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In this work, the effect of different mixing techniques on thermal and mechanical properties of graphene nanoplatelets (GNPs) and graphene nanofibers (GANFs) loaded epoxy nanocomposites was investigated. Three dispersion methods were employed: a high shear rate (HSR), ultrasonication (US) and the fluidized bed method (FBM). The optical microscopy has revealed that the most suitable dispersion, in terms of homogeneity and cluster size, is achieved by implementing the US and FBM techniques, leading to nanocomposites with the largest increase of glass transition temperature, as supported by the DMA analysis data. The fracture toughness results show a general increase of both the critical stress intensity factor (KIC) and the critical strain energy release rate (GIC), likely due to the homogeneity and the low scale dispersion of the carbonaceous nanostructures. Based on the nanocomposite fracture toughness improvements and also assuming a potential large scale up production of the nanocomposite matrix, a single mixing technique, namely the FBM, was employed to manufacture the carbon fiber reinforced composite (CFRC). This method has resulted in being less time-consuming and is potentially most suitable for the high volume industrial production. The CFRCs were characterized in terms of tensile, flexural and interlaminar fracture toughness properties and the results were analyzed and discussed.

The aim of this paper is to study the effect of strain rate on the compressive behavior of the highly cross-linked RTM6 epoxy resin used in advanced aerospace composites. Dynamic compression tests were performed using a split Hopkinson pressure bar, along with reference quasi-static compression tests, to cover a strain rate range from 0.001 to 1035 s−1. Special attention was paid to the optimization of the test methodologies in order to obtain material data free of bias related to the use of different load introduction techniques and sample geometries over the considered strain rate range. In addition, the use of full-field 3D deformation measurements allowed the validation of traditional test and material assumptions. A novel self-alignment tool was developed to enable perfect interfacial contact during compression loading. The 3D digital image correlation technique was used to measure the instantaneous deformation of the sample during compression at different strain rates. Results showed a pronounced strain rate sensitivity of the RTM6 epoxy in compression. The peak yield strength increased with increasing strain rate, while the elastic modulus and Poisson’s ratio in compression were independent of the strain rate. The barreling of the sample in compression, quantified by the barreling ratio, showed an increase during the progression of the compression tests. However, the barreling ratio significantly decreased with the increasing strain rate. Finally, it was shown that neglecting the significant volume change in the yield stages gave rise to a non-negligible underestimation of the strength of the material.

Two different hyperbranched polymer (HBPs) fillers were synthesized and dispersed within an aeronautical graded epoxy matrix as toughening agents. The first typology, identified as HBPG (HBP Glassy) is a glassy polyester characterized by a higher glass transition temperature (Tg) then room temperature (∼90 °C) and obtained by means of bulk polycondensation reaction starting from a diphenolic acid as precursor. The second hyperbranched polymer, labelled HBPR (HBP Rubbery) was a polyamide ester with a Tg of about 20 °C and synthesized by bulk polycondensation of sebacic acid and diisopropanolamine. HBP/epoxy systems were prepared considering two concentration levels, respectively 0.1 and 5 wt%, and the effects on rheological, thermal stability, mechanical properties and fracture toughness were investigated and analyzed in respect to the corresponding neat epoxy. Rheological results revealed that the HBPG filler induces relevant effects on the viscosity of the epoxy matrix compared to HBPR limiting the potential usage of the system for composite manufacturing. Nevertheless, HBPG induces optimal results in term of thermal stability, mechanical and fracture performances, with a limited reduction of the Tg and a higher increase of degradation activation energy along with enhanced fracture behavior as indicated by an enhanced critical stress intensity factor (KIC) and critical strain energy value (GIC). The main result of this work suggests that the HBPG/RTM6 epoxy could be suitably used as polymer matrix for carbon-reinforced composites preserving the advantages of infusion process but at the same time enhancing the matrix-driven mechanical property.

The aim of this paper is to investigate the effect of strain rate and filler content on the compressive behavior of the aeronautical grade RTM6 epoxy-based nanocomposites. Silica nanoparticles with different sizes, weight concentrations and surface functionalization were used as fillers. Dynamic mechanical analysis was used to study the glass transition temperature and storage modulus of the nanocomposites. Using quasi-static and split Hopkinson bar tests, strain rates of 0.001 s−1 to 1100 s−1 were imposed. Sample deformation was measured using stereo digital image correlation techniques. Results showed a significant increase in the compressive strength with increasing strain rate. The elastic modulus and Poisson’s ratio showed strain rate independency. The addition of silica nanoparticles marginally increased the glass transition temperature of the resin, and improved its storage and elastic moduli and peak yield strength for all filler concentrations. Increasing the weight percentage of the filler slightly improved the peak yield strength. Moreover, the filler’s size and surface functionalization did not affect the resin’s compressive behavior at different strain rates.

Synthesized silica nanoparticles (SiO2) were coated with a thin polydopamine (PDA) shell by a modified one-step procedure leading to PDA coated silica nanoparticles (SiO2@PDA). Core-shell (CSNPs) characterization revealed 15 nm thickness of PDA shell surrounding the SiO2 core (~270 nm in diameter). Different weight percentages of CSNPs were employed as filler to enhance the final properties of an aeronautical epoxy resin (RTM6) commonly used as matrix to manufacture structural composites. RTM6/SiO2@PDA nanocomposites were experimentally characterized in terms of thermal stability and mechanical performances to assess the induced effects by the synthesized CSNPs on pristine matrix. Thermal stability was investigated by thermogravimetry and data were modelled by the Doyle model and Kissinger methods. An overall enhancement in thermal stability was achieved and clearly highlighted by modelling results. Dynamic Mechanical Analysis has revealed an improvement in the nanocomposite performances compared to the neat matrix, with an increase in the glassy (+9.5%) and rubbery moduli (+32%) as well as glass transition temperature (+10 &deg, C). Fracture Toughness tests confirmed the positive effect in damage resistance compared to unloaded resin with an impressive variation in critical stress intensity factor (KIC) and critical strain energy (GIC) of about 60% and 138%, respectively, with the highest SiO2@PDA content.

The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using a bulk poly-condensation reaction, reveals a glassy state at room temperature. Indeed, according to differential scanning calorimetry measurements, the glass transition temperature (Tg) of AHBP is 95 &deg, C. Three different adduct weight percentages were employed to manufacture the AHBP/epoxy samples, respectively, 0.1, 1, and 5 wt%. Dynamical Mechanical Analysis tests revealed that the addition of AHBP induces a negligible variation in terms of conservative modulus, whereas a slight Tg reduction of about 4 &deg, C was observed at 5 wt% of filler content. Fracture toughness results showed an improvement of both critical stress intensity factor (+18%) and critical strain energy release rate (+83%) by adding 5 wt% of AHBP compared to the neat epoxy matrix. Static and dynamic compression tests covering strain rates ranging from 0.0008 to 1000 s&minus, 1 revealed a pronounced strain rate sensitivity for all AHBP/epoxy systems. The AHBP composites all showed an increase of the true peak yield compressive strength with the best improvement associated with the sample with 0.1 wt% of AHBP.

The following data describe the thermal properties of two different typologies of Hyperbranched Polymers (HBPs): the first one is a polyester (HBPG – Hyperbranched Polymer Glassy) with a glass transition temperature (Tg) higher than room temperature (∼90 °C) whereas the second one is a polyamide ester (HBPR – Hyperbranched Polymer Rubbery) characterized by Tg of about 20 °C. The nanocomposites manufactured using these HBPs as filler were characterized using Optical Microscopy and Differential Scanning Calorimetry. The raw data for the evaluation of fracture toughness properties are reported for the listed materials. This article provides data related to “The effect of Glassy and Rubbery Hyperbranched Polymers as Modifiers in Epoxy Aeronautical Systems” (Zotti et al.). Keywords: Thermosetting matrix, Polymer matrix composites (PMC), Hyperbranched polymers (HBPs), Thermal stability, Fracture toughness

Synthesized silicon oxide (silica) nanoparticles were functionalized with a hyperbranched polymer (HBP) achieving a core/shell nanoparticles (CSNPs) morphology. CSNPs were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), and Thermogravimetric Analysis (TGA). A core diameter of about 250 nm with a 15 nm thick shell was revealed using TEM images. An aeronautical epoxy resin was loaded with the synthesized CSNPs at different percentages and thermal properties, such as thermal stability and dynamic mechanical properties, were investigated with the use of different techniques. Although the incorporation of 2.5 wt% of CSNPs induces a ~4 &deg, C reduction of the hosting matrix glass transition temperature, a slight increase of the storage modulus of about ~10% was also measured. The Kissinger Method was employed in order to study the thermal stability of the nanocomposites, the degradation activation energies that resulted were higher for the sample loaded with low filler content with a maximum increase of both degradation step energies of about ~77% and ~20%, respectively. Finally, fracture toughness analysis revealed that both the critical stress intensity factor (KIC) and critical strain energy release rate (GIC) increased with the CSNPs content, reporting an increase of about 32% and 74%, respectively, for the higher filler loading.

This work aimed to investigate the effect of hybrid carbon nanofillers (e.g., carbon nanotubes/carbon nanofibers in the ratio 1:1 by mass) over the electrical and flexural properties for an epoxy matrix and corresponding basalt fibre reinforcing composite (BFRC) subjected to full-year seasonal water absorption. Hydrothermal ageing was performed by full immersion of the tested materials into distilled water according to the following model conditions (seasons). The mechanical properties were measured in three-point bending mode before environmental ageing and after each season. Upon environmental ageing, the relative change of flexural strength and elastic modulus of the epoxy and NC was within 10–15%. For nanomodified BFRCs, the slightly higher effect (approx. by 10%) of absorbed moisture on flexural characteristics was found and likely attributed to higher defectiveness (e.g., porosity, the formation of agglomerates etc.). During flexural tests, electrical resistance of the nanocomposites (NC) and BFRC/NC samples was evaluated. The electrical conductivity for UD BFRC/NC, before and after hydrothermal ageing, was by 2 and 3 times higher than for the NC, accordingly, revealing the orientation of electrically conductive nanoparticles and/or their agglomerates during lay-up manufacturing which was evaluated by the rules of the mixture. Based on all results obtained it can be concluded that the most potentially applicable for damage indication was UD BFRC/NC along fibres since full-year hydrothermal ageing improved its electrical conductivity by approx. 98% and, consequently, the ability to monitor damages was also enhanced.

The effects of temperature and moisture on flexural and thermomechanical properties of neat and filled epoxy with both multiwall carbon nanotubes (CNT), carbon nanofibers (CNF), and their hybrid components were investigated. Two regimes of environmental aging were applied: Water absorption at 70 &deg, C until equilibrium moisture content and thermal heating at 70 &deg, C for the same time period. Three-point bending and dynamic mechanical tests were carried out for all samples before and after conditioning. The property prediction model (PPM) was successfully applied for the prediction of the modulus of elasticity in bending of manufactured specimens subjected to both water absorption and thermal aging. It was experimentally confirmed that, due to addition of carbon nanofillers to the epoxy resin, the sorption, flexural, and thermomechanical characteristics were slightly improved compared to the neat system. Considering experimental and theoretical results, most of the epoxy composites filled with hybrid carbon nanofiller revealed the lowest effect of temperature and moisture on material properties, along with the lowest sorption characteristics.

The aim of this work was to establish the effect of environmental factors (moisture and temperature) on some mechanical, electrical and thermal properties of epoxy-based composites filled with carbon nanofillers: nanotubes (CNT), nanofibers (CNF) and hybrid nanofiller (nanotubes/nanofibers in the ratio 1:1) and to reveal the most environmentally stable NC. First, the nanocomposites (NC) containing different nanofiller contents were prepared to evaluate electrical percolation threshold and to choose NC at certain electrical conductivity for further characterization of the physical properties in initial state and during/after environmental ageing. The environmental ageing consisted of water absorption at 70 °C until equilibrium moisture content reached all samples in 4 weeks and 2) heating at 70 °C for the same time, and 3) freezing at -20 °C for 8 weeks. Two concurrent factors, temperature and moisture, led to post-curing of all materials studied without significant plastization. Some positive nanofiller effects were found for sorption, mechanical and thermophysical characteristics of RTM6 epoxy resin. Based on experimental results, the most environmentally stable NC was epoxy filled with 0.1 wt. % of CNT/CNF hybrid, which had the lowest effect of temperature and moisture on thermal and electrical conductivities, along with the lowest equilibrium water content and diffusivity.The aim of this work was to establish the effect of environmental factors (moisture and temperature) on some mechanical, electrical and thermal properties of epoxy-based composites filled with carbon nanofillers: nanotubes (CNT), nanofibers (CNF) and hybrid nanofiller (nanotubes/nanofibers in the ratio 1:1) and to reveal the most environmentally stable NC. First, the nanocomposites (NC) containing different nanofiller contents were prepared to evaluate electrical percolation threshold and to choose NC at certain electrical conductivity for further characterization of the physical properties in initial state and during/after environmental ageing. The environmental ageing consisted of water absorption at 70 °C until equilibrium moisture content reached all samples in 4 weeks and 2) heating at 70 °C for the same time, and 3) freezing at -20 °C for 8 weeks. Two concurrent factors, temperature and moisture, led to post-curing of all materials studied without significant plastization. Some positive nanofiller e...

In this work, basalt microfiber reinforced poly(lactic acid) (PLA) composites filled with talc nanoplatelets (2D) and sepiolite nanofibers (1D) were prepared at different compositions and tested to assess the effects of filler geometry. Thermal analysis results show that crystallinity of amorphous PLA can be enhanced up to 24% by adding basalt and talc. Thermal stability of PLA is increased by basalt microfibers whereas talc and sepiolite prompted early degradation in binary composites. In ternary systems, i.e. PLA/basalt/talc and PLA/basalt/sepiolite, thermal stability was further increased. Mechanical tensile and flexural properties were remarkably increased for a specific composition basalt (30 wt%) and talc (10 wt%) with a final enhancement of 176% and 261% for modulus and 46% and 43% for strength respectively in tensile and bending configuration. For the composition, the coefficient of thermal expansion is significantly reduced up to 54% of the corresponding pristine PLA value. The increase of thermal conductivity is mainly related to the presence of 1D sepiolite, with a variation of ∼54% for the 10 wt% PLA/sepiolite binary system. Finally, a significant increment of impact property was observed by unnotched Charpy impact tests for talc (+97%) and basalt (+140%) composites.

Metal nanoparticles (NPs) were prepared from acrylamide complex of iron and nickel nitrates by controlled thermolysis at constant temperature in a self-generated atmosphere and used to fabricate epoxy resin nanocomposites. X-ray diffraction performed on the nanoparticles revealed a metal core/polymeric shell structure for the nanoparticles thermolysed at higher temperature as also confirmed by cross analysis of thermo-gravimetrical and vibrating magnetometer data. Optical microscopy was used to investigate the achieved dispersion of the nanoparticles within the uncured resin and transmission electronic microscopy was used to analyse the morphology and the average dimensions of the nanoparticles. Thermal stability of manufactured nanocomposites was studied by thermo-gravimetric analysis in inert and oxidative conditions, reporting that negligible variations are induced by the presence of nanofillers. A complete thermo-mechanical and fracture characterization was carried out to assess the effect of nanoparticles on final nanocomposite system. A slight increase of the modulus is recorded at room temperature whereas a significant variation is induced for higher temperature. The presence of nanoparticles induces a global increase in the fracture energy of nanocomposite associated to different failure mechanisms. Magnetic data indicate that iron particles based nanocomposites display room-temperature ferromagnetic behaviour with saturation magnetization and coercivity depending on the diameter of the metal core.

In this work, we report the in-field demonstration of a liquefied petroleum gas monitoring system based on optical fiber technology. Long-period grating coated with a thin layer of atactic polystyrene (aPS) was employed as a gas sensor, and an array comprising two different fiber Bragg gratings was set for the monitoring of environmental conditions such as temperature and humidity. A custom package was developed for the sensors, ensuring their suitable installation and operation in harsh conditions. The developed system was installed in a real railway location scenario (i.e., a southern Italian operative railway tunnel), and tests were performed to validate the system performances in operational mode. Daytime normal working operations of the railway line and controlled gas expositions, at very low concentrations, were the searched realistic conditions for an out-of-lab validation of the developed system. Encouraging results were obtained with a precise indication of the gas concentration and external conditioning of the sensor.

The aim of this paper was to estimate the effect of moisture and temperature on the flexural properties of the epoxy filled with single and hybrid carbon nanofillers (CNTs and CNFs) and to reveal the most environmentally stable NC. Water absorption at 70 °C until equilibrium moisture content and heating at 70 °C for 4 weeks were followed by freezing at -20 °C for 8 weeks. Microstructural characterization of optical images revealed homogeneous dispersion of all carbon nanofillers in the epoxy resin at microscale. Positive nanofiller effects were found for sorption, flexural and thermophysical characteristics of the epoxy resin. The most environmentally stable NC was epoxy filled with 0.1 wt. % of CNTs/CNFs hybrid, which had the lowest effect of temperature and moisture on mechanical characteristics, along with the lowest equilibrium water content and diffusivity.

Fracture toughness is generally considered as the main properties of a polymer or a polymer adhesive system for measuring the material resistance to the extension of cracks. Epoxy adhesives are generally brittle in nature; however, the addition of a second dispersed phase could induce a remarkable increase of damage tolerance performance by an enhancement of the material fracture toughness. The fracture behavior of a filled epoxy resin is strongly affected by the dimensions, the shape, and the chemical nature of the considered filler? The chapter describes the different toughening mechanisms for polymer adhesives with special attention toward innovative nanofiller such as graphene nanoplatelets and hyperbranched polymer nanoparticles.

The aim of this paper is to study the compressive behavior of a typical aeronautical epoxy composite matrix filled with silica nanoparticles at high strain rates. The weight percentage of the silica nanoparticles was 1% of the epoxy resin and the average size of the nanoparticles was approx. 800 nm, as measured by SEM image analysis. Reference quasi-static experiments (at strain rates 0.0008, 0.008, and 0.08 s -1 ) and high strain rate experiments (up to 1050 s -1 ) were carried out using both neat and silica nanoparticle filled epoxy resins. Results showed that the addition of silica nanoparticles improved the compressive yield strength and reduced the maximum strain of the epoxy resin at quasi-static and high strain rates. In addition, results revealed that strain rate sensitivity at higher strain rates was also negatively affected.. The effect of strain rate on the compressive yield strength of silica nanoparticles filled epoxy reasonably followed a power law, which is characterised by a strain rate exponent value of approx. 0.0227. This work is carried out within the scope of EU H2020 funded EXTREME project.