Hemp fiber

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Hemp fiber
Hemp fibers
Fiber type

Natural fiber

origin

Industrial hemp

colour

gray, brown

characteristics
Fiber length Single fiber 5–55, avg. 25 mm; Fiber bundle 1–3 m
Fiber diameter 10–50 µm, avg. 25 µm
density 1.48 g / cm³
tensile strenght 310-390 N / mm²; other specification: 580 - 1110 N / mm²
modulus of elasticity 69 GPa
Elongation at break 1.6-2.7%
Water absorption 8% or 8.5-10%
Chemical resistance resistant to bases, not resistant to strong acids
Fabric made from hemp fiber

Hemp fibers are fibers from the bast of the hemp plant . The fibers of the industrial hemp varieties are used as fiber material for various applications. The oldest evidence of the use of hemp fibers goes back to approx. 2800 BC. BC back. Due to their properties, especially their strength, they were used for the production of canvas , ropes and hemp ropes well into the 20th century. Today they are also used in textiles, cellulose , paper and natural fiber-reinforced plastics . Fabric made from hemp fibers in a plain weaveis also referred to as "hemp linen", not to be confused with hemp linen (cord, rope).

Fiber structure, ingredients and properties

Hemp stem with fibers and woody interior

Hemp fibers form the outer layer of the stem and are arranged in several layers and as fiber bundles parallel to the stem axis and in a ring in the phloem . They consist of long bast fiber cells (elementary fibers ) arranged one above the other and next to one another . The bundles consist of 2 to 40 cell units, which are called primary fibers . The fibers in the inner bundles are usually shorter and finer than those of the outer fiber bundles. The individual cells have a diameter of 10 to 50 micrometers and lengths of 5 to 55 millimeters with an average of about 25 millimeters. They are more or less strongly connected by pectin substances , whereby a fiber bundle can reach a total length of one to three meters.

Male and female hemp plants differ in their fiber morphology and quality . The female plants have a longer growing season and form thicker and firmer fiber cells, while the proportion of primary fibers in the male plants is higher. Accordingly, the fibers of the male hemp plants are finer and can be woven into finer fabrics. Those of the female plants, on the other hand, are much stronger and can be used for coarser fabrics and ropes. Today fibers of both sexes are processed together for a medium fiber quality.

Ingredients of the fibers
ingredient percent
Cellulose 75.0
Hygroscopic water 10.0
Pectin , lignin 9.5
Mineral substance 0.8
Vegetable oil and wax 0.6
Water soluble
substances 		2.1
Other components 2.0

As the plant continues to grow, secondary fibers form, especially in the lower stem area , which increase the stability of the stem and, with an average length of two millimeters, are significantly shorter than the primary fibers . Modern industrial hemp varieties contain between 30 and 40% fiber, which means that yields of 1.5 to 2 tons per hectare of cultivated area can be achieved.

Depending on the state of maturity of the plant, the fibers consist of 60–70% cellulose and 10–20% hemicelluloses . These proportions can vary due to harvesting processes and subsequent production steps such as roasting and fiber opening up to the end product. Other substances in the fibers are pectins , lignin (2 to 5%), minerals, fats and waxes . The fiber contains more lignin than flax fiber and accordingly less cellulose. It is comparatively insensitive to chemicals: it is completely insensitive to bases and only strong acids can damage the fiber.

The mechanical properties of the hemp fiber may vary relatively strongly and are only given as mean values depending on the starting material, as with all natural products. The breaking strength of the hemp fiber is 23% a little higher than that of the comparable flax fiber and the specific breaking strength is about 30 breaking kilometers . The stretchability , on the other hand, is only two to three percent and the flexibility depends on the bundle structure and the fineness of the fibers. In yarns , strength and flexibility are increased by spinning hemp and flax fibers together and thus using the properties of both fibers. The water absorption capacity of the hemp fiber is around 8% of its own weight, without water escaping and the material feeling wet; It is to this property that hemp owes its importance as a material for ropes, ropes, nets and sailcloth in shipping. It is also very suitable as summer and winter clothing.

Fiber digestion

Hemp harvest

The hemp harvest for fiber production usually takes place during the flowering period of the male plants. The hemp fibers are separated from the rest of the plant by breaking and rolling the stems, this process is called fiber digestion . The hemp straw is separated into fibers and shives . Depending on the length of the fibers obtained in this way, a distinction is made between long fiber digestion and short fiber and total fiber line . The production of long fibers is the more complex, traditional digestion process, while the short fiber line is the more cost-effective alternative to the extraction of fibers for technical applications, primarily due to the lack of water roasting and the parallel position of the straw, as well as the extensive automation.

Long fiber digestion

Traditional long fiber digestion is only rarely used today and is mainly used in Eastern Europe , China and India . After harvesting, the hemp straw is laid out parallel to fiber production ( longitudinal fiber ) and dried. Drying is followed by roasting with water and renewed drying in the field. The straw, which is still lying parallel, is then broken and the long fibers are extracted by swinging and panting the straw, which should be 150 millimeters to 1500 millimeters in length as spinnable fibers . Shives from the broken wood core as well as tow and super short fibers or dust are produced as by-products of the long fibers . Processing long fibers causes high costs across the entire value chain . Above all, the high workload and the expensive use of machines make this processing unprofitable in countries with high personnel costs. Added to this are the ecological pollution caused by the roasting water and the very high failure rate of the fibers.

Short fiber and total fiber line

Short fibers are produced in modern digestion systems and optimized for technical use. As a pretreatment for the fiber breakdown of the short fiber and total fiber line, the hemp straw is cut and roasted in the field and then pressed into round and square bales; water roasting as with traditional long fiber processing is not required. The bales are fed to a fiber disintegration system in a random layer ( random fiber ) and opened. The straw is then broken in the crushing units, which are made up of toothed rollers of different sizes , to enable the fibers and wood core to be separated. In several steps, the wood components are separated from the fibers as shives, with the partially deforested straw being passed through pre-openers , cleaners , pre-dissolvers and finally shaking and needle opening units and thus broken up into smaller fiber bundles. The fiber bundles are further broken up and refined into individual fibers via further stage cleaning , rollers , carding devices and opening units .

The very strong mechanical stresses during the dissolution inevitably lead to damage to the hemp fibers, which can be different depending on the degree of ripeness and roasting. On average, the fiber losses as super short fibers or dust are 20% to 25%. There is no tow as a by-product, as all fibers are processed into short fibers.

Use and cultivation

Historical use

Hemp plants

The use of hemp fibers can be traced back over several millennia. The oldest finds come from China around 2800 BC. BC, where ropes were made from hemp fibers. The plant has been used since the Yangshao culture in the 4th millennium BC. Since about 900 BC In BC, hemp was also found in West Asia and India. The oldest textile fragment made of hemp fibers comes from a grave of the Zhou dynasty (1122–770 BC), near Ankara , hemp textiles from the 8th century BC were found. Found. Around 500 BC The cultivation of hemp for the area between China and the Caspian Sea can be assumed. In Europe, the manufacture of hemp textiles was also proven by grave finds; Here the oldest woven fragment comes from a Celtic burial mound near Stuttgart from a time around 500 BC. BC and another with processed hemp fibers from around the year 570 was found near Paris. Until the 3rd century BC Hemp found its way to Italy , especially in the form of ropes and similar products . For the late Middle Ages , a particular concentration of hemp cultivation can be observed in the Baltic States and the adjacent areas of Russia , Poland , Northern Germany and the Netherlands , Brittany and Burgundy . At that time, alongside flax, it was the most important industrial crop . It was also mostly grown with flax on smaller, garden-like areas. However, hemp was easier to process than flax. Because of its high tensile strength, it was mainly used to make sailcloth , ropes and sacks, but because of its coarseness, it was rarely made into cloth.

The oldest evidence of paper made from hemp fibers also comes from China from 140–87 BC. BC, making it the oldest paper find in China. Hemp paper became popular in China from around the year 105, but did not reach Europe via the Middle East until the 13th century . It was first detected in Germany in the 14th century.

Hemp rope

Hemp fibers reached their peak in use in the 17th century, when they were mainly used for the production of ropes and sailcloth for shipping; Many tons of hemp fiber were required for a normal sailing ship and the materials were replaced every two years on average. Until the 18th century, hemp fibers were the most important raw materials for the European textile industry, alongside flax , nettle and wool , with hemp mainly used in the manufacture of outerwear and workwear due to the coarser bundles of fibers. Hemp processing played a key role in textile processing before the introduction of cotton and other exotic fibers such as jute , sisal and ramie .

Above all, the development of cotton spinning machines in the 19th century and the cheap imports of cotton and jute, especially from Russia and Asia, ended the use of hemp and flax as textile fibers. At the same time, the demand in shipping also decreased, as many ships were converted to steam power and sailcloth was no longer needed. In papermaking, too, a cheaper alternative developed through the manufacture of paper from wood. The cultivation of hemp declined sharply in the 19th century and was only able to regain importance for a short time through the trade embargoes for exotic fibers during the world wars in Germany. After the Second World War , industrial hemp was only grown on very small areas. Between 1982 and 1995 the cultivation of hemp was completely banned by the Narcotics Act in Germany in order to prevent the illegal use of cannabis as an intoxicant . Although the industrial hemp grown in the 1950s and 1960s is harmless due to the almost complete lack of THC , its cultivation has been banned in Germany and many other countries. In France , the industrial hemp varieties continued to be used for the production of cigarette paper , and hemp continued to be grown on a small scale in several Eastern European countries. The most important producer of hemp fibers at this time was the Soviet Union with 140,000 hectares of hemp cultivation area, which, however, had been reduced to 40,000 hectares by 1990. Cultivation in Romania , Poland, Hungary and the former Yugoslavia was also important .

In the 1990s, the bans were withdrawn due to the growing interest of agriculture and industry in the raw material and in 1996 hemp was again allowed to be grown in Germany. Today the cultivation of low-THC industrial hemp varieties is legalized in all European countries as well as in countries such as Canada and Australia , only in the USA the cultivation is still completely prohibited.

Usage today

Inner door trim made of hemp fiber reinforced plastic (matrix polyethylene PE)
Hemp fiber trousers

The worldwide cultivation areas for industrial hemp are around 60,000 to 100,000 hectares today and vary greatly from year to year. For 2005, the global cultivation area was estimated at around 115,000 hectares, of which around 80,000 hectares in Asia (mainly China and North Korea ), 14,000 hectares in EU countries , 5,700 hectares in other European countries, 10,000 hectares in North America (excluding Canada), 4,300 hectares are in South America and 250 hectares in Australia. The leading growing countries are China, Russia, Canada and France, while in other countries the cultivation is rather low.

In Europe, until the beginning of the 1990s, hemp was grown almost exclusively in France (around 6,000 hectares) and used for the production of cigarette paper, while small exports came from Spain to France. Especially in the search for alternatives to the stagnating and sometimes declining food cultivation on increasingly fallow agricultural land , hemp, like other renewable raw materials, was promoted across Europe after the ban on cultivation was abolished ; at the same time, hemp gained increasing scientific and economic backing as a useful plant, including through various book publications the hemp plant. By 1998, the cultivation of industrial hemp in Europe (excluding Spain) quadrupled to almost 40,000 hectares. In Spain from 1997 to 1999 high cultivation figures of up to 20,000 hectares were achieved through premium payments, but most of the subsidized harvest was not processed. In 2006, around 14,000 hectares of industrial hemp were grown in the countries of the European Union , 8,000 of them in France alone and over 1,000 each in Germany, Great Britain and the Czech Republic . Forecasts assume that hemp cultivation will increase to around 20,000 hectares across Europe due to the increasing demand for hemp fiber-reinforced materials and insulation material as well as the price increases for exotic fibers.

Long hemp fibers are almost exclusively used in the production of textiles today. They are very tear-resistant and are particularly suitable for the clothing industry. Hemp textiles achieve better values ​​for abrasion resistance than cotton textiles and therefore also have a longer service life. A classic application for the tow as a loose long fiber material is the sealing when screwing pipe threads .

Due to their low tendency to rot , harmless to health and resistance to pests, hemp fibers are used as insulation , e.g. B. for house building, well suited and popular. Today, short fibers are also used in cellulose , nonwovens , such as rearing nonwovens for cress seeds , special papers and natural fiber-reinforced plastics . One focus is the use of hemp fibers in automobile construction, where they are used as reinforcement for plastics for door and trunk linings . Above all, the further expansion of the insulation market and the use of natural fiber-reinforced plastics outside the automotive industry are currently determining the growth of the European hemp market. For example, they are used in the production of suitcases, laptop cases and grinding wheels . Today, these plastics are no longer used solely for their mechanical properties , but are also used as design elements, for example in the Eco Elise from Lotus Cars presented in July 2008 . Cubic cannon strokes are bandaged with hemp splits .

  • Insulation block made of hemp fibers

  • Hemp fabric sack, Japan

  • B-pillar made of hemp fiber reinforced plastic (matrix polypropylene PP)

  • Glove box made of hemp fiber reinforced plastic (matrix polypropylene PP)

Byproducts

Shives

In the production of hemp fibers are obtained as by-product scrapings on. They are the remains of the woody parts of the plant that cannot be used for fiber production. They occur in large quantities and thus have a significant share in the added value in hemp fiber processing. The 31,000 tons of hemp shives, which were produced by European hemp farmers in 2003, are mainly used as bedding . Horse owners particularly appreciate the absorbency and easy compostability of the hemp litter. The shives can also be used as a building material, mixed with quicklime and sand .

The super short fibers with their length from a few millimeters to one centimeter are by-products or losses of the hemp fiber digestion. As a rule, they cannot be used like short fibers. Super-short fibers are primarily added to cattle feed as dietary fiber ; an alternative use is their use as reinforcement fibers in injection-molded plastics .

Full products of industrial hemp in addition to fiber are hemp seeds , hemp oil and essential hemp oil .

literature

Web links

Individual evidence

  1. ↑ a b c d e f g h Comparative physical, chemical and morphological characteristics of certain fibers. In: Robert R. Franck (Ed.): Bast and other plant fibers. Woodhead Publishing, Cambridge 2005, pp. 4-23.
  2. ↑ Menachem Lewin (Ed.): Handbook of Fiber Chemistry. Third edition. Taylor & Francis Group, Boca Raton 2007, ISBN 978-0-8247-2565-5 , p. 498
  3. ↑ a b c d e Heyland u. a.
  4. ↑ a b c Peter Schütt : Weltwirtschaftspflanzen. Paul Parey Publishing House, Berlin / Hamburg 1972, ISBN 978-3-489-78010-6 , p. 156.
  5. ↑ a b J. Sponner, L. Toth, S. Cziger, R. R. Franck: Hemp. In: Robert R. Franck (Ed.): Bast and other plant fibers. Woodhead Publishing, Cambridge 2005, pp. 176-206.
  6. ↑ nova Institute.
  7. ↑ Hemp . In: Hans Zoebelein (Ed.): Dictionary of Renewable Resources. 2nd Edition. Wiley-VCH, Weinheim / New York 1996, ISBN 3-527-30114-3 , p. 137.
  8. ↑ on the early days , see: Jürgen Schultze-Motel: Hanf. In: Lexicon of Early Cultures Vol. 1: A - L , Pahl-Rugenstein, 1984, ISBN 3-7609-0913-2 , p. 344.
  9. ↑ on antiquity , see: Christian Hünemörder : Hanf . In: The New Pauly . Vol. 5, 1998, p. 151 f.
  10. ↑ on the Middle Ages , see: Christian Reinicke: Hanf . In: Lexicon of the Middle Ages . Vol. 4, 1999, p. 1918 f.
  11. ↑ W. Hingst, H. Mackwitz: Reiz-lingerie. Our clothes: fashion, poisons, eco-look. Campus-Verlag, Frankfurt 1996, ISBN 978-3-593-35471-2 .
  12. ↑ Second law amending the Narcotics Act (Second BtMG Amendment Act - 2nd BtMG-Amendment Act)
  13. ↑ Bócsa: pp. 11-20, and Carus: pp. 17-21.
  14. ↑ Carus: Worldwide cultivation areas for hemp in 2005 (estimate). P. 34.
  15. ↑ especially Jack Herer: The Emperor Wears no Clothes . The Authoritative Historical Record of Cannabis and the Conspiracy Against Marijuana. Ah Ha Publishing, Van Nuys 1985, ISBN 1-878125-00-1 ; 1 edition in Germany 1993 as Hemp & The Marijuana Conspiracy: The Emperor Wears no Clothes ISBN 0-9524560-0-1 and German, extended translation Hemp - The rediscovery of the useful plant hemp, cannabis, marijuana. Heyne, 1996, ISBN 978-3-453-11566-8 .
  16. ↑ a b c Carus: Hemp cultivation in the EU. Pp. 25-28.
  17. ↑ Carus: Hanf - A Historical Contemplation P. 17–21.
  18. ↑ Lotus Eco Elise: Lightweight with natural materials . Auto-News.de
This version was added to the list of articles worth reading on August 1, 2008 .