Wood lignin samples

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

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). 

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. 

It has been suggested that quinones are present in milled wood lignins [30]. However, their occurrence in wood and pulps is doubtful. The quinone models studied, 3-methoxy-o-benzoquinone (sample 23) and 2-methoxy-p-benzoquinone (sample 24), did not show any Raman bands when studied using 514.5-nm laser excitation. These compounds were fluorescent and degraded in the laser beam. Nevertheless, such structures, if present, are not expected to survive various bleaching treatments. Quinones are easily attacked chemically and probably do not survive peroxide and borohydride bleaching [19, 31, 32]. 

The natural content of stilbenes is considered to be very low in spruce wood lignin and this was confirmed in the present work (Figure 5). Analysis of the aqueous extracts after mild acidic hydrolysis revealed, however, that from wood to unbleached pulps and further to bleached pulps a stepwise conversion of diarylpropane to diguaiacyl stilbene structures takes place (Figure 5). The content of diarylpropane structures was found to be 25% less in the unbleached pulp samples than in the wood with a simultaneous increase in the content of stilbene structures. After hydrogen peroxide bleaching, the content of diarylpropane structures further decreased and the... 

Ribbon Probe Compared to Quartz Tubes or Boats. Positioning of a wood or lignin sample is of paramount importance. Soluble lignins may be applied directly to the surface of the ribbon probe with a microliter syringe. A solution (2p ) of 10 mglp concentration is transferred to the ribbon probe. The solvent is evaporated either by air-drying or by heating the ribbon at an appropriate temperature. 

Milled wood lignin is carefully packed into a quartz sample tube and inserted into the ESR cavity. Turn on the instrument and by following the procedure described above, a singlet signal with a g-value of 2.0023 and a line width of 16 gauss will be detected (Fig. 5.5.5) The concentration of this particular lignin... 

Irrespective of whether the starting material is a wood, plant, or pulp sample, an isolated lignin sample, or a lignin model compound, it is essential that all free phenolic hydroxyl groups be protected by alkylation prior to oxidation to prevent degradation of the phenolic units. This is usually accomplished by methylation or ethylation in an alkaline solution with dimethyl sulfate or diethyl sulfate, respectively. The reaction step should be performed in a well-ventilated hood. 

The GC internal standard is usually hexacosane (C26) and/or tetracosane (C24) For complex samples, such as those represented by lignocellulose residues, it is advisable to add both of these internal standards The amount of each internal standard (C26 and/or C24) to be added is 0 5 mg/20 mg of extractive-free wood, 0 25mg/20mg of extractive-free straw, and lmg/5mg of milled wood lignin (Note 6)... 

When the sample under investigation is an isolated protolignin, e.g., milled wood lignin, the syringyl nuclei content can be directly calculated from the analytical composition expressed on a C9(OCH3)x basis. 

Fig. 8.1.2. High-performance size-exclusion chromatography of silylated samples of pine kraft lignin (—), birch kraft lignin (—) and milled wood lignin from spruce (—). (Mansson 1981)...

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