1,721,024 research outputs found
A one-pot biomimetic synthesis of selectively functionalized lignins from monomers: A green functionalization platform
Full text linkLignin is the most abundant renewable source of phenolic compounds with great application potential in renewable materials, biofuels and platform chemicals. The current technology for producing cellulose-rich fibers co-produces heterogeneous lignin, which includes an untapped source of monomeric phenolics. One such monomer also happens to be the main monomer in soft wood lignin biosynthesis, namely coniferyl alcohol. Herein, we investigate the potential of coniferyl alcohol as a platform monomer for the biomimetic production of tailored functionalized oligolignols with desirable properties for material synthesis. Accordingly, a bifunctional molecule with at least one carboxyl-ended functionality is included with coniferyl alcohol in biomimetic lignin synthesis to, in one pot, produce a functionalized lignin. The functionalization mechanism is a nucleophilic addition reaction to the quinone methide intermediate of lignin polymerization. The solvent system applied was pure water or 50% aqueous acetone. Several bi-functional molecules differing in the second functionality were successfully inserted in the lignin demonstrating the platform component of this work. Detailed characterization was performed by a combination of NMR techniques which include1H NMR, COSY-90,31P NMR,13C NMR,13C APT, HSQC, HMBC and HSQC TOCSY. Excellent selectivity towards benzylic carbon and a high functionalization degree were noted. The structure of lignin was tailored through the solvent system choice, with 50% aqueous acetone producing a skeletal structure favorable for a high degree of functionalization. Finally, material concepts are demonstrated using classical thiol-ene- and Diels-Alder-chemistries to show the potential for the thermoset and thermoplastic concepts, respectively. The functionalization concept presents unprecedented opportunities for the green production of lignin-based recyclable biomaterials
Ski Boot Soles Based on a Glass Fiber/Rubber Composite with Improved Grip on Icy Surfaces
Full text linkAbstractA study on the effect of glass fibers/rubber composites on the grip on ice has been conducted in order to develop new materials for ski boot soles with increased grip in winter environments. The study has been conducted analyzing the friction of a composite material and of a ski boot sole containing an insert made of the composite material and comparing the results with those obtained using rubber and a thermoplastic elastomer. The analysis of the morphology of the composite surface, by Scanning Electron Microscopy, shows a homogenous distribution of glass fibers of approximately 10μm of diameter in the rubber matrix. Moreover, the measure of the contact angle shows that the composite material has a higher water repellency compared to the rubber matrix. The measure of the coefficient of friction indicates a significant effect of the glass fibers on the grip on icy surfaces. The increased grip can be ascribed to the stiffness of the glass fibers that are able to have a mechanical grip on the ice surface and to the increased contact angle and water repellency of the composite that decrease the formation of a water layer below the sole
Recent Strategies for Lignin-Based Thermosets
No full textLignin has gained interest in academia as a raw material for advanced materials such as thermosets. Attractive features include its natural and technical abundances, its structural compositions, distribution of functionalities and most importantly its origin from renewable sources, i.e. lignocellulosic biomass. In this chapter, we will focus on lignin-based thermosets, specifically reviewing the recent strategies for such applications in polyurethanes, phenol-formaldehyde resins and epoxy thermosets. In these contexts, the advantages and competitiveness of lignin over conventional petrol-based will be discussed based on comparisons with benchmark properties. The chapter emphasizes the unique polymer chemistries adopted by different researchers, the effects of the chemical and physical properties of lignin on both reactivities during synthesis and thermomechanical properties of materials. Furthermore, the direct use of lignin in the unmodified state is contrasted with the use of selectively modified lignins in these polymer systems. The use of multifunctional lignin oligomers as raw material is also contrasted with the use of lignin platform monomers obtained through de-polymerization approaches. Finally, the challenges of lignin or monomers thereof, as a raw material in these applications are discussed to direct the future outlook of this research area
Method of regioselective synthesis of polyesters from asymmetric diols
No full textThe present invention belongs to the field of polymer synthesis. In particular, the present invention relates to a method for the synthesis of regioregular polyesters, wherein the polymer ordered structure provides them with advantageous physical-chemical properties, starting from asymmetric diols. More particularly, by the method of the present invention it is possible to obtain regioregular polyesters having high glass transition temperatures Tg and crystalline properties. In the case in which the asymmetric diols are used in a pure enantiomeric form, with respect to the chiral carbon bound to the secondary hydroxyl, through the above-mentioned method it is possible to obtain regioregular and stereoregular polyesters, characterized by thermal and crystalline properties further ameliorative with respect to non-chiral regioregular polymers
Chemical recycling of post-consumer compact discs towards novel polymers for powder coating applications
No full textNew processes for the chemical recycling of bisphenol A polycarbonate (PC), directly from post-consumer compact discs, have been developed. The first recycling method is based on the use of molecules that can be derived from renewable resources (isosorbide, ethylene carbonate and succinic acid). A second procedure involves a one-pot reaction of post consumer PC with ethylene carbonate, without complete degradation to low molecular weight products. The final polymers feature properties that make them suitable for powder coating 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
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
- …
