CA1069264A - Manufacture of fibrids of polyolefins - Google Patents
Manufacture of fibrids of polyolefinsInfo
- Publication number
- CA1069264A CA1069264A CA215,799A CA215799A CA1069264A CA 1069264 A CA1069264 A CA 1069264A CA 215799 A CA215799 A CA 215799A CA 1069264 A CA1069264 A CA 1069264A
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- CA
- Canada
- Prior art keywords
- fibrids
- solvent
- polyethylene
- pressure
- solution
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
- D01D5/11—Flash-spinning
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
- D21H13/10—Organic non-cellulose fibres
- D21H13/12—Organic non-cellulose fibres from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
- D21H13/14—Polyalkenes, e.g. polystyrene polyethylene
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
- D21H5/00—Special paper or cardboard not otherwise provided for
- D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
- D21H5/20—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of organic non-cellulosic fibres too short for spinning, with or without cellulose fibres
- D21H5/202—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials of organic non-cellulosic fibres too short for spinning, with or without cellulose fibres polyolefins
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- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Textile Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Artificial Filaments (AREA)
- Nonwoven Fabrics (AREA)
- Spinning Methods And Devices For Manufacturing Artificial Fibers (AREA)
- Paper (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
Discrete fibrids of polyethylene having lengths of 1 to 50 mm and thicknesses between 2 and 30 µm, are produced by (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 140°C. 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, cyclo-pentane and neopentane; (b) maintaining the vapor pressure in the pressure vessel at 4 to 60 atmospheres and maintaining the temperature of the polyethylene solution in the pressure vessel at temperature of 80 to 250°C 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) flashing 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;
and (e) drying the resultant polyethylene fibrids. The fibrids directly obtained may be used, for example, for the manufacture of paper or for the manufacture of textile-like webs.
Discrete fibrids of polyethylene having lengths of 1 to 50 mm and thicknesses between 2 and 30 µm, are produced by (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 140°C. 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, cyclo-pentane and neopentane; (b) maintaining the vapor pressure in the pressure vessel at 4 to 60 atmospheres and maintaining the temperature of the polyethylene solution in the pressure vessel at temperature of 80 to 250°C 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) flashing 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;
and (e) drying the resultant polyethylene fibrids. The fibrids directly obtained may be used, for example, for the manufacture of paper or for the manufacture of textile-like webs.
Description
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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 _ .
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 . ~ , . . .
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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~9~;4 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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- 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 ~9~
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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 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.
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 ~ 9~
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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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~ 6g 2 6 4 O.Z0 30,284 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.
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 : ; ' ' - - ~
~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 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 ~0~926~ o.z. 30,2~4 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.
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 ~ 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.
.-In a polymerization plant, an ethylene copolymer with n-butyl-. .
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 .
~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 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/
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 , ' ~ ~ ~ ' , ~ . .''," .
, :
~ ~6926~
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;
:, . ~' and - "
(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 _ .
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 . ~ , . . .
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 ' .
L~
- 5 ~
l.. .. . . . . . . . . . . . . . . . .
~9~;4 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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` ~6926~
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, -~' .
. .
- 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 ~9~
~ z. 30,2~
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 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.
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 ~ 9~
~ ~ ;
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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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' '`'` '` ' ~ .~. ',.
~ 6g 2 6 4 O.Z0 30,284 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.
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 ;
~ .
~ 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 : ; ' ' - - ~
~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 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 ~0~926~ o.z. 30,2~4 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.
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. -.
.
~ 69~64 0,ZO 30,2~4 ~ 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.
.-In a polymerization plant, an ethylene copolymer with n-butyl-. .
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 .
~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 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.
.. ~ - , ' . .
; 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.
.. ~ - , ' . .
Claims (4)
1. A process for the manufacture of discrete fibrids of polyethylene having lengths of 1 to 50 mm and thicknesses between 2 and 30 µm, which 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 140°C. and containing pentanes in an amount of from 5 to 50% by weight, said pentanes being selected from the group consisting of n-pentane, isopentane, cyclopentane and neopentane;
(b) maintaining the vapor pressure in said pressure vessel at 4 to 60 atmospheres and maintaining the temperature of the polyolefin solution in said pressure vessel at temperature of 80 to 250°C and above the boiling point of said solvent at standard pressure;
(c) passing said polyethylene solution from said pressure vessel through an orifice into a space maintained at lower temperature and pressure than those in said pressure vessel;
(d) flashing off said solvent in said space from the solution passed through said orifice to produce a tangled mass of said fibrids, said amount of said pentanes in said solvent further being sufficient to cause the polyethylene to separate in form of discrete fibrids upon the flashing off of said solvent in said space; and (e) drying the resultant polyethylene fibrids.
(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 140°C. and containing pentanes in an amount of from 5 to 50% by weight, said pentanes being selected from the group consisting of n-pentane, isopentane, cyclopentane and neopentane;
(b) maintaining the vapor pressure in said pressure vessel at 4 to 60 atmospheres and maintaining the temperature of the polyolefin solution in said pressure vessel at temperature of 80 to 250°C and above the boiling point of said solvent at standard pressure;
(c) passing said polyethylene solution from said pressure vessel through an orifice into a space maintained at lower temperature and pressure than those in said pressure vessel;
(d) flashing off said solvent in said space from the solution passed through said orifice to produce a tangled mass of said fibrids, said amount of said pentanes in said solvent further being sufficient to cause the polyethylene to separate in form of discrete fibrids upon the flashing off of said solvent in said space; and (e) drying the resultant polyethylene fibrids.
2. A process as claimed in claim 1, which comprises the further step of disentangling the dried fibrids by combing, brushing or picking to obtain a free flowing and transportable mass of said polyethylene fibrids having said lengths and said thicknesses.
3. A process as claimed in claim 1, wherein said polyethylene has a density in the range of 0.915 to 0.965 g/cm3.
4. A process as claimed in claim 1, wherein said poly-ethylene has a melt index (as determined by ASTM D 1238-65 T at 190°C and a load of 2.16 kg) in the range of 100 g/10 minutes to 0.01 g/10 minutes.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2363672A DE2363672C3 (en) | 1973-12-21 | 1973-12-21 | Process for the production of short fibers from low-pressure polyethylene and their use |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1069264A true CA1069264A (en) | 1980-01-08 |
Family
ID=5901457
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA215,799A Expired CA1069264A (en) | 1973-12-21 | 1974-12-11 | Manufacture of fibrids of polyolefins |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5094234A (en) |
| BE (1) | BE823440A (en) |
| CA (1) | CA1069264A (en) |
| DE (1) | DE2363672C3 (en) |
| FR (1) | FR2255400B3 (en) |
| GB (1) | GB1477378A (en) |
| IT (1) | IT1025794B (en) |
| SE (1) | SE406332B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4181794A (en) * | 1978-08-28 | 1980-01-01 | Gulf Oil Corporation | Method for manufacture of olefin polymer fibrils |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DK116229B (en) * | 1957-06-11 | 1969-12-22 | Du Pont | Continuously extruded or spun filament product and process for its manufacture. |
| US3227664A (en) * | 1961-12-07 | 1966-01-04 | Du Pont | Ultramicrocellular structures of crystalline organic polymer |
| US3081519A (en) * | 1962-01-31 | 1963-03-19 | Fibrillated strand | |
| NL300881A (en) * | 1962-11-23 | |||
| US3904804A (en) * | 1968-10-14 | 1975-09-09 | Mitsubishi Rayon Co | Polyolefin micro-flake aggregation useful for manufacturing synthetic papers and polyolefin synthetic papers obtainable therewith |
| FR1596107A (en) * | 1968-12-13 | 1970-06-15 | ||
| JPS4813722B1 (en) * | 1970-07-14 | 1973-04-28 | ||
| JPS4813723B1 (en) * | 1970-07-16 | 1973-04-28 | ||
| BE787032A (en) * | 1971-08-06 | 1973-02-01 | Solvay | |
| BE787033A (en) * | 1971-08-06 | 1973-02-01 | Solvay | |
| NL169760C (en) * | 1972-04-22 | 1982-08-16 | Stamicarbon | PROCESS FOR PREPARING POLYMER FIBERS |
-
1973
- 1973-12-21 DE DE2363672A patent/DE2363672C3/en not_active Expired
-
1974
- 1974-11-18 IT IT29556/74A patent/IT1025794B/en active
- 1974-12-11 CA CA215,799A patent/CA1069264A/en not_active Expired
- 1974-12-17 BE BE151576A patent/BE823440A/en not_active IP Right Cessation
- 1974-12-18 FR FR7441758A patent/FR2255400B3/fr not_active Expired
- 1974-12-18 JP JP49144597A patent/JPS5094234A/ja active Pending
- 1974-12-19 GB GB5485474A patent/GB1477378A/en not_active Expired
- 1974-12-19 SE SE7416069A patent/SE406332B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5094234A (en) | 1975-07-26 |
| BE823440A (en) | 1975-06-17 |
| SE406332B (en) | 1979-02-05 |
| FR2255400B3 (en) | 1977-09-16 |
| DE2363672A1 (en) | 1975-07-10 |
| DE2363672B2 (en) | 1975-10-30 |
| IT1025794B (en) | 1978-08-30 |
| DE2363672C3 (en) | 1982-08-05 |
| FR2255400A1 (en) | 1975-07-18 |
| GB1477378A (en) | 1977-06-22 |
| SE7416069L (en) | 1975-06-23 |
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| Date | Code | Title | Description |
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| MKEX | Expiry |