In 1995, the United States produced about 1,260,000 metric tons of rice hulls at about 50 mills located in Louisiana, Texas, Arkansas, Missouri, Mississippi, Florida and California. More than 100,000,000 metric tons of rice hulls are generated each year throughout the world. Since rice is grown on every continent except Antarctica, since it ranks second only to wheat in terms of worldwide area and production, and since the hull represents on average about 20% of the rough harvested weight of rice, our planet ends up with an abundance of this scaly residue. Such a high percentage of silica is very unusual within nature, and this intimate blend of silica and lignin makes the rice hull not only resistant to water penetration and fungal decomposition, but also resistant to the best efforts of man to dispose of it. The rice hull contains approximately 20% opaline silica in combination with a large amount of the phenyl propanoid structural polymer called lignin. Of all cereal byproducts, the rice hull has the lowest percentage of total digestible nutrients (less than10%). Nowhere could we ever find a cereal by-product so low in protein and available carbohydrates, and yet, at the same time, so high in crude fiber, crude ash and silica. When nature decided how to package a grain of rice, she wrapped this tiny bundle of nutrients with what is often referred to as a "biogenic opal." The chemical structure of the rice hull, containing amorphous silica bound to water, closely resembles that of the opal, and this gives the rice hull some fairly amazing properties. This paper also explains how the structure of such a house can be fashioned out of a variety of engineered lumber products derived from sugarcane rind. In their raw and unprocessed state, rice hulls constitute a Class A or Class I insulation material, and therefore, they can be used very economically to insulate the wall, floor and roof cavities of a super-insulated Rice Hull House. Recent ASTM testing conducted R&D Services of Cookville, Tennessee, reveals that rice hulls do not flame or smolder very easily, they are highly resistant to moisture penetration and fungal decomposition, they do not transfer heat very well, they do not smell or emit gases, and they are not corrosive with respect to aluminum, copper or steel. This abundant agricultural waste has all of the properties one could ever expect of some of the best insulating materials. They contain approximately 20% opaline silica in combination with a large amount of the phenyl propanoid structural polymer called lignin.
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