New alkylated xanthan gum as amphiphilic derivatives: Synthesis, physicochemical and rheological studies

This research aims to develop new hydrophobically modified derivatives of xanthan gum with amphiphilic character by the grafting of octyl chains onto xanthan gum (XG) backbone using a Williamson synthesis. The etherification reaction between 1-Octyl chloride and the hydroxyl groups of XG at a reagent/monomer ratio (R = 1) was carried out in two different reaction media: Ethanol and Dimethylsulfoxyde (DMSO). The two derivatives HMXG1 and HMXG2, obtained respectively in ethanol and DMSO were subsequently subjected to various physicochemical and rheological characterization techniques. According to the results of FTIR and H1-NMR spectroscopy, the grafting of the alkyl groups onto XG was successfully achieved. The obtained results showed that the HMXG1 derivative prepared in ethanol presented a higher degree of substitution and molecular weight than HMXG2. The SEM and XRD analyses revealed some changes in morphology and crystalinity of xanthan after modification. Additionally, Thermogravimetric Analysis and its derivative (TGA/DGA) and Differential Scanning Calorimetric analysis (DSC) demonstrated that the degradation temperature decreases with decreasing Degree of Substitution (DS). Moreover, the rheological study confirmed that HMXG derivatives exhibited a shear-thinning fluids and that the viscosity decreases with decreasing DS. The amphiphilic properties of HMXG derivatives were assessed by determining the critical aggregation concentration (CAC) and by the emulsifying power test which demonstrated respectively that HMXG1 presents a lower value of the CAC (0.2%) compared with HMXG2 (0.35%) and a higher emulsion stabilizing capacity.