Abstract
A shift towards an economically viable biomass biorefinery concept requires the use of all biomass fractions (cellulose, hemicellulose, and lignin) for the production of high added-value products. As lignin is often underutilized, the establishment of lignin valorization routes is highly important. In-house produced organosolv as well as commercial Kraft lignin were used in this study. The aim of the current work was to make a comparative study of thermoplastic biomaterials from two different types of lignins. Native lignins were alkylate with two different alkyl iodides to produce ether-functionalized lignins. Successful etherification was verified by FT-IR spectroscopy, changes in the molecular weight of lignin, as well as 13C and 1H Nuclear Magnetic Resonance (NMR). The thermal stability of etherified lignin samples was considerably improved with the T2% of organosolv to increase from 143 °C to up to 213 °C and of Kraft lignin from 133 °C to up to 168 °C, and glass transition temperature was observed. The present study shows that etherification of both organosolv and Kraft lignin with alkyl halides can produce lignin thermoplastic biomaterials with low glass transition temperature. The length of the alkyl chain affects thermal stability as well as other thermal properties.
Highlights
Lignin is an aromatic heteropolymer, the second most abundant biopolymer in the world after cellulose
Kraft lignin is produced through the sulphate cooking process, in which fibers are treated at temperatures of 165–175 ◦ C for 1–2 h in the presence of sodium hydroxide and sodium sulphite [5]
The ethanol was removed under vacuum in a rotary evaporator and, lignin was separated from the liquor by centrifugation at 29,416× g for 1 min at 4 ◦ C
Summary
Lignin is an aromatic heteropolymer, the second most abundant biopolymer in the world after cellulose. It constitutes 15–35% w/w of a plant’s cell wall and plants are estimated to generate. The global annual production of lignin is estimated at approximately 100 million tons, of which only 2% is used commercially (primarily in dispersants, adhesives, and surfactants); whereas the rest is burned as low-value fuel [3,4,5]. Ligno-sulphonates are a by-product of sulphite cooking in which the fibers are treated by HSO3 − and SO3 2− ions and the digestion is typically operated at 120–180 ◦ C for 1–5 h [1,5]
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