Plastic and nonmetallic article shaping or treating: processes – Forming articles by uniting randomly associated particles
Patent
1996-02-05
1998-06-23
Edwards, Newton
Plastic and nonmetallic article shaping or treating: processes
Forming articles by uniting randomly associated particles
156 622, 156312, B27N 300, C09J 500
Patent
active
057701377
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method for preparing biodegradable natural fiber materials (wood, textile fibers, paper, etc.) comprising binders from renewable raw materials. Such methods are gaining more and more importance, for example, in the production of environmentally compatible and formaldehyde-free particle boards.
BACKGROUND OF THE INVENTION
The majority of composite materials made of wood chips or wood fibers is used in the form of flat boards in the furniture or construction business. Unlike in the paper or textile industry, starch paste is not used at all in the wood industry or merely to serve as extender for synthetic resin glue.
So far, organic binders from basic petrochemical materials have mainly been employed in the production of board-like wood products. Even if only small portions of such synthetic binders are replaced by binders made of renewable raw materials, substantial ecological and macroeconomic advantages will result.
In conventional processes for the production of board-like materials, for example, wood fibers have been prepared by hot-pressing using synthetic binders. The synthetic binders are crosslinked or cured by chemical reactions (polymerization, polyaddition, etc.). During those chemical reactions the wood particles are caused by external pressure to exhibit a degree of compression higher than that corresponding to their bulk density. By curing the synthetic binders, the elastic recovery of the wood particles is reduced. The pressing process is completed when the restoring forces have been fully absorbed by the binders. All conventional methods of preparation have in common that the wood particles are cured prior to the application of glue. Depending on the portion of synthetic binder, a wood chip humidity of 10 to 15% will result after the glue has been applied. Due to the vapor pressure resulting during hot pressing, higher wood chip humidities in conventional preparatory methods will cause tension in the material in excess of the tensile strength in the transverse direction of the board. After the press is opened, the board will crack.
SUMMARY OF THE INVENTION
The object underlying the present invention is to provide an environmentally compatible and cost-efficient method for preparing fully biodegradable natural fiber materials free from harmful substances.
This object is achieved by providing the features indicated in the claims.
In achieving the object, the invention is based on the concept of utilizing starch-based binders in the method for preparing fully biodegradable natural fiber materials, coordinating and controlling the procedural steps and selecting a recipe for the amount of binder, water and, if desired, further additives, based on the amount of dry wood chips or wood fibers, thus optimizing the residence time during hot pressing and shaping the mechanical properties of the composite materials prepared in accordance with the desired usage. The humidity of the wood chips used as fibrous material is used as solvent and swelling agent in the production of the natural fiber mixture.
DETAILED DESCRIPTION OF THE INVENTION
Starch and/or dextrin gums can be economically useful for the preparation of composite materials made of wood chips and wood fibers especially if the necessary procedural requirements are converted to industrial manufacture to enable the preparation of substitutable products in amounts comparable to raw materials for use in synthetic resin binders.
Native starch obtainable from various plants is insoluble in cold water and therefore cannot be used as binder in such state. A chemical and/or physical process is required to impart binding properties to the starch. Irrespective of the process used, the starch is meant to be converted to a colloidal system. Evaporation of the solvent (water) yields a solid matrix that may bond more or less strongly to other substances by adhesion.
Advantageously, the materials, boards, molded articles and profiles based on natural fibers and prepared in accordance with the present in
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Heuer Joachim
Klenke Kurt
Lorcks Jurgen
Pommeranz Winfried
Schmidt Harald
Biotec Biologische Naturverpackungen GmbH & Co.
Edwards Newton
Rauchfuss, Jr. George W.
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