Examinando por Autor "Prolongo, S.G."

Mostrando 1 - 7 de 7

Double percolation approach for hybrid graphene Nanoplatelet-Carbon black nanocomposites based on electrical impedance Spectroscopy
(Elsevier, 2024-09) Sánchez-Romate, X.F.; Jiménez-Suárez, A.; Sanz-Ayet, J.M.; García-Martínez, V.; Gude, M.R.; Prolongo, S.G.
A double-percolation model for predicting electrical properties in hybrid carbon black (CB)-graphene nanoplatelet (GNP) nanocomposites is proposed. This model is based on DC and EIS measurements. From DC measurements, a non-ohmic behavior is observed for low-filled nanocomposites whereas at high-filled ones, an ohmic behavior is noticed. From EIS analysis, the behavior of the system can be modeled by an equivalent circuit formed by a series of inductance-resistance capacitance (LRC), for contact and intrinsic electrical mechanisms, and resistance–capacitance (RC) elements, for tunneling transport, where the capacitances are substituted by Constant Phase Elements (CPEs) due to the presence of scattering effects. The complex impedance analysis shows a GNP-dominated electrical behavior at a high CB/GNP ratio. At a medium CB/GNP ratio a double percolating network is formed. At a low CB/GNP ratio, the electrical transport is CB-dominated. The proposed model based on the classical percolation theory with a double threshold properly fits the electrical measurements
Electroactive shaping and shape memory of sequential dual-cured off-stoichiometric epoxy/CNT composites
(Elsevier, 2021) Prolongo, S.G.; Díaz-Maroto, C.G.; Jiménez-Suárez, A.
Sequential dual-cured epoxy composites, based on off-stoichiometric thiol–epoxy mixtures catalysed by 1-methylimidazole, have been developed by adding carbon nanotubes (CNT). The epoxy curing process initially consists in two thermally activated curing stages: a first thiol–epoxy reaction and later homopolymerization at a higher temperature. This system presents easy shaping/conforming and shape memory properties through thermo-mechanical treatments. Addition of the electrical CNT network into the epoxy matrix allows electrical switching, which increases its performance and in-situ applicability. The obtained results confirmed that CNTs catalyse the homopolymerization epoxy reaction, hindering the sequential curing process, due to the π–π anchoring of imidazole catalyser over the CNTs surface, enhanced by donor–acceptor interaction. Non-doped off-stoichiometric resins present relatively high thermal strength, with a glass transition temperature in the range of 73–109 °C, and high stiffness, with a storage modulus close to 2–3 GPa. They can be easily conformed at low temperature, 60 °C, before their second curing stage, showing a high shaping efficiency (around 90%) and full fixing efficiency (>98%). Nanocomposites with 0.2% CNT present efficient Joule heating, triggering the shape memory at low voltage, <80 V, with fixing and recovery efficiencies of 60–85%. In addition to its high in-situ applicability, the electrical resistive heating is faster and more efficient than conventional heating in an oven.
Enhancing efficiency and sustainability of digital light processing 3D-Printing by novel two-stage processing of carbon nanotube reinforced nanocomposites
(Elsevier, 2024-03) Cortés, A.; Bañón-Veracruz, M.; Jiménez-Suárez, A.; Campo, M.; Prolongo, M.G.; Prolongo, S.G.
3D printing has gained a spot within the industry during the last decade due to the advantages it presents regarding conventional manufacturing technologies. Nevertheless, the high processing time and the material waste due to the use of printing supports are still some of the main challenges that have to be addressed. In this research work, a simple strategy to minimize the processing time and the material waste is carried out through a two-stage processing method. Here, a flat specimen is obtained using a vat photopolymerization 3D printer, presenting a low curing degree. Then, the specimen is bent and subsequent post-curing treatments are performed to increase the cross-link density, thus fixing the desired shape. Furthermore, carbon nanotubes were used as nanoreinforcement for increasing the mechanical properties and exploiting their Joule heating capabilities for the thermal post-curing treatment, being way less energy-consuming (around 1W) than using a conventional oven (around 750 W). The results obtained with a proof-of-concept evinced the suitability of the proposed two-stage processing method to enhance the efficiency and sustainability of the 3D printing process. The printing time and the material waste were reduced by 94.3 % and 16.7 % on average, respectively, with regard to printing the part directly on its final desired shape, as well as showing a shape fixity ratio of around 98 %. Furthermore, an enhancement of the mechanical properties was obtained due to the reorientation of the printed layers during the two-stage processing
Mechanical recycling and electro-thermal welding of epoxy vitrimer nanocomposites
(Wiley, 2024-02-03) Lorero, I.; Mujica, A.; Campo M.; Prolongo, S.G.
Vitrimers constitute a new class of recyclable thermosets based on the incorporation of associative dynamic covalent bonds, such as disulfide bonds, into the crosslinked matrix. These reversible bonds usually require excess dynamic bonds to confer proper self-healing and recycling capabilities to the thermoset. In that way, we manufacture epoxy resins cured with 4-aminophenyl disulfide (AFD) in a stoichiometric ratio, and with 10 and 20 wt% of AFD excesses to analyze the effect of composition on resin properties. Beyond the neat vitrimers analysis, we manufacture nanocomposites doped with carbon nanotubes (CNT) to obtain electroactive vitrimers. These epoxy resins and nanocomposites can be mechanically recycled by milling and hot-pressing. The recycled nanocomposites conserve partially CNT integrity and dispersion. Even more, recycled nanocomposites with AFD excesses maintain the mechanical strength of the pristine nanocomposites. Vitrimer nanocomposite samples can be also electrically welded, due to their heating by the Joule effect, through a relatively low voltage application, and therefore with low energy consumption, to obtain a monolithic specimen. In summary, the manufactured epoxy vitrimers and nanocomposites are recyclable and sustainable epoxy materials, which can be processed and reprocessed using technologies easily implementable, fast, and with low energy consumption
Recycling development and shaping of a thermo-reversible epoxy resin with partial contents of Diels-Alder bonds
(Elsevier, 2024-05) Lorero, I.; Rico, B.; Campo, M.; Prolongo, S.G.
Thermo-mechanical recycling and reshaping of dynamic covalent networks is a promising field under development that could help to increase thermoset sustainability. Herein, the reprocessing of a partially reversible epoxy resin with a 0.6 Diels-Alder crosslink ratio, which has a relatively high Tg and a simplified manufacturing route, is studied to determine the optimal conditions for its thermomechanical recycling through milling and hot-pressing, and reshaping. Thus, in this work, we have studied the influence of compaction time, pressure, and temperature on recycled bulk properties. Meanwhile, different heating temperatures and times are also tested to evaluate the cured resin shaping to fix a new geometry and to observe its shape-recovering capability. Their characterization reveals that the recycling method generates dense thermosetting polymers with similar crosslinking structure and behavior, comparable to the virgin resin, inducing light post-curing that increases their glass transition temperature (Tg). The most efficient thermo-mechanical recycling conditions consist of the application of isothermal compaction at 130 °C and 150 bar for 30 min, which leads to resin bulks with comparable properties to the neat resin even after 3 cycles of milling and hot-pressing. On the other hand, the synthesized resin has shown excellent shaping due to the structural relaxation induced by the initiation of retro Diels-Alder reaction, adopting new geometries easily when the samples are heated above their Tg (91 °C) and preserving them after cooling to ambient temperature. Moreover, the samples also show high shape-recovering after heating again up to Tg. This reshaping and recovery have been maintained for several cycles without observing an irreversible lack of shape fixing or shape recovery
Sequential and selective shape memory by remote electrical control
(Elsevier, 2021) Cortés, A.; Pérez-Chao, N.; Jiménez-Suárez, A.; Campo, M.; Prolongo, S.G.
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.
Temperature-dependent synergistic self-healing in thermoplastic-thermoset blends: Unraveling the role of thermoplastics and dynamic covalent networks
(Elsevier, 2024-03) Jiménez-Suárez, A.; Buendía Sanchez, G.; Prolongo, S.G.
Two different self-healing approaches are studied in this work to analyze the possible contribution of each of the self-healing mechanisms at different temperatures and the possible synergetic effects between them. Thermal and mechanical properties were differently affected by the addition of each of the thermoplastic polymers. This was caused by different phase separations induced during the curing reaction in terms of size and number of the thermoplastic phase domains dispersed within the epoxy matrix and due to the different amounts of thermoplastic polymer that remain solved in the matrix. When using the vitrimeric matrix, phase separation only occurred at the nanometer scale when utilizing poly(bisphenol-A-co-epichlorohydrin) (PBAE) as a thermoplastic agent or higher contents of polycaprolactone (PCL). Self-healing capabilities showed a strong dependence on the temperature used and the type of crack. Low temperatures allowed the thermoplastic phase to flow and fill partially the cracks with moderate levels of self-healing which were only available when phases were separated. Higher temperatures allowed dynamic bonds to induce material healing reaching very high efficiencies but, more importantly, a synergic effect was observed when material was removed from the cracks. In these cases, the flow of the thermoplastic phase filled better the crack and there was an enhanced cooperation between the two healing mechanisms. At higher self-healing temperatures, materials with nanometric size phase separation enabled greater self-healing efficiencies (above 90 %) due to the vitrimeric self-healing capability while the thermoplastic phase helped fill the gaps due to material removal