From 05/18/2015 through 2/16/2013
“Wood is a hard, fibrous structural tissue found in the stems and roots of trees and other woody plants. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers (which are strong in tension) embedded in a matrix of lignin which resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or it is defined more broadly to include the same type of tissue elsewhere such as in tree roots or in other plants such as shrubs. In a living tree it performs a support function, enabling woody plants to grow large or to stand up for themselves. It also mediates the transfer of water and nutrients to the leaves and other growing tissues. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, or wood chips or fiber.
The earth contains about one trillion tonnes of wood, which grows at a rate of 10 billion tonnes per year. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as a source of renewable energy. In 1991, approximately 3.5 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction.”
(Wood, Wikipedia, 2/16/2013)
“Wood-plastic composites are widely used in residential and commercial structures for decking board, fencing, railing and so forth. In the manufacture of these products, wood flour or wood fiber is mixed with a resin and the composite is extruded. Warm extruded profiles may be embossed to create a real wood or wood grain appearance. Adding wood flour or wood fiber helps reduce cost, improve flex modulus and add wood appearance.
Initially, these products represented a marked cost savings over actual wood when used for the same purposes. Over time, however, the cost of wood flour and wood fiber has increased dramatically. A decade ago, wood flour and wood fiber were little-used by-products of the paper and lumber industries. Today, the opposite is true; trees are grown for the specific purpose of direct conversion into wood flour or wood fiber for use in wood-plastic composites.
In addition to their increasing cost, wood-plastic composites have several drawbacks. The use of wood as a reinforcing filler in composites creates a strong wood color that is very difficult to change in the presence of a plastic resin. For example, significant amounts of titanium dioxide are needed in formulations where a light color is desired. Titanium dioxide is an expensive additive, and its use in large quantities creates an unnatural look with a lackluster appearance. Further, abundant quantities of lubricant are needed to allow the composite to be extruded into a board, and the resulting board is not completely hydrophobic. Wood flour and wood fiber can both adsorb a large amount of water. Wood-plastic composite profiles also have a stronger than normal wood smell due to high process temperatures used in the production process. This makes wood-plastics composites unattractive for many in-house applications.
In an attempt to replace wood flour and wood fiber in composites, various agricultural materials have been used. For example, pure cellulose fibers have been used to impart a light color on composite profiles. However, pure cellulose fibers are very costly and difficult to process at high fiber content. Composite profiles with high cellulose fiber content are thus not commercially viable as replacement construction materials.”
8,802,754 (8/12/2014) (Nie et al)
Starch-plastic composite resins and profiles made by extrusion
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Roger D. Corneliussen
Maro Polymer Links
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Copyright 2013 by Roger D. Corneliussen.
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* Date of latest addition; date of first entry is 2/16/2013.