I am always amazed at how little I know about the wood industry. With over 30 years experience in forestry and retail wood sales, only yesterday did I learn about "wood flour".
Wood flour is pulverized and screened dry (8% - 10% moisture content) sawdust and wood shavings the finest grinds of which look like wheat flour. Edgings, slabs, and trimmings may also be used but have to be dry, bark and dirt free. Most of the industry demands an end product that is light in color and weight, highly absorptive and resin free. In the U.S., 75% of wood flour comes from our Eastern White Pine and from the Western White and Sugar Pines. The balance is derived from Spruce, Fir, Hemlock, Aspen, Cottonwood, and from a few other light colored hardwoods.
My 1962 text tells me that wood flour was first produced in 1906 in Norway. I was a history major and if I remember correctly, dynamite was invented there. Since wood flour's most important use as an absorbent is in the manufacture of dynamite, that probably explains its origin.
Four different types of mills produce wood flour: the attrition mill grinds it, the hammer and beater mills essentially pound it, and the roller mill crushes it. There are also three grades of wood flour. The non-technical grade uses mixed wood species for the linoleum, dynamite, and plastic-wood markets. The technical grade has standards that are more rigid and is mostly produced from White Pine. It is used as filler in resinoid plastics. Finally, there is granular metric grade wood flour, which is a special and refined technical grade that is very expensive and hard to produce. Some other interesting uses of wood flour include cleaning of furs where it is a mild abrasive and oil absorbent, it is also an abrasive in soaps - especially those used by mechanics, and relatively coarse wood flour is used in silverware cleaners. Other uses include doorknobs, ornaments, and molded furniture parts.