From rather high molecular-weight cellulose and very low molecular-weight hemicellulose

Fractions owing to the heterogeneous degradation of the wood pulp constituents

Across the cell wall layers. Intrinsic strength properties from a polymeric

Material are always related to the weakest part in the polymer, which is represented

By the short-chain molecules. A detailed evaluation of the numerical data from

GPC measurement revealed that zero-span tensile strength correlates well with

the weight percent of the DP <120 fraction, as illustrated in Fig. 11.4.

The intrinsic viscosity as well as standard information from GPC measurements

Such as PDI or DPw and DPn are not suited to predict the fiber strength

Properties accurately. However, the amount of low molecular-weight fraction comprising

The DP range between 100 and 150 is a suitable measure to estimate fiber

Strength properties, regardless of the origin of pulp (wood species, pulping,

Bleaching processes). This example clearly demonstrates that the macromolecular

Properties are a decisive element of strength characteristics of a pulp fiber. These

Results are in good agreement with the findings of Kettunen et al. that tearing

Strength of a pulp increased with increasing amounts of high molecular-weight

xylan [24].

However, sheet properties are determined by many other parameters such as

the cellulose:hemicellulose ratio, as previously discussed. Another important factor

For pulp sheet properties is fiber morphology, characterized by fiber length,

Fiber length distribution, and coarseness. It is widely accepted that especially

Pulp Properties and Applications

2 4 6 8

Zero-Span tensile index, dry [Nm/g]

Weight fraction < DP 120

Fig. 11.4 Relationship between zero-span tensile index and

the weight fraction <DP 120 of a representative selection of

Commercial hardwood and softwood kraft and sulfite pulps

[17]. For more detailed information on these pulps, see

Tabs. 11.1 and 11.2.

Tearing strength is influenced by fiber length. Based on the comparison between

Hardwood and softwood kraft pulps, the poorer tearing strength of the former is

Generally attributed to the shorter fiber length. The results of the measurement of

The fiber dimensions of the selected paper pulps are provided in Fig. 11.5 and

Tab. 11.3.

By comparing the fiber length distribution of both spruce pulps, it is apparent

That the sulfite pulp shows a higher proportion of short fibers as compared to the

Kraft pulp. This may be attributed to the degraded cellulose fraction formed during

The late stage of cooking. The beech pulp shows the characteristic peak at a

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