Handbook of Size Exclusion Chromatography and Related ...

Table 2 The Relative Composition of the Main Polymers of Softwood and Hardwood
Species, and of Kraft-Pulped Pine Wood and Birch Wood a
Cellulose (%) Hemicellulose (%) Lignin (%)
Softwood 33–42 21–29 27–32
Hardwood 38–51 17–33 21–31
Pine kraft pulp b
35 (39) 9 (25) 3 (27)
Birch kraft pulp b
34 (40) 17 (33) 2 (20)
a
The figures in parentheses refer to the original wood composition.
b
Unbleached.
Source: Refs. 3. and 20.
The relation between DP and the molecular mass (M) of a cellulose molecule can
thus be calculated by using the molecular mass of the glucan unit, that is,
anhydroglucose, M ¼ 162 DP.
The M average of dissolved cellulose can be obtained by various techniques.
The “zeta average” (Mz) from sedimentation equilibrium data is achieved by
ultracentrifugation, the “weight average” (M w) by light scattering, the “number
average” (M n) by osmometry, and “viscosity average” (M v) from viscosity
measurement. One clear advantage with SEC is the possibility to get all of the
averages from the molecular distribution and in addition a measure of the
polydispersity (Mw/Mn) of the cellulose sample.
As is true for the determination of the cellulose content, the reported M
average of a cellulose sample depends on the source and origin, the isolation
method, the solvent system, and conditions during dissolution. Because of this,
reported DP averages of native cellulose differ widely. In Table 3 average DP v is
exemplified for some cellulose samples.
© 2004 by Marcel Dekker, Inc.
Table 3 DPv of some Cellulose Fibers
Samples DPv
Valonia 27,000
Acetobacter xylinum 4,000–6,000
Cotton fiber, open–unopened 8,000–15,000
Cotton linters, bleached 1,000–5,000
Bast fiber 8,000–9,600
Ramie fiber 6,500–11,000
Flax 8,800
Wood fiber 8,000–10,000
Source: Refs. 21–23.