Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
3179
HOECHST AKTIENGESE~LSCHAFT HOE 92/F 361 Dr.AC
Description
Acrylic fibers of improved dispersibility in vi~cous
matrices and process for producing fiber-reinforced
composites
':
The present invention relates to new fiber bundles ba~ed
on acrylic fibers and to a process for producing fiber-
reinforced composites.
It is known that mixing short synthetic fibers into
viscous matrices, such as concrete or mortar, presents
problems. Unless special measures are taken, it is usual
for clumping to occur; that is, the fiber bundles do not
disperse sufficiently, if at all, and remain in the
matrix and thus in the composite later produced there-
from. Undisper~ed bundle i~ generally not desirable,since it gives rise to regions of weakness in the com-
posite material.
Various ways have already been tried to improve the
dispersion of fiber bundles on mixing into such matrices.
For instance, special mixing apparatus can be used; this
solution is frequently machine- and time-intensive and
accordingly cost-intensive.
It i8 al80 already known to treat the fiber bundles with
an adhesive which holds the bundle together before it i8
mixed in and allows the bundle to b~ dispersed u~ing
conventional mixing apparatus. For instance, EP-A-235,577
describe~ acrylic fiber bundles having such a property
profile. These fiber bundles are characterized in that
the fibers used have diameters of less than 50 ~m and
lengths of more than 3 mm and have been provided with an
adhesive. The adhesives u ed are water-~oluble or
-swellable, for example carboxymethylcellulose, or
organic solvent-soluble, for example polyurethane resins.
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It has now been surprisingly found that the treatment of
short acrylic fiber~ with selected agents lead~ to fiber
bundles and that these fiber bundle~ are particularly
readily dispersible in viScou~ matrices into individual
fiber~.
The pre~ent invention accordingly provides a fiber bundle
compri~ing staple fiber~ of acrylonitrile polymers which
is provided with an agent that causes the fiber bundle to
hold together and which separates into its individual
fibers on mixing into vi9cou8 matrix materials, wherein
the agent i8 a water-soluble alkali metal silicate and/or
an organosilane adhesion promoter.
The acrylic fibers to be u~ed according to the invention
can be fiber~ from any de~ired acrylonitrile polymer.
Thu~, the~e fiber~ can be made of acrylonitrile contain-
ing at least 40 mol%, ba~ed on the polymer, of recurring
acrylonitrile units and otherwise containing recurring
structural units derived from monomers that are co-
polymerizable with acrylonitrile, ~uch a~ acrylic or
methacrylic acid derivatives or a-olefins.
Preferably the acrylonitrile polymers contain at least
85 mol%, based on the polymer, of recurring acrylonitrile
units.
The acrylic fibers to be used according to the invention
u~ually have a staple length from 2 to 24 mm, preferably
~ from 6 to 12 mm.
¦ Their fiber linear density is u~ually from 1.0 to
100 dtex, preferably from 1.5 to 50 dtex.
The acrylic fibers to be used according to the invention
can have any cross-sectional shape, for example tri-
angular, tri- or multilobal or in particular round.
The acrylic fibers to be used according to the invention
.~,
1 7 ~
are usually high-strength types. Fibers of thi~ type
generally have a tenacity (measured according to
DI~ 53816) of more than 20 cN/tex, preferably of from 35
to 90 cN/tex. Dependent on the linear density there are still higher .
tenecity values possible. : : .
Particular preference i~ given to using high-strength
high-modulus acrylic fiber types, for example fibers
having a tenacity of from 50 to 90 c~/tex and an initial -
modulus (measured according to DIN 53816), based on 100
extension, of more than 10,000 N/mm2, preferably more
than 15,000 N/mm2.
Such fiber types preferably have breaking extensions
(measured according to DIN 53816) of from 4 to 30%, in
particular of from 5 to 11~.
The agent causing the fiber bundle to hold together is
applied to the fibers in such an amount that the desired
effect i8 obtained. Typical amount~ for thi6 agent range
from 0.1 to 5.0~ by weight, preferably from 0.3 to 3.0%
by weight, based on the fiber bundle. Particular pre- ~ ;
ference is given to using from 0.7 to 1.5% by weight of
the agent.
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The agent to be used according to the invention is a
water-soluble alkali metal silicate and/or an organo-
silane adhesion promoter. Both types of adhesives are
known per se; see for example Ullmanns Encyclopadie ter
technischen Chemie, 4th revised and extended edition,
volume 21, pages 409-414 and pages 496-500, Verlag Chemie
(1980).
The water-~oluble alkali metal silicate is particularly
preferably a sodium silicate which usually contains from
2 to 4 mol of SiO2 per mole of alkali metal oxide.
The organosilane adhesion promoter is preferably a com-
pound of the formula I
~ 21~317~
_ 4 _
X-~CH2)~-Si-(Y)3 (I)
where n is an integer from 1 to 5, in particular 3, X is
a group of the formula -COORl, -CN, -(CH2)m-~R2R3 or
halogen, Y is alkyl, alkoxy or halogen, R', R2 and R3 are
independently of each other hydrogen, alkyl, cycloalkyl,
aryl or aralkyl, and m is an integer from 0 to 5, in
particular 2.
Alkyl can be branched or in particular straight-chain. `~
Examples are alkyl radicals having from 1 to 6 carbon
atoms, such a~ methyl, ethyl, n-propyl, n-butyl, n-pentyl
and n-hexyl.
Alkoxy can be branched or in particular ~traight-chain.
Example~ are alkoxy radicals having from 1 to 6 carbon
atom~, such as methoxy, ethoxy, n-propoxy, n-butoxy,
n-pentoxy and n-hexoxy.
Cycloalkyl i8 generally a radical having fro~ 5 to 8 ring
carbon atoms, in particular cyclohexyl.
Aryl iB generally a mono- or polycyclic carbocyclic
aromatic radical, which may be fused or anellated, in
20 particular phenyl. `
." ,:
Aralkyl i8 generally a radical having from 7 to 9 carbon
atom~, in particular benzyl.
Halogen can be fluorine, chlorine, bromine or iodine;
preferably it is chlorine.
Particular preference i~ given to treating acrylic fiber~
¦ with organosilane adhe~ion promoters of the above-defined
formula I where X is a group of the formula -(CH2)~-NR2R3
where R and R3 are independently of each other hydrogen
or C1-C6alkyl, Y i~ Cl-C6alkyl or in particular
C~-C6alkoxy, and m is n or 2.
The fiber bundles of the invention are used with
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preference for producing composite materials. ~he process
for producing these composite material~ compri~es the
steps of
a) introducing a viscous matrix material in a dry or
moist state into a mixing apparatu~ as the initial
charge, ~ `
b) adding an effective amount of a reinforcing
material in the form of fiber bundles as claimed in ~ ~
claim 1, and ~ ~;
c) mixing said reinforcing material into ~aid finely
divided matrix material so that the fiber bundles
are es~entially separated into the individual
fibers.
The above-defined process and the use of the fiber
bundles ~or producing compo~ite materials form part of
the subject-matter of the present invention.
The fiber bundles of the invention can be used mixed with
inorganic and/or organic viscous matrix materials.
A~ used herein, the term "viscous matrix material" is to
20 be understood as meaning materials whose viscosity is 80 ~`
high that the use of conventional short fibers and of
conventional mixing apparatus is likely to result in
appreciable clumping of the mixture.
Examples of organic matrix materials are vi~cous
pla~tics, i.e. heated thermoplastics or thermosets, into
which the fiber bundles of the invention are to be mixed
and uniformly dispersed.
Examples of inorganic matrix materials are air- and/or
water-setting mixtures of inorganic materials, in par-
ticular hydraulically setting materials. The fiberbundle~ of the invention are preferably used in mixtures
with mortar, concrete, cement, gypsum or organic sealing
compositions, i.e. building material compositions in the
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widest sense.
The mixing of the fiber bundles of the invention into the
matrix material can be by conventional mixing apparatu~.
Exampleg are customary forced-circulation, plough share
and other such mixers.
The matrix material can be present in a finely divided
form, as in the form of a granulation, a powder or a
dust, or in the form of a vi8CoU8 melt. Preferably it is
in the form of a finely divîded inorganic material. The
mixing of the fiber bundles into finely divided inorganic
material can take place in the dry or in the moist state.
The Examples which follow illu~trate the invention
without limiting it.
Numerous experiments were carried out mixing prepared
lS short-fiber bundles of the type described into various
mortar and concrete matrices. The fibers used were high-
~trength high-modulus acrylic fiber~ prepared with from
about 0.5 to 1% by weight of N-aminoethyl-3-aminopropyl-
trimethoxysilane or with from 0.8 to 5% by weight of
~odium silicate. The fiber bundles were found to be ea~y
to di~per~e homogeneously using commercial forced-
circulation mixers of the type customary in the building
indu~try, the fibers being poured in weighed-out amounts
from the pack onto the ready-mixed matrix.
Finished fiber-reinforced parts were examined, inter alia
under W light, in respect of the homogeneity of fiber
distribution in the matrix. The distribution was found to
be homogeneous. Flexural tensile strength and energy
absorption capacity are up, crack initiation and crack
widening are down.
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