CA1072278A - Process for the production of polyolefin fibers - Google Patents
Process for the production of polyolefin fibersInfo
- Publication number
- CA1072278A CA1072278A CA219,069A CA219069A CA1072278A CA 1072278 A CA1072278 A CA 1072278A CA 219069 A CA219069 A CA 219069A CA 1072278 A CA1072278 A CA 1072278A
- Authority
- CA
- Canada
- Prior art keywords
- composition
- fibers
- polyolefin
- diluent
- range
- 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
- D01D5/40—Formation of filaments, threads, or the like by applying a shearing force to a dispersion or solution of filament formable polymers, e.g. by stirring
Abstract
ABSTRACT
A process and apparatus for manufacturing polyolefin fibers from a composition of the said polyolefins dissolved in a diluent, by subjecting the composition to flow at a velocity above a critical value in a tube or bundle of tubes, the tempera-ture of the composition being within the range of critical temp-eratures of the said composition over at least a portion of the length of the tube or bundle of tubes and separating the fibers from the liquid diluent. The critical temperature range is below the temperature of solution of the polyolefin in the molten state in a diluent and is more specifically the range of temperatures in which the polyolefin remains in dissolved condition when the solution mixture is maintained at rest but precipitates when the mixture is subjected to certain disturbances such as, for instance, shearing. The critical velocity and the lower critical temperature are determined by the appearance of powder co-precipitating with the fibers. In a variation the composition contains fibrous material (e.g. cellulose) insoluble in the diluent, yielding an interlaced fiber mix (useful in paper making, among other things).
A process and apparatus for manufacturing polyolefin fibers from a composition of the said polyolefins dissolved in a diluent, by subjecting the composition to flow at a velocity above a critical value in a tube or bundle of tubes, the tempera-ture of the composition being within the range of critical temp-eratures of the said composition over at least a portion of the length of the tube or bundle of tubes and separating the fibers from the liquid diluent. The critical temperature range is below the temperature of solution of the polyolefin in the molten state in a diluent and is more specifically the range of temperatures in which the polyolefin remains in dissolved condition when the solution mixture is maintained at rest but precipitates when the mixture is subjected to certain disturbances such as, for instance, shearing. The critical velocity and the lower critical temperature are determined by the appearance of powder co-precipitating with the fibers. In a variation the composition contains fibrous material (e.g. cellulose) insoluble in the diluent, yielding an interlaced fiber mix (useful in paper making, among other things).
Description
~72;~7i3 This invention ~elates to a process of manufacturing polyolefin fibers from a solution of these polyolefins.
French Patents Nos. 1,596,107 and 2,141,748 describe processes for the manufacture of polyolefin fibers by adiabatic expansion of a solution of polyolefins. This expansion takes place by passage of the solution through a spinneret. The solvent is at least partially volatilized and the fibers are then collected.
French Patent No. 2,132,903 concerns the preparation of polyolefin fibers of high molecular weight by dispersing a solution of polyolefins under a high shearing rate in a precipitant. The polyolefin solutionr before being introduced into the precipitant, must be at a temperature above the temperature of dissolving of the molten mass of the polyolefins. In one particular embodiment of this process, the solvent and the precipitant are the same chemical substance.
French Patent No. 2,181,952 describes a process for pre-cipitating polymer fibers from a solution of said polymer by in-troducing a stream of solvent tangentially to the outer surface of the precipitation enclosure. The shearing of the solution created by the rotation in the enclosure produces the precipitation of the polymer in fiber form.
French Patent No. 2,131,145 describes a process for obtaining fibrous gel containing 30~ polyolefins or more by weight by polymerization of olefins, the reaction mixture being subjected to a shearing force created by mechanical agitation. The fibrous gel may also be obtained by cooling a solution of a preformed polymer under a high shearing rate created by mechanical agitation, said solution being initially at a temperature above the tempera-ture of solution of the molten mass of the polyolefin.
An advantage of the present invention is the developmentof a process for the formation of polyolefin fibers which is not ~C~7Z~
accompanied by the vaporization of a solvent and which does not require the use either of a precipitant or of means of mechanical agitation intended to create a high rate of shear in the solution~
The applicants discovered that polyolefin fibers are obtained when a composition consisting of a polyolefin and a diluent flows under special conditions and when the temperature of the composition is within certain limits.
Therefore a preferred embodiment of the present invention is a process for the manufacture of polyolefin fibers from a com-position of said polyolefins dissolved in a diluent. Said processcomprises subjecting the composition to flow, at a velocity higher than a critical value, in a tube or bundle of tubes, the tempera-ture of the composition being within a range of critical tempera-tures of said composition over at least a portion of the path of -the tube or bundle of tubes and by separating the fibers from the liquid diluent.
A further embodiment of the present invention is apparatus for carrying out of the process of the invention, which apparatus will be described in detail further below in the present ~-application.
The invention is not limited to obtaining fibers from amacroscopically homogeneous liquid composition. The applicants have also carried out the process by cooling a pclyolefin compo-sition in a diluent containing furthermore fibers which are in-.. . . .
soluble in the diluent. Thus, from a polyolefin composition dissolved in cyclohexane and furthermore containing cellulose fibers one can obtain an interlacing of polyolefin and cellulose fibers. This particular application of the process for the manu-facture of polyolefin fibers forms another object of the invention.
The mixtures of fibers thus obtained constitute still another embodiment of the invention.
Finally, the use of the fibers or mixtures of fibers for ; -2-, , . . , : . . . .
: , -. , . , : . .: . . , : .. : .. .
~2278 the manufacture of papers in accordance with the known techniques and the papers thus obtained also constitute embodiments of t~e present invention.
In order to define the zone of critical -temperatures which is characteristic for the proc ss of manufacturing polyole-fin fibers in accordance with the invention, it is necessary first of all to define the temperature of solution of a polyolefin in molten state. -By temperature of solution of the polyolefin in molten state in a diluent is meant the temperature at which upon heating a macroscopically homogeneous phase of the molten polyolefin in the diluent appears. It is known that one does not have a true solution at this temperature and that one would tend towards a :~
true solution by increase in the temperature, such increase being furthermore accompanied by an increase in the viscosity of the composition.
The temperature of solution of the polyolefin in molten state in a diluent obviously depends on the polyolefin, on -the diluent, and on the concentration of the polyolefin in the diluent.
The range of critical temperatures is a range of temperatures lower than the solution temperature previously de-fined. It is the range of temperatures in which the polyolefin remains in dissolved condition when the solution mixture is main-tained at rest but precipitates when the mixture is subjected to certain disturbances such as, for instance, shearing. The amp-litude of the range of critical temperatures depends on the poly-olefin, on the diluent, on the concentration of the polyolefin in the diluent and on the velocity of flow of the mixture. The range may extend o~er 1 to 10 C for solutions of polyethylene of a density of more than 0.935, for example.
The critical phase of the process for the manufacture of fibers is the flow under specific conditions of the composition ' ~
~L~7~7~
at a temperature which must be within the range of critical temperatures or posslbly slightly above the upper limit of the range of critical temperatures when said flow is accompanied by heat losses.
When it is desired to obtain only fibers, the velocity of flow of the composition must be greater than a critical value which depends on the nature of the polyolefin, on the nature of the diluent, and on the concentration of the poly-olefin in the diluent. Within this critical value of the velocity, a mixture of polyolefin fibers and powder ls obtained. One simple method is to effect this flow in a tube or a bundle of tubes. The flow may be isothermal or nonisothermal. If it is isothermal, the temperature of introduction of the composition into the tube or bundle of tubes must be within the range of critical temperatures. If the flow is nonisothermal, the tube or the bundle of tubes then operates as heat exchanger, cooIing the composition. The temperature of introduction of the composition -may then be above the range of critical temperatures. In this latter case it is advantageous for the cooling to be effected homogeneously within the composition by the use of a bundle of tubes. The composition may or may not flow at a velocity greater than the critical value in a linear tube or bundle of tubes. The length of the tube or tubes is not determinative for the obtaining of the fibers. The "useful" length is the length at which the composition is within the range of crltical temperatures.
The velocity necessary for the formation of the flbers may be reached in several ways. A first manner consists in initially impressing this velocity on the composition by means of a circulating pump, the circulation line being of constant diameter. A second method consists in obtaining this velocity by a decrease in the cross section of the line downstream of the pump circulating the composition. In this latter case, only the - : .:
... ,, .. . , . ., . .. : . , . . . ~ :
` ~07;2Z7~
portion of the line which is of reduced diameter, and which may be a tube or a bundle of tubes, will be the place of the forma-tion of fibers. It should be noted that everything else being equal, the larger the number of tubes which a bundle has, the smaller the diameter of the tubes must be.
The temperature at which the fibers are formed is gener-ally obtained by cooling from the temperature of solution of the polyolefin in molten s-tate. This is particularly the case when the polyolefin from which one starts is initially in the form of `-~
powder or granulates which are dissolved in a diluent.
The accompanying drawing is a schematic illustration of the apparatus used in the process of the present invention.
Referring to the drawing, an enclosure 1 containing a polyolefin in a diluent under a nitrogen pressure of 3 bars is connected, via lines 2 and 3, to a straight tube 4 having ends A
and s. The tube 4, which is the place of formation of the fibers, has a cross section~which is less than that of the lines 2 and 3.
Downstream of the tube 4, there is an enclosure 5 for ti~e recovery of the fibers, which enclosure has a grid 6 on which the fibers -deposit. The diluent is recovered in the lower portion 7 of the enclosure 5. A part of the diluent recovered is recycled via the line 8 while another part is forwarded, via the line 9, into the enclosure 1 when the latter is used as a solution enclosure for the polyolefin. The recycling through the line 8 can be eliminated .t..... '''.. ' when~the diluent recovered at 7 does not contain any polyolefin.
The lines 2 and 3 contain pumps, 10 and 11 respectively.
The pressure in the enclosure 5 is 3 bars. The loss of heat in -~
the tube 4 ~epends upon the geometry of this tube and the material of which it is made. The formation of the fibers in the tube 4 ~ -takes place in a quasi-isothermal manner. The .. ., ., . . . .:: ~ , , .. .. . . . . . . . .. : . . .
. .: . : . : . . . . , , , . . ........... . :. . , . : .
,.:.. .. . . . . . : . ... . . .: , . . . . . . . . .
~7~Z7~3 temperature of the composition at the point A is therefore sub-stantially the same as at the point B, which means that the temperature of the composition at the point A is within the region of critical temperatures. The enclosure 5 is advantageously at the same temperature as the tube 4. The line 12 extending be-tween the point B and the enclosure 5 may be eliminated, the tube 4 then discharging directly into the enclosure 5. Likewise, the end A may be connected directly to the outlet of the circulating pump 11. The carrying out of the process may require the use of a cooler (not shown in the figure) in the path of the line 2 or of the line 3 in the event that the temperature of the composition at the point A, in the absence of such cooler, would be above the upper limit of the range of critical temperatures and there is no, or practically no, heat loss in the tube 4.
The enclosure 5 fulfills the function of receiving the solution containing the fibers after their precipitation in the tube 4, as well as the function of recovering these fibers by filtration through the grid ~. However, it is possible to carry out these two functions in two different enclosures -- a first enclosure which receives the solution and the fibers which it contains and permits the recycling of the solution to the precipitation tube; a second enclosure, fed continuously or inter-mittently, from the first enclosure via a line, effecting the recovery proper of the fibers (for instance by filtration). The filtrate recovered in the second enclosure is then sent to the ~-polymer solution enclosure or is possibly recycled in the precipi-tation tube. -~
In another embodiment of the process, the tempera-ture of the composition at the point A is above the upper limit of the range of critical temperatures. In this case it is necessary for there to be heat losses in the tube or bundle of tubes where the fibers are formed. This tube or bundle of tubes operates as , . : . . . , , : , 7zz7~ -a heat exchanger cooling the composition to a temperature within the range of critical temperatures. In this case also the line for the introduction of the composition into the tube or bundle of tubes may possibly contain a cooler.
The process may also be carried out in intermediate manner, that is to say in the presence of a tube or bundle of tubes producing only a small heat exchange. In this case, the solution will be introduced into the heat exchanger at a tempera-ture within the range of critical temperature$ or very close to the upper limit of said range.
When the tube or bundle of tubes acts as a heat ex-; changer, the jacket in which the heat-removing fluid flows may be formed of a single chamber or of several separate chambers fed with heat-removing fluids at the same temperature or at different temperatures.
The polyolefin subjected to the process of the in-; vention may be polyethylene of a density of more than 0.935 ob-tained by the lo~-pressure polymerization process and whose molecular weight distribution may be very broad (for instance polyethylene of a density of 0.950 and for which Mn is 8300 and Mw is 300,000) or the molecular weight distribution of which is narrower (polyethylene of a density of 0.960 and for which Mn i5 11, 500 and Mw is 801000). Polyethylenes of very high molecular weight may also be used. Crystalline polyolefins may also be ~
used such as polypropylene or polybutene. The copolymers of ole- -fins may also be subjected to the process of the invention.
The diluent used may be a solvent, the solubility ~ -parameter of which is preferably close to that of the polyolefin.
In the case of polyethylene, one such solvent is commercial hexane or cyclohexane or mixtures of xylenes. However, the solubility parameter of the diluent may also be substantially different from ; i that of the polyolefin.
: ~
,~-, . ~ , '" , ... , , ' .
-~7~71~
The concentration of the polyolefin in the diluent is a parameter which has an effect on the position and amplitude of the range of critical temperatures. By way of example, in the case of polyethylene of a density of more than 0.935, the concentration of the polyolefin may vary between 0.5% and 10% of the weight of the diluent.
One can operate with a higher concentration of poly-olefin; however, the compositions become more viscous and the mechanical energy which must be expended for the circulating of the composition becomes substantial.
It is also possible to add soluble adjuvants to the diluent, such as polyisobutylenes of low molecular weight or polyvinyl alcohol. These adjuvants do not precipitate upon the formation of the polyolefin fibers. The concentration of the adjuvants may be between 0.1% and 50% of the polyolefins. These adjuvants are added in order to obtain fibers which can be more easily separated from each other.
The process of the invention makes it possible to prepare fibers of a length of between 0.1 mm and 2 cm and of a diameter of between 5~ and 200~. This last value does not correspond to the diameter of an individual fiber obtained by the process but to the diameter of bundles of individual fibers formed.
The fibers obtained by the process of the invention may find numerous industrial applications. They may in particular ~-be used for the making of non-woven sheets, or as aggregates for adsorption of hydrocarbons or aqueous products. Furthermore, as indicated above, the polyolefin fibers obtained in accordance with the invention may be used alone or in mixtures with cellulose fibers for the manufacture of different papers in accordance with known techniques.
The invention is further illustrated by the follow-ing examples, given solely by way of illustration.
.
' ": ' ~, : , . . .
~07~æ~Z~s EXAMPLE I
20 g of polyethylene marketed under the trademark "VESTOLEN 6016" having the properties d = 0.960, Mn = 11,500, Mw = 80,000 are dissolved in an enclosure of a volume of 1 liter at a temperature of 130C in 600 ml of cyclohexane, corresponding to a concentration of 5~ expressed by weight. The enclosure is connected, via a reciprocating pump, to a copper coil of a length of 10 m and a diameter of 4 mm placed in a thermostatic oil bath ;
in such a manner that the flow in the coil is isothermal. The temperature of the coil is therefore fixed. For a pumping rate of 70 liters/hour (which corresponds to a maximum linear velocity of the composition in the coil of 3 m/sec), fibers appear in the composition while it passes through the coil when the temperature of the compositlon at the entrance to the coil is between 82 and 78C. These two values of the temperature define the range of critical temperatures.
~hen the temperature is above 82C, all other things being equal, one does not note any precipitation of polyethylene in any form whatsoever.
When the temperature is below 78C, all other things being equal, there is noted the precipitation of a mixture of fibers and powder, the proportion of powder being higher the lower the temperature.
Within the same temperature range when the rate of the pump is fixed at 35 l/hour (which corresponds to a maximum linear velocity of 1.5 m/sec of the composition in the coil), the fibers obtained are shorter, and they are obtained mixed with ~ : .
powder. The velocity is therefore below the critical value.
EXAMPLE Il ' An apparatus similar to that described in Example I, in which the copper coil of a length of 10 m is replaced by a linear Teflon (trademark) tube of a length of 40 cm and a diameter ' ' .-. ' .', '. ' . , .. . . : :
-~72~
of 1.5 mm, is fed with a solution formed of 2% polyethylene (identical ~o that described in Example 1), 1% Oppanol B (trade-mark for polyisobutylene of low molecular weight marketed by B.A.S.F.~, and 97% commercial hexane. It is noted that the range of critical temperatures extends from 93C to 97C.
EXAMPLE III
An apparatus similar to that of Example I, in which the copper coil of a length of 10 m is replaced by a linear steel tube of a length of 40 cm and a diameter of 2 mm, is fed by a composition formed of 1% polyethylene (identical to that des-cribed in Example I), 1% of cellulose fibers and 98% cyclohexane.
It is noted that the range of critical temperatures extends from 78C to 82C, in which range an intermeshing of polyethylene and cellulose fibers is obtained.
EXAMPLE IV
A composition formed of 1% polyethylene (identical to that described in Example I), 0.5% cellulose fibers and 98.5%
cyclohexane is treated in accordance with Example III. The range of critical temperatures is between 78 and 82C.
MPLE V -In an enclosure of a volume equal to 2 liters, 110 g of polypropylene mar~eted under the trademark "MOPLEN Q 30 P" and having the following properties:
~Mn 28,000 -Mw 450,000 -proportion of atactic polypropylene 5.3%, are dissolved at the temperature of 140C in 1.5 liters of heptane, which corresponds to a concentration by weight of 5%. The enclo-sure is connected, via a reciprocating pump having a rate of flow of 70 l/hour, with a linear tube of stainless steel of a length :~
of 40 cm and a diameter of 2 mmO Fiber intermeshings are obtained for the range of critical temperatures of 80 -to 88C.
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- . , ........................... . ' . .
. . . . . . . . .
~C~7~'~7~
EXAMPLE VI
By means of a reciprocating pump of a rate of flow of 70 l/hour, a 5% solution of polyethylene identical to that described in Example I in commercial cyclohexane is passed into a tube of a length of 90 cm and a diameter of 2 mm provided with `
an outer jacket formed of three independent successive chambers of lengths of 20, 30, and 40 cm respectively. This device makes it possible to circulate a fluid at a desired temperature in each of the chambers constituting the outer jacket. The chamber whose length is equal to 20 cm surrounds the initial part of the tubes.
The chambers of 30 and 40 cm in length surround the central por-tion and the final portion of the tube respectively.
The formation of fibers is noted within a range of critical temperatures of between 80 and 92C. The temperature of the fluid circulating in the chamber surrounding the initial, central and final regions of the tube being equal to 125C, 67C
and 67C respectively.
EXAMPLE VII
A 5% solution of the same polyethylene in an industrial solvent having the composition:
; -49.4% normal hexane -19 % 3-methyl pentane -18.9% 2-methyl pentane - 7.8% methyl cyclopentane, ~-
French Patents Nos. 1,596,107 and 2,141,748 describe processes for the manufacture of polyolefin fibers by adiabatic expansion of a solution of polyolefins. This expansion takes place by passage of the solution through a spinneret. The solvent is at least partially volatilized and the fibers are then collected.
French Patent No. 2,132,903 concerns the preparation of polyolefin fibers of high molecular weight by dispersing a solution of polyolefins under a high shearing rate in a precipitant. The polyolefin solutionr before being introduced into the precipitant, must be at a temperature above the temperature of dissolving of the molten mass of the polyolefins. In one particular embodiment of this process, the solvent and the precipitant are the same chemical substance.
French Patent No. 2,181,952 describes a process for pre-cipitating polymer fibers from a solution of said polymer by in-troducing a stream of solvent tangentially to the outer surface of the precipitation enclosure. The shearing of the solution created by the rotation in the enclosure produces the precipitation of the polymer in fiber form.
French Patent No. 2,131,145 describes a process for obtaining fibrous gel containing 30~ polyolefins or more by weight by polymerization of olefins, the reaction mixture being subjected to a shearing force created by mechanical agitation. The fibrous gel may also be obtained by cooling a solution of a preformed polymer under a high shearing rate created by mechanical agitation, said solution being initially at a temperature above the tempera-ture of solution of the molten mass of the polyolefin.
An advantage of the present invention is the developmentof a process for the formation of polyolefin fibers which is not ~C~7Z~
accompanied by the vaporization of a solvent and which does not require the use either of a precipitant or of means of mechanical agitation intended to create a high rate of shear in the solution~
The applicants discovered that polyolefin fibers are obtained when a composition consisting of a polyolefin and a diluent flows under special conditions and when the temperature of the composition is within certain limits.
Therefore a preferred embodiment of the present invention is a process for the manufacture of polyolefin fibers from a com-position of said polyolefins dissolved in a diluent. Said processcomprises subjecting the composition to flow, at a velocity higher than a critical value, in a tube or bundle of tubes, the tempera-ture of the composition being within a range of critical tempera-tures of said composition over at least a portion of the path of -the tube or bundle of tubes and by separating the fibers from the liquid diluent.
A further embodiment of the present invention is apparatus for carrying out of the process of the invention, which apparatus will be described in detail further below in the present ~-application.
The invention is not limited to obtaining fibers from amacroscopically homogeneous liquid composition. The applicants have also carried out the process by cooling a pclyolefin compo-sition in a diluent containing furthermore fibers which are in-.. . . .
soluble in the diluent. Thus, from a polyolefin composition dissolved in cyclohexane and furthermore containing cellulose fibers one can obtain an interlacing of polyolefin and cellulose fibers. This particular application of the process for the manu-facture of polyolefin fibers forms another object of the invention.
The mixtures of fibers thus obtained constitute still another embodiment of the invention.
Finally, the use of the fibers or mixtures of fibers for ; -2-, , . . , : . . . .
: , -. , . , : . .: . . , : .. : .. .
~2278 the manufacture of papers in accordance with the known techniques and the papers thus obtained also constitute embodiments of t~e present invention.
In order to define the zone of critical -temperatures which is characteristic for the proc ss of manufacturing polyole-fin fibers in accordance with the invention, it is necessary first of all to define the temperature of solution of a polyolefin in molten state. -By temperature of solution of the polyolefin in molten state in a diluent is meant the temperature at which upon heating a macroscopically homogeneous phase of the molten polyolefin in the diluent appears. It is known that one does not have a true solution at this temperature and that one would tend towards a :~
true solution by increase in the temperature, such increase being furthermore accompanied by an increase in the viscosity of the composition.
The temperature of solution of the polyolefin in molten state in a diluent obviously depends on the polyolefin, on -the diluent, and on the concentration of the polyolefin in the diluent.
The range of critical temperatures is a range of temperatures lower than the solution temperature previously de-fined. It is the range of temperatures in which the polyolefin remains in dissolved condition when the solution mixture is main-tained at rest but precipitates when the mixture is subjected to certain disturbances such as, for instance, shearing. The amp-litude of the range of critical temperatures depends on the poly-olefin, on the diluent, on the concentration of the polyolefin in the diluent and on the velocity of flow of the mixture. The range may extend o~er 1 to 10 C for solutions of polyethylene of a density of more than 0.935, for example.
The critical phase of the process for the manufacture of fibers is the flow under specific conditions of the composition ' ~
~L~7~7~
at a temperature which must be within the range of critical temperatures or posslbly slightly above the upper limit of the range of critical temperatures when said flow is accompanied by heat losses.
When it is desired to obtain only fibers, the velocity of flow of the composition must be greater than a critical value which depends on the nature of the polyolefin, on the nature of the diluent, and on the concentration of the poly-olefin in the diluent. Within this critical value of the velocity, a mixture of polyolefin fibers and powder ls obtained. One simple method is to effect this flow in a tube or a bundle of tubes. The flow may be isothermal or nonisothermal. If it is isothermal, the temperature of introduction of the composition into the tube or bundle of tubes must be within the range of critical temperatures. If the flow is nonisothermal, the tube or the bundle of tubes then operates as heat exchanger, cooIing the composition. The temperature of introduction of the composition -may then be above the range of critical temperatures. In this latter case it is advantageous for the cooling to be effected homogeneously within the composition by the use of a bundle of tubes. The composition may or may not flow at a velocity greater than the critical value in a linear tube or bundle of tubes. The length of the tube or tubes is not determinative for the obtaining of the fibers. The "useful" length is the length at which the composition is within the range of crltical temperatures.
The velocity necessary for the formation of the flbers may be reached in several ways. A first manner consists in initially impressing this velocity on the composition by means of a circulating pump, the circulation line being of constant diameter. A second method consists in obtaining this velocity by a decrease in the cross section of the line downstream of the pump circulating the composition. In this latter case, only the - : .:
... ,, .. . , . ., . .. : . , . . . ~ :
` ~07;2Z7~
portion of the line which is of reduced diameter, and which may be a tube or a bundle of tubes, will be the place of the forma-tion of fibers. It should be noted that everything else being equal, the larger the number of tubes which a bundle has, the smaller the diameter of the tubes must be.
The temperature at which the fibers are formed is gener-ally obtained by cooling from the temperature of solution of the polyolefin in molten s-tate. This is particularly the case when the polyolefin from which one starts is initially in the form of `-~
powder or granulates which are dissolved in a diluent.
The accompanying drawing is a schematic illustration of the apparatus used in the process of the present invention.
Referring to the drawing, an enclosure 1 containing a polyolefin in a diluent under a nitrogen pressure of 3 bars is connected, via lines 2 and 3, to a straight tube 4 having ends A
and s. The tube 4, which is the place of formation of the fibers, has a cross section~which is less than that of the lines 2 and 3.
Downstream of the tube 4, there is an enclosure 5 for ti~e recovery of the fibers, which enclosure has a grid 6 on which the fibers -deposit. The diluent is recovered in the lower portion 7 of the enclosure 5. A part of the diluent recovered is recycled via the line 8 while another part is forwarded, via the line 9, into the enclosure 1 when the latter is used as a solution enclosure for the polyolefin. The recycling through the line 8 can be eliminated .t..... '''.. ' when~the diluent recovered at 7 does not contain any polyolefin.
The lines 2 and 3 contain pumps, 10 and 11 respectively.
The pressure in the enclosure 5 is 3 bars. The loss of heat in -~
the tube 4 ~epends upon the geometry of this tube and the material of which it is made. The formation of the fibers in the tube 4 ~ -takes place in a quasi-isothermal manner. The .. ., ., . . . .:: ~ , , .. .. . . . . . . . .. : . . .
. .: . : . : . . . . , , , . . ........... . :. . , . : .
,.:.. .. . . . . . : . ... . . .: , . . . . . . . . .
~7~Z7~3 temperature of the composition at the point A is therefore sub-stantially the same as at the point B, which means that the temperature of the composition at the point A is within the region of critical temperatures. The enclosure 5 is advantageously at the same temperature as the tube 4. The line 12 extending be-tween the point B and the enclosure 5 may be eliminated, the tube 4 then discharging directly into the enclosure 5. Likewise, the end A may be connected directly to the outlet of the circulating pump 11. The carrying out of the process may require the use of a cooler (not shown in the figure) in the path of the line 2 or of the line 3 in the event that the temperature of the composition at the point A, in the absence of such cooler, would be above the upper limit of the range of critical temperatures and there is no, or practically no, heat loss in the tube 4.
The enclosure 5 fulfills the function of receiving the solution containing the fibers after their precipitation in the tube 4, as well as the function of recovering these fibers by filtration through the grid ~. However, it is possible to carry out these two functions in two different enclosures -- a first enclosure which receives the solution and the fibers which it contains and permits the recycling of the solution to the precipitation tube; a second enclosure, fed continuously or inter-mittently, from the first enclosure via a line, effecting the recovery proper of the fibers (for instance by filtration). The filtrate recovered in the second enclosure is then sent to the ~-polymer solution enclosure or is possibly recycled in the precipi-tation tube. -~
In another embodiment of the process, the tempera-ture of the composition at the point A is above the upper limit of the range of critical temperatures. In this case it is necessary for there to be heat losses in the tube or bundle of tubes where the fibers are formed. This tube or bundle of tubes operates as , . : . . . , , : , 7zz7~ -a heat exchanger cooling the composition to a temperature within the range of critical temperatures. In this case also the line for the introduction of the composition into the tube or bundle of tubes may possibly contain a cooler.
The process may also be carried out in intermediate manner, that is to say in the presence of a tube or bundle of tubes producing only a small heat exchange. In this case, the solution will be introduced into the heat exchanger at a tempera-ture within the range of critical temperature$ or very close to the upper limit of said range.
When the tube or bundle of tubes acts as a heat ex-; changer, the jacket in which the heat-removing fluid flows may be formed of a single chamber or of several separate chambers fed with heat-removing fluids at the same temperature or at different temperatures.
The polyolefin subjected to the process of the in-; vention may be polyethylene of a density of more than 0.935 ob-tained by the lo~-pressure polymerization process and whose molecular weight distribution may be very broad (for instance polyethylene of a density of 0.950 and for which Mn is 8300 and Mw is 300,000) or the molecular weight distribution of which is narrower (polyethylene of a density of 0.960 and for which Mn i5 11, 500 and Mw is 801000). Polyethylenes of very high molecular weight may also be used. Crystalline polyolefins may also be ~
used such as polypropylene or polybutene. The copolymers of ole- -fins may also be subjected to the process of the invention.
The diluent used may be a solvent, the solubility ~ -parameter of which is preferably close to that of the polyolefin.
In the case of polyethylene, one such solvent is commercial hexane or cyclohexane or mixtures of xylenes. However, the solubility parameter of the diluent may also be substantially different from ; i that of the polyolefin.
: ~
,~-, . ~ , '" , ... , , ' .
-~7~71~
The concentration of the polyolefin in the diluent is a parameter which has an effect on the position and amplitude of the range of critical temperatures. By way of example, in the case of polyethylene of a density of more than 0.935, the concentration of the polyolefin may vary between 0.5% and 10% of the weight of the diluent.
One can operate with a higher concentration of poly-olefin; however, the compositions become more viscous and the mechanical energy which must be expended for the circulating of the composition becomes substantial.
It is also possible to add soluble adjuvants to the diluent, such as polyisobutylenes of low molecular weight or polyvinyl alcohol. These adjuvants do not precipitate upon the formation of the polyolefin fibers. The concentration of the adjuvants may be between 0.1% and 50% of the polyolefins. These adjuvants are added in order to obtain fibers which can be more easily separated from each other.
The process of the invention makes it possible to prepare fibers of a length of between 0.1 mm and 2 cm and of a diameter of between 5~ and 200~. This last value does not correspond to the diameter of an individual fiber obtained by the process but to the diameter of bundles of individual fibers formed.
The fibers obtained by the process of the invention may find numerous industrial applications. They may in particular ~-be used for the making of non-woven sheets, or as aggregates for adsorption of hydrocarbons or aqueous products. Furthermore, as indicated above, the polyolefin fibers obtained in accordance with the invention may be used alone or in mixtures with cellulose fibers for the manufacture of different papers in accordance with known techniques.
The invention is further illustrated by the follow-ing examples, given solely by way of illustration.
.
' ": ' ~, : , . . .
~07~æ~Z~s EXAMPLE I
20 g of polyethylene marketed under the trademark "VESTOLEN 6016" having the properties d = 0.960, Mn = 11,500, Mw = 80,000 are dissolved in an enclosure of a volume of 1 liter at a temperature of 130C in 600 ml of cyclohexane, corresponding to a concentration of 5~ expressed by weight. The enclosure is connected, via a reciprocating pump, to a copper coil of a length of 10 m and a diameter of 4 mm placed in a thermostatic oil bath ;
in such a manner that the flow in the coil is isothermal. The temperature of the coil is therefore fixed. For a pumping rate of 70 liters/hour (which corresponds to a maximum linear velocity of the composition in the coil of 3 m/sec), fibers appear in the composition while it passes through the coil when the temperature of the compositlon at the entrance to the coil is between 82 and 78C. These two values of the temperature define the range of critical temperatures.
~hen the temperature is above 82C, all other things being equal, one does not note any precipitation of polyethylene in any form whatsoever.
When the temperature is below 78C, all other things being equal, there is noted the precipitation of a mixture of fibers and powder, the proportion of powder being higher the lower the temperature.
Within the same temperature range when the rate of the pump is fixed at 35 l/hour (which corresponds to a maximum linear velocity of 1.5 m/sec of the composition in the coil), the fibers obtained are shorter, and they are obtained mixed with ~ : .
powder. The velocity is therefore below the critical value.
EXAMPLE Il ' An apparatus similar to that described in Example I, in which the copper coil of a length of 10 m is replaced by a linear Teflon (trademark) tube of a length of 40 cm and a diameter ' ' .-. ' .', '. ' . , .. . . : :
-~72~
of 1.5 mm, is fed with a solution formed of 2% polyethylene (identical ~o that described in Example 1), 1% Oppanol B (trade-mark for polyisobutylene of low molecular weight marketed by B.A.S.F.~, and 97% commercial hexane. It is noted that the range of critical temperatures extends from 93C to 97C.
EXAMPLE III
An apparatus similar to that of Example I, in which the copper coil of a length of 10 m is replaced by a linear steel tube of a length of 40 cm and a diameter of 2 mm, is fed by a composition formed of 1% polyethylene (identical to that des-cribed in Example I), 1% of cellulose fibers and 98% cyclohexane.
It is noted that the range of critical temperatures extends from 78C to 82C, in which range an intermeshing of polyethylene and cellulose fibers is obtained.
EXAMPLE IV
A composition formed of 1% polyethylene (identical to that described in Example I), 0.5% cellulose fibers and 98.5%
cyclohexane is treated in accordance with Example III. The range of critical temperatures is between 78 and 82C.
MPLE V -In an enclosure of a volume equal to 2 liters, 110 g of polypropylene mar~eted under the trademark "MOPLEN Q 30 P" and having the following properties:
~Mn 28,000 -Mw 450,000 -proportion of atactic polypropylene 5.3%, are dissolved at the temperature of 140C in 1.5 liters of heptane, which corresponds to a concentration by weight of 5%. The enclo-sure is connected, via a reciprocating pump having a rate of flow of 70 l/hour, with a linear tube of stainless steel of a length :~
of 40 cm and a diameter of 2 mmO Fiber intermeshings are obtained for the range of critical temperatures of 80 -to 88C.
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. . . . . . . . .
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EXAMPLE VI
By means of a reciprocating pump of a rate of flow of 70 l/hour, a 5% solution of polyethylene identical to that described in Example I in commercial cyclohexane is passed into a tube of a length of 90 cm and a diameter of 2 mm provided with `
an outer jacket formed of three independent successive chambers of lengths of 20, 30, and 40 cm respectively. This device makes it possible to circulate a fluid at a desired temperature in each of the chambers constituting the outer jacket. The chamber whose length is equal to 20 cm surrounds the initial part of the tubes.
The chambers of 30 and 40 cm in length surround the central por-tion and the final portion of the tube respectively.
The formation of fibers is noted within a range of critical temperatures of between 80 and 92C. The temperature of the fluid circulating in the chamber surrounding the initial, central and final regions of the tube being equal to 125C, 67C
and 67C respectively.
EXAMPLE VII
A 5% solution of the same polyethylene in an industrial solvent having the composition:
; -49.4% normal hexane -19 % 3-methyl pentane -18.9% 2-methyl pentane - 7.8% methyl cyclopentane, ~-
2,2-dimethyl pentane and 2,4-dimethyl pentane - 4.9% miscellaneous is passed into an apparatus identical to that described in Example VI.
The formation of fibers is noted in a range of critical temperatures of between 95 and 102C. The temperature of the fluid flowing in the chamber surrounding the initial, ~ ;
central and final portions of the tube being equal to 200C, . .. . . .
.: : , , - ~)7;~ 78 90C and 90C respectively.
EXAMPL~
.
Sheets of laboratory paper ("formettes") were prepared using a mixture of cellulose fibers and polyethylene fibers prepared in accordance with the invention.
Bleached coniferous Kraft pulp was beaten in the laboratory to a degree of beating of 45 SR (degree Schopper Riegler, AFNOR Specification NF-Q 50-003). To this pulp there were added polyethylene fibers which had been previously dis-integrated in the dry state. The composition obtained (60~polyethylene fibers; 40~ wood pulp) had an SR degree of 30 and made it possible to produce formettes with a Rapid Kothern ~
apparatus, being careful not to aerate the suspension. After -drying, these sheets were heat-sealed without pressure in an oven at 136C for 15 minutes.
The physical characteristics of these sheets were measured in accordance with the AFNOR specifications. The results -are indicated in the following table, as compared with a ~-composition of cellulose fibers of coniferous woods and broad-leaved woods. They relate to formettes of 70 g/m2.
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The formation of fibers is noted in a range of critical temperatures of between 95 and 102C. The temperature of the fluid flowing in the chamber surrounding the initial, ~ ;
central and final portions of the tube being equal to 200C, . .. . . .
.: : , , - ~)7;~ 78 90C and 90C respectively.
EXAMPL~
.
Sheets of laboratory paper ("formettes") were prepared using a mixture of cellulose fibers and polyethylene fibers prepared in accordance with the invention.
Bleached coniferous Kraft pulp was beaten in the laboratory to a degree of beating of 45 SR (degree Schopper Riegler, AFNOR Specification NF-Q 50-003). To this pulp there were added polyethylene fibers which had been previously dis-integrated in the dry state. The composition obtained (60~polyethylene fibers; 40~ wood pulp) had an SR degree of 30 and made it possible to produce formettes with a Rapid Kothern ~
apparatus, being careful not to aerate the suspension. After -drying, these sheets were heat-sealed without pressure in an oven at 136C for 15 minutes.
The physical characteristics of these sheets were measured in accordance with the AFNOR specifications. The results -are indicated in the following table, as compared with a ~-composition of cellulose fibers of coniferous woods and broad-leaved woods. They relate to formettes of 70 g/m2.
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Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for manufacturing polyolefin fibers from a composition containing said polyolefin dissolved in a liquid diluent, which is cyclohexane, hexane, pentane, heptane, xylenes, or mixtures thereof, at a concentration of about 1 to about 5% by weight, which fibers generally have a length of between 0.1 mm and 2 cm and a diameter of bundles of such fibers of between 5µ
and 200µ, comprising flowing said composition through at least one elongated zone circumscribed by a stationary boundary having a length of about 40 cm to about 10 m and a diameter of about 1.5 mm to about 4 mm, said composition having a temperature in a range such that while in said zone said range is below the temperature of solution of said polyolefin in the molten state and within, but not below, the range of critical temperatures in which said polyolefin would remain dissolved under the given conditions and with the composition at rest but precipitates when subjected to shear, whereby polyolefin fibers are formed in said diluent, said range of critical temperatures being between about 78°C and about 102°C, said composition in said zone being flowed at a velocity greater than the velocity for the given conditions at which polyolefin powder would be formed with said fibers, and beyond said zone separating the fibers from suspension in the diluent which is still liquid.
and 200µ, comprising flowing said composition through at least one elongated zone circumscribed by a stationary boundary having a length of about 40 cm to about 10 m and a diameter of about 1.5 mm to about 4 mm, said composition having a temperature in a range such that while in said zone said range is below the temperature of solution of said polyolefin in the molten state and within, but not below, the range of critical temperatures in which said polyolefin would remain dissolved under the given conditions and with the composition at rest but precipitates when subjected to shear, whereby polyolefin fibers are formed in said diluent, said range of critical temperatures being between about 78°C and about 102°C, said composition in said zone being flowed at a velocity greater than the velocity for the given conditions at which polyolefin powder would be formed with said fibers, and beyond said zone separating the fibers from suspension in the diluent which is still liquid.
2. A process according to claim 1, wherein the flow in said zone is effected isothermally or quasi-isothermally and the temperature of introduction of the composition into said zone is within the range of critical temperatures.
3. A process according to claim 1, wherein the flow in said zone is effected in a non-isothermal manner and the temperature of the composition decreases along the zone in the direction of flow.
4. A process according to claim 3, wherein the temper-ature of introduction of the composition into said zone is greater than the upper limit of the range of critical tempera-tures.
5. A process according to claim 1, wherein said com-position contains from 0.5 to 10 parts of polyethylene of a density of more than 0.935.
6. A process according to claim 1, wherein said com-position contains from 0.5 to 10 parts of polyethylene of a density of more than 0.935 in 100 parts of a diluent and further-more contains an adjuvant means soluble in the diluent in an amount of between 0.1 and 50% of the polyethylene for increasing the viscosity of the composition.
7. A process according to claim 1, wherein said com-position contains polypropylene.
8. A process according to claim 5, wherein said diluent is chosen from the group consisting of cyclohexane, hexane, and mixture of xylenes.
9. A process according to claim 1, wherein said diluent is chosen from the group consisting of cyclohexane, hexane, and mixtures of xylenes.
10. A process according to claim 1, wherein said polyolefin is chosen from the group consisting of polyethylene, polypropylene, and polybutene, and copolymers thereof.
11. A process according to claim 1, wherein said polyolefin is chosen from the group consisting of polyethylene having a density of at least 0.935, crystalline polypropylene, crystalline polybutene, and copolymers thereof.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7403338A FR2259923B1 (en) | 1974-01-31 | 1974-01-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1072278A true CA1072278A (en) | 1980-02-26 |
Family
ID=9134318
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA219,069A Expired CA1072278A (en) | 1974-01-31 | 1975-01-30 | Process for the production of polyolefin fibers |
Country Status (10)
| Country | Link |
|---|---|
| JP (1) | JPS50157620A (en) |
| BE (1) | BE824870A (en) |
| CA (1) | CA1072278A (en) |
| DE (1) | DE2502458A1 (en) |
| FR (1) | FR2259923B1 (en) |
| GB (1) | GB1452041A (en) |
| IT (1) | IT1028383B (en) |
| NL (1) | NL7501030A (en) |
| NO (1) | NO750293L (en) |
| SE (1) | SE7500853L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19922944A1 (en) * | 1999-05-14 | 2000-11-16 | Bgb Ges Tu Berlin | Acceleration of phase separation of liquid polymer-containing phases used for polyolefins involves using branched solvents to increase speed |
-
1974
- 1974-01-31 FR FR7403338A patent/FR2259923B1/fr not_active Expired
-
1975
- 1975-01-15 IT IT19289/75A patent/IT1028383B/en active
- 1975-01-22 DE DE19752502458 patent/DE2502458A1/en active Pending
- 1975-01-27 SE SE7500853A patent/SE7500853L/xx unknown
- 1975-01-28 BE BE152785A patent/BE824870A/en unknown
- 1975-01-29 NL NL7501030A patent/NL7501030A/en not_active Application Discontinuation
- 1975-01-30 NO NO750293A patent/NO750293L/no unknown
- 1975-01-30 GB GB411675A patent/GB1452041A/en not_active Expired
- 1975-01-30 CA CA219,069A patent/CA1072278A/en not_active Expired
- 1975-01-31 JP JP50013259A patent/JPS50157620A/ja active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB1452041A (en) | 1976-10-06 |
| NL7501030A (en) | 1975-08-04 |
| BE824870A (en) | 1975-07-28 |
| NO750293L (en) | 1975-08-25 |
| SE7500853L (en) | 1975-08-01 |
| IT1028383B (en) | 1979-01-30 |
| FR2259923B1 (en) | 1978-10-27 |
| JPS50157620A (en) | 1975-12-19 |
| FR2259923A1 (en) | 1975-08-29 |
| DE2502458A1 (en) | 1975-08-14 |
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