1,721,014 research outputs found
Effect of compatibilization on thermal degradation kinetics of HDPE-based composites containing cellulose reinforcements
No full textDynamic thermogravimetric analysis under nitrogen flow was used to investigate the thermal decomposition process of high-density
poly(ethylene) (HDPE)-based composites reinforced with cellulose fibers obtained from the recycling of multilayer carton scraps,
as a function of the cellulose content and the compatibilization. The Friedman, Flynn–Wall–Ozawa, and Coats–Redfern methods
were used to determine the apparent activation energy (E
a) of the thermal degradation of the cellulose component into the composites. E
a has been found dependent on the cellulose amount and on the cellulose/polymer matrix interfacial adhesion. In particular,
it has been evidenced an increase of the cellulose thermal stability as a consequence of the improved interfacial adhesion
between the components in NFR composites
Poly(vinyl chloride)/CaCO3 nanocomposites: Influence of surface treatments on the properties
No full textPoly(vinyl chloride) (PVC)-based nanocomposites containing calcium carbonate nanoparticles (CaCO3) were prepared. Different nanoparticle surface modifiers were selected and tested to promote matrix/filler interactions and, consequently, to obtain high- performance materials. In particular, the nanoparticles were modified with poly(acrylic acid) (PAA) and poly (butadiene-co-acrylonitrile-co-acrylic acid) (PBAA). For comparison, PVC-based materials, with the addition of commercial neat and stearic acid modified CaCO3, were also prepared. The influence of CaCO3 and surface modifiers on the gelation, thermal properties, thermal stability, and mechanical properties of PVC was studied. The gelation time of the rigid PVC/CaCO3 composites decreased as a function of the percentage and surface treatment of CaCO3. Morphological analysis proved the effectiveness of PAA and PBAA as surface modifiers; they obtained for the corresponding materials a typical nanostructured morphology. A significant improvement in the PVC thermal stability was recorded with the addition of neat and stearic acid modified CaCO3. Finally, mechanical tests showed an increase in the flexural strength and toughness of PVC as a function of the nanoparticle surface modifier. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 201
Recycled multilayer cartons as cellulose source in HDPE-based composites: Compatibilization and structure-properties relationships
No full textIn this article, an alternative mechanical recycling of multilayer carton scraps (MC), consisting in the use of MC without the physical separation of its different fractions (cellulose fibers and low-density polyethylene, 80/20 wt/wt), is proposed. In particular, MC was considered as a source of cellulose fibers in the obtainment of high-density polyethylene (HDPE)-based composites. Composites containing up to 60 wt % of milled MC were prepared by reactive processing, i.e., by adding different amount (5 and 10 wt %) of a linear low-density polyethylene grafted with maleic anhydride (coupling agent, maleated linear low-density polyethylene) during HDPE/MC mixing. Then, structure/properties relationships were deeply investigated as a function of MC and coupling agent content. The coupling agent was able to induce a complete polymeric covering of cellulose fraction as well as a strong HDPE/cellulose interfacial adhesion. As a consequence, a significant improvement of mechanical properties at low and high deformation rates as well as a very interesting response of composites to water vapor permeability was obtained
Probing the effect of high energy ball milling on PVC through a multitechnique approach
No full textThe effects induced by ball milling treatment on PVC features and properties were deeply investigated through a multitechnique approach. SEM analysis showed a drastic change in PVC morphology; the hierarchical structure of PVC grains was partially destroyed as well as the domain size strongly reduced. A X-ray diffraction and DSC comparative study proved a structural modification in the PVC crystalline phase. Moreover, it was found that these morphological and structural changes strongly affected the gelation behavior, the microstructure and the mechanical parameters of PVC. In particular, the gelation time increased with increasing the ball milling time; the residual primary crystallite content doubled with respect to neat PVC and the toughness improved up to 25% as a function of the resulting microstructure. © 2011 Elsevier B.V. All rights reserved
Up-cycling end-of-use materials: Highly filled thermoplastic composites obtained by loading waste carbon fiber composite into fluidified recycled polystyrene
No full textCarbon fibers reinforced epoxy resins are used in a wide range of applications, such as automotive and aerospace industry. Because of their thermosetting nature, recycling at the end of the life cycle is a difficult issue. However, lack of recyclability poses environmental concerns to the use of these composite materials. In this article, a sustainable, cost-effective technological approach aiming at recycling postconsumer carbon fibers reinforced thermosets (CFRT) is proposed. Composites containing 50 and 70 wt% of CFRT particles were prepared by incorporating the filler fraction into a fluidified postconsumer expanded polystyrene matrix. A cold mixing approach consisting in the use of a low boiling solvent as a binder to guarantee the dispersion homogeneity on micro- and macroscopic level was set up. For comparison, analog composites were also prepared through melt mixing process. Morphological, mechanical, and thermal analyses allowed to prove the effectiveness of the cold mixing approach and to evaluate the influence of particle size on the performance of new recycled composites. Thermogravimetric analysis and thermal conductivity tests of samples highlighted further peculiarities of the cold mixing process. The approach proposed is an effective recycling technology for CFRT and could be extended to other postconsumer materials
The chemistry of polydopamine film formation: The amine-quinone interplay
Full text linkDespite extensive investigations over the past decade, the chemical basis of the extraordinary underwater adhesion properties of polydopamine (PDA) has remained not entirely understood. The bulk of evidence points to PDA wet adhesion as a complex process based on film deposition, and growth in which primary amine groups, besides catechol moieties, play a central role. However, the detailed interplay of chemical interactions underlying the dynamics of film formation has not yet been elucidated. Herein, we report the results of a series of experiments showing that coating formation from dopamine at pH 9.0 in carbonate buffer: (a) Requires high dopamine concentrations (>1 mM); (b) is due to species produced in the early stages of dopamine autoxidation; (c) is accelerated by equimolar amounts of periodate causing fast conversion to the o-quinone; and (d) is enhanced by the addition of hexamethylenediamine (HMDA) and other long chain aliphatic amines even at low dopamine concentrations (<1 mM). It is proposed that concentration-dependent PDA film formation reflects the competition between intermolecular amine-quinone condensation processes, leading to adhesive cross-linked oligomer structures, and the intramolecular cyclization route forming little adhesive 5,6-dihydroxyindole (DHI) units. Film growth would then be sustained by dopamine and other soluble species that can be adsorbed on the surface
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
Degradation of Biodegradable Plastic in Marine Environment
No full textIn the recent years, a growing attention has addressed to compostable and biodegradable polymers, in order to reduce plastic pollution. arding these latter, very few data on their biodegradability and toxicity in the marine environment are available as well as on their impact on marine invertebrates. In this study, we investigated the behaviour and degradation of five biodegradable polymers (BPs): Poly(butylene succinate) (PBS); Poly(butylene succinate-co-adipate) (PBSA); Polycaprolactone (PCL); Polyhydroxy butyrate (PHB); Polylactic acid (PLA) in marine environment
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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