Читайте также:
|
|
angles (0°–10°) [13].
Fibers, particularly of low fibril angle between 0° and 10°, have shown that the
shape of the stress–strain curve depends on the pulping process. Figure 11.1 illustrates
The decreasing modulus with increasing proportion of amorphous cellulose.
The modulus decreases in the order holocellulose > acid sulfite > 60% kraft >
bleached kraft + 7% NaOH > bleached kraft + 16% NaOH, which corresponds
Well with the order of decreasing beating rate and increasing tear strength. The
Rate at which a pulp beats is virtually a measure of the rate at which the wet cell
Wall splits and breaks up while applying mechanical stress. Fibers of amorphous
Structure thus containing viscoelastic properties are more likely to withstand
Stress without fracture, since the stresses will be relaxed and the energy dissipated
In the viscoelastic regions. Fibers of high modulus and elasticity tend to peel their
Bonds at low strains, while those of low modulus will peel at larger strains because
Pulp Properties and Applications
Paper-Grade Pulp
They relax stresses in viscoelastic elements. From that it has been concluded that
Higher tearing strength is likely to be associated with a higher proportion of amorphous
Regions.
The differences between sulfite and kraft pulps are also reflected in their chemical
And macromolecular properties. Representative fully bleached commercial
Soft- and hardwood kraft and sulfite paper pulps have been selected for comprehensive
Chemical and macromolecular characterization. Additionally, elemental
Chlorine-free (ECF) and totally chlorine-free (TCF) -bleached pulps have been chosen
From each softwood kraft and sulfite pulps. A comparison of the four categories
Of chemical paper pulps, including TCF and ECF variants for both softwood
Kraft and sulfite pulps and two representatives of hardwood kraft pulps, on the
Basis of extended chemical characterization, is provided in Tab. 11.1.
Tab. 11.1 Comprehensive chemical characterization of a
representative selection of commercial paper-grade pulps [17].
Parameter Pine Spruce Eucalyptus Beech Spruce Spruce Beech
Kraft Kraft Sulfite Sulfite
ECF TCF ECF ECF TCF ECF TCF
Basic characteristics
Kappa number – 0.5 0.5 0.5 0.8 2.7 0.3 6.2
Brightness % ISO 89.0 90.7 89.7 87.6 85.9 92.7 90.3
Viscosity mL g–1 793 635 833 802 1020 868 1123
Extractives
DCM % od pulp 0.03 0.03 0.12 0.17 0.15 0.10 0.15
Acetone % od pulp 0.05 0.02 0.16 0.18 0.12 0.12 0.18
Alkali resistancies
R10 content % od pulp 87.0 87.2 91.9 90.0 87.7 87.4 84.6
R18 content % od pulp 87.1 88.0 94.6 93.6 89.8 90.5 87.6
Carbohydrates
Glucose % od pulp 84.7 86.1 80.4 73.3 89.7 91.6 84.9
Mannose % od pulp 6.6 5.8 0.3 0.2 5.2 5.0 1.2
Galactose % od pulp 0.2 0.2 0.1 0.1 0.0 0.0 0.0
Xylose % od pulp 7.3 6.9 18.4 25.5 4.1 2.7 12.2
Arabinose % od pulp 0.5 0.5 0.0 0.0 0.0 0.0 0.0
Pulp Properties and Applications
Дата добавления: 2015-10-21; просмотров: 89 | Нарушение авторских прав
<== предыдущая страница | | | следующая страница ==> |
Two major characteristics. First, kraft pulps show a much higher resistance | | | Tab. 11.1 Continued. |