Influence of the reaction conditions on the degree of substitution of carboxymethyl seriguela gum for application as a flocculant aid

Abstract

Seriguela gum is a barely explored polysaccharide, whose carboxymethylation can expand its applications for water treatment by the increase of negative charges in the chain. This work aimed to extract gum from seriguela’s exudate and to produce carboxymethyl derivatives under different reaction condition, aiming for increased substitution degree to apply as a flocculation aid in water treatment. The derivatives were characterized by titration, FTIR, NMR and GPC techniques. The reaction condition parameters, NaOH concentration and chloroacetic acid molar ratio, were significant on the degree of substitution, with values between 0.35 and 0.51. Optimal results were achieved using lower levels of NaOH and intermediate chloroacetic acid levels. Based on the results, the derivative with the highest degree of substitution was used as a flocculation aid, combined with Aluminum Sulfate, where tests demonstrated that the use of 5 mg.L− 1 of the carboxymethyl seriguela gum achieved a maximum turbidity removal rate of 99.62%, reducing turbidity to levels accepted by legislation, being more efficient than Aluminum Sulfate. The study showed that carboxymethylated seriguela gum with increased negative charges can be obtained with a high degree of substitution by a simple and high-yield process, and the tests showed high potential for application as a flocculation aid in water treatment processes.