Note: Descriptions are shown in the official language in which they were submitted.
-
~198~
DESCRIPTION
COAT D EXTENDED CHAIN POLYOLEFIN FIBER
BACKGROUND OF THE INVENTION
Extended chain polyethylene and extended chain
polypropylene fibers o~ extremely high tenacity and
modulus values are known materials, having been des-
cribed by various publications of Professor Penningsand co-workers, Smith and Lemstra, and in certain co-
pending commonly assigned patent applications of Kavesh,
et al. These mechanical properties are due, at least in
part, to the high degree of crystallinity and orienta-
tion imparted to the fiber by the production processes,which include either drawing an ultrahigh molecular
weight polyolefin from a supersaturated solution or
spinning a hot solution of the ultrahigh molecular
weight polyoleEin through a dye to fo~m a gel fiber.
Subsequent processin~/ including especially a stretch-
ing step, impart a high crystallinity and orientation
to the polyolefin.
Unfortunately, such extended chain polyolefin
fibers have two disadvantageous properties that result
directly from a high crystallinity and orientation.
First, the high orientation in the longitudinal direc-
tion gives the fibers extermely low transverse strengths,
with a corresponding tendency of the fibers to fibril-
late especially when subjected to abrasion or self-
abrasion, particularly when twisted or processed into afabric. This fibrillation is an undesirable feature in
many applications, such as rope~ sutures or fabrics
~9 ~ ~3
--2--
A second disadvantageous property of the extended chain
polyolefin fibers is that their crystallinity causes
these fibers to have poor adhesion to most matrix mate-
rials. This tends to limit the usefulness of these
fibers in composite structures.
BRIEF DESCRIPTION OF THE INVENTION
It has been discovered that coatiny extended chain
polyethylene or polypropylene fibers with a poly-
ethylene, polypropylene, ethylene copolymer or propylene
copolyrner material substantially reduces the tendency of
the fibers to fibrillate, increases their transverse
strength, enables the fibers to be used in composite
structures alone or with a variety of matrix materials
and achieves these results without any signiEicant loss
of the tenacity and modulus values for the fiber alone,
and in scme instances with some improvement in these
properties which may be attributable to annealing of
fiber defects. The coated fibers may be used alone
: under appropriate conditions of temperature and pres-
sures to produce simple composite structures, which
single composite structures are the subject of an appli-
cation "COMPOSITE CONTAINING POLYOLEFIN FIBER AND POLY-
MER MATRIX" Canadian patent application 423,587, filed
March 15, 1983.
Accordingly, the present includes a coated
polyolefin fiber comprising:
(a) a monofilament or multifilament fiber of
polyethylene or pol~propylene of weight average molecu-
lar weight at least about 500,000 having, in the case of
polyethylene, a tenacity of at least about 15 g/denier
and a tensile modulus of at least about 300 g/denier
and, in the case of polypropylene, a tenacity of at
least 8 g/denier and a tensile modulus of at least about
160 g/denier; and
(b) a coating on the monofilament and on at least
a portion of the filaments of the multifilament
containing a polymer having ethylene or propylene
crystallinity, said coating being present in an amount
,~ ~
between about 0.1~ and about 200%, by weiyht of Eiber.
The present invention further includes a compositestructure comprising a network of the above-described
coated fibers in a matrix which is not a material with
ethylene or propylene crystallinity.
DETAILED DESCRIPTION OF THE INVENTION
The coated fiber of the present invention (which
forms a part of the composite structure of the present
invention) includes an e~tended chain polyolefin fiber,
which may be ultrahigh molecular weight polyethylene or
ultrahigh rnolecular weight polypropylene. Suitable
polyethylene fibers are made of polyethylene having a
weight average molecùlar weight at least about 500,000,
preferably a-t least about 1 million and more preferably
between about 2 million and about 5 million. The fiber
may be grown by solution techniques, is described in
more detail in pending U.S~ Patent 4,356,138 of Kavesh
et al. or by other solution processes in which the poly-
olefin is drawn from a supersaturated solution, includ-
ing those described in various publications of Pennings,
et al and in U.S. Patent 4,137,394 to Meihuisen, et
al. The polyolefin fiber may also be produced by pro-
cesses involving the spinning of polyolefin solutions to
form a gel structure upon cooling, and especially in
such a process as described in U.S. Patent 4,413,110 of
Kavesh et al. (November 1, 1983) and Canadian patent ap-
plication 401,450, filed April 22, 1982. Other solution
spinning (gel) processes may also be usedl such as those
described in various other works of Pennings and co
workers, in various publications and applications of
Smith and Lemstra including UK application GB 2,051~667
and Ger. Off. 3004699 or by similar techniques. Poly-
ethylene fibers formed by melt spinning under controlled
conditions, such as described in U.SO Patent 4,228,118
or British Patent 1,469,526 may also be used, bu-t are
86~
generally less preferred than fibers produced either by
drawing from supersaturated solutions or by spinning
solutions via a gel.
The polyethylene fibers used have tenacity values
of at least about 15 g/denier, preEerably at least about
20 g/denier, more preferably at least about 25 or 30
g/denier and most preferably at least about 40
g/denier. Correspondingly, the preferred tensile
modulus values for -the polyethylene fibers are at least
about 300 g/denier, preferably at least about 500
g/denier, more preferably at least about 750 or 1,000
g/denier and most preferably at least about 1,500
g/denier. In general, the tenacity and modulus values
are directly related and rise together in a relatively
linear fashion for most of the processes used, but it is
con-templated that for certain applications fibers
selected for particularly high tenacities, without
regard to modulus, or with particularly high modulus,
; without regard to tenacity, such as are produced by melt
spinning, may be used. Thus, for example, in the
application of coated fibers for sutures, the elongation
value is particularly important. For coated fibers and
composites used in ballistic applications, as described
in greater detail in U.S Patent 4,403,012 of Harpell et
al., and Canadian patent application 423j592, filed
March 19, 1982, hoth tenacity and modulus values are
extremely important.
The melting point of the polyolefin fiber is not a
particularly critical value in the present invention,
but the melting point is generally above about 138C
(e.g. 145-155C) for polyethylene fibers and above about
168C (e.g. 170-173C) for polypropylene fibersO Other
properties, which are not critical but may have
importance for particular applications, include work to
break values (as measured by ANSI/ASTM D-2256), creep
values (as measured, for example, under 10~ of breaklng
load for 50 days at room temperature), elongation to
18~
break, elongation at yield, ~V stability, oxidative
stability, thermal stability ahd hydrolytic stability.
It is expected that most, if not all, of these other
properties obtained by the polyolefin fiber will corres-
pond to similar, linearly dependent or enhanced valuesfor the coated polyolefin fiber.
The polyethylene fiber used in the present
invention may be either a monofilament or a multifila-
ment, with multifilaments of from 2-500 or more strands
being contemplated, and with arrangements varying from
totally parallel filaments, to wound filaments, to
braided and twisted strands also being contemplated. In
the case of multifilaments of other than parallel
arrangement, it is contemplated that the winding or
other rearrangement of the filament may occur before,
during or after application of the coating. Further-
more, it is contemplated tha~ the coated fibers of the
present invention may either be extremely long fibers
(referred to sometimes as being of substantially indefi-
nite length), of relatively short pieces, or even ofextremely short pieces as, for e2ample, in resins rein-
forced by short fibers (e.g. 9 bulk molding compounds or
sheet molding compounds).
Similarly, extended chain polypropylene fibers
may be used with generally the same geometries, molecu-
lar weights, fiber-forming processes and filament
structure as the extended chain polyethylene fibers.
The major difference resides in the properties of the
fiber, with polypropylene fibers of tenacity at least
about 8 g/ denier, and preerably at least about 15 g/
denier, and of tensile modulus at least about 160 g/
denier, preferably at least about 200 g/denier, being
suitable. In addition, the extended chain polypropylene
fibers will have a main melting point significantly
higher than the corresponding polyethylene fibers,
although the melting point is not a critical feature of
the polypropylene fiber~ Representative main melting
points for extended chain polypropylene fibers are from
about 168 to about 180C, or typically between about 16
8~
and abo~t 173C, preferably at least about 170C.
Suitable coating materials for the coated
fibers of the present invention include polyethylene of
various ~orms, polypropylene of various forms, eth~lene
copolymers of various forms having at least 10% ethylene
crystallinity, propylene copolymers of various forms
having at least 10% propylene crystallinity and various
ethylene-propylene copolymers. Polyethylene coatinys
may be either low density (having, for example, about
0~90-0.94 specific gravity), high density (having, for
example, about 0.94-0.98 specific gravity), with various
amounts o~ branching, linearity, relatively minor co-
monomers as found in materials generally labeled as
"polyethylene", molecular weights, melt viscosities, and
other values. For certain applications high density
polyethylene is pre~erred, ~hile for other applications
low density is preferred. Suitable polypropylene coat-
ings include isotactic, atactic and syndiotactic poly-
propylene. The isotactic or amorphous polypropylene is
generally less preerred, however, compared to the two
crystalline forms.
Suitable ethylene copolymer coatings include
copolymers of ethylene with one or more other olefin-
ically unsaturated monomers from several broad classes~
Similarly suitable propylene copolymers include co-
polymers of propylene with one or more olefinically
unsaturated monomers from several broad classes:
l-monoolefins, olefins containing one terminal poly-
merizable double bond and one or more internal double
bond or bonds.
For many applications~ the ethylene or
propylene content of the copolymers is preferably higher
than that minimum necessary to achieve about 10 volume
percent ethylene or propylene crystallinity. Especially
when strong adherence of the coating to the ~iber is
desired, it is pre~erred that the ethylene or propylene
crystallinity be at least about 25 volume percent, more
preferably at least about 50 volume percent, and most
~g8~6~
preferably at least about 70 volume percent. These
values are achieved, Eor example, in the ethylene-
butene-l copolymers indicated on page 355 of the
Encyclopedia of Polymer Technology as 3, 9, and 18
branches/1000 carbon atoms, corresponding to 90~, 80%
and 70% ethylene crystallinity. Ethylene-vinyl acetate
copolymers oE 5, 10 and 15 mol ~ vinyl acetate corre-
spond to approximately 55%, ~0% and 25% crystallinity.
The proportion of coating compared to fiber
may vary over a wide range depending upon the
application for which the coated fibers are to be used.
A general broad range is from about 0.1 to about 200%
coating, by weight of fiber. For coated fibers to be
used in purely fiber applications, as in rope~ sutures
and the like, a preferred coat-ng amount is between
ahout 10 and about 50%, by weight of fiber. The same or
lower proportion of coating may be used when the coated
fiber is to be used to form a simple composite in which
the coating is fused into a continuous matrix. Higher
amounts of coating may be preferred for other applica-
tions such as composites containing other fibers (e~g.
glass fibers) and/or fillers, in which coating amounts
of 50-200%, 75-150% and 75-100% are preferred, more
pre~erred and most preferred.
The coating may be applied to the fiber in a
variety of ways. One method is ~o apply the neat resin
of the coating ma~erial to the stretched high modulus
fibers either as a liquid, a sticky solid or particles
in suspension or as a fluidized bed. ~lternatively, the
coating may be applied as a solution or emulsion in a
suitable solvent which does not adversely affect the
properties of the fiber at the temperature of applica-
tion. While any solvent capable of dissolving or dis-
persing the coating polymer may be used, preferred
groups of solvents include paraffin oils, aromatic
solvents or hydrocarbon solvents, with illustrative
specific solvents including paraffin oil, xylene,
toluene and octane. The techniques used to dissolve or
38~i~
--8--
disperse the coating polymers in the solvents will be
those conventiona]ly used for -the coating of similar
polymeric materials on a varie-ty of substrates.
Other techniques for applying the coating to the
fibers may be used including coating of the high modulus
precursor before the high temperature stretching opera-
tion, either before or after removal of the solvent from
the fiber. The Eiber may then be stretched at elevated
temperatures to produce the coated fibersO The extruded
gel fiber may be passed throuyh a solution of the appro-
priate coating polymer (solvent May be paraffin oil,
aromatic or aliphatic solvent) under conditions to
attain the desired coatiny. Crystallization of the high
molecular weight polyethylene in the gel fiber may or
may not have taken place before the fiber passes into
the cooling solution. Alternatively, the fiber may be
extruded into a fluidized bed of the appropriate
polymeric powder.
In addition to polymeric coatings, fillers such as
carbon black, calcium carbonate, silica or barium fer-
rite may also be incorporated to attain desired physicalpropeLties, e.g. incorporation of carbon black to obtain
U.V. protection and/or enhanced electrical conductivity.
Furthermore, if the polyolefin fiber achieves its
final properties only after a stretchiny operation or
other manipulative process, e.g. solvent exchanging,
drying or the like, it is contemplated that the
coating may be applied to a precursor material of
the final fiber. In such cases, the desired and
preferred tenacity, modulus and other properties of
the fiber should be judged by continuing the
manipulative process on the fiber precursor in a manner
corresponding to that employed on the coated fiber
precursor. ~hus, for example, if the coating is applied
to the xerogel fiber described in U.S~ Patent 4,413,110
of Kavesh et al, and the coated xerogel fiber is then
stretched under defined temperatuxe and stretch ratio
conditions, then the fiber tenacity and fiber modulus
values would be measured on uncoated xerogel fiber which
is similarly stretched.
The coated fibers of the present invention may be
further processed for use in a variety of applications
such as preparation of composites using coated fibers
alone, weaving, felts, fabrics and non-woven and knitted
articles~
In addition, the coated fibers of the present
invention may be used to form the complex composite
structures of the present invention~ Such complex
composites contain the coated fibers (either
monofilament or multifilament) described above, formed
into a network of conventional type, such as completely
parallel fibers, layers of parallel fibers rotated
between layers in a variety of ways, randomly oriented
lengths of fibers (including felts) and other
arrangements. In addition to such coated fiber network,
the complex composites include a matrix different from
the coating material which may be a thermosetting
polymeric material, a thermoplastic polymeric material,
an elastomeric polymeric material or even various non-
polymeric materials. Suitable matrices include
thermoset polymers such as epoxies, unsaturated
polyesters, polyurethanes, polyfunctional allyl polymers(e.g. diallyl phthalate), urea-formaldehyde polymers,
phenol-formaldehyde polymers and vinyl ester resins;
thermoplastic matrices such as poly-l-butene,
polystyrene, styrene copolymers, polyvinyl chloride and
ABS resin (it will be appreciated that polyethylene,
polypropylene, ethylene copolymers and propylene
copolymers, as matrices, are covered in our Canadian
patent application 423,587); elastomers matrices such as
polybutadiene, butadiene copolymers, thermoplastic
elastomers (e.g. polystyrene-polyisoprene-polystryene t
polystyrene-polybutadiene-polystyrene and polystyrene-
hydrogenated diene-polystyrene), sulfonated ethylene-
~19~
--10--
propylene-diene terepolymer and metal salts of this
terpolymer and silicone elastomers, and non-polymeric
substrates such as concrete. Such complex composite
structures have special utility in ballistic applica-
tions, boat hulls, motorcycle helmets, road surfacing,building constructions~ films/ hoses and belts.
Composite structures may be prepared using chopped
coated fiber of this invention alone (simple composites)
or together with other thermoplastics and thermoset
matrices (called complex composites and described more
fully herein)~
In addition to the coated fiber and the
matrix, other materials may be present in the complex
composite, including lubricants, ~illers, adhesion
agents, other fiber materials (e.g. aramids, boron
fibers, glass fibers~ glass microballoons, graphite
fibers and mineral fibers such as mica, wollastonite
and asbestos) in various regular or irregular geometric
arrangements. For those composite structures in which
strong adherence between the coated polyloefin fiber and
matrix is desired, the coating should be selected for
good adhesion with the matrix material. In general,
adhesion can be improved by using ethylene copolymers or
propylene copolymers having comonomers with similar
ionic character, aromatic character or other properties
of the matrix. For example, in the case of epoxy
matrices, relatively ionic monomers such acrylic acid,
vinyl acetate or methacrylic acid will, in general,
improve the adhesion of the coated fiber to the epoxy
matrix compared to the adhesion of the corresponding
uncoated fiber with the same epoxy matrix. In the case
of polyester matrices, some preferred comonomers in the
coating include acrylic acid~ 1,4-hexadiene, vinyl
alcohol and unreacted free radically pol~merizable
3~ monomers (e.g. acrylates). Also suitable are block and
graft copolymers of polyethylene with polybutadiene and
the reaction product of ethylene-acrylic acid copolymer
with glycidol methacrylate. In the case of matrices
~a8~
composed of polyurethanes, preferred coatings include
hydroxyl-containing polyethylene copolymers such as
ethylene-vinyl alcohol copolymers. Various suitable
thermoplastic matrices and corresponding representative
preferred comonomers for the coating material are
indicated in Table 1 below.
TABLE 1
Matrix Preferred Coatings
1. ~BS, polystyrene 1~ Ethylene-polystyrene block
or polystyrene-poly- and graft copolymers
10 butadiene-polystyrene
2. Sulfonated polyethy- ~. Ethylene-acrylic acid
lene and its salts copolymers
3. Polyvinyl chloride 3. Ethylene-vinyl chloride
graft copolymers
4. Thermoplastics con- 4. Ethylene-acrylic (or meth-
15 taining carboxylic acids acrylic) acid copolymers
5. Sulfonate ethylene- 5. Ethylene-acrylic acid
propylene-diene copolymers or sulfonated
elastomers polyethylene
6. Concrete 6. Ethylene-acrylic acid
copolymer
The properties of the~e complex composites
will generally include various advantageous properties
derived from the coated fiber, and especially for the
extended chain polyolefin fiber component of the coated
fiber~ including especially tenacity and modulus but in
some instances also including dimensional stability, low
water absorption and chemical stability. The complex
composites may also have advantageous properties derived
from the matrix material includin~, for example, high
heat distortion temperature, appropriate flexibility or
stiffness and abrasion resistance. The coating compo- -
nent generally does not contribute substantially ko the
mechanical or other properties of the composite except
insofar as it improves the inherent properties of the
extended chain polyolefin as described above in con-
nection with the novel coated fiber, e.g. by improvingthe transverse strength of a multifilament fiber.
Furthermore, the proportion of coated fiber
(or for that mattery extended chain polyolein fiber)
8~
-12-
in the composite is not critical, but may have preferred
values for various applications.
The coated fibers and complex composite structures
of the present invention may be formed into a variety of
articles. For example, vests may be made containing
either knitted or woven or non-woven fabric of the
present coated fiber, relatively rigid portions of the
composite of the present invention, or a combination of
these. Helmets may be fabricated employing the complex
composites of the present invention using a thermo-
setting matrix. Shielding for helicopters, tanks and
other articles where ballistic-resistance articles are
desired may also be formed out of either the coated
fiber or complex composite of the present invention,
with the matrix material especially being selected based
upon the desired physical properties of the shielding
material. Such articles are described in more detail in
U~S. Patent 4,~03,01 2 ~
For other applications, complex composites of the
present invention may be formed into a variety of
conventional geometric arrangements.
The polyethylene/ethylene copolymer coatings rnay be
crosslinked by crosslinking techniques known in the art
such as the use of peroxides, sulfur or radiation cure
systems, or may be reacted with polyfunctional acid
chlorides or isocyanates in order to obtain a
crosslinked coating on the high modulus fibers.
EXAMPLES
An ultrahigh molecular weight polyethylene
30 (intrinsic viscosity of 17 dL/g in decalin at 135C)
was dissolved as a 7 weight % solution in paraffin oil
at 220Co The solution was extruded through a 16 hole
die (with one millimeter diameter holes) to produce a
gel fiber at the rate of 1.8 m/min. The fiber was
extracted with trichlorotrifluoroethane and dried. lhe
~ 3
-13-
filament~s were stretched in a one meter long tube at
145C at a feed roll speed of 25 cm/min to a stretch
ratio of 19:1 to produce a 625 denier yarn having a
tenacity of 19 g/denier, a modulus of 732 g/denier and
an elongation to hreak of 4.4%. These fibers were used
in Example 2.
A similar fiber preparation (but as a mono-
filament) involved dissolving the same polymer to a 5
weight ~ solution at 200C and extruding through a
single two millimeter diameter die to produce a gel
fiber at 598 cm/minO The extracted and dried fiber was
stretched in the one meter long tube at 130C at a
stretch ratio of 19:1 to produce a 65 denier fiber
having a tenacity of 14.5 g/denier, a modulus of 366
g/denier and an ultimate elongation of 6%. This mono-
filament fiber was used in Example 3.
A similar multifilament fiber employed an 18
IV polyethylene dissolved to 6 weight % in paraffin oil
at 220C. Extruding the solution through a 16 hole die
20 (with 0.76 mm hole diameters) produced gel fiber at 3.08
m/min. The wet gel fiber was stretched at 100C to a
stretch ratio of 11:1, extracted and dried. The 198
denier yarn produced had a tenacity of 25 g/deniery a
modulus of 971 g/denier and an elongation of 4~5% and
was used in Example 4.
EXAMPLE 1
Preparation of Gel Fiber
A high molecular weight linear polyethylene(intrinsic viscosity o~ 17.5 in decalin at 135C) was
dissolved in paraffin oil at 220C to produce a 6 weight
% solution. This solution was extruded through a
sixteen-hole die (hole diameter 1 mm) at ~he rate of 3.2
m/minute~ The oil was extracted from the fiber with
trichlorotrifluoroethane and then the fiber was
subsequently dried~
Coating of Cel Fiber
The multifilament fibers was passed through a
solution of low density polyethylene (Union Carbide DPDA
-14-
6169WT; Density 0.93; MI2 = 6), 35 9 dissolved in 500 mL
of toluene at 75C at the rate of 1.5 m/minute and then
-twice through a bath of trichlorotrifluoroethane and
finally dried. The Eiber increased in weight b~ 19.5%.
Stretchîng of Fiber
The coated fiber was stretched to a stretch
ratio of 20:1 in a 100 cm long tube heated to 140C,
using a eed roll speed of 25 cm/minute to produce a
single filament of 208 denier. Tensile testing of the
coated fiber showed a tensile strength of 19.9 g/denier
and a modulus of 728 g/denier.
Uncoated fiber was stretched in an identical
manner to produce a multifilament yarn. Tensile testing
of this uncoated fiber showed a tensile strength ~tena-
15 city) of 18.9 g/denier and a modulus of 637 g/denier~
As can be seen from the data, the coated
fiber has a higher tensile strength and modulus in
spite of the fact that 20% of the fiber weight consists
of low density polyethylene coating.
By contrast, the Rule of Mixing would suggest
(ignoring second order e~fects3 that the coated fiber
modulus would be 0.8 x ~38 = 509 g/denier and that the
coated fiber tensile strength would be 0.8 x 18.9 = 1501
g/denier~ The a~tual values are 143% and 132% of
theory.
The coated fiber was then tied around a small
post, making five knots (each knot drawn down on the
previous knot). Examination under an optical micro-
scope indicated that no fibrillation occurred, a result
particularly significance for suture applications.
EXAMPLE 2
Single 13 denier ECPE filaments (modulus 732
g/denier, tensile strength 19 g/denier) were dipped into
a solution of ethylene-acrylic acid copolymer (~ow EAA-
35 455, containing 0.932 milliequivalents acrylic acid/g
polymer) in toluene under condi~ions shown in Table 1
The fiber was removed, allowed to dry in air and then
subsequently embedded in an epoxy resin~ Devkon 5
36~
minute epoxy manuEactured by Devkon Corporation (Devkonbeing their -trademark), to a depth of 5 mm. ~he resin
was cured at room temperature Eor one hour, and then
heated in an air-circulating oven for 30 minutes at
100C.
The fibers were pulled on an Instron (a tradernar~)
tensile tester at 1 inch/minute (2.54 cm/min). Results
given in Table 2 (each the average of two runs) indicate
that, under all conditions of dipping evaluated,
improvement of adhesion over that of the unmodified
fiber occurred. Under best conditions (one run of
Sample C), the fiber broke rather than being pulled out
of the resin.
TA13LE 1
15Polymer Dip Dip A~hesive Force
Sample ConcO(g/L) Time Temp (pounds-Newtons)
A 20 2 sec 95C 0.34 - 1.51
6 sec 95C 0,43 - 1.91
C 20 15 min95-75C 0.79 - 3.52
D undipped control -- 0.14 - 0.62
E 40 30 sec 104C 0.52 - 2.31
F 40 2 min 105C 0.41 - 1.82
G 40 5 sec 95C 0.71 - 3.16
H 40 2 sec 85C n . 47 - 2.09
I 40 2 sec 750C 0-47 ~ 2.09
J undipped con-trol -- -- 0.19 - 0.85
K 60 30 sec 105C 0.63 ~ 2.80
L 60 2 min 105C 0,79 - 3.52
M 60 5 sec 104C 0.58 - 2.58
N 60 5 sec 95C 0.46 - 2.05
O 60 2 min 85C 0.66 - 2,94
P undipped control - -- 0,18 - 0.80
EXAMPLE 3
An extended chain polyethylene fiber of lA.5
g/denier tenacity and 366 g/denier modulus prepared by
stretching a xerogel at a 19:1 stretch ratio at 130C
was cut into approximately 40 cm pieces~ Some of the
pieces were tied into knots and thereupon fibrillated
'~
-15A-
extensively, with examination under an optical micro-
scope at 50 x magniEication showing microfibrillae
approximately 8-9 micrometers in diameter.
' `~
-16-
Other pieces of the fiber were dipped one, two or
three times (two each for six total coated fibers) in a
8 weight % solution of PAXON EA-55-180 polyethylene (an
ethylene hexene-l copolymer having density oE 0.955 and
a MI2 = 18) in xylene at 100C (PAXON being a registered
trademark of Allied Corporation).
Five knots were then tied in each fiber (aro~nd a
small post) each knot drawn down on the previous
knot). The coating on the once-dipped fibers appeared
about one micrometer thick. One fibril was seen on one
once-dipped fiber, no fibrils on the other. The
coatings on the twice-dipped fibers appeared about -three
micrometers thick. No fibrillatlon was observed, but
the coating on one section of one fiber detached and
ended about three micrometers from the fiber. The
coating on the thrice-dipped fibers varied in thickness
(six micrometers in the thickest portion) and showed no
fibrillation after five knots.
EXA~PLE 4
An extended claim polyethylene fiber of 25g/ denier
tenacity and 971 g/denier modulus was coated in one of
two treatment regimes with various polymers in xylene
solution tat 60 or 120 g/L concentration). The first
regime was to dip the fiber in the solution for two
minutes and then dry. The second reglme was to dip for
30 seconds, dry in air for three minutes and then (for
four repetitions) dip for two seconds and dry for three
rninutes. All of the coated fibers were then placed in a
rectangular parallelopiped mold of an epoxy resin (the
same resin as Example 2) which was then cured at 25C
for 24 hours.
A force was then applied to the fiber end sticking
out of the cured epoxy resin at a rate of 2
inches/minute (5.1 cm/min). ~ force at pull-out ("Fpol')
was measured and a Shear Stress At Break ('ISB'')
calculated. The results are displayed in Table 2.
TABLE 2
Run Polymer* Conc Temp Regime Fpo S~
(g/L) C N kPa
A EAAO 60 87 First 0. 93 1580
B EAAO 60 87 Second 1.20 2000
C PE-AA 60 105 First 1. 38 2270
D PE-AA 60 205 Second lo 56 2620
E EAA2 60 95 First 1. 33 2340
F EAA5 60 95 First 1. 42 2340
10 G OPE2 60 95 First 1. 25 2070
H OPE2 120 95 First 1. 56 2620
I OPE6 60 95 First 1~ 47 2400
3 OPE6 120 95 First 1. 38 2270
uncoated fiber - ~ - 0. 67 1100
*The polymers used were:
EEAO - a low molecular weight ethylene-acry-
llc acid copolymer of acid number 120 sold
by Allied Corporation as AC~-5120 copolymer
PE-AA - a polyethylene graft acrylic acid
: 20 having 6% acrylic acid sold by ReichhGld
Chemical as PE-452
EAA2 - an ethylene-acrylic acid copolymer
~: of acid number 49. 2 sold by Dow Chemical as
Dow-PE-452~
EAA5 - an ethylene-acrylic acid copolymer
of acid number 52 sold by Dow Chemical as
EAA-455
OPE2 - an oxidized polyethylene of acid
number 28 sold by Allied Corporation as
AC~-392 oxidized polyethylene
OPE6 - ~n oxidized polyethylene of acid
number 16 sold by Allied Corporation as
AC~ 316A oxidized polyethylene
EXAMPLE 5
Continuous Coating of Polyethylene Fibers
With Ethylene Acrylic Acid Copolymer
Preparation of Gel Fiber
An ultrahigh molecular weight polyethylene ~intrinsic
~88~i~
-18-
~iscosity of 17.5 dL/g in decalin at 135C) was dis-
solved as a 6 weight % solution in paraffin oil at
220C. The solution was extruded through a 16 hole
die (with 1.0 millimeter diameter holes) to produce
a gel fiber at the rate of 3.2 m/min. The fiber was
extracted with trichlorotrifluoroethane and dried.
Coating Eiber
The dry undrawn fiber ~7.0 g) was passed
through a 600 mL of toluene containing 24 g of a
dissolved ethylene-acrylic acid copolymer (Dow EAA-
455 copolymer having Acid No. = 52.3, i.e. requires
52.3 mg of potassium hydroxide to neutralize 1 g of
sample) at 105C at the rate of 1.5 meters/min. After
passing through the solution, the fiber passed through
a trichlorotrifluoroethane and -then dried, giving a
fiber weight o 8.06 g. This fiber was then stretched
in a 100C tube at 140C, using a feedroll speed of
25 cm/min. The resultant fiber had a denier of 234,
tenacity of 20.2 g/d, modulus of 696 g/d and ultimate
elongation of 3.9%.
Adhesion to Epoxy Resin
Adhesion to epoxy matrix was determined in the
same manner as in Example 4. Force required to pull
fiber out of the matrix was 1.33 N (0.30 lb) and shear
25 stress was 2340 kPa (340 lb/in).
