Hemp hurds, also known as shives or hemp wood, are an agricultural product made from hemp. Hurds consist of "the woody inner portion of the hemp stalk, broken into pieces and separated from the fiber in the processes of breaking and scutching" and "correspond to the shives in flax, but are coarser and usually softer in texture". Hurds have traditionally been a by-product of fiber production.
Decortication separates bast fiber from the hurd. The fine bast fiber is used to make textiles. Decortication is accomplished by manually crushing, a labor-intensive process, or by a hemp decorticator machine.
Hurds can be used as stock in papermaking; particleboard, hempcrete, and other construction composites; or bedding for animals, particularly in horse stalls, which is the most common use (by weight) in Europe.
Development of water-repellent coatings
Hemp shiv is a renewable organic raw material used for the production of insulation boards. The use of biomaterials for insulation boards in walls is attracting increasing interest, but wider acceptance in the construction industry has so far been slowed-down by adverse material properties. Because such materials consist mainly from cellulose, they are flammable and their hydrophilic surface leads to high water uptake, which can lead to mold or rot.
Therefore, engineering studies have investigated whether a coating with a water-repellent thin film provides the desired benefits. For the hydrophobic coating with silica particles, a colloidal sol-gel dispersion was successfully synthesized by the Stöber process, characterized and deposited on hemp shiv. These samples passed a 72-hour test in the humidity chamber without loss of their hydrophobic property and no signs of mold growth.
When the hemp shiv was coated several times with functionalized silica particles, uniform and complete coverage of the surface was achieved. Such a treatment provided the hemp shiv with a comprehensive water repellency: The hydrophilic character of the untreated hemp shiv was modified to durably hydrophobic, once the bio-materials were coated with functionalised silica particles. Mould growth was delayed when exposed to humidity, whilst the liquid water repellent property of the treated hemp shiv was maintained despite the humid conditions. The treatment developed in this study could be a viable solution for use on bio-materials that need to repel liquid water, whilst preserving the integrity of the insulation panel in common environmental conditions. There are of course still further tests to be carried out before adopting this treatment in the construction sector, such as additional moisture tests, mechanical tests, biodegradation tests, etc. However, the promising results described here give a good first assessment of feasibility. Before being fully adopted in the construction sector, these treatments and materials must be fully tested in accordance with the building codes. In addition, with the recent recent use of biomaterials, new standards and test methods for these specific materials should be developed.
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- Nadjla Mostefai, Rabah Hamzaoui, Sofiane Guessasma, Amadou Aw and Hedi Nouri: Microstructure and mechanical performance of modified hemp fibre and shiv mortars: Discovering the optimal formulation. In: Materials & Design, Volume 84, 5 November 2015, Pages 359-371. DOI: 10.1016/j.matdes.2015.06.102.
- 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, 15 March 2018, Pages 850-860 DOI: 10.1016/j.apsusc.2017.10.210
- Stephan W. Kallee: Entwicklung von wasserabweisenden Siliciumdioxid-Partikeln zum Schutz von Hanfschnittgut als Isoliermaterial. German translation of an English Open Access article 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 21 December 2017, retrieved on 25 November 2017. DOI: 10.3390/ma11010004. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
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- Media related to Hemp shives at Wikimedia Commons