U.S. patent application number 11/000414 was filed with the patent office on 2006-03-02 for expanded ptfe articles and method of making same.
Invention is credited to Norman Ernest Clough, David Isaac Lutz.
Application Number | 20060047311 11/000414 |
Document ID | / |
Family ID | 35944402 |
Filed Date | 2006-03-02 |
United States Patent
Application |
20060047311 |
Kind Code |
A1 |
Lutz; David Isaac ; et
al. |
March 2, 2006 |
Expanded PTFE articles and method of making same
Abstract
Unique PTFE structures comprising islands of PTFE attached to an
underlying expanded polytetrafluoroethylene (ePTFE) structure and
to methods of making such structures is disclosed. The ePTFE
material may or may not have been exposed to amorphous locking
temperatures. These unique structures exhibit islands of PTFE
attached to and raised above the expanded PTFE structures.
Inventors: |
Lutz; David Isaac; (Newark,
DE) ; Clough; Norman Ernest; (Landenberg,
PA) |
Correspondence
Address: |
W.L. Gore & Associates, Inc.
551 Paper Mill Road
P.O. Box 9206
Newark
DE
19714-9206
US
|
Family ID: |
35944402 |
Appl. No.: |
11/000414 |
Filed: |
November 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60605127 |
Aug 26, 2004 |
|
|
|
Current U.S.
Class: |
606/228 |
Current CPC
Class: |
Y10T 428/2967 20150115;
Y10T 428/2978 20150115; Y10T 428/3154 20150401; Y10T 428/13
20150115; A01K 91/00 20130101; Y10T 428/29 20150115; Y10T 428/2925
20150115; A61C 15/041 20130101; A61L 17/04 20130101; Y10T 428/2929
20150115; Y10T 428/249921 20150401; Y10T 428/2913 20150115; Y10T
428/24479 20150115 |
Class at
Publication: |
606/228 |
International
Class: |
A61L 17/00 20060101
A61L017/00 |
Claims
1. An article comprising: a first PTFE material having a
microstructure characterized by nodes interconnected by fibrils,
and islands of a second PTFE material on the surface of the first
PTFE material.
2. The article of claim 1 in the form of a fiber.
3. The article of claim 1 in the form of a membrane.
4. The article of claim 1, further comprising at least one filler
material.
5. The article of claim 4, wherein the at least one filler is in
the first PTFE material.
6. The article of claim 4, wherein the at least one filler is in
the second PTFE material.
7. The article of claim 1, wherein said islands of said second PTFE
material are oriented on said first PTFE in a patterned
configuration.
8. A process for forming a PTFE article comprising: subjecting an
expanded PTFE article to a plasma treatment; and subjecting the
plasma treated material to a heat treatment.
9. An article comprising: a first PTFE material having a
microstructure characterized by nodes interconnected by fibrils,
and islands of a second PTFE material on the surface of the first
PTFE material, wherein said article is in the form of a dental
floss.
10. The article of claim 9, wherein said dental floss has a drag
resistance of at least 0.17.
11. A dental floss comprising a fluoropolymer, said dental floss
having a drag resistance of at least 0.175.
12. The dental floss of claim 11, wherein said dental floss has a
drag resistance of at least 0.190.
13. The article of claim 9, wherein said dental floss incorporates
at least one filler.
14. An article comprising: a first PTFE material having a
microstructure characterized by nodes interconnected by fibrils,
and islands of a second PTFE material on the surface of the first
PTFE material, wherein said article is in the form of a fishing
line.
15. The article of claim 14, wherein said fishing line has a
fishing line fray score of less than 100.
16. The article of claim 14 wherein said fishing line comprises a
monofilament fiber.
17. The article of claim 14 wherein said fishing line comprises a
multifilament fiber.
18. The article of claim 14, wherein said fishing line comprises
twisted fiber.
19. The article of claim 14, wherein said fishing line has a
density of at least 1.9 g/cc.
20. A fishing line comprising PTFE having a fishing line fray score
of less than 50.
21. An article comprising: a first PTFE material having a
microstructure characterized by nodes interconnected by fibrils,
and islands of a second PTFE material on the surface of the first
PTFE material, wherein said article is in the form of a suture.
22. The article of claim 21, wherein said suture has a diameter of
about 0.025 mm.
23. The article of claim 21, wherein said suture has a diameter of
about 0.015 mm.
24. An article comprising a monofilament fluoropolymer fiber having
a density greater than 1 g/cc and a fiber fray score of less than
about 100.
25. The article of claim 24, wherein said monofilament
fluoropolymer fiber has a fiber fray score of less than about
20.
26. The article of claim 24, further comprising a plurality of said
monofilament fluoropolymer fibers combined in a twisted
configuration.
27. A dental floss comprising a fluoropolymer, said dental floss
having a density greater than 1 g/cc and a fiber fray score of less
than about 100.
Description
RELATED APPLICATIONS
[0001] The present application is a regular application based on
co-pending U.S. Provisional Patent Application 60/605,127 filed
Aug. 26,2 004.
FIELD OF THE INVENTION
[0002] The present invention relates to unique expanded PTFE
articles. More specifically, it is directed to novel structures of
expanded PTFE and a novel process for preparing the structures.
BACKGROUND OF THE INVENTION
[0003] The structure of expanded PTFE ("ePTFE") is well known to be
characterized by nodes interconnected by fibrils, as taught in U.S.
Pat. Nos. 3,953,566 and 4,187,390, to Gore, and which patents have
been the foundation for a significant body of work directed to
ePTFE materials. The node and fibril character of the ePTFE
structure has been modified in many ways since it was first
described in these patents. For example, highly expanded materials,
as in the case of high strength fibers, can exhibit exceedingly
long fibrils and relatively small nodes. Other process conditions
can yield articles, for example, with nodes that extend through the
thickness of the article.
[0004] Surface treatment of ePTFE structure has also been carried
out by a variety of techniques in order to modify the ePTFE
structure. Okita (U.S. Pat. No. 4,2308,745) teaches exposing the
outer surface of an ePTFE tube, specifically a vascular prosthesis,
to a more severe (i.e., higher) thermal treatment than the inner
surface in order to effect a finer structure on the inside than on
the outside of the tube. One of ordinary skill in the art will
recognize that Okita's process is consistent with prior art
amorphous locking processes, the only difference being preferential
exposure of the outer surface of the ePTFE structure to greater
thermal energy.
[0005] Zukowski (U.S. Pat. No. 5,462,781) teaches employing plasma
treatment to effect removal of fibrils from the surface of porous
ePTFE in order to achieve a structure with freestanding nodes on
the surface which are not interconnected by fibrils. No further
treatment after the plasma treatment is disclosed or contemplated
in the teachings.
[0006] Martakos et al. (U.S. Pat. No. 6,573,311) teach plasma glow
discharge treatment, which includes plasma etching, of polymer
articles at various stages during the polymer resin processing.
Martakos et al. distinguish over conventional processes by noting
that the prior art techniques operate on finished, fabricated
and/or finally processed materials, which are "ineffective at
modifying bulk substrate properties, such as porosity and
permeability." Martakos et al. teach plasma treating at six
possible polymer resin process steps; however, no such treatment
with or subsequent to amorphous locking is described or suggested.
Again, the focus of Martakos et al. is to affect bulk properties
such as porosity and/or chemistry quality in the finished
articles.
[0007] Other means of creating new surfaces on porous PTFE and
treating the surface of porous PTFE abound in the prior art.
Butters (U.S. Pat. No. 5,296,292) teaches a fishing flyline
consisting of a core with a porous PTFE cover that can be modified
to improve abrasion resistance. Abrasion resistance of the flyline
is improved by modifying the outer cover either through adding a
coating of abrasion resistant material to it or by densifying the
porous PTFE cover.
[0008] In a further example, Campbell et al (U.S. Pat. No.
5,747,128) teach a means of creating regions of high and low bulk
density throughout a porous PTFE article. Additionally, Kowligi et
al. (U.S. Pat. No. 5,466,509) teach impressing a pattern onto an
ePTFE surface, and Seiler et al. (U.S. Pat. No. 4,647,416) teach
the scoring PTFE tubes during fabrication in order to create
external ribs.
[0009] However, none of the prior art references teach applicants'
unique combination of processing to create a unique surface on PTFE
which has heretofore not been seen.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to a unique PTFE structure
comprising islands of PTFE attached to an underlying expanded
polytetrafluoroethylene (ePTFE) structure and to methods of making
such a structure. The ePTFE material may or may not have been
exposed to amorphous locking temperatures. These unique structures
exhibit islands of PTFE attached to and raised above the expanded
PTFE structures. By "raised" is meant that when the article is
viewed in cross-section, such as in a photomicrograph of the
article cross-section, the islands are seen to rise above the
baseline defined by the outer surface of the underlying node-fibril
structure by a length, "h." Referring to FIG. 1, which shows a
cross-section of an expanded PTFE fiber 10 with island 12, the
height of the island 12 rises a height "h" above the surface 14, or
"baseline," of the underlying ePTFE structure.
[0011] These raised regions, or islands, are connected at their
bases to the underlying ePTFE structure. The islands are
distinguishable from the underlying nodes and fibrils because of
their much larger size. The largest length dimension of the islands
is at least twice that of the same dimension of the underlying
nodes. This length difference can even exceed 100 times that of the
underlying nodes. Further, the morphology of the islands tends to
distinguish them from the underlying ePTFE structure. This island
structure is unique to the surface of the article and is not
present below the surface.
[0012] The morphology of the PTFE structures of the present
invention may also vary widely with respect to the number of
islands present on a given surface area. In many cases, the islands
are large and not interconnected. In other embodiments, the islands
are interconnected and may appear as a porous covering or web atop
the ePTFE structure. Given the expanse of the web, its size greatly
exceeds that of underlying nodes.
[0013] The unique character of the present articles and processes
enable the formation of improved products not seen to date. For
example, PTFE fibers can be made according to invention having
improved performance in such areas as dental floss, fishing line,
sutures, and the like. PTFE articles in membrane, tube, sheet and
other forms can also provide unique characteristics in finished
products. These and other unique features of the present invention
will be described in more detail herein.
DETAILED DESCRIPTION OF FIGURES
[0014] The operation of the present invention should become
apparent from the following description when considered in
conjunction with the accompanying drawings, in which:
[0015] FIG. 1 is perspective view of a cross-section of a fiber in
accordance with the present invention showing islands of PTFE above
the surface of the underlying ePTFE structure.
[0016] FIG. 2 is perspective view of a fixture set-up for measuring
mechanical properties of materials of the present invention as
described in more detail herein.
[0017] FIG. 3 is a schematic of the different comparative and
inventive samples and treatments referred to in the Examples and
Comparative Examples.
[0018] FIGS. 4-6 are photomicrographs of the prior art precursor
material used in Example 1.
[0019] FIGS. 7-10 are photomicrographs of the inventive material
made in accordance with Example 1.
[0020] FIG. 11 is a photomicrograph of a prior art plasma-treated
only material made in accordance with Comparative Example 1A.
[0021] FIG. 12 is a photomicrograph of a prior art heat-treated
only material made in accordance with Comparative Example 1B.
[0022] FIG. 13 is a photomicrograph of the inventive material made
in accordance with Example 2.
[0023] FIGS. 14 and 15 are photomicrographs of the precursor
material used in Example 3.
[0024] FIGS. 16-18 are photomicrographs of the inventive material
made in accordance with Example 3.
[0025] FIG. 19 is a graph showing the differential scanning
calorimetry (DSC) scans comparing the features of the inventive
materials with prior art materials, and described in more detail
herein.
[0026] FIG. 20 is a photomicrograph of the precursor material used
in Example 4.
[0027] FIGS. 21 and 22 are photomicrographs of the inventive
material made in accordance with Example 4.
[0028] FIG. 23 is a photomicrograph of the precursor material used
in Example 5.
[0029] FIG. 24 is a photomicrograph of the inventive material made
in accordance with Example 5.
[0030] FIG. 25 is a photomicrograph of the precursor material used
in Example 6.
[0031] FIG. 26 is a photomicrograph of the inventive material made
in accordance with Example 6.
[0032] FIGS. 27 and 28 are photomicrographs of the precursor
material used in Example 7.
[0033] FIGS. 29 and 30 are photomicrographs of the inventive
material made in accordance with Example 7.
[0034] FIG. 31 is a photomicrograph of the inventive material made
in accordance with Example 8.
[0035] FIGS. 32 and 33 are photomicrographs of the inventive
material made in accordance with Example 9.
[0036] FIG. 34 is a photomicrograph of the inventive material made
in accordance with Example 10.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The PTFE articles of the present invention comprise islands
of PTFE attached to an underlying ePTFE structure. No prior art
material exhibits these unique structures of PTFE islands attached
to underlying ePTFE material. The identity of the island material
can be confirmed by a variety of techniques. For instance, the
island material can be assessed by scraping bits of just the island
material off the surface with a razor blade, or by other suitable
means, then performing a thermal analysis on the sample.
Differential Scanning Calorimetry (DSC) analysis of the islands,
described later herein, indicates the absence of a node and fibril
structure.
[0038] Articles of the present invention are also unique in that
the islands of PTFE are of lower molecular weight than the PTFE of
the underlying ePTFE structure. This difference in molecular weight
can be inferred from measuring and comparing the exotherms of the
cooling curves obtained from differential scannning calorimetry.
Furthermore, the heating curves indicate that the underlying ePTFE
material possesses melt temperatures at or about 327.degree. C. and
380.degree. C. The raised islands do not exhibit the melt
temperature at or about 380.degree. C.
[0039] The fundamental process for practicing the present invention
is to first subject precursor ePTFE articles to a high-energy
surface treatment followed by a heating step to achieve the unique
PTFE islands on the surface of the underlying ePTFE material.
Solely for convenience the term "plasma treatment" will be used to
refer to any high-energy surface treatment, such as but not limited
to glow discharge plasma, corona, ion beam, and the like. It should
be recognized that treatment times, temperatures and other
processing conditions may be varied to achieve a range of island
sizes and appearances. For example, the PTFE surface can be plasma
etched in an argon gas or other suitable environment, followed by a
heat treating step. Neither heat treating the ePTFE alone nor
plasma treating alone without subsequent heat treating results in
articles of the present invention.
[0040] This inventive process can be applied to a vast array of
types and shapes of articles including, but not limited to, tubes,
fibers, including but not limited to twisted, round, flat and towed
fibers, membranes, tapes, sheets, rods, and the like, each
possessing any of a variety of cross-sectional shapes. Depending on
the morphology of the precursor ePTFE material, the appearance of
the islands can vary significantly, and the process produces a more
dramatic effect in certain precursor materials. For example, larger
islands appear to be produced in precursor materials possessing
long fibrils and small nodes when processed in accordance with the
teachings of the present invention.
[0041] In a further embodiment, the present invention also includes
the step of filling just the surface of ePTFE with other materials.
Filler particles can be applied to the surface of the ePTFE article
after the plasma treatment step, before the heat treatment step.
This process is referred to as surface filling, as distinguished
from conventional means of filling the pores of porous ePTFE
articles, which may include such techniques as blending or
co-coagulation of the filler material with PTFE, impregnating the
pores with filler, and altering the surface then bonding other
materials to that surface. The particles were primarily contained
within the islands as opposed to lying on the surface, as they were
prior to the heat treating step.
[0042] Articles of the present invention possess surprising and
valuable features heretofore unobtainable. In one embodiment,
dental floss materials consisting essentially of PTFE are found to
have significantly increased grippabililty and abrasive
characteristics. Grippability refers to the ability to firmly grip
the floss during use such that it does not slide between the user's
fingers. The abrasiveness provides the user with an improved
cleaning sensation, if not with improved cleaning, as well. These
characteristics have not been realized to this degree in
conventional PTFE floss materials.
[0043] The abrasiveness feature affords the creation of articles
consisting essentially of PTFE that possess all of the advantages
of PTFE and ePTFE, without being lubricious. Lubricity is not a
desirable feature in all applications.
[0044] Surprisingly, articles of the invention can simultaneously
exhibit increased abrasiveness evidenced by an increased drag
coefficient and improved abrasion resistance, as evidenced by
improved durability in abrasion tests. Durability tests described
herein quantify the fray resistance of articles.
[0045] Even though the precursor material is subjected to a plasma
treatment step that would otherwise be expected by one of skill in
the art to compromise the abrasion resistance of the article, by
virtue of the subsequent heat treating step, the inventive article
is surprisingly more abrasion resistant than the precursor article.
This degree of abrasion resistance had heretofore only been
achieved with ePTFE floss materials with bulk densities less than
about 0.8 g/cc.
[0046] The abrasion resistance also is particularly useful in
solving fraying problems associated with ePTFE fibers, especially
with ePTFE fishing lines.
[0047] The islands of PTFE have also been demonstrated to improve
the knot holding strength of suture materials made in accordance
with the inventive process.
[0048] The presence of the islands may also enhance bonding
inventive articles to other articles, especially perfluoropolymer
articles, PTFE articles in particular.
[0049] The present invention will be further described with respect
to the non-limiting Examples provided below.
Test Methods
Drag Resistance Test
[0050] Dynamic drag resistance was determined using a fixture 180
as shown in FIG. 2 using three 12.7 mm (0.50 inch) diameter
cylindrical shafts mounted on a rigid beam which was cantilevered
from a standard tensile tester, Model 5567 from INSTRON Company
(Canton, Mass.). The fixture arm support 176 was drilled and reamed
nominal 12.7 mm diameter (nominal 0.500 inch diameter) for a
running fit of three cylinders 170, 172 and 174 (available from
McMaster-Carr Supply Company, Dayton, N.J., Part Number 8524-K24,
off-white, G-7 Garolite Glass Silicon Rod material nominal 12.7 mm
diameter, and parted off at nominal lengths of 25 mm) in the
fixture arm support, which were secured using set-screws
compressing radially on the cylinders at the cylinder-support
interface. The cylinders were secured such that they did not rotate
during a test iteration and extended out of the test fixture
approximately 17 mm. All three cylinders were parallel which each
other and perpendicular with the cantilever fixture arm support
176.
[0051] The surface roughness (R.sub.a.) of the three cylinders was
measured both axially and radially using a Perthometer Model M4P
(Feinpruef Perthen, GmbH, Postfach 1853, D-3400 Goettingen,
Germany). R.sub.a was measured in the cylinder axial direction at 4
quadrants 90 degrees apart measured using a stroke 0.03 inch. For
the R.sub.a in the cylinder radial direction, 3 to 4 measurements
were taken using a 0.01 inch stroke randomly along the length of
the cylinder. The results are presented in the table below.
TABLE-US-00001 R.sub.a Measurements - Axial R.sub.a Measurements -
Cylinder Number (microinches) Radial (microinches) 1 93/122/102/103
55/56/59 2 32/27/67/55 101/53/48/69 3 52/57/118/66 60/98/68/40
Average R.sub.a: 74.5 64.3 Standard Deviation: 32.3 19.2
[0052] Before each sample was tested, the cylinders were removed
from the fixture, completely submerged in a beaker containing 99.9%
isopropanol alcohol for 1 minute, replaced in the test fixture and
permitted to air dry completely.
[0053] The INSTRON 5567 tensile tester was outfitted with a one
yarn style clamping jaw suitable for securing filament samples
during the measurement in the mode of tensile loading. The jaw was
connected to a 100 Newton rated load cell (not shown) which was
secured on the tester's cross-head. The cross-head speed of the
tensile tester was 30.48 cm per minute, and the gauge length was 50
mm (measured from the tangent point of the yarn clamp down to the
tangent point of the test specimen resting against the first of the
three cylinders 170). The fixture 176 was secured to the tensile
tester such that the test specimen secured in the clamping jaw was
perpendicular to the axis of cylinder 170.
[0054] The test article was threaded around the three cylinders
170, 172 and 174 in the manner depicted in FIG. 2. Consequently,
the sample was wrapped halfway around cylinder 170 and a quarter of
the way around cylinders 172 and 174. Hence, a total cumulative
wrap angle of one full wrap (i.e., 2.pi. radians) was achieved.
[0055] The vertical distance between the center points of cylinders
170 and 172 tangent points was 25.4 mm. The horizontal distance
between the center points of the same two cylinders was 12.7 mm.
The horizontal distance between the center points of cylinders 172
and 174 was 360.4 mm.
[0056] Since the inventive material may be produced to provide
islands on only one side of the material, the samples were all
twisted so that the same side contacted the surface of all three
cylinders. This results in placing a one turn twist in all test
specimens between cylinders 170 and 172. The test specimens had no
twist between cylinders 172 and 174. A 300 gram weight 186 was
fixed to the end of the test specimen. The length of the test
specimen extending past cylinder 174 and down to the suspended 300
gram weight 186 was at least 110 mm, but no more than 510 mm.
[0057] In order to determine drag resistance of samples, five
samples long enough to conduct the test were randomly selected and
tested. To begin the test, the tensile tester cross-head was set to
move upwards, thus causing the 300 gram weight to move upwards as
well. The test specimen slid over the three cylinders for at least
a travel length of 80 mm, but no more than 510 mm. The load cell
was connected to a data acquisition system such that the load
induced as the test specimen slid over the cylinders during the
upward motion of the cross-head was recorded at a rate of at least
10 data points per second. The data acquisition system recorded the
corresponding cross-head displacement during the testing as well.
The drag resistance at each cross-head displacement was then
calculated by the following formula: e.sup.(60)=T.sub.2/T.sub.1,
which reduces to: .delta.=[ln(T.sub.2/T.sub.1)]/.theta.,
[0058] where:
[0059] .delta.=Drag Resistance
[0060] .theta.=Cumulative Wrap Angle in Radians=2.pi. radians
[0061] T.sub.1=average input tension=300 grams
[0062] T.sub.2=average output tension as recorded by data
acquisition in gram force
[0063] (Note: In is the natural logarithm base on e=2.71828)
[0064] Data were obtained for displacements between 0 mm to 76mm.
The dynamic drag resistance was determined by using the arithmetic
mean-calculated drag resistance over the displacement between 25.4
and 50.8 mm.
[0065] Note that samples possessing a wax or other coating can be
tested after removing the coating material. Wax coating, for
example, can be removed by soaking the floss in a heated bath at 60
deg C. of reagent grade isopropanol alcohol for 10 minutes and then
wiping the wax away using a soft cotton cloth.
Knot Holding Capacity Test for Sutures
[0066] Samples were prepared in the following manner: A length of
the sample suture material was wrapped twice around a 2-inch
diameter smooth surfaced (for example, Delrin) cylinder. The ends
were tied together using 4 sliding throws, and one
alternate-sliding throw to lock. Throws were tensioned so that the
knot was positioned against the cylinder. The "ears" (ears are the
two free ends of the suture after the knot is tied) were trimmed to
lengths between 1/8 and 3/16-inch. The sample was slipped off of
the cylinder and the loop was cut in half at a location opposite
the knot.
[0067] Samples were tested using an INSTRON Model 5500R testing
machine at a 200 mm/min cross-head speed and 229 mm gauge length.
Yarn grips and a 10-kg load cell were used. At least ten samples
were tested and the peak force results were averaged (regardless of
whether peak force occurred by breaking or slippage of the knot).
All samples were tested in the temperature range of 22-24.degree.
C.
Island Height Measurement
[0068] Island height was measured from scanning electron
micrographs of longitudinal cross-sections of the samples.
Individual values of island height were measured as the shortest
distance from the node-fibril ePTFE structure to the highest point
of the overlying island. A line was drawn across the top surface of
the node-fibril structure adjacent to the island. A perpendicular
line was then dropped from the highest point on the island to the
line on the surface of the node-fibril structure.
[0069] The length of the dropped line is the island height.
Measurements were preferably taken from micrographs taken at
sufficiently high magnification to enable a clear determination of
the height, taking into account the magnification of the scale bar
at the bottom corner of the figure. Individual measurements were
taken for five randomly chosen islands that were representative of
all the islands. The reported island height value is the average of
those five individual measurements.
Test Method for Determination of Crystalline Phases in
Polytetrafluoroethylene Material Based on Differential Scanning
Calorimetry
[0070] Differential Scanning Calorimetry (DSC) can be used to
identify the crystalline phases of polytetrafluoroethylene (PTFE).
The presence of endothermic peaks during a heating scan, at
approximately 320-340.degree. C. shows the typical melting phases
of PTFE. In addition, an endotherm at approximately 380.degree. C.
is a consequence of PTFE having been expanded, thereby creating a
node-fibril structure. This peak (or endotherm) is widely
recognized to be indicative of the presence of fibrils in the test
sample.
[0071] This test was performed using a TA Instruments Q1000 DSC and
TA Instruments standard aluminum pans and lids for Differential
Scanning Calorimetry (DSC). A TA Instruments Sample Encapsulation
Press (Part No. 900680-902) was used to crimp the lid to the pan.
Weight measurements were performed on a Sartorius MC 210P
microbalance.
[0072] Calibration of the Q1000 was by performed by utilizing the
Calibration Wizard available through the Thermal Advantage software
supplied with the device. All calibration and resulting scans were
performed under a constant helium flow of 25 ml/min.
[0073] Samples were prepared by either cutting pieces (6 mm or
smaller) of fiber or by loading already prepared surface and core
material using a scraping method (described elsewhere herein). One
pan and lid were weighed on the balance to 0.01 mg precision. The
sample material was loaded into the pan and also recorded to 0.01
mg precision, with samples ranging from slightly under 1.0 mg for
surface scraping samples to nearly 3.0 mg for some fiber samples.
These values were entered into the Thermal Advantage control
software for the Q1000. The lid was placed on the pan and was
crimped using the press. Care was taken to ensure that no sample
material was caught in the crimp between the lid and the pan. A
similar pan for reference was prepared, with the exception of the
sample article, and its weight was also entered into the software.
The pan containing the sample article was loaded onto the sample
sensor in the Q1000 and the empty pan was loaded onto the reference
sensor. The samples were then subjected to the following procedure:
[0074] 1: Equilibrate at -30.00.degree. C. [0075] 2: Ramp
10.00.degree. C./min to 400.00C [0076] 3: Mark end of cycle 0
[0077] 4: Isothermal for 5.00 min [0078] 5: Mark end of cycle 0
[0079] 6: Ramp 10.00.degree. C./min to 200.00.degree. C. [0080] 7:
End of method
[0081] Data were analyzed, unaltered, using Universal Analysis 2000
v.4.0C from TA Instruments. Where data were being analyzed
qualitatively (for the presence and temperature location of peaks),
scans run under T4P mode were used. In the case of quantitative
interpretation of crystallization peaks (specifically, for the
measurement of enthalpy), scans were run under T1 mode.
Tensile Break Load and Matrix Tensile Strength (MTS) for Membrane
Examples
[0082] Tensile break load was measured using an INSTRON 5567
tensile test machine equipped with flat-faced grips and a 10 kN
load cell. The gauge length was 2.54 cm and the cross-head speed
was 25.4 cm/min. The sample dimensions were 6.35 cm.times.0.635 cm.
For longitudinal MTS measurements, the larger dimension of the
sample was oriented in the machine (also known as the down web)
direction. For the transverse MTS measurements, the larger
dimension of the sample was oriented perpendicular to the machine
direction, also known as the cross web direction. Each sample was
weighed using an A&D scale, (Milpitas, Calif.), Model #FR-300,
then the thickness of the samples was taken using the Heidenhain
thickness gauge Model # MT-60M (Schaumburg, Ill.). The samples were
then tested individually on the tensile tester. Five different
sections of each sample were measured. The average of the five
break load (i.e., the peak force) measurements was used. The
longitudinal and transverse MTS were calculated using the following
equation: MTS=(break load/cross-section area)*(density of
PTFE)/bulk density of the porous article), wherein the density of
PTFE is taken to be 2.2 g/cc. MTS Calculation and Tenacity
Measurement for Fiber and Suture Examples
[0083] For fiber materials, matrix tensile strength was derived
from tenacity values. Tenacity was calculated using break load and
sample weight data. Prior to tensile testing, the fiber denier was
determined by weighing a 9 m length sample of the fiber using an
analytical balance (model AA160, Denver Instruments. Inc.,
Gottingen, Germany). The mass of the fiber expressed in grams was
multiplied by 1000 to arrive at the denier value. The 9 m long
fiber sample was cut into five lengths for subsequent break load
testing. Tensile testing was conducted at ambient temperature on an
INSTRON 5567 tensile test machine equipped with fiber grips and a
10 kN load cell, set to a sample length of 269 mm. The sample was
loaded into the grips and clamped. The break load was recorded as
the grips move apart at a speed of 254 mm/min. The tenacity of each
fiber sample (expressed in grams/denier) was calculated by dividing
the break load (expressed in grams) by the denier value of the
fiber. The tenacity values for five samples were calculated and
then averaged. Matrix tensile strength was then calculated by
multiplying the tenacity value (in grams/denier) by 26,019.
Density Measurement
[0084] Fiber density was determined using one of two techniques.
For fiber densities greater than 1, the "principle of buoyancy," or
Archimedes principle, was used, which states that a body immersed
in a fluid will be subjected to a buoyancy force equal to the
weight of the displaced fluid. Buoyancy force, or the weight of the
displaced fluid, is calculated from the initial fiber sample mass
and the fiber sample mass during full immersion in the fluid. From
the mass of the displaced fluid and the fluid density, the fluid
volume displaced can be calculated and represents the total volume
of the fiber. Using the initial "dry" mass of the fiber and the
fiber volume, the fiber sample density can be calculated.
[0085] A Duran glass volume standard was used to determine water
density. This glass standard was certified to have a volume of
10.+-.0.001 cubic centimeters (cc). During the experiment, the room
temperature was recorded at 71.degree. F. (22.degree. C.). The
glass standard was placed on a Mettler-Toledo AG204 series balance
equipped with an integral immersion densitometer, previously tared
to zero, and the mass was noted at 30.0409 g. A support was then
placed over the balance base to allow a deionized water container
to be placed over, but not in contact with, the balance. A support
crucible was then suspended from the center of the balance into the
water container and not allowed to contact the sides of the
container. Any air bubbles attached to the crucible were removed by
gentle agitation. The balance was then tared to zero. The glass
standard was then carefully placed on the crucible and fully
immersed in the water container, avoiding contact with the sides of
the container. Any air bubbles attached to the glass standard after
immersion in the water container were removed by gentle agitation
of the glass standard on the crucible. The mass of the fully
immersed glass standard was noted at 20.0465 g. The density of
water was calculated as follows: buoyancy mass for the 10 cc glass
standard=30.0409 g-20.0465 g=9.9944 g water density=9.9944/10
cc=0.9994 g/cc.
[0086] All fibers with a density greater than 1 were tested using
the following procedure. A fiber sample was placed on a
Mettler-Toledo AG204 series balance equipped with an integral
immersion densitometer, and the mass was noted in grams (A).
[0087] As described above in the density determination of water, a
support was placed over the balance base to allow a water container
to be placed over but not in contact with the balance. A support
crucible was then suspended from the center of the balance into the
water container and not allowed to contact the sides of the
container. Any air bubbles attached to the crucible after immersion
in the water container were removed by gentle agitation. The
balance was then tared to zero. The fiber sample was then carefully
placed on the crucible and fully immersed in the water container
avoiding contact with the sides of the container. Any air bubbles
attached to the fiber after immersion in the water container were
removed by gentle agitation of the fiber on the crucible. The mass
of the fully immersed fiber was noted in grams (B). The density of
the fiber sample was calculated as follows: fiber sample density
(g/cc)=A/((A-B)/0.9994).
[0088] For fiber densities less than 1, the fiber volume was
calculated from the average thickness and width values of a fixed
length of fiber and the density calculated from the fiber volume
and mass of the fiber. For fibers with a density less than 1, a 1.8
meter length of fiber was placed on an A&D FR-300 balance and
the mass noted in grams (C). The thickness of the fiber sample was
then measured at 4 points along the fiber using a Heindenhain
thickness gauge. The width of the fiber was also measured at 4
points along the fiber using a graduated eyepiece from Edmund
Scientific Co. Average values of thickness and width were then
calculated, and the volume of the fiber sample was determined (D).
The density of the fiber sample was calculated as follows: fiber
sample density (g/cc)=C/D. Dimensional Measurements
[0089] Thickness was measured between the two plates of a
Mitutoyo/MAC micrometer, unless indicated otherwise. Three
different sections were measured on each sample. The average of the
three measurements was used.
[0090] Diameter was measured using a single beam laser measuring
device (LaserMike optical micrometer Model Number 60-05-06). Five
different sections were measured on each sample. The average of the
five measurements was used.
[0091] Width was measured using a digital caliper. Three different
sections were measured on each sample. The average of the three
measurements was used.
Scraping Procedure
[0092] Scrapings of the islands of PTFE for DSC analysis were
obtained in the following manner. A portion of the sample was
wrapped around a glass slide and positioned such that the islands
faced upwards, then the ends were taped to the slide to prevent the
sample from moving. Only the islands were scraped from the sample
using fresh razor blades, with the aid of magnification
(20-30.times. under a stereoscope). To ensure that only island
material was collected, it was visually confirmed that island
material remained in each section from which scrapings were taken.
This visual confirmation ensured that scrapings did not extend into
the underlying node and fibril structure. Multiple samples were
scraped to collect island material until approximately 1 mg of
scrapings was so gathered for DSC analysis.
Fiber Fray Test Method Description
[0093] Fiber samples were tested using the fixture in FIG. 2 used
for the Drag Resistance Test, described earlier, which provides the
details of this fixture. Before each sample was tested, the
cylinders were removed from the fixture, completely submerged in a
beaker containing 99.9% isopropanol alcohol for 1 minute, replaced
in the test fixture and permitted to air dry completely.
[0094] The test article was threaded around the three cylinders
170, 172 and 174 in the manner depicted in FIG. 2. Consequently,
the sample was wrapped halfway around cylinder 170 and a quarter of
the way around cylinders 172 and 174. Hence, a total cumulative
wrap angle of one full wrap (i.e., 2.pi. radians) was achieved. The
sample did not have any twists between cylinders.
[0095] An INSTRON Model 5567 tensile tester outfitted with one yarn
style clamping jaw was used. The gauge length was 50 mm (measured
from the tangent point of the yarn clamp down to the tangent point
of the test specimen resting against the first of the three
cylinders 170). The fixture 180 was secured to the tensile tester
such that the test specimen secured in the yarn style clamp was
perpendicular to the axis of cylinder 170.
[0096] A 400 gram weight 186 was fixed to the end of the test
specimen by tying a looped knot around a 400 gram weight. The
length of the test specimen extending past cylinder 174 and down to
the suspended 400 gram weight 186 was at least 150 mm. The tensile
tester pulled the sample over the three cylinders a distance of
50.8 mm at a cross-head speed of 50.8 cm/min and then returned to
its starting position to complete one cycle. Five consecutive
cycles were run per sample.
[0097] The tested portion of the sample was marked by securing a
piece of tape on the sample 12 mm past cylinder 170 toward the yarn
style jaw and securing another piece of tape on the sample 63 mm
past cylinder 172 toward cylinder 174.
[0098] The test method should be modified for fibers that do not
have enough tensile strength to survive the test. If any of the
desired number of samples break during the five cycles the weight
should be lowered by 100 gram increments and the test should be
started over until a weight is arrived at that does not cause any
of the desired number of samples to break during the five
cycles.
[0099] Upon completion of the test, the test samples were examined
between the two pieces of tape for evidence of hairing. A hair is
any part of the sample that has become frayed from the sample but
is still attached at one end. Examination of the surface of the
sample was performed using either a light ring with a 2.times.
magnification lens or with a microscope (10.times. magnification).
A caliper was used to measure the length of the hair, i.e., the
length from the free end of the hair to the point where the hair is
attached to the rest of the sample. The choice of magnification
used, if any, is dependent on the ability to accurately detect and
measure the length of the hairs.
[0100] The Fiber Fray Score for each sample was calculated from the
length of the hairs coming off of the samples by the following
equation: Fiber Fray Score=sum of the lengths in millimeters of the
hairs Fishing Line Fray Test
[0101] The fishing line to be tested was cut to a length of about
7.62 meters. One end of the sample to be tested was tied using a
fisherman's double Uni-knot to the free end of typical 12 lb test
nylon fishing line that had been spooled onto a Shakespeare
Tidewater 10LA bait casting reel (Shakespeare Fishing Tackle, Inc.,
Columbia, S.C.). The length of the nylon line was such that it
filled 1/4 of the spool on the reel. The reel was securely attached
to the reel holder of a commercially available fishing pole (7 ft
Gold Cup Inshore rod rated for 12-25 lb lines and 3/4-3 oz. lures;
Bass Pro Model GC171225, Springfield, Mo.). The pole was secured at
approximately a 10-degree angle. The pole was secured 20 mm behind
the last eyelet (toward the reel end of the pole) and 90 mm in
front of the reel (toward the tip end of the pole). The tip was
therefore allowed to move and vibrate by the tensions of the line
and the inherent stiffness of the pole, as in a real fishing
situation. The pole was secured in such a way that the line did not
touch the securing devices during the test.
[0102] The other end of the sample fishing line to be tested was
threaded through the pole guides and tied to a 16.83 cm diameter,
about 50 mm wide, silicone coated take-up wheel in such a way that
it did not slip or break during the test. The center of the wheel
was located 15.24 cm beyond the pole tip (in the horizontal
direction) and 34.3 cm below the pole tip (in the vertical
direction). The 50 mm wide part of the wheel was positioned
perpendicular to the fishing rod in such a way that the line could
wind onto the 50 mm wide surface. This take-up wheel was attached
to a DC motor that accelerated to 1750 rpm in approximately 1/4
second. The rpm of the motor was measured with a digital hand
tachometer (Ametek model 1726, Largo, Fla.) applied to the outside
surface of the silicone take-up wheel.
[0103] The reel was set to the casting, or open, position. The
motor was turned on and the line was wound onto the 50 mm wide part
of the take-up wheel. This was intended to simulate casting the
line during fishing. The motor was turned off after the entire
sample had been wound onto the take-up wheel. Pressure was applied
to the exposed metal side of the spool by hand with a piece of PFTE
tape and a sponge to prevent the spool from over spinning while the
take-up wheel was decelerating. The reel was switched to the closed
or reeling position. An air drill (Matco Model MT1889, Stow, Ohio)
attached to the handle of the reel in order to re-spool the line
was turned on. The drill re-spooled the line at a rate of 85 to 88
feet per minute as measured by a digital hand tachometer (Ametek
model 1726, Largo, Fla.) on the silicon surface of the wheel and
with a back tension of 1800-2000 g applied to the wheel. The back
tension was intended to simulate the resistance of a fish on the
line and was measured by placing a SaxI Tension Meter Model TR-4000
(Tensitron, Inc., Harvard Mass.) onto the sample between the reel
and the first eyelet as the sample was being reeled up by the air
drill. A cycle was complete once the sample fishing line was
respooled on the reel, minus the amount strung through the rod and
tied onto the wheel. The air drill was turned off. Each line was
subjected to 5 such test cycles.
[0104] Upon completion of the test, the test samples were examined
over their entire length for evidence of hairs. A hair is any part
of the line that has frayed and become separated from the line, but
is still attached at one end. Examination of the surface of the
sample was performed using either a light ring with a 2.times.
magnification lens or with a microscope (10.times. magnification).
A caliper was used to measure the length of the hair, i.e., the
length from the free end of the hair to the point where the hair is
attached to the rest of the sample. The choice of magnification
used, if any, is dependent on the ability to accurately measure the
length of the hairs.
[0105] A Fishing Line Fray Score for each sample was then
calculated from the length of the hairs coming off of the samples
using the following equation: Fishing Line Fray Score=sum of the
lengths in millimeters of hairs over 4 mm in length. Moisture Vapor
Transmission Rate (MVTR)
[0106] The samples (measuring larger than 6.5 cm in diameter) were
conditioned in a 23.degree. C., 50%.+-.2% RH test room. Test cups
were prepared by placing 70 grams of a Potassium Acetate salt
slurry into a 4.5 ounce polypropylene cup having an inside diameter
of 6.5 cm at the mouth. The slurry was comprised of 53 grams of
potassium acetate crystals and 17 g of water. The slurry was
thoroughly mixed with no undissolved solids present and stored for
16 hours in a sealed container at 23.degree. C. An expanded PTFE
membrane (ePTFE), available from W. L. Gore and Associates,
Incorporated, Elkton, Md., was heat sealed to the lip of the cup to
create a taut, leakproof microporous barrier holding the salt
solution in the cup. A similar ePTFE membrane was mounted taut
within a 12.7 cm embroidery hoop and floated upon the surface of a
water bath in the test room. Both the water bath and the test room
were temperature controlled at 23.degree. C.
[0107] Samples to be measured were laid upon the floating membrane,
and a salt cup inverted and placed upon each sample. The salt cups
were allowed to pre-condition for 10 minutes. Each salt cup was
then weighed, inverted and placed back upon the sample. After 15
minutes, each salt cup was removed, weighed, and the moisture vapor
transmission rate was calculated from the weight pickup of the cup
as follows: MVTR g/(m.sup.2.times.24 hours)=Weight (a) water pickup
in cup [Area (m.sup.2) of cup mouth.times.Time (days) of test]. The
average of five tests was used.
EXAMPLES
[0108] In order to demonstrate the unique surfaces of the materials
of the present invention as compared to prior art surfaces and
treatments, surface and longitudinal cross-section scanning
electron micrographs were taken, in many cases, for each of the
following three "comparative" materials and for the inventive
material of the present invention: (A) precursor material; (B)
plasma-treated only material, (C) heat-treated material only, and
(D) inventive material that was subjected to the unique combination
of plasma treating then heat treating to effect a unique surface on
the inventive material. FIG. 3 is a schematic, for reference only,
of the different comparative and inventive samples and treatments
described in the following examples. Higher magnification images
were taken in the same region that the low-magnification images
were taken. Samples were thoroughly scanned to ensure that the
images were representative of the sample.
Example 1
Precursor material:
[0109] Expanded PTFE dental floss material made in accordance with
the teachings of U.S. Pat. No. 5,518,012 was the precursor for the
two continuous processing techniques performed in this example,
described below as (a) and (b). This dental floss was an ePTFE flat
fiber possessing the following properties: bulk density of 1.52
g/cc, thickness of 0.05 mm, width of 1.2 mm, and matrix tensile
strength of 81,401 psi in the length direction, drag resistance of
0.148 and Fiber Fray Score of greater than 200 (exact numbers were
not calculated because of the abundance of hairs). Representative
scanning electron photomicrographs of the precursor material, all
taken at 500.times. magnification, appear in FIGS. 4 through 6. The
dashed bars present at the lower right of these and all other
micrographs presented herein indicate the magnification scale. For
example, the distance between the first and last dash marks in FIG.
4 corresponds to a length of 100 microns. The precursor material
was produced by stretching PTFE over heated plates. FIGS. 4 and 5
show both of the surfaces of the precursor material, namely, the
surface that did contact the plate and the surface that did not
contact the plate, respectively. Islands of PTFE are not evident in
either of these photomicrographs. FIG. 6, which shows a
cross-section of the precursor material, also confirms the absence
of islands in the precursor material. These three photomicrographs
of the precursor material depict an ePTFE structure that is
representative of highly longitudinally-expanded materials.
Experimental Procedures:
[0110] (a) Long lengths of the precursor material were first plasma
treated using argon gas in conjunction with a Plasma Treatment
System PT-2000P (Tri-star Technologies, El Segundo, Calif.). A
T-section was affixed to the end of the nozzle of the unit. Plasma
treatment occurred within the straight length of the T-section. The
precursor floss material was fed through the straight section,
which measured 59 cm long and 3.7 mm inner diameter. The floss
material was drawn through the unit at a linear speed of 30 fpm,
and the power was set between 2.1 and 2.2, per the "Plasma Current"
display on the front of the unit. The argon flow rate was set at
about 25 SCFH. The plasma-treated material was next subjected to a
heat-treating step by passing it over a heated plate set to
390.degree. C. at a line speed of 60 fpm. The length of the heated
plate was 86 inches (2.2 m).
[0111] Photomicrographs of the plasma-treated, then heat-treated
materials appear in FIGS. 7 through 10. FIG. 7 was taken at
200.times. magnification, and FIGS. 8 through 10 were taken at
500.times.. FIGS. 7 and 8 are surface shots taken of the plate side
of the material, FIG. 9 is a surface shot taken of the non-plate
side of the material, and FIG. 10 is a cross-sectional
photomicrograph. The surface images indicate the smooth,
island-like appearance of the PTFE material on top of the
node-fibril structure of the underlying ePTFE floss material. These
images demonstrate that the individual islands have a much larger
surface area than any of the nodes of the underlying node-fibril
ePTFE structure. The island height was determined to be about 17
microns.
[0112] The inventive article had the following properties: bulk
density of 1.52 g/cc, longitudinal matrix tensile strength of
62,113 psi, width of 1.1 mm, and thickness of 0.05 mm. The
inventive material had a drag resistance of 0.196, which was
consistent with the perception of increased grippability and
improved cleaning sensation experienced upon handling and using the
inventive material. Three inventive samples were subjected to the
Fiber Fray Test and were found to have no visible hairs, resulting
in a Fiber Fray Score of 0.
[0113] (b) Another sample of the precursor material was processed
in the same way as described above in procedure (a), except that
faster line speeds of 200 feet per minute for both the plasma
treating and subsequent heat treating were employed. The resulting
inventive material had a drag coefficient of 0.192, and island
height of 6 microns.
Comparative Example 1A
[0114] The same precursor material as described in Example 1,
above, was used in this comparative example. A long length of the
precursor material was plasma treated using argon gas in
conjunction with a Plasma Treatment System PT-2000P (Tri-star
Technologies, El Segundo, Calif.). A T-section was affixed to the
end of the nozzle of the unit. Plasma treatment occurred within the
straight length of the T-section. The precursor floss material was
fed through the straight section, which measured 59 cm long and 3.7
mm inner diameter. The floss material was drawn through the unit at
a linear speed of 30 fpm, and the power was set between 2.1 and
2.2, per the "Plasma Current" display on the front of the unit. The
argon flow rate was set at about 25 SCFH.
[0115] This plasma treatment resulted in a material possessing the
following properties: bulk density of 1.52 g/cc, thickness of 0.1
mm, width of 1.2 mm, and matrix tensile strength of 69,998 psi.
FIG. 11 is a photomicrograph of this plasma-treated only material,
showing a surface devoid of islands.
Comparative Example 1B
[0116] The same precursor material as described in Example 1,
above, was used in this comparative example. A long length of the
precursor material was subjected to a heat-treating step by passing
it over a heated plate set to 390.degree. C. at a line speed of 60
fpm. The length of the heated plate was 86 inches (2.2 m). FIG. 12
is a photomicrograph taken at 500.times. of the non-plate side of
this heat-treated material. This image shows that the material
surface is devoid of islands.
Example 2
[0117] The same precursor material as described in Example 1 was
used in this example. The precursor material samples were subjected
to the same plasma treatment described in Example 1, part (a), then
the plasma-treated samples were axially restrained and placed in a
forced air oven set to 335.degree. C. for about 10 minutes.
[0118] Surface and longitudinal cross-section scanning electron
photomicrographs were obtained for this inventive material. FIG. 13
is a surface photomicrograph of the floss material sample taken at
1000.times. magnification. The islands that are characteristic of
articles of the present invention are evident in this
photomicrograph. As with the islands observed in Example 1, the
island surfaces appear smooth and the individual islands are of
greater surface area than any of the underlying nodes.
[0119] The inventive article had the following properties: bulk
density of 1.46 g/cc, longitudinal matrix tensile strength of
64,345 psi, width of 1.1 mm, and thickness of 0.17 mm. The
inventive floss material, when tried by several individuals, gave
the perception of improved grippability and cleaning sensation
compared to the precursor material.
Example 3
Precursor material:
[0120] Expanded PTFE dental floss made in accordance with the
teachings of U.S. Pat. No. 6,539,951 was the precursor material for
this example. This dental floss consisted essentially of ePTFE and
possessed the following properties: bulk density of 0.80 g/cc,
thickness of 0.08 mm, width of 1.9 mm, matrix tensile strength of
63,949 psi, and drag coefficient of 0.172. Photomicrographs of the
surface and cross-section, respectively, of this precursor material
appear in FIGS. 14 (500.times.) and 15 (1000.times.).
Experimental procedure:
[0121] For the present example, the precursor material was
plasma-treated, then heat treated in accordance with the steps
described in Example 1, part (a). FIG. 16 (surface, 200.times.),
FIG. 17 (surface, 500.times.), and FIG. 18 (cross-section,
1000.times.) are photomicrographs of the microstructure of the
inventive material. As with the prior examples, the individual
islands are seen to have a much larger surface area than any of the
nodes of the underlying node-fibril ePTFE structure, and the
islands exhibit a smooth surface. The inventive material had the
following properties: bulk density of 0.82 g/cc, longitudinal
matrix tensile strength of 36,707 psi, width of 1.8 mm, and
thickness of 0.08 mm.
[0122] The average island height for the inventive material was
determined to be about 13 microns. The drag coefficient for the
inventive material was measured to be 0.220, thus indicating that
the inventive article was more grippable than the precursor article
and had an improved cleaning sensation.
[0123] Differential Scanning Calorimetry (DSC) was used to
determine whether multiple crystalline phases of PTFE existed in
the islands and in the underlying core, or non-island, component of
the material made in this example. Scrapings of the islands were
taken by following the Scraping Procedure described herein. FIG. 19
herein includes the DSC scans for the inventive material as a
whole, as well as for the scrapings alone and the underlying core
alone. The results are described in more detail later herein, along
with comparisons with Comparative Example 3A and 3B material
scans.
Comparative Example 3A
[0124] The precursor material described in Example 3 was used for
this comparative example. This precursor material was subject to
the same plasma treatment described in Comparative Example 1A.
Comparative Example 3B
[0125] The precursor material described in Example 3 was used for
this comparative example. This precursor material was subject to
the same heat treatment described in Comparative Example 1B.
[0126] FIG. 19 shows six DSC heating scans for the inventive
materials of Example 3 (labeled (1), (2) and (3) on the figure),
the precursor material for Example 3 (labeled (4)), and for
Comparative Example 3A (labeled (5)) and 3B (labeled (6)). All
samples were tested in the manner described in the Test Method for
Determination of Crystalline Phases in Polytetrafluoroethylene
Material based on Differential Scanning Calorimetry. The curves
were overlaid on the same graph and shifted on the y-axis for
clarity. The curve corresponding to the inventive sample is labeled
as (1). Islands from a section of this sample were scraped off the
surface per the Scraping Procedure, and the heating scan for this
island material is labeled (2). A scan was also prepared by
obtaining core material from the center of the inventive material
sample, ensuring that all island material was removed, and the
curve for this core material is labeled (3).
[0127] All but one of the scans in this FIG. 19 exhibit the
approximately 380.degree. C. peak in the heating curves. The only
sample that did not exhibit this peak was the island material
obtained by scraping (scan (2)). The absence of this endotherm in
this DSC curve indicates that the islands do not contain the node
and fibril structure that is present in all of the other materials.
This result is consistent with the absence of discernable fibrils
in the islands evidenced in the micrographs.
[0128] From the DSC cooling scan, the exothermic enthalpy (as
expressed in units of J/g) represented by the area of the peak at
approximately 316.degree. C. provides information regarding the
molecular weight of the PTFE. Lower molecular weight PTFE has
higher enthalpic values because the material can recrystallize more
readily during cooling than higher molecular weight PTFE. The
exothermic enthalpy of the core of the inventive material devoid of
all islands, represented by the area of the peak at approximately
316.degree. degree C., was 33.5 J/g. The exothermic enthalpy of the
island scrapings had an exothermic enthalpy, represented by the
area of the peak at approximately 316.degree. C., of 60.5 J/g. The
higher exothermic enthalpy of the islands as compared to the core
indicated that the islands were comprised of lower molecular weight
PTFE than the core.
Example 4
[0129] Expanded PTFE fiber was obtained (Part Number V112765,
available from W. L. Gore and Associates, Inc., Elkton, Md.), and
two such fibers were twisted together to provide the precursor
material for this example. The precursor material possessed the
following properties: bulk density of 1.29 g/cc, longitudinal
matrix tensile strength of 138,278 psi, and diameter of 0.483 mm.
FIG. 20 (100.times.) is a photomicrograph of the surface of the
precursor material.
[0130] In this example, the precursor material was plasma treated
and heat treated in the same manner as described in Example 1, part
(a), except that the plasma treatment line speed was set at 100
fpm, and the heat treatment was performed over a series of three
heated plates, measuring 9 feet total, all set to 440.degree. C. to
effect a modest amount of shrinkage by applying an overall stretch
ratio of 0.92:1.
[0131] The inventive article had the following properties: bulk
density of 2.17 g/cc, longitudinal matrix tensile strength of
92,285 psi, diameter of approximately 0.41 mm. The cross-section of
the article was of oblong shape. The island height was determined
to be about 6 microns. FIG. 21 (100.times.) and FIG. 22
(1000.times.) are surface photomicrographs of the inventive
material. Both figures show raised, smooth-surfaced islands.
[0132] In addition, three samples of the inventive fishing line
material were subjected to the Fishing Line Fray Test, and all of
the inventive fishing lines exhibited only small hairs ranging from
0.5 mm to 6 mm in length. Fishing Line Fray Scores for these three
samples were 4, 5, and 10, respectively.
Comparative Example 4A
[0133] The precursor material described in Example 4 was used for
this comparative example. Comparative fishing line material were
made by heat treating the precursor over a series of three heated
plates, all set to 440.degree. C. to effect a modest amount of
shrinkage by applying an overall stretch ratio of 0.92:1.
[0134] Three comparative fishing line samples were subjected to the
Fishing Line Fray Test. Each of the three samples had many hairs of
varying lengths from 0.5 mm to as long as 38 mm, with at least 10
hairs over 10 mm in length and at least two hairs over 20 mm in
length. The Fishing Line Fray Scores for these samples were all
over 160 (exact numbers were not obtained because of the abundance
of hairs).
Example 5
[0135] The precursor material for this example was expanded PTFE
suture material possessing the following properties: bulk density
of 1.13 g/cc, longitudinal matrix tensile strength of 56,382psi,
and diameter of 0.3 mm. FIG. 23 is a photomicrograph taken at
200.times. of the precursor material.
[0136] This precursor material was plasma treated in the same
manner as described in Example 1(a); however, the subsequent heat
treating was performed in a continuous manner, drawing the plasma
treated article through a 92-inch-long forced air oven set to
415.degree. C. at a line speed of about 15 ft/minute. The resulting
inventive article had the following properties: bulk density of
1.07 g/cc, longitudinal matrix tensile strength of 44,986 psi, and
a diameter of 0.33 mm. The island height was determined to be about
11 microns. FIG. 24 is a photomicrograph taken at 200.times. of the
inventive material.
[0137] FIGS. 23 and 24 demonstrate the difference in the surface
appearance between the precursor and inventive materials,
respectively. The inventive material clearly exhibits the raised
islands of PTFE, in which the islands are smooth and are of greater
size than the nodes of the underlying structure. As with all of the
images included herein, samples were thoroughly scanned to ensure
that the images were representative of the sample.
[0138] The inventive materials were subjected to the Knot Holding
Capacity Test, and the knotted inventive article retained 59% of
its material peak force, and the inventive suture broke at the knot
in 70% of the cases.
[0139] For comparison purposes, a sample of the knotted precursor
suture material, when subjected to the Knot Holding Capacity Test,
retained only 27% of its material peak force and in each test the
knot slipped without the suture breaking.
Example 6
[0140] The precursor material for this example was an expanded PTFE
fiber material, suitable for use as a suture, having a diameter of
0.023 mm. FIG. 25 is a photomicrograph taken at 500.times. of the
precursor material.
[0141] The precursor material was first plasma treated using argon
gas in conjunction with a Plasma Treatment System PT-2000P
(Tri-star Technologies, El Segundo, Calif.). A T-section was
affixed to the end of the nozzle of the unit. Plasma treatment
occurred within the straight length of the T-section. The precursor
floss material was fed through the straight section, which measured
59 cm long and 3.7 mm inner diameter. The floss material was drawn
through the unit at a linear speed of 5 fpm, and the power was set
at 1.8, per the "Plasma Current" display on the front of the unit.
The argon flow rate was set at about 25 SCFH. The plasma-treated
material was next restrained from shrinking by tying it to a metal
frame, then subjected to a heat-treating step by placing it in a
forced air oven set to 335.degree. C. for 10 minutes. Islands of
PTFE are evident on the inventive material, as shown in FIG. 26,
which is a photomicrograph taken at 500.times..
Example 7
[0142] The precursor material for this example was an expanded PTFE
membrane possessing the following properties: moisture vapor
transmission rate of 68,149 g/m.sup.2-day, thickness of 0.023 mm,
bulk density of 0.80 g/cc, longitudinal matrix tensile strength of
8,740 psi, and transverse matrix tensile strength of 15,742 psi.
FIGS. 27 and 28 are photomicrographs of the surface and the
cross-section, respectively, of the precursor membrane, both taken
at 2000.times. magnification.
[0143] The membrane material was then processed to provide articles
of the present invention. The precursor membrane was subjected to a
plasma treatment using argon gas by passing the membrane through an
atmospheric plasma treatment unit set to a power of 2.5 kilowatts.
The membrane was passed through the unit at a speed of 5 meters per
minute, and the argon gas flow rate was 50 liters per minute. The
plasma-treated membrane was subsequently restrained from skrinking
by securing it on a pin frame and heat treated in a forced air oven
set to 335.degree. C. for about 10 minutes.
[0144] The resulting inventive material had the following
properties: bulk density of 0.81 g/cc, longitudinal matrix tensile
strength of 10,070 psi, transverse matrix tensile strength of
14,375 psi, and thickness of 0.023 mm. FIGS. 29 and 30 are surface
and cross-sectional photomicrographs, respectively, of the
inventive material taken at 2000.times., showing smooth, raised
islands. The island height of the inventive material was determined
to be about 3 microns.
Example 8
[0145] The same precursor membrane material described in Example 7
was used for this example. The precursor was processed in the same
manner described in Example 7, except that round silica particles
(Admatechs, Product Number SO-E2, Seto, Japan) were applied to the
surface of the plasma-treated membrane by sprinkling, then the
particles were spread out by a gloved hand to form a thin,
substantially even coating on the membrane prior to the
heat-treating step.
[0146] A photomicrograph of the surface of the inventive article
taken at 2000.times. appears in FIG. 31. Upon examination of the
photomicrograph, it was observed that the raised islands contained
silica particles.
Example 9
[0147] The precursor membrane material described in Example 7 was
used for this example. The membrane was processed in the same
manner as described in Example 7, except that a mask material
comprising a polyester film tape with a rubber adhesive (3M.TM.
Polyester Protective Tape 335, Minnesota Mining and Manufacturing,
Inc., St. Paul, Minn.) having a pattern of substantially
regularly-spaced holes was taped to the surface of the precursor
material prior to the plasma-treatment step. The mask was removed
after the plasma-treatment, but prior to the heat treatment
step.
[0148] FIGS. 32 and 33 are surface shots taken at 70.times. and
2000.times., respectively, of the resulting article of this
example. FIG. 32 shows the dot pattern effected by masking the PTFE
during the plasma-treating process. Specifically, the areas that
appear as dots (darker) 501 are areas that were plasma-treated then
heat-treated; hence, these regions were processed in accordance
with the present invention. The masked (lighter) regions 502 were
subjected only to heat treatment. A representative higher
magnification image of the boundary between the masked 502 and
unmasked 501 regions is presented in FIG. 33. Note the smooth
islands 503 on the plasma-treated and heat-treated area, as
compared to the masked region 502.
Example 10
[0149] A precursor material comprising expanded PTFE fiber which
had never been subjected to amorphous locking temperatures was
obtained having the following properties: bulk density of 1.2 g/cc,
longitudinal matrix tensile strength of 71,000 psi, width of 1.2
mm, and thickness of 0.2 mm.
[0150] The precursor material was processed in the same manner as
part (a) of Example 1. The resulting inventive article had the
following properties: bulk density of 1.4 g/cc, longitudinal matrix
tensile strength of 64,400 psi, width of 0.9 mm, and thickness of
0.2 mm. A photomicrograph taken at 500.times. of the surface of the
resulting inventive material appears in FIG. 34. This figure shows
the raised islands of PTFE on the material, thus demonstrating that
articles of the present invention are created even with ePTFE
precursor materials which have not been subjected to amorphous
locking temperatures. While the invention has been disclosed
herein, in connection with certain embodiments and detailed
descriptions, it will be clear to one skilled in the art that
modifications or variations of such detail can be made without
deviating from the gist of the invention and such modifications or
variations are considered to be within the scope of the claims
herein below.
* * * * *