Characterization of Lignin Derivatives in Alkaline Polyethylene Glycol-treated Soda Cooking Black Liquor Powder

Abstract

To improve the thermal properties of softwood soda lignin, we studied a method of lignin modification using black liquor powder and polyethylene glycol (PEG). In this process, the black liquor powder was directly treated with PEG under alkaline conditions to produce a thermal melting material (alkaline PEG treatment). A model experiment was performed to determine the reaction of the lignin. The lignin in the black liquor powder consisted of 62.16% acid-insoluble lignin (purified lignin) and 37.84% acid-soluble lignin. After alkaline PEG treatment using purified lignin, the samples exhibited weak thermal melting during softening point analysis but did not exhibit appropriate thermal melting during thermal mechanical analysis (TMA). Nuclear magnetic resonance (NMR) data suggest that there was no linkage between lignin and PEG in the alkaline PEG-treated lignin prepared from the purified lignin. On the other hand, when using acidsoluble lignin, NMR data suggest that PEG was introduced to the lignin at its α-carbon position. Acid-soluble lignin PEG derivatives could work as plasticizers to induce the thermal melting of the alkaline PEG-treated lignin prepared from black liquor powder. Tsukuba, Tsukuba, Ibaraki, Japan; b: Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan; *Corresponding author: yamadat@affrc.go.jp Keywords INTRODUCTIONLignin is a major component in wood cell walls and can be isolated from wood via chemical pulping. Wood can be regarded as a lignin plastic reinforced by cellulose fibers (Hoyt and Goheen 1971). Many million tons of wood are processed annually in the chemical pulping industry to separate lignin from cellulose fibers. Spent liquors (black liquor) from pulping operations such as kraft, soda, and sulfite processes are some of the available sources of lignin. Lignin prepared from the black liquor of industrial pulping processes is called technical lignin. Some types of technical lignin can be used as dispersants, binders, and surfactants (Dizhbite et al. 1999;Gargulak and Lebo 2000;Lora and Glasser 2002;Gosselink et al. 2004;El Mansouri and Salvadό 2006;Stewart 2008;El Mansouri et al. 2011). However, only approximately 2% of the technical lignin produced from industrial pulp manufacturing is utilized for commercial purposes (Gargulak and Lebo 2000). In the industrial pulping process, most of the lignin in black liquor is combusted to generate energy and recover chemicals. To activate the commercial utilization of lignin, the mechanical properties of technical lignin must be improved, a key point in the preparation of these value-added products.PEER-REVIEWED ARTICLE bioresources.com Yoon et al. (2016). "Alkaline PEG-treated lignin," BioResources 11(3), 6426-6437. 6427Polymer blending is a simple modification method used to upgrade the thermoplastic properties of lignin (Feldman et al. 1995;Feldman 2002). Li et al. (1997) reported that lignin-based polymeric materials blended with polyvinyl acetate exhibited improved mechanical and thermoplastic properties. Kadla...

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