RESUMO
Methylation is a well-established means of enhancing the thermal stability, improving the compatibility in polymer blends, and lowering the glass-transition temperature of lignins. This process normally involves reagents that are costly, associated with poor atom economy and/or highly toxic. Herein, we report the methylation of softwood and hardwood kraft lignins using chloromethane in alkaline aqueous media. This reaction proceeds in high yields at 90-110 °C under moderate pressure (40 psi) while generating environmentally benign sodium chloride and water as by-products.
RESUMO
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 1.62meq/g and DS of 0.21 was produced under the optimal conditions of 0.75M NaOH concentration, 1.0mol/mol sodium chloroacetate (SCA)/xylan ratio, 2h reaction time, 70°C and 15g/L xylan concentration. The carboxylate group of the product was 1.48mmol/g. The attachment of the carboxymethylated group to xylan was confirmed by Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance ((1)H 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.