1,720,987 research outputs found
Thermal stability of high density polyethylene-fumed silica nanocomposites
No full textHigh-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations
Thermo-mechanical characterization of epoxy/clay nanocomposites as matrices for carbon/nanoclay/epoxy laminates
No full textMicrostructural and thermo-mechanical characterization were performed on epoxy-clay nanocomposites, to be used as matrix for continuous carbon fiber reinforced composites, containing various amounts of clays having different hydrophilicity. XRD tests displayed that the dispersion degree of the clay lamellae was strictly correlated to their hydrophilicity, while DSC tests revealed that the crosslinking degree was negatively affected by the presence of most hydrophilic clays. Therefore, the balance between polymer-filler interaction and crosslinking degree influenced the final properties of the resulting composites. The mechanical behaviour, both under quasi-static and impact conditions, was positively affected by resin nanomodification. Fracture toughness and threshold to crack initiation under cyclic loading were also interestingly improved
Electrospun Poly(butylene 2,5-furanoate) and Poly(pentamethylene 2,5-furanoate) Mats: Structure–Property Relationships and Thermo-Mechanical and Biological Characterization
Full text linkThis study explores, for the first time, the application of electrospun biobased poly(butylene 2,5-furanoate) (PBF) and poly(pentamethylene 2,5-furanoate) (PPeF) mats in biomedical and drug delivery fields, through a careful investigation of their structure-property relationship. PBF mats, with a glass transition temperature (T-g ) of 25-30 degrees C and an as-spun crystallinity of 18.8%, maintained their fibrous structure (fiber diameter similar to 1.3 mu m) and mechanical properties (stiffness similar to 100 MPa, strength similar to 4.5 MPa, strain at break similar to 200%) under treatment in physiological conditions (37 degrees C, pH 7.5). In contrast, PPeF mats, being amorphous with a T-g of 14 degrees C, underwent significant densification, with geometrical density increasing from 0.68 g/cm(3) to 1.07 g/cm(3), which depressed the specific (i.e., normalized by density) mechanical properties. DSC analysis revealed that the treatment promoted crystallization in PBF (reaching 45.9% crystallinity), while PPeF showed limited, but interestingly not negligible, structural reorganization. Both materials promoted good cell adhesion and were biocompatible, with lactate dehydrogenase release not exceeding 20% after 48 h. The potential of PBF mats for drug delivery was evaluated using dexamethasone. The mats exhibited a controlled drug release profile, with similar to 10% drug release in 4 h and similar to 50% in 20 h. This study demonstrates the versatility of these biopolyesters in biomedical applications and highlights the impact of polymer structure on material performance
Uncharted development of electrospun mats based on bioderived poly(butylene 2,5-furanoate) and poly(pentamethylene 2,5-furanoate)
Full text linkSustainable and bioderived furanoate polyesters are emerging as promising substitutes for petrochemical-derived polyesters, which are mainly applied in packaging, textile, and biomedical fields. This work presents the successful production, for the first time, of electrospun nanofibrous mats based on two furan-based polyesters, i.e., poly(butylene 2,5-furanoate) (PBF) and poly(pentamethylene 2,5-furanoate) (PPeF), which have very similar chemical structure but remarkably different physical and mechanical properties. The feasibility to produce nanofibrous mats of PBF and PPeF by electrospinning was systematically investigated, by optimizing (i) the solubility of the polymers in different solvent mixtures, (ii) the viscosity and concentration of the spinning dopes, evaluated through rheological measurements of the polymeric solutions, (iii) the spinning rate, and (iv) the applied voltage. A detailed morphological analysis of the resulting non-vowen mats, carried out through field-emission scanning electron microscopy (FESEM), allowed the screening of the best processing conditions for PBF and PPeF, in order to produce electrospun mats suitable for biomedical applications
High-density polyethylene reinforced with titania nanoparticles
No full textTitania nanoparticles were prepared by means of two different synthetic procedures in order to obtain different particle size (diameter ranging from 20 nm to 350 nm), shapes and morphologies (amorphous or crystalline). Titania nanoparticles were surface modified with octadecylsilane in order to improve their compatibility with respect to polymeric matrices. High density polyethylene (HDPE) - titania nanocomposites were prepared by melt blending by using an internal mixer. The obtained nanocomposites were mechanically characterized and quasi static and creep tensile conditions. The presence of titania nanoparticles (1%vol) led to a significant increase of elastic modulus (20-25%) together with a slight increase of yield stress and a decrease of ultimate elongation. An interesting reduction of for both elastic and viscoelastic creep compliance components was also evidenced
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
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