Characteristics of Lignin from Flax Shives as Affected by Extraction Conditions

Abstract

Lignin, a polyphenolic molecule, is a major constituent of flax shives. This polyphenolic molecular structure renders lignin a potential source of a variety of commercially viable products such as fine chemicals. This work compares the performance of different lignin isolation methods. Lignin from flax shive was isolated using both conventional alkaline extraction method and a novel experimental pressurized low polarity water (PLPW) extraction process. The lignin yields and chemical composition of the lignin fractions were determined. The conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h, extracted 92 g lignin per kg flax shives, while lignin yields from the PLPW extracts ranged from 27 to 241 g lignin per kg flax shives. The purity and monomeric composition of the lignins obtained from the different extraction conditions was assessed via UV spectroscopy and alkaline nitrobenzene oxidation. Lignin obtained from conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h was of low purity and exhibited the lowest yields of nitrobenzene oxidation products. With respect to alkali assisted PLPW extractions, temperature created an opposing effect on lignin yield and nitrobenzene oxidation products. More lignin was extracted as temperature increased, yet the yield of nitrobenzene oxidation products decreased. The low yield of nitrobenzene oxidation products may be attributed to either the formation of condensed structures or the selective dissolution of condensed structures of lignin during the pressurized alkaline high temperature treatment. Analytical pyrolysis, using pyroprobe GC-MS, was used to investigate the molecular composition of the lignin samples. The total yield of pyrolysis lignin products was 13.3, 64.7, and 30.5% for the 1.25 M NaOH extracted lignin, alkaline assisted PLPW extracted lignin, and the unprocessed flax shives, respectively. Key lignin derived compounds such as guaiacol, 4-vinyl guaiacol, 4-methyl guaiacol, syringol, eugenol, isoeugenol, catechol, homocatechol, and vanillin were detected in all of the samples.

Capillary effects on flax fibers – Modification and characterization of the wetting dynamics

“…Those free radicals tend to create cross-linking in lignins when they are generated in wood. Flax fibers are containing a very low amount of lignin [30] and the measured amount of lignin can depend on the extraction method [35]. The process of free radicals stabilization could thus be different.…”

Comparative moisture and heat sorption properties of fibre and shiv derived from hemp and flax

“…This paper aims to study the effects of the microstructure, chemical composition, pore size distribution and porosity on the hygroscopic behaviour of fibre and shiv. In addition, the moisture sorption properties (sorption Table 1 Chemical composition of selected fibre and shiv (Garcia et al 1998;Bledzhi and Gassan 1999;Vignon et al 1995;Ross and Mazza 2010;Kostic et al 2008;Kymäläinen and Sjöberg 2008;Viel et al 2018 isotherms) and the enthalpy of heat sorption were evaluated for both shiv and fibre of flax and hemp during the sorption process.…”

The impact of lignin source on its self-assembly in solution

“…8 The monolignol composition of lignin varies from one plant source to another, further complicating the use of lignin in targeted value added applications. [11][12][13] In addition to the limited knowledge of the chemical and physical properties of lignin, there is limited information available that defines the association behavior in solution, which depends on the solvent conditions and lignin structure. The differences in monolignol composition and the randomness of oxidative coupling results in high polydispersity of molecular weight and p-coumaryl coniferyl sinapyl alcohol Figure 1.…”