Handbook of Size Exclusion Chromatography and Related ...

The determination of MMD by HPSEC using crosslinked polystyrene gels as
column packing materials (19) and THF as eluent has been investigated in detail for
acetylated and underivatized lignins. Also investigations with mixed solvent systems
such as chloroform and dioxane were used. DMF and other polar eluents were also
investigated and it was seen that for solvents such as DMF or a DMF/THF mixture, a
strong association between lignin molecules occurred. However, the addition of LiCl
breaks up the associates. A comparison of THF and DMF as solvents was performed
for several purified kraft lignins from slash pine (20) using vapor pressure
osmometry (VPO) and low-angle laser light scattering (LALLS). The molar mass
distribution by high-temperature size exclusion chromatography (SEC) was
investigated in THF, DMF, DMF with 0.1 M LiBr, and pyridine at conditions
above the theta temperature. It was concluded that VPO may be used to determine Mn
for kraft lignins if the purity of the lignins and the identity of the impurities are
known. LALLS can be used to determine Mw for kraft lignins if measurements are
made at or above the theta temperature of the lignin–solvent pair. SEC should be
used at temperatures at, or above, the theta temperature of the lignin–solvent pair.
The separation according to molecular size is highly dependent on the solvent used,
and DMF is a much better solvent than THF for SEC at higher temperatures.
The molar masses of lignins from cork (21) and wine (22) have been
determined. The cork lignin was significantly more crosslinked than wood-derived
lignins. Also, lignins isolated from wheat straw (23) were investigated using this
HPSEC system. The MMDs of lignin isolated from spruce wood at 50–1108C
with mono-, di-, and trichloroacetic acid (24) were studied using THF and
conventional calibration. Similar MMD measurements were performed for aspen
and loblolly pine lignin samples (25) recovered from the spent liquor of several
acetic acid-based pulping processes.
According to a new lignin isolation method (26), wood and pulp were
subjected to ball milling, swelled in an organic solvent, and then treated with a
cellulase. The MMDs of the lignins were determined using HP/SEC and THF as
eluent. The thioacidolysis is used in the characterization of lignin structures and by
determination of the MM for the reaction products indications of the degree of
condensation of lignin and, hence, its reactivity toward pulping chemicals are
obtained (27).
The molar masses of the residual lignin in softwood kraft pulp isolated by
both enzymatic hydrolysis and acid hydrolysis extraction were characterized and
their molar masses were determined using an HPSEC system including THF as
eluent and a UV detector (28).
The MMD of chlorinated compounds of bleached kraft mill effluents
(BKME) were studied by aqueous and nonaqueous SEC using THF as eluent and
by ultrafiltration (29). In total 90% of the BKME halogenated organics, which
originated from lignin, were soluble in THF, which was used as eluent when
determining the MMD of these products.
© 2004 by Marcel Dekker, Inc.