Solvent-Free One-Pot Synthesis of Epoxy Nanocomposites Containing Mg(OH)2 Nanocrystal−Nanoparticle Formation Mechanism

[Image: see text] Epoxy nanocomposites containing Mg(OH)(2) nanocrystals (MgNCs, 5.3 wt %) were produced via an eco-friendly “solvent-free one-pot” process. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and thermogravimetric analysis (TGA) confirm the presence of well-dispersed MgNCs. HRTEM reveals the presence also of multisheet-silica-based nanoparticles and a tendency of MgNCs to intergrow, leading to complex nanometric structures with an intersheet size of ∼0.43 nm, which is in agreement with the lattice spacing of the Mg(OH)(2) (001) planes. The synthesis of MgNCs was designed on the basis of a mechanism initially proposed for the preparation of multisheet-silica-based/epoxy nanocomposites. The successful “in situ” generation of MgNCs in the epoxy via a “solvent-free one-pot” process confirms the validity of the earlier disclosed mechanism and thus opens up possibilities of new NCs with different fillers and polymer matrix. The condition would be the availability of a nanoparticle precursor soluble in the hydrophobic resin, giving the desired phase through hydrolysis and polycondensation

Hybrid Hemp Particles as Functional Fillers for the Manufacturing of Hydrophobic and Anti-icing Epoxy Composite Coatings

The development of hydrophobic composite coatings is of great interest for several applications in the aerospace industry. Functionalized microparticles can be obtained from waste fabrics and employed as fillers to prepare sustainable hydrophobic epoxy-based coatings. Following a waste-to-wealth approach, a novel hydrophobic epoxy-based composite including hemp microparticles (HMPs) functionalized with waterglass solution, 3-aminopropyl triethoxysilane, polypropylene-graft-maleic anhydride, and either hexadecyltrimethoxysilane or 1H,1H,2H,2H-perfluorooctyltriethoxysilane is presented. The resulting epoxy coatings based on hydrophobic HMPs were cast on aeronautical carbon fiber-reinforced panels to improve their anti-icing performance. Wettability and anti-icing behavior of the prepared composites were investigated at 25 °C and −30 °C (complete icing time), respectively. Samples cast with the composite coating can achieve up to 30 °C higher water contact angle and doubled icing time than aeronautical panels treated with unfilled epoxy resin. A low content (2 wt %) of tailored HMPs causes an increase of ∼26% in the glass transition temperature of the coatings compared to pristine resin, confirming the good interaction between the hemp filler and epoxy matrix at the interphase. Finally, atomic force microscopy reveals that the HMPs can induce the formation of a hierarchical structure on the surface of casted panels. This rough morphology, combined with the silane activity, allows the preparation of aeronautical substrates with enhanced hydrophobicity, anti-icing capability, and thermal stability

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an In Situ Process

Organic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an “in situ” sol–gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol–gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol–gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles

Structure and Bottom-up Formation Mechanism of Multisheet Silica-Based Nanoparticles Formed in an Epoxy Matrix through an in Situ Process

[Image: see text] Organic/inorganic hybrid composite materials with the dispersed phases in sizes down to a few tens of nanometers raised very great interest. In this paper, it is shown that silica/epoxy nanocomposites with a silica content of 6 wt % may be obtained with an “in situ” sol–gel procedure starting from two precursors: tetraethyl orthosilicate (TEOS) and 3-aminopropyl-triethoxysilane (APTES). APTES also played the role of a coupling agent. The use of advanced techniques (bright-field high-resolution transmission electron microscopy, HRTEM, and combined small- and wide-angle X-ray scattering (SAXS/WAXS) performed by means of a multirange device Ganesha 300 XL+) allowed us to evidence a multisheet structure of the nanoparticles instead of the gel one typically obtained through a sol–gel route. A mechanism combining in a new manner well-assessed knowledge regarding sol–gel chemistry, emulsion formation, and Ostwald ripening allowed us to give an explanation for the formation of the observed lamellar nanoparticles

Thermal and fire behavior of a bio-based epoxy/silica hybrid cured with methyl nadic anhydride

Thermosetting polymers have been widely used in many industrial applications as adhesives, coatings and laminated materials, among others. Recently, bisphenol A (BPA) has been banned as raw material for polymeric products, due to its harmful impact on human health. On the other hand, the use of aromatic amines as curing agents confers excellent thermal, mechanical and flame retardant properties to the final product, although they are toxic and subject to governmental restrictions. In this context, sugar-derived diepoxy monomers and anhydrides represent a sustainable greener alternative to BPA and aromatic amines. Herein, we report an “in-situ” sol–gel synthesis, using as precursors tetraethylorthosilicate (TEOS) and aminopropyl triethoxysilane (APTS) to obtain bio-based epoxy/silica composites; in a first step, the APTS was left to react with 2,5-bis[(oxyran-2-ylmethoxy)methyl]furan (BOMF) or diglycidyl ether of bisphenol A (DGEBA) monomers, and silica particles were generated in the epoxy in a second step; both systems were cured with methyl nadic anhydride (MNA). Morphological investigation of the composites through transmission electron microscopy (TEM) demonstrated that the hybrid strategy allows a very fine distribution of silica nanoparticles (at nanometric level) to be achieved within a hybrid network structure for both the diepoxy monomers. Concerning the fire behavior, as assessed in vertical flame spread tests, the use of anhydride curing agent prevented melt dripping phenomena and provided high char-forming character to the bio-based epoxy systems and their phenyl analog. In addition, forced combustion tests showed that the use of anhydride hardener instead of aliphatic polyamine results in a remarkable decrease of heat release rate. An overall decrease of the smoke parameters, which is highly desirable in a context of greater fire safety was observed in the case of BOMF/MNA system. The experimental results suggest that the eect of silica nanoparticles on fire behavior appears to be related to their dispersion degree

Non Monotonous Effects of Noncovalently Functionalized Graphene Addition on the Structure and Sound Absorption Properties of Polyvinylpyrrolidone (1300 kDa) Electrospun Mats

Graphene is an attractive component for high-performance stimuli-responsive or 'smart' materials, shape memory materials, photomechanical actuators, piezoelectric materials and flexible strain sensors. Nanocomposite fibres were produced by electrospinning high molecular weight Polyvinylpyrrolidone (PVP-1300 kDa) in the presence of noncovalently functionalised graphene obtained through tip sonication of graphite alcoholic suspensions in the presence of PVP (10 kDa). Bending instability of electrospun jet appears to progressively increase at low graphene concentrations with the result of greater fibre stretching that leads to lower fibre diameter and possibly conformational changes of PVP. Further increase of graphene content seams having the opposite effect leading to greater fibre diameter and Raman spectra similar to the pure PVP electrospun mats. All this has been interpreted on the basis of currently accepted model for bending instability of electrospun jets. The graphene addition does not lower the very high sound absorption coefficient, α, close to unity, of the electrospun PVP mats in the frequency range 200⁻800 Hz. The graphene addition affects, in a non-monotonous manner, the bell shaped curves of α versus frequency curves becoming sharper and moving to higher frequency at the lower graphene addition. The opposite is observed when the graphene content is further increased

Benefits and Harms of Lung Cancer Screening by Chest Computed Tomography: A Systematic Review and Meta-Analysis

PURPOSE This meta-analysis aims to combine and analyze randomized clinical trials comparing computed tomography lung screening (CTLS) versus either no screening (NS) or chest x-ray (CXR) in subjects with cigarette smoking history, to provide a precise and reliable estimation of the benefits and harms associated with CTLS. MATERIALS AND METHODS Data from all published randomized trials comparing CTLS versus either NS or CXR in a highly tobacco-exposed population were collected, according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Subgroup analyses by comparator (NS or CXR) were performed. Pooled risk ratio (RR) and relative 95% CIs were calculated for dichotomous outcomes. The certainty of the evidence was assessed using the GRADE approach. RESULTS Nine eligible trials (88,497 patients) were included. Pooled analysis showed that CTLS is associated with: a significant reduction of lung cancer-related mortality (overall RR, 0.87; 95% CI, 0.78 to 0.98; NS RR, 0.80; 95% CI, 0.69 to 0.92); a significant increase of early-stage tumors diagnosis (overall RR, 2.84; 95% CI 1.76 to 4.58; NS RR, 3.33; 95% CI, 2.27 to 4.89; CXR RR, 1.52; 95% CI, 1.04 to 2.23); a significant decrease of late-stage tumors diagnosis (overall RR, 0.75; 95% CI, 0.68 to 0.83; NS RR, 0.67; 95% CI, 0.56 to 0.80); a significant increase of resectability rate (NS RR, 2.57; 95% CI, 1.76 to 3.74); a nonsignificant reduction of all-cause mortality (overall RR, 0.99; 95% CI, 0.94 to 1.05); and a significant increase of overdiagnosis rate (NS, 38%; 95% CI, 14 to 63). The analysis of lung cancer-related mortality by sex revealed nonsignificant differences between men and women (P = .21; I-squared = 33.6%). CONCLUSION Despite there still being uncertainty about overdiagnosis estimate, this meta-analysis suggested that the CTLS benefits outweigh harms, in subjects with cigarette smoking history, ultimately supporting the systematic implementation of lung cancer screening worldwide

DEVELOPMENT OF INNOVATIVE ELECTROSPUN COMPOSITES VIA SOL-GEL PROCESS

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