CA1053871A - Manufacture of thermoplastics fibrids - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A process for the manufacture of thermoplastic fibrids by shredding a solution of a polymeric thermoplastic in a field of shearing forces, said shredding being performed by passing a homogeneous solution of the thermoplastic in an organic solvent, which is a solvent for said thermoplastic only at elevated temperature, through a nozzle having one or more orifices in the form of an annular die into a zone having the form of an impulse exchange chamber which has a mean inlet diameter of from 2 to 20 times that of the circular area equal to the total cross-sectional area of the nozzle orifices through which the homogeneous solution is extruded and a length of from 2 to 30 times its hydraulic diameter, in which chamber the homogeneous solution is cooled such that the thermoplastics material precipitates and in which a turbulent field of shear forces exists, this being produced by the introduction of one or more jets of a gaseous or liquid medium, which jets are located centrally to the annular orifice, into said impulse exchange chamber at a velocity of from 5 to 500 m/s.

Description

1~5~
, ~ This invention relates to a process for the manufacture of thermoplastics fibrids by shredding a solution of a thermo-plastic in a zone of shear.
A large number of processes have been proposed for the manufacture of staple fibrids of thermoplastics, for example the ~
aerodynamic spinning process. In this process, the plastics ~ -material is melted either in a worm extruder or in a pressuri~ed container and is fed to the fiber-forming station through heated pipes. There a high-speed stream of gas or vapor is directed onto the extruded melt at a specific angle.
German Published Application 1,~69,120 discloses a `
process for the manufacture of a suspension of fibrids in which a solution of a synthetic organic polymer is dispersed in a precipitant for the polymer and the polymer precipitates under the action of high shear forces. , -However, the prior art processes are not free from drawbacks, slnce either the said processes cause formation of powdery or crumb-like particles in addition to the fibrids or -~
they require the use of large amounts of gaseous medium. The ' prior art processes make use of expensive apparatus and are thus frequently not economical. The fibrids obtained show a broad spectrum of dimensions. Those processès which provide fibrids in the desired size distribution have, however, the drawback that the resulting fibrids have only a relatively small specific surface area.
It is an object of the present invention to provide a ,`
process of the above kind-in which the drawbacks of the prior art processes are substantially obviated and in which fibrids are produced which are similar to natural fibrids, e.g. ground cellulose, as regards morphology and size and which have a large specific surface area.
This object is achieved by the present invention by - 1- ~ -', - ~OS~B7iL
passing a homogeneous solution of a thermoplastic in an organic solvent which is a solvent for said thermoplastic only at elevated temperature, through a nozzle haviny one or more orifices in the form of an annular die into a zone having the form of an impulse exchange chamber which has a mean inlet diameter of from

2 to 20 times that of the circular area equal to the total - cross-sectional area of the nozzle orifices through which the homogeneous solution is extruded and a length of from 2 to 30 times its hydraulic diameter, in which chamber the homogeneous solution is cooled such that the thermoplastics material precipitates and in which a turbulent field of shear forces exists, this being produced by the introduction of one or more jets of a gaseous or liquid medium, which jets are located centrally to the annular orifice, into said impulse exchange chamber at a velocity of from 5 to 500 m/s.
Suitable thermoplastics are all polymers from which fibrids can be prepared, for example polyolefins, polyamides, polymers of styrene and polymers of substituted styrenes. Parti-cularly suitable are polyolefins such as polyethylene and polypropylene. The density of the polyethylene may be from 0.915 to 0.965 g/cm3. The melt index of the polyethylene is from 0.01 to 100 gjlO min. (190C/2.16 kg), as determined according to ASTM D 1238-65 T. Suita~le polyethylenes are commercially available. They are prepared by well-known high-pressure and low-pressure-polymerization processes. The poly-propylene has an intrinsic viscosity (measured at 130C in decalin) of from 1.5 to 8 dl/g. Alternatively, polyvinyl chloride or chlorinated polyethylene may be used for the manufacture of the fibrids. Another important process is the manufacture of fibrids from copolymers of ethylene. Suitable ethylene copolymers are well known. They are prepared by copolymerization of ethylene with other ethylenically unsaturated compounds by the high-pressure polymerization process. As examples there may be mentioned copolymers of ethylene and vinyl acetate, copolymers o~ ethylene '~:
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~ L053871 and n-butyl acrylate, copolymers of ethylene and acrylic acid and copolymers containing polymerized units of a number of ethylenically unsaturated comonomers such as copolymers of ethylene, acrylic acid and vinyl acetate or copolymers of ethylene, acrylic acid and t-butyl acrylate. It is of course also possible to prepare fibrids from mixtures of thermoplastics, for example from a mixture of high-pressure and low-pressure polyethylenes in a ratio of 1:1 or a 4:1 mixture of high-pressure polyethylene and an ethylene/vinyl acetate copolymer having a vinyl acetate content of 15~ by weight. -;
The-thermoplastics are dissolved in an organic solvent.
Suitable solvents are only those in which the ther~moplastic is soluble at elevated temperatures and separates out on cooling.
Since each polymer/solvent system requires a different tempera-ture for the preparation of the solution, it is not possible to give a general value of the temperature at which the homogeneous solution is prepared. It is important, however, that the polymer precipitates at a temperature which is below that at which the homogeneous solution is prepared. Here again, it is not possible to give a general value, because the temperature at which ~ -precipitation begins depends on the solvent, the polymer and the - concentration of the latter. However, we prefer to prepare the homogeneous solution of the thermoplastic, or the mixture of molten thermoplastic with a solvent, at temperatures above the crystallite melting point or the softening point of the polymer. `
The temperature used does not exceed 300C.
Suitable solvents are for example hydrocarbons such as pentane, hexane, heptane, isooctane, n-octane, decalin, tetra-lin, cyclohexane and aromatic hydrocarbons such as benzene, xylene, toluene, chlorobenzene and halohydrocarbons such as -ethylene chloride, 1,2-dichlorotetrafluoroethane and hexachloro ethane. Other suitable solvents are acetone, cyclohexanone,

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methyl ethyl ketone and tetrahydrofuran. It is advantageous, in some cases, to use mixtures of said solvents. The ratio of thermoplastic to solvent may be varied within wide limits. The concentration of the polymer in the organic solvent may be from 1 to 99%. Advantageously polymer solutions are used in which from 1 to 30~ by weight of thermoplastic is dissolved homo-geneously. ~-In this way there is obtained a polymer solution or a - ~-mixture of a polymer melt and solvent. For the purposes of the present invention, a mixture of molten polymer with solvent, ~ ' for example a homogeneous mixture of 99% by weight of a thermo-plastic and 1% by weight of an organic solvent, is also regarded as a polymer solution.
In a preferred embodiment of the process-of the invention, the aforementioned organic solvents are supplemented ~
by expanding agen-ts. By expanding agents we mean those gaseous, ~-liquid or solid substances which are used as foaming agents in `~
the known processes for the manufacture of foams. Up to 75%
by weight and preferably from 20 to 60% by weight of the organic ;~
solvent may be replaced by an expanding agent or mixture of expanding agents. ~`
Suitable expanding agents are inert gases such as nitrogen, carbon dioxide and inert liquids such as water and low-boiling hydrocarbons and halohydrocarbons. The melting points of the hydrocarbons concerned are preferably from 25 to 150C
below the melting point of the thermoplastic. That is to say, these compounds have a high vapor pressure at room tempera-ture.
Examples of suitable expanding agen-ts are aliphatic and olefinic hydrocarbons of from 1 to 4 carbon atoms such as methane, ethane, propane, butane and ethylene, propylene and butene. It is also possible to use hydrocarbons containing from 5 to 7 carbon atoms and having at least two lateral methyl groups and boiling points

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between -10C and 60C. Examples thereof are isopentane, isohexane and 2,2-dimethylbutane. Particularly suitable halo-hydrocarbons are those having 1 or 2 carbon atoms such as methyl chloride, dichlorodifluoromethane, dichloromethane, fluorotri-chloromethane, monoEluorochloromethane, 1,2,2-trifluorotri-chloroethane and 1,1,2,2-tetrafluorodichloroethane. The said expanding agents are such as are used, for example, as foaming agents in the manufacture of foams. Some of these expanding agents may be used alone as solvents, as in the case of dichloromethane and pentane. In other cases it is possible to replace the organic solvent used within wide limits by one or more of said expanding agents.
The expanding agents used may also be solids which, on heating to temperatures above their decomposition point, disinte-grate to form gaseous products. Examples of suitable substances of this kind are azodicarbonamide, azoisobutyronitrile and aromatic sulhydrazides. It is also possible to use mixtures of carbonates and acids, for example a mixture of sodium carbonate and citric acid.
The homogeneous solution of thermoplastic in an organic solvent is prepared either batchwise in a stirred auto-clave or possibly, in the case of higher boiling solvents, in an open vessel, or it is prepared continuously in a single-worm or twin-worm extruder. When preparing the homogeneous polymer ~
solution, we generally operate at pressures above the pressure '~ ' of the solvent at the solution temperature with the result that the solvent remains liquid under these conditions. By the pressure of the solvent we mean the vapor of the solvent above the dissolved or molten polymer. When dissolution is complete, the resulting homogeneous polymer solution is passed to the fibrid-production point, where the polymer is shredded.
The homogeneous polymer solution is passed through a ;-

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single smooth tube of small cross-section, which narrows sharply at the end of the feed line, or alternatively through specially designed nozzles to a liquid or to a gas atmosphere. Suitable nozzles have one or more orifices ~n the form of an annular die. The diameter of the nozzle orifices is usually from - 0.3 to 5 mm. Shredding of the polymer solution leaving the nozzles is carried out under the influence of shearing forces exerted on a small volume. The said polymer solution is fed to a zone of high energy dissipation, in which the polymer is then shredded to fibrids of the desired sizè.
In order to produce high shear stress in a small volume and thus high energy di-ssipation, it has been found ad-vantageous to use an apparatus consisting of a two-component nozzle projecting into a tank in which there is disposed a tube which is small compared with the volume of the tank and which forms an impulse exchange chamber of any desired cross-section arranged with its longitudinal axis in line with the axis of the nozzle and at such a short distance from the nozzle orifices that it accommodates the media emerging from said orifices (homo-geneous polymer solution and propulsive jet). Apart from theextruded homogeneous polymer solution, high-speed jets of a gaseous or liquid medium are also directed toward the small tube disposed in the tank near the nozzle orifices. The nozzle orifices through which the gaseous or liquid medium emerges usually have a diameter of from 1 to 10 mm. The velocity of the jets of gaseous or liquid medium directed toward the impulse exchange chamber i3 preferably from 10 to 100 m/s.
The small tubular chamber is usually cylindrical and constitutes an impulse exchange chamber because virtually all of the impulse energy of the propulsive jets is dissipated within this chamber. This arrangement of nozzles and impulse exchange chamber in a larger tank causes the medium in the tank not to be ' i - . ,, ~)S38~71 simply entrained by the jet in its general direction of flo~, as in the case of a free jet, but to be entrained into the inlet of the impulse exchange chamber at a rate depending on the energy.
The impulse exchange chamber generally has a constant crosa-section.
Alternatively, the impulse exchange chamber may be of a shape such that its cross-section increases in the direction of flow. Usually, cylindrical tubes or frusta are used. The impulse exchange is generally designed so as to have a length which is from 2 to 30 times its hydraulic diameter. The impulse exchange chamber should have a mean inlet diameter which is from 2 to 20 times that of a circular ` `-area equal to the total area of the nozzle orifices from which the homogeneous polymer solution emerges. In our invention, the energy dissipation densities achieved in the impulse exchange chamber are from 10 to 106 kw/m3.
The process of the invention is carried out industrially in the manner described below with reference to the accompanying Figures 1 and 2. These figures are schematic views illustrating apparatuses which may be used to carry out the process according to the present invention.

, For the sake of clarity, the nozzles and the impulse ~-exchange chamber shown in the figures are drawn on a larger scale than the tank. The reference numerals in the Figures have the following meanings:
1 is the propulsive jet outlet, 2 is the outlet for the homogeneous solution of thermoplastic, 3 is the impulse exchange chamber, 4 is the tank, 5 is the inlet for the gaseous or liquid medium and

6 is the inlet for the homogeneous solution. ~ -Figure 2 shows an apparatus which dispenses with a large tank. In this Figure, reference numeral 7 denotes the inlet for the slower fluent gaseous or liquid medium. In this case, shredding of the polymer is effected in tube 3 acting as impulse exchange chamber.

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1~38'71 The turbulent field of shearing forces acting on the polymer solution in the impulse exchange chamber may be in an inert liquid or in a gaseous phase. This means that the impulse exchange chamber is filled with a gas and/or a liquid. Suitable liquids are water and the solvents in which the polymer is dissolved. It is particularly advantageous to use water as propulsive medium. The use of water is particularly advantageous in the process of the invention, since it has a density which is greater than that of a gaseous medium such as air by a factor of lO , so that a given pulse is achieved at a much lower velocity of the driving jets and of the volume of water used than is the case when air is used. Another advantage of the use of ~ater is that the fibrids are subsequently suspended in water for treatment with, say, substances rendering them hydrophilic.
The temperature of the gaseous or liquid shredding medium depends on the temperature of the solution of thermo-plastic and on the type and size of fibrids to be produced. It is important that the polymer solution cools quickly to enable the dissolved thermoplastic to precipitate. The temperature of the auxiliary media is generally between -20 and 90C and preferably between 1 and 60C. The-difference in temperature between the homogeneous solution and the gaseous or liquid auxiliary medium is at least 30C. The velocity of the driving water jet or the jets of other liquids or gaseous media directed toward the impulse exchange chamber for the production of the field of shearing forces depends on the shear gradient required and on the desired structure of the fibrids.
According to the process of the invention, fibrids are formed which have a narrow distribution of sizes (lengths, thicknesses~ and a large specific surface area. The fibrids thus obtained are of various shapes and sizes depending on the conditions of the process and on the concentration of polymer in ~, . .
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.` 1()53871 the solvent and are swollen with solvent to a greater or lesser ~egree. The fibrids must be worked up and treated further depending on the use to which they are to be put.
The fibrids produced in the process of the invention are used, for example, in the manufacture of a wide variety of non-wovens. Typical examples are webs of paper and non-woven fabrics. In the manufacture of paper and non-woven fabrics, the fibrids prepared in the present invention may, in conjunction with natural and synthetic fibrids of all kinds, contribute to the texture or act as bonding fibrids, depending on their shape and size, particularly fine fibrids being required for the latter ` ~-purpose. The fibrids improve the strength of the webs when they are subjected to suitable heat treatments when the webs are being made.
Since non-wovens are frequently manufactured by wet-processes involving the use of very dilute aqueous suspensions, the polymeric fibrids must have a hydrophilic surface if they are -~
to be uniformly dispersed in the suspension and thus in the resulting non-wovens. It has been found particularly advantageous to carry out the process of the invention in such a manner that substances capable of rendering the fibrids hydrophilic can be -added during the shredding operation. These substances can then act on the natant fibrids when their surface area is at its largest, without having to pass through long diffusion paths.
However, this does not exclude the possibility of adding such agents directly to the polymer solution or, at a subsequent point, to the fibrids themselves during working up.
The in~ention is illustrated below with reference to the following Examples.

A linear polyethylene having a density of 0.960 g/cm3, a melt index of 5 (190C/2.16 kg) and a melting point of 132C is -~

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dissolved in cyclohexane in a stirred autoclave at a temperature of 155C and a pressure of 6 atmospheres. A 1~ homogeneous so-lution is produced which is then passed through a heated pipeline to a fibrid producer of the kind shown diagrammatically in Figure 1. The polymer solution is extruded through a nozzle having a - circle of orifices each of a diameter of 0.7 nlm. A tube having a length of 15 cm and a diameter of 2.5 cm is situated at a distance of 8 mm from said nozzle. A water jet is directed toward this tube, which serves as an impulse exchange chamber, at a velocity of 34 m/s from an-orifice 1 having a diameter of 2 mm.
The water contains a surfactant (a commercially available adduct of ethylene oxide and propylene oxide) in a concentration of `
0.1% by weight, based on the water, and has a temperature of 25C. In this way, the polymer solution is suddenly cooled at the point of fibrid formation. The resulting entangled fibrids or bundles of fibrids swollen with cyclohexane are mechanically disentangled in a water/cyclohexane emulsion at a pulp density of 0.4~ by weight for 3 minutes by mechanical high-frequency treatment by the method proposed by P. Willems (see DECHEMA
Monographie, Vol. 28 (1956), pp. 173-I90). The slurry of fibers is thèn distilled at atmospheric pressure and at temperatures of up to 100C to remove the solvent and is then again subjected to mechanical high-frequency treatment as above for 2 minu-tes to disentangle any slight fibrid agglomerations which may have formed during distillation.
The fibrids thus produced are very finely fibrillated and are thin and crimped. Some of the individual microfibrids converge on each other in the longitudinal direction to form thicker single fibrids. The fiber diameter is from 5 to 50,um.
The lengths of the fibrids are between 350 and l,OOO,um. The fibrids have an appearance very similar to cellulose fibrids.
Due to the high velocity of the jet of water leaving 1 - 10 - .
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~OS3871 the nozzle, a high energy dissipation density of about 1,600 kw/m3 is achieved in a very small volume within the impulse exchange chamber. In this way fibrids having a large specific surface area are produced. In this case, nitrogen adsorption measurements gave a value of about 30 m2/g.

Example 1 is repeated except that the polymer solution ~
used is a 5% solution in cyclohexane prepared at a temperature of ' ' 145C and a pressure of 4.5 atmospheres, and that the velocity of the water jet is 22 m/s. There are obt~ained fibrids having thicknesses of from 30 to 250~um and lengths of from 400 to 1,600,um. The energy dissipation density in the impulse exchange -chamber is 500 kw/m3 and the specific surface area of the fibrids ;~
is about 10 m2/g.

Example 2 is repeated except that a 10% solution in cyclohexane is prepared at a temperature of 185C and a pressure -~
of 10 atmospheres. The energy dissipation density is 1,600 kw/m .
There are obtained fibrids having diameters of from 10 to lOO,um and lengths of from 400 to 2,000,um.
Similar results are obtained when the turbulent field of shearing forces is produced not in water but in cyclohexane.

Example 1 is repeated except that a 10% solution in cyclohexane is prepared which contains 3% by weight of water, based on the weight of solvent. The resulting fibrids are relatively long and have very fine fibrillations. They show, in the longitudinal direction, relatively thick agglomerates of fine fibrids and also flatter structures. The fibrld diameter ranges from 10 to 100 ~m and the lengths of the fibrids range from 400 to 5,000,um. Very similar fibrids may be prepared by `~
adding to the polymer solution not water but 0.05% by weight of .` ` 1~53~71 ~" of nitrogen based on the solvent.

A polyethylene having a density of 0.96 g/cm , a melt index of 5 (190C/2.16 kg) and a melting point of 132C is dis-solved in a solvent mixture consisting of 79% by weight of cyclo-hexane and 21~ by weight of pentane, in a stirred autoclave at a temperature of 155C and a pressure of 9 atmospheres. There is formed a 3.3% polymer solution which is fed to the fibrid producer of Example 1 through a heated pipeline. The velocity of the water jet is 22 m/s and its temperature is 25C. The energy dissipation is 500 kw/m .
The fibrids, swollen with solventr are subjected to a mechanical high-frequency treatment by the method proposed by P. Willems (see DECHEMA Monographie, Vol. 28 tl956), pp. 173-190) for 3 minutes in the presence of 3% by weight, based on the poly-mer, of a surface-active substance and at a pulp density of 1.1~ by weight. The solvent is then removed at a pressure of 100 mm of Hg and temperatures of up to 60C, whereupon the fibrids ~ t are again subjected to said mechanical high-frequency treatment.
The resulting fibrids are finely fibrillated and ramified. The finest ramifications have thicknesses of less than 10 ~m, whilst the flbrids themselves have diameters of from 10 to 80~u and lengths ranging from 300 to 4,000 ~m.

A high molecular weight polyethylene having a density of 0.952 g/cm3, a melt index of 2 (I90 C/2.16 kg) and a crystallite melting point of 136C is dissolved in cyclohexane in a stirred autoclave at a pressure of 7 atmospheres and a temperature of 165C. There is produc~d a 3% polymer solution which is fed to the fibrid producer-described in Example 1 through a heated pipeline. The velocity of the water jet is 22 m/s and its tempera-ture is 25C. The energy dissipation is 500 kw/m3. -, .... - . , .. .- . - .. .. . , . ~ ,, OS387~
: The fibrids obtained are swollen with solvent. The entangled fibrids and bundles thereof are subjected, for 3 minutes, to a mechanical hiyh-frequency treatment by the method proposed by P. Willems (see DECHEMA Monographie, Vol. 28 (1956), pp. 173-190) in the presence of 5~ by weight (based on the polymer) of a surfactant and at a pulp density of 1.1% by weight. The solvent is then removed as described in Example 5. There are obtained fibrids which are very finely fibrillated. The fibrid diameters - -are from 5 to 20,um and the lengths of the fibrids range from 2,000 to 6,000,um.

Branched-chain polyethylene having a density of 0.918 g/cm3, a melt index of 20 (190C/2.16 kg) and a melting point of 105C is melted in a twin-worm extruder. The extruder worms have a length/diameter ratio of 34 and a diameter of 2 inches. Pentane is fed to the polyethylene melt by a metering pump such that the extrudate consists of a homogeneous polymer solution consisting of 84% by weight of pentane and 17% by weight of polyethylene. The homogeneous solution resides in the extruder for about 3 minutes at a temperature of 125C and is then fed to the fibrid producer of Example 1. The velocity of the water jet is 40 m/s and its temperature is 18C. The energy dissipation is 2,500 kw/m3. There are obtained fibrids, which are subjected, for 3 minutes, to a mechanical high-frequency treatment as proposed b~ P. Willems (see DECHEMA Monographie, Vol. 28 (1956~ pp. 173-190) in the presence of a water/pentane emulsion and a pulp density of 1.7% by weight. The pentane is distilled off at temperatures of up to 45C. The fibrids are - finely fibrillated and have a foam-like structure. The individual fibrids show fine ramifications and are slightly crimped. Their thicknesses range from about 10 to 150,um and their lengths from 250 to 3,000 ~m. The specific surface area of the fibrids is 1 1 m2/g . , - ' ' '' ' '. ' -: . ' . :
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Polyethylene having a density of 0.918 g/cm3, a melt index of 20 (190C/2.16 kg) and a me].ting point of 105C is melted in the extruder described in Example 7. Cyclohexane is fed to the polyethylene melt by means of a pump at such a rate that the extruder worm feeds a homogeneous polymer solution containing 60~ by weight of cyclohexane and having a temperature of 190C
to the fibrid produced illustrated in Figure 1. In addition, when the polyethylene has been melted, nitrogen is added thereto at a pressure of 10 atmospheres and at a rate of 9 l/kg (STP).
The pressure built up upstream of the fibrid producer by the extruder is 27 atmospheres and the velocity of the water jet is 40 m/s. Energy dissipation is 2,500 kw/m3 and the water temperature is 55C. There are produced fibrids having the character of individual fibrids of solidified polyethylene and having highly cracked surfaces and a slightly flat appearance. `

A 13% solution in pentane of a branched-chain poly-ethylene having a density of 0.918 g/cm3, a melt index of 1.5 .
(lqOC/2.16 kg) and a melting point of 108C is produced in a stirred autoclave at a temperature of 90C and a pressure of 4.5 atmospheres and is then fed to the fibrid producer described in Example 1. The velocity of the water jet is 10 m/s and its ~ -temperature is 26C (energy dissipation 40 kw/m3~. The water contains a surface-active substance in a concentration of O.L% - :
by weight. The resulting pentane-containing fibrids are - disentangled in a water!pentane mixture at a pulp density of 3.5 by weight by subjection, for 3 minutes, to a mechanical high-frequency treatment as proposed by P. Willems (see DECHEM~
Monographie, Vol. 28 (1257~, pp. 173-190~. The remaining -~
solvent is then distilled off at temperatures of up 40C and the residue is again subjected to said mechanical high-frequency ~ ~ .

105387~L
~reatment. There are obtained fibrids which are finel~ fibril-lated. They are similar to the well known spruce/cellulose fibers.
The thicknesses of the fibrids range from 10 to 60~um and their lengths from 250 to 1,500~um. During the manufacture of the fibrids, the energy dissipation in the impulse exchange tube is 40 kw/m3. The specific surface area of the fibrids is 64 m2/g.
Similar results are obtained if a 5% solution of the same polymer in pentane or a 10% solution of the polymer given in Example 7 in pentane is used.
If the mechanical high-frequency treatment proposed by P. Willems (see DECHEMA Monographie, Vol. 28 (1956), pp. 173-190) is omitted after distillation, the fibrids produced are longer, having lengths of up to about 10 mm. These fibrids are particular-ly suitable for the manufacture of non-woven webs.

Example 9 is repeated except that a 10% solution of the polymer is prepared and that the velocity of the water jet is 22 m/s and its temperature is 50C (energy dissipation 500 kw/m3).
There are obtained long fibrids of a foamy structure, which are very uniform. They are suitable for the manufacture of coarser non-wovens, to which they impart resilient, flexible and soft characteristics. The diameters of these fibrids depend on the dimensions of the outlet orifices of the fibrid producer. When said orifices have a diameter of 1 mm, the thickness of the fibrids is from 2 to 3 mm.

The procedure described in Example 1 is followed. The polymer used is a highly crystalline propylene homopolymer having a density of 0.908 g/cm3 and a melt index of 2.5 (190C/2.16 kg), this being dissolved in cyclohexane in a stirred autoclave at a temperature of 160C and a pressure of 6 atmospheres. There is obtained a 3~ solution which is then fed to the fibrid producer.

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7~ velocity of the water jet is 34 m/s and its temperature is 25C. The energy dissipation is 1,600 kw/m3. The resulting entangled fibrids swollen with cyclohexane are disentangled in a water/cyclohexane emulsion at a pulp density of 1% by weight by subjection, for 3 minutes, to a mechanical high-frequency treat-ment. To the emulsion there is added 1% (based on the fibrids) - -of a commercial surfactant (adduct of ethylene oxide and propylene oxide~. The slurry of fibrids is heated at temperatures of up to 60 C under reduced pressure to distill off the cyclohexane.
The fibrid suspension is then again treated for 1 minute with said mechanical high-frequency treatment. There are obtained fibrids which are very finely fibrillated. The thickness of the "
fibrids is from 5 to 50~um and their lengths range from 250 to 3,000~um.

Standard polystyrene having a density of 1.05 g/cm3 and a dimensional stability of 101C (measured by the Vicat method, DIN 53,460) is fed to a twin-worm extruder in the form of granules.
Isobutyl alcohol is fed, as solvent, to the polystyrene melt by means of a metering pump such that the extrudate consists of a ~ ~
homogeneous polymer solution consisting of 95 parts by weight of ~ -isobutyl alcohol and 5 parts by weight of polystyrene. The temperature of the polymer solution is 175C. On leaving the extruder, the homogeneous solution is fed to the fibrid producer of Example 1. The nozzle orifices have a diameter of 0.7 mm.
The velocity of the water jet is 34 m/s and its temperature is 25C (energy dissipation 1,600 kw/m3). There are obtained very fine fibrids, which are disentangled in a water/isobutyl alcohol mixture for 3 minutes by means of a mechanical high-frequency process. The disentangled fibrids have a thickness of from 50 to 500~um and a length of fxom 250 to 3,000~um. The specific surface area, determined by the BET method, has a value :- ,, ' ` ;
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o~ about 150 m /g of fibrids.

Polyethylene having a density cf 0.918 g/cm3 and a melt index of 20 (190C/2.16 kg) is fed iIl the form of granules to a twin-worm extruder. Pentane is metered, as solvent, to the resulting polyethylene melt at such a rate that the extrudate consists of a homogeneous polymer solution consisting of 95 parts by weight of pentane and 5 parts by weight of polyethylene. The temperature of the polymer solution is 140C. On leaving the extruder, the homogeneous solution is fed to the fibrid producer of Example 1. The nozzle orifices have a diameter of 0.5 mm.
The propulsive jet consists of nitrogen (pressure 6 atm. gage).
There are obtained short fibrids having diameters ranging from ~ `
40 to 500jum and lengths ranging from 500 to 6,000/um. The energy diss pati~n density in the impulse exchan3e chambe= is 80 ~w~m3.

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Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the manufacture of thermoplastic fibrids by shredding a solution of a polymeric thermoplastic in a field of shearing forces, said shredding being performed by passing a homogeneous solution of the thermoplastic in an organic solvent, which is a solvent for said thermoplastic only at elevated temperature, through a nozzle having one or more orifices in the form of an annular die into a zone having the form of an impulse exchange chamber which has a mean inlet diameter of from 2 to 20 times that of the circular area equal to the total cross-sectional area of the nozzle orifices through which the homogeneous solution is extruded and a length of from 2 to 30 times its hydraulic diameter, in which chamber the homogeneous solution is cooled such that the thermoplastic material precipitates and in which a turbulent field of shear forces exists, this being produced by the introduction of one or more jets of a gaseous or liquid medium, which jets are located centrally to the annular orifice, into said impulse exchange chamber at a velocity of from 5 to 500 m/s.

2. A process as claimed in claim 1, wherein the energy dissipation densities in the zone having the form of an impulse exchange chamber range from 10 to 106 kw/m3.

3. A process as claimed in claim 1, wherein the homogeneous solution additionally contains an expanding agent.