Search results for "Ethylene"

Some Features of Polymeric Membranes for Water Purification via Membrane Distillation

2011

Polymeric membranes are currently adopted in water purification processes, such as reverse osmosis (RO) and membrane distillation (MD). This latter technique is very promising for separation effectiveness and energy savings. A valuable and effective MD unit must be equipped with polymeric membranes that exhibit specific properties, for example, hydrophobicity, a narrow pore size range, a high water penetration pressure, and a large vapor permeability. In this work, we present and examine the main features of membranes for MD processes, with the aim of experimentally evaluating the related performances. Scanning electron microscopy analysis was carried out for a first estimate of the pore si…

Synthesis and characterization of redox-sensitive polyurethanes based on L-glutathione oxidized and poly(ether ester) triblock copolymers

2021

Abstract Segmented polyurethanes, based on PCL-PEG-PCL copolymers, 1,4-diisocyanatobutane and l -glutathione oxidized, used as chain extender, were synthetized. Three different reactions conditions were investigated using three different copolymers having ɛ-CL/polyethylene glycol molar ratios equal to 12, 24 and 36 and three different reaction conditions. As investigated by size exclusion chromatography analyses and quantification of l -glutathione, the polymerization and the extension phase's efficiency depended on the ɛ-CL/PEG ratio and the extension phase's operating temperature. Three selected polyurethanes were characterized by spectroscopic, differential scanning calorimetry (DSC) and…

A facile and eco-friendly route to fabricate poly(Lactic acid) scaffolds with graded pore size

2016

Over the recent years, functionally graded scaffolds (FGS) gaineda crucial role for manufacturing of devices for tissue engineering. The importance of this new field of biomaterials research is due to the necessity to develop implants capable of mimicking the complex functionality of the various tissues, including a continuous change from one structure or composition to another. In this latter context, one topic of main interest concerns the design of appropriate scaffolds for bone-cartilage interface tissue. In this study, three-layered scaffolds with graded pore size were achieved by melt mixing poly(lactic acid) (PLA), sodium chloride (NaCl) and polyethylene glycol (PEG). Pore size distr…

Pressure-Induced Binding Sites in Molecularly Imprinted Network Polymers

1997

Molecular imprinting in network polymers under high pressure was studied as a means of inducing selective binding sites for molecular recognition. Network polymers of methacrylic acid and ethylene ...

(Liquid + liquid) equilibria of polymer-salt aqueous two-phase systems for laccase partitioning : UCON 50-HB-5100 with potassium citrate and (sodium …

2012

Aqueous two-phase systems (ATPS) are recognized as very suitable techniques for the recovery of target solutes in biological applications. Three new phase diagrams of (UCON 50-HB-5100 + potassium citrate + water), (UCON 50-HB-5100 + sodium formate + water), and (UCON 50-HB-5100 + potassium formate + water) systems were measured at 23 C. The binodal curves were successfully described using the empirical equation suggested by Merchuk and co-workers. The reliability of the tie-line data experimentally determined was evaluated using the equations reported by Othmer–Tobias and Bancroft and satisfactory linearity was obtained for all ATPS. Among the salts studied, potassium citrate proved to be t…

The influence of preservation method and time on theδ13C value of dissolved inorganic carbon in water samples

2009

The precise delta(13)C value of dissolved inorganic carbon (DIC) is important for various types of ecological studies. Without a preservation agent, microbial degradation of organic compounds continues in water samples and the delta(13)C value of DIC will become more depleted with time. HgCl(2) or acidification is often used to prevent microbial activity in water samples collected for carbon isotope ratio analyses of DIC. Mercury compounds are toxic and result in waste disposal problems. Other inhibiting agents or preservation methods are therefore needed. Two possible solutions are to use copper sulphate (CuSO(4)) as a preservative agent or to acidify water samples with phosphoric acid (H(…

1989

Heat of crystallization significantly slows down polymer cooling and thus pressure drop increase during mould filling with thermoplastic crystalline polymers. If a correction of thermal diffusivity can account for such a cooling slow down at least as far as the effect on pressure drop is concerned, the use of nonisothermal crystallization kinetics may be avoided in the simulation of mould filling. A procedure to identify such a correction is outlined in this work. Pressure drop values during cavity filling calculated by using a corrected thermal diffusivity in the model proposed by Lord and Williams favourably compare with literature data taken with polypropylene and polyethylene resins. Be…

Five-Membered 2-Methylene-2,3-dihydro Heterocycles from Ruthenium Butatrienylidene Intermediates and 2-(Dimethylamino)methyl-Substituted Furans, Thio…

2003

Trapping of the primary butatrienylidene intermediate trans-[Cl(dppm) 2 Ru=C=C=C=CH 2 ] + with five-membered 2-(dimethylamino)methyl-substituted heterocycles provides an easy and efficient route to aminoallenylidene complexes with appended 2-methylene-2,3-dihydrofuran, -thiophene, or -selenophene moieties. Upon warming or acid catalysis isomerization to the aromatic 2-methylated isomers is observed.

Agglomerated non-porous silica nanoparticles as model carriers in polyethylene synthesis

2004

Abstract Non-porous submicron silica particles (250 and 500 nm) with high monodispersity were agglomerated to form spherical agglomerates via spray drying. As a binder, 25 nm sized monodisperse silica spheres were selected from a variety of colloidal systems including Levasil-type and Aerosil-type silica nanoparticles. The use of such binders led to an increase of the specific surface area of the agglomerated carriers. All materials were characterised by nitrogen sorption, mercury intrusion and scanning electron microscopy. The silica agglomerates, with highly defined geometrical and pore structural parameters, were employed as model carriers in the heterogeneous polymerization of ethylene …

Cytotoxicity and induction of DNA double-strand breaks by components leached from dental composites in primary human gingival fibroblasts

2012

Abstract Introduction The public interest steadily increases in the biological adverse effects caused by components released from resin-based dental restorations. Objective In this study, the cytotoxicity and the genotoxicity were investigated of following released components from dental resin restorations in human gingival fibroblasts (HGF): tetraethyleneglycol dimethacrylate (TEEGDMA), neopentylglycol dimethacrylate (Neopen), diphenyliodoniumchloride (DPIC), triphenyl-stibane (TPSB) and triphenylphosphane (TPP). Methods XTT based cell viability assay was used for cytotoxicity screening of substances. γ-H2AX assay was used for genotoxicity screening. In the γ-H2AX assay, HGFs were exposed …