The industrial hemp plant produces one of the world’s most versatile fibers. It can be used to make high-quality fabric, stuff furnishings, and much more.
Hemp plants have two fiber-producing areas: the outer “bast” layers of the stem and the “hurd” core inside it. Bast fibers are much longer and workable than hurd fibers. The fiber production process involves three main steps: harvesting, retting, and separation.
The quality of finished hemp fiber depends in no small extent on the genetics of the plant. Crops raised expressly for textile use deliver better quality fiber than “dual-purpose” hemp crops. As suggested by the name, dual-purpose hemp is grown to produce both fiber and seeds. Hemp seeds also have a range of different applications, including food and biofuel.
Hemp grown expressly for fiber is harvested quickly to catch the fibers at the highest possible level of quality. This generally happens between 70 and 90 days after the plants are seeded when they are just starting to flower. Harvesting occurs long before the plants even start producing new seeds.
The hemp grown for CBD extraction purposes is harvested during its maturity, the biomass often contains from 5%-11% cannabinoids if the genetics are present to produce the cannabinoid concentration.
A dual-purpose hemp crop is left in the ground to mature longer. The fibers it produces have a higher amount of lignin, which makes them poorly suited to textile use. There are still productive uses for these more robust fibers; they are often used in the creation of paper, pulp, and other non-textile products.
Whenever they are harvested, hemp plants are cut roughly an inch above the soil. The harvested plants are set aside for a short drying period; this usually only takes a few days.
As noted above, hemp plant stems contain two different fiber-producing regions (bast and hurd) in their outer and inner layers. Retting is the process used to separate the two parts of the stem chemically. Retting typically relies on the application of water and microbial action, but it can be carried out in several different ways:
- Water retting: This involves immersing the plants entirely in water.
- Field retting: This means letting hemp decompose in the field thanks to original mold and bacteria. Field retting takes between four and six weeks, and the process needs to be monitored carefully.
- Enzyme retting
After hemp plants have been retted, the stalks are thoroughly dried out (aiming for moisture content of less than 15 percent) and bound up in bales.
Separating Hemp Fiber
Dried hemp stalks are next “broken.” They’re passed through fluted rollers which break the hurd and shake it out of the bast. This process also starts to separate some of the fiber. Traditionally, breaking hemp was a difficult process done by hand. Modern hemp separation is considerably faster thanks to an automated machine designed specifically for fiber separation: the decorticator. Decorticators are used with many different fiber-producing plants; the video included here shows one being used on jute plants.
Decorticators can break hemp stalks before their leaves are removed. This is a time-saving step, but it requires extra sorting before the separation process is finished.
The final sorting, scraping, and separating process is known as “scutching.” After this, the majority of the short fibers and hurd material have been removed from the long fibers.
Hemp Fiber: Line And Tow
Once hemp plants have been processed and separated, the two resulting fibers are called “tow” and “line” based on their length. The maximum potential length of line fiber is restricted only by how high the hemp plant grows. Single line strands of 15 feet in length are not uncommon.
After the separation process, line fiber is cleaned, carded to size, cut, and bailed for further processing. Tow fiber is collected more simply, merely compressed and packed into bails. Hemp tow can be used for pulp products, stuffing, or coarse yarn.
Line fiber is the key to creating quality hemp products including fabrics for clothing, furnishings, and carpets. Good line fiber processed with care can produce a fine fabric with a texture like that of linen. This is a sharp contrast to the undeserved reputation for roughness that some people ascribe to clothing made out of hemp fabric.
USDA statistical data indicates that when “green” (i.e., unprocessed) industrial hemp is separated and dried, 3.5 percent of the plant’s total weight becomes line fiber. Tow fiber represents about one percent of the plant. Don’t think that the rest of the plant is wasted; every bit of an industrial hemp plant can be turned to a useful purpose.
Hemp leaves can be taken back to the field and used as fertilizer. Solid hurd material can be processed into pulp products, plastics, and insulation. Even the dust created by fiber processing can be collected, compressed into pellets, and used as a renewable fuel resource.
The Advantages Of Hemp Fiber
Hemp has many unique benefits and advantages that easily make it the equal of other fiber plants, and some supporters argue that it is superior. Some of the most important of hemp’s advantages:
- Hemp requires fewer inputs and less water than cotton.
- The fast-growing time of hemp makes it less vulnerable to pests and plant diseases.
- Because it has little lignin, hemp fiber can be bleached without environmentally-hazardous chlorine.
- In terms of land area cultivated, hemp is far more productive than cotton or flax.
- Hemp is stronger than many other natural fibers.
- Hemp fibers are inelastic, resulting in clothes that retain shape better.
- Hemp fabric gets softer over time.
- Hemp fabric holds dye better than cotton.
- Hemp fiber has formidable insulation and anti-bacterial properties
- Hemp fabric resists mold, mildew, and abrasion damage.
- Hemp fabric is breathable yet blocks UV radiation.
In many markets, hemp clothing and other hemp products are currently more expensive than those made of different fibers. This is likely to change as industrial hemp cultivation grows more popular.
A range of external factors – everything from drug paranoia to lobbying by the cotton industry – has held industrial hemp production back over the last hundred years. Were it not for these impediments, the value and utility of hemp fibers would doubtless already be widely known and celebrated.