Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~15~
~W094/20~2 PCT~S93/02250
A FIR~ QR~n Gr~SS COMPOSTT~ FOR PROTECTI~G
POrYMERIC SUBSTRAT~
Prior Art
The invention relates generally to composites
in which a matrix material is reinforced with fibers
and applied as a protective layer to polymeric
substrates.
Polymers are commonly reinforced with fibers
and the resulting composites are widely used for many
purposes where lightweight, high strength and ease of
fabrication are needed. However, polymers are useful
at low temperatures, typically being limited to
applications where they are ex~ to temperatures no
higher than about 400-C. For many polymers the
temperatures cannot exceed 250-C. Exten~g the
usef~ sc of such polymeric compositQs into higher
temperature uses would be most desirable.
It has now been found that adding a unigue
f~ber-reinforced composite as a protective layer to
polymeric substrates provides substantial resistance
for short-term exposure to quite high temperatures.
Matrices having enh~nce~ performance have
been suggested for use with fibers having high strength
at ~levated temperature~. Examples of such matrix
material~ are the glass and glass ceramics ~Prewo et
al., Ceramic Bulletin, Vol. 65, No. 2, 1986).
In USSN 002,049 a ceramic composition
designated "black glass" is disclosed which has an
empirical formula ~sicxoy where x ranges from 0.5 to
about 2.0 and y ranges from about 0.5 to about 3.0,
preferably x ranges from o.9 to 1.6 and y ranges from
0.7 - 1.8. Such a ceramic material has a higher carbon
content than prior art materials and is very resistant
to high temperatures - up to about 1400-C. This black
W094/20~2 PCT~S93/02250
21545g8
glass material is produced by reacting in the presence
of a hydrosilylation catalyst a cyclosiloxane having a
vinyl group with a cyclosiloxane having a hydrogen
group to form a polymer, which is subsequently
pyrolyzed to black glass. The present invention
involves the application of such black glass with
reinforcing fibers to form a protective layer for
polymeric substrates.
In U.S. Patent 4,460,638 a fiber-reinforced
gl~ss composita is disclosed which employs high modulus
fibers in a matrix of a pyrolyzed silazane polymer.
Another possible matrix material is the refiin 801 of an
organosilsesquioxane, as described in U.S. 4,460,639.
However, such materials are hydrolyzed, and since they
release alcohols and contain excess water, they must be
carefully dried to avoid fissures in the curing
E'l ~-- .
Another U.S. Patent 4,460,640, disclosed
related fiber-reinforced glass composites using
organopolysilox~ne resins of U.S. Patent 3,944,519 and
U.S. Patent 4,234,713 which employ cro~slinking by the
reaction of ~SiH ~o~ to CH2-CHSir yLou~. These
later two patents have in common the use of
organosilsesquiQY~nes having C6H5Si~J2 units, which have
been considered n~ces-~ry by the patentees to achieve
a flowable resin capable of forming a laminate. A
~ vantagQ of ~uch C6H5Si~2 units is their te~ cy
to produce free carbon when pyrolyzed. The present
invention requires no such C6HsSi~/2 units and still
W094/20432 PCT~S93/022S0
~ ~15~4588
provides a flowable resin, and does not produce easily
Q~i ~ i 7ed carbon.
Another disadvantage of the
organopolysiloxanes used in the '640 patent i8 their
fiensitivity to water as indicated in the reguirement
that the solvent used be essentially water-free. The
resins contain silanol ~LO~ and when these are
hydrolyzed they form an infusible and insoluble gel.
The present invention requires no such silanol yLou~s
and is thus in^ensitive to the pre-?nce of water. In
addition, the organopolysiloxAnes of the '640 patent
may not have a long shelf life while those of the
present invention remain stable for extsn~P~ period~.
Still another disadvantage for the organopolysilQxAn~
disclosed in the '640 patent is that th-y require a
partial curing step before pressing and final curing.
This operation is difficult to carry out and may
pr~vent ~atisfactory lamination if the polymer is over
cured. The present invention can be carried out After
coating the fibers and requires no ~L c ~ring st~p.
Y of th~ Tnvention
A protective layer for polymeric ~ubstrates
i~ a fiber-reinforcQd glass composite comprising (a) at
least one refractory fiber select~d from the group
consisting o~ boron, silicon carbide, graphite, silica,
quartz, S-glass, E-glass, alumina, aluminosilicate,
boron nitride, s$1icon nitride, silicon carbonitride,
~ilicon oxycArhQ~itride, boron carbide, titanium
boride, titanium carbide, zirconium oxide, and
zirconia-to~qh~n-~ alumina and, (b) a carbon-contA~ing
black glass ceramic composition having the empirical
formula sicxoy where x ranges from about o.s to about
2.0, preferably from 0.9 to 1.6, and y ranges from
W094/20432 PCT~S93/02250
215~5~8
about 0.5 to about 3.0, preferably from 0.7 to 1.8.
The fibers optionally may be coated with carbon, boron
nitride or other coatings to affect the bond between
the fiber and the black glass matrix.
In a preferred embodiment, the bl2ck glass
ceramic composition (b) is the pyrolyzed reaction
product of a polymer prepared from (1) a cyclosiloxane
monomer having the formula
R'
-- (si--O) n
R
where n i8 an integer from 3 to about 30, R is
hyd~vyen, and R' is an Al ken~ of from 2 to about 20
carbon atoms in which one vinyl c~r~on atom i8 directly
bonded to silicon or (2) two or more different
cyclosiloxane monomers having the formula of (1) where
for at lea~t one monomer R is l,y~Lo~en and R' i5 an
lkyl group having from 1 to ~bout 20 carbon atoms and
for the other ~onomers R is an ~lkPne from about 2 to
about 20 carbon atoms in which one vinyl carbon is
dirQCtly h~ to silicon and R' is an alkyl group of
from 1 to about 20 carbon atoms, or (3) cyclosiloxane
monomer~ having the formula of (1) where R and R' are
ind~pend~ntly sQlæcted from hydrogen, an Al~e~e of from
2 to ~bout 20 c~rbon atoms in which one vinyl carbon
atom i5 directly ~onA~ to silicon, or an alkyl group
of from 1 to about 20 carbon atoms and ~t least some of
said monomers contain each of said hydrogen, ~1 kQne ~
and alkyl moieties, said polymerization reaction taking
place in the pre~ence of an effective amount of
094/20~2 PCT~S93/02250
g
~ , , ,
hydrosilylation catalyst. The polymer product i8
pyrolyzed at a temperature in the range of about 800 C
to about 1400-C to produce the black glass ceramic,
preferably in a non-oxidizing atmosphere.
In another ~ho~iment the invention comprises
a method of applying a fiber-reinforced black glass
matrix composite wherein the cyclosiloxane reaction
product described above is combined with refractory
fibers, which may be in the form of woven fabric or
lo ~ni~irectionally aligned fibers. Plies of the resin
impregnated fibers may be laid-up to form a green
l~minate and then pyrolyzed at a temperature between
about 800-C and about 1400-C, preferably about 850-C,
to form the black glass composite. The composite may
be reimpregnated with precursor and repyrolyzed in
order to increase density. The resulting black glass
composite i8 then applied to an uncured polymer
laminate and cured using heat and pressure suitable for
the polymer selected in order to bond the two
component~ into a composite capable of withst~nAing
higher temperatures than possible with the polymer
alone. A curable hon~i~g agent may be usad as an
intermediate layer to assist in bonding the two layers.
The polymeric substrate may be glas~ fi~er,
organic f~ber, or carbon fiber-reinforced organic
matrices, such as epoxy, bismaleimides, phenolic
triazines, poly (phenylen~ sulfide),
poly(etheretherketone), poly(ethersulfone), liquid
crystal polymers, phenolics, PMR polyimides, and the
like.
Descri~tion of the Preferred ~hodi~ents
Rlack Glass Ceramic
The black glass ceramic used as the matrix
has an empirical formula sicxoy wherein x ranges from
W094/20432 PCT~S93/02250 ~
2~5~588
about O.5 to about 2.0, preferably O.9 - 1.6, and y
ranges from about 0.5 to about 3.0, preferably 0.7 -
1.8, whereby the carbon content ranges from about 10%
to about 40% by weight. The black glass ceramic i~ the
product of the pyrolysis, preferably in a non-oxidizing
atmosphere, at temperatures between ~bout 800 C and
about 1400-C of a polymer made from certain siloxane
monomers.
The polymer precursor of the black glass
ceramic may be prepared by sub~cting a mixture
contAini~g cyclosiloxanes of from 3 to 30 silicon atoms
to a temperature in the range of from about lO-C to
about 300-C in the pre~Qnce of 1-200 wt. ppm of a
pl~tinum hyd~c-ilylation catalyst for a time in the
rang~ of from about 1 minute to about 600 minutea.
When the polymer i~ pyrolyzed ~t a temperature in the
range from about 800-C to about 1400-C for a time in
the range of from about 1 hour to about 300 hours,
black glass results. The polymer formation takes
advantage of the fact that a silicon-hydride will react
with a ~illcon-vinyl group to form a
~ilicon-ca ~ carbon-silicon hon~ chain, thereby
forming a n~.~olk polymer. For this reason, each
mono~er cyclosiloxane must contain either a
s~ hyd~id~ bond or a silicon-vinyl bond or both.
A ~ilicvn hy~ide bond refers to a silicon atom bonded
directly to a hydrogen atom and a silicon-vinyl bond
refers to a silicon atom bonded directly to an alkene
carbon, i.e., it is con~ected to another c~rbon atom by
a double bond.
The polymer precursor for the black glas~
ceramic may be defined generally as the reaction
product of (1) a cyclosiloxane monomer having the
formula
~ 094/20432 2 1 5 ~ 5 8 8 PCT~S93/022~0
(si--O) n
R
where n is an integer from 3 to 30, R is hydrogen, and
R' is an alkene of from 2 to 20 carbon atoms in which
one vinyl carbon atom is directly bonded to silicon or
(2) two or more different cyclosiloxane monomers having
the formula of (1) where for at least one monomer R is
hydrogen and R' is an alkyl group having from 1 to 20
carbon atoms and for the other monomers R is an Alkenq
from about 2 to 20 carbon atoms in which one vinyl
~5 carbon i~ directly bonded to silicon and R' i~ an alkyl
group of from 1 to 20 carbon atoms, or (3)
cyclosiloxane monomers having the formula of (1) where
R and R' ~re ;nAep~n~Pntly selected from hydrogen, an
alkene of from 2 to about 20 carbon atoms in which one
vinyl carbon atom is directly bonded to silicon, or an
alkyl group of from 1 to about 20 carbon atoms and at
least some of said monomers contain each of said
hydrogen, alken~, and alkyl moieties, said reaction
~in~ place in the presence of an effective amount of
hydrosilylation catalyst.
The black glass ceramic may be prepared from
a cyclosiloxane polymer precursor wherein both the
requisite silicon-hydride bond and the silicon-vinyl
bond are present in one molecule, for example,
1,3,5,7-tetravinyl-1,3,5,7-tetrahydro-cyclo-
tetrasiloxane. Such monomers may also contain alkyl
groups such as, for example, 1,3-divinyl-1,5-dihydro-
3,S,7,7-tetramethylcyclotetrasiloxane. Alternatively,
W094/20432 PCT~S93/02250 ~
21S~5~8
two or more cyclosiloxane monomers may be polymerized.
Such mono~ers would contain at least either a silicon
hydride bond or a ~ilicon-vinyl bond and the ratio of
the two types of ~onds should be a~out 1:1, more
broadly about 1:9 to 9:1.
Examples of such cyclosiloY~n6~ include, but
~re not limited to:
1,3,~,7-tetramethyltetrahydrocyclotetrasiloxane,
1,3,5,7-tetravinyltetrahydrocyclotetra~iloxane,
1,3,5,7-tetravinyltetraethylcyclotetrasiloxane,
1,3,5,7-tetravinyltetramethylcyclotetrasiloxane,
1,3,5-tri~ethyltrivinylcyclotrisiloxane,
1,3,5-trivinyltrihydrocyclotrisiloxane,
1,3,5-trimethyltrihydrocyclotrisiloxane,
1,3,5,7,9-pentavinylpentahydrocyclopentasiloxane,
1,3,5,7,9 pentavinylpentamethylcyclopent~siloxane,
1,1,3,3,5,5,7,7-octav~nylcyclotetrasiloxane,
1,1,3,3,5,5,7,7-octahydrocyclotetrasiloxane,
1,3,5,7,9,11-hexavinylhexamethylcyclo~Y~iloxane,
1,3,5,7,9,11-hexa~ethylhexahydrocyclo~eY~iloxane,
1,3,5,7,9,11,13,15,17,19-decavinyldecahydrocyclodeca-
siloxane,
1,3-divinyl-1,5-dihydro-3,5,7,7-
tetramethylcyclotetrasiloxane
1,3,5-tri~inyl-1,3,5,7,7-
pentamethylcyclotetrasiloxane
1,~,5-tril,~o 1,3,5,7,7-
penta~ethylcyclotetrasiloxane
1,3,5,7,9,11,13,15,17,19,21,23,25,27,29-pent~eca-
vinyl-1,3,5,7,9,11,13,15,17,19,21,23,25,27,29-
E~ent~e~ahy~l~G~ lopenta~ecAciloxane
1,3,5,7-tetrapropenyltetrahydrocyclotetrasiloxane,
1,3,~,7-tetrapentenyltetrapentylcyclotetrasiloxane
and
1,3,5,7,9-pent~decenylpentapropylcyclopentasiloxane.
~ 094/20432 PCT~S93/02250
., , ~ .
It will be understood by those skilled in the
art that while the siloxane monomers may be pure
species, it will be frequently desirable to use
mixtures of such monomers, in which a single species is
predominant. MixLu~ eB in which the tetramers
predominate have been found particularly useful.
While the reaction works best if platinum is
the hydrosilylation catalyst, other catalysts such _s
cobalt, rhodium (Wilkincon~s catalyst) and manganese
carbonyl will perform adequately. The catalyst can be
dispersed as a solid or can be u~ed as a solution when
added to the cyclosiloxane monomer. With platinum,
about 1 to 200 wt. ppm, preferably 1 to 50 wt. ppm as
the metal will be employed as the catalyst.
Black glass precursor polym~r may be prepared
from either bulk or ~olution polymerization. In bulk
polymerization, neat monomer liquid, i.e., without
solvents, reacts to form oligomers or high molecular
weight polym~rs. In ~ulk polymerization, a solid gel
can be formed without entrapping solvent. It is
particularly useful for impregnating porous composites
to increasQ density. Solution polymerization refers to
polymerizing monomers in the p.~ nce of An unreActive
solvent.
The resin used in impregnating fibers to form
~_~r ~g in our invention preferably is pr~pared by
~olution polymerization. The advantage of solution
polymerization is the ease of ~G~ olling resin
characteristics. It is possible but very difficult to
produce B-stage resin suitable for ~L~e~ with
consistent characteristics by bulk polymerization. In
the p.~~e~t invention, soluble resin with the desirable
viscosity, ~ ne~5, and flowability shitable for
prepregging and laminating can be obt~inA~ consistently
W094/20~2 PCT~S93102250 ~
~1~4588
using solution polymerization process. The production
of easily handleable and consistent resin is very
critical in composite fabrication.
F~hers
Reinforcing fibers useful in the protective
layers of the invention are refractory fibers which are
of interest for ~pplications where superior physical
propertie~ are ~ee~e'3. They include such materials a
boron, silicon carbide, graphite, silica, quartz,
S-glass, E-gla~s, alumina, aluminosilicates, boron
nitride, silicon carbonitride, silicon oxycarbonitride,
silicon nitride, boron carbide, titanium boride,
titaniu~ c~rbide, zirconium oxide, and
zirconia-to~gh~ne~ alumina. The fibers may have
various sizes ~nd forms. They may be monofilaments
from 1 ~m to 200 ~m diameter or tows of 200 to 2000
filaments. When used in composites of the invention
they may be woven into fabrics, p..- -5^'3 into mats, or
~n~3~ectionally aligned with the fibers oriented as
desired to obtain the needed physical properties.
An important factor in the performance of the
black gla~s composites is the bond between the fibers
and the hl ~k glass matrix. ConAe~uently, where
improved me~An~cal strength and to~ghness are desired,
the fiber~ are provided with a carbon, boron nitride,
or other coating which reduces the honA~g between the
fibQrs and th~ black glass matrix. The surface sizings
found on fibers as received or pro~3~cD~ may be removed
by solvent w~h~g or heat treatment and the coating
applied. Yarious methods of depositing carbon coatings
may be used, including chemical vapor deposition,
solution coating, and pyrolysis of organic polymers
such as car~on pitch and phenolics. One preferred
~ 094/20432 PCT~S93/02250
2~54588
~e~hnique is ehemieal vapor deposition using
deeomposition of methane or other hydroearbons.
Another method is pyrolysis of an organie polymer
eoating sueh as phenol-formaldehyde polymers
eross-linked with ~ueh agents as the monohydrate or
sodium salt of paratoluenesulfonic aeid. Still ~nother
method uses toluene-soluble and toluene-insoluble
earbon piteh to eoat the fibers. Deposition of boron
nitride may be aeeomplished by reaetion of boron
eompo~nAC ~ueh as boron ehloride with ammonia.
o-,e3si nc~
As previously ~ , the blaek glass
preeursor is a polymer. It may be shaped into fibers
and eombined with reinforeing fibers or the blaek glass
preeursor may be used in solution for eoating or
impregnating reinforeing fibers. Various ~ethods will
~uy~e_L themselves to those skilled in the art for
eombining the hl ~ck glass preeursor with reinforeing
fibers. It would, for example, be feasible to eombine
fibQrs of the polymer with fibers of the reinforeing
material and then to eoat the resulting fabrie or mat.
Alternatively, the reinforcing fibers eould be coated
Yith ~ ~olution of the polymer and then formed into the
deaired shape. Coating may be done by dipping,
~praying, brushing, or the like.
In one method, a contitlt~o~ fiber is eoated
with ~ solution of the black glas~ pr~cur~or polymer
~nd then wound on ~ rotating drum covered with a
release film whieh is easily separated from the eoated
fibers. After suffieient fiber has been built up on
the drum, the proeess is stopped and the uni-
direetional fiber mat removed from the drum and dried.
W094/20~2 PCT~S93/02250 ~
2~59~
The resulting mat (i.e., "prepreg") then may be cut ~nd
laminated into the desired ~AreC.
In ~ second method, a woven or pressed f~bric
of the reinforcing fibers is coated with a solution of
S the black gla~s precursor polymer and then dried, after
which it may be formed into the desired ~hA~e, by
procedures which are familiar to those skilled in the
art of fabricating structures with the prepreg sheets.
For example, layers of prepreg sheets may be laid
together, heated and pressed into the n~-~e~ shape.
The orientation of the fibers may be chosen to
strengthen th~ composite part in the principal
load-bearing directions.
Solvents for the black glass precursor
polymers include hydrocarbons, such aS isooctane,
tolu~ne, benzene, ~nd xylene, ~nd ethers, such as
tetrahydrofuran, and ketones such a8 methyl ethyl
ketone, etc. rQ~Gentration of the prepregging solution
may vary from about 10% to about 70% of resin by
weight. r~e_~.;o~ polymer used in i~pregnating the
fibers i5 ~ -ally prepared from solution polymerization
of the ~e~e_~ive monomers.
Si~ce the precursor polymers do not contain
any hydrolyzable functional ~oups, such as silanol,
chlorosilane, or alkoxysilane, the pr~cursor polymer is
not watQr sens$tive. No particul~r precaution is
n~e~ to exclude water from the solvent or to control
relative humidity during processing.
The resin ages very slowly when stored at or
below room temperatures as is evident from its shelf
life of more than three months at these temperatures.
The resin is ~table both in the solution or in the
prepreg. Prepregs stored in a refrigeiator for three
months have been used to make laminates without any
~0 94/20432 2 1 ~ 4 ~ ~ 8 PCT~S93/02250
r
difficulty. Also, resin solutions stored for months
have been used for making prepregs s~cce~sfully.
Large and complex shape fiber-reinforced
glass composites can be fabricated from laminating
prepregs. One method is hand lay-up. Several plies of
prepregs cut to the desired shape are laid-up to
achieve the required thickness of the component. Fiber
orientation can be tailored to give maximum strength in
the preferred direction. Fibers can be oriented
unidirectionally t0~, at 90- angles t0/90], at 45-
angles t0/45 or 45/90], and in other combinations as
desired. The laid-up plies are then bonded by vacuum
compaction before autoclave curing. Another
fabrication method is tape laying which uses
pre-impregnated ribbons in forming composites. The
resins can be controlled to provide the desired
tac~in~sF and viscosity in the prepreg for the lay-up
pl OC~dul e~.
After the initial lay-up of the pLe~Le~ ~ the
composites are consolidated and cured by heating to
temperatures up to about 250-C under pressure. In one
method, the composited prepreg is placed in a bag,
which is then evacuated and the outside of the bag
placed under a pressure sufficient to bond the layered
prepreg, say up to about 1482 kPa. The resin can flow
into and fill up any voids between the fibers, forming
a void-fre~ green laminate ~kin. The resulting
polymer-fiber composite is dense and is ready for
conversion of the polymer to black gla~s ceramic. If
an eY~cFively cured prepreg is used, as is possible
with the method of U.S. ~at. No. 4,460,640, there will
be no adhesion ~etween the plies and no flow of resin
material and no bonding will occur.
W094/20432 PCT~S93/02250
.
21545~8
14
Heating the composite to temperatures from
about 800-C up to about ~400-C (pyroly~is) converts the
polymer into a black glass ceramic containing
essentially only carbon, silicon, and oxygen.
5 Pyrolysis is preferably carried out in an inert
atmosphere, although oxygen may be present provided the
heating is carried out very rapidly, as disc~c~e~ in
co-pen~;n~ application having a docket number 82-2966.
It is characteristic of the black glass prepared by
pyrolyzing the cyclosiloxanes described above that the
resulting black glass has a large carbon content, but
is able to withstand exposure to temperatures up to
about 1400-C in air without oxidizing to a significant
degree. Pyrolysis is usually carried out with a
heating to the maximum temperature selected, holding at
that temperature for a period of time determined by the
size of the ætructure, and then cooling to room
temperature. Little bulk shrinkage is observed for the
black glass composites and the resulting structure
typically has about 70-80% of its theoretical density.
Conversion of the polymer to black glass
takes place between 430-C and 9SO-C. Three major
pyrolysis steps were identified by thermogravimetric
analysis at 430-C-700-C, 680-C- 800-C and 780-C-9SO-C.
The yield of the polymer-glass conversion up to 800-C
is about 83~; the third pyrolysis mechAnism occurring
between 780-C and 950-C contributed a final 2.5% weight
loss to the final product.
Since the pyrolyzed co~rocite structure still
retains voids, the structure may be increased in
density by im~Le~.lating with a neat monomer liquid or
solution of the black glass precursor polymer. The
solution is then gelled by heating to about 50-C-120-C
for a sufficient period of time. Following gelation,
W094/20432 PCT~S93/02250
215~88
the polymer i5 pyrolyzed as described above. Repeating
these steps, it is feasible to increase the density up
to about 95~ of the theoretical. Alternatively! a
porosity suitable for bonding to the polymer substrate
may be produced.
~olYmeric Substrates
~ he polymeric substrates may include a wide
variety of polymers used as matrices for reinforcing
fibers, which in this class of materials are typically
glass or carbon fibers, although other fibers such as
those used in the black glass comrocites or organic
fibers such as polyester, nylon, Spectra~,
polyethylene, aromatic polyamide (e.g. Kevlar-),
polybenzoxazole, and poly(etheretherketone) may be
chosen if desired. Polymers which might be used as
matrices include epoxy, bismaleimides, phenolic
triazines, poly (phenylene sulfide),
poly(etheretherketone), poly(ether sulfone), liquid
crystal polymers, phenolics, PMR polyimides,
polyure~h~ne~, silicones, polycarbonate, polyamide-
amide and the like. In general, there is believed to
be no limitation on the nature of the polymer
substrates. The polymeric substrates are protected by
applying a pyrolyzed fiber-reinforced black glass layer
to B stage or partially cured polymer substrate and
then curing the polymer, which also bonds the cured
polymer substrate to the prote~tive layer of reinforced
black glass matrix.
Several methods familiar to those skilled in
the art are useful for bonding the polymer substrate to
the black glass layer. In one method the black glass
layer is bonded to the polymer substraté by using heat
and pressure. In another method a curable bonding
W094/20432 PCT~S93/02250
.
4588
16
agent is applied as an intermediate layer and cured.
A third method is similar to the first but the poly~er
is applied as a f~ber-reinforced prepreg to the black
glass layer and then the two are vacuum autoclaved,
autoclave cured, or hot-pressed to consolidate ~he
layers and to cause the polymer to flow into pores of
the black glass layer. The conditions for such curing
will depend upon the polymer selected and the degree to
which the polymer has been given a partial cure beforeO contacting the reinforced black gl~ss composite.
~Y~ml~le 1
Polymer Precursor Preparation
The cyclosiloxane having silicon-vinyl bond
was poly(vinylmethylcyclosiloxane) (ViSi). The
cyclosiloxane with a silicon-hydride bond was
poly(methylhydrocyclosiloxane) (HSi). Both
cyclosilQY~n~ were mixtures of oligomers, about 85% by
weight being the cyclotetramer with the remainder being
principally the cyclopentamer and cyclohexamer. A
volume ratio of 59 ViSi/41 HSi was mixed with 22 wt.
ppm of platinum as a platinum-cyclovinylmethylsiloxane
complex in isooctane to give a lO vol. percent solution
of the cyclosiloxane monomers. The solution was heated
to reflux conditions (about lOO-C) and refluxed for
about 1 hour. Then, the solution was conre~trated in
a rotary evaporator at 50-C to a 25-35% co~ntration
suit~blQ for use in prepregging. The resin proAltr~
was poly(methylmethylenecyclosiloxane) (PMMCS). It was
tacky at room temperature and flowable at temperatures
of about 70-C or higher and thus suitable for use as a
B-stage resin.
F~XAm~le ~
A black glass ro~ro~ite layer ~as prepared by
applying a 35 wt.% solution of the black glass
W094/20~2 PCT~S93/022S0
21~.8~
, i . .
precursor polymers of Example 1 in isooctane to 6" x 6"
(152.4 mm x 152.4 mm) squares of a carbon coated
Nicalon~ -ni~;rectional fiber fabric, six layers of
which were laid up with t0/90] orientation. This
prepreg was cured in an autoclave by heating to 65-C at
2-C/min, holding for 30 minutes, then heating to 135-C
at 2-C/min, holding for 30 minutes, and then cooling to
room temperature at 2-C/min. No weight loss was found.
The cured composite was next pyrolyzed by heating in a
furnace in a nitrogen atmosphere to 350-C over 2.7
hours, holding for 10 minutes and then heating to 450-C
over 2.7 hours, holding again for 10 minutes and then
heating to 850-C over 6.7 hours, holding for 10 minutes
and cooling down to 200-C over 5 hours. After the
pyrolyzed composite was free cooled to room temperature
the black glass composite was infiltrated three times
with a neat solution of ViSi/HSi cyclosiloxane in a
ratio of 59 to 41 in the presence of 22 wt. ppm of
platinum. After such application of the precursor
solution, the black glass composite was heated to 50-C
to cure the infiltrated liquid and then pyrolyzed as
described. The weight of the consolidated composite
initially was 55.41 gms. It decreased to 52.74 gm
after pyrolysis and then increased with the subsequent
~dditions of black glass precursors to 67.14 gms, 72.1
gms, and finally 76.39 gms, respectively, after the
pyrolysis.
The polymeric substrate selected was a
Magnamite- AS4/3501-6 unidirectional graphite fiber-
reinforced epoxy resin o~tained from Hercules. Theepoxy resin is stated to be stable up to 177-C and
makes up 30% of the weight of the prepreg. Twelve
layers of 6" x 6" (152.4 mm x 152.4 mm) squares of the
Magnamite prepreg were laid up in a t0/90] orientation.
Then, the black glass composite described above was
W094/20432 PCT~S93/02250
~15~5~8
18
placed on top of the epoxy prepreg layers with the
fibers in contacting layers oriented in the same
direction. The composite was then placed in a vacuum
bag and a vacuum applied of 28 in (711 mm) of mercury.
The bag was heated to 116-C at 2.8-C/min in an
autoclave at 85 psig (586 kPa gauge), then after
holding for 60 minutes, the temperature was raised to
177-C at 2.8-C/min and lOO psig (689.5 kPa gauge) while
venting the vacuum bag to atmospheric pressure. The
temperature was reduced to 116-C and held there for 120
minutes, after which it was cooled to 93-C at
2.8-C/minute. The pressure was released and the
co-~losite allowed to free cool to room temperature.
The initial weight was 138.75 gms, but After curing the
weight was 129.06 gms, of which 76.39 gms represented
the black glass-Nicalon composite ~nd 52.67 gms
represented t~e epoxy-carbon composite. Of the
combined composites black glass was 28.7 wt.~, Nicalon
30.5 wt.%, epoxy 9.4 wt.%, and carbon 31.4 wt.%.
A control laminate was prepared with only
twelve plies of Magnamite AS4/3501-6 as described
above, but without applying a black glass-Nicalon
layer.
~Y~mple 3
The composites prepared in Example 3 were cut
into 3n x 3n (76.2 mm x 76.2 mm) samples for testing
for flame resistance when contacted with the flame from
a 0.5" (12.7 mm) Bunsen burner fueled by natural gas
and adjusted to provide temperatures of about 480-530 C
and 380-420-C. The flame covered an area about 1.3"
(33 mm) in diameter in the middle of each sample. When
heating the hybrid composites, the flame impinged on
the black glass side. The results of comparisons
between the epoxy laminate and the black glass-epoxy
composites are given in the following table.
2~ 54~88
~0 94/20432 PCT/US93/02250
19
tJ
~~ 0 ~
~. . . .
~ o _~ o o
I I I I
a
_~ C o ~ ~
a) o
o
e ~ c~ 0
0 0 o ~ o
~ C C C ~~ C C ~ '
0 _I ~ ~ o
C ~0 C C
~ ~ C
o ~ i o ~ ~ o ~ U ~
Z ~ ~ ~ ~Z ~ ~ Z o o 0
E~
~ o o
_~ ~ U~
E~ u~ ~ ~~
a~ o o
~ e c~ ~ o o O~
~ E~
- -
h
0 ~ ~ 0 ~ J~
oq ~ c 0 ~ c
~
U U 0
G ~. O~ ~ C :~ O
_I ~ O ~ O _I ~ O ~ O
0
E~ Z 1~1 ~
l~ 0 1~ 0
W094/20432 PCT~S93/022~0 ~
215458~ 20
~xam~le 4
The samples were cut into 3" x 0.5 (76.2 mm
x 12.7 mm) test bars after the flame testing of Example
3. Three bars were tested from each sample. One from
the center of each sample where the flame had tol~ch~A
and one each from either side of the center piece. A
3-point bend test was done in an Instron tester to
determine the effect of flame contact on the strength
of the laminates. The results of the tests are given
in the following table.
Table 2
Flame Bend Strength,
Sa~le ~e~sure, C Ii~ Xs~ fMPa)
Epoxy Composite
(control)
(as-prepared) N/A N/A 181 (1248)
Epoxy Composite 390 7 min. Center 29 (200)
(control) Left 159 (1096)
(flame ~Yrose~) Right 47 (324)
Epoxy Composite 506 135 sec Center 5 (34.5)
(CG11L~ 01) Left 33 (227.5)
(flame exposed) Right 8 (55.2)
Black glass/ N/A N/A 60 (414)
epoxy Composite
(invention)
(as prepared)
Black gla~s/ 400 7 min. Center 47 (324)
epoxy Composite Side 60 (414)
(invention)
(flame exposed)
~W094/20~2 ~15 ~ 5 8 8 PCT~S93/02250
81ack glass/ 534 158 min. Center 23 (159)
epoxy Composite Left 51 ~352)
(invention) Right 38 (262)
(flame o~rore~)
It will be seen that the black glass-epoxy composite
ret~ne~ much of its initial strength while the
strength of the epoxy composite control was
significantly reduced even at the low temperature
exposure where no burning occurred. ~on~e~uently, it
is concluded that the black glass covered epoxy
laminate can be used above temperature range normally
permitted for the epoxy alone.
