Probing the molecular weights of sweetgum and pine kraft lignin fractions

The present investigation undertook a systematic investigation of the molecular weight (MW) of kraft lignins throughout the pulping process to establish a correlation between MW and lignin recovery at different extents of the kraft pulping process. The evaluation of MW is crucial for lignin characterization and utilization, since it is known to influence the kinetics of lignin reactivity and its resultant physicochemical properties. Sweetgum and pine lignins precipitated from black liquor at different pHs (9.5 and 2.5) and different extents of kraft pulping (30–150 min) were the subject of this effort. Gel permeation chromatography (GPC) was used to deter- mine the number average molecular weight (Mn), mass average molecular weight (Mw), and polydispersity of the lignin samples. It was shown that the MW of lignins from both feedstocks follow gel degradation theory; that is, at the onset of the kraft pulping process low molecular weightlignins were obtained, and as pulping progressed, the molecular weight peaked and subsequently decreased. An important finding was that acetobromination was shown to be a more effective derivatization technique for carbohydrates containing lignins than acetylation, the technique typically used for derivatization of lignin.

Defining lignin nanoparticle properties through tailored lignin reactivity by sequential organosolv fragmentation approach (SOFA)

Sequential organosolv fragmentation approach (SOFA) enhances the self-assembling process of high-quality lignin nanoparticles (LNPs) by tailoring the lignin chemistry in biorefineries.

Reactivity improvement by phenolation of wheat straw lignin isolated from a biorefinery process

This work describes an effective phenolation process to improve wheat straw biorefinery lignin reactivity.

Study of the Ability of Reducing Saccharides to Chemically Transform Lignin

The efficiency of chemical transformations of lignin obtained from Picea excelsa wood under the action of galactose, galacturonic acid and xylose (which can be obtained by enzymatic hydrolysis of hemicelluloses and pectin containing in plant material) was evaluated. The results were compared with use of traditional reducing agent which was borohydride sodium. Using the method of differential UV-spectroscopy was confirmed the increase of a number of phenolic hydroxyl units by Xyl, Gal and GA. The increase of lignin reactivity was controlled to sulfuric acid and to peroxide hydrogen. Similarly to NaBH4, a nucleophilic addition mechanism for the reaction of the reducing saccharides with lignin was revealed. Reduction by NaBH4, Xyl, GA and Gal increased the lignin reactivity to acid solubilisation and to peroxide oxidation.

Lignin oxidation mechanisms under oxygen delignification conditions. Part 1. Results from direct analyses

Oxidation of softwood and hardwood kraft lignins was observed under conditions of oxygen delignification (90°C and 110°C; 0.6 and 0.9 MPa) as a function of time by means of a number of analysis techniques and quantitative information was obtained on the degradation and formation of various compounds and structures. The decrease in reactor pressure was monitored during a 4-h reaction period. During the first 60 min, lignin reactivity was high, while a very intense stage took place during the first 20 min. The reactions decelerated after the first 60 min and after 120 min the reactions did not significantly advance. The oxygen consumption after 4-h reaction was 1.3–1.5 mole O2 per 1 mole lignin depending on the conditions. In the first 20 min, 50%–60% of the oxygen was consumed and the consumption increased only slightly after 60 min. At 90°C, the changes in all observed quantities were smaller throughout the whole 4-h reaction period than at 110°C. Under the studied conditions, increasing the reaction temperature, rather than the pressure, had primary significance in the increasing rate of lignin degradation. Hardwood kraft lignin was more reactive than softwood kraft lignin. The results obtained in this study are the basis for the development of a mechanistic model for the oxygen delignification process of pulps to be published in subsequent papers.

Ozonation of conventional kraft and SuperBatch residual lignins in methanol/water and water

The chemistry of ozone bleaching of chemical pulps was explored by ozonating residual lignins isolated from conventional kraft and SuperBatch pulps in methanol/water medium to detect possible differences in the reactivity of the two types of lignin. SuperBatch lignin was ozonated also in water to study the effect of ozonation medium on the lignin reactivity. The residual lignins were found to display similar reactivities in methanol/water, implying that ozonation should result in equal delignification rates for both conventional kraft and SuperBatch pulps unless the rates of reagent diffusion in the pulps are different. The lignins were partly oxidized to volatile and nonvolatile low-molecular weight oxidation products by the so-called “peeling mechanism”, according to which oxidation products go into solution and insoluble reaction products resemble the starting lignins. The reaction products obtained upon ozonation of SuperBatch lignin in neutral water resembled those formed in methanol/water, but their yield was much lower. This is probably due to the better solubility of lignin in methanol/water than in water and/or higher degradability of lignin by ozone than by radicals formed as ozone decomposition products.