Process for the control of the physical and chemical characteristics of cellulose fiber containing molded articles

Abstract

A process is disclosed for engineering the architectural arrangement and inter-fiber bonding of fibers within an article being molded form a pulp. This allows for optimal structural characteristics and additive disposition within the article. Complex forms can be fabricated, articles so made having regional variations in chemical and physical parameters as well as those defined by the gross structural form of the article. The addition of osmotic gradients as well as electrical and hydrostatic potentials applied during molding control the migration of additives and solvents through the body of the article in preset directions, thereby controlling the spatial arrangements and bonding of fiber material

Description

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO A MICROFICHE APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention is a method/process whereby a cellulose based pulp in aqueous or other solution/emulsion is handled during molding in a fashion that controls the inter and intra-fiber architectural arrangement and inter-fiber bonding thereby controlling the physical and other material properties of a formed end article.

[0005] Molding of cellulose pulp materials into objects has a long tradition and uses simple processes. The primary control of the end product characteristics are primarily set by the composition of the cellulose pulp and additives utilized and the physical shape of the mold, whether a casting, pouring, press or spray forming mold. The drying process of a pulp material is primarily aimed at controlling shrinkage without adversely affecting any additive characteristics. Various designs for de-watering cellulose pulp in stages have been proposed, these allowing various molding techniques such as press molding. The end article material characteristics are largely predetermined by the chemical composition of any additives and coarseness of fiber size and form. These material characteristics are generally homogenous throughout the body of the molded article and no process to date is described whereby these properties can be varied at will across or within the body of an article. The processes described below outline a method of engineering the architecture of a cellulose fiber based article, allowing a mixture of physical and chemical characteristics within a single molded form.

SUMMARY OF THE INVENTION

[0006] Through the use of locally applied forces comprising (osmotic, electrostatic, hydrostatic) to a drying cellulose based pulp, local ion concentration, hydration envelope and orientation of cellulose fibers and fibrils as well as rate and extent of inter-fiber hydrogen bonding is controlled. Further, the local disposition of additives, such as chalks, waxes or other or more complex macromolecules can be controlled, thus effecting local engineering of a molding article allowing for complex structures to be built.

DESCRIPTION OF THE INVENTION

[0007] Generally, the rate of drying of cellulose pulps used to form molded articles is controlled by ambient humidity, mold permeability and temperature and any vacuum or external pressure applied to the mold or pulp material (U.S. Pat. No. 4,683,028). The use of an electric current to speed drying and to limit temperatures the material is exposed to have been described (U.S. Pat. No. 5,151,226) and a variety of other de-watering techniques using electricity are well known in the building industry for drying masonry materials (U.S. Pat. Nos. 5,368,709, 5,015,351). Applied to a cellulose pulp this gives a limited degree of control over the inter-fiber bonding on the gross or aggregate level. Rather the intent is to gain control overall of the natural shrinkage of the material that occurs on de-watering, while not damaging any inclusion bonding material setting characteristics and or to maintain pliability or working characteristics of the pulp mixture (U.S. Pat. No. 5,883,025). The nature of the pulp and its fiber form (degree of fibrillation and particle size of the cellulose fibers which effects matting and felting characteristics and inter fiber hydrogen bonding) affect gross characteristics of the end article, such as thermal insulation properties. More usually, however the nature and quantities of additives such as polyolefins, polyamides, cellulose acetates etc define the end articles' material physical characteristics. Additional characteristics may be set by the nature of other additives to the pulp for example chalks, waxes etc. These physical characteristics are generally homogenous across the molded form. Thus the full potential of inter-fiber bonding is not utilized and the nature of the end article fall some way short of a truly environmentally friendly or complex form, because of the need to include additives and the lack of control of their distribution (and therefore total amount per article). It is known that careful processing or raw cellulose sources such as jute, flax, hemp etc, can increase the fibers' ability to hydrogen bond to its neighbors and other materials. What is proposed here is a system that utilizes the ability of cellulose fibers, particularly those that are milled to have a high surface area and fibril structure, to form hydrogen bonds between fibers and to felt, in order to construct deliberate architectural arrangements of fibers and additives. By doing this the contribution to the material properties of an end article by the cellulose material itself is extended and the use of additives confined to the areas where they are needed. This is done by effecting a regional or local control of the hydrogen bonding extent, fiber disposition and felting, particle behavior and characteristics as well as the general disposition of additives (or finely ground cellulose). The process in so doing allows a lower use of potentially harmful additives. It is known that direction of fluid flow and electrostatic fields can affect fiber orientation (U.S. Pat. No. 4,060,449) and indeed electrostatic fields are the basis of control of large molecule migration (electrophoresis) through gels.

[0008] I propose the addition of other effects and forces in order to control general, regional or local characteristics of an article during the molding process to control fiber architecture and additive localization hence end material and article characteristics. The use of geometrically orientated osmotic gradients of selected ions and chemicals and or hydrostatic pressures and or electric fields applied across a permeable, semi permeable mold or membrane or directly to the pulp material controls fiber orientation, flocculation or emulsion characteristics and hydrogen bonding of cellulose pulp. Both electrostatic and osmotic gradients will cause movement of ions and both therefore can be used to effect de-watering and fiber orientation, but they also affect the hydration shell of the cellulose fibers and thus control the amount and rate of inter-fiber hydrogen bonding. This shell of hydration is also affected by the nature of ions in the vicinity of the fibers. This effect is taken advantage of in the pottery industry, where the handling characteristics of various clays are deliberately manipulated by modulating the pH and various ion concentrations within the clay. A description of these effects and their uses can be found in “The Potter's Dictionary of Materials and Techniques” by Frank Hamer. By using these recognized separate and unconnected techniques a novel system emerges, allowing for the deliberate engineering the architecture of the fibers of cellulose material within a cellulose containing pulp and therefore complex physical characteristics of an end article based on more than its constituent or gross structural form. Reiterating, as the pulp material dries through varying degrees, inter particle hydrogen bonding can occur in a controlled fashion, hydrogen bonding characteristics being defined by particle size and preparation, hydration sphere around the particle and local ion concentrations as well as any chemical additives. Thus, chemical concentration gradients, Electro-osmosis and solvent flow rate and direction allow regional ion control, fiber orientation and felting arrangement and inter-particle bonding. In addition as a result of the egress of solvent (usually water) from the pulp, the ingress of new materials into the pulp (such as water proofing agents) can be encouraged in a controlled and specific fashion, rendering local and varying characteristics across the molding article. Further, the addition of other fluids or solids to the pulp material can be effected before, or during the molding process and their spatial disposition and physical and chemical properties within the pulp can be controlled. For example, on one side of the material a hyper-tonic solution may draw out solvent in one direction while on the other side or surface of the pulp may be exposed to a different additive such as a water proofing material. The latter will be drawn into the pulp by the relative negative pressure caused by elution of solvent in one direction or may be forced in by the addition of pressure on its side of the molding article. The use of osmotic or hydrostatic pressures during the molding process, leads to a controlled ingress or egress of material into or from the pulp. Thus the disposition of new additives is brought under control and if so required these additives can be caused to form local chemical reactions within the pulp by controlling the local medium in which they reside. These effects allow the specific engineering of physical and chemical properties of an end article, either as a whole or on a regional basis, through the specific local application of these forces to the molding article. Numerous mold forms have been described including the incorporation of ports to either side of a molding article (mainly to allow the egress of water) (U.S. Pat. No. 4,683,028). It is here envisaged that any one internal surface of a mold may have an array of access ports to individual areas of the internal mold or form surface or mesh. Thus a defined area of pulp could be exposed to a specific chemical, electric or hydrostatic potential which may be different to that of its neighbor. The counter surface of the mold for the article, or some other area of the article would have its surface exposed to an opposite or neutral potential (chemical, physical or electrical). Alternatively a port or ports may be provided to the internal surface of the molding article (if it is to be hollow) or into the body of the pulp itself, which may act as the neutral for application of the above forces or gradients. By applying chemical, electrical or pressure potential to an array of these surfaces, the intervening pulp may be exposed to varying ion, osmotic, flow and electrical potentials in a controlled fashion. These varying forces may be applied concurrently or sequentially. Regional or local control of the inner environment of the pulp is thereby gained allowing the ability to control the fiber architecture as outlined above. Consequently a none homogenous article may be formed where not just shape but internal composition may be effectively engineered.

Claims

1) the engineering of the architectural and spatial arrangement of fibers and additives within the body of an article being molded from a pulp containing cellulose.

2) the use of chemical osmotic gradients applied through a mold or form to control the localized internal arrangement and bonding of fibers within an article being molded from a pulp containing cellulose.

3) the use of ion concentrations gradients applied through a mold or form to control the internal arrangement and bonding of fibers within an article being molded from pulp containing cellulose.

4) the use of osmotic gradients applied through a mold or form to control the internal arrangement, disposition and bonding of additives within an article being molded from a pulp containing cellulose.

5) the use of ion concentration gradients applied through a mold or form to control the internal arrangement, disposition and bonding of additives within an article being molded from a pulp containing cellulose.

6) the use of an electric field or current applied through a mold surface to control the internal arrangement and bonding of fibers within an article being molded from a pulp containing cellulose.

7) the use of an electrical field or current applied through a mold surface to control the local concentration of ions within an article being molded from a pulp containing cellulose.

8) the use of an electrical field or current applied through a mold surface to control the local concentration of additives within an article being molded from a pulp containing cellulose.

9) the use of a mold having a matrix of porous or semi-permeable surfaces through which a pulp can be exposed to varying ion, osmotic, chemical, electrical or hydrostatic pressure to effect the structural, chemical and physical nature of a cellulose containing pulp forming an article.