rice hull

{{Short description|Protective husk of rice grains}}

Image:rice chaffs.jpg

Rice hulls or husks are the hard protecting coverings of grains of rice. In addition to protecting rice during the growing season, rice hulls can be put to use as building material, fertilizer, insulation material, or fuel. Rice hulls are part of the chaff of the rice.

Production

Rice hulls are part of the rice seed. The hull protects the grain during the growing season from pests. The hull is formed from hard materials, including opaline silica and lignin. The hull is hard to eat or swallow (unless finely ground) and mostly indigestible to humans because of its enriched fibre components. However, during times of food scarcity in ancient China, a common daily meal was a pastry made from rice husks, wild vegetables, and soybean powder. This led to the idiom "meals of cereal, hulls, and vegetables for half a year", indicating poverty and food insecurity.{{citation needed|date=June 2020}} Testing and commercialization of human grade anti-caking agents were done in the early 2000s. The material is approved for use in USDA Certified Organic products to replace silicon dioxide.{{fact|date=May 2024}}

Winnowing, used to separate the rice from hulls, consists of putting the whole rice into a pan and throwing it into the air while the wind blows. The light hulls are blown away while the heavy rice falls back into the pan. Later, pestles and a simple machine called a rice pounder were developed to remove hulls. In 1885 the modern rice hulling machine was invented in Brazil. During the milling processes, the hulls are removed from the raw grain to reveal whole brown rice, which is then usually milled further to remove the bran layer, resulting in white rice.

Uses

{{stack|File:Bata Candi-candi Batujaya.JPG in Indonesia (5th century CE) were built with bricks containing rice hulls.]]}}

=Ash=

Combustion of rice hulls affords rice husk ash (acronym RHA). This ash is a potential source of amorphous reactive silica, which has a variety of applications in materials science. Most of the ash is used in the production of Portland cement.{{cite book |first1=Otto W. |last1=Flörke |display-authors=etal |chapter=Silica |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2008 |location=Weinheim |publisher=Wiley-VCH |doi=10.1002/14356007.a23_583.pub3 |isbn=978-3-527-30385-4 }} When burnt completely, the ash can have a Blaine number of as much as 3,600 compared to the Blaine number of cement (between 2,800 and 3,000), meaning it is finer than cement. Silica is the basic component of sand, which is used with cement for plastering and concreting. This fine silica will provide a very compact concrete. The ash also is a very good thermal insulation material. The fineness of the ash also makes it a very good candidate for sealing fine cracks in civil structures, where it can penetrate deeper than the conventional cement sand mixture.{{fact|date=May 2024}}

Rice husk ash has long been used in ceramic glazes in rice-growing regions in the Far East, such as China and Japan.{{cite book |last1=Tichane |first1=Robert |title=Ash Glazes |date=1998 |publisher=Krause Publications |isbn=0873416600 |url=https://books.google.com/books?id=oPLh75SOqI0C&pg=PA34}} Being about 95% silica, it is an easy way of introducing the necessary silica into the glaze, and the small particle size helps with early melting of the glaze.{{fact|date=May 2024}}

Possible uses for RHA include absorbents for oils and chemicals, soil ameliorants, a source of silicon, insulation powder in steel mills, repellents in the form of "vinegar-tar" release agent in the ceramics industry, and as an insulation material.

More specialized applications include use as a catalyst support.J. Chumee et al. "Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation" Sci. Technol. Adv. Mater. 9 (2008) 015006 [https://dx.doi.org/10.1088/1468-6996/10/1/015006 free download]

Goodyear announced plans to use rice husk ash as a source for tire additive.{{cite web|url=http://www.goodyear.com/cfmx/web/corporate/media/news/story.cfm?a_id%3D1028 |title=Goodyear Converts Waste from Rice Harvest to Fuel-Efficient Tire Treads |access-date=February 9, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150124021752/http://www.goodyear.com/cfmx/web/corporate/media/news/story.cfm?a_id=1028 |archive-date=January 24, 2015 }}{{cite AV media | date = 2015-06-09 | title = Goodyear Reaches Supply Agreements for Rice Husk Ash Silica | medium = YouTube | language = en | url = https://www.youtube.com/watch?v=iYwUyLplByE | access-date = 2016-05-26 | format = Online video | publisher = Goodyear Tire and Rubber Company}}

Rice hulls are a low-cost material from which silicon carbide "whiskers" can be manufactured. The SiC whiskers are then used to reinforce ceramic cutting tools, increasing their strength tenfold.{{cite web |url=http://www.ms.ornl.gov/researchgroups/process/cpg/sic.htm |title=SiC Whisker-Reinforced Ceramic Composites |work=Materials Science and Technology Division - Physical Sciences Directorate|archive-url=https://web.archive.org/web/20090816181003/http://www.ms.ornl.gov/researchgroups/process/cpg/sic.htm |archive-date=2009-08-16 |publisher=Oak Ridge National Laboratory |location=Oak Ridge, TN, USA |access-date=2013-06-06}}

=Tooth powder=

In southern India, charred rice hull, known as umikkari in Malayalam and Tamil, was traditionally used for cleaning teeth before the advent of toothpaste.{{Cite web |title=ഉമിക്കരി ഉപയോഗിച്ച് പല്ല് തേക്കുന്നത് നല്ലതാണോ? |url=https://malayalam.samayam.com/lifestyle/health/is-it-good-to-brush-your-teeth-with-charcoal/articleshow/100851136.cms |access-date=2024-06-05 |website=Samayam Malayalam |language=ml}}

=Rice bran oil=

{{Main|Rice bran oil}}

Rice bran oil is the oil extracted from the hard outer brown layer of rice called chaff (rice husk). It is popular as a cooking oil in the Indian subcontinent and East Asian countries, including India, Nepal, Bangladesh, Indonesia, Japan, Southern China, and Malaysia.{{fact|date=May 2024}}

=Brewing=

Rice hulls can be used in brewing beer to increase the lautering ability of a mash. Rice husk is also used in one step of traditional preparation processes of kaoliang (sorghum) liquid. After fermentation, rice husk can be added into the wine tank to increase the void, which is advantageous for distillation.{{fact|date=May 2024}}

= Fertilizer and substrate =

Rice hulls can be composted, but their high lignin content can make this a slow process. Sometimes earthworms are used to accelerate the process. Using vermicomposting techniques, hulls can be converted to fertilizer in about four months.{{fact|date=May 2024}}

Rice hulls that are parboiled (PBH) are used as a substrate or medium for gardening, including certain hydrocultures. The hulls decay over time. Rice hulls allow drainage, and retain less water than growstones.{{cite web |date=2011-12-04 |title=Growstones ideal alternative to perlite, parboiled rice hulls |work=(e) Science News|url=http://esciencenews.com/articles/2011/12/14/growstones.ideal.alternative.perlite.parboiled.rice.hulls |access-date=2013-06-06}} It has been shown that rice hulls do not affect plant growth regulation.{{cite web | url=http://www.purdue.edu/newsroom/research/2010/101025LopezHulls.html | title=Rice hulls a sustainable drainage option for greenhouse growers | publisher=Purdue University | date=2010-10-25 | access-date=2012-08-30 | author=Wallheimer, Brian}}

=Fireworks=

Rice hulls are coated with fine-grained gunpowder and used as the main bursting charge in aerial fireworks shells.{{fact|date=May 2024}}

=Fuel=

{{stack|

File:Packaging of woodfire made by rice residue.jpg

File:Kiln in Vietnam in Chau Thanh District, 13.webm

}}

With proper techniques, rice hulls can be burned and used to power steam engines. Some rice mills originally disposed of hulls in this way.{{Citation needed|date=July 2011}}

The direct combustion of rice hulls produces large quantities of smoke. An alternative is gasification. Rice hulls are easily gasified in top-lit updraft gasifiers. The combustion of this rice hull gas produces a blue flame, and rice hull biochar makes a good soil amendment.{{cite web |first1=Paul |last1=Olivier |first2=Todd |last2=Hyman |title=Biomass Gasification and the Benefits of Biochar |url=http://esrla.com/pdf/landfill_06.pdf |date=2012-03-27 |publisher= Engineering, Separation and Recycling LLC |access-date=2013-06-06}}

Traditional brickmaking kilns in Mekong Delta are using rice hulls as fuel.{{fact|date=May 2024}}

=Juice extraction=

Rice hulls are used as a "press aid" to improve extraction efficiency of apple pressing.{{cite web|archive-date=2010-01-09|archive-url=https://web.archive.org/web/20100109021522/http://www.vincentcorp.com:80/press_design/issue198.html|publisher=Vincent Corp|title=Press aids|url=http://www.vincentcorp.com/press_design/issue198.html}}

=Pet food fiber=

Rice hulls are an inexpensive byproduct of human food processing, serving as a source of fiber that is considered a filler ingredient in pet foods.{{cite web|url=http://www.dogfoodproject.com/index.php?page=badingredients |title=Ingredients to avoid |publisher=The Dog Food Project |access-date=2013-06-04|archive-date=2018-04-04|archive-url=https://web.archive.org/web/20180404183633/http://www.dogfoodproject.com/index.php?page=badingredients}}

=Pillow stuffing=

Rice hulls are used as pillow stuffing. The pillows are loosely stuffed and considered therapeutic as they retain the shape of the head.{{fact|date=May 2024}}

=Insulating material=

Rice hulls themselves are a class A thermal insulating material because they are difficult to burn and less likely to allow moisture to propagate mold or fungi.{{cite web|url=http://www.appropedia.org/Rice_hulls_in_construction |title=Rice hulls in construction - Appropedia: The sustainability wiki |publisher=Appropedia |date=2013-02-23 |access-date=2014-02-23}} It is also used as roofing after mixing it with mud and water.{{fact|date=May 2024}}

=Particle boards and cardboard=

Rice hulls are used to make particle boards and cardboard. The silica in rice husk make the particle boards less attractive to termites.{{cite web |last1=Coxworth |first1=Ben |title=Rice husks may find use in cheaper, greener, longer-lasting particleboard |url=https://newatlas.com/rice-husk-particleboard/37730/ |website=New Atlas|date=2015-05-28 |publisher=GIZMAG PTY LTD 2017 |access-date=2017-12-04 }}

=Geopolymers=

Due to high amorphous silica content, the RHA (rice husk ash) can be used as a precursor material for geopolymer concrete.{{cite journal |last1=Das |first1=Shaswat Kumar |last2=Mishra |first2=Jyotirmoy |last3=Singh |first3=Saurabh Kumar |last4=Mustakim |first4=Syed Mohammed |last5=Patel |first5=Alok |last6=Das |first6=Sitansu Kumar |last7=Behera |first7=Umakanta |display-authors=3|title=Characterization and utilization of rice husk ash (RHA) in fly ash – Blast furnace slag based geopolymer concrete for sustainable future |journal=Materials Today: Proceedings |date=2020-03-29 |volume=33 |pages=5162–5167 |doi=10.1016/j.matpr.2020.02.870|s2cid=216202502 }}

=Rice concrete=

To achieve the best pozzolanic properties the combustion of the husks has to be carefully controlled by keeping the temperature below {{convert|700|C|K}} and to create conditions to minimize carbon formation by feeding sufficient air.{{Cite web|title=Effects of exposure to elevated temperatures on properties of concrete containing rice husk ash|url=https://www.researchgate.net/publication/296706983|accessdate=2022-10-10|work=researchgate.net}}{{Cite journal|title=Fire resistance evaluation of rice husk ash concrete|journal= Heliyon|year=2018 |pmc=6299146 |last1=Umasabor |first1=R. I. |last2=Okovido |first2=J. O. |volume=4 |issue=12 |pages=e01035 |doi=10.1016/j.heliyon.2018.e01035 |doi-access= free|pmid=30582051 |bibcode= 2018Heliy...401035U}}

At a given water-cement ratio, the addition of small amounts of rice hull ash (2 to 3% of cement mass) may be useful to improve the workability of concrete mixtures by reducing the cement milk separation and segregation and increasing the strength and durability of concrete.{{Cite web|title=Rice concrete: characteristics and composition|url=https://www.concretersmelbourne.net/rice-concrete-characteristics-and-composition/|accessdate=2022-10-10|work=concretersmelbourne.net|date=2022-03-05 }} However, the introduction of large quantities of this additive may result in poor workability of the concrete mixture if strong water-reducing additives are not used.{{Cite journal|title=Investigation of the effect of mineral additives on concrete strength using ANN|journal=Asian Journal of Civil Engineering|year=2022 |doi=10.1007/s42107-022-00431-1 |last1=Al-Gburi |first1=Majid |last2=Yusuf |first2=Salim A. |volume=23 |issue=3 |pages=405–414 |s2cid=247428142 |doi-access=free }}

See also

References

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Bibliography

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