1,721,005 research outputs found
The effects of cold plasma treatments on LDPE wettability and curing kinetic of a polyurethane adhesive
No full textA cold plasma feed with either oxygen or nitrogen was used to modify thin Low Density Polyethylene films. The treatment improved both the surface wettability and the curing kinetic of a polyurethane based adhesive spread on the surface. The chemical functionalities responsible of the observed behaviours were investigated and monitored over time by high resolution x-ray photoelectron spectroscopy. Atomic force microscopy were used to compare the effects of the two feeding gases on the surface morphology of films exposed (to the plasma) for equal times. The effect on the treated films of the atmosphere exposure and of the aging time were also considered
Polymerization Kinetics and Characterization of Dual Cured Polyurethane-Acrylate Nanocomposites for Laminates
No full textFour different types of montmorillonites have been dispersed by sonication at 50° C into a propoxylated aromatic epoxy diacrylate oligomer to achieve interlayered or exfoliated nanocomposites. A thermally-induced cross-linking reaction, forming a polyurethane network in the presence of 7 wt.-% of a montmorillonite, has been promoted by addition of an allophanate modified polyisocyanurate based on hexamethylene diisocyanate. The kinetic behavior of the network formation has been studied at 25, 40 and 60° C by following the disappearance of the isocyanate vibrational band found at 2 270 cm(-1). A tight crosslinked polyurethane acrylate network has been achieved by a subsequent dual UV curing promoted by a photoinitiator mixture (0.6 wt,-%) added to the reactive mixture because of further reactions occur to the acrylate double bonds. The photopolymerization kinetic has been investigated on the different thermally treated polyurethane nanocomposite networks by Real Time FTIR spectroscopy monitoring the changes of the IR band at 810 cm(-1) assigned to the acrylate double bond vibrations. The influence of the different montmorillonite clays on the final nanocomposite morphology has been investigated by using XRD and SEM. Finally, the use of these mixtures as internal layer between two modified surface PET films has been also studied for the laminate production. The based-PET laminate films have been characterized by determining the bending resistance and optical properties as a function of different nanofiller
Pulp Cellulose Fiber Modification by Grafting with Ethyl Acrylate
No full textWe report the results of an investigation on the controlled modification of cellulose fibres by grafting with a synthetic polymer. The first step was the controlled esterification of cellulose fibre surface with -bromoisobutyryl bromide (BIBB), an ATRP initiator. Ethyl acrylate (EA) was grafted-polymerised from functionalised cellulose under ATRP conditions using CuBr/tris(2-dimethyl amine ethyl)amine (Me6TREN) as the catalyst in ethyl acetate, with or without the presence of a sacrifical free radical initiator (ethyl -bromoisobutyrate). The adopted polymerisation methods allowed to control grafting degree, grafted polymer chain length and, in perspective, grafted polymer structure, namely random and block copolymers. The obtained materials were characterised by ATR/FT-IR spectroscopy, thermal gravimetric analysis (TGA), energy dispersive x-ray spectroscopy (EDXS), scanning electron microscopy (SEM)
Highly thermostable and crystalline poly(butylene adipate) bionanocomposites prepared by in situ polycondensation with organically modified Moroccan Beidellite clay
No full textBionancomposites from bioplastics and nanoclays are of great interest for packaging, agricultural, and other large volume and niche applications due to their enhanced physical, thermal, mechanical, and processing characteristics compared to the parent polymer. In this study, the biodegradable polyester poly(butylene adipate) (PBA) was synthesized by in situ polycondensation catalyzed by titanium tetrabutoxide in the presence of the natural Moroccan clay Beidellite (BDT). Optimisation of the nanoclay exfoliation in the bionanocomposite was achieved by cation exchange of BDT with cetyltrimethylammonium bromide, CTA, and by selecting the most effective among a range of organically modified xCTA-BDT (x=CTA/BDT equivalent feed ratio). FT-IR, 1H NMR, and SEC analyses confirmed the effectiveness of the in situ polymerization, yielding structurally regular PBA with narrow molecular weight polydispersity and 7750>M ̅_n>30360 g/mol, depending on the organoclay load. XRD and TEM analyses showed best clay dispersion and homogeneous distribution at 2 wt% 3CTA-BDT. From TGA and DSC results the thermal stability of PBA is greatly improved even at 1 wt% 3CTA-BDT, its glass transition temperature is nearly unaffected while crystallinity is increased by the organoclay nucleating action. These results, along with a bionanocomposite hydrophilicity only moderately higher than that of PBA, make this preparation approach particularly promising
Injectable polyurethane-based hydrogels for smart drug release in the treatment of chronic skin wounds
No full textInjectable thermosensitive gels for the localized and controlled delivery of biomolecules in tissue engineering/regenerative medicine.
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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
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