Hemp is a significant crop with pulpy fiber. Uses for hemp fiber range from making bio-plastics, paper, bio-fuels, building materials, ropes, and fabric. The industrial hemp plant produces natural and organic fiber, that is eco-friendly in comparison to synthetic fibers made from fossil fuels. The hemp fiber is also more eco-friendly in comparison to other natural fibers like cotton, which uses a lot of water and herbicides in cultivation. Hemp stalk produces the fiber. After harvesting hemp, the crop has to undergo retting and separation. The outer hemp plant contains hemp fiber bast while the inner part has short fiber.
What is Retting?
Hemp fiber retting is a process of separating the fiber from the stalk. The process uses moisture and microbes to break down pectin, a chemical bond that usually holds the industrial stem together. Pectin is a carbohydrate soluble gelatinous glue-like substance. Then, it becomes easy to separate the hemp bast from the hemp woody core. Primary hemp fiber makes reinforcements, paper, pulp, and composites, while the wood-like core fiber makes fuel, building materials, garden mulch, and animal bedding. There are three main methods of separating hemp fiber from the stalk. However, to minimize environmental impact, it is important to choose eco-friendly retting methods, which are the natural retting methods.
Hemp Retting Methods
There are three common methods of hemp retting. Namely
- Water retting which involves full immersion in water
- Field retting where you will leave the hemp plant to decompose through actions of bacteria, molds, and dew
- Direct use of enzymes.
When retting, you need to monitor the process to prevent under retting or over retting. Under retting makes the next production process difficult while over retting lowers the quality of the fiber. After retting, you should dry and bail the hemp stalks with a moisture content of 15%.
This is the most popular method. In water retting, you put the stalks in water for ten days. Usually, the water penetrates the stalks causing swelling and then bursting. This results in the absorption of moisture and bacteria. The process is more effective in warm water that has a good amount of bacteria. In natural water retting, you can use natural water sources like ponds, rivers, or streams.
i) Double Water Retting
It is a more gentle process. In this process, retting is done twice. The first time, the stalks are removed from the water before the retting is complete. The stalks have to dry for several months before undergoing retting again.
ii) Dew Retting
In dew retting, a natural process is triggered using wet dew. Usually, you put the hemp stalks in field grounds for several weeks. The process can take three weeks to ten weeks. How long the retting process takes depends on the availability of air temperature and moisture. Warm weather accelerates the process. For effectiveness, you need to turn over the stems for even rotting to occur. The process is complete after the appearance of white, and it becomes easy to separate the fiber from the stalk. Retting is complete when pectins are decomposed by microbes and it becomes easy to separate the fiber from the stalk. The stalks are then dried, and processed by the decortications machine.
For chemical retting, different chemicals are used, which include mineral acids, soaps, sodium hydroxide, and sodium carbonate. The process takes a few hours. Although the process produces high-quality fiber, the practice is not eco-friendly.
Factors that Affect the Quality of Hemp Fiber
Different hemp crops and varieties of hemp have different qualities of fiber. Noteworthy, dual-purpose crops grown for the production of both fiber and seed have a lower quality fiber than plants grown specifically for fiber because they have high lignin content. The time of hemp harvesting also has an impact on the quality of the fiber.
The time of harvesting hemp fiber depends on the purpose of the crop. Hemp grown for fiber is harvested earlier than dual-purpose hemp. This results in higher quality fiber suitable for making hemp fabric. On the other hand, dual-purpose hemp fiber is of low quality. It is not fit for textiles manufacturing, but it is commonly used for non-woven products, making pulp and paper.
Hemp Fiber Processing
After retting, the stalks have to undergo further processing to separate the fiber from the stalks. The process of separating hemp fiber from the stalks was once labor-intensive. Decorticator machines have simplified the process. After fiber separation, the fiber is processed further into raw material after cleaning. It can then be spun or processed into textiles or other hemp materials. If you do not have the necessary mechanisms to process the fiber into a finished product, then you can hire or buy a hemp fiber processing machine. Alternatively, you can contract one of the hemp fiber processing companies to process the fiber.