1,721,317 research outputs found
Hydrolytic degradation of PLA/Posidonia Oceanica green composites: A simple model based on starting morpho-chemical properties
No full textIn this work, we studied the degradability of PLA-based biocomposites containing Posidonia Oceanica flour at different loading levels and aspect ratios. Hydrolytic tests were carried out in neutral (pH = 7.4) and alkaline (pH = 10) environment. Time-dependent evolution of some key features, including residual mass and solution uptake, was monitored, and correlated with the changes observed in both morphology and chemical structure of the matrix. The results pointed out that biocomposites degraded much faster than neat PLA in both conditions, up to lose 70% of their initial weight after 1000 h immersion. A complex mechanism was unveiled, evidencing the crucial role of the fillers, capable of both imparting degradation to PLA during processing with enhancement of hydrophilicity and offering preferential gateways for solution penetration through filler-matrix interface by capillarity and swelling-aided polymer cracking. Based on data collected, we propose a new model allowing to predict the triggering and final extent of degradation pathways by considering starting morphological and chemical features of composites via the use of a novel yet simple indicator of chemical stability, which we called morphochemical parameter
Melt stabilization of wet polyamide 6
No full textMelt processing of polycondensate polymers must be carried out after careful drying in order to avoid any hydrolytic chain scission caused by the presence of water or other small molecules. In this work, the effect of two different antioxidants on the processing and flow properties of a polyamide 6 sample not dried before processing operations has been studied. One of these stabilizers seems to protect the wet polymer from hydrolytic chain scission. This action has been interpreted considering that the stabilizer hydrolyses instead of the polyamide macromolecules
Structure–property relationship and controlled drug release from multiphasic electrospun carvacrol-embedded polylactic acid/polyethylene glycol and polylactic acid/polyethylene oxide nanofiber mats
Full text linkElectrospinning technologies gained considerable interest over the last decade. In this study, it is proposed a systematic study of polylactic acid/polyethylene glycol (PLA/PEG) and polylactic acid/polyethylene oxide (PLA/PEO) electrospun blends at different concentrations. The effect of blend composition and PEG molecular weight on the morphological and mechanical properties of the mats was evaluated. Furthermore, the kinetic release of carvacrol as model drug in phosphate buffer saline at 37°C was studied and the data were then fitted using an exponential model. The scanning electron microscopy revealed that the morphology of the mats was strongly dependent on the relative ratio PLA:PEG, PLA:PEO and in the presence of carvacrol. Furthermore, the mechanical properties of the mats as well as their carvacrol release rate were successfully tuned by changing the relative ratio of the blend components
Highly porous hollow 3D devices obtained by a combined melt-wet processing for long-term controlled release
Full text linkThe possibility to obtain resistant and reusable hollow devices with differentiated high porosity for storage and tunable long-term controlled release of substances is difficult to achieve efficiently. To solve this problem, we propose a combined melt-wet processing, which allows predictable and tunable morphologies. The process consists in combining Material Extrusion (MEX) with an eco-friendly salt leaching in distilled water, by using a biostable polymer and high percentages of saline porogen. Three blends with PA6/NaCl-30/70wt% composition were extruded, varying the salt particles size, that shows good dispersion in all the filaments, with a spontaneous tendency for bigger particles to accumulate in the central region of the cross-sections, attributable to fluid-dynamic reasons. Blends rheological and mechanical properties appeared suitable for the printing process. The hollow devices were then printed and successfully leached, resulting in homogeneously dispersed pores, with size ranges comparable to those of the porogen for each blend; therefore, the morphology of the pores can be directly predicted by the porogen and it was not altered during processing. Leaching occurred completely, in fact the real porosity for each device was consistent with the theoretical one. Despite the high percentage of voids, the hollow devices appeared to be mechanically resistant and therefore suitable for the application. Controlled release up to 11 days of a model molecule (methylene blue) was tested and predictable kinetics related to pore size were achieved so, therefore, they are easily tunable and versatile. Release data were fitted according to Peppas-Korsmeyer-model to describe the release mechanism related to porosity
Reliability and Fabrication of Molds for Nanoimprinting
No full textDuring the last decade there has been a growing attention to nanoscaled materials and to the related technologies to produce them. The problems to overcome in the manufacturing of these kinds of items increase dramatically on decreasing the dimension of the devices. In this sense, the scientific research has been strongly stimulated to try to improve and optimize all the critical issues. One of the most attractive fields in nanomanufacturing is related to nanoimprinting, i.e. to the possibility to transfer a nanoscaled pattern from a mold to another substrate. In this technology, among the others, there are two main critical steps: the preparation of a good mold and the use of a correct releasing agent to reduce the sticking between the mold and the imprinted substrate. In this review paper the authors will describe the most recent advances on the preparation of the mold, including the studies on the releasing agents used during the manufacturing
Characterization of monopolymer blend of virgin and recycled polyamide 6
No full textIt is a common industrial practice to blend virgin polymer with the same recycled polymer coming from plastic scraps that, in general, has not undergone relevant degradation. In this work, the characteristics of blends of virgin and recycled polyamide have been considered by changing the amount of recycled polymer and the presence of humidity and a stabilizer. Neither dry nor wet stabilized recycled polyamide samples show significant variations of the molecular weight, but the melt Newtonian viscosity of the blends are slightly different from that predicted by an additive rule, despite the same chemical nature of the two components. This holds true even more for the humid unstabilized sample, as its noticeably lower molecular weight implies values lower than those expected on a linearity basis. The situation is different for the mechanical properties; here the morphology reached in the solid state determines a more rigid and brittle material, compared to the pure components, with relevant deviations from linearity for all the recycled samples used to prepare the blends. A different crystallinity as a function of the composition can be invoked to explain this phenomenon. The blends containing dry and wet stabilized recycled polyamide show almost the same behavior, confirming the reduced degradation of these samples
Nanofibrous Polymeric Membranes for Air Filtration Application: A Review of Progress after the COVID‐19 Pandemic
Full text linkAir pollution is one of the major global problems causing around 7 million dead per year. In fact, a connection between infectious disease transmission, including COVID-19, and air pollution has been proved: COVID-19 consequences on human health are found to be more severe in areas characterized by high levels of particulate matter (PM). Therefore, after the COVID-19 pandemic, the production of air filtration devices with high filtration efficiency has gained more and more attention. Herein, a review of the post-COVID-19 pandemic progress in nanofibrous polymeric membranes for air filtration is provided. First, a brief discussion on the different types of filtration mechanism and the key parameters of air filtration is proposed. The materials recently used for the production of nanofibrous filter membranes are presented, distinguishing between non-biodegradable polymeric materials and biodegradable ones. Subsequently, production technique proposed for the fabrication of nanofibrous membranes, i.e., electrospinning and solution blow spinning, are presented aiming to analyze and compare filtration efficiency, pressure drop, reusability and durability of the different polymeric system processed with different techniques. Finally, present challenges and future perspectives of nanofibrous polymeric membranes for air filtration are discussed with a particular emphasis on strategies to produce greener and more performant devices
Thermo-oxidative ageing of an organo-modified clay and effects on the properties of PA6 based nanocomposites
No full textIn this work a careful investigation on the degradation of an organically modified montmorillonite sample (Cloisite 15A) thermal treated under different atmospheres, namely nitrogen, air and oxygen enriched atmosphere was performed. The exposure time of the thermal treatment ranged between 5 and 300 min. The chemical composition evolution as function of the thermal treatment conditions of the clay organic modifier was monitored by means of combined thermogravimetry/Fourier transform infrared spectroscopy (TGA-FTIR). Moreover, the morphological behaviour of treated Cloisite 15A samples as function of the time and of the decomposition atmosphere was investigated by X-ray diffraction analysis (XRD). In order to understand the possible different interactions of neat and degraded modified clay with a polymeric matrix, PA6 based composites containing 5% of clay were prepared in the melt and fully characterized by a rheological, mechanical and morphological point of view. The results showed t..
Ionic tactile sensors as promising biomaterials for artificial skin: Review of latest advances and future perspectives
Full text linkIonic tactile sensors (ITS) are an emerging subfield of wearable electronics, capable of mimicking the human skin, including not only the typical anisotropic structure, mechanical behaviour, and tactile functions but even the mechanosensitive ionic channels that are crucial for the human sense of touch. With the rapid development of intelligent technology, such bioinspired materials constitute the core foundation of intelligent systems and are a candidate to be the next generation e-skins, offering a more accurate and evolved biointerface. In the latest years, a wealth of novel ultra-stretchable ITS was proposed, progressively refining the choice of soft materials, including ion gels, ionic liquids and hydrogels, and fabrication techniques. Regardless of materials and methods adopted, all these tactile sensors can feel mechanical solicitations and external stimuli, thus behaving as – or even better than – human skin. In this review, an overview of the very latest advances in high-performance ITS applied in intelligent systems is reported. First, generality of ITS will be summarized. After, ion gel, ionic liquid, hydrogel, and elastomer ITS will be discussed focusing first on composition, fabrication, type and mode of sensing and then on their characteristics and application. In this perspective, the advantages that biomimetic approaches brought in terms of sensitivity, speed of response and multimodality of sensing will be highlighted, with a particular focus on the development of electrochromic, thermochromic, self-powered and self-healing devices. In conclusion, the prospects of tactile sensors for intelligent systems in biomedicine and robotics will be discussed, along with the possible strategies to overcome the current shortcomings, in terms of biocompatibility, durability, mechanical performance, adhesion to biological substrates, which represent the future challenges
Innovative 3D-printed devices for water pollutant removal: Comprehensive review on printing parameters, composition, properties and performances of the latest 3D-systems
Full text linkWater pollution is one of the most pressing problems of our time; in fact, it contributes to 24 % of global deaths. Therefore, finding an effective and efficient solution is crucially important. In this regard, systems based on polymers and containing, often, fillers, intended for potential water pollutant removal are well established. Recently, simultaneously with the impressive spread of 3D printing, the production of these systems by various additive manufacturing processes is gaining popularity, enabling the rapid production of complex geometries, high porosity, large surface area and mechanical strength. These systems, to date, are becoming particularly competitive with 2D or 1D systems produced by other methods, so understanding them fully is essential. Therefore, here we provide a review of the most recent advances in the field of manufacturing 3D systems for water remediation. First, a brief introduction is proposed on the cathegory of 3D printing, making a distinction between Material Extrusion (MEX) and non-Material Extrusion (non-MEX) systems, and the main performance parameters of water pollutant removal. Next, the process parameters, composition, and morphological and chemical-physical properties of the latest 3D systems are discussed in detail. In the last part, an overview is given of the functional properties of these systems, in terms of removal efficiency and reusability, which is crucial in an ideal life cycle of such systems. In conclusion, the main outcomes and future perspectives for the production of more efficient systems are provided
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