Obtaining jute fabrics with enhanced sorption properties and “closing the loop” of their lifecycle

Abstract The objective of this investigation was to obtain jute fabrics with enhanced sorption properties (by using simple and cost-effective alkali and oxidative modifications) and a long life cycle. The applied alkali modifications lead to hemicellulose removal and decreased the fibers’ crystallinity, both contributing to enhanced fibers’ sorption properties, i.e., water retention power and degree of fibers’ swelling up to 49 % and 70 %, respectively. A connection between cellulose polymorphs’ (cellulose I and cellulose II) contents (determined by XRD), fibers’ surface morphology (verified by FESEM), fabrics’ crimp, and capillarity of jute fabrics modified with 17.5 % NaOH was established. During the oxidative modifications, significant changes in jute fibers’ chemical composition and structure (i.e., lignin removal and more homogeneous middle lamellae) occurred which further resulted in enhanced jute fabrics’ water retention power and capillarity as well as fibers’ swelling up to 80 %, 75 %, and 54 %, compared to the raw jute, respectively. In order to move towards a circular economy and to ensure the recycling and re-use of recycled fabrics, the jute fabrics with enhanced sorption properties were evaluated as biosorbents for anthraquinone dye C. I. Acid Blue 111. The obtained results revealed that the jute fabrics’ maximum biosorption capacities for this dye ranged from 12.94 to 18.97 mg/g, while the equilibrium adsorption data were highly consistent with the Langmuir isotherm model. Moreover, based on the predicted dye pKa values, the fabric zeta potential, content of carboxyl and aldehyde groups as well as hydrogen bond intensity (determined by ATR-FTIR), a possible mechanism of the dye biosorption onto jute fabric waste was proposed.

1. Experimental 1.1.Method used for the measurement of jute fabrics' capillarity The jute fabrics' capillarity measurements were performed on an appliance which is presented in Fig. S1.Namely, the jute fabrics (25 cm x 2 cm in warp direction) were placed in a vertical position.Their one end was fixed with a clip on the horizontal bar, while the other end was pre-loaded with a tag of 2 g and immersed approximately 2 cm in depth into 0.1% aqueous solution of eosin (red-colored) which level was above tag and overlapped with 0 cm at rulers printed along with the vertical plate.When the samples were immersed in eosin, the GoPro Hero 4 camera started to take pictures at time intervals of 1 min in the first 10 min and every 5 min up to attaining capillary rise equilibrium.

Fig. S1 Appliance used for capillary rise measurements
Based on the experimental data obtained by capillarity measurements and methodology described by Pejić et al. (2020), the three wettability parameters were determined by using Eqs. (1-4).
where: D (mm 2 /s) is a capillary diffusion coefficient; where: C (mm/s) is a coefficient related to the mean hydrodynamic pores radius and the liquid nature, while H values were determined as: Coefficient R, which confirms the validity of assumption θ≅θeq is given by: where: θ and θeq (°) are the dynamic and static contact angles of the liquid on the solid.The carboxyl group content was determined using the calcium-acetate method (Knežević et al., 2020).The cellulose carboxyl groups react with calcium acetate (weak acid salt), forming a salt of the cellulose and releasing an equivalent amount of the weaker acid.The cellulose should be obtained in the acidic form by replacement of its cations with hydrogen ions by the treatment of jute sample (0.5 g) with 100 mL of 0.01 M HCl solution for 1 h followed by washing with distilled water.In the next step, 50 ml of distilled water and 30 ml of 0.25 M calcium acetate were added and the mixture was stirred for 2 h.Thereafter, 30 ml portions of the liquid were titrated with 0.01 M NaOH solution, using phenolphthalein as an indicator.The quantity of carboxyl groups (Q(COOH), mmol/g) was calculated as follows, Eq. 5:

Jute fabrics' structural characteristics
where 0.01 is NaOH concentration, mol/l, V (NaOH) is the volume of NaOH solution used for titration, ml, m is the weight of absolutely dry jute fabric, g.
The content of aldehyde groups was determined according to the method described by Saito and Isogai (2004).In order to selectively oxidize the sample's aldehyde groups to carboxyl groups, 1 g of a sample was added to a mixture containing 0.905 g NaClO2, 10 ml of 5 M CH3COOH solution, and 50 ml of distilled water.Oxidation was carried out by mixture stirring at room temperature for 48 h, and thereafter, the sample was thoroughly washed with distilled water and acetone.Further, the previously described calcium acetate method for determining the content of carboxyl groups was applied.The content of aldehyde groups was calculated by subtracting the content of carboxyl groups determined in the starting sample from that of chlorite oxidized one.Ivanovska, A., Cerovic, D., Maletic, S., Jankovic Castvan, I., Asanovic, K., Kostic, M., 2019.
Influence of the alkali treatment on the sorption and dielectric properties of woven jute fabric.
Influence of potassium permanganate oxidation on structure and properties of cotton.J. Nat.

Fig
Fig. S2 ATR-FTIR spectra of raw and some alkali modified jute fabrics

Fig. S4
Fig. S4 Predicted pKa values for ionizable groups of C. I. Acid Blue 111

Table S2
Wettability coefficients D, C, and R determined from capillary rise measurements