1,720,958 research outputs found
Bio-Based Epoxy Adhesives Reinforced with Recycled Fillers
Full text linkThis study explores the potential of a bio-based thermosetting adhesive system incorporating recycled fillers to enhance structural bonding applications while promoting sustainability. Diglycidylether of vanillyl alcohol (DGEVA) was selected as the resin matrix due to its favorable thermomechanical properties and low moisture absorption. To improve mechanical performance and support circular economy principles, recycled carbon fibers (RCFs) and mineral wool (MW) were integrated into the adhesive formulation in varying proportions (10, 30, and 50 phr). A cationic thermal initiator, ytterbium (III) trifluoromethanesulfonate (YTT), was used to permit polymerization. Comprehensive characterization was performed to assess the curing behavior, thermal stability, and mechanical performance of the adhesive. FTIR spectroscopy monitored the polymerization process, while DSC and dynamic DSC provided insights into reaction kinetics, including activation energy, and curing rates. The mechanical and thermomechanical properties were evaluated using dynamic mechanical thermal analysis (DMTA) and shear lap testing on bonded joints. Additionally, SEM imaging was employed to examine fillers’ morphology and joint interfaces. The results indicated that increasing filler content slowed polymerization and raised activation energy but still permitted high conversion rates. Both RCF- and MW-containing formulations exhibited improved stiffness and adhesion strength, particularly in CMC joints. These findings suggest that DGEVA-based adhesives reinforced with recycled fillers offer a viable and sustainable alternative for structural bonding, contributing to waste valorization and green material development in engineering applications
Biobased Epoxidized Castor Oil Covalent Adaptable Networks Adhesives Reinforced with Recycled Carbon Fibers
Full text linkThe development of sustainable, smart, and functional adhesives is crucial in advancing environmentally friendly materials. In
this study, a fully biobased adhesive based on Covalent Adaptable Networks (CANs) is presented, integrating epoxidized castor oil
(ECO) as the bio-based monomer and a novel eugenol-based phosphate ester (EUGP) as the transesterification catalyst. The system
was further enhanced with Recycled Carbon Fibers (RCF) as reinforcing filler. The curing process was thermally initiated using
Ytterbium(III) trifluoromethanesulfonate (YTT), enabling efficient crosslinking even at room temperature over 24 h, permitting
an eco-friendly production. Extensive characterizations were conducted. FT-IR confirmed high conversion rates, even with 20 phr
of RCF, proving the curing efficiency. DSC revealed curing kinetics, and DMTA revealed a tunable glass transition temperature
(0–10 ◦◦C) depending on the filler content. Rheological stress-relaxation tests demonstrated rapid stress relaxation (1000 s at
70 ◦◦C), confirming dynamic bond exchange and reprocessability. Contact angle analysis confirmed the presence of hydrophobic
surfaces, which enhance moisture resistance. TGA indicated thermal stability up to 105 ◦◦C. Mechanical tests performed on
different joined substrates (metals and ceramic composites) showed that both adhesive bulk and joint strength at room temperature
increased with fiber loading. Rebonded joints retained 74–91% of their initial strength after two repair cycles. By exploiting
transesterification chemistry, bio-based materials, and recycled conductive fillers, this study highlights a sustainable alternative
to conventional adhesives. The results indicate that the analyzed fully biobased adhesive offers promising applications in flexible
electronics, smart adhesives, and advanced composites, supporting the transition toward more environmentally responsible
materials
Ternary formulations of bio-based grapeseed oil-based monomers for 3D printing: Effect of thiol-ene reaction on acrylic radical photopolymerization
No full textThe development of new renewable resin formulation for VAT 3D printing is one of the most actively researched topics in chemistry and materials science. In this sense, a good balance of sustainability and final properties should be developed. Therefore, this work aims to use grapeseed oil-GSO, acrylated seed oil-AGSO, and Trimethylolpropane tris(3-mercapto propionate) – 3SH as monomers for new printable formulations. These formulations were investigated to understand the types of reactions that can occur during photopolymerization. Therefore, two reactions can occur depending on the system: thiol-ene polymerization (TEP) and free radical polymerization (FRP). All formulations showed conversion values superior to 80% and are feasible to be applied in VAT 3D printing to print complex structures. Moreover, formulations containing a higher quantity of GSO-3SH presented biobased carbon content superior to 72% and gel content higher than 99%. Last, the amount of the TE part (GSO-3SH) affects the glass transition temperature, mechanical properties (toughness, stress, strain), and hydrophobicity. Therefore, materials with different stress, strain, and toughness can be designed using various concentrations of each monomer
Green Design of Renewable Dual-Curing Polymers with Self-Healing and Recyclable Networks for 3D Printing
Full text linkThis work presents a green design approach for a novel class of dual-curing, self-healing polymers derived from vegetable oils for additive manufacturing. The polymer network is constructed from methacrylated and epoxidized monomers derived through environmentally friendly transformations, allowing for UV-curing radical polymerization followed by thermal curing via acid–epoxy reactions. The resulting materials exhibit self-healing behavior, supporting thermal reprocessing and chemical recycling via transesterification. Designed for circularity, polymers containing the vegetable oil derivatives─methacrylated and epoxidized─reached a biobased content of up to 98% and a biobased carbon content above 77%, far exceeding industry standards. The materials also display alkaline hydrolytic degradation, aligning with end-of-life strategies under a circular economy model. Dual-curing systems achieved an epoxy conversion of over 90% and gel contents above 97%, resulting in stable polymer networks suitable for reprocessing. The formulations were successfully processed using 3D printing platforms, producing well-defined structures despite viscosities exceeding the ideal printability window. The system containing the maleinized/methacrylated grapeseed oil and epoxidized castor oil showed the most favorable behavior, with lower overcuring and the lowest critical energy (37 mJ cm– 2). Successful printing confirms the applicability of these systems
3D printing with biobased epoxidized formulations based on vegetable oils with dynamic polymer network properties
No full textIn this work, we developed and characterized bio-based formulations derived from functionalized vegetable oils, aiming to create sustainable resins suitable for 3D printing with dynamic polymer network (DPN) properties. Epoxidized castor oil (ECO), known for its inherent DPN behaviour due to the presence of hydroxyl groups enabling transesterification, was used as the primary component. However, its high viscosity at room temperature limits its printability. To address this, epoxidized soybean oil (ESO), a less viscous and equally bio-based alternative, was blended with ECO in varying weight ratios: 100% ECO, 100% ESO, ECO–ESO 70–30, and ECO–ESO 50–50. UV-curing characterization of the prepared formulations was performed through FTIR and photo-DSC. Their thermal and mechanical properties were investigated through DMTA and tensile tests, while rheological analyses were conducted to assess their printability. DPN behaviour was evaluated via stress relaxation tests in the presence of a bio-based transesterification catalyst, eugenol-based phosphate ester (EUGP). Among the blends, the ECO–ESO 70–30 formulation retained good DPN dynamics, while in the 50–50 blend, this feature decreased due to the lack of hydroxyl groups in ESO. The DPN systems demonstrated successful 3D printability and were proven to be thermally reprocessable. This work highlights the potential of renewable, plant-oil-based materials in advancing circular and sustainable additive manufacturing technologies
Advancing green additive manufacturing: Epoxidized vegetable oils for room-temperature photopolymerization 3D printing
No full textThis work reports, for the first time, renewable biobased epoxy formulations specifically designed for conventional VAT 3D printing under low light intensity, at room temperature, and in the complete absence of acrylic
monomers. No previous study has described photocurable systems with these combined characteristics. The
epoxy monomers were synthesized from three renewable feedstocks—macaw palm, grapeseed, and castor oils—via a green, efficient, and rapid epoxidation route that achieved full conversion of double bonds. Epoxidized
macaw palm oil (EMPO), due to its low viscosity, was employed as a reactive diluent in binary formulations.
Cationic photopolymerization was initiated through charge transfer complexes (CTCs) formed by either
isopropyl-9H-thioxanthen-9-one (ITX) or curcumin (CUR), combined with an iodonium borate photoinitiator.
The photocurable systems reached epoxy conversions of 60–78 % within 120 s of irradiation. All formulations
exhibited high renewability metrics, with bio-based content >97 %, bio-based carbon >50 %, and gel fractions
>99 %. DMA confirmed the influence of epoxidized grapeseed and castor oils on glass transition temperature and
crosslinking density. Notably, all ITX-based systems enabled the successful 3D printing of complex structures,
establishing a novel route for sustainable, high-performance resins in additive manufacturing
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
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
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