Synthesis and characterization of carboxymethylated xylan and its application as a dispersant

• Carboxymethylated xylan (CMX) was produced under alkali conditions.
• The reaction led to the maximum charge density of 1.62 meq/g and DS of 0.21.
• The properties of CMX were characterized using GPC, FTIR, TGA and NMR.
• The dispersion of clay suspension was significantly improved by adding CMX.

In this study, carboxymethylated beechwood xylan was produced under alkali conditions using sodium chloroacetate. Taguchi orthogonal design was used to explore the influence of the process parameters, i.e. NaOH concentration, time, temperature, the molar ratio of sodium chloroacetate to xylan and the concentration of the reaction medium on the charge density and degree of substitution (DS) of xylan. Carboxymethylated xylan (CMX) with the maximum charge density of 1.62 meq/g and DS of 0.21 was produced under the optimal conditions of 0.75 M NaOH concentration, 1.0 mol/mol sodium chloroacetate (SCA)/xylan ratio, 2 h reaction time, 70 °C and 15 g/L xylan concentration. The carboxylate group of the product was 1.48 mmol/g. The attachment of the carboxymethylated group to xylan was confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The molecular weight of xylan increased and its thermal stability was improved via carboxymethylation. The dispersion performance of the carboxymethylated xylan in clay suspensions was determined by photometric dispersion analyzer (PDA). CMX showed better performance than sodium carbonate-polyacrylic acid (Na2CO3-PAA) in dispersing the clay suspension. The unmodified xylan did not show any dispersion performance.