## 3 Results and Discussion  
### Characterization of Raw and Chitosan Treated Fabrics' Surface Chemistry  
The ATR-FTIR spectroscopy was used to characterize the fabrics' surface chemistry and to assess the changes that occurred due to the treatment with chitosan solution. The spectra of J and J2.0% CS (chosen as a representative of chitosan-treated fabrics) show typical bands corresponding to jute fiber main constituents and chitosan (Figure 3).  
Considering both spectra in parallel, it is evident that the major chitosan band at 1560 cm\({}^{-1}\) (related to stretching vibration of its -NH\({}_{2}\) groups, [12]) appeared, while that at 1651 cm\({}^{-1}\) (corresponding to amide I overlapped with -OH bending of adsorbed water [15]), it become intensified after the treatment with 2.0% chitosan solution, Figure 3b. The formation of the intermolecular hydrogen bonds between the jute hydroxyl groups (present in cellulose) and chitosan was confirmed by the decreased intensity of the broadband between 3000-3600 cm\({}^{-1}\) assigned to -O-H stretching vibrations overlapped with chitosan -NH\({}_{2}\) stretching [16], Figure 3a. Furthermore, a high-intensity band at 1735 cm\({}^{-1}\) originating from -C = O stretching vibration of carboxyl groups or ester groups present in hemicellulose [17], as well as aldehyde groups, can be observed in the spectra of raw jute fabric (J). Relocation of the mentioned band to lower wavenumber (1729 cm\({}^{-1}\)) and a significant decrease in its intensity suggest the formation of Schiff base between jute aldehyde groups and chitosan -NH\({}_{2}\) groups to some extent [18]. In brief, the deposition of the chitosan onto jute fabric could be ascribed to the different mechanisms involving interactions, such as ionic and hydrogen bonding, further supported by the cross-linking of the chains through the chemical bondings to form Schiff bases.  
Besides jute fiber groups that participate in the chitosan binding, it should be mentioned that the ATR-FTIR spectra of J and J2.0% CS showed bands originating from cellulose, hemicellulose, and lignin as the main jute fiber constituents. They are also presented in Figure 3 and summarized in Table 1.  
Figure 3: ATR-FTIR spectra of selected fabrics in the range: (a) 4000–600 cm\({}^{-1}\) and (b) 1750–1400 cm\({}^{-1}\).  
The previously discussed changes in the fabrics' surface chemistry caused by chitosan treatment should undoubtedly affect their surface charge. Therefore, electrokinetic measurements were done (Figure 4) to give information about the fabric surface charge as a function of pH and indirectly about surface acidic-base functional groups and their reactivity in an aqueous medium [26]. Exactly, the fabric surface charge represents a key parameter responsible for dye adsorption, which is chosen as an indicator for polysaccharide-based fabrics' sorption properties. The results presented in Figure 4 revealed that after the treatment with chitosan, the pH vs. zeta potential curve was shifted to higher pH values and the fabric isoelectric point (IEP) was shifted from 2.80 to 3.52 due to the incorporation of positively charged chitosan -NH\({}_{3}\)+ groups (since -NH\({}_{2}\) groups of chitosan are protonated in acidic medium).  
The successful functionalization of jute fabrics with chitosan was confirmed through the notable changes observed in the fabric surface chemistry and electrokinetic properties.