[0001] This invention relates generally to a rubber composition useful for rubber products such as belts and hose, more particularly to a composition that is a blend of polyvinylpyrrolidone in an elastomer, reinforced with cellulosic fibers.

[0002] Belts for power transmission include V-belts, multi-v-ribbed belts, and synchronous or toothed belts. High-performance, synthetic, short-fiber reinforcements, such as aramid fibers, are often used in the rubber formulations used in such belts. These fibers tend to be expensive and from non-renewable sources, but are considered necessary to meet performance requirements.

SUMMARY

[0003] The present invention is directed to systems and methods which provide elastomeric compositions useful for power transmission belts or hose which utilize environmentally friendly cellulosic reinforcing fibers.

[0004] The elastomeric or rubber compositions include an elastomer,

polyvinylpyrrolidone, a cellulosic fiber, and a curative.

[0005] The elastomer may be one or more selected from ethylene elastomers, nitrile elastomers, and polychloroprene elastomers. The elastomer may be an ethylene-alpha-olefin elastomer.

[0006] The polyvinylpyrrolidone may be present in an amount of 5 to 50 parts weight per hundred parts ("PHR") of the elastomer.

[0007] The cellulosic fiber may be one or more selected from kenaf, jute, hemp, flax, ramie, sisal, wood, rayon, acetate, triacetate, and cotton. The cellulosic fiber may be a natural fiber or man-made material. The cellulosic fiber may be a bast fiber. The

cellulosic fiber is present in an amount of 1 to 50 parts weight per hundred parts of the elastomer.

[0008] The invention is also directed to a power transmission belt utilizing the reaction product of the inventive rubber composition. The rubber composition may be vulcanized or cured.

[0009] The invention may contribute to providing relatively high value rubber compounds, for example, achieving a relatively high compound modulus with a relatively low-cost fiber from a renewable natural resource.

[0010] Embodiments of the invention based on polychloroprene elastomer may exhibit a modulus plateau on cure instead of a marching modulus.

[0011] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its

organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which are incorporated in and form part of the specification in which like numerals designate like parts, illustrate embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings:

[0013] FIG. 1 is a partially fragmented perspective view of a power transmission V-belt according to an embodiment of the invention;

[0014] FIG. 2 is a cross-section view of a power transmission V-ribbed belt according to an embodiment of the invention; and

[0015] FIG. 3 is a partially fragmented perspective view of a toothed power transmission belt according to an embodiment of the invention.

DETAILED DESCRIPTION

[0016] The invention is directed to rubber compositions useful for dynamic products such as power transmission belts or hose. The rubber compositions have a base elastomer blended with polyvinylpyrrolidone (PVP) and have a cellulosic fiber component.

[0017] The term "rubber" refers to a material capable of recovering from large deformations quickly and forcibly (i.e., is "elastomeric"), and which is essentially insoluble in boiling solvents (due the presence of covalent crosslinks). Other useful definitions may be found in ASTM D-1566, which is hereby incorporated herein by reference. "Elastomer" refers to an elastomeric polymer, which when crosslinked may form a rubber.

[0018] Rubber or elastomeric "composition" or "formulation" refers to the combination of raw materials used to make a rubber material. Rubber "compound" refers to the mixture of the materials in a rubber composition after mixing but before curing or vulcanization. Rubber compositions may include a number of additional ingredients besides the elastomer(s), such as curatives, fillers, extenders, softeners, anti-degradants, colorants, process aids, curatives, accelerators, retardants, coagents, flame retardants, and the like. "Base elastomer" refers to the elastomeric polymer used in the rubber composition, and it may be a blend of elastomers.

[0019] The inventive rubber may be based on any suitable base elastomer, but exemplary elastomers are natural rubber, polychloroprene (CR), polyisoprene, styrene-butadiene rubber, ethylene elastomers, nitrile elastomers, polyurethane elastomers, and the like. Ethylene elastomers include ethylene-vinylacetate elastomer, ethylene acrylic elastomers, and ethylene-alpha-olefin elastomers. Nitrile elastomers include acrylonitrile-butadiene rubber (NBR), hydrogenated nitrile (HNBR), carboxylated NBR and HNBR,

and the like. The invention is particularly advantageous when the exemplary rubber compositions are based on non-polar elastomers such as the ethylene-alpha-olefin elastomers, such as ethylene propylene diene elastomer (EPDM), ethylene propylene elastomer (EPM), ethylene octene elastomers (EOM), ethylene butene elastomer (EBM), and the like. The rubber compositions may also be based on blends of two or more elastomers.

[0020] The inventive rubber is based on a blend of a base elastomer and polyvinylpyrrolidone as the polymeric matrix in which all other ingredients are mixed. Polyvinylpyrrolidone (PVP) is a white, hygroscopic powder with a weak characteristic odor. In contrast to most polymers, it is readily soluble in water and a large number of organic solvents, such as alcohols, amines, acids, chlorinated hydrocarbons, amides and lactams. On the other hand, the polymer is insoluble in the common esters, ethers, hydrocarbons and ketones. The hygroscopic property combined with outstanding film formation, initial tack and adhesion to different materials, high capacity for complex formation, good stabilizing and solubilizing capacity, insensitivity to pH changes, ready radiation-induced crosslinkability as well as good biological compatibility have made PVP a frequently used specialty polymer especially in solutions, emulsions, coatings, and films.

[0021] PVP is synthesized by free-radical polymerization of N-vinylpyrrolidone in water or alcohols with a suitable initiator and method of termination. By selecting suitable polymerization conditions, a wide range of molecular weights can be obtained, extending from low values of a few thousand daltons to approximately 2.2 million daltons. Selected comonomers can be incorporated into the PVP polymer during polymerization to modify its properties. Such comonomers include vinylacetate (VA) and N-vinylcaprolactam (VCAP). For example, Luvitec® VA64 contains about 40% of VA comonomer and is less hygroscopic than PVP homopolymer. Table 1 shows weight average and number average molecular weight in Daltons of some commercial PVP homo- and co-polymer grades from BASF sold under the Kollidon® mark and the Luvitec® mark.

[0022] TABLE 1.

Number

Grade Weight Average

Average

Kollidon( D 12PF 2000-3000 1300

Kollidon( D 17PF 7000-11000 2500

Kollidon( D 25 28,000-34,000 6000

Kollidon( D 30 44,000-54,000 12,000

Kollidon( D 90F 1,000,000-1,500,000 360,000

Luvitec® K17 9000 2000

Luvitec® K30 50,000 14,000

Luvitec® VA64 65,000 15,000

[0023] The present invention is directed to the use of cellulosic fibers, which are naturally occurring plant-derived fibers or man-made fibers with a major component based on cellulose, such as wood, kenaf, jute, hemp, ramie, and flax, in rubber compositions useful for flexible power transmission belts or hose. The bast fibers from the bark section of the plants are of primary interest, although some leaf and seed fibers may also be useful. Other bast fibers include sunn, urena or cadillo, and roselle. Leaf fibers include abaca, cantala, henequen, istle, phromium, sanseviera, and sisal. Useful seed fibers include cotton and kapok. Wood fibers include those derived from hardwood or softwood species. Man-made cellulosic fibers include rayon (regenerated cellulose), viscose, acetate (cellulose acetate), triacetate (cellulose triacetate), and the like.

[0024] Kenaf {Hibiscus cannabinus L.) is an annual herbaceous plant originally from Africa. It is a newer crop to the United State. Kenaf is mainly cultivated in southern temperate regions such as Mississippi, Texas, California, Louisiana, New Mexico, and Georgia. It has a growing period of 90-150 days and may grow to 2.4-6 m in height. Its single, straight stem consists of an outer fibrous bark and an inner woody core which yields two distinct types of fibers: bast and core fibers respectively. The bast fiber constitutes about 26-35 wt% (weight percentage) of its stem, and genetic strains have been developed which yield 35 wt% or greater bast portions. The harvested kenaf stems are usually first decorticated to separate the bark from the core, producing ribbons of kenaf bast fibers. These ribbons can be retted into fiber bundles or single fibers. It is preferable to harvest the kenaf crop once the fiber has been air-dried (approximately 10% moisture content). Drying may be achieved by leaving the crop standing in the field.

[0025] In general, the kenaf bast fibers are hollow tubes averaging 2.6 mm in length, 21 μπι in diameter with an average length/diameter aspect ratio of 124, very similar to softwood species. The core fibers, with an average length of 0.5 mm, closely match those of hardwoods.

[0026] The major constituents of kenaf bast fiber bundles (KBFB) are cellulose, hemicellulose and lignin. The amount of each constituent can vary significantly due to cultivation environments, geographic origins, age, locations in the plant (from root to tip), and retting and separating techniques. Lloyd E. H. and D. Seber, "Bast fiber applications for composites," (1996), available at

http://www.hempology.org/CURRENT%20HISTORY/1996%20HEMP%20COMPOSIT ES.html, reported weight percentages of 60.8 for cellulose, 20.3 for hemicellulose, 11.0 for lignin, 3.2 for extractives, and 4.7 for ash. Mohanty et al, "Biofibres, biodegradable polymers and biocomposites: an overview," Macromolecular materials and engineering, 276-277(1): 1-24 (2000), reported lower cellulose (31-39 wt%) and higher lignin (15-19 wt%) amounts. Rowell et al., "Characterization and factors effecting fiber properties," In: Frollini E, Leao AL, Mattoso LHC, editors. "Natural polymers and agrofibers based composites: preparation, properties and applications," San Carlos, Brazil: L.H.C., Embrapa. pp. 115-134 (2000) reported 44-57 wt% cellulose, and 15-19 wt% lignin.

Other sources cite cellulose contents of about 71 to 76% for kenaf, jute, hemp and flax fibers, with lower (<8%) lignin contents and 13-19%) hemicellulose.

[0027] Kenaf is a cellulosic source with ecological and economical advantages, abundant, exhibiting low density, nonabrasive during processing, high specific mechanical properties, biodegradable and cheap pricing. Historically, kenaf fiber was first used as cordage. Industry is now exploring the use of kenaf in papermaking and nonwoven textiles. Potential applications of kenaf products include paper pulp, cordage, grass erosion mats, animal bedding, oil sorbents, potting media, animal litter, insulation boards, fillers for plastics, and textiles.

[0028] Table 2 compares mechanical properties of kenaf and other cellulosic fibers with some common synthetic fibers. Kenaf, flax, hemp, and jute are bast fibers, while sisal is a leaf fiber and cotton is a seed hair fiber. In terms of tensile strength and elongation, the cellulosic fibers compare quite favorably with nylon and polyester. The outstanding feature of kenaf fiber is its Young's modulus, which is close to that of E-glass fiber and aramid fiber. These cellulosic fibers' tensile strength is not high enough for belt tensile cord applications, but according to an embodiment of the invention, they are suitable for using as a filler to reinforce rubber belt compounds to provide belt shape stabilization or stiffening or cord support.

[0029] TABLE 2.

Tensile Young's Elongation

Density Diameter

Fiber strength Modulus at break

(g/cc) (μιη)

(MPa) (GPa) (%)

Kenaf (bast) 1.45 14-23 930 53 1.6

Flax (bast) 1.5 40-600 345-1500 27.6 2.7-3.2

Hemp (bast) 1.48 13-30 810 1-6

Jute (bast) 1.50 15-25 350-700 1.5

Sisal (leaf) 1.5 511-635 9.4-22 2-3

Cotton (seed hair) 1.5-1.6 12-38 287-800 5.5-12.6 7-8

Nylon (synthetic) 1.0-1.2 40-90 3-5 20-60

Polyester 1.2-1.5 40-90 2-4.5 12-47

E-glass 2.55 <17 3400 73 2.5

Kevlar 1.44 3000 60 2.5-3.7

Carbon 1.78 5-7 3400-4800 240-425 1.4-1.8

[0030] Preferred bast fibers, including kenaf fibers, for practicing the present invention are the longer bast fibers from bark, separated from the shorter core fibers, and chopped to a useful length for use in belt compositions. Suitable fiber lengths may be in the range from 0.5 to 5 mm, or from 1 to 4 mm, or 1 to 3 mm or 2 to 3 mm. Preferred loadings will depend on the amount of reinforcement desired, but may advantageously be in the range of 0.5 to 50 parts weight per hundred parts of the base elastomer (PHR), or from 1 to 30 PHR. Suitable fibers may be obtained, for example, from Procotex

Corporation SA, Kenactiv Innovations, Inc., or International Fiber Corporation.

[0031] Flax fiber (Linum usitatissimum L.) comes from the annual plant by that name grown in temperate, moist climates. Harvesting and processing of the flax bast

fibers is similar to Kenaf. Boiled and bleached flax may contain over 95% cellulose. Suitable fibers may be obtained for example from Procotex Corporation SA.

[0032] Hemp fiber comes from the plant Cannabis sativa which originated in China, but is now grown in Asia and Europe as well.

[0033] Jute comes from two plants, Corchorus capsularis and C. olitorius. It is grown mainly in India, Bangladesh, Burma, Nepal, and Brazil. Kenaf and jute contain lignocellulose, which contributes to their stiffness. Roselle is derived from H. Sabdarifa, which is closely related to kenaf.

[0034] Ramie bast fiber comes from the bark of Boehmeira nivea. Because of the high gum content, it cannot be retted like kenaf. Instead, the fibers are separated by boiling in alkaline solution, followed by washing, bleaching, neutralizing, and drying. Thus degummed ramie may contain over 95% cellulose. Such chemical treatments may also be used to prepare other types of fibers, and may include enzyme treatments.

[0035] Sisal is obtained from Agave sisalana and is the most commercially important of the leaf fibers.

[0036] A number of other plant fibers have been studied for possible use in composites. To the extent they are cellulosic and have suitable physical and dimensional properties, they may also be useful in rubber compositions. Among these others are banana plant fibers, pineapple, palm, bamboo, and the like.

[0037] Wood fiber (also known as cellulose fiber or wood pulp or just "pulp") can be obtained from any number of wood species, both hardwood and softwood. The fibers may be separated by any of the known pulping processes to obtain suitable fibers for reinforcing rubber compositions. Recycled pulp may be used.

What is claimed is:

1. A rubber composition comprising a base elastomer, polyvinylpyrrolidone, a cellulosic fiber, and a curative.

2. The rubber composition of claim 1 wherein the base elastomer is one or more selected from the group consisting of ethylene elastomers, nitrile elastomers, and polychloroprene elastomer.

3. The rubber composition of claim 1 wherein the base elastomer is an ethylene- alpha-olefin elastomer.

4. The rubber composition of claim 1 wherein the base elastomer is a

polychloroprene elastomer.

5. The rubber composition of claim 1 wherein the cellulosic fiber is one or more natural fiber selected from the group consisting of kenaf, jute, hemp, flax, ramie, sisal, wood and cotton.

6. The rubber composition of claim 1 wherein the cellulosic fiber is one or more selected from the group consisting of kenaf, jute, hemp, and flax.

7. The rubber composition of claim 1 wherein the cellulosic fiber is one or more bast fiber selected from the group consisting of kenaf, jute, hemp, flax, and ramie.

8. The rubber composition of claim 1 wherein the cellulosic fiber is one or more bast fiber selected from the group consisting of kenaf, jute, and flax.

9. The rubber composition of claim 1 wherein the cellulosic fiber is a man-made material.

10. The rubber composition of claim 1 wherein the polyvinylpyrrolidone is

present in an amount of 5 to 50 parts weight per hundred parts of the base elastomer.

11. The rubber composition of claim 1 wherein the cellulosic fiber is present in an amount of 1 to 50 parts weight per hundred parts of the base elastomer.

12. A power transmission belt comprising the reaction product of the rubber composition of claim 1.

13. The rubber composition of claim 1 after having been vulcanized or cured.

14. A rubber composition comprising an ethylene-alpha-olefin elastomer,

polyvinylpyrrolidone, a cellulosic bast fiber selected from the group consisting of flax, jute and kenaf, and a curative.

15. The rubber composition of claim 14 wherein the polyvinylpyrrolidone is present in an amount of 5 to 50 parts weight per hundred parts of the elastomer.

16. The rubber composition of claim 15 wherein the cellulosic fiber is present in an amount of 1 to 50 parts weight per hundred parts of the elastomer.

17. A power transmission belt comprising the reaction product of the rubber

composition of claim 16.