1,720,972 research outputs found
Synthesis, Characterization, Application And Recycling of Bio-based Polyesters
No full textThe PhD research programme focused on the development of new formulations based on bioplastic using polymers with linear and stellar geometry, commercial and ad hoc synthetized. Specifically, these systems were studied starting from two bioplasticss, polycaprolactone (PCL) and polylactic acid (PLA), which, due to their versatility, have been considered among the best alternatives to traditional polymers. In addition, several polymers obtained by enzymatic synthesis starting from a cardanol-based monomer, which is a waste product of the food industry, have been studied. For all the systems prepared, the effects of the chemical nature of the biopolymers on the final properties of the formulations analysed have been extensively studied, and in some cases the end-of-life of these has been investigated by verifying their actual biodegradability. In this research project,two aspects of particular importance were the use of polymers with a star molecular topology, commonly referred to as ‘star-shaped’ polymers, characterised by a low molecular mass, and the study of new sustainable synthesis routes as an alternative to the traditional ones. The star-shaped molecular configuration makes it possible to modulate certain fundamental physical properties of polymers, such as crystallinity, solubility, and the viscosity of the melt and the resulting solutions. In particular, it makes it possible to obtain systems with a higher quantity of functional groups than linear polymers with the same molecular mass, and it is precisely the combination of these characteristics that makes these polymers particularly suitable for combination with other polymer matrices. Specifically, the research activities carried out during the PhD focused on the development of three different systems, two contain polymers with a star-shaped geometry, one PCL-based and one PLA-based, while the last one contains linear cardanol-based polyesters with low molecular, prepared by means of enzymatic synthesis. The first project focused on the development of cross-linked materials characterised by dynamic covalent bonds, starting with a star-shaped polycaprolactone with numerous terminal hydroxyl groups (PCL-OH) used for the development of nanostructured systems based on reduced graphite oxide (rGO). The cross-linking reaction was carried out using methylenediphenyl diisocyanate (MDI) to create systems capable of exchanging bonds through transesterification and transcarbamoylation reactions, in the presence of a tin-based catalyst. In this regard, the combination of dynamic network and the use of rGO, resulted in a material characterised by recycling and self-healing properties with interesting rheological properties at high temperatures. The second project focused on the development of an environmentally friendly synthesis of cardanol-based polyesters to be used as plasticisers for polylactic acid (PLA), starting with a cardanol-based diol and various dimethyl esters such as dimethyl succinate (DMS) and dimethyl adipate (DMA). The innovative aspect of the work involved the use of cardanol-derived diol and the development of an enzymatic polycondensation, which was carried out under milder conditions (85 °C) than those generally used in industry. Finally, the last project focused on one of the most critical aspects for the wide application of polylactic acid (PLA): its recycling. An innovative and effective approach was developed to obtain star-shaped polymers starting from a commercial PLA, using an environmentally friendly solvent-free process based on compounds derived from renewable sources. In particular, starting from a high-mass linear commercial PLA, a depolymerization route based on a bulk alcoholysis reaction in the molten state was developed. For this purpose two polyalcohols, pentaerythritol and dipentaerythritol, and an catalyst from renewable sources, i.e., zinc stearate, were utilized. The polymers thus obtained were then blended with an epoxide derived from castor oil (GE-35H) in order to obtain homogeneous systems with better mechanical properties than the starting polymers
Environmentally Friendly Synthesis of Cardanol-Based Polyesters and Their Application as Poly(lactic acid) Additives
No full textByproducts derived from the food industry are an interesting biomass to valorize as they are cheap to source, their generation does not compete with food and feed production, and their utilization solves the waste disposal issue. In this work, we
focused on the production of a series of polyesters using a cardanol-derived diol produced from the inedible shell of cashew nuts.
The synthesized polymers are 100% biobased since the diacid components of the structure (adipic acid and succinic acid) can also
be bio-derived monomers. Moreover, the overall process is a paradigm for a green circular economy as the synthesis was conducted via mild enzymatic catalysis (T < 90 °C) in a solventless system. The final workup procedure to recover the materials was conducted using the biomass-derived solvent methyl-tetrahydrofuran, therefore presenting a methodology that does not include any petroleumbased component. This work led to the biocatalyzed synthesis of linear cardanol-based polyesters having mean average molecular
weights between 1800 and 4100 g mol−1 and low dispersity values (2 < D̵), which were used to plasticize poly(lactic acid), leading to an increase in the elongation at break of the resulting ble
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
On the Development of Nanocomposite Covalent Associative Networks Based on Polycaprolactone and Reduced Graphite Oxide
Full text linkIn this work, the development of nanocomposite systems based on reduced graphite oxide (rGO) was combined with the development of crosslinked materials characterized by dynamic covalent bonds, i.e., a covalent associative network, starting from ad-hoc synthesized hydroxyl terminated polycaprolactone (PCL-OH). The crosslinking reaction was carried out using methylenediphenyl diisocyanate (MDI) to create systems capable of bond exchanges via transesterification and transcarbamoylation reactions, in the presence of stannous octoate as a catalyst. The above materials were prepared at two different temperatures (120 and 200 °C) and two PCL-OH:MDI ratios. FT-IR measurements proved the formation of urethane bonds in all the prepared samples. Crosslinking was demonstrated by contacting the samples with a solvent capable of dissolving the star-shaped PCL. These tests showed a significant increase in the crosslinked fraction with increasing the temperature and the PCL-OH:MDI ratio. In order to evidence the effect of crosslinking on rGO dispersion and the final properties of the material, a nanocomposite sample was also prepared using a linear commercial PCL, with the nanofiller mixed under the same conditions used to develop the crosslinked systems. The dispersion of rGO, which was investigated using FE-SEM measurements, was similar in the different systems prepared, indicating that the crosslinking process had a minor effect on the dispersibility of the nanofiller. As far as the thermal properties are concerned, the DSC measurements of the prepared samples showed that the crosslinking leads to a decrease in the crystallinity of the polymer, a phenomenon which was particularly evident in the sample prepared at 200 °C with a PCL-OH: MDI ratio of 1:1.33 and was related to the decrease in the polymer chain mobility. Moreover, rGO was found to act as a nucleating agent and increase the crystallization temperature of the nanocomposite sample based on linear commercial PCL, while the contribution of rGO in the crosslinked nanocomposite samples was minor. Rheological measurements confirmed the crosslinking of the PCL-OH system which generates a solid-like behavior depending on the PCL-OH:MDI ratio used. The presence of rGO during crosslinking generated a further huge increase in the viscosity of the melt with a remarkable solid-like behavior, confirming a strong interaction between rGO and crosslinked PCL. Finally, the prepared nanocomposites exhibited self-healing and recyclability properties, thus meeting the requirements for sustainable materials
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
Functional outcomes after transoral CO2 laser treatment for posterior glottic stenosis: a bicentric case series
Full text linkPurpose The aim of this study is to evaluate functional outcomes in terms of decannulation rate and quality of life of patients affected by PGS (Grades I-IV) treated only by transoral CO2 laser microsurgery (TOLMS) in two tertiary centers. Methods An observational retrospective study was carried out, enrolling 22 patients affected by PGS who were treated by a transoral approach at two tertiary referral centers. Surgical treatment included TOLMS with tailored laser resection of the scar tissue combined with posterior cordotomy, resurfacing of the raw area with mucosal microflap, or placement of a Montgomery T-tube or Keel stent. All patients were evaluated and staged preoperatively and postoperatively, at least 6 months after the surgery. Functional outcomes were objectively evaluated by the Airway-Dysphonia-Voice-Swallowing (ADVS) staging system, Voice Handicap Index-30 (VHI-30), and Eating Assessment Tool-10 (EAT-10) questionnaires. Results Quality of life significantly improved as measured by the VHI-30 questionnaire with a median variation of - 31.0 (p = 0.003), the EAT-10 with a median variation of - 4.0 (p = 0.042), and the ADVS with a median variation of - 3.5 (p < 0.001). No significant changes were observed in swallowing scores. We were able to decannulate 7 of 9 patients (almost 80%) with previous tracheotomy. Conclusion In conclusion, even if there is still no general agreement on an exact therapeutic algorithm to treat PGS, our results confirm that transoral surgery, in terms of scar tissue removal, combined in selected patients with posterior cordotomy and pedicled local flaps and/or placement of stents, represents a safe and effective surgical approach even for more severe PGS
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