U.S. patent application number 11/205951 was filed with the patent office on 2006-07-13 for drawn gel-spun polyethylene yarns and process for drawing.
This patent application is currently assigned to Honeywell International Inc.. Invention is credited to Charles R. JR. Arnett, Thomas Yiu-Tai Tam, Chok B. Tan, Qiang Zhou.
Application Number | 20060154059 11/205951 |
Document ID | / |
Family ID | 35405109 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060154059 |
Kind Code |
A1 |
Tam; Thomas Yiu-Tai ; et
al. |
July 13, 2006 |
DRAWN GEL-SPUN POLYETHYLENE YARNS AND PROCESS FOR DRAWING
Abstract
Gel-spun multi-filament polyethylene yarns possessing a high
degree of molecular and crystalline order, and to the drawing
methods by which they are produced. The drawn yarns are useful in
impact absorption and ballistic resistance for body armor, helmets,
breast plates, helicopter seats, spall shields, and other
applications; composite sports equipment such as kayaks, canoes,
bicycles and boats; and in fishing line, sails, ropes, sutures and
fabrics.
Inventors: |
Tam; Thomas Yiu-Tai;
(Richmond, VA) ; Tan; Chok B.; (Richmond, VA)
; Arnett; Charles R. JR.; (Richmond, VA) ; Zhou;
Qiang; (Chesterfield, VA) |
Correspondence
Address: |
Honeywell International Inc.
15801 Woods Edge Road
Colonial Heights
VA
23834
US
|
Assignee: |
Honeywell International
Inc.
|
Family ID: |
35405109 |
Appl. No.: |
11/205951 |
Filed: |
August 17, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10934675 |
Sep 3, 2004 |
6969553 |
|
|
11205951 |
Aug 17, 2005 |
|
|
|
Current U.S.
Class: |
428/364 |
Current CPC
Class: |
D01F 6/04 20130101; Y10T
428/2913 20150115; Y10T 428/29 20150115; Y10T 428/2967
20150115 |
Class at
Publication: |
428/364 |
International
Class: |
D02G 3/00 20060101
D02G003/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. A polyethylene multi-filament yarn comprising a polyethylene
having an intrinsic viscosity in decalin at 135.degree. C. of from
about 5 dl/g to 35 dl/g, fewer than about two methyl groups per
thousand carbon atoms, and less than about 2 wt. % of other
constituents, said multi-filament yarn having a tenacity of at
least 17 g/d as measured by ASTM D2256-02, wherein filaments of
said yarn have a peak value of the ordered-sequence length
distribution function, F(L), at a straight chain segment length L
of at least 40 nanometers as determined at 23.degree. C. from the
low frequency Raman band associated with the longitudinal acoustic
mode (LAM-1), and a parameter of intrachain cooperativity of the
melting process, .nu., of at least 535 as determined by
differential scanning calorimetry (DSC) of the first polyethylene
melting endotherm at a heating rate extrapolated to 0.degree.
K./min from at least 3 melting scans at heating rates less than
2.degree. K./min, said DSC calorimetry being conducted of a
filament segment of about 0.03 mg mass cut into pieces of about 5
mm length wrapped in parallel array in a Wood's metal foil and
placed in an open sample pan.
19. (canceled)
20. (canceled)
21. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a process for drawing gel-spun
polyethylene multi-filament yarns and to the drawn yarns produced
thereby. The drawn yarns are useful in impact absorption and
ballistic resistance for body armor, helmets, breast plates,
helicopter seats, spall shields, and other applications; composite
sports equipment such as kayaks, canoes, bicycles and boats; and in
fishing line, sails, ropes, sutures and fabrics.
[0003] 2. Description of the Related Art
[0004] To place the invention in perspective, it should be recalled
that polyethylene had been an article of commerce for about forty
years prior to the first gel-spinning process in 1979. Prior to
that time, polyethylene was regarded as a low strength, low
stiffness material. It had been recognized theoretically that a
straight polyethylene molecule had the potential to be very strong
because of the intrinsically high carbon-carbon bond strength.
However, all then-known processes for spinning polyethylene fibers
gave rise to "folded chain" molecular structures (lamellae) that
inefficiently transmitted the load through the fiber and caused the
fiber to be weak.
[0005] "Gel-spun" polyethylene fibers are prepared by spinning a
solution of ultra-high molecular weight polyethylene (UHMWPE),
cooling the solution filaments to a gel state, then removing the
spinning solvent. One or more of the solution filaments, the gel
filaments and the solvent-free filaments are drawn to a highly
oriented state. The gel-spinning process discourages the formation
of folded chain lamellae and favors formation of "extended chain"
structures that more efficiently transmit tensile loads.
[0006] The first description of the preparation and drawing of
UHMWPE filaments in the gel state was by P. Smith, P. J. Lemstra,
B. Kalb and A. J. Pennings, Poly. Bull., 1, 731 (1979). Single
filaments were spun from 2 wt. % solution in decalin, cooled to a
gel state and then stretched while evaporating the decalin in a hot
air oven at 100 to 140.degree. C.
[0007] More recent processes (see, e.g., U.S. Pat. Nos. 4,551,296,
4,663,101. and 6.448.659) describe drawing all three of the
solution filaments, the gel filaments and the solvent-free
filaments. A process for drawing high molecular weight polyethylene
fibers is described in U.S. Pat. No. 5,741,451. The disclosures of
these patents are hereby incorporated by reference to the extent
not incompatible herewith.
[0008] Although gel-spinning processes tend to produce fibers that
are free of lamellae with folded chain surfaces, nevertheless the
molecules in gel-spun UHMWPE fibers are not free of gauche
sequences as can be demonstrated by infra-red and Raman
spectrographic methods. The gauche sequences are kinks in the
zig-zag polyethylene molecule that create dislocations in the
orthorhombic crystal structure. The strength of an ideal extended
chain polyethylene fiber with all trans --(CH.sub.2).sub.n--
sequences has been variously calculated to be much higher than has
presently been achieved. While fiber strength and multi-filament
yarn strength are dependent on a multiplicity of factors, a more
perfect polyethylene fiber structure, consisting of molecules
having longer runs of straight chain all trans sequences, is
expected to exhibit superior performance in a number of
applications such as ballistic protection materials.
[0009] A need exists for gel-spun multi-filament UHMWPE yarns
having increased perfection of molecular structure. One measure of
such perfection is longer runs of straight chain all trans
--(CH.sub.2).sub.n-- sequences as can be determined by Raman
spectroscopy. Another measure is a greater "Parameter of Intrachain
Cooperativity of the Melting Process" as can be determined by
differential scanning calorimetry (DSC). Yet another measure is the
existence of two orthorhombic crystalline components as can be
determined by x-ray diffraction. It is among the objectives of this
invention to provide methods to produce such yarns by drawing, and
the yarns so produced.
SUMMARY OF THE INVENTION
[0010] The invention comprises a process for drawing a gel-spun
multi-filament yarn comprising the steps of: [0011] a) forming a
gel-spun polyethylene multi-filament feed yarn comprising a
polyethylene having an intrinsic viscosity in decalin at
135.degree. C. of from about 5 dl/g to 35 dl/g, fewer than about
two methyl groups per thousand carbon atoms, and less than about 2
wt. % of other constituents; [0012] b) passing the feed yarn at a
speed of V.sub.1 meters/minute into a forced convection air oven
having a yarn path length of L meters, wherein one or more zones
are present along the yarn path having zone temperatures from
130.degree. C. to 160.degree. C.; [0013] c) passing the feed yarn
continuously through the oven and out of the oven at an exit speed
of V.sub.2 meters/minute wherein the following equations 1 to 4 are
satisfied 0.25.ltoreq.L/V.sub.1.ltoreq.20, min Eq. 1
3.ltoreq.V.sub.2/V.sub.1.ltoreq.20 Eq. 2
1.7.ltoreq.(V.sub.2-V.sub.1)/L.ltoreq.60 min.sup.-1 Eq. 3
0.20.ltoreq.2L/(V.sub.1+V.sub.2).ltoreq.10, min Eq. 4
[0014] The invention is also a novel polyethylene multi-filament
yarn comprising a polyethylene having an intrinsic viscosity in
decalin at 135.degree. C. of from about 5 dl/g to 35 dl/g, fewer
than about two methyl groups per thousand carbon atoms, and less
than about 2 wt. % of other constituents, the multi-filament yarn
having a tenacity of at least 17 g/d as measured by ASTM D2256-02,
wherein filaments of the yarn have a peak value of the
ordered-sequence length distribution function F(L) at a straight
chain segment length L of at least 35 nanometers as determined at
23.degree. C. from the low frequency Raman band associated with the
longitudinal acoustic mode (LAM-1).
[0015] In another embodiment, the invention is a novel polyethylene
multi-filament yarn comprising a polyethylene having an intrinsic
viscosity in decalin at 135.degree. C. of from about 5 dl/g to 35
dl/g, fewer than about two methyl groups per thousand carbon atoms,
and less than about 2 wt. % of other constituents, the
multi-filament yarn having a tenacity of at least 17 g/d as
measured by ASTM D2256-02, wherein filaments of the yarn have a
value of the "Parameter of Intrachain Cooperativity of the Melting
Process", .nu., of at least about 535.
[0016] In yet another embodiment, the invention is a novel
polyethylene multi-filament yarn comprising a polyethylene having
an intrinsic viscosity in decalin at 135.degree. C. of from about 5
dl/g to 35 dl/g, fewer than about two methyl groups per thousand
carbon atoms, and less than about 2 wt. % of other constituents,
the multi-filament yarn having a tenacity of at least 17 g/d as
measured by ASTM D2256-02, wherein the intensity of the (002) x-ray
reflection of one the filament of the yarn, measured at room
temperature and under no load,shows two distinct peaks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is the low frequency Raman spectrum and extracted
LAM-1 spectrum of filaments of a commercially available gel-spun
multi-filament UHMWPE yarn (SPECTRA.RTM. 900 yarn).
[0018] FIG. 2(a) is a plot of the ordered sequence length
distribution function F(L) determined from the LAM-1 spectrum of
FIG. 1.
[0019] FIG. 2(b) is a plot of the ordered sequence length
distribution function F(L) determined from the LAM-1 spectrum of a
commercially available gel-spun multi-filament UHMWPE yarn
(SPECTRA.RTM. 1000 yarn).
[0020] FIG. 2(c) is a plot of the ordered sequence length
distribution function F(L) determined from the LAM-1 spectrum of
filaments of the invention.
[0021] FIG. 3 shows differential scanning calorimetry (DSC) scans
at heating rates of 0.31. 0.62 and 1.25.degree. K./min of a 0.03 mg
filament segment taken from a multi-filament yarn of the invention
chopped into pieces of 5 mm length and wrapped in parallel array in
a Wood's metal foil and placed in an open sample pan.
[0022] FIG. 4 shows an x-ray pinhole photograph of a single
filament taken from multi-filament yarn of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0023] In one embodiment, the invention comprises a process for
drawing a gel-spun multi-filament yarn comprising the steps of:
[0024] a) forming a gel-spun polyethylene multi-filament feed yarn
comprising a polyethylene having an intrinsic viscosity in decalin
at 135.degree. C. of from about 5 dl/g to 35 dl/g, fewer than about
two methyl groups per thousand carbon atoms, and less than about 2
wt. % of other constituents; [0025] b) passing the feed yarn at a
speed of V.sub.1 meters/minute into a forced convection air oven
having a yarn path length of L meters, wherein one or more zones
are present along the yarn path having zone temperatures from about
130.degree. C. to 160.degree. C.; [0026] c) passing the feed yarn
continuously through the oven and out of the oven at an exit speed
of V.sub.2 meters/minute wherein the following equations 1 to 4 are
satisfied 0.25.ltoreq.L/V.sub.1.ltoreq.20, min Eq. 1
3.ltoreq.V.sub.2/V.sub.1.ltoreq.20 Eq. 2
1.7.ltoreq.(V.sub.2-V.sub.1)/L.ltoreq.60, min.sup.-1 Eq. 3
0.20.ltoreq.2L/(V.sub.1+V.sub.2).ltoreq.10 min. Eq. 4
[0027] For purposes of the present invention, a fiber is an
elongate body the length dimension of which is much greater than
the transverse dimensions of width and thickness. Accordingly,
"fiber" as used herein includes one, or a plurality of filaments,
ribbons, strips, and the like having regular or irregular
cross-sections in continuous or discontinuous lengths. A yarn is an
assemblage of continuous or discontinuous fibers.
[0028] Preferably, the multi-filament feed yarn to be drawn
comprises a polyethylene having an intrinsic viscosity in decalin
of from about 8 to 30 dl/g, more preferably from about 10 to 25
dl/g, and most preferably from about 12 to 20 dl/g. Preferably the
multi-filament yarn to be drawn comprises a polyethylene having
fewer than about one methyl group per thousand carbon atoms, more
preferably fewer than 0.5 methyl groups per thousand carbon atoms,
and less than about 1 wt. % of other constituents.
[0029] The gel-spun polyethylene multi-filament yarn to be drawn in
the process of the invention may have been previously drawn, or it
may be in an essentially undrawn state. The process for forming the
gel-spun polyethylene feed yarn can be one of the processes
described by U.S. Pat. Nos. 4,551,296, 4,663,101, 5,741,451, and
6,448,659.
[0030] The tenacity of the feed yarn may range from about 2 to 76.
preferably from about 5 to 66, more preferably from about 7 to 51,
grams per denier (g/d) as measured by ASTM D2256-97 at a gauge
length of 10 inches (25.4 cm) and at a strain rate of 100%/min.
[0031] It is known that gel-spun polyethylene yarns may be drawn in
an oven, in a hot tube, between heated rolls, or on a heated
surface. WO 02/34980 A1 describes a particular drawing oven. We
have found that drawing of gel-spun UHMWPE multi-filament yarns is
most effective and productive if accomplished in a forced
convection air oven under narrowly defined conditions. It is
necessary that one or more temperature-controlled zones exist in
the oven along the yarn path, each zone having a temperature from
about 130.degree. C. to 160.degree. C. Preferably the temperature
no within a zone is controlled to vary less than .+-.2.degree. C.
(a total less than 4.degree. C.), more preferably less than
.+-.1.degree. C. (a total less than 2.degree. C.).
[0032] The yarn will generally enter the drawing oven at a
temperature lower than the oven temperature. On the other hand,
drawing of a yarn is a dissipative process generating heat.
Therefore to quickly heat the yarn to the drawing temperature, and
to maintain the yarn at a controlled temperature, it is necessary
to have effective heat transmission between the yarn and the oven
air. Preferably, the air circulation within the oven is in a
turbulent state. The time-averaged air velocity in the vicinity of
the yarn is preferably from about 1 to 200 meters/min, more
preferably from about 2 to 100 meters/min, most preferably from
about 5 to 100 meters/min.
[0033] The yarn path within the oven may be in a straight line from
inlet to outlet. Alternatively, the yarn path may follow a
reciprocating ("zig-zag") path, up and down, and/or back and forth
across the oven, around idler rolls or internal driven rolls. It is
preferred that the yarn path within the oven is a straight line
from inlet to outlet.
[0034] The yarn tension profile within the oven is adjusted by
controlling the drag on idler rolls, by adjusting the speed of
internal driven rolls, or by adjusting the oven temperature
profile. Yarn tension may be increased by increasing the drag on
idler rolls, increasing the difference between the speeds of
consecutive driven rolls or decreasing oven temperature. The yarn
tension within the oven may follow an alternating rising and
falling profile, or it may increase steadily from inlet to outlet,
or it may be constant. Preferably, the yarn tension everywhere
within the oven is constant neglecting the effect of air drag, or
it increases through the oven. Most preferably, the yarn tension
everywhere within the oven is constant neglecting the effect of air
drag.
[0035] The drawing process of the invention provides for drawing
multiple yarn ends simultaneously. Typically, multiple packages of
gel-spun polyethylene yarns to be drawn are placed on a creel.
Multiple yarns ends are fed in parallel from the creel through a
first set of rolls that set the feed speed into the drawing oven,
and thence through the oven and out to a final set of rolls that
set the yarn exit speed and also cool the yarn to room temperature
under tension. The tension in the yarn during cooling is maintained
sufficient to hold the yarn at its drawn length neglecting thermal
contraction.
[0036] The productivity of the drawing process may be measured by
the weight of drawn yarn that can be produced per unit of time per
yarn end. Preferably, the productivity of the process is more than
about 2 grams/minute per yarn end, more preferably more than about
4 grams/minute per yarn end.
[0037] In another embodiment, the invention is a novel polyethylene
multi-filament yarn comprising a polyethylene having an intrinsic
viscosity in decalin at 135.degree. C. of from 5 dl/g to 35 dl/g,
fewer than two methyl groups per thousand carbon atoms, and less
than 2 wt. % of other constituents. the multi-filament yarn having
a tenacity of at least 17 g/d as measured by ASTM D2256-02, wherein
filaments of the yarn have a peak value of the ordered-sequence
length distribution function F(L) at a straight chain segment
length L of at least 40 nanometers as determined at 23.degree. C.
from the low frequency Raman band associated with the longitudinal
acoustic mode (LAM-1).
[0038] In yet another embodiment, the invention is a novel
polyethylene multi-filament yarn comprising a polyethylene having
an intrinsic viscosity in decalin at 135.degree. C. of from 5 dl/g
to 35 dl/g, fewer than two methyl groups per thousand carbon atoms,
and less than 2 wt. % of other constituents, the multi-filament
yarn having a tenacity of at least 17 g/d as measured by ASTM
D2256-02, wherein filaments of the yarn have a value of the
"Parameter of Intrachain Cooperativity of the Melting Process",
.nu., of at least 535.
[0039] In a further embodiment, the invention is a novel
polyethylene multi-filament yarn comprising a polyethylene having
an intrinsic viscosity in decalin at 135.degree. C. of from about 5
dl/g to 35 dl/g, fewer than about two methyl groups per thousand
carbon atoms, and less than about 2 wt. % of other constituents,
the multi-filament yarn having a tenacity of at least 17 g/d as
measured by ASTM D2256-02, wherein the intensity of the (002) x-ray
reflection of one filament of the yarn, measured at room
temperature and under no load, shows two distinct peaks.
[0040] Preferably, a polyethylene yarn of the invention has an
intrinsic viscosity in decalin at 135.degree. C. of from about 7
dl/g to 30 dl/g, fewer than about one methyl group per thousand
carbon atoms, less than about 1 wt. % of other constituents, and a
tenacity of at least 22 g/d.
Measurement Methods
1. Raman Spectroscopy
[0041] Raman spectroscopy measures the change in the wavelength of
light that is scattered by molecules. When a beam of monochromatic
light traverses a semi-transparent material, a small fraction of
the light is scattered in directions other than the direction of
the incident beam. Most of this scattered light is of unchanged
frequency. However, a small fraction is shifted in frequency from
that of the incident light. The energies corresponding to the Raman
frequency shifts are found to be the energies of rotational and
vibrational quantum transitions of the scattering molecules. In
semi-crystalline polymers containing all-trans sequences, the
longitudinal acoustic vibrations propagate along these all-trans
seqments as they would along elastic rods. The chain vibrations of
this kind are called longitudinal acoustic modes (LAM), and these
modes produce specific bands in the low frequency Raman spectra.
Gauche sequences produce kinks in the polyethylene chains that
delimit the propagation of acoustic vibrations. It will be
understood that in a real material a statistical distribution
exists of the lengths of all-trans seqments. A more perfectly
ordered material will have a distribution of all-trans seqments
different from a less ordered material. An article titled,
"Determination of the Distribution of Straight-Chain Segment
Lengths in Crystalline Polyethylene from the Raman LAM-1 Band", by
R. G. Snyder et al, J. Poly. Sci. Poly. Phys. Ed., 16, 1593-1609
(1978) describes the theoretical basis for determination of the
ordered-sequence length distribution function, F(L) from the Raman
LAM-1 spectrum.
[0042] F(L) is determined as follows: Five or six filaments are
withdrawn from the multi-filament yarn and placed in parallel
alignment abutting one another on a frame such that light from a
laser can be directed along and through this row of fibers
perpendicular to their length dimension. The laser light should be
substantially attenuated on passing sequentially through the
fibers. The vector of light polarization is collinear with the
fiber axis, (XX light polarization).
[0043] Spectra are measured at 23.degree. C. on a spectrometer
capable of detecting the Raman spectra within a few wave numbers
(less than about 4 cm.sup.-1) of the exciting light. An example of
such a spectrometer is the SPEX Industries, Inc, Metuchen, N.J.,
Model RAMALOG.RTM. 5, monochromator spectrometer using a He--Ne
laser. The Raman spectra are recorded in 90.degree. geometry, i.e.,
the scattered light is measured and recorded at an angle of 90
degrees to the direction of incident light. To exclude the
contribution of the Rayleigh scattering, a background of the LAM
spectrum in the vicinity of the central line must be subtracted
from the experimental spectrum. The background scattering is fitted
to a Lorentzian function of the form given by Eq. 5 using the
initial part of the Raman scattering data, and the data in the
region 30-60 cm.sup.-1 where there is practically no Raman
scattering from the samples, but only background scattering. f
.function. ( x ) .times. ) = H 4 ( x - x 0 w ) 2 + 1 Eq . .times. 5
##EQU1## [0044] where: x.sub.0 is the peak position [0045] H is the
peak height [0046] w is the full width at half maximum
[0047] Where the Raman scattering is intense near the central line
in the region from about 4 cm.sup.-1 to about 6 cm.sup.-1, it is
necessary to record the Raman intensity in this frequency range on
a logarithmic scale and match the intensity recorded at a frequency
of 6 cm.sup.-1 to that measured on a linear scale. The Lorentzian
function is subtracted from each separate recording and the
extracted LAM spectrum is spliced together from each portion.
[0048] FIG. 1(a) shows the measured Raman spectra for a fiber
material to be described below and the method of subtraction of the
background and the extraction of the LAM spectrum.
[0049] The LAM-1 frequency, is inversely related to the straight
chain length, L as expressed by Eq. 6. L = 1 2 .times. c .times.
.times. .omega. L .times. ( E .times. .times. g c .rho. ) 1 / 2 Eq
. .times. 6 ##EQU2## [0050] where: c is the velocity of light,
3.times.10.sup.10 cm/sec [0051] .omega..sub.L is the LAM-1
frequency, cm.sup.-1 [0052] E is the elastic modulus of a
polyethylene molecule, g(f)/cm.sup.2 [0053] .sigma. is the density
of a polyethylene crystal, g(m)/cm.sup.3 [0054] g.sub.c is the
gravitational constant 980 (g(m)-cm)/((g(f)-sec.sup.2)
[0055] For the purposes of this invention, the elastic modulus E,
is taken as 340 GPa as reported by Mizushima et al., J. Amer.
Chem., Soc., 71, 1320 (1949). The quantity (g.sub.cE/p).sup.1/2 is
the sonic velocity in an all trans polyethylene crystal. Based on
an elastic modulus of 340 GPa, and a crystal density of 1.000
g/cm.sup.3, the sonic velocity is 1.844.times.10.sup.6 cm/sec.
Making that substitution in Eq. 6, the relationship between the
straight chain length and the LAM-1 frequency as used herein is
express by Eq. 7. L = 307.3 .omega. L , nanometers Eq . .times. 7
##EQU3##
[0056] The "ordered-sequence length distribution function", F(L),
is calculated from the measured Raman LAM-1 spectrum by means of
Eq. 8. F .function. ( L ) = [ 1 - exp .function. ( - hc .times.
.times. .omega. L kT ) .times. .omega. L 2 .times. I .omega. ] ,
arbitrary .times. .times. units Eq . .times. 8 ##EQU4## [0057]
where: h is Plank's constant, 6.6238.times.10.sup.-27 erg-cm [0058]
k is Boltzmann's constant, 1.380.times.10.sup.-16 erg/.degree. K.
[0059] I.sub..omega. is the intensity of the Raman spectrum at
frequency .omega..sub.L, [0060] arbitrary units [0061] T is the
absolute temperature, .degree. K. [0062] and the other terms are as
previously defined.
[0063] Plots of the ordered-sequence length distribution function,
F(L), derived from the Raman LAM-1 spectra for three polyethylene
samples to be described below are shown in FIGS. 2(a), 2(b) and
2(c).
[0064] Preferably, a polyethylene yarn of the invention is
comprised of filaments for which the peak value of F(L) is at a
straight chain segment length L of at least 45 nanometers as
determined at 23.degree. C. from the low frequency Raman band
associated with the longitudinal acoustic mode (LAM-1). The peak
value of F(L) preferably is at a straight chain segment length L of
at least 50 nanometers, more preferably at least 55 nanometers, and
most preferably 50-150 nanometers.
2. Differential Scanning Calorimetry (DSC)
[0065] It is well known that DSC measurements of UHMWPE are subject
to systematic errors cause by thermal lags and inefficient heat
transfer. To overcome the potential effect of such problems, for
the purposes of the invention the DSC measurements are carried out
in the following manner. A filament segment of about 0.03 mg mass
is cut into pieces of about 5 mm length. The cut pieces are
arranged in parallel array and wrapped in a thin Wood's metal foil
and placed in an open sample pan. DSC measurements of such samples
are made for at least three different heating rates at or below
2.degree. K./min and the resulting measurements of the peak
temperature of the first polyethylene melting endotherm are
extrapolated to a heating rate of 0.degree. K./min.
[0066] A "Parameter of Intrachain Cooperativity of the Melting
Process", represented by the Greek letter .nu., has been defined by
V. A. Bershtein and V. M. Egorov, in "Differential Scanning
Calorimetry of Polymers: Physics, Chemistry, Analysis, Technology",
P. 141-143, Tavistoc/Ellis Horwod, 1993. This parameter is a
measure of the number of repeating units, here taken as
(--CH.sub.2--CH.sub.2--), that cooperatively participate in the
melting process and is a measure of crystallite size. Higher values
of .nu. indicate longer crystalline sequences and therefore a
higher degree of order. The "Parameter of Intrachain Cooperativity
of the Melting Process" is defined herein by Eq. 9. v = 2 .times. R
.times. .times. T .omega. .times. .times. 1 2 .DELTA. .times.
.times. T .omega. .times. .times. 1 .DELTA. .times. .times. H
.omega. , dimensionless Eq . .times. 9 ##EQU5## [0067] where: R is
the gas constant, 8.31 J/.degree. K.-mol [0068] T.sub.m1 is the
peak temperature of the first polyethylene melting [0069] endotherm
at a heating rate extrapolated to 0.degree. K./min, .degree. K.
[0070] .DELTA.T.sub.m1 is the width of the first polyethylene
melting endotherm, .degree. K. [0071] .DELTA.H.sup.0 is the melting
enthalpy of --CH.sub.2--CH.sub.2-- taken as 8200 J/mol
[0072] The multi-filament yarns of the invention are comprised of
filaments having a "Parameter of Intrachain Cooperativity of the
Melting Process", .nu., of at least 535, preferably at least 545.
more preferably at least 555, and most preferably from 545 to
1100.
3. X-Ray Diffraction
[0073] A synchrotron is used as a source of high intensity
x-radiation.
[0074] The synchrotron x-radiation is monochromatized and
collimated. A single filament is withdrawn from the yarn to be
examined and is placed in the monochromatized and collimated x-ray
beam. The x-radiation scattered by the filament is detected by
electronic or photographic means with the filament at room
temperature (.about.23.degree. C.) and under no external load. The
position and intensity of the (002) reflection of the orthorhombic
polyethylene crystals are recorded. If upon scanning across the
(002) reflection, the slope of scattered intensity versus
scattering angle changes from positive to negative twice, i.e., if
two peaks are seen in the (002) reflection, then two orthorhombic
crystalline phases exist within the fiber.
[0075] The following examples are presented to provide a more
complete understanding of the invention. The specific techniques,
conditions, materials, proportions and reported data set forth to
illustrate the principles of the invention are exemplary and should
not be construed as limiting the scope of the invention.
EXAMPLES
Comparative Example 1
[0076] An UHMWPE gel-spun yarn designated SPECTRA.RTM. 900 was
manufactured by Honeywell International Inc. in accord with U.S.
Pat. No. 4,551,296. The 650 denier yarn consisting of 60 filaments
had an intrinsic viscosity in decalin at 135.degree. C. of about 15
dl/g. The yarn tenacity was about 30 g/d as measured by ASTM
D2256-02, and the yarn contained less than about 1 wt. % of other
constituents. The yarn had been stretched in the solution state, in
the gel state and after removal of the spinning solvent. The
stretching conditions did not fall within the scope of equations 1
to 4 of the present invention.
[0077] Filaments of this yarn were characterized by Raman
spectroscopy using a Model RAMALOG.RTM. 5, monochromator
spectrometer made by SPEX Industries, Inc., Metuchen, N.J., using a
He--Ne laser and the methodology described herein above. The
measured Raman spectrum, 1, and the extracted LAM-1 spectrum for
this material, 3, after subtraction of the Lorenzian, 2, fitted to
the Rayleigh background scattering are shown in FIG. 1(a). The
ordered-sequence length distribution function, F(L), for this
material determined from the LAM-1 spectrum and equations 7 and 8
is shown in FIG. 2(a). The peak value of the ordered-sequence
length distribution function, F(L), was at a straight chain segment
length L of approximately 12 nanometers (Table I).
[0078] Filaments of this yarn were also characterized by DSC using
the methodology described hereinabove. The peak temperature of the
first polyethylene melting endotherm at a heating rate extrapolated
to 0.degree. K./min. was 415.4.degree. K. The width of the first
polyethylene melting endotherm was 0.9.degree. K. The "Parameter of
Intrachain Cooperativity of the Melting Process", .nu., determined
from Eq. 9 was 389 (Table I).
[0079] A single filament taken from this yarn was examined by x-ray
diffraction using the methodology described hereinabove. Only one
peak was seen in the (002) reflection (Table 1).
Comparative Example 2
[0080] An UHMWPE gel-spun yarn designated SPECTRA.RTM. 1000 was
manufactured by Honeywell International Inc. in accord with U.S.
Pat. Nos. 4,551,296 and 5,741,451. The 1300 denier yarn consisting
of 240 filaments had an intrinsic viscosity in decalin at
135.degree. C. of about 14 dl/g. The yarn tenacity was about 35 g/d
as measured by ASTM D2256-02, and the yarn contained less than 1
wt. % of other constituents. The yarn had been stretched in the
solution state, in the gel state and after removal of the spinning
solvent. The stretching conditions did not fall within the scope of
equations 1 to 4 of the present invention.
[0081] Filaments of this yarn were characterized by Raman
spectroscopy using a Model RAMALOG.RTM. 5, monochromator
spectrometer made by SPEX Industries, Inc. Metuchen, N.J. using a
He--Ne laser and the methodology described hereinabove. The
ordered-sequence length distribution function, F(L), for this
material determined from the LAM-1 spectrum and equations 7 and 8
is shown in FIG. 2(b). The peak value of the ordered-sequence
length distribution function, F(L), was at a straight chain segment
length L of approximately 33 nanometers (Table I).
[0082] Filaments of this yarn were also characterized by DSC using
the methodology described hereinabove. The peak temperature of the
first polyethylene melting endotherm at a heating rate extrapolated
to 0.degree. K./min, was 415.2.degree. K. The width of the first
polyethylene melting endotherm was 1.3.degree. K. The "Parameter of
Intrachain Cooperativity of the Melting Process", .nu., determined
from Eq. 9 was 466 (Table I).
[0083] A single filament taken from this yarn was examined by x-ray
diffraction using the methodology described hereinabove. Only one
peak was seen in the (002) reflection (Table 1).
Comparative Examples 3-7
[0084] UHMWPE gel spun yarns from different lots manufactured by
Honeywell International Inc. and designated either SPECTRA.RTM. 900
or SPECTRA.RTM. 1000 were characterized by Raman spectroscopy, DSC,
and x-ray diffraction using the methodologies described
hereinabove. The description of the yarns and the values of F(L)
and v are listed in Table I as well as the number of peaks seen in
the (002) x-ray reflection.
EXAMPLE OF THE INVENTION
[0085] An UHMWPE gel spun yarn was produced by Honeywell
International Inc. in accord with U.S. Pat. No. 4,551,296. The 2060
denier yarn consisting of 120 filaments had an intrinsic viscosity
in decalin at 135.degree. C. of about 12 dl/g. The yarn tenacity
was about 20 g/d as measured by ASTM D2256-02. and the yarn
contained less than about 1 wt. % of other constituents. The yarn
had been stretched between 3.5 and 8 to 1 in the solution state,
between 2.4 to 4 to 1 in the gel state and between 1.05 and 1.3 to
1 after removal of the spinning solvent.
[0086] The yarn was fed from a creel, through a set of restraining
rolls at a speed (V.sub.1) of about 25 meters/min into a forced
convection air oven in which the internal temperature was
155.+-.1.degree. C. The air circulation within the oven was in a
turbulent state with a time-averaged velocity in the vicinity of
the yarn of about 34 meters/min.
[0087] The feed yarn passed through the oven in a straight line
from inlet to outlet over a path length (L) of 14.63 meters and
thence to a second set of rolls operating at a speed (V.sub.2) of
98.8 meters/min. The yarn was cooled down on the second set of
rolls at constant length neglecting thermal contraction. The yarn
was thereby drawn in the oven at constant tension neglecting the
effect of air drag. The above drawing conditions in relation to
Equations 1-4 were as follows,
0.25.ltoreq.[L/V.sub.1=0.59].ltoreq.20, min Eq. 1
3.ltoreq.[V.sub.2/V.sub.1=3.95].ltoreq.20 Eq. 2
1.7.ltoreq.[(V.sub.2-V.sub.1)/L=5.04].ltoreq.60, min.sup.-1 Eq. 3
0.20.ltoreq.[2L/(V.sub.1+V.sub.2)=0.24].ltoreq.10 min Eq. 4
[0088] Hence, each of Equations 1-4 was satisfied.
[0089] The denier per filament (dpf) was reduced from 17.2 dpf for
the feed yarn to 4.34 dpf for the drawn yarn. Tenacity was
increased from 20 g/d for the feed yarn to about 40 g/d for the
drawn yarn. The mass throughput of drawn yarn was 5.72 grams/min
per yarn end.
[0090] Filaments of this yarn produced by the process of the
invention were characterized by Raman spectroscopy using a Model
RAMALOG.RTM. 5, monochromator spectrometer made by SPEX Industries,
Inc., Metuchen, N.J., using a He--Ne laser and the methodology
described hereinabove. The ordered-sequence length distribution
function, F(L), for this material determined from the LAM-1
spectrum and equations 7 and 8 is shown in FIG. 2(c). The peak
value of the ordered-sequence length distribution function, F(L),
was at a straight chain segment length L of approximately 67
nanometers (Table I).
[0091] Filaments of this yarn were also characterized by DSC using
the methodology described hereinabove. DSC scans at heating rates
of 0.31.degree. K./min, 0.62.degree. K./min, and 1.25.degree.
K./min are shown in FIG. 3. The peak temperature of the first
polyethylene melting endotherm at a heating rate extrapolated to
0.degree. K./min, was 416.1.degree. K. The width of the first
polyethylene melting endotherm was 0.6.degree. K. The "Parameter of
Intrachain Cooperativity of the Melting Process", .nu., determined
from Eq. 9 was 585 (Table I).
[0092] A single filament taken from this yarn was examined by x-ray
diffraction using the methodology described hereinabove. An x-ray
pinhole photograph of the filament is shown in FIG. 4. Two peaks
were seen in the (002) reflection. TABLE-US-00001 TABLE I L, nm No.
of Ex. or at (002) Comp. Denier/ peak .nu., X-Ray Ex. No.
Identification Fils of F(L) dimensionless Peaks Comp. SPECTRA .RTM.
650/60 12 389 1 Ex. 1 900 yarn Comp. SPECTRA .RTM. 1300/240 33 466
1 Ex. 2 1000 yarn Comp. SPECTRA .RTM. 650/60 28 437 1 Ex. 3 900
yarn Comp. SPECTRA .RTM. 1200/120 19 387 1 Ex. 4 900 yarn Comp.
SPECTRA .RTM. 1200/120 20 409 1 Ex. 5 900 yarn Comp. SPECTRA .RTM.
1200/120 24 435 1 Ex. 6 900 yarn Comp. SPECTRA .RTM. 1300/240 17
467 1 Ex. 7 1000 yarn Exam- Inventive 521/120 67 585 2 ple
Fiber
[0093] It is seen that filaments of the yarn of the invention had a
peak value of the ordered-sequence length distribution function.
F(L), at a straight chain segment length, L, greater than the prior
art yarns. It is also seen that filaments of the yarn of the
invention had a "Parameter of Intrachain Cooperativity of the
Melting Process", .nu., greater than the prior art yarns. Also,
this appears to be the first observation of two (002) x-ray peaks
in a polyethylene filament at room temperature under no load.
[0094] Having thus described the invention in rather full detail,
it will be understood that such detail need not be strictly adhered
to but that further changes and modifications may suggest
themselves to one skilled in the art, all falling with the scope of
the invention as defined by the subjoined claims.
* * * * *