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Objetivo: describir modelos de negocio digitales mediante la variante de suscripción freemiun como necesidad social en Cuba. Método: el estudio se realizó desde enero a diciembre de 2022 sobre siete empresas en la categoría de servicios de La Habana, Cuba. se valoró la prestación de servicios o accesibilidad a contenidos gratuitos de parcialidad (free) para cualquier usuario y tipo de cobro por contenido o servicio de exclusividad (premium) para clientes con mejores prestaciones. Las características que se analizan fueron: ingresos, clientes, relaciones, precios, canales, recursos clave. Asimismo, se considera la venta de información. Resultados: no se encontró modelos digitales de servicios free y tampoco premium en las empresas de servicios, a pesar que en sus carteras de servicios se identificaron las características de los modelos digitales de suscripción. Del mismo modo, existió ausencia de ventas efectivas al consumidor desde la información empresarial. Discusión: se necesita que las empresas de servicios implementen los contenidos para la satisfacción de los consumidores. En el caso del contenido free se requiere que exista mayor publicidad y en el premium analizarse su restricción. Conclusiones: se demanda que las empresas de servicios consultadas la suscripción freemium debe implementarse como modelo de negocio digital para su competitividad.

The shape memory (SM) capabilities of nanocomposites based on two photocurable acrylated/methacrylated resins, doped with carbon nanotubes (CNTs), and manufactured by digital light processing 3D printing were investigated. The mechanical properties and glass transition temperature (Tg) can be tailored in a broad range by varying the weight ratio of the two resins (Tg ranging from 15 to 190 °C; Young’s modulus from 1.5 to 2500 MPa). Shape fixity (SF) and recovery (SR) ratios are strongly influenced by the temperature being significantly higher at temperatures close to the Tg. The results confirm that the SF strongly depends on the stiffness of chain segments between cross-linking points, whereas the SR mainly depends on the cross-link density of the network. CNT addition barely affects the SF and SR in the conventional oven, whereas the recovery speed using IR heating is significantly increased for the doped nanocomposites due to their higher IR absorbance.

The importance of proper CNT dispersion is still the main challenge in CNTs doped epoxy nanocomposites. Therefore, this study was aimed to investigate the effect of toroidal stirring-assisted sonic...

The use of polymer and polymer-based composites has increased over the last decades [...]

Over the last 30 years, the study of the cellular response to ionizing radiation (IR) has increased exponentially. Among the various signaling pathways affected by IR, p38 MAPK has been shown to be activated both in vitro and in vivo, with involvement in key processes triggered by IR-mediated genotoxic insult, such as the cell cycle, apoptosis or senescence. However, we do not yet have a definitive clue about the role of p38 MAPK in terms of radioresistance/sensitivity and its potential use to improve current radiotherapy. In this review, we summarize the current knowledge on this family of MAPKs in response to IR as well as in different aspects related to radiotherapy, such as their role in the control of REDOX, fibrosis, and in the radiosensitizing effect of several compounds.

Self-heating GNPs-based electrical networks were successfully obtained for their use in electrothermal applications. The electrical resistance of the GNPs-networks created on glass fiber fabrics was strongly dependent on fiber direction. The electrothermal response was fast and the maximum temperature was achieved in the system after ∼20 s. Increments in temperature above 80°C were obtained at the surface of the coated glass fiber fabric at relatively low intensity currents. Cyclic self-heating did not cause appreciable diminution in performance. Additionally, their potential application in evaluation of the quality of dispersion of the nanoreinforcement was demonstrated, as regions with lower contents in GNPs showed higher temperature due to weak links between GNPs located in highly conductive paths forming the electrical network.

The influence of the average surface area of different graphene nanoplatelets (GNP) on the thermo-electrical behaviour, associated with Joule heating, and the attenuation of electromagnetic signals of epoxy composites has been studied, analysing the effect of the morphology obtained as a function of the dispersion time by ultrasonication and the GNP content added. Gravity moulding was used as the first stage in the scaling-up, oriented to the industrial manufacture of multilayer coatings, observing a preferential self-orientation of nanoparticles and, in several conditions, a self-stratification too. The increase of sonication time during the GNP dispersion provides a decrease in the electrical conductivity, due to the GNP fragmentation. Instead, the thermal conductivity is enhanced due to the higher homogeneous distribution of GNPs into the epoxy matrix. Finally, the lower surface area of GNPs reduces the thermal and electrical conductivity due to a greater separation between nanosheets. Regarding the study of the attenuation of electromagnetic waves, it has been discovered that in the frequency range from 100 Hz to 20 MHz, this attenuation is independent of the direction of analysis, the type of graphene, the sonication time, and the state of dispersion of the nano-reinforcement in the matrix. Furthermore, it has also been observed that the conservation of the constant shielding values for the three types of GNPs are in a range of average frequencies between 0.3 and 3 MHz.

The present work studies the electrical and electrothermal properties of CNT/GNP-doped nanocomposites for optimizing their anti-icing and de-icing capabilities. Here, a comparison between 3D-printed circuits and coatings based on these materials is carried out. In this regard, the higher electrical conductivity that is achieved by the specimens when increasing the nanoparticle content and the higher cross-sectional area of the coatings with regard to the 3D-printed circuits induces a higher heat generated by the Joule’s effect. Moreover, the successful de-icing test performed by the specimen with the highest self-heating capability, evinces that the studied nanocomposites are suitable for de-icing purposes.

This paper reports on an investigation of the critical parameters which determine the electrical and electromechanical properties of carbon nanotube (CNT) nanocomposites. For this purpose, a novel analytical model, based on the tunnelling mechanisms of CNTs, is proposed. Three dispersion parameters are introduced in the model to reflect the CNT aggregation state. Microscopy analysis and electrical and strain monitoring tests were carried out on CNT nanocomposites manufactured by toroidal stirring and three roll milling. It is observed that electrical conductivity is greatly affected by dispersion procedure as well as strain sensitivity, measured by the gauge factor (GF). Generally, well dispersed materials have higher conductivities and GF. In this regard, the aggregate ratio has a prevalent effect. Experimental data and theoretical predictions allow the correlation of dispersion parameters given by manufacturing procedures with electrical properties to develop highly sensitive nanocomposites. This demonstrates the potential and applicability of the proposed model.

The effect of the addition of carbon nanotubes (CNTs) to adhesive films in composite joints has been studied due to their potential in structural health monitoring (SHM) applications. Carbon nanotube dispersion has been prepared by sonication in an aqueous media using sodium dodecyl sulfate (SDS) as surfactant. A dispersion procedure has been developed to promote a homogeneous dispersion of CNTs within an adhesive. Studies of aqueous dispersions have been carried out by FEG-SEM analysis, proving the disaggregation effect that SDS has on the CNT dispersion and the breakage induced by sonication. By mechanical testing of adhesive joints, it has been observed that the addition of CNTs does not have a significant effect on lap shear strength (LSS), with the best results being achieved in the case of dispersions made with 0.25 wt%. A microstructural study of fracture surfaces shows that the main failure mode is cohesive although in some areas adhesive failure has been observed. In this regard, there is no significant difference between doped and non-doped joints. In addition, electrical conductivity through the bonding line is highly improved, making the adhesive joint electrically conductive, which proves its potential for SHM applications.

This paper presents a process where carbon fibers and hydrogen can be recovered simultaneously through a two-stage thermal treatment of an epoxy-carbon fiber composite. For this purpose, some pieces of epoxy resin reinforced with carbon fiber fabrics have been fabricated and, after curing, have been pyrolyzed in an installation consisting of two reactors. In the first one, the thermal decomposition of the resin takes place, and in the second one, the gases and vapors coming from the first reactor are thermally treated. Once this process is completed, the solid generated is oxidized with air to eliminate the resin residues and carbonaceous products from the fibers surface. The recovered carbon fiber fabrics have been reused to make new cured parts and their electrical and mechanical properties have been measured. The results show that it is possible to obtain carbon fiber fabrics that can be processed as they leave the recycling process and that retain 80% of the tensile modulus, 70% of the flexural strength, and 50% of the interlaminar shear strength. At the same time, a gaseous stream with more than 66% by volume of hydrogen can be obtained, reaching a maximum of 81.7%. This research was funded by the Ministry of Science and Innovation of the Spanish Government through the project with reference PID2019-110770RB-I00 and by the Basque Government through the project with reference KK-2020/00107 (ELKARTEK program). Besides, the Basque Government also contributed to this work by means of the regular funding granted to consolidated research teams (IT993-16) and the researcher training grant awarded to Naia Gastelu.

Shape memory (SM) materials have been widely investigated for several years. Most polymers present SM behaviour based on their thermo-mechanical properties. However, they are usually stimulated by an external heating source, hindering their industrial application. The addition of carbon nanotubes (CNT) allows turning conventional SM polymers into electro-active actuators. In this regard, the resistive heating by the Joule effect is considerably fast with a low energy cost. The most used epoxy resins cured at high temperature are based on diglycidyl ether of bisphenol A (DGEBA) cured with aromatic amine hardeners, such as diaminodiohenylsulfone (DDS) and 4,4′diamine-diphenylmetane (DDM). In this work, they were synthesised with modification of the epoxy/amine ratio to vary the crosslinking density of networks so as to build up different viscoelastic properties in order to tailor their SM behaviour. Electrically conductive nanocomposites were manufactured by adding a CNT percentage above the percolation threshold. A comparison of SM behaviour stimulated by traditional convection and resistive heating was carried out, confirming the higher recovery ratio, speed, and applicability of the electrical stimuli. In addition, the configuration of electrodes allows the design of self-deployable materials with remote control. In this way, the most common dual-shape SM polymers (one permanent shape and one temporary shape) can easily develop several stable temporary shapes. Moreover, the electrical remote control provides sequential and selective actuators, enhancing their performance for developing smart structures with shape memory capability.

The capabilities of Digital Light Processed CNT doped nanocomposites for electrothermally triggered selective shape memory have been explored. Here, selective shape memory enables fixing the temporary shape and recovering the original one of different regions of a specimen individually, without affecting the other regions. In this regard, the shape memory capabilities of different matrices based on mixtures of rigid and elastic resins, consisting in hard segments (HS) and soft segments (SS), respectively, doped with CNTs have been investigated. A decrease in the HS:SS ratio leads to a decrease in the glass transition temperature, which constitutes the transformation temperature needed for fixing the temporary shape and recovering the original one. However, the electrical conductivity experiences a sudden drop, reaching values below the percolation threshold at 0:100 samples. Therefore, only the 100:0 and 80:20 samples were valid for shape memory triggered by Joule's effect. Furthermore, selective shape memory tests were conducted by placing different electrodes throughout the material by dividing the specimen in one, two or three individual regions that could be activated selectively. Here, it has been observed that the shape recovery ratio was above 75% in every case, proving the potential of the proposed materials and technique for selective shape memory activation by Joule's heating.

Functionalized graphene nanoplatelets networks created through glass fiber fabrics were used to detect and locate damage in multiscale composite materials. The electrical behavior of multiscale composite materials was strongly influenced by microstructural features. Coated fabrics presented high sensitivity to breakage of fibers due to the preferential orientation of f-GNPs through fibers. This sensitivity was higher when damage was induced perpendicular to the fiber direction and the region where damage could be detected was bigger in the case of locating the measuring electrical channels perpendicular to fiber direction. These phenomena are related again to the morphology of the electrical network through the coating. Due to the insulating character through thickness of composites, detection and location was limited to layers of fabric of the composite. Nevertheless, self-sensors had the capacity of detecting and locating damage with high sensitivity by means of abrupt increases in electrical resistance induced by breakage.

Chromatin remodeling plays a key role in the establishment and maintenance of gene expression patterns essential for plant development and responses to environmental factors. Post-translational modification of histones, including acetylation, is one of the most relevant chromatin remodeling mechanisms that operate in eukaryotic cells. Histone acetylation is an evolutionarily conserved chromatin signature commonly associated with transcriptional activation. Histone acetylation levels are tightly regulated through the antagonistic activity of histone acetyltransferases (HATs) and histone deacetylases (HDACs). In plants, different families of HATs are present, including the MYST family, which comprises homologs of the catalytic subunit of the Nucleosome Acetyltransferase of H4 (NuA4) complex in yeast. This complex mediates acetylation of histones H4, H2A, and H2A.Z, and is involved in transcriptional regulation, heterochromatin silencing, cell cycle progression, and DNA repair in yeast. In Arabidopsis and, other plant species, homologs for most of the yeast NuA4 subunits are present and although the existence of this complex has not been demonstrated yet, compelling evidence supports the notion that this type of HAT complex functions from mosses to angiosperms. Recent proteomic studies show that several Arabidopsis homologs of NuA4 components, including the assembly platform proteins and the catalytic subunit, are associated in vivo with additional members of this complex suggesting that a NuA4-like HAT complex is present in plants. Furthermore, the functional characterization of some Arabidopsis NuA4 subunits has uncovered the involvement of these proteins in the regulation of different plant biological processes. Interestingly, for most of the mutant plants deficient in subunits of this complex characterized so far, conspicuous defects in flowering time are observed, suggesting a role for NuA4 in the control of this plant developmental program. Moreover, the participation of Arabidopsis NuA4 homologs in other developmental processes, such as gametophyte development, as well as in cell proliferation and stress and hormone responses, has also been reported. In this review, we summarize the current state of knowledge on plant putative NuA4 subunits and discuss the latest progress concerning the function of this chromatin modifying complex.

This work aims to investigate the crack propagation monitoring capacity of carbon nanotube (CNT) reinforced adhesive films in joints with dissimilar materials. To achieve this purpose, Mode-II standard tests have been carried out while the electrical response has been determined in terms on electrical resistance measurements. It has been observed that electrical and mechanical response show a good agreement, with an increase of the electrical resistance with crack length due to the breakage of electrical pathways. Brushed and grit-blasted metallic substrates were tested and some significant differences between electrical response have been observed. Samples with poorer surface treatment showed a more unstable response due to a continuous creation and breakage of electrical pathways while grit-blasted specimens present a uniform electrical resistance increase. These results were also stated by microstructural analysis, showing the presence of weak areas in case of brushed substrates. In addition to that, skin-stringer elements were also tested at static conditions, showing a good electrical continuity. Therefore, the potential and applicability of the proposed technique for SHM of bonded joints have been demonstrated

The addition of functionalized graphene nanoplatelets (f-GNPs) into the epoxy resin of glass fiber multiscale composite materials creates an electrically conductive network. This electrical network is highly sensitive to strain induced in the material. For this reason, it is a competitive material to be used in structural health monitoring (SHM). Sensitivity of multiscale composite materials is ∼50 under tensile loads and the behavior under compression loads differs, making possible the detection of different load conditions. Independency of the strain rate is related to the enhanced interface between f-GNPs and the epoxy matrix due to functionalization. Additionally, the electrical behavior is reversible without the loss of efficiency in sensorial properties.

The aim of this study was to explore whether children with and without learning difficulties use orthographic rules to write words. To study this, two types of tasks from the Early Grade Writing As...

En el presente artículo encontraremos algunas de las acciones realizadas por las mujeres colombianas para acceder a la educación superior y cómo estas enmarcan la necesidad de visibilizar y reflexionar acerca de la construcción de una sociedad donde se supere el discurso de la igualdad y se inicie la lucha por la equidad, como característica fundamental del reconocimiento de la mujer. Para ello, abordaremos históricamente el acceso de las mujeres a la educación superior y posteriormente validaremos dos escenarios específicos para realizar un análisis que permita develar el ingreso de las mujeres a las instituciones de educación superior y el compromiso de estas últimas al respecto. Finalmente, será necesario recrear dos historias que trascienden a la acción este derecho ganado por muchas, reconfigurando el papel de la mujer en la sociedad y en la construcción de un país en el que la apuesta fundamental es la educación como una vía posible de cualquier transformación social.

Hybrid multi-material joints of titanium alloy (Ti6Al4V) bonded to carbon fibre reinforced polymer (CFRP) are really interesting for lightweight high-performance structures, i.e., aeronautical and marine applications. Co-bonding technique, in which the joining takes place at the same time as the manufacturing of the CFRP, could be a great solution for easy manufacturing fibre metal laminate (FML) and complex structures, or a time saving process. One of the biggest challenges in this type of multi-material structures is to be able to confirm the structural health in service. The present work deals with the use, as matrix, of an epoxy resin reinforced with multiwalled carbon nanotubes (MWCNT) for manufacturing of Ti-CFRP joints by co-bonding. The aim is the structural health monitoring (SHM) of these hybrid structures, enhancing their mechanical properties. The obtained results show an improvement of more than 140% in fracture resistance of the multi-material joints with optimal surface preparation, by incorporating CNT. Furthermore, electrical monitoring makes it possible to discern the quality of the manufactured joints, increasing their reliability and performance. Besides, the ability to localize crack propagation and stresses prior to joint failure has been confirmed, so CNT addition results in a powerful tool for SHM multi-material joints.

Sensing capabilities of carbon nanotube (CNT) epoxy materials have been studied in order to develop multifunctional coatings for damage detection. For that purposes CNT doped epoxy nmixtures have been manufacturing using toroidal stirring. The microstructural characterization of CNT dispersion has been carried out by optical microscopy, showing the good homogenization effect induced by toroidal stirring. Then, electromechanical tests have been carried out on bulk nanocomposites and strain gauges. From tensile tests, it has been noticed that the Gauge Factor (GF) of strain gauges is much higher than those of bulk nanocomposites and conventional metallic gauges. Bending tests, which gauges made over tensile or compressive faces of the samples show that strain gauges have different behaviors while bulk materials show similar ones due to electrical volume interactions, proving the potential of strain gauges for monitoring complex load states. Damage sensing of CNT/epoxy materials has been also proved by inducing artificial defects on a monitored coating as changes in electrical resistance related to damage size. Thus damage detection, location and quantification have been achieved.

Subunit II of cytochrome c oxidase (Cox2) is usually encoded in the mitochondrial genome, synthesized in the organelle, inserted co-translationally into the inner mitochondrial membrane, and assembled into the respiratory complex. In chlorophycean algae however, the cox2 gene was split into the cox2a and cox2b genes, and in some algal species like Chlamydomonas reinhardtii and Polytomella sp. both fragmented genes migrated to the nucleus. The corresponding Cox2A and Cox2B subunits are imported into mitochondria forming a heterodimeric Cox2 subunit. When comparing the sequences of chlorophycean Cox2A and Cox2B proteins with orthodox Cox2 subunits, a C-terminal extension in Cox2A and an N-terminal extension in Cox2B were identified. It was proposed that these extensions favor the Cox2A/Cox2B interaction. In vitro studies carried out in this work suggest that the removal of the Cox2B extension only partially affects binding of Cox2B to Cox2A. We conclude that this extension is dispensable, but when present it weakly reinforces the Cox2A/Cox2B interaction.

Electromechanical sensing devices, based on resins doped with carbon nanotubes, were developed by digital light processing (DLP) 3D printing technology in order to increase design freedom and identify new future and innovative applications. The analysis of electromechanical properties was carried out on specific sensors manufactured by DLP 3D printing technology with complex geometries: a spring, a three-column device and a footstep-sensing platform based on the three-column device. All of them show a great sensitivity of the measured electrical resistance to the applied load and high cyclic reproducibility, demonstrating their versatility and applicability to be implemented in numerous items in our daily lives or in industrial devices. Different types of carbon nanotubes—single-walled, double-walled and multi-walled CNTs (SWCNTs, DWCNTs, MWCNTs)—were used to evaluate the effect of their morphology on electrical and electromechanical performance. SWCNT- and DWCNT-doped nanocomposites presented a higher Tg compared with MWCNT-doped nanocomposites due to a lower UV light shielding effect. This phenomenon also justifies the decrease of nanocomposite Tg with the increase of CNT content in every case. The electromechanical analysis reveals that SWCNT- and DWCNT-doped nanocomposites show a higher electromechanical performance than nanocomposites doped with MWCNTs, with a slight increment of strain sensitivity in tensile conditions, but also a significant strain sensitivity gain at bending conditions.

The incorporation of graphene nanoplatelets (GNPs) as a coating on glass fibre fabrics for strain monitoring applications was analysed. Non-functionalized and functionalized GNPs were used in order to study the effect of the functionalization in the morphology of the coating and the electrical behaviour of the material. In contrast with non-functionalized GNPs, when NH 2 -functionalized GNPs were used, the nanoparticles adapted to the surface of the fibres causing a major effectiveness of the electrical network created along the fibres, achieving an electrical conductivity in the order of 10 −2 S/m. The sensitivity values, obtained under tensile loads, reached values in the order of 840 up to 16400.

The mechanical and crack sensing capabilities of CFRP-metal Mode-II coupons and skin-stringer T-joints under bending conditions with carbon nanotube (CNT) doped adhesive films are explored. Different surface treatments of the aluminium substrate are tested (grit blasting and sandpaper brushing). Mode-II energy fracture slightly increases with CNT addition due to the nanoparticle toughening effect when the surface treatment is adequate. However, in the case of brushed specimens, the enhanced lubricant properties of CNTs leads to the promotion of weak interfaces between adhesive and metal substrate. The electrical resistance increases with the load nose displacement with a good correspondence to the crack length. A crack opening effect is herein noticed in the last stages of the Mode-II tests due to the difference between the stiffness of metal and CFRP adherents, which is reflected in a sudden increase of the electrical resistance. These results have been also validated by theoretical analysis. Electromechanical response of T-joints shows a similar behaviour with an increasing sensitivity when placing a CFRP stringer, due to a more prevalent crack opening observed in this type of specimens. Therefore, crack sensing capabilities are demonstrated at both coupon and sub-element level.

The strain-sensing, self-curing and self-heating capabilities of a 3D printed circuit made of a graphene nanoplatelet and carbon nanotube reinforced resin, have been widely explored. These materials exhibit high Joule’s heating effect capabilities that can be used for post-curing processes. More specifically, the values of glass transition temperature reached by Joule’s heating post-curing were very similar to those obtained by conventional oven heating. The temperature profile along each individual ribbon was relatively homogeneous, being an indicative of a good nanoparticle dispersion, confirmed by field emission gun scanning electron microscope analysis. Furthermore, the proposed printed circuits showed excellent strain-sensing capabilities with a much higher strain sensitivity, with a gauge factor of 6–8, in comparison to conventional metallic gauges or bulk nanocomposites, with a gauge factor of around 2, showing also good linearity. In addition, the breakage of individual ribbons can be easily detected by the strain-sensing system as a sharp increase of the electrical resistance. Finally, temperature compensation tests showed that, in case of printed ribbon breakage, it is possible to keep constant the average temperature of the circuit by raising the applied voltage to avoid ice accretion. Thus, with none to two broken ribbons, the 3D printed circuit can act as an efficient anti-icing and de-icing system.

A performance mapping of GNP/epoxy composites was developed according to their electromechanical and electrothermal properties for applications as strain sensors and Joule heaters. To achieve this purpose, a deep theoretical and experimental study of the thermal and electrical conductivity of nanocomposites has been carried out, determining the influence of both nanofiller content and sonication time. Concerning dispersion procedure, at lower contents, higher sonication times induce a decrease of thermal and electrical conductivity due to a more prevalent GNP breakage effect. However, at higher GNP contents, sonication time implies an enhancement of both electrical and thermal properties due to a prevalence of exfoliating mechanisms. Strain monitoring tests indicate that electrical sensitivity increases in an opposite way than electrical conductivity, due to a higher prevalence of tunneling mechanisms, with the 5 wt.% specimens being those with the best results. Moreover, Joule heating tests showed the dominant role of electrical mechanisms on the effectiveness of resistive heating, with the 8 wt.% GNP samples being those with the best capabilities. By taking the different functionalities into account, it can be concluded that 5 wt.% samples with 1 h sonication time are the most balanced for electrothermal applications, as shown in a radar chart.

This paper studies the development and characterization of 3D printed conductive circuits based on epoxy inks doped with carbon nanotubes (CNTs) and/or graphene nanoplatelets (GNPs), which could be used in applications such as electronic circuits, heated seats, Anti-icing and De-Icing Systems (ADIS) or Structural Health Monitoring (SHM) systems, among others. A design of experiments (DOE) has been carried out by the Taguchi method to develop and optimize an ADIS based on a 3D printed circuit, using a conductive ink doped with CNTs/GNPs to achieve Joules heating. The target of the DOE is based on reaching the highest average temperature, which was measured by infrared thermographic analysis, taking also into account the quality of the 3D printed circuits. The DOE factors were the CNT and GNP content, the voltage applied to the circuit and its geometry, proposing two alternative designs. Finally, a de-icing test was carried out with the optimal parameters obtained from the DOE. Results evince the viability of the system developed, being able to melt an ice layer of 2.5 mm thick in 3 min and 30 s.

Many studies were performed to improve CNT dispersion into epoxy using different mechanical dispersion methods as well as CNT functionalization. In this study, a novel method is introduced to enhance CNT dispersion using 2D nanoclay as a secondary filler. Hence, this study was aimed to investigate the effect of nanoclay platelets on electrical, mechanical, and piezoresistive characteristics of the SWCNTs doped epoxy nanocomposites. Two different types of nanocomposites were prepared for comparison including binary (SWCNT/epoxy) and hybrid (SWCNT-nanoclay/epoxy) states. CNT content of 0.1 wt% was used for the binary and hybrid states while two different nanoclay loadings (0.5 wt% and 1.0 wt%) were employed in the hybrid nanocomposites. Tensile and mode I fracture tests were performed for the mechanical and electromechanical characterization using two probe techniques while electron microscopy and X-ray diffraction were used for microstructural analysis. Results showed severe CNT agglomeration in the binary state whilst a homogenous CNT dispersion was achieved in the ternary states. The binary nanocomposite showed weak performance in terms of electrical, mechanical and piezoresistive properties caused by severe CNT aggregates. On the other hand, addition of nanoclay into CNTs doped epoxy manifested a significant increase in the electrical, mechanical and piezoresistive-sensitivity performance of the hybrid nanocomposites compared to the binary one. The best performance was achieved at 0.5 wt% nanoclay loading where electrical conductivity increased by six orders of magnitude, UTS increased by 37%, KIC and GIC increased by 34% and 64%, respectively, with respect to the binary nanocomposite. Crack-pinning and crack deflection were accounted for the fracture toughness increase in ternary composites. Nonlinear piezoresistivity resulting from the predominate effect of tunneling resistance ruled piezoresistivity in the hybrid nanocomposites. A sensitivity of 2.1 and 2.0 at strain of 0.01 were obtained for 0.5 wt% and 1.0 wt% nanoclay contents, respectively, whereas no sensitivity was achieved for the binary composite.

The present study investigates, through experimental and numerical approaches, the incorporation effect of different weight concentrations of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of epoxy. Tensile and mode I fracture tests were performed to investigate the effect of the addition of MWCNTs on Young’s modulus, Ultimate Tensile Strength (UTS), critical stress intensity factor (KIC) and critical strain energy release rate (GIC). Different carbon nanotubes (CNTs) contents were employed to compare the effect of the resulting microstructures (well-dispersed and agglomerated CNTs) on the mechanical properties. Field Emission Scanning Electron Microscopy (FESEM) and Scanning Electron Microscopy (SEM) were used for microstructural analysis and fractography. Experimental results showed that UTS was improved (28%) by incorporation of MWCNTs while the KIC and GIC were substantially increased by 192% and 614%, respectively. CNT pullout and crack bridging were the main contributing mechanisms in toughening the epoxy at low CNT contents (0.1 and 0.25 wt%). In contrast, a combination of crack bridging and crack branching was responsible for the resin toughening in the case of 0.5 wt% loading. The significant increase for KIC and GIC demonstrated the excellent performance of the dispersion approach used in this study. Finite Element modelling was used to provide a more robust analysis of the effect of CNT incorporation in tension tests and of the toughening mechanism of the nanocomposites in mode-I fracture tests.

Carbon fibers reclamation from waste composites by pyrolysis is developing fast. Pyrolysis allows the reclamation of the fibers by thermal decomposition of the polymeric resin, but the material value of these resins is not yet recovered. In this research work, the possibility of obtaining high-value gaseous fractions by treating the vapors generated in the decomposition of a poly(benzoxazine) containing carbon fiber waste composite has been studied. The experiments have been carried out in a lab-scale facility consisting of two reactors in series. In the first reactor, the pyrolysis of the waste is carried out at 500 °C, while in the second reactor the vapors coming from the first reactor are treated at 900 °C. Such treatment enables to triple the amount of gas in comparison to conventional pyrolysis. Besides, this gas contains 56% by volume of H2, which means the recovery of approximately 60% of the hydrogen contained in the resin. On the other hand, clean carbon fibers with mechanical properties within commercial values have been also obtained.

The influence of dispersion procedure and nanofiller geometry on thermal and electrical properties of graphene nanoplatelet (GNP) based composites has been investigated. A theoretical model, based on the contacts between adjacent nanoparticles, has been proposed aiming to connect thermal and electrical properties. It has been observed that GNP overlapping (type I) induces a decrease on thermal conductivity. Its effect on electrical conductivity is more complex and depends on the areas of overlap and in-plane contacts (type II). A higher type I area in comparison to type II implies an increase of electrical conductivity with overlapping whereas the opposite effect is found when type II area is higher than type I. The predicted results of the theoretical model fitted experimental measurements at different GNP contents and three roll milling processing conditions, giving a better overview of the influence of GNP geometry and interactions on electrical and thermal properties of nanocomposites.

Carbon nanotubes (CNT) were added to epoxy/polycaprolactone (PCL) blends in order to get electrically conductive blends. As it was expected, an increase of CNT content promotes a higher electrical conductivity due to the creation of more electrical pathways. Furthermore, it was observed that the enhancement is also observed with increasing PCL content, reaching values of around 0.2 S/m for 0.2 wt % CNT and 20 wt % PCL samples, due to its effect on rheological properties of the mixture, which affect positively to the CNT dispersion process, thus leading to more homogeneous and well dispersed nanocomposites, as observed by microstructural analysis. Thermal conductivity also increases with CNT content but decreases with PCL addition due to its insulating properties. A study of the voltage required to reach the above-mentioned self-healing temperature for each material has been performed by thermography monitoring. It has been observed that the samples with the highest amount of both CNT and PCL, have the best resistive heating capabilities due to a higher thermoresistive efficiency of the electrical network, reaching temperatures above 100 °C, at voltages below 150 V.

The electrical behaviour and mechanical properties of functionalized graphene nanoplatelets (GNPs) reinforced epoxy-based composites were evaluated. These properties were analysed scaling up from the nanocomposite to the multiscale composite material. The electrical conductivity of 12 wt % GNPs reinforced nanocomposites was in the order of 10 −4 S/m, in contrast to the in-plane conductivity of multiscale composite materials with the same GNPs content, which was found to be ∼10 −3 S/m. This was attributed to microstructural features that also provoke the electrical conductivity through the thickness diminish down to ∼10 −4 S/m in multiscale composites. Additionally, mechanical properties were enhanced by the dispersion of GNP in nanocomposites but experienced a reduction in glass fibre composites because of the formation of a weak interface between the GNPs filled matrix and fibres.

The addition of graphene nanoplatelets (GNPs) into the epoxy adhesives has been studied in order to increase their thermal conductivity. Thermally conductive adhesives are often used as thermal interface materials (TIMs). The incorporation of 8 and 10 wt% GNPs reinforcement caused a thermal conductivity enhancement of ~206 and ~306%, respectively. The wettability seems to decrease with low GNPs content (2–3 wt%) in comparison with the neat epoxy adhesive but the contact angle remains constant for higher GNPs contents. Lap shear strength remains constant for neat adhesives and resins doped with GNPs. The lack of enhancement of adhesive properties of doped resins is due to a weak interface reinforcement-matrix. In fact, the joint failure is in the adhesive except for high GNPs content (10 wt%) where a cohesive failure mode is observed.