HARVESTING HEMP
Fibre harvesting of hemp for paper pulp and textiles occurs as the female plant is in flower and before seed formation. Harvesting for seed production occurs 4 to 6 weeks after flowering. If fibre is obtained after seed formation it is of a poorer quality.
RETTING is the process used to ensure the long bast fibres are undamaged. It involves decomposition by bacteria and moulds by which the pectin (binds the fibrous and non-fibrous portion of the stalk) is broken down. Once the pectin is broken down the fibre and the stalk can be easily seperated. There is a period of drying following the decomposition period. There are several differing retting processes:-
- Dew Retting
The tradtional method. It relies on frequent rain and dew. Once the stalks are cut, they are spread evenly over the ground, allowing the rain and dew to induce the breakdown of the pectin. This method, without proper equipment, is labour intensive. There is a fine line between retted and rotted, so the hemp must be lifted at the right time otherwise it will be useless. This process may take one to two weeks with favourable weather (humid and warm), but usually four weeks is necessary. After this retting there is a period of drying and the fibres are then stored for further processing. Dew retting produces a coarse fibre, light brown in colour. Main use is for twine, cordage and fine paper.
- Water Retting
Hemp stalk bundles are submerged in clear water low in calcium and chlorides. The average time for this period is 7 to 10 days. The bundles are rinsed, washed, sun-dried and stored for fibre extraction. This process is more costly than the dew retting process, but the fibre obtained is of a higher quality. It can be combed one or more times, refined, dyed, spun and woven into whatever extent is requires for cable, rope, string, thread, cloth etc.
- Warm Water
This is similar to water retting, but the hemp is soaked for 24 hours when new water is added and brought to an elevated temperature for about 2 or 3 days. A very uniform and clean fibre is produced.
- Green Retting
Green stalks are mechanically processed, seperating the fibre from the stalk. The high quality fibre can be refined for the textile industry, while the remaining stalk can be used in the paper and fibre board industries.
- Chemical Retting
Stalks are processed using chemical agents to dissolve the pectin. This process can reduce retting period to 48 hours and produce a high quality fibre.
After retting the hemp fibre and stalk are loosely held together. They must be decorticated, scutched, hackled, and combed to remove remaining pieces of stalk, broken fibres and extraneous material. Mechanical equipment can be used to produce the hemp stalks into consumer products, like this thread on the right.
After retting the hemp fibre and stalk are loosely held together. They must be decorticated, scutched, hackled, and combed to remove remaining pieces of stalk, broken fibres and extraneous material. Mechanical equipment can be used to produce the hemp stalks into consumer products, like this thread on the right.
