1,720,957 research outputs found
Fully bio-based furan/maleic anhydride epoxy resin with enhanced adhesive properties
No full textEpoxy resins are widely used in a variety of application fields, thanks to their good mechanical strength, chemical resistance and adhesion to several substrates. Nowadays, the quite majority of epoxy resins are based on derivatives of bisphenol A (BPA), which poses serious health concerns. This issue is pushing the research towards suitable bio-based alternatives to this product, being furan-based epoxies very promising in this respect. In a previous work, 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan (BOMF) was cured with methyl nadic anhydride (MNA), and successfully used as tinplate coating. Herein, in a view of increasing the sustainability of these epoxy resins, we have replaced MNA with maleic anhydride (MA), which can be derived from vegetable feedstocks, thus obtaining a fully bio-based epoxy resin. This latter has then been used as adhesive for carbon fiber-reinforced thermosetting plastics (CFRP). The curing process of the resin was monitored by differential scanning calorimetry (DSC) and chemo-rheological analysis. The results highlighted the significantly higher reactivity of BOMF towards MA compared to the diglycidyl ether of BPA (DGEBA). The crosslinked samples were characterized in their thermal, mechanical and adhesive properties. In comparison to DGEBA/MA and BOMF/MNA, BOMF/MA showed higher ultimate strain and slightly lower glass transition temperature, tensile modulus and ultimate strength. Interestingly, BOMF/MA displayed outstanding adhesive strength on CFRP joints, outperforming the DGEBA-based counterpart by three times. Indeed, by properly selecting the anhydride curing agent, a highly ductile fully bio-based material was developed for high performance adhesive applications. The overall results demonstrate that the properties of BOMF-based epoxy resins can be tailored to meet technical and safety requirements of downstream applications, representing a sustainable alternative to traditional systems containing DGEBA
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
Curing Behavior and Properties of Sustainable Furan-Based Epoxy/Anhydride Resins
No full textThe last two decades have witnessed a significant growth in using bioderived materials, driven by the necessity of replacing fossil-derived precursors, reducing the fossil fuel consumption, and lowering the global environmental impact. This is possible thanks to the availability of abundant resources from biomasses and the development of optimized technologies based on the principles of sustainability and circular economy. Herein, we report on the synthesis and characterization of new carbohydrate-derived epoxy resins. In particular, 2,5-bis[(oxiran-2-ylmethoxy)methyl]furan has been synthesized and cured with methyl nadic anhydride. The effect of different initiators was studied, in order to identify the most efficient curable formulations. A series of resins was then prepared varying the epoxide–anhydride ratios. The results gathered from physicochemical, mechanical, morphological analyses have demonstrated that the produced furan-based thermosets have the potential to be proposed as sustainable alternatives to the traditional, bisphenol A-containing epoxy resins
Biobased furan-based epoxy/TiO2 nanocomposites for the preparation of coatings with improved chemical resistance
No full textBiobased, solvent-free thermosetting coating systems are developed from epoxidized hydroxymethylfuran (BOMF) crosslinked with methyl nadic anhydride (MNA) filled with TiO2 nanoparticles. The effect of 1 to 5 wt% of TiO2 on the curing behavior of the resin and the overall performance of the resulting coatings is studied by means of rheological, thermal, mechanical, morphological, and chemical resistance tests. TiO2 particles shift the curing reaction to higher temperatures and reduce the reaction enthalpy, resulting in lower crosslinking degrees and glass transition temperatures. The resins are applied as tinplate coatings, exhibiting optimal adhesion to the metal substrate (5A according to ASTM D3359), and performing well in pencil hardness tests (9H and 7H in gouge and scratch hardness, respectively). Morphological characterization highlights homogeneous distribution of TiO2 nanoparticles even at the highest loading. Finally, the chemical resistance of the coatings to ethanol and acetic acid solutions used as simulants is significantly enhanced by the addition of TiO2, resulting in an efficient protection of the tinplate from corrosion. Overall, these results demonstrate that the proposed furan-based thermosets show potential for use as coatings
Bio-based epoxy resin/carbon nanotube coatings applied on cotton fabrics for smart wearable systems
No full text: Electroactive coatings for smart wearable textiles based on a furan bio-epoxy monomer (BOMF) crosslinked with isophorone diamine (IPD) and additivated with carbon nanotubes (CNTs) are reported herein. The effect of BOMF/IPD molar ratio on the curing reaction, as well as on the properties of the crosslinked resins was first assessed, and it was found that 1.5:1 BOMF/IPD molar ratio provided higher heat of reaction, glass transition temperature, and mechanical performance. The resin was then modified with CNT to prepare electrically conductive nanocomposite films, which exhibited conductivity values increased by eight orders of magnitude upon addition of 5 phr of CNTs. The epoxy/CNT nanocomposites were finally applied as coatings onto a cotton fabric to develop electrically conductive, hydrophobic and breathable textiles. Notably, the integration of CNTs imparted efficient and reversible electrothermal behavior to the cotton fabric, showcasing its potential application in smart and comfortable wearable electronic devices
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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