1,721,050 research outputs found
The aliphatic counterpart of PET, PPT and PBT aromatic polyesters: effect of the molecular structure on thermo-mechanical properties
No full textThe aliphatic counterparts of the most used aromatic polyesters (PET, PPT, and PBT) have been synthesized by a two-stage polycondensation process, starting from dimethyl 1,4-cyclohexane dicarboxylate and different diols. The fully aliphatic polyesters are characterized by two cis/trans isomeric ratios (50 and 90 mol%) of the 1,4-cycloaliphatic rings. According to the cis/trans content, the properties of the materials notably change. Indeed, polymers rich in trans isomer are semicrystalline, whereas polymers with low trans content are fully amorphous, due to the presence of kinks along the chain. Trans isomer is characterized by higher rigidity than the cis one and the corresponding polymers have high glass transition temperatures. Moreover, the length of the methylene sequences in the diol has a notable influence on the final thermal and mechanical properties. Therefore, tunable properties can be easily obtained. This characteristic, in association with good mechanical performances, potential sustainability of the monomers and biodegradability, makes these aliphatic polyesters an interesting class of polyesters for some specific applications
Fully biobased poly(propylene 2,5-furandicarboxylate) for packaging applications: excellent barrier properties as a function of crystallinity
No full textHigh molecular weight, amorphous poly(propylene 2,5-furandicarboxylate) has been aged at 135 °C for different times. The crystal phase contributes to achieve exceptionally low oxygen transmission rates and also good impermeability to water vapors, making PPF one of the most interesting fully biobased polyesters for packaging applications
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
Poly(1,4-dimethylcyclohexane adipate) nanocomposites with organoclays modified with ionic liquid based on phosphonium salt
Full text linkVariations 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
Use of ionic liquids based on phosphonium salts for preparing biocomposites by in situ polymerization
No full textA sodium montmorillonite, Dellite HPS, was modified with ionic liquids based on phosphonium salts, such as octadecyltriphenylphosphonium
tetrafluoroborate and octadecyltriphenylphosphonium bromide. Thanks to their high thermal stability, these
salts can be used during in situ polymerization, a method that favors the achievement of a good dispersion of the clay. Poly(1,4-dimethylcyclohexane
adipate) (PCHA), was chosen as an example of aliphatic polyester which can be a suitable matrix for new biocomposites
with organo-clays. The organo modified clays prepared were characterized by X-ray diffraction (XRD), ATR-FTIR spectroscopy,
and thermal gravimetric analysis (TGA) while biocomposites were analyzed in terms of molecular structure, thermal and thermomechanical
properties. The degree of dispersion of the clays in the polymer matrix was studied by XRD. The results show that the clays
are well dispersed in the biocomposites, despite an intercalated structure highlighted by XRD analysis. Moreover, the clays confer a
certain improvement in mechanical properties to the final materials
Block and random copolyamides of poly(m-xylylene adipamide) and poly(hexamethylene isophthalamide-co-terephthalamide): Methods of preparation and relationships between molecular structure and phase behavior
No full textCopolymerization of poly(m-xylylene adipamide) (MXD6) and poly(hexamethylene isophthalamide-co-terephthalamide) (PA6I-6T) was used as an efficient strategy to prepare amorphous homogeneous systems with improved properties mainly for packaging applications. The preparation of block copolymers was first of all tried by co-extrusion of the two polymers and then by thermal treatments at high temperatures in DSC or mixing in Brabender, also in the presence of a catalyst. The occurrence of transamidation reactions led to macromolecular structures with different randomness degrees. Further, random copolymers, with the full range of compositions, were synthetized from monomers, by a fast and simple two-stage melt polycondensation. For all the copolymers, the sequence distribution was studied by using a H-1 NMR method developed by the Authors. The effects of preparation procedures, of mixing temperature and time, of the presence of a catalyst on the chemical structure, and, then, on final properties were studied. Interesting correlations among block length, monomer distribution and phase behavior were discussed
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
Effect of 1,4-cyclohexylene units on thermal properties of poly(1,4-cyclohexylenedimethylene adipate) and similar aliphatic polyesters
Full text linkIn the field of aliphatic polyesters there is a great interest in building novel macromolecular structures that may effectively
feature the requiredproperties for specific applications. For this reason, it is extremely important to understand the correlations between chemical structure and final performance. Monomers based on the 1,4-cyclohexylene unit are interesting as they are potentially bio-based and rigid enough to improve glass transition and melting temperatures. The present paper describes the preparation of samples of poly(1,4-cyclohexylenedimethylene adipate), characterized by different cis/trans isomeric ratio of the cyclic units, the analysis of their thermal properties and the comparison with the properties of similar polymers such as poly(butylene adipate), poly(butylene-1,4-cyclohexanedicarboxylate) and poly(1,4-cyclohexylenedimethylene-1,4- cyclohexanedicarboxylate). The effect of the rigidity and of the stereochemistry of the 1,4-cyclohexylene unit on the thermal properties was analysed. Such an effect reaches its maximum level when the cyclic-containing monomers are the diacid or the diester and when the trans isomers predominate. Starting from such a result, the combination of specific cyclic building blocks with the correct cis/trans ratiomakes it possible to build macromolecular structures with the required final properties
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