546 research outputs found

    New understanding of the shape-memory response in thiol-epoxy click systems: towards controlling the recovery process

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    Our research group has recently found excellent shape-memory response in ‚Äúthiol-epoxy‚ÄĚ thermosets obtained with click-chemistry. In this study, we use their well-designed, homogeneous and tailorable network structures to investigate parameters for better control of the shape-recovery process. We present a new methodology to analyse the shape-recovery process, enabling easy and efficient comparison of shape-memory experiments on the programming conditions. Shape-memory experiments at different programming conditions have been carried out to that end. Additionally, the programming process has been extensively analysed in uniaxial tensile experiments at different shape-memory testing temperatures. The results showed that the shape-memory response for a specific operational design can be optimized by choosing the correct programming conditions and accurately designing the network structure. When programming at a high temperature (T ¬Ľ Tg), under high network mobility conditions, high shape-recovery ratios and homogeneous shape-recovery processes are obtained for the network structure and the programmed strain level (eD). However, considerably lower stress and strain levels can be achieved. Meanwhile, when programming at temperatures lower than Tg, considerably higher stress and strain levels are attained but under low network mobility conditions. The shape-recovery process heavily depends on both the network structure and eD. Network relaxation occurs during the loading stage, resulting in a noticeable decrease in the shape-recovery rate as eD increases. Moreover, at a certain level of strain, permanent and non-recoverable deformations may occur, impeding the completion and modifying the whole path of the shape-recovery process.Postprint (author's final draft

    Laboratory 3.0: manufacturing technologies laboratory virtualization with a student-centred methodology

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    This paper presents a blended-learning strategy for improving the teaching method applied in the laboratory subject Manufacturing Technologies. The teaching method has been changed from a predominantly teacher-centred to an active learning system with a student-centred focus and e-learning activities. In face-to-face classes, a game-based learning platform has been used. This methodology ensured engaging classes at the same time that provided a useful live feedback for students and teachers. The virtualization of the laboratory was achieved by two different e-learning activities, self-assessment tasks and video clips. These e-learning tools have been used not only to improve the students’ learning but also to enhance their motivation. The results from academic outputs show a significant improvement after the new blended learning method is applied. Moreover, a student satisfaction survey shows the positive impact of the methodology on the students’ engagement and motivationPeer Reviewe

    Laboratori 3.0: virtualització del laboratori amb una metodologia centrada en l'estudiant

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    This paper presents an improvement introduced to a laboratory subject by means of a student - centered blended - learning teaching strategy. The implemented virtual tools (videos and questionnaires) help to prepare the practical sessions and allow the sel f - assessment before and after each practical session. Students have shown a great satisfaction with the method. The analysis of the qualifications obtained has allowed an assessment of the degree of correlation between the different techniques used.Postprint (published version

    Novel hybrid organic/inorganic poly(thiourethane) covalent adaptable networks

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    Organic-inorganic hybrid materials combine the advantages of both phases: hardness and strength of inorganic phase and elasticity and toughness of the organic matrix. In the present study, we have prepared nanocomposites with a poly(thiourethane) polymeric matrix and silsesquioxane-type structures, with thiols as reactive groups (POSS-A or POSS-B, synthesized in different pressure conditions), looking for a covalent interaction between both phases, and good dispersion. Due to the click behavior of the reaction between the isocyanate and the thiol groups, highly homogeneous materials are obtained. Both monomers, catalyst (dibutyltin dilaurate, DBTDL), and the POSS precursor (3-mercaptopropyl trimethoxysilane, MPTMS), are commercially available, which present the advantage of being industrially scalable. The incorporation of POSS leads to an increase in glassy and rubbery storage moduli and the temperature of the maximum of tan delta curve. The vitrimeric behavior of the poly(thiourethanes) improved with the POSS incorporation, getting lower relaxation times. With a higher proportion of closed cages, POSS-B leads to the most significant improvements. All the materials prepared showed high transparency and the fracture of POSS modified materials indicates an improved toughness.This work is part of the R & D projects PID2020-115102RB-C21 and PID2020-115102RB-C22 funded by MCINAEI/10.13039/501100011033. We acknowledge these grants and the Generalitat de Catalunya (2017-SGR-77 and BASE3D) . The authors declare the following financial interests/personal re-lationships which may be considered as potential competing interests: Angels Serra reports financial support was provided by Spain Ministry of Science and Innovation

    Preparation and Characterization of a Series of Self-Healable Bio-Based Poly(thiourethane) Vitrimer-like Materials

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    A series of poly(thiourethanes) (PTUs) from biobased monomers have been synthesized. Limonene and squalene were transformed into polyfunctional thiols by thiol-ene reaction with thioacetic acid and further saponification. They were then reacted in different proportions with hexamethylene diisocyanate (HDI) in the presence of a catalyst to prepare bio-based poly(thiourethane) vitrimer-like materials. The different functionalities of squalene and limonene thiols (six and two, respectively) allow for changing the characteristics of the final material by only varying their relative proportions in the reactive mixture. The proportions of thiol and isocyanate groups were stoichiometric in all the formulations tested. An acidic and a basic catalyst were tested in the preparation of the networked polymers. As the acidic catalyst, we selected dibutyltin dilaurate (DBTDL), and as the basic catalyst, a tetraphenylborate salt of 1,8-diazabicyclo(5.4.0)undec-7-ene (BGDBU), which has the advantage of only releasing the base at high temperatures. The materials obtained were characterized by thermogravimetry and thermomechanical analysis. The vitrimeric-like behavior was evaluated, and we could see that higher proportions of the limonene derivative in the formulations led to faster stress relaxation of the material. The use of the base catalyst led to a much shorter relaxation time. The materials obtained demonstrated good self-healing efficiencyPeer ReviewedPostprint (published version

    New bio-based materials obtained by thiol-ene/thiol-epoxy dual curing click procedures from eugenol derivates

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    Novel bio-based and dual-curable thermosets were prepared from eugenol derivatives. The curing sequence combined two click reactions, a photoinduced radical thiol-ene reaction followed by a thermally activated thiol-epoxy reaction. Eugenol was transformed into a triallyl (3A-EU) and a diallyl glycidyl derivative (2AG-EU) with high yields, and they were used as starting monomers in order to study the thiol-ene reaction and the dual-curing process, respectively. Three different thiol crosslinkers were tested, one commercially available tetrathiol derived from pentaerythritol (PETMP) and two other that were also synthesized: a trithiol derived from eugenol (3SH-EU) and a hexathiol derived from squalene (6SH-SQ). FTIR and DSC were used to monitor both curing stages and analyze the obtained materials. The results evidenced the occurrence of side reactions that led to incomplete thiol-ene reaction. The dual-curable materials showed higher Tgs than the materials obtained by a simple thiol-ene process and presented higher mechanical and thermomechanical performance.Postprint (author's final draft

    The use of lanthanide triflates in the preparation of poly(thiourethane) covalent adaptable networks

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    Covalent adaptable networks (CANs) are new polymeric materials with the mechanical properties of thermosets and the possibility of being recycled like thermoplastics. Poly(thiourethane) networks have demonstrated vitrimeric-like behavior at high temperatures due to the trans-thiocarbamoylation process, which Lewis acids and bases can accelerate. In this study, we report the use of lanthanide triflates (La, Sm, Dy, Er, and Yb) as Lewis acid catalysts, a greener alternative to other metallic catalysts as dibutyltin dilaurate (DBTDL) widely used in poly (urethane) and poly(thiourethane) networks. Moreover, they are not as reactive as DBTDL, and the curing mixture can be manipulated for a longer time at room temperature. As monomers, trimethylolpropane tris(3- mercapto propionate) (S3), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI) have been used. We have demonstrated that the materials prepared with lanthanum triflate present the lowest relaxation times than those prepared with other lanthanide triflates or DBTDL. Calorimetry (DSC) and infrared spectroscopy (FTIR) were applied to study the curing process. The materials obtained were fully characterized by thermog- ravimetric analysis (TGA) and thermomechanical tests (DMA).This work is part of the R&D projects PID2020-115102RB-C21 and PID2020-115102RB-C22 funded by MCNI/AEI/10.13039/ 501100011033. We acknowledge these grants and to the Generalitat de Catalunya (2021-SGR-00154 and BASE3D). F.G. thanks to MCNI/AEI for the grant PRE2018-084192.Postprint (published version

    Sequential curing of off-stoichiometric thiol-epoxy thermosets with a custom-tailored structure

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    A new dual-curing system based on sequential thiol-epoxy click polycondensation and epoxy anionic homopolymerization was studied. Formulations of diglycidyl ether of bisphenol A and trimethylolpropane tris(3-mercaptopropionate) with 1-methylimidazole as a base catalyst and excess of epoxy groups were prepared and characterized. The curing process is sequential: fast thiol-epoxy polycondensation takes place first, followed by slower homopolymerization of excess epoxy groups. This makes it possible to define curing sequences with easy time-temperature control for both curing stages. The network buildup process during the first curing stage can be easily modelled assuming ideal polycondensation, which allows tailoring the structure and properties of the intermediate materials. The homopolymerization of the excess epoxy groups in the second curing stage results in a higher glass transition temperature (T-g) in comparison with the stoichiometric thiol-epoxy material, thus extending the application of thiol-epoxy thermosets to wider temperature ranges.Postprint (published version

    Tribological Behavior of Microalloyed Cu50Zr50 Alloy

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    Promoting the martensitic transformation through optimum microalloying with Fe and/or Mn was observed to be an effective method to enhance the wear resistance of the Cu50Zr50 at% shape memory alloy (SMA). Among all the potential microelements and concentrations, partial replacement of Cu by up to 1 at% Fe and Mn is of interest since from density functional-based calculations, large minimization of the stacking fault energy (SFE) of the B2 CuZr phase is predicted. For this reason, an effective martensitic transformation is expected. The largest decrease of the SFE from 0.36 J/m2 to 0.26 J/m2 is achieved with partial replacement of Cu by 0.5 at% Fe. This results in the highest martensitic transformation upon wear testing, especially at highest load (15 N) for which the mass loss is 0.0123 g compared to 0.0177 g for Cu50Zr50 and a specific wear-rate of 5.9 mm3/Nm, compared to 8.5 for mm3/Nm for Cu50Zr50. This agrees with the low coefficient of friction of 0.48 ¬Ī 0.05 and low roughness of 0.200 ¬Ī 0.013 ¬Ķm of the Fe-containing alloy compared to that for Cu50Zr50, 0.55 and 0.415 ¬Ī 0.026 ¬Ķm, respectively. All the worn surfaces show the formation of abrasive grooves, being shallowest for the more wear resistant 0.5 at% Fe alloy. The second more wear resistant alloy contains 0.5 at% Mn. Wear mechanisms of abrasion, adhesion, and delamination have been identified

    Measuring universal health coverage based on an index of effective coverage of health services in 204 countries and territories, 1990‚Äď2019: a systematic analysis for the Global Burden of Disease Study 2019

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    Background Achieving universal health coverage (UHC) involves all people receiving the health services they need, of high quality, without experiencing financial hardship. Making progress towards UHC is a policy priority for both countries and global institutions, as highlighted by the agenda of the UN Sustainable Development Goals (SDGs) and WHO's Thirteenth General Programme of Work (GPW13). Measuring effective coverage at the health-system level is important for understanding whether health services are aligned with countries' health profiles and are of sufficient quality to produce health gains for populations of all ages. Methods Based on the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019, we assessed UHC effective coverage for 204 countries and territories from 1990 to 2019. Drawing from a measurement framework developed through WHO's GPW13 consultation, we mapped 23 effective coverage indicators to a matrix representing health service types (eg, promotion, prevention, and treatment) and five population-age groups spanning from reproductive and newborn to older adults (‚Č•65 years). Effective coverage indicators were based on intervention coverage or outcome-based measures such as mortality-to-incidence ratios to approximate access to quality care; outcome-based measures were transformed to values on a scale of 0‚Äď100 based on the 2¬∑5th and 97¬∑5th percentile of location-year values. We constructed the UHC effective coverage index by weighting each effective coverage indicator relative to its associated potential health gains, as measured by disability-adjusted life-years for each location-year and population-age group. For three tests of validity (content, known-groups, and convergent), UHC effective coverage index performance was generally better than that of other UHC service coverage indices from WHO (ie, the current metric for SDG indicator 3.8.1 on UHC service coverage), the World Bank, and GBD 2017. We quantified frontiers of UHC effective coverage performance on the basis of pooled health spending per capita, representing UHC effective coverage index levels achieved in 2019 relative to country-level government health spending, prepaid private expenditures, and development assistance for health. To assess current trajectories towards the GPW13 UHC billion target‚ÄĒ1 billion more people benefiting from UHC by 2023‚ÄĒwe estimated additional population equivalents with UHC effective coverage from 2018 to 2023. Findings Globally, performance on the UHC effective coverage index improved from 45¬∑8 (95% uncertainty interval 44¬∑2‚Äď47¬∑5) in 1990 to 60¬∑3 (58¬∑7‚Äď61¬∑9) in 2019, yet country-level UHC effective coverage in 2019 still spanned from 95 or higher in Japan and Iceland to lower than 25 in Somalia and the Central African Republic. Since 2010, sub-Saharan Africa showed accelerated gains on the UHC effective coverage index (at an average increase of 2¬∑6% [1¬∑9‚Äď3¬∑3] per year up to 2019); by contrast, most other GBD super-regions had slowed rates of progress in 2010‚Äď2019 relative to 1990‚Äď2010. Many countries showed lagging performance on effective coverage indicators for non-communicable diseases relative to those for communicable diseases and maternal and child health, despite non-communicable diseases accounting for a greater proportion of potential health gains in 2019, suggesting that many health systems are not keeping pace with the rising non-communicable disease burden and associated population health needs. In 2019, the UHC effective coverage index was associated with pooled health spending per capita (r=0¬∑79), although countries across the development spectrum had much lower UHC effective coverage than is potentially achievable relative to their health spending. Under maximum efficiency of translating health spending into UHC effective coverage performance, countries would need to reach 1398pooledhealthspendingpercapita(US1398 pooled health spending per capita (US adjusted for purchasing power parity) in order to achieve 80 on the UHC effective coverage index. From 2018 to 2023, an estimated 388¬∑9 million (358¬∑6‚Äď421¬∑3) more population equivalents would have UHC effective coverage, falling well short of the GPW13 target of 1 billion more people benefiting from UHC during this time. Current projections point to an estimated 3¬∑1 billion (3¬∑0‚Äď3¬∑2) population equivalents still lacking UHC effective coverage in 2023, with nearly a third (968¬∑1 million [903¬∑5‚Äď1040¬∑3]) residing in south Asia. Interpretation The present study demonstrates the utility of measuring effective coverage and its role in supporting improved health outcomes for all people‚ÄĒthe ultimate goal of UHC and its achievement. Global ambitions to accelerate progress on UHC service coverage are increasingly unlikely unless concerted action on non-communicable diseases occurs and countries can better translate health spending into improved performance. Focusing on effective coverage and accounting for the world's evolving health needs lays the groundwork for better understanding how close‚ÄĒor how far‚ÄĒall populations are in benefiting from UHC
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