08.08.2015   BIOENERGY. RESEARCH:. ADVANCES AND. APPLICATIONS

Molecular Weight Distribution

The accurate determination of lignin Mw is an impor­tant aspect of lignin characterization. The lignin Mw is

TABLE 18.7 Amounts of Different Structural Units per 100 Ar (per 100 Monomeric Units) Quantified by Combi­nation of 13C and HSQC NMR Techniques

Units

PSDL

PKRL

EKRL

EKDL

1-G

0.7

5.2

5.8

1.7

1-S

na

na

21.8

2.2

C

1.1

2.8

2.3

0.8

5

1.3

1.8

0.8

0.7

6

2.7

4.0

7.5

4.6

18

1.5

6.4

1.2

17

2.9

4.2

1.3

10

1.4

2.4

28

6.9

3.8

7.2

1.5

20

3.5

0.6

tr

30

4.1

25.2

3.4

13.1

29

2.0

nd

nd

tr

21—26

4.7

2.1

nd

2.4

13

—

3.1

nd

0.2

16

2.8

2.2

nd

0.3

S/G

na

na

3.0

2.1

PSDL, pine soda dissolved lignin; PKRL, pine kraft residual lignin; EKRL, Eucalyptus globulus kraft residual lignin; EKDL, Eucalyptus grandis kraft dissolved lignin. See Figure 18.2 for lignin structural units numbering reference.

Source: Capanema et al, 2008.

typically analyzed by a combination of size-exclusion HPLC and a detection method (refractive index, evapora­tive light scattering, or others) using calibrants which mimic the typical Mws and chemistry of lignins. Howev­er, lignin Mw determination still remains a challenge. For instance, a recent joined study by seven major European lignin research groups reported a reasonably small (<15%) intralab variability in the determination of lignin Mw. However, the interlab differences were very large, up to 49 times(!) difference even under standardized con­ditions (Baumberger et al., 2007).

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