Hemp Fiber Production & Processing
Hemp belongs to the Moracea family (the Mulberry family) and the commercially cultivated species are Cannabis sativa. Notes on hemp growing, yields and structure:
- Sowing: industrial hemp is usually seeded at approximately 1,000 to 1,350 seeds per hectare (60 to 80 kg of seed/ha.)
- Growing: the growing season is usually 95 to 115 days in temperate climates from sowing to harvest. Usually hemp stalks are 1.5 to 2.5 m high with stalks 4 – 10 mm in diameter. In some cases, the plants can grow as high as 3- 4 m high and the stalks as thick as 20 to 25 mm.
- Stalk Yield: is usually 6.5 to 12 tonnes per hectare.
- Fiber Yield: 23 to 35% of stalk mass under ideal growing and processing conditions and depending on the variety of plant. Approximately 1.5 to 4.2 tonnes of fiber per hectare. Note: 1.5 to 4 times higher fiber yield than flax. Only 10 to 20% of cotton fiber yields.
- Fiber Bundles: can be as long as 100 to 300 cm.
Fundamentally, hemp fiber extraction for technical fiber purposes involve the following main steps:
- Retting Harvested Fiber: Keeping the baled fiber in the field for some wet period of time to instill some bacteria-induced delaminating of the bast fiber from the core; once retted, the middle lamella is substantially degraded and the woody plant core is dry and brittle.
- Decortication: Processing the field feedstock via special machinery — the Decorticator — to separate the outer bast fiber from the inner core hurd fiber
- Refinement of Bast Fiber: Processing the Bast fiber after decortication through special machinery to:
- Remove non-structural fiber
- Align the fiber
- Surface Treatment & Sizing of Fiber: Using special machinery, as required for applications
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