Shives

Hemp shives

As shives (singular: shiv) are referred to the relatively evenly broken, similar to wood particles in the production of bast fibers , especially flax - or hemp fibers , in the mechanical process of delignification of (decortication) plant stem incurred. They come from the woody core of the stem, which is surrounded by the fibers. Their length varies from less than one to a few centimeters. They are a by- product or by- product of fiber production that is mainly used as animal bedding .

Ingredients and properties

Shives make up around 50 to 60 percent of the stalk of hemp, while the proportion of shives is lower at 45 to 55 percent in flax. This makes them the most extensive product of fiber digestion in terms of quantity. Hemp shives have an elongated shape and are made up of around 35 percent cellulose , 18 percent hemicellulose and 21 percent lignin . Proteins , pectins and carbohydrates are about 18 percent in total, the water content of dry hemp shives is less than 10 percent.

Hemp shives can absorb up to four times their own weight in moisture and are easily compostable. Compared to other natural fiber materials, shives are characterized by their low weight, high porosity and thus a high insulating effect and high elasticity .

During the processing process, five fractions or qualities arise with hemp:

1. Thirty to forty percent coarser, slightly darker shives
2. Thirty to thirty-five percent smaller, almost fiber-free, light-colored shives
3. Ten to fifteen percent very small shives
4. Five to ten percent dust and fiber residues
5. Five to ten percent waste

High quality shives are light and ivory in color. The color can shift into dark gray due to mold growth and roasting, which means that the shives lose their value.

Extraction

Hemp stalks; the woody core is broken into pieces when broken

→ Main article : fiber digestion

Shives are produced in the extraction of flax and hemp fibers in addition to tow and super short fibers or dust. The roasted and dried plant stems (straw) are separated into fibers and shives in a fiber digestion system. This digestion is usually done purely mechanically: The lignified inner part of the straw is broken, creating the shives, which are then separated from the fibers in several process steps. The shives are produced or extracted differently depending on the fiber digestion technology used. The higher the proportion of shives that are produced during fiber production, the lower the proportion of shives in the product “fiber” (with the same plant material).

As a cleaned product, shives are a marketable product, whereas in the flax or hemp fiber itself, a lower shives content is usually aimed for. In the case of technical short fibers, from which nonwovens , felts and composite materials are made, shives contents of a maximum of five percent can be tolerated, which can be achieved through production in the so-called random fiber line . If a shives content of up to 25 percent is tolerated , as is the case with hemp fibers for pulp production , simpler technologies such as hammer mills can be used.

Applications

Hemp shives lightweight panel

Historically, shives were mainly used as fuel and for chipboard or lightweight board production. Today, cleaned and dedusted hemp and flax shives are mainly used in animal husbandry because of their high water absorption capacity and their compostability. Larger shives are mostly used as horse litter, while smaller, light-colored shives are used in keeping small animals. Very small shives are used in poultry farming and - after pelleting - as cat litter. The high cellulose fiber residues and dusts are used as a fiber-rich extender in animal feed. The waste is used as organic fertilizer or pressed into briquettes and incinerated.

Hemp shives are also used as filler , low-quality cellulose , bio-fuel or in construction and insulation materials. In chipboard , shives are advantageous because of their low weight - the density of shives, at 300 to 340 kilograms per cubic meter, is less than half that of commercially available chipboard. Mixtures of shives with bitumen and cork have been on the market as bulk insulation for floors since 1957 - the good impact sound insulation due to the high elasticity of the shives favors this application. Other uses in the construction sector are as an aggregate in clay and lime as well as in hemp shives. Pre-treated shives can serve as a substitute for peat in potting soil.

In 2006, 70 percent of the hemp shives produced in Europe were used as litter for animals, around 87 percent of which went to horse owners. Applications in the construction sector were less important with 16 percent and incineration for energy generation with 8 percent. While 4 percent of the shives were used as tools in horticulture, the growing market for material panels only accounted for 1 percent of sales. Flax shives have similar sales markets as hemp shives. However, shives from flax processing in France and Belgium, the main European processing countries, go to the chipboard industry in large quantities and are only used to a lesser extent as animal bedding.

Development of water-repellent coatings

Colored water droplets on hemp shives coated with silicon dioxide as an insulating material. The 130 ° water contact angle shows the water-repellent effect of the coating.

Hemp shives are already used industrially for the production of insulation boards. The use of biomaterials for insulation panels in walls is attracting increasing interest, but its wider acceptance in the construction industry has so far been hampered by disadvantageous material properties. Since such materials are mainly made of cellulose, they are flammable and their hydrophilic surface leads to high water absorption, which can lead to mold or rot.

For this reason, engineering research was carried out to determine whether a coating with water-repellent silicon dioxide particles would bring the desired advantages. For the hydrophobic coating with silicon dioxide particles, a colloidal sol-gel dispersion was successfully synthesized using the Stöber process, characterized and deposited on hemp shives. These samples passed a 72 hour test in the humidity chamber with no loss of their hydrophobic nature and no evidence of mold growth.

By repeatedly coating hemp shives with functionalized silicon dioxide particles, an even and complete coverage of the surface was achieved. This made the hemp shives water-repellent: the hydrophilic character of the untreated hemp shives was permanently hydrophobized after the biomaterials were coated with functionalized silicon dioxide particles. The growth of mold was delayed when it was exposed to moisture, while the water-repellent properties of the treated hemp shives were retained despite the damp conditions. The treatment developed in this study could be a viable solution for using biomaterials that need to repel liquid water while maintaining the integrity of the insulation panel under normal ambient conditions. Of course, there are other tests that need to be done before this treatment is done in the construction sector, such as additional moisture tests, mechanical tests, biodegradation tests. The results of the study are promising. Before being fully adopted in the construction sector, the treatment procedures and materials must be fully checked according to the building regulations. In addition, given the recent use of biomaterials, new standards and test methods for these materials should be developed.

Economic importance, market development

Shives production (flax and hemp) in the EU

Depending on the type of plant and the pulping fibers, shives are an economically subordinate by-product or a co-product of hemp and flax fiber production that is economically equal to the main product natural fiber. In the production of high-quality flax long fibers, shives as well as short fibers are considered by-products, which together have to generate a comparatively low added value, hemp shives in the widespread random fiber line are economically roughly equivalent to the main product hemp fiber. They have about half the value of hemp short fibers per unit weight, but are about twice as much.

In 2004, around 370,000 tons of flax shives and around 45,000 tons of hemp shives were produced in the European Union (EU). In line with the importance of hemp and flax processing, France and Belgium are the main producing countries for flax shives in the EU, with Germany following France a long way behind when it comes to hemp shives.

Energy demand

The primary energy input required for the production of hemp shives is given as around 2.5 megajoules per kilogram of shives (this corresponds to around 0.7 kWh), with the energy consumption for the production of fibers and shives being calculated based on the market value of the products. Around two thirds of the energy consumption is used in hemp cultivation (fertilization and use of machines).

Trivia

If the shives are not completely removed when the fibers are broken down, the result is an inferior fiber known as “shabby”. This word - detached from its original meaning - entered common usage as a derogatory term.

supporting documents

literature

• Michael Carus et al .: Study on the market and competitive situation for natural fibers and natural fiber materials (Germany and EU) . Ed .: Fachagentur Nachwachsende Rohstoffe e. V. (=  Gülzower technical discussions series of publications . Volume 26 ). Die Werkstatt, Gülzow 2008 ( online [PDF; 10.0 MB ; accessed on August 20, 2012]).

Individual evidence

Most of the information in this article has been taken from the sources given under literature; the following sources are also cited:

1. ↑ Duden: The German orthography. 24th edition, Duden-Verlag, 2006. ISBN 3-411-04014-9
2. ↑ ^{a b c} Michael Carus et al: "Study on the market and competitive situation for natural fibers and natural fiber materials (Germany and EU)." 2008, p. 42.
3. ↑ ^{a b c} Stephan W. Kallee: Development of water-repellent silicon dioxide particles to protect hemp shives as insulating material. German translation of the English publication by Marion A. Bourebrab, Géraldine G. Durand and Alan Taylor: Development of Highly Repellent Silica Particles for Protection of Hemp Shiv Used as Insulation Materials, published on December 21, 2017, accessed on November 25, 2018. DOI : 10.3390 / ma11010004 .
4. ↑ CAVAC Biomaterials: Applications.
5. ↑ Mahmoud Khazma, Adeline Goullieux, Rose-Marie Dheilly and Michèle Quéneudec: Coating of a lignocellulosic aggregate with pectin / polyethylenimin mixtures: Effects on flax shive and cement-shive composite properties. In: Cement and Concrete Composites , Volume 34, Issue 2, February 2012, pp. 223-230 DOI: 10.1016 / j.cemconcomp.2011.07.008 .
6. ↑ Nadjla Mostefai, Rabah Hamzaoui, Sofiane Guessasma, Amadou Aw and Hedi Nouri: Microstructure and mechanical performance of modified hemp fiber and shiv mortars: Discovering the optimal formulation. In: Materials & Design , Volume 84, November 5, 2015, pp. 359–371. DOI: 10.1016 / j.matdes.2015.06.102 .
7. ^ Atif Hussain, Juliana Calabria-Holley, Diane Schorr, Yunhong Jiang, Mike Lawrence and Pierre Blanchet: Hydrophobicity of hemp shiv treated with sol-gel coatings. In: Applied Surface Science. Volume 434, March 15, 2018, pp. 850-860. DOI: 10.1016 / j.apsusc. 2017.10.210

Web links

Wiktionary: Schänke  - explanations of meanings, word origins , synonyms, translations

This version was added to the list of articles worth reading on August 1, 2008 .