US3920509A

US3920509A - Process of making polyolefin fibers

Info

Publication number: US3920509A
Application number: US340140A
Authority: US
Inventors: Hayato Yonemori
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-10-05
Filing date: 1973-03-12
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18

Abstract

An improved process of manufacturing fibers by the technique of forming a mixture of polymer, solvent for such polymer and, optionally, water or other flashing aids, at a temperature (flash temperature) which is high enough to bring the polymer to a plastic state and which will permit substantially complete vaporization of the solvent when the mixture is flashed and flashing the mixture into a flash zone to produce a fibrous product. In the improved process (a) the flash zone is established at a pressure of 600 mm Hg or below and, advantageously, between 50 and 500 mm Hg, and (b) the flash temperature, the components of the mixture and the concentration of each in the mixture (with respect to the heat capacity of said components and with respect to the heat of vaporization of those components in the mixture which will be volatilized in flashing) are all chosen relative to each other so as to produce in the flashed product a temperature which is less than 94* C., and, advantageously, below 80* C. when the mixture is flashed into said flash zone and substantially all of the solvent vaporized. In an additional feature of the invention, said flash zone pressure and the solvent in the mixture are selected so as to produce a vapor condensation point in the flash zone when the mixture is flashed thereinto which is at or below 60* C., an aqueous mixture of the flashed product is produced in the flash zone by introduction thereinto of dilution water at a temperature below 70* C. and, advantageously, within the range of 10* C. to 60* C., which temperature is at or above said condensation point in said flash zone, and refining the aqueous mixture at a temperature below 70* C. and, advantageously, between 10* C. and 60* C. Advantageously, at least a part of the refining may be carried out while the aqueous mixture is in pressure communication with the flash zone and subjected to the ambient pressure condition in the flash zone.

Description

United States Patent [191 Yonemori Nov. 18, 1975 1 PROCESS OF MAKING POLYOLEFIN FIBERS [76] Inventor: Hayato Yonemori, 2-2, l-chome Muronoki-cho, Iwakuni, Japan [22] Filed: Mar. 12, 1973 [21] Appl. No.: 340,140

Related US. Application Data [63] Continuation-impart of Ser. No. 295,339, Oct. 5,

Primary ExaminerS. Leon Bashore Assistant Examiner-Peter Chin Attorney, Agent, or Firm-Stanley M. Tiegland; Corwin R. Horton; Robert E. Howard [57] ABSTRACT An improved process of manufacturing fibers by the technique of forming a mixture of polymer, solvent for such polymer and, optionally, water or other flashing aids, at a temperature (flash temperature) which is high enough to bring the polymer to a plastic state and which will permit substantially complete vaporization of the solvent when the mixture is flashed and flashing the mixture into a flash zone to produce a fibrous product. In the improved process (a) the flash zone is established at a pressure of 600 mm Hg or below and, advantageously, between 50 and 500 mm Hg, and (b) the flash temperature, the components of the mixture and the concentration of each in the mixture (with respect to the heat capacity of said components and with respect to the heat of vaporization of those components in the mixture which will be volatilized in flashing) are all chosen relative to each other so as to produce in the flashed product a temperature which is less than 94 C., and, advantageously, below 80 C. when the mixture is flashed into said flash zone and substantially all of the solvent vaporized. In an additional feature of the invention, said flash zone pressure and the solvent in the mixture are selected so as to produce a vapor condensation point in the flash zone when the mixture is flashed thereinto which is at or below 60 C., an aqueous mixture of the flashed product is produced in the flash zone by introduction thereinto of dilution water at a temperature below 70 C. and, advantageously, within the range of 10 C. to 60 C., which temperature is at or above said condensation point in said flash zone, and refining the aqueous mixture at a temperature below 70 C. and, advantageously, between 10 C. and 60 C. Advantageously, at least a part of the refining may be carried out while the aqueous mixture is in pressure communication with the flash zone andsubjected to the ambient pressure condition in the flash zone.

11 Claims, 2 Drawing Figures US. Patent Nov. 18, 1975 PROCESS OF MAKING POLYOL'EFIN FIBERS CROSS-REFERENCE T of APPLICATION This is a continuation-in-part of Ser. No. 295,339

filed Oct. 5, 1972.. I I v BACKGROUND OF THE INVENTION Numerous processes have been proposed for preparing synthetic fibrous materials by flashing polymer solutions or dispersions held at high temperature and pressure into a zone of reduced pressure. In various patent literature, such as German Offenlegungsschrift No. 1,958,609and Japanese patent applicaton having publication No. 71-34921, processes are proposed in which a polymer is dissolved in a solvent therefor and heated under at least autogenous pressure and then flashed into a zone of lower pressure to thereby vaporize the solvent and form fibrous materials. In the latter mentioned patent, the fibrous material thus formed is quenched with a water spray at a temperature between 60 c, and 80 c.

Similar processes are presented in US. patent application Ser. No. 295,339, filed Oct. 5, 1972, (assigned to the assignee of the present application) and as well in German OLS No. 2,121,512 and German OLS No. 2,144,409. In these processes a polymer dissolved in a solvent is mixed with water or other liquid non-solvents for the polymer to form an emulsion of thepolymer solution in a continuous waterphase and this emulsion is heated and flashed to a reduced pressure zone to produce fibers.

Another approach is described in U.S. patent application Ser. No. 285,386 and now abandoned, filed Aug. 30, 1972, (assigned to the assignee of the present application) wherein a polymer. solution in which water is dispersed as a discontinuous phase is flashed to form fibers. In this process, the water concentration is held between 30 and 70% of the entire mixture and in forming the mixture it is preferable'to add the water to the preformed polymer solution totinsure that the water forms the discontinuous phase.

OLS No. 2,147,461 describes a process in which molten polymer is emulsified with water (optionally, with a minor amount of solvent in the polymer phase) and then heated and'flashed to a reduced pressure zone to form fibers.

While many variations are evident, it is seen that the common feature of all these fiber-making processes is the flashing into a zone of reduced pressure of a heated mixture containing a polymer and a solvent for such polymer. Various conditions of flashing are suggested in the referenced processes including temperature and pressure ranges for the mixture to be flashed and various solvents, flashing aids, etc. Most of the references contemplate flashing into .a zone held at atmospheric pressure. Others suggest the possibility of flashing into a zone which is above or below atmospheric pressure, in some cases with the application of heat in such zone. All of these processes may lead to the production of fibrous material. However, each suffersfrom the shortcoming that a specific set ofconditions of flashing, particularly with regard to temperature-and pressure, and

interrelationship of such conditions are not provided which will'permit manufacture, in a practical manner, "of fibers having the optimum properties desirable for their use as a synthetic:pulp in the manufacture of paper by conventional techniques.

Fibrous materials produced under the general process conditions described in these references tend to be interconnectedor bundled together to an undesirable degree and the paper produced therefrom is undesirably low in strength (e.g., tensile strength). Such fibrous material is more difficult to separate, cut or refine in preparation for paper making and contains a high content of gels and chunks of polymer which cause undesirable fish eyes'or transparent spots in 0 paper manufactured therefrom.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The purpose of the present invention is to provide an economical technique involving a specific interrelated set of flashing conditions, applicable to all of the foregoing described processes, which will produce a product capable of being readily separated and refined for paper making and which, upon refining in accordance with the invention, will yield a pulp useful for producing synthetic paper by conventional paper making techniques whic has surprisingly improved properties and a low content of gels and chunks.

Briefly, the present process comprises establishing a flash zone at a pressure of 600 mm Hg or below and, advantageously, between 50 and 500 mm Hg, forming a mixture of polymer, solvent for such polymer and, optionally, water and/or other flashing aids, at a temperature which is high enough to bring the polymer to a plastic state and which will result in substantially complete vaporization of the solvent upon flashing of the mixture into the flash zone held at between 50 and 600 mm Hg pressure, flashing the mixture at such temperature through a nozzle to the flash zone to form a fibrous product. 7

In this process, the flash temperature, the components of the mixture and the concentration of each in the mixture (with respect to the heat capacity of the components and with respect to the heat of vaporization of those components in the mixture which will be volatilized in flashing) are all chosen so as to produce in the flashed product a temperature which is less than 94 C., and advantageously, below C when the mixture is flashed into said flash zone. Desirably, the solvent or solvents selected have a normal boiling point at one atmosphere pressure between 20 and 130 C. and, preferably, between 50 C. and C. The polymer may be any polymer capable of forming fiber, preferably, a crystalline or partially crystalline polymer. The preferred polymers are crystalline or partially crystalline polyolefins, especially polyethylene and polypropylene.

In an additional feature of the invention, said flash zone pressure and the solvent (or solvents) in the mixture are selected so as to produce a vapor condensation point in the flash zone when the mixture is flashed thereinto which is at or below 60 C., an aqueous mixture of the flashed product is produced in the flash zone by introduction thereinto of dilution water at a temperature below 70 C. and, advantageously, within the range of 10 C. to 60 C., which temperature is at or above said solvent boiling point in said flash zone, and refining the aqueous mixture in a continuous manner at a'temperature below 70 C. and, advantageously, between 10 C and 60 C. Advantageously, at least a part of the refining may be carried out while the aqueous mixture is in pressure communication with the flash zone and subjected to the ambient pressure condition in the flash zone.

DESCRIPTION OF PREFERRED EMBODIMENTS ln practicing the process of the present invention, any polymer or copolymer may be employed which is capable of forming fibers by conventional spinning techniques. It is preferred to employ crystalline or par tially crystalline polyolefins such as low pressure polyethylene, isotactic or partially isotactic polypropylene, and ethylene-propylene copolymers. Additionally, polybutenes and polymethyl pentenes may be employed in the practice of this invention. Crystalline or partially crystalline polyamides and polyesters may also be used. Noncrystalline polymers such as polycarbonates, polysulfones, polyvinyl chloride, polymethylmethacrylate, polyacrylonitrile and polystyrene may be used. Mixtures of the foregoing with each other or other polymers may also be employed.

The preferred polyolefins employed are those having an intrinsic viscosity above about 0.7 dl/g., which for polyethylene corresponds to a viscosity average molecular weight of about 30,000 to 40,000.

The polymers employed in practicing the present process may be in the form of dried powder or pellets or, preferably, as a wet cake, slurry or solution of polyolefin in the reaction solvent as obtained after polymerization.

Generally, any substituted or unsubstituted aliphatic, aromatic or cyclic hydrocarbon which is a solvent for the polymer at elevated temperatures and pressures, which is relatively inert under the conditions of operation and which has a boiling point at atmospheric pressure that is between C and 130 C, preferably between 50 C and 100 C, and at the flash zone pressure that is less than the softening point of the polymer may be employed in practicing the present process. Illustrative of the solvents which may be utilized are aromatic hydrocarbons, e.g., benzene and toluene; aliphatic hydrocarbons, e.g., pentane, hexane, heptane, octane and their isomers and homologues; alicyclic hydrocarbons, e.g., cyclohexane; chlorinated hydrocarbons, e.g., methylene chloride, carbon tetrachloride and chloroform; higher alcohols; esters; ethers; ketones; nitriles; amides; fluorinated compounds, e.g., fluoro-hydrocarbons; nitromethane; and mixtures of the above solvents and other solvents having a boiling point between 20 C and 130 C at one atmosphere pressure.

The polymer-solvent mixture may be formed by any one of several methods. One may start with a solution of polymer in solvent as it comes from a solution polymerization process, either at the same concentration, diluted or concentrated. Alternatively, one may start with a slurry of polymer particles in the solvent such as is produced by a slurry polymerization procedure and the appropriate amount of water is added to the slurry or vice versa. A further alternative would be to start with a dry polymer powder, or granules, or a wet cake such as might be produced at some stage of solvent removal in the polymer plant, and the appropriate amounts of solvent is admixed therewith.

The polymer concentration relative to the solvent is not critical, the solvent being present in an amount that is greater than 100 percent by weight of the polymer and sufficient to give a viscosity at the flash temperature employed that can be easily handled. Frequently, this viscosity will be between 500 and 3,500 centipoises. Generally, the polymer concentration will vary from about 2 to about 30% by weight of the solvent 4 plus polymer, and preferably is in the range of about 5 to about 15%.

In one preferred embodiment water is employed as a flashing aid. In this embodiment the water may be in a continuous phase or discontinuous phase, depending upon the amount of water added to the polymer-solvent mixture and the manner of addition. If the water is to form the discontinuous phase it should be present in an amount less than To form a continuous water phase the water should be present in an amount greater than 30% by volume of the mixture and preferably between 50 and 70%. The particular method of mixing is not critical, but if it is desired to have the water form a discontinuous phase it has been found to be advantageous to have the solvent present prior to water addition since the solvent or polymer solution will form the continuous phase of the mixture to be formed. This latter approach is particularly desirable when one employs an amount of waterwhich is near the borderline of an inversion occurring, i.e., at the point where the amount of water is approaching that level where it would form the continuous phase. Conversely, if the water is added with or before ths solvent, it will tend to form the continuous phase.

A primary function of the water is to provide energy to aid the vaporization of the solvent during flashing since it is not desirable to have the temperature so high that there is sufficient energy imparted to the solvent alone to effect its complete vaporization. However, the amount of water should not be so great as to require the expenditure of unnecessary heat values in attaining the desired flashing temperature, i.e., once that amount of water required to form an aqueous solution or dispersion of the agent having a suitable viscosity is determined, additional water may be employed to a certain extent since it helps to lower the mixture viscosity and aids solvent vaporization but the additional amount need not be great.

Another function of the water is to reduce the temperature of the fibrous mass in the zone immediately following the nozzle (flash zone). The addition of water increases the total vapor pressure of the system at the moment of flashing, thus reducing the boiling point of the flashing mixture. This is independent of the amount of water employed, and very small quantities may thus be employed'for this purpose. As a practical matter, however, water would be employed in the amount of at least about 1% by volume of the solvent-water mixture. Lowering the boiling point of the mixture in this fashion will assist in establishing proper temperature conditions in the fibrous mass formed upon flashing in accordance with this invention, as discussed in detail at a later point.

Another function of the water is to act as the carrier for a hydrophilic water-dispersing agent for the fibers to be formed. It has been found that it is most advantageous to have the water-dispersing agent present during flashing and precipitation of the fibrous polymer. An equivalent amount of the same agent added at a later stage to the already formed fibers does not give the same degree of dispersibility and the presence of the agent enhances the reflnability of the fibers. Therefore, the water should be present in an amount sufficient to carry that amount of the hydrophilic agent employed to impart to the fibrous polymer the desired level of water dispersibility, preferably as a solution thereof. Additional water above such minimum amount required to carry the agent may be employed to impart a suitable viscosity to the aqueous solution or dispersion agent,

i.e., the aqueous solution of the water-dispersion agent should not be so viscous as to present problems of handling or incorporation into the polymer solution as a dispersed phase. Also, the water can aid in reducing the viscosity of the mixture to a level less than that of the polymer solution alone, thus permitting higher polymer concentrations.

The agents which may be added to the mixture to impart water dispersibility to the fibrous polymer are preferably watersoluble or partially water-soluble high molecular weight materials. However, they may also be materials which are soluble or partially soluble in the solvent so long as they are somewhat hydrophilic and impart water dispersibility to the fibers. The amount of water-dispersing agent employed may range from 'about 0.1% to about by weight of the polymer, preferably from about 0.1% to about 5% by weight.

The preferred water-dispersing agent is an at least partially water-soluble polyvinyl alcohol (PVA) having a degree of hydrolysis greater than about 77% and, preferably, greater than about 85 mol. and having a viscosity (in a 4% aqueous solution at C.) greater than about 2 centipoises. Desirably the PVA has a degree of polymerization in the range of 200 to 4000 and preferably between 300 and 1500. If desired, the PVA may be chemically modified to enhance its adhesion to the polymer, dispersion and other properties. The polyvinyl alcohol is preferably added with the water at the time the mixture is formed. illustrative of other water-dispersing agents that may be employed are cationic guar, cationic starch, potato starch, methyl cellulose and Lytron 820 (a styrene-maleic acid copolymer).

Such water dispersing agents are also advantageous in developing the fiber properties during refining of the flashed product in accordance with this invention as described at a later point. Alternatively for this purpose, such agents may be added subsequent to flashing, such as with the dilution water for refining. It is particularly advantageous to add at least 1% and preferably .between I%% and 5% by weight of the flashed polymer of polyvinyl alcohol, either before and/or after flashing (but prior to refining).

the mixture will quickly separate into two distinct and separate phases.

The ingredients are then heated to a suitable temperature and preferably agitated if water is present to form a uniform mixture wherein water is present as a discontinuous or dispersed phase within a continuous phase of polymer solution or as a continuous phase with polymer solution dispersed uniformly therein, depending upon the water concentration and mode of addition as previously discussed. The temperature employed is preferably above the melt dissolution .temperature of the polymer in the solvent employed. The melt dissolution temperature of any particular solvent is deter mined by placing low concentrations of the polymer (e.g., 0.1 and 1.0% by weight) into the solvent in a vial which is then sealed and placed in an oil bath. The temperature of the oil bath is raised slowly (e.g., 10

C/hour) until the last trace of polymer disappears. This temperature is the melt dissolution temperature. In some instances, it may be desirable to operate at a temperature below the melt dissolution temperature. In this case the temperature should be high enough under the operating conditions so that the polymer is dissolved in the solvent or at least is in a swollen state with sufficient fluidity to be discharged from nozzle, i.e., in a plastic state.

Flashing is preferably carried out substantially adiabatically, utilizing the heat (enthalpy) in the heated mixture to provide the heat of vaporization for vaporizing substantially all of the solvent when the mixture is discharged to the flash zone held at a suitable lower pressure. Accordingly, for adiabatic flashing the temperature of mixture prior to flashing should be high enough to provide sufficient heat content or enthalpy for vaporization adiabatically of substantially all solvent upon flashing to the flash zone. However, the maximum temperature employed should be less than the critical temperature of the solvent and/or the decomposition temperature of the polymer.

It is also possible to carry out the flashing to some extent in a non-adiabatic fashion, for example, by the addition of heat to the material as it is flashed from the nozzle. For instance, low pressure steam (e.g., below 20 psi) or water at 100 C. may be added to the fibrous noodle in the flashing zone as by injection thereof in a conduit immediately following the flash nozzle into which the flashed noodle is also injected. In this case, the flashing temperature should be chosen so the heat content in the mixture to be flashed plus the heat added to the flashed material is sufficient to vaporize substantially all of the solvent in the flash zone.

The pressure-employed in the vessel containing the heated mixture is preferably substantially autogenous. While pressures substantially higher than autogenous may be employed, they are not preferred as in some cases poor fiber formation may result. It may be desirable, particularly in batch operations, to employ an inert gas such as nitrogen during the flashing operation to maintain substantially autogenous pressure in the vessel and thus maintain the velocity of the mixture through the nozzle at a fairly constant level.

Flashing is preferably effected through a nozzle which has a substantial longitudinal dimension in order to efficiently impart shear to the mixture (particularly the polymer component thereof) immediately prior to flashing. Such shearing action aids fiber formation and enhances fiber properties for paper making purposes. The nozzle may be circular or noncircular in crosssection and may be an annulus.

in addition to the foregoing more general parameters for the flashing operation, an important feature of this invention is the maintenance of certain pressure and temperature conditions in the flash zone and the interrelationship of these conditions with the temperature and other conditions of the mixture prior to flashing. In accordance with this invention the flash zone is maintained at a pressure of between 50 mm Hg and 600 mm Hg and the other conditions of flashing are selected so that the temperature of the flashed product is almost immediately lowered in the flash zone, by evaporation of substantially all of the solvent (and a portion of the flashing aids, if employed), to a temperature below 94 C. and, preferably, below C. It will be appreciated that a portion of the solvent may still be unvaporized in the close vicinity of the flash nozzle so in this case the appropriate point at which the temperature of the flash product should be below 94 C is that point downstream of the nozzle where substantially all (above 95%) of the solvent has vaporized. In a typical flashing procedure in accordance with this invention vaporization may be substantially complete 10 to 100 cm downstream of the nozzle. However, this can vary widely depending upon the flow velocity, flash zone pressure, flash temperature, solvent, etc.

Importantly, in the mixture to be flashed, all of the components of the mixture and the concentration of each in the mixture are chosen with respect to the heat capacity of each, with respect to the heat of vaporization of each component which will be volatilized in flashing, and with respect to the flash temperature chosen so as to produce in the flashed product a temperature below 94 C. and, preferably, below 80 C. upon flashing of the mixture into the flash zone held at 50-600 mm Hg pressure. Expressed in another way, the heat content of the mixture to be flashed and the heat to be removed through vaporization of the vaporizable components (solvent and any flashing aids vaporized, if employed) should be adjusted so that the residual heat in the flashed product, after removal of the heat of vaporization of the vaporized components, will impart a temperature in the flashed product which is below 94 C. and, preferably, below 80 C. Selection of the appropriate flashing temperature and of the components of the mixture and their concentrations for this purpose will depend upon the pressure within the range of 50 -600 mm Hg selected for the flash zone and the amount of heat added to the flash material during flashing if the flashing is performed non-adiabatically. If the flash temperature is too high or if the components of the flash mixture and their concentrations with respect to their heat capacity and heat of vaporization (for the vaporizable components) are improperly chosen, the temperature of the flashed product, upon substantially complete evaporation of the solvent, will remain above 94 C. If the flash temperature is too low or, again, the components are improperly chosen with respect to heat capacity and heat of vaporization, there will be incomplete evaporation of the solvent. For the purposes of this invention, appropriate selection of these variable 45 parameters, namely, the flash temperature, components and concentrations thereof in the flash mixture, may be determined for a given pressure condition in the flash zone by making a heat balance for the flashing operation which will produce the desired noodle tem- 50 perature below 94 C. Advantageously, these variable parameters may be selected so as to satisfy the following equation:

V,= Enthalpy of vaporization of flashing aids vapor- 65 ized (if any) W Weight of polymer in the flashed product C,,= Heat capacity of polymer in the flashed product W',.= Weight of the flashing aids, adjuvants, and/or nonvolatile components other than polymer in the flashed product (if any) C',= Heat capacity of the flashing aids in the flashed product (if any) and where such enthalpy values are based on the same temperature datum plane and the heat capacities are those applicable between such datum plane and the temperature of the flashed product.

In using this formula, the heat capacity values and weights of the flash components may be substituted into this formula, for example, as follows for the specific case where a single polymer, solvent and flashing aid are present in the flash mixture:

where the additional terms are:

W Weight of the solvent in the flash mixture C, Heat capacity of the solvent in the flash mixture W,= Weight of the flashing aid in the flash mixture C;= Heat capacity of the flashing aid in the flash mixture C Heat capacity of the polymer in the flash mixture AH, Enthalpy of vaporization of solvent under flash conditions AH,= Enthalpy of vaporization of flashing aid under flash conditions T,= Flash temperature, C. and where the indicated heat capacities are those applicable between the flash temperature and the previously mentioned temperature datum plane.

In practice, the heat capacity and enthalpy of vaporization values for the desired components can be substituted into this equation. Then, a flash temperature and the concentrations of the flash mixture components may be selected relative to each other to satisfy the equation for a desired flashed product temperature. For ease of calculation it can be useful to program these variables for computer analysis to select the desired components and flash temperature.

It may not be necessary to actually measure the noodle temperature (which is a cumbersome procedure under the flash zone conditions). All that is necessary for control purposes is to maintain the indicated parameters for the flash procedure at values that satisfy this equation for the noodle temperature below 94 C.

- which is desired. Of course, the various parameters should also satisfy the other conditions for proper flashing as previously discussed, e.g., the flash temperature should be above the melt dissolution temperature, substantially all of the solvent should be vaporized, etc.

During flashing, the polymer is precipitated as a fibrous noodle, which is a loose aggregation of fibers which is sometimes continuous. The fibrous noodle is collected in a suitable receiving vessel, preferably one which permits the vaporized solvent to be separated therefrom.

Fibrous material may be formed in accordance with the foregoing procedures which has improved proper ties, which will be discussed at a later point. The mechanisms by which the combined parameters of the pressure conditions in the flash zone and the flash conditions which produce a noodle temperature below 94 C. canresult in improved fiberformation have not been fully elucidated. However, in addition to other possible mechanisms, it is believed that the more rapid and pronounced cooling of the precipitating polymer combined with the relatively violent flashing caused by the prescribed pressure conditions in the flash zone are at least, in part, responsible. I

The fibrous noodle formed in accordance with this invention may be processed, by the various conven- .tional procedures, for use such as for paper making. However, it is an additional advantageous feature of this invention to process the noodle in a manner which is interrelated with the conditions of flashing and wherein water is introduced into the flash zone for processing of the flashed product. In this procedure the solvent and flashing aid if employed in the flash mixture and the pressure in the flash zone at the location where the introduced water is in contact'with the flashed product (between 50-600 mm Hg) areappropriately selected so that the temperature at which vapor condensation would occur (condensation point) in the flash zone during flashing is maintained at or below 60 and, advantageously, below 55 C. For this reason, the solvent and flashing aid (if employed) selected should have a combined vapor pressure at 60 C. which is at least 600 mm Hg, or higher. correspondingly, the pressure in the flash zone at and following the location of introduction of the processing water should be maintained at least as low as the combined vapor pressure at or below 60 C of the solvent and any flashing aid employed. For convenience, reference may be made to easily available vapor pressure tables for solvents and flashing aids to make appropriate selectionof solvents and flash zone pressures in accordance with the forego- While utilizing the foregoing flashing conditions to produce a solvent boiling point in the flash zone at or below 60 C., dilution water may be introduced into the flash zone at a temperature which is (a) below 70 C. and advantageously within the range of 10 and 60 C., and (b) at or above the condensation point of the vapor in the flash zone. It is desirable, particulary in a large scale operation, for the dilution water to be at a temperature at least and preferably between and C. higher than the boiling point of the solvent in the flash zone as'a safety factor to prevent any solvent condensation by the dilution water. The dilution water forms an aqueous mixture with the noodle in the flash zone and this mixture is then refined. Advantageousiy, at least the initial part of this refining is carried out while the mixture is still indirect flow communication with the flash zone and subjected to the pressure condition of the flash zone. That is to say, the initial refining is preferably conducted in a continuous fashion while the aqueous mixture is subjected to the ambient pressure of the flash zone (between 50 and 600 mm Hg) and immediately following such refining. I

Desirably, the dilution water added to the flash noodle in the flash zone is at a temperature and in sufficient quantity so that the aqueous mixture assumes a temperature below 70 C. and preferably between l0 C. and

60 C. In the case where'the noodle has a temperature prior to' dilution which is 70 C. or above, it is desirable to add dilution water at a temperature below 70 C. in a quantity sufficient to create a temperature below 70 C. in the aqueous mixture formed therewith.

The total dilution "water' added is desirably sufficient to provide an appropriate aqueous mixture or slurry for refining of the flashed product; Typically, an aqueous mixture with a consistency of l to 10%, or higher, by weight of the flashed product may be formed for refining. Preferably, refining is conducted in a disc or conical refiner and is, preferably, conducted in a fashion to place the fibers in a form optimumly suitable for paper making. The refining of the fibrous noodle separates discrete fibers and also may be used to control the length of the fibers. Preferably, refining is carried out in two or more stages with multiple passes through the refiner in the latter stages. It may be desirable in the latter stages of refining to conduct such refining outside the flash zone. That is to say, the latter stages of refining may, preferably, be conducted under atmospheric pressure.

importantly, this refining is carried out at a temperature below 70 C. and preferably between 10 C. and C., which has been found to cause an unexpected degree of fibrillation or fiber development, particularly when conducted in the presence of a dispersing agent such as polyvinyl alcohol, thereby greatly enhancing the strength of the fibers for paper making use.

The foregoing flashed noodle processing procedure provides a unique and industrially practical mode of continuously producing a flashed noodle and refining same at a temperature below 70 C. Establishing a vapor condensation point in the flash zone of 60 C., or below, makes possible the addition of dilution water in the flash zone at a temperature below 70 C. If the vapor condensation point were appreciably above 60 C., addition of dilution water at these temperatures would cause condensation of solvent on the flashed product resulting in unacceptable agglomeration or flocculation of the fibers. Additionally, by selecting a dilution water temperature and amount which will lower the aqueous mixture to be refined to a temperature below 70 C., refining may be accomplished at the desired temperatures on a practical, continuous basis even in the case where the flashed noodle has a temperature of 70 C., or higher. Becuase of the difficulty of cooling the noodle, which has low heat conductivity, to the desired refining temperature, other than by use of dilution water and because of the difficulty of extracting the semisolid flashed product (which tends to float in water) from the reduced pressure flash zone other than in the form of an aqueous, at least partially refined, slurry, the foregoing procedures are particularly suitable for a practical continuous operation. This procedure has additional advantages in that by conducting at least the initial refining under ambient pressure of 50-600 mm Hg, removal of residual minor amounts of solvent, which may be entrapped in the flashed noodle and cause fiber flocculation, is facilitated.

As mentioned previously, a principal advantage of the process of this invention is the ability to improve the properties of the fibers produced as compared to made by the process of the present invention is the 1 1 length, various strength properties of paper made therefrom increase with the drainage factor of such fibers.

Another indication of improvement of the fibers made in accordance with this invention is their slenderness relative to fibers prepared by typical conventional technique. It is desirable to produce fibers which are relatively thin (or of low coarseness) as these fibers will impart higher opacity, density and better formation to the paper prepared therefrom.

Generally, the set of operating parameters of the present invention will result in improved fiber properties such as thinness and drainage factor compared with fibers prepared using typical conventional parameters. Because other process variables in addition to the specific parameters of this invention also influence fiber properties (e.g., flash nozzle size and configuration, polymer type and molecular weight, solvent, flashing aids, dispersants, etc.), such resulting fiber comparisons are appropriately made with the other process variables held constant.

For the same reason, i.e., the influence of other process conditions besides the parameters specific to this invention on the resulting fiber properties, no absolute fiber property values can be assigned to the fibers which may be prepared by the process of this invention. However, with appropriate selection of all parameters, it has been found that pulps can be produced in accordance with this invention which have a drainage factor in excess of 1 and as high as 50 to 100 seconds per gram and which have an average coarseness below decidrex (as measured by TAPPI Test 234 SU 67) and frequently between 1 and 10 decidrex (m/lOO m). For paper making use, a drainage factor between 2 and 10 may be the preferred range as an appropriate balance between increased strength and ease of water removal from the fibers. Higher drainage factors can be obtained and may be useful where the enhanced strength is more important than rapid water removal.

In the accompanying drawing, the

FIG. 1 represents a schematic representation of apparatus suitable for use in carrying out the process of this invention, and

FIG. 2 is a detailed representation of the flash nozzle schematically shown in FIG. 1.

In FIG. 1, 1 is a steam jacketed vessel, provided with an agitator 1a, which may be charged with solvent, polymer (or polymer solution) and, if desired, flashing aids such as water. Conduit 2 is provided at the bottom of vessel 1 in communication with flash nozzle 3 through shut-off valve 2a (a ball valve). As seen in FIG. 2, flash nozzle 3 is a circular orifice of substantially smaller diameter than conduit 2. After the mixture is heated to the desired temperature and agitated, if necessary, to dissolve the polymer and/or disperse the flashing aids, valve 2a is opened and the mixture thus formed is forwarded from vessel 1 to flashing nozzle 3 under autogenous pressure of the heated mixture. As the mixture discharges from vessel 1, nitrogen or other inert gas may be introduced into the head space thereof through line 4 in order to maintain the pressure in the vessel at autogenous or higher pressure. The mixture flashed through nozzle 3 into the flash zone which is comprised of a separation vessel, cyclone 6, and connecting conduit 5. Conduit 5 is a pipe having an internal cross-sectional area larger than that of flash nozzle 3 and of sufficient internal diamter to permit rapid, unrestricted passage of the flashed noodle to cyclone 6, preferably 12 having an internal cross-sectional area many times larger than that of the nozzle 3.

Vaporized solvent and water leaving cyclone 6 pass through line 7 to scrubbing tower 8 in which water and any entrained polymer is removed from the vapor stream. The solvent vapor leaving scrubbing tower 8 passes to condenser 10 through condenser conduit 9, where such vapor is condensed, and passes via conduit 11 to solvent collection tank 12.

In order to provide reduced pressure throughout the system downstream of nozzle 3, a vacuum generating device, steam ejector 14, is connected by conduit 15 to solvent collection tank 12. It will be appreciated that there will be a pressure gradient between the flash nozzle 3 and cyclone 6 due to the constricting effect of conduit 5. Therefore, the vacuum generated by ejector 14 should be adjusted so that the pressure condition in conduit 5 in the vicinity of nozzle 3 is below 600 mm Hg.

The flashed fibrous noodle entering cyclone 6 through conduit 5, together with the unvaporized portion of water or other flashing aid present, passes downward through conduit 16 into disc refiner 17 where it is refined. Conduit 18 is provided in cyclone 6 for introduction of nitrogen prior to start-up and to maintain an oxygen-free atmosphere therein during operation. Nitrogen may also be introduced during operation for the same purpose and also to assist in regulating the pressure condition in the flash zone. Conduit 19 is provided for introduction of water at an appropriate low temperature to form a mixture of slurry with the fibrous material having an appropriate consistency for disc refining.

The refined material leaving the refiner passes through conduit 20 to first receiving tank 21. To provide reduced pressure in receiving tank 21 (and disc refiner 17) conduit 22 connects receiving tank 21 with condenser conduit 9. Maintenance of the reduced pressure throughout the refining operation in this manner promotes removal from the flashed product any small residual amount of solvent which may remain therein. It is thus seen that this refining stage is in direct pressure communication with and a part of the flash zone.

The water slurry of refined fibers may be withdrawn from receiving tank 21 through line 23 utilizing pump 24, for a second refining step in disc refiner 25 under atmospheric pressure conditions. The fibrous slurry leaving refiner 25 passes through conduit 26 to second receiving tank 27, which is maintained at atmospheric pressure, where it is collected prior to further processing for shipment or for paper making use. If desired, the fibrous slurry leaving refiner 25 may be recycled through line 28 for one or more additional passes through refiner 25.

The fibers after refining may be diluted to a suitable consistency and made into synthetic paper webs either alone or blended with normal cellulose paper making fibers. Alternatively, the fibers can be dewatered, pressed into bales, stored and shipped to the ultimate user.

The illustrated apparatus may be operated on a batch basis as described or on a continuous basis by continuously feeding vessel 1 with polymer solution and any flashing aids desired as flow rates to maintain the appropriate mixture in the vessel for flashing, while heating the vessel to maintain the mixture at the appropriate flash temperature. In order to insure uniform dispersion of flashing aids, it may be desirable to place an inline mixing device in line 2 between vessel 1 and flash nozzle 3.

Optionally, instead of using a stirred heated vessel such as vessel 1, it is also possible to prepare the mixture on a continuous basis by blending a polymer solution with any flashing aids desired (as by adding superheated water) continuously in an in-line mixing device just prior to flashing through the nozzle. It is also possible to utilize an in-line mixer.

An adiabatic operation has been described but for non-adiabatic operation low pressure steam or water at 100 C. may be injected into conduit immediately downstream of nozzle 3 through a tee connection therein (not shown) in an appropriate amount to add heat to the flashing mixture consistent with the prescribed parameters of operation of the invention.

The following examples will illustrate the invention:

EXAMPLE 1 The apparatus employed in this example 'is that illustrated in the drawing previously described, except that scrubbing tower 8 was omitted. The dissolution vessel was a 250 liter, stainless steel, baffled tank having a centrally disposed three h.p. rotating stirrer having three blade back-swept impellers located therein, each impeller being 50 cm. long. This stirrer was operated throughout the run.

The vessel was charged with 9.6 kg of high density polyethylene having an intrinsic viscosity of 1.4 dl/gm and a melt index of5.58 (Mitsui 2,200 P) and 120 liters of water containing polyvinyl alcohol (grade NL-OS from Nippon Gosei Chemical Industries, viscosity 4.6-6 centipoise measured at 4% in water at 20 C. and having a degree of saponification of 98.5-100 mol.%) in the amount of 3% by weight based on the polymer in the vessel. Then 120 liters of n-hexane were added and the vessel was sealed and heated to 150 C. and held with stirring for 2-3 hours to dissolve the polyethylene and to form a dispersion of the polymer solution, with the water assuming the continuous phase.

The water-to-hexane ratio in the mixture was 1:1 by

'volume and the polyethylene concentration was 80 gm per liter of hexane. With the mixture heated to 150 C. and a pressure in the vessel of 175 p.s.i. the valve 2a at the bottom of the vessel was opened and the mixture was flashed through nozzle 3 into conduit 5 (which has an internal diameter of one inch and a length of ten meters) and conveyed to cyclone 6. The flash nozzle consisted of a circular orifice having an internal diameter of 3 mm and a length of 20 mm. The mixture flowed through the nozzle at the rate of 10.4 kg of polyethylene per hour. Steam ejector 14 was activated to provide a flash zone pressure of 350 mm Hg measured immediately downstream of flash nozzle 3. 1n cyclone 6 the pressure was about 200 mm Hg and the condensation point of the vapor was about 27 C. The temperature of the flashed noodle in conduit 5 at the point where substantially all of the solvent was'vaporized was estimated to be about 63 C. Dilution water at 50 C. was introduced through line 19 at a rate to provide a consistency of between 1 and 5 gm of polyethylene per liter of water. The mixture of water and fibrous noodle, at a temperature of 50 C., was continuously fed to refiner 17, a 12 in. diameter single disc refiner manufactured by Kumagaya Riki Kogyo, for a single pass at a plate clearance of 150 microns.

The plates of the refiner had brushing-type tackle consisting of one-sixth inch wide, 1 to 2 inch long bars separated by one-sixteenth inch wide, three-sixteenth inch deep grooves, the grooves being offset about 10 from the radial direction, withno dams. The ambient pressure in refiner 17 and receiving tank 21 was about 300 mm Hg. The resulting slurry in receiving tank 21 was pumped intorefiner 25 for a second stage of refining at atmospheric pressure for a total of seven passes at a consistency adjusted to 5.9 gm polyethylene per liter of water, and at the same temperature and plate clearance and with the same type of refiner plates as in refiner 17. The plate clearance of refiner 25 was then adjusted to microns and the slurry recycled therethrough for an additional 8.5. (average) passes.

The resulting fibers had a classified fiber length of 1.35 mm and a fiber fractionation, when tested according to TAPPl Standard T233su64, as shown in Table l.

TABLE I Mesh Weight Through 150 fied web pressing (400 p.s.i.) and a heat-bonding step (121 C. at minimum pressure).

TABLE 11 Density 0.380 Breaking length 1.53 Stretch 18.9 Zero span (Km) 2.10 Tear strength (gm/sheet) 92 Porosity (Gurley secs) In the foregoing example and subsequent examples, the density, stretch and breaking length were determined by TAPPI Standard T-220, tear strength by TAPPI Standard T-414 and zero span by TAPPl Standard T-231. Porosity is reported in Gurley seconds.

The drainage factor in this and following examples was determined substantially in accordance with TAPPI Test T221 05-63 with a slight modification in the method of calculation. Briefly, approximately 10 grams of a fiber sample is weighed and dispersed in water. Theslurry is then added to the standard sheet mold and water added to the mark. The slurry is stirred by four up-and-down strokes of the standard stirrer, which is then-removed. Thewater temperature in the mold is measured and the drainage valve opened. The time between the opening of the valve and the first sound of suction is noted. The procedure is repeated with water only (no fiber) in the sheet mold and the temperature and drainage time noted. The drainage factor in seconds pergram is then calculated as follows:

where D'F drainage factor, seconds/gram D drainage time with pulp in mold, seconds d drainage time without pulp in mold, seconds V viscosity of water at temperature T W weight of fibers employed in test, grams The quantityll/V llis tabulated in the aforementioned TAPPl Test T221 08-63. This quantity is multiplied by 0.3 which has been empirically determined for the present fibers.

EXAMPLE 2 To compare the effect of utilizing flash zone pressure of 600 mm Hg the procedure described in Example 1 was repeated employing identical apparatus, materials, concentrations and conditions, except that the pressure in the flash zone was held at approximately 600 mm Hg in the vicinity of the flash nozzle and 420 mm Hg in the cyclone. The resulting flash noodle temperature at the point of substantially complete solvent vaporization was estimated to be about 73 C. The condensation point of the vapor in the cyclone was about 46 C., and the dilution water was added at approximately 62 C.

The flashed product was refined to produce a fibrous product with fiber length characteristics substantially equivalent to those of the product of Example 1. Specifically, following dilution with water at 60 C. to a consistency of between 1 to 5 gms/liter, the fibrous material was refined for one pass to refiner 17 with a plate clearance of 100 microns and of a temperature of 62 C. and then with passes through refiner 25 at a plate clearance of 100 microns, at an average temperature of 60 C. and consistency of 8 vicinity complete The resulting fiber had a classified fiber length of 1.33 mm and a fiber fraction distribution as shown in Table III.

TABLE III Mesh Weight On 16.57 On 35 39.29 On 65 24.80 On 150 13.10 Through 150 6.25

The fibers had a drainage factor of 6.85 sec/gm. Handsheets were prepared and tested with the result Comparison of the above results with'Example 1 shows that the drainage factor in this'example is less than that for the product in Example 1 and strength properties of the handsheets show a similar decline. This example by way of comparison, illustrates the advantages of more preferred range of 50-500 mm Hg pressure in the flash zone.

EXAMPLE 3 The example which follows illustrates practice of the invention with a flashing system employing water as a flashing aid and wherein the water assumes the discontinuous phase. The same materials, concentrations and flashing conditions were used as described in Example 1, except as follows:

a. At start-up the dissolution vessel was charged by first adding polymer solution followed by the PVA- containing water in order to establish the water as the discontinuous phase;

b. The flashed noodle was adjusted to a slightly higher consistency (6.7 gm/liter) prior to secondary refining.

The resulting fibers had a classified fiber length of 1.14 and a fiber fractionation as shown in Table V.

TABLE V Mesh Weight On 20 4.77 On 35 41.37 On 30.40 On 16.21 Through 150 7.31

The fibers had a drainage factor of 16.5 sec/gm. Handsheets prepared from these fibers had the properties shown in Table VI-.

EXAMPLE 4 To demonstrate the beneficial effects of the invention in decreasing the degree of entanglement of the flashed fiber product, the flashing procedures of Example 2 were repeated in a series of three runs utilizing in each case the same flashing conditions, concentrations, and materials, except for the pressure conditions maintained in the flash zone. In each of these runs samples of the flashed fibrous product were taken from cyclone 6 in the unrefined state and these samples were tested as will be described. In run 1, the flash zone was maintained at 360 mm Hg; in run 2, at 500 mm Hg; and in run 3, for comparison, at 760 mm Hg.

Another series of three runs were made following the flashing conditions, concentrations and materials of Example 3 but with the flash zone maintained at 360 mm Hg for run 4, 500 mm Hg for run 5, and at 760 mm 5 Hg, for comparison, in run 6. In these three runs the flashing nozzle was of the same length as that used in Example 3 but its internal diameter was 2 mm. Unrefined samples of the flashed product were collected and TABLE VII of Product Flash Zone "Passing Through Run No K (Pressure (mm-Hg) -mesh Screen.

3 (comparison) 760 22.3

6 (comparison) 760. 3.2

It can beseen that the percentage of fibers able to v H l 8 bu tyl -4 hydroxytoluenein an amount equal to 0.2% of the polypropylene.

This mixture was heated to a temperature of approximately 140C and flashed to a flash nozzle which was a circular orifice 5 mm in diameter and 1000 mm long into the flash zone which was maintained at approximately 400 mm Hg pressure in conduit 5 in the vicinity of the flash zone and at approximately 240 mm Hg in cyclone 6. The vapor condensation point in cyclone 6 was approximately 32C. Dilution water was added to the flashed product in cyclone 6 at a temperature of 44C to provide a consistencyof between 1 and 5 gm per liter and this mixture was refined by a single pass at pass through a lO-mesh screen is markedly greater for the runs made in accordance with this invention (runs 1, 2, 4 and 5). This demonstrates thatby utilizing the interrelated parametersof'thisinvention'the degree of entanglement of the flashed fibrous product can be materially'decre'ased.

EXAMPLE 5 The procedure of Example '3 was repeated utilizing a higher molecular weight polyethylene as the polymer,

specifically Mitsui Petrochemical Co grade 7000P which has a melt flow-index of 0.04. In this run the amount of polyethylene was adjusted to provide a concentration of the polyethylene in the solvent in the dissolution tank of 35 gm per liter. All the other conditions of flashing were the same as in Example 3 except that the flash zone pressure in the vicinity ofthe nozzle was held at 360 mm Hg. The flashed product was refined at 50C at a slurry concentration of 1.1 gm per liter as in Example 3 to a classified fiber length of 1.40 mm. The resulting fibers had a drainage factor of 40.7 sec/gm. Handsheets made therefrom had the properties listed in Table VIII.

The procedures of Example 1 were repeated utilizing polypropylene as the polymer, specifically a polypropylene having an intrinsic viscosity of 1.90-centipoise, melt flow index of 14.5 gm/minute and anisotacticity index of-.94 .7%. The amount of polypropylene added to the dissolutionyessel was adjusted to give a polymer concentration in the hexane of 100 gm per liter. The volume ratio of solvent. to water was 1:1. The polyvinyl alcohol (added in an amount equal to 3% of theweight of the polypropylene) had a degree saponification of 95-100 ml. percent. and a viscosity (4% -inwater at 20C) of'-25- 29c.p;;-Also added;with the .water, as a heat stabilizer for the polypropylene, was 3,5 -ditertiary 44C in refiner l7 utilizing cutting type refining plates (plates having more widely spaced, higher tackle than the brushing type plate) with a plate spacing of microns. The mixture was then allowed to settle in receiving tank 21 and the dilution water drawn off. Then lower temperature water was added to bring the temperature of the slurry to 22C and the consistency thereof'to 4.0 gm per liter. This mixture was refined in refiner 25 using the brushing type plates of Example 1 for two passes at a zero plate clearance and at a temperature between 22 and 30C and then for nine passes at a plate clearance of 50 u and at a temperature of approximately 30C.

The resulting fibers had a classified fiber length of 1.66 sec/gm and a drainage factor of 1.66.

' Handsheets made from the fibrous product had the properties listed in Table IX] When it was attempted to produce polypropylene fibers under similar conditions but utilizing flash zone pressures of 760 mm Hg and above, the result was the formation of an endless unfibrilated noodle or weak powder like fibers.

EXAMPLES 7 11 A series of four runs were carried out on a continuous basis in equipment as described in Example 1.

During each run the dissolution vessel was continuously charged with an n-hexane solution of high density polyethylene at C having a concentration of 59 gm of polyethylene per liter of hexane. The polyethylene had a melt flow index of 5.5. An equal amount of polyvinyl alcohol containing water at 150C was also continuously metered into the vessel during the run to provide a mixture in the vessel having a water to hexane ratio by volume 1:1. The polyvinyl alcohol (grade AL-04 having a degree of polymerization of 450 160,

viscosity of approximately 4 centipoise measured at 4% in water at 20C and a degree of saponification of solution assuming the continuous phase. When the vessel was fully charged and the mixture well dispersed at a temperature of 150C, the valve at the bottom of the vessel was opened and the mixture continuously fed to flash nozzle 3.

Flash nozzle 3 was an angle valve (Yamatake Honeywell Model No. 1010) which had internal dimensions as follows: Valve seat section 8mm in diameter and 10mm in length with a V" cut shaped valve body adapted to nest in the valve seat. During flashing the 10 valve is partially opened and adjusted for the desired rate of flow.

Conduit 5 had an internal diameter of 21 mm and a length of about 10 meters.

The flashed product in each run was refined in refiner 17 utilizing the refining plates described in Example 1 and in refiner 25 utilizing similar brushing type plates but which had a minor number of more widely spaced deeper cutting type tackle. 1n Example 10, additional PVA was added to the flashed product. After pri- 20 mary refining in refiner 17, the material was permitted to settle in receiving tank 21 and dilution water drawn off. Then additional dilution water was added prior to secondary refining in refiner 25, in order to adjust the temperature and consistency as indicated. The other 25 flashing conditions and refining conditions and the properties of the resulting products are shown in Table X.

To evaluate the fibers of the foregoing example with respect to the amount of gels and chunks of polymer therein, samples were taken from the fibers of Example 9, 10 and 11 and each was mixed with bleached kraft hardwood fiber to form a mixture of 60% by weight wood fiber and 40% polyethylene fiber. Handsheets were made of each sample in the manner previously described and these handsheets were subjected to calendering with linear pressures from 14 to 31.5 kg/gm. The handsheets were visually inspected for transparent spots resulting from gels and chunks. In comparison with similar handsheets made from the comparison fibers described above, these handsheets had a much lower number of tansparent spots.

What 1 claim is:

l. A process for manufacturing papermaking pulp of synthetic fibers comprising forming a mixture ofa polymer and a solvent for such a polymer, flashing said mixture at a temperature which is high enough to bring said polymer to a plastic state and which will permit substantially complete vaporization of the solvent when the mixture is flashed, flashing said mixture into into a flash zone to produce a fibrous product, and refining the fibrous product, characterized in that a. said flash zone is maintained at or below 600 mm Hg pressure, b. said flashing temperature, the components of said mixture and the concentration of each in the mix- TABLE X Flash Conditions Example 7 8 9 1O 1 1 PVA in flash mixture by weight of polymer) 1.5 1.5 3 1.5 1.5 Flash zone pressure in proximity of flash nozzle (mm Hg) 590 560 585 560 570 Flash zone in cyclone (mm Hg) 320 320 360 350 310 Vapor condensation point in cyclone (C) 39 39 42 4| 38 Temperature of dilution water added in cyclone (C) 50 70 50 5O PVA added with dilution water by weight of polymer) 0 0 0 1.0 0 Calculated temp. of flashed product m. from nozzle (C) 73 72 73 73 72 Primary Refining Temperature (C) 50 50 70 50 50 Plate clearance (microns) 50 50 5 200 200 Passes 2.8 4 4 4 4 Consistency (gm/L) 5 5 S 5 5 Secondary Refining Temperature (C) 46 46 62 48 44 Plate Clearance (microns) 50 50 50 100 100 Passes 6 8 8 10 10 8 Consistency (gm/L) 3.7 3.3 3.7 3.7 3.7

Product Characteristics Classified fiber length 1 15 1 15 0.99 l 39 1.30 Drainage factor (gm/sec) 0 6.1 4 3.1

Handsheet Properties Density (gm/cc) Tear strength (gm/sheet) Breaking length Stretch TEA lnternal Bond C Range (Scott units) Brightness Opac'ity ture, with respect to their heat capacity and with respect to the heat of vaporization of the components vaporized during flashing, are all selected relative to each other to produce a temperature of less than 94C in the flashed fibrous product upon evaporation of substantially all of said solvent,

0. the solvent has a vapor condensation point in the flash zone below C,

d. dilution water is introduced into the flash zone at a temperature above the vapor condensation point 21 p of the solventbut below 70C to form an aqueous "mixture, v e. the aqueous mixture is passed directly to a refiner which is in direct pressure communication with the flash zone,'and f. the aqueous mixture isrefined-in the refiner at a temperature below 70Ctoproduce the papermaking pulp.

2. A process as in claim 1 and wherein the flash zone pressure is maintained between 50 and 500 mm Hg pressure.

3. A process as in claim 1 and wherein saidflashing temperature, the components of said mixture and the concentration of each in the mixture, with respect to their heat capacity and with respect to the heat of vaporization of the components vaporized during flashing, are all selected relative to each other to produce a temperature less than 80C in the flashed fibrous product upon evaporation of substantially all of said solvent.

4. A process as in claim 1 and wherein said flash mixture contains v a. water as a flashing aid in an amount between about 30 and 70% by volume of the mixture,

b. a saturated hydrocarbon solvent having a boiling point between C and 130C at. atmospheric pressure, and

c. a crystallizable pol'yolefin in an amount between 2 and of the combined weight of the solvent and polymer.

5. A process as in claim 4 and wherein said mixture contains between about 1 and 5% by weight of the polymer therein of a polyvinyl alcohol having a degree of hydrolysis greater than 77 mols. and a degree of polymerization between 200 and 4000. Y

6. A process as in claim 4 and wherein said solvent has a boiling point at atmospheric pressure which is be tween 50C and lO0C.

7. A process as in claim 6 and wherein said polymer is high density polyethylene.

8. A process as in claim 6 and wherein said polymer is polypropylene which is predominently isotactic.

9. A process as in claim 1 and wherein said dilution water is at least 5C above said vapor condensation point.

10. A process as in claim 1 and wherein said aqueous mixture is refined in the presence of between about 1 and 5% of an at least partly water soluble polyvinyl alcohol having a degree of hydrolysis greater than 77% and a degree of polymerization of between 200 and 11. A process as in claim 1 and wherein said flash zone is maintained at a pressure between 50 and 500 7 mm Hg, said dilution water added to the flash zone is at a temperature between 10C and 60C and said refining is conducted at a temperature between 10C and 60C.

Claims

1. A PROCESS FOR MANUFACTURING PAPERMAKING PULP OF SYNTHETIC FIBERS COMPRISING FORMING A MIXTURE OF A POLYMER AN A SOLVENT FOR SUCH A POLYMER, FLASHING SAID MIXTURE AT A TEMPERATURE WHICH IS HIGH ENOUGH TO BRING SAID POLYMER TO A PLASTIC STATE AND WHICH WILL PERMIT SUBSTANTIALLY COMPLETE VAPORIZATION OF THE SOLVENT WHEN THE MIXTURE IS FLASHED, FLASHING SAID MIXTURE INTO A FLASH ZONE TO PRODUCE A FIBROUS PRODUCT, AND REFINING THE FIBROUS PRODUCT, CHARACTERIZED IN THAT A. SAID FLASH ZONE IS MAINTAINED AT OR BELOW 600 MM HG PRESSURE, B. SAID FLASHING TEMPERATURE, THE COMPONENTS OF SAID MIXTURE AND THE CONCENTRATION OF EACH IN THE MIXTURE, WITH RESPECT TO THEIR HEAT CAPACITY AND WITH RESPECT TO THE HEAT OF VAPORIZATION OF THE COMPONENTS VAPORIZED DURING FLASHING, ARE ALL SELECTED RELATIVE TO EACH OTHER TO PRODUCE A TEMPERATURE OF LESS THAN 94*C IN THE FLASHED FIBROUS PRODUCT UPON EVAPORATION OF SUBSTANTIALLY ALL OF SAID SOLVENT, C. THE SOLVENT HAS A VAPOR CONDENSATION POINT IN THE FLASH ZONE BELOW 60*C. D. DILUTION WATER IS INTRODUCED INTO THE FLASH ZONE AT A TEMPERATURE ABOVE THE VAPOR CONDENSATION POINT OF THE SOLVENT BUT BELOW 70*C TO FORM AN AQUEOUS MIXTURE, E. THE AQUEOUS MIXTURE IS PASSED DIRECTLY TO A REFINER WHICH IS IN DIRECT PRESSURE COMMUNICATION WITH THE FLASH ZONE, AND F. THE AQUEOUS MIXTURE IS REFINED IN THE REFINER AT A TEMPERATURE BELOW 70*C TO PRODUCE THE PAPERMAKING PULP.

3. A process as in claim 1 and wherein said flashing temperature, the components of said mixture and the concentration of each in the mixture, with respect to their heat capacity and with respect to the heat of vaporization of the components vaporized during flashing, are all selected relative to each other to produce a temperature less than 80*C in the flashed fibrous product upon evaporation of substantially all of said solvent.

4. A process as in claim 1 and wherein said flash mixture contains a. water as a flashing aid in an amount between about 30 and 70% by volume of the mixture, b. a saturated hydrocarbon solvent having a boiling point between 20*C and 130*C at atmospheric pressure, and c. a crystallizable polyolefin in an amount between 2 and 30% of the combined weight of the solvent and polymer.

5. A process as in claim 4 and wherein said mixture contains between about 1 and 5% by weight of the polymer therein of a polyvinyl alcohol having a degree of hydrolysis greater than 77 mols. % and a degree of polymerization between 200 and 4000.

6. A process as in claim 4 and wherein said solvent has a boiling point at atmospheric pressure which is between 50*C and 100*C.

9. A process as in claim 1 and wherein said dilution water is at least 5*C above said vapor condensation point.

10. A process as in claim 1 and wherein said aqueous mixture is refined in the presence of between about 1 and 5% of an at least partly water soluble polyvinyl alcohol having a degree of hydrolysis greater than 77% and a degree of polymerization of between 200 and 4000.

11. A process as in claim 1 and wherein said flash zone is maintained at a pressure between 50 and 500 mm Hg, said dilution water added to the flash zone is at a temperature between 10*C and 60*C and said refining is conducted at a temperature between 10*C and 60*C.