US3904728A

US3904728A - Method of preparing fibrils having properties for making improved paper sheets

Info

Publication number: US3904728A
Application number: US298085A
Authority: US
Inventors: Joseph C Davis; Francis R Galiano; Robert W Hill
Original assignee: Gulf Research and Development Co
Current assignee: Chevron USA Inc; Gulf Research and Development Co
Priority date: 1972-10-16
Filing date: 1972-10-16
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

An improvement in the fibril formation process which includes dissolving at an elevated temperature an olefin polymer having an inherent viscosity of at least 3.5 in a hot hydrocarbon solvent, shearing the hot polyolefin solution to thereby orient the polymer molecules therein, passing the sheared solution through a cooling zone maintained below the precipitation temperature of the solution while maintaining the orientation of the polymer molecules within the solution to thereby precipitate by thermal means the polymer in the form of a solvent swollen fibrous mass, separating a substantial portion of the polymer solvent from the fibrous mass, beating the fibrous mass in a liquid which is a non-solvent for the polymer and which is soluble in the polymer solvent for a time sufficient to break down the fibrous mass into a plurality of fibrils, and separating the fibrils from the nonsolvent liquid. The improvement consists of incorporating from about 5 up to about 15 weight percent based on the weight of the polyolefin of a surfactant selected from the group consisting of those nonionic surfactants having an HLB value from 7 to 12 and those anionic surfactants having an HLB value greater than 13 into the hot polyolefin/hydrocarbon solvent solution prior to the fibril formation steps of the process whereby the resultant fibrils containing the surfactant possess improved hydrophilic properties and paper sheets fabricated from these fibrils possess improved physical properties, particularly increased tensile strength.

Description

United States Patent [191 Davis et al.

[4 1 Sept. 9, 1975 METHOD OF PREPARING FIBRILS HAVING PROPERTIES FOR MAKING IMPROVED PAPER SHEETS [75] Inventors: Joseph C. Davis, De Soto; Francis R. Galiano, Overland Park; Robert W. Hill, Leawood, all of Kans.

[73] Assignee: Gulf Research & Development Company, Pittsburgh, Pa.

[22] Filed: Oct. 16, 1972 [21] Appl. No.: 298,085

Primary Examiner-Robert F. White Assistant Examiner-J. R. Hall [57] ABSTRACT An improvement in the fibril formation process which includes dissolving at an elevated temperature an olefin polymer having an inherent viscosity of at least 3.5 in a hot hydrocarbon solvent, shearing the hot polyolefin solution to thereby orient the polymer molecules therein, passing the sheared solution through a cooling zone maintained below the precipitation temperature of the solution while maintaining the orientation of the polymer molecules within the solution to thereby precipitate by thermal means the polymer in the form of a solvent swollen. fibrous mass, separating a substantial portion of the polymer solvent from the fibrous mass, beating the fibrous mass in a liquid which is a non-solvent for the polymer and which is soluble in the polymer solvent for a time sufficient to break down the fibrous mass into a plurality of fibrils, and separating the fibrils from the nonsolvent liquid. The improvement consists of incorporating from about 5 up to about 15 weight percent based on the weight of the polyolefin of a surfactant selected from the group consisting of those nonionic surfactants having an HLB value from 7 to 12 and those anionic surfact-ants having an HLB value greater than 13 into the hot polyolefin/hydrocarbon solvent solution prior'to the fibril formation steps of the process whereby the resultant fibrils containing the surfactant possess improved hydrophilic properties. and paper sheets fabricated from these fibrils possess improved physical properties, particularly increased tensile strength.

8 Claims, No Drawings METHOD OF PREPARING FIIBRILS HAVING PROPERTIES FOR MAKING IMPROVED PAPER SHEETS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for the formation of improved fibrils from high molecular weight polymers used to make improved paper sheets fabricated from the resultant fibrils. More particularly, the present invention pertains to an improvement, in the method of making fibrils from very high molecular weight polyolefins, particularly linear polyethylenes, whereby the resulting fibrils and paper or other nonwoven sheet-like structures into which these fibrils or fibril material are incorporated have improved qualities. In greater detail, the subject invention is concerned with a modification in the fibril-forming process from very high molecular weight polyolefins, especially linear polyethylenes, which includes the blending with the olefin polymer of a certain, particular additive or modifier and then the producing of improved fibrils from this polymer and additive blend, which may then be fabricated into paper sheets possessing improved properties. The fibrils produced by the invention, particularly when employing the improvement therein, possess an improved capability of forming coherent, selfsupporting water leaves which can be used for the production of paper and other nonwoven sheetlike structures according to known methods of paper manufacturing which possess improved properties.

2. Description of the Prior Art During recent years, a need has developed throughout industry for a better paper or paper product containing synthetic fibers of improved quality. Several synthetic fiber paper compositions and processes by which such fibers and paper can be made have been proposed. For certain rather limited and specialized purposes, the prior art compositions have been successful. However, because the synthetic fibers containing these compositions are not at all similar in structure to natural paper-making fibers, the compositions have not been successful in the vast number of situations where a product isrequired which has essentially paper-like characteristics in addition to certain qualities not found in natural fiber paper. Such papers should have improved flexing qualities, high tensile and bursting strengths, both when wet and dry, and be simply and economically produced.

The synthetic, hydrophobic fibers that were developed principally for textile end uses are now being employed in the development of numerous novelty and specialty papers, plus other nonwoven fibrous products not traditionally associated with the paper industry. Particular emphasis has been placed on the preparation of paper and paper-like webs from these polymeric fibrous products either to be ultimately used in unconverted form in specialty paper end uses or to be combined with other materials as in a laminate structure for its structural or aesthetic characteristics. To this end, for obvious reasons, including availability and economy, it has been advantageous to utilize conventional paper-making equipment and techniques which are well known.

In Davis et al, Ser. No. 193,716, filed Oct. 29, 1971, entitled improved Fibril and Process', Davis et a1, Ser. No. 202,302, filed Nov. 26, 1971, entitled 1mproved Fibril Process; and Davis et al, Ser. No. 21 1,562, filed Dec. 23, 1971, entitled Fibril Process," all now abandoned, there have been disclosed a number of processes or methods for producing high quality fibrils which are especially suitable for and readily adaptable to incorporation into paper or other nonwoven sheet-like structures which may be manufactured by known paper-making processes. The invention disclosed herein relates to changes or modifications in those fibril and paper-making processes which result in improvements in the produced fibrils and in the paper or other nonwoven sheet-like structures fabricated from these improved fibrils produced by those processes.

In each of those previously mentioned processes, fibrils are produced from a solution of a very high molecular weight polyolefin, such as polyethylene or polypropylene and more particularly linear polyethylene, in which the solution is sheared or subjected to a shearing action whereby the polymer molecules therein are oriented and immediately thereafter the polymer solute is made to precipitate from the solution by purely thermal means, which is attained by rapidly lowering the temperature, as in a quenching bath or by other cooling means. As set forth therein, the most useful systems for this type of fibril production are those systems employing polyolefins and suitable liquid hydrocarbon solvents for theses polyolefins. The cooling or quenching of these oriented solutions is usually carreid out under conditions of zero shear and at temperatures well below the precipitation temperatures of the polymer solutions to result in the formation of solvent swollen fibrous masses. These fibrous masses are then normally converted into fibrils by a series fo subsequent operations which may and usually do include the removal of excess solvent from the fibrous mass, the cutting of the fibrous mass into pieces of desired length, and the bearing and refining of the cut or chopped fibrous mass into individual fibrils for use in the production of paper or other nonwoven sheet material on paper-making machinery by the normally employed methods and techniques of paper production,

While the papers or other nonwovensheet-like structures fabricated in each of the hhereinabove-identified disclosures, from a plurality of the fibrils produced by the process of each of the respective inventions, and the fibrils themselves, are of good quality, it has been observed that some of the physical properties of the fibrils and the paper sheets so produced were somewhat less than might be desired and could stand improve ment. It would be desirable, and it is the general object and concern of this invention, to produce fibrils and paper sheets from synthetic polymers by the processes set forth in the above-identified disclosures which possess improved physical properties when compared to the physical properties of the fibrils and paper sheets produced'in those disclosures. It is particularly desirable to produce fibrils from purely synthetic or manmade materials and paper sheets fabricated therefrom which, respectively, possess improved hydrophilic properties, are more readily water-dispersible, are more readily adaptable to use in conventional papermaking equipment utilizing the normally employed methods and techniques of paper production, and possess improved tensile strength, burst strength, elongation and fold endurance when compared to the previously produced fibrils and fabricated paper sheets from these type materials.

SUMMARY OF THE INVENTION We have found that fibrils and paper, or other similar nonwoven sheet-like structures, of higher quality and possessing improved properties over those fibrils and paper sheets fabricated in the hereinabove-identified disclosures, can be proudced if a minor amount of a certain additive or modifier is incorporated into the starting hot polyolefin/hydrocarbon solvent solution from which the fibrils that are to be incorporated into the paper sheets are formed prior to the fibril formation steps of the process. By the incorporation of minor amounts of the additive or modifier, the resultant fibrils are more hydrophilic and more readily waterdispersible; and paper sheets fabricated therefrom possess improved properties, such as higher tensile strength, increased burst strength, increased stretch and greater fold endurance, and are generally of a higher quality and grade. The particular additive or modifier incorporated into the starting or beginning polymer solution is a surfactant. The particular surfactant incorporated may be a nonionic surfactant or an anionic surfactant. The nonionic surfactant employed should have an HLB value or number of from about 7 up to about 12, and the anionic surfactant used should have an HLB value or number greater than 13. The additive surfactant may be incorporated at levels of from about 2 weight percent up to about 20 weight percent based on the weight of the high molecular weight polyolefin, particularly linear polyethylene. added to the hydrocarbon solvent of the beginning solution, to impart the desirable improvements to the resultant fibrils formed during the process and the paper sheets fabricated therefrom. More particularly, it is preferred to incorporate in the range of from about up to weight percent of the modifying surfactant to impart the desired increase in hydrophilic properties of the fibrils and the higher quality and grade to the resultant paper sheets.

DETAILED DESCRIPTION In order that the complete fibril formation process and the method of fabrication of paper sheets therefrom is completely and readily understood, the disclosure of Davis et al, Ser. No. 193,716 (more completely identified hereinabove) is incorporated herein by reference.

By the invention disclosed herein, paper sheets or other similar nonwoven sheet-like structures may be fabricated from improved fibrils which are formed or obtained from a process or method like that disclosed in Davis et al, Ser. No. 193,716, from wholly man-made or synthetic polymeric materials which fibrils and sheets possess improved properties and are of a better or higher quality and grade than those fibrils and sheets obtained in the previously-identified disclosures. The invention contemplates the addition of a certain, particular additive or modifier material to the polyolefin and hydrocarbon solvent beginning solution prior to the formation of fibrils therefrom by one of the processes set forth in the hereinabove-identified disclosures. The modifier or additive incorporated into the polyolefin and solvent solution is incorporated in minor amounts to attain the unexpected and desirous improvements in the resultant fibrils and improvement in many of the physical properties of the paper sheets formed from the fibrils produced. The additive employed is a surfactant and is employed at levels of from about 2 weight percent up to about 20 weight percent, and preferably from about 5 up to about 15 weight percent based on the amount of the polyolefin, particularly high molecular weight linear polyethylene, dissolved in the hydrocarbon solvent to form the starting solution. The surfactant incorporated may be a nonionic surfactant or an anionic surfactant.

The nonionic surfactants which are effective in this invention are those with an HLB number or value between 7 and 12. The HLB, or hydrophilic-lipophilic balance, refers to the relative degree of water solubility and oil solubility of an emulsifier or surfactant; these properties determine the usefulness of a given surfactant for a particular chemical system. The HLB is described on a scale from 1 to 20, an HLB number of 1 indicating a highly oil-soluble surfactant, and a value of 20 indicating a high degree of water solubility. As indicated above, the nonionic surfactants which perform well in this invention have HLB values between 7 and 12. Those which lie outside this range either do not disperse the polymer fibers well in an aqueous medium, are insufficiently soluble in the kerosene (Speedsol) solvent, or do not impart desirable properties to the finished paper.

The HLB system applied to anionic surfactants gives somewhat different results. In this case, the best results have been obtained where the surfactant is quite soluble in water, i.e., the HLB number or value is greater than 13. The fact that the HLB requirements for this invention for anionic surfactants is quite different than for nonionics is not surprising, since the ionic nature of the former changes their water solubility relative to the nonionics to a much greater extent than it effects the oil solubility. Reasons for this are discussed in the publication, The Atlas HLB System, 2nd edition, 1963, published by Atlas Chemical Industries, Inc. This publication also describes (p. 19) a method for determining the HLB values or numbers for anionic surfactants the water-dispersibility method which has been used for determining the values reported herein.

The HLB values or numbers reported herein for the nonionic surfactants were obtained from McCutcheons Detergents and Emulsifiers Annual, 1972, published by McCutcheons Division, Allured Publishing Corp., Ridgewood, N. .1.

Among those additive or modifier surfactants which have been used in this invention and successfully incorporated into the beginning polyolefin and hydrocarbon solvent solution to impart the unexpected and desirable improvements in the resultant fibrils produced during the process and the paper sheets fabricated therefrom are the following: I

Igepal CO-210, nonylphenoxypo1y(ethylneoxy)ethanol, a nonionic surfactant obtained from GAF Corporation, having an HLB value of 7.0.

Atlas 6-1086, polyoxyethylene sorbitol hexaoleate, a nonionic surfactant obtained from Atlas Chemical Industries, having an HLB value of 10.2.

Aerosol AY, diamyl ester of sodium sulfosuccinic acid, an anionic surfactant obtained from American Cyanamid Company. having an HLB value greater than Conoco SA-697, straight-chain tridecylbenzene sulfonic acid, an anionic surfactant obtained from Continental Oil Company, having an HLB value greater than 13.0.

Tween 81, polyoxyethylene sorbitan monooleate, a nonionic surfactant obtained from Atlas Chemical lndustries, having an HLB value of 10.0.

Tween 65, polyoxyethylene sorbitan tristearate, a nonionic surfactant obtained from Atlas Chemical lndustries, having an HLB value of 10.5.

Aerosol OT, dioctyl ester of sodium sulfosuccinic acid, an anionic surfactant obtained from American Cyanamid Company, having an HLB value greater than 13.0.

Tween 61, poly(ethyleneoxy)sorbitan monostearate, a nonionic surfactant obtained from Atlas Chemical 1ndustries, having an HLB value of 9.5.

lgepal CO-430, nonylphenoxypoly (ethyleneoxy)ethanol, a nonionic surfactant obtained from GAF Corporation, having an HLB value of l l O.

The additive or modifying surfactant may be added to the hydrocarbon solvent when the same is hot or prior to the heating thereof and may be added thereto along with the high molecular weight linear polyethylene, prior thereto or after the linear polyethylene has been dissolved in the hydrocarbon solvent. In order to be useful in this invention, the surfactant should be soluble to a degree in the hot polyolefin/hydrocarbon solvent solution but not overly soluble therein. The surfactant must be soluble in an amount of up to at least 2 percent on a weight basis in the hot polyolefin/hydrocarbon solvent solution to be employable in the invention.

In order to illustrate the invention and the improvments in the resultant fibrils and the paper sheets improvements from the fibrils produced with greater particularity, the following specific examples are included. These examples are intended to be illustrative of the invention only and are not intended to limit the same in any way.

EXAMPLE 1 In this example, fibrils were produced by the process set forth in Ser. No. 193,716 (more completely identified hereinabove) without employing the improvement of this invention, and the resultant fibrils were used to fabricate paper sheets on the Noble and Wood sheetforming machine, physical properties of which were measured and are set forth hereinbelow. This example is included as a control for comparative purposes with the fibrils prepared in accordance with the invention and the improvement thereof and with the paper sheets fabricated from these improved fibrils.

A glass vessel equipped with a stirrer was charged with 3.0 liters of the substantially aliphatic hydrocarbon solvent Speedsol (boiling range l55l 80 C.) containing 0.018 gram of an anti-oxidant mixture consisting of equal parts by weight of lonol, Santonox R (trademarks) and dilauryl thiodipropionate. The solvent/anti-oxidant mixture was heated to 150 C. and

then 15.0 grams ofa linear high molecular weight poly Inherent Viscosity ln I/M/c wherein I fall time or time for passage through the viscosimeter of the polymer solution, 1,, fall time of the solvent and c =concentration of the polymer in the solvent. All inherent viscosity measurements set forth herein are made at a concentration of 0.05 gram of polymer per milliliters of decalin at C.

The slurry was held at the C. temperature with stirring for a time period sufficient to completely dissolve the polyethylene and result in a solution suitable for the formation of fibrils by the methods of the hereinabove-identified disclosures. This solution was then charged to a centrifugal spinning apparatus, such as the hammermill shown at reference numeral 22 in Ser. No. 193,716, whose rotor was rotating at approximately 1 1,140 rpml Fibrils suitable for paper production were then produced by carrying out the remainder of the method steps set forth in the process of Ser. No. 193,716 wherein the temperature of the fibrils coming from the spinning apparatus was -10 C. and the refining was carried out in isopropanol in a Waring blender. The fibrils were used to make paper sheet which were obtained by slurrying the fibril product produced to the head box of the Noble and Wood sheet-forming machine. Handsheets were then formed on the Noble and Wood machine by the usual and normal methods em ployed in the use of this sheet-forming machine. A number of physical properties of the resultant sheets formed in this example were determined and calculated and are set forth hereinbelow in Table l.

Water-dispersibility studies for the fibrils produced in this and the following examples were undertaken and results thereof are set forth hereinbelow in Table 11. The dispersiblity in water of the fibrils obtained in the examples was checked by dispersing 3.0 grams (weight of a squeezed but not dried sample of the fibrils) of tibril pulp in 250 milliliters of water in a Waring blender.

The fibril pulp derived from purely linear high molecular Weight polyethylene without any additives or modifiers (Example 1) is almost completely unwet and the essentially dry fibril pulp floats on the surface of the water in a Waring blender. The varying degrees of improvement attainedwith the various modifiers or additives of the invention were readily apparent when fibril pulp samples of the same were dispersed as above in 250 milliliters of water in'a Waring blender.

In order to attain some numerical comparisons of the dispersibility of the fibril pulp obtained from the various blends of high molecular weight linear polyethylene and the various surfactant additives, the water and pulp suspension obtained in the Waring blender for each of the examples was transferred to a 250 milliliter graduated cylinder and the water level adjusted to 250 milliliters. If there was any of the substantially dry fibrils in the pulp, the approximate fraction of the substantially dry fibril material was noted and is recorded hereinbelow in Table ll. As can be noted from the table, substantially dry fibrils within the pulp are greatest when the poorest of blends of the additive or modifying surfactants are employed.

- The next step in the dispersibility study was to vigorously shake the suspension in the graduated cylinder and thereafter note and record the volume occupied within the graduated cylinder by the wet pulp after time intervals of 30 seconds, 60 seconds and 10 minutes. The values observed and recorded are reported hereinbelow in Table li.

Yet another measure of the fibril puips dispersibility undertaken in these water-dispersibility studies was that ofthe rise time of the fibril pulp. The rise time of the fibril pulp was observed and recorded at two differ- Speedsol ent levels within the 250 milliliter graduated cylinder after the suspension therein had been vigorously shaken. The two levels within the graduated cylinder at which the times were observed and recorded were the 100 milliliter level and the 80 milliliter level. The time required for the wet pulp volume within the graduated cylinder to reach or decrease to 100 milliliters and also to 80 milliliters were recorded and are reported hereinbelow in Table 11.

EXAMPLE 2 In this example, fibrils and paper sheets fabricated therefrom were prepared by the process set forth in Ser. No. 193,716 and as set forth in Example I employing the improvement of the invention, i.e., the addition of a modifying surfactant to the starting or beginning polymer solution from which the improved fibrils are formed.

The apparatus employed and the process used in this example were identical to that used in Example 1 with the exception that an additive, a nonionic surfactant, was used and added in a minor amount to the starting hot polyethylene/hydrocarbon solvent solution.

The vessel used in Example 1 was charged with 3.0 liters of Speedsol solvent containing 0.018 gram of the anti-oxidant mixture of Example 1 to which 1.5 grams of lgepal CO-210 (nonylphenoxypo1y(ethyleneoxy)ethanol, a nonionic surfactant obtained from GAF Corporation, having an HLB value of 7.0) was added. This mixture was then heated to 150 C. To the resulting solvent/additive surfactant solution was added 15.0 grams of a linear high molecular weight polyethylene having an inherent viscosity of 13.33. This mixture was then held with stirring at the 150 C. temperature for a time sufficient to completely dissolve the polyethylene, thereby resulting in a solution suitable for the formation of fibrils by the method set forth in Example 1, and containing about weight percent of the surfactant additive based on the weight of the linear polyethylene. Water-dispersibility studies, as in Example 1, were carried out on the fibrils produced by the method set forth in Example 1, and these fibrils were used to make paper sheets on the Noble and Wood sheet-forming machine as was done in Example 1. Some of the physical properties of the resultant sheets fabricated in this example were obtained and are recorded in Table l below, and the data collected in the water-dispersibility studies are reported in the following Table I1.

EXAMPLE 3 In this example, fibrils were prepared and refined by the methods and procedures carried out in Examples 1 and 2 and paper sheets were prepared therefrom in the manner identical to that employed in Examples 1 and 2 with a single exception. In this example, the additive or modifying surfactant employed was a different surfactant but was employed at the same level or concentration. The nonionic surfactant used was Atlas 6-1086 (polyoxyethylene sorbitol hexaoleate, a nonionic surfactant obtained from Atlas Chemical Industries, having an HLB value of 10.2) and was employed in an amount of 1.5 grams in 3.0 liters of the Speedsol solvent of Example 1. The resultant Speedsol solvent/surfactant additive/linear high molecular weight polyethylene solution contained approximately 10 weight percent of the surfactant additive based on the weight of the linear polyethylene. Fibrils were then produced by the method set forth in Examples 1 and 2, water-dispersibility studies were carried out as in Example l, and paper sheets were prepared from the fibrils as was done in Examples 1 and 2. The physical properties of the resultant sheets fabricated on the Noble and Wood sheet-forming machine was determined and are recorded hereinbelow in Table I, and the data collected in the water-dispersibility studies are reported in the following Table II.

EXAMPLE 4 Fibrils were prepared and refined by the methods and procedures carried out in Example 2 and paper sheets were prepared therefrom in a manner identical to the employed in Example 2 with the exception that the additive or modifying surfactant employed was a different surfactant. The surfactant used was Aerosol AY (a diamyl ester of sodium sulfosuccinic acid, and anionic surfactant obtained from American Cyanamid Company, having an HLB value greater than 13.0), which was employed in an amount of 1.5 grams. The resultant solvent/surfactant/linear high molecular weight polyethylene solution contained about 10 weight percent of the surfactant additive based on the weight of the linear polyethylene. Fibrils were then produced from this solution by the processes set forth in Examples 1 and 2, water-dispersibility studies were undertaken and carried out on the fibrils as in Example 1, and paper sheets were fabricated from the resultant fibrils as was done in Examples 1 and 2. The physical properties of the paper sheets fabricated on the Noble and Wood sheet forming machine were determined and are reported in the following Table I, and data collected in the water-dispersibility studies were recorded and are set forth hereinbelow in Table II.

EXAMPLE 5 In this example, fibrils were parepared and refined in a fashion similar to that employed in Example 2 and paper sheets were prepared therefrom in a manner identical to that employed in Example 2, with. the ex ception that a different surfactant additive was used and was employed at the same level or concentration. The surfactant additive used was Conoco SA-697 (a straight-chain tridecylbenzene sulfonic acid, an anionic surfactant obtained from Continental Oil Company, having an HLB value greater than 13.0) and was employed in the amount of 1.5 grams. The resulting solvent/surfactant additive/linear high molecular weight polyethylene solution contained approximately 10 weight percent of the surfactant additive based on the weight of the linear polyethylene. Fibrils were thereafter produced by the method set forth in Examples 1 and 2, water-dispersibility studies of the fibrils were undertaken as in Example 1, and paper sheets were fabricated from the resultant fibrils as was done in Examples 1 and 2. The physical properties of the resultant sheets prepared on the Noble and Wood sheet-forming machine were determined and are set forth herienbelow in Table l and the resultsof the water-dispersibility studies are recorded in the following Table II.

and II and a study and comparison of the results recorded thereimthe practice of this invention and the improvement thereof, i.e.. the incorporation of a minor amount of an additive or modifying surfactant into the beginning or starting solution from which the fibrils are formed, results in improved hydrophilic properties in and improved water-dispersibility of the fibrils produced'and in improved and increased physical properties in the resultant paper sheets fabricated from saids fibrils. By a comparison of the examples set forth in Tables l and Il above, it is readily seen that the fibrils produced possess improved hydrophilic properties and linear polyethylene/hydrocarbon solvent solution from which the fibrils are formed and sheets are fabricated.

by the addition of a minor amount of a surfactant additive. The improvement in quality and grade of the resultant sheets is particularly evident in the increase in tensile strength, as indicated by the tensile factor and fthe stretch Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is; therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described therein.

What is claimed as new and what is desired to secure by Letters Patent by the United States is:

I. In a process for preparing fibrils which may subsequently be used to prepare paper sheets having improvements in tensile strength, tensile factor and stretch properties, comprising:

a. forming a heated solution of an olefin polymer having an inherent viscosity of at least 3.5 by dissolving said polymer in a heated hydrocarbon solvent,

b. subjecting said solution to a shearing action whereby the polymer molecules therein are oriented,

Table l Example Example Example Example Example Property* l 2 3 4 5 t Basis Weight 45.15 40.46 514x 50.70 56.14

lbs/3000 11. Tensile Strength, 5.50 LL40 12.57 7.19 10.02

)li Tensile Factor 0.12 0.23 0.24 0.14 0.17 Stretch. 4.7x 31.70 20.00 9.57 12.30 Elmentlurf Tear. 182.00 148.00 178.00 324.00 147.00 g./shect Elmcndorl' Tear 4.04 3.66 3.56 6.10 2.74 Factor Tappi Procedure Nu T220 c. cooling said heated solution to a temperature Table II 15 below which said polymer solute is made to precipitate in the form of a solvent-swollen fibrous mass, Time (sec.) (1. removing excess solvent from said fibrous mass, Requ'red e. cutting said fibrous mass into pieces of selected Volume (ml) Volume of Wet len ths and 2 Dry of Wet Fibrils Fihrils m i fibrils Aft Deena-1Sta to 20 f. beating sa1d cut fibrous mass 1nto individual fibrils, Exam On Water 30 0 10 100 the improvement consisting essentially of: P Surface g. incorporating in said solution of step (a) about 1 9O 5 5 5 1 1 220% by weight, based upon said polymer. of a 2 trace 95 75 15 360 surfactant belng partially soluble in an amount of Z s 25 up to at least 2% by weight in said heated solution, 5 5 g 55 5 3 4 and be ng selected from the group consisting of nonlomc surfactants and anionic surfactants, sa1d nonionic surfactants having an HLB value from 7 to 12 and said anionic surfactants having an HLB As can be readily observed from the above Tables I 30 value greater than 13 2. In a process as defined in claim 1 wherein said olefin polymer is linear polyethylene.

3. In a process as defined in claim 2 wherein said linear polyethylene has an inherent viscosity of at least 5.0 and is present in said polyolefin/hydrocarbon solvent solution in an amount of from about 0.25 up to about 5.0 weight percent and said surfactant additive is a nonionic surfactant.

4. In a process as defined in claim 3 wherein said linear polyethylene has an inherent viscosity of at least 10.0 and is present in said polyolefin/hydrocarbon sol vent solution in an amount of from about 0.25 up to about 3.0 weight percent, said nonionic surfactant additive is present in an amount of from about 5 up to about 15 weight percent based on the weight of said linear polyethylene.

5. In a process as defined in claim4 wherein said non ionic surfactant is a surfactant selected from the group consisting of alkylphenoxypoly (ethyleneoxy) ethanols, polyoxyethylene sorbitol hexaoleates, polyoxyethylene sorbitan monooleates, polyoxyethylene sorbitan tristearates, and poly( ethyleneoxy)sorbitan monostearates.

6. In a process as defined in claim 2 wherein said linear polyethylene has an inherent viscosity of at least 5.0 and is present in said polyolefin/hydrocarbon solvent solution in an amount of from about 0.25 up to about 5.0 weight percent and said surfactant.

7. In a process as defined in claim 6 wherein said linear polyethylene has an inherent viscosity of at least 10.0 and is present in said polyolefin/hydrocarbon solvent solution in an amount of from about 025 up to about 3.0 weight percent, said anionic surfactant additive is present in an amount of from about 5 up to about 15 weight percent based on the weight of said linear polyethylene.

8. In a process as defined in claim 7 wherein said anionic surfactant is a surfactant selected from the group consisting of diamyl ester of sodium sulfosuccinic acid, straight-chain alkylbenzene sulfonic acids, and dioctyl ester of sodium sulfosuccinic acid.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. I 3,904,728

D E I September 9, 1975 INVENTO I Joseph C. Davis, Francis R. Galiano and Robert W. Hill It rs certrtred that error appears In the above-Identified patent and tnat said Letters Patent are hereby corrected as shown below:

COL. 10, line 57, delete and insert additive is an anionic surfactant.

Signed and Scaled this ninth Day of March 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner of Parents and Trademarks

Claims

1. IN A PROCESS FOR PREPARING FIBRILS WHICH MAY SUBSEQUENTLY BE USED TO PREPARE PAPER SHEETS HAVING IMPROVEMENTS IN TENSILE STRENGTH, TENSILE FACTOR AND STRETCH PROPERTIES COMPRISING : A. FORMING A HEATED SOLUTION OF AN OLEFIN POLYMER HAVING AN INHERENT VISCOSITY OF AT LEAST 3.5 BY DISSOLVING SAID POLYMER IN A HEATED HYDROCARBON SOLVENT, B. SUBJECTING SAID SOLUTION TO A SHEARING ACTION WHEREBY THE POLYMER MOLECULES THEREIN ARE ORIENTED, C. COOLING SAID HEATED SOLUTION TO A TEMPERATURE BELOW WHICH SAID POLYMER SOLUTE IS MADE TO PERCIPITATE IN THE FORM OF A SOLVENT-SWOLLEN FIBROUS MASS, D. REMOVING EXCESS SOLVENT FROM SAID FIBROUS MASS, E. CUTTING SAID FIBROUS MASS INTO PIECES OF SELECTED LENGTHS, AND F. BEATING SAID CUT FIBROUS MASS INTO INDIVIDUAL FIBRILS, THE IMPROVEMENT CONSISTING ESSENTIALLY OF: G. INCORPORATING IN SAID SOLUTION OF STEP (A) ABOUT 2-20% BY WEIGHT, BASED UPON SAID POLYMER, OF A SURFACTANT BEING PARTIALLY SOLUBLE IN AN AMOUNT OF UP TO AT LEAST 2% BY WEIGHT IN SAID HEATED SOLUTION, AND BEING SELECTED FROM THE GROUP CONSISTING OF NONIONIC SURFACTANTS AND ANIONIC SURFACTANTS, SAID NONIONIC SURTACTANTS HAVING AN HLB VALUE FROM 7 TO 12 AND SAID ANIONIC SURFACTANTS HAVING AN HLB VALUE GREATER THAN 13.

2. In a process as defined in claim 1 wherein said olefin polymer is linear polyethylene.

4. In a process as defined in claim 3 wherein said linear polyethylene has an inherent viscosity of at least 10.0 and is present in said polyolefin/hydrocarbon solvent solution in an amount of from about 0.25 up to about 3.0 weight percent, said nonionic surfactant additive is present in an amount of from about 5 up to about 15 weight percent based on the weight of said linear polyethylene.

5. In a process as defined in claim 4 wherein said nonionic surfactant is a surfactant selected from the group consisting of alkylphenoxypoly (ethyleneoxy) ethanols, polyoxyethylene sorbitol hexaoleates, polyoxyethylene sorbitan monooleates, polyoxyethylene sorbitan tristearates, and poly(ethyleneoxy)sorbitan monostearates.

7. In a process as defined in claim 6 wherein said linear polyethylene has an inherent viscosity of at least 10.0 and is present in said polyolefin/hydrocarbon solvent solution in an amount of from about 0.25 up to about 3.0 weight percent, said anionic surfactant additive is present in an amount of from about 5 up to about 15 weight percent based on the weight of said linear polyethylene.