1,720,958 research outputs found
Rubber Seed Oil-Based UV-Curable Polyurethane Acrylate Resins for Digital Light Processing (DLP) 3D Printing
Get PDFNovel UV-curable polyurethane acrylate (PUA) resins were developed from rubber seed oil (RSO). Firstly, hydroxylated rubber seed oil (HRSO) was prepared via an alcoholysis reaction of RSO with glycerol, and then HRSO was reacted with isophorone diisocyanate (IPDI) and hydroxyethyl acrylate (HEA) to produce the RSO-based PUA (RSO-PUA) oligomer. FT-IR and 1H NMR spectra collectively revealed that the obtained RSO-PUA was successfully synthesized, and the calculated C=C functionality of oligomer was 2.27 per fatty acid. Subsequently, a series of UV-curable resins were prepared and their ultimate properties, as well as UV-curing kinetics, were investigated. Notably, the UV-cured materials with 40% trimethylolpropane triacrylate (TMPTA) displayed a tensile strength of 11.7 MPa, an adhesion of 2 grade, a pencil hardness of 3H, a flexibility of 2 mm, and a glass transition temperature up to 109.4 ◦C. Finally, the optimal resin was used for digital light processing (DLP) 3D printing. The critical exposure energy of RSO-PUA (15.20 mJ/cm2) was lower than a commercial resin. In general, this work offered a simple method to prepare woody plant oil-based high-performance PUA resins that could be applied in the 3D printing industry
From Glassy Plastic to Ductile Elastomer: Vegetable Oil-Based UV-Curable Vitrimers and Their Potential Use in 3D Printing.
No full textCurrent UV-curable resins based on acrylate or methacrylate monomers are mostly derived from nonrenewable petroleum feedstocks, and the cured resins are not easily repairable or reprocessable due to the stable cross-linked network. In this work, bio-based UV-curable di methacrylate compounds are synthesized via a reaction of the vegetable oil-derived dimer acid with glycidyl methacrylate. The length and flexibility of the chain segment between the two methacrylate groups are manipulated to tune the properties of the cross-linked polymer materials. The UV-cured materials exhibit a tensile strength of up to 9.2 MPa and an elongation at break of up to 66.4%. At elevated temperatures (\u3e160 oC), the thermally induced dynamic trans-esterification reaction (DTER) between hydroxyl groups and ester bonds in the network structure provides repairability to the material. The use of the UV-resin for three-dimensional (3D) printing is demonstrated. The printed objects exhibit unique welding and shape-changing properties owing to the thermally induced DTER. This work integrates the concepts of UV curing, vitrimer preparation, 3D printing, and bio-based polymers, demonstrating a feasible approach for the sustainable design of polymer materials
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Trade-offs Between Limonene & Geraniol-Based Reprocessable and Non-Reprocessable Epoxy Thermosets: Role of Aliphatic Diamines in Polymer Networks Design.
No full textThe growing demand for sustainable materials, driven by environmental concerns and the rapid depletion of fossil fuels, has garnered significant attention in bio-based thermosets fabrication. Petroleum-derived thermosetting polymers can be replaced with renewable alternatives such as limonene and geraniol-derived epoxy prepolymers. The present study focuses on the synthesis and characterization of limonene and geraniol-based epoxy prepolymers over a two-step process and their thermally crosslinked thermosets using different aliphatic diamines. Incorporating cystamine, a disulfide-containing diamine, introduced a covalent adaptable network via disulfide metathesis, achieving a reprocessable thermoset with self-healing capabilities, recyclability, and extended lifespan. In contrast, traditional aliphatic diamines produced a permanently crosslinked thermoset with superior mechanical strength, thermal stability, and chemical resistance, ideal for high-performance applications requiring durability with maximum tensile strength of 11.62 MPa and 17.9 MPa for limonene and geraniol derived epoxy thermoset, respectively. Differential scanning calorimetry (DSC) elucidated the curing kinetics and crosslinking behavior, while thermogravimetric analysis (TGA) confirmed excellent thermal stability. Dynamic mechanical analysis (DMA) and tensile testing also demonstrated desirable mechanical properties. The glass transition temperature (Tg) of the limonene- and geraniol-derived malleable thermosets was determined by dynamic mechanical analysis (DMA) at 18C and 25℃, respectively. Above these temperatures, the malleable thermosets exhibited dynamic behavior facilitated by disulfide bond exchange. In addition, the developed materials displayed maximum tensile strengths of 3.1 MPa and 3.66 MPa, highlighting their mechanical robustness and potential for reprocessable applications
Trade-off Between Limonene-based Reprocessable and Non-Reprocessable Epoxy Thermosets: Role of Aliphatic Diamines in Polymer Networks Design
No full textThe increasing demand for sustainable materials, driven by environmental concerns and the rapid depletion of fossil fuel resources, has led to significant advancements in the fabrication of bio-based thermosets. Renewable alternatives, such as limonene-derived epoxy prepolymers, offer a promising replacement for petroleum-based thermosetting polymers, exhibiting comparable mechanical strength, thermal stability, and chemical resistance for applications in films, composites, coatings, and adhesives. This study presents the synthesis and characterization of limonene-based epoxy prepolymers through a two-step process, followed by their thermal crosslinking with various aliphatic diamines to fabricate thermosets. Incorporating cystamine, a disulfide-containing diamine, facilitated the formation of a covalent adaptable network via disulfide metathesis, yielding a reprocessable thermoset with self-healing capabilities, recyclability, and an extended lifespan. In contrast, thermosets cured with conventional aliphatic diamines formed permanently crosslinked networks with enhanced mechanical strength, thermal stability, and chemical resistance, making them suitable for high-performance applications requiring long-term durability with a maximum tensile strength of 11.62 MPa at an elongation of 22.2 %. Differential scanning calorimetry (DSC) was employed to elucidate the curing kinetics and crosslinking behavior, while thermogravimetric analysis (TGA) confirmed the excellent thermal stability of the synthesized materials. Additionally, dynamic mechanical analysis (DMA) and tensile testing demonstrated desirable mechanical properties. The absolute value of the glass transition temperature (Tg) determined from DMA analysis was 18 ℃, above which the malleable thermoset exhibited dynamic behavior due to disulfide bond exchange. Furthermore, the reprocessable thermoset exhibited a maximum tensile strength of 3.1 MPa at an elongation of 65 % and excellent reprocessability. Overall, this study highlights the potential of limonene-derived epoxy thermosets as sustainable alternatives, offering robust properties such as reprocessability, self-healing, and high-performance networks
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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