PROPERTIES OF HEMP
About 10% of fibers used in papermaking come from fiber crops, agricultural crop residue and a few other sources such as stalks.
Hemp is herbaceous annual plant with a single, straight un-branched hollow stem that grows over 4 to 5 months growing season to a height of 1 to 5 metres or 3 to 16 ft. and a diameter of 10 - 60 mm or 0.4 to 2.3 inch. The stem is characterized by a relatively thin outer layer (referred to as bark or bast) and a wood like core that surrounds a hollow center.
The bast constitutes on average about 30 to 35% of the dry weight of the stem. The bast proportion may vary from 12 to 48%. Primary bast fibers are highly variable in length, ranging from 10 to 100mm with an average length of 20 to 40mm. These fibers are thick walled and rigid. Secondary bast fibers are relatively short, about 2 mm in length. The woody core makes up the remaining 65-70% of the stem weight and consist of short fibers that are reportedly a rather constant 0.50 to 0.55mm in length.
Chemically, the bark fibers of hemp stalk contains significantly more cellulose and holocellulose and significantly less lignin than either of hardwood or softwood. Hemp core on the other hand contains less cellulose than wood.
Hemp is one of the fastest growing plants and was one of the first plants to be spun into usable 10,000 years ago.
Hemp Plant Hemp Plant Hemp Fibers
Physical Characteristics of Hemp and Softwood/Hardwood
| Characteristics | Hemp Bark | Softwood | Hardwood | ||
| Primary | Secondary | Hemp Core | |||
| Length (mm) | 10 - 100 | 2.0 | 0.55 | 2.5-5.5 | 0.8-1.9 |
| Alfa Cellulose (%) | 67+/-5 | 38+/-2 | 40.6 | 42+/-2 | 67+/-5 |
| Holocellulose (%) | 80+/-1 | 69+/-3 | 74.9 | 69+/-4 | 80+/-1 |
| Lignin (%) | 4+/-2 | 20+/-2 | 16.0 | 28+/-3 | 4+/-2 |
| Extractives (%) | 3+/-2 | 5+/-3 | |||
| Ash Content (%) | <0.5 | <0.5 | |||
Currently there is a small niche market for hemp pulp, for example cigarette tissue. Hemp fiber is mixed with other fibers. World hemp pulp production was believed to be around 120,000 tons per year in 1991. The total world production of hemp fiber had in 2003 declined to about 60,000. The cost of hemp pulp is approximately six times that of wood pulp. Hemp pulp is bleached with hydrogen peroxide.
