Note: Descriptions are shown in the official language in which they were submitted.
~106~Z~;~
This invention relates to a process for the manufacture of
fibrids of polyolefins by dissolving a polyolefin in an organic
solvent under pressure and at a temperature which at standard
pressure is abovetheboiling point of the solvent, and flashing the
solution by passing it through an orifice into a space which is at
a lower pressure.
Fibrids of polyethylene are produced, for example, by
dissolving polyethylene in an organic solvent at an elevated
temperature under pressure and then flashing the solution through a
nozzle. The primary products are coherent masses of fibers or
plexus filaments (German Published Application No. 1,290,040
of February 27, 1969, to E.I. Dupont de Nemours & Co.) or fibrous
gels (German Published Applications No. 2,117,370 of October 28,
1971, to Crown Zellerbach Corp.; No. 2,227,021 of January 4, 1973,
to Crown Zellerback International Inc. and No. 2,237,606 of
Febrùary 15, 1973, to Crown Zellerback Corp.).
In order to obtain fibrids from the ple~us filaments or
the coherent masses, it is first necessary to cut these into staple
lengths and then to dlsentangle them in liquids by the action of
highshearing forces to obtain discrete fibrids. The fibrids
liberated in this manner are relatively short and show only a low
degree of ~ibrillation.
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The ~ibrous gels contain a high proportion of solvent
and turn into hard crumbly masses, no longer of a ~ibrous
nature, when left in the air. The fibrous gels shrink and
stick together when left in the air.
However, discrete fibrids may be obtained from the
fibrous gels if the solvent-containing gel is subjected to thé
action of mechanical shearing forces in a liquid medium. The
liquid medium conslsts of solvent and/or dispersion-containing
water.
On removal of the liquid medium, the residual solvent
and/or water is removed from the disentangled fibrids by
evaporation or by steam distillation. However, this must be
effected in the presence of surfactants such as polyhydroxyl
compounds (German Published Application 2,237,606), and, possibly,
anti-foaming agents, as the heat treatment will otherwise cause
the fibrids to agglomerate and lose their fibrous characterr
The solvent-free fibrids contain a high proportion of auxiliaries
and therefore have only restricted application. For example,
when sheets of paper àre prepared from polyolefin fibrids
obtained in this manner, fiber bonding and the initial wet
strength of the sheets are impaired by the presence of surfactants
and anti-foaming agents.
In another well-known process, the solvent residues
are removed by solvent exchange. In this method, the solvents,
primarily cyclohexane and n-hexane, are replaced, in a first
extraction stage, by some other solvent, such as isopropanol,
which is then washed out in a second extraction stage by means
of water. This method is expensive and time-consuming.
The fibrids obtained by the prior art processes
cannot be disentangled, for example with the aid of an opener,
willey, card or spiked rolle~
It is an object of the invention to modify the process
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described above in such a manner that the drawbacks of the
prior art processes are obviated. It is desired to produce,
directly, fibrids which are morphologically similar to cellulose
fibers. This means that they
- ~692~L
should have a high degree of fibrillation, should have a high
specific surface area, should not agglomerate on evaporation of the
solvent, should not (substantially) shrink when left in the air and
should be capable of being isolated in the absence of auxiliaries.
In accordance with the invention, there is thus provided a
process for the manufacture of discrete fibri'ds of polyethylene
having lengths of l to 50 mm and thicknesses between 2 and 30 ,um,
t~hich comprises:
(a) dissolving in a pressure vessel polyethylene, obtained
by low-pressure polymerization of ethylene, in a solvent
which is a mixture of pentanes and a naphtha cut boiling at 25 to
140C and containing pentanes in an amount of from 5 to 50% by
weight, the pentanes being selected from the group consisting of n-
pentane, isopentane, cyclopentane and neopentane;
(b) maintaining the vapor pressure in the pressure ~essel
at 4 to 60 atmospheres and maintaining the temperature of the poly-
ethylene solution in the pressure vessel at temperature of 80 to ~ '
250C and above the boiling point of the solvent at standard
' pressure;
(c) passing the polyethylene'solution from the pressure
vessel through an orifice into a space maintained at lower
temperature and pressure than those in the pressure vessel~
(d) 1ashing off the solvent in the space from the
solution passed through the orifice to produce a tangled mass of ' '
polyethylene fibrids, the amount of pentanes in the solvent further~ '
being sufficient to cause the polyethylene to separate in form of ' ''
' ~ discrete fibrids upon the flashing off of the solvent in the space;
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(e) drying'the resultant polyethylene fibrids. '
30~ Unlike the prior art processes, this method produces '~
individual fibrillated fibrids. They are produced as a tangled mass.'
Surprisingly, the polyethylene fibrids of the invention do not
agglomerate when, for example, dried at an elevated temperature or :~
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when the residual solvent is distilled off from an ~queous
fiber suspension.
The immediate product is a fiber which is no long,er
swollen by solvent. No fibrous gel is formed~
The polyethylenes used in the process of the invention
are obtained by the well-known low-pressure polymerization of
ethylene. Suitable partially crystalline ethylené polymers have
an X-ray crystallinity of more than 5% w/w at a temperature of
25C. We prefer to use polyethylenes having densities of from
0.915 to 0.965 g/cm3.-The molecular weight of the polyethylenes
- is characterized by their melt index, the maximum molecular weight
being indicated by a melt index of 0.01 g/10 min (as measured at
a temperature of 190C and a load of 21.6 kg), and the minimum
molecular weight bein~ indicated by a melt index of 100 g/10 min
(190C/2.16 kg). The melt index is determined by the method
laid down in ASTM D 1238-65 T. The polyethylenes are commer-
cially available, the molecular weight of which is character-
ized by an intrinsic viscosity of, preferably, from 1.5 to 8
dl/g ~as measured in decalin at 130C).
Also suitable are copolymers of ethylene with other
ethylenically unsaturated compounds, for example copolymers~of
.
ethylene and propylene, copolymers of ethylene and butylene, copo-
lymers of ethylene and 4-methylpentene-1 and copolymers of ethy-
lene and vinyl esters derived, for example, from saturated carbo-
xylic acids of from 2 to 4 carbon atoms, copolymers of ethylene
and acrylates of from 1 to 3 carbon atoms, copolymers of ethylene
and methacrylates of from 1 to 8 carbon atoms, copolymers of
ethylene and fumaric acids, maleic acid, itaconic acid and their
esters, and copol~mers containing polymerized units of acrylic
acid and methacrylic acid. Particularly significant are copolymers
of ekhylene and vinyl acetate, copolymers of ethylene and n-,iso-
or tert.-butylacrylate, copolymers of ethylene and acrylic acid
and copolymers containing polymerized units of 2 or more of said
4 _
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69Z64
ethylenically unsaturated comonomers, for example comonomers
of ethylene, acrylic acid and vinyl acetate and comonomers of
ethylene, acrylic acid and tert.-butyl acrylate. It is, of course,
also possible to produce fibrids from mixtures of various polymers,
for example from a blend of high-pressure and low-pressure poly-
ethylenes at a ratio of 1:1 or a blend of 80% of high-pressure poly-
ethylene and 20~ w/w of an ethylene-vinyl acetate copolymer having
a vinyl acetate content of 15~ by weight. Usually, the ethylene
copolymers contain up to 50~ w/w of one or more comonomers,
preferably from 5 to 40~ w/w of comonomers.
According to the invention, the solvent used for the poly-
olefins is a solvent mixture containing pentane. For the purposes
of the present invention, we mean, by pentane, all isomers of `
pentane such as n-pentane, isopentane, cyclopentane and neopentane.
Use will usually be made of an isomeric mixture, for example a
mixture of n-pentane and isopentane, although pure n-pentane, iso-
pentane or neopentane may of course be used.
The solvent mixtures contain at least sufficient pentane
to cause the polyolefin to separate in the form of discrete fibrids
when the homogeneous solution is flashed in a space which is at a
lower temperature. Suitable solvent mixtures are obtained by adding
pentane to naphtha cuts boiling at from 25 to 140C. Particul~ ly
advantageous are ligroin (b.p. 30 to 60 C) and low-boiling naphtha
(b.p. 55 to 95C). Mixtures of said solvents may also be used if
desired.
In order to obtain fibrids from the polyolefins, the
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latter are dissolved in an organic solvent. The solubility of the
polyolefins in said organic solvent is greatly dependent on the
temperature. In order to obtain a highly concentrated solution -
the polyolefin :is preferably dissolved at atemperature which is ~
above the boiling point of the solvent used. It is therefore `
necessary to produce the polyolefin solution in a pressure vessel.
For examplè, this may be stirred pressure tank, or the polyolefin
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may first be melted in a screw machine, e.g. a twir.-shaft screw
kneader, the molten polyolefin then being mixed with the solvent
under pressure. In order to obtain fibers from the polyolefin
solutions in accordance with the present invention, the concen-
tration of the polyolefin in the solution may be fr~m 0.5 to 30
and preferably from 10 to 25% by weight.
- The amount of pentane required in the sol~lent mix-ture is
dependent on the molecular weight and molecular weight distribution
of the polyolefin used, on the solvent action of the solvent used
10 and on the processing conditions. The required amount of pentane
in the solvent mixture may be readily determined, for each poly-
olefin, by simple tests in which, for example, polyethylene is
dissolved, with heating, in various naphtha-pentane mixtures and
observations are made to discover the mixtures from which the
polyethylene no longer separates in a gelled condition. Suitable
naphtha-pentane mixtures contain
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from 5 to 50% and preferably from 10 to 30% by weight of pentane.
In order to obtain maximum concentrations of polyolefin in the
solution, it is necessary to employ those solvents since they
are very good solvents for the polyolefins.
According to the invention, the polyolefin solutions
are generally prepared in such proportions that the vapor
pressure above the mixture is from about 4 to 60 and preferably
from 10 to 20 atmospheres at ternperatures of from 80 to 250C
and preferably from 100 to 180C. However, the solution may be
prepared at lower temperatures and/or under inert gas pressure,
for example nitrogen pressure of up to 60 atmospheres.
The homogeneous polyolefin solutions are then flashed
by passage through an orifice, for example a nozzle or a tube,
into a space which is at a lower pressure. Preferably, the
polyolefin solution is flashed into a nitrogen-filled chamber.
The pressure in that chamber may be atmospheric or subatmospheric.
Alternatively, however, the homogeneous solution may
be flashed into a container containing a precipitant such as the
same solvent or solvent mixture as that in which the-polyolefin -
is dissolved. Alternatively, the space into which the homogene-
ous solution is flashed may, if desired, be filled with water or
an organic solvent known to be a non-solvent for the polyolefin
used.
Suitable non-solvents (precipitants) are for example
naphtha cuts, pentane, water, acetone, methylethylketone,
methanol, isopropanol and n-hexanol.
The orifice through which the homogeneous solution is
flashed may have any desired cross-section and any desired
geometrical shape. If, for example, a cylindrical tube is used,
the internal cliameter of said tube can be, for example, from 1
to 20 and preferably from 3 to 10 mm.
If the homogeneous solution is flashed, for example,
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264
- into a space ~illed with one of the above liquids acting as
precipitant, a constant level of, liquid may be maintained
above the outlet of the tube through which the solution is
passed. Flashing of the pressurized polymer solution is
preferably carried out isothermally with evaporative cooling,
the excess heat being removed by means of a cooler. The
resulting slurry of fibrids is adjusted, if necessary, to a
different density, for example, one at which the product may be
hydraulically transported, by the addition of further amounts
of the solvent in which the polymer is dissolved.
In another embodiment of the process of the invention,
the polyolefin solution is flashed by passage into a cylindrical --
chamber either tangential~y or centrally thereto. This chamber
is at the top of a vertical tube, down which the ~ibrids fall
when the solvent has evaporated. The solvent vapors released
by the flash are condensed by cooling. The fibrids formed
by the flash are dried by means of warm nitrogen which is passed
countercurrently through the tube arrangement. Virtually
solvent-free polyolefin fibrids are discharged at the bottom
of the tube.
If, in the process of the invention, a mush of fibrids
is obtained the fibrids are substahtially separated from the~
solvent for example by evaporation, filtration, centrifuging
and suction or pressure filter~ing. The solvent may be immediately
re-used.
The fibrids of the invention may be disentangled
immediately after drying by combing, brushing or picking. The
fibrids thu9 obtained are free-flowing and transportable. They
show high values of specific surface area, these being from
about 10 to S0 m2/g (as measured by the BET-method by nitrogen
adsorp~ion). The lengths of the fibrids are generally~from 1
to 5 mm and their thickness is between 2 and 30 fum. ~
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The main advantage of the process of the invention
is that it is no longer necessary to disentangle the coherent
mass of fibrids or a gel by mechanical means. It is thus no
longer necessary to add dispersing or stabilizing auxiliaries
or an additional solvent fo:r solvent exchange in order to
obtain discrete solvent-free fibrids. Another advantage of
the process of the invention is that the fibrids
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may be further processed immediately or once they have been trea~ed
with an agent sui~able for the purposa in hand.
The tangled mass of polyDlef'in fibrids of the invention may be
used, for example, for the manufacture of paper or textile-like webs.
To manufacture paper, the fibrids are suspended in, say, water and
the aqueous suspension is processed in a paper machine to form sheets
of paper. Sheets of paper may alternatively be prepared from mixtures
of the polyolefin fibrids and cellulose fibers. The two types of
fibers may be blended in any desired proportions. For the preparation
of the aqueous suspensions of polyolefinifibrids, disparsing agents
are used in amounts of up to 2% by weight, based on the dry weight
of th~ polyolefin fibrid~. Suitable dispersing agents are for example
melamine-formaldehyde polycondensates prepared by polycondensation
of melamine, formaldahyde and aminocarboxylic acids or alkali metal
salts thereof in aqueous solution. Another suitabla dispersing agent
is an anionic protective colloid, which is also used in amounts of
up to 2% by weight, based on the dry weight of the polyolefin fibrids.
Suitable anionic protective col~loids are for example condensates of
formaldehyde and the sodium salt of ~-naphthalene sulfonic acid,
polycondensates of urea, formaldehyde and the sodium salt of phenol
sulfonic acid, urea-formaldehyde polycondensates which have been
modified with sodium bisulfate or melamine-formaldehyde polyconden-
sates which have been modified with sodium hydrogen sulf~te, alkali
metal salts of carboxymethyl cellulose, copolymers of maleic acid
and vinyl isobutyl ether and ammonium salts of copolymers of styrene
and acrylic acid.
Paper webs produced with the polyolefin fibrids of the invention
are distinguished by good fiber bonding and high dry and wet strength.
The high degree of fibrillation o~ ~he fibrids may be deter-
mined, for example, by assessing the freeness by the Schopper-Riegler ~;
mathod ~Korn/Burg~taller, ~IHandbuch der WerkstoffprUfung~, 2nd
adition, 1953, Vol. 4, "Papier- und ZellstoffprUfung~, pp. ~88 et
seq., published by Springer-Verlag). To carry out this test, the
69264
fibrids must be treated with dispersing agents and converted
to an aqueous suspension of constant density (2 g/l at 20C.
That amount of water is determined which is retained by the
suspended fibrids under specific conditions. The retained
amount of water ~Schopper-Riegler, SR) is greater, the higher
the degree of fibrillation of the fibrids. For example, the
Schopper-Riegler values of fibrids of linear polyethylene of
the invention are from 15 to 30"SR.
The invention is further described with reference to
the following Examples, in which the parts are by weight.
EXAMPLE 1
In a pressure vessel provided with a stirrer, 14 parts
of a linear polyethylene having a density of 0.96 g/cm3, a melt
index of 4.5 g/10 min (190/2.16 kg) and a melting point of
130C are dissolved in a mixture of 51.6 parts of low-boiling
naphtha (b.p. 65 to 95C) and 34.4 parts of pentane consisting
of 80 parts of n-pentane ~nd 20 parts isopentane, at 165C.
The autogenous pressure is from 18 to 20 atmosphares gage.
This solution is then passed through a pipeline having a length
of 120cm and an internal diameter of 4 mm to enter a cylindrical
chamber tangentially, in which the solution is flashed in the
precipitant contained in the chamber, this being the same solvent
mixture as that in which the polymer is dissolved. The outlet
orifice of the tube, through which flashing occurs, is below
the surface of the liquid. The liquid boils under reflux,
excess heat being removed via a cooler. The mush of fibers is
continuously discharged by way of an overflow. The diameter
of the flash chamber is 30 cm and its height is 50 cm, the
overflow being provided so as to give a constant level of liquid `
,
of about 15 cm.
The mush of fibrids is substantially freed from
adhering solvent by filtration. The residual solvent is
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~ 926~
removed in a dryer by means of a stream of nitrogen at a
temperature of from 40 to 45C. There is obtained a soft loose
fibrous product (bulk density 18 gji), which is opened out on
a carding machine to a product having the nature of cotton
wool and having a bulk density of 10 g/l. The
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langth of fibrids is from 5 to 25 mm ar.d their thicknes~ is from 3
to 6 /um. The specific surface area is 11.2 m2/g and the degree of
fibrillation is found to ba 24SR.
EXAMPLE 2
14 parts of tha linear polyethylene used in Example 1 are melted
in a twin-shaft worm kneader. At a point one third of the way along
the working portion of the extruder there is added, by means ~f a
met~ring pump, a mixture of 43 parts of naphtha (b.p. 65 to 95C) and
43 parts of pentane consisting of ao parts of n-pentane and 20 parts
of isopentane The pressure measured at the head of the extrudar is
about 25 atmospheres gage. The polymer solution is passed through a
- tub~ having a length of 50 cm and an internal diameter of 6 mm to be
relaxPd in a cylindrical chamber as described in Example 1 and which
it ~nters tangentially. The flash chamber is ~illed with the same
solvent mixture as ~hat in which the polymer is dissolved. The
process is continued as described in Example 1.
There is obtained a soft loose fibrous ma~s (bulk density 15 gil)
which may ba opened out to a free-flowing fibrous product by combing
`~ and picking by means of a roll provided with fine taeth. The fibride
`~ hava a length of from 5 to 30 mm and a thickness of about 5 /um. The
specific surface area was found to be 14.3 m2/g. The Schopper-Riegler
value is 22SR.
EXAMPLE 3 ;
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~ xample 1 is repeated and the same starting materials are used
to produce a polyethylene solution in a mixture of naphtha and
pentane, which solution contains 15% w/w of polymer. This solution
is held at 165C under a pressure of 18 to 20 atmospheres gage. The
solution is flashed through a pipe having a length of 5 m and a
diameter of 6 mm, ~he solution passing tangentially into a cylindri-
cal chamber havin~ a diameter of 3 m and a height of 1 m. This
chamber is at the top end of a ~artical tube having a diameter of
3 m and a length ofi 6 m, which tube i~ cooled. The solvent relea8ed
by tha flash condensas on these cooling surfaces. The fibrids fall
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~69Z64 o.z. 30,284
down a concentric perforated inner tube having a diameter of 2 m.
Nitrogen having a temperature of about 60C is passed countercurrently
through the tuba arrangement, at the bottom of which the fibridS are
dischargad. The fibrids are loose and soft and have a bulk dansit;y of
15 g/l and are virtually free from solvent. Their lengths are ~rom
3 tO 25 mm and they have a thicknass of 5 /um. The fibrids have a
specific surface area of 10.2 m2/g and give a Schopper-Riegler value
of 21SR.
EXAMPLE 4
Example 1 is repeated and 6 parts of polyethylene are dissolved
in a solvent mixture of 27 parts of cyclohexane and 67 parts of
pentane consisting o~ 80% w/w of n-pentane and 20% w/w of isopentane,
at 165C. The autogenous pressura is about 10 atmospheres gage. This
solution is relaxed as described in Example 1, the liquid precipitant
being the same cyclohexane-pentane mixture, this boiling under reflux
at $rom 40 to 45C. The mush of' ~'ibars i3 subs~antially freed f`rom
adhering solvant by filtration. The residual solvent is removed in a
dryar by means of a stream of nitrogen having a temperature of f'rom
40 to 45C. There is obtained a soft loose ~'ibrous product having a
bulk density o~ 25 g/l. The lengths of the fibrids range from 2 to
20 mm and their thicknesses ~rom 3 to ~ /um.
COM~ARATIVE EXAMPLE
A linear polyethylene having the physlcal properties stated in
,~ ~xample 1 and pro~uced by po}ymerization in solution ~n cyclohexane
~, is diluted with cyclohexane at 1~5C until a solution iB obtained
which contains 3% w/w of polymer homogeneously dissolved therein~ A
pressure of from ~ to 7 atmospheres gage is measurod above the
~ solution. This solution i8 flashed as described in Example 1, the
'' liquid precipitant baing cyclohexane boiling under re~lux at 80 to
~1C. There is obtained an opaque slimy product of a substantially
amorphous and gelat;inous nature. When the ~olvent evaporates, the
product shrinks oonsidarably to form a hard sheet no longer
showing fibrous character. With relatively thick filter ¢akes, cracks
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form on drying and a hard crumbly opaque ma~s is produced.
If tha polyethylena concentration is raised to ~ or 14~ w/w,
there is likewisa obtained a gelatirous product, from which9 on
drying, hard crumbly masses form.
EXRmple 5
A linear polyethylene having the physical properties stated in
Example 1 is dissolved in low-boiling naphtha (b.p. 35 to 75C), as
described in Example 1. The polyethylena concentration is selected
so as to give 8 parts of polymer for every 82 parts of naphtha. The
~pressure above the solution at 165C is found to be 15 to 1~ atmos-
; 10 pheres gage. This solution is flashed as described in Example 1, the
liquid precipitant being naphtha ~b.p. 35 to 95C) boiling under
reflux at 50 to 55C. There i obtained a white fibrous product.
Following evaporation of the solvent, there is obtained a mass of
loose fibrids having a harder handla than those obtained in Example
1. Th~ fibrids have a length of from 5 to 15 mm and a thickness of
from 10 to 25 /um. The specific surface area is 26.9 m2/g. The
Schopper-Riegler value is found to be 17SR.
EXAMPLE 6
A linear polyethylene having the physical properties stated in
;Example 1 is dissolved in a mixture of low-boiling naphtha and
20 pentane so as to give 9 parts of polymer for every 74 parts of ; ;
naphtha (b.p. 35 to 75C) and for every 18 parts Of pentane, this
consisting of 60% w/w of n-pentane and 40% w~w of isopentane. The
pressure above the solution at 1~5C is found to be 1~ to 20 atmos-
pheres gage. This solution i9 flashed in the manner described in
,` Example 1, the liquid precipitant consisting of the same mixture of
,
naphtha and pentane, this boiling undar reflux at from 45 to 50C.
The fibrous product is dried as described in Example 1 and there are
.
obtained fibrids having a length of from 2 to 20 mm and a thickness
of-about 5 /um. The specific surface area is 9.7 m'/g and the
30 Schopper-Riegler value is 28SR. -
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~ 69~64 0,ZO 30,2~4
EXAMPLE 7
~ xample 1 is repeated and the same starting materials are used
to produce a polyethylene solution in a mixture of naphtha and
pentane, containing 15~ w/w of polymer The pressure above the
solution at 165C is 1~ to 20 atmospheres gage. The solution is
flashed in a tube having a length of 6 m, a diameter of 8 mm and
taparing to 4 mm at its end. Flashing takes place tangentially in a
cylindrical chamber haYing a diameter of 1 m and a height of 0.5 m,
this being filled with water up to a level of 15 cm. The outlet end
of the tube is about 10 cm b~low the surface of tha water. By
continuous addition of fresh water, the temperature of the mush of
fibrids is maintained at from 30 to 40C during flashing. The mush
of fibrids is continuously passed to a vaporizer, in which the
solvent mixture is distilled off under reduced pressure at a tempera-
ture of from 60 to 70C. The fibrous product is separated from water
on a sieva having a mesh width of 0.5 mm.
For the manufacture of paper, the moist fibrous product is
placed in water together with cellulose in a ratio of 1:1 by weight,
the water con~aining 2% w/w, based on the dry weight of the poly-
olefin fibrids, of a dispersing agent, prod~ced by polycondensation
of melamine, formaldehyde and the sodium salt of ~-aminocapr~C
acid. The mush of fibers is milled in a conical refiner. The sus-
pension of milled fibers is used to produce a paper web showing good
fiber bonding and high wet and dry strength.
.-
EXAMPLE 8
In a polymerization plant, an ethylene copolymer with n-butyl-
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acrylate is prepared by the high-pressure process, which copolymer
contains 20% w/w o~ n-butyl acrylate and ha~ a density of 0.926
g/cm3 and a melt index of 1.6 g/10 min (190/2.16 kg)o The copolymer
is produced in the ~orm of a melt. Pentane consisting of 80 parts of
n-pentane and 20 parts of isopentane is add~d to the melt at a tem-
perature of 145C in a screw extruder so that a solution containing25% w/w of polymer is obtained. The pressure at the head af the
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~69Z64 o . z ~ 30, 28l1
extruder is found to be 20 to 25 atmospheres gage. This solution is
passed through a tube having a length of 1.5 m and an intarnal dia-
meter of 10 mm tapering to 3 mm at the end of the tube and passes
centrally in a vertical tube having a diameter of 2.5 mm and a length
of 6 m. Nitrogen is passed countercurrently through the tube arrange-
ment at a temperature of 50C. Fibrids which are virtually free of
solvent are discharged at the bottom of the tube. The SDlvent vapors
entrained by the nitrogen are condensed by cooling and returned to the
extruder.
The fibrids are soft and elastic and have a bulk density of 20
to-25 g/l. Their lengths are found to be from 3 to 40 mm and their
thicknesses from 5 to 15 /um.
EXAMPLE 9
Example 1 is repeated, and 20 parts of polyethylene having a
densi~y of 0.918 g/cm3 and a melt index of 1.5 g/10 min (190C/
2.16 kg) are dissolved, at 145C in a pressure vessel, in 80 parts of
pentane consisting of 80 parts of n-pentana and 20 parts of isopentane.
; A pressure of about 18 atmospheres gage is measured above this
solution. The solution is flashed as in Exampie 8 and it is dried
with a countercurrent of nitrogen at 60C. There is obtained a fibrous
product which is soft and has the nature of cotton wool. It has a
~bulk density of about 15 g/l and the length of the fibrids is fr~om
5 to 20 mm, the thickness of the fibrids being ~ /um.
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