Green composites, i.e. biodegradable polymers reinforced with natural fibers, are attracting interest as potential substitutes for conventional composites based on petroleum derived plastics. The ...role of the inherently complex morphology of natural fibers in their reinforcing mechanisms is not completely understood and this is the topic of the present study. The selected system was poly-(lactic acid) filled with 3 and 6 wt% of short hemp fibers. Such a low fiber amount was chosen to help visualization of the fiber – matrix interface at the scanning electron microscope. Remarkable differences in the mechanical behavior were found between composites containing fibers that were alkali treated with respect to untreated fiber filled materials, but unexpectedly it was found that the quality of the fiber – matrix interface was only marginally influenced by the alkaline treatment. Interface properties were thus not exhaustive in explaining the observed differences. On the other hand, the main difference between treated and untreated fibers was the presence, in the untreated fibers population, of a volumetrically relevant sub-population of thick fiber bundles. It was further argued that this fraction did not carry the loads transferred across the fiber-matrix interface uniformly in its cross section, thus determining a reduction in the effective fiber volume fraction. In contrast, the combined action of alkalization and the mechanical stresses during melt mixing resulted in a narrow distribution of isolated elementary fibers, which were more effective in providing higher mechanical properties, in agreement with theoretical predictions. The key message for the scientific community interested in maximizing the mechanical performances of green composites is that, besides trying to improve the quality of the fiber-matrix interface, one should also aim at minimizing the amount of fiber bundles.
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•CS and CS/GO aerogels are prepared by crosslinking before or after freeze-drying.•Crosslinking after freeze-drying improves the dye removal ability of CS aerogels.•GO addition ...significantly improves the mechanical properties.•GO addition also provides a high uptake capacity towards cationic dyes.•The crosslinking strategy is crucial to optimize the properties of CS/GO aerogels.
Chitosan (CS) aerogels were prepared by freeze-drying as potential adsorbents for water purification, and the effect of the strategy of crosslinking was investigated by varying the amount of crosslinker (glutaraldehyde) and the sequence of steps for the preparation of the aerogel. Two procedures were compared, in which the crosslinking step was carried out before or after the freeze-drying of the starting CS solution. When crosslinking was postponed after the freeze-drying step, the adsorption capacity towards an anionic dye, such as indigo carmine, considerably increased (up to +45%), reaching values as high as 534.4 ± 30.5 mg g−1. The same crosslinking strategy ensured a comparable improvement also in nanocomposite aerogels containing graphene oxide (GO), which was added to enhance the mechanical strength and provide adsorption capacity towards cationic dyes. Besides possessing good mechanical strength (compressive modulus higher than 1 MPa), the CS/GO aerogels were able to bind also cationic pollutants such as methylene blue. The maximum uptake capacity increased from 4.3 ± 1.6 to 168.6 ± 9.6 mg of cationic dye adsorbed per gram of adsorbent with respect to pristine CS aerogels.
Different amounts of organoclay, sepiolite, and carbon nanotubes are added to an immiscible blend of poly(lactic acid) (PLA) and polyamide 11 (PA11) with drop-matrix morphology aiming at elucidating ...the mechanisms through which unevenly distributed nanoparticles may induce co-continuity. Morphological and dynamic-mechanical analyses show that the three fillers, preferentially located inside the minor PA11 phase, are all able to convert the drop-matrix morphology of the blend into a stable, highly co-continuous one provided a critical nanoparticle loading is exceeded. The cross-checking of the experimental results reveals that co-continuity occurs when the strength of the particle network encapsulated inside the PA11 is sufficient to balance the inclination of the stretched polymer domains to retract back towards lower aspect ratio shapes driven by interfacial tension. A single dimensionless group that combines the yield stress of the filled PA11, the bending resistance of the nanoparticles, and the PLA-PA11 interfacial tension, seems able to rationalize our data, providing a general criterion for the optimal selection of fillers suitable to induce co-continuity in immiscible polymer blends.
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Cyclin-dependent kinase 12 (CDK12) overexpression is implicated in breast cancer, but whether it has a primary or only a cooperative tumorigenic role is unclear. Here, we show that transgenic CDK12 ...overexpression in the mouse mammary gland per se is sufficient to drive the emergence of multiple and multifocal tumors, while, in cooperation with known oncogenes, it promotes earlier tumor onset and metastasis. Integrative transcriptomic, metabolomic and functional data reveal that hyperactivation of the serine-glycine-one-carbon network is a metabolic hallmark inherent to CDK12-induced tumorigenesis. Consistently, in retrospective patient cohort studies and in patient-derived xenografts, CDK12-overexpressing breast tumors show positive response to methotrexate-based chemotherapy targeting CDK12-induced metabolic alterations, while being intrinsically refractory to other types of chemotherapy. In a retrospective analysis of hormone receptor-negative and lymph node-positive breast cancer patients randomized in an adjuvant phase III trial to 1-year low-dose metronomic methotrexate-based chemotherapy or no maintenance chemotherapy, a high CDK12 status predicts a dramatic reduction in distant metastasis rate in the chemotherapy-treated vs. not-treated arm. Thus, by coupling tumor progression with metabolic reprogramming, CDK12 creates an actionable vulnerability for breast cancer therapy and might represent a suitable companion biomarker for targeted antimetabolite therapies in human breast cancers.
Thermal and thermo-oxidative degradation of polyamide 11 (PA11) in the melt state (T = 215 °C) are studied by resorting to time-resolved mechanical spectroscopy. Such an approach allows to elude the ...changes in the rheological properties occurring while testing, thus enabling the rigorous study of polymer degradation in the melt state. Different concurrent degradation reactions in oxidative (air) and non-oxidative (N2) environment are promptly guessed by studying the time evolutions of rheological functions. In particular, changes in the zero–frequency complex viscosity reflects changes in the average molecular weight, while the appearance of a yield stress in the complex viscosity curve is identified as the rheological fingerprint of cross-linking reactions. Size exclusion chromatography corroborates the hypotheses based on rheological analyses, and matrix assisted laser desorption/ionization mass spectrometry sheds light on the chemical aspects of degradation. Specifically, post-condensation (in N2), chain scission, hydrolysis and cross-linking reactions (in air) are identified as the dominant degradation mechanisms of PA11 in the melt state. Overall, our study demonstrates that rheology is a valuable tool to detect and discriminate among different degradation mechanisms in polymer melts. In particular, rheology promptly identifies cross-linking reactions, which can be difficult to be detected through common analytical techniques that envisage the solubilization of the polymer sample.
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•Degradation of PA11 in the melt state is studied through time-resolved rheology.•Post-condensation is the dominant thermal degradation mechanism in N2.•Post-condensation, chain scission and cross-linking simultaneously occur in air.•Rheology is very sensitive to cross-linking reactions.
We study the structure and linear viscoelasticity of interacting polymer nanocomposites based on mixtures of poly(ethylene oxide) and fumed silica particles. The filler is dispersed within the ...polymer using two different techniques which lead to different dispersion states. The analysis of the dynamic response of our systems highlights the formation of a stress-bearing network above a critical volume fraction, Φc. Extending a two-phase model used to describe weakly interacting systems, we show that above Φc the melt-state elasticity of the composites arises from the independent contributions of a polymer–particle network and a viscous matrix. We also find that, although Φc depends on the initial state of dispersion, the network elasticity scales with volume fraction following a universal power-law, with an exponent ν ≈ 1.8. Such a scaling law has been recently predicted for the stress-bearing mechanism governed by polymer-mediated interactions.
Thermal and thermo-oxidative degradation of nanocomposites based on polyamide 11 (PA11) and organo-modified clay (Cloisite® 30B) are studied in the melt state (T = 215 °C) via time-resolved ...mechanical spectroscopy (TRMS). The goal is assessing the potentiality of rheological analysis for studying polymer degradation in complex systems such as polymer nanocomposites, whose rheological response stems from the combination of the contributions of polymer and nanoparticles. We prove that a thorough analysis grounded on TRMS allows to isolate the effect of degradation of the polymer matrix, whose progress can be hence profitably monitored. Essentially the same degradation mechanisms as in neat PA11 are identified for the nanocomposite, but the kinetics of the thermo-oxidation processes are much faster in the presence of organo-clay. In particular, rheology promptly identifies cross-linking reactions since the early stage of the treatment in air. Matrix-assisted laser desorption/ionization and oxidative induction time measurements corroborate the conclusions drawn on the basis of rheological analyses, shedding light on the chemical aspects of PA11 degradation. Overall, rheological analysis confirms to be a valuable tool for monitoring polymer degradation even in case of inherently complex systems such as nanocomposites. In this case, however, the analysis can be difficult if the dynamics of the nanoparticles prevail over those of the polymer matrix, which is the case of nanocomposites at high filler contents.
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•Degradation of PA11/Clay nanocomposites is studied through rheology in N2 and air.•The nanocomposites experience the same degradation mechanisms as neat PA11.•Nanoparticles accelerate PA11 thermo-oxidative degradation.•At high particle loadings the filler masks the degradation pathways of the polymer.
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.
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•Nano-SiO2 was used for improving shear mechanical properties of superfine cement grouts.•Shear strength parameters and rheological properties of different grouts were determined.•The ...optimal SP amounts of 1.5% and 0.75% were recommended for different grouts.•Superfine cement grout property optimization and grouting effectiveness were discussed.
The subsoil consolidation in the archaeological sites or in areas with historic existing buildings (e.g. Pompeii) needs the use of ground improvement techniques that must guarantee the safeguarding of such relevant areas and structures. One of the best approaches in such cases is low pressure grouting. An experimental multidisciplinary study was carried out with the aim to design and characterize a sustainable chemical grout sodium silicate-based catalysed by NaHCO3. The evolution from sol-to-glassy phase of the grouts was carefully investigated, furthermore the effectiveness of the grout has been verified either by lab tests or by real-scale field trials. The experimental findings suggested that it is possible to properly control the viscosity and gel-time of the grout modulating the amount of catalyst without affecting the final consolidation performances. Furthermore, the results at real-scale validate the safety of the above approach in cultural heritage applications, since it allowed a complete permeation of the soil without worsening its final properties.
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