Note: Descriptions are shown in the official language in which they were submitted.
Z001475
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
--2--
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
--4--
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
--5--
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.
,............... .
2(~0~475
--6--
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
--8--
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
--1 1 --
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
-12-
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
-14-
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
-15-
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.
2~3()1~7S
-16-
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.
