Nonwood Plant Fiber Characteristics
By Robert W. Hurter, P. Eng., MBA, President, HurterConsult Incorporated
Extracted from "Agricultural Residues", TAPPI 1997 Nonwood Fibers Short Course Notes, updated and expanded February 2006.
(requires Adobe Reader).There is considerable variability within a particular species of nonwood plant fiber raw material. Unlike wood which takes years to grow to pulpwood size, most commonly used nonwood plant fibers (some exceptions include bamboo, sisal, hesperaloe) are annual plants and the entire plant develops within a fairly short growing period. Plant genus, climate, soil conditions and farming practices all have a large impact on the plants and the ultimate pulp fiber.
Generally, nonwood plant fiber pulps can be grouped into two broad categories:
common nonwoods or hardwood substitutes such as cereal straws, sugarcane bagasse, bamboo, reeds and grasses, esparto, kenaf, corn stalks, sorghum stalks etc.specialty nonwoods or softwood substitutes such as cotton staple and linters; flax, hemp and kenaf bast fibers; sisal; abaca; bamboo; hesperaloe etc.Physical Characteristics
Softwoods are relatively uniform consisting of over 90% tracheid fibers and only 10% stubby ray cells and other fines. Hardwoods by comparison are more heterogeneous and contain only about 50% tracheid fibers and a large number of vessel cells and ray cells.
Nonwoods, however, have large differences in their physical and chemical characteristics, and they all contain to varying degrees a wide variety of fiber and cell types. Monocots such as cereal straws, sugarcane bagasse and corn stalks are more similar to hardwoods as the “fiber” fraction is in the same order; however, they are much more heterogeneous and contain a large proportion of very thin-walled cells, barrel-shaped parenchymous cells, and vessel and fine epidermal cells in a wide range of dimensions. Dicots such as flax straw, kenaf and hemp contain two distinct fiber types: an inner core of short fibers surrounded by a layer of longer bast fibers. Core fibers typically contain more lignin and are more difficult to pulp.
Fiber dimensions of various nonwoods are provided in the following table.
Fiber dimensions of various nonwoods
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Fiber Source
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Length (microns)
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Diameter (microns)
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L/D
Ratio
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Maximum
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Minimum
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Average
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Maximum
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Minimum
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Average
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Bast Fibers
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Common industrial hemp
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55000
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5000
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20000
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50
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16
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22
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1000:1
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Jute (1)
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4520
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470
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1060
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72
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8
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26
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45:1
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Jute (2)
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5000
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500
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2000
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68
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8
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20
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100:1
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Kenaf
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7600
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980
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2740
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|
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20
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135:1
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Oilseed flax tow
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45000
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10000
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27000
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30
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16
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22
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1250:1
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Textile flax tow
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55000
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16000
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28000
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28
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14
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21
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1350:1
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Core Fibers
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Common industrial hemp
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|
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510
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|
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31
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16:1
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Kenaf
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1100
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400
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600
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37
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18
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30
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20:1
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Leaf Fibers
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Abaca
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12000
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2000
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6000
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36
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12
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20
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300:1
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Hesperaloe funifera
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3200
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15
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213:1
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Sisal
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6000
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1500
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3030
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17
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180:1
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Seed Hull Fibers
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Cotton staple
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50000
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20000
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30000
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30
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12
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20
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1500:1
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Cotton linters
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6000
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2000
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3500
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27
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17
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21
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165:1
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Stalk Fibers
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Canes
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sugarcane bagasse
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2800
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800
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1700
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34
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10
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20
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85:1
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bamboo (wide range)
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3500 - 9000
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375 - 2500
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1360 - 4030
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25 - 55
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3 - 18
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8 - 30
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135 - 175:1
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Cereal straw
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wheat, rye, oats, barley, mixed
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3120
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680
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1480
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24
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7
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13
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110:1
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rice
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3480
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650
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1410
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14
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5
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8
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175:1
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Grasses
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esparto
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1600
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600
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1100
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14
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4
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9
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120:1
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lemon
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1320
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9
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145:1
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sabai
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4900
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450
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2080
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28
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4
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9
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230:1
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switchgrass
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1370
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12.5
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110:1
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Reeds
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arundo donax
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|
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1180
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|
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15
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78:1
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papyrus
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8000
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300
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1500
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25
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5
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12
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125:1
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phragmites communis
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3000
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100
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1500
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37
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6
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20
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75:1
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Stalks
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corn
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2800
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680
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1260
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20
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10
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16
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80:1
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cotton
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2000
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700
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860
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|
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19
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45:1
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grain sorghum
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|
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1650
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80
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30
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47
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35:1
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Woods - for comparison
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Coniferous (softwood)
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3600
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2700
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3000
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43
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32
|
30
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100:1
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Deciduous (hardwood)
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1800
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1000
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1250
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50
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20
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25
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50:1
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Sources:
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1. Hurter, Robert W., “Agricultural Residues”, TAPPI 1997 Nonwood Fibers Short Course.
2. Hurter, A.M., “Utilization of Annual Plants and Agricultural Residues for the Production of Pulp and Paper”, Nonwood Plant Fiber Pulping Progress Report #19, TAPPI Press, pp. 49-70.
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Chemical Characteristics
The chemical composition of nonwood plant fibers varies widely depending on the type of plant and the soil and growing conditions. The following table gives chemical characteristics of various nonwoods for well-cleaned raw materials. Regarding chemical composition,
all nonwoods are characterized by a lower lignin content than wood and a higher pentosan or hemicellulose content stalk fibers are closer to hardwoods in chemical properties than to softwoods - the major difference is in the higher ash and silica content of these nonwoodsoilseed flax bast fiber has similar chemical properties to hardwoods; however, it has physical properties superior to softwoods.cotton staple and linters fibers are in a class of their own with respect to chemical properties - they contain an alpha cellulose content double that of softwoods and only a fraction of the lignin contained in all of the other fibers.Chemical properties of various nonwoods
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Fiber Source
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Cross & Bevan Cellulose
(%)
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Alpha Cellulose
(%)
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Lignin
(%)
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Pentosans
(%)
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Ash
(%)
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Silica
(%)
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Bast Fibers
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Common industrial hemp - bast
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55 - 65
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2 - 4
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4 - 7
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5 - 7
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< 1
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Common industrial hemp - core
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39 - 49
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17 - 22
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16 - 23
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3 - 4.5
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< 1
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Common industrial hemp - whole stalk
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43 - 51
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11 - 14
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9 - 13
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4.5 - 6
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<1
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Jute (1)
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57 - 58
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39 - 42
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21 - 26
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18 - 21
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0.5 - 1
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<1
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Jute sticks (whole jute)
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43
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Kenaf - bast
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47 - 57
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31 - 39
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7.5 - 9.5
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16 - 23
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2 - 5.5
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Kenaf - core
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34
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17.5
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19.3
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2.5
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Oilseed flax tow
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47
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34
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23
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25
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2 - 5
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Textile flax tow
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76 - 79
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50 - 68
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10 - 15
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6 - 17
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2 - 5
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<1
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Leaf Fibers
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Abaca
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78
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61
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9
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17
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1
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<1
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Sisal
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55 - 73
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43 - 56
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8 - 9
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21 - 24
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0.6 - 1
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<1
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Seed Hull Fibers
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Cotton staple
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85 - 90
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3 - 3.3
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1 - 1.5
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<1
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Cotton linters
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80 - 85
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3 - 3.5
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1 - 1.2
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<1
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Stalk Fibers
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Canes
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sugarcane bagasse
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49 - 62
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32 - 44
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19 - 24
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27 - 32
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1.5 - 5
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0.7 - 3
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bamboo
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57 - 66
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26 - 43
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21 - 31
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15 - 26
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1.7 - 5
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1.5 - 3
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Cereal straw
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barley
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47 - 48
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31 - 34
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14 - 15
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24 - 29
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5 - 7
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3 - 6
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oat
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44 - 53
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31 - 37
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16 - 19
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27 - 38
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6 - 8
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4 - 7
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rice
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43 - 49
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28 - 36
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12 - 16
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23 - 28
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15 - 20
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9 - 14
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rye
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50 - 54
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33 - 35
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16 - 19
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27 - 30
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2 - 5
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0.5 - 4
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wheat
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49 - 54
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29 - 35
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16 - 21
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26 - 32
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4 - 9
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3 - 7
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Grasses
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arundo donax
|
|
29 - 33
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21
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28 - 32
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4 - 6
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1.1 - 1.3
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esparto
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50 - 54
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33 - 38
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17 - 19
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27 - 32
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6 - 8
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2 - 3
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|
sabai
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54 - 57
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17 - 22
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18 - 24
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5 - 7
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3 - 4
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switchgrass
|
|
43
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34 - 36
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22 - 24
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1.5 - 2
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Reeds
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phragmites communis
|
57
|
45
|
22
|
20
|
3
|
2
|
Woods - for comparison
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Coniferous (softwood)
|
53 - 62
|
40 - 45
|
26 - 34
|
7 - 14
|
1
|
<1
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Deciduous (hardwood)
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54 - 61
|
38 - 49
|
23 - 30
|
19 - 26
|
1
|
<1
|
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Note: For well cleaned raw material - the composition of uncleaned raw material will be different with respect to pentosans, solubles, ash and silica content in many cases.
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Sources:
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1. Hurter, Robert W., “Agricultural Residues”, TAPPI 1997 Nonwood Fibers Short Course.
2. Hurter, A.M., “Utilization of Annual Plants and Agricultural Residues for the Production of Pulp and Paper”, Nonwood Plant Fiber Pulping Progress Report #19, TAPPI Press, pp. 49-70.
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Papermaking
The wide variety of physical and chemical properties offered by nonwood plant fibers provides virtually endless opportunities for papermaking. Combinations of common and specialty nonwood pulps will permit the production of virtually any grade of paper to meet any quality requirements demanded in the global market. Adding possible combinations which include wood pulp, nonwood pulp and recycled wastepaper pulp increases the possibilities for developing paper with specific sheet properties designed to meet specific customers needs. Nonwood Plant Fiber Uses in Papermaking provides just some of the many possibilities for the use of various nonwoods in papermaking.
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