CA2001475A1 - Short fibers and reinforced elastomeric composition and articles containing short fibers - Google Patents

Abstract

SHORT FIBERS AND ELASTOMERIC
COMPOSITION CONTAINING SHORT FIBERS

Abstract of the Disclosure A short fiber of from 0.1 to 1.0 inches in length having a modulus of less than 1X1011 dynes/cm2, preferably less than 0.6x1011 dynes/cm2. Preferably the fiber is a polyamide having a birefringence value of from 0.02 to 0.04. Elastomeric compositions containing the short fiber exhibit improved fatigue resistance, lower heat generation upon cyclic estraining and improved modus.

Description

SHORT FIBERS AND ELASTOMERIC
_ _ _ COMPOSITION REINFORCED CONTAININC SHORT FIBERS

8ack~round of the Invention This invention is in the field of fibers and elastomeric compositions; more particularly, the invention relates to low modulus short fibers and elastomeric compo~itions comprising the elastomer such short fibers.
U.S. Patent No. 4,389,361 contains a definition for the term ela~tomer as a substance that can be stretched at room temperature to at least twice its original length and, after having been ~tretched and the stress removed, returns with force to approximately its 15 original length in a short time. (Glossary of terms as prepared by ASTM Committee D-11 on Rubber and Rubber-like material~, published by the American Society ~or Testing Materials).
Elastomers are also referred to in Billmeyer, Textbook of Polymer Science, second edition, John Wiley and Sons, Inc. ~1971), at pages 242-243 and 533-550 hereby incorporated by reference. Elastomer~ are considered as a class of high poiymers which are amorphous when unstretched and must be above the glass transition temperature to be elastic. Typically, ela~tomeric polymers have networks Or cros~links.
Crosslinks can be obtained by a vulcanization process.
Crosslinking tran~forms an elastomer from a weak thermoplastic mass into a strong elastic, tough rubber material.
An indication oP the meohanical properties of elastomer~ i9 the measurement oP elongatlon under load, commonly characterized by the stress-strain behavior of the rubber. As the load is increased and the elongation is measured a curve results which is considered the stress-~train curve of the rubber. The elongation of the rubber ~ample is measured with increased load.

2~0i47S

Correspondingly a stress-strain curve develops as the load i9 removed. Difference~ between the stress-~train curve during loading and unloading represent energy losses due to internal heat generatlon and is commonly called a hyteresis 1099. As ~uccessive cycle~ take place, the changes to resistance to stretching, tensile strength, energy absorption, and permanent set become smaller.
A common type of testing is to subject elastomeric materials to cyclical mechanical ~tresses. Most materials fail at a stress considerably lower than that required to cause rupture in a single stress cycle.
~his phenomena is called ~atigue. Various modes of fatigue testing in common use include alternating tensile and compressive stress and cyclic flexural stress. Results are reported as plots of cyclic stress amplitude versus number of cycles to fail. Fatigue testing is reviewed in Billmeyer at page 128.
Elastomeric compositions can include a variety of additives to improve processing, crosslinking, physical properties and age resistance. Such additiveg include the u~e of oil, vulcanization agents such as sulphur, acceleration aids to enhance vulcanization, activators to attain the full effect o~ the organic accelerators.
Elastomeric compositions have been filled with a variety of materials including oil~ and other fillers.
Additionally, fillers are used as reinforcement agents to improve physical properties. A widely used form of filler in common rubber~ is carbon black. Reference is made to the Vanderbilt Rubber Handbook for typloal elastomerio compositions.
Attempts have been made to stiffen elastomeric compositions by incorporating short fibers. While the fiber stiffened the composition, it was deleterious to properties such as the ability to withstand cyclic strain (fatigue).
Patents disclosing flber reinforced polymer composites include U.S. Patent Nos. 4,389,361 , 2C~01475 4,728,698, 4,711,282, 4,393,154, 4,014,969 and 3,969,568. The patents of interest relating ~o fiber loaded rubber compositions generally disclose that fibrous reinforcements are used to stiffen, and strengthen elastomeric compositions.
U.S. Patent No. 4,389,361 discloses a process for molding fiber loaded rubber compounds. This patent i~
directed to an elastomeric compound that has chopped fibers dispersed throughout the compound. The orientation of the chopped ~ibers within the rubber matrix increases the modulus and strength of the compound. The orientation i9 achieved by milling the fiber loaded compound to break up the fibers and thereafter mold and then vulcanize the resulting product. The filaments are initially approximately 1.6 inche~ in length and have a diameter of 11 micronq. The resulting composition has fibers of small length of approximately 0.125 inches. The fibers are used as a reinforcing additive to improve physical properties such as tensile strength and to stiffen the composition by reducing elongation and increasing the "low strength modulus". U.S. Patent No. 4,711,285 di~closes a bead filler compo~ition which contain3 short fiber of an organic polymer. It can be from 15 to 70 parts the short fiber based on the rubber. Short fibers are used to increase the elastic modulus of the rubber.
U.S. Patent 4,393,154 discloses a process for blending 5 to 50% by weight of a chopped fiber from about 0.4 to 1.3 cm in length with 95 to 50% by welght of a particulate unvulcanized rubber. It is a goal of this patent to lmprove uniform mixing of ~ibers and rubber.
U.S. Patent No. 3,969,568 dlscloses aramid flock reinforcement of rubber u~ing a particular adhesive.
The composition is disclosed to contain rubber and adhesive compositions and a fibrou~ rein~orcement. The composition has improved physical properties such as Z(X)1475 compression modulu~ and lower elongation, and a stiffer rubber.

';UMMARY OF THE INVENTION
. . ~
The present invention includes a polyamide fiber f`rom 0.1 to 1.0 inches long having a birefringence value of from 0.02 to 0.04. The fiber preferably has a fiber modulus of le~s than 1X1011 dyne/cm2 and more preferably less than 0.6x1011 dyne/cm2. The polyamide is preferably selected from polycaprolactam and poly (hexamethylene adipamide), The present invention is a composition comprising an elastomer and from 1 to 25%, preferably from Z to 10%, and more preferably 4 to 6% by weight based on the elastomer of a fiber up to 1 inches long, preferably from .1 to 1 inches long, more preferably from .125 to 1 inches long, and most preferably from .25 to 0.5 inches long.
Preferably, the fiber in general has a fiber modulus of less than 1X1011 dyne~cm2 as measured by ASTMD 2256-80. The fiber is preferably a polyamide fiber having a birefringence value of le3s than 0.1 preferably from 0.01 to 0.05 and more preferably from 0.02 to 0.04. The birefringence value is a measure of molecular orientation effected by drawing or stretching. The birefringence is measured according to ASTM 858-82.
The composition of the present invention can have sufficient amount of a polyamide fiber having a birefringence value of from 0.02 to 0.04 to result ln the compo~ition having a greater fatigue llfe, as mea~ured acoording to modlfied ASTM-D 3479-76 when compared to a composition without the fiber.
In an alternate embodiment of the present invention the composition comprise3 from 1 to 25% by weight of an elastomer of a fiber from 0.1 to 1 inches long having sufficient molecular orientation to result in a composition having equal or a greater fatigue life, 2(~147S

mea~ured according to modified ASTMD-3479-7, when compared to a compo~ition without the fiber. The orientation should be low enough to have equal or better fatigue resistance as the compo~ition without the short fiber, but high enough to improve the stiffness (modulus) of the elastomeric composition.
A preferred composition comprises an elastomer, and 1 to 25% by weight based on the elastomer of a polyamide fiber from 0.1 to 1 inches long having a birefringence value of le99 than 0.1 preferably 0.02 to 0.04.
The compositlon can additionally contain other additives conventionally used in elastomeric composition including but not limited to processing aids, crosslinking agents including curing agents, accelerators and other types of curing promoters, and age resistors. The composition can comprise other types of fillers such as particulate ~illers including carbon black aq well aq extenders ~uch as oil.

BRIEF DESCRIPTION OF THE DRAWING
The figure is a graph of the heat generation rate, 104 Erg/cc/sec versus temperature.

DETAILED_DESCRIPTION OF THE.INVENTION
The present invention is a composition comprising an elastomer and from 1 to 25 percent by weight of elastomer of fiber from 0.1 to 1.0 inches in length.
The fiber modulu~ i9 preferably less than 1xlO11dynes/cm2 preferably le99 than 0.6x1011 dynes/cm2 and more preferably from 0.1 to .6x101l dynes/cm2. The composition ha3 equal or better fatigue reslstanoe and is stiffer than the ela~tomeric composition without the fiber.
The improvement can be obtained by controlling the degree of molecular orientation attained during drawing or stretching of the fiber. Thi~ property is measured as the bire~ringence of the fiber.

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2(~0~475 The composition is preferably a homogeneous distribution of ribers in the elastomeric compo~ition matrix. Preferably, the fibers are randomly oriented.
However, the fibers can be oriented. Such orientation 5 can occur or be induced during proce~sing the elastomeric composition. The composition can be made by methods such as coagulation of the ela~tomer in the presence of the fiber and other components of the ~omposition. The composition can be solution lO blending. Preferably, the composition is made by melt blending. The elastomeric composltion comprising the elastomer and fibers can be cured or crosslinked in accordance wit~h methods known in the art.
Typical conditions for vulcanizing natural rubber and/or synthètic rubber compositions including styrene-butadiene rubber compositions are to heat the composition during molding to temperatures of from 250F
to 4000F under pressure of greater than 150 psi preferably greater than 200 psi and typically from 200 to 400 psi. The time to vulcanize will vary depending on the size article being treated.
Elastomers useful in the composition of the present invention include elastomers as characterized above in the Background of the Inventlon. Elastomers include those disclo9ed in Billmeyer, Textbook of Polymer Science; Babbit, the Vanderbilt Rubber Handbook, publi hed by the R.T. Vanderbilt Company, Inc., Connecticut, 1978, and the various U.S. Patents listed above including U.S. Patent No. 4,389,361.
Useful elastomers include but are not limited to natural rubber, synthetic polyisoprene, copolymer~ Or styrene and butadiene, copolymers o~ butadiene and acrylonitrile, copolymers o~ butadiene and alkyl acrylates, butyl rubber, bromo butyl rubber, chlorobutyI
rubber, neoprene (chloroprene, 2-chloro-1, 3-butadiene), olefinic rubber~ such as ethylene propylene rubber and ethylene propylene diene monomer (EPDM) rubbers, nitrile elastomers, polyacrylic elastomer~, poly~ulfide 2()Q1~7.~

polymer~, silicone elastomers, thermoplastic elastomer~, thermopla~tic copolye~ters, ethylene acrylic elastomers, vinyl acetate ethylene copolymers, epichlorohydrin, chlorinated polyethylene, and chemically crosslinked polyethylene.
The fiber can be any fibrou~ material including monofilament yarn, or multi-filament yarn. Fibers useful in the composition of the present invention are short fibers up to 1 inch long, preferably 0.1 to 1 inch, more preferably 0.125 to 1 inch and most preferably 0.25 to 0.5 inches long. There i9 from 1 to 25~ preferably 2 to 10%, and more preferably 4 to 6% by weight ba~ed on the elastomer of the fiber in the composition of the present invention. The short fiber filament~ are preferably homogeneously distributed in the elastomer. When multi-filament yarn is used, preferably the individual yarn filaments are dispersed.
The fiber Pilaments useful in the composition of the present invention typically have a diameter of from 0.0001 to 0.01 inches, preferably 0.0004 to 0.002 inches. Typical multi-filament yarn~ contain from 50 to 1500 filaments, preferably 100 to 1000 filament~. The denier per filament i~ prePerably from 1 to 25 preferably 2 to 10, where denier i9 grams per 9000 meters.
Polyamide fibers useful in the composition oP the present invention are preferably drawn or oriented in order to have a birefringence value of less than 0.1, prererably Prom 0.01 to 0.1, more preferably 0.01 to 0.05 and most preferably 0.02 to 0.04.
Blrefringence is an optical term meanlng double refraction. lt i9 used in the examination of Pibers to measure the degree of molecular orientatlon effected by stretching or drawing. For the purpose of the present invention birefringence values were measured in accordance with ASTM E 858-82.

Z(01~75 The fiber can be selected from the group including acetate based fiber~ such as cellulo~e acetate including rayon, acrylic fibers, polyvinyl chloride fibers, fluorocarbon fiber~ including fibers made from polytetrafluoroethylene, polychlorotrifluoroethylene and copolymer of fluoropolymers with ethylene and other monomers, nylon including nylon 6 (polycaprolactam) and nylon 6,6 (polyhexamethylane adipamide), thermoplastic polyesters including polyethylene terephthalate, polypropylene, polyurethane, polyvinyl alcohol, polyvinylidene chloride, polyaramid~ and the like.
Preferred polymer are polyamides and polyesters with polycaprolactam being most preferred.
The polyamide useful as the short fiber of the present invention, has a molecular weight sufficient to form fiber. Preferably, the molecular weight is from 10,G00 to 40,000 preferably 20,000 to 35,000 number average molecular weight as measured by membrane osmonetry. As noted, preferred polyamides include polycaprolactam and poly(hexamethylene adipamide).
Generally, polyamides are polyamides capable of forming fiber selected from the lo~ng chain synthetic polymers which have regularly occuring amide groups. Useful polyamides can be prepared by defunction monomers or it~
equivalent its cyclized lactam; or by the reaction of a conjugate pair of monomers for example diamide and dicarboxylic acid, or a linear aminoaliphatic acid such as omega-amino undecanoic acid.
Suitable polylactam3 can be produced by polymerization of lactam molecules of the formula ~,--C~~
~.J
where R is an alkylene group having 3 to 12, preferably 5 to 12 carbon ions, The polyamide fiber useful in the present invention is preferably ~pun and drawn in one process to an amount of drawing sufficient to be within a range of elongation to re~ult in the birefringence values of less than 0.04,-2(~1475 preferably from 0.01 to 0.04 and most preferably from 0.02 to 0.04. The fiber i9 considered to be only partially oriented yarn (POY). Typically, fibers are spun and quenched and optionally this can be followed by a separate drawing step. In the present process there is a restriction on the total amount that the fiber is clrawn. Undrawn fiber can also be used. The yarn can have a denier per filament of from 1 to 50. The yarn preferably has a denier per filament of from 1 to 10, more preferably from 2 to 8. The fiber is from 0.1 to 1.0 inches long, preferably from 0.1 to 0.250 inches long. The birefringence is less than 0.1 preferably from 0.02 to 0.04. The total amount the fiber is drawn, whether by stack drawn or in combination with a separate draw step is such that the fiber modulus i~q less than lxlOlldyne/cm2 preferably less than 0.6xlO1ldyne/cm2.
The fiber can be cut by any suitable means to chop or cut fiber known in the art. A preferred method is to feed the yarn to between two rolls. One roll has a plurality of knives parallel to the axis of the roll and perpendicular to the direction of the fiber. The other roll is a backing roll, preferably made of rubber. The knives press against and cut through the fiber as it presses to the nip of the rolls. The necessary pres~ure to accomplish the cutting i~ attained by the knives pressing against the fiber which presses against sthe backing roll.
Preferably the fiber is coated with an adhesive and/or the host matrix ela~tomeric composition contains an adhesive promoting material whioh enhances adhesion between the fiber and the host elastomeric oomposltion.
Adhesive compositions known in the art to adhere fiber and fabrics to elastomeric compositions oan be used. A preferred composition is ba~ed on resorcinol formaldehyde latex. This is preferred when using nylon fiber. When using fiber such as polyester a diisocyanate-epoxy composition is preferred. The diisocyanate-epoxy composition can be used to coat 2~ 47~
--1 o --polyester fiber followed by a coating with the resorcinol formaldehyde late~ composltlon. The dii~ocyanate-epoxy composition is first applied to the fiber and can adhere to resorcinol formaldehyde latex which is used as a second coating. The resorcinol formaldehyde latex can then adhere to the elastomeric composition. The resorcinol formaldehyde latex can be used alone with fibers such as nylon and rayon while the use of the diisocyanate-epoxy system is used with polyaramide and polyesters.
The composition of the present invention results in an elastomeric compound that has equal or greater fatigue life as measured by a cyclic strain test such as the modified ASTM-D-3479-76 test compared to the composition without the fiber.
The modified ASTM-D-3479-76 test is used to measure the fatigue resistance of oriented fiber in resin matrix composites. Method 8 was used. A sample was prepared from a composition formed into a sheet on a laboratory mill roll. The composition is vulcanized (crosslinked). The sample was 0.6 cm high, and 1cm wide. The length of the sample was in the milling direction or longitudinal direction of the sheet off of the mill. The ~ample is long enough,so that there is a 25 length of 2 cm between clamps. Fatigue condition used are: strain amplitude; 8.5%; pretension force, 8kg;
frequency 10Hz, and 130C. Results are reported in cycles to break.
The short fibers improve the stiffness of the composition. Stiffness i9 indicated by yarn modulus.
Modulus and other tensile properties Or the yarn were measured in accordance with ASTM D-.2256-80. There ls improved resistance to interrace failure between the fiber and rubber due to the use of the adhesive system as well as the properties 'of the fibers. It is believed that by using the yarn of the present invention, the properties of the fibers are closer to that of the matrix composition than otherwise.

2(~ 75 The compo9ition of the present invention has lower heat generation upon cyclic tensile straining. The amount of heat generation during cyclic straining is measured as the hysteresis 1099. The hysteresis 1099 is the area in a loop on a stress v. strain curve. A
sample is stressed to a given strain. The stress is removed. A loop is formed between the streAs v. strain curve upon straining the sample and the stress v. strain curve upon the stress being released. The area of this loop is lost energy which is characterized as hysteresis energy resulting in heat generation. The heat generation of the sample of the pre~ent invention was measured using an Allied Hlgh Strain Dynamic Viscoelastometer made by RJS Corporation of Akron, Ohio. A sample made in the same manner as that used in the modified ASTM D 3479-76 fatigue test is clamped with a sample 2 cm long between clamps. The sample is cyclically stained + 2% at a rate of 10 cycles per minute. The temperature i9 raised from room temperature to 160C at 2C/min. The stress strain curve is read on an oscilloscope and the heat generation in erg/cc/sec (corrected for modulus) is measured. Preferably, the composition of the present invention has lower heat generation than a composition which is equivalent except that it does not contain the fiber used in the composition of the present invention.
The fiber of the present invention can be uniformly or randomly aligned in the elastomeric matrix. The fiber can be oriented within the composition by prooe9sinB suoh as oalandering.
The present lnvention results in a oompo 9 i tion whioh has improved flexihility, low heat generation and improved resistance to fatigue as well as improved elongatLon to break. This is attributed to the fiber having the claimed modulus and/or birefringence values, resulting in lower modulus and longer breaking elongation. The fiber has improved flexibility, There is less ~tress concentration at the fiber-rubber 2V01~75 interface during cyclic straining. The composLtion is useful in a variety of rubber products which undergo continual cyclic stress including compositions used in various portions. It can be used in tires and in ho3e.
Several examples are set forth below to illustrate the nature of the invention and the manner of carrying it out. However, the invention should not be considered as being limited to the details thereof. All parts are by weight unless otherwise indicated.
Examples A useful method to make fiber of the present invention is to extrude polycaprolactam having a nominal formic acid ~iscosity (FAV) of about 90 through a conventional spinning pot having a round pack filter and a spinnerette. The spinnerette had 204 capillaries.
The capillary dimensions were 0.040 inche~ length x 0.040 inches diameter. The extrusion temperature was 265C + 3C and the takeup speed was about 2800 meters per minute. The fiber was quenched with air using a radial infiow quench as the filaments travel down through a quench stack (tube). The stretching or drawing of the fiber occured while it was moving through the stack. The amount of draw was controlled by the ratio of polymer throughput to the take up speed of the fiber. A through put of 48 pounds per hour produced a 6 denier per filament (dpf) product. A throughput of 60 pounds per hour produced an 8 dpf product. Lubricating oils were applied using a finish applicator roll, and the yarn taken up on a speed controlled winder.

Example~ 1-7 Following are examples of polycaprolactam flbers useful in the present invention. The fibers of Examples 1-6 were made from polycaprolactam having a nominal FAV
of about 90. Examples 1 and 3 were made uqing the above described proce~s. Example 2 was made u~ing a modified spinnerette to produce a fiber with about 3 dpf. The 20~ 1~7 5 -l3-fiber of Exampl~ 7 was made of fiber ~rade poly(ethylene terephthalate) having a nominal intrinsic viscosity of about 0.90.
Example~ l-3 were nylon 6 fibers only drawn as they 5 moved through the stack. Examples 4 and 5 were nylon 6 fiber which were initiaily undrawn at low stack draw (estimated takeup speed o~ 300-500 meters per minute).
This had a birefringence value of about 0.015. This yarn was then drawn in a separate step using pairs of lO godet rolls with speeds selected such that the draw ratio wa~ about 2:1. Draw ratio is the final unit length divided by the original unit length. Example 6 is nylon 6 fiber drawn to about 90% of it~ maximum draw ratio in a separate step after leaving the stack. The draw ratio was between 4:1 and 5:l. Thi~ is typical of high strength nylon 6 used for tlre cords. Example 7 is poly(ethylene terephthalate) (PET) fiber only drawn as it moved through the stack to give equivalent elongation and tensile strength to the Examples 1-3.
Stress strain properties were measured according to ASTM 2256-80. Free shrink was measured according to ASTM 885-85. Birefringence was measured according to ASTM 858-82. Properties are ~ummarized in Table 1. In Table 1 the following abbreviation~ were used: BIREFRIN
- birefringence; DPF - denier per filament; UTS ~-lfl7~i ultlmate tensile stren~th; and Free Sh - f'ree ~hrinkage. The results are ~ummarized in Table i below:

Table I
.

.. _ . . . , . _ . . _ ~F ~æ~. U~ ~ ~L~ ~ESH
- g/~ t%) g~ ~%) (10~d~e/~) (10 ~e/~) 1 8~2 0.0~2 3.9 ~ ~ 4.8 ~3.~) (o.~O

2 2.8 0.0~ 4,1 46 ~ 1~,3 (4.15) (.~3) 3 6.6 0.0Z~2 2.3 ~ 23 3.9 (2.33) (0.~3) 4 5.6 0.0~ 3.0 ~ 19 4.7 - (3.~) (0.177) ~ 5 2.0 0.~1~ 2.2 5~ ~ 4.3 (2.23) (~3) 6 6.6 0.~5-0.~ 8.8 18 40 13.5 (8.~) (o.~O
7 ~ 0.1~-0.12 3.2 55 '~ 0.7 -- (3.76) (0.~5) Exam~le 8-14 The fibers of Exa~ples 1-7 were coated with a re~orcinol formal dehyde latex (RFL,) adhe~ive system in a single en~ treating unit~ Example 7 was precoated with a diisocyanate epoxy composition~ The resulting fibers were then cut to 1/4 inch length. The cut fibers were and melt blended in a rubber composition using a laboratory internal mixer. The composition contained 100 phr natural rubber (parts per hundred of rubber~, 70 phr of filler tcarbon black and silica); a resorcinol bonding agent, a cobalt salt additive; 5 phr pine tar and a sulfur and sulfonamide curing system~ Each example contained 6 phr of fiber. The melt blended composition was cured at 290F for 90 mlnutes into sheets userul for testing for fatiuge resi~tance according to the modified ASTM D3479-76 test reviewed above. Tear testing was conducted according to ASTM

5 D31ô2. Result~ are summarized in Table 2 below.
Comparative 1 (Comp 1) was the rubber composition without any short fiber.
Table 2 Fiber Fa~igue ~esist.
From 10 Cycles to 10 Ex Ex Break Tear .
~psi) Comp 1 0.43 8 1 0.54 482 9 2 0.52 365 3 0.50 333 11 4 0.40 333 12 5 0.30 348 20 13 6 0.39 14 7 0.15 287 Examples 15-16 Compositions were made based on the same rubber 25 composition as in Examples ô-14 above using the same process. Example 15 contained the same nylon 6 as used in Example 1. Example 16 contained the fully drawn nylon 6 as used in Example 6. Comparative 2 was the rubber composition without short fiber. Comparatives 3-30 5 were compositions containing ribers having a fibermodulus of greater than lxlO11 dyne per square cm according to ASTM D 2258-80. Comparative 3 contained Santoweb cellulose fiber mode by Monsanto. Comparative 4 was PET fiber having and intrinsic vescosity o~ about 0.9 spun and drawn to a draw ratio of between 4 :1 and 5:1. Comparative 5 was Kevlar polyaramide, grade 29 fiber qold by DuPont. All of the fiber was about 1/4 inch in length.

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The composltions were tested for flber modulus according to ASTMD 2256-80; ~atigue re~istance according to modified ASTMD 3479-76, and Examples 15 and 16 and Comp 2 for heat generation according- to the process recited above. The fiber modulus and fatigue resistance are reported in Table 3 below. The heat generation results are reported in the accompanying Figure.

Table 3 Fa~igue Resist. Fi~r Modulu~
10 Cycles to Break lO dyne/cm Ex 15 0.756 0.6 Ex 16 0.387 0.6 15 Gomp 2 0.324 0.0013 Comp 3 0.096 1,7 Comp 4 0.017 1.3 Comp 5 0.015 6.4 A review of Tables 2 and 3 ~how that where the ~iber modulus was lower than 1X101l dynes/cm2 the fatigue resistance wa~ equal to or better than the comparative rubber without fiber. When nylon 6 fiber had a birefringence value below 0.05 the fatigue resistance was much better than the control.

Claims (21)

1. A composition comprising an elastomer, and from 1 to 25% by weight based on the elastomer of a polyamide fiber from 0.1 to 1.0 inches long having a birefringence value of less than 0.1.

2. The composition result in claim 1 having a birefringence of from 0.02 to 0.04.

3. A composition comprising an elastomer and a sufficient amount of polyamide fiber up to 1.0 inch long have a birefringence value of Prom 0.02 to 0.04 to result in a composition having equal or greater fatigue life, as measured according to modified ASTM-D 3479-76, when compared to a composition without fiber.

4. A composition comprising an elastomer and from 1 to 25% by weight based on the elastomer, of a fiber from 0.1 to 1.0 inches long having sufficient orientation to result in a composition having a greater fatigue life, as according to modified ASTM-D 3479,76, when compared to a composition without fiber.

5. The composition as recited in claim 4 wherein the fiber is a polyamide fiber having a birefringence value is from 0.01 to 0.05.

6. The composition as recited in claim 5 wherein the birefringence value is from 0.02 to 0.04.

7. The composition as recited in claim 3 wherein there is from 2 to 10% fiber.

8. The composition as recited in claim 7 wherein there is from 4 to 6 % fiber.

9. The composition as recited in claim 4 wherein the fiber is from 0.125 to 1.0 inches long.

10. The composition as recited in claim 9 wherein the fiber is from 0.25 to 0.50 inches long.

11. The composition as recited in claim 4 wherein the elastomer is selected from the group consisting of: natural rubber, rubber, a copolymer of butadiene and acrylonitrile, copolymer of butadiene and styrene, a copolymer of butadiene and alkyl acrylate, butyl rubber, an olefin rubber such as ethylene-propylene and EPDM

rubber, flurocarbon rubber, flurosilifone rubbers, silicone rubbers, chlorosulfonated polyethylene, polyacrylates, polybutadiene, polychloroprene and mixtures thereof.

12. The composition as recited in claim 4, further comprising crosslinking agents.

13. The composition as recited in claim 4 further comprising particulate fillers.

14. The composition as recited in claim 13 further comprising carbon black.

15. A composition comprising an elastomer, and from 1 to 25% by weight based upon the elastomer of a fiber from 0.1 to 1.0 inches long having a fiber modulus of less than 1X1011 dyne/cm2.

16. The composition as recited in claim 15 wherein the fiber modulus is less than 0.6x1011 dyne/cm2.

17. A polyamide fiber from 0.1 to 1.0 inches long having a birefringence value of from 0.02 to 0.04.

18. The polyamide fiber as recited in claim 17 having a fiber modulus of less than 1x1011 dyne/cm2.

19. The polyamide fiber as recited in claim 18 having a fiber modulus of less than 0.6x1011 dyne/cm2.

20. The polyamide fiber as recited in claim 17 wherein the polyamide is selected from polycaprolactam and poly (hexamethylene adipamide).

21. The polyamide fiber as recited in claim 17 wherein the fiber is coated with an adhesive.