Xg Synthesis

‘Xanthan gum (XG) is a hetero-polysaccharide consisting of a cellulosic backbone (β-(1→4)-D-glucopyranose glucan) with two mannose and one glucuronic acid side chains (-(3→1)-α-linked-D-mannopyranose-(2→1)-β-D-glucuronicacid-(4→1)-β-D mannopyranose) on every second glucose residue’[1]. XG is stable over a wide range of pH and temperatures and is soluble in both cold and hot water. The rheology of water based systems can be controlled by XG. Even at very low concentration, XG gives viscous solutions compared with other polysaccharides. Hence it can be used as highly effective stabilizer and thickener [2]. Therefore it finds many applications in pharmaceutical, food and cosmetic industries [2-4]. XG is a natural anionic polyelectrolyte due to

The PEC obtained as precipitate in each beaker was separated by filtration, washed several times with water and dried at 40°C for 24h. The % yield of the PEC obtained in each case was measured. The results obtained are presented in Table 4.1. Experiments were also performed by varying the pH of two solutions (using 0.1 M HCl and 0.1 M NaOH) and the results are given in Table 4.2. The maximum yield of TMC/XG-PEC was obtained by mixing TMC and XG in the ratio 1 : 4 at pH

Thus, the formation of TMC/XG-PEC occurs mainly due to the ion-dipole forces existing between the carboxylic groups of XG molecules and +NH3, +NM (monomethylated), +ND (dimethylated) and +NT (trimethylated) sites of the TMC. On the other hand, the formation of TMC/XG-PEC is significantly less in basic and neutral pH, probably due to the low availability of +NH3, +NM, +ND sites and, at alkaline conditions, to high proportion of ionized carboxylic groups in the structure of XG. In the alkaline conditions or close to pH 6.5, the NM, ND, NH3 groups are deprotonated, according to the reactions +NM + −OH → NM + H2O; +ND + −OH → ND + H2O and + NH3 + −OH → NH2 + H2O. These factors prevented the formation of TMC/XG-PEC. So, the complexation of XG and TMC at neutral or alkaline conditions occurs primarily with the +NT quaternized sites of TMC and COO− groups of XG [18]. The structure of PEC from TMC and XG is shown in Fig.