Patent Application
20080096017
In one preferred embodiment of the present invention, a super absorbent polymer or fiber (“SAP”) generally having a swell factor of about 25% or greater is formed into a composite core yarn strand. The SAP selected preferably can be a modified hydrophilic polyacrylate, but also could include any other SAP that could be extruded as a filament such as starch grafted copolymers or cross-linked carbon methylcellulose, and also could include SAPs having a greater or lesser swell factor, depending on the particular application or use desired for the fabric structure formed using the composite SAP core yarn of the present invention. The SAP polymer material is extruded into filaments and cut into staple fibers that can range in length from about 0.05″ to about 2.0″, although other size fibers also can be formed. This fiber is characterized by very low tensile strength and elongation. The composite core yarn strand containing the SAP fiber is formed by blending the SAP fibers with textile fibers in proportions ranging from about 20% to about 80% SAP and about 80% to about 20% conventional fibers that could include, but are not limited to, cotton, rayon, flax, jute, knaf, ramie, polyester, polyolefin, polyamide, acrylic, polyethylene, PLA, and PTT fibers and/or blends thereof.
The composite core yarn strand generally is prepared by conventional cotton system spinning methods that could include, but are not limited to, carded sliver, drawn sliver, roving, rotor spinning, ring spinning, air jet spinning, or friction spinning. The composite core yarn strand is then encapsulated by a membrane generally composed of cotton, rayon, flax, jute, knaf, ramie, polyester, polyolefin, polyamide, acrylic, polyethylene, PLA, PTT, and/or blends thereof, or other similar encapsulating material. The membrane will be selected as having a defined porosity of typically between about 5 microns to about 220 microns, although greater or letter porosities also can be used, and generally is sealed about the core strand by one of various sealing/encapsulating methods including thermal bonding, adhesive bonding, sonic welding, needle punching, or sewing.
In an alternative embodiment of the present invention, a composite core yarn containing a hydrophilic polyacrylate or other suitable SAP fiber is formed by intimately blending the SAP fiber in a ratio ranging from approximately 20% to approximately 80% with conventional textile fibers, said conventional fibers generally including, but are not limited to, cotton, rayon, flax, jute, wool, polyester, polyolefin, polyamide, acrylic, fibers and/or blends thereof by a spinning process using the ring, rotor, air jet, or friction methods. Strands of fibers are prepared for the sheath formed about the core and generally can include, but are not limited to, cotton, rayon, flax, jute, wool polyester, polyolefin, polyamide, acrylic, fibers and/or blends thereof. These sheath fibers are fed into the back of a Dref spinning machine with the core fibers for spinning together to form a composite spun yarn. For example, the present invention can utilize a Dref 3000, Dref 2, 2000 or Dref 3 spinning machine that is capable of producing the desired composite yarns depending upon the yarn size and the fiber lengths utilized. Several strands of the composite yarns are fed together to compose a total weight of about 220-400 grains per yard.
As these composite yarns with SAP fibers enter the spinning zone of the Dref spinning machine, a carding drum covered with a saw-toothed wire reopens and individualizes the fibers and propels them into the nip or crotch between two perforated drums. The perforated drums are rotated in the same direction at a predetermined rate ranging from 1,500 RPM to 4,000 RPM with an adjustable negative vacuum in the range from about 70 to about 110 millibars being applied at the crotch between the perforated drums where the fibers are received from the carding drum, although greater or lesser pressures also can be used. A membrane ribbon, that generally will comprise from about 5% to about 30% or more of the weight of the entire structure, generally formed from cotton, rayon, flax, jute, knaf, ramie, polyester, polyolefin, polyamide, acrylics and/or blends thereof or other, similar encapsulating materials, and the core yarn are fed in parallel at one end of the rotating drums and are pulled through the spinning zone of the spinning machine by an outlet roller at the rear of the spinning zone.
As the membrane/core yarn structure passes through the spinning zone of the spinning machine, the composite core yarn with SAP fiber sheath is pre-positioned so that the membrane substantially completely encapsulates the core structure with the individualized fibers being rotated or spun around the membrane, completely covering it to a desired percentage and substantially keeping it from unraveling. The number of strands of the card sliver, the weight per unit length, and the denier of the core yarn can be varied to determine the percentage of membrane, core, and sheath fibers in the overall composite fiber structure.
This process results in a composite yarn structure where the membrane is held in place by the mechanical tension of the outer sheath of staple fibers. It has been demonstrated that this generally will effectively seal the membrane, locking in most of the SAP fibers over repeated absorptive/desorptive cycles. However, because the SAP fibers still could eventually breach the mechanical membrane seal, it is envisioned that an ultrasonic or thermal sealing head also can be mounted at the exit of the Dref spinning zone to thermally seal the membrane by sonic friction. This sealing method has been demonstrated to produce a substantially total and permanent containment of the SAP fiber subject only to the permeability characteristics of the membrane material. It also has been envisioned that the utilization of one or more sewing heads or an adhesive application also can be used to bond the membrane to the outer sheath, so as to seal about the core yarn of SAP fibers, either in conjunction with or in place of the ultrasonic or thermal sealing mechanism.
The membrane material utilized in the present invention generally will be selected based upon its having a desired porosity in the range from about 5 to about 200 microns (although other porosities also can be used, depending upon the application for the encapsulated yarns) that permits the transpiration of water freely without allowing the hydrated gel particles of the membrane to escape. The membrane material also generally is very thin and sufficiently pliable to allow the Dref spinning elements to form it around the core without tangling or unduly tearing the membrane material. The membrane material also can include a thermoplastic material to permit sealing via sonic or heat welding. Examples of nine polyolefin thermally bonded filtration substrates were acquired having porosity ratings ranging from about 5.0 microns to about 220 microns. Experiments dictated that pretreatment with a liquid synthetic surfactant to negate surface tension present that would inhibit transpiration of water.
The resultant composite yarn structure with encapsulated SAP fibers formed according to the principles of the present invention is now ready to be assembled into an open configuration fabric for use in sub-soil water retention application. This can be done by conventional weaving or knitting techniques or by various nonwoven processes such as heat bonding, needle punching or melt extrusion processes, provided that the assembly process leaves an open grid-work having defined open spaces or gaps of between ⅛″ to about 6″ between the yarn strands, although greater or lesser size spaces also can be used, and capable of allowing excess water and plant roots to pass by the fabric. Another configuration could incorporate the present invention into a three dimensional fabric with large diameter fibers in the denier ranges generally between about 9 and about 300 denier in a random, omni-directional arrangement, or on an open grid-work configuration having open spaces of approximately 1/16″-⅛″ up to about 6″ or more therebetween to create a fabric more resilience to soil pressure. This generally will help the membrane-coated yarn strands not to become compacted over time and retain a large working area. However, care has to be taken that soil or sand has to be used to fill in the voids of the fabric to prevent root fungi from developing.
The preferred and alternative embodiments of the present invention further are disclosed herein as containing non-biodegradable materials and generally are intended to remain functional in their subterranean environment long term. However, it is anticipated and should be understood that certain applications could require the structures of the present invention to be fabricated of one hundred percent biodegradable textile materials that would eventually decompose under the ground. The life span and rate of such decomposition could be predetermined by specifying the content of cellulose-based textile fibers utilized in forming the SAP fiber blended yarn structure.
A sample of a Dref-spun composite core yarn made from staple fibers according to the present invention was produced from a modified hydrophilic polyacrylate polymer blended with conventional 3 denier polyester staple fibers. A polyolefin membrane having a porosity of about 120 micron was sonically welded around the composite core yarn utilizing an off-line sonic bonding machine. This yarn then was tested for water absorption and retention in comparison to testing with a similar size strand cut from a conventional Aquamat™ (100% polyester) product.
It can be observed that although the Aquamat™ (100% polyester) takes on a relatively large amount of water initially, a significant amount of the trapped water is not retained over time. This is because the polyester fibers are actually hydrophobic and the water is only temporarily captured within the interstices of the structure. With the present invention, however, the SAP composite core yarn swells and retains a large majority of the water absorbed even after significant time lapse.
In a second series of tests, boxes of sand and topsoil were prepared with composite core yarns of the present invention prepared in accordance with the alternative embodiment discussed above (a Dref spun yarn with a polyacrylate SAP core, 120 micron polyolefin membrane, and staple polyester outer sheath) laid in a matrix form below the surface. Control test boxes were also prepared that: 1) did not contain any matter other than equal amounts of sand and dirt; and 2) had a matrix of 100% cotton yarn of approximately the same weight and configuration as the Dref spun composite SAP yarn.
It can be readily observed from the presented testing that the invention, represented as the test sample, caused the sand and the topsoil to retain significantly more water than the control samples containing no yarn. Likewise, the topsoil containing the composite SAP yarn retained significantly more water than the soil containing a conventional cotton absorbent yarn. It also will be understood that composite SAP yarn of the present invention further can be woven, knitted or otherwise formed into a fabric structure having an open configuration with defined spaces or voids, or can be formed with a strand arranged in a substantially random configuration. When used as a subterranean fabric structure or material, the resultant fabric structure substantially retains moisture while permitting normal root growth and allowing excess water to pass through and beneath the fabric and facilitating movement of collected water from lower levels of plant root structure toward the surface of the soil.
It will be further understood by those skilled in the art that while the present invention has been described above with reference to preferred embodiments, numerous variations, modifications, and additions can be made thereto without departing from the spirit and scope of the present invention as set forth in the following claims.
The present patent application is a formalization of previously filed, co-pending U.S. provisional patent application Ser. No. 60/862,673, filed Oct. 24, 2006, by the inventors named in the present application. This patent application claims the benefit of the filing date of the cited provisional patent application according to the statutes and rules governing provisional patent applications, particularly USC § 119(e)(1) and 37 CFR § 1.78(a)(4) and (a)(5). The specification and drawings of the provisional patent application are specifically incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60862673 | Oct 2006 | US |
