Effect of alkaline preswelling on the structure of lignins from Eucalyptus

Study on the green extraction of lignin and its crosslinking and solidification properties by geopolymer pretreatment

Different delignification processes lead to significant differences in the structure and activity of lignin. Consequently, complex modifications are necessary before lignin to be applied. In this paper, a green process for the selective catalytic extraction of lignin by geopolymer is proposed based on biomass refining. This process can obtain lignin with ideal performance on activity, crosslink ability and curability. Taking eucalyptus, fir and bagasse as examples, the optimal lignin yields reach 46.5 %, 34.8 % and 48.7 % respectively (mFiber/mGeopolymer = 3, 120 min, and 130 °C). Moreover, lignin isolated with geopolymer (GL) shows a similar narrow molecular weight distribution range to that of Milled Wood Lignin (MWL). Studies on crosslinking solidification mechanisms have demonstrated that the phenolic hydroxyl groups of GL participate in the formation of a multi-stage amine crosslinking and solidification network structure. GL does not rely on flexible chains in the crosslinking and solidification of wood adhesives. Since highly active lignin can condense with phenolic hydroxyl groups on the surface of wood, it provides the adhesive with higher bonding strength (3.8 MPa). This study presents a novel approach to fabricating lignin-based formaldehyde-free wood adhesives.

Discrepancy of lignin dissolution from eucalyptus during formic acid fractionation

Understanding the structure and properties of lignin has important practical significance for its further applications. In this case, eucalyptus was fractionated with 88% formic acid at 101 °C for different durations, and the removal efficiency as well as the chemical structure of lignin at various stages were comparatively analyzed. The obtained data indicated that with increasing reaction time, lignin was continuously removed and the process could be divided into three stages. The lignin dissolution rate was fast first and then slow, and the molecular weight of the dissolved lignin increased with time. The lignin structure was condensed and the molecular weight increased with prolonged of reaction time. Structural analysis indicated that the β-O-4' structure was largely destroyed, the G-type lignin dissolved early, and the degradation of the S-type lignin became more intensive with increasing reaction time. This is of great help for reaction control as well as the further processing of lignin byproducts.

Structural Features of Alkaline Dioxane Lignin and Residual Lignin from Eucalyptus grandis × E. urophylla

In the present study, lignin from eucalyptus was extracted with 80% alkaline dioxane (0.05 M NaOH) from ball-milled wood and subsequently fractionated by gradient acid precipitation from the filtrate. Meanwhile, the residual lignin was prepared by a double enzymatic hydrolysis process. The yield of the lignin extracted by alkaline dioxane (L_A-2) was 29.5%. The carbohydrate contents and molecular weights of the gradient acid precipitated lignin fractions gradually decreased from 4.90 to 1.36% and from 7770 to 5510 g/mol, respectively, with the decline of the pH value from 6 to 2. Results from two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (NMR) and ³¹P NMR spectroscopy showed an evident reduction of β- O-4 ' linkages with the pH value decrease, while the contents of aliphatic -OH, phenolic -OH, and carboxylic groups displayed an increasing trend. Moreover, the residual lignin exhibited the highest molecular weight (11690 g/mol), the most abundant β- O-4 ' linkages (71.1%), and the highest S/G ratio (4.68).

Hydrazine hydrate and organosolv synergetic pretreatment of corn stover to enhance enzymatic saccharification and co-production of high-quality antioxidant lignin

Hydrazine hydrate and organosolv synergetic pretreatment of corn stover was developed. With the aid of alkaline and reductive hydrazine hydrate, a high delignification rate (77.94%) and total sugar yield of 90.27% (96.60% glucose, 78.82% xylose) based on the pulp could be obtained using hydrazine hydrate (10 mmol/g corn stover) and aqueous ethanol (60 vt%) as the solvent system. Analysis techniques such as FT-IR, SEM, XRD, and NMR were employed to characterize the structure and property changes of stock before and after pretreatment to evaluate the effect of hydrazine hydrate. A mechanism is proposed for the presented system.

Structural characterization of Chinese quince fruit lignin pretreated with enzymatic hydrolysis

Lignin is an increasingly valuable raw material for industrial, pharmaceutical and the food industries; natural antioxidants are also being used more and more widely. The Chinese quince fruits have an abundance of lignins with antioxidant properties; however, the lignins cannot be isolated by the methods conventionally used on other sources (e.g., wood, straw). In this investigation, multi-enzymatic hydrolytic pretreatments were used to isolate lignins from Chinese quince fruit, and the structures of these multi-enzyme mixture lignin (EML) fractions were then analyzed and compared with conventional cellulolytic enzyme lignin (CEL). EML fractions are structurally similar to CEL fractions except for an increased S/G ratio, greater number of β-O-4 linkages, higher average molecular weight and decreased thermal stability. The EML-2 fraction in particular seemed most representative of the lignins isolated, and it exhibited the highest antioxidant activity in comparison with CEL and other EML fractions.