Mirjana Kostic

The effects of hemicelluloses and lignin removal on water uptake behavior of hemp fibers.

This study investigated the individual influences of hemicelluloses and lignin removal on the water uptake behavior of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. Various tests (capillary rise method, moisture sorption, water retention power) were applied to evaluate the change in water uptake of modified hemp fibers. The obtained results show that when the content of either hemicelluloses or lignin is reduced progressively by chemical treatment, the capillary properties of hemp fibers are improved, i.e. capillary rise height of modified fibers is increased up to 2.7 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increases the moisture sorption and decreases the water retention values of hemp fibers, while lignin removal decreases the moisture sorption and increases the water retention ability of hemp fibers.

Decolorization of reactive textile dyes using water falling film dielectric barrier discharge

Decolorization of reactive textile dyes Reactive Black 5, Reactive Blue 52, Reactive Yellow 125 and Reactive Green 15 was studied using advanced oxidation processes (AOPs) in a non-thermal plasma reactor, based on coaxial water falling film dielectric barrier discharge (DBD). Used initial dye concentrations in the solution were 40.0 and 80.0mg/L. The effects of different initial pH of dye solutions, and addition of homogeneous catalysts (H(2)O(2), Fe(2+) and Cu(2+)) on the decolorization during subsequent recirculation of dye solution through the DBD reactor, i.e. applied energy density (45-315kJ/L) were studied. Influence of residence time was investigated over a period of 24h. Change of pH values and effect of pH adjustments of dye solution after each recirculation on the decolorization was also tested. It was found that the initial pH of dye solutions and pH adjustments of dye solution after each recirculation did not influence the decolorization. The most effective decolorization of 97% was obtained with addition of 10mM H(2)O(2) in a system of 80.0mg/L Reactive Black 5 with applied energy density of 45kJ/L, after residence time of 24h from plasma treatment. Toxicity was evaluated using the brine shrimp Artemia salina as a test organism.

Biosorption of heavy metal ions from aqueous solutions by short hemp fibers: Effect of chemical composition

Sorption potential of waste short hemp fibers for Pb(2+), Cd(2+) and Zn(2+) ions from aqueous media was explored. In order to assess the influence of hemp fiber chemical composition on their heavy metals sorption potential, lignin and hemicelluloses were removed selectively by chemical modification. The degree of fiber swelling and water retention value were determined in order to evaluate the change in accessibility of the cell wall components to aqueous solutions due to the fiber modification. The effects of initial ion concentration, contact time and cosorption were studied in batch sorption experiments. The obtained results show that when the content of either lignin or hemicelluloses is progressively reduced by chemical treatment, the sorption properties of hemp fibers are improved. Short hemp fibers are capable of sorbing metal ions (Pb(2+), Cd(2+) and Zn(2+)) from single as well as from ternary metal ion solutions. The maximum total uptake capacities for Pb(2+), Cd(2+) and Zn(2+) ions from single solutions are the same, i.e. 0.078mmol/g, and from ternary mixture 0.074, 0.035 and 0.035mmol/g, respectively.

Studies on oxidative modifications of cellulose in the periodate system: Molecular weight distribution and carbonyl group profiles

Abstract The effects of periodate oxidation on cellulose were studied by means of gel permeation chromatography (GPC) using multiple detection and carbonyl-selective fluorescence labeling according to the CCOA methodology profiling of carbonyl groups. At low degrees of oxidation, the molecular weight distribution was fully maintained. Upon more pronounced oxidation the molecular weight even increased due to cross-linking effects. More condensed structures were identified by means of light scattering. Periodate oxidation also affects crystalline regions of cellulose, as demonstrated by comparison of homogeneous and heterogeneous carbonyl labeling. Highly ordered regions in cellulose were affected by oxidation even below an oxidation degree of 2%. Two different phases for the oxidation kinetics were identified in the early stages of periodate treatments.

Dissolution Behavior of Different Celluloses

Celluloses from different origins were dissolved stepwise in N,N-dimethylacetamide/lithium chloride (9% v/w; DMAc/LiCl) with the aim to study the time course of the dissolution process, completeness of dissolution in the dissolved fractions, possible discrimination effects, and differences between the celluloses. Cellulosic pulps from both annual plants and different wood species were analyzed. The obtained fractions were subject to gel permeation chromatography (GPC) with multiple detection to monitor the development of molecular mass distribution (MMD), molecular mass, and recovered mass. The dissolution behavior of accompanying xylans was followed by quantitative analysis of the uronic acids by fluorescence labeling--GPC. The morphological changes at the remaining fibers in the stepwise dissolution were addressed by SEM. The time needed to dissolve completely the cellulosic pulp differed from species to species, mainly between pulps from annual plants and pulps from wood. Annual plants generally needed much longer to dissolve completely. In the beginning of the dissolution, the dissolved fractions of annual plants showed a distinct discrimination effect because they were enriched in hemicellulose. By contrast, wood pulps dissolve fast and without distinct changes in the MMD of the dissolved fractions over time. Bagasse pulp is an exception to the observation for annual plants and rather resembled the behavior of wood celluloses. Prolonged dissolution times, as often practiced in cellulose GPC, do not lead to any improvements regarding the determination of molecular mass, MMD, and recovered mass of injected sample, so that the dissolution times required for reliable GPC analysis can be significantly shortened, which will be important for biorefinery analytics with high numbers of samples.

Oxidative modifications of cellulose in the periodate system - Reduction and beta-elimination reactions

Abstract The conversion of cellulose to dialdehyde cellulose (DAC) by treatment with aqueous periodate was studied by the CCOA method, which is a combination of gel permeation chromatography and carbonyl-selective fluorescence labeling. The beta-alkoxy-elimination reaction under alkaline conditions was used as a diagnostic tool to address the regioselectivity of the oxidation at low degrees of conversion. The oxidation proceeded by random oxidant attack; cluster-like or isolated oxidation patterns were excluded. The beta-alkoxy-elimination proceeded as a competitive process during reduction of DAC by sodium borohydride. Reduction was thus inevitably accompanied by a significant loss in molecular weight. The borohydride treatment decompacted the molecules by reducing the aldehyde groups and destroying hemiacetal crosslinks. As a result, highly flexible chains were produced.

Silver incorporation on viscose and cotton fibers after air, nitrogen and oxygen DBD plasma pretreatment

Dielectric barrier discharge (DBD) pretreatments in air, nitrogen and oxygen plasma of viscose and cotton fabrics with subsequent immobilization of silver were studied. Surface activation of treated fibers was evaluated through subsequent sorption of silver from aqueous AgNO3 solution, after which changes in the surface morphology were monitored and quantity of silver deposition on fabric was measured. The plasma treatment was done in volume DBD discharge with the gap distance between electrodes of 0.5 and 2 mm. Depending on the gas used in pretreatment, significant difference in the way silver bonds to the textile surface was found. Nitrogen plasma pretreatment with gap distance of 0.5 mm led to the homogeneous fiber coating by silver nanoparticles with average size up to 300 nm estimated by SEM, while fibers treated in oxygen plasma adsorbed silver in a form of ions. The plasma pretreatment in air leads to changes that contain features of fibers treated in both nitrogen and oxygen DBD plasma. Distinct difference of used configuration of the plasma source is a use of gap distance 0.5 mm, which is in order of textile thickness. Observed results allow us to report a new way how to immobilize silver nanoparticles onto textile fibers using plasma pretreatment with subsequent sorption of silver from aqueous solution.Graphical Abstract

Influence of chemically modified short hemp fiber structure on biosorption process of Zn2+ ions from waste water

Short hemp fibers, acquired as a waste from textile industry, were used as an efficient biosorbent for removal of zinc ions from polluted water. In order to obtain the material with better sorption properties, short hemp fibers were subjected to oxidative and alkali treatment. The following factors that may influence the sorption properties of short hemp fibers were examined: fiber structure and morphology were characterized by iodine sorption, water retention and scanning electron microscopy, while specific surface area was determined by BET method. Additionally, the amount of carboxyl groups was determined by calcium-acetate method, and the point of zero charge of the short hemp fibers samples was determined by the solid addition method. Biosorption of zinc ions was evaluated through the total uptake capacity, equilibrium and kinetic data. Obtained data were analyzed by nonlinear Langmuir and Freundlich isotherms, as well as pseudo-first and pseudo-second order kinetic models, and the best fitting model was chosen using Akaike information criterion. Chemical modification, used in this work, leads to structural and morphological changes of short hemp fibers, and improvement of their sorption properties. It was found that sorption properties of short hemp fibers are predominantly influenced by surface acidity and the amount of functional groups, while fiber structure and specific surface area have a secondary role in the biosorption of zinc ions. Akakike information criterion values showed that biosorption of zinc ions on all tested hemp fiber samples obey the pseudo-second order adsorption kinetics, while experimental isotherm data fit better with Langmuir model. Biosorption of zinc ions on the hemp fibers is a predominantly chemical process, which mainly follows the mechanism of ion exchange on acidic functional groups, and occurs through the fast surface adsorption, intraparticle diffusion and final equilibrium stage.

Microalbuminuria in relation to metabolic control and blood pressure in adolescents with type 1 diabetes

Introduction The objective of this study was to assess the frequency of microalbuminuria and the relationship with other risk factors for the development of diabetic nephropathy. Material and methods Our cross-section study involved a group of 60 adolescence of both sexes, mean age 15.3 ±2.43 years with mean duration of diabetes 7.74 ±3.44 years. Albumin excretion rate was measured on 2-3 samples of the first morning urine in the period below 6 months and persistent microalbuminuria was defined if its increased in two out of three urine specimens. Ambulatory blood pressure was monitored (ABPM, SpaceLabs 90207). Results Microalbuminuria developed in 13.3% of adolescents with mostly completed sexual development, statistically significantly poorer metabolic control (9.79% vs. 8.7%) and higher BMI (23.59 kg/m2 vs. 20.85 kg/m2) than in the patients with normoalbuminuria. The mean night-time systolic blood pressure (SBP) was statistically significantly higher in microalbuminuric patients than in normoalbuminurics. The nocturnal dip was reduced in 41.7% of our patients; 38.5% of nondippers were in normoalbuminuric and 62.5% in microalbuminuric patients. Conclusions Diabetic adolescents require particular attention in order to minimize the factors such as high HbA1c, elevated body mass index and night-time SBP in the development of incipient nephropathy.

Factors affecting graft function in pediatric and adult recipients of adult live donor kidney transplants.

Abstract:  The aims of this investigation were to compare changes of function of adult living kidney grafts transplanted into adult and child recipients and to analyze factors associated with graft function during the first post‐transplant year. The study involved 53 adult and 23 pediatric recipients with immediate graft function and without complications that could influence graft function. In comparison to children, adult recipients and their donors were older, and having been longer on hemodialysis they had received more transfusions. Although similar baseline graft function – GFR0 was transplanted in both groups, absolute and relative GFR in adults rose and maintained stable, while in children absolute GFR decreased and remained similar to the GFR0 until the end of the study. Significant predictors of kidney function in both adult and child recipients were donor age, ratio between GFR0 and recipient BSA, induction immunosuppression, and systolic hypertension. In conclusion, the function of adult live kidney grafts changed differently in children and adults because of different functional requirements of recipients but donor age, induction immunosuppression and hypertension are significant predictor of graft function in both adults and children.