U.S. patent application number 15/213564 was filed with the patent office on 2018-01-25 for composite carbon fibers.
The applicant listed for this patent is Hexcel Corporation. Invention is credited to Michael Yurchenko.
Application Number | 20180023244 15/213564 |
Document ID | / |
Family ID | 59738379 |
Filed Date | 2018-01-25 |
United States Patent
Application |
20180023244 |
Kind Code |
A1 |
Yurchenko; Michael |
January 25, 2018 |
COMPOSITE CARBON FIBERS
Abstract
A composite carbon fiber having a carbon fiber to which an
amine-functionalized polymer is electro-grafted onto a surface
thereof is provided. Electro-grafting the amine-functionalized
polymer onto the surface of the carbon fiber results in a composite
carbon fiber in which the polymer is covalently bonded to the
fiber, and in which a significant number of reactive amine groups
are available for subsequent reactions, such as for reacting with a
resin matrix in the production of a fiber reinforced composite. As
a result, the composite carbon fibers may be particularly useful in
producing fibers reinforced composites that exhibit improved
interlaminar strength. Fiber reinforced composites are also
provided.
Inventors: |
Yurchenko; Michael;
(Decatur, AL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hexcel Corporation |
Dublin |
CA |
US |
|
|
Family ID: |
59738379 |
Appl. No.: |
15/213564 |
Filed: |
July 19, 2016 |
Current U.S.
Class: |
442/60 |
Current CPC
Class: |
D06M 15/59 20130101;
D06M 10/10 20130101; D06M 23/12 20130101; D06M 15/55 20130101; D06M
2400/01 20130101; D01F 11/14 20130101; D06M 15/3562 20130101; D10B
2505/12 20130101; C08J 5/06 20130101; D06M 2101/40 20130101; C08J
5/042 20130101; D06M 14/36 20130101; D06M 15/61 20130101 |
International
Class: |
D06M 14/36 20060101
D06M014/36; D06M 15/59 20060101 D06M015/59; D06M 15/55 20060101
D06M015/55; D01F 11/14 20060101 D01F011/14 |
Claims
1.-56. (canceled)
57. A composite carbon fiber comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof.
58. The composite carbon fiber of claim 57, wherein the composite
carbon fiber has a nitrogen/carbon (N/C) ratio that is at least
0.125.
59. The composite carbon fiber of claim 57, wherein the composite
carbon fiber has a N/C ratio that is from about 0.15 to 0.3.
60. The composite carbon fiber of claim 57, wherein the composite
carbon fiber exhibits an increase in nitrogen surface concentration
that is at least 50% in comparison to the original carbon fiber
that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber.
61. The composite carbon fiber of claim 57, wherein the composite
carbon fiber exhibits an increase in nitrogen surface concentration
that is from about 50 to 500% in comparison to the original carbon
fiber that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber.
62. The composite carbon fiber of claim 57, wherein the composite
carbon fiber exhibits an increase in nitrogen surface concentration
that is from about 150 to 500% in comparison to the original carbon
fiber that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber.
63. The composite carbon fiber of claim 57, wherein the
amine-functionalized polymer is selected from the group consisting
of linear polyethyleneimines (PEI), branched polyethyleneimines
(PEI), branched polypropyleneimine, linear poly(allylamine) (PAA),
polyamidoamine (PAMAM) dendrimer, branched poly(allylamine)
prepared by branching of poly(allylamine) with divinylbenzene
(PAADVB), and block-copolymers, core-shell particles, and
combinations thereof.
64. The composite carbon fiber of claim 57, wherein the
amine-functionalized polymer comprises a branched
polyethyleneimine.
65. The composite carbon fiber of claim 57, wherein the carbon
fiber has a tensile strength of at least 400 ksi.
66. The composite carbon fiber of claim 57, wherein the carbon
fiber has a tensile strength from about 600 to 1,050 ksi.
67. The composite carbon fiber of claim 57, wherein the
amine-functionalized polymer has a weight average molecular weight
ranging from about 5,000 to 35,000.
68. A fiber reinforced composite comprising the composite carbon
fiber of claim 57.
69. A composite carbon fiber comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof, and wherein the composite carbon fiber is characterized
by: a) a nitrogen/carbon (N/C) ratio that is at least 0.125; and b)
an increase in nitrogen surface concentration that is from about 50
to 3,000% in comparison to the original carbon fiber that does not
include an amine-functionalized polymer electro-grafted onto the
surface of the carbon fiber.
70. The composite carbon fiber of claim 69, wherein the composite
carbon fiber exhibits a nitrogen/carbon (N/C) ratio that is from
about 0.15 to 0.3, and an increase in surface of nitrogen
concentration of any one or more of at least 75%, at least 100%, at
least 125%, at least 150%, at least 175%, at least 200%, at least
225%, at least 250%, at least 275%, at least 300%, at least 325%,
at least 350%, at least 375%, at least 400%, at least 425%, at
least 450%, at least 475%, or at least 500%, in comparison to the
original carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface.
71. The composite carbon fiber of claim 69, wherein the composite
carbon fiber exhibits an increase in surface of nitrogen
concentration ranging from about 100 to 500% in comparison to the
original carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface.
72. The composite carbon fiber of claim 69, wherein the
amine-functionalized polymer is selected from the group consisting
of linear polyethyleneimines (PEI), branched polyethyleneimines
(PEI), branched polypropyleneimine, linear poly(allylamine) (PAA),
polyamidoamine (PAMAM) dendrimer, branched poly(allylamine)
prepared by branching of poly(allylamine) with divinylbenzene
(PAADVB), and a combination thereof.
73. The composite carbon fiber of claim 69, wherein the carbon
fiber has a tensile strength from about 600 to 1,050 ksi, and the
amine-functionalized polymer has a weight average molecular weight
ranging from about 5,000 to 35,000.
74. A fiber reinforced composite comprising a carbon fiber having
an amine-functionalized polymer electro-grafted onto a surface
thereof, and a resin matrix infused into the carbon fiber, wherein
the fiber reinforced composite exhibits an interlaminar strength of
about 17 to 25 ksi as characterized by Short Beam Shear (SBS)
testing.
75. The fiber reinforced composite of claim 74, wherein the
interlaminar strength of the fiber reinforced composite is about 20
to 22 ksi as characterized by SBS.
76. The fiber reinforced composite claim 74, wherein the fiber
reinforced composite exhibits an increase in SBS ranging from about
5 to 25% in comparison to a similar fiber reinforced composite in
which the carbon fibers are identical with the exception that the
surfaces of the carbon fibers do not include an
amine-functionalized polymer.
77. The fiber reinforced composite claim 74, wherein a surface of
the composite carbon fiber has a nitrogen/carbon (N/C) ratio that
is from about 0.15 to 0.3.
78. The fiber reinforced composite of claim 77, wherein the
composite carbon fiber exhibits an increase in surface of nitrogen
concentration of any one or more of least 25%, at least 50%, at
least 75%, at least 100%, at least 125%, at least 150%, at least
175%, at least 200%, at least 225%, at least 250%, at least 275%,
at least 300%, at least 325%, at least 350%, at least 375%, at
least 400%, at least 425%, at least 450%, at least 475%, or at
least 500%, in comparison to the original carbon fiber that has not
had an amine-functionalized polymer electro-grafted onto its
surface.
79. The fiber reinforced composite of claim 77, wherein the
composite carbon fiber exhibits an increase in surface of nitrogen
concentration ranging from about 100 to 500%, in comparison to the
original carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface.
80. The fiber reinforced composite of claim 74, wherein the resin
is selected from the group consisting of epoxy based resins,
bismaleimide based resins, cyanate ester based resins, and phenolic
based resins.
81. The fiber reinforced composite of claim 74, wherein the carbon
fiber has a tensile strength from about 600 to 1,050 ksi.
82. The fiber reinforced composite of claim 74, wherein the
amine-functionalized polymer is selected from the group consisting
of linear polyethyleneimines (PEI), branched polyethyleneimines
(PEI), branched polypropyleneimine, linear poly(allylamine) (PAA),
polyamidoamine (PAMAM) dendrimer, branched poly(allylamine)
prepared by branching of poly(allylamine) with divinylbenzene
(PAADVB), and a combination thereof.
83. An aerospace part comprising the fiber reinforced composite of
claim 74.
84. A method of preparing a composite carbon fiber comprising
passing a carbon fiber through a bath comprising an
amine-functionalized polymer; applying an electro-potential to the
cell; electro-grafting the amine-functionalized polymer onto the
carbon fiber to produce a composite carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof, and wherein the composite carbon fiber is characterized
by: a) a carbon/nitrogen (N/C) ratio that is at least 0.125; and/or
b) an increase in nitrogen surface concentration that is from about
50 to 500% in comparison to the original carbon fiber that does not
include an amine-functionalized polymer electro-grafted onto the
surface of the carbon fiber.
85. The method of claim 84, wherein the composite carbon fiber
exhibits a nitrogen/carbon (N/C) ratio that is from about 0.15 to
0.3, and wherein the composite carbon fiber exhibits an increase in
surface of nitrogen concentration of any one or more at least 100%,
in comparison to the original carbon fiber that has not had an
amine-functionalized polymer electro-grafted onto its surface.
86. The method of claim 84, wherein the step of electro-grafting
the amine-functionalized polymer onto the carbon fiber lasts for a
period of time between 30 seconds and two minutes.
87. The method of claim 84, wherein the step of electro-grafting
the amine-functionalized polymer onto the carbon fiber lasts for a
period of time between 45 seconds and 90 seconds.
Description
FIELD
[0001] The present invention relates generally to carbon fibers for
use in the preparation of fiber reinforced composites, and in
particular, to a composite carbon fiber comprising a carbon fiber
having an amine-functionalized polymer electro-grafted onto a
surface thereof.
BACKGROUND
[0002] Fiber reinforced composites are increasingly being used in a
wide variety of applications due to their relative low weight and
high strength. An example of one such application is the aviation
industry where there is a desire to improve fuel efficiency by
reducing vehicle weight. Fiber reinforced composite structures
provide a material having a lower density than a corresponding
structure comprising a metallic alloy while retaining mechanical
properties comparable with steel and aluminum.
[0003] Generally, fiber reinforced composites comprise a resin
matrix that is reinforced with a fibers, such as carbon fibers. The
fiber reinforced composites are typically prepared in a process in
which a fabric or tow comprising fibers is impregnated with the
resin to form a so called prepreg. The term prepreg is commonly
used to describe a reinforced composite comprising fibers that are
impregnated with a resin, and that is in an uncured or partially
cured state. The prepreg can then be molded into a final or
semifinal molded part by subjecting the prepreg to conditions
sufficient to cure the resin. Typically, curing takes place by
heating the prepreg in a mold at a sufficient temperature and for a
sufficient amount of time to cure the resin. Epoxy resins are
commonly used in the productions of fiber reinforced
composites.
[0004] Adhesion of the carbon fibers to the resin matrix is of
critical importance in maintaining the mechanical strength of the
part, and to prevent delamination of the fiber-carbon interface. To
improve adhesion, the carbon fibers are typically treated with a
surface treatment prior to impregnation with the resin. A common
surface treatment method involves pulling the carbon fiber through
an electrochemical or electrolytic bath that contains solutions,
such as ammonium bicarbonate, and applying potential, which results
anodic oxidation of the carbon fiber surface. Such treatments
etches or roughens the surface of each filament, which increases
the surface area available for interfacial fiber/matrix bonding.
The increase in fiber surface area helps to mechanically interlock
the resin matrix to the fiber. In addition, the surface treatment
may also oxidize the surface of the fibers, which results in the
formation of reactive chemical groups, such as carboxylic acids, on
the surface of the fibers.
[0005] There are however some disadvantages which may be associated
with the surface treatment. For example, in some circumstances the
surface treatment may result in undesirable deterioration of the
fibers, which results in a practical limitation on how much surface
treatment to which the carbon fiber may be subjected. As a result,
the surface treatment may not adequately provide the desired level
of reactive chemical groups on the surface of the fibers.
[0006] Accordingly, there still exists a need for improved carbon
fibers and methods of preparing same.
SUMMARY
[0007] Embodiments of the invention are directed to amine
functionalized carbon fibers, and to processes for preparing amine
functionalized carbon fibers. Additional aspects of the invention
are directed to reinforced composites comprising a resin matrix and
the amine functionalized fibers, and to processes of making such
reinforced composites.
[0008] In one embodiment, aspects of the present invention are
directed to a composite carbon fiber comprising a carbon fiber
having an amine-functionalized polymer electro-grafted onto a
surface thereof. The inventor has discovered that by
electro-grafting amine functionalized polymers onto a carbon fiber
surface, a fiber reinforced composite having improved interlaminar
properties can be prepared.
[0009] Embodiments of the present invention may provide composite
carbon fibers comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof. In one embodiment, the composite carbon fiber has a
nitrogen/carbon (N/C) ratio that is at least 0.125, and in
particular, a N/C ratio that is from about 0.15 to 0.3, and even
more particularly, a N/C ratio that is from about 0.15 to 0.2. In
one embodiment, the composite carbon fiber has a N/C ratio that is
at least 0.150, such as a N/C ratio that is from about 0.15 to
0.3.
[0010] In one embodiment, the composite carbon fiber exhibits an
increase in nitrogen surface concentration that is at least 50%, at
least 75%, at least 100%, at least 125%, at least 150%, at least
175%, at least 200%, or at least 250% in comparison to the original
carbon fiber that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber. In one
particular embodiment, the composite carbon fiber exhibits an
increase in nitrogen surface concentration that is at least 495%,
in comparison to the original carbon fiber that does not include an
amine-functionalized polymer electro-grafted onto the surface of
the carbon fiber.
[0011] In some embodiments, the composite carbon fiber exhibits an
increase in nitrogen surface concentration that is from about 50 to
500% in comparison to the original carbon fiber that does not
include an amine-functionalized polymer electro-grafted onto the
surface of the carbon fiber. For example, in one embodiment, the
composite carbon fiber may exhibit an increase in nitrogen surface
concentration that is from about 100 to 500% in comparison to the
original carbon fiber that does not include an amine-functionalized
polymer electro-grafted onto the surface of the carbon fiber. In
other embodiments, the composite carbon fiber the composite carbon
fiber exhibits an increase in nitrogen surface concentration that
is from about 150 to 500% in comparison to the original carbon
fiber that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber. In still yet
another embodiment, the composite carbon fiber may exhibit an
increase in nitrogen surface concentration that is from about 100
to 250%, such as from about 125 to 200%, in comparison to the
original carbon fiber that does not include an amine-functionalized
polymer electro-grafted onto the surface of the carbon fiber.
[0012] In one embodiment, the amine-functionalized polymer is
selected from the group consisting of linear polyethyleneimines
(PEI), branched polyethyleneimines (PEI), branched
polypropyleneimine, linear poly(allylamine) (PAA), polyamidoamine
(PAMAM) dendrimer, branched poly(allylamine) prepared by branching
of poly(allylamine) with divinylbenzene (PAADVB), and
block-copolymers, core-shell particles, and combinations thereof.
In a preferred embodiment, the amine-functionalized polymer
comprises a branched polyethyleneimine.
[0013] Preferably, the amine-functionalized polymer has a weight
average molecular weight ranging from about 5,000 to 35,000.
[0014] A wide variety of different carbon fibers may be used in
accordance with the present invention. In one embodiment, the
carbon fiber may have a tensile strength of at least 400 ksi. For
example, the carbon fiber for preparing the composite carbon fiber
may have a tensile strength from about 600 to 1,050 ksi.
[0015] The composite carbon fiber in accordance with the present
invention may be used to prepare a variety of different articles.
For example, the composite carbon fiber may be used to prepare a
fiber reinforced composite, such as prepreg, or a structural
element formed from a prepreg.
[0016] In one embodiment, the present invention may provide a fiber
reinforced composite comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof, and a resin matrix infused into the carbon fiber. In one
such embodiment, the fiber reinforced composite may exhibit an
interlaminar strength of about 17 to 25 ksi as characterized by
Short Beam Shear (SBS) testing. In some embodiments, the
interlaminar strength of the fiber reinforced composite is about 20
to 22 ksi as characterized by SBS.
[0017] In one embodiment, the present invention may provide a fiber
reinforced composite exhibiting an increase in SBS ranging from
about 5 to 25% in comparison to a similar fiber reinforced
composite in which the carbon fibers are identical with the
exception that the surfaces of the carbon fibers do not include an
amine-functionalized polymer.
[0018] In one embodiment, the fiber reinforced composite may
include a resin selected from the group consisting of epoxy based
resins, bismaleimide based resins, cyanate ester based resins, and
phenolic based resins.
[0019] In one embodiment, the composite carbon fiber for preparing
fiber reinforced composites may exhibit an increase in surface of
nitrogen concentration of any one or more of least 25%, at least
50%, at least 75%, at least 100%, at least 125%, at least 150%, at
least 175%, at least 200%, at least 225%, at least 250%, at least
275%, at least 300%, at least 325%, at least 350%, at least 375%,
at least 400%, at least 425%, at least 450%, at least 475%, or at
least 500%, in comparison to the original carbon fiber that has not
had an amine-functionalized polymer electro-grafted onto its
surface. In some embodiments, the composite carbon fiber exhibits
for use in the fiber reinforced composite may exhibit an increase
in surface of nitrogen concentration ranging from about 50 to
3,000%, such as from about 100 to 500%, from about 150 to 500%,
from about 100 to 250%, or from about 125 to 200%, in comparison to
the original carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface.
[0020] In one embodiment, fiber reinforced composites in accordance
with embodiments of the present invention may be used in the
manufacture of an aerospace part.
[0021] Other aspects of the invention are directed to a composite
carbon fiber comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof, and wherein the composite carbon fiber is characterized
by:
[0022] a) a nitrogen/carbon (N/C) ratio that is at least 0.125;
and/or
[0023] b) an increase in nitrogen surface concentration that is
from about 50 to 500% in comparison to the original carbon fiber
that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber. In such
embodiments, the composite carbon fiber may exhibit a
nitrogen/carbon (N/C) ratio that is from about 0.15 to 0.3, such as
from about 0.15 to 0.2, and from about 0.165 to 0.195, and an
increase in surface of nitrogen concentration of any one or more of
at least 75%, at least 100%, at least 125%, at least 150%, at least
175%, at least 200%, at least 225%, at least 250%, at least 275%,
at least 300%, at least 325%, at least 350%, at least 375%, at
least 400%, at least 425%, at least 450%, at least 475%, or at
least 500%, in comparison to the original carbon fiber that has not
had an amine-functionalized polymer electro-grafted onto its
surface.
[0024] In one embodiment, the composite carbon fiber in accordance
with the preceding paragraph may exhibit an increase in surface of
nitrogen concentration ranging from about 50 to 3,000%, such as
from about 100 to 500%, from about 150 to 500%, from about 100 to
250%, or from about 125 to 200%, in comparison to the original
carbon fiber that has not had an amine-functionalized polymer
electro-grafted onto its surface.
[0025] In another aspect, embodiments of the invention are directed
to a method of preparing a composite carbon fiber comprising:
[0026] passing a carbon fiber through a bath comprising an
amine-functionalized polymer;
[0027] applying an electro-potential to the cell;
[0028] electro-grafting the amine-functionalized polymer onto the
carbon fiber to produce a composite carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof, and wherein the composite carbon fiber is characterized
by:
[0029] a) a carbon/nitrogen (N/C) ratio that is at least 0.125;
and/or
[0030] b) an increase in nitrogen surface concentration that is
from about 50 to 500% in comparison to the original carbon fiber
that does not include an amine-functionalized polymer
electro-grafted onto the surface of the carbon fiber.
[0031] In one aspect of the method, the composite carbon fiber
exhibits a nitrogen/carbon (N/C) ratio that is from about 0.15 to
0.3, such as from about 0.15 to 0.2, and from about 0.165 to
0.195.
[0032] In another aspect of the method, the composite carbon fiber
exhibits an increase in surface of nitrogen concentration of any
one or more of at least 75%, at least 100%, at least 125%, at least
150%, at least 175%, at least 200%, at least 225%, at least 250%,
at least 275%, at least 300%, at least 325%, at least 350%, at
least 375%, at least 400%, at least 425%, at least 450%, at least
475%, or at least 500%, in comparison to the original carbon fiber
that has not had an amine-functionalized polymer electro-grafted
onto its surface.
[0033] In one embodiment of the method of making the composite
carbon fibers, the composite carbon fiber may exhibit an increase
in surface of nitrogen concentration ranging from about 50 to
3,000%, such as from about 100 to 500%, from about 150 to 500%,
from about 100 to 250%, or from about 125 to 200%, in comparison to
the original carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface.
[0034] In one embodiment of the method of making a composite carbon
fiber, the amine-functionalized polymer is selected from the group
consisting of linear polyethyleneimines (PEI), branched
polyethyleneimines (PEI), branched polypropyleneimine, linear
poly(allylamine) (PAA), polyamidoamine (PAMAM) dendrimer, branched
poly(allylamine) prepared by branching of poly(allylamine) with
divinylbenzene (PAADVB), and a combination thereof. In a preferred
embodiment, the amine-functionalized polymer comprises a branched
polyethyleneimine.
[0035] In one embodiment, the amine-functionalized polymer has a
weight average molecular weight ranging from about 5,000 to
35,000.
[0036] Advantageously, the steps of electrografting the
amine-functionalize polymer to the surface of the carbon fiber may
be completed in a relatively short period of time. For example, in
one embodiment, the step of electro-grafting the
amine-functionalized polymer onto the carbon fiber may take a
period of time that lasts between 30 seconds and two minutes, and
in particular, for a period of time that lasts between 45 seconds
and 90 seconds, and in particular, about 60 seconds.
[0037] Embodiments of the invention may be directed to composite
carbon fibers, and molded parts prepared therefrom. The invention
also covers methods of preparing the composite carbon fibers, and
methods of preparing a fiber reinforced composite that incorporates
the composite carbon fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Reference will now be made to the accompanying drawing,
which is not necessarily drawn to scale, and wherein:
[0039] FIG. 1 is a schematic illustration of a system for
electro-grafting an amine-functionalized polymer onto a carbon
fiber.
DETAILED DESCRIPTION
[0040] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
some, but not all embodiments of the invention are shown. Indeed,
the invention may be embodied in many different forms and should
not be construed as limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
satisfy applicable legal requirements.
[0041] The terms "first," "second," and the like, "primary,"
"exemplary," "secondary," and the like, do not denote any order,
quantity, or importance, but rather are used to distinguish one
element from another. Further, the terms "a," "an," and "the" do
not denote a limitation of quantity, but rather denote the presence
of "at least one" of the referenced item.
[0042] Each embodiment disclosed herein is contemplated as being
applicable to each of the other disclosed embodiments. All
combinations and sub-combinations of the various elements described
herein are within the scope of the invention.
[0043] It is understood that where a parameter range is provided,
all integers within that range, and tenths and hundredths thereof,
are also provided by the invention. For example, "5-10%" includes
5%, 6%, 7%, 8%, 9%, and 10%; 5.0%, 5.1%, 5.2% . . . 9.8%, 9.9%, and
10.0%; and 5.00%, 5.01%, 5.02% . . . 9.98%, 9.99%, and 10.00%.
[0044] As used herein, "about" in the context of a numerical value
or range means .+-.10% of the numerical value or range recited or
claimed.
[0045] In one aspect, embodiments of the present invention provide
a composite carbon fiber comprising a carbon fiber having an
amine-functionalized polymer electro-grafted onto a surface
thereof. As explained in greater detail below, electro-grafting the
amine-functionalized polymer onto the surface of the carbon fiber
results in a composite carbon fiber in which the polymer is
covalently bonded to the fiber, and in which a significant number
of reactive amine groups are available for subsequent reactions,
such as for reacting with a resin matrix in the production of a
fiber reinforced composite. As a result, the composite carbon
fibers may be particularly useful in producing fibers reinforced
composites that exhibit improved interlaminar strength.
[0046] Composite carbon fibers in accordance with the present
invention may be used in a wide variety of applications where a
fiber reinforced composite having high interlaminar strength as
characterized by Short Beam Shear (SBS) testing is desired.
Although the composite carbon fibers may be used alone, the
composite carbon fibers are generally combined with a resin to form
a fiber reinforced composite material. The fiber reinforced
composite materials may be in the form of a prepreg or cured final
part. Although the fiber reinforced composite materials may be used
for any intended purpose, they are preferably used in aerospace
applications for both structural and non-structural parts.
[0047] For example, the composite carbon fibers may be used to form
fiber reinforced composite materials that are used in structural
parts of the aircraft, such as fuselages, wings and tail
assemblies. The composite carbon fibers may also be used to make
composite material parts that are used in non-structural areas of
the airplane. Exemplary non-structural exterior parts include
engine nacelles and aircraft skins. Exemplary interior parts
include the aircraft galley and lavatory structures, as well as
window frames, floor panels, overhead storage bins, wall
partitions, wardrobes, ducts, ceiling panels and interior
sidewalls.
[0048] As noted previously, the composite carbon fibers provide a
large number of reactive amine groups that are available for
subsequent reactions. The presence of the available reactive amine
groups on the composite carbon fiber may be characterized by the
carbon/nitrogen (N/C) ratio of the composite carbon fibers. For
example, composite carbon fibers in accordance with the present
invention typically exhibit a nitrogen/carbon (N/C) ratio that is
at least 0.125, and more typically, a N/C ratio that is at least
0.150. In one embodiment, the composite carbon fiber has a N/C
ratio that is from about 0.15 to 0.3, such as from about 0.15 to
0.2, and from about 0.165 to 0.195. In some embodiments, the
composite carbon may have a N/C ratio that is at least 0.120, such
as from 0.120 to 0.200. The N/C ratio of the composite carbon
fibers may be determined using analytic methods that are known in
the art, such as X-ray photoelectron spectroscopy (XPS).
[0049] Composite carbon fibers in accordance with embodiments of
the present invention may also exhibit increases in surface
nitrogen concentration in comparison to an identical carbon fiber
(e.g., in comparison to the original carbon fiber prior to
electro-grafting of the amine-functionalized polymer) that does not
include an amine-functionalized polymer electro-grafted to its
surface. For example, composite carbon fibers in accordance with
embodiments of the invention may exhibit an increase in nitrogen
surface concentration of at least 25% in comparison to an identical
carbon fiber that has not had an amine-functionalized polymer
electro-grafted onto its surface.
[0050] More particularly, the composite carbon fibers may exhibit
increases in nitrogen surface concentration of at least 25%, at
least 50%, at least 75%, at least 100%, at least 125%, at least
150%, at least 175%, at least 200%, at least 225%, at least 250%,
at least 275%, at least 300%, at least 325%, at least 350%, at
least 375%, at least 400%, at least 425%, at least 450%, at least
475%, and at least 500%, in comparison to an identical carbon fiber
that has not had an amine-functionalized polymer electro-grafted
onto its surface.
[0051] In one embodiment, the composite carbon fiber may exhibit an
increase in nitrogen surface concentration ranging from about 50 to
5,000% in comparison to an identical carbon fiber that has not had
an amine-functionalized polymer electro-grafted onto its surface.
Preferably, the composite carbon fiber exhibits an increase in
nitrogen surface concentration ranging from about 50 to 500%, and
more preferably, from about 100 to 500%, and even more preferably,
from about 150 to 500%, in comparison to an identical carbon fiber
that has not had an amine-functionalized polymer electro-grafted
onto its surface. In other embodiments, the composite carbon fiber
may exhibit an increase in nitrogen surface concentration ranging
from about 100 to 250%, and more typically, from about 125 to 200%,
and even more typically, from about 150 to 200%, in comparison to
an identical carbon fiber that has not had an amine-functionalized
polymer electro-grafted onto its surface. The surface nitrogen
concentration of the composite carbon fibers may also be determined
using analytic methods that are known in the art, such as X-ray
photoelectron spectroscopy (XPS).
[0052] In addition, fiber reinforced composites prepared from the
composite carbon fibers may exhibit improved interlaminar strength.
In one embodiment, fiber reinforced composites in accordance with
embodiments of the present invention may exhibit increases in SBS
ranging from about 5 to 25% in comparison to a similar fiber
reinforced composite in which the carbon fibers are identical with
the exception that the surfaces of the carbon fibers have not been
modified to include an amine-functionalized polymer (hereinafter
referred to as a "non-grafted carbon fiber"). Preferably, the fiber
reinforced composites exhibit increases in SBS ranging from about 7
to 25%, and more preferably, from about 10 to 25% in comparison to
a composite comprising a non-grafted carbon fiber. In one
embodiment, the fiber reinforced composites may exhibit increases
in SBS ranging from about 15 to 25% in comparison to a composite
comprising a non-grafted carbon fiber.
[0053] In one embodiment, the fiber reinforced composites prepared
from the composite carbon fibers exhibit an interlaminar strength
that is from about 17 to 25 ksi as characterized by SBS, and in
particular, from about 18 to 24 ksi, and more particularly, from
about 20 to 22 ksi.
[0054] Composite carbon fibers in accordance with aspects of the
invention may be prepared by immersing the carbon fiber through a
bath solution comprising the amine-functionalized polymer. The bath
may be aqueous or non-aqueous, and may include one or more
electrolytes.
[0055] Examples of suitable non-aqueous solvents may include
methanol, ethanol, dimethylformamide, dimethylsulfoxide, sulfolane,
tetrahydrofuran, and acetonitrile, among others.
[0056] Examples of suitable electrolytes may include
tetraethylammonium tetrafluoroborate, tetrabutylammonium
tetrafluoroborate, tetraethylammonium hexafluorophosphate,
tetrabutylammonium hexafluorophosphate, tetrabutylphosphonium
hexafluorophosphate, tetraethylammonium perchlorate,
tetrabutylammonium perchlorate, tetraethylammonium
trifluoromethanesulfonate, tetrabutylammonium
trifluoromethanesulfonate, lithium perchlorate, lithium
hexafluorophosphate, lithium tetrafluoroborate, lithium triflate,
lithium bis(trifluoromethanesulfonyl)-imide, and lithium
bis(trifluoroethanesulfonyl)imide, among others.
[0057] The concentration of the electrolyte in the bath may range
from about 0.01 to 1 M, based on the total volume of the
electrolyte solution in the bath. In one embodiment, the amount of
the electrolyte in the bath is from about 0.01 to 0.5 M, and in
particular, from about 0.015 to 0.1 M, and more particularly, from
about 0.02 to 0.05 M.
[0058] The concentration of the amine-functionalized polymer in the
bath may range from about 0.5 to 5 weight percent, based on the
total weight of the bath. In one embodiment, the amount of the
amine-functionalized polymer in the bath is from about 0.5 to 2.5
weight percent, and in particular, from about 0.75 to 2 weight
percent, and more particularly, from about 1.0 to 2.0 weight
percent.
[0059] As shown in FIG. 1, a system for electro-grafting an
amine-functionalized polymer onto a carbon fiber is represented by
reference character 10. The system 10 includes an electrolytic bath
12, a power source 14, a cathode 16, and a carbon fiber 18. The
power source 14 is connected to the cathode(s) 16 via a lead 20,
and to the carbon fiber 18 via a lead 22. The system may also
include one or more TEFLON.RTM. coated pulleys over which the
carbon fiber is directed. The system may also include a pump (not
shown) to recirculate the bath solution. After the carbon fiber is
drawn through the bath, it is directed to wash station (washer) 30
where the fiber is rinsed with deionized water. The composite fiber
may then be passed through a dryer 32, and then wound on an uptake
spooler 34 for later use. In some embodiments, the bath may also
include a reference electrode 24 that is connected to a voltmeter
(e.g., digital multimeter) 28, which in turn may be connected to a
cathode 16 via lead 26.
[0060] The carbon fiber may be exposed to the bath for a period of
time from about 30 seconds to 5 minutes. Advantageously, it has
been discovered that the amine-functionalized polymer may be
electro-grafted onto the carbon fiber in an exposure time ranging
from about 1 to 2 minutes, and in particular, about 1 minute.
[0061] The applied voltage typically ranges from about 0.1 to 10
volts with a voltage from about 0.5 to 5 volts being preferred.
[0062] A wide variety of amine-functionalized polymers may be used
in embodiments of the invention. Preferably, the
amine-functionalized polymers include a plurality of amine groups
distributed along the backbone or branches of the polymer that are
available for being electro-grafting to the carbon fiber surface or
are available for subsequent reactions with a resin matrix. For
example, in a preferred embodiment the amine-functionalized polymer
includes a plurality of pendant, terminal primary, secondary,
tertiary, amino-groups, or mixtures thereof that are incorporated
into polymer structure.
[0063] In one embodiment, the amine-functionalized polymer
comprises a polymer of formulas (I) and (II):
##STR00001##
[0064] In formulas (I) and (II), the R group may independently
represent a hydrogen, a linear, branched, cyclic or alkyl group
(saturated or unsaturated), aliphatic group, aromatic group, or
mixture thereof. In some embodiments, R in addition to the
abovementioned groups may also include ethoxylated segments,
heterocyclic compounds, and heteroatoms.
[0065] In some embodiments, R may also comprise an amine protecting
groups, such as a carbobenzyloxy, methoxybenzyl carbonyl,
tert-Butyloxycarbonyl, 9-fluorenylmethyloxycarbonyl, acetyl,
benzoyl, benzyl, carbamate, methoxybenzyl, 3,4-dimethoxybenzyl,
p-methoxyphenyl, tosyl, and sulfonamides.
[0066] In a preferred embodiment, the amine-functionalized polymer
comprise a carbon (e.g., organic) based polymer back-bone, such a
back-bone comprising hydrocarbon-based moieties which may be
aromatic or aliphatic (saturated or unsaturated). Such a backbone
may be connected via C--C, C--O, C--N, C--S, and N--N bonds. In
some embodiments, the back-bone may include hydrocarbon moieties in
which heteroatoms, such as O, N, S are incorporated. The
aforementioned moieties can be also of heterocyclic nature. In
other embodiments, the back-bone of the amine-functionalized
polymer may be derived from siloxane based polymers. The back-bone
may be crosslinked or substantially free of crosslinks.
[0067] In general, it may be desirable for the amine-functionalized
polymer to have a weight average molecular weight (Mw) that is
greater than about 2,000, and in particular, greater than about
2,500. While there is no general practical limit on the Mw of the
amine-functionalized polymer, the polymer may have a Mw ranging
from about 5,000 to 1,000,000, with a Mw ranging from about 15,000
to 750,000 being somewhat more typical, and a Mw ranging from about
15,000 to 100,000 being even more typical. As is known in the art,
the Mw of a polymer may be determined with static light scattering
techniques.
[0068] In one embodiment, the amine-functionalized polymer is
selected from the group consisting of linear polyethyleneimines
(PEI), branched polyethyleneimines (PEI), branched
polypropyleneimine, and linear poly(allylamine) (PAA), branched
poly(allylamine) prepared by branching of poly(allylamine) with
divinylbenzene (PAADVB), and mixtures thereof. In a preferred
embodiment, the amine-functionalized polymer is a branched
polyethyleneimine.
[0069] In one embodiment, the amino-functionalized polymer may
comprise a copolymer. For example, the amine-functionalized polymer
may comprise a polymer structure that is derived from a mix of
monomers that contain an amine function and monomers which do not.
Examples of such a copolymers include block copolymers and
core-shell particles derived from such copolymers. Both block
copolymers (see, for example, U.S. Pat. No. 6,894,113) and
core-shell particles (see, for example, EP 1632533A1, U.S. Patent
Publication No 2008/0251203 A1, EP 2123711A, EP 2135909A1, and EP
2256163A1) are extensively described in literature as toughening
additives to epoxy-based resins. One of the most interesting and
relevant example of such copolymers and core-shell particles that
are described in literature by Berg et al. (Nguyen, F.; Saks, A.;
Berg, J. C. J. Adhesion Sci. Technol. 2007, 21, pp. 1375-1393;
Leonard, G. C.; Hosseinpour, D.; Berg, J. C. J. Adhesion Sci.
Technol. 2009, 23, pp. 2031-2046.), where the outer-shell is
comprised of polyethyleneimine polymerized onto a core particle
made of polystyrene.
[0070] In one embodiment the amine-functionalized polymer can be
based on polysiloxane polymeric back-bone. One of the examples of
such polymers can be found in WO2004/035675A1 where authors
described preparation of sol gel particles bearing amine
functionality on a surface and a cross-linked polysiloxanes
structure as a core.
[0071] In one embodiment, the amine-functionalized polymer may
comprise a polyamidoamine (PAMAM) dendrimer. PAMAM dendrimers are
hyperbranched polymers typically comprising an ethylenediamine
core, a repetitive branching amidoamine internal structure and a
primary amine surface. The dendrimers are grown off a central core
in an iterative process in which each step produces a new
generation of dendrimer having approximately twice the number of
reactive surface sites, and approximatedly double the molecular
weight of the preceding generation. An example of Generation 0 and
Genaration 1 for a PAMAM dendrimer is shown below.
##STR00002##
[0072] In yet another embodiment, the amine-functionalized polymer
may comprise highly branched poly-amido-amines described by Buchman
et al. (Dodiuk-Kenig, H.; Buchman, A.; Kenig, S. Composite
Interfaces 2004, 11, pp. 453-469 and references therein). There the
synthesis of highly branched amine-functional polymer is based on
amine-epoxy reactions.
[0073] In some embodiments, the amine-functionalized polymer may
include block-copolymers and core-shell particles. For example, in
one embodiment, the amine-functionalized polymer may comprise
block-copolymers and core-shell particles of linear
polyethyleneimines (PEI), branched polyethyleneimines (PEI),
branched polypropyleneimine, and linear poly(allylamine) (PAA),
branched poly(allylamine) prepared by branching of poly(allylamine)
with divinylbenzene (PAADVB), and combinations thereof.
[0074] A wide variety of different carbon fibers may be used in
accordance with embodiments of the present invention. In one
embodiment, the carbon fiber may be considered aerospace grade
carbon and have a tensile strength of at least 400 ksi (2,758 MPa).
For example, the carbon fiber may have a tensile strength of at
least one of 450 ksi, 500 ksi, 550 ksi, 600, ksi, 650 ksi, 700 ksi,
750 ksi, 800 ksi, 850 ksi, 900 ksi, 950 ksi, and 1,000 ksi. In one
embodiment, the carbon fiber may have a tensile strength from about
400 to 1,200 ksi, and in particular from about 600 to 1,050 ksi,
and more particularly, from about 700 to 950 ksi.
[0075] Preferably, the carbon fibers are arranged in tows. The
"tows" (sometimes referred to as "rovings" or simply `fibers") are
multifilament fibers. The number of filaments per tow may be, for
example, 100 to 30,000. The tows should be thermally and chemically
stable under conditions of prepreg formation (e.g., curing of the
matrix resin composition).
[0076] Typically the fibers will have a circular or almost circular
cross-section with a diameter in the range of from 0.5 to 30
microns, preferably from 2 to 20 microns, and more preferably, from
2 to 15 microns. In terms of weight, the individual tows may have a
weight of, for example, 200 to 3,000 g/1000 meters, 600 to 2,000
g/1000 meters, or 750 to 1750 g/1000 meters. In a preferred
embodiment, the individual tow may have a weight that is from 200
to 500 g/1,000 meters.
[0077] In some embodiments, the carbon fibers may be surface
treated prior to electro-grafting the amine-functionalized polymer
onto the fibers. In other embodiments, the carbon fibers may be
untreated prior to electro-grafting. Preferably, the carbon fibers
are not subjected to any treatment prior to electro-grafting that
would reduce the tensile strength of the fibers. For example, in
various embodiments the carbon fibers are not subjected to a high
temperature treatment in a steam atmosphere, such as at a
temperature above 800.degree. C., or a plasma treatment.
[0078] In some embodiments, it may be desirable that the fiber is
not sized or at least de-sized prior to attachment of the
amine-functionalized polymer to the carbon fiber. In one
embodiment, composite carbon fiber may be used as either sized or
unsized by formulations known to the ones skilled in art, depending
on application.
[0079] Examples of suitable carbon fibers include HEXTOW.RTM. AS-4,
AS-7, IM-7, IM-8, IM-9, and IM-10, and HM-63 carbon fibers, all of
which are PAN based continuous fibers available from Hexcel
Corporation (Dublin, Calif.). IM-7 through IM-10 are continuous,
high performance, intermediate modulus, PAN based carbon fibers
available in 12,000 (12K) filament count tows having minimal
tensile strengths of 820 ksi, 880 ksi, 890 ksi, and 1,010 ksi,
respectively.
[0080] Carbon fibers from other carbon manufacturers may also be
used in some embodiments of the invention. For example, in some
embodiments, suitable carbon fibers may include Aksaca 3K A-38, 6K
A-38, 12K A-42, 24K A-42, 12 K A-49 and 24 K A-49 carbon fibers
available from Dow Aksa Ileri Kompozit Malzemeler Saai Ltd, Sti,
Istanbul, Turkey. These product designations indicate the
approximate number of filaments/roving in thousands (3K being 3,000
filaments, for example), and the approximate tensile strength of
the fibers in hundreds of MPa (A-38 indicating a tensile strength
of 3,800 MPa). Other carbon fibers that may be used in accordance
with embodiments of the invention are believed to include T700 and
T800, which are available from Toray Industries.
[0081] Composite carbon fibers in accordance with embodiments of
the invention may be used in a wide variety of reinforcement
structures, For example, the composite fibers may arranged to form
reinforcing structures that are unidirectional, bidirectional or
multidirectional depending on the desired properties required in
the final reinforced composite. The composite carbon fibers may be
in the form of tows or fabrics and may be in the form of random,
knitted, non-woven, multi-axial (e.g., non-crimped fabric), braided
or any other suitable pattern.
[0082] When unidirectional fiber layers are used, the orientation
of the composite fibers may be the same or vary throughout a
prepreg stack to form a so called non-crimp fabric (NCF). However,
this is only one of many possible orientations for stacks of
unidirectional fiber layers. For example, unidirectional fibers in
neighboring layers may be arranged orthogonal to each other in a
so-called 0/90 arrangement, which signifies the angles between
neighboring fiber layers. Other arrangements, such as 0/+45/-45/90
are of course possible, among many other arrangements. In one
embodiment, the carbon fibers may comprise a braided or non-crimp
fabric having a basis weight from 150 to 2,000 g/m.sup.2, and in
particular from 300 to 1600 g/m.sup.2.
[0083] Prepregs in accordance with embodiments of the present
invention may be produced by infusing the carbon fibers or a fabric
comprising the carbon fibers with a resin composition, such as an
epoxy resin.
[0084] A wide variety of different resin compositions may be used
in the practice of the invention. Preferably, the resin composition
comprises a cross-linkable thermoset system. Suitable examples of
the thermoset resins may include epoxy based resins, bismaleimide
based resins, cyanate ester based resins, and phenolic based
resins. Examples of suitable bismaleimide (BMI) resins that may be
used in the invention is available from Hexcel Corporation under
the tradename HEXPLY.RTM..
[0085] In some embodiments, the resin composition may comprise a
thermoplastic resin. Examples of suitable thermoplastic resins may
include polyaryletherketones (PAEK), such as polyetheretherketones
(PEEK) and Polyetherketoneketones (PEKK), polyamides, such as
nylons, polyphenylene sulfides (PPS), polyetherimides (PEI),
polyphenylene oxides (PPO), polyether sulfones (PES),
polybenzimidazole s (PBI), and polycarbonates (PC).
[0086] In one embodiment the resin composition may comprise an
epoxy resin composition. Typically, the resin composition may
include from 55 to 75 weight percent of an epoxy resin component
that includes one or more epoxy resins. The epoxy resins may be
selected from any of the epoxy resins that are used in high
performance aerospace epoxies. Difunctional, trifunctional and
tetrafunctional epoxy resins may be used. In one embodiment, the
epoxy resin may be made up substantially of a trifunctional epoxy
compound. If desired, tetrafunctional epoxies may be included. The
relative amounts of trifunctional and tetrafunctional epoxies may
be varied as is known to one of skill in the art.
[0087] A trifunctional epoxy resin will be understood as having the
three epoxy groups substituted either directly or indirectly in a
para or meta orientation on the phenyl ring in the backbone of the
compound. A tetrafunctional epoxy resin will be understood as
having the four epoxy groups in the backbone of the compound.
Suitable substituent groups, by way of example, include hydrogen,
hydroxyl, alkyl, alkenyl, alkynyl, alkoxyl, aryl, aryloxyl,
aralkyloxyl, aralkyl, halo, nitro, or cyano radicals. Suitable
non-epoxy substituent groups may be bonded to the phenyl ring at
the para or ortho positions, or bonded at a meta position not
occupied by an epoxy group.
[0088] Suitable trifunctional epoxy resins, by way of example,
include those based upon: phenol and cresol epoxy novolacs;
glycidyl ethers of phenol-aldelyde adducts; aromatic epoxy resins;
dialiphatic triglycidyl ethers; aliphatic polyglycidyl ethers;
epoxidised olefins; brominated resins, aromatic glycidyl amines and
glycidyl ethers; heterocyclic glycidyl imidines and amides;
glycidyl ethers; fluorinated epoxy resins or any combination
thereof. A preferred trifunctional epoxy is the triglycidyl ether
of para aminophenol, which is available commercially as Araldite MY
0500 or MY 0510 from Huntsman Advanced Materials (Monthey,
Switzerland). A particularly preferred trifunctional epoxy is a
triglycidyl ether of meta-aminophenol, which is available
commercially from Huntsman Advanced Materials (Monthey,
Switzerland) under the trade name Araldite MY0600, and from
Sumitomo Chemical Co. (Osaka, Japan) under the trade name
ELM-120.
[0089] Suitable tetrafunctional epoxy resins, by way of example,
include those based upon: phenol and cresol epoxy novolacs;
glycidyl ethers of phenol-aldelyde adducts; aromatic epoxy resins;
dialiphatic triglycidyl ethers; aliphatic polyglycidyl ethers;
epoxidised olefins; brominated resins, aromatic glycidyl amines and
glycidyl ethers; heterocyclic glycidyl imidines and amides;
glycidyl ethers; fluorinated epoxy resins or any combination
thereof. A preferred tetrafunctional epoxy is
N,N,N',N'-tetraglycidylmethylenedianiline, which is available
commercially as Araldite MY0720 or MY0721 from Huntsman Advance
Materials (Monthey, Switzerland).
[0090] If desired, the epoxy resin component may also include a
difunctional epoxy. such a Bisphenol-A (Bis-A) or Bisphenol-F
(Bis-F) epoxy resin.
[0091] Examples of suitable epoxy resins may include the diglycidyl
ethers of polyhydric phenol compounds such as resorcinol, catechol,
hydroquinone, bisphenol, bisphenol A, bisphenol AP
(1,1-bis(4-hydroxylphenyl)-1-phenyl ethane), bisphenol F, bisphenol
K, bisphenol M, tetramethylbiphenol, diglycidyl ethers of aliphatic
glycols and polyether glycols such as the diglycidyl ethers of
C.sub.2-24 alkylene glycols and poly(ethylene oxide) or
poly(propylene oxide) glycols; polyglycidyl ethers of
phenol-formaldehyde novolac resins, alkyl substituted
phenol-formaldehyde resins (epoxy novalac resins),
phenol-hydroxybenzaldehyde resins, cresol-hydroxybenzaldehyde
resins, dicyclopentadiene-phenol resins and
dicyclopentadiene-substituted phenol resins, and any combination
thereof.
[0092] Suitable diglycidyl ethers include diglycidyl ethers of
bisphenol A resins such as are sold by The Dow Chemical Company
under the designations D.E.R..RTM. 330, D.E.R..RTM. 331,
D.E.R..RTM. 332, D.E.R..RTM. 383, D.E.R..RTM. 661 and D.E.R..RTM.
662 resins, and as Araldite GY6010 (Huntsman Advanced Materials).
Exemplary Bis-F epoxy resin is available commercially as Araldite
GY281 and GY285 (Huntsman Advanced Materials).
[0093] Commercially available diglycidyl ethers of polyglycols
include those sold as D.E.R..RTM. 732 and D.E.R..RTM. 736 by Dow
Chemical.
[0094] Epoxy novolac resins may also be used. Such resins are
available commercially as D.E.N..RTM. 354, D.E.N..RTM. 431,
D.E.N..RTM. 438 and D.E.N..RTM. 439 from The Dow Chemical
Company
[0095] The epoxy resin component may optionally include from 5 to
20 weight percent of a thermoplastic toughening agent.
Thermoplastic toughening agents are well-known for use in preparing
high performance epoxy resins. Exemplary toughening agents include
polyether sulfone (PES), polyetherimide (PEI), polyamide (PA) and
polyamideimide (PAI). PES is available commercially from a variety
of chemical manufacturers. As an example, PES is available from
Sumitomo Chemical Co. Ltd. (Osaka, Japan) under the tradename
Sumikaexcel 5003p. Polyetherimide is available commercially as
ULTEM 1000P from Sabic (Dubai). Polyamideimide is available
commercially as TORLON 4000TF from Solvay Advanced Polymers
(Alpharetta, Ga.). The thermoplastic component is preferably
supplied as a powder that is mixed in with the epoxy resin
component prior to addition of the curative agent.
[0096] The epoxy resin composition may also include additional
ingredients, such as performance enhancing and/or modifying agents.
The performance enhancing or modifying agents, for example, may be
selected from: flexibilizers, particulate fillers, nanoparticles,
core/shell rubber particles, flame retardants, wetting agents,
pigments/dyes, conducting particles, and viscosity modifiers.
[0097] In some embodiments, the infusion process may be carried out
at an elevated temperature so that the viscosity of the resin
composition is further reduced. However it must not be so hot for
sufficient length of time that an undesirable level of curing of
the resin composition occurs.
[0098] In a preferred embodiment of the invention, the
infusion/impregnation of the resin composition into the carbon
fibers is carried out at temperatures sufficient for the resin to
flow into and between the fibers. For example, the infusion
temperature of the resin composition may be in the range of from
100 to 200.degree. C., with a range of 120 to 180.degree. C., and
in particular, a temperature of about 150.degree. C. being more
preferred. It should be recognized that temperature ranges outside
the above ranges may also be used. However, the use of higher or
lower infusion temperatures typically requires adjusting the
machine speed at which the infusion process is carried out. For
example, at temperatures greater than about 175.degree. C., it may
be necessary to carry out the infusion process at a higher machine
speed in order to reduce the duration of time to which the resin
composition is exposed to an elevated temperature to avoid
undesirable crosslinking of the resin composition.
[0099] Similarly, to obtain a desired level of infusion and thereby
decrease void spaces in the prepreg, the use of lower infusion
temperatures will typically require a lower machine speed for
infusing the epoxy resin composition into the fibrous material.
[0100] Typically the resin composition will be applied to the
carbon fibers at a temperature in this range and consolidated into
the fibers by pressure, such as that exerted by passage through one
or more pairs of nip rollers.
[0101] A further aspect of the invention is directed to a process
of preparing prepregs in accordance with embodiments of the
invention. In a first step, the epoxy resin composition is extruded
onto a sheet material to form a thin film coating thereon. The
sheet material comprises a release film or paper from which the
film coating of the epoxy resin composition may be transferred to
the fibrous material during the prepregging process. After the film
of the epoxy resin composition has been deposited on the sheet
material, the sheet material with the film coating may be passed
over a chill roll to cool the epoxy resin composition. The sheet
material is then typically wound on a roll for future use.
EXAMPLES
[0102] Test Methods
[0103] X-Ray Photoelectron Spectroscopy (XPS).
[0104] XPS analysis of carbon fiber samples was performed on
instrument PHI 5701LSci with X-ray source of monochromated Al
k.alpha. 1486.6 eV, with acceptance angle .+-.7.degree. and
take-off angle of 50.degree.. Analysis area was 2 mm.times.0.8 mm.
Resulting values were normalized to 100% using the elements
detected. Trace elements were not reported.
[0105] Test samples were prepared by cutting a 20 cm sample from a
spool followed by sonication for 30 minutes in solvent. The solvent
was changed to fresh after 15 minutes. The fiber samples were dried
at 80.degree. C. at reduced pressure overnight.
[0106] Tensile Strength
[0107] Tensile strengths of the carbon fiber samples were measured
in accordance with the procedures set forth in ASTM D-4018.
[0108] Short Beam Shear (SBS)
[0109] Various laminate panels were prepared to evaluate the
interlaminar strength of fiber reinforced composites using SBS
accordance with ASTM D 2344. Sample widths were 0.25.+-.0.005
inches. 4:1 span to depth ratio was used. Nine replicates were
tested per each sample.
[0110] Laminate panel samples were prepared using either BMI or
epoxy resins. The BMI infused laminates had a basis weight of 190
g/m.sup.2, and were prepared by laying down 12 plies of the carbon
fibers. The epoxy infused laminates had a basis weight of 145
g/m.sup.2, and were prepared by laying down 16 plies of the carbon
fibers. The carbon fibers were laid down by hand or with a tension
stand. All plies had 0.degree. orientation and were laid onto BMI
or epoxy tapes. The panels were then cut and pressed to form a
prepreg. Carbon fiber lengths were approximately 30 meters. The
laminates panels were cured according to the following:
[0111] Epoxy infused laminate panels were cured in an autoclave
using two cycles:
[0112] 1) cure cycle: the laminate panels were heated to
240.degree. F., which was held for a duration of 65 minutes at a
pressure of 85 PSI. The panels were then heated to 350.degree. F.,
and held for a duration of 120 minutes at a pressure of 100 PSI.
The panels were then cooled to 140.degree. F. at a rate of
3.degree. F. per minute.
[0113] 2) post cure cycle: The panels were then heated to
350.degree. F., which was held for a duration of 4 hours. The
panels were then cooled down to 140.degree. F.
[0114] BMI infuse laminates were similarly cured in an autoclave
using two cycles:
[0115] 1) cure cycle: the laminate panels were heated to
250.degree. F., which was held for a duration of 30 minutes at a
pressure of 85 PSI. The panels were then heated to 375.degree. F.,
and held at this temperature for a duration of 250 minutes at
pressure of 85 PSI. The panels were cooled to 140.degree. F. at a
rate of 3.degree. F. per minute.
[0116] 2) post cure cycle: The panels were then heated to
465.degree. F., which was held for 6 hours and 30 minutes. The
panels were then cooled down to 140.degree. F.
[0117] The materials used in the adhesive compositions are
identified below. All percentages are weight percents unless
indicated otherwise. All physical property and compositional values
are approximate unless indicated otherwise.
[0118] "B-PEI-1" refers to a branched polyethyleneimine (having an
average Mw of approximately 25,000 and an average Mn of
approximately 10,000) available from SIGMA-ALDRICH.RTM..
[0119] "B-PEI-2" refers to a branched polyethyleneimine (having an
average Mw of approximately 800 and an average Mn of approximately
600) available from SIGMA-ALDRICH.RTM..
[0120] "L-PEI" refers to a linear polyethyleneimine (having an
average Mw of approximately 2,500), available from Polysciences,
Inc.
[0121] "PAA" refers to poly(allyl amine) polyethyleneimine (having
an average Mw of approximately 15,000), available from
Polysciences, Inc.
[0122] "TAEA" refers to tris(2-aminoethyl)amine (96%), available
from SIGMA-ALDRICH.RTM..
[0123] "TEABF" refers to tetraethylammonium tetrafluoroborate
(99%), available from SIGMA-ALDRICH.RTM..
[0124] "MEOH" refers to methanol (anhydrous), available from
SIGMA-ALDRICH.RTM..
[0125] Na.sub.2SO.sub.4" refers to sodium sulfate (.gtoreq.99.0%,
A.C.S. reagent grade, anhydrous) available from
SIGMA-ALDRICH.RTM..
[0126] "IM-7" refers to a 100% nominal surface treated PAN based
continuous carbon fiber (12,000 (12K) filament count tows having a
minimal tensile strength of 820 ksi) available from Hexcel
Corporation under the tradename HEXTOW.RTM.. The carbon fiber was
unsized.
[0127] "IM-X" refers to a 5% nominal surface treated PAN based
continuous carbon fiber (12,000 (12K) filament count tows having a
minimum tensile strength of 825 ksi), prepared by Hexcel
Corporation. The carbon fiber was unsized.
[0128] "IM-U" refers to a non-surface treated PAN based continuous
carbon fiber (12,000 (12K) filament count tows that were prepared
by Hexcel Corporation. The carbon fiber was unsized.
[0129] "BMI" refers to a bismaleimide resin available from Hexcel
Corporation under the name HX1624.
[0130] "EPDXY" refers to a proprietary epoxy resin available from
Hexcel Corporation.
[0131] Composite carbon fibers were prepared in accordance with the
following procedures.
[0132] A bath similar to the one depicted in FIG. 1 was used to
electro-graft the amine-functionalized polymers onto the surface of
the carbon fibers. The power supply used in the electro-grafting
process was a DC Power Supply 1030 from BK Precision. Carbon
cathodes were used in the process. The cathodes had a generally
elongated rectangular shape, and were supplied by Americarb (grade
AX-50). Dimensions of the cathodes were: 21 cm.times.2.5
cm.times.1.2 cm. The experiment employed either non-aqueous Ag/Ag+
reference electrodes or aqueous Ag/AgCl reference electrodes. The
non-aqueous Ag/Ag+ reference electrodes (CHI 112) were purchased
from CH instruments, Austin Tex., and were filled with 10 mM silver
nitrate and 20 mM supporting electrolyte solutions in organic
solvent. The aqueous Ag/AgCl reference electrodes (CHI 112) were
purchased from the same source and filled with 1M KCl solution.
[0133] Carbon fiber tow was fed from a controlled tension feed
spooler over a steel roller. The steel roller was connected to the
positive terminus of the power supply. The carbon cathodes were
immersed in the bath and connected to the negative terminus of the
power supply. The carbon fiber tow fed over a TEFLON.RTM. coated
roller disposed in the bottom of the bath, and then was passed over
a second steel roller outside of the bath. The carbon fiber was
then washed with deionized water, dried, and then wound on a
take-up spool.
[0134] The applied voltage was adjusted so that the potential read
by the silver reference electrode placed in a close proximity of
the carbon fiber tow was approximately 1.6 Volts. The distance
between the cathodes was 2.5 cm and fiber travel path length was 61
cm (2 feet). The bath solution was recirculated by a peristaltic
pump and replenished as needed to maintain a constant volume. The
duration of the exposure of the carbon fiber to the bath was varied
from 1 to 4 minutes depending on the experimental trial.
[0135] The volume of the bath was approximately 1 liter. The
washing bath employed deionized water and included a multi-path and
a multi-roller system with total volume of water of about 2 liters.
The washing bath was purged and completely changed over every 30
minutes with fresh deionized water. The dryer was a drying tower
which utilized hot air at 125.degree. C.
[0136] In the following Examples, the difference between simple
adsorption of the amine-functionalized polymer (B-PEI-1) in
comparison to electro-grafting of the same polymer was evaluated.
The electro-grafting was performed as described above. The same
bath chemistry was used in both the adsorption method and
electro-grafting process, with the exception of an electrolyte. The
concentration of the B-PEI-1 in the bath was approximately 1.25
weight percent. A B-PEI-1 concentration of 1.25 weight percent was
found to generally provide the best results for electrografting.
Increases in polymer concentration did not appear to result in
nitrogen concentration increase on the fiber surface. The bath was
non-aqueous and used MEOH. For electrografting, the bath contained
TEABF as a supporting electrolyte. The carbon fiber tows were
exposed to the bath for a duration of one to two minutes. The
carbon fibers were then evaluated using XPS to determine the carbon
(C), nitrogen (N), and oxygen (O) atomic concentration percent. The
control carbon fiber tow was not subjected to the bath treatment.
The results are summarized in Table 1 below.
TABLE-US-00001 TABLE 1 Comparison of N/C ratio of electro-grafted
carbon fibers vs. adsorption Bath exposure Carbon time N/C Sample
No. Process fiber (min.) C (%) N (%) O (%) ratio Control 1 -- IM-7
N/A 83 6.3 10.4 0.075 Comparative-1 Adsorption IM-7 2 78.7 9.5 10.9
0.121 Comparative-2 Adsorption IM-7 1 82.6 6.7 9.1 0.081
Comparative-2A Adsorption IM-7 2 75.1 8.7 13.8 0.115 Comparative-3
Adsorption IM-7 2 82.2 8.2 9.1 0.099 Example 1 Electro-graft IM-7 1
71.6 11.9 12.1 0.166 Example 2 Electro-graft IM-7 4 70.5 13.4 12.5
0.190
[0137] The adsorption method, which is also known as the "Wet
Chemistry" approach utilizes reactions of organic molecules
containing several amine functions with the fiber. Generally, it is
believed that amines react with surface functionalities on the
carbon fibers, such as carboxylic acids (resulting in salts and/or
amides) or others, which results in adsorption of the polymers onto
the carbon fibers. From the results in Table 1, it can be seen that
the adsorption method results in a significantly lower
concentration of amine groups (as evidenced by the nitrogen atomic
concentration) on the surface of the composite carbon fibers.
Further, it was observed that even though, it was possible to
immobilize the B-PEI-1 onto carbon fiber by simple adsorption from
organic solution, this type of deposition was highly uneven in many
cases. The XPS results were irreproducible, as it is shown in Table
1, some samples showed a nitrogen surface concentration increase of
various degrees and some showed relatively none (e.g.,
Comparative-2) in comparison to the control carbon fiber
(Control-1).
[0138] In contrast, the electro-grafted carbon fibers were observed
to be very reproducible, which implies that the electro-grafting of
the B-PEI-1 is much more homogeneous on the carbon fiber surface in
comparison to the adsorption approach. It was also established that
only half of the time period (1 minute vs. 2 minutes) was necessary
to introduce nitrogen surface concentration higher than in the best
case of adsorbed B-PEI-1.
[0139] In the following examples various composite fibers were
prepared in which an amine-functionalized polymer was
electro-grafted onto a carbon fiber as previously described. The
resulting composite carbon fibers were then used to prepare
laminate panels as discussed previously.
Example 3: Electro-Grafting of B-PEI-1 onto IM-7 Carbon Fiber
Tow
[0140] A bath comprising a MEOH solution 20 mM in
tetraethylammonium tetrafluoroborate as a supporting electrolyte
(S.E.), and 1.25 wt. % of B-PEI-1 was prepared. The B-PEI-1 was
electro-grafted onto IM-7 carbon fiber tow according to the
procedure described above. A laminate panel was prepared with the
resulting composite carbon fiber and an epoxy resin. The laminate
panel was then evaluated for interlaminar strength using SBS
testing. The results are summarized in Table 2 below.
TABLE-US-00002 TABLE 2 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-1 Bath Carbon exposure C O N SBS Sample
No. fiber time (min.) (%) (%) (%) (ksi) Control-2 IM-7 -- 83.8 11.9
4.1 18.67 .+-. 0.85 Example 3 IM-7 1 77.8 8.9 12.0 20.11 .+-.
0.43
[0141] As can be seen in Table 2, the XPS analysis indicated a
significant increase in nitrogen surface concentration in
comparison to the control fiber (i.e., Control-2). In particular,
Table 2 shows that the electro-grafted carbon fiber (Example 3)
exhibited an increase of surface nitrogen concentration of 192.7%
in comparison to the control carbon fiber. This nitrogen
concentration remained unchanged upon prolonged sonication (30
minutes) in methanol, indicating that the B-PEI-1 was covalently
bonded to the surface of the carbon fibers. The electro-grafted
carbon fiber also contained trace amounts of fluorine and boron
from the supporting electrolyte, which was easily removed by
sonication.
[0142] In addition, the laminate panel prepared from the composite
carbon fiber also exhibited improved interlaminar strength as
evidenced by the SBS results shown in Table 2. As can be seen,
laminates prepared from the composite carbon fiber in Example 3
showed an increase of more than 7% in interlaminar strength over
the control fiber.
Example 4: Electro-Grafting of Branched PEI onto IM-712K Fiber Tow
and SBS Evaluation of Laminates Prepared with BMI Resin
[0143] In this example, a laminate panel was prepared with the
composite carbon fiber of Example 3 and BMI resin. As in Example 3,
above the panel was evaluated with SBS. The results are summarized
in Table 3 below.
TABLE-US-00003 TABLE 3 Summary of SBS and XPS Data for
Electro-grafting of BMI Bath Carbon exposure C O N SBS Sample No.
fiber time (min.) (%) (%) (%) (ksi) Control-3 IM-7 -- 83.8 11.9 4.1
18.33 .+-. 0.31 Example 4 IM-7 1 77.8 8.9 12.0 16.69 .+-. 0.21
[0144] As in Example 4, laminates prepared with the composite
carbon fiber showed improvements in interlaminar strength in
comparison to the laminates prepared from the control carbon fiber.
Laminates prepared from the composite carbon fiber in Example 3
showed an increase of nearly 10% in interlaminar strength in
comparison to the control fiber.
[0145] Comparative Examples 4 and 5: Electro-grafting of
tris(2-aminoethyl)amine (TAEA) onto IM-712K fiber tow and SBS
evaluation of laminates prepared with EPDXY resin.
[0146] In Comparative Examples 4 and 5, TAEA was grafted onto the
surface of the carbon fiber to produce a composite carbon fiber.
Laminate panels were then prepared with EPDXY resin (Comparative
Example 4) or BMI resin (Comparative Example 5) and evaluated with
SBS. A bath comprising a MEOH solution 20 mM in tetraethylammonium
tetrafluoroborate as a supporting electrolyte (S.E.), and 1.25 wt.
% of TAEA was prepared. The TAEA was electro-grafted onto IM-7
carbon fiber tow according to the procedure described above. The
composite carbon fibers were also evaluated with XPS.
TABLE-US-00004 TABLE 4 Summary of SBS and XPS Data for
Electro-grafting of TAEA Bath Carbon exposure C O N SBS Sample No.
fiber time (min.) (%) (%) (%) (ksi) Control-4 IM-7 -- 83.8 11.9 4.1
18.67 .+-. 0.85 Comparative IM-7 1 82.0 10.5 7.2 18.71 .+-. 0.84
Example 4 Control-5 IM-7 -- 83.8 11.9 4.1 16.69 .+-. 0.21
Comparative IM-7 1 82.0 10.5 7.2 17.13 .+-. 0.27 Example 5
[0147] XPS analysis (Table 4) indicated an increase in surface
nitrogen concentration of 75.6%, when compared to the control
fiber. This concentration remained unchanged upon prolonged
sonication (30 minutes) in methanol, indicating that TAEA was
covalently attached to the surface. The composite carbon fiber also
contained trace amounts of fluorine and boron from the supporting
electrolyte, which was removed by sonication.
[0148] Although, the composite carbon fiber exhibited a modest
increase in nitrogen content due to the electro-grafting of the
TAEA, this increase did not translate into an increase in
interlaminar strength as evident from the SBS results shown in
Table 4. Accordingly, it can be seen the importance of using an
amine-functionalized polymer in order to achieve improvements in
interlaminar strength of the laminates.
Examples 6 and 7: Electro-Grafting of B-PEI-2 onto IM-712K Fiber
Tow and SBS Evaluation of Laminates Prepared with BMI and EPDXY
Resins
[0149] In this example, a composite carbon fiber was prepared with
B-PEI-2. B-PEI-2 has a weight average molecular weight of
approximately 800. The composite carbon fiber was prepared as
described in Example 3 and evaluated with XPS. Laminate panels were
also prepared with EPDXY and BMI resins, and then evaluated with
SBS. The results are summarized in Table 5 below.
TABLE-US-00005 TABLE 5 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-2 Bath Carbon exposure C O N SBS Sample
No. fiber time (min.) (%) (%) (%) (ksi) Control-6 IM-7 -- 83.8 11.9
4.1 18.67 .+-. 0.85 Example 6 IM-7 1 81.5 8.8 9.3 17.33 .+-. 1.53
Control-7 IM-7 -- 83.8 11.9 4.1 16.69 .+-. 0.21 Example 7 IM-7 1
81.5 8.8 9.3 16.92 .+-. 0.80
[0150] XPS analysis from Table 5 showed an increase in surface
nitrogen concentration of 126.8% in comparison to the control
fiber. This nitrogen concentration increase was smaller in
comparison to the electro-grafting of higher molecular weight
polymers (see, for example, Example 3 above). The nitrogen
concentration remained unchanged upon prolonged sonication (30
minutes) in methanol, indicating that the B-PEI-2 was covalently
attached to the surface of the carbon fibers. Grafted fiber also
contained trace amounts of fluorine and boron from the supporting
electrolyte, which were removed by sonication.
[0151] SBS data showed a very slight increase in interlaminar
strength for both EPDXY laminate panels (Example 6) and for BMI
laminate panels (Example 7) in comparison to the control carbon
fiber. From Table 5, it can be seen that the low molecular weight
PEI did not statistically improve the interlaminar strength
properties of the laminate panels.
Example 8: Electro-Grafting of Branched B-PEI-1 onto IMU 12K Fiber
Tow, and SBS Evaluation of Laminates Prepared in BMI Resin
[0152] In the following example, the interlaminar strength property
of laminates comprising electro-grafted IMU carbon fiber (untreated
12,000 filament tow) was evaluated. Composite carbon fiber was
prepared by passing an IMU carbon fiber through a bath comprising
MeOH solution 20 mM in tetraethylammonium tetrafluoroborate
supporting electrolyte (S.E.) containing 1.25 wt. % branched
B-PEI-1. The composite carbon fibers were evaluated with XPS.
Laminate panels were prepared with the composite carbon fiber and
BMI resin. The laminate panels were evaluated with SBS. The results
are summarized in Table 6 below.
TABLE-US-00006 TABLE 6 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-1 Bath Carbon exposure C O N SBS Sample
No. fiber time (min.) (%) (%) (%) (ksi) Control-8 IMU -- 95.8 2.0
2.2 -- Example 8 IMU 1 72.0 9.2 13.1 12.54 .+-. 0.50 Control-9 IMU
-- 91.1 5.0 2.7 10.20 .+-. 0.20
[0153] The XPS analysis in Table 6 indicated a significant increase
in nitrogen concentration, when compared to the carbon fiber of
Control-8. In particular, the electro-grafted carbon fiber of
Example 8 exhibited an increase in surface nitrogen concentration
of 495.5% in comparison to the control carbon fiber. This
concentration remained unchanged upon prolonged sonication (30
minutes) in methanol, indicating that B-PEI-1 was covalently
attached to the surface of the carbon fiber. The electro-grafted
fiber also contained trace amounts of fluorine and boron from the
supporting electrolyte, which could be removed by sonication.
[0154] In addition, it was observed that the electro-grafted fiber
(Example 8) had a rather significant increase in oxygen surface
concentration in comparison to previous examples. It is believed
that this phenomenon may be due to the presence of water in
reagents (especially PEI), which cannot be completely eliminated,
even though anhydrous solvent was used and the reactive nature of
the IMU fiber surface itself. Also a formation of a small amount of
a precipitate of carbon nature was noticed at the end of all IMU
runs in electro-treatment bath. This may be the result of several
unidentified processes that are simultaneously occurring on the
surface of the IMU fiber. Even during blank runs (without PEI or
TAEA) some surface etching and surface oxidation appeared to have
occurred.
[0155] In response, a blank run was prepared in which the bath did
not include any polymer (Control-9). The carbon fiber of Control-9
was found to have a somewhat increased amount of oxygen, most
likely due to the presence of water during electro-grafting. As a
result, it was determined to compare SBS data for Example 8 and
Control-9. SBS data for the fiber of Control-8 was not evaluated.
As can be seen, the untreated IMU carbon fiber also exhibited
improvements in interlaminar strength in comparison to the carbon
fiber of Control-9. In this case, the inventive composite carbon
fiber exhibited an improvement in SBS of more than almost 23% in
comparison to Control-9.
[0156] It should be noted that it is difficult to unequivocally
interpret the results for the above examples in Table 6 because of
the above-described complications. In all cases of IMU-fibers, SBS
strengths observed are much lower than those for laminates based on
grafted and feed IM-7 fibers (both treated electrochemically by
standard methods). This is an interesting observation, because both
IM-7 and IMU grafted fibers appeared to have comparable amounts of
grafted PEI or TAEA (XPS). This result appears to emphasize the
significance of surface topology (roughness) of the fibers.
Comparative Example 6: Electrografting of TAEA onto IMU 12K Fiber
Tow, and Evaluation of Laminates Prepared with BMI Resin
[0157] In this example, TAEA was electro-grafted onto an untreated
IMU carbon fiber. The resulting composite fiber was used to prepare
a laminate with BMI resin. The composite carbon fibers and laminate
panels were evaluated with XPS and SBS, respectively. The results
are summarized in Table 7 below.
TABLE-US-00007 TABLE 7 Summary of SBS and XPS Data for
Electro-grafting of TAEA Bath Carbon exposure C O N SBS Sample No.
fiber time (min.) (%) (%) (%) (ksi) Control-8 IMU -- 95.8 2.0 2.2
-- Comparative IMU 1 88.0 5.3 6.1 11.23 .+-. 0.54 Example 6
Control-9 IMU 1 91.1 5.0 2.7 10.2 .+-. 0.20
[0158] XPS analysis (Table 7) indicated an increase in surface
nitrogen concentration of 177.3%, when compared to the control
fiber. This concentration remained unchanged upon prolonged
sonication (30 minutes) in methanol, indicating that TAEA was
covalently attached to the surface. The electro-grafted fiber also
contained trace amounts of fluorine and boron from the supporting
electrolyte, which were removed by sonication. As in the preceding
example, an increase in oxygen surface concentration was noticed
for the electro-grafted fiber and therefor a blank (without TAEA in
the bath) was prepared. The blank carbon fiber (Control-10) was
found to have a somewhat increased amount of oxygen, most likely
due to the presence of water during electrografting. SBS evaluation
was performed on Comparative Example 6 and Control fiber 9. The
results are summarized in Table 7 above. Although TAEA grafted
fiber exhibited an SBS increase of 10%, improvements for PEI
grafted carbon fibers (Example 8) were much more significant. Both
examples (Example 8 and Comparative Example 5) employed same
controls.
[0159] In the following examples, composited carbon fibers were
prepared in which the carbon fibers comprised IM-X carbon fibers.
As in the preceding examples, the composite carbon fibers were
evaluated with XPS, and laminate panels prepeared therefrom were
evaluated with SBS.
Examples 9 and 10: Electro-Grafting of B-PEI-1 onto IM-X Untreated,
12K Fiber Tow and SBS Evaluation of Laminates Prepared with BMI and
EPDXY Resins
[0160] In this example, a composite carbon fiber was prepared with
B-PEI-1 and IM-X carbon fiber. The composite carbon fiber was
prepared as described in Example 3 and evaluated with XPS.
Specifically, a bath comprising MeOH solution 20 mM in
tetraethylammonium tetrafluoroborate supporting electrolyte (S.E.),
and 1.25 wt. % of B-PEI-1 was prepared. The composite carbon fibers
were prepared as discussed previously. The fibers were then
evaluated with XPS. The results are summarized in Table 8 below. As
can be seen in Table 8, the electro-grafted carbon fiber had an
increase in surface N concentration of 53.2% in comparison to the
control carbon fiber.
[0161] Laminate panels were also prepared with EPDXY (Example 9)
and BMI (Example 10) resins, and then evaluated with SBS. The
results for the XPS and SBS evaluation are summarized in Table 8
below.
TABLE-US-00008 TABLE 8 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-1 on IM-X Bath Carbon exposure C O N SBS
Sample No. fiber time (min.) (%) (%) (%) (ksi) Control-10 IM-X --
81.6 10.5 6.2 17.39 .+-. 0.30 Example 9 IM-X 1 79.2 9.8 9.5 19.68
.+-. 0.26 Control-11 IM-X -- 81.6 10.5 6.2 10.83 .+-. 0.30 Example
10 IM-X 1 79.2 9.8 9.5 15.81 .+-. 0.65
[0162] For the epoxy-based laminate (Example 9), the SBS results
indicated a 12% improvement in interlaminar strength in comparison
to a laminate prepared from the Control carbon fiber. The BMI-based
laminate (Example 10), exhibited an improvement in interlaminar
strength of more than 45.9% in comparison to a laminate prepared
from the Control carbon fiber.
Examples 11 and 12: Aqueous Electro-Grafting of Branched B-PEI-1
onto IM-X Untreated, 12K Fiber Tow, and Evaluation of Laminates
Prepared in EPDXY and BMI Resin
[0163] A bath of an aqueous solution 0.5 M in sodium sulfate
supporting electrolyte (S.E.) and 1.25 wt. % branched B-PEI-1 was
prepared. The B-PEI-1 was electrografted onto the carbon fiber with
the processes and conditions described previously. "Blank run"
fibers (Control-13 and Control 15) were also prepared in which the
bath did not contain a polymer. The resulting carbon fibers were
prepared into laminate panels with EPDXY resin (Example 11) and BMI
resin (Example 12). The composite carbon fibers and laminate panels
were evaluated with XPS and SBS, respectively, as previously
described. The results are summarized in Table 9 below. As can be
seen in Table 9, the electro-grafted carbon fiber had an increase
in N surface concentration of 106.5% in comparison to the control
carbon fiber (Control 12).
TABLE-US-00009 TABLE 9 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-1 on IM-X Bath Carbon exposure C O N SBS
Sample No. fiber time (min.) (%) (%) (%) (ksi) Control-12 IM-X --
81.6 10.5 6.2 17.39 .+-. 0.30 Control-13 IM-X 1 70.6 20.8 7.4 18.61
.+-. 0.34 Example 11 IM-X 1 72.3 14.4 12.8 20.19 .+-. 0.43
Control-14 IM-X -- 81.6 10.5 6.2 10.83 .+-. 0.30 Control-15 IM-X 1
70.6 20.8 7.4 15.87 .+-. 0.26 Example 12 IM-X 1 72.3 14.4 12.8
17.31 .+-. 0.44
[0164] Aqueous grafting was somewhat more complicated. Like the IMU
(surface untreated) fiber and unlike IM-7 (100% surface treated),
IM-X fiber is easy to modify further, which has been revealed by
XPS analysis of the "Blank run" fiber (Control 13 and 15). A very
significant change in surface chemistry, namely almost a two-fold
increase in O concentration was observed. For that reason, just as
in case of IMU fibers, a "Blank run" fiber was made for comparison
of SBS properties. This addition was justified, as an improvement
of SBS properties in laminates based on "Blank run" fiber were
observed, when compared to laminates from the feed fiber. It is
believed that this result is due to additional surface treatment of
the IM-X feed fiber in aqueous Blank conditions. However, it was
still observed that fibers grafted with PEI (aqueous) still showed
a much more significant increase in SBS properties than the "Blank
run" fibers, when compared to the initial IM-X 12K fiber and to
each other in both epoxy and BMI composites.
[0165] From Table 9, it can be seen that aqueous electro-grafting
of B-PEI-1 onto a carbon fiber results in an increase of 106.5% in
nitrogen concentration on the surface of the fibers in comparison
to Control-12, as well as, and increase in the interlaminar
strength of the laminate panels prepared with the composite carbon
fibers. In particular, the EPDXY based laminate panel (Example 11)
exhibited an increase in interlaminar strength of greater than 16%
in comparison to the Control fiber (Control-12). Similarly, the
BMI-based laminate panels (Example 12) exhibited an increase in
interlaminar strength of more than 59% in comparison to the Control
fiber (Control-14).
Examples 13 and 14: Electro-Grafting of Linear PAH onto IM-7
Treated, 12K Fiber Tow, and Evaluation of Laminates Prepared in
EPDXY and BMI Resin
[0166] In this example, electro-grafting using PAH as the
amine-functionalized polymer was evaluated. A bath of MEOH solution
20 mM in tetraethylammonium tetrafluoroborate supporting
electrolyte (S.E.), and 1.25 wt. % of PAH was prepared. PAH was
electro-grafted onto IM-7 12,000 filament tow according to the
procedure described above. The resulting carbon fibers were
prepared into laminate panels with EPDXY and BMI resin. The
composite carbon fibers and laminate panels were evaluated with XPS
and SBS, respectively, as previously described. The results are
summarized in Table 10 below.
TABLE-US-00010 TABLE 10 Summary of SBS and XPS Data for
Electro-grafting of PAH on IM-7 Bath exposure Sample Carbon time C
N SBS No. fiber (min.) (%) O (%) (%) (ksi) Control-16 IM-7 -- 83.0
10.4 6.3 17.62 .+-. 0.31 Example 13 IM-7 1 81.3 7.6 10.1 18.64 .+-.
0.45 Control-17 IM-7 -- 83.0 10.4 6.3 16.68 .+-. 0.50 Example 14
IM-7 1 81.3 7.6 10.1 18.80 .+-. 0.45
[0167] From Table 10, it can be seen that electro-grafting of PAH
onto a carbon fiber results in an increase in nitrogen
concentration on the surface of the carbon fibers of 60.3% in
comparison to the control carbon fiber. In addition,
electro-grafting of PAH onto a carbon fiber also resulted in an
increase in the interlaminar strength of the laminate panels
prepared with the composite carbon fibers. In particular, the EPDXY
based laminate panel (Example 13) exhibited an increase in
interlaminar strength of greater than 5% in comparison to the
Control fiber (Control-16). Similarly, the BMI-based laminate
panels (Example 14) exhibited an increase in interlaminar strength
of more than 12% in comparison to the Control fiber
(Control-17).
Example 15: Electro-Grafting of L-PEI onto IM-7 12K Fiber Tow, and
Evaluation of Laminates Prepared in EPDXY Resin
[0168] In this example, electro-grafting using L-PEI as the
amine-functionalized polymer was evaluated. A bath of MEOH solution
20 mM in tetraethylammonium tetrafluoroborate supporting
electrolyte (S.E.), and 1.25 wt. % of L-PEI was prepared. L-PEI was
electro-grafted onto IM-7 12,000 filament tow according to the
procedures described above. The resulting carbon fibers were
prepared into laminate panels with EPDXY resin. The composite
carbon fibers and laminate panels were evaluated with XPS and SBS,
respectively, as previously described. The results are summarized
in Table 11 below.
TABLE-US-00011 TABLE 11 Summary of SBS and XPS Data for
Electro-grafting of L-PEI on IM-7 Bath exposure Sample Carbon time
C N SBS No. fiber (min.) (%) O (%) (%) (ksi) Control-18 IM-7 --
83.0 10.4 6.3 17.62 .+-. 0.31 Example 15 IM-7 1 80.7 9.1 9.8 18.82
.+-. 0.34
[0169] From Table 11, it can be seen that electro-grafting of L-PEI
onto a carbon fiber results in an increase in nitrogen
concentration on the surface of the fibers, as well as, and
increase in the interlaminar strength of the laminate panels
prepared with the composite carbon fibers. In particular, the
electro-grafted carbon fibers exhibited an increase in surface
nitrogen concentration of 55.5% in comparison to the control, and
the EPDXY based laminate panel (Example 15) exhibited an increase
in interlaminar strength of greater than 6% in comparison to the
Control fiber (Control-18).
[0170] Notably, the polymer had quite a different structure from
branched polyethyleneimine (PEI), in that only secondary amine
groups were present. Secondary amines were known to electrograft to
substrates, but less efficiently than primary amines. Nevertheless,
these types of polymers could be grafted onto fibers and a clear
improvement of interlaminar properties was observed in the case of
an epoxy composite.
Example 16: Spontaneous Grafting of B-PEI-1 onto IM-712K Fiber Tow,
and Evaluation of Laminates Prepared in EPDXY Resin
[0171] A bath of MEOH solution 20 mM in tetraethylammonium
tetrafluoroborate supporting electrolyte (S.E.), and 1.25 wt. % of
B-PEI-1 was prepared. B-PEI-1 was grafted onto IM-7 12,000 filament
tow by passing tow through the bath. No voltage was applied to the
bath. The resulting carbon fibers were prepared into laminate
panels with EPDXY resin. The composite carbon fibers and laminate
panels were evaluated with XPS and SBS, respectively, as previously
described. The results are summarized in Table 12 below.
TABLE-US-00012 TABLE 12 Summary of SBS and XPS Data for grafting of
B-PEI-1 on IM-7 Bath Carbon exposure C O N SBS Sample No. fiber
time (min.) (%) (%) (%) (ksi) Control-19 IM-7 -- 83.0 10.4 6.3
17.62 .+-. 0.31 Example 16 IM-7 1 80.8 7.6 11.1 19.17 .+-. 0.36
[0172] To the surprise of the inventor, XPS analysis indicated a
significant increase in surface nitrogen concentration (76.2%),
when compared to the control carbon fiber (Control-19). Notably,
this concentration increase was comparable to that of the examples
in which B-PEI-1, L-PEI and PAH were electro-grafted onto the
carbon fibers.
[0173] In Example 16, the inventor evaluated the possibility of
spontaneous grafting/attachment of amine-containing polymers onto
the carbon fiber. It appeared that even without any potential
applied to the cell, branched PEI could be attached in significant
enough amounts to IM-7 fiber to improve Short Beam Shear strength
of the resulting laminate in epoxy resin. It must be noted that,
even though no potential was applied to the cell, a potential of
0.7-0.8V was usually measured at fiber (open circuit potential),
which could be enough to generate cation radicals, especially in
case of PEI, which contained secondary and tertiary amino-groups,
which are known to generate radical cations at lower potentials
then primary amines (usually 1.5-1.6V range for primary
aminogroups). Others have reported that spontaneous grafting of
amines is much less efficient than classic electrografting.
However, it must be pointed out that only "small" molecules were
investigated so far, and that tor "large" polymeric molecules it
may not be necessary to form a lot of bonds with the fiber surface
to introduce a lot of functionality to the surface. That is why
even low-efficiency grafting, as has been shown for secondary
amines (Example 15) and spontaneous grafting (Example 16) could be
sufficient to introduce enough amine functionality for further
reactions with resin matrices and improvement of interlaminar
properties.
Example 17: Grafting of B-PEI-1 onto HM-63 12K Fiber Tow and
Evaluation of Laminates Prepared in EPDXY Resin
[0174] In this example, electro-grafting using B-PEI-1 as the
amine-functionalized polymer was evaluated. A bath of MEOH solution
20 mM in tetraethylammonium tetrafluoroborate supporting
electrolyte (S.E.), and 1.25 wt. % of B-PEI-1 was prepared. B-PEI-1
was electro-grafted onto HM-63 12,000 filament tow according to the
procedures described above. The resulting carbon fibers were
prepared into laminate panels with EPDXY resin. The composite
carbon fibers and laminate panels were evaluated with XPS and SBS,
respectively, as previously described. The results are summarized
in Table 13 below.
TABLE-US-00013 TABLE 13 Summary of SBS and XPS Data for
Electro-grafting of B-PEI-1 on HM-63 Bath Carbon exposure C O N SBS
Sample No. fiber time (min.) (%) (%) (%) (ksi) Control-20 HM-63 --
94.9 4.4 0.2 11.9 .+-. 0.45 Example 17 HM-63 1 87.5 4.9 6.0 12.59
.+-. 0.23
[0175] From Table 13, it can be seen that electro-grafting of
B-PEI-1 onto a carbon fiber results in an increase in nitrogen
concentration on the surface of the fibers, as well as, and
increase in the interlaminar strength of the laminate panels
prepared with the composite carbon fibers. In particular, the
electro-grafted carbon fiber exhibited an increase in surface
nitrogen concentration of 2,900%, and the EPDXY based laminate
panel (Example 17) exhibited an increase in interlaminar strength
of greater than 5% in comparison to the Control fiber
(Control-20).
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