1,721,089 research outputs found
Diels-Alder Macromolecular Networks in Recyclable, Repairable and Reprocessable Polymer Composites for the Circular Economy – A Review
Full text linkIn the expanding field of high-performance materials, polymer-based thermoset composites play an important role due to their favorably-high strength/weight ratio and their mechanical performance, thermal stability, and chemical resistance. However, their chemically-crosslinked nature hampers their re-processability and efficient recyclability, thus making them not compliant with the principles of the circular economy and of end-of-life valorization. Dynamic covalent polymers able to modify their network topology upon thermal stimulus can be considered valid alternatives to commonly used thermosets as they offer advantages in terms of recyclability and reusability, normally not achievable with conventional cross-linked systems. Within the broad field of dynamic polymers, thermally-triggered Diels-Alder based materials represent reliable platforms with enormous technological and industrial potential as repairable, reusable and recyclable matrices in composites given their chemical versatility, suitable mechanical performance and ease of production and processing. In this review, a comprehensive discussion of the most recent demonstrations of the reversibility, reprocessability and recyclablability of such systems is provided, in the context of their use as polymer matrices in composites. It is hoped that this work will stimulate further discussion and research in the area of reversible polymer composites with increased functionality and extended lifetime, in view of their application in future circular economy scenarios
Fluoropolymeric luminescent downshifters for organic-dye-sensitized solar cells
No full textAs a feasible option for photovoltaic technology to meet the growing energy demand, dye-sensitized solar cells (DSSCs) have attracted much attention due to their low cost, ease of fabrication and good performance. In particular, metal-free organic dyes are currently under investigation because of their low cost and high molar extinction coefficient; thus, they are ideal sensitizer for large-scale applications. However, their absorption range is often narrow, so that an important portion of the solar spectrum is not absorbed. In this context, we think that luminescent materials, which are capable of converting a broad spectrum of light into photons of a particular wavelength, can be used to improve the light harvesting efficiency of the solar-cell-based energy conversion process. In this work, for the first time ever new crosslinked fluoropolymeric systems are employed as luminescent downshifters for organic-dye-sensitized solar cells. The effect of these parameters on the photovoltaic cells and the study of devices aging will be presente
Stimuli-responsive polymer nanocomposites: Reversibility as a tool for advanced manufacturing of functional devices
No full textOver the past decade, rapid developments and advancements in the electronic industry have led to a sharp increase in electronic waste (e-waste) disposed in landfills and not reusable. A wide and diversified range of advanced materials are present in e-waste. Among them, polymer nanocomposites represent a valuable example of high-added-value materials that can have however negative environmental consequences. Although thermoset polymer nanocomposites have demonstrated various beneficial properties such as high chemical resistance, and good mechanical strength, owing to their covalently crosslinked network, their potential damage could shorten the lifespan of electronic devices, increasing the amount of e-waste. To extend their service life, polymer matrices with self-healing abilities, and a good recovery of mechanical properties after healing have been developed. In this context, polymer matrices with dynamic covalent bonds activated by a thermal stimulus stand out as an attractive choice because they combine the re-processability of thermoplastics with the high mechanical performance of thermoset polymers. This chapter will discuss two emerging categories of polymer matrices with thermally reversible covalent bonds: Diels-Alder (DA)- and vitrimer-based systems. Within these two classes of dynamic polymer nanocomposites, the focus will be on the reaction mechanisms enabling self-healing, the types of nanofillers used, the recovery of mechanical and functional properties after damage, and the potential applications in devices and sensors. This work will therefore foster new studies and discussions in the field of repairable electronic and functional devices to prolong their lifetime and reduce their environmental impact
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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