MXPA99001591A - Poly(p-phenylene terephthalamide) articles of high flame strength - Google Patents

Abstract

Articles made from poly(p-phenylene terephthalamide) polymer having an inherent viscosity of 1.5 to 4 dL/g, 5 to 20 mols of sulfur, as sulfonate, per 100 mols of polymer repeat units, and at least 0.5 weight percent of tungsten oxides or molbydenum oxides;and the process for making such articles.

Description

ARTICLES OF POLI (P-PHENYLENE TEREFTALAMIDE) OF HIGH RESISTANCE TO THE FLAME Field of Invention This invention relates to poly (p-phenylene terephthalamide) articles that exhibit increased flame resistance.

Background of the Invention U.S. Patent No. 4,112,016, filed on April 3, 1975, discloses polyamide fibers having improved fire protection capabilities where fibers, such as poly (p-phenylene terephthalamide), are grafted with certain compounds of the invention. match.

U.S. Patent No. 4,198,494, filed September 30, 1974, discloses a mixture of poly (p-phenylene terephthalamide) and poly (m-i softalamide) which exhibit improved resistance to heat flow.

REF .: 29342 U.S. Patent Number 4,741,740, filed September 9, 1986, discloses the increased flame resistance of aramid fibers by fire retardant compounds of organic introduction by means of swollen fiber organic liquids.

Description of the invention.

The present invention provides an article of poly (p-phenylene terephthalamide) of high flame resistance having an inherent viscosity from about 1.5 to 4 dL / g and from 5 to 20 moles of sulfide, as sulfonate groups, per 100 moles of repeating units of polymer, with from 0.5 - 15 weight percent, based on the total weight of the article, of a metal, wherein the metal is presented as oxides, selected from the group consisting of tungsten oxide and molybdenum oxide, uniformly distributed around the article, the article exhibiting a flame resistance of at least five times greater than the flame resistance of the same article without the metal compound.

The present invention also provides a process for manufacturing articles of high flame resistance of pol i (p-pheny1-ene terephthalamide) comprising the steps of contacting a never-dried article of poly (p-phenylene terephthalamide) with an aqueous solution of metal ions selected from the group consisting of tungsten ions and molybdenum ions to introduce a sufficient amount of the metal into the article to increase the flame resistance of the article, and dry the article.

Detailed description of the invention Articles made of poly (p-phenylene t erephthalamide) (PPD-T) are well known for their extreme flame resistance and high modulus. For some terminal applications, however, there is a need for sustained strength through the flame conditions. "Articles", as used herein, refers to fibers, fabrics, films, cords, tapes, and the like, all exhibiting the features and capabilities of this invention. "Articles", in this, most frequently means fibers, fabrics, and films; and where the mention is made in this of fibers, fabrics, or films, those terms include articles, generally.

Although PPD-T fibers are inherently flame resistant, it is often desirable to have PPD-T articles that maintain strength in the presence of a flame, thereby providing an enhanced enhanced flame barrier. A protective garment made of the fibers of this invention exhibits an integral physical improvement in the flame.

It has now been found that fibers made using sulfonated PPD-T have an inherent viscosity of about 1.5 to 4 dL / g, and contain from 5 to 20 moles of sulfide, as sulfonated groups, per 100 moles of p-phenylene terephthalamide units (the repeated units of the polymer chain) possesses the high resistance to the desired flame when PPD-T of the article is a particular metallic compound distributed around. In an experimental result, the flame resistance of the PPD-T articles of this invention is increased by at least five times over the flame resistance of the same article are the presence of the metal compound.

By PPD-T we have the poly (p-phenylene terephthalamide) homopolymer. PPD-T is more frequently prepared by the polymerization of p-phenylene diamine and terephthalate chloride, or else copolymers result from the incorporation of small amounts of other diamines with p-phenylene diamine or from small amounts of other chlorides diacids with terephthaloyl chloride. As a general rule, other diamines and other diacid chlorides can be used in amounts well above about 10 mole percent of p-phenylene diamine or terephthaloyl chloride, with the proviso that the other diamines and diacid chlorides do not have reactive groups that interfere with the polymerization reaction. The preparation of PPD-T is described in U.S. Patent Nos. 3,869,429; 4,308,374; and 4,698,414.

In a convenient manner for making the fibers for the practice of this invention, an inherent high-viscosity PPD-T (greater than about 5) is mixed with sulfuric acid of a concentration of 100.2 to 102% to cause the desired degree of sulfonation of the PPD-T molecules. The conditions are carefully controlled such that the molecular weight of PPD-T is reduced to an inherent viscosity level (IV) from about above 1.5 to 4 dL / g (as measured from PPD-T yarn) dissipated, at the same time, executing the desired degree of sulfonation.

The degree of sulfonation and the degree of degradation of the PPD-T form a balance that is controlled by the concentration of sulfuric acid, the concentration of polymer in sulfuric acid, the exposure time of the polymer to the acid, and the temperature of the sulfuric acid during The exhibition .

This is useful for using sulfuric acid of concentrations between about 100.2% and 102% to dissolve the PPD-T and the sulfonate. Acid concentrations above about 103% can cause unacceptable severe polymer degradation; and concentrations below 100.2% require unacceptable long times to execute the desired degree of sulfonation.

The time and temperature at which the polymer is exposed to acid will affect the degree of sulfonation and the degree of degradation of the polymer. Temperatures in the range of 75 to 120 ° C and periods of time from 10 minutes to 2 hours are useful.

The inherent viscosity, which is determined as described below, is a measure of the molecular weight of the polymer and serves as an indication of the reduction in molecular weight that the polymer undergoes in the sulfonation process.

In the preparation of fibers of this invention, the spinning solution is conveniently made by dissolving PPD-T at the desired concentration in concentrated sulfuric acid. The concentration of polymer in the acid is generally about 9 to 15% by weight, and preferably about 12% by weight; and the acid concentration is around 100 to 102% The sulfonation conditions employed in the present invention result in sulfur levels of 5 to 20 moles of sulfur, such as sulfonate groups, per 100 moles of polymer repeating units. Below 5 moles the fibers seem unable to inhibit significant amounts of the metal and above 20 moles, the polymer invariably shows an unacceptably low molecular weight.

The fibers of the present invention can be spun using the air layer spinning conditions of U.S. Pat. 3,767,756 or the wet spinning conditions of U.S. Pat. 3,671,542. If desired, the fibers of this invention can be produced in colors by incorporating pigments or other dyes into the solution to be spun. The sulfonated PPD-T solution can be extruded through spinners with holes in the range of about 0.025 to 0.25 mm in diameter. The number, size, shape and configuration of the holes may vary to execute the desired fiber product. The extruded adjuvant is emptied into a coagulation bath with or without passing it previously through a non-coagulating fluid layer. The non-coagulating fluid layer, if used, is generally air; but it can be any other inert gas or liquid that is a non-coagulant for the adjuvant. The non-coagulating fluid layer is generally from 0.1 to 10 centimeters thick.

The coagulant bath is aqueous and may contain a maximum of 80% sulfuric acid. The bath temperature can be as low as -10 ° C; but it can be in a range of around 25 to 80 ° C or slightly higher.

Then, the extruded adjuvant can be conducted around the coagulation bath and the adjuvant is coagulated in acid / fibers swollen with water, the fibers are thoroughly washed to extract the acid and neutralizing acid groups. The solution for washing the fiber can be water, followed by alkaline water.

After spinning the fibers from the sulfonated PPD-T, low inherent viscosity, those fibers, in the "never dry" form, are contacted with an aqueous solution of a metal compound to impregnate the metal and, by the presence of metal, increase the flame resistance of articles. Various metals are found to increase the flame resistance of the fibers using the process of this invention; but molybdenum and tungsten are found to produce truly outstanding improvements. Other metals tested and found to produce some degree of improvement in flame resistance include palladium, vanadium, and zirconium.

The contact of the article with the aqueous metal cation solution can be performed after the coagulation step in the spinning process or the aqueous metal compound solution can be used directly as a liquid fiber coagulant in the spinning process.

Any molybdenum or tungsten compound that can form a stable aqueous solution can be used here; The compounds that assist in dissolving the metal compounds can also be added to the aqueous solution. Useful tungsten compounds include tungsten tetrachloride (with citric acid to stabilize the solution), as well as tungsten such as phosphoric acids, homopolytungs such as ammonium tungstate and sodium tungstate. Any tungsten compound can be used along if it is soluble in water, and if it does not precipitate during the conduction of the process. The preferred tungsten compounds are acid phosphungs, and ammonium ta tungs tatos. Preferred molybdenum compounds are fomolybdic fos acids.

The concentration of the metal in the aqueous solution, the temperature of the solution, and the duration of contact between the solution and the never-dried fiber is not critical to provide an effective amount of the metal if it is impregnated into the fiber structure. Concentrations (measured as elemental metals) greater than about 1 weight percent or more, over saturation in aqueous solution, are preferred. The temperature at which this contact step is executed can be any within the range at which the solution is liquid - 25 ° C to 100 ° C is preferred. The duration of the contact can be from one or two seconds to an hour; - Long fibers require more time. All the above variables can be adjusted as for the final concentration in the article (measures as elemental metals) is from Q.5 - 15 percent by weight based on the final article; - at least 1.0 percent by weight is preferred.

By "never dry" it is meant that the fiber is formed from an aqueous system and coagulant in an aqueous system and the water is not removed from the fiber for at least about 100 weight percent. The never dried fibers have an opening, such as sponge, of molecular structure with typical bonds of 100 to 300 or more percent by weight based on the weight of the dried polymer. When the fibers are dried by at least about 20 weight percent water, the molecular structure collapses irreversibly and the process of this invention no longer runs immediately.

It is believed that the use of PPD-T which is both sulfonated and of inherent low viscosity results in a material that is surprisingly high in attraction to certain metals and, in combination with such metals, exhibit amazing increases in flame resistance. The tungsten and molybdenum solutions are more easily taken up in aramid structures when the structures are never dry and the aramid is of inherent low viscosity; and the metals taken in the aramid structures never dry are more effectively supported if the aramid is sulfonated and of low inherent viscosity.

The swollen and wet fibers, which contain a metal in solution, are then conducted to a drying step, as desired for the final increase in the quality of the fibers. The metal, which occurs in the aramid fibers during the drying step, remains in the fibers after the drying step in the form of oxides. No special conditions are required for drying the fibers. Any reasonable temperature can be used with care by exercising a condition to avoid damaging the fibers by excessive heat. It is preferred to dry the fibers in a vacuum on heat rollers or in an atmosphere of inert gas in motion, although not required; and air is usually used in an atmosphere.

The sulfonated, low inherent viscosity PPD-T, metal oxide-containing fibers of this invention exhibit improved flame resistance and are especially useful in fabrics for fire protective garments and the like which maintain flame resistance.

Test Methods Inherent viscosity (IV) is defined by the equation: where c is the concentration (0.5 grams of polymer in 100 ml of solvent) of a solution of the tested polymer and? Rei (relative viscosity) in the range of time between the floating time of the solution of the polymer and the floating range of the solvent, alone, as measured at 30 ° C in a capillary viscometer. The inherent viscosity values reported and specified here are based on the use of concentrated sulfuric acid (96% H2SO4) as the solvent.

Sulfur Content A sample of yarn of a small amount (about 0.5 grams) is dissolved in about 96% sulfuric acid, and then water is added to precipitate the polymer. The water is further added later, to thoroughly wash the polymer to remove any free sulfate, such as sodium sulfate, from the polymer. The resulting polymer sample is dried and carefully weighed before being placed in the flask for combustion with pure oxygen. S02 and S03 generated by combustion are absorbed in water to form sulfuric acid. The acid is titrated using barium chloride to determine the sulfur content, such as a bound sulfonic acid or sulfonate groups, in the original spinning sample. Sulfur is reported as moles of sulfur, in the form of sulfonate groups, per 100 moles of PPD-T in repeated units.

Flame Resistance Test The end of the dry spinning sample is attached to a stationary folder, spread horizontally over another stationary folder, and held taut with a weight. A flame is kept below a horizontal portion of the yarn and the time for spinning to burn through and the weight to fall is recorded. In the tests reported here, the flame temperature was around 700 ° C. Because this can mean variations in the test conditions, the tests reported here are usually conducted simultaneously in a spin of the invention and, as a control, in the same spin without the metal. Flame resistance is reported as a range of times required for the spin test and yarn control to break the same weight used; or, alternatively, the weights in the yarns can be adjusted to produce almost the same times of exposure to the flame before breaking and, in this case, the flame resistance can be reported in a range of weights in the spinning test in yarn control.

Metal content.

The metal content is determined by inductive coupling of plasma-atomic spectroscopic emissions as described in ASTM-C 1111-88.

Description of the Preferred Modalities.

The following examples are illustrative of the invention and are constructed as limiting factors.

EXAMPLE 1 In this example, the tungsten-treated fibers were made and tested to resist the flame.

Four different solutions of poly (p-phenylene terephthalamide) spin (PPD-T) were prepared in 100.1 percent sulfuric acid: 1. A solution of 19.4 weight percent of PPD-T was made using PPD-T having an inherent viscosity of 6.37 dL / g and 0.7 moles per sulfur per 100 moles of PPD-T of repeating units. 2. A 10 weight percent solution of PPD-T was made using PPD-T having an inherent viscosity of 3.40 dL / g and essentially zero moles of sulfur per 100 moles of PPD-T of repeating units. 3. A 19.4 weight percent solution of PPD-T was made using PPD-T having an inherent viscosity of 5.17 dL / g and 6.0 moles of sulfur per 100 moles of PPD-T of repeating units. 4. A 10 weight percent solution of PPD-T was made using PPD-T having an inherent viscosity of 1.97 dL / g and 6.9 moles of sulfur per 100 moles of PPD-T of repeating units.

The four PPD-T spinning solutions were spun in accordance with the procedure carried out in U.S. Pat. No. 3,767,756.

The portions of each of the PPD-T spun fibers, in the never-dried form, were contacted for 5 seconds with a phosphoric acid solution and then washed thoroughly. The phosphoric acid solution was made by the addition of 247.5 parts by weight of sodium tungstate and 23.75 parts by weight of disodium phosphate for 500 parts by weight of water; adjusting the pH to 1.1 with sulfuric acid; and heating to boil after which the solution was clarified with a pH of about 2.6. Equivalent portions of each of the spun PPD-T yarns were not contacted with the tungstic acid solution and were used here as control fibers.

Tungsten treated fibers and control fibers were dried overnight under vacuum at 80 ° C and then subjected, in triplicate, to the Flame Resistance Test by determining the times to break the weight constant and reporting the range of time to treat the fibers and time to control the fibers. The results of the Flame Resistance Test, as an average of the triplicate values, were as follows: Solution Burned Weight Resistance Content of Yarn around used (g) to the tungsten flame (% No. (sec.) By weight) 1. treated 8.5 20 < 0.1 1. control 20 2. treated 9.0 20 < 0.1 2. control 9.0 20 treated 8.4 20 < 0.1 control 8. 20 4. treated 12.0 100 7.21 4. 7.2 control 20 It is notable that only the treated fibers made from the spun solution number 4 are the fibers of this invention made in this Example. For reasons not entirely understood, the fibers made from the other spun solutions are not improved by the tungsten treatment. The PPD-T in the spinning solutions numbers 1 and 3 has an inherent viscosity above 4 dL / g apparently too high to allow adequate impregnation of the treated metal. The PPD-T in the spinning solutions numbers 1 and 2 have a sulfonation of less than 5 moles per 100 moles of PPD-T of repeating units - appear too low to dock or retain the treated metal. The PPD-T in spinning solution number 1 has both an inherent viscosity that is too high and a sulfonation that is too low.

EXAMPLE 2 The fibers made using the spun solution number 4 of Example 1 were treated, by contact for 5 seconds, with a solution of phosphomolybdic acid. The phosphomolybdic acid solution was made by adding 49.5 parts by weight of sodium molybdate and 4.75 parts by weight of disodium phosphate for 100 parts by weight of water; adjusting the pH to 2.5 with sulfuric acid; and heating to boil after which the solution was washed.

The fibers treated with molybdenum and the corresponding untreated control fibers were dried in a vacuum oven at 80 ° C and subjected, in triplicate, to the Flame Resistance test by adjusting the weights in the yarns to produce exposure times almost equal to break and report the range of the weight break for the treated fibers and the weight break for the control fibers. The results of the Flame Resistance test, as an average of the tripled values, are like s igue: Exposure Content of the Flame Weight Resistance molybdenum (% Items (sec) used (g) to the flame in weight) treated 150 6.3 control 10 15 not detected EXAMPLE 3 The spun fibers of solution number 4 were treated, by contact for 5 seconds, with a solution of vanadium, in one instance, and with palladium solution in another instance. The vanadium solution was made by, first, adding 49.5 parts by weight of sodium vanadate and 4.75 parts by weight of disodium phosphate to 100 parts by weight of water and adjusting the pH to 3 with sulfuric acid, and then combining 18 parts by weight. weight of the solution with 45 parts by weight of acetic acid and 37 parts by weight of water. The palladium solution was made by adding 1.4 parts by weight of palladium chloride and 12 parts by weight of citric acid to 100 parts by weight of water, and heating the solution to clarify.

Improvements in Flame Resistance are exhibited by fibers treated with vanadium with about 2x and with palladium with, also, around 2x.

EXAMPLE 4 In this example, aramid fibers such as the courses of solution number 4 in Example 1 are treated by contact with tungsten solutions of different concentrations in accordance with the present invention and the fibers are then tested by Flame Resistance.

The tungsten solutions are made by diluting a master solution, in amounts listed in the Table, for a total volume of 50 milliliters with water. The master solution was 49.5 grams of sodium tungstate, and 4.75 grams of sodium phosphate in 100 milliliters of water adjusted to a pH of 2.0 with sulfuric acid. The master solution was stirred for thirty minutes at 80 ° C before making the solutions.

A sample of never-dried fibers was immersed for five seconds in each tungsten solution and rinsed immediately with water and dried. The tungsten contained in the fibers was determined and the Flame Resistance was determined. In this example, the Flame Resistance was established to show the improvement in flame resistance of the fibers of this invention as compared to the same fibers that do not have tungs t eno.

To determine the Flame Resistance a test yarn and a control yarn were simultaneously subjected to the flame of the Flame Resistance Test in which the control yarn was weighed with 10 grams and, by trial and error, the The weight of the test yarn was adjusted such that both yarns were burned together about 3 seconds of each. Yarns are usually burned in about 7 to 10 seconds. This Flame Resistance is the weight range in the test yarn for the weight in the control yarn. In this test, a tungsten concentration of about 1 weight percent in the fibers results in a Flame Resistance of about 5.

TABLE Solution Tungsten Master Point Resistance Solution (%) Fiber (%) Flame A 40 5, .96 10.1 20 B 30 4, .81 8.36 22 C 20 3. .69 7.31 22 D 10 2. .55 4.80 25 E 7 1. .24 3.18 25 F 5 0. .94 3.69 20 G 3 0. .67 2.34 12 H 2 0. .41 1.75 10 I 1 0. .14 0.58 4 J 0.5 0. .07 0.31 1 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (11)

Claims

1. An article of high resistance to the flame of pol i (p-phenylene terephthalamide) polymer, characterized in that it has: (i) an inherent viscosity of 1.5 to 4 dL / g; (ii) from 5 to 20 moles of sulfur, as sulfonate groups, per 100 moles of polymer of repeat units; and (iii) at least 0.5 weight percent, based on the total weight of the article, of a metal wherein the metal is presented as oxides selected from the group consisting of tungsten oxides and molybdenum oxides, uniformly distributed around the article .

2. The article according to claim 1, characterized in that the metal is tungsten dye.

3. The article according to claim 1, characterized in that the metal is mol ibdeno.

4. The article according to claim 1, as a fiber, characterized in that the flame resistance of the article is at least five times greater than the flame resistance of a fiber made by the same substantial processes, using the same substantial materials in the absence of metal.

5. The article according to claim 1, characterized in that the metal is present in the amount of 1.0 to 15 weight percent.

6. The article according to claim 1, characterized in that it is in the form of a fiber.

7. A process for increasing the flame resistance of an article of poly (p-phenylene terephthalamide) polymer, characterized in that it comprises: (a) contacting a never-dried article of poly (p-phenylene terephthalamide) polymer having an inherent viscosity of 1.5 to 4 dL / g and 5 to 20 moles of sulfur, such as sulfonate groups, per 100 moles of repeating unit polymer, with an aqueous solution of a water-soluble metal compound selected from the group consisting of a compound of water-soluble tungsten and a water-soluble molybdenum compound in a concentration of one percent by weight for a saturation for two seconds to one hour; and (b) drying the article.

8. The process according to claim 7, characterized in that the metal is tungsten.

9. The process according to claim 7, characterized in that the metal is molybdenum.

10. The process according to claim 7, characterized in that the never dry article has from 100 to 300 percent water, based on the weight of the dried polymer.

11. The process according to claim 7, characterized in that the article is in the form of a fiber.