Abstract
A large-scale glycol lignin (GL) production process (50 kg wood meal per batch) based on acid-catalyzed polyethylene glycol (PEG) solvolysis of Japanese cedar (JC) was developed at the Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Japan. JC wood meal with various particle size distributions (JC-S < JC-M < JC-L) (average meal size, JC-S (0.4 mm) < JC-M (0.8 mm) < JC-L (1.6 mm)) and liquid PEG with various molecular masses are used as starting materials to produce PEG-modified lignin derivatives, namely, GLs, with various physicochemical and thermal properties. Because GLs are considered a potential feedstock for industrial applications, the effect of heat treatment on GL properties is an important issue for GL-based material production. In this study, GLs obtained from PEG400 solvolysis of JC-S, JC-M, and JC-L were subjected to heating in a constant-temperature drying oven at temperatures ranging from 100 to 220 °C for 1 h. All heat-treated GL series were thermally stable, as determined from the Klason lignin content, TMA, and TGA analyses. SEC analysis suggests the possibility of condensation among lignin fragments during heat treatment. ATR-FTIR spectroscopy, thioacidolysis, and 2D HSQC NMR demonstrated that a structural rearrangement occurs in the heat-treated GL400 samples, in which the content of α–PEG-β–O-4 linkages decreases along with the proportional enrichments of β–5 and β–β linkages, particularly at treatment temperatures above 160 °C.
Highlights
Lignin is known as the most abundant aromatic biopolymer in nature, representing 15%–35% of the cell wall components of typical vascular plants including trees, where it functions as a bonding agent between cells to provide cell walls with outstanding resistance against external physical, chemical, and biological reactions [1]
Utilizing the abundance of Japan’s softwood plantation forests, 50% of which are occupied by Japanese cedar (Cryptomeria japonica; JC), we have developed a large-scale (50 kg wood meal per batch) lignin production process based on technically feasible and environmentally benign acid-catalyzed polyethylene glycol (PEG) solvolysis of JC
0.4–1.6 mm washigher applied in the present studya range) rise to glycol lignin (GL) with higher average molecular mass, yield of present β–O–4study range) gives rise to
Summary
Lignin is known as the most abundant aromatic biopolymer in nature, representing 15%–35% of the cell wall components of typical vascular plants including trees, where it functions as a bonding agent between cells to provide cell walls with outstanding resistance against external physical, chemical, and biological reactions [1]. Depending on the type of biomass resource used (e.g., softwood, hardwood, or grass), different proportions of phenylpropane units and diverse interunit linkages occur, resulting in wide variations in lignin macromolecules, with a high degree of complexity and heterogeneity [6,7,8] Because of these heterogeneous features, high-value applications of technical lignins are rather limited. Numerous studies and developments on effective isolation methods to obtain lignin with specific properties have been reported [9,10,11,12,13], and some of these approaches have been integrated in chemical pulping processes and realized in large-scale plants [9,10,11]. The effectiveness of the production process has been elucidated by investigating the influence of these two main raw materials on the yield, chemical structure, average molecular mass, and thermal properties of the resulting GLs when operating under constant reaction conditions. Functional group distribution, ether linkages and intermonomeric linkages,average and thermal transition frequency of ether linkages and intermonomeric linkages, and thermal transition temperatures
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