Search

Your search keyword '"Christova, Darinka"' showing total 43 results
Start Over Author "Christova, Darinka"
43 results on '"Christova, Darinka"'

2. Flat ultrafiltration PAN/BNE membranes with temperature-responsive performance obtained by modification with 'smart' PVA copolymer

Author

Miteva Мilena and Christova Darinka

Subjects
Engineering (General). Civil engineering (General), TA1-2040
Abstract

The ultrafiltration (UF) composite polyacrylonitrile (PAN)/ butadiene–acrylonitrile elastomer (BNE) membrane obtained by the phase inversion method was modified with temperature sensitivity by physicochemical immobilization of hydrophobically modified poly(vinyl alcohol) (HMPVA). HMPVA was prepared by partial acetalization of poly(vinyl alcohol) (PVA) with a molar mass of 75000 g/mol, resulting in a temperature-sensitive copolymer with a phase transition temperature (Ttr) of 40.2oC. Modification of the membranes was performed by introducing aqueous HMPVA solutions of different concentrations into the membrane structure, followed by its immobilization by cross-linking with glutaraldehyde. The composition, technological and structural characteristics of the membranes before and after the modification were investigated. Scanning electron microscopy (SEM) and barodynamic determinations were used in the typical UF operating pressure range (0–0.5 MPa), evaluating permeability (J, l/m2.h) and rejection (R, %) of water and albumin as a calibrant (molecular mass ~76 kDa). Temperature-sensitive HMPVA in the membrane structure optimizes the energy and material efficiency of the membrane process, including membrane service life and maintenance.

Published
2023
Full Text
View/download PDF

33. Heavy metal biosorption sites in Penicillium cyclopium

Author

Tsekova, Kolishka, Christova, Darinka, and Ianis, Maria

Abstract

The biomass of Penicillium cyclopium was subjected to chemical treatment to study the role of the functional groups in the biosorption of heavy metal ions. The modifications of the functional groups were examined with infrared spectroscopy. Hydroxyl groups were identified as providing the major sites of heavy metal deposition, augmented by secondary binding by amides and carboxylates. Phosphate groups and the lipids fraction of the biomass did not play significant role in biosorption of the metal ions in the studied biomass. Biosorption of copper and cobalt ions displaced K+, Mg2+ and Ca2+ present on the biosorbents indicating that biosorption took place as a result of an ion-exchange process. Journal of Applied Sciences and Environmental Management Vol. 10(3) 2006: 117-121

Published
2006

41. Polyester-Based (Bio)degradable Polymers as Environmentally Friendly Materials for Sustainable Development.

Author

Rydz, Joanna, Sikorska, Wanda, Kyulavska, Mariya, and Christova, Darinka

Subjects
BIODEGRADABLE plastics, SUSTAINABLE development, POLYESTERS, WASTE management, POLYAMIDES, ENVIRONMENTAL impact analysis
Abstract

This review focuses on the polyesters such as polylactide and polyhydroxyalkonoates, as well as polyamides produced from renewable resources, which are currently among the most promising (bio)degradable polymers. Synthetic pathways, favourable properties and utilisation (most important applications) of these attractive polymer families are outlined. Environmental impact and in particular (bio)degradation of aliphatic polyesters, polyamides and related copolymer structures are described in view of the potential applications in various fields. [ABSTRACT FROM AUTHOR]

Published
2015
Full Text
View/download PDF

43. Removal of Cu(II), Co(II) and Fe(III) Ions from Ternary Solution by Free and Entrapped in PVA-Hydrogel Biomass of Penicillium Cyclopium

Author

Tsekova, Kolishka, Christova, Darinka, Todorova, Dessislava, and Ivanova, Sijka

Abstract

ABSTRACTBatch sorption equilibrium experiments using free and immobilized Penicillium cyclopium biomass in PVA-hydrogel were carried out using ternary mixture of corresponding metal ion solutions. The metal binding ability of the hybrid hydrogel for Cu(II), Co(II) and Fe(III) ions was determined by atomic absorption spectrophotometer. The performance of free and immobilized biosorbent was evaluated by sorption kinetics and sorption capacities for different metal ions in the mixture. The immobilized system showed higher removal efficiency (expressed as mg metal ions removed per mg metal ions added) in comparison to the free-cell system. In addition, the immobilized system showed two-fold shorter time for reaching the equilibrium in comparison to the free cells. The pseudo-second order kinetic model was applied to the multi-component experimental data and important kinetic parameters of the biosorption process were calculated. The data obtained are in agreement with the assumption that the external mass transfer limitation in the immobilized system can be neglected and biosorption is chemisorption controlled. The immobilized system of organic polymer with entrapped fungal biomass showed high biosorption performance and may be used successfully for the removal of Cu(II), Co(II) and Fe(III) ions from ternary mixed solutions.

Published
2011
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results