Fibre

Fibre is one of the most common raw materials derived from hemp. Fibre harvesting is usually done when the plant is about to finish producing pollen and nearly before the first seeds appear. Harvesting during this time usually produces finer fibre typically used in textile.

Harvesting soon after pollination would typically produce coarse fiber. This is perfect for products requiring stronger fiber such as fiberboard or ropes. Males plants which die soon after pollination produce coarse yet strong fiber materials.

Harvesting Fibre

Hemp crops farmed for fibre production are typically longer. The stalks are often well developed. Moreover, harvesting starts well before most of the seeds develop. It can be cut during harvest using discbine or sickle bar mower. Most stalks cuts leave the stalks long for longer fibres.

Retting

Retting can be done naturally or biologically. It is the process of breaking down the gummy substance, such as pectin, which binds the fibers together and to the plant core. Common retting method is leaving the steams spread over the surface of the field right after harvest. Some refer to this method as “dew retting.” This allows even exposure to light and moisture. Retting begins when microorganisms attack the stalk and break down the “flesh.” Stems are normally turned a couple of times for even retting until it turns black and the fibers are exposed. Then, it is collected and stored using a baler.

Winter retting is common in areas with a harsh winter season. The hemp stalks are left during the cold winter season. The freezing weather opens the fiber surface and allows microorganisms to break down the pectin. The stalks are then baled during spring.

Artificial forms of retting may be done indoors and often involve water, enzymes, and chemicals.

The retted stems are then baled and dried to easily separate the fiber from the core.

Hurds

Hurds, also known as shives or hemp wood consists of the inner portion of the hemp stalk. It is often tough and breakable.  Hurds are popular especially in the UK for its use in animal husbandry. In most areas, it is used in papermaking, particle boards, hempcrete, and other construction materials.

Breaking and Scutching

Once retted, dried, and baled, the stalks are ready for further processing. It will undergo breaking using mechanical separation. Stalks pass between rollers to crush and break the core to produce hurds. This makes it easy to separate the fiber as well. During breaking, some of the hurds will separate right away.

The remaining hurds and fibers are separated during scutching. Fiber bundles are gripped between chains or rubber belts. Then, the bundles will pass through revolving drums with projecting bars. This effectively separates the hurds and short fibers from the long fibers.

Decorticating

Decortication refers to the overall process of separating the hurd and the fiber. This is typically done after some retting has taken place. Modern-day decortication is usually done by different types of machinery with varying degrees of success. It produces both the fine bast fibers and the tough, woody hurds. Different processors apply different decorticating methods but the most common are the dry and the wet processing.

Some farms use the process of breaking and scutching as described above. However, most bring their dried and baled stalked to be processed using a decorticator. Processors typically involve manual labor from skilled workers who spin the fibers into twines or refine them into bales.

Seeds

Hempseed is quite tricky to harvest and process. However, due to its nutrient value and usability, a lot of hemp farmers consider planting hemp for seeds over fiber.

Harvesting Seeds

Mature hemp seeds shatter very easily. While it makes good birdseed at this point, farmers would want to get more out of the seeds than that. Modern combine machines are typically used to harvest hemp seeds. Farmers need to study the moisture and climate as seeds need to be combined between 18% to 20% moisture to avoid shattering the hull during harvest.

It is necessary to aerate the seeds right after harvest to 9% moisture. This prevents molds and preserves the quality of the seeds. Farmers often reduce combine speed to avoid too much damage to the seeds and wrapping of raw fiber and stems.

Seeds should be dried using heated air dryers. This helps preserve and aerate the seeds making it ready for storage. At this point, the seeds will need close monitoring to maintain moisture below 9% which prepares the seeds for long-term storage.

Cleaning and Dehulling

Seeds are clean de-hulled through a processor. Most processors would use input hoppers, de-hulling and separating units, and re-separator units to control the entire process. The first clean-up would remove leaves, fibers, and other non-seed particles before the hard shells are removed.

Next, the seeds are processed through the dehulling and separating units. Simply, it consists of centrifugal force created by the machine. This force will crack the shell and separate the nut. Take note that both the hull (or the shell) and the nut are raw materials.

De-hulled hemp seeds below 9% moisture can last up to 12 months while maintaining its quality. The hulls should be stored as well as it can make great raw material for food and other products.

Pressing/Crushing

Pressing, or crushing, are considered secondary processes. Most modern processors press de-hulled seeds to produce better hemp oils. More on this process on manufacturing section.

Final Thoughts

Fibres, hurds, and seeds are the three main raw materials derived from hemp. Through various secondary and tertiary processes, these materials can be sourced to produce countless products. It’s important to note that no artificial elements or chemicals are added or used during the first few processes of the raw hemp materials.

Sources

(1) Alberta, Government of. 2017. Industrial hemp enterprise. Alberta Agriculture and Forestry. Alberta, Canada.

(2) Buoloc, P. 2013. The industrial hemp economy. Hemp: Industrial production and uses.

(3) Bystrom, T., and James, B. 2015. Industrial hemp harvest and storage: Best management practices. Agriculture and Forestry. Alberta, Canada.

(4) Horne, M.R.L. 2012. Bast fibres: Hemp cultivation and production § fibre extraction. In: Kozlowski, R.M. Handbook of natural fibres: Types, properties and factors affecting breeding and cultivation. Woodhead Publishing, Elsevier.

(5) Meidavilla, V., Jonquera, M., Schmid-Slembrouck, I., and Soldati, A. 1998. A decimal code for growth stages of hemp (Cannabis sativa L.). Journal of the International Hemp Association. 65, 68-74.

(6) Pecenka, R., Lühr, C., and Gusovious, H.J. 2012. Design of competitive processing plants for hemp fibre production. Agronomy. 2012 (5). doi:10.5402/2012/647867

(7) Schreiber, G. 1997. The Hemp Handbook. Munich, Germany: Wilhelm Heyne Verlag GMBH & Co. KG.