1,720,996 research outputs found
An innovative process for mass production of multi-wall carbon nanotubes by means of low-cost pyrolysis of polyolefins
No full textAn innovative process for a mass production of multi-wall carbon nanotubes (MWCNTs) by means of pyrolysis of virgin or recycled polyolefins is described. The technique uses solid-gas fluidised bed reactors, continuously operated under conditions which allow high heating rates of the polymers, high heat and material exchange coefficients and a reliable control of residence times in the reactor. The obtained MWCNTs have been characterized by TGA, SEM and TEM microscopy as well as X-ray diffractometry and Raman spectroscopy. The results demonstrate that the proposed process allows the production of MWCNTs compatible with most of the already known applications, in large quantities and at low cost. This makes extremely wider the field of possible applications of these nanostructured materials. © 2005 Elsevier Ltd. All rights reserved
Polypropylene containing Ti- and Al-Polyhedral Oligomeric Silsesquioxanes: Crystallization Process and Thermal Properties
No full textThis paper deals with the preparation and characterization of isotactic polypropylene (PP) containing different metal-polyhedral oligomeric silsesquioxanes (M-POSS). Two M-POSS, Ti(IV)- and Al(III)-isobutyl-POSS, defined by a monomeric structure, were selected for dispersion, and particular attention was paid to the assessment of the morphology, crystallization process and thermal behavior of M-POSS/PP composites, using SEM and TEM microscopy, x-ray diffraction (XRD), FTIR and Raman spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and gas chromatography/mass spectrometry. The study of M-POSS/PP thermal degradation showed that Ti-POSS and Al-POSS induce different effects on the thermoxidative behavior of the polypropylene matrix, showing a clear specificity of the metal center on the PP degradation pathway. In particular, Ti-POSS showed a significant stabilization of PP when heating under air, whereas limited effects were observed with Al-POSS. Moreover, Ti-POSS was also found to affect PP crystallization, driving the crystallization process along specific crystallographic directions
The use of POSS-based nanoadditives for cable-grade PVC: Effects on its thermal stability
No full textPlasticized-Poly(vinyl chloride) (P-PVC) for cables and insulation requires performances related to outdoor, indoor and submarine contexts and reduction of noxious release of HCl-containing fumes in case of thermal degradation or fire. Introducing suitable nanomaterials in polymer-based nanocomposites can be an answer to this clue. In this work, an industry-compliant cable-grade P-PVC formulation was added with nanostructured materials belonging to the family of Polyhedral Oligomeric Silsesquioxane (POSS). The effects of the nanomaterials, alone and in synergy with HCl scavenging agents as zeolites and hydrotalcites, on the thermal stability and HCl evolution of P-PVC were deeply investigated by thermogravimetric analysis and reference ASTM methods. Moreover, hardness and mechanical properties were studied in order to highlight the effects of these additives in the perspective of final industrial uses. The data demonstrated relevant improvements in the thermal stability of the samples added with nanomaterials, already with concentrations of POSS down to 0.31 phr and interesting additive effects of POSS with zeolites and hydrotalcites for HCl release reduction without losing mechanical performances
On the use of Me-Isobutylsilsesquioxanes (Me=Ti, V) as additives for enhancing thermal stability of polypropylene
No full textIncorporation of Antimony Ions in Heptaisobutyl Polyhedral Oligomeric Silsesquioxanes
No full textThe direct incorporation of Sb(V) ions into a polycondensed silsesquioxane network based on heptaisobutyl POSS units (Sb(V)-POSSs) through a corner-capping reaction is reported for the first time in this work. As a reference sample, a completely condensed monomeric Sb(III)-POSS was prepared using a similar synthetic protocol. The chemical properties of both Sb-containing POSSs were investigated with different analytical and spectroscopic techniques. The analyses confirm the success of the corner-capping reaction for both samples and indicate that an Sb(V)-POSS sample is characterized by a heterogenous multimeric arrangement with an irregular organization of POSS cages linked to Sb(V) centers, and has a more complex structure with respect to the well-defined monomeric Sb(III)-POSS
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
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