Lignin samples

Finally, the sulfonate content of lignin is deterrnined by two main methods one typified by conductometric titration in which sulfonate groups are measured direcdy, and the other which measures the sulfur content and assumes that all of the sulfur is present as sulfonate groups. The method of choice for determining the sulfonate content of lignin samples that contain inorganic or nonsulfonate sulfur, however, is conductometric titration (45). 

Other lignins can be reacted with this chemistry. Table 7 shows synthesis data for the preparation of poly(lignin-g-(1-amido-ethylene)) from several different lignins. Sample 1 is a kraft pine lignin grafted in a reaction coinitiated with sodium chloride. 

Lignin Sample No. of entering groups Molecular Methoxyl % ... 

Recent determinations carried out by W. J. Schubert and Mary Bolton in this laboratory indicate the following molecular weights for certain of our lignin samples native White Scots pine Si 5, enzymatically liberated White Scots pine 695, native Oak 910, enzymatically liberated Oak 855-... 

The electrophoretic analyses of our various lignin samples has thus yielded results, which could not be obtained as yet by any other method. As in the case of proteins, electrophoresis supplies us with valuable information on the purity and homogeneity of the lignin preparations. The main limitation to a wider application of this method to lignin lies in the comparatively close mobility of all the samples thus far investigated (100). 

In this study the percentage of vanilhn present in the soda lignin sample will be determined. Next, the vanillin compound will be separated from soda lignin via crystallization technique. 

Table 9.1 Oxide peak identifieation in the lignin sample...

Lignin Samples. Ball-milled (BM) aspen lignin was prepared following the procedure of Lundquist et al. (21). The yield of purified milled wood lignin obtained was usually about 10% w/w that of ethanol/benzene-extracted aspen wood. 

Alkaline-extracted/steam-exploded (AESE) aspen lignin samples were prepared from steam exploded wood samples (55 s residence time at 240°C) obtained from Iotech Corp. Exploded wood pulp was treated with a series of carbon tetrachloride and alkaline extractions (12). 

Alkaline-extracted/acid hydrolysis (AH/NaOH) lignin samples were prepared by subjecting aspen wood flour to a one hour cook at 120°C in 0.05N sulfuric acid (22), followed by mixing the clarified supernatant with 1% w/w NaOH at 25°C with a Waring blender. The insoluble lignins were precipitated by addition of acid and water washes (32% yield). 

Narrow and broad MW standards were injected onto the HPSEC-DV system at concentrations near 1 mg/mL and 2 mg/mL, respectively. Initially, in order to obtain a usable differential pressure chromatogram, the lignin samples were injected at concentrations near 20 mg/mL, with an instrument (A-D amplifier) gain setting of 1 (0-1.0 volt Full Scale). As the... 

Universal Calibration. The aspen wood lignin samples chosen for this study were prepared by organosolv, steam explosion, dilute acid hydrolysis, and ball-milling procedures. 

Values for system peak parameters were found using a narrow distribution polystyrene standard (PS68K) before calculating MWD data for the lignin samples from universal calibration. To check software and instrument operation, several narrow MWD polystyrene and one broad MWD polymethylmethacrylate standards were treated as unknown samples and subjected to analysis with the universal calibration curve assembled from all polymer standards files. It was found that the MWD could be estimated for the recalculated polymer standards with errors between 5 and 10% of the original value indicated by the supplier of the standard (e.g., Mw for PS11K and Mw and M for PMMA17K-6). 

Table I illustrates the molecular weight averages found from universal calibration (narrow standards) for four aspen lignins and two quinonemethide-derived polymers using the Unical software. The poly-dispersities were the same within the experimental errors for all lignin samples. In contrast, the polydispersities found for the quinonemethide-derived polymers by universal calibration were near 1.1. The molecular weight averages found for the four acetylated lignins studied by universal calibration were substantially larger than those determined from previous work using conventional GPC (e.g., AESE and BM lignins from refs. 7 and 12 had approximately one-third those values found by HPSEC-DV in the present study).

This experiment was designed to examine the possible bias the broad polydispersities of the lignin samples may have on estimation of MWD by universal calibration. These data indicate that no such contribution exists, since the summation of the individual fractions of narrow(er) dispersity lead to values of MWD similar to those found using Unical software for the unfractionated lignin sample. 

We would like to thank Professor Wolfgang G. Glasser of the Department of Wood Science and Forest Products at Virginia Polytechnic Institute and State University for providing the lignin samples and the National Science Foundation for financial support of this project through grant CBT-8512636. 

Given the sensitivity of colligative methods to the presence of low molecular weight impurities, particular care was taken to isolate lignin samples free of such foreign contaminants. Thus, for example, the extraction... 

Associative/Dissociative Homology among Kraft Lignin Samples... 

Figure 7. Association of predissociated kraft lignin sample (92% retained by nominally 500 molecular weight cutoff ultrafiltration membrane) during incubation at 160 gL 1 in 1.0 M ionic strength aqueous 0.40 M NaOH for (l)0h, (2) 50 h and (3) 480 h.

Figure 10. Molecular weight calibration curves for kraft lignin samples differing in degree of association eluted from Sephadex G100 with aqueous 0.10A/ NaOH ( ) associated sample after 385 h at 180 gL 1 in 1.0 M ionic strength aqueous 0.40 M NaOH (O) orig nal preparation ( ) dissociated sample precipitated upon acidification to pH 3.0 after 2000 h at 0.50 gL 1 in aqueous 0.10 M NaOH.

---