The main objective of this study was to perform laboratory experiments on calcium nitrate addition to sediments of a tropical eutrophic urban reservoir (Ibirité reservoir, SE Brazil) to immobilize ...the reactive soluble phosphorus (RSP) and to evaluate possible geochemical changes and toxic effects caused by this treatment. Reductions of 75 and 89% in the concentration of RSP were observed in the water column and interstitial water, respectively, after 145 days of nitrate addition. The nitrate application increased the rate of autotrophic denitrification, causing a consumption of 98% of the added nitrate and oxidation of 99% of the acid volatile sulfide. As a consequence, there were increases in the sulfate and iron (II) concentrations in the sediment interstitial water and water column, as well as changes in the copper speciation in the sediments. Toxicity tests initially indicated that the high concentrations of nitrate and nitrite in the sediment interstitial water (up to 2300 mg L−1 and 260 mg L−1, respectively) were the major cause of mortality of Ceriodaphnia silvestrii and Chironomus xanthus. However, at the end of the experiment, the sediment toxicity was completely removed and a reduction in the 48 h-EC50 of the water was also observed. Based on these results we can say that calcium nitrate treatment proved to be a valuable tool in remediation of eutrophic aquatic ecosystems leading to conditions that can support a great diversity of organisms after a restoration period.
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► Nitrate addition cause iron oxidation, which reduces the RSP flow from sediments to water column. ► AVS oxidation, alkalinity and nitrate consumption indicate autotrophic denitrification process. ► Nitrate addition as sediment restoration technology may cause toxicity to aquatic organisms.
Degradation of polymer blends: A brief review La Mantia, F.P.; Morreale, M.; Botta, L. ...
Polymer degradation and stability,
November 2017, 2017-11-00, 20171101, Letnik:
145
Journal Article
Recenzirano
The usefulness of any material, including polymer blends, depends on its degradability and durability. The blend composition can significantly affect the degradative behavior of a polymer blend and ...can differ from the degradation routes of the pure components since the interactions among different species in the blends during degradation, and among the degradation products, can occur. These reactions can lead either to an acceleration of the degradation rate or to a stabilizing effect in comparison with the pure components. Thus, the additive rule cannot be often applied in case of degradation of polymer blends and, therefore, it is difficult to predict the degradative behavior of a polymer blend on the base of the properties of pure components.
This review aims to report the status of the research on degradation of polymer blends focusing on thermal, thermomechanical and photo-oxidative degradation.
The photo-oxidation behaviour of polymer nanocomposites depends not only on the photo-oxidation behaviour of the matrix, but also on the chemical composition, on the physical properties of the ...nanoparticles and on the possible interactions between the two phases. In the case of nanocomposites with carbonaceous particles, the main effect is a photo-stabilization due to the absorption of the UV energy and the radical scavenging action. In this work we investigated the effect of the presence of graphene nanoplatelets on the photo-oxidation behaviour of the polypropylene. The presence of the graphene nanoplatelets improves the photo-resistance of the polypropylene and this effect increases with the graphene content. This behaviour has been correlated with the exposed surface of the graphene and not to the dimensions of the graphene nanoplatelets.
•PP/GnP nanocomposites were subjected to accelerated weathering.•Nanocomposites viscosity as function of the irradiation time decreases more slowly in comparison with the neat PP.•The presence of the GnP improves the photo-stability of the matrix.•The photo-stabilizing action improves with increasing the content of GnP.
Bio-based, biodegradable polymers can dramatically reduce the carbon dioxide released into the environment by substituting fossil-derived polymers in some applications. In this work, prototypes of ...trays for aquaculture applications were produced via injection molding by using a biodegradable polymer, Mater-Bi
. A characterization carried out via calorimetric, rheological and mechanical tests revealed that the polymer employed shows properties suitable for the production of tools to be used in aquaculture applications. Moreover, the samples were subjected to a biodegradation test in conditions that simulate the marine environment. The as-treated samples were characterized from gravimetrical, morphological and calorimetric point of views. The obtained data showed a relatively low biodegradation rate of the thick molded samples. This behavior is of crucial importance since it implies a long life in marine water for these manufacts before their disappearing.
Coatings of a Fe43.2Co28.8B19.2Nb4Si4.8 alloy on AISI 1020 steel substrates were produced by laser cladding. By properly selecting the processing parameters adherent tracks with negligible dilution ...could be obtained. For the processing conditions used the clad material presents a graded structure consisting of 5 layers with different microstructures, resulting from the prevalent material solidification path. Solidification starts by epitaxial growth of Fe–Co δ-ferrite on the δ-ferrite resulting from heating of the substrate near the fusion line into the δ-ferrite stability temperature range. This first stage of solidification leads to the formation of consecutive layers consisting predominantly of δ-ferrite and formed by plane front, cellular and columnar dendritic solidification. The solidification of Fe–Co δ-ferrite leads to the segregation of B and Nb first frontally, to the bulk of the liquid, then to the interdendritic regions, resulting in the precipitation of a boride containing eutectic. Initially, the eutectic precipitates in the interdendritic regions, resulting in a layer of material comprised of δ-ferrite dendrites and interdendritic eutectic, then in a layer of material where the eutectic is the bulk alloy constituent. Eventually, a layer of amorphous material with homogeneously dispersed dendrites of Fe–Co δ-ferrite forms in most of the coating thickness. These embedded dendrites form by equiaxed solidification within the supercooled liquid at the trailing edge of the melt pool, from δ-ferrite dendrite fragments and boride particles carried from the growing columnar layer into the liquid bulk by Marangoni convection, driven by the temperature gradients existing within the melt pool. They play a critical role in defining the excellent properties of the coating material: a very high hardness of 1040±16 HV0.5 associated to a reasonable ductility, allowing the formation of crack-free coatings, in contrast with the bulk alloy prepared by spray forming, either in the as-prepared condition or after laser melting.
•Fe-based glassy matrix composite coatings were produced by laser cladding.•The coating consists mainly of amorphous phase with δ-ferrite dendrites.•The defect-free coatings exhibit hardness 6 times higher than the steel substrate.
Summary
Background
In liver transplant recipients with hepatitis C virus recurrence, there is concern about renal safety of sofosbuvir‐based regimens. Changes in serum creatinine or in the estimated ...glomerular filtration rate (eGFR) under treatment are used to look for possible renal toxicity. However, serum creatinine and eGFR are highly variable.
Aim
To analyse renal function trajectory with numerous assays of serum creatinine over a long period of time.
Methods
In a multicentre cohort of 139 patients, the eGFR was obtained from serum creatinine using the Chronic Kidney Disease–Epidemiology Collaboration (CKD‐EPI) equation. Slopes of eGFR were defined as a change in eGFR during a period divided by time. Pre‐treatment, on‐treatment and post‐treatment periods were 9 months, 3‐9 months and 4.5 months. Interactions between eGFR slopes and the pre‐treatment eGFR, use of ribavirin or mycophenolate mofetil, and stage of fibrosis were addressed. On‐treatment eGFR slopes were separated in tertiles. Pre‐ and post‐treatment eGFR slopes were compared globally and according to tertiles.
Results
The post‐treatment eGFR slope was significantly better than pre‐treatment eGFR slope (+0.18 (IQR −0.76 to +1.32) vs −0.11 (IQR −1.01 to +0.73) mL/min/1.73 m2/month, P = 0.03) independently of the pre‐treatment eGFR (P = 0.99), ribavirin administration (P = 0.26), mycophenolate mofetil administration (P = 0.51) and stage of fibrosis (F3 and F4 vs lower stages, P = 0.18; F4 vs lower stages, P = 0.08; F4 Child‐Pugh B and C vs lower stages, P = 0.38). Tertiles of on‐treatment eGFR slopes were −1.71 (IQR −2.54 to −1.48), −0.78 (IQR −1.03 to −0.36) and +0.75 (IQR +0.28 to +1.47) mL/min/1.73 m2/month. Pre‐ and post‐treatment eGFR slopes were not significantly different according to tertiles (respectively, P = 0.34, 0.08, 0.73).
Conclusion
The eGFR varies during treatment and gives a confusing picture of the renal safety of sofosbuvir‐based regimens. In contrast, longitudinal assessment of the eGFR shows a rising trajectory over longer time, meaning that these therapies are safe for the kidneys in our cohort of liver transplant recipients.
In this work the effect of multiple reprocessing was studied on molecular structure, morphology and properties of poly(lactic acid)/hydrotalcites (PLA/HT) nanocomposites compared to neat PLA. In ...addition, the influence of two different kinds of HT - organically modified (OM-HT) and unmodified (U-HT) - was evaluated. Thermo-mechanical degradation was induced by means of five subsequent extrusion cycles. The performance of the recycled materials was investigated by mechanical and rheological tests, differential scanning calorimetry (DSC), intrinsic viscosity measurements and SEM observation. The results indicated that the best morphology was achieved in the systems incorporating OM-HT. On increasing the extrusion reprocessing cycles, the properties showed behavior due to two opposite effects: i) chain scission due to thermo-mechanical degradation and ii) filler dispersion effect resulting from multiple processing. In particular, at low reprocessing cycles, both tensile and rheological properties seem to be mainly affected by HT dispersion, especially when OM-HT was added. After five reprocessing cycles, on the contrary, chain scission, i.e. thermo-mechanical degradation, dominated. As regards the effect of the presence of organic modifier in HT, the results indicated that this variable apparently did not affect the macroscopic performance of the nanocomposites, especially at high reprocessing cycles.
This study aimed to analyze laboratory and field data to assess the ecotoxicological risks of calcium nitrate exposure to freshwater tropical biota. Short-term laboratorial tests resulted in ...estimated EC50 values of 76.72 (67.32–86.12)mg N-NO3-L−1 for C. silvestrii and 296.46 (277.16–315.76)mg N-NO3-L−1 for C. xanthus. Long-term laboratorial tests generated IC25 values of 5.05 (4.35-5.75) and 28.73 (26.30–31.15)mg N-NO3-L−1 for C. silvestrii and C. xanthus, respectively. The results from in situ mesocosm experiments performed in the Ibirité reservoir (a tropical eutrophic urban water body located in SE Brazil) indicated that C. silvestrii and C. xanthus were not under severe deleterious acute impact due to the treatment because the higher nitrate concentrations determined were 5.2mg N-NO3-L−1 (t=24h; sediment-water interface) and 17.5mg N-NO3-L−1 (t=600h; interstitial water). However, an abrupt decrease in the densities of Cyanophyceae members and other benthic taxa was observed. In summary, the present work contributes greatly to the toxicity data linked to two taxonomically distinct organisms that have never been screened for calcium nitrate sensitivity. Furthermore, considering the problem of the management and restoration of eutrophic environments, our study reports a comprehensive field assessment that allows the elucidation of the possible toxic impacts caused by the addition of calcium nitrate (a remediation technique) on aquatic and benthic organisms as well as the implications on the aquatic ecosystem as a whole, which may greatly allow expanding the current knowledgebase on the topic.
•Ceriodaphnia silvestrii: 48h-EC50=76.72 (67.32–86.12)mg N-NO3−L−1.•Ceriodaphnia silvestrii: 7d-IC25=5.05 (4.35–5.75)mg N-NO3−L−1.•Chironomus xanthus: 96h-EC50=296.46 (277.16–315.76)mg N-NO3−L−1.•Chironomus xanthus: 20d-IC25=28.73 (26.30–31.15)mg N-NO3−L−1.•No acute effect was observed to C. silvestrii and C. xanthus in treated mesocosms.
In this work the effect of the presence of graphene nanoplatelets (GnP) on the morphology and mechanical properties of polypropylene/GnP nanocomposites has been investigated when these polymer ...systems are subjected to non-isothermal elongational flow in a melt spinning operation. The presence of the GnP magnifies the effect of the elongational flow. Indeed, the elastic modulus and the tensile strength of nanocomposites increases with the orientation more than that observed for the pure matrix. Moreover, the elongation at break increases at low values of the draw ratio for the nanocomposites, while, the matrix shows the expected decrease in deformability. These effects have been correlated with the decrease in the dimensions of the nanoplatelets caused by the elongational flow. The increase of contact surface between matrix and dispersed phase is responsible for these behaviours since the larger contact area improves the transfer of the stress from matrix to GnP. The best performance was observed for the nanocomposite with the lower GnP content and this phenomenon has been again correlated with the minor size of the GnP in this nanocomposite sample.
•PP/GnP nanocomposite fibers were prepared by melt spinning.•The effect of the elongational flow on the morphology of these nanocomposites was studied.•The elongational flow caused the reduction of GnP aggregates size.•The presence of the GnP enlarged the effect of the elongational flow on the mechanical properties.•The best performance was observed for the nanocomposites with the lower GnP content.
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