1,720,958 research outputs found
Castor oil-based UV curable acrylate resins for digital light processing (DLP) 3D printing technology
No full textBiobased resins are a promising sustainable alternative to traditional petroleum-based polymers in Digital Light Processing (DLP) 3D printing. This study focuses on developing a castor oil-based UV-curable acrylate resin that is renewable. Castor oil was chemically modified with methacrylic anhydride (MAA) via an esterification process to synthesize castor oil-based methacrylate ester (CO_MAA), enhancing its photopolymerization efficiency and crosslinking potential. To comprehensively evaluate the resin\u27s properties, several characterization techniques such as FT-IR and NMR spectroscopy were conducted that confirmed the successful chemical modification. Furthermore, the viscosity measurements of the CO_MAA resins were investigated to gain insight into the printability of the synthesized photocurable resins. Indeed, the dynamic mechanical analysis (DMA) of the UV-cured film of CO_MAA exhibits a glass transition temperature (Tg) of 10.44 oC. Moreover, the thermal properties of the UV-cured object were examined by TGA analysis, demonstrating that the resin can withstand high temperatures before degradation. Tensile testing showed the tensile strength of CO_MAA film is 1.8 MPa, confirming the material\u27s elasticity and mechanical strength. Additionally, gel content and swelling behavior validated the resin\u27s crosslinking efficiency and solvent resistance. The results indicate that this castor oil-derived resin exhibits excellent UV-curability, strong mechanical properties, and high-resolution printability, making it a promising material for DLP 3D printing applications
Effect of Diamine and Triamines Crosslinkers on the Adhesive Properties of Soybean Oil-Based Non-Isocyanate Polyurethane
No full textNowadays, polyurethanes (PUs) play a major role in the polymer industry and are more and more popular due to their advantages and unique mechanical and chemical properties in different applications like foams, paint, coatings, elastomers, and adhesives, Bio-based sources have recently gained attention as sustainable alternatives to conventional petroleum-based material. Due to growing environmental concerns and the excessive use of petroleum-based products, this study explores non-isocyanate polyurethanes (NIPUs) as sustainable, low-toxicity alternatives to traditional PUs. To achieve this, as a starting material, soybean oil (SBO) was used, and it was converted into epoxidized soybean oil (ESBO). ESBO was then converted into CSBO using a Parr autoclave reactor in the presence of tetrabutylammonium bromide (TBAB). Then synthesized CSBO was characterized using physicochemical experiments, e.g. FT-IR, Oxirane oxygen percentage (%EOC content), viscosity analysis, gel permeation chromatography (GPC), and also the 1H NMR spectra further verified the formation of CSBO, Following the successful synthesis of CSBO, we used solvent-free and catalyst-free methods to synthesize NIPU. For that, we used two different diamines, namely Isophorone diamine (IPDI) and Meta-xylylene diamine (m-XDA), or one triamine, e.g. Tris(2-aminoethyl)amine (TAA). The NIPU adhesive specimens containing IPDA and m-XDA as curing agents exhibit lap shear strength of 1.1 MPa and 4.97 MPa respectively on the wood coupon. However, TAA containing adhesive sample shows excellent shear strength of 7.62 MPa on stainless-steel metal coupon under the optimized condition. The thermal transition of all fabricated adhesive samples was investigated by DSC analysis which shows higher glass transition temperature (Tg) of 35.12 oC and 34.58 oC for CSBO_IPDA (1:4) and CSBO_TAA (1:2.5) respectively compared to CSBO_m-XDA (1:3.5) specimen (Tg 16.33C) indicating higher cross-linking in the polymer network
Geraniol-Derived Mechanically Robust, Self-Healable, and Reprocessable Epoxy Vitrimer Based on Dynamic Boronic Esters
No full textCovalent Adaptable Networks (CANs) are a pioneering family of polymers that have garnered significant attention in recent years and are characterized by covalent crosslinks that exhibit reversible dynamic alterations by external stimuli. Additionally, unlike traditional thermosets, CANs-particularly vitrimers-exhibit self-healing, reprocessability, shape-memory, and recycling capabilities due to the dynamic feature of covalent crosslinks. Recently, an increasing trend in the global production of thermosets involves rapid consumption of petroleum-based resources, which has become a growing environmental concern. From this perspective, the development of eco-friendly thermosets from bio-based feedstocks is a possible way to overcome these drawbacks. In this context, geraniol is one of the monoterpenoid alcohols, a primary component of several plant oils that become a valuable replacement for petroleum-based resources. In this study, for the first time, a geraniol-derived epoxy vitrimer has been developed by a thermally triggered thiol-epoxy click reaction between the geraniol-based epoxy resin and dynamic diboronic ester dithiol (DBDT) cross-linker. The resulting vitrimer exhibits excellent self-healing properties driven by the topology alteration through the dynamic transesterification of boronic ester bonds. The fabricated epoxy vitrimers possess superior thermal stability and significant mechanical properties with the absolute value of glass transition temperature (Tg) of 38.43 oC determined by DMA analysis. Incorporating dynamic boronic ester linkages imparts an enhanced tensile strength of ~19 MPa, enabling the vitrimer to recover its original shape after deformation (shape memory), solvent recycling ability, and excellent reprocessability with the maximum restoration of mechanical strength. Moreover, the vitrimer was further characterized by a remarkably short relaxation time of 9 s at 140 oC and an activation energy of 22.44 kJ/mol
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
Mechanically Robust, Self-Healing, and Reprocessable Geraniol Based Epoxy Vitrimer by Dynamic Boronic Ester Bonds
No full textCovalent Adaptable Networks (CANs) are an emerging class of polymers with reversible covalent crosslinks that respond dynamically to external stimuli. Unlike conventional thermosets, CANs-particularly vitrimers- exhibit self-healing, reprocessability, shape memory, and recyclability due to their adaptable crosslinking chemistry. The widespread use of thermosets has led to growing concerns over the depletion of petroleum-based resources and environmental impact. To address these challenges, bio-based alternatives offer a sustainable pathway for developing high-performance materials. Geraniol, a naturally occurring monoterpenoid alcohol found in various plant oils, serves as a promising renewable feedstock for polymer synthesis. This study presents the first development of a geraniol-based epoxy vitrimer synthesized via a thermally activated thiol-epoxy click reaction between a geraniol-derived epoxy resin and a diboronic ester dithiol (DBDT) cross-linker. The incorporation of dynamic boronic ester bonds facilitates topological rearrangements, enabling efficient self-healing and reprocessability. The vitrimer demonstrates excellent thermal stability and mechanical strength, with a glass transition temperature (Tg) of 38.43℃ determined through Dynamic Mechanical Analysis (DMA). Additionally, it exhibits a tensile strength of approximately 19 MPa, shape memory behavior, solvent-based recyclability, and outstanding mechanical strength retention after reprocessing. The vitrimer also features a rapid relaxation time of 9 seconds at 140C and an activation energy of 22.44 kJ/mol, highlighting its efficient bond exchange capability. These attributes make the developed vitrimer a strong candidate for sustainable, high-performance applications, offering a viable alternative to traditional thermosets with enhanced environmental benefits
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-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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