First of all, it is important to understand that there are two main types of hemp fibre. A typical hemp stalk comes with an outer material that has bast fibres and the hurd, or the inner part contains short fibres.
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Thanks to the versatile nature of hemp products, the plant’s cultivation has a long-drawn history in the United States dating back to the times of the early colonists. The quality of hemp fibre is largely determined by the initial purpose for which it was first cultivated. That is to say, hemp plants are generally cultivated either exclusively for making textile fibres or for multi-purpose usage.
The process of acquiring hemp fibres –
The extraction of fibres from industrial hemp is a three-stage process involving harvesting, retting and separation. At each of these stages, adequate caution is to be exercised to get supreme quality hemp fibres. With the growing demand for hemp products worldwide, there is a greater emphasis on adopting standard procedures in cultivation to ensure the proper maturation of hemp crops.
1. Harvesting
On average, hemp crops mature in about 100 days from the date of seeding. Taking into account varying factors like seed variety, time of seeding, climatic conditions, and growing conditions; the maturity date of hemp crops can slightly differ.
The time of harvesting industrial hemp is instrumental in determining the quality of hemp fibre obtained. Consequently, industrial hemp crops need to be harvested early in the flowering stage, sometimes before the seed is produced.
On the other hand, multipurpose hemp is intended to be used to make paper, pulp and other non-woven products. For this very reason, harvesting time is usually much later for these hemp plants. Regardless of the type, hemp plants are required to be cut a little above 2 to 3 cm above the soil. Following the cutting, hemp crops are usually left to dry for a few days.
2. Retting
2. RettingA chemical substance called pectin is responsible for holding together a hemp stalk. To obtain hemp fibres it is important to break down this glue-like substance. The degradation of pectin is usually carried out with the help of microbes present in the stem or soil, acids/bases and even special enzymes.
Most cultivators find chemical retting a tedious process as it involves the use of special facilities. The most preferred type of retting is field retting also known as dew retting. This process requires the active supervision of the cultivator thereby lending it the epithet of ‘controlled rotting’.
Field retting is carried out by exposing the harvested hemp stalks to weather conditions in the open. The atmospheric moisture and temperature are critical factors that help determine the duration of the retting process. Experts point to the role of intermittent precipitation in aiding moisture maintenance within the stalks and also accelerating microbial activity.
To ensure that uniform retting takes place, the hemp stems should be turned over when they start changing in colour. This change in colour is usually observed anywhere between two to three weeks post-harvesting. Turning over of stems is a crucial step for hemp meant for textiles. As discussed earlier, hemp fibres meant for this purpose should be uniformly retted while retaining the thickness of its layers.
3. Separating
After the stalks are retted and allowed to dry for a sufficient time. The final stage of separation of fibres needs to be carried out. The mechanical process of separation is also called breaking.
In this process, the stalks are brought to a central location and after selecting the stalks they are passed between fluted rollers. This results in the breaking of the woody core into hurds and the bast fibres are released from the outer material.
The fluted rollers are efficient only in the separation of stalks of considerable quality. The remnants of the process are further separated by scutching. Scutching involves beating the fibre bundles held together by chains. The process exhorts a lot of pressure on the fibres that eventually separates the short and long fibres.
The entire process of separating is quite labour-intensive. The development of a machine called a decorticator has greatly simplified the separation of the bast fibres and the hurd.
A decorticator
Characteristics of fibres from hemp plants –
Fibres obtained from hemp has a distinct dark brown colour rendering it almost impossible to bleach. Certain industries like to add hues of vivid colours to suit their respective requirements. Hemp fibre often displays nodes similar to that of linen. The marked difference being hemp’s wide central canal.
Fibres from hemp have variable length. Fibres obtained from industrial hemp measure few inches, while hemp fibres used for textile production are generally about an inch in length. The elasticity rate of hemp fibre is very low.
Moth resistant hemp fibres usually respond to sunlight in the same way as most other fibres like cotton or linen. What distinguishes hemp fibre from other fibres is the former’s excellent insulation properties.
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Within the same species of hemp plants, the fibres have shown staggering differences worldwide. Although, every variety has more or less the same chemical properties; only fibres with high durability and lustre are commercially desirable. The physical appearance of the hemp plant resembles the flax plant and hemp fibres are commonly confused with that of linen.
Owing to poor elasticity, fine fabrics can not be woven from hemp. The low elasticity component is compensated by extreme durability – making hemp a great choice for carpet manufacturing industries.
Another interesting feature of hemp fibre is its ability to block out the Sun’s ultraviolet rays. This means that dyed hemp fibres are likely to last longer as they don’t fade away with usage or exposure to Sunlight.
General usage of Hemp fibres –
Hemp fibre production had seen a sharp decline until being eventually rediscovered in the 1980’s. Regardless, hemp was a preferred choice among natural fibres because of its obvious advantages
The rougher variety of hemp fibres are woven into ropes, sacks and cordage commonly. Some European countries are famous for their fine hemp fibres based interior design as well as apparel fabrics. Furthermore, different varieties of shawls, hats, posters, towels and carpets are made from hemp fibres.
Craft items like rugs and crochets that often require colors and patterns make use of dyed hemp. When compared to the average jute and linen fibre, hemp fibre is much stronger. This makes hemp an ideal choice for making twines, cables and ropes.
Experts are constantly coming up with various uses of hemp-based products. Hemp products have the potential to replace commonly used commercial materials. By virtue of being eco-friendly, hemp products can go a long way in sustainable development.
Source –
https://hempgazette.com/industrial-hemp/hemp-fiber-production/
https://www.hempbasics.com/shop/general-hemp-information
http://www.madehow.com/Volume-6/Industrial-Hemp.html
http://www.hemptrade.ca/eguide/harvest-management/crop-condition-for-harvest
Thanks to the versatile nature of hemp products, the plant’s cultivation has a long-drawn history in the United States dating back to the times of the early colonists. The quality of hemp fibre is largely determined by the initial purpose for which it was first cultivated. That is to say, hemp plants are generally cultivated either exclusively for making textile fibres or for multi-purpose usage.
