Abstract
Softwood kraft lignin is a renewable type of woody material that can be converted to value-added products, for example, as a paper strength additive in the paper industry. In this study, the monomers of methacryloxyethyltrimethyl ammonium chloride (DMC), acrylic acid (AA), and acrylamide (AM) were grafted on softwood kraft lignin (SKL) to prepare three different SKL copolymers. Fourier-transform infrared, proton nuclear magnetic resonance, charge density, elemental, and molecular weight analyses confirmed that the monomers were successfully grafted onto SKL. The grafting rates of SKL-DMC, SKL-AA, and SKL-AM copolymers were 80.35%, 82.70%, and 79.48%, respectively. The application of SKL copolymers as a paper additive for enhancing paper physical properties was studied. The results indicated that at a 2 wt % dosage of SKL copolymers, the increase in the physical properties of paper is maximum.
Highlights
Lignin is the second-most abundant natural aromatic polymer in nature after cellulose and is used in several industrial operations with significant sustainability [1,2]
Methacryloxyethyltrimethyl ammonium chloride (DMC), acrylic acid (AA), and acrylamide (AM) were all purchased from Sigma-Aldrich Co. (Shanghai, China)
Fourier-transform infrared (FTIR) analysis was conducted on the softwood kraft lignin (SKL) and SKL copolymer samples using a FTIR spectrophotometer (Bruker VERTEX70, Rheinstetten, Germany)
Summary
Lignin is the second-most abundant natural aromatic (phenolic) polymer in nature after cellulose and is used in several industrial operations with significant sustainability [1,2]. In order to fully utilize this low-cost resource, chemical modification is considered one of the effective techniques for altering the properties of lignin and promoting the value-added nature of the products [9]. Copolymerization, which is one of the most effective chemical modification techniques, was applied in the preparation of water-soluble kraft lignin–acrylic acid copolymer [14]. Nguyen and co-workers reported the preparation of lignin-based thermoplastic copolyester for eco-friendly polymers using kraft lignin [16]. Wang and co-workers developed a soda lignin–acrylamide (AM) copolymer as a paper dry-strength additive [18]. The use of lignin and its derivatives as strength additives in the paper-making industry as a pulp-strengthening agent is still
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