Aggregation and adsorption behaviors of carboxymethylated lignin (CML) in aqueous solution

Abstract

Carboxymethylated lignin (CML) as a watersoluble lignin derivative is a multipurpose adsorbent and dispersant. In this article, the aggregation and adsorption behaviors of CML have been investigated in aqueous solution using fluorescence spectroscopy, dynamic light scattering, and a quartz crystal microbalance combined with dissipation monitoring techniques. It was found that CML forms aggregates when its concentration exceeds the critical aggregation concentration (CAC). The CAC of CML1 with a carboxylic (COOH) group content of 2.8 mmol g -1 was 0.022 g l -1 , and that of CML2 with a COOH group content of 2.0 mmol g -1 was 0.026 g l -1 . The adsorption behavior of CML on the gold surface was strongly dependent on the pH and ionic strength of the solution. At low pH and ionic strength, more CMLs were adsorbed at the gold/water interface, and the layers were rigid. The results could be used not only from the theoretical but also from the application point of view.

Production of carboxymethylated lignin and its application as a dispersant

“…% led to a decrease in the carboxylate group content [16]. In other reports, a higher SCA to lignin or starch molar ratio was claimed to lead to the production of sodium glycolate [1,41,42]. …”

“…The peak at 4.7 ppm corresponds to the D 2 O. Compared to unmodified lignin, peaks at 7 and 3.5 ppm were somehow weaker in the carboxymethylated lignin, which might be due to the breakage of aromatic ring and methoxyl groups during carboxymethylation [1]. Furthermore, the peak at 3.8 ppm in carboxymethylated lignin corresponds to the protons of carboxymethyl groups attached to lignin, which is absent in unmodified lignin [50].…”

“…The gradual depletion and the availability of oil are major concerns these days [1]. As natural products are renewable, the production of natural based products and the replacement of these products for oil based products would help develop more sustainable society [2].…”

Influence of carboxylic group content on the solution behavior of carboxymethylated lignin (CML) in water

“…It is also obvious that the decrease in surface tension of water is larger at a higher COOH content of CML. Gan et al (2013b) also found that the CAC of CML in aqueous solution decreased slightly with increasing COOH content. Thus, it can be safely concluded that the surface tension effect is higher at an elevated COOH content of CML.…”

“…The contents of COOH and phenolic hydroxyl groups (OH phen ) were determined by automatic potentiometric titration (809 Titrando; Metrohm Co., Herisau, Switzerland) based on nonaqueous titration, and the M w was determined by GPC (Waters Co., Milford, MA, USA) (Gan et al 2013b). The test data are listed in Table 1.…”