Acid wash of polyarylene sulfides

Abstract: In one embodiment, a process is provided for treating virgin poly(arylene sulfide) resins, wherein a heated polymeric slurry, comprising a virgin poly(arylene sulfide) resin and water is contacted by an acidic treating solution comprising an acidic component and an aqueous component, wherein the amount of the acidic component in the acidic treating solution is less than the amount necessary to result in a partial curing of the virgin poly(arylene sulfide) resin. In a second embodiment, the process is provided for treating a virgin poly(arylene sulfide) resin, wherein the virgin poly(arylene sulfide) resin is slurried in an acidic treating solution comprising an acidic component and an aquoues component and the concentration of the acidic component in the aqueous treating solution is less than the amount necessary to result in a partial curing of the virgin poly(arylene sulfide) resin. The polymeric slurry is then heated to an elevated temperature, below the melting point of the virgin resin, while in the substantial absence of a gaseous oxidizing atmosphere.

Description: This invention relates to poly(arylene sulfide)s. It relates broadly to a method for preparing poly(arylene sulfide)s. In a specific aspect, the invention relates to the production of thermally stable poly(arylene sulfide) resins and products produced therefrom having improved melt flow rates, and/or cure rates. In the years following their initial development, poly(arylene sulfide)s (henceforth PAS) have become commercially important resins and the products prepared therefrom are finding increasing utility because of their outstanding durability, toughness, inertness, and versatility. Such resins, although having relatively high melting points, are thermoplastic. While PAS polymers have many desirable properties, the virgin PAS resins generally have a relatively high melt flow, e.g., about 2000 to about 15,000 grams/10 minutes. While, for some purposes, such an encapsulation and coating, it is desirable to have a PAS resin with a melt flow greater than about 15,000 grams/10 minutes, for other purposes, such as molding, film making and fiber making, the resins should have a melt flow in the range from about 10 to about 3,000 grams/10 minutes. Since virgin PAS resins generally have a melt flow ranging from about 3000 to about 10,000 grams/10 minutes, if such a resin is to be employed in moldings or the making of polymeric films and/or fibers, the resin must have its melt flow value decreased. Conversely, if such a polymeric resin is to be employed for the purposes of encapsulations and/or coatings, the resin must have its melt flow value increased. One conventional method of decreasing the melt flow of PAS resins is by a process referred to as "curing". The extent of cure and the final melt flow which is obtained depend upon the intended end use of the polymer. Generally, one method of curing a PAS resin is to subject the resin to an elevated temperature below its melting point while in the presence of a gaseous oxidizing atmosphere. It should be noted that the term "curing", with respect to PAS resins, is not necessarily synonymous with the meaning of that term when applied to other polymers, such as in the curing of natural or synthetic rubber with sulfur as the vulcanizing agent, or the curing of unsaturated polyester compositions with styrene as the crosslinking agent. The complete curing of such rubber or unsaturated polyester compositions results in an irreversible conversion from the thermoplastic state to the thermoset state. The curing of PAS resins, on the other hand, differs in that these resins are thermoplastic, both before and after such curing, although not necessarily to the same degree. Thus, the curing of PAS resins, and objects formed therefrom, produces changes in extrudability, toughness, and other important properties. EP-A-189927 describes PAS coating compositions having para- as well as ortho- or meta polymerized aromatic units and optionally trifunctionally polymerized aromatic units. Washing the copolymers with hot water has been described. Curing at lower temperatures has been mentioned. Although curing the PAS resin results in decreasing its melt flow, which is synonomous with increasing the resin's molecular weight, this method of improving the processability of the polymeric resin is generally long and tedious. It is known that curing rate is generally proportional to the temperature at which the polymer is being cured. Therefore, a method of increasing the curing rate of a resin is by using a higher curing temperature. However, since it is desirable to maintain the curing temperature below the melting point of the resin, the amount that the temperature may be increased is limited to the specific resin's melting point. Accordingly, it is an object of this invention to provide a process for increasing the rate at which polymeric resins cure without increasing the temperature at which the resins are to be cured. Although, for certain applications, polymers with increased rates of cure are economically attractive, it is also desirable to have polymeric resins which are thermally stable in the melt. In other words, it is desirable to have resins whose melt flow values do not substantially change while the resins are held at a temperature above their melting point for a period of time. Accordingly, another object of this invention is to provide a process for preparing thermally stable polymeric resins. A further object of this invention is to provide a process producing PAS polymers having varying melt flow properties which have specific fields of utility. Other objects, aspects and advantages of the invention will be apparent to those skilled in the art upon reading the specification and appended claims. In accordance with one embodiment of this invention, a process is provided as defined as claim 1 for treating poly(arylene sulfide) resin. This process involves (a) preparing a virgin poly(arylene sulfide) resin, (b) contacting the virgin poly(arylene sulfide) resin with an acidic treating solution to form a polymeric slurry, wherein the acidic treating solution comprises an acidic component and an aqueous component and the concentration of the acidic component in the acidic treating solution is less than the amount necessary to result in at least a partial curing of the virgin poly(arylene sulfide) resin, (c) heating the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature below the melting point of the virgin poly(arylene sulfide) resin, to treat the virgin PAS resin, and (d) recovering the treated poly(arylene sulfide) resin from the polymeric slurry. In accordance with the second embodiment of this invention, a process is provided as defined in claim 2 for treating poly(arylene sulfide) resin. This process involves (a) preparing a virgin poly(arylene sulfide) resin, (b) contacting the virgin poly(arylene sulfide) resin with an aqueous solution to form a polymeric slurry, (c) heating the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature below the melting point of the virgin poly(arylene sulfide) resin, (d) adding to the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, an acidic treating solution comprising at least an acidic component, to treat the virgin poly(arylene sulfide) resin, wherein the amount of the acidic component in the acidic treating solution is less than the amount necessary to result in at least a partial curing of the virgin poly(arylene sulfide) resin, and (e) recovering the treated poly(arylene sulfide) resin from the polymeric slurry. Both above embodiments of this invention result in thermally stable polymeric resins which have higher melt flow values and which cure faster than their untreated counterparts. Brief Description of the Drawings A more complete appreciation of the invention and many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying figures briefly described below. FIGURE 1 is a schematic representation of a process for preparing a treated poly(phenylene sulfide) resin in accordance with the embodiments of this invention. FIGURE 2 is a semi-log graph demonstrating the effectiveness of contacting a heated polymeric slurry, comprising a virgin poly(arylene sulfide) resin and water, with an acidic treating solution. FIGURE 3 is a semi-log graph demonstrating the effectiveness of treating a virgin poly(arylene sulfide) resin by slurrying the virgin resin in an acidic treating solution and then subjecting the polymeric slurry to an elevated temperature. The terms "arylene sulfide polymer" and "poly(arylene sulfide)" abbreviated as "PAS", as used in this specification are intended to include polymers of the type which are prepared by reacting polyhaloaromatic compounds with an alkali metal sulfide in the presence of a polar organic compound. The resulting polymers contain the aromatic structure of the polyhalo compound coupled in repeating units through a sulfur atom. The term "virgin", when used to identify a type of PAS resin, refers to substantially linear, low molecular weight polymeric resin which has not been subjected to any oxidative heat treatment (i.e., curing), and wherein no molecular weight modifying agents have been used in the production of the resin. Examples of a molecular weight modifying agents includes, but are not limited to, alkali metal carboxylates and trichlorobenzene. As used herein, the terms "melt flow" and "flow rate" refer to the rate at which a melted PAS resin flows through an orifice when subjected to a downward pressure. In this invention, flow rate is recorded in units of grams of extrudate collected over a 10 minute interval (g/10 min), and is based on a modified version of ASTM D1238, Procedure B. For example, in determining the flow rate for poly(phenylene sulfide) resins, having a melting point of about 285°C (515°F), the resin is subjected to test conditions 315/3.0, where the temperature in degree Celsius is shown first followed by the weight in kilograms. The modification is that the preheating time is 5 minutes as opposed to the minimum 6 minute period. As used herein, the term "thermal stability" refers to the degree of change in the melt flow values of a resin sample, while the resin is held at a temperature above its melting point for different periods of time. As the thermal stability of a given resin improves (i.e., increases), the degree at which the resin's melt flow value changes over time, decreases. The phrase "polymeric slurry", as used herein, refers to a slurry comprising a particulate polymeric resin and a liquid medium. Generally the amount of polymeric resin present in the polymeric slurry will range from about 1 weight percent to about 50 weight percent, preferably from about 5 weight percent to about 40 weight percent, even more preferably from about 10 weight percent to about 30 weight percent. The above weight percentages are based on the total weight of the polymeric slurry. In accordance with a first embodiment of this invention, a process is provided for preparing a treated PAS resin comprising: (a) preparing a virgin PAS resin, (b) contacting the virgin PAS resin with a acidic treating solution to form a polymeric slurry, wherein the acidic treating solution comprises an acidic component and an aqueous component and the concentration of the acidic component in the acidic treating solution is less than the amount necessary to result in at least a partial curing of the virgin PAS resin, (c) heating the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature below the melting point of the virgin PAS resin, to treat the virgin PAS resin, and (d) recovering the treated PAS resin from the polymeric slurry. In accordance with a second embodiment of this invention, a process is provided for preparing a treated PAS resin comprising: (a) preparing a virgin PAS resin, (b) contacting the virgin PAS resin with an aqueous solution to form a polymeric slurry, (c) heating the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature below the melting point of the virgin PAS resin, (d) adding to the polymeric slurry, while in the substantial absence of a gaseous oxidizing atmosphere, an acidic treating solution comprising at least an acidic component, to treat the virgin PAS resin, wherein the amount of the acidic component in the acidic solution is less than the amount necessary to result in at least a partial curing of the virgin PAS resin, and (e) recovering the treated PAS resin from the polymeric slurry. Both above embodiments of this invention result in thermally stable polymeric resins which have higher melt flow values and which cure faster than their untreated counterparts. Any suitable organic or inorganic acids can be used as the acidic treating solution. Examples of suitable organic acids include, but are not limited to, acetic acid, formic acid, oxalic acid, fumaric acid, and monopotassium phthalic acid. The presently preferred organic acid is acetic acid. Examples of suitable inorganic acids include, but are not limited to, hydrochloric acid, monoammonium phosphate, sulfuric acid, phosphoric acid, boric acid, nitric acid, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, carbonic acid, and H₂SO₃(SO₂). The presently preferred inorganic acid is hydrochloric acid. The amount of the acidic component within the acidic treating solution, which can be used in practicing either embodiment of this invention, must be such that no oxidative curing of the resin will occur during the treating process. In other words, the amount of the acidic component, present in the acidic treating solution, must be such that, when the acidic treating solution contacts the virgin PAS resin, at an elevated temperature, below the melting point of the virgin resin, the amount of the acidic component does not result in a decrease of the resin's melt flow value. The maximum amount of the acidic component which can be used in treating a virgin PAS resin in accordance with the embodiments of this invention, will depend upon the oxidative strength of the acid. In other words, the maximum amount of an acidic component having strong oxidative characteristics, which can be used in treating a virgin PAS resin in accordance with the embodiments of this invention will be less than the maximum amount of an acidic component having low oxidative characteristics. Generally, when practicing the first embodiment of this invention, the amount of the acidic component present in the acidic treating solution will not be greater than about 10 weight percent of the total weight of the acidic treating solution. Preferably, the amount of the acidic component present in the acidic treating solution will range from about 0.01 weight percent to about 10 weight percent, more preferably, from about 0.05 weight percent to about 1 weight percent, and even more preferably from about 0.1 weight percent to about 0.5 weight percent, wherein the above weight percentages are based on the total weight of the acidic treating solution. When treating a virgin PAS resin in accordance with the second embodiment of this invention, the amount of the acidic component present in the acidic treating solution will not, generally, exceed 10 weight percent of the sum of the weights of the aqueous solution and the acidic treating solution. Preferably, the amount of the acidic component present will range from about 0.01 weight percent to about 10 weight percent, more preferably from about 0.05 weight percent to about 1 weight percent, and even more preferably from about 0.1 weight percent to about 0.5 weight percent, wherein the above weight percentages are based on the sum of the weights of the aqueous solution and the acidic treating solution. When treating a virgin PAS resin in accordance with this invention, the treating process is conducted at a temperature below the melting point of the virgin PAS resin. Generally, the treating process will be conducted at a temperature within the range from about 1°C to about 165°C below the melting point of the virgin PAS resin, preferably, in the range from about 14°C to about 150°C below the melting point of the virgin PAS resin. The concentration of the virgin PAS resin in the polymeric slurry is such that the acidic treating solution sufficiently contacts the virgin PAS resin. Generally, the concentration of the virgin PAS resin in the polymeric slurry will range from about 1 weight percent to about 50 weight percent. Preferably from about 5 weight percent to about 40 weight percent, and even more preferably from about 10 weight percent to about 30 weight percent, wherein the above weight percentages are based on the total weight of the polymeric slurry. This invention can be used to treat virgin PAS resins at any point in time after the resin has been polymerized but before the resin has been subjected to an oxidative curing process. In commercial application, however, it is preferable to treat the virgin PAS resin during the recovery process of the particulate resin. To demonstrate one method of incorporating the embodiments of this invention, a polymerization reaction process is described below. The polymerization process is illustrated by FIGURE 1 which is a schematic representation of a process for producing a virgin poly(phenylene sulfide) and treating the virgin poly(phenylene sulfide) in accordance with this invention. Referring now to FIGURE 1 aqueous solutions of a caustic solution (e.g., NaOH) and an alkali metal hydrosulfide (e.g., NaSH) are fed into stirred vessel 1 through lines 3 and 5, respectively and allowed to react. A polar organic solvent (e.g., N-methyl-2-pyrrolidone "NMP") is fed through line 7 into stirred vessel 1 to flush all of the material from vessel 1 through line 9 into stirred vessel 11 which serves as a dehydration/polymerization reactor. A second charge of a polar organic solvent (e.g., NMP) is fed through line 13 into line 15 which introduces the solvent into the dehydration/polymerization vessel 11. The contents of vessel 11 are then heated by heating coils 19 to a temperature sufficient to dehydrate the mixture therein. Rising vapors, passing through line 21, are fractionated in distillation column 23. Condensed water is passed through line 25 to be collected in dehydration accumulator 27. After the dehydration process, the distillation column 23 is isolated from vessel 11 by closing valves 22 and 24. The monomer (e.g., p-dichlorobenzene "DCB") is then added through line 29 into line 15 which introduces the monomer into vessel 11. The mixture in vessel 11 is then stirred while being heated, by heating coils 19, to a temperature sufficient to effect the polymerization of the monomeric material. After the polymerization reaction is completed, a sufficient amount of a phase separation agent is added into vessel 11 through line 12 to facilitate the separation of the molten poly(phenylene sulfide) phase from the second liquid phase comprising the solvent, phenylene sulfide oligomers, salt, and unreacted reactants. During the phase separation, the reaction mixture is vigorously stirred by agitator 33 to disperse the polymer phase and the temperature of the reactor is reduced so that after the separation, the liquid polymeric phase gradually solidifies as the temperature of the resin drops below the polymer transition temperature. The reaction mixture effluent, comprising the particulate virgin polymeric resin, solvent, salt, and water, is then transferred through line 35 into stirred dilution tank 37. Water is added through line 39 in a sufficient quantity to dissolve the major portion of soluble salts. Steam is then introduced through line 41 at the bottom of tank 37 mainly for the purpose of driving off unreacted monomer as vapor through line 43. Steam and unreacted monomer are condensed in heat exchanger 45 and collected in receiver 47 from which they can be fed into a fractionator (not shown) for monomer and water recovery. The effluent slurry from dilution tank 37 is charged through line 49, pump 51 and line 53 into stirred tank 55. Here, further deashing (i.e., dissolving of salt and other impurities), is carried out. The slurry is transferred through line 57, pump 59 and line 61 to porous metal screen 63 where solids are collected as a filter cake, comprising of particulate virgin poly(phenylene sulfide) resin, water, and small amounts of solvent and impurities, while the filtrate is passed through line 65 and sent for solvent recovery. The polymeric filter cake, comprising the virgin resin, from porous metal screen 63 is passed through line 83 along with deionized water added through line 85 to be slurried in wash tank 87 which is an agitated tank providing contact between the slurry and the wash water to further deash the virgin poly(phenylene sulfide) particles. Effluent from tank 87 is passed through line 89, pump 91 and line 93 to a second porous metal screen 95 where solids are again collected as a polymeric filter cake and comprising a virgin resin. The filtrate is passed through line 96 and is generally either recycled (not shown) or discarded. The polymeric filter cake from porous metal screen 95 comprising virgin resin is passed through line 97 to wash tank 99 which is another agitated vessel. It is in this wash vessel that the virgin poly(phenylene sulfide) resin will be treated in accordance with the processes of this invention. Specifically, if the virgin resin is treated in accordance with the first embodiment of the invention, the virgin poly(phenylene sulfide) filter cake is passed through line 97 along with an acidic treating solution added through line 98 to be reslurried in wash tank 99. Wash tank 99 is then blocked off using valves 90, 92 and 94. The polymeric slurry is heated by means of heat transfer coils 100, to a temperature not exceeding the melting point of the virgin poly(phenylene sulfide) resin. The polymeric slurry is then cooled and the wash tank vented through valve 94 and line 104. The cooled effluent from wash tank 99 is passed through line 101, pump 103, and line 105 to a third porous metal screen 107. Solids are again collected comprising a now treated poly(phenylene sulfide) resin. The filtrate is passed through line 106 and is generally either recycled (not shown) or discarded. The polymeric filter cake, comprising the now treated poly(phenylene sulfide) resin, is washed with water from line 109. The treated poly(phenylene sulfide) resin is transferred through line 111 as recovered, treated poly(phenylene sulfide) which is then dried and, optionally, air-cured. When practicing the second embodiment of this invention, the virgin poly(phenylene sulfide) filter cake from porous metal screen 95 is reslurried in wash tank 99 with a sufficient amount of water being added through line 98. Wash tank 99 is then blocked off using valves 90, 92 and 94. The polymeric slurry in wash tank 99 is heated, by means of heat transfer coils 100, to a temperature not exceeding the melting point of the virgin poly(phenylene sulfide) resin. An acidic treating solution is then added to the heated slurry in wash tank 99 through line 102. The polymeric slurry containing the acidic treating solution is then agitated while being maintained at the elevated temperature. The polymeric slurry is then cooled and the wash tank vented through valve 94 and line 104. The cooled effluent from wash tank 99 is then passed through line 101, pump 103 and line 105 to a third porous metal screen 107. Solids are again collected comprising a now treated poly(arylene sulfide) resin. The filtrate is passed through line 106 and is generally either recycled (not shown) or discarded. The polymeric filter cake, comprising the now treated poly(phenylene sulfide) resin, is washed with water from line 109. The treated poly(phenylene sulfide) resin is then transferred to line 111 as recovered, treated poly(phenylene sulfide) which is then dried and, optionally, air-cured. In either of the above embodiments, the drying process of the treated, recovered poly(phenylene sulfide) should result in substantially no oxidative curing of the polymeric resin. Therefore, if the drying process is conducted at a temperature at or above 100°C, the drying vessel should be substantially free of any gaseous oxidizing atmosphere. If, however, the drying process is conducted at a temperature below 100°C, drying must be done in a vacuum so that the aqueous component of the polymeric filter cake can be vaporized. Moreover, if drying is below 100°C, the presence of a gaseous oxidizing atmosphere will generally not result in a curing of the treated resin. As stated above, after the treated, recovered poly(phenylene sulfide) resin has been dried, it can optionally be cured. The curing process of a PAS resin generally entails subjecting the resin to an elevated temperature, below its melting point, while in the presence of gaseous oxidizing atmosphere. Any suitable gaseous oxidizing atmosphere can be used. Examples of such include, but are not limited to, oxygen, any mixture of oxygen and an inert gas, such as nitrogen, or air. Generally, due to economic feasability, air is often preferred. The curing temperature is generally in the range from about 1°C to about 110°C below the melting point of the treated resin, preferably, from about 14°C to about 85°C below the melting point of the treated resin. As stated earlier, treating a virgin PAS resin in accordance with this ivnention results in a treated resin which cures faster than its untreated counterpart. This result is desirable since it enables one to cure a PAS resin to a desired melt flow value either (a) in a shorter period of time and/or (b) at a lower curing temperature. Another advantage of treating a virgin PAS resin in accordance with this invention is that a treated PAS resin will have a melt flow value greater than its untreated counterpart. In other words, a virgin resin which has been treated in accordance with this invention will have greater flowing tendencies (i.e., will be less viscous) than its untreated counterpart. This result is also desirable, especially if the PAS resin is to be employed for encapsulating and/or coating various objects. Depending upon the specific acidic treating solution and/or the concentration of the acidic treating solution used in treating a virgin PAS resin, the degree at which the melt flow value of the treated resin increases will vary. For example, if the same virgin resin is treated, the specific acidic solution employed in the treating process can result in the melt flow value of the treated resin being from about 50% to about 250% greater than the melt flow value of the resins untreated counterpart. As stated earlier, resins which are useful for encapsulation and/or coating purposes, generally have melt flow values greater than 15,000 g/10 min. Therefore, in the preparation of a PAS resin, suitable for encapsulation and/or coating purposes, the virgin PAS resin, prior to being treated, will generally have a melt flow value greater than 4500 g/10 min., preferably, greater than 6000 g/10 min., more preferably greater than 7500 g/10 min, and even more preferably greater than 9000 g/10 min. This invention is broadly applicable to PAS resins wherein polyhalo-substituted aromatic compounds are reacted with sulfur-containing reactants in a polar organic solvent, either in batch or continuous operations. Generally, the polymers which are prepared for use in this invention, because of the availability of the materials from which they are prepared, are those having the repeating unit R-S, wherein R is phenylene, biphenylene, naphthylene, biphenylene ether, or a lower alkyl-substituted derivative thereof. The phrase "lower alkyl", as used herein, refers to alkyl groups having 1 to 6 carbon atoms. Examples of such lower alkyls include, but are not limited to, methyl, propyl, isobutyl, n-hexyl, and the like. Moreover, preferred polymers generally have melting points above 200°C (392°F), more preferably, in the range from about 200°C (392°F) to about 500°C (932°F). Although other polymeric resins are not excluded, in general, the poly(arylene sulfide) polymers, treated by the process of this invention, are those wherein the arylene group is a phenylene group. Generally, the process of this invention can be used to improve the properties of phenylene sulfide polymers selected from the group comprising poly(phenylene sulfide), poly(phenylene sulfide ketone), poly(phenylene sulfide diketone), and poly(biphenylene sulfide). The invention will still more fully be understood from the following examples. These examples are only intended to demonstrate select embodiments of the invention. Example I This Example demonstrates treating a virgin poly(phenylene sulfide) (henceforth PPS) resin, commercially available from Phillips Petroleum Company as Ryton®, having a melting point of about 285°C (545°F) and an initial melt flow rate ranging from about 2,000 to about 6,000 g/10 min as determined by modified ASTM D1238 Procedure B to use a 5 minute preheat time (henceforth, modified ASTM D1238). In this example, the virgin PPS resin was treated by contacting a heated polymeric slurry comprising the virgin PPS resin and water, with an acidic treating solution. To simulate commercial conditions, 800 grams of a polymeric filter cake, comprising the virgin PPS resin (i.e., approximately 400 grams virgin PPS resin and approximately 400 mL. water) were charged to a stirred 7.6 ℓ (2-gallon) autoclave reactor. The polymeric filter cake was then slurried by adding approximately 3.6 liters of water to the autoclave reactor as the aqueous solution. The polymeric slurry was then heated to 185°C (365°F) while being stirred. After stirring the heated slurry for approximately 15 minutes, 2.7 grams of glacial acetic acid was added to the reactor as the acidic treating solution. The amount of the acidic component present in the acidic treating solution (i.e., 2.7 grams glacial acetic acid) is 0.075 weight percent of the sum of the weights of the aqueous solution (i.e., 3.6 liters water) and the acidic treating solution (i.e., 2.7 grams glacial acetic acid). As the virgin PPS resin was being treated with the acidic treating solution, the temperature of the polymeric slurry contents was maintained at about 185°C (365°F). The treating process continued for approximately one hour, after which time the polymeric slurry was cooled to approximately 21°C (70°F). The treated PPS resin was recovered from the polymeric slurry by filtration. The treated recovered, PPS resin was then washed several times with distilled water, and allowed to dry at 121°C (250°F) for approximately 4 hours while purging the drying vessel with nitrogen gas. Hereinafter, this resin will be referred to as Resin 1. A series of 12-gram samples of Resin 1 were cured by being heated at 264°C (507°F) for approximately 6 hours while in the presence of air. At various time intervals, during this 6-hour curing period, one sample, from the series of 12-gram samples, was removed from the oven. The melt flow value of this particular 12-gram sample of Resin 1 was measured according to modified ASTM D1238. The observed results are recorded in Table I. Two additional samples of the same virgin PPS resin contacted by an acidic treating solution, recovered, dried, and cured in accordance with the same procedure as set out for Resin 1. The resulting PPS resins will be referred to as Resins 2 and 3. The only significant difference between the treatment of Resin 1 and that of the remaining two resin samples was the amount of glacial acetic acid added. Specifically, Resin 2 was treated with 4.5 grams of glacial acetic acid resulting in a 0.125 weight percent solution; and, Resin 3 was treated with 5.4 grams of glacial acetic acid resulting in a 0.15 weight percent solution. The varying concentrations of the acidic components employed and the resulting melt flow values of their respective treated resins at varying time intervals during the curing process are also recorded in Table I. For the purposes of demonstrating the effectiveness of this invention, the melt flow values of a control resin (hereinafter referred to as Resin 4), which was washed with distilled water as opposed to being treated by an acidic treating solution, are also recorded in Table I. To visually implement the demonstration of the invention's effectiveness, the data from Table I has been plotted on the graph shown in FIGURE 2. When comparing the melt flow values of inventive Resins 1-3 with those of control Resin 4, the data clearly shows that contacting a heated polymeric slurry, comprising a virgin PPS resin, with an acidic treating solution results in a pronounced acceleration of the rate at which the PPS resin cures. Example II This Example demonstrates illustrates treating a virgin poly(phenylene sulfide) (henceforth PPS) resin, commercially available as Ryton®, having a melting point of about 285°C (425°F) and a melt flow rate ranging from about 2,000 to about 6,000 g/10 min. as determined by modified ASTM D1238. In this example, the virgin PPS resin was treated by slurrying a polymeric filter cake comprising the virgin PPS resin, with an acidic treating solution and then subjecting the slurry to an elevated temperature below the melting point of the virgin PPS resin. To simulate commercial conditions, 800 grams of a polymeric filter cake, comprising the virgin PPS resin (i.e., approximately 400 grams virgin PPS resin and approximately 400 mL. water), were charged to a stirred 7.6 ℓ (2-gallon) autoclave reactor. The polymeric filter cake was then stirred by adding approximately 3.6 liters of a 0.05 weight percent aqueous acetic acid solution (HOAc) to the autoclave reactor. In this example, the 3.6 liters of 0.05 wt. percent acetic acid is the acidic treating solution. The polymeric slurry was then heated to 185°C (365°F) while being stirred. The treating process continued for approximately one hour, at 185°C (365°F), after which time the polymeric slurry was cooled to approximately 21°C (70°F). The treated PPS resin was recovered from the polymeric slurry by filtration. The treated, recovered, PPS resin was then washed several times with distilled water, and allowed to dry at 121°C (250°F) for approximately 4 hours while purging the drying vessel with nitrogen gas. Hereinafter, this resin will be referred to as Resin 5. A series of 12-gram samples of Resin 5 were cured by being heated at 264°C (507°F) for approximately 6 hours, while in the presence of air. At various time intervals during this 6-hour curing period, one sample, from the series of 12-gram samples, was removed from the oven. The melt flow value of this particular 12-gram sample of Resin 5 was measured according modified ASTM D1238. The observed results are recorded in Table II. Five additional samples of the same virgin PPS resin were contacted by an acidic treating solution, recovered, dried, and cured in accordance with the same procedure as set out for Resin 5. The resulting PPS resins will be referred to as Resins 6-10. The only significant difference between the treatment of Resin 5 and that of the remaining 5 resin samples, was the acidic treating solution added. Specifically, Resins 6-8 were treated with varying concentrations of an aqueous acetic acid solution; Resin 9 was treated with an aqueous hydrochloric acid solution; and Resin 10 was treated by adding carbon dioxide to the autoclave reactor. The varying concentrations of the acidic components present in the respective acidic treating solution and the resulting melt flow values of their respective treated resins at varying time intervals during the curing process are also recorded in Table II. For the purposes of demonstrating the effectiveness of this invention, the melt flow values of the control resin from Example I (i.e., Resin 4), which was washed with distilled water, as opposed to being treated by an acidic treating solution, are also recorded in Table II. To visually implement the demonstration of this invention's effectiveness, the data from Table II has been plotted on the graph shown in FIGURE 3. When comparing the melt flow values of inventive Resins 5-10 with those of control Resin 4, the data clearly shows that slurrying a virgin PPS resin in an acidic treating solution and then heating the polymeric slurry to a temperature below the melting point of the resin, results in a pronounced acceleration of the rate at which a PPS resin cures. Example III This example provides data which demonstrates the thermal stability of a virgin poly(phenylene sulfide) (henceforth PPS) resin, commercially available as Ryton®, after the virgin resin had been contacted by an acidic treating solution in accordance with the procedure set out in Example II. In this example, the thermal stabilities of seven treated PPS resin (Resins 11-17, inclusive) were assessed by noting the changes in the respective melt flow values for each Resin after being maintained at 315°C (600°F), in the barrel of the melt index apparatus of ASTM D1238, for 5 minutes and for 30 minutes. Resins 11-13 were treated by slurrying the virgin PPS resin in a 0.5 weight percent acetic acid solution and then heating the slurry to 185°C (365°F). The thermal stability of Resins 11-13 was then observed and recorded at various degrees of cure. Specifically, the data associated with Resin 11 is that of a treated PPS resin, after the Resin had been cured at 264°C (507°F) for 0.25 hr. The data associated with Resin 12 is that of a treated PPS resin, after the Resin had been cured at 264°C (507°F) for 0.5 hr. The data associated with Resin 13 is that of a treated PPS resin, after the Resin had been cured at 264°C (507°F) for 0.25 hr. Resins 14-17 were treated by slurrying the virgin PPS resin in a 0.1 weight percent acetic acid solution and then heating the slurry to 185°C (365°F). The thermal stability of Resins 14-17 was the observed and recorded at various degrees of cure. Specifically, the data associated with Resin 14 is that of a treated PPS resin, after the Resin had been cured at 264°C (507°F) for 0.75 hr. The data associated with Resin 15 is that of a treated PPS resin, after the Resin had been cured at 264°C (507°F) for 1 hr. The data associated with Resin 16 is that of a treated PPS resin after the resin had been cured at 264°C (507°F) for 1 hr. The data associated with Resin 17 is that of a treated PPS resin after the resin had been cured at 264°C (507°F) for 1.25 hrs. The observed melt flow values of Resin 11-17 are recorded in Table III. For the purposes of demonstrating the effectiveness of this invention, the thermal stability of a control resin sample (hereinafter referred to as Resin 18) was also determined. Control Resin 18 was prepared in accordance with the same procedure set out in Example II and washed with distilled water, as opposed to being treated with an acidic treating solution. Control Resin 18 was cured at 264°C (507°F) for 6 hours. The thermal stability of Resin 18 was then determined and is recorded in Table III. Effect of Contacting a Virgin PPS Resin with an Acidic Treating Solution on Thermal Stability Resin No. Treating Agent Flow Rate (g/10 min.) Net Change (%) After 5 min. at 315°C. After 30 min. at 315°C. 11 0.5 wt-% HOAc 440 500 12 12 0.5 wt-% HOAc 237 219 〈8〉 13 0.5 wt-% HOAc 418 540 30 14 0.1 wt-% HOAc 207 238 15 15 0.1 wt-% HOAc 98 95 〈3〉 16 0.1 wt-% HOAc 45 59 31 17 0.1 wt-% HOAc 14 9 〈36〉 18 H₂O (control) 67 75 12 The data in Table III clearly demonstrates that, regardless of the desired degree of cure, the melt flow values of inventive Resins 11-17 do not vary by more than 40 percent. Therefore, for the purposes of this invention, this example demonstrates that slurrying a virgin PPS resin in an acidic treating solution and then heating the slurry to a temperature below the virgin resin's melting point, will not substantially effect the thermal stability of the resin. Example IV As stated earlier, the rate at which a poly(arylene sulfide) resin cures is directly proportional to the temperature at which the resin is cured. This example illustrates that, regardless of the curing temperature, virgin PAS resins, which have been treated in accordance with this invention, cure faster than their untreated counterpart. The PAS resin used to demonstrate this feature of the invention is a virgin poly(phenylene sulfide), commercially available under the trade name Ryton® having a melting point of 285°C (545°F) and a melt flow value within the range from about 2,000 g/10 min. to about 6,000 g/10 min. according to modified ASTM D1238. To simulate commercial conditions, 800 grams of a polymeric filter cake, comprising the virgin PPS resin (i.e., approximately 400 grams virgin PPS resin and approximately 400 mL. water), were charged to a stirred 7.6 ℓ (2-gallon) autoclave reactor. The polymeric filter cake was then slurried by adding approximately 3.6 liters of a 0.1 weight percent aqueous acetic acid solution (HOAc), to the autoclave reactor. The polymeric slurry was then heated to 185°C (365°F) while being stirred. The treating process continued for approximately one hour, at 185°C (365°F), after which time the polymeric slurry was cooled to approximately 21°C (70°F). The treated PPS resin was recovered from the polymeric slurry filter cake by filtration. The treated, recovered PPS resin was then washed several times with distilled water, and allowed to dry at 121°C (250°F) for approximately 4 hours while purging the drying vessel with nitrogen gas. Hereinafter, this resin will be referred to as Resin 19. Six 12-gram samples of Resin 19 were cured by being heated at various temperatures for various time periods while in the presence of air. The final melt flow value of each of these six Resin 19 cured samples was measured, at the end of their respective curing period, according to modified ASTM D1238. The observed results are recorded in Table IV. In order to demonstrate the effectiveness of this invention, a control resin (henceforth Resin 20) was prepared by being washed with distilled water, as opposed to being treated with an acidic treating solution. Six 12-gram samples of control Resin 20 were cured for the same time and at the same temperature as each of the six Resin 19 samples. The final melt flow value of each of the six Resin 20 cured samples was measured, at the end of their respective curing period, according to modified ASTM D1238. The observed results are also recorded in Table IV. Effect of Temperature and Time on Curing Acid-Treated Polymers Resin No. Melt Flow (g/10 min.) After Curing at Temperature (time) (Initial) 357°F. (191°C) (75 Hrs.) 425°F. (219°C) (30 Hrs.) 400°F. (205°C) (3 Hrs.) 425°F. (219°C) (25 Hrs.) 475°F. (248°C) (3 Hrs.) 507°F. (263°C) (6 Hrs.) 19 (invention) 6450 95 --- 930 0 10 0 20 (control) 4200 379 303 660 130 140 15 As can be seen, Table IV demonstrates that contacting a virgin PPS resin with an acidic treating solution results in a faster curing resin, regardless of the temperature of cure. Example V This Example demonstrates a method of treating a virgin poly(arylene sulfide) resin, such that the treated resin can be used for encapsulation and/or coating purposes. Specifically, this example demonstrates that treating a virgin poly(phenylene sulfide) resin (henceforth PPS), having an initial melt flow value ranging from about 10,000 g/10 min. to about 14,500 g/10 min, with an acidic treating solution, results in a treated PPS resin having an initial melt flow value ranging from about 15,000 g/10 min. to about 35,000 g/10 min. The virgin PPS resin used in this example was prepared in a 340 ℓ (90-gallon) stirred polymerization reactor and had an initial melt flow value of approximately 13,500 g/10 minutes as determined by modified ASTM 1238. To simulate commercial conditions, 800 grams of a polymeric filter cake, comprising the above virgin PPS resin (i.e. 400 grams of the above PPS resin and 400 mL water) were charged into a stirred 2-gallon autoclave reactor. The polymeric filter cake was then slurried by adding approximately 2 liters of a 0.2 weight percent aqueous acetic acid solution (HOAc) to the autoclave reactor. The polymeric slurry was then heated to 185°C (365°F) while being stirred. The treating process continued for approximately one hour, at 185°C (365°F), after which time the polymeric slurry was cooled to approximately 21°C (70°F). The treated PPS resin was recovered from the polymeric slurry by filtration. The treated, recovered PPS resin was then washed several times with distilled water, and allowed to dry at 121°C (250°F) for approximately 4 hours while purging the drying vessel with nitrogen gas. Hereinafter, this resin will be referred to as Resin 21. The melt flow value of Resin 21 was then measured according to modified ASTM D1238. This value is recorded in Table V. For the purposes of demonstrating the effectiveness of this invention, the melt flow value of a control resin (henceforth Resin 22), which was washed with distilled water, as opposed to being treated by an acidic treating solution, is also recorded in Table V. Control Resin 22 was prepared using the same virgin PPS resin employed in the preparation of Resin 21. Effect of Acid-Treating a Polymer on Melt Flow Value Resin No. Treating Agent Melt Flow (g/10 min.) 21 (invention) 0.2 wt. % HOAc 24,750 22 (control) Water 13,800 As can clearly be seen, Table V demonstrates that a virgin PPS resin, which is initially not suitable for encapsulation and/or coating purposes, can be converted to a suitable encapsulation resin by contacting the virgin PPS resin with an acidic treating solution in accordance with the embodiments of this invention. Example VI This Example further demonstrates the effectiveness of this invention by providing data illustrating the thermal stability of invention Resin 21 of Example V. A 12-gram sample of Resin 21 of Example V was cured by being heated to 264°C (507°F) for 2.5 hours while being exposed to air. The thermal stability of cured Resin 21 was then assessed by noting the changes in the melt flow values after the Resin has been maintained at 185°C (365°F), while in the barrel of the melt index apparatus of ASTM D1238, for 5 minutes and for 30 minutes. The 5 minute and 30 minute melt flow values of cured Resin 21 are recorded in Table VI. Thermal Stability of a PPS Resin Contacted by an Acidic Treating Solution Resin No. Treating Agent Melt Flow (g/10 min) Net Change (%) After 5 min. at 316°C. After 30 min. at 316°C. 21 0.2 wt-% HOAc 1136 1430 7 The data of Table VI clearly demonstrates that contacting a virgin PPS resin with an acidic treating solution will not substantially affect the thermal stability of the resin. It is evident from the foregoing that various modifications can be made to the embodiments of this invention without departing from the spirit and scope thereof which will be apparent to those skilled in the art. Having thus described the invention, it is claimed as follows.

Claims: A process for treating a virgin poly(arylene sulfide) resin being a substantially linear, low molecular weight polymeric resin, which has not been subjected to an oxidative heat treatment and has not been produced with a molecular weight modifying agent, said process comprising: (a) contacting said virgin resin having a melt flow of 2000 to 15000 g/10 min as determined by ASTM D1238 Procedure B modified to employ a preheating time of 5 min. with an acidic treating solution to form a polymer slurry, wherein said acidic treating solution comprises an acidic component and an aqueous component and the concentration of said acidic component in said acidic treating solution is 0.1 to 0.5 weight percent based on the total weight of the acidic treating solution, said acidic treating solution having a pH greater than 2, (b) heating said polymer slurry mixture, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature within the range of 1°C to 175°C below the melting point of said virgin resin, to treat said virgin resin, and (c) recovering said treated resin from said polymer slurry. A process for treating a virgin poly(arylene sulfide) resin being a substantially linear, low molecular weight polymeric resin, which has not been subjected to an oxidative heat treatment and has not been produced with a molecular weight modifying agent, said process comprising: (a) contacting said virgin resin having a melt flow of 2000 to 15000 g/10 min as determined by ASTM D1238 Procedure B modified to employ a preheating time of 5 min. with an aqueous solution to form a polymer slurry, (b) heating said polymer slurry, while in the substantial absence of a gaseous oxidizing atmosphere, to an elevated temperature within the range of 1°C to 175°C below the melting point of said virgin resin, (c) adding to said polymer slurry, while in the substantial absence of a gaseous oxidizing atmosphere, an acidic treating solution comprising an acidic component and an aqueous component, to treat said virgin resin, wherein the concentration of said acidic component in said acidic treating solution is 0.1 to 0.5 weight percent based on the total weight of the acidic treating solution, said acidic treating solution having a pH greater than 2, and (d) recovering said treated resin from said polymer slurry. A process as claimed in claim 1 wherein, prior to contacting said virgin resin with said acidic treating solution, said virgin resin is recovered from a polymerization reaction effluent comprising said virgin poly(arylene sulfide) resin, salt, a polar organic solvent, and water. A process as claimed in claim 2 wherein, prior to contacting said virgin resin with said aqueous solution, said virgin resin is recovered from a polymerization reaction effluent comprising said virgin poly(arylene sulfide) resin, salt, a polar organic solvent, and water. A process as claimed in claim 1 or 2 wherein, after said treated resin is recovered from said polymer slurry, said treated resin is dried, while in the substantial absence of a gaseous oxidizing atmosphere, at an elevated temperature below the melting point of said treated resin. A process as claimed in claim 1 or 2 wherein, after said treated resin is recovered from said polymer slurry, said treated resin is dried at a temperature not exceeding 100°C and under vacuum conditions sufficient to vaporize any liquid component. A process as claimed in claim 5 wherein, after said treated resin is dried, said treated resin is heated to an elevated temperature, below the melting point of said treated resin, while in the presence of a gaseous oxidizing atmosphere, in particular in the presence of air. A process as claimed in claim 6 wherein, after said treated resin is dried, said treated resin is heated to an elevated temperature, below the melting point of said treated resin, while in the presence of a gaseous oxidizing atmosphere, in particular in the presence of air. A process as claimed in claim 1 or 2 wherein said polymer slurry is heated to a temperature within the range from 14°C to 150°C below the melting point of said virgin resin. A process as claimed in claim 1 or 2 wherein said acidic treating solution is a solution of an organic acid selected from the group comprising acetic acid, formic acid, oxalic acid, fumaric acid, and monopotassium phthalic acid, in particular wherein said organic acid is acetic acid. A process as claimed in claim 1 or 2 wherein said acidic treating solution is a solution of an inorganic acid selected from the group comprising hydrochloric acid, monoammonium phosphate, sulfuric acid, phosphoric acid, boric acid, nitric acid, sodium dihydrogen phosphate, carbonic acid and H₂SO₃, in particular wherein said inorganic acid is hydrochloric acid. A process as claimed in claim 1 or 2 wherein the concentration of said virgin resin in said polymer slurry ranges from 1 weight percent to 50 weight percent; in particular from 5 weight percent to 40 weight percent, and more particularly from 9 weight percent to 20 weight percent, said weight percentages being based on the total weight of said polymer slurry. A process as claimed in claim 1 wherein; prior to contacting said virgin resin with said acidic treating solution, said virgin resin has a melt flow value of at least 4,500 grams/10 minutes, in particular of at least 6,000 grams/10 minutes, more particularly of at least 7,500 grams/10 minutes, and even more particularly of at least 9,000 grams/10 minutes, said melt flow measured according to ASTM D1238, Procedure B, modified to have a pre-heating time of 5 minutes. A process as claimed in claim 2 wherein, prior to contacting said virgin resin with said aqueous solution, said virgin resin has a melt flow value of at least 4,500 grams/10 minutes, in particular of at least 6,000 grams/10 minutes, more particularly of at least 7,500 grams/10 minutes, and even more particularly of at least 9,000 grams/10 minutes, said melt flow measured according to ASTM D1238, Procedure B, modified to have a pre-heating time of 5 minutes. A process as claimed in any of the preceding claims wherein said virgin poly(arylene sulfide) is poly(phenylene sulfide). A process as claimed in any of the preceding claims wherein said acidic treating solution has a pH of greater than 4.0.

Inventors: NESHEIWAT AFIF MICHAEL, SENATORE GUY, SHERK FRED THEODORE, NESHEIWAT, AFIF MICHAEL, SENATORE, GUY, SHERK, FRED THEODORE
Applicants: PHILLIPS PETROLEUM CO, PHILLIPS PETROLEUM COMPANY
Application year: 1989
Main classification: C08G75
IPC codes: C08G75, C08G85