Chemical Properties of Dissolving Pulps from Nonwood Fibers
By Alfred M. Hurter, P. Eng., "Utilization of Annual Plants and Agricultural Residues for the Production of Pulp and Paper", TAPPI 1988 Pulping Conference Proceedings, pages 139 - 160.
Updated by Robert W. Hurter, P. Eng., MBA, President, HurterConsult Incorporated, January 2003.
(requires Adobe Reader).Dissolving pulps are high alpha cellulose, low ash pulps that are used to produce various products such as viscose rayon, cellulose esters (acetates, proprionates, butyrates, nitrates) and cellulose ethers (carboxymethyl, ethyl, methyl).
Because of the high pentosan content of most nonwood fiber raw materials, the prehydrolized kraft process has been used for most of the laboratory testing conducted to date and for the very few commercial dissolving pulp mills that have been built based on nonwood fiber raw materials (primarily cotton and bamboo). This process, however, is complicated and expensive from both a capital and operating viewpoint. Depending on the nonwood fiber raw material, it may be possible to reduce the capital and operating costs by using a prehydrolized soda-anthraquinone process but this would have to be tested prior to developing a commercial facility.
Hurter provided the following data on dissolving pulps from various fiber raw materials.
Chemical Properties
|
Bagasse
|
Bamboo
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Cotton
|
Sisal
|
Prehydrolized
Hardwood Kraft
|
Softwood
Sulphite
|
|
Ash
|
%
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0.04 - 0.15
|
0.06 - 0.11
|
0.10 - 0.15
|
|
0.08 - 0.15
|
0.06 - 0.08
|
Pentosan
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%
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4.0 - 6.0
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2.5 - 3.5
|
|
|
1.6 - 2.5
|
3.0 - 5.0
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Alpha Cellulose
|
%
|
92 - 94
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90 - 94
|
97 - 98
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92 - 93
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93 - 96
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93 - 95
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Beta Cellulose
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%
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3.5 - 5.0
|
1.6 - 3.0
|
|
0.1
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2.1
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1.5 - 2.6
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Gamma Cellulose
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%
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1.8 - 3.2
|
2.5 - 3.5
|
|
7.3
|
1.0 - 3.0
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3.2 - 8.7
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Alcohol-Benzene Extraction
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%
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0.3 - 0.5
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0.3 - 0.5
|
|
0.2 - 0.3
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0.03 - 0.26
|
0.2 - 0.4
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Degree of Polymerization
|
|
525 - 840
|
1026 - 1030
|
1440
|
|
500 - 1000
|
500 - 1000
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Viscosity
|
cp
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13 - 14
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|
|
31.9
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8 - 12
|
15 - 45
|
Copper Number
|
|
0.23
|
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0.06
|
|
0.3 - 0.6
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0.5 - 1.5
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