1,720,962 research outputs found
Nuove strategie per la preparazione di polimeri Bio-based ad alte prestazioni - Conferenza premio AICIng 2018 Tesi di Dottorato
No full textInsights into the synthesis of PEF from FDCA: steps toward environmental and food safety excellence in packaging applications
No full textPoly(ethylene 2,5-furandicarboxylate) (PEF) is considered today as a very promising biobased polymer for packaging applications. The main reason lies in its extraordinary barrier properties: oxygen permeability in PEF is reduced by a factor of about 10 with respect to poly(ethylene terephthalate) (PET) (1). In terms of the synthesis of PEF, scientific literature describes synthetic procedures based on the transesterification of the dimethylester of the 2,5-furandicarboxylic acid (2,3,4). This research, instead, aims at studying the possibility of a practical and profitable synthetic route of PEF starting from the 2,5-furandicarboxylic acid. In this respect two catalysts, zinc acetate (ZnAcO) and aluminum acetylacetonate (Al(acac)3), chosen for their compatibility with food contact applications and for featuring a potentially reduced environmental impact, were investigated. The synthesis was performed by using tight reaction conditions: low excess of diol and short reaction time. Indeed, the use of high amount of glycol could lead to the ether-bridges (DEG) formation, which significantly reduces the extremely valuable barrier performances of PEF; high polymerization times lead to material yellowing, indicating the occurrence of by-side reactions. Different catalyst amounts and addition times were tested and the obtained polymers were characterized in terms of inherent viscosity, color (absorbance at 400 nm), and diethylene glycol content, as summarized in Table 1. Since titanium (IV) butoxide (TBT) is the most used catalyst in the PEF syntheses, PEF samples prepared with it were reported as a reference for the present study. Results show that ZnAcO and Al(acac)3 are very promising catalysts for the PEF polymerization from FDCA, because the use of ZnAcO allows them to reach relatively high inherent viscosity in the usual polymerization procedure, while the use of Al(acac)3 leads to materials characterized by very low yellowing. In this case, the moderate molecular weight obtained for aluminum-based PEF was overcome by a final step of solid state polymerization (SSP), which increases the viscosity from 0.25 to 0.39 dL/g in just 3 days. Finally, the obtained amorphous PEF samples result filmable and therefore suitable for the manufacturing of various packaging articles
Insights into the Synthesis of Poly(ethylene 2,5-Furandicarboxylate) from 2,5-Furandicarboxylic Acid: Steps toward Environmental and Food Safety Excellence in Packaging Applications
No full textPoly(ethylene 2,5-furandicarboxylate)
(PEF) is considered today
as a very promising biobased polymer for packaging applications. Most
often, scientific literature describes synthetic procedures based
on the transesterification of the dimethylester of the 2,5-furandicarboxylic
acid, whereas this paper aims at studying the possibility of a practical
and profitable synthetic route for PEF comprising a direct esterification
stage of 2,5-furandicarboxylic acid. In that respect two catalysts,
zinc acetate and aluminum acetylacetonate, chosen for their compatibility
with food contact applications and for featuring a potentially reduced
environmental impact, were investigated. The synthesis was performed
by using tight reaction conditions: low excess of diol and short reaction
time. Interesting results were obtained in terms of final PEF viscosity,
color, and diethylene glycol content, that may strongly influence
thermal and barrier properties. Furthermore, the obtained amorphous
polymers are potentially suitable for the manufacturing of various
packaging articles such as oriented films and bottles
Scarti Agricoli e agro-industriali:una risorsa da sfruttare per nuovi-biopolimeri nell'ambito dei progetti europei NoAw e Agrimax
No full text
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
Biobased vanillic acid and ricinoleic acid: building blocks for fully renewable copolyesters
No full textNew fully biobased polyether/esters have been synthesized by a one-pot polymerization reaction of ricinoleic acid (RA), vanillic acid (VA) and ethylene carbonate (EC). In particular, EC selectively reacts with the phenolic group of VA to obtain in-situ 4-(2-hydroxyethoxy)-3-methoxybenzoate (EV), suitable for subsequent copolymerization with RA. The procedure was carried out in a single step, without any solvent. Chemical structure and thermal properties of the new materials were studied in order to explore relationships between composition and final performances. The combination of EV, bearing a rigid aromatic structure, with RA, characterized by high flexibility and potential biocidal activity, allows the production of a novel class of fully biobased aliphatic-aromatic polymers presenting tuneable thermal properties and suitable for a range of applications, for example, in active packaging and biomedical fields
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
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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