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• the isothermal TGA behaviour of different PEs gives dissimilar residue and stability. • hydroperoxidation and dehydrogenation reactions compete during PE thermo-oxidation. • Macromolecular architecture of polyethylenes affects its charring ability. The induction period preceding the ignition is a fundamental stage in controlling the protection of polymeric materials from fire. In fact, at this stage, the formation of a non-pyrolyzable carbonaceous layer (char) onto the material surface could prevent the development of a sustained flame, hence delaying or preventing polymer burning. In this work, the charring ability of four samples of high- and low-density polyethylene was evaluated in different scenarios, namely isothermal oxidative conditions and cone calorimetry tests at different heat fluxes, aiming at assessing the possible influence of the polymer macromolecular architecture on their charring ability. First, the selected polymers were characterized from a thermal and rheological point of view; the obtained results allowed for disclosing the different microstructure of the materials, in terms of molecular weight and possible presence of short- or long-chain branching. Then, isothermal thermogravimetric analyses and cone calorimetry tests were performed, demonstrating a different charring ability of the investigated polyethylenes. Finally, the observed behaviours were correlated to the different chemical structure and to the specific macromolecular architecture of the polymers, allowing a systematic evaluation of the relationship between the molecular weight or the presence of branched structures and the mechanism and rate of char formation. [ABSTRACT FROM AUTHOR]

Nanohybrid (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. [ABSTRACT FROM AUTHOR]

Hindered 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. [ABSTRACT FROM AUTHOR]

Warming over Mongolia and Central Asia has been unusually rapid over the past few decades, particularly in the summer, with surface temperature anomalies higher than for much of the globe. With few temperature station records available in this remote region prior to the 1950s, paleoclimatic data must be used to understand annual-to-centennial scale climate variability, local response to large-scale forcing mechanisms, and the significance of major features of the past millennium such as the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) both of which can vary globally. Here we use an extensive collection of living and subfossil wood samples from temperature-sensitive trees to produce a millennial-length, validated reconstruction of summer temperatures for Mongolia and Central Asia from 931 to 2005 CE. This tree-ring reconstruction shows general agreement with the MCA (warming) and LIA (cooling) trends, a significant volcanic signature, and warming in the 20th and 21st Century. Recent warming (2000–2005) exceeds that from any other time and is concurrent with, and likely exacerbated, the impact of extreme drought (1999–2002) that resulted in massive livestock loss across Mongolia. [ABSTRACT FROM AUTHOR]

Quercetin (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. [ABSTRACT FROM AUTHOR]

Abstract: α-Tocopherol, a natural antioxidant molecule, was physically immobilized on the outer surface of multi-walled carbon nanotubes (CNTs), and the resulting functionalised particles (f-CNTs) were dispersed in ultra-high molecular weight polyethylene aiming at improving its thermo-oxidation resistance. The success of the functionalization was assessed through spectroscopic and thermal analysis, and the influence of the filler on the thermo-oxidative stability of the nanocomposites was investigated through rheological analyses and infrared spectroscopy. We found that the addition of only 1wt.% of f-CNTs brings about a surprisingly high oxidation resistance, with a five/ten-fold increase of the induction time of the degradation phenomena. Rather than to the inherent stabilizing action of the α-tocopherol, such a notable result is believed to be due to its specific chemical interactions with the CNTs, which could exhibit a considerable radical scavenging activity due to the formation of structural defects on their outer surface. The latter represent acceptor-like localized states, which radically improve the thermo-oxidative resistance of the f-CNTs-based polymer nanocomposites. [Copyright &y& Elsevier]

Highlights: [•] Nanocomposites based on commercial biodegradable polymer were investigated. [•] Effect of the orientation during non-isothermal elongational flow was assessed. [•] Different clay nanofillers lead to different rheological behaviour due to their polarity. [•] Mechanical properties are significantly dependent on the draw ratio. [•] Nanocomposites subjected to significant non-isothermal elongational flow can behave like a polymer blend. [ABSTRACT FROM AUTHOR]

Abstract: Pd nanoparticles deposited by sol-immobilization on N-doped nanocarbon are studied in the direct synthesis of H2O2 and compared with undoped catalysts or prepared by the same Pd deposition method on active carbon (Vulcan XC-72). The Pd on N-CNT-like gives high productivities to H2O2, comparable to the best literature results. The introducing of nitrogen in the CNT-like material favors not only the dispersion of Pd (with a consequent improvement of the activity), but also the specific turnover. However, the introduction of these N functionalities on the surface has also a negative effect on the rate of H2O2 consecutive conversion to water. [ABSTRACT FROM AUTHOR]

Abstract: The photo-ageing behaviour of Polyhedral Oligomeric SilSequioxane (POSS)-polystyrene (PS) nanocomposites has been investigated for the first time. POSS having different inorganic framework and pendant organic groups have been used in the PS nanocomposite preparation and the formulated films were subjected to accelerated weathering. Compared to pristine PS, the POSS-containing PS developed a lower level of carbonyl and hydroxyl groups as a function of the exposure time, indicating a significantly improved resistance of the nanocomposites to photo-degradation. The results suggest that all of the investigated POSS molecules play a protective role and may extend the in-use lifetime of the polymeric matrix. The protection efficiency seems to depend on the structure of the POSS used, i.e. the type of their inorganic framework and organic pendant groups. The efficacy of the protection provided by POSS is more pronounced for the open-cage POSS-triols than for the closed-cage POSS, suggesting an active role of the POSS-triol free OH group in the PS stabilisation process. The pendant organic groups significantly influence the nanocomposite''s local morphology by controlling the formation of POSS re-aggregates and/or the POSS dispersion into the matrix, and its response to photo-oxidation. [Copyright &y& Elsevier]

Abstract: In this paper two systems, polyethylene (LDPE) and polyethylene/commercial organo-modified montmorillonite (LDPE/OMMT) nanocomposite, were subjected to e-beam irradiation at different doses and both the molecular modifications and mechanical properties have been investigated through solubility, FT-IR, calorimetric and tensile tests. Moreover, in some of the irradiated systems photo-oxidation aging was performed and its effects were studied. The results show an enhancement with irradiation of the positive effect of the nano-filler loading, related to the increase of the mechanical properties, due to the increase of the nano-filler polymer interaction. Nevertheless calorimetric and FT-IR data indicate that the well known reduction of LDPE/OMMT nanocomposite resistance to photo-oxidation ageing, with respect to LDPE, is amplified by ionizing radiation. [Copyright &y& Elsevier]

Abstract: The characteristics of Fe-[B,Al]MFI catalysts prepared by changing: (i) the gel composition during the hydrothermal synthesis (Si/Al and Si/B ratio) and (ii) other synthesis aspects (silica source, use of phosphoric acid to complex iron) were studied. The samples were investigated in terms of composition, structural (X-ray diffraction (XRD), Fourier transform-IR (FT-IR)) and morphological (scanning electron microscopy (SEM)) aspects and distribution of the iron species determined by UV–vis DR spectroscopy. The results were correlated with the reactivity of these samples (phenol productivity and selectivity during benzene hydroxylation with N2O). A linear relationship was observed between Si/B ratio and phenol maximum productivity. This indicates that the main factor determining the catalytic performances is the amount of B introduced in the zeolite which in turn depends on the gel composition during hydrothermal synthesis and the preparation method. The linear relationship could be interpreted considering that the role of B is related to its easier migration from framework to extra-framework position with respect to Al and therefore easier creation of defect sites during heat treatment. These defect sites are important, because during the initial stage of the catalytic reaction, iron ions migrate to these sites creating highly active iron sites responsible of the initial increase in the phenol productivity. The presence of Al in the gel influences negatively the catalytic performances, because both Al competes with B to be introduced in the MFI structure as T atom. Furthermore, the presence of Al as T atom determines a lowering of the selectivity to phenol with respect to both carbon oxides and carbonaceous deposits formation. [Copyright &y& Elsevier]

Highlights • Operando photoelectron spectroscopy of Ir NPs under OER conditions in aqueous electrolyte. • Electron-hole shared between Ir 5d and O 2p as key in formation active species in the OER. • DFT calculations of the amount of hole character in Δp and Δd depending on the oxidation state. Abstract An electrode for the oxygen evolution reaction based on a conductive bi-layered free standing graphene support functionalized with iridium nanoparticles was fabricated and characterized by means of potentiometric and advanced X-ray spectroscopic techniques. It was found that the electrocatalytic activity of iridium nanoparticles is associated to the formation of Ir 5d electron holes. Strong Ir 5d and O 2p hybridization, however, leads to a concomitant increase O 2p hole character, making oxygen electron deficient and susceptible to nucleophilic attack by water. Consequently, more efficient electrocatalysts can be synthesized by increasing the number of electron-holes shared between the metal d and oxygen 2p. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract: The catalytic performances of Fe-[Al, B]MFI zeolites in benzene hydroxylation with N2O are studied as a function of the nature of the T atom (Al, B) and compared with the characterization of the nature of iron species determined by UV–vis diffuse reflectance spectroscopy. The results indicate that the mechanism for generation of iron species highly active in this reaction is the creation of hydroxyl nests in the zeolite framework due to framework to extra-framework migration of the T atom. The process is favoured when B is present as T atom, but occurs also in the case of Fe and Al as T atoms. Iron atoms migrate to these zeolite defect sites forming highly active Fe3+ isolated species in square pyramidal or highly distorted octahedral coordination. The process occurs during the catalyst pre-treatment as well as during the initial half an hour of time on stream, leading to an increase in the phenol productivity during this step. A model of these active sites is presented. The effect of the silica source in the preparation of these catalysts is also reported. [Copyright &y& Elsevier]

Linked to major volcanic eruptions around 536 and 540 CE, the onset of the Late Antique Little Ice Age has been described as the coldest period of the past two millennia. The exact timing and spatial extent of this exceptional cold phase are, however, still under debate because of the limited resolution and geographical distribution of the available proxy archives. Here, we use 106 wood anatomical thin sections from 23 forest sites and 20 tree species in both hemispheres to search for cell-level fingerprints of ephemeral summer cooling between 530 and 550 CE. After cross-dating and double-staining, we identified 89 Blue Rings (lack of cell wall lignification), nine Frost Rings (cell deformation and collapse), and 93 Light Rings (reduced cell wall thickening) in the Northern Hemisphere. Our network reveals evidence for the strongest temperature depression between mid-July and early-August 536 CE across North America and Eurasia, whereas more localised cold spells occurred in the summers of 532, 540-43, and 548 CE. The lack of anatomical signatures in the austral trees suggests limited incursion of stratospheric volcanic aerosol into the Southern Hemisphere extra-tropics, that any forcing was mitigated by atmosphere-ocean dynamical responses and/or concentrated outside the growing season, or a combination of factors. Our findings demonstrate the advantage of wood anatomical investigations over traditional dendrochronological measurements, provide a benchmark for Earth system models, support cross-disciplinary studies into the entanglements of climate and history, and question the relevance of global climate averages., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2022 Science China Press. Published by Elsevier B.V. All rights reserved.)