Adhesion is attracting increasing interest in the aerospace field since composite materials have become, together with aluminium alloys, the main structural materials for aircraft primary structures. Nano-graphite was demonstrated to improve the mechanical performance of several polymers used as composite matrices. In this work Single Lap Joints (SLJs) of unidirectional composite laminates were manufactured, tested and simulated: two families of specimens were investigated and compared, one joined using conventional epoxy resin, the other joined with an adhesive obtained mixing the same epoxy resin with nano-graphite particles. The dispersion of expanded and sonicated graphene stacks (EGS, 3% wt) in the epoxy matrix was obtained by the swelling method, dispersing first the filler in acetone and then mixing it with the epoxy oligomers. Finally the solvent was evaporated and the filler-epoxy mixture was degassed under vacuum before adding an amine curing agent in a stoichiometric quantity. The research demonstrates the superior mechanical properties of the adhesive with the addition of nano-graphite through experimental characterization of its behaviour in terms of strength and energy absorption. Finite element numerical simulations have been carried out using the Cohesive Zone Model (CZM) element, obtaining as parameters the maximum shear stress and the critical fracture energy for the two adhesives. A good correlation between numerical and experimental results has been achieved and the criteria for developing reliable and accurate non-linear models of the adhesive failure have been established.

ABSTRACT: The aim of this work is to characterize the rheological and permeability behavior of nanocomposites based on amorphous poly(ethylene terephthalate) (PETg) and organically modified montmorillonites (omMMT), obtained by melt intercalation. The use of PETg instead of semicrystalline PET is believed to reduce the risks associated to organic modifier degradation during processing at high temperatures. X-ray and transmission electron microscopy analysis performed on the PETg nanocomposites showed that processing for long time at temperatures lower than melting of semicrystalline PET allowed to obtain a partially intercalated structure with some degree of exfoliation. The rheological behavior of PETg nanocomposites was studied as a function of shear rate in a cone– plate rheometer in order to correlate the viscosity with the aggregation state of omMMT. A simple model accounting for an apparent increase of rheological units size, associated with the intercalation of PETg macromolecules into omMMT galleries, is proposed. The glass transition temperature, Tg, as a function of the volume fraction of omMMT content of the nanocomposite, was measured using differential scanning calorimetry. Finally, the water vapour permeability of PETg nanocomposites was correlated to the volume fraction of the impermeable inorganic part of the omMMT.

This study is aimed at the synthesis of antimicrobial hydroxyapatite (HAP)‐based composites for dental application by stereolithography (SLA). A micron‐sized commercial HAP was modified by methacrylate and quaternary ammonium salt, and, then, it was used in different amounts (namely 2.5, 5, and 10 wt%) as filler for a photocurable custom made resin for SLA. Thermal stability, microstructure, and particles size of the pristine (HAP) and modified HAP (mHAP) were evaluated by thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and particle size analyser (CILAS). The suitability of each formulation for stereolithography process was assessed by measuring viscosity, degree of conversion (DC%) by Fourier transform infrared spectroscopy (FTIR), glass transition temperature, and thermal stability. Photo‐cured specimens for physical, mechanical, and antimicrobial testing were built by SLA. The flexural strength of the samples was measured using a 3‐point bending test method, and the fractured surface was analysed by scanning electron microscopy (SEM). The antimicrobial activity of samples was investigated against some standard microorganisms (Staphylococcus aureus, Escherichia coli, and Candida albicans), as representative Gram positive and Gram negative bacteria and fungus, respectively. The flexural strength increased with a filler content up to 5% and slightly decreased for higher content. SEM analysis confirmed the presence of uniformly distributed HAP. The incorporation of mHAP reduced the bacterial and fungal growth in dose‐dependent manner in comparison with the neat samples. Finally, a prototype of dental bite was built by SLA.

The strong influence of graphite oxide (GO) nanofiller on the glass transition temperature (Tg) of epoxy resins, generally attributed to restricted molecular mobility of the epoxy matrix by the nanofiller or to the crosslinking of GO layers via the epoxy chains, is investigated. The study confirms that large increases of the glass transition temperature of the nanocomposite can be observed in presence of GO. However, similar Tg increases are observed, when the filler is a high-surface-area graphite (HSAG), lacking oxidized groups. Moreover, these Tg differences tend to disappear as a consequence of aging or thermal annealing. These results suggest that the observed Tg increases are mainly due to a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and diamine), rather than to reaction of the epoxide groups with functional groups of GO. This hypothesis is supported by investigating the catalytic activity of graphite-based materials on reactions between analogous monofunctional epoxide and amine compounds

This article compares the catalytic activities of oxidized carbon black (oCB) and graphene oxide (eGO) samples on the kinetics of a reaction of diglycidyl ether of bisphenol A (DGEBA) with a diamine, leading to crosslinked insoluble networks. The study is mainly conducted by rheometry and Differential Scanning Calorimetry (DSC). Following the same oxidation procedure, CB samples are more efficiently oxidized than graphite samples. For instance, CB and graphite samples with high specific surface areas (151 and 308 m2/g), as oxidized by the Hummers’ method, exhibit O/C wt/wt ratios of 0.91 and 0.62, respectively. Due to the higher oxidation levels, these oCB samples exhibit a higher catalytic activity toward the curing of epoxy resins than fully exfoliated graphene oxide.

Abstract: In materials research, the development of polymer nanocomposites (PN) is rapidly emerging as a multidisciplinary research field with results that could broaden the applications of polymers to many different industries. PN are polymer matrices (thermoplastics, thermosets or elastomers) that have been reinforced with small quantities of nano-sized particles, preferably characterized by high aspect ratios, such as layered silicates and carbon nanotubes. Thermal analysis (TA) is a useful tool to investigate a wide variety of properties of polymers and it can be also applied to PN in order to gain further insight into their structure. This review illustrates the versatile applications of TA methods in the emerging field of polymer nanomaterial research, presenting some examples of applications of differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical thermal analysis (DMTA) and thermal mechanical analysis (TMA) for the characterization of nanocomposite materials.

tWater vapour flux into the porous microstructure represents a crucial factor capable of influencingthe degradation of porous materials. This fact is of utmost importance especially considering materialsinstalled in cultural heritage. The necessity to preserve stone artworks pushes to perform surface pro-tective coatings that create an intermediate sacrificial layer between stone and the environment. Highhydrophobicity and high permeability of water vapour must be one of the most important requirements ofa protective film. These features depend upon the nature of coatings as well as the porous microstructures.In order to control coatings’ effects and their influence on final water vapour permeability (ı) properties,a new modelling procedure has been proposed. The study is conducted on a porous limestone, namelyPietra Leccese, which is being largely used for historical constructions in Mediterranean. The averageexperimental water vapour permeability ıexpis 4.83 × 10−4and 3.86 × 10−4(g/m d Pa) respectively foruntreated and treated PL stone, while the average model prediction ıIFUis 4.87 × 10−4and 3.77 × 10−4(g/m d Pa) respectively for untreated and treated PL stone. The good agreement between experimen-tal and calculated data shows that the proposed modelling procedure could represent a good tool fordesigning and controlling protection activity on cultural heritage.

A significant effort was directed to the synthesis of graphene stacks/epoxy nanocomposites and to the analysis of the effect of a graphene precursor on cure reaction of a model epoxy matrix. A comparative thermal analysis of epoxy resins filled with an exfoliated graphite oxide eGO were conducted. The main aim was to understand the molecular origin of the influence of eGO on the Tg of epoxy resins. The higher Tg values previously observed for low curing temperatures, for epoxy resins with graphite-based nanofillers, were easily rationalized by a catalytic activity of graphitic layers on the reaction between the epoxy and amine groups of the resin, which leads to higher crosslinking density in milder conditions. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based filler was performed by isothermal DSC measurements. The DSC results showed that the addition of graphite based filler greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an auto-catalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller.

Novel photopolymerizable formulations, able to photopolymerize with a dual mechanism (cationic and radical), were developed and characterized as potential resins for stereolithography (SL) process. The influence of the presence of organically modified boehmite nanoparticles on the properties of the photopolymerizable mixtures was also analyzed. The main important properties required to a liquid SL resin are an high reactivity and a low viscosity. All the experimental formulations produced, even in presence of boehmite nanoparticles, are able to satisfy these significant requirements. Physical-mechanical and thermal properties of the photocured samples, obtained starting from the experimental formulations, were finally measured. The cured nanocomposite bars show an high transparency, confirming the good dispersion of the nanofiller in the polymeric matrix and posses improved glass transition temperature and mechanical performances, compared to the unfilled system and to a commercial stereolithographic resin. This result suggest the possibility to use the novel nanofilled photopolymerizable suspensions in the stereolithographic apparatus to build, not only esthetical, but also functional prototypes.

The need for reconstructing complex bone defects in the maxillofacial region as a result of trauma, tumor surgery or congenital malformation has become a hot topic in the field of tissue engineering. Tools such as 3D computer aided design (CAD) systems and rapid prototyping (RP) machines can be exploited to fabricate custom made bone scaffolds. RP techniques allow the construction of complex physical models based on 3D clinical images elaborated by suitable software and CAD systems. Hydroxyapatite (HA) is one of the most commonly used materials for bone reconstruction because of its close similarity in composition to human bone and teeth. Thus, producing a custom-made scaffold from a ceramic material directly by RP represents an exciting challenge. The aim of this paper is the development of a suspension of HA powder dispersed in an UV curable epoxy based resin, suitable for stereolithography (SLA). The influence of different HA concentrations within the ceramic suspension on the kinetics of the photochemical reaction was firstly investigated. The rheological behavior of the same ceramic suspensions was also analyzed by verifying the effect of HA on the viscosity and the stability of the suspensions as a function of the shear rate and the time from preparation. After the selection of a suitable suspension, simple green ceramic bars built by stereolithography and sintered with an appropriate thermal cycle, were built and characterized, showing good mechanical properties. A complex prototype, starting from a CAD model, was finally built by a SLA apparatus

This work is aimed to study the diffusion process in oriented nanocomposites, characterized by the presence of permeable lamellar stacks, by FEM analysis. To this purpose, a geometrical model, based on a random distribution of non-interpenetrating stacks, was used to calculate the coefficient of diffusion. The main novelty of the developed analysis is that each nanofiller particle is made by a stack of individual platelets, separated by galleries of varying thickness. Consequently, the nanofiller particles are not considered to be completely impermeable to the diffusing species, thus allowing to account for mass transport between stacks, as well as within each stack. Simulations were run at different nanocomposites morphologies, varying nanofiller volume fraction, orientation angle, lamellar gallery thickness and number of platelets in each stack. An analytical model was developed, which is able to predict the evolution of coefficient of diffusion as a function of the four morphologic features of the nanocomposites. The developed model can account for the multi scale diffusion mechanism, showing a very good agreement with the simulation data. The developed analytical model was used to estimate the orientation angle of graphene stacks in epoxy matrix by comparison with experimental permeability data.

Abstract This paper is aimed to study the morphology of intercalated nanocomposites, by coupling experimental permeability data with different analytical models. X-Ray diffraction provided the reference morphological features of the nanocomposite, including gallery thickness and aspect ratio of the lamellar stacks. Afterward, the water permeability of two intercalated nanocomposites was used for the calculation of the nanofiller aspect ratio, following different approaches. The obtained results indicate that an assumption of impermeable stacks involves a significant over- estimation of the nanofiller aspect ratio. Further, when the morphological features determined in the assumption of impermeable particles are used for estimation of the nanocomposite diffusivity by the use of the Fricke model, results do not show a satisfactory agreement with experimental data. On the other hand, fitting experimental permeability data with an analytical model accounting for intra-stack diffusion provided an estimation of the nanofiller aspect ratio in excellent agreement with that obtained by XRD. Further, applying the Fricke equation with the morphological features determined by the permeable stack model, an excellent agreement to the experimental data was obtained. The results indicate the relevance of intra-stack diffusion in intercalated nanocomposite, and the need to account for it when modeling mass transfer in nanocomposites.

Graphene stacks/epoxy nanocomposites were produced and characterized in order to analyse the effect of different graphene precursors on cure reaction of a model epoxy matrix. A kinetic analysis of the cure mechanism of the epoxy resin associated to the catalytical activity of the graphite based fillers was performed by isothermal DSC measurements. The DSC results showed that the addition of all graphite based fillers greatly increased the enthalpy of epoxy reaction and the reaction rate, confirming the presence of a catalytic activity of graphitic layers on the crosslinking reaction between the epoxy resin components (epoxide oligomer and di-amine). A kinetic modelling analysis, arising from an autocatalyzed reaction mechanism, was finally applied to isothermal DSC data, in order to predict the cure mechanism of the epoxy resin in presence of the graphite based nanofiller.

The aim of this paper is a comparison of the effectiveness of different macrocharacterization techniques for the prediction of the degree of dispersion and intercalation of bidimensional nanofillers in an amorphous thermoplastic matrix. Organically modified montmorillonites (omMMT) were used as bidimensional nanofillers, whereas amorphous polyethylene-terephthalate copolymer (PETg) was used as matrix. Wide angle xray diffraction analysis showed no relevant difference between the samples processed at different temperatures, all characterized by a predominantly intercalated structure. On the other hand, transmission electron microscopy (TEM) analysis showed the presence of some degree of exfoliation, as well as the presence of lamellar stacks of different thickness. The aspect ratio of lamellar stacks was estimated by means of rheological, mechanical, and gas permeability analysis. All techniques provided values which are in quite good agreement with TEM analysis. Furthermore, all techniques were able to capture the increase in the lamellar stack aspect ratio with decreasing processing temperature.

An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings of stone substrates. The kinetics of the radical photopolymerization mechanism induced by UV radiations in presence of a suitable photoinitiator was studied by a calorimetric analysis by varying the atmosphere (oxygen or nitrogen) and the composition of the mixtures, in particular of the UV photoinitiator. The reactivity, expressed in terms of both heat developed and rate of reaction, was generally found to decrease when the photopolymerization was carried out in air, due the inhibiting action of the oxygen towards the free radical polymerization. The addition of a proper thiol to the acrylic modified resin was found to reduce the adverse effect of oxygen on the kinetic reaction and on the degree of conversion. This result allowed to reduce the content of the photoinitiator and to increase the content of the siloxane in the acrylic based mixtures. The effect of the change of the composition of the formulations on the kinetic behaviour of the acrylic based resins was also analysed by calorimetric analysis. Calorimetric experimental data were fitted to a simple kinetic model for radical photopolymerization reactions. Finally, a proper relationship between the glass transition temperature and the total extent of reaction was applied to the experimental data. A good agreement between the experimental data and both the theoretical models was generally found.

In this work glucose (G), α-cyclodextrin (α-CD) and sodium salt of carboxymethyl cellulose (CMCNa) are used as dispersing agents for graphene oxide (GO), exploring the influence of both saccharide units and geometric/steric hindrance on the rheological, thermal, wettability and electrochemical properties of a GO/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) nanocomposite. By acting on the saccharide-based additives, we can modulate the rheological, thermal, and wettability properties of the GO/PEDOT:PSS nanocomposite. Firstly, the influence of all the additives on the rheological behaviour of GO and PEDOT:PSS was investigated separately in order to understand the effect of the dispersing agent on both the components of the ternary nanocomposite, individually. Subsequently, steady shear and dynamic frequency tests were conducted on all the nanocomposite solutions, characterized by thermal, wettability and morphological analysis. Finally, the electrochemical properties of the GO/ PEDOT composites with different dispersing agents for supercapacitors were investigated using cyclic voltammetry (CV). The CV results revealed that GO/PEDOT with glucose exhibited the highest specific capacitance among the systems investigated.

The influence of different graphite-based nanofillers on epoxide ring opening reactions, as induced by amines for diglycidyl ether of bisphenol A (DGEBA), is studied. Direct kinetic studies, with full chemical characterization and quantitative evaluation of the low molecular mass products, for reactions of DGEBA with primary and secondary monoamines as well with alcohols, are conducted. Moreover, the kinetic behavior of a commercial epoxy resin based on DGEBA and a diamine, leading to crosslinked insoluble networks, is studied by indirect methods, such as differential scanning calorimetry (DSC) and rheometry. The reported results show a relevant catalytic activity of graphene oxide on epoxy resin crosslinking by amines. For instance, for a graphene oxide content of 3 wt%, the exothermic crosslinking DSC peak is shifted (upon heating at 10 C min1) from 113 C down to 96 C, while the gel time at 50 C is reduced by a factor of 2.5. This behavior is due to the ability of graphene oxide to catalyze primary amine–epoxy, secondary amine–epoxy and mainly hydroxyl–epoxy additions.

A study was made of the effects of calcarenitic stone particles, known as pietra gentile, inclusions on the rheological behavior of photopolymerizable siloxanemodified acrylic formulations, intended as protective for the calcarenitic stone structures. Different amounts of stone particles (ranging from 15% wt to 35% wt) were added to the modified acrylic mixture to achieve a natural color matching for calcarenitic stone substrates. The presence of stone particles was expected to modify the rheological behavior of the protective formulation. Therefore, the viscosity of the mixtures was studied at ambient temperature as function of the shear rate and the solid volume fraction. A relationship was obtained to predict the modification of viscosity of each formulation as a consequence of inclusions of different amounts of stone.

An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings. The kinetics of the radical photopolymerization mechanism induced by UV and visible radiations in presence of suitable photoinitiators was studied by a calorimetric analysis by varying the testing conditions (temperature, light power emission, atmosphere). The reactivity, expressed in terms of both heat developed and rate of reaction, was generally found to decrease when the photopolymerization was carried out in air, due the inhibiting action of the oxygen towards the free radical polymerization. The addition of both a silane coupling agent or a high molecular weight polysiloxane monomer to the acrylic resin was found to reduce the heat of reaction. Experimental data were fitted to a kinetic model to quantify the effects of light intensity and temperature on reaction rates and extent of reaction. A good agreement between the experimental data and the theoretical model was generally found.

A deep study on the possibility to increase the quality of the dispersion of organically modified Boehmite nanoparticles into photo-polymerizable methacrylic-siloxane monomers, to be used as coatings, was conducted using unconventional indirect analyses. The nanocomposite were produced using two different procedures, starting from the conventional ‘‘solvent dispersion method.’’ The two procedures used differ for the technique used to obtain the dispersion of Boehmite, i.e., sonication or magnetic stirring and for the time used in each procedure. The efficiency of each method of preparation of nanostructured systems was analyzed, both in the liquid (uncured) and ultraviolet (UV) cured state. First, dynamic light scattering and rheological measurements were performed on the liquid suspensions, supplying experimental data used in proper theoretical models to estimate the dimensions and distribution of Boehmite particles. The suspensions obtained with the two different methods were, then, UV cured obtaining thin and thick films, on which scanning electron microscopy and transmittance measurements were performed.

An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was firstly carried out. The O-I hybrid first proposed in this study was obtained from organic precursors with a high siloxane content, which are mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silica nanodomains dispersed within the crosslinked organic phase, as a result of the sol-gel process. The first part of the research deals with the selection and optimization of suitable systems through appropriate chemical modifications, in order to ensure that curing reactions can be carried out at room temperature and in the presence of UV radiation. Firstly, the silica domains are formed, followed by crosslinking reactions of the acrylic groups in the oligomer via a free radical polymerization. The crosslinking reaction was controlled with the use of a suitable photoinitiator. Most of the experimental work was devoted to understanding the morphology of the hybrid system, both in uncured and cured states, and to assess its final thermal and optical properties, using different experiential techniques.

The work is addressed to investigating the potentiality of calcination of organic-inorganic (O-I) hybrids as a feasible approach to produce silica particles, at mild temperature conditions and with tailored morphology. Two different innovative hybrid systems were obtained through sol-gel process with a siloxane content ranging from 6 to 26wt%. The two O-I hybrids differed for i) the organic matrix (methacrylic or epoxy), ii) its crosslinking mechanism (photopolymerization for methacrylic systems or thermal cold-cure for epoxy systems) and iii) the rate ratio between solgel and crosslinking reactions. Different characterization techniques were used to understand the effect of composition and curing method on the morphology of the silica obtained from O-I hybrids after calcination in air. The results confirm the morphology and properties of silica particles in terms of surface and porosity may be tailored over a wide range by varying the composition and nature of organic and inorganic precursors of hybrids

Bioactive food-preserving materials are based on the use of a natural antimicrobial compound loaded in a carrier material, which is able to trigger its release when requested and to modulate the rate of release, thus using either toxic or inhibitory properties against pathogens or bacteria due to food decomposition. In this study, the Schiff base formation for chitosan functionalization was achieved by the reaction of chitosan with cinnamaldehyde at different concentrations. Cinnamaldehyde is an aromatic α,β-unsaturated aldehyde, and the major component in essential oils from some cinnamon species. It has been shown to exert antimicrobial action against a large number of microorganisms including bacteria, yeasts, and mould. The formation of the Schiff base is reversible under suitable conditions, and this might allow the release of the active cinnamaldehyde from chitosan, used as the carrier. The reaction kinetics was investigated by means of rheological measurements, while infrared spectroscopy was used to assess the efficacy of the functionalization. The addition of nanometric graphene stacks to the cinnamaldehyde-functionalized chitosan films was evaluated with the aim to increase the mechanical properties of the film. Finally, the films were tested for antifungal properties with bread slices against a selected mould line.

The application of hydrophobic polymers to stone materials is an effective way to preserve stone artifacts and protect Cultural Heritage from decay. To improve the characteristics and performance of waterrepellent treatments, and to avoid the use of harmful solvents, new solutions have been recently explored. The authors have recently proposed experimental photopolymerizable hybrid organic–inorganic (O–I) protective coatings, mainly intended for the surface protection of porous stones. In this paper, different analytical techniques (contact angle, colorimetric measurements, water absorption measurements, ESEM–EDS analyses) were employed to fully characterize the innovative water-repellent coatings applied on a calcareous stone substrate, typical of Apulia Region (Pietra Leccese, PL). The research work consists of two parts: the first one concerns the evaluation of the appropriate amount of the novel photopolymerizable O–I hybrid coating applied on Lecesse Stone in order to achieve better protective properties; the second one refers to the comparison of the properties of this latter coating with two commercial waterrepellent products. The final performances of the innovative free-solvent photopolymerizable coating, in terms of hydrophobicity and color change, are found to be comparable to those of the commercial products.

Low-molecular-weight organic gelators are widely used to influence the solidification of polymers, with applications ranging from packaging items, food containers to organic electronic devices, including organic photovoltaics. Here, this concept is extended to hybrid halide perovskite-based materials. In situ time-resolved grazing incidence wide-angle X-ray scattering measurements performed during spin coating reveal that organic gelators beneficially influence the nucleation and growth of the perovskite precursor phase. This can be exploited for the fabrication of planar n-i-p heterojunction devices with MAPbI3 (MA = CH3NH3 +) that display a performance that not only is enhanced by ≈25% compared to solar cells where the active layer is produced without the use of a gelator but that also features a higher stability to moisture and a reduced hysteresis. Most importantly, the presented approach is straightforward and simple, and it provides a general method to render the film formation of hybrid perovskites more reliable and robust, analogous to the control that is afforded by these additives in the processing of commodity “plastics.”

Novel photopolymerizable nanocomposite formulations, able to photopolymerize with a dual curing mechanism (cationic and radical), were developed, characterized and used in the stereolithography (SL) process for the construction of 3D objects with a very simple geometry. The influence of the presence of organically modified montmorillonite (OM) nanoparticles on the reactivity of the photopolymerizable liquid mixtures was firstly analyzed, as function of the amount of nanofiller, by photocalorimetric analysis (p-DSC). The basal distance of OM before and after mixing with the photocurable formulation was characterized by X-ray diffraction. Composites with higher content of OM show an intercalated structure. An exfoliated structurewas instead observed in the compositeswith the lowestOMcontent, after photocuring in the SL apparatus. These results were also confirmed by the morphological analysis performed by SEM. The glass transition temperature of nanocomposites, photocured by stereolithography, was finally measured by TMA and DSC techniques, confirming that the photocurable formulation loaded with the lowest amount of OM presents improved properties than the unloaded formulation.

Transparent nanocomposite films were prepared using bacterial cellulose (BC) as reinforcement and diethylene glycol bis(allyl carbonate) polymer (DEAC) as matrix by vacuum infiltration and UV polymerization. The BC/DEAC nanocomposites exhibit excellent transparency up to 88% at wavelength of 550 nm. The uniform dispersion of resin in BC 3D network was evidenced from SEM and ATR-FTIR analyses, confirms the complete photo-polymerization of diethylene glycol bis(allyl)carbonate monomer to Poly (diethylene glycol bis(allyl carbonate) in BC network. The BC/DEAC composites have good mechanical properties, reaching a tensile strength of 130 MPa and a Young’s Modulus of 6.4 GPa. Applying a micromechanic modeling approach, the elastic modulus of the composite was used in order to determine the average aspect ratio of BC fibers. These flexible transparent BC/DEAC

In this study, free-standing expanded graphite chitosan (EG-chitosan) nanocomposite films have been prepared using a novel green and simple preparation method, starting from a commercial expandable graphite (GIC). The in situ exfoliation of GIC by a solvent-free sonication method was monitored as a function of the process parameters using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS) and UV-visible transmittance (UV-VIS) analyses. The optimal process parameters were selected in order to obtain an efficient dispersion of EG in chitosan solutions. The effective EG amount after the in situ exfoliation was also determined by thermogravimetric analyses.

Several innovative photopolymerizable siloxane-modified acrylic formulations were characterized, both in presence or absence of organically Boehmite (OMB) nanoparticles, in order to assess their rheological and kinetic behavior. The experimental formulations were mainly intended for the surface protection of porous stones or wood elements. The importance of the experimental investigation lies in the specific requirements necessary for the proposed applications, i.e. the innovative UV coatings developed should possess adequate viscosity, photopolymerization reaction rate and time. The kinetics of the radical photopolymerization mechanism, induced by UV radiations, was studied by calorimetric analysis and FTIR spectroscopy as function of the mixtures composition and test conditions (air or nitrogen atmosphere). The addition of a silane coupling agent or a high molecular weight polysiloxane monomer to the acrylic resin was found to reduce the heat of reaction. On the other hand, the presence of Boehmite nanoparticles in the UV photopolymerizable formulations does not seem to modify the reactivity of the siloxane-modified acrylic formulations. The effect of the presence of oxygen on the kinetic reaction was also investigated and correlated to the composition of the systems. Finally, the viscosity of the formulations was studied at ambient temperature with a parallel plates rheomether as a function of composition and shear rate. The viscosity curves were also fitted according to theoretical models as function of shear rate and composition, obtaining a good agreement between experimental data and model predictions.

In this work, the influence of graphene oxide (GO) doped Poly(3,4 ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) thin nanocomposite on an indium–tin-oxide (ITO) anode, as hole transport layer (HTL) in perovskite solar cells, was investigated. Different concentrations of GO were added into the PEDOT:PSS in order to enhance its conductivity. In particular, the influence of GO content on the rheological and thermal properties of Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/ GO nanocomposites was initially examined. The GO filler was prepared by using modified Hummers method and dispersed into PEDOT:PSS in different quantity (ranging from 0.05 to 0.25%wt/wt). The obtained nanocomposite solutions were analyzed by rheological characterizations in order to evaluate the influence of the GO filler on the viscosity of the PEDOT:PSS matrix. The wettability of solutions was evaluated by Contact Angle (CA) measurements. The quality of GO dispersion into the polymer matrix was studied using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Thermal characterizations (DSC and TGA) were, finally, applied on nanocomposite films in order to evaluate thermal stability of the films as well as to indirectly comprehend the GO influence on PEDOT:PSS-water links

Polymer nanocomposites are usually studied by means of different techniques, being wide angle X - ray diffraction (WAXD) and transmission electron microscopy (TEM) the most commonly used. Although WAXD offers a convenient method to determine the interlayer spacing of the silicate layers in the intercalated nanocomposites, little can be said about the spatial distribution of the silicate layers or any structural non-homogeneities in nanocomposites. On the other hand, TEM is very time-intensive, and only gives qualitative information on the sample as a whole, due to the small investigable area [ ]. In this work, PETg nanocomposites were produced by melt intercalation of omMMT at different temperatures. Nanocomposites were characterized by means of WAXD and TEM analysis, showing that XRD is only able to capture some of the basic features of the nanocomposite morphology. Further, DSC analysis revealed the relevance of the degree of intercalation on the relaxation times of the nanocomposite.

Novel UV-photopolymerizable siloxane-modified methacrylate/ Boehmite nanocomposites were experimented as possible protective coatings for different substrates. To this aim, unfilled and Boehmite-filled suspensions were applied and photocured on a glass substrate. A subsequent detailed experimental characterization was performed in order to evaluate the effect of the presence of Boehmite nanoparticles on the surface properties of the coatings and on their durability characteristics. In particular, transparency, glass transition temperature, scratch, and surface hardness, contact angle, and color change were measured on the coatings applied on glass support before and after QUV accelerated weathering cycles.

We have developed a novel and straightforward approach for the green synthesis of reduced graphite oxide (rGO). First, graphite oxide (GO) was prepared by the Hummers' oxidation method, starting from high-surface-area graphite. Then, rGO was generated from GO in aqueous suspension through a UV-irradiation treatment. The influence of different process parameters (including type of UV source, irradiation time and atmosphere) on the GO reduction efficiency was explored and evaluated on the basis of the data acquired by several experimental techniques, such as infrared spectroscopy in attenuated total reflectance mode, X-ray diffraction, UV-vis absorption spectrophotometry, X-ray photoelectron spectroscopy and thermogravimetry. The acquired results allowed identifying appropriate sets of reaction conditions under which GO reduction yield could be maximized. In particular, the highest reduction degree was obtained by exposing GO to UV light in a UV oven for 48 h under inert atmosphere. The reduction strategy developed by us represents an innovative low-cost and easy route to graphene-based nanomaterials, which does not require any stabilizer, photocatalyst or reducing agent. For this reason, our method represents an attractive environmentally friendly alternative approach for the preparation of stable rGO dispersions in large-scale amounts, to be utilizable in disparate engineering applications.

The improvement of physical and mechanical properties of nanofilled matrices significantly depends on the average size of dispersed fillers. In particular, the aspect ratio of lamellar nanofillers, such as graphene stacks, results from a combination of both filler morphology and processing techniques. In this study, nanocomposites were obtained dispersing three different graphene precursors in an epoxy resin: expanded graphite, commercial graphene nanoplatelets, and natural graphite. Epoxy matrix nanocomposites reinforced with graphene stacks, ranging from 1 wt% to 3 wt% were prepared and characterized. The structural, mechanical, and thermal properties of expanded graphitebased nanocomposites, as well as the rheological properties of liquid resin/filler suspensions, were studied and compared with those of the unfilled epoxy matrix and of the matrix filled with natural graphite and commercial nanoplatelets. The comparison of mechanical and rheological properties with simple mathematical models indicated that the aspect ratio of expanded graphite is in the order of 1000, i.e., a dispersion of nanoscale graphene stacks was obtained. This result suggests that the measurement of engineering properties of nanocomposites not only represents an objective but can also provide information about the average degree of dispersion.

The engineering aspects associated with nanocomposite development are strongly dependent on the final properties that can be achieved as well as on their processability. Both features are affected by the average distribution of nanofiller in the matrix, or in other words by its dispersion. Furthermore, characterization of intercalation or exfoliation of organic modified montmorillonite (omMMT) or graphene lamellae by X-ray or transmission electron microscopy cannot be easily related to nanocomposite macroscopic properties (mechanical, rheological etc.), the most relevant from an engineering point of view. On the other hand mechanical and rheological analysis shows that properties of nanocomposites are not only dependent from lamellar spacing but also the aspect ratio plays a key role. Even if single graphene sheets or single omMMT are not observed in the matrix bulk, a high aspect ratio of the filler can generate a significant improvement of macroscopic properties. Finally, the measurements of engineering properties of nanocomposites not only represent an objective but can provide information about the average degree of dispersion. Comparison of mechanical and rheological properties with simple mathematical models can be used to determine the average aspect ratio of nanofillers. It may be concluded that macrocharacterization can represent a valuable and complementary tool for the morphological characterization of nanocomposites being capable of providing information about the level of dispersion of nanocomposites.

tThis study presents an intermingled fractal model (IFU) capable of simulating the porous microstructureof natural calcareous stone substrate, typical of Apulia Region (Pietra Leccese, PL) used in historical build-ings. The developed model is aimed at predicting, by an analytical approach, the thermal conductivity ofthese materials. To verify the actual ability of the proposed method to predict stone thermal conductiv-ity, the intermingled fractal units model was applied to untreated natural stone, and to the same stone,treated with a novel UV-light curable O–I hybrid coating. The application of hydrophobic polymers tostone materials is, in fact, an effective way to preserve stone artifacts and protect cultural heritage fromdecay. To this aim, a novel experimental photopolymerizable organic–inorganic (O–I) hybrid protectivecoating, mainly intended for the protection of PL stone, was previously developed by some of the authors.The innovative hybrid product evidenced an extraordinary hydrophobicity, able to guarantee a very highpreservation of the stone from water actions, as well as another important property required to a pro-tective, i.e., a high traspirability of the stone substrate. Furthermore, the experimental product proposedwas able to equal the performance of commercial available products, with the adjunctive advantage tobe free-solvent.

In this study nanocomposites were prepared by dispersing three different grades of graphite particles, expanded graphite, commercial graphene nanoplatelets and natural graphite, in a commercial epoxy matrix. Dielectric properties, thermal conductivity and permeability to oxygen of the composites were studied and compared to those of the unfilled epoxy matrix. An increase of all properties is obtained using expanded graphite, suggesting the presence of a good dispersion of the filler in the matrix and a strong polar interactions of the filler with the matrix, attributed to the partially oxidised surfaces of the expanded graphite. All the measured transport properties were fitted with simple mathematical models obtaining good agreement between the experimental results and theoretical predictions. The model parameters were related to the aspect ratio of the filler, defined as the ratio between the in-plane average dimension and the thickness of the reinforcement. An aspect ratio between 1250 and 1550 indicates that graphite thin platelets (or graphene stacks), characterized by a thickness of the order of a few tens of nanometers, were dispersed in the epoxy matrix.

Novel nanocomposite UV - cured coatings, based on photopolymerizable siloxane-modified acrylic formulations with the addition of organo-modified Boehmite (OMB), are proposed as potential protective coatings for porous stones and wood elements. The OMB nanofiller has been dispersed into an optimized acrylic-based formulation in the presence of a proper photoinitiator for UV-curing. This represents the first example of the use of Boehmite-based UV-cured nanocomposite in the field of Cultural Heritage. The advantages offered by UV-cured coatings with respect to traditional heat-cured ones mainly reside in the attainment of superior performance achievable in less time. The use of a nanocomposite protective coating will guarantee better surface properties and durability characteristics. In this chapter, the characterization of the innovative liquid photopolymerizable siloxane-modified acrylic formulations, both in presence or absence of OMB nanoparticles, is presented in order to assess the suitability of the proposed products for the specific applications. A wide experimental characterization of the solid coatings, applied on different substrate and photo-cured by using a medium pressure Hg UV lamp, is illustrated, in order to assess the attainment of the expected superior properties in terms of transparency, hydrophobicity, surface resistance, glass transition temperature, among the most important. An accelerated weathering procedure is proposed as a means to evaluate the weathering resistance of the coatings.

An organo-modified Boehmite (OMB) was used to prepare nanocomposite UV-cured coatings, based on an innovative photopolymerizable siloxane-modified acrylic formulation, for possible use as protective coatings. 3 wt.% of the nanofiller was dispersed into the mixture in the presence of a proper photoinitiator for UV curing. Different amounts of a silane coupling agent were added to the mixture in order to enhance the compatibility between the nanofiller and the siloxane-modified acrylic formulation. The kinetics of the radical photopolymerization reaction, induced by UV radiations, was studied by photo-calorimetric analysis. The rheological behaviour of the formulations produced was studied as function of the shear rate using a plate and plate rheometer. The formulations, coated on a glass substrate, were photo-cured by using a medium pressure Hg UV lamp. On the coatings photo-polymerized in air were measured: gel content, transparency, scratch and surface hardness. The water absorption effect of the coating based on the novel organic photo-curable nanocomposite on walnut wood elements was evaluated.

Inthis paper, we have investigated the possibility to realize a nanocomposite buffer layer for perovskite solar cells, based on polyelectrolyte poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) PEDOT:PSS and graphene oxide (GO). To this aim, GO, prepared by a modified Hummers method, was mixed with PEDOT: PSS by solvent swelling method and reduced in situ into the polymer matrix through a green and simple method, by using UV radiation. Thin nanocomposite layers were spin coated on different substrates and characterized by several techniques. GO reduction was first analyzed by XPS analyses, monitoring the decrease of the intensity of the peak of the oxygen groups linked to carbon. The grade of the dispersion of GO into PEDOT: PSS was also analyzed by scanning electron microscopy. Sheet resistance measurements of the films with and without GO before and after UV treatment was performed. The thermal stability of the nanocomposites was then evaluated by thermogravimetric analyses. The nanocomposite layer was finally employed in a perovskite solar cell to evaluate the effect of GO reduction on power conversion efficiency. The interface interaction between the nanocomposite and the perovskite precursors was analyzed by contact angle measurements.

tThe kinetic behavior of innovative photopolymerizable UV-cured methacrylic–silica hybrid formula-tions, previously developed, was studied and compared to that of a reference control system. Theorganic–inorganic (O–I) hybrids proposed in this study are obtained from organic precursors with a highsiloxane content mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silicanano-domains dispersed within a cross-linked organic phase, as a result of the hydrolysis and condensa-tion reactions. The kinetics of the radical photopolymerization mechanism induced by UV-radiations, inpresence of a suitable photoinitiator, was studied by calorimetric, FTIR and Raman spectroscopic analy-ses, by varying the composition of the mixtures and the atmosphere for reactions. The well known effectof oxygen on the kinetic mechanism of the free radical photopolymerization of the methacrylic–siloxanebased monomers was found to be strongly reduced in the hybrid system, especially when a properthiol was used. The experimental calorimetric data were fitted using a simple kinetic model for radicalphotopolymerization reactions, obtaining a good agreement between the experimental data and the the-oretical model. From the comparison of the kinetic constants calculated for control and hybrid systems,it was possible to assess the effect of the composition, as well as of the atmosphere used during thephoto-polymerization process, on the kinetic of photopolymerization reaction.

An experimental study was carried out for the development and characterization of novel photopolymerizable siloxane-modified methacrylic formulations containing hydroxyapatite (HA) powders for possible use as protective coating for carbonate stone substrates. The experimental formulations were mainly intended for the surface protection of porous stones, in particular those employed in Apuliam monumental, archeological and historical constructions, or wood supports. Amounts of HA particles ranging from 2.5 wt.% to 20 wt.% were added to a siloxane-modified methacrylic mixture, previously investigated. The effect of inclusion of HA particles in the methacrylic mixture on the final properties of the photopolymerizable systems, applied on glass support and on two different carbonate stone elements, was investigated. To this aim, the transparency and scratch hardness characteristics of the coatings, photo-cured on a glass substrate, were firstly measured. Then, the hydrophobic properties and

An experimental study was carried out for the development and characterization of innovative photopolymerizable siloxane-modified acrylic formulations for possible use as protective coatings for stone substrates. Two amounts of calcarenitic stone particles (25 wt.% and 35 wt.%) were added to a siloxane-modified acrylic mixture. The effect of stone particles inclusion on the reactivity and surface properties of the photopolymerizable systems was investigated. To this aim, the kinetics of the radical photo-polymerization reaction, induced by UV radiations in the presence of a suitable photoinitiator, was studied by calorimetric analysis, both in air and nitrogen atmosphere. The formulations, coated on a glass substrate, were photo-cured by using a medium pressure Hg UV lamp in air. On the coatings photo-polymerized in air were measured: gel content, transparency, scratch and surface hardness.

In this work nanocomposites based on amorphous poly(ethylene terephthalate) (PETg) were developed using melt intercalation. X-ray analysis performed on the PETg nanocomposites showed that intercalation and exfoliation took place during static mixing. The water vapor permeability of PETg nanocomposites was correlated to the volume fraction of the impermeable inorganic part of the omMMT.