How to Make Hemp Fiber: Growing, Harvesting, and Processing Hemp for Fiber

Posted: 11/27/24 | Author: Lawrence Serbin

Growing Hemp for Fiber: Traditional Methods and Modern Advancements

Growing hemp for fiber involves a series of traditional steps combined with modern advancements, aimed at maximizing fiber quality and quantity. Each phase, from seeding to retting and fiber processing, plays a vital role in determining the final product's quality.

Below, we dive deeper into these processes to provide a thorough understanding of hemp fiber production.

Seeding Rates and Plant Density

The first step in growing hemp for fiber is managing the seeding rates and stalk density. Most hemp-producing regions use a seeding rate of 100-140 kg per hectare, which results in 500-700 plants per square meter. This dense seeding promotes thinner stalks, leading to higher fiber content.

• High Seeding Rate: A high seeding rate increases plant mortality, but it also produces stalks with smaller diameters, which is ideal for finer fiber production.

For more information about hemp fiber, visit Hemp Traders.

Hemp Maturation Period

Hemp takes about 80-150 days to mature, depending on the variety and location. The majority of hemp varieties mature within 120 days. Harvesting at the right time is crucial for high-quality fiber.

• Early Harvest: Leads to low yield and weak fibers.
• Late Harvest: Results in tough stems that are hard to process, producing coarse fibers with little luster.

Harvesting Hemp Stalks

Traditional and Modern Harvesting Methods

The next step involves cutting down the hemp stalks.

Traditionally, this was done manually with a sickle or a modified hoe. In places like China, manual harvesting is still widely used.

• Modern Harvesting: Modern machinery, such as large tractor-mounted hedge trimmers, have been developed to make the harvesting process more efficient. These machines significantly reduce time and labor costs compared to manual methods.

Retting: The Key to Bark Removal

The process of removing the bark from hemp stalks starts with retting. This step allows for easier separation of the bark by partially decomposing the stalks.

Types of Retting

• Dew Retting: Dew retting involves leaving the stalks out in the field, allowing dew and atmospheric moisture to decompose the stalk. This natural process requires bacteria and moisture to soften the bark.
• Water Retting: Water retting involves submerging the stalks in water for several days. The bacteria in the water help break down the components of the stalk, particularly the middle section, known as the hurd.

Once retting is complete, the stalks are dried, and the bark is peeled away.

Removing the Bark from the Stalk

Traditional and Mechanical Methods

Traditionally, removing the bark from the hemp stalk was a labor-intensive process often performed by hand. In some regions, it still is.

• Modern Machinery: Flax processing machinery has been adapted to handle hemp. These machines cut the stalks to a uniform length of about three feet, making it easier to strip the bark and extract the fibers.

Separating Hemp Fibers

Physical and Chemical Fiber Separation

After the bark is removed, the next challenge is separating the fibers from each other. Raw hemp bark resembles long strips of corn husk, with fibers held together by lignin, a plant-based glue that provides structural rigidity.

• Combing Method: Traditionally, the fibers were combed manually, which was laborious and inefficient, leaving most fibers stuck together. Such irregular and thick fibers were mainly used for twine, ropes, and coarse canvas cloth.
• Chemical Degumming: In 1985, technicians in China pioneered a chemical separation method using a mild base of sodium hydroxide (NaOH) or lye. This process, known as degumming, was a significant advancement that allowed fibers to be completely separated.

Degumming removes lignin, enabling the individual fiber bundles to be fully separated and used in higher-quality textile applications.

Importance of Fiber Length and Thickness

The length and thickness of hemp fibers are crucial quality factors. One hemp fiber can be as long as the entire stalk, up to 14 feet (168 inches). The thickness of the individual fibers is usually determined by the thickness of the stalks.

• Thin Stalks for Textiles: Thinner stalks produce finer fibers, ideal for textiles, while thicker stalks produce coarse fibers.
• Seed Strain: The type of seed strain also affects fiber thickness. Specific strains are selected to produce either finer or thicker fibers, depending on the intended use. Learn more about different hemp products.

Sorting Hemp Fibers by Length

Fiber Combing and Separation

Hemp fibers come in various lengths and thicknesses, which requires sorting into uniform groups for specific applications. Modern combing machines separate fibers into different lengths.

• Long Fibers (4-6 inches): Primarily used for making 100% hemp yarns with specialized spinning equipment initially developed for flax. These strong, smooth fibers are used in high-quality textiles.
• Short Fibers (3/4 to 1.5 inches): Often blended with cotton and spun on conventional cotton spinning machinery. While 100% hemp yarn can be spun with short fibers, it is not as strong or luxurious as long-fiber yarn.

Cottonization of Hemp Fibers

The term cottonization refers to the process of converting all hemp fibers to lengths of 3/4 to 1.5 inches, making them suitable for cotton spinning systems.

This method aims for maximum fiber utilization with minimal waste, although excessively short fibers (less than 1/2 inch) become unsuitable for spinning and are redirected for use in paper production.

Short hemp fibers may be blended with other fibers to combine their different properties.

Blending hemp with other fibers is not a new concept—mills in China have been blending hemp with cotton since the mid-1990s. For more on hemp blends, check out this page.

• Hemp and Cotton Blends: Hemp adds stability and strength, making the resulting fabric stronger and less prone to shrinkage.
• Other Blends: Hemp can be blended with wool, silk, flax, bamboo, tencel, nylon, rayon, and polyester. Hemp adds absorbency, breathability, and durability, while the other fibers add flexibility, smoothness, and stability.

Conclusion to How to Make Hemp Fibers

The process of growing, harvesting, and processing hemp for fiber is both labor-intensive and fascinating.

With the combination of traditional techniques and modern innovations, hemp fiber is increasingly being used in a wide array of products, from textiles to ropes and composites.

By understanding the seeding rates, retting techniques, and fiber separation methods, we can make the most of what hemp offers as a sustainable and versatile material.