1,720,973 research outputs found
Constrained amorphous interphase in poly(l-lactic acid): Estimation of the Tensile elastic modulus
No full textThe mechanical properties of semicrystalline PLLA containing exclusively α′- or α-crystals have been investigated. The connection between experimental elastic moduli and phase composition has been analyzed as a function of the polymorphic crystalline form. For a complete interpretation of the mechanical properties, the contribution of the crystalline regions and the constrained amorphous interphase or rigid amorphous fraction (RAF) has been quantified by a three-phase mechanical model. The mathematical approach allowed the simultaneous quantification of the elastic moduli of (i) the α′- and α-phases (11.2 and 14.8 GPa, respectively, in excellent agreement with experimental and theoretical data reported in the literature) and (ii) the rigid amorphous fractions linked to the α′- and α-forms (5.4 and 6.1 GPa, respectively). In parallel, the densities of the RAF connected with α′- and α-crystals have been measured (1.17 and 1.11 g/cm3, respectively). The slightly higher value of the elastic modulus of the RAF connected to the α-crystals and its lower density have been associated to a stronger chain coupling at the amorphous/crystal interface. Thus, the elastic moduli at Troom of the crystalline (EC), mobile amorphous (EMAF), and rigid amorphous (ERAF) fractions of PLLA turned out to be quantitatively in the order of EMAF < ERAF < EC, with the experimental EMAF value equal to 3.6 GPa. These findings can allow a better tailoring of the properties of PLLA materials in relation to specific 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
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
Coexistence of two lamellar populations in poly(ethylene vanillate) reorganized upon heating
Full text linkThe structural evolution of poly(ethylene vanillate) (PEV) crystals, after isothermal crystallization at T-c = 180 degree celsius, was explored by synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS) measurements. The WAXS/SAXS analyses proved that an additional more perfect crystal population starts to grow exactly in correspondence of the exotherm displayed by the specific heat capacity curve. The study ascertained that two different reorganization/recrystallization mechanisms occur upon heating: the more perfect crystals originate from a recrystallization process, whereas the original crystals undergo small and progressive perfection maybe without previous complete fusion. Deconvolution of the double Lorentz-corrected SAXS profiles was performed to calculate the temperature evolution of the lamellar thickness for the original and additional crystal populations. The two crystal populations appear to differ substantially in the temperature evolution of the lamellar and amorphous thicknesses. Hypotheses on the relative location of the two different crystal stacks as well as on the possible thermodynamic reason that triggers the formation of the more perfect crystal population have been formulated
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
Evaluation of mussel shells powder as reinforcement for pla-based biocomposites
Full text linkThe use of biopolyesters, as polymeric matrices, and natural fillers derived from wastes or by-products of food production to achieve biocomposites is nowadays a reality. The present paper aims to valorize mussel shells, 95% made of calcium carbonate (CaCO3 ), converting them into high-value added products. The objective of this work was to verify if CaCO3, obtained from Mediterranean Sea mussel shells, can be used as filler for a compostable matrix made of Polylactic acid (PLA) and Poly(butylene adipate-co-terephthalate) (PBAT). Thermal, mechanical, morphological and physical properties of these biocomposites were evaluated, and the micromechanical mechanism controlling stiffness and strength was investigated by analytical predictive models. The performances of these biocomposites were comparable with those of biocomposites produced with standard calcium carbonate. Thus, the present study has proved that the utilization of a waste, such as mussel shell, can become a resource for biocomposites production, and can be an effective option for further industrial scale-up
Binary green blends of poly(Lactic acid) with poly(butylene adipate-co-butylene terephthalate) and poly(butylene succinate-co-butylene adipate) and their nanocomposites
Full text linkPoly(lactic acid) (PLA) is the most widely produced biobased, biodegradable and biocompatible polyester. Despite many of its properties are similar to those of common petroleum-based polymers, some drawbacks limit its utilization, especially high brittleness and low toughness. To overcome these problems and improve the ductility and the impact resistance, PLA is often blended with other biobased and biodegradable polymers. For this purpose, poly(butylene adipate-co-butylene terephthalate) (PBAT) and poly(butylene succinate-co-butylene adipate) (PBSA) are very advantageous copolymers, because their toughness and elongation at break are complementary to those of PLA. Similar to PLA, both these copolymers are biodegradable and can be produced from annual renewable resources. This literature review aims to collect results on the mechanical, thermal and morphological properties of PLA/PBAT and PLA/PBSA blends, as binary blends with and without addition of coupling agents. The effect of different compatibilizers on the PLA/PBAT and PLA/PBSA blends properties is here elucidated, to highlight how the PLA toughness and ductility can be improved and tuned by using appropriate additives. In addition, the incorporation of solid nanoparticles to the PLA/PBAT and PLA/PBSA blends is discussed in detail, to demonstrate how the nanofillers can act as morphology stabilizers, and so improve the properties of these PLA-based formulations, especially mechanical performance, thermal stability and gas/vapor barrier properties. Key points about the biodegradation of the blends and the nanocomposites are presented, together with current applications of these novel green materials
From Biomass to Bio-Based Polymers: Exploitation of Vanillic Acid for the Design of New Copolymers with Tunable Properties
Full text linkVanillic acid represents a potentially interesting bio-based building block for the production of new aliphatic-aromatic polymers, characterized by thermal properties similar to those of the analogous terephthalic polyesters. However, poly(ethylene vanillate) proved to be a very brittle material, probably due to a very high degree of crystallinity, and, then, not suitable for melt processing. Therefore, the synthesis of copolymers, based on vanillic acid and pentadecalactone is considered as a strategy to obtain new polymeric materials with a low degree of crystallinity, tunable properties, and better performances. The synthesis of these fully bio-based random copolymers is successful. The thermal properties have been studied in order to correlate chemical structure and final performances. The polymers proved to be processable and films are obtained, suggesting possible applications of the copolymers in a new sustainable flexible packaging
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