Water soluble kraft lignin–acrylic acid copolymer: synthesis and characterization

Abstract

Lignin produced in the kraft pulping process is insoluble in water at neutral pH, which limits its application in industry. In this paper, kraft lignin (KL) was copolymerized with acrylic acid (AA) in an aqueous solution to produce a water soluble lignin-based copolymer. The copolymerization was carried out using K 2 S 2 O 8 -Na 2 S 2 O 3 as the initiator under alkaline aqueous conditions, and the influence of the reaction parameters, i.e. initiator dosage, reaction time and temperature, mole ratio of acrylic acid to lignin and reaction concentration, on resultant lignin copolymers were investigated. The mechanism of copolymerization of kraft lignin with acrylic acid was also discussed in this work. The resultant lignin copolymer was characterized by Fourier Transform Infrared (FTIR) spectrophotometry and Nuclear Magnetic Resonance (NMR). The successful copolymerization of AA and KL was confirmed by the new absorption peak of carboxyl anions in the FTIR spectrum and new peaks in the 1 H-NMR spectrum. At optimal conditions, the charge density and molecular weight of lignin copolymer reached 1.86 meq g −1 and 46 421 g mol −1 , respectively, and the solubility of lignin after reaction was increased from 1.80 g L −1 to 100 g L −1 at neutral pH. † Electronic supplementary information (ESI) available. See

Synthesis and Characterization of Carboxyethylated Lignosulfonate

“…To identify selectivity in the alkylation of aliphatic hydroxylg roups, methylation was performed [57,58] (Scheme 4a). To identify selectivity in the alkylation of aliphatic hydroxylg roups, methylation was performed [57,58] (Scheme 4a).…”

“…[57,58] In this work, methylated lignosulfonate (MLS) and carboxyethyl methylated lignosulfonate (CEMLS)w ere produced for the first time and their properties were determined and compared with those of LS and CELS. [57,58] In this work, methylated lignosulfonate (MLS) and carboxyethyl methylated lignosulfonate (CEMLS)w ere produced for the first time and their properties were determined and compared with those of LS and CELS.…”

Novel pathway to produce high molecular weight kraft lignin–acrylic acid polymers in acidic suspension systems

“…Aer the reactions, the solution was treated according to the procedure used in our earlier paper 21 (available in ESI †).…”

“…19,40 In our previous work, we described that the polymerization did not occur on those groups in alkaline homogenous reaction of KL and AA. 21 Due to the lowest bond dissociation energies of C 6 the predominant lignin radicals, which are induced by the initiator radicals SO 4 2À c through the homolytic rupture of a bond in KL during acidic polymerization reaction, are phenoxyl radicals from phenolic lignin units, and with smaller probability, benzylic radicals from non-phenolic lignin units. It was also reported in the literature 42 that acetylated lignin models had signicantly lower free radicals (benzylic radicals) than the untreated lignin samples.…”

“…The purication of lignin-AA polymer was carried out according to the procedure developed in our earlier paper. 21 The reaction solution was rstly acidied to pH of 1.5 to precipitate the lignin-AA polymer from the solution, and then centrifuged to remove the formed PAA homopolymer and unreacted AA monomer from lignin-AA polymer. The detailed procedure was stated in the ESI.…”