Biljana Pejic

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.

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.

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.

Wetting Properties of Hemp Fibres Modified by Plasma Treatment

Abstract The influence of dielectric barrier discharge (DBD) on the physico-chemical properties of hemp fibres was studied in this paper. Plasma-modification of hemp fibres was performed at atmospheric pressure. The source of the DBD was developed in the Quantum Optics Laboratory of the Faculty of Physics in Belgrade as a device prototype with plane-parallel geometry, for the continuous plasma-modification or treatment of textile materials. The capillary rise method was applied to evaluate the improvement in water uptake of the DBD treated hemp fibres. The plasmamodified hemp fibres have highly improved wetting properties without changing physico-mechanical properties (tensile strength and elongation).

New functionalities in cellulosic fibers developed by chemical modification

This paper gives an overview of the current state in the field of cellulosic fibers functionalization by chemical modification. The emphasis is placed on the selective (periodate and TEMPO oxidation) and non-selective (permanganate and peroxide) cellulose oxidation, non-conventional methods for obtaining man-made cellulosic fibers, methods for obtaining antimicrobial cellulosic fibers, as well as method for obtaining two-component polysaccharide fibers. To provide evidence on the achieved functionalities we mainly used capillary rise method, moisture and iodine sorption method, water retention power, NaOH uptake, different ions sorption, Cu-number, carbonyl-and carboxyl-selective labelling and antimicrobial tests.

Oxidized cotton as a substrate for the preparation of hormone-active fibers-characterization, efficiency and biocompatibility

Oxidized cellulose has a long history of safe and effective use in medical applications. In this paper, research has been directed towards obtaining hormone-active cellulose fibers in the form of an artificial insulin depot, and examination of its biocompatibility regarding cytotoxicity, sensitization, and irritation. The procedure of obtaining the fibrous insulin depot is based on the modification of cotton fibers with sodium periodate, followed by chemisorption of insulin from insulin aqueous solutions. In order to optimize the insulin chemisorption process, the influence of the fiber structure parameters, i.e. the aldehyde group content and iodine sorption value (ISV) on the chemisorption capacity was examined. The obtained artificial depot, containing ≈55 mg insulin/g of fibers, has been characterized in vitro by investigation of the desorption kinetics of the insulin from the fibrous depot. It has been shown that insulin is controllably released in quantities of 1.3-1.6 mg of insulin during 24 hours, in the course of 20 days. The results of biocompatibility tests have shown that the examined artificial depot neither shows irritating effects nor provokes sensitizing or cytotoxic effects. Therefore, these materials are acceptable for use in a direct contact with tissue of a living organism.

Influence of hemicelluloses and lignin content on structure and sorption properties of flax fibers (Linum usitatissimum L.)

In this work, alkali and oxidative treatments were employed to obtain flax fibers with different content of hemicelluloses and lignin, in order to study the influence of chemical composition on structure and sorption properties of flax fibers. The flax fibers were characterized using FTIR spectroscopy and FESEM microscopy, and by determination of chemical composition, carboxyl group content, electrokinetic and sorption properties. Adsorption of silver ions was used to evaluate flax fiber sorption properties, but also to obtain antimicrobial fibers whose antimicrobial activity was tested against Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus and fungi Candida albicans. The progressive removal of hemicelluloses or lignin influenced the sorption properties through the increased liberation of elementary fibers and accessibility of functional surface groups of flax fibers. Removal of hemicelluloses led to increase of iodine sorption without significant change in functional groups content and electrokinetic properties. On the other hand, lignin removal led to an increase of functional groups content, namely carboxyl groups, which in turn influenced better moisture and silver ions sorption. Flax fibers with incorporated silver exhibit fair antimicrobial activity against Gram (−) E. coli, Gram (+) S. aureus and fungi C. albicans.