1,720,971 research outputs found
Preparation of gelatin/polyoxypropylene grafted copolymers by isocyanate promoted "grafting onto" reaction
No full textA "grafting onto" method for the synthesis of protein-based grafted copolymers is here described. Monofunctional oligo(oxypropylene) chains carrying a terminal isocyanate group were prepared and coupled with gelatin likely by reaction with hydroxyl or primary amino groups. A grafting yield higher than 85% was obtained by using an amount of isocyanate terminated oligo(oxypropylene) of 0.2 mmol per gram of gelatin. A tailored purification procedure based on fractionation with selective solvents was set up to remove homo-coupling products, affording water soluble gelatin-oligo(oxypropylene) graft copolymers having up to 19% wt of grafted oligo(oxypropylene) chains, as indicated by elemental analysis. The composition of all sample fractions were accomplished through NMR, FT-IR and elemental analysis. A negligible insoluble fraction and a water soluble gelatin fraction having a higher modification degree were obtained when the unreacted 1,6-diisocyanatehexane was removed by distillation from the intermediate reagents.The solid films of the graft copolymers showed single-phase morphology by scanning electron microscopy (SEM) observation, confirming the covalent bond formation between oligo(oxypropylene) and gelatin. Simple oligo(oxypropylene)/gelatin blends were prepared and characterized by SEM and stress-strain measurements for comparison. (C) 2012 Elsevier Ltd. All rights reserved
Easy detectable isocyanate in the reaction with gelatin RID E-9799-2011
No full textGelatin reactivity with isocyanate was studied by using the easy detectable 1-naphthyl-isocyanate (NphI). Four different NphI/gelatin feed ratios were investigated with NphI molar amount ranging between 1/10 and 1/1 with respect to the possible reactive groups of gelatin. The reactions were carried out at 45 A degrees C in DMSO as solvent, under nitrogen atmosphere. Modified gelatin samples were characterized by IR, UV-VIS, fluorescence spectroscopies as well as by proton and DOSY NMR. Spectroscopy results allow to evidence the presence of both bonded and unbonded naphthyl derivatives in the gelatin samples. Unbonded species were present particularly at the highest NphI/gelatin feed ratio and their formation was correlated to the increasing competition of the reaction with water since the amount of available reactive groups on gelatin was comparable or smaller than the amount of residuum water in dry gelatin.Gelatin reactivity with isocyanate was studied by using the easy detectable 1-naphthyl-isocyanate (NphI). Four different NphI/gelatin feed ratios were investigated with NphI molar amount ranging between 1/10 and 1/1 with respect to the possible reactive groups of gelatin. The reactions were carried out at 45 °C in DMSO as solvent, under nitrogen atmosphere. Modified gelatin samples were characterized by IR, UV-VIS, fluorescence spectroscopies as well as by proton and DOSY NMR. Spectroscopy results allow to evidence the presence of both bonded and unbonded naphthyl derivatives in the gelatin samples. Unbonded species were present particularly at the highest NphI/gelatin feed ratio and their formation was correlated to the increasing competition of the reaction with water since the amount of available reactive groups on gelatin was comparable or smaller than the amount of residuum water in dry gelatin. © 2010 Springer-Verlag
Multiscale characterization of corrosion in archaeological artefacts from Motya (Sicily, Italy) through X-ray microscopy
No full textHere we presented a multi-analytical approach (Multiscale X-ray Microscopy, Micro-Raman, SEM, HR- FESEM- EDS and EMPA) to explore corrosion mechanisms in different type of metal artefacts from Motya (Sicily, Italy) to gain the maximum information with the minimum sampling. Indeed, the elemental analysis provides key information on the role of alloying elements in production technology and corrosion process, whereas the structure information from Multiscale Xray Microscopy (XRM) enables multilength scale visualization of whole objects and provides the spatial distribution of corrosion phases.
The results revealed the internal structure of the artefacts and the structural discontinuities which lead the corrosion, highlighting the compositional differences between the tip and the head of the iron nail (Bernabale et al., 2022). All copper-based artefacts were exposed to bronze disease corrosion induced by the presence of the reactive cuprous chloride (CuCl) located at the interface between external corrosion layers and the surviving metal core. In a Cu nail arsenic was forced outwards along inter-granular channels and it combined with Fe atoms at Cu grain boundaries, leading to the formation of copper-iron arsenate. Binary and ternary alloys revealed marked Cu and Sn selective corrosion and thicker patina compared with Cu metal due to the presence of Sn in chlorine-rich environment. The dissolution factor of copper in these alloys showed a great variability. In addition, the occurrence of cracks inside the bronze needle acted as new corrosion interfaces and involved the formation of complex and periodic stratified corrosion layers, leading to a complete mineralized structure (Bernabale et al. 2023)
Preparation and characterisation of gelatine-g-PPG copolymers
No full textGelatine is a natural polymer from collagen denaturation used from long time as adhesive, food additive, colloidal stabiliser and in photographic films.
Its use in packaging materials has been until now prevented by its scars mechanical properties: its film are hard and brittle. To overcame this drawback much efforts have been dedicated to make gelatine thermoplastic by mixing with plasticizers or by blending with polyolefins. Different chemical modification methods have also been proposed to provide gelatine with new properties in particular for biomedical application.
In this work we study the polymer grafting modification approach as possible method to get gelatine based materials suitable as adhesive for packaging.
Comb like gelatine-graft-polypropylen glycol copolymers were prepared in a two steps process. In the first step (6-Isocyanato-hexyl)-carbamic acid 2-{butoxy-polyoxopropylene}-1-methyl-ethyl ester (PPG-NCO) was prepared by reacting poly(propylene glycol) monobutyl ether with 1,6-diisocyanatohexane (HDI) with dibutyldilauryltin (DBTL) as catalyst in ethyl acetate as solvent under dry conditions. PPG-NCO was then grafted to gelatine in the second reaction step in DMSO as solvent. Copolymers at different gelatine/PPG ratio were obtained as revealed by FT-IR analysis. They were characterised by GPC, TGA and NMR analyses. All prepared copolymers were soluble in water at room temperature whereas pristine gelatine is a gel under the same conditions. Moreover, the hydrodynamic volume of copolymer in water was lower then that of gelatine and showed a clear dependence on the PPG content.
Films of the comb copolymers were prepared by solvent casting from thifluoroethanol and their material mechanical properties were investigated by stress-strain analysis, while their morphology was investigated by SEM microscopy. Films made by gelatine/PPG and gelatine/PPG-HDI-PPG were also prepared for comparison.
All prepared mixtures and copolymer provided homogeneous materials down to the SEM resolution while mechanical properties indicated a plasticization effect of PPG and PPG-HDI-PPG, with better efficiency for the later
Lo sviluppo delle abilità di prima comunicazione e la 'lingua dell’accoglienza'
No full textIl contributo discute le coordinate teorico-metodologiche principali che hanno guidato la realizzazione di percorsi di facilitazione linguistico-culturale, presentati nell'opera, frutto di un corso di qualifica promosso dalla Provincia di Ascoli Piceno
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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