FIBER WITH SACRIFICIAL JUNCTIONS

Abstract

A fiber composition, along with a method for toughening fiber compositions, are described. A fiber composition contains at least three loops along the length of said fiber, wherein the loops are bonded using sacrificial junctions comprising a bonding material that is chemically distinct from the fiber material. In some preferred embodiments, the loops have a circumference of at least one centimeter, and the bonding material is an ultraviolet light-cured adhesive. When a suitable force is applied, one or more sacrificial junctions can break without breaking the continuous fiber. The fiber compositions described herein have a toughness that is many times greater than the toughness of otherwise equivalent compositions of the fiber material which lack any such loops.

Claims

1. A fiber composition comprising: A) a continuous fiber having a length of at least 5 meters, and B) at least 3 fixed loops along the length of said fiber; wherein said continuous fiber is made from a fiber material; wherein said loops have a circumference of at least 1 millimeter; and wherein said loops are welded with a loop weld material that is chemically distinct from the fiber material.

2. The composition of claim 1, wherein said loops are welded with an ultraviolet light curing adhesive.

3. The composition of claim 1, wherein said continuous fiber comprises a fiber selected from the group consisting of natural fibers, man-made fibers, and semi-synthetic fibers.

4. The composition of claim 1, wherein said composition comprises at least ten loops along the length of said fiber; wherein said loops have a circumference of at least one centimeter; and wherein said composition has a toughness that is at least two times the toughness of an otherwise equivalent composition of the fiber material that lacks any welded loops.

5. A method for enhancing toughness of a fiber composition comprising the steps: A) selecting a continuous fiber having a length of at least 5 meters, and B) introducing at least three fixed loops along the length of said fiber; wherein said continuous fiber is made from a fiber material; wherein said loops have a circumference of at least 1 millimeter; and wherein said loops are welded with a loop weld material that is chemically distinct from the fiber material.

6. The method of claim 5, wherein at least 10 fixed loops are introduced along the length of said fiber.

7. The method of claim 5, wherein said loops have a circumference of at least one centimeter.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0014] FIG. 1 is a schematic diagram showing a representative looped fiber composition as described herein.

[0015] FIG. 2 is a stress-strain curve of a looped Loxosceles strand with L.sub.0=5 mm. The first two peaks show the response of the apparent length of the strand until a loop unraveling event (*), and the last peak (having darker fill) shows the response of the unraveled strand.

[0016] FIG. 3 is a graph showing an experimentally measured stress-strain curve of a looped fiber with non-zero adhesive mass.

DETAILED DESCRIPTION OF THE INVENTION

[0017] Suitable looped fiber compositions as described herein can in theory be made from any type of fiber, although the advantages conferred by the methods are more apparent for some fibers than others. Representative fibers include, but are not limited to, natural fibers such as cellulosic fibers (e.g., cotton, hemp, jute, flax, ramie, sisal) and animal fibers (e.g., wool, silk), and man-made fibers including metallic fibers (e.g., copper, aluminum), carbon fibers, glass fibers, synthetic polymer fibers (e.g., polyamide, polyvinyl chloride, polyolefin, aromatic polyamide, acrylic, polyester), and semi-synthetic fibers (e.g., cellulose acetate, rayon).

[0018] The methods provided have practical utility only when used with a continuous fiber having a length of at least 5 meters, having at least 3 loops along the length of said fiber, wherein (i) said continuous fiber is made from a fiber material; (ii) said loops have a circumference of at least 1 mm; and (iii) said loops are welded with a loop weld material that is chemically distinct from the fiber material such that the welded area is positionally fixed until sufficient force is applied such that the weld is broken. In some embodiments, production of the toughened fiber is facilitated when the loops have a circumference of at least one centimeter. In some embodiments, commercial viability is increased when the continuous number of loops is at least 20, or at least 100.

[0019] Suitable adhesives used to weld the loops can be any type of adhesive, but preferred adhesives are inexpensive, have quick setting times, and create sacrificial junctions having a breaking strength less than the strength of the selected unlooped fiber, preferably between 1% of the breaking strength of the unlooped fiber and 99% of the breaking strength of the unlooped fiber. Adhesives can be non-reactive adhesives such as drying adhesives, pressure-sensitive adhesives, contact adhesives, and hot-melt adhesives; or reactive adhesives such as multi-component adhesives or one-part adhesives.

[0020] Drying adhesives set through a drying process, and can be solvent-based adhesives or emulsion adhesives. Solvent-based adhesives entail a mixture of ingredients dissolved in a solvent, and upon evaporation of the solvent, the adhesive hardens. Pressure-sensitive adhesives form a bond by application of pressure (e.g., conventional tapes). Contact adhesives are generally used to form strong bonds with high shear resistance, and include compounds such as natural rubber and neoprene. Hot-melt adhesives comprise thermoplastic agents applied in molten form which solidify upon cooling to form sacrificial junctions as described herein.

[0021] Reactive adhesives include multi-component adhesives which harden when two or more different components react (e.g., epoxy adhesives), as well as one-part adhesives which harden via a chemical reaction with an external source, typically oxygen, light, or water.

[0022] Ultraviolet light curing adhesives, also known as light curing materials, are particularly well-suited to the methods of the invention because of their rapid cure times and strong bond strengths. For example, light curing materials can cure in as little as one second. They are often acrylic-based polymers.

[0023] Comparing the looped fiber compositions described herein to unlooped fibers (which can be used as starting materials), experimental and theoretical analysis of the looped material's tensile properties demonstrates significant enhancement in toughness due to the looped structure.

[0024] Referring now to FIG. 1, a continuous fiber 10 has a series of loops 11 along the length of said fiber. The loops are fixed into place with a series of sacrificial junctions 12, which are made with a loop weld material that is distinct from the chemical composition of the continuous fiber 10. When a sufficient force is applied, the sacrificial junctions are broken, resulting in a fiber having increased distance between its two ends. All loops can have the same size, or, as shown in FIG. 1, they can have different sizes. All loops can have the same shape, e.g., a circle, or they can have different shapes, as shown in FIG. 1. All sacrificial junctions can require the same breaking force, or they can have different breaking forces. In the representative diagram shown in FIG. 1, there are three loops having sacrificial junctions, but in other representative embodiments, the number of loops could be at least 10, at least 100, or at least 1000.

[0025] We have identified this enhanced toughness in experimental studies of the recluse genus of spiders (Loxosceles), which produce a biological metamaterial: its ribbon-like silk is woven into serial micro-loops by an intricate spinneret motion. This looped architecture enhances toughness. As shown in an example stress-strain curve of an experimentally measured strand of Loxosceles silk with two loops (FIG. 2), opening the first loop at a strain of 0.1 and loop opening stress a fully relaxed the ribbon (first asterisk). Further extension exhausted the slack and built stress in the fiber until the next loop unraveled (second asterisk, FIG. 2). After the last loop was opened, the fiber was ultimately stretched to failure at stress .sub.u. Notably, this strain cycling needed to unravel serial loops significantly increases the total energy required to fracture the fiber (FIG. 2).

EXAMPLES

[0026] The examples that follow are intended in no way to limit the scope of this invention but are provided to illustrate the methods of the present invention. Many other embodiments of this invention will be apparent to one skilled in the art.

Example 1

[0027] Loops (of approximately 1 cm in total perimeter length, also referred to herein as circumference) were introduced into 24 gauge copper wire by soldering using a 60/40 PbSn solder. The sample was then loaded into wire clamps in an Instron 5848 MicroTester with a 500 N load cell. After the sample's initial length was measured, it was extended at a rate of 1 mm/min until fracture, and the results are depicted in the stress-strain curve shown in FIG. 3. A control test was also conducted with a length of non-looped wire, and is shown as the dark (and thicker) curve in FIG. 3, while the results of the looped fiber appear as the lighter curve in FIG. 3. The significant breaking strength of the loops relative to the ultimate strength of the wire is apparent in the height of the stress peaks, indicating that the wire underwent substantial strain-cycling before fracture.

Example 2

[0028] Looped strands of tape were fabricated that successfully released all hidden length before fracture and displayed no decrease in strength after loop unravelling. Heavy-duty trapping tape (with a width of 24.2 mm and thickness of 0.130 mm, comprising a polypropylene film reinforced with fiberglass fibres and coated on one side with a rubber-based adhesive) was utilized for this model study based on its elastic behaviour, ribbon morphology, and high resistance to torsional tearing due to its fibrillar composition. When a single loop of normalized size 1.5 (wherein a is the loop circumference divided by the initially loaded length of the strand) was introduced, no significant decrease in strength was detected, and toughness was significantly increased. Tensile testing on these folded fibres was conducted using a 5848 MicroTester (Instron) with a 1 kN load cell. The mean toughness gain of 30% was in good agreement with the 22% gain predicted by a mathematical model, and much larger increases can be obtained in systems with more loops.

INCORPORATION BY REFERENCE

[0029] All publications, patents, and patent applications cited herein are hereby expressly incorporated by reference in their entirety and for all purposes to the same extent as if each was so individually denoted.

EQUIVALENTS

[0030] While specific embodiments of the subject invention have been discussed, the above specification is illustrative and not restrictive. Many variations of the invention will become apparent to those skilled in the art upon review of this specification. The full scope of the invention should be determined by reference to the claims, along with their full scope of equivalents, and the specification, along with such variations.

[0031] The articles a and an are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, a fiber means one fiber or more than one fiber.

[0032] Any ranges cited herein are inclusive, e.g., between five percent and seventy-five percent includes percentages of 5% and 75%.