The influence of alkali treatment on the chemical composition, sorption and electrokinetic properties of jute woven fabrics

Abstract

In this investigation, the influence of alkali treatment on the chemical composition (content of hemicelluloses), sorption properties and surface charge of jute woven fabrics were studied. In order to partially remove hemicelluloses, jute fabric was alkali modified with NaOH solutions of different concentrations (5%, 10% and 17.5%) during 5 min at room temperature. With increasing the NaOH concentration, the content of hemicelluloses decreased. Untreated jute fabric has 21.76% hemicelluloses, while after alkali treatments, the content of hemicelluloses decreased down to 13.76%.The content of hemicelluloses has impact on various sorption properties, which can be evaluated by determination of moisture sorption and water retention value. Moisture sorption values provide information on the extent of areas accessible to water vapor within the fiber, while water retention value represented the total water holding capacity of fibers (i.e. all water absorbing and holding surfaces, cracks and cavities in jute fibers structures). Higher availability of hydroxyl groups which occurs as a result of removal of hemicelluloses, contributes to higher moisture sorption of alkali treated jute woven fabrics in relation to untreated. The moisture sorption of alkali treated jute fabrics increased for 17.3-21.6% in comparison with untreated fabric. Removal of hemicelluloses causes increase in water retention values. This is a consequence of structure changes (changes in the size and number of pores and microcracks in fibers) and effective removal of hydrophobic layer on the fabric surface (fats and waxes), which should enable better hydrophilicity. Alkali treatments during only 5 min can improve the water retention value up to 49%. The changes of the fabric surface chemistry caused by removal of hemicelluloses also have influence on the electrokinetic properties, i.e. surface charge. Zeta potential measurements in a wide pH range were used for studying the surface charge of textile fabrics, including presence, availability and nature of surface groups. Untreated jute woven fabric has negative zeta potential in a wide range of pH due to the presence of hydroxyl and carboxyl groups on the surface subjected to dissociation in a high pH range. The greater accessibility of dissociated surface functional groups increases the ζpotential. Alkali treated jute fabrics display a positive ζplateau-value (zeta potential value in a basic range of pH) as a result of removal of fats, waxes and pectin from the fibers surfaces. Also, the effectiveness of such an alkali treatment process in order to increase the accessibility of surface groups can clearly be seen from the drastic change of the ζ-potential at low pH values as compared to untreated fabric. With increasing the concentration of NaOH from 5 to 17.5%, ζ-potential values decreased. Furthermore, isoelectric point (IEP, a pH value were ζ value is 0) as an indicator of the nature of functional groups of alkali treated jute fabrics are shifted toward higher pH. This indicates that after alkali treatment, contribution of acidic groups on the fiber surface become lower.