Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Reexamination Certificate
2000-04-03
2002-04-30
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
C106S162510, C106S137100, C524S013000, C524S015000
Reexamination Certificate
active
06379446
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates to short-sequence methods for obtaining aqueous compositions having uniformly dispersed fibers. More particularly, the present invention relates to methods for obtaining aqueous compositions having uniformly dispersed plant-based fibers in a single mixing step.
2. The Relevant Technology
When manufacturing biodegradable articles of manufacture using a biodegradable water-dispersible binder, it has been found desirable to incorporate plant-based fibers therein for reinforcement. Plant-based fibers are themselves biodegradable. Uniformly dispersed fibers, especially longer-length fibers and/or fibers of high aspect ratio, result in articles having substantially the same amount, concentration, and distribution of fibers throughout the entire bonding matrix. Articles so manufactured have greatly increased strength, toughness, and ductility, and such articles attain substantially all of their final strength, flexibility, toughness, and other critical properties immediately or shortly after being demolded without the need for subsequent processing steps or the inclusion of synthetic polymers.
A description of compositions and methods for obtaining substantially homogeneously dispersed fibers within compositions for manufacturing biodegradable articles of manufacture may be found in any one of the following U.S. Pat. Nos. 5,580,624; 5,545,450; 5,662,731; 5,683,772; 5,709,827; 5,679,145; 5,618,341; and 5,848,155. For purposes of disclosing compositions and methods for dispersing fibers within compositions used to manufacture biodegradable articles of manufacture, the foregoing patents are incorporated herein by specific reference.
One method for dispersing fibers employs a pseudo plastic or an approximately Binghamian fluid that is able to impart shear from a mechanical mixing apparatus down to the fiber level to obtain a starch-based composition having substantially uniformly dispersed fibers. This type of fluid is characterized by having an appropriately high viscosity and yield stress, which is typically achieved by blending a viscosity or yield stress increasing agent with water to form a fluid fraction that has the requisite viscosity, yield stress and other desired rheological properties. The viscosity or yield stress increasing agent may comprise a variety of organic thickening agents, an example of which is gelatinized starch. The water is included to form a fluid fraction or aqueous phase in order to gelate the thickening agent and to disperse the fibers in conjunction with the gelatinized thickening agent.
One of the problems encountered when attempting to disperse plant-based fibers has been the form in which such fibers have typically been commercially available. For example, virgin wood fibers are typically sold in large rolls, while recycled paper is typically in the form of newsprint or sheets of paper.
In order to disperse such fibrous rolls or sheets, they are first typically mixed in water under high conditions for 3-10 minutes to yield a water-fiber mixture having the consistency of hamburger. In this condition the fibers are still bound together in large clumps. In order to further separate the fibers and homogeneously disperse them throughout the mixture, a thickening agent such as pregelatinized starch is then added to the water-fiber mixture in order to create the aforementioned Binghamian fluid fraction and the resulting mixture subjected to high shear mixing conditions for an additional 12 minutes. The high viscosity and yield stress of the fluid fraction is able to transfer the shearing action of the mixing apparatus down to the fiber level, thus pulling apart and separating the fibers and also homogeneously mixing them throughout the mixture.
While the foregoing provides an excellent process for separating and dispersing plant-based fibers, it would be an advancement in the art to provide compositions and methods for dispersing plant-based fibers in significantly shorter periods of time.
It would be a further improvement in the art if such compositions and methods for dispersing plant-based fibers in a significantly shorter period of time could also be performed in a single step.
It would yet be an advancement in the art if such compositions and methods for dispersing plant-based fibers imparted less overall shear to the composition, thus reducing the mechanical stresses and potential damage experienced by the fibers and other solid components that may be added to the composition.
Such compositions and methods for dispersing plant-based fibers are disclosed and claimed herein.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention is directed to compositions and methods for obtaining aqueous compositions having substantially uniformly dispersed plant-based fibers. The compositions include water, a thickening agent, and specially treated plant-fibers that are much more easily dispersed than conventional fiber rolls, newsprint, or other sheet-like fibrous materials.
The key to efficiently dispersing plant-based fibers within aqueous compositions in a shorter period of time is to first obtain fibers that are mechanically separated in the first instance, while in a dry state, rather than being bound together in a fiber roll or in a sheet-like form. Fibers in a roll or sheet are mechanically intertwined and held together by web physics. In addition, there may even be some hydrogen bonding between the cellulose molecules comprising the plant-based fibers depending on how the fibers are initially processed. In such a state, a considerable amount of force is necessary just to break down the mechanical and chemical bonds between the fibers even prior to dispersing them throughout the mixture, thus increasing the time and quantity of shear forces that must be applied to achieve homogeneous dispersion of such fibers. Increasing the mixing time and shearing forces applied to the aqueous mixture naturally leads to increased damage to the fibers and any optional solid components within the mixture.
The solution is to at least partially separate the plant-based fibers before they are added to the mixture into which they are to be homogeneously dispersed. This can be done during initial manufacture of plant-based fibers during plant pulping, or else it can be done after formation of rolls or sheets of plant-based fibers but prior to adding the fibers to the aqueous mixture.
Fibers are liberated from plant materials by means of conventionally known pulping processes which utilize highly aqueous slurries. In many cases, such as when pulping trees or other relatively large plant-based raw materials, strong chemicals are required in order to break down the lignins and cellulosic polymers that chemically bind the fibers together and which otherwise prevent the separation of fibers in water. The fibrous slurries resulting from pulping processes are typically dried on a forming wire to yield paper or paperboard sheets, which are rolled up as long sheets or rolls. In some cases, thicker mats may be produced in which the fibers are more loosely bound and which are formed into rolls, typically 3 ft. wide rolls.
More recently, some manufacturers of plant fibers have began producing what are known as “flash-dried” fibers. Instead of laying the fibrous slurry onto a forming wire, as is typically done, the fibrous slurry is partially dried, such as by decantation or vacuum filtration, and then dried within an oven or drying chamber by means of countercurrent hot drying gases. The fibers dried in this manner are not mechanically intertwined and/or chemically bound together as in wet-laid processes, but are loosely bunched together. The dried fibers are compressed into bails for shipment. Such fibers are much more easily dispersed than fibrous rolls or sheets because they are not mechanically intertwined to any appreciable degree.
Alternatively, fibrous rolls or sheets can be mechanically broken down, at least partially, in order to yield a dry fibrous product that is more easily dispersed througho
Andersen Per Just
Hodson Simon K.
Brunsman David
E. Khashoggi Industries, LLC.
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