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[EN] This work focuses on the manufacturing and characterization of highly environmentally friendly lightweight sandwich structures based on polylactide (PLA) honeycomb cores and PLA-flax fabric laminate skins or facings. PLA honeycombs were manufactured using PLA sheets with different thicknesses ranging from 50 to 500 mu m. The PLA sheets were shaped into semi-hexagonal profiles by hot-compression molding. After this stage, the different semi-hexagonal sheets were bonded together to give hexagonal panels. The skins were manufactured by hot-compression molding by stacking two Biotex flax/PLA fabrics with 40 wt% PLA fibers. The combined use of temperature (200 degrees C), pressure, and time (2 min) allowed PLA fibers to melt, flow, and fully embed the flax fabrics, thus leading to thin composite laminates to be used as skins. Sandwich structures were finally obtained by bonding the PLA honeycomb core with the PLA-flax skins using an epoxy adhesive. A thin PLA nonwoven was previously attached to the external hexagonal PLA core, to promote mechanical interlock between the core and the skins. The influence of the honeycomb core thickness on the final flexural and compression properties was analyzed. The obtained results indicate that the core thickness has a great influence on the flexural properties, which increases with core thickness; nevertheless, as expected, the bonding between the PLA honeycomb core and the skins is critical. Excellent results have been obtained with 10 and 20 mm thickness honeycombs with a core shear of about 0.60 and facing bending stresses of 31-33 MPa, which can be considered as candidates for technical applications. The ultimate load to the sample weight ratio reached values of 141.5 N center dot g(-1) for composites with 20 mm thick PLA honeycombs, which is comparable to other technical composite sandwich structures. The bonding between the core and the skins is critical as poor adhesion does not allow load transfer and, while the procedur

[EN] This research is focused on manufacturing and characterization of hybrid composite laminates obtained different stacking sequences of basalt and flax fabrics with silane treatments embedded in a partially bio-sourced epoxy resin as matrix. They were manufactured by the vacuum-assisted resin infusion molding and mechanical properties were tested in tensile, flexural and impact conditions. The effect of the coupling agent on the fiber/matrix interface was studied by FESEM. The effect of temperature on mechanical properties was evaluated by DMTA and TMA. FESEM images revealed improved fiber/matrix interactions with silane treatment, having a more satisfactory effect on basalt fibers than on flax fibers because of its silica-based structure, leading to improved mechanical properties. It is worthy to note that the hybrid stacking sequence has no remarkable influence on the elongation at break. On the contrary, the hybrid stacking sequence offered a great influence on both the elastic modulus and the tensile strength.

[EN] Eco-effcient Wood Plastic Composites (WPCs) have been obtained using poly(hydroxybutyrate-co-hexanoate) (PHBH) as the polymer matrix, and almond shell flour (ASF), a by-product from the agro-food industry, as filler/reinforcement. These WPCs were prepared with different amounts of lignocellulosic fillers (wt %), namely 10, 20 and 30. The mechanical characterization of these WPCs showed an important increase in their stiffness with increasing the wt % ASF content. In addition, lower tensile strength and impact strength were obtained. The field emission scanning electron microscopy (FESEM) study revealed the lack of continuity and poor adhesion among the PHBH-ASF interface. Even with the only addition of 10 wt % ASF, these green composites become highly brittle. Nevertheless, for real applications, the WPC with 30 wt % ASF is the most attracting material since it contributes to lowering the overall cost of the WPC and can be manufactured by injection moulding, but its properties are really compromised due to the lack of compatibility between the hydrophobic PHBH matrix and the hydrophilic lignocellulosic filler. To minimize this phenomenon, 10 and 20 phr (weight parts of OLA-Oligomeric Lactic Acid per one hundred weight parts of PHBH) were added to PHBH/ASF (30 wt % ASF) composites. Differential scanning calorimetry (DSC) suggested poor plasticization effect of OLA on PHBH-ASF composites. Nevertheless, the most important property OLA can provide to PHBH/ASF composites is somewhat compatibilization since some mechanical ductile properties are improved with OLA addition. The study by thermomechanical analysis (TMA), confirmed the increase of the coeffcient of linear thermal expansion (CLTE) with increasing OLA content. The dynamic mechanical characterization (DTMA), revealed higher storage modulus, E¿, with increasing ASF. Moreover, DTMA results confirmed poor plasticization of OLA on PHBH-ASF (30 wt % ASF) composites, but interesting compatibilization effects.

[EN] This works focuses on the development of environmentally friendly composites with a partially biobased polyamide 610 (PA610), containing 63% biobased content, and a natural inorganic filler at the nanoscale, namely, halloysite nanotubes (HNTs). PA610 composites containing 10, 20, and 30 wt% HNTs were obtained by melt extrusion in a twin screw co-rotating extruder. The resulting composites were injection-molded for further characterization. The obtained materials were characterized to obtain reliable data about their mechanical, thermal, and morphological properties. The effect of the HNTs wt% on these properties was evaluated. From a mechanical standpoint, the addition of 30 wt% HNTs gave an increase in tensile modulus of twice the initial value, thus verifying how this type of natural load provides increased stiffness on injection molded parts. The materials prepared with HNTs slightly improved the thermal stability, while a noticeable improvement on thermomechanical resistance over a wide temperature range was observed with increasing HNTs content. The obtained results indicate that high biobased content composites can be obtained with an engineering thermoplastic, i.e., PA610, and a natural inorganic nanotubeshaped filler, i.e., HNTs, with balanced mechanical properties and attractive behavior against high temperature.

[EN] The purpose of this paper is to study and outline the effects of infill parameters (percentage and pattern) using fused deposition manufacturing on mechanical properties of PLA printed samples. Three infill patterns were tested (rectilinear, honeycomb and Hilbert curve) while infill percentage was tested at three levels (20, 60 and 90 per cent). The properties examined were tensile strength, tensile modulus, elongation, Charpy impact test, morphology of the fractures of tensile and impact test and thermo mechanical analysis. Also, a thermal analysis was done using differential scanning calorimetry to the raw polymer in order to determine the processing temperature. Results showed the influence of the filling parameters in 3D printing on the mechanical properties of the obtained part. The filling pattern greatly influences the mechanical properties of parts with low filling percentages. Honeycomb filling pattern is the one with better mechanical results. The complexity of the filling pattern influences on the processing time. Nozzle direction changes in complex patterns lengthen processing time. Results can significantly influence custom design and manufacturing of parts using material fused deposition modeling., [ES] El propósito de este trabajo es estudiar y esbozar los efectos de los parámetros del relleno (porcentaje y patrón) de la fabricación por deposición fundida sobre las propiedades mecánicas de probetas de PLA. Se han analizado tres patrones de relleno (rectilíneo, panal de abeja y curva Hilbert), y tres porcentajes de relleno distintos (20, 60 y 90 por ciento). Las propiedades examinadas fueron resistencia a la tracción, módulo de tracción, alargamiento, tenacidad utilizando ensayo Charpy, morfología de las fracturas de los ensayos de tracción e impacto y análisis termomecánico. Además, se realizó un análisis térmico utilizando calorimetría diferencial de barrido al polímero virgen para determinar la temperatura de procesamiento. Los resultados mostraron la influencia de los parámetros de llenado en la impresión 3D sobre las propiedades mecánicas de la pieza obtenida. El patrón de llenado influye en gran medida en las propiedades mecánicas de las piezas con bajos porcentajes de relleno. El patrón de relleno de panal de abeja es el que tiene mejores resultados mecánicos de los tres analizados. La geometría del patrón de relleno también influye sobre el tiempo de procesado. Los cambios de dirección de las boquillas en patrones complejos alargan el tiempo de procesamiento. Los resultados obtenidos pueden influir significativamente en el diseño y la fabricación de piezas a medida mediante el modelado de la deposición de material fundido.

[EN] In the present study, partially bio-based polyethylene terephthalate (bio-PET) was melt-mixed at 15-45 wt% with recycled polyethylene terephthalate (r-PET) obtained from remnants of the injection blowing process of contaminant-free food-use bottles. The resultant compounded materials were thereafter shaped into pieces by injection molding for characterization. Poly(styrene-co-glycidyl methacrylate) (PS-co-GMA) was added at 1-5 parts per hundred resin (phr) of polyester blend during the extrusion process to counteract the ductility and toughness reduction that occurred in the bio-PET pieces after the incorporation of r-PET. This random copolymer effectively acted as a chain extender in the polyester blend, resulting in injection-molded pieces with slightly higher mechanical resistance properties and nearly the same ductility and toughness than those of neat bio-PET. In particular, for the polyester blend containing 45 wt% of r-PET, elongation at break (epsilon(b)) increased from 10.8% to 378.8% after the addition of 5 phr of PS-co-GMA, while impact strength also improved from 1.84 kJm(-2) to 2.52 kJm(-2). The mechanical enhancement attained was related to the formation of branched and larger macromolecules by a mechanism of chain extension based on the reaction of the multiple glycidyl methacrylate (GMA) groups present in PS-co-GMA with the hydroxyl (-OH) and carboxyl (-COOH) terminal groups of both bio-PET and r-PET. Furthermore, all the polyester blend pieces showed thermal and dimensional stabilities similar to those of neat bio-PET, remaining stable up to more than 400 degrees C. Therefore, the use low contents of the tested multi-functional copolymer can successfully restore the properties of bio-based but non-biodegradable polyesters during melt reprocessing with their recycled petrochemical counterparts and an effective mechanical recycling is achieved.

[EN] In the present work, green¿composites from a partially biobased epoxy resin (BioEP) reinforced with lignocellulosic particles, obtained from flax industry by¿products or wastes, have been manufactured by casting. In this study, the flaxseed has been crushed by two different mechanical milling processes to achieve different particle sizes, namely coarse size (CFF), and fine size (FFF) particle flaxseed flour, with a particle size ranging between 100¿220 ¿m and 40¿140 ¿m respectively. Subsequently, different loadings of each particle size (10, 20, 30, and 40 wt%) were mixed with the BioEP resin and poured into a mold and subjected to a curing cycle to obtain solid samples for mechanical, thermal, water absorption, and morphological characterization. The main aim of this research was to study the effect of the particle size and its content on the overall properties of composites with BioEP. The results show that the best mechanical properties were obtained for composites with a low reinforcement content (10 wt%) and with the finest particle size (FFF) due to a better dispersion into the matrix, and a better polymer¿particle interaction too. This also resulted in a lower water absorption capacity due to the presence of fewer voids in the developed composites. Therefore, this study shows the feasibility of using flax wastes from the seeds as a filler in highly environmentally friendly composites with a wood¿like appearance with potential use in furniture or automotive sectors.

[EN] This study describes an experienced teaching method in the subject of Materials Science, which is studied in the framework of different degrees at the Universitat Politècnica de València, Spain. The main objective of this method was to motivate and stimulate the student's interest through to study relevant and real consequences of materials failures. The method was conducted by analysing real examples of aeronautics failures that occurred in the aerospace and aeronautical industry. The case studies described in this experience were the Challenger shuttle and the comet plane catastrophic failures. In order to verify the validity of the teaching experience, the students' perception compared to the traditional teaching method was taken into account. On the other hand, the positive results were seen through the evaluation proposed in the curriculum. Collaterally, the ethical sense and good practice is commented and worked on, a subject that is very important and sometimes little worked on in our classrooms. It can be concluded that the use of reverse engineering is of high interest to students and allows some basic concepts of materials science to be explained in a more global way than when they are traditionally explained in the master class.

[EN] A doctoral thesis is a major work that lasts approximately 3 years. During this period, the doctoral student faces with a large number of tasks that must be planned and structured in order to increase the productivity of work of this nature. In this paper it is presented an experience of using a set of a free web and mobile application (Trello) for the management and planning of the tasks of the thesis, with the aim of increasing the motivation and productivity of doctoral students in the development of their PhD. With the application of these computer tools in a systematic and planned way during the development of the research work, it has been proven that the results are improved as a result of the structuring, the student assumes more responsibility and is more inclined to take the initiative, the task planning also facilitates the subsequent documentation of results. Therefore, the use of these tools makes it easier to achieve the final objective of the development of a doctoral thesis, which is that the student demonstrates that can generate knowledge.

[EN] In the present study, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] was reinforced with hydroxyapatite nanoparticles (nHA) to produce novel nanocomposites for potential uses in bone reconstruction. Contents of nHA in the 2.5¿20 wt % range were incorporated into P(3HB-co-3HHx) by melt compounding and the resulting pellets were shaped into parts by injection molding. The addition of nHA improved the mechanical strength and the thermomechanical resistance of the microbial copolyester parts. In particular, the addition of 20 wt % of nHA increased the tensile (Et) and flexural (Ef) moduli by approximately 64% and 61%, respectively. At the highest contents, however, the nanoparticles tended to agglomerate, and the ductility, toughness, and thermal stability of the parts also declined. The P(3HB-co-3HHx) parts filled with nHA contents of up to 10 wt % matched more closely the mechanical properties of the native bone in terms of strength and ductility when compared with metal alloys and other biopolymers used in bone tissue engineering. This fact, in combination with their biocompatibility, enables the development of nanocomposite parts to be applied as low-stress implantable devices that can promote bone reconstruction and be reabsorbed into the human body

[ES] Este trabajo se centra en la fabricación y caracterización de nuevos materiales tipo sándwich híbridos de bajo peso, con diferentes configuraciones de apilamiento de refuerzo de basalto y lino tratadas previamente con silanos. Para aligerar el peso y facilitar la fabricación, se empleó un núcleo de poliéster no tejido que, además de aligerar el peso del compuesto también actuó como medio de difusión de la resina. Se empleó una resina epoxi de origen parcialmente renovable con un diluyente reactivo derivado de aceites vegetales epoxidados que contribuye a un 31 % de origen renovable. Los compuestos híbridos se fabricaron mediante moldeado por infusión de resina asistida por vacío (VARIM), donde el núcleo se utilizó como medio de infusión de la resina. Las propiedades mecánicas se evaluaron en condiciones de impacto y de flexión. La interacción en la intercara fibra-matriz se evaluó por medio de microscopía electrónica de barrido de emisión de campo (FESEM). Los datos revelaron que el tratamiento de silanos funciona mejor en las fibras de basalto que en las fibras de lino, resultando en propiedades a flexión superiores en las estructuras donde estas fibras están presentes. Cabe mencionar que la distribución de apilamiento influye directamente en las propiedades a flexión, pero no afecta en la absorción de energía en condiciones de impacto., [EN] This work focuses on the manufacturing and characterization of novel and lightweight hybrid sandwichtype structures, using different stacking sequences of flax and basalt fabrics as reinforcement fibers, both of them previously silanized. To reduce the overall weight and facilitate the manufacturing process, a polyester non-woven core, was used which, besides reducing the weight of the composite it also acts as a media to spread the resin. These composites were manufactured with a partially bio-based epoxy resin with a reactive diluent derived from epoxidized vegetable oils that contributes to a 31 % of biobased content. The hybrid composites were obtained by vacuum-assisted resin infusion moulding (VARIM), where the core was used as a media to spread the resin. The mechanical properties were evaluated in flexural and impact conditions. The interactions in the fiber-matrix interface were studied through field emission scanning electron microscopy (FESEM). The obtained data revealed that the silane (coupling agent) treatment works better on basalt fibers than on flax fibers, resulting in superior flexural properties on structures where these fibers are present. It is noteworthy to mention that the stacking sequence of plies directly influences the flexural properties, but it does not significantly affect the energy absorbed when these composites work on impact conditions.

In the present study, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HHx)] was reinforced with hydroxyapatite nanoparticles (nHA) to produce novel nanocomposites for potential uses in bone reconstruction. Contents of nHA in the 2.5–20 wt % range were incorporated into P(3HB-co-3HHx) by melt compounding and the resulting pellets were shaped into parts by injection molding. The addition of nHA improved the mechanical strength and the thermomechanical resistance of the microbial copolyester parts. In particular, the addition of 20 wt % of nHA increased the tensile (Et) and flexural (Ef) moduli by approximately 64% and 61%, respectively. At the highest contents, however, the nanoparticles tended to agglomerate, and the ductility, toughness, and thermal stability of the parts also declined. The P(3HB-co-3HHx) parts filled with nHA contents of up to 10 wt % matched more closely the mechanical properties of the native bone in terms of strength and ductility when compared with metal alloys and other biopolymers used in bone tissue engineering. This fact, in combination with their biocompatibility, enables the development of nanocomposite parts to be applied as low-stress implantable devices that can promote bone reconstruction and be reabsorbed into the human body.

[EN] This research work aims to study the influence of the reprocessing cycles on the mechanical, thermal, and thermomechanical properties of polylactide (PLA). To this end, PLA was subjected to as many as six extrusion cycles and the resultant pellets were shaped into pieces by injection molding. Mechanical characterization revealed that the PLA pieces presented relatively similar properties up to the third reprocessing cycle, whereas further cycles induced an intense reduction in ductility and toughness. The effect of the reprocessing cycles was also studied by the changes in the melt fluidity, which showed a significant increase after four reprocessing cycles. An increase in the bio-polyester chain mobility was also attained with the number of the reprocessing cycles that subsequently favored an increase in crystallinity of PLA. A visual inspection indicated that PLA developed certain yellowing and the pieces also became less transparent with the increasing number of reprocessing cycles. Therefore, the obtained results showed that PLA suffers a slight degradation after one or two reprocessing cycles whereas performance impairment becomes more evident above the fourth reprocessing cycle. This finding suggests that the mechanical recycling of PLA for up to three cycles of extrusion and subsequent injection molding is technically feasible.