There is considerable variability within a particular species of nonwood plant fibre raw material. Unlike wood, which takes years to grow to pulpwood size, most commonly used nonwood plant fibres (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 fibre. Generally, nonwood plant fibre 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 fibres; sisal; abaca; bamboo; hesperaloe etc.

Physical Characteristics
Softwoods are relatively uniform consisting of more than 90% tracheid fibres and only 10% stubby ray cells and other fines. Hardwoods by comparison are more heterogeneous and contain only about 50% tracheid fibres 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 fibre and cell types. Monocots such as cereal straws, sugarcane bagasse and corn stalks are more similar to hardwoods as the “fibre” 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 fibre types: an inner core of short fibres surrounded by a layer of longer bast fibres. Corn fibres typically contain more lignin and are more difficult to pulp.

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.