HIGH THROUGHPUT DIE FOR POLYAMIDE STRAND SYNTHESIS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61/818,126, filed May 1, 2013, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

[0002] In various continuous polyamide manufacturing processes, molten polyamide is formed into strands, which when hardened can be cut into pellets. To increase polyamide output, one or more parts of the polyamide manufacturing system can be modified to improve the function of rate-limiting steps of the process. However, a continuous manufacturing system has numerous parts that must operate in concert. Swapping out one part to better optimize its function can require adaptation of other parts, leading to expensive refitting, retooling, alignment and adjustment of the entire system. Hence, the benefits of attempted optimization of one part of a system can be negated by the costs of changing not only that one part but other parts of the system. SUMMARY

[0003] The number of polyamide strands can be related to the output of polyamide in that more strands may allow more polyamide pellets to be made.

However, the strands also should be wide enough to have structural integrity so that strand breakage is reduced. Hence, the diameter of a polyamide strand cannot be reduced below the diameter needed to generate stable polyamide strands. For an existing system with a fixed die capillary size selected to generate polyamide strands with satisfactory strand integrity, polyamide strand manufacture could be increased by increasing the number of capillaries in the die.

[0004] However, merely increasing the number of capillaries through which the polyamide is extruded can place the capillaries too close together, causing the resulting rather sticky polyamide strands to fuse. Strand fusion is a common problem that complicates pellet formation by automatic strand cutting devices. One could increase the size of the polyamide strand die so that more surface area is available for the added capillaries, but this would likely require retooling of the manufacturing system so that the larger die can be fitted into the system. Hence, it is generally not economical to increase the rate of polyamide manufacture in an existing manufacturing system by adding additional capillaries to a strand die.

[0005] The problem of increasing polyamide production without causing polyamide strand fusion and without retooling more than one component of a continuous polyamide manufacturing system is solved by increasing the length and width of capillaries in a polyamide strand die. This solution to the problem not only improves polyamide output but also improves polyamide strand stability.

Surprisingly, the pressure drop across the polyamide strand die is low despite the longer capillary length. Strand fusion is also reduced, which is surprising because the capillaries in the strand die are closer together.

[0006] A strand die is described herein that has a multiplicity of capillaries, each capillary having a length that is about 6.1 to about 6.5 times its diameter. The capillaries of the strand die can have an oval or a circular cross-section

approximately perpendicular to the longitudinal axis of the capillary. The diameter of about 5.5 - 6.5 mm refers to the largest dimension of the capillary cross- section approximately perpendicular to a longitudinal axis of the capillary. For example, each capillary can have a length of about 3 - 4.5 cm and a diameter of about 5.5 - 6.5 mm, where the capillary has a circular cross- section approximately

perpendicular to a longitudinal axis of the capillary. The strand die can extrude about 20-60% by weight more polyamide than a die that has capillaries with diameter 4.5 mm and length of 0.5 inches (1.27 cm). The strand die can also extrude polyamide strands with a lower strand-fusion incidence than polyamide strands extruded from a die that has capillaries of diameter 4.5 mm and length of 0.5 inches (1.27 cm). The strand die can also extrude polyamide strands that break less than polyamide strands extruded from a die that has capillaries with diameter 4.5 mm and length 0.5 inches. For example, the strand die can be configured to synthesize strands of nylon 6; nylon 7; nylon 11; nylon 12; nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; or copolymers thereof.

[0007] Also described herein is a method of increasing polyamide strand manufacture that includes: replacing a polyamide extrusion die with the strand die described herein in an extruder unit of a continuous polyamide manufacturing system, to thereby increase polyamide strand manufacture.

[0008] A method is described herein that avoids polyamide strand fusion that includes: replacing a polyamide extrusion die with the strand die described herein in an extruder unit of a continuous polyamide strand manufacturing system, to thereby avoid polyamide strand fusion;

[0009] A method is described herein that improves polyamide strand stability and that involves: replacing a polyamide extrusion die with the strand die described herein in an extruder unit of a continuous polyamide strand manufacturing system, to thereby improve polyamide strand stability.

DETAILED DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a diagram of a conventional polyamide strand forming die with smaller capillaries through which polyamide can be extruded to form polyamide strands.

[0011] FIG. 2 is a diagram illustrating a polyamide strand die of the invention with larger capillaries through which polyamide can be extruded to form polyamide strands with improved properties.

[0012] FIG. 3 is a polyamide strand formation unit that includes a polyamide strand die plate.

DETAILED DESCRIPTION

[0013] An improved system is described herein having a polyamide strand formation unit that includes a polyamide strand die plate with a plurality of capillaries (e.g., holes or bores), each capillary width and length sufficient to produce a structural intact polyamide strand when molten polyamide is forced through the capillary, and each capillary spaced away from every other capillary by a distance sufficient to avoid strand fusion. Also described is a process that involves production of polyamide strands using such a strand forming unit.

[0014] FIG. 1 is a diagram of a conventional polyamide strand forming die with capillaries, each having diameter Dl and length LI , through which polyamide can be extruded to form polyamide strands. An extruder unit extrudes molten polyamide into an extrusion chamber which includes multiple stand forming dies from which the strands are ultimately extruded. FIG. 2 is a diagram illustrating an embodiment of a polyamide strand die with capillaries each having diameter D2 and length L2. In some embodiments, D2 can equal Dl . In some embodiments, L2 can equal LI . In some embodiments, the capillaries of the polyamide strand die shown in FIG. 2 can have a larger diameter D2 than the diameter Dl of the conventional polyamide strand forming die shown in FIG. 1, and in some embodiments the length L2 can be larger than length LI . Surprisingly, the larger capillary diameters of embodiments of the polyamide strand formation unit can increase polyamide production without increased strand fusion even though the capillaries are closer together than in currently available strand formation units having similar die size. Currently available dies for polyamide strand formation have a smaller capillary size where the length of capillary is about 2.8 times its width (e.g., a diameter of 4.5 mm, and a length of about 1.27 cm). Such smaller capillary dies generate less polyamide product, and the polyamide strands tend to fuse, which complicates pellet formation.

[0015] For example, the strand die described herein can extrude about 20-60% by weight more polyamide than such currently available strand dies. The polyamide strand dies and processes described herein solve the problems of low polyamide production, polyamide strand fusion and polyamide strand breakage that are commonly observed with currently available polyamide strand formation units.

[0016] The polyamide strand formation unit can therefore have a polyamide strand die with a plurality of capillaries, the individual capillaries each have a round (circular), oval, square, or triangular cross- section approximately perpendicular to a longitudinal axis of the capillary. For example, the individual capillaries can each have a round (circular), or oval cross- section approximately perpendicular to a longitudinal axis of the capillary.

[0017] The polyamide strand die can have a shape that is interchangeable with strand dies now employed to extrude polyamide. For example, the polyamide strand die can be a circular, square or rectangle plate configured to fit into an extruder of a continuous polyamide manufacturing system.

[0018] The polyamide strand die provided herein can have a plurality of capillaries, where the capillaries have a diameter greater than 4.5 mm. In general, the length of the capillaries in the polyamide strand die can be about 6.3 times its width.

[0019] For example, the diameter of the capillaries can be greater than 4.7 mm, greater than 4.8 mm, be greater than 4.9 mm, greater than 5.0 mm, greater than 5.1 mm, greater than 5.2 mm, greater than 5.3 mm, greater than 5.4 mm, be greater than 5.5 mm, greater than 5.6 mm, greater than 5.7 mm, greater than 5.8 mm, or greater than 5.9 mm. The capillaries in the polyamide strand die can have a diameter smaller than 7.0 mm, smaller than 6.9 mm, smaller than 6.8 mm, smaller than 6.7 mm, smaller than 6.6 mm, smaller than 6.5 mm, smaller than 6.4 mm, smaller than 6.3 mm, or smaller than 6.2 mm. For example, the polyamide strand formation unit can have capillaries with a diameter of about 6.0 mm. In some embodiments, the diameter of the capillary can be substantially constant from one end of the capillary to the other. In other embodiments, the capillary can have a smaller diameter at the entrance and a larger diameter at the exit, or a larger diameter at the exit and a smaller diameter at the entrance. In capillaries having different entrance and exit diameters, the diameter in the section of the capillary between the entrance and the exit can be any suitable diameter, such as a gradual transition between the entrance and the exit diameters, or any other suitable shape that allows the die to be used as described herein.

[0020] The capillaries in the polyamide strand die can have a length that is sufficient to stabilize strands as they form. For example, the capillaries can have the length that reduces polyamide build-up at the exit of the die plate. The capillaries can, for example, have the length that modulates the pressure gradient along the length of capillary. Such modulation of pressure reduces the incidence of polyamide splatter or build-up at the capillary outlet. In general a longer capillary length can reduce the pressure differential across the length of capillaries in the polyamide strand die. The polyamide strand die can have capillaries with a length greater than 1.5 cm. For example, the length of the capillaries can be greater than 1.6 cm, greater than 1.7 cm, greater than 1.8 cm, greater than 1.9 cm, greater than 2.0 cm, greater than 2.1 cm, greater than 2.2 cm, greater than 2.3 cm, greater than 2.4 cm, greater than 2.5 cm, greater than 2.6 cm, greater than 2.7 cm, greater than 2.8 cm, greater than 2.9 cm, greater than 3.0 cm, greater than 3.1 cm, greater than 3.2 cm, greater than 3.3 cm, greater than 3.4 cm, greater than 3.5 cm, greater than 3.6 cm, or greater than 3.7 cm.

[0021] The polyamide strand die can have capillaries with a length less than 5.0 cm. For example, the length of the capillaries can be less than 4.9 cm, less than 4.8 cm, less than 4.7 cm, less than 4.6 cm, less than 4.5 cm, less than 4.4 cm, less than 4.3 cm, less than 4.2 cm, less than 4.1 cm, less than 4.0 cm, or less than 3.9 cm. For example, the polyamide strand die can have capillaries with a length of about 3.81 cm.

[0022] Fourne (SYNTHETIC FIBERS at pg. 242 (Hanser Publishers, Munich 1999)) recommends that the clearance between strands be 14.4 mm. However, the spacing between capillaries in the polyamide strand die described herein can be less than 14.4 mm or greater than 14.4 mm. For example, the strands generated using the polyamide strand die and processes described herein do not readily fuse so the spacing between capillaries in the polyamide strand die described herein can be less than 14.4 mm. Thus, the spacing between capillaries in the polyamide strand die described herein can vary from about 3 mm to 14 mm, or about 4 mm to 13 mm, or about 5 mm to 12 mm, or about 6 mm to 11 mm, or about 7 mm to 13 mm, or about 8 mm to 12 mm, or any value between about 4 mm to 13 mm.

[0023] The number of capillaries in the polyamide strand die can vary. For example, when the face of the polyamide strand die has a larger surface area, more capillaries can be present in the polyamide strand die. However, when the face of the polyamide strand die has a smaller surface area, fewer capillaries can be present in the polyamide strand die. For example, the polyamide strand die can have about 10-200 capillaries, 20-150, 50-100, 25-40, or about 30 capillaries, or about 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, or about 200 capillaries.

[0024] The polyamide strand die can be composed of a material that is substantially inert to the polyamide reactants and products. Materials employed for the polyamide strand die can transfer heat such that the molten polyamide entering the capillaries of the polyamide strand die remains sufficiently molten to pass through the capillaries but emerges with sufficient cohesiveness to form a structurally sound polyamide strand. For example, the polyamide strand die can be composed of materials such as stainless steel, such as such as austenitic steel, ferritic steel, martensitic steel, and combinations thereof in any suitable proportion. Stainless steels can include any suitable series of stainless steel, such as for example 440A, 440B, 440C, 440F, 430, 316, 409, 410, 301, 301LN, 304L, 304LN, 304, 304H, 305, 312, 321, 321H, 316L, 316, 316LN, 316ΤΪ, 316LN, 317L, 2304, 2205, 904L, 1925hMo/6MO, 254SMO. Austenitic steels can include 300 series steels, for example having a maximum of about 0.15% carbon, a minimum of about 16% chromium, and sufficient nickel or manganese to retain an austenitic structure at substantially all temperatures from the cryogenic region to the melting point of the alloy. Austenitic steel can include, for example, 304 and 316 steel, such as 316L steel. In some examples, the strand die can include corrosion-resistant materials. Examples of corrosion-resistant materials can include superalloys, such as nickel- copper alloys containing small amounts of iron and trace amounts of other elements such as Monel® 400, precipitation- strengthened nickel-iron-chromium alloys such as Incoloy® brand alloys, for example Incoloy® 800 series, or austenitic nickel- chromium-based Inconel® brand alloys, or nickel-chromium-molybdenum alloys such as Hastelloy® brand alloys, for example, Hastelloy® G-30®. Examples of corrosion-resistant materials can include any suitable corrosion-resistant material, such as super austenitic stainless steels (e.g. AL6XN, 254SMO, 904L), duplex stainless steels (e.g. 2205), super duplex stainless steels (e.g. 2507), nickel-based alloys (e.g. alloy C276, C22, C2000, 600, 625, 800, 825), titanium alloys (e.g. grade 1, 2, 3), zirconium alloys (e.g. 702), Hasteloy 276, duplex 2205, super duplex 2507, Ebrite 26-1, Ebrite 16-1, Hasteloy 276, Duplex 2205, 316 SS, 316L and 304SS, zirconium, zirconium clad 316, Ferralium 255, or any combination thereof.

[0025] In some embodiments, the surfaces of the die can be cleaned or polished. The capillaries or the die can have any suitable roughness average. The term "roughness average" (R _a ) is the measured average from the surface peaks and valleys of those irregularities and expressed in micrometers (μιη) and in micro- inches (μίη). Surface texture measurement is known to those of ordinary skill in the art and employs a surface profile instrument. A known surface profiler instrument is available from TAYLOR-HOBSON, a company of AMETEK, INC., 1100 Cassatt Road, RO. Box 1764, Berwyn, Pennsylvania, 19312 USA. In some examples, the capillaries or the die can have an average surface roughness of no greater than about 6.00 μιη, of between about 1.00 μιη and about 6.00 μιη, of between about 0.90 μιη and about 1.50 μιη, of between about 0.60 μιη and about 1.00 μιη, of no greater than about 0.5 μιη, of no greater than about 0.10 μιη, of between about 0.10 μιη and about 0.80 μιη, or of between about 0.90 μιη and about 1.50 μιη.

[0026] The flow rate of material passing from the extruder and through the die is generally uniform and constant. Flow uniformity depends both on the characteristics of the polymer (that is, its viscoelastic properties) and on the level of shear stress imposed on the polymer during transport through the polyamide strand die. A precision gear pump can be used to provide steady pressure and accurate metering so the polyamide reaches the die head in a controlled and surge-free manner. Such a gear pump can be installed between an extruder device (e.g., a screw extruder) and the polyamide strand die, or upstream of the extruder. The gear pump can be a primary extruder control device, to reduce inefficiencies that may be inherent in conventional extrusion systems. Discharge pressure variation, and thus mass-flow variations, can be held to less than 3% or less than 1%, to facilitate uniform strand production and avoid shrinkage, imperfections, and gel formation.

[0027] The heating chamber heats the polyamide to an appropriate temperature for extrusion through the polyamide strand die. In general, if the extrusion temperature is not high enough, the melted polymer will not be sufficiently homogeneous, and some solid or crystalline polyamide may be present. Conversely, if the extrusion temperature is too high, the risk of degradation increases, and it may be difficult to extrude the polyamide because it can have a low viscosity at higher temperatures. In general, the heating chamber temperature can be about 185-350 °C to maintain the polyamide at a temperature of about 180-300 °C when it passes through the polyamide strand die. The temperature at which the polyamide is maintained can vary with the type of polyamide to be made into strands. For example, nylon 6 can be maintained at a temperature of about 225 - 260 °C when passing through the polyamide strand die, while the nylon 6,6 can be maintained at a temperature of about 270 - 295 °C when passing through the polyamide strand die. In one example, nylon 11 can be maintained at a temperature of about 190 - 220 °C when passing through the polyamide strand die, while the nylon 12 can be maintained at a temperature of about 185 - 215 °C when passing through the polyamide strand die.

[0028] After emergence from the polyamide strand die, the polyamide strands can be chilled to a temperature of about 10-100 °C. For example, the strands emerging from the polyamide strand die can be sprayed or immersed in water to quickly cool and harden them. The hardened strands can be cut or otherwise processed into easily packaged lengths or sizes. In general, the polyamide is dried before packaging to reduce the water content to 1% or less, or 0.7% or less, or 0.5% or less, or 0.2% or less, or 0.1% or less.

[0029] The polyamide strand die and methods of using such a die unexpectedly increase polyamide production while also reducing strand fusion even though the capillaries are closer together than in currently available strand formation units. Gel formation is reduced. Gel can be any solid material formed from the polymeric material that accumulates or clogs equipment or that contaminates the polyamide product, such as a disordered solid formed from oxidative or thermal degradation of polymer. Gel can form in stagnant pockets as well as irregularities or eddies in the flow of polymer through the system. The polyamide strand die facilitates flow of the polyamide and thereby reduces gel formation. Example polyamide strand forming unit

[0030] FIG. 3 shows an example embodiment of a polyamide strand forming unit. Molten polyamide 10 from a continuous polyamide manufacturing system is transported by at least one transfer line 20 to an inlet 30 of the polyamide strand forming unit. The inlet 30 can include an extruder or a gear pump (e.g., a precision gear pump) to facilitate transport of the polyamide into the extrusion chamber 45 and through the polyamide strand die 60. In some embodiments, the gear pump can occur upstream of line 20. The gear pump can help to buffer surging in flow, such as caused by an extruder. A heating chamber 40 can be used to maintain the temperature of the extrusion chamber 45 at an appropriate temperature so that the polyamide to be extruded 50 remains molten but also has an appropriate viscosity for strand formation upon passage through the polyamide strand die 60. Polyamide strands 70 are formed by passage of the polyamide through the polyamide strand die 60.

Polyamide manufacture

[0031] The term "polyamide" means a polymer containing a plurality of amide linkages. Polyamides, for example, aliphatic linear polyamides having at least 85 per cent aliphatic linkages between repeating amide units are also known as nylon. The term "linear" means that the polyamides are obtainable from bifunctional reactants where the structural units are linked end-to-end and in chain-like fashion. As such, this term is intended to exclude three-dimensional polymeric structures that might be present in polymers derived from triamines or from tribasic acids. See, Wallace H. Carothers, United States Patent Number 2,130,948, entitled "Synthetic Fiber."

[0032] The aliphatic polyamides can be obtained from dibasic carboxylic acids and other amide-forming derivatives of dibasic carboxylic acids (such as

anhydrides, amides, acid halides, half esters, and diesters) when reacted with a primary or secondary amine. The formation of substantially all aliphatic polyamides polymers, from monomers consisting of dicarboxylic acids and diamines, can be accomplished by reaction of a primary or secondary diamine (diamines having at least one hydrogen attached to each nitrogen) and either a dicarboxylic acid or an amide-forming derivative of a dibasic carboxylic acid.

HOOC-R-COOH + H ₂ N-R'-NH ₂ → -[NH-R'-NH-CO-R-CO] _m - + nH ₂ 0 where R and R' represent divalent hydrocarbon radicals.

[0033] The product generated is composed of long chains built up from a series of identical units consisting of:

-NH-R'-NH-CO-R-CO- where water is the only co-product of polymer formation.

[0034] A naming convention for diamine and diacid polyamides provides that the "structural unit" of the polymer derived from one molecule each of diacid and diamine is named for the number of carbon atoms in the respective radicals, R and R'. The polyamide from hexamethylene-l,6-diamine and adipic acid is called "nylon 6,6" (polyhexamethylene adipamide).

[0035] Commercial processes for preparing polyamides can include continuously passing an aqueous solution of a diamine-dibasic carboxylic acid salt at super- atmospheric pressure through a continuous reaction zone. See, e.g., U.S. Patent No 2,361,717 to Taylor; U.S. Patent No. 2,689, 839 to Heckert.

[0036] Polyamides can be prepared by heating substantially equimolecular amounts of diamine and dicarboxylic acid or an amide forming derivative of a dibasic carboxylic acid under condensation polymerization conditions. Such condensation polymerization conditions generally include temperatures of about 180°C to 300° C.

[0037] For example, in a nylon 6,6 process, the continuous polymerization reactor can be fed an aqueous solution of hexamethylene diammonium adipate (nylon 6,6 salt) having a concentration in a range of between 35 and 65% by weight. The concentration of hexamethylene diammonium adipate is adjustable in an optional evaporator upstream of the reactor. The effluent from the flasher stage (which is also referred to as the secondary reactor) includes polyamide pre-polymer, typically with a relative viscosity of about 9-20. This stream is fed into a finishing apparatus. Control variables in the finishing apparatus can include temperature, pressure and hold-up volume. These control variables are adjustable such that a final polymer of the desired relative viscosity, typically in the range of 30 to 100, is obtained. Temperature in the finishing apparatus is maintained in the range of 270° to 290° C. Pressure is maintained at 25 KPa to 64 KPa. Hold-up volumes are approximately 20 to 40 minutes.

[0038] The product has fiber-forming properties when a sufficiently high molecular weight is achieved. For example, such fiber-forming occurs when polyamides have an intrinsic viscosity range of about 0.5 and 2.0; as measured in m- cresol solution.

[0039] Polymerization is complete when the desired degree of polymerization is achieved. The degree of polymerization is indirectly expressed in terms of polymer viscosity. The degree of polymerization, often measured as relative viscosity or RV, is a proxy measurement for viscosity and molecular weight in turn.

[0040] At elevated temperatures, the degree of polymerization is a function of and is limited by the amount of water present. A dynamic equilibrium exists between polymer and water on the one hand, and depolymerized polymer (or even the reactants) on the other. Polyamides having an RV considerably higher than that attainable through equilibration with steam at atmospheric pressure are often desirable.

[0041] The properties of a given polyamide can vary, especially with the molecular weight of the polyamide. The polyamide properties are also influenced by the nature of its terminal groups, which in turn is dependent upon which reactant is used in excess, the diamine or the diacid.

[0042] The average molecular weight of a polyamides can be difficult to determine, but precise knowledge of average molecular weights is generally not important for most purposes. In general, two stages or degrees of polymerization exist: low polymers whose molecular weights probably lie in the neighborhood of 1000 to 4000, and fiber forming polyamides whose molecular weights probably lie above at least 7000. A distinction between low polymers and the high polymers or "superpolymers" is that the former when molten are relatively less viscous. The high polymers are quite viscous, even at temperatures 25° C above their melting points. [0043] In contrast to low polymers, the high polymers of polyamides are readily spun into strong, continuous, pliable, permanently oriented fibers. However, the low polymers, for example those having a smaller unit length than about 9, can be converted into high polymers by continuing the polymerization reaction.

[0044] Fiber-forming polyamides generally have high melting points and low solubility. Those derived from the simpler types of amines and acids are generally opaque solids that melt or become transparent at a fairly definite temperatures. Below their melting points the fiber-forming polyamides generally exhibit sharp X- ray crystalline powder diffraction patterns, which is evidence of their crystalline structure. The densities of these polyamides generally lie between 1.0 and 1.2. The density of nylon 6,6 is usually identified as 1.14 grams per cubic centimeter.

[0045] Polyamides can have individual units of similar structure. The average size of these individual units, the average molecular weight of the polymer, is subject to deliberate control within certain limits. The further the polymerization reaction has progressed the higher the average molecular weight (and intrinsic viscosity) will be. If the reactants are used in exactly equimolecular amounts during polymerization, and heating is continued for a long time under conditions that permit the escape of the volatile products, polyamides of very high molecular weight are obtained. However, if either reactant is used in excess, the

polymerization can proceed to a certain point and then essentially stop. A point at which polymerization ceases is dependent upon the amount of diamine or dibasic acid (or derivative) used in excess.

[0046] A convenient method of preparing polyamides can include making a salt by mixing approximately chemically equivalent amounts of the diamine and the dicarboxylic acid in a liquid. The liquid can be a poor solvent for the resultant salt. The salt that separates from the liquid can then be purified, if desired, by crystallization from a suitable solvent. These diamine-dicarboxylic acid salts are crystalline and have definite melting points. They are soluble in water and can be crystallized from certain alcohols and alcohol- water mixtures.

[0047] The preparation of fiber-forming polyamides from the diamine- dicarboxylic acid salts can be carried out in a number of ways. The salt can be heated in the absence of a solvent or diluent to a reaction temperature (180° - 300° C) under conditions that permit the removal of the water formed in the reaction.

[0048] The polyamide polymerization reaction can be subjected to reduced pressure, for example, an absolute pressure equivalent to 50 to 300 mm of mercury (67 to 400 millibar) to facilitate substantially complete polymerization. For example, the reaction vessel in which the polyamide is prepared can be evacuated before allowing the polymer to solidify.

[0049] In general, no added catalysts are required in the above described processes of polyamide formation. However, certain phosphorus containing materials can exert a certain degree of catalytic function. The phosphorus containing materials can include metal phosphonates. The use of added catalysts can facilitate production of high molecular weight materials.

Test Methods

[0050] Thermal degradation index (TDI) is a measurement that correlates with a polymer's thermal history. A lower TDI indicates less severe temperature history during manufacture. A TDI determination method available to the skilled person measures the optical absorbance of a 1% (by weight) solution of the polymer in 90% formic acid at a wavelength of 292 nm.

[0051] Oxidative degradation index (ODI) is a measurement that correlates with a polymer's exposure to oxidizing conditions during its high temperature manufacture. A lower ODI indicates less severe oxidative degradation during manufacture. It is determined by measuring the optical absorbance of a 1% (by weight) solution of the polymer in 90% formic acid at a wavelength of 260 nm.

[0052] Relative viscosity (RV) refers to the ratio of solution and solvent viscosities measured in a capillary viscometer at 25°C. RV by ASTM D789-06 is the basis for this test procedure and is the ratio of viscosity (in centipoises) at 25°C. of 8.4% by weight solution of polyamide in 90% formic acid (90% by weight formic acid and 10% by weight water) to the viscosity (in centipoises) at 25°C of 90% formic acid alone. Definitions

[0053] The term "about" as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0054] The term "substantially" as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

[0055] The term "solvent" as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Nonlimiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

[0056] The term "air" as used herein refers to a mixture of gases with a composition approximately identical to the native composition of gases taken from the atmosphere, generally at ground level. In some examples, air is taken from the ambient surroundings. Air has a composition that includes approximately 78% nitrogen, 21% oxygen, 1% argon, and 0.04% carbon dioxide, as well as small amounts of other gases.

[0057] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1% to about 5%" or "about 0.1% to 5%" should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y," unless indicated otherwise. Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z," unless indicated otherwise.

[0058] In this document, the terms "a," "an," or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section.

[0059] The strand forming unit and a process of making polyamides using such a unit are illustrated by the following Examples, which are not intended to be limiting of the invention.

Example la: Process using a Capillary Extrusion Die Having Capillaries with a Length about 2.8 Times the Diameter and Having a Diameter of 4.5 mm

[0060] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 4.5 mm, and a land length (i.e., the length of the capillary) of 0.5 inches (1.27 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 12 M/min. The emerging fibers have a 4.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm-long pellets.

[0061] Strand fusion is significant, with approximately 0.000,1 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking

approximately every 10 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 6 months.

Example lb: Process using a Capillary Extrusion Die Having Capillaries with a Length about 2.8 Times the Diameter and Having a Diameter of 6 mm

[0062] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 0.66 inches (1.68 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0063] Strand fusion is significant, with approximately 0.000,09 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 15 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 8 months.

Example 2a: Process using a Capillary Extrusion Die Having Capillaries with a Length about 5.6 Times the Diameter and Having a Diameter of 4.5 mm

[0064] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min through an extruder from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 4.5 mm, and a land length of 0.992 inches (2.52 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 12 M/min. The emerging fibers have a 4.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm-long pellets.

[0065] Strand fusion is significant, with approximately 0.000,08 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 30 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months.

Example 2b: Process using a Capillary Extrusion Die Having Capillaries with a Length about 5.6 Times the Diameter and Having a Diameter of 6 mm

[0066] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 1.32 inches (3.36 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0067] Strand fusion is significant, with approximately 0.000,07 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 50 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 11 months.

Example 2c: Process using a Capillary Extrusion Die Having Capillaries with a Length about 5.6 Times the Diameter and Having a Diameter of 7 mm

[0068] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 7 mm, and a land length of 1.54 inches (3.92 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 5 M/min. The emerging fibers have a 7 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0069] Strand fusion is significant, with approximately 0.000,08 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 30 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months.

Example 3a: Process using a Capillary Extrusion Die Having Capillaries with a Length about 7 Times the Diameter and Having a Diameter of 4.5 mm

[0070] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 4.5 mm, and a land length of 1.24 inches (3.15 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 12 M/min. The emerging fibers have a 4.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0071] Strand fusion is significant, with approximately 0.000,08 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 30 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months. Example 3b: Process using a Capillary Extrusion Die Having Capillaries with a Length about 7 Times the Diameter and Having a Diameter of 6 mm

[0072] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 1.65 inches (4.2 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0073] Strand fusion is significant, with approximately 0.000,07 wt% of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 50 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 11 months. Example 3c: Process using a Capillary Extrusion Die Having Capillaries with a Length about 7 Times the Diameter and Having a Diameter of 7 mm

[0074] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 7 mm, and a land length of 1.92 inches (4.9 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 5 M/min. The emerging fibers have a 7 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0075] Strand fusion is significant, with approximately 0.000,08 wt of the pellets being fused. Significant strand breakage occurs, with 1 strand breaking approximately every 30 minutes. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months.

Example 4: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.35 Times the Diameter and Having a Diameter of 6 mm

[0076] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 1.5 inches (3.81 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0077] Strand fusion is improved over Examples 1-3, with approximately 0.000,02 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 1 day. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 18 months.

Example 5a: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.35 times the Diameter and Having a Diameter of 5.5 mm

[0078] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 5.5 mm, and a land length of 1.38 inches (3.49 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 8.2 M/min. The emerging fibers have a 5.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm-long pellets.

[0079] Strand fusion is improved over Examples 1-3, with approximately 0.000,03 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 20 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 15 months.

Example 5b: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.35 times the Diameter and Having a Diameter of 6.5 mm

[0080] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6.5 mm, and a land length of 1.63 inches (4.13 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 5.8 M/min. The emerging fibers have a 6.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm-long pellets.

[0081] Strand fusion is improved over Examples 1-3, with approximately 0.000,03 wt of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 20 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 15 months.

Example 6a: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.1 times the Diameter and Having a Diameter of 6 mm

[0082] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 1.5 inches (3.81 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0083] Strand fusion is improved over Examples 1-3, with approximately 0.000,03 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 20 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 15 months.

Example 6b: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.1 times the Diameter and Having a Diameter of 4.5 mm

[0084] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 4.5 mm, and a land length of 1.1 inches (2.75 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 12 M/min. The emerging fibers have a 4.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0085] Strand fusion is improved over Examples 1-3, with approximately 0.000,05 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 10 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months. Example 6c: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.1 times the Diameter and Having a Diameter of 7 mm

[0086] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 7 mm, and a land length of 1.68 inches (4.27 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 5 M/min. The emerging fibers have a 7 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0087] Strand fusion is improved over Examples 1-3, with approximately 0.000,05 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 10 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months.

Example 7a: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.5 times the Diameter and Having a Diameter of 6 mm

[0088] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 6 mm, and a land length of 1.5 inches (3.81 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 6.8 M/min. The emerging fibers have a 6 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0089] Strand fusion is improved over Examples 1-3, with approximately 0.000,03 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 20 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 15 months.

Example 7b: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.5 times the Diameter and Having a Diameter of 4.5 mm

[0090] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 4.5 mm, and a land length of 1.15 inches (2.93 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 12 M/min. The emerging fibers have a 4.5 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0091] Strand fusion is improved over Examples 1-3, with approximately 0.000,05 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 10 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months.

Example 7c: Process using a Capillary Extrusion Die Having Capillaries with a Length about 6.5 times the Diameter and Having a Diameter of 7 mm

[0092] Nylon 6,6 polymer is prepared and discharged as a molten material at a rate of about 58 L/min from an extruder, which includes an screw-type extruder that discharges material into extrusion chamber that includes multiple capillary extrusion dies through which nylon strands are extruded. The extruder has 10 dies, each having 30 capillaries. Each capillary has a diameter of 7 mm, and a land length of 1.79 inches (4.55 cm). The die has a diameter of about 10 cm. The fibers emerge from each capillary at a rate of about 5 M/min. The emerging fibers have a 7 mm diameter, a temperature of 270 °C, and have a total weight percent water of about 0.1%, which is primarily internal water. Strands are extruded at an angle from the horizontal plane of about 45° and water is sprayed onto the strands as they emerge from the die. The strands travel to a pelletizer which chops the strands into 2.5 mm- long pellets.

[0093] Strand fusion is improved over Examples 1-3, with approximately 0.000,05 wt% of the pellets being fused. Strand breakage is improved over

Examples 1-3, with 1 strand breaking approximately every 10 hours. Each die is taken out of service for cleaning after about 5 g of gel or polymer accumulates thereon, about every 10 months. [0094] All patents and publications referenced or mentioned herein are indicative of the levels of skill of those skilled in the art to which the present subject matter pertains, and each such referenced patent or publication is hereby specifically incorporated by reference to the same extent as if it had been incorporated by reference in its entirety individually or set forth herein in its entirety. Applicants reserve the right to physically incorporate into this specification any and all materials and information from any such cited patents or publications.

[0095] The specific methods, devices and compositions described herein are representative of preferred embodiments and are examples and not intended as limitations on the scope of the present subject matter. Other objects, aspects, and embodiments will occur to those skilled in the art upon consideration of this specification, and are encompassed by the present subject matter. It will be readily apparent to one skilled in the art that varying substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

[0096] The present subject matter illustratively described herein suitably may be practiced in the absence of any element or elements, or limitation or limitations, which is not specifically disclosed herein as essential. The methods and processes illustratively described herein suitably may be practiced in differing orders of steps, and the methods and processes are not necessarily restricted to the orders of steps indicated herein or in the claims.

[0097] Under no circumstances may the patent be interpreted to be limited to the specific examples or embodiments or methods specifically disclosed herein. Under no circumstances may the patent be interpreted to be limited by any statement made by any Examiner or any other official or employee of the Patent and Trademark Office unless such statement is specifically and without qualification or reservation expressly adopted in a responsive writing by Applicants.

[0098] The terms and expressions that have been employed are used as terms of description and not of limitation, and there is no intent in the use of such terms and expressions to exclude any equivalent of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention as claimed. Thus, it will be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims and statements of the invention.

[0099] The invention has been described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the invention. This includes the generic description of the invention with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. In addition, where features or aspects of the invention are described in terms of Markush groups, those skilled in the art will recognize that the invention is also thereby described in terms of any individual member or subgroup of members of the Markush group.

Statements:

[00100] The following statements summarize aspects of the inventive subject matter.

[00101] 1. A polyamide strand die comprising a multiplicity of capillaries, each capillary independently having a capillary length that is about 6.1 to about 6.5 times its capillary diameter.

[00102] 2. The strand die of statement 1, wherein the diameter refers to the largest dimension of a cross-section perpendicular to a longitudinal axis of the capillary.

[00103] 3. The strand die of statement 1 or 2, wherein each capillary has an oval or circular cross- section perpendicular to a longitudinal axis of the capillary.

[00104] 4. The strand die of any of statements 1-3, where each capillary has a length of about 3 - 4.5 cm and a diameter of about 5.5 - 6.5 mm. [00105] 5. The strand die of any of statements 1-4, wherein each capillary length is about 3.7 to about 3.9 cm.

[00106] 6. The strand die of any of statements 1-5, wherein each capillary has a diameter of about 5.75 - 6.25 mm.

[00107] 7. The strand die of any of statements 1-6, wherein each capillary has a diameter is about 6 mm.

[00108] 8. The strand die of any of statements 1-7, comprising about 10-200 capillaries.

[00109] 9. The strand die of any of statements 1-8, comprising about 25-40 capillaries.

[00110] 10. The strand die of any of statements 1-9, wherein the die extrudes about 20-60% more polyamide by weight than a die that has capillaries with diameter 4.5 mm and length of 1.27 cm.

[00111] 11. The strand die of any of statements 1-10, wherein the die extrudes polyamide strands with a lower strand- fusion incidence than polyamide strands extruded from a die that has capillaries of diameter 4.5 mm, and capillary length of 1.27 cm.

[00112] 12. The strand die of any of statements 1-11, wherein the die extrudes polyamide strands that break less than polyamide strands extruded from a die that has capillaries with diameter 4.5 mm, and capillary length 1.27 cm.

[00113] 13. The strand die of any of statements 1-12, configured to synthesize strands of nylon 6, nylon 11; nylon 12; nylon 6,6; nylon 6,9; nylon 6,10; nylon 6,12; or copolymers thereof.

[00114] 14. The strand die of any of statements 1-13, integrated into a continuous polyamide manufacturing system.

[00115] 15. An extruder comprising the strand die of any of statements 1-13.

[00116] 16. A polyamide manufacturing system comprising the strand die of any of statements 1-14.

[00117] 17. The system of statement 16, wherein the system is integrated into a continuous polyamide manufacturing system. [00118] 18. A method of increasing polyamide strand manufacture comprising: replacing a polyamide extrusion die with the strand die of any of statements 1-14 in an extruder unit of a continuous polyamide manufacturing system, to thereby increase polyamide strand manufacture.

[00119] 19. A method of avoiding or reducing polyamide strand fusion comprising: replacing a polyamide extrusion die with the strand die of any of statements 1-14 in an extruder unit of a continuous polyamide strand manufacturing system, to thereby avoid polyamide strand fusion;

[00120] 20. A method of improving polyamide strand stability comprising: replacing a polyamide extrusion die with the strand die of any of statements 1-14 in an extruder unit of a continuous polyamide strand manufacturing system, to thereby improve polyamide strand stability.

[00121] 21. The method of any of statements 18-20, wherein the polyamide extrusion die and the strand die have an identical number of capillaries.

[00122] 22. The method of any of statements 18-21, wherein the polyamide extrusion die capillary length is shorter than the strand die capillary length.

[00123] 23. The method of any of statements 18-22, wherein the strand die has larger diameter capillaries than the polyamide extrusion die.

[00124] 24. The method of any of statements 18-23 wherein the polyamide extrusion die and the strand die are equivalent in size.

[00125] 25. The method of any of statements 18-24, wherein the polyamide extrusion die can be replaced by the strand die in an extruder unit of the system.

[00126] 26. The method of any of statements 18-25, wherein fewer polyamide strands extruded from the strand die fuse than do polyamide strands extruded from the polyamide extrusion die.

[00127] 27. The method of any of statements 18-26, wherein the strand die capillaries are about 2-4 times longer than the capillaries of the polyamide extrusion die.

[00128] 28. The method of any of statements 18-27, wherein the strand die capillaries are about 3 times longer than the capillaries of the polyamide extrusion die. [00129] 29. The method of any of statements 18-28, wherein the strand die has capillaries with diameters that are about 1.25 - 1.5 larger than the capillaries of the polyamide extrusion die.

[00130] 30. The method of any of statements 18-29, wherein the strand die has capillaries with diameters that are about 1.33 larger than the capillaries of the polyamide extrusion die.

[00131] 31. The method of any of statements 18-30, wherein the polyamide extrusion die and the strand die each have 10-200 capillaries.

[00132] 32. The method of any of statements 18-31, the polyamide extrusion die and the strand die each have 25-40 capillaries.

[00133] 33. The method of any of statements 18-32, wherein the strand die extrudes about 20-60% more polyamide by weight than the polyamide extrusion die.

[00134] 34. The method of any of statements 18-33, wherein the strand die extrudes about 30-50% more polyamide by weight than the polyamide extrusion die.

[00135] 35. The method of any of statements 18-34, wherein capillaries in the strand die and in the polyamide extrusion die have a circular cross-section perpendicular to a longitudinal axis of the capillary.

[00136] The following claims summarize features of the systems and methods described herein.