Treatment of arylene sulfide polymer fiber
BACKGROUND OF THE INVENTION p This invention relates to arylene sulfide polymer fibers and monofilaments having improved properties. 
     In the years following their initial development, poly(arylene sulfide) resins have become commercially important and the products produced therefrom are finding increasing utility due to their outstanding durability, toughness, inertness and versatility. To extend the value of such poly(arylene sulfide) resins and the utility of products prepared therefrom, still further improvements have been sought with regard to improving the properties of fibers to meet the requirements of certain applications. 
     Fibers of poly(arylene sulfide) possess many desirable properties because of the strength, high melting point, and non-burning characteristics of the polymer. Articles made from fibers of poly(arylene sulfide) are attractive for use in corrosive atmospheres and applications because the polymers from which the fibers are made are highly resistant to most chemicals including commonly used acids and bases. Multifilament and staple fibers can be formed into fabrics by knitting, weaving, or non-woven processes. Monofilament fiber can be woven into belts or screens for use in various applications, such as in the paper-making industry. 
     However, these fibers, while known to be useful, are also known to have limited physical strength. This lack of strength limits the applications and use of poly(arylene sulfide) fibers. Thus, increasing the polymer strength, as shown by increasing the tensile strength, abrasion resistance, and density, would be a desirable improvement to these poly(arylene sulfide) fibers. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of this invention to improve the physical properties of arylene sulfide polymers. 
     It is another object of this invention to improve the tensile strength and abrasion resistance of poly(arylene sulfide) fibers. 
     It is yet another object of this invention to increase the density of poly(arylene sulfide) fibers. 
     It is a further object of this invention to provide poly(arylene sulfide) fibers having improved structural characteristics in a simple, economic, and expedient manner. 
     It is yet a further object of this invention to provide a process of treating, in the presence or absence of heat, arylene sulfide polymers to improve their physical properties. 
     It has now been found that poly(arylene sulfide) fibers can be treated with an organic halide to improve their physical properties. If said treatment is carried out at an elevated temperature, the resultant physical properties can be further improved. Furthermore, if said organic halide treatment is used in conjunction with pre- or post-heating, i.e. annealing, of the poly(arylene sulfide) fiber, additional physical improvements to the polymer are possible. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The terms &#34;poly(arylene sulfide)&#34; and &#34;arylene sulfide polymers&#34; as used in this specification are intended to include crystallizable poly(arylene sulfide). Examples of such polymers are described in U.S. Pat. No. 3,354,129, issued Nov. 21, 1967, to Edmonds and Hill (incorporated herein by reference). As disclosed in this patent, these polymers can be prepared by reacting a polyhalosubstituted cyclic compound containing unsaturation between adjacent ring atoms and an alkali metal sulfide in a polar organic compound. The resulting polymer contains the cyclic structure of the polyhalo-substituted compound coupled in repeating units through a sulfur atom. The polymers which are preferred for use in this invention, because of their high thermal stability and availability of the materials from which they are prepared, are those polymers having the repeating unit -R-S- where R is phenylene, biphenylene, naphthylene, benzophenone, or a lower alkyl-substituted derivative thereof. By the term &#34;lower alkyl&#34; is meant alkyl groups having one to six carbon atoms, such as methyl, propyl, isobutyl, n-hexyl, and the like. The preparation of such polymers is disclosed in the above patent of Edmonds et al. The most preferred poly(arylene sulfide) polymers used in the making of fibers are disclosed in U.S. Pat. No. 3,919,177, issued on Nov. 11, 1975, to Campbell (incorporated herein by reference). 
     The terms &#34;poly(arylene sulfide)&#34; and &#34;poly(arylene sulfide polymers&#34; are also meant to indicate not only homopolymers but also normally solid arylene sulfide copolymers and terpolymers. 
     The polymers used in this invention are those which have differential scanning calorimeter (DSC) melting temperatures in the range of about 200° to about 500° C. Preferably, these poly(arylene sulfide) polymers have DSC melting temperatures in the range of about 250° to about 320°. If the poly(arylene sulfide) is comprised primarily of poly(phenylene sulfide), the most preferred DSC melting temperature is in the range of about 265° to about 295° C., which is indicative of appropriate properties for the ease in production of monofilament. 
     As produced, poly(arylene sulfide) is a crystalline polymer, which is usually converted into pellets for ease of handling. Pellets are formed by extruding under heat and pressure and mechanically cutting the extrudate into the desired size. The pellets are dried, or heated, fed into yet another extruder, through a gear pump, which regulates polymer throughput, and finally, through a die to form poly(arylene sulfide) fiber. The fiber is immediately quenched in water or air. Air quenching is preferred in the production of finer, lower denier, fiber. The thus cooled fiber enters a drawing zone where it is heated slightly and drawn to about two to about five times the original fiber length resulting in orientation, but not substantial crystallization of the polymer molecules. The drawn fiber can be wound onto a spool to be used as is, or to be incorporated into or made into a final product. 
     As used in this disclosure, the term &#34;fiber&#34; includes all types of monofilament, multifilament, as well as staple fibers. A &#34;monofilment&#34; is a single filament, i.e., one strand; a &#34;multifilament&#34; is two or more monofilaments assembled and held together; a &#34;staple&#34; is discontinuous lengths of fibers which have been cut or broken into desired lengths from longer monofilaments or multifilaments. 
     Treating Agents 
     Any organic halide, in gaseous or liquid form, can be used to treat poly(arylene sulfide) fibers and monofilaments. Liquid treatment is preferred because a higher concentration of treating agent can contact the fiber. The organic halide, if a liquid, can be used in the pure, undiluted form or diluted in an appropriate diluent. If the organic halide is solid, an appropriate liquid solvent for the organic halide can be used. 
     The organic halide can be either an aliphatic halide or aromatic halide, wherein the halide is selected from the group consisting of chloride, bromide, iodide, or mixtures thereof. Preferably an aliphatic halide is used as the treating agent. Most preferably, the aliphatic halide is an aliphatic chloride. The most preferred aliphatic chloride is dichloromethane (CH 2  Cl 2 ) because it is readily available, easy to handle, and can be used without any dilution. 
     Treatment Conditions 
     The conditions under which the process of the present invention can be carried out can vary according to the specific organic halide, or treating compound, used, and the desired results. Although the specific mechanisms involved in the chemical transformations of the present invention are not understood completely, there is, nevertheless, a direct relationship between the severity of the treatment and the level of the chemical and physical changes produced. The treatment severity depends upon the combination of operating parameters used in the process, namely, the temperature of treatment, the time of treatment, the concentration of the treating agent in the treating diluent, and pre- or post- heat treatment. Thus, it is clear that no single condition can alone control the level of the organic halide treatment severity. 
     Treatment with a treating agent can change the appearance of the fiber. The treating agent can cause the fiber to change from transparent to opaque. The fiber can initially appear transparent and, depending on the treatment conditions, can become hazy, then milky, and finally opaque. Organic halide treatment of the fiber or monofilament can occur either before or after the fiber or monofilament is drawn. Preferably, treatment with the treating agent is done after drawing, for best polymer property improvement. 
     The organic halide treatment can be for a time which ranges from about one minute to about 72 hours, preferably from about 5 minutes to about 50 hours. Most preferably, the treatment time ranges from about 15 minutes to about 3 hours for the most chemical and physical change relative to treatment time. The treatment temperature of the organic halide can range from about 0° to about 150° C., preferably from about 5° to about 100° C. Most preferably, the organic halide temperature ranges from about 10° to about 50° C. for ease of handling and operability. Ordinarily, pressures in the range of about 0 to about 500 psig can be used. Operation at atmospheric pressure is convenient. 
     Optionally, the fiber can be heat treated, i.e., annealed, in addition to the organic halide treatment. Annealing of the fiber, if desired, can be done before or after the organic halide treatment. As with the organic halide treatment, the heat treatment parameters can be adjusted to accommodate specific needs or limitations. For example, high temperatures and short times can be employed, or lower temperatures and longer times can be used. Usually, the poly(arylene sulfide) fiber can be annealed at a temperature in the range of about 100° to about 270° C, preferably from about 130° to about 240° C., either before or after subjecting the fiber to the organic halide treatment. Most preferably, the annealing temperature is within the range of about 160° C. to about 220° C, for best property improvements. The length of time for the heat treatment of the poly(arylene sulfide) can varY from about one-half second to about 30 minutes, preferably from about one-half second to about 20 minutes. Most preferably, for convenience, the heat treatment time is within the range of about one second to about 15 minutes. Furthermore, in order to achieve the best property improvements, annealing is done after the organic halide treatment. 
     As stated earlier, the operating parameters can be varied in order to obtain specifically desired results. The operating parameters also can be varied depending on the equipment processing capabilities. For example, higher temperatures and/or longer treatment times can be used if lower concentrations of treating agent are appropriate. Similarly, with lower temperature, higher concentrations and/or longer treating times can be used. Likewise, with shorter treating times, higher concentrations and/or higher temperatures can be used. Because there are several parameters available in the invention process, many suitable combinations of conditions can be chosen not only to obtain the result desired, but also to provide convenience and ease of operation. For example, high treating temperature with a low treatment time can be traded for a lower treatment temperature and a longer treatment time, if such is more convenient. 
     The contact of the treating fluid with the article comprising poly(arylene sulfide) resin can be carried out using any suitable mode, such as immersion, and using any suitable apparatus that is compatible with the conditions described above. The contact can be carried out either batchwise or continuously. 
     The quantity of treating fluid with respect to the extent of the surface area of the fiberous article or articles being treated can vary widely. If desired, a measured amount of treating agent can be contacted with a measured amount of total surface area to be treated such as in a batch treatment operation. Alternatively, the articles to be treated can be contacted batchwise or continuously, with a large excess of the treating fluid under conditions which are sufficient to obtain the desired improvement. As shown in the examples, the specific amounts of treating agent or the specific conditions required to achieve the desired result can be determined by experimentation using a given poly(arylene sulfide) fiber and a given treating fluid. 
    
    
     EXAMPLES 
     A further understanding of the present invention and its advantages is provided by reference to the following examples. The poly(arylene sulfide) monofilament fibers used in the following examples were prepared from poly(para-phenylene sulfide) polymer (PPS). 
     EXAMPLE I 
     Table I shows the effect on the density of poly(phenylene sulfide) (PPS) monofilament with treating compounds. The monofilament was submerged in each compound for one hour at room temperature. 
     
                       TABLE I                                                     
______________________________________                                    
Run No. Treating Compound    Density, g/cc                                
______________________________________                                    
101     None                 1.338                                        
102     Freon 113            1.335                                        
103     Triphenyl phosphate  1.338                                        
104     Sodium hypochlorite  1.339                                        
        (10% by weight in water)                                          
105     Nitrobenzene         1.340                                        
106     N,N--dimethylformamide                                            
                             1.340                                        
107     Toluene              1.340                                        
108     m-Cresol             1.340                                        
109     Ethylacetate         1.340                                        
110     Acetonitrile         1.340                                        
111     2-Propanol           1.341                                        
112     Tetrahydrofuran      1.341                                        
113     Methylethylketone    1.341                                        
114     Analine              1.341                                        
115     Hydrochloric acid (concentrated)                                  
                             1.341                                        
116     Sulfolane            1.342                                        
117     Dimethylsulfoxide    1.342                                        
118     Sodium hydroxide     1.342                                        
        (15% by weight in water)                                          
119     Glacial acetic acid  1.342                                        
120     Sodium chloride      1.342                                        
        (10% by weight in water)                                          
121     Sodium hypochlorite  1.343                                        
        (5% by weight in water)                                           
122     Dichloromethane      1.350                                        
______________________________________                                    
 
    
     The data in Table I indicate that organic halides, especially aliphatic halides, such as dichloromethane, can increase the density of PPS. Inorganic halides and unhalogenated organic compounds are not as effective in increasing the density of poly(phenylene sulfide) monofilament. 
     EXAMPLE II 
     Table II shows the effect on PPS monofilament density when the length of treatment time is varied. The PPS monofilament was treated with dichloromethane at room temperature. 
     
                       TABLE II                                                    
______________________________________                                    
Run No.      Treatment Time                                               
                         Density, g/cc                                    
______________________________________                                    
201          None        1.338                                            
202           5 minutes  1.339                                            
203          15 minutes  1.342                                            
204          30 minutes  1.342                                            
205          60 minutes  1.350                                            
206          120 minutes 1.350                                            
______________________________________                                    
 
    
     The data in Table II show that increasing treatment time can increase the density of poly(phenylene sulfide) monofilament. 
     EXAMPLE III 
     The data in Table III lists the drawing conditions used to produce monofilaments used for the analyses in this example. The results of these analyses are listed in Table IV. Denier, or linear density, represents the mass, in grams, of 9,000 meters of fiber. Tenacity, as defined in ASTM D2101, is tensile strength expressed as force per unit of linear density (denier) of the unstrained specimen. The testing procedure of ASTM D2101-82 was used to determine tenacity; however, the scale loads used were from about 3500 to about 5000 grams and only one sample per reported result was analyzed, i.e., average values were not determined. Elongation, as defined by ASTM D2101, is the increase in length of a specimen expressed as a percentage of the nominal gage length. The testing procedure of ASTM D2101-82 was followed to determine elongation; however, only one sample per reported result was analyzed, i.e., average values were not determined. Toughness is determined by multiplying the tenacity and elongation analysis results. Density, reported in grams per cubic centimeter (g/cc), was determined in a gradient density column in accordance with ASTM D1505. 
     Abrasion resistance test results are reported in the number of cycles required to break the fiber or monofilament. Round rod abrasion testing is done by contacting the fiber or monofilament with a rotating round rod testing unit. This testing unit is similar to a hollow tube with a diameter of about six inches. However, the testing unit comprises about 12, 0.175 inch diameter, substantially parallel, equidistant stainless steel rods. One end of each of these steel rods is connected to the circumference of a disc. The other end of each of these steel rods is connected to the circumference of a second disc, which is parallel to the first disc, to give a structure which is similar in design to a circular &#34;bird cage&#34;. The steel rods are uniformly spaced in this &#34;bird cage&#34; structure. One end of the fiber to be tested is attached to a stationary point. The fiber is draped over the exterior surface of the &#34;bird cage&#34; testing unit at an approximate 90 degree angle. The lower, free-hanging, vertical portion of the fiber is attached to a 250 gram weight. The &#34;bird cage&#34; testing unit rotates at a rate of 100 revolutions per minute until the fiber breaks. One complete revolution constitutes one cycle. 
     Another abrasion test, corner abrasion, is performed with a commercially available type of testing unit. This testing unit is available from Custom Scientific Instruments, Inc. in Cedar Knolls, N.J. The testing unit is a 3 inch by 0.5 inch by 0.0312 inch piece of aluminum. All of the corners of the testing unit are approximately right angles. The fiber is suspended over a corner of the testing unit at approximately 90 degrees. The horizontal, upper portion of the fiber is attached to a moveable rod. The lower, free-hanging, vertical portion of the fiber is attached to a 50 gram weight. The moveable rod is moved horizontally to raise and lower the 50 gram weight about three inches, 30 times per minute until the fiber breaks. One complete oscillation, of raising and lowering the 50 gram weight, constitutes one cycle. 
     
                       TABLE III                                                   
______________________________________                                    
Drawing Polymer            Roll 1 Heater,                                 
                                         Draw                             
Condition                                                                 
        Lot      Roll 1, °C.                                       
                           ft/min °C.                              
                                         Ratio                            
______________________________________                                    
A       1        55        20     106-107                                 
                                         3.3                              
B       1        45        20     104    4.4                              
C       2        45        20     108    4.4                              
______________________________________                                    
 
    
     
                                           TABLE IV                                
__________________________________________________________________________
     Drawing         Tenacity,                                            
                           Elongation, Density                            
                                            Round Rod                     
                                                  Corner                  
Run No.                                                                   
     Condition                                                            
           Processing                                                     
                 Denier                                                   
                     (g/denier)                                           
                           %     Toughness                                
                                       (g/cc)                             
                                            Abrasion                      
                                                  Abrasion                
__________________________________________________________________________
301  A     solvent,.sup.(1)                                               
                 2323                                                     
                     1.7   15    25.5  1.354                              
                                            35,100                        
                                                  679                     
           drawn                                                          
302  A     solvent,.sup.(1)                                               
                 2675                                                     
                     1.5   28    42.0  1.369                              
                                            15,300                        
                                                  2589                    
           drawn,                                                         
           HS.sup.(3)                                                     
303  B     drawn 1615                                                     
                     3.1   14    43.4  1.334                              
                                            --    121                     
304  B     drawn,                                                         
                 1879                                                     
                     2.4   24    57.6  1.355                              
                                             9,800                        
                                                  694                     
           HS.sup.(3)                                                     
305  B     drawn,                                                         
                 1906                                                     
                     2.3   24    55.2  1.352                              
                                            13,200                        
                                                  1340                    
           HS,.sup.(3)                                                    
           solvent.sup.(4)                                                
306  B     drawn,                                                         
                 1825                                                     
                     1.9   20    38.0  1.365                              
                                            20,000                        
                                                  1033                    
           solvent,.sup.(4)                                               
           HS.sup.(2)                                                     
307  B     drawn,                                                         
                 1708                                                     
                     1.8   15    27.0  1.351                              
                                            24,100                        
                                                  523                     
           solvent.sup.(4)                                                
308  C     drawn 1643                                                     
                     2.5   13    32.5  --   19,000                        
                                                  339                     
309  C     drawn,                                                         
                 1699                                                     
                     2.5   11    27.5  --   24,360                        
                                                  459                     
           solvent.sup.(4)                                                
310  --    undrawn                                                        
                 --  --    --    --    --    5,860                        
                                                    50                    
311  --    undrawn,                                                       
                 --  --    --    --    --    6,100                        
                                                  &gt;2400                   
           solvent.sup.(4)                                                
__________________________________________________________________________
 .sup.(1) Solvent was CH.sub.2 Cl.sub.2. Treatment for 2 hours; however, n
 visible change after first hour.                                         
 .sup.(2) HS = heatset at conditions equivalent to 200° C. for 10  
 minutes.                                                                 
 .sup.(3) Heatset continuously, inline, at conditions equivalent to       
 200° C. for 10 minutes.                                           
 .sup.(4) Solvent was CH.sub.2 Cl.sub.2. Treatment for 1 hour.            
 
    
     The data in Table IV show the changes in the physical properties of the PPS monofilament after solvent and/or heatset treatment. Denier and density, in all instances, were increased after treatment. Toughness changed after treatment and increased in some instances and decreased in others. 
     Round rod abrasion improved after treatment, except in one treatment sequence. If the monofilament was heatset after being solvent treated, the round rod abrasion was lower than monofilment that had been only solvent treated. Similar results were observed for the corner abrasion test. 
     These two abrasion resistance tests are laboratory simulations of abrasion on an actual fiber end product in use. When abrasion resistance is improved in both tests, the fiber end product is predicted to have a better abrasion resistance during actual use. 
     EXAMPLE IV 
     Table V shows the effect of various gasses on PPS monofilament. The samples were either heatset or heatset and treated with methylene chloride for one hour at 25° C. The treated sample was placed in a bomb and pressurized to about 0.5 atmospheres of the designated gas. The pressurized bombs were placed in an oven at about 220° C for about 24 hours. At the end of the 24 hour time period, the samples were analyzed for physical properties. The analyses shown in Table V were performed in the same manner as described in Example III. 
     
                                           TABLE V                                 
__________________________________________________________________________
                      Tenacity,                                           
                            Elongation, % Loss Of                         
                                              Density,                    
Run No.                                                                   
     Gas                                                                  
        Heatset.sup.(1)                                                   
             CH.sub.2 Cl.sub.2.sup.(2)                                    
                  Denier                                                  
                      (g/denier)                                          
                            %     Toughness                               
                                        Toughness                         
                                              (g/cc)                      
__________________________________________________________________________
401  No Treatment 1904                                                    
                      2.5   27    67.5  --    1.347                       
402  Air                                                                  
        Yes  No   1994                                                    
                      2.2   19    41.8  38.1  1.363                       
403  N.sub.2                                                              
        Yes  No   1987                                                    
                      2.1   17    35.7  47.1  1.365                       
404  SO.sub.2                                                             
        Yes  No   1941                                                    
                      1.5   10    15.0  77.8  1.365                       
405  No Treatment 1939                                                    
                      2.4   26    62.4  --    1.347                       
406  Air                                                                  
        Yes  Yes  1909                                                    
                      2.6   23    59.8   4.2  1.364                       
407  N.sub.2                                                              
        Yes  Yes  1958                                                    
                      2.6   24    62.4  0     1.363                       
408  SO.sub.2                                                             
        Yes  Yes  1953                                                    
                      2.5   21    52.5  15.9  1.366                       
__________________________________________________________________________
 .sup.(1) Heatset at conditions equivalent to 200° C. for 10       
 minutes.                                                                 
 .sup.(2) Treatment for one hour at 25° C.                         
 
    
     Examination of the results listed in Table V show that nearly every monofilament sample lost toughness after the gas treatment. However, run numbers 506, 507, and 508, wherein the samples that were heatset and solvent-treated, had a lower percent loss of toughness than those samples that were only heatset, run numbers 502, 503, and 504. Once again, it is shown that treatment of a poly(arylene sulfide) fiber with an organic halide improves the physical properties of the fiber. 
     While this invention is described in detail for the purpose of illustration, it is not to be construed or limited thereby. These detailed examples are intended to cover all changes and modifications within the spirit and scope of the invention.