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La sintesi sol-gel non-idrolitica e il metodo della sospensione reattiva: un approccio innovativo alla preparazione di materiali nanocompositi magnetici a matrice epossidica
No full textNell’ambito della scienza e dell’ingegneria dei materiali l’emergere delle nanotecnologie ha rappresentato una vera e propria rivoluzione per le possibilità sia di fabbricare nuovi materiali dalle interessanti e peculiari proprietà sia di modificarne le caratteristiche chimiche e fisiche in funzione del settore di applicazione e delle necessità tecnologiche e industriali.
Di particolare rilievo è l’apporto delle nanotecnologie al settore dei compositi, perché questi materiali sono ottenuti combinando tra loro materiali eterogenei.
La combinazione tra matrici polimeriche e particelle inorganiche di dimensioni nanometriche, pensate come fase dispersa di rinforzo, permette di ottenere sistemi ibridi di natura sia funzionale che strutturale in cui le proprietà meccaniche, termiche e di processabilità dei polimeri si uniscono a quelle ottiche, elettriche e magnetiche di nanofiller costituiti, generalmente, da ossidi inorganici.
Lo studio dei materiali nanocompositi a base polimerica apre la porta a numerosi sviluppi tecnologici e produttivi. Infatti le potenziali applicazioni riguardano diversi settori di attività, da quello alimentare a quello ambientale, da quello chimico a quello elettronico, da quello farmaceutico e biomedicale ai trasporti, dall’automotive al packaging.
In questo contesto si inserisce il presente progetto di ricerca che consisterà nella preparazione e caratterizzazione di nanocompositi basati sull’incorporazione di nanoparticelle di magnetite in matrici termoindurenti a base epossidica.
Per la sintesi delle nanoparticelle è stata presa in considerazione la tecnica sol-gel di tipo non-idrolitico (NHSG). La flessibilità di questo approccio sintetico è molto importante perhè sperimentalmente permette la formazione di un intorno chimico il più possibile compatibile con la caratteristiche organiche della resina epossidica.
Inoltre in una reazione NHSG, il solvente non solo reagisce con il precursore organometallico ma nello stesso tempo agisce come legante superficiale, permettendo il controllo della crescita delle nanoparticelle e la loro funzionalizzazione superficiale, senza il bisogno di ulteriori reagenti in soluzione.
Nella seconda fase sperimentale, tutti i componenti del composito sono miscelati nella sospensione liquida del solvente, e la formazione del nanocomposito è subordinata alla polimerizzazione del precursore monomero per dare la struttura polimerica, in cui la fase nanometrica dispersa è inglobata. A questo scopo è stata sviluppata una tecnica di preparazione in-situ che prevede un solo passaggio reattivo, ottimizzando così la dispersione e la distribuzione del nanofiller nella matrice polimerica.
La polimerizzazione produce una struttura tridimensionale in cui l’eccesso di solvente, che non ha reagito nella precedente reazione NHSG e ancora presente nella sospensione di magnetite, agisce sia come mezzo disperdente della sospensione di nanoparticelle che come sostanza reattiva nei confronti del monomero organica nella successiva reazione di polimerizzazione.
Questo doppio ruolo del solvente è alla base del metodo della sospensione reattiva, utilizzato nella preparazione del polimero caricato con nanoparticelle magnetiche.
Sperimentalmente anche le microonde sono state utilizzate per l’attivazione termica delle reazioni coinvolte, perchè negli ultimi anni sono apparse come una valida e promettente sorgente termica alternativa sia nella sintesi organica e inorganica che in altri campi della scienza dei materiali. I risultati sono stati confrontali con quelli ottenuti con un riscaldamento conduttivo tradizionale.
La caratterizzazione microscopica e spettroscopica delle nanoparticelle e quella dinamico-termico-meccanica dei nanocompositi ha permesso di correlare la microstruttura dei nanocompositi con le loro proprietà funzionali e strutturali.In the field of materials science and engineering the emergence of nanotechnologies represents a real revolution with regard to the possibility of producing new materials with attractive and distinctive properties and modifying their physical and chemical characteristics depending on technological and industrial requirements.
The contribution of nanotechnology to the area of nanocomposites is particularly important, since these materials are obtained combining heterogeneous materials.
The combination between a polymeric matrix and inorganic nanoparticles, as reinforcing phases, allows obtaining hybrid systems with both functional and structural characteristics. In these systems mechanical and thermal properties of polymers join optical, electric and magnetic features, usually characterizing the inorganic oxide nanofillers.
The research on polymeric nanocomposite materials permits remarkable developments in many technologic and productive fields. Indeed, potential applications of nanocomposites regard many industrial areas, such as alimentary, environmental, chemical, electronic, pharmaceutical, biomedical, automotive and packaging ones.
In this context the present research work finds its justification: in details it consisted in the preparation and characterization of nanocomposites based on the incorporation of magnetite nanoparticles in thermosetting epoxy-based polymer matrices.
Non-hydrolytic sol-gel route (NHSG) was used for the synthesis of targeted nanoparticles. The flexibility of this synthetic approach is very important because experimentally it allowed the formation of the chemical environment as much as possible compatible with the organic characteristics of the epoxy resin.
Indeed in the NHSG reaction, the solvent not only reacts with the organometallic precursor but at the same time it acts as a surface ligand, allowing the control of the nanoparticles growth and the functionalization of the nanoparticles surface without the need of any additional reagents in the solution.
In the second experimental phase, all the components are mixed in the liquid solvent suspension, and the development of the nanocomposite is related to the polymerization of the monomer precursors to get a polymer matrix, within which the dispersed phase is frozen.
In situ preparation technique was developed for one step nanocomposites synthesis, optimizing nanofiller distribution and dispersion into the polymer matrix.
The polymerization produces a three-dimensional network in which the excess solvent, unreacted in the magnetite suspension, acts as suspending medium of the nanoparticles suspension and reactive substance towards organic monomers in the subsequent polymerization reaction.
This double role of the solvent is the basis of the “reactive suspension method”, used to prepare magnetic nanoparticles filled polymer.
Microwaves was also used for the activation of the reactions involved, since during the last decades it appeared as a promising alternative energy source in organic as well as inorganic syntheses and in different other fields of materials science. A comparison with traditional heating techniques was however performed.
Microscopic, spectroscopic and structural characterization of nanoparticles and the dynamic, thermo-mechanical analysis of nanocomposites were performed with the specific aim to correlate the composite microstructures with their functional and structural properties
Non-hydrolytic sol–gel synthesis and reactive suspension method: an innovative approach to obtain magnetite–epoxy nanocomposite materials
No full textInnovative magnetite–epoxy nanocomposites were prepared starting from magnetite nanoparticles suspended in alcoholic or amino reactive solvents, synthesized by non-hydrolytic sol–gel process from iron (III) acetylacetonate. The obtained suspensions, also synthesized using microwave heating, were mixed with an epoxy monomer (bisphenol A diglycidyl ether, DGEBA), and the formulations were subsequently cured. The thermally activated ring-opening polymerization produced a three-dimensional network in which the suspending medium was covalently linked to the epoxy network according to the chain or step polymerization mechanisms during the cross-linking reaction. This synthetic strategy allowed to obtain nanocomposites in which the nanoparticles play an active role in the polymeric structure, affecting the structural (mechanical and thermal) and functional (magnetic) properties of the final system. The presence of magnetite nanoparticles in the composite resulted in distinct reinforcing effects, acting as rigid filler and/or as cross-linking point, depending on the different chemical environment at the nanoparticle–polymer interphase
Durability of SiO2-TiO2Photocatalytic Coatings on Ceramic Tiles
No full textThe aim of this investigation was the evaluation of the durability of photocatalytic sol–gel coating deposited on industrial
ceramic tiles. In particular, the effect of substrate roughness on photocatalytic performance before and after different aging tests
was determined. The results showed that the photodegradation process was clearly affected by the surface roughness of the substrate.
In particular, the smoother surface had a higher photocatalytic activity, faster hydrophilicity but a lower durability to abrasion
with respect to the matt surface
Antibacterial and Self-Cleaning Coatings for Silicate Ceramics: A Review
No full textThe development of advanced materials is increasingly leading to integration of functions
into materials and components. This drive in technological innovation is strongly felt in many
traditional fields, like textiles or ceramics. Over the last twenty years, the so-called "traditional"
ceramics industry for tile production has undergone a profound technological reorganization, both in
production technologies and automation of the different production phases, but new products and
possible new applications are still needed, thereby opening up new markets.
In this paper a critical review of the industrial and scientific effort to obtain antibacterial and selfcleaning
coating for ceramic tiles is reported. The main patents and scientific papers in the field are
reported as well as some final results obtained by the authors on the evaluation of the durability of
photocatalytic coating deposited on industrial ceramic tiles
Accurate Energy Consumption Prediction for Cleaner Fused Deposition Modeling (FDM)
No full textAdditive Manufacturing (AM) has revolutionized rapid prototyping and mechanical production in a range of different fields, including e-mobility and aerospace, as well as personalized medical devices. In an era dominated by increasing environmental awareness, requirements to reduce CO2 emissions and climate change associated with manufacturing energy consumption are paramount, further to the development of clean energy systems. With the aim of achieving cleaner production, accurate prediction of energy consumption during additive manufacturing processes is the first step in obtaining tangible reductions in manufacturing-related emissions. Energy optimization not only promotes environmental sustainability, but also gives an additional competitive advantage to additive manufacturing processes in today's market, bringing considerable benefits to these technologies. The present work provides an in-depth study into energy consumption during additive manufacturing, applying a novel and highly accurate methodology for evaluating electrical energy usage during Fused Deposition Modeling (FDM) as a test case for applying this approach to a wider range of additive manufacturing technologies such as Laser Powder Bed Fusion (LPBF), Selective Laser Sintering (SLS), Stereolithography (SLA) and others. FDM is renowned for its popularity in multiple sectors due to its versatility in achieving customized results at low cost with relative ease and safety. To date, the vast majority of scientific literature relating to additive manufacturing has focused on the mechanical properties of printed objects, topology optimization, support structures and energy consumption. Investigations into the energy consumption during additive manufacturing have mainly focused on the measurement and estimation of total energy consumption over the entire printing process based on general considerations and, in some cases, machine learning algorithms. The present study distinguishes itself from previous works by providing precise and detailed analysis of each individual step in the printing process. Experimental evaluation of each machine action was performed, allowing translation of the machine instructions (G-code) employed for printing an object into distinct energy contributions for each action during the process. This approach makes it possible to estimate the total energy consumption very accurately as the sum of all energy contributions, allowing an additional energy optimization parameter to be introduced. Such a detailed analysis allows the main drivers of energy consumption during FDM to be identified, leading to relatively simple solutions to dramatically reduce energy consumption during the process. The presented approach was developed as a test bed for detailed evaluation of energy consumption during additive manufacturing, with potential for application over a wide range of different technologies with similar approaches
Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles
Full text linkThe limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles
Influence of process parameters on temperature field and residual strain in FFF-printed parts
No full textAmongst the low-cost additive manufacturing processes available, fused filament
fabrication (FFF) is one of the most widely used configurations not only for prototypes but
also for functional components. Despite such extensive uptake, there are few comprehensive
numerical tools available to aid in the design and structural optimization of components obtained
with this technology. To address this shortfall, the present work embraces a methodology
for thermal and structural simulation of the filament deposition process, with particular emphasis
on the influence of process parameters and deposition strategy on the resulting residual
stresses and distorsion to allow optimization of outcomes in terms of structural integrity and
build accuracy. The developed finite elements simulation considers both material properties
and process parameters, as well as environmental conditions. Comparison between simulation
outcomes, thermal measurements and optical profiler acquisitions confirms good alignment,
suggesting that such an approach is likely to prove valuable in improving process outcomes
Acrylate-based silver nanocomposite by simultaneous polymerization-reduction approach via 3D stereolithography
No full textThis study demonstrates the feasibility of printing 3D composite objects based on acrylic photocurable formulations, containing in situ generated silver nanoparticles (AgNPs). In fact, the laser radiation of a commercial stereolithography printer was used to both selectively cure, layer by layer, the acrylic resin and to reduce a silver salt to AgNPs (having dimensions ranging between 10 and 25 nm). The most suitable formulation was developed using silver acetate to obtain 1% by weight of AgNPs in the final 3D structures. The presence of the filler causes an increase in the physical and mechanical properties of the samples that become significantly stiffer and stronger than the pristine matrix. Antibacterial properties and electrical conductivity measurements performed on the printed samples gave promising results for the use of the developed formulation for the building of 3D polymeric structures with improved multifunctional properties
Effects of nano-silica treatment on the flexural post cracking behaviour of polypropylene macro-synthetic fibre reinforced concrete
Full text linkThe effects of a surface nano-silica treatment, carried out with the sol gel method, on the post-cracking behaviour of polypropylene macro-synthetic fibre reinforced concrete are experimentally investigated here for the first time. The present study extends previous experimental and analytical investigations on the corresponding improvement of the bonding properties of a single synthetic macro fibre, performed by means of pull-out test. Scanning electron microscopy is adopted here to explore the changes in the morphological characteristics of polypropylene macro synthetic fibres, before and after mixing in the concrete matrix. A comparative analysis, carried out with three-point bending tests on notched beam specimens, is used to evaluate the effects of the nano-silica treatment on the concrete post cracking behaviour. Increase in concrete toughness and residual post-cracking strength is recorded due to improved adhesion between fibres and the concrete matrix and to the consequent increase in the frictional shear stress generated during the fibre pull-out, especially for large crack opening. As shown by the SEM images, the nano-treatment favours the bonding of the concrete hydration products to the surface of the treated fibres, thus ensuring strengthening of the interface transition zone. In addition, the links between the nano-silica coating and the concrete hydration products improve the frictional shear stress and thus the overall energy absorption, as denoted by the increase of the residual strength during the post-cracking phase
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