1,721,148 research outputs found
Multi-functional hindered amine light stabilizers-functionalized carbon nanotubes for advanced ultra-high molecular weight Polyethylene-based nanocomposites
Full text linkHindered Amine Light Stabilizer (HAS) molecules have been covalently linked on the outer surface of multi-walled carbon nanotubes (CNTs), and the so-obtained multi-functional fillers (HAS-f-CNTs) have been compounded with Ultra High Molecular Weight Polyethylene (UHMWPE) to get composite films. The success of the grafting reaction of the HAS molecules has been confirmed through spectroscopic and thermo-gravimetric analyses. Morphological analyses reveal a segregated microstructure, in which CNT-rich channels surround the polymer domains. This morphology results in improved mechanical properties and appreciable electrical conductive features. More importantly, the addition of only 1 wt.% of HAS-f-CNTs brings about a significant improvement of the photo-oxidation resistance, which neither HAS nor CNTs can provide if used separately. The origin of this synergic effect is discussed. Overall, our results demonstrate the possibility of using properly functionalized CNTs as multi-functional fillers to get high-performance polymer composites
On the effectiveness of different additives and concentrations on the re-building of the molecular structure of degraded polyethylene
No full textMechanical recycling is an easy and economic way to re-use plastic waste as secondary materials, but, in general, their properties are worse with respect to the reclaimed materials and the virgin polymer. The aim of this work was to study the effect of concentration and reaction kinetics of two additives, an ethylene-co-glycidyl methacrylate (Lotader) and a hydroxylamine derivative (CGX), in the re-building of a degraded polyethylene. CGX is a nitroxyl radical generator able to form branching in polyolefins while the epoxy groups of Lotader can react with the functional groups present in the recycled polyethylene. The results indicate that the CGX has a higher reaction rate than Lotader, probably due to its lower molecular weight and the different reaction path. As for the effect of concentration, as expected, a higher amount of additive accelerates and increases re-building, especially when CGX is used. The melt strength increases with the additive content and the mechanical properties show a significant reduction at the highest concentrations of both additives due to excessive cross-linking
Slow pyrolysis as a method for biochar production from carob waste: Process investigation and products’ characterization
Full text linkThe zero-waste city challenge of the modern society is inevitably addressed to the development of model’s waste-to-energy. In this work, carob waste, largely used in the agro-industrial sector for sugar extraction or locust beangum (LBG) production, is considered as feedstock for the slow pyrolysis process. According to the Food and Agriculture Organization of the United Nations (FAO), in 2012, the world production of carobs was ca. 160,000 tons, mainly concentrated in the Mediterranean area (Spain, Italy, Morocco, Portugal, and Greece). To evaluate the biomass composition, at first, the carob waste was subjected to thermo-gravimetric analysis. The high content of fixed carbon suggests that carobs are a plausible candidate for pyrolysis conversion to biochar particles. The thermal degradation of the carob waste proceeds by four different steps related to the water and volatile substances’ removal, degradation of hemicellulose, lignin and cellulose degradation, and lignin decomposition. Considering this, the slow pyrolysis was carried out at three different temperatures, specifically, at 280, 340, and 400◦C, and the obtained products were characterized. Varying the processing temperature, the proportion of individual products’ changes with a reduction in the solid phase and an increase in liquid and gas phases, with an increase in the pyrolysis temperature. The obtained results suggest that carob waste can be considered a suitable feedstock for biochar production, rather than for fuels’ recovery
Rheological Percolation Threshold in High-Viscosity Polymer/CNTs Nanocomposites
No full textPolystyrene (PS)/multi-walled carbon nanotubes (CNT) nanocomposites have been prepared through melt mixing processing
aiming at obtaining a uniform and homogeneous dispersion of the used nanoparticles within the polymeric matrix. Optical and scanning
electron microscopy has been employed to determine the dispersion and distribution of CNTs at different length scales. Furthermore, the
linear viscoelastic behavior of formulated nanocomposites has been deeply investigated. As a result of CNTs added, the nanocomposites
experience a transition from liquid-like to solid-like rheological behavior, and a disappearance of relaxation processes at low frequency can be
noticed. By plotting G’ versus CNTs loading and fitting with a power-law function, the rheological threshold of PS-based nanocomposites has
been calculated. Moreover, the mechanical behavior of nanocomposites has been investigated and related to the formed CNTs network within
polymer matrix
Thermo-oxidative resistant nanocomposites containing novel hybrid-nanoparticles based on natural polyphenol and carbon nanotubes
Full text linkQuercetin (Q), a natural antioxidant molecule, is physically immobilized onto multi-walled carbon nanotubes (CNTs) bearing covalently-linked long-chain alkyl functional groups, and the so obtained hybrid-nanoparticles are used to prepare Ultra High Molecular Weight PolyEthylene-based nanocomposite films with enhanced thermo-oxidation resistance. The effective immobilization of the Q molecules is confirmed by spectroscopic (micro-Raman, ATR-FTIR, and FTIR) and thermo-gravimetric analyses, and the influence of the nanoparticles on the rheological behaviour and thermo-oxidative stability of the nanocomposites are investigated. Rheological analyses (linear viscoelasticity and stress relaxation tests) and morphological observations reveal that the Q-functionalized CNTs disperse better than bare CNTs in the host matrix. Quercetin confirms to be an excellent anti-oxidant for polyethylene, but the study of the thermo-oxidation behaviour shows that a remarkable stabilizing action only emerges when Q is physically immobilized on the CNTs. In particular, a ten-fold increase of the onset of degradation phenomena in thermo-oxidative environment was found. Such an excellent result is due to a synergic effect stemming from the physical interaction between Q and CNTs, which cannot provide a similar stabilizing action if used separately. In particular, we argue that the process of physical immobilization of the Q molecules causes the formation of structural defects onto outer CNTs surfaces, thus remarkably improving the CNTs radical scavenging activity and probably promoting Q regeneration. In addition, CNTs seem acting as efficient nano-carriers for the quercetin molecules, improving the dispersion of the latter in the host matrix in spite of their poor solubility
Multi-functional polyhedral oligomeric silsesquioxane-functionalized carbon nanotubes for photo-oxidative stable Ultra-High Molecular Weight Polyethylene-based nanocomposites
No full textNanohybrid (phPOSS-f-CNTs) based on Carbon Nanotubes (CNTs) and Phenyl Polyhedral Olygomenric Silsesquioxane (phPOSS) have been synthesized to be used as multifunctional filler for polymer nanocomposites. The success of the functionalization procedure has been demonstrated via accurate spectroscopic, spectrometric and thermo-gravimetric analyses. The results reveal that a large portion of phPOSS is covalently linked to CNTs, while a small amount of phPOSS remains physically adsorbed due to the strong interactions coming from π electron coupling between the CNTs and phenyl rings in phPOSS. Small amounts (1 wt.%) of phPOSS-f-CNTs have been dispersed in Ultra High Molecular Weight Polyethylene (UHMWPE), aiming at improving the photo-stability of the resulting nanocomposite. The rheological and thermo-mechanical behavior of UHMWPE/phPOSS-f-CNTs nanocomposite reflects two different opposite contributions, namely the reinforcement effect of CNTs and the plasticizing action of phPOSS molecules. Concerning the photo-oxidative behavior, phPOSS-f-CNTs show a remarkable protective ability, which is absolutely much higher than those exerted by CNTs and phPOSS molecules when added one by one. Such unexpected results could be explained considering (i) a synergic effect between phPOSS and CNTs, (ii) the possibility of phPOSS to act at the polymer-nanoparticles interface, which is a critical region for the degradation processes, and (iii) the formation of a phPOSS-rich layer that may hinder the oxygen diffusion within the polymeric matrix
Low-density polyethylene/polyamide/clay blend nanocomposites: Effect of morphology of clay on their photooxidation resistance
Full text linkThe photooxidation behaviour of low-density polyethylene (LDPE)/polyamide (PA) blends, containing polyamide 11 (PA11) or polyamide 6(PA6), has been investigated in the absence and presence of a small amount of commercial organomodified clay (OMMT). The polymer blends LDPE/PA11 and LDPE/PA6 at 75/25 wt./wt.%, with and without OMMT, have been prepared by a two-step procedure: extrusion and sheet formulation. The formulated complex systems have been subjected to accurate morphological analysis in order to evaluate the effect of the OMMT presence on the refinement of the blend morphology. Furthermore, the produced sheets have been subjected to arterial UVB exposure and the variations of the mechanical properties and chemical structure of all the investigated samples have been monitored as a function of the exposure time. Finally, the rate of the photodegradation of the complex systems has been related to the morphological changes of these systems upon OMMT addition
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
Reprocessing and restabilization of greenhouse films
No full textFrom the ecological and economical points of view, reprocessing of polyethylene greenhouse films is a promising solution to reduce discarded materials and to produce useful, or potentially useful, objects for service. Films exposed outdoors, however, show inferior mechanical properties and the melt processing worsens these properties. The addition of stabilizers and antioxidants to recycled plastic products prevents inherent thermal instabilities from occurring within the time frame of proper processing. In this study, we attempt to explore ways for improving product performance by the addition of four different additives when the recycled films undergo intensive shear processing. The process is evaluated by measuring the changes in chemical structure (carbonyl evolution) as well as rheological and mechanical characteristics (tensile properties). The effectiveness of the various additives was estimated and the one with the best antioxidant ability was identified. The analysis of processing conditions allowed us to find that the best results are emphasized by the continuous addition of the stabilizer at each step of reprocessing. (C) 2002 Elsevier Science Ltd. All rights reserved
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