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Handbook of Size Exclusion Chromatography and Related ...

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Figure 2 Elution curves <strong>of</strong> a residual lignin from an unbleached kraft pulp using 0.5 M<br />

NaOH as eluent <strong>and</strong> measured with the same column after 1 month (KP ProRL 1) <strong>and</strong> after<br />

3 months (KP Pro RL2). (From Ref. 46.)<br />

lignins obtained during flow-through kraft cooking <strong>of</strong> birch wood has also been<br />

studied (35). Underivatized <strong>and</strong> acetylated samples were investigated in DMAC/<br />

LiCl <strong>and</strong> compared to the MMDs <strong>of</strong> acetylated samples obtained when THF is<br />

used as eluent in a similar chromatographic system. The apparently larger molecular<br />

size obtained with the DMAc/LiCl system, as compared to the THF system,<br />

may be caused by interactions between the polystyrene st<strong>and</strong>ards <strong>and</strong> column<br />

matrix in combination with a more extensive conformation <strong>of</strong> the lignin polymer<br />

<strong>and</strong> or a higher degree <strong>of</strong> swelling <strong>of</strong> the polystyrene–divinylbenzene matrix.<br />

The MMDs <strong>and</strong> structures <strong>of</strong> dehydrogenation polymer models <strong>of</strong> lignin<br />

(DHPs) (36) were analyzed using DMF as eluent. The selection <strong>of</strong> solvents for<br />

MMD measurements was considered to be important because some solvents, for<br />

example, DMF alone, are not able to destroy lignin aggregates. In this work the<br />

association effects were highly reproducible <strong>and</strong> influenced by the polymerization<br />

mode <strong>of</strong> the precursors. It was suggested that the mechanism <strong>of</strong> the association <strong>of</strong><br />

lignin molecules should be investigated in detail.<br />

© 2004 by Marcel Dekker, Inc.

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