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Handbook of Size Exclusion Chromatography and Related ...

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Figure 4 MMD<strong>of</strong>birchkraftpulpdegradedbyozone.Reference ¼untreatedpulp.The<br />

arrow indicates the gradual change <strong>of</strong> MMD obtained on increasing ozone dosage.<br />

Chromatographic conditions as in Fig. 2. (From Ref. 200.)<br />

cellulose part <strong>of</strong> ozone-treated unbleached kraft pulp was obtained. Radicals<br />

formed in lignin–ozone reactions were suggested to cause heterogeneous<br />

degradation<strong>of</strong>thecelluloseinthepulpfiberasvisualizedbythebimodalMMD<strong>of</strong><br />

the cellulose fraction. In contrast, the cellulose part <strong>of</strong> the MMD <strong>of</strong> bleached<br />

hardwoodkraftpulps,thatis,lignin-freesamples,showedaGaussianshape(200).<br />

In another study concerning the aging <strong>of</strong> cotton linters, the MMD was shown to<br />

gradually change from amonomodal to abimodal pr<strong>of</strong>ile, but returned to the<br />

monomodal pr<strong>of</strong>ile at alimiting DP value <strong>of</strong> 150–200 (197).<br />

Tosummarize, when using LiCl/DMAc as solvent, the type <strong>and</strong> origin <strong>of</strong><br />

the sample are <strong>of</strong> great importance to consider for applying adequate dissolution<br />

conditions. It seems that LiCl/DMAc is less suitable for direct dissolution <strong>of</strong><br />

s<strong>of</strong>twood kraft pulp samples. For this type <strong>of</strong> sample, derivatization <strong>and</strong> SEC in<br />

LiCl/DMAc provide abetter way to study its MMD. Taken the new findings<br />

concerning the dissolution process into account, LiCl/DMAc <strong>of</strong>fers aconvenient<br />

way to characterize cellulosic samples by SEC in areliable way.<br />

6 DETECTORS AND CALIBRATION METHODS<br />

The chromatogram obtained by SEC using differential refractive index (DRI) or<br />

UVabsorbancedetectorsismerelyaconcentrationpr<strong>of</strong>ile<strong>of</strong>thepolymericsample<br />

withthelargermoleculeselutingfirst,thatis,itdoesnotprovidedirectinformation<br />

about M. Thus, to evaluate the MMD <strong>and</strong> the Maverages <strong>of</strong> asample, the elution<br />

© 2004 by Marcel Dekker, Inc.

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