Wyniki wyszukiwania - BazTech

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Rozwój komunikacji miejskiej w Polsce w latach 2009–2015

Wolański M., Pieróg M.

Autobusy : technika, eksploatacja, systemy transportowe

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2017

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R. 18, nr 6

25--29

PL

Niniejszy artykuł podsumowuje zmiany w polskiej komunikacji miejskiej w latach 2009–2015 w sferze produktowej oraz oddziaływania. Był to okres intensywnych inwestycji odtworzeniowych i rozwojowych, których duża część była znacząco wsparta funduszami Unii Europejskiej. Umożliwiło to poprawę jakości usług przewozowych w wielu miastach oraz pozwoliło na realizację wielu przełomowych projektów. Liczne inwestycje, wsparte zwiększaniem nakładów na komunikację miejską i rozwojem oferty przewozowej, pozwoliły na zahamowanie spadku lub nieznaczny wzrost przewozów w komunikacji miejskiej w największych miastach. W pozostałych ośrodkach zauważalny jest jednak trend spadkowy w przewozach, wynikający zarówno z zaniedbań inwestycyjnych, jak i braku jednoznacznej i kompleksowej polityki mającej na celu skuteczne wdrożenie zrównoważonego transportu miejskiego.

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Modyfikacja chitozanu : krótki przegląd

Ostrowska-Czubenko J., Pieróg M., Gierszewska M.

Wiadomości Chemiczne

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2016

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[Z] 70, 9-10

657--679

EN

Chitosan is the most important derivative of chitin, a polysaccharide found in the exoskeleton of shellfish like shrimp and crab. It is a product of deacetylation of chitin under alkaline conditions or enzymatic hydrolysis in the presence of chitin deacetylase. Both chitin and chitosan are linear polysaccharides and are chemically defined as copolymers consisting of varying amounts of β-(1→4)- linked 2-acetamido-2-deoxy β-D-glucopyranose (GlcNAc) and 2-amino-2-deoxy- β-D-glucopyranose (GlcN). The difference between chitin and chitosan lies in the content of GlcNAc and GlcN units. Chitin samples contain a high content of Glc- NAc units. Due to excellent properties of chitosan, such as biocompatibility, biodegradability, hydrophilicity, non-toxicity, cationicity, ease of modification, film forming ability, affinity to metals, protein and dyes, etc., this polymer has found applications in medicine and pharmacy, as food additive, antimicrobial agent, in paper and textile industry, in environmental remediation and other industrial areas. The presence of functional groups, reactive amino and hydroxyl groups, in chitosan backbone makes it suitable candidate for chemical modification. Chemical modification of chitosan to generate new polymers with useful physicochemical properties and distinctive biological functions is of key interest because it would not change the fundamental skeleton of the polymer. In this article the main three methods of chitosan modification: substitution reactions, reactions leading to the chain elongation and/or molecular weight increasing and methods of depolymerization are shortly characterized. Moreover, the selected methods of chitosan modification, i.e. quaternization, alkylation, acylation, carboxyalkylation, phosphorylation, sulfation, graft copolymerisation, crosslinking and depolymerization are discussed in more detail. A special attention is drawn to chitosan crosslinking with low and high molecular compounds. Chitosan modification by covalent and ionic crosslinking allows to obtain polymer materials with improved mechanical and chemical resistance and suitable for example for chitosan hydrogel membranes formation. Keywords: chitosan, chitosan modification, chitosan derivatives, crosslinking

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Equilibrium swelling behavior of crosslinked chitosan hydrogels

Ostrowska-Czubenko J., Pieróg M., Gierszewska-Drużyńska M.

Polish Journal of Applied Chemistry

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2011

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Vol. 55, nr 2

49-56

EN

Chemically and physically crosslinked chitosan hydrogels were obtained by treating chitosan (Ch) with glutaraldehyde (GA) and sodium tripolyphosphate or GA and sodium citrate, GA and sulfuric acid and GA and sulfosuccinic acid, respectively. The formation of covalent and ionic crosslinks between Ch, GA and low molecular ionic compounds was confirmed by FTIR spectroscopy. There was examined the equilibrium degree of swelling of membranes formed from uncrosslinked and crosslinked chitosan hydrogels in buffer solutions of different pH. It was observed that the swelling of all studied membranes was highly dependent on pH.

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Synthesis and characteristics of chemically modified chitosan membranes with sulfuric acid

Ostrowska-Czubenko J., Pieróg M.

Polish Journal of Applied Chemistry

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2009

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Vol. 53, nr 2

155-160

EN

Chemically modified chitosan membranes were obtained by treatment of chitosan membranes with sulfuric acid. The effect of chemical modification conditions on molecular and supcrmolecular structure and some physicochemical properties of synthesized membranes were studied using FTIR spectroscopy, X-ray diffraction method, SEM and elemental analysis. FTIR spectra of unmodified and modified chitosan membranes were compared and conclusions concerning the formation of ionic crosslinks between protonated amine groups of chitosan and sulfate anions were drawn out. X-ray analysis indicates that strong interactions between chitosan -NH3~ groups and SO42' ions influence chitosan membrane crystallinity.