerospace applications it was reported. On the basis of characterizations results, it was concluded that PVP/SiO2Np electrospun composites are more suitable for sound adsorption properties, in the lower frequency range, as compared to other materials (e.g. glass wool) normally used as fuselage coating in aircrafts. Moreover, PVP/SiO2Np electrospun composites showed an excellent fire barrier property due to the presence of silica sol-gel nanoparticles. Regarding environmental applications, novel PVP-based ternary electrospun composite mats containing silica sol-gel nanoparticles (SiO2Np) and sol-gel TiO2-acetylacetonate (TiO2acac) microparticles (up to 90 µm) it is also reported. The presence of hybrid titania made this ternary electrospun composites a promising membrane for adsorption/degradation of water pollutant in absence of light irradiation. This work is structured in the following six chapters: In Chapter 1.0 the fundamentals of sol-gel chemistry, with particular attention to metal oxides particles such as silica and titania are reported. In Chapter 2.0 the main aspects of the electrospinning process and its applications in the industrial field are explained. In Chapter 3.0 it is reported the state of art of this work and its objectives. In particular the importance of using electrospun composite materials in aerospace or environmental applications is emphasized. The reason why it was decided to produce electrospun composite materials by incorporating sol-gel particles is then reported. In Chapter 4.0 materials and methods employed to produce and characterize the electrospun composite samples PVPSi and PVPSi_Tiacac are listed. In Chapter 5.0 and Chapter 6.0 are discussed the promising results obtained for both samples. In particular, the successful fabrication of novel polymer electrospun fibers using silica sol-gel nanoparticles for aerospace applications and also using titania particles for removal of pollutants are reported in detail.

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