WO2005023955A2

WO2005023955A2 - Biodegradable nets, methods of manufacture and uses thereof, particularly as an erosion blanket

Info

Publication number: WO2005023955A2
Application number: PCT/US2004/029500
Authority: WO
Inventors: William S. Shelton; John P. Pocher
Original assignee: Atlantech International, Inc.
Priority date: 2003-09-09
Filing date: 2004-09-09
Publication date: 2005-03-17
Also published as: WO2005023955A3

Abstract

A lightweight, highly porous, biodegradable uniaxially or biaxially oriented net, and a method of making same, by stretching a cast integral net of a modified biodegradable polymer such as a corn polymer or a polypropylene polymer having been made biodegradable by use of an additive or other biodegradable resins, and an erosion blanket preferably including a sandwich of a pair of such nets containing an erosion-controlling material such as a quantity of straw, coconut fibers, wood excelsior or the like.

Description

BIODEGRADABLE NETS, METHODS OF MANUFACTURE AND USES THEREOF, PARTICULARLY AS AN EROSION BLANKET [0001] This application claims priority to U.S. provisional application Serial No. 60/501,013 filed September 9, 2003 and U.S. provisional application Serial No. 60/575,407 filed June 1, 2004 and both are incorporated by reference herein as if fully set forth in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

[0002] This invention relates to the production of polymer nets and relates more particularly to nets made of biodegradable polymers and their uses, especially as blankets for minimizing erosion on steepened slopes or the like.

Description of the Related Art

[0003] Erosion blankets or mats are usually laid over sloped terrain to minimize erosion caused by man-made or environmental conditions and to beautify the area. Commonly, such mats include straw, coconut fibers, wood excelsior, as well as such biodegradable fibers or other materials used to retain moisture. Such mats may also facilitate germinating seeds such as grass seeds and may include fertilizers or the like to enhance such growth.

[0004] In the production of erosion blankets, a quantity of erosion-controlling biodegradable materials is attached to a supporting layer of a polymeric netting, or captured between a pair of such nets, to retain the materials while the seeds take root. The germinating grass or other ground cover may grow up while the roots may grow down through the netting to help anchor the top soil and provide erosion control .

[0005] While the straw and other materials tend to decompose over time by exposure to sunlight and moisture, the polymeric netting currently in use does not, and remains either on the surface or buried just beneath the new grass seedlings. The almost indestructible nature of such polymeric netting material, particularly when not subjected to sunlight, i.e., buried, causes problems during subsequent operations, such as mowing of the grass where even a few strands of netting can become tangled in the grass cutting equipment.

[0006] "Soil nails" or spikes have sometimes been used to retain erosion blankets in place, particularly when the blankets are laid on slopes of a sharp angle. Depending on the material from which the nails are made, it may have been necessary to remove the same once the grass starts to grow to avoid interference with subsequent operations. More recently, however, some soil nails have been molded from a biodegradable, corn-based polymer, so that, after a period of time, the soil nails themselves tend to degrade due to exposure to moisture and sunlight, as well as the soil microbes.

[0007] It would be desirable to render the erosion mat netting biodegradable as well, but the production of integral nets by extruding corn-based polymers or other such biodegradable polymer materials is much more difficult than the molding of the soil nails. Simply casting unoriented net is too expensive for such applications, requiring excessive quantities of polymeric material, producing thick net strands which decrease the biodegradability of the erosion blanket, and providing inadequate porosity or open spaces between the strands to permit the seedlings and roots to grow through the relatively small openings. Moreover, commercial net- forming extrusion equipment is generally too small to provide a practical width of "as cast" netting for use in extrusion blankets where relatively large areas must be covered. Attempts to stretch nets cast from commercially available corn-based polymers to provide larger sheets of highly porous nets having finer strands for use in erosion blankets have resulted in destruction of the nets due to the inherent brittleness of such materials.

[0008] Other biodegradable materials are not well suited for this purpose. For example, in U.S. Patent No. 6,573,340 to Khemani et al., the subject matter of which is incorporated herein in its entirety by reference, biodegradable sheets and films are disclosed, but such materials are simply not practical for use in the production of erosion blankets which require high porosity materials of great widths and lengths to minimize expense and maximize erosion control and biodegradability.

SUMMARY OF THE INVENTION

[0009] Accordingly, it is an object of the present invention to produce an integral, biodegradable net material which, as cast, is capable of being stretched at least one and one-half or two times its original size uniaxially, and preferably up to six times its original size or more, uniaxially or biaxially, to provide large sheets of light weight, thin strand netting material with substantial open areas from limited quantities of starting material . [0010] Another object of this invention is to produce an erosion blanket having one or two layers of a porous, integral net with highly oriented biodegradable strands retaining a core of erosion-controlling materials such as straw, coconut fibers, wood excelsior or other biodegradable materials of this nature.

[0011] A further object of this invention is to produce an integral netting of a biodegradable polymer, such as corn resin or the like, by incorporating an additive which acts as a plasticizer to minimize brittleness of the "as cast" net, thereby facilitating significant uniaxial and/or biaxial stretching to orient the molecules and thereby strengthen the net while minimizing the quantity of polymer material needed to cover large areas and increasing the porosity of the resultant net by reducing the strand size to a point where the erosion-controlling material is retained, but the ground cover can grow through the open areas .

[0012] Still another object of this invention is to produce a biodegradable polymer netting for erosion control using polypropylene which has been made biodegradable by the addition of one or more additives. One such additive is ECM 6.0701 available from ECM Biofilms, Inc., 1 Victoria Square - Suite 304, Painesville, Ohio 44077. Other biodegradable resins that may be applicable for the production of lightweight, thin strand, netting material in accordance with the present invention include Ecoflex F BX7011 resin available from BASF Plastics, 3000 Continental Drive-North, Mount Olive, New Jersey 07828, Biomax 4026 resin available from Dupont, Wilmington, Delaware and Mater-Bi biodegradable resin available from Novamont N.A., P.O. Box 1039, Ridgefield, Connecticut 06877.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other objects, features and many of the attendant advantages of the invention will be better understood upon a reading of the following detailed description when considered in connection with the accompanying drawings herein.

[0014] Figure 1 schematically illustrates portions of an erosion blanket incorporating the principles of the present invention laid on the steepened slope of a hillside for initiating growth of grass to minimize soil erosion. [0015] Figure 2 is a top plan view of an erosion blanket according to this invention.

[0016] Figure 3 is an enlarged view of a portion of the erosion blanket of Figure 2.

[0017] Figure 4 is a bottom plan view of the portion of the erosion blanket illustrated in Figure 3. [0018] Figure 5 is a transverse cross-sectional taken along lines 5-5 of Figure 4.

[0019] Like reference characters refer to like parts throughout the several views of the drawings .

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] In describing preferred embodiments of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose . [0021] As seen in Figure 1, a soil erosion blanket 10 according to preferred embodiments of the instant inventive concepts, is laid on a slope 12 on the side of a hill 14 to minimize soil erosion. Although such erosion control blankets have particular utility on steepened slopes where erosion is paramount, they may also be used on embankments or bases where erosion from foot or vehicle traffic or even rain, snow, wind or other forces of nature can occur. The erosion blanket 10 may be secured by a plurality of soil nails or spikes (not shown) which may be molded of a biodegradable corn-polymer or the like such as are currently available from Almar Molded Products of Nashville, Tennessee, or other such securing means.

[0022] The erosion blanket 10, as discussed above, generates or promotes the growing of grass or other such ground cover to minimize the loss of top soil resulting from such erosion.

[0023] As seen particularly in Figures 2-5, the erosion blanket 10 includes inner and outer layers 16, 18 of a biodegradable net according to this invention containing therebetween a layer of erosion-controlling material 20 which may be any of the aforementioned, generally fibrous, biodegradable materials such as straw, coconut fibers, wood excelsior and the like, or mixtures of these materials with each other and seeds or chemicals, as desired. The dimensions of the erosion blanket 10 are only limited by the size of the extrusion equipment and the level of stretching, whether uniaxially or biaxially, imparted to the "as cast" net prior to incorporating the erosion- controlling material 20 in the netting sandwich. As is well known, the erosion blanket 10 may be transported to the site in roll form (not shown) and cut to size. A s indicated above, the use of a polymeric net material in the production of erosion blankets is well known. Such net materials may be integrally cast and then stretched using any of a variety of well known techniques such as those seen, for example, in U.S. Patent Nos . 2,919,467 to Mercer, 3,070,840 to Mercer, 3,252,181 to Hureau, 3,317,951 to Hureau, 3,384,530 to Mercer et al . , 3,384,692 to Gait et al., ^'3,496,965 to Hureau, 3,749,535 to Gaffney et al . , 3,917,889 to Gaffney et al . , and 4,756,946 to Mercer, the subject matters of all of which are incorporated herein in their entireties by reference. These patents are cited as illustrative, and are not considered to be all inclusive, or to exclude other techniques known in the art for the production of integral net materials.

[0024] The polymeric materials used in the production of such netting for erosion control blankets heretofore are not biodegradable and, therefore, remain in the soil for an indeterminate period of time and produce an obstacle to subsequent maintenance and other operations. The key to the instant invention is the provision of a biodegradable polymer capable of extrusion according to any of the well known techniques for producing integral net, with the "as cast" net being uniaxially or biaxially stretchable to expand the overall sheet size beyond the capacity of currently available equipment for this purpose.

[0025] The aforementioned biodegradable soil nails are produced by molding a polylactide resin (PLA) , also known as "corn polymer", commercially available from Cargill-Dow of Minnetonka, MN. Resins of this nature are derived from naturally-occurring plant starch, in this instance, corn starch. Other readily available plants that may be used to make biodegradable polymers are wheat, beets and rice, to name a few. DuPont is developing a corn-based fiber called Sorona, and Metabolix is developing a biodegradable material using hydroxyalkanoates (PHAs) . It is anticipated that any of these materials, and others, could be used to produce a biodegradable net according to the instant inventive concepts.

[0026] Attempts to produce integral, biodegradable plastic net from the Cargill-Dow PLA using the techniques of the aforementioned patents were unsuccessful because of the poor extrudability of these materials and the relatively brittle nature of the "as cast" net. This brittleness of the "as cast" net precludes significant stretching to thin the strands, which would otherwise increase the strength through orientation and improve the porosity. However, according to the instant inventive concepts, the corn resin can be modified to enable significant uniaxial or biaxial orientation, that is, at a stretch ratio of at least 1.5:1 or 2:1 in one direction, or up to as much as 6:1 or more in one or both directions.

[0027] The preferred PLA material for this purpose is available from Cargill-Dow under the name Nature Works Polylactide Resin, product code 5429B, CAS No. 9051-89-2. This PLA corn resin must be dried, preferably at about 170^CF for four to five hours, as it is hygroscopic in nature, to produce a moisture content preferably of less than about 0.025% (250 ppm) . The PLA resin preferably has a melt index of about 1.0-10.0 g/10 min. and is fully biodegradable making it particularly advantageous for use in the production of an erosion blanket netting according to this invention.

[0028] In order to enable the Cargill-Dow PLA to be stretched as needed for use in an erosion blanket according to this invention, a key secondary resin is required to eliminate the "as cast" net brittleness. An example of an acceptable secondary resin is available from Eastman Chemical, a product coded Eastman Bio™ GP Copolyester. The chemical name for this additive modifier is 1, 4- benzenedicarboxlic acid polymer with 1, 4-butanediol and hexanedioic acid. This additive is available under several product ID's, namely: 21154, P21154FC, P21154F2, P21154FF, P21154FJ, P21154FZ, P21154FA, P21154FB and P21154XZ.

[0029] The modifier additive is added at a level of from about 10% to about 35%, preferably about 8% to about 10%, by weight of the final resin content. With the incorporation of Eastman Bio™ GP Copolyester or other suitable additives, the netting may be cast according to a selected process of the prior art as discussed in the aforementioned U.S. patents and is then readily stretched, uniaxially or biaxially, to produce a light-weight, highly porous, biodegradable netting material particularly useful in the production of erosion blankets.

[0030] Examples of other modifier additives that could be blended with the Cargill-Dow PLA or other similar resins from as low as 2% to as high as 70% by weight for increased elasticity and toughness are polypropylene glycol (PPG) ; epoxy functionalized PPG (PPG-E) ; polyethylene glycol

(PEG) ; polybutylene succinate adipate random copolymer

(PBSU-AD0), also known by the trade name Bionolle#3000; and polyhydroxyalkanoate (PHA) polyester.

[0031] In addition to the "corn polymer" and modifier additives as described above, the instant inventive concept also includes the modification of polypropylene to make it biodegradable for the production of biodegradable lightweight, thin strand nets for erosion control and the like. Polypropylene can be made biodegradable by the addition of known and more recently developed biodegradable additives, such as ECM 6.0701 concentrate available from ECM Biofilms, Inc., 1 Victoria Square - Suite 304, Painesville, Ohio 44077. ECM 6.0701 is an additive concentrate composed of ethylene-vinyl acetate copolymer with added ingredients of organoleptic-organic chemical names/cultured colloids, and natural fiber. The following product coded ingredients are cited by the manufacturer for the concentrate : Reactor grade bining agent: (EVA) Ethylene-Vinyl Acetate Mixture of fatty acid soaps; Calcium; Accelerator; Organoleptic; sg/14/FCC-LBGVWG; Processed Fiber ash/Husk; Acid; Insoluble Ash; Accelerator Suspended: /V3200.

The ECM 6.0701 additive concentrate is added to the polypropylene at a level from about 0.5% to about 10%, by weight, and preferably from about 0.5% to about 3%, by

weight, in order to modify the polypropylene and make it biodegradable in accordance with the present invention. [0032] Other biodegradable resins that may be applicable to produce lightweight, thin strand netting materials for erosion control and other applications in accordance with this invention are Ecoflex F BX7011 resin available from BASF Plastics, 3000 Continental Drive-North, Mount Olive, New Jersey 07828, Biomax 4026 resin available from Dupont, Wilmington, Delaware and Mater-Bi biodegradable resin available from Novamont N.A., P.O. Box 1039, Ridgefield, Connecticut 06877.

[0033] According to BASF product literature, Ecoflex F BX7011 resin is a biodegradable, statistical aliphatic-aromatic copolyester based on the monomers butane diol, adipic acid ^• and terephthalic acid. Ecoflex has properties similar to PELD because of its high molecular weight and its branched molecular structure. DuPont ' s Biomax resins are biodegradable, modified-PET resins. The Mater-Bi biodegradable resins are mainly derived from corn, wheat and potato starch to produce thermoplastic materials which can be processed with the same machines currently used to process conventional plastics. [0034] Preferred processing of the modified resin according to this invention facilitates the extrusion and subsequent orientation of the "as cast" net. The pre-dried resin components as described are fed to an extrusion system consisting of a basic 24:1 or 32:1 length/diameter (L/D) extruded screw or other L/D sizes as are available or chosen to be used. This will convert the polymer ingredients into a molten resin that will then be fed to a die system, whether oscillating or reciprocating, of the prior art integral net extrusion system selected, preferably the systems of the aforementioned Hureau patents, to convert the resin into a molten cast tube in the form of machine direction (MD) and cross-machine direction (CMD) polymer strands integrally joined at their intersections to form perforations or openings in the cast tube.

[0035] The perforated cast tube then flows over a sizing mandrel, which imparts a small amount of melt orientation, into a water filled quenching tank in which the tube is solidified and slit open into a cast net sheet. At controlled temperatures, the cast net sheet is then fed to a uniaxial or biaxial stretching machine where the MD and CMD cast strands are oriented from about 1.5 to 6.0 times in one or both directions to form the finished net. [0036] The preferred finished product characteristics are as follows :

Strand Count - Minimum MD strands/20cm: 8.0 Maximum MD strands/20cm: 24.0 Minimum CMD strands/20cm: 8.0 Maximum CMD strands/20cm: 24.0. [0037] The biodegradable netting of the present invention preferably has a minimum cross-sectional area for the MD and CMD strands of about 0.0000125 square inches. The nodal junctions have a preferred cross-sectional area of about 0.0004 square inches. A preferred percentage of pores or open areas will be at least about 85%, preferably about 90% and higher.

[0038] The formation of the oriented strands is preferably carried out under low temperature cast extrusion and orientation conditions. Unlike polypropylene or high density polyethylene polyolefins, the extrusion profile temperatures are set to as low as about 350^CF, with the melt temperature below 400^CF, preferably less than about 350^CF. The uniaxial and biaxial stretching is preferably done at a temperature of less than about 250^CF, preferably about 180-200^CF. [0039] The finished net is fully, naturally and completely biodegradable. When installed or exposed to moisture and humidity the net reverts back to a sugar starch and is totally depleted by soil microbes.

[0040] Although other applications for the biodegradable net produced hereby are discussed below, the preferred use is in the production of an erosion blanket as seen in Figures 1-5 hereof wherein at least one layer of such net material is stitched to a layer of erosion-controlling material, with the preferred embodiment including a sandwich formed by a pair of layers of net material such as seen at 16, 18.

[0041] In the illustrated embodiment, each of the nets has been biaxially stretched by well known techniques, to provide cross-machine direction strands 16a, 18a and machine direction strands 16b, 18b, integrally interconnected by nodes 16c, 18c in a well known manner. Formation of the erosion control blanket from the nets 16, 18 and the erosion-controlling material 20 may be identical to the techniques used in the production of blankets heretofore using non-biodegradable plastic netting.

[0042] During use, one or more blankets 10 according to the present invention, is positioned on a hillside as seen in Figure 1, to control soil erosion. Optionally, biodegradable stakes are used to secure the blanket 10 in position. After a period of time, sunlight, rainfall and/or exposure to the soil will cause the netting 16, 18 to decompose leaving the straw or other fibrous core materials in place. Germinating ground cover seeds will hold the entire assembly in place until eventually the straw or the like also decomposes leaving behind firmly entrenched grass or other suitable ground cover with no remaining netting material to act as an obstacle to future maintenance.

[0043] Although the lightweight biodegradable netting of this invention has particular utility as a supporting material in the production of erosion blankets, other uses for such unique materials will be obvious to those with ordinary skill in this art. For example, the net may be used as a scrim for sod, as a packaging material, e . g. , for hay bales, and in any other environment where it's highly porous and biodegradable properties would be useful.

[0044] The foregoing description should be considered as illustrative only of the principles of the invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

What is claimed is:

1. A biodegradable polymer netting comprising an unaxially or biaxially oriented net made of a polymer composition selected from the group consisting of: a) a polylactide resin (PLA) or similar resin derived from naturally-occurring plant starch, which is combined with an effective amount of an additive to make the final resin extrudable and reduce the as cast net brittleness; b) a modified polypropylene resin which is combined with an effective amount of an additive to produce a biodegradable polypropylene resin; and c) a biodegradable resin selected from the group consisting of Ecoflex F BX7011 resin and Biomax 4026 resin .

2. The biodegradable polymer netting of claim 1, wherein said biodegradable polymer netting has a uniaxial or biaxial orientation at a stretch ratio of at least 1.5:1 in one direction, and up to as much as 6:1 or more in one or both directions and a minimum cross-sectional area for the MD and CMD strands of about 0.0000125 square inches, the nodal junctions have a preferred cross- sectional area of about 0.0004 square inches, and the percentage of pores or open areas will be at least about 85%.

3. A biodegradable polymer netting comprising a polylactide resin (PLA) or similar resin, derived from naturally-occurring plant starch, which is combined with an additive comprising about 2% to 70% by weight of the final resin content, wherein said additive is selected from the group consisting of: 1, 4-benzenedicarboxylic acid polymer with 1, 4-butanediol and hexanedioic acid; polypropylene glycol (PPG) ; epoxy functionalized PPG (PPG-E) ; polyethylene glycol (PEG) ; polybutylene succinate adipate; and random copolymer (PBSU-AD0) , also known by the trade name Bionolle#3000; and polyhydroxyalkanoate (PHA) polyester.

4. The biodegradable polymer netting of claim 3, wherein said biodegradable polymer netting has a uniaxial or biaxial orientation at a stretch ratio of at least 1.5:1 in one direction, and up to as much as 6:1 or more in one or both directions and a minimum cross-sectional area for the MD and CMD strands of about 0.0000125 square inches, the nodal junctions have a preferred cross- sectional area of about 0.0004 square inches, and the percentage of pores or open areas will be at least about 85%.

5. A biodegradable polymer netting comprising a modified polypropylene resin which is combined with an effective amount of ECM 6.0701 concentrate as an additive to increase extrudability and reduce as cast net brittleness of said resin.

6. The biodegradable polymer netting of claim 5, wherein said biodegradable polymer netting has a uniaxial or biaxial orientation at a stretch ratio of at least 1.5:1 in one direction, and up to as much as 6:1 or more in one or both directions and a minimum cross-sectional area for the MD and CMD strands of about 0.0000125 square inches, the nodal junctions have a preferred cross- sectional area of about 0.0004 square inches, and the percentage of pores or open areas will be at least about 85%.

7. An erosion blanket having an inner layer and an outer layer, wherein said inner layer comprises generally fibrous, biodegradable materials such as straw, coconut fibers, wood excelsior or similar materials, and said outer layer is comprised of the biodegradable polymer netting of claim 1, and wherein said erosion blanket is capable of being held in the location of interest by use of spikes or nails.

8. The erosion blanket of claim 7 wherein said outer layer is comprised of the biodegradable polymer netting of claim 2.

9. The erosion blanket of claim 8 wherein said inner layer further comprises seeds.

10. The erosion blanket of claim 7 wherein said outer layer is comprised of the biodegradable polymer netting of claim 4.

11. The erosion blanket of claim 7 wherein said outer layer is comprised of the biodegradable polymer netting of claim 6.

12. The erosion blanket of claim 10 wherein said inner layer further comprises seeds.

13. A process for making a biodegradable polymer netting comprising the steps of: a) extruding pre-dried resin components of claim 1 into a molten cast tube in the form of machine direction (MD) and cross-machine direction (CMD) polymer strands integrally joined at their intersections to form perforations or openings in said cast tube; b) causing said perforated cast tube to flow over a sizing mandrel to impart a small amount of melt orientation, and into a water filled quenching tank in which the polymer resin in the tube is solidified; c) slitting open the tube into a cast net sheet; and d) uniaxially or biaxially stretching the cast net sheet such that the MD and CMD cast strands are oriented from about 1.5 to 6.0 times in one or both directions to form the finished net.

14. The biodegradable polymer netting of claim 1 wherein said netting has the following dimensions: a) Minimum MD strands/20cm: 8.0; Maximum MD strands/20cm: 24.0; Minimum CMD strands/20cm: 8.0; Maximum CMD strands/20cm: 24.0; a minimum cross-sectional area for the MD and CMD strands of about 0.0000125 square inches; and the percentage of pores or open areas will be at least about 85%.

15. The biodegradable polymer netting of claim 3 wherein the polylactide resin (PLA) or similar resin is combined with 1, 4-benzenedicarboxylic acid polymer with 1, 4- butanediol and hexanedioic acid comprising about 8% to 10% by weight of the final resin content.

16. The biodegradable polymer netting of claim 5 wherein the modified polypropylene resin or similar resin is combined with a sufficient amount of ECM 6.0701 concentrate.

17. The biodegradable polymer netting of claim 5, wherein said ECM 6.0701 concentrate is added to polypropylene in an amount by weight from about 0.5% to about 10%, preferably about 0.5% to about 3.0%.