Lignin concentration

When the proper conditions are met, UV microscopy can provide a quantitative measure of the lignin concentration in a microscopic area of wood tissue according to the Beer-Lambert law  

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The methods of oxidant consumption are used exclusively in the analysis of residual lignin in unbleached pulps. These procedures are all based on the common principle that lignin consumes the appHed oxidants at a much faster rate than the carbohydrates, and oxidant consumption under carefully specified conditions can be regarded as a measure of lignin concentration in the pulp. 

Wood Morphological region Tissue volume (%) Lignin (% of total) Lignin concentration (%)... 

L., Macromolecules, in press) had shown that this membrane did not allow associated complexes to pass through the membrane. The cell is pressurized with nitrogen. The first 5 mL of permeate are discarded, and then a 2 mL sample is taken for analysis. The ultrafilter conditions were adjusted to minimize concentration polarization, CP (16), by using a stirrer rate of 390 rpm and 60 kPa pressure drop across the membrane. At high lignin concentrations CP could not be avoided and many different stirrer rates and pressures were used to provide a correction for CP. 

Figure 2. Rejection coefficient distribution on the XM300 membrane showing the association caused by an increase in the concentration of large molecules at constant total lignin concentration.

Lignin Concentration. Lignin concentrations have been examined in the range of 10 to 100 g/L. These concentrations represent concentrations normally present in black liquors and therefore are of industrial relevance. Typical lignin concentrations in black liquor range from 50 g/L for 15% solids to over 300 g/L at firing. 

The results based on bulk lignin concentration demonstrate that the degree of association increases as the concentration of the solute increases. This result is observed at all alkalinities. The degree of association increases as the alkalinity decreases at any solute concentration. 

The simple solubility model would predict that the concentration in the permeate would remain constant as the total lignin concentration increases. 

Higher lignin concentrations and higher ionic strengths increase the degree of association. 

Fukushima, R. S., and Hatfield, R. D., 2001, Extraction and isolation of lignin for utilization as a standard to determine lignin concentration using the acetyl bromide spectrophotometric method, J. Agric. Food Chem. 49 3133-3139. 

Hatfield, R. D., Grabber, J., Ralph, J., and Brei, K., 1999, Using the acetyl bromide assay to determine lignin concentrations in herbaceous plants some cautionary notes, J. Agric. Food Chem. 47 628-632. 

It is concluded that all of the results presented above discredit the phenol-furfural condensation mechanism and that the source of wet strength in hardboards is thermoplastic-fusion of lignin concentrated on the surfaces of the fibers. 

The lignin concentration is high in the middle lamella and low in the secondary wall. Because of its thickness, at least 70% of the lignin in softwoods is, however, located in the secondary wall as shown by quantitative UV microscopy (Fig. 4-11 and Table 4-4). The picture is very similar for... 

Of the methods for determining lignin in solution based on a specific chemical reaction, that involving nitrosation, the so-called Pearl-Benson method, has found the widest application. In this procedure, reaction of the phenolic units in lignin with acidified sodium nitrite leads to the formation of a nitrosophenol which, upon addition of alkali, is tautomerized to an intensely colored quinone mono-oxime. The absorbance of the latter structure is measured at 430 nm and related to lignin concentration by calibration with a standard lignin. The procedure described below is essentially that developed by Barnes et al. (1963), who modified the original Pearl-Benson method (Pearl and Benson 1940) to improve its sensitivity. 

Lignin concentration is calculated from the Beer-Lambert equation ... 

Kleinert TN, Joyce CS (1957b) Short wavelength absorption of various lignins and related substances III The flow-micro cuvette for continuous measurement of lignin concentration in sulfite cooking liquors Pulp Pap Mag Can 58(7) 215-219 Kolboe S, Ellefsen O (1962) Infrared investigations of lignin A discussion of some recent results Tappi 45 163-166... 

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