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Extraction, processing, properties and use of hemp fiber

Natural and organic fibers become more and more popular these years. Most of the people come to realize that nature, soft and healthy are the most important things of the textile. Hemp fiber is naturally one of the most environmentally friendly fibers and also the oldest. The Columbia history of the world states that the oldest relics of human industry are bits of Hemp fabric discovered in tombs dating back to approximately 8000 B.C.

Hemp is called a fiber of hundred uses. The significance of Hemp to the economic and day to day lives of our ancestors is increasingly being recognized. It was important for textile, paper, rope and oil production. Indeed, Hemp was so important in England in the sixteenth century that King Henry VIII passed an act on parliament which fined farmers who failed to grow the crop. Besides fabrics, Hemp is also used in the production of paper. The oldest piece of paper – over 2000 yrs old – was discovered in China and is made from Hemp. Until 1883, between 75% and 90% of all paper in the world was made with Hemp fiber. Hemp paper can also be recycled more times than wood-based paper.

Erica McBride and Geoff Whaling of the Pennsylvania Hemp Industry Council check the growth in a hemp field near Bethlehem
Figure 1: Erica McBride and Geoff Whaling of the Pennsylvania Hemp Industry Council check the growth in a hemp field near Bethlehem. The picture is credited to www.whyy.org.

Hemp is a bast fiber plant similar to Flax, Kenaf, Jute, and Ramie. Long slender primary fibers on the outer portion of the stalk characterize bast fiber plants. It was probably used first in Asia. Hemp is also one of the bast fibers known to ancient Asians, long before the birth of Christ.

The primary hemp fiber is attached to the core fiber by Pectin – a glue-like soluble gelatinous carbohydrate. The primary hemp fibers can be used for composites, reinforcements, and specialty pulp and paper. The wood-like core Hemp fiber can be used for animal bedding, garden mulch, fuel and an assortment of building materials. Hemp also produces an oil seed that contains between 25 to 35% oil by weight, which is high in essential fatty acids considered to be necessary to maintain health.

The composition of Hemp
Table 1: The composition of Hemp.

Hemp (Cannabis sativa) could be an important crop enabling the production of environmentally – friendly, locally produced, high-quality textiles.  Hemp is an annual plant that grows from seed. It can be grown on a range of soils but tends to grow best on land that produces high yields of corn. The soil must be well drained, rich in nitrogen, and non-acidic. Hemp requires limited pesticides because it grows so quickly and attracts few pests. Hemp is a traditional fiber crop which for centuries was important in meeting our needs for textiles, paper, and oils. It is easy to grow organically. That is, without a need for artificial pesticides, herbicides or fertilizers, so it can make an important contribution to a sustainable future. The production of cotton, on the other hand, needs a lot of pesticides.

Hemp is environmentally friendly in many ways. It can displace the use of cotton, which requires a massive amount of chemicals harmful to people and the environment. The production of cotton consumes 50% of the pesticides sprayed in the entire world. Hemp has a deep root system that helps to prevent soil erosion, removes toxins, provides a disease break, and aerates the soil to the benefit of future crops.  True hemp is a fine, light-colored, lustrous, and strong bast fiber, obtained from the hemp plant, “cannabis sativa.” It is a plant similar to jute, grown in many countries. When spun, it is rather like flax but thicker and coarser. It is a very strong fiber and is used in the manufacture of carpets, rugs, ropes etc., but has limited use because bleaching is difficult.

Hemp is a renewable resource which grows more quickly and easily than trees making hemp more cost effective than waiting decades for trees to grow to be used in man-made fiber products such as Lyocell and Rayon from wood pulps. The bark of the hemp stalk contains bast fibers, which are among the earth’s longest natural soft fibers and also rich in cellulose.

The term “Hemp” is often incorrectly used in a generic sense for fibers from different plants eg; Manila “Hemp”, Sisal “Hemp”, Sunn “Hemp” etc. Hemp is grown in countries like Canada, USA, France, Hungary, Belgium, Holland, Thailand, Austria, Italy, China, Philippine island, Russia, Mexico, Germany, West Indies and India.  In India, Deccan Hemp is grown both as crop and hedge plant. It is cultivated largely in Maharastra, Tamil Nadu, and north Gujarat.  It can be grown in all temperature and tropical countries of the world.  Currently, the bulk of our demand for textiles is met by cotton and synthetics, both of which have serious environmental problems associated with them.

Following are the steps required for Hemp processing in textiles.

  1. Retting – Harvesting is done with a conventional combine harvester machine. Once cut, the plants, which are composed of two types of fiber – long outer fibers suitable for textiles, and short inner fiber suitable for paper or industrial applications – are left in the field for about 10 to 20 days to ‘ret’.                          

Retting is of two types.

  • Water Retting– It involves lying the stems in water in tanks, ponds or in streams for around 10 days–it is more effective if the water is warm and bacteria-laden.
  • Dew Retting– It is a natural process that is triggered by dew that falls on the crop each morning. After cutting, the hemp stems were laid parallel in rows to dew ret. The stems needed turning at least once (sometimes) twice in order to allow for even Retting (or rotting) being the name given to the process whereby bacteria and fungi is break down the pectins that bind the fibers to the stem allowing the fiber to be released. Retting is complete when the fiber bundles appear white, separate from the woody core and divide easily into individual finer fibers for their full length. Once this process is complete (dry), the stalks are collected and sent to the “decortication” machine. The major Hemp varieties are called F 34, F 56, Uniko BF and Kompolti.

2. Decortication– In this process the de-leafed Hemp stems are then dried, i.e. conditioned and freed from the wood kernel in a sequence of a squeeze, break and scutching processes. In other words, it is described as breaking the stems by passing through a “breaker” or fluted rollers. Then the fiber is separated from the woody core (“scotching”) by beating the broken stems with a beech stick or passing through rotary blades.

3. Softening– By using a so-called Hemp softener or roller, the decorticated fibers are made softer and suppler.

4. Combing– The shortening of the initial fiber lengths from up to 3 m down to 650 mm is done on a special cutting machine. Then the short and tangled fibers are combed out, the long fibers are parallelized and smoothed using a hackling machine. In other words “hackling” (combing) means to remove any woody particles and to further align the fibers into a continuous “sliver” for spinning.

5. Spinning– After several drawing and doubling passages, the manufactured slivers are pre-spun roving yarns and according to quality and the desired yarn fineness, spun into Hemp yarn by wet or dry spinning processes. Although as Hemp is coarser than Flax, the pins on the board for drafting the combed fiber into a sliver needed to be set differently. The rove produced was then boiled in caustic soda to refine it and most of the yarn was bleached with hydrogen peroxide. As it is similar to Flax fibers, generally the best yarns are obtained by wet spinning. In which fibers are allowed to pass through a trough of hot water before being spun. This softens the Pectin allowing a greater drawing out and separation of the fibers and producing a finer yarn (greater than 12 Nm). Dry spinning is cheaper, producing yarns and fabrics with a different appearance and handle.  Using the above process two types of 100% Hemp yarn is made known as long yarn and short yarn. Normally the counts are Nm 7/1, Nm 8.5/1, Nm 10/1, Nm 16/1, Nm 18/1, Nm 24/1 and Nm 36/1.

The above preparatory processing of Hemp fiber incur considerable waste and add significantly to the cost of the fiber which could be made available as a raw textile fiber for 3500 USD /tons.  The Hemp was successfully processed to produce nonaligned fibers, with a yield of 20-25%.

Properties of Hemp fiber

Hemp fiber is dark tan or brown and is difficult to bleach, but it can be dyed bright and dark colors. Hemp fiber is a lustrous fiber, has characteristic nodes and joints of linen, but the central canal is wider. The cells are blunt-ended when the fiber is viewed under a microscope. The Hemp fibers vary widely in length, depending upon their ultimate use. Industrial fibers may be several inches long, while fibers used for domestic textiles are about a ¾ inch to 1 inch (1.9 to 2.54 cm) long. The elongation (1 to 6%) is low and its elasticity poor. The thermal reactions of Hemp and the effect of sunlight are the same as for Cotton. Hemp is moth resistant, but it is not impervious to mildew. Furthermore, Hemp has the best ratio of the heat capacity of all fibers giving it superior insulation properties. As a fabric, Hemp provides all the warmth and softness of other natural textiles but with a superior durability seldom found in other materials. Natural organic Hemp fiber “breathes” and is biodegradable.

Hemp fiber is longer, stronger, more absorbent, more mildew resistant and more insulative than Cotton fiber. There are thirty varieties of Hemp fiber. It is a tall plant with a natural woody fiber. All these varieties resemble one another in general appearance and properties, but only those having fibers of high tensile strength, fineness, and high luster have commercial value. It resembles flax closely, and its fiber is easily mistaken for linen. Hemp is harsh and stiff and cannot be bleached without harm to the fiber. As Hemp is not pliable and elastic, it cannot be woven into fine fabrics. Hemp is durable and is used in rug and carpet manufacturing. It is especially suitable for ship cordage as it is not weakened or rotted by water, this means that Hemp will keep you warmer in winter and cooler in summer than Cotton. Hemp is more effective at blocking the sun‘s harmful ultraviolet rays. The nature of Hemp fibers make them more absorbent to reactive dyes, vat dyes and sulfur dyes, which coupled with Hemp’s ability to better screen out ultraviolet rays, means that Hemp material is less prone to fading than cotton fabrics are.

Cotton was known for their naturalness but look at the comparison
Table 2: Cotton was known for their naturalness but look at the comparison.

The blending of Hemp fiber   

Like Cotton, Hemp can be made into a variety of fabrics, including high-quality Linen. When blended with materials such as Cotton, Linen, and Silk. Hemp provides a sturdier, longer lasting product while maintaining quality and softness.

Hemp Active, an Austrian company supplies Hemp blended yarn which is made of Hemp with cotton/organic cotton. Nowadays few mills in Europe are making Hemp/Polyester 60/40 blends and Hemp/Wool/Polyester 40/40/20 blends.

Hemp Textiles Intl., Canada supplies blend of Hemp/Wool 50/50. Hemp blended with other fibers easily incorporate the desirable qualities of both textiles. When combined with the natural strength of Hemp, the soft elasticity of Cotton or the smooth texture of Silk creates a whole new genre of fashion design.

Uses of Hemp fiber

Coarse Hemp fibers and yarns are woven into cordage, rope, sacking and heavy –duty tarpaulins. In Italy, fine Hemp fibers are used for interior design and apparel fabrics. Hemp is used in tapestry, hats, shawls, rugs, posters, and towel.

Dyed hemp yarn from Hungary is suitable for rug weaving, placemats, crochet and other craft items. It has been found that 3 plies, 6 plies, and 12 plies are used for weaving, knitting or crochet. Hemp is stronger than linen and jute fiber, hence it is ideal for making twine, ropes, cables, carpets, canvas, ship cordage, sailcloth, etc. Central American Hemp is chiefly used for cordage. Manila “Hemp” is a fiber from the leaves of the Abaca plant; it is very strong, fine, white, lustrous and, though brittle, it is adaptable for the weaving of coarse fabrics.

Lastly, more research work has to be done on Hemp fiber like scouring/bleaching using enzymes without affecting the strength of the fiber.

Trials can be taken in cotton and synthetic spinning by adding Hemp fiber in many value-added items and make various types of fancy yarn which can be sold in the market at a premium rate.

Acknowledgment The author is thankful to Mr. Subhash Bhargava FSDC (UK) MD, Colorant Ltd., Ahmedabad for giving permission to publish this article.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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