Note: Descriptions are shown in the official language in which they were submitted.
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This invention ~elates to a process of manufacturing
polyolefin fibers from a solution of these polyolefins.
French Patents Nos. 1,596,107 and 2,141,748 describe
processes for the manufacture of polyolefin fibers by adiabatic
expansion of a solution of polyolefins. This expansion takes
place by passage of the solution through a spinneret. The
solvent is at least partially volatilized and the fibers are then
collected.
French Patent No. 2,132,903 concerns the preparation of
polyolefin fibers of high molecular weight by dispersing a solution
of polyolefins under a high shearing rate in a precipitant. The
polyolefin solutionr before being introduced into the precipitant,
must be at a temperature above the temperature of dissolving of the
molten mass of the polyolefins. In one particular embodiment of
this process, the solvent and the precipitant are the same chemical
substance.
French Patent No. 2,181,952 describes a process for pre-
cipitating polymer fibers from a solution of said polymer by in-
troducing a stream of solvent tangentially to the outer surface of
the precipitation enclosure. The shearing of the solution created
by the rotation in the enclosure produces the precipitation of
the polymer in fiber form.
French Patent No. 2,131,145 describes a process for
obtaining fibrous gel containing 30~ polyolefins or more by weight
by polymerization of olefins, the reaction mixture being subjected
to a shearing force created by mechanical agitation. The fibrous
gel may also be obtained by cooling a solution of a preformed
polymer under a high shearing rate created by mechanical agitation,
said solution being initially at a temperature above the tempera-
ture of solution of the molten mass of the polyolefin.
An advantage of the present invention is the developmentof a process for the formation of polyolefin fibers which is not
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accompanied by the vaporization of a solvent and which does not
require the use either of a precipitant or of means of mechanical
agitation intended to create a high rate of shear in the solution~
The applicants discovered that polyolefin fibers are
obtained when a composition consisting of a polyolefin and a
diluent flows under special conditions and when the temperature
of the composition is within certain limits.
Therefore a preferred embodiment of the present invention
is a process for the manufacture of polyolefin fibers from a com-
position of said polyolefins dissolved in a diluent. Said processcomprises subjecting the composition to flow, at a velocity higher
than a critical value, in a tube or bundle of tubes, the tempera-
ture of the composition being within a range of critical tempera-
tures of said composition over at least a portion of the path of -
the tube or bundle of tubes and by separating the fibers from the
liquid diluent.
A further embodiment of the present invention is
apparatus for carrying out of the process of the invention, which
apparatus will be described in detail further below in the present ~-
application.
The invention is not limited to obtaining fibers from amacroscopically homogeneous liquid composition. The applicants
have also carried out the process by cooling a pclyolefin compo-
sition in a diluent containing furthermore fibers which are in-
.. . . .
soluble in the diluent. Thus, from a polyolefin composition
dissolved in cyclohexane and furthermore containing cellulose
fibers one can obtain an interlacing of polyolefin and cellulose
fibers. This particular application of the process for the manu-
facture of polyolefin fibers forms another object of the invention.
The mixtures of fibers thus obtained constitute still
another embodiment of the invention.
Finally, the use of the fibers or mixtures of fibers for
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the manufacture of papers in accordance with the known techniques
and the papers thus obtained also constitute embodiments of t~e
present invention.
In order to define the zone of critical -temperatures
which is characteristic for the proc ss of manufacturing polyole-
fin fibers in accordance with the invention, it is necessary first
of all to define the temperature of solution of a polyolefin in
molten state. -
By temperature of solution of the polyolefin in molten
state in a diluent is meant the temperature at which upon heating
a macroscopically homogeneous phase of the molten polyolefin in
the diluent appears. It is known that one does not have a true
solution at this temperature and that one would tend towards a :~
true solution by increase in the temperature, such increase being
furthermore accompanied by an increase in the viscosity of the
composition.
The temperature of solution of the polyolefin in
molten state in a diluent obviously depends on the polyolefin, on -
the diluent, and on the concentration of the polyolefin in the
diluent.
The range of critical temperatures is a range of
temperatures lower than the solution temperature previously de-
fined. It is the range of temperatures in which the polyolefin
remains in dissolved condition when the solution mixture is main-
tained at rest but precipitates when the mixture is subjected to
certain disturbances such as, for instance, shearing. The amp-
litude of the range of critical temperatures depends on the poly-
olefin, on the diluent, on the concentration of the polyolefin in
the diluent and on the velocity of flow of the mixture. The range
may extend o~er 1 to 10 C for solutions of polyethylene of a
density of more than 0.935, for example.
The critical phase of the process for the manufacture
of fibers is the flow under specific conditions of the composition
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at a temperature which must be within the range of critical
temperatures or posslbly slightly above the upper limit of the
range of critical temperatures when said flow is accompanied by
heat losses.
When it is desired to obtain only fibers, the
velocity of flow of the composition must be greater than a
critical value which depends on the nature of the polyolefin, on
the nature of the diluent, and on the concentration of the poly-
olefin in the diluent. Within this critical value of the velocity,
a mixture of polyolefin fibers and powder ls obtained. One
simple method is to effect this flow in a tube or a bundle of
tubes. The flow may be isothermal or nonisothermal. If it is
isothermal, the temperature of introduction of the composition
into the tube or bundle of tubes must be within the range of
critical temperatures. If the flow is nonisothermal, the tube or
the bundle of tubes then operates as heat exchanger, cooIing the
composition. The temperature of introduction of the composition -
may then be above the range of critical temperatures. In this
latter case it is advantageous for the cooling to be effected
homogeneously within the composition by the use of a bundle of
tubes. The composition may or may not flow at a velocity greater
than the critical value in a linear tube or bundle of tubes. The
length of the tube or tubes is not determinative for the obtaining
of the fibers. The "useful" length is the length at which the
composition is within the range of crltical temperatures.
The velocity necessary for the formation of the
flbers may be reached in several ways. A first manner consists in
initially impressing this velocity on the composition by means
of a circulating pump, the circulation line being of constant
diameter. A second method consists in obtaining this velocity
by a decrease in the cross section of the line downstream of the
pump circulating the composition. In this latter case, only the
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portion of the line which is of reduced diameter, and which may
be a tube or a bundle of tubes, will be the place of the forma-
tion of fibers. It should be noted that everything else being
equal, the larger the number of tubes which a bundle has, the
smaller the diameter of the tubes must be.
The temperature at which the fibers are formed is gener-
ally obtained by cooling from the temperature of solution of the
polyolefin in molten s-tate. This is particularly the case when
the polyolefin from which one starts is initially in the form of `-~
powder or granulates which are dissolved in a diluent.
The accompanying drawing is a schematic illustration of
the apparatus used in the process of the present invention.
Referring to the drawing, an enclosure 1 containing a
polyolefin in a diluent under a nitrogen pressure of 3 bars is
connected, via lines 2 and 3, to a straight tube 4 having ends A
and s. The tube 4, which is the place of formation of the fibers,
has a cross section~which is less than that of the lines 2 and 3.
Downstream of the tube 4, there is an enclosure 5 for ti~e recovery
of the fibers, which enclosure has a grid 6 on which the fibers -
deposit. The diluent is recovered in the lower portion 7 of the
enclosure 5. A part of the diluent recovered is recycled via the
line 8 while another part is forwarded, via the line 9, into the
enclosure 1 when the latter is used as a solution enclosure for
the polyolefin. The recycling through the line 8 can be eliminated .t..... '''.. '
when~the diluent recovered at 7 does not contain any polyolefin.
The lines 2 and 3 contain pumps, 10 and 11 respectively.
The pressure in the enclosure 5 is 3 bars. The loss of heat in -~
the tube 4 ~epends upon the geometry of this tube and the material
of which it is made. The formation of the fibers in the tube 4 ~ -
takes place in a quasi-isothermal manner. The
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temperature of the composition at the point A is therefore sub-
stantially the same as at the point B, which means that the
temperature of the composition at the point A is within the
region of critical temperatures. The enclosure 5 is advantageously
at the same temperature as the tube 4. The line 12 extending be-
tween the point B and the enclosure 5 may be eliminated, the tube
4 then discharging directly into the enclosure 5. Likewise, the
end A may be connected directly to the outlet of the circulating
pump 11. The carrying out of the process may require the use of
a cooler (not shown in the figure) in the path of the line 2 or
of the line 3 in the event that the temperature of the composition
at the point A, in the absence of such cooler, would be above the
upper limit of the range of critical temperatures and there is no,
or practically no, heat loss in the tube 4.
The enclosure 5 fulfills the function of receiving
the solution containing the fibers after their precipitation in
the tube 4, as well as the function of recovering these fibers
by filtration through the grid ~. However, it is possible to
carry out these two functions in two different enclosures -- a
first enclosure which receives the solution and the fibers which
it contains and permits the recycling of the solution to the
precipitation tube; a second enclosure, fed continuously or inter-
mittently, from the first enclosure via a line, effecting the
recovery proper of the fibers (for instance by filtration). The
filtrate recovered in the second enclosure is then sent to the ~-
polymer solution enclosure or is possibly recycled in the precipi-
tation tube. -~
In another embodiment of the process, the tempera-
ture of the composition at the point A is above the upper limit of
the range of critical temperatures. In this case it is necessary
for there to be heat losses in the tube or bundle of tubes where
the fibers are formed. This tube or bundle of tubes operates as
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a heat exchanger cooling the composition to a temperature within
the range of critical temperatures. In this case also the line
for the introduction of the composition into the tube or bundle
of tubes may possibly contain a cooler.
The process may also be carried out in intermediate
manner, that is to say in the presence of a tube or bundle of
tubes producing only a small heat exchange. In this case, the
solution will be introduced into the heat exchanger at a tempera-
ture within the range of critical temperature$ or very close to
the upper limit of said range.
When the tube or bundle of tubes acts as a heat ex-
; changer, the jacket in which the heat-removing fluid flows may be
formed of a single chamber or of several separate chambers fed
with heat-removing fluids at the same temperature or at different
temperatures.
The polyolefin subjected to the process of the in-
; vention may be polyethylene of a density of more than 0.935 ob-
tained by the lo~-pressure polymerization process and whose
molecular weight distribution may be very broad (for instance
polyethylene of a density of 0.950 and for which Mn is 8300 and
Mw is 300,000) or the molecular weight distribution of which is
narrower (polyethylene of a density of 0.960 and for which Mn
i5 11, 500 and Mw is 801000). Polyethylenes of very high molecular
weight may also be used. Crystalline polyolefins may also be ~
used such as polypropylene or polybutene. The copolymers of ole- -
fins may also be subjected to the process of the invention.
The diluent used may be a solvent, the solubility ~ -
parameter of which is preferably close to that of the polyolefin.
In the case of polyethylene, one such solvent is commercial hexane
or cyclohexane or mixtures of xylenes. However, the solubility
parameter of the diluent may also be substantially different from ; i
that of the polyolefin.
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The concentration of the polyolefin in the diluent
is a parameter which has an effect on the position and amplitude
of the range of critical temperatures. By way of example, in
the case of polyethylene of a density of more than 0.935, the
concentration of the polyolefin may vary between 0.5% and 10% of
the weight of the diluent.
One can operate with a higher concentration of poly-
olefin; however, the compositions become more viscous and the
mechanical energy which must be expended for the circulating of
the composition becomes substantial.
It is also possible to add soluble adjuvants to the
diluent, such as polyisobutylenes of low molecular weight or
polyvinyl alcohol. These adjuvants do not precipitate upon the
formation of the polyolefin fibers. The concentration of the
adjuvants may be between 0.1% and 50% of the polyolefins. These
adjuvants are added in order to obtain fibers which can be more
easily separated from each other.
The process of the invention makes it possible to
prepare fibers of a length of between 0.1 mm and 2 cm and of a
diameter of between 5~ and 200~. This last value does not
correspond to the diameter of an individual fiber obtained by the
process but to the diameter of bundles of individual fibers formed.
The fibers obtained by the process of the invention
may find numerous industrial applications. They may in particular ~-
be used for the making of non-woven sheets, or as aggregates for
adsorption of hydrocarbons or aqueous products. Furthermore, as
indicated above, the polyolefin fibers obtained in accordance
with the invention may be used alone or in mixtures with cellulose
fibers for the manufacture of different papers in accordance with
known techniques.
The invention is further illustrated by the follow-
ing examples, given solely by way of illustration.
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EXAMPLE I
20 g of polyethylene marketed under the trademark
"VESTOLEN 6016" having the properties d = 0.960, Mn = 11,500,
Mw = 80,000 are dissolved in an enclosure of a volume of 1 liter
at a temperature of 130C in 600 ml of cyclohexane, corresponding
to a concentration of 5~ expressed by weight. The enclosure is
connected, via a reciprocating pump, to a copper coil of a length
of 10 m and a diameter of 4 mm placed in a thermostatic oil bath ;
in such a manner that the flow in the coil is isothermal. The
temperature of the coil is therefore fixed. For a pumping rate
of 70 liters/hour (which corresponds to a maximum linear velocity
of the composition in the coil of 3 m/sec), fibers appear in the
composition while it passes through the coil when the temperature
of the compositlon at the entrance to the coil is between 82 and
78C. These two values of the temperature define the range of
critical temperatures.
~hen the temperature is above 82C, all other things
being equal, one does not note any precipitation of polyethylene
in any form whatsoever.
When the temperature is below 78C, all other things
being equal, there is noted the precipitation of a mixture of
fibers and powder, the proportion of powder being higher the
lower the temperature.
Within the same temperature range when the rate of
the pump is fixed at 35 l/hour (which corresponds to a maximum
linear velocity of 1.5 m/sec of the composition in the coil), the
fibers obtained are shorter, and they are obtained mixed with
~ : .
powder. The velocity is therefore below the critical value.
EXAMPLE Il
'
An apparatus similar to that described in Example I,
in which the copper coil of a length of 10 m is replaced by a
linear Teflon (trademark) tube of a length of 40 cm and a diameter
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of 1.5 mm, is fed with a solution formed of 2% polyethylene
(identical ~o that described in Example 1), 1% Oppanol B (trade-
mark for polyisobutylene of low molecular weight marketed by
B.A.S.F.~, and 97% commercial hexane. It is noted that the
range of critical temperatures extends from 93C to 97C.
EXAMPLE III
An apparatus similar to that of Example I, in which
the copper coil of a length of 10 m is replaced by a linear steel
tube of a length of 40 cm and a diameter of 2 mm, is fed by a
composition formed of 1% polyethylene (identical to that des-
cribed in Example I), 1% of cellulose fibers and 98% cyclohexane.
It is noted that the range of critical temperatures
extends from 78C to 82C, in which range an intermeshing of
polyethylene and cellulose fibers is obtained.
EXAMPLE IV
A composition formed of 1% polyethylene (identical
to that described in Example I), 0.5% cellulose fibers and 98.5%
cyclohexane is treated in accordance with Example III. The range
of critical temperatures is between 78 and 82C.
MPLE V -
In an enclosure of a volume equal to 2 liters, 110 g
of polypropylene mar~eted under the trademark "MOPLEN Q 30 P" and
having the following properties:
~Mn 28,000
-Mw 450,000
-proportion of atactic polypropylene 5.3%, are
dissolved at the temperature of 140C in 1.5 liters of heptane,
which corresponds to a concentration by weight of 5%. The enclo-
sure is connected, via a reciprocating pump having a rate of flow
of 70 l/hour, with a linear tube of stainless steel of a length :~
of 40 cm and a diameter of 2 mmO Fiber intermeshings are obtained
for the range of critical temperatures of 80 -to 88C.
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EXAMPLE VI
By means of a reciprocating pump of a rate of flow
of 70 l/hour, a 5% solution of polyethylene identical to that
described in Example I in commercial cyclohexane is passed into
a tube of a length of 90 cm and a diameter of 2 mm provided with `
an outer jacket formed of three independent successive chambers
of lengths of 20, 30, and 40 cm respectively. This device makes
it possible to circulate a fluid at a desired temperature in each
of the chambers constituting the outer jacket. The chamber whose
length is equal to 20 cm surrounds the initial part of the tubes.
The chambers of 30 and 40 cm in length surround the central por-
tion and the final portion of the tube respectively.
The formation of fibers is noted within a range of
critical temperatures of between 80 and 92C. The temperature of
the fluid circulating in the chamber surrounding the initial,
central and final regions of the tube being equal to 125C, 67C
and 67C respectively.
EXAMPLE VII
A 5% solution of the same polyethylene in an
industrial solvent having the composition:
; -49.4% normal hexane
-19 % 3-methyl pentane
-18.9% 2-methyl pentane
- 7.8% methyl cyclopentane, ~-
2,2-dimethyl pentane and
2,4-dimethyl pentane
- 4.9% miscellaneous
is passed into an apparatus identical to that described in
Example VI.
The formation of fibers is noted in a range of
critical temperatures of between 95 and 102C. The temperature
of the fluid flowing in the chamber surrounding the initial, ~ ;
central and final portions of the tube being equal to 200C,
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90C and 90C respectively.
EXAMPL~
.
Sheets of laboratory paper ("formettes") were
prepared using a mixture of cellulose fibers and polyethylene
fibers prepared in accordance with the invention.
Bleached coniferous Kraft pulp was beaten in the
laboratory to a degree of beating of 45 SR (degree Schopper
Riegler, AFNOR Specification NF-Q 50-003). To this pulp there
were added polyethylene fibers which had been previously dis-
integrated in the dry state. The composition obtained (60~polyethylene fibers; 40~ wood pulp) had an SR degree of 30 and
made it possible to produce formettes with a Rapid Kothern ~
apparatus, being careful not to aerate the suspension. After -
drying, these sheets were heat-sealed without pressure in an
oven at 136C for 15 minutes.
The physical characteristics of these sheets were
measured in accordance with the AFNOR specifications. The results -
are indicated in the following table, as compared with a ~-
composition of cellulose fibers of coniferous woods and broad-
leaved woods. They relate to formettes of 70 g/m2.
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