Search results for "CARBONATE"
showing 10 items of 920 documents
Damage monitoring on carbonate stones: Field exposure tests contributing to pollution impact evaluation in two Italian sites
2017
During the last decades, many studies have been carried out on environmental monitoring in specific sites aiming at their protection and conservation; however, researches focused on the direct implications, in terms of quantitative evaluation of stone deterioration, of these monitoring actions are still scarce. This experimental work aims at monitoring the degradation processes affecting historical buildings constituted by carbonate stones. Specifically, specimens of Carrara marble and two limestones largely used in the Sicilian Baroque architecture, namely Noto and Comiso stones, were exposed outdoor in two Italian sites (Catania and Palermo), which are characterized by different environme…
Bioavailability and assessment of heavy metal pollution in sediment cores off the Mejerda River Delta (Gulf of Tunis): How useful is a multiproxy app…
2016
International audience; Three core samples were taken from zones offshore from the Mejerda River Delta (Tunisia) and analyzed formajor and trace elements to assess their relationships with organic matter, monosulfides and carbonates, aswell as for pollution and bioavailability. Chemical speciation,ΣSEM/AVS, the enrichment factor (EF) and thegeo-accumulation index (I-geo) were used. Iron, cadmium, lead and zinc – the most frequently mined metalsin the Mejerda catchment – were found as contaminants in the offshore areas. Estimations of trace elementaccumulation using the EF and the I-geo index show that lead, and to a lesser extent zinc, are the most pollutingmetals off the Mejerda outlet. Ac…
Heavy metals in rivers of Latvia☆
2000
Abstract Total heavy metal concentrations in waters and sediments (HNO 3 digestible Pb, Cu, Co, Ni, Mn, Zn) and their speciation forms in sediments (exchangeable, carbonate bound, iron–manganese oxide bound, organic matter bound and residual) in major and common small watercourses (31 sampling stations) along their flow in Latvia were determined. The metal loads entering the Baltic Sea from Latvia were calculated. Increased metal concentrations were found only in lower reaches of the largest rivers and locally around known industrial pollution sources. Differences in metal concentrations and loads in rivers from different regions of Latvia were related to natural geochemical processes. Meta…
Controlled Synthesis of Multi-Arm Star Polyether-Polycarbonate Polyols Based on Propylene Oxide and CO2
2013
Multi-arm star copolymers based on a hyperbranched poly(propylene oxide) polyether-polyol (hbPPO) as a core and poly(propylene carbonate) (PPC) arms are synthesized in two steps from propylene oxide (PO), a small amount of glycidol and CO2 . The PPC arms are prepared via carbon dioxide (CO2 )/PO copolymerization, using hbPPO as a multifunctional macroinitiator and the (R,R)-(salcy)CoOBzF5 catalyst. Star copolymers with 14 and 28 PPC arms, respectively, and controlled molecular weights in the range of 2700-8800 g mol(-1) are prepared (Mw /Mn = 1.23-1.61). Thermal analysis reveals lowered glass transition temperatures in the range of -8 to 10 °C for the PPC star polymers compared with linear …
Blends of polyamide 6 and bisphenol-A polycarbonate. Effects of interchange reactions on morphology and mechanical properties
1992
Blends of polyamide 6 (PA6) and polycarbonate (PC) were prepared in a Brabender mixer, at 240°C, applying long mixing time, for 45 min. It was observed that the morphology and the mechanical properties tend to resemble those of a homogeneous material as the mixing time and PA6 concentration increase. This is attributed to chemical reactions taking place between the two homopolymers. Acidolysis, amidolysis, and aminolysis, catalyzed by the terminals and the amide groups of the polyamide, should in principle be possible. Our results indicate that the aminolysis is the main process, inducing simultaneously scission of PC chains and formation of PC-PA6 copolymer chains. The latter act as interf…
Preparative fractionation and characterization of polycarbonate/eugenol-siloxane copolymers
2002
Bisphenol-A polycarbonate/eugenol-siloxane copolymers were fractionated at the preparative scale by the continuous polymer fractionation (CPF) technique. It is the first example of copolymer fractionation by CPF. The distribution of siloxane species across the fractions was assessed for copolymers differing in initial siloxane concentration and block length. On- and off-line combinations of size exclusion chromatography and infrared spectroscopy were used to analyze chemical composition (CC) of the unfractionated samples across the molecular weight distribution enabling comparison with the fractions. A polycarbonate-siloxane copolymer containing 10 wt% of very short siloxane blocks (dp = 2)…
Multiarm Polycarbonate Star Polymers with a Hyperbranched Polyether Core from CO2 and Common Epoxides
2017
Multiarm star copolymers, consisting of hyperbranched poly(ethylene oxide) (hbPEO) or poly(butylene oxide) (hbPBO) polyether copolymers with glycerol branching points as a core, and linear aliphatic polycarbonate arms generated from carbon dioxide (CO2) and epoxide monomers, were synthesized via a “core-first” approach in two steps. First, hyperbranched polyether polyols were prepared by anionic copolymerization of ethylene oxide or 1,2-butylene oxide with 8–35% glycidol with molecular weights between 800 and 389,000 g·mol–1. Second, multiple arms were grown via immortal copolymerization of CO2 with propylene oxide or 1,2-butylene oxide using the polyether polyols as macroinitiators and (R,…
Dual removal and selective recovery of phosphate and an organophosphorus pesticide from water by a Zr-based metal-organic framework
2021
The authors express their thanks for the financial support provided by the Marie Sklodowska-Curie Individual Fellowships (H2020-MSCA-IF-2019-EF-ST-888972-PSustMOF, F.J.C.; H2020-MSCA-IF-2016-GF-749359-EnanSET, N.M.P.) within the European Union H2020 programme and EU FEDER. MINECO (CTQ2017-84692-R, PID2020-113608RB-I00, PEJ2018-004022-A), Universidad de Granada (Plan Propio de Investigacion and Programa Operativo FEDER Andalucia 2014-2020: B-FQM-364-UGR18), Junta de Andalucia (P18-RT-612) and 2020 Post-doctoral Junior Leadere-Retaining Fellowship, la Caixa Foundation (ID 100010434 and fellowship code LCF/BQ/PR20/11770014, N.M.P.) are also acknowledged for funding. Funding for open access cha…
Rigid Hyperbranched Polycarbonate Polyols from CO2 and Cyclohexene-Based Epoxides
2017
Hyperbranched, multifunctional polycarbonate polyols based on CO2, cyclohexene oxide (CHO), and the “inimer” (initiator–monomer) (4-hydroxymethyl)cyclohexene oxide (HCHO) were prepared in one-pot syntheses. The related linear poly(hydroxymethyl cyclohexene carbonate) structures based on protected HCHO and postpolymerization deprotection were also synthesized as model compounds. The content of hydroxyl functionalities was adjustable for both linear and hyperbranched terpolymer systems. All CO2/epoxide polymerizations were catalyzed by the (R,R)-(salcy)-Co(III)Cl complex. The polycarbonates obtained were comprehensively investigated using various 1D and 2D NMR techniques, SEC, FT-IR, UV–vis s…
Polyphosphate: A Morphogenetically Active Implant Material Serving as Metabolic Fuel for Bone Regeneration
2015
The initial mineralization centers during human bone formation onto osteoblasts are composed of CaCO3 . Those bioseeds are enzymatically formed via carbonic anhydrase(s) in close association with the cell surface of the osteoblasts. Subsequently, the bicarbonate/carbonate anions are exchanged non-enzymatically by inorganic phosphate [Pi ]. One source for the supply of Pi is polyphosphate [polyP] which is a physiological polymer, formed in the osteoblasts as well as in the platelets. The energy-rich acid anhydride bonds within the polyP chain are cleaved by phosphatase(s); during this reaction free-energy might be released that could be re-used, as metabolic fuel, for the maintenance of the …