Note: Descriptions are shown in the official language in which they were submitted.
. :
.
106Z418
.
~ .
.. . . ~ .
.
Proc.ases h~ve b~en described for producing iibrids or
. fibrils of synthetic thermoplastic polymeric materials by flash-
spinning solutlons, emulsions or suspensions of the polymeric
1¦ materials under the actlon of a fluid in the gas or vapor pha3e
: i and at high speed.
. ~ By "~lash-spinning" i9 generally meant the process of
; ~ extruùing a solution, dispersion, emulsion or suspension of a
thermoplastic polymer in a liquid medium through an orifice under . .l pFessure and temperature aonditions such that instantaneous, or
1~ 1 ' ~
~'' ' . ' . ~ '` ~ ;
~ , ' . , .
~o6z~il8 -
` practically instantaneous, evaporation of the liquid medium
occurs in the extrusion ambient, resu1ting in the precipitation
of the polymer in the form of numerous fibrils connected to
each other to form a more or less continuous tridimensional
fibrous network having a surface area (specific area) greater
than 1 m2/g.
The flash-spinning of homogeneous solutions of thermo-
plastic polymers in organic solvents, of emulsions of the
polymers in solvents and non-solvents (such as water), or of
10 ` dispersions of the molten polymers in solvents and/or non-
solvents are described, for instance, in British Paten~s Nos.
891,943 and 1,262,531; in U.S. Patents Nos. 3,402,231,
3,081,519, 3,227,784, 3,227,794, 3,770,856, 3,740,383 and
3,808,091; in Belgian Patent No. 789,808, in French Patent
No. 2,176,858, and in German Patent (DOS) 2,343,543 (Kozlowski
et al) published March 21, 1974.
According to a more recent method, described in
Canadian Patent Application Serial No. 164,491, filed on
February 23, 1973, single ibrils of the kind described here-
inabove are obtained directly by subjecting a solution of a
polyolefin being extruded under "flash" conditions, to the
disrupting action of a high-speed gaseous jet having an angular
direction with respect to the direction of extrusion of the
polyolefin solution.
An analo~ous proces9, but in which the starting materiàl ~.
i~ a two-phase mixture~made up o a molten polymer and a solvent, ;
is disclosed in British Patents Nos. 1,355,912.and 1,355,913.
,
.
.
- 2 -
. '-~;"''~1 .
: ~ . ~.,;~ .
" ~ ,~,................................................................. ..
~624~8
` Finally, German Patent (DOS) No. 2,339,044 (Drake et
al) published February ~1, 1974 discloses a process for preparing
fibrils which consists in extruding a polyolefin solution at
high temperature and hitting the extruded solution by a fluid
jet at an angle lower than 30 and at particular speed ratios.
Among the processes available so far for obtaining
microfibers ox fibrils of synthetic thermoplastic polymers for
use in paper-making pulps, most suitable have proved to be the
processes in which the extruded polymer composition is hit by
a jet of gas or vapor disposed at an angle to the direction of
extrusion of the polymer composition. This is both because of
the simplicity of the apparatus required, and the possibility
of utilizing those processes to obtain microfibers or fibrils
of any thermoplastic polymer.
The possibility of using such process in commercial
practice in order to obtain fibrous products which are morpho-
logically suitable and competitive with cellulose fibers depends,
essentially, on the proper use of the fluid jet in relation to
the polymeric solutions, emulsions or dispersions employed.
In this connection, several operating methods have been proposed,
- one of which is described in the above-mentioned Canadian
; application 164,491 and consists in using the fluid in the form
.
of a jet coaxial with the nozzle through which the polymer
solution is extruded.
Another method is suggested in the aforementioned
~1 British Patent No. 1,355,913. It involves the use of two-phase
polymer/soIvent mixtures and consists in conveying the fluid into
,, ' . ,
. ~ : , ,
: . :
106Z418
I . .
a duct comprising, in the order stated, a convergent portion, a
¦ narrow portion and, optionally, a divergent portion, extruding the
two-phase mixture into either the convergent portion or the
¦ narrowed portion of the duct, and causing impact between the
1 fluid jet and the two-phase mixture in either of those portions
¦! of the duct, depending on which is the portion into which the
two-phase mixture is extruded.
Il The results of both the process of the pending applica-
I! tion and of the British Patent are unsa~isfactory from the
Il, economical point o~ view, due to the low yields of fibrous product
I obtained with respect to the consumption of fluid. The
... ,,~.~,j ~,~
uneconomical aspects of those methods ta~d~ to increase when
¦ higher speeds of the fluid are employed, in particular when the
!I fluid is steam, whereas it would be profitable to use the fluid
15 ll at high speeds.
., ,~. .
¦l THE ~RESENT INVENTIO~
One object of this invention is to provide an improved
¦ process for obtaining the microfibers or fibrils in which the
I fluid which hits the extruding polymeric material is used at hlgh
speed but which is free of the aforesaid disadvantages.
This and other objects are achieved by the present
invention in accordance with which considerably improved yield~
of fibrous product made up of microfibers or fibrils having ! ;
suitable characteristics, especially as regards homogeneity, by
employing the fluid jet under particular conditions, are obtained.
. .
1, ' . . , . '' :
-4-
:lC)624~3
The particular conditions consist in causing the fluid
jet to expand through a nozzle or duct of the convergent-
divergent type and in extruding a polymer solution, emulsion
or dispersion in flash conditions at an angle toward the fluid
jet in expansion in the divergent portion of the nozzle.
Thus, the invention provides a process for producing
microfibers or fibrils of synthetic polymers for use in making
paper according to conventional paper-making techniques, in which
solutions, emulsions or dispersions of thermoplastic synthetic
fiber-forming polymers in a liquid medium are extruded through
a nozzle, under conditions such that instantaneous vaporization
of the liquid medium occurs in the ambient of extrusion, and the
extruded material is impacted in said ambient of extrusion by
a high-speed jet of gaseous fluid having an angular direction
with respect to the direction of extrusion of the polymqric
material, characterized in that the gaseous fluid is expanded
initially through a nozzle of the convergent-divergent type
and the polymeric material (solution, emulsion or dispersion)
is extruded inta the divergent portion of said nozzle.
In a presently preferred embodiment of the invention,
the po~ymer in the liquid medium is extruded into the zone of
the divergent portion of the convergent-divergent nozzle where
,i .
the fluid jet reaches the maximum speed consistent with the
thermodynamic conditions of the fluid upstream of the divergent
portion of the nozzle.
Additional preferred conditions consist in expanding
"
the gaseous fluid in such a way that it may reach its maximum
,,
.,. . ' .
~, :
,~ , .
~ ' ' ' .
! - 5 D
~',;~ j~ ' ' . . .
`~
` -ll
6Z4~8
speed at, or in proximity to, the terminal zone of the divergent
portion of the nozzle, and in extruding the polymer solution,
emulsion or dispersion into such terminal zone.
¦ By the term "convergent-divergent nozzle", we mean any
! type of nozzle or pipe comprising, in the order stated, a conver-
gent portion, a narrowed portion and a divergent portion. The
l section of the narrowed portion of such a nozzle is also defined
I as the "critical section" when a compressible fluid is expanded,
the pressure in the narrowed portion ("critical pressure") being
l higher than the pressure existing downstream of the divergent
Iportion of the nozzle.
¦ An example of a nozzle of the convergent-divergent type,
¦usually employed for bringing about the above-described conditions
¦l in a gaseous fluid, and which can be used also in the practice of
1 this invention, is the nozzle known as a "De Laval" no~zle.
¦ The present process can be used to obtain the microfiber~
or fibrils from homogeneous polymer solutions, as well as from
¦ dispersions, emu~sions, suspensions and, in general, heterogeneous
: I mixtures of polymer and liquid solvents and/or non-solvents.
While, for obtaining fibrils which are of more uniform
and suitable dimensions, it is preferable to extrude the polymeric
¦composition in proximity to the terminal section of the divergent
,portion o the nozzle, in practice the polymeric composition may
be extruded into any section of said divergent portion.
For similar reasons, and as aiready mentioned, it i~
¦preferred to have the fluld jet, in proximity to the terminal
section of the divergent portion of the nozzle, at the maximum
., . .
~ ~ -6-
,,~ , ,: . ' . ,.. '
s .... ~ ~ ... .. . . .
~ 106Z~8
speed attainable compatibly with its temperature and pressure
conditions upstre~m of the narrowed nozzle portion. This can be
achieved by suitably dimensioning the nozzle as a function of the
initial thermodynamic state of the fluid utilized and of the
downstream conditions.
The dimensions can be obtained by simple thermodynamic
calculations or, optionally, by direct experiments, which is to
say empirically.
~¦ By operating according to the modalities described
,I herein, it is possible, a~ong~other things, to utilize the fluid
i jet at very high speeds, ranging from the velocity of sound in the
critical section of the nozzle to values several times higher in
the terminal portion thereo.
There is an optimum velocity of the fluid jet for each
j type of polymeric solution, emulsion or dispersion, depending on
; ¦ the polymer and the solvent or liquid carriers employed, as well
as on the thermodynamic characteristics of the given solution,
l I emulsion or dispersion.
¦ Generally, it is preferable to use several extrusion
l~ nozzles for the polymer composition, circularly arranged around
the divergent portion of the convergent-divergent nozzle for the
gaseous fluid.
The accompanying drawing illustrates a device which can
be used in practicing the invention. ~n the drawing, the ~et of
fluid runs, in the direction indicated by arrow (6) through
convergent portion ~2), narrowed portion ~3) and divergent portion
~4) of nozzle (1). ~he polymer composition is extruded through
' . .
~ _7_
.. , ... , . - . :
: ll` .
~l ~
~0~;2~18 :::
nozzles (5) in the di~ection indicated'by arrow (7) and leading . ~ '.
. into the divergent portion (4) of nozzle (1). Nozzles ~5) may
. have a uniform diameter or, although not necessarily, may have a
larger diameter in proximity to divergent portion ~4)'in order to :
permit a partial expansion of the polymer composition before it is
impacted by the fl~id jet.
~owever, a surprising aspect of the improved process of
this invention is that no preliminary expansion of the polymer ::
solution, emulsion or dispersion is necessary for obtalnlng sult- :~
able fibrous products. ::
In the device illustrated in the drawing, nozzles (5)
are arranged to form an anyle of about 90 with respect to the
longitudinal axis of nozzles ~1). Nozzles ~5) may also be arrang- . :~.
ed at a different angle with respect to said axis, the angle being
preferably comprised between about 5 and about 90.
Any gaseous or vaporous'fluld may be used, such as those
. described in the above mentioned appllcatlon Serlal No. GOG,4;3,' including the solvents or llquid media contained in the polymer .: .
., composition being extruded, in vapor form, provided they are in .
' 20 such condition as to be a~. a temperature lower than the dissolu-
., tion and/or softening temperature of the'polymer/resldual solvent
.l system at the time they hlt the extrudate.
Steam, and particularly dry steam, is preferably employed ~ , '.
~:3 as the impactlng fluid. n-hexane is an example of a solvent whlch,
in the form of superheated steam, ls ,advantageously utlll2ed as
~:j . , . the flu1d ~et. ~ :
''`I ' : : ` . ' ' -'8 - ' ' .'
.,, . , ' . ' ~ , ~
r: ;.- :-
s.. t~
~L~6Z~3;8
. . , : ,.
The present process can be used to obtaln the mlcro-
flbers or flbrlls from any fiber-formlng, synthetic, thermoplastic
polymer, such as homopolymers of olefins, acrylonltrile, acrylates,
vinylchloride, vinylacetate, styrene, copolymers o~ such monomers
with each other, and mixtures of such homopolymers and copolymers.
The following examples are given to illustrate the in-
vention in more detail and are not intended to be limiting.
EXAMPLE 1
This example relates to the preparation of polyethylene :
fibrils starting from a solution of the polymer in n-hexane,
using dry saturated steam as fluid and operating with a device of
the kind shown in the drawlng.
To this purpose, a solution contalning 100 g of high
density polyethylene (M~I. = 4.5) for 1 liter of solution was
j 15 used, at a temperature of 180 C and at a pressure differ~nce wlth
respect to the outside of 14 atmospheres.
At the inlet of the nozzle's convergent portion the
steam employed has a pressure of 18 ~gjcm gauge and a temperature
of 205C. The steam flow-rate was 300 Kg/h.
The nozzle exhlbited a clrcular narrowed sectlon ~cri--
tlcal) having a diameter of 6.5 mm, and a maximum ~termlnal~ sec-
tlon, ln the divergent portion, having a 15.42 mm dlameter. The
l dis~ance between the narrowed section and the terminal sectlon
i was 31.8 mm.
Undes these conditlons the steam pressure, in proxlmlty
to the termlnal ection o~ the divergent portlon, was sllghtly
,! _ 9 _
.. .. . -
1062~ï~3 ` :;
~i.e. few mmH~) higher than the atmospheric pressure, and the
steam had the maximum speed consistent with its conditions up-
stream of the critical section, and equal to 900 m/sec. The
steam expansion corresponded to an enthalpy drop of 115 Kcal/Xg.
The polymeric solution was fed, at a total flowrate of
960 ~g/h, through 8 cylindrical nozzles arranged symmetrically
around the terminal section of the divergent portion of the
convergent-divergent nozzle, each of them having a dlameter of
2 mm.
After a 1-hour operation, 120 Kg of fibrils having a
length between 3 and 4 mm, an apparent diameter of 40 microns and
a surface area of 7 m /g were obtained.
The steam consumption was 2.5 Rg per Kg of 1brils.
I EXAMPLE 2
A solution of polyethylene in n-hexane like that of
e~Xample 1, under the same temperature, pressure and hourly
capacity conditions, was utilized.
Steam at a pressure of 2.7 Kg/cm gauge, superheated up
to a temperature o~ 200 C and at a flowrate of 300 Kg/h wa3
employed as fluid.
The devlce used was of the kind illustrated in the ~ ;
drawlng, having a nozzle characterlzed by a crltlcal section
diameter of 7.3 mm and by a maximum section dlameter, in the
i nozzle's divergent portion, of 8.7 mm, in which maximum section
^,, 25 the steam was in the superheated state, at a pressure slightly
hlgher than the atmospheric pressure and at lts maximum velooity
:~ ! 10
,.,,,1, .~ , ' '. '
106Z4~8
., ~ .
of 607 m/sec. The distance between mlnimum and maximum section
was 22.4 mm. 8 nozzles for the extrusion of the polymeric solu-
tion, having a diameter of 2 mm, were used.
After a 1-hour operation, 120 Kg of fibrils having a
length of 4-5 mm, an apparent diameter of 40 microns and a sur-
face area of 8 m /g were obtained; the steam consumption was
2.5 Kg per ~g of fibrils.
EXAMPLE 3
This example illustrates the preparation of fibrlls
starting fro~ an emulsion formed by a solution of polypropylene
in n-pentane and water. The polypropylene used had a M.I. = 10.
The concentration of polypropylene in the emulslon was 50 g for 1
liter of emulsion. The weight ratio n-pentane/water in the
emulsion was ~ 1.
~l 15 The device used was of the kind shown in the drawing,
.fi having a nozzle i'or the fluid characterized by a critlcal sectioni diameter of 11.5 mm, a terminal maximum section di~meter, in the
nozzle's divergent portion, of 15.7 mm, and by a distance ~etween
critical and maximum section of about 21 mm.
;~ 20 The emulsion was extruded, at a temperature of 155C
and pressure of 21.4 Kg/cm2 gauge, through 8 cylindrical nozzle~
arranged symmetrically around tha terminal ~maxlmum) section of
the convergent-divergent nozzle, each of them having a dlameter
of`2 mm.
2S The emulsion was fed through the 8 cylindrical nozzles
at a total flowrate of 2,200 Kg/h. The steam flowrate was 300
''', . ' .
. ~;. ' ~
106Z~18
Kg/h. Dry saturated steam was used as fluid, havlng, at the lnlet
of the nozzle's convergent portion, a pressure of 6 Xg/cm gauge
and a temperature of 200 C.
Under these conditions the steam pressure, at the terml-
nal section of the divergent portion of the nozzle, was slightly
higher than the atmospheric pressure, and the steam was at its
maximum speed consistent with its conditions upstream of the cri-
tical section, and equal to 715 m/sec.
After a 1-hour operation, about 150 Xg of fibrils having
a length of 1.5 - 2.5 m~, mean ~apparent) diameter of 20 microns
and surface (specif~c) area of 4.1 m /g, were obtained.
he steam consumption was 2 Kg/Kg of flbrils.
EXAM2LE 4
This example illustrates the preparatlon of fibrlls
starting from a two-phase polymer composition, wherein one phase
is formed by molten polyethylene ~M.I. = 5) which contalns liquid
n-hexane, and the other phase ls formed by liquid n-hexane which
contains polyethylene ln the dissolved state, the former phase
being homogeneously dispersed into the latter phase. Such a two-
~ 20 phase compasition was obtained by heating a polyethylene solutlon
; ln n-hexane, contalnlng 100 g of polymer for 1 liter of solutlon,
at a temperature of 200 C and under a pressure of 17 Xg/cm2 gauge.
Under such temperature and pressure condltlons, the two-
` phase compositlon is extruded through the 8 nozzles of the device
described in Example 1, wlth a total flowrate of 1,200 Xg/h.
Steam at a temperature of 205C and at a pressure of 18 Kg/cm
''.~' ., . . . , ...
;~ _ - 12 -
, . , . " '
--
' ` . :,11 ' .' . ' '
1 ~06Z418 . '~ .
gauge at the inlet of the nozzle's convergent portion was used as . ~ .
fluid, at a flowrate of 300 ~g/h.
The pressure value of the steam at the terminal diver-
gent portlon of the nozzle, where impact with the extruded po-
lymer composition occurred, was slightly higher than the atmo- .:
spheric pressure, and the steam was at its maximum velocity of
900 m/sec.
After a 1-hour operatlon about t50 Kg of fibrils, hav-
. ing length of 2 - 2.5 mm, apparent diameter of about 25 microns
and surface area of 8 m /g, were obtained.
~ he steam ~onsump lon was 2 ~g ~g of fibrl}~.
''' . ' ~. . `.'
: . . .
~',' .
''' ' ~' ' ' ' . .
. . . - 13.-
. I .
.
, 11 , .
1.
