TECHNICAL FIELD

The present disclosure relates to methods and apparatuses for manufacturing of polyamide pellets using vacuum pre-casting and a method of casting polyamide pellets.

BACKGROUND A particular class aliphatic polyamides having at least 85 percent aliphatic linkages between repeating amide units describes nylon polyamides. These aliphatic polyamides are known to be derivable from dibasic carboxylic acids and other amide-forming derivatives of dibasic carboxylic acids, such as anhydrides, amides, acid halides, half esters, and diesters, and are typically reacted with a primary or secondary amine. More specifically, the formation of aliphatic polyamide polymers from monomers such as dicarboxylic acids and diamines, is known to 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. An example reaction scheme is shown below:

HOOC-R-COOH + H ₂ N-R'-NH ₂ →

-[NH-R'-NH-CO-R-CO]- _n - + nH ₂ 0 where R and R' represent divalent hydrocarbon radicals, and n represents the number of repeating units and the number of molecules of water.

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'. Thus, a polyamide from hexamethylene-1 ,6-diamine and adipic acid is "nylon 6,6" (polyhexamethylene adipamide).

The fiber-forming 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, generally 180 °C to 300 °C. This product exhibits fiber-forming properties wherein sufficiently high molecular weight can be achieved.

The properties of a given polyamide can vary over a considerable range and can depend upon molecular weight. In part, the polyamide properties are influenced by the nature of its terminal groups, which in turn is dependent upon which reactant is used in excess, diamine or diacid.

Two characteristics of fiber-forming polyamides relate to their high melting points and low solubility. Those derived from the simpler types of amines and acids are almost invariably opaque solids melting or become transparent at a fairly definite temperature. Below their melting points the fiber-forming

polyamides when examined by X-ray generally furnish sharp X-ray crystalline powder diffraction patterns, clear evidence of their crystalline structure in the massive state. Densities of these polyamides generally lie between 1 .0 and 1 .2, and more particularly, the density of nylon 6,6 is recognized today as 1 .14 grams per cubic centimeter.

In common with other condensation polymerization products, polyamides generally include individual units of closely similar structures. 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, polymerization and heating is continued for a long time under conditions which permit the escape of the volatile products, and polyamides of very high molecular weight can be obtained. However, if either reactant is used in excess, the polymerization proceeds to a certain point and then essentially stops. The point in time at which polymerization ceases can be dependent upon the amount of diamine or dibasic acid (or derivative) that is used in excess. A convenient method of preparing polyamides includes making a salt by mixing approximately chemical equivalent amounts of the diamine and the dicarboxylic acid in a liquid, which may be by choice a poor solvent for the resultant salt. The salt which 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 may conveniently be crystallized from certain alcohols and alcohol- water mixtures.

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

It may become desirable to subject a polyamide to reduced pressure, e. g., an absolute pressure equivalent to 50 to 300 mm of mercury (67 to 400 millibar), before using it in making filaments and other shaped-objects. This is conveniently done by evacuating the reaction vessel in which the polyamide is prepared before allowing the polymer to solidify.

In general, no added catalysts are necessarily required in the above described processes of polyamide formation. However, certain phosphorus containing materials, e.g. metal phosphonates, and phosphates, are known to exert a certain degree of catalytic function. The use of added catalysts sometimes confers additional advantages for making high molecular weight materials.

The commercial preparation of most linear condensation polymers, polyamides, typically involves heating monomeric starting materials to cause progressive condensation of the polymers. This process is usually carried out in several stages, with the intermediate formation of low-molecular weight, low viscosity polymeric liquid by the removal of volatiles. The low-molecular weight, low-viscosity polymeric liquid is processed at various vacuum and residence times and temperatures to allow the polymer to reach the desired final molecular weight and viscosity.

While a desired final molecular weight and viscosity can be achieved generally, reducing reaction times and obtaining consistent uniformity of the polymeric material during casting can be problematic. Thus, it would be an advancement in the art to discover and utilize various techniques for

manufacturing polymeric materials more efficiently and having improved uniformity.

SUMMARY

The present disclosure relates to methods and devices for producing polyamide pellets using a cyclic process. In one embodiment, a method of casting a polyamide polymer can comprise steps of maintaining a vacuum during a pre-casting polymerization cycle, extruding the reactive polyamide polymer during a casting cycle, and cutting the extruded polymer. More specifically, the method can include maintaining a vacuum during a pre-casting polymerization cycle of the cyclic process such that the pre-casting polymerization cycle produces a reactive polyamide polymer with decreased pre-casting

polymerization cycle time. The method also includes extruding the reactive polyamide polymer during a casting cycle by adjusting process parameters including vessel pressure and extrusion valve opening to generate a throughput of extruded polymer. Cutting the extruded polymer at a cutting speed

substantially proportional to the throughput to provide polyamide pellets can be carried out to generate uniformity.

In another example, an apparatus for manufacturing polyamide pellets can comprise and autoclave vessel, a cutter, and a process controller. The autoclave vessel can include an extrusion valve and a pressure controller (e.g., inlet valve, vent valve, heating component, or any other device other than the extrusion valve that can be used to modulate pressure within the autoclave). The cutter can be adapted to cut polyamide polymer extruded from the autoclave vessel to form polyamide pellets. The process controller can include a pressure control module for controlling the pressure controller, a cutting speed module for controlling cutter speed, and an extrusion valve module for controlling the extrusion valve. The apparatus can be configured to maintain a vacuum during a pre-casting polymerization cycle of the cyclic process such that the pre-casting polymerization cycle produces a reactive polyamide polymer with decreased pre- casting polymerization cycle time.

In one embodiment of the disclosed process, the problem of a prolonged pre-casting polymerization cycle is addressed by operating the pre-casting cycle under at least partial vacuum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A is a schematic cross-sectional view of an autoclave vessel that is usable in accordance with examples of the present disclosure;

FIG. 1 B is a schematic cross-sectional view of another autoclave vessel that is usable in accordance with examples of the present disclosure;

FIG. 2 is a diagram of a system in which the apparatus of the present disclosure is usable in accordance with examples of the present disclosure;

FIG. 3 is an exemplary graph depicting a pressure profile of a five cycle autoclave process in accordance with examples of the present disclosure; and

FIG. 4 is a sample casting plot of a polyamide in accordance with one embodiment of the present disclosure.

It should be noted that the figures are merely exemplary of embodiments of the present invention and no limitations on the scope of the present disclosure are intended thereby.

DETAILED DESCRIPTION Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the herein disclosed embodiments.

Accordingly, the following embodiments are set forth without any loss of generality to, and without imposing limitations upon any claimed invention. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as this may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a polyamide" includes a plurality of polyamides.

In this disclosure, "comprises," "comprising," "containing" and "having" and the like can have the meaning ascribed to them in U.S. Patent law and can mean "includes," "including," and the like, and are generally interpreted to be open ended terms. The term "consisting of" is a closed term, and includes only the devices, methods, compositions, components, structures, steps, or the like specifically listed, and that which is in accordance with U.S. Patent law.

"Consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure, refers to elements like those disclosed herein, but which may contain additional structural groups, composition components, method steps, etc. Such additional devices, methods, compositions, components, structures, steps, or the like, etc., however, do not materially affect the basic and novel characteristic(s) of the devices, compositions, methods, etc., compared to those of the corresponding devices, compositions, methods, etc., disclosed herein. In further detail, "consisting essentially of or "consists essentially" or the like, when applied to devices, methods, compositions, components, structures, steps, or the like encompassed by the present disclosure have the meaning ascribed in U.S. Patent law and the term is open- ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments. When using an open ended term, like "comprising" or "including," it is understood that direct support should be afforded also to "consisting essentially of language as well as "consisting of language as if stated explicitly. The term "polymerizable composition" or "polymerizable solution" refers to the solution that is added to the agitated autoclave in accordance with examples of the present disclosure, that upon processing within the autoclave under certain heat and pressure profiles, a polyamide polymer is formed that can be extruded or otherwise harvested for further use.

The term "polyamide salt" refers to the salt that is included in the polymerizable composition (along with other additives) that provides the basic polymerizable material for forming the polyamide polymer. If the polyamide polymer is nylon 6,6, for example, then the salt can be prepared from adipic acid and hexamethylenediamine. Other additives can also be present in the polyamide solution, either introduced prior the reactor vessel, or introduced in the reactor vessel. Titanium dioxide, for example, is typically introduced directly into the vessel, whereas other additives, such as catalysts, optical brighteners, anti- foaming additives, etc. are introduced prior to introducing the polymerizable composition into the vessel, though this sequence or even the presence of these additives is not required.

The term "cycle" refers to the stages of a batch polymerization process as defined primarily by the pressure profile within the vessel. A first cycle (Cycle 1 ) occurs at the beginning of the batch process while the pressure is being increased from an ambient low press to a relative high pressure. A second cycle (Cycle 2) occurs as the relative high pressure is maintained for a period of time. A third cycle (Cycle 3) occurs as the relative high pressure is reduced back to a relative low pressure. A fourth cycle (Cycle 4) occurs as the relative low pressure is maintained for a period of time, which in this example, occurs under a vacuum. A fifth cycle (Cycle 5) occurs as the prepared polymer is being extruded from the vessel. The present disclosure uses the terms "fourth cycle", "Cycle 4" and "pre- casting cycle" interchangeably.

Phrases such as "suitable to provide," "sufficient to cause," or "sufficient to yield," or the like, in the context of methods of synthesis, refers to reaction conditions related to time, temperature, solvent, reactant concentrations, and the like, that are within ordinary skill for an experimenter to vary to provide a useful quantity or yield of a reaction product. It is not necessary that the desired reaction product be the only reaction product or that the starting materials be entirely consumed, provided the desired reaction product can be isolated or otherwise further used.

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, 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 includes "about 'x' to about 'y'". To illustrate, a concentration range of "about 0.1 % to about 5%" should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1 %, 2.2%, 3.3%, and 4.4%) within the indicated range. In an

embodiment, the term "about" can include traditional rounding according to significant figures of the numerical value. In addition, the phrase "about 'x' to 'y " includes "about 'x' to about 'y'".

The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range.

In addition, where features or aspects of the disclosure are described in terms of a list or a Markush group, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. For example, if X is described as selected from the group consisting of bromine, chlorine, and iodine, claims for X being bromine and claims for X being bromine and chlorine are fully described as if listed individually. For example, where features or aspects of the disclosure are described in terms of such lists, those skilled in the art will recognize that the disclosure is also thereby described in terms of any combination of individual members or subgroups of members of list or Markush group. Thus, if X is described as selected from the group consisting of bromine, chlorine, and iodine, and Y is described as selected from the group consisting of methyl, ethyl, and propyl, claims for X being bromine and Y being methyl are fully described and supported. As used herein, all percent compositions are given as weight-percentages, unless otherwise stated. When solutions of components are referred to, percentages refer to weight-percentages of the composition including solvent (e.g., water) unless otherwise indicated.

As used herein, all molecular weights (Mw) of polymers are weight- average molecular weights, unless otherwise specified.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

Generally, a method of casting a polyamide polymer can comprise steps of maintaining a vacuum during a pre-casting polymerization cycle, extruding the reactive polyamide polymer during a casting cycle, and cutting the extruded polymer. More specifically, the method can include maintaining a vacuum during a pre-casting polymerization cycle of the cyclic process such that the pre-casting polymerization cycle produces a reactive polyamide polymer with decreased pre- casting polymerization cycle time. Additional steps can include extruding the reactive polyamide polymer during a casting cycle by adjusting process parameters including vessel pressure and extrusion valve opening to generate a throughput of extruded polymer, and cutting the extruded polymer at a cutting speed substantially proportional to the throughput to provide polyamide pellets.

Likewise, an apparatus for manufacturing polyamide pellets can comprise and autoclave vessel, a cutter, and a process controller. The autoclave vessel can include an extrusion valve and a pressure controller (e.g., inlet valve, vent valve, heating component, or any other device other than the extrusion valve that can be used to modulate pressure within the autoclave). The cutter can be adapted to cut polyamide polymer extruded from the autoclave vessel to form polyamide pellets. The process controller can include a pressure control module for controlling the pressure controller, a cutting speed module for controlling cutter speed, and an extrusion valve module for controlling the extrusion valve. The apparatus can be configured to maintain a vacuum during a pre-casting polymerization cycle of the cyclic process such that the pre-casting

polymerization cycle produces a reactive polyamide polymer with decreased pre- casting polymerization cycle time.

It is noted that when discussing the present apparatuses and methods, each of these discussions can be considered applicable to each of these examples, whether or not they are explicitly discussed in the context of that example. Thus, for example, in discussing a polyamide polymer with respect to the apparatus, that discussion is also applicable to the methods, and vice versa.

Returning now to the apparatuses and methods of the present disclosure generally, the present manufacturing processes, casting processes, apparatuses, etc., can be used with polymer systems comprising polyamides. In one embodiment, the polyamide polymer can comprise, consist essentially of, or consist of nylon 6,6. The nylon 6,6 can be neat polymer, or can be modified by any of a number of additives, including optical brighteners, dyes, etc. Generally, the manufacturing processes referred to herein can include continuous and batch processes unless otherwise specified. Such processes are generally performed in reactor vessels, e.g., an autoclave. In one embodiment, the manufacturing process can be a batch process. Without specific limitation, such a batch process is typically a 5 cycle process, as described herein.

With reference to nylon 6,6 in particular, a typical batch size in accordance with examples of the present disclosure can be from about 1000 Kg to about 3000 Kg, and can be cycled during the batch within the autoclave at from about 100 to 120 minutes. Batch sizes and timing outside of these ranges can also be used, depending on equipment and polymer choices, or other considerations within the knowledge of one skilled in the relevant arts. Generally, the nylon of the polyamide can be added as a salt. In one embodiment, the nylon can be a nylon 6,6 salt and can be present in the polyamide in an amount ranging from about 50 wt% to 95 wt%.

Various processing parameters can be used in the polymerization of the present polyamides including temperature and pressure. In one embodiment, the temperature can range from about 190°C to about 290°C and the autogenous or other pressure during certain cycles can range from about 250 pounds per square inch absolute (psia) to about 300 pounds per square inch absolute (psia). Additionally, in another embodiment, during certain cycles, heating can be performed under vacuum at a pressure of less than 10 torr.

As used herein, the terms "RV" and "formic acid RV" refer to ASTM D789- 07e1 "Standard Test Methods for Determination of Solution Viscosities of Polyamide (PA)".

In accordance with the invention, we have discovered that the pressure in the pre-casting step to below atmospheric pressure addresses the problem of undesirably long residence time in the pre-casting step. The effect appears more pronounced with higher RV nylon-6,6 formulations. For example, while the process is useful for making nylon-6,6 with RV from about 20 to about 60, it is especially advantageous for making nylon-6,6 polymers with RV above 30, for example above 40 or 50. In one embodiment, the process produces a nylon-6,6 polymer having RV of 40 to 250, for example about 50 to about 60.

The process includes operating the pre-casting step at slightly to markedly below atmospheric pressure. In accordance with the invention, the pressure in the pre-casting step can be reduced in increments of about 1 psi, for example 1 .2, 1 .4, 1 .6, 1 .7, 1 .8, 1 .9 or 2 psi. The resulting reduction in the required pre- casting cycle time is more pronounced with higher RV nylon-6,6 formulations, and is also more pronounced when the reaction mixture contains additives that are either substantially inert or polymerization inhibiting.

Generally, the present process for producing polyamide pellets may be made by an autoclave and extrusion/cutting process. In one embodiment, the process may start with a concentrated slurry or polyamide solution prepared from an aqueous solution of a polyamide salt, e.g. a nylon 6,6 salt, that is provided to an autoclave vessel. Optionally, the slurry may be dilute and become more concentrated by means of an evaporation step. In one embodiment, the slurry may be prepared from an aqueous solution of the monomers hexamethylene diamine and adipic acid, in the manner known in the art. In another specific embodiment, the slurry may contain a minor amount of nylon 6 monomer with the aqueous solution of the nylon 6,6 monomers in the form of an aqueous caprolactam solution. The autoclave vessel may then be heated to about 230°C (or some other functional temperature) allowing the internal autogenous pressure to rise, in one example. A delusterant, titanium dioxide (ΤΊΟ2) may optionally be injected into the autoclave and monomer mixture as an aqueous dispersion.

The polyamide solution or thickening slurry mixture may then be heated in the autoclave to about 245 C (or some other functional temperature). While at this temperature, the autoclave pressure may be reduced to atmospheric pressure and further reduced in pressure by application of a vacuum in the known manner, to form the polyamide composition. The autoclave, containing the polyamide composition, would be maintained at this temperature and/or pressure for about 30 minutes. This step may be followed by further heating of the polyamide polymer composition in the autoclave to about 285°C, for example, and introducing dry nitrogen to the autoclave vessel and pressurizing the autoclave by introducing dry nitrogen to about 4 to about 5 Bar absolute pressure.

In accordance with the general heating and pressure cycles discussed herein, generally, the present methods include the use of a pre-casting polymerization cycle immediately preceding a casting cycle. The pre-casting cycle occurs under vacuum such that a reactive polymer is formed with a decreased cycle time. Thus, the term "pre-casting cycle" is defined herein to include the cycle immediately preceding the casting cycle. Thus, for example, in a five cycle polymerization cycle, such as the five cycle polymerization cycle described herein, the pre-casting cycle can be Cycle 4 and the casting cycle can be Cycle 5. Cycles 1-3 in this example are not considered to be the "pre-casting cycle," as they do not immediately precede the casting cycle.

Furthermore, the pre-casting cycle is characterized as having a

"decreased cycle time." Thus, the decreased cycle time is determined as compared to the same cycle performed under the same conditions with the same equipment, except that the cycle is performed under ambient temperature. Thus, in determining whether there is in fact a "decreased cycle time" during the pre- casting cycle, one can carry out two polymer preparation runs, one which uses a vacuum and one which does not. If the polymerization time can be decreased because of the sole variable change of using a vacuum vs. ambient pressure, then the pre-casting cycle can be said to have a "decreased cycle time." In one embodiment, the decreased pre-casting polymerization cycle time is decreased by at least 10%, 20%, 40%, or 50%, for example. In real time, the decreased cycle time can be by a time increment of at least 1 minute, 2 minutes, 4 minutes, 6 minutes, 8 minutes, or 10 minutes, for example, compared to a pre-casting polymerization cycle performed under the same conditions and with the same equipment except that the pre-casting polymerization cycle is performed under ambient pressure. These amounts of time may not seem like much, but when run over and over again during essentially 2 hour runs, this time savings can add up quickly, increasing efficiency of the system as a whole.

The present polyamide polymers can be reactive polyamide polymers. In another embodiment, the reactive polyamide polymer can continue to polymerize after extruding. As such, various types of polymers can be produced by the present methods and apparatuses. Notably, such reactive polymers can be difficult to process and maintain uniformity during casting. As such, the present methods and apparatuses further provide uniform casting.

Regarding uniform casting, the present methods can include adjusting process parameters including vessel pressure, extrusion valve opening, and cutting speed to maintain uniformity during the casting process. Generally, each process parameter can be individually controlled such that the throughput of the reactive polyamide polymer is proportional to the cutting speed thereby providing uniform polyamide pellets. Typically, uniformity is based on pellet mass measurements. By proportional, the present cutting speed can match that of the throughput such that the when the throughput decreases the cutting speed decreases or when the throughput increases the cutting speed increases. The proportionality can be substantially proportional such that the uniformity of the polyamide pellets can be measured as a batch of pellets having an average mass with at least 95% of the individual pellets having an individual mass within 10% of the average mass. In one aspect, the pellets can have an average mass with at least 99% of the individual pellets having an individual mass within 5% of the average mass.

The polyamide polymers described herein can be prepared as well using a catalyst. In one embodiment, the catalyst can be present in the polyamide in an amount ranging from 10 ppm to 1 ,000 ppm by weight. In another aspect, the catalyst can be present in an amount ranging from 10 ppm to 100 ppm by weight. The catalyst can include, without limitation, phosphoric acid, phosphorous acid, hypophosphoric acid arylphosphonic acids, arylphosphinic acids, salts thereof, and mixtures thereof. In one embodiment, the catalyst can be sodium

hypophosphite, manganese hypophosphite sodium phenylphosphinate, sodium phenylphosphonate, potassium phenylphosphinate, potassium

phenylphosphonate, hexamethylenediammonium bis-phenylphosphinate, potassium tolylphosphinate, or mixtures thereof. In one aspect, the catalyst can be sodium hypophosphite.

The polyamides and polyamide compositions in accordance with embodiments disclosed herein can be improved in whiteness appearance through the addition of an optical brightener. Such polyamides can exhibit a permanent whiteness improvement and can retain this whiteness improvement through operations such as heat setting. In one embodiment, the optical brightener can be present in the polyamide in an amount ranging from 0.01 wt% to 1 wt%. In one aspect, the optical brightener can be titanium dioxide.

In addition, these polyamide polymers can be prepared with antioxidant stabilizers, antimicrobial additives, etc. Additionally, the polyamide polymers may be prepared using anti-foaming additives. In one embodiment, the anti-foaming additive can be present in the polyamide in an amount ranging from 1 ppm to 500 ppm by weight.

The polyamide polymers in accordance with embodiments disclosed herein are inherently acid dyeable, but may also be rendered into a basic dyeing form by modifying these polymers or copolymers with a cationic dye

copolymerized in the polymer. This modification makes compositions particularly receptive to coloration with base dyes.

Turning now to FIGS. 1 A and 1 B, schematic cross-sectional views of two exemplary agitated autoclaves are shown. This FIG. is not necessarily drawn to scale, and does not show each and every detail that is typically present in an agitated autoclave, opting instead to show schematic representations of features particularly relevant to the present disclosure. Thus, an agitated autoclave 10 can include an autoclave vessel 20 and an agitator or auger 22 in this example.

Although shown, the agitator or auger is not required. The vessel includes a vessel wall 24, which is typically a cladded vessel wall, and the vessel wall and/or other structures are adapted to support one or more type of heating components 26a, 26b. In this example, external jacket heating components are shown at 26a and internal heating components are shown at 26b. It is noted that the heating component in FIG. 1 A is positioned relatively close to the agitator, which can be typical, whereas the heating component FIG 1 .B is positioned closer to the vessel wall, which may be more typical of non-agitated autoclaves. However, this being stated, positioning of the heating elements can be carried out by one skilled in the art after considering the present disclosure. In still further examples, there may be heating elements in both locations, i.e. near the vessel wall and near the agitator.

The external jacket heating components 26a can be used to raise the temperature of the polymerizable composition or polymer contained within the vessel, and the internal heating components 26b in particular can be used to prevent polymer from becoming adhered to an interior surface of the vessel wall and/or to the agitator. As shown in FIG. 1 A, in addition to the internal heating component shown, there is also a pair of refresher bars 1 8 that work with the central agitator or auger 22 to refresh the polymer. The agitator works to move the polymer upward along a center portion, and the pair of refresher bars are used to refresh the molten polymer by removing the polymer from the side wall surfaces as the molten polymer is churned. This arrangement can improve the heat transfer within the system, and can reduce the height of the vortex caused by the agitation. In either case, it is noted that the interior heating components are shown schematically in cross-section, but it is understood that any shape or configuration of interior heating components could be used. It is also noted that the heating components can be configured or adapted to carry any fluid known in the art for providing heat to autoclaves, including gases and/or liquids. An inlet valve 28 and an autoclave vent 30 are also shown and can be used to together or alone as the pressure controller (along with the heating components 26a, 26b, which also control pressure). A pressurizing device or pressure source is not shown, but is understood to be present when pressure is to be added externally. Alternatively, pressure can be increased by the addition of heat and reduced by venting, as is understood in the art. Furthermore, at the bottom end of the autoclave vessel is a valve opening 32. The extrusion valve is not shown in this FIG., but this is the location where polymer prepared in the autoclave is extruded for further processing. It is noted that irrespective of the description and shown location of these inlets, valves, vents, etc., these or other ports can be used differently than shown for any purpose designed by the user, as would be appreciated by one skilled in the art. It is also noted that this exemplary autoclave vessel and methods of forming the polyamide polymer within the autoclave are provided for exemplary purposes only, as any of a number of other process procedures, autoclaves, and additives may be used to generate the polyamide polymer. That being described generally, it is at this point in the process, regardless of how the polymer was prepared in the autoclave vessel that is the primary subject of the present disclosure, i.e. casting of the polymer from the polymerization vessel.

As discussed herein, the present disclosure provides apparatuses and methods for forming pellets of polyamide polymers by cutting an extruded polyamide polymer and adjusting various processing parameters. Particularly, the present method allows for adjusting process parameters including vessel pressure and extrusion valve opening to generate a throughput of extruded polymer. Additionally, cutting speed can be adjusted to coordinate with the throughput so that mass can be within a predetermined narrow range, as described herein. Generally, the throughput can be controlled at least partially by the extrusion valve opening. Notably such process parameters can be adjusted to maintain uniformity during the casting process. As such, in one embodiment, the present method can include adjusting the cutting speed in response to a change in the extrusion valve opening and/or the vessel pressure to maintain the uniformity of the polyamide pellets. In another embodiment, the cutting speed can be substantially proportional to or coordinated with the throughput to provide a uniformity of the polyamide pellets.

Turning now to FIG. 2, an apparatus for manufacturing polyamide pellets can comprise a vessel 20, such as an autoclave similar to that shown in FIGS. 1 A and 1 B, including a pressure controller (which can be in the form of an inlet line/valve 28, vent line/valve 30, and/or heating component(s) 26). It is noted that the heating component is shown as an external jacket, but could alternatively or additionally be an internal heating component. Also shown is an extrusion valve 34 for extruding polymer through a die plate or other extrusion configuration. The apparatus can also include a cutter 36 adapted to have a cutting speed suitable for cutting uniform polyamide pellets. The cutter can be a circular cutter adapted to cut very quickly as the extruded polymer is passed thereby, for example. The apparatus can also include a process controller 60, which can include a pressure control module 70, a cutting speed module 80, and an extrusion valve module 90. The apparatus can also include trays 38, slurry collection devices 40, a slurry pipe 42, and a drier/spinner 44.

In further detail regarding the process controller 60 of the apparatus, the various modules 70, 80, 90 can be used to automatically carry out the general functions or process steps of the automated apparatus. For example, an inlet valve 28, autoclave vent 30, and a heating component 26 can be controlled by a pressure control module 70 allowing for adjustment of pressure. The cutter 36 can be controlled by the cutting speed module 80. The extrusion valve 34 can be controlled by the extrusion valve module 90. Other modules (not shown) can be present including without limitation an agitation module, a drier module, a heating component module, etc. The modules can work together to provide an automated system in a manner to cause uniform polyamide pellets.

FIG. 3 is provided to show a single example of a five cycle process defined by the pressure profiles of each cycle. Specifically, a first cycle (Cycle 1 ) occurs at the beginning of the batch process while the pressure is being increased from an ambient low pressure 1 10a to a relative high pressure 120. A second cycle (Cycle 2) occurs as the relative high pressure is maintained for a period of time. A third cycle (Cycle 3) occurs as the relative high pressure is reduced to an even lower pressure 1 10b than initially present, which can be in accordance with examples of the present disclosure, reduced below the initial ambient pressure using a vacuum. A fourth cycle (Cycle 4) occurs as the lower (vacuum) pressure is maintained for a period of time. In this specific example, Cycle 4 is the "pre- casting cycle." A fifth cycle (Cycle 5) occurs as the pressure is increased again for the purpose of extruding the polymer from the agitated autoclave vessel. In this specific example, Cycle 5 is the "casting cycle."

It is noted that there are many other pressure profiles that can be used to prepare and cast polymers, and the example shown in FIG. 3 is merely exemplary. It is also noted that there will be other devices that are used in order to achieve this pressure profile, such as venting profiles, heating profiles, agitator profiles (when an agitator is used), etc., as is understood by those skilled in the art. For example, heat can be used to raise the pressure in the autoclave vessel. Likewise, venting can be used to maintain the relative high pressure at a relatively constant level during the second cycle. Furthermore, a vacuum can be used to reduce the pressure to below ambient pressure during the fourth cycle, as has been described herein.

FIG. 4 is sets forth a plot that illustrates an example where such modules work together to achieve exceptional uniformity in accordance with examples of the present disclosure. Specifically, FIG. 4 depicts a casting plot, e.g., Cycle 5, of processing parameters of an apparatus in accordance with an embodiment of the present disclosure. Specifically, the plot provides autoclave pressure through a single batch casting process, throughput of the polyamide polymer from the autoclave, a linearized extrusion valve plot, and cutting speed as a function of time during casting. As shown, the various process parameters are adjusted to provide substantially constant throughput at a high cutting speed thereby providing an automated process that maintains uniformity of the pellets while also maintaining high production rates.

It is also noted in the graph of FIG. 4 that the cutting speed is modified and is substantially proportional to the throughput, i.e. when the throughput moves upward or downward (as shown graphically), the cutting speed likewise moves upward and downward, respectively. The term "substantially" as it relates to the proportionality or relative matching of the throughput to the cutting speed can be defined as any degree of matching where the uniformity of a batch of pellets have an average mass with at least 95% of the individual pellets having an individual mass within 10% of the average mass. It is by substantially matching the relative movements of the cutting speed to the throughput, the uniformity can be maintained. As a result, it is the use of the pressure controller and the extrusion valve that keeps the throughput within a reasonable range for achieving an efficient cutting profile. For example, in an efficient system with high throughput provided by an appropriate pressure and linearized valve opening, cutting speed can be relatively matched with respect to the throughput. Note that when the throughput increases, so does the cutting speed. Returning now to FIG. 2, as discussed herein, the vessel 20 pressure can be autogenous or can be generated from an outside pressure source.

Additionally, the pressure can be adjusted using heat, a pressure source (not shown), and/or the vent 30. The extrusion valve 34 generally controls the opening from which the polyamide polymer is extruded. In some aspects, the extrusion valve opening can be referred to as a linearized opening of the extrusion valve. As used herein, "linearized" refers to a mathematical manipulation that equates the opening of the valve, i.e., unblocked area, to the percent of the material that is extruded through the opening. As such, a "linearized" opening of 50% refers to 50% material extruding from the opening from a total amount of 100% (100% referring to the maximum capacity when the valve is completely open), even though the valve opening (i.e., unblocked area) may not be 50% of the total available opening. It is noted that there is much more control of throughput of the polyamide polymer when the valve is not set near 100% open. As the valve approaches 70% or 80% opening, the control throughput is significantly reduced. For example, modifying the opening of the valve from 40% to 50% has a relatively significant effect on throughput, whereas opening a valve from 80% to 90% has minimal effect on throughput. As a result, it can be desirable to keep the valve, to the extent possible within a range of about 30% to 70% open, and more typically from 35% to 60% open during the polymer casting process. To accomplish this, pressure and/or cutting speed may be changed to keep the valve opening within a desirable range. That being described, this is not strictly required. This merely provides a mechanism to retain maximum flexibility with respect to the extrusion valve opening.

Returning to the various adjustments to process parameters that can be carried out in response to changes in other process parameters, it is noted that adjustments to the process parameters can be performed sequentially or simultaneously (or in an overlapping time sequence). In one embodiment, more than one process parameter can be adjusted in response to a third process parameter change. To provide an example of why such process parameters may benefit from modification, it is noted that once the extrusion process is begun from an autoclave vessel, often, the polyamide polymer contained therein has not completely finished with its polymerization process. Thus, the polyamide polymer may continue to thicken further during the extrusion process. It has been discovered that throughput, and more significantly, pellet uniformity cannot simply be maintained under these conditions by increasing pressure alone. Likewise, merely opening the extrusion valve 34 up further will not always adequately compensate for the thickening polymer. Further, even by controlling both of these parameters together, if the cutting speed is not modulated based on throughput changes, uniformity of polyamide pellets may suffer. Notably, maintain uniformity for reactive polymers can be even more challenging as their characteristics can be even more dynamic.

Thus, the present apparatuses and methods include controlling

throughput, and thus, pellet uniformity using varying pressure, varying valve opening, and varying cutting speed to achieve uniform pellets in an efficient manner. Thus, in one specific example, exemplary throughputs can range from 2 to 10 tons per hour, or from 5 to 9 tons per hour, or more particularly, from 6 to 8 tons per hour. Exemplary pressures during extrusion can range from 0 to 12 Bar, from 1 to 10 Bar, or from 5 to 10 Bar. Exemplary valve opening levels can range from 30% to 70%, or from 45% to 65%. Exemplary cutting speeds using a helical cutter or other similar rotational cutter can range from 100 to 2000 RPM, from 400 to 1800 RPM, or from 600 to 1500 RPM. Typically, these process

parameters are kept within these ranges during the casting process, and by adjusting the parameters within these ranges, uniformity of polyamide pellets can be achieved. That being stated, process parameters outside of these ranges can also be used, provided the pellet uniformity can be maintained as described herein.

The throughput can be controlled, at least in part, by the extrusion valve

34 opening, the cutting speed can be controlled by the cutter 36, and the pressure can be controlled by one or more pressure controller 26, 28, 30. While more than one process parameter can be adjusted to maintain uniformity of the polyamide pellets, in one specific embodiment, the pressure and/or cutting speed can allow for the extrusion valve to operate with a linearized opening at from 30% to 70%, from 35% to 65%, or from 40% to 60%. Additionally, to provide desirable efficiency, in one embodiment, the throughput can be at least 5 ton/hour, or at least 7 ton/hour in large systems, and the adjusting of the process parameters can maintain the target throughput varying no more than 10% by weight.

The process controller 60 is generally networked to the cutter 36 and the vessel via a computer, other computing device, or other networked device. The present apparatus can be automated using various modules. In one embodiment, the pressure control module 70 can modulate the pressure controller 26, 28, 30 in response to a change in the cutting speed or an opening of the extrusion valve 34. In one aspect, the pressure control module can modulate the pressure controller in response to changes in the cutting speed and an opening of the extrusion valve. In another embodiment, the cutting speed module 80 can modulate the cutting speed of the cutter 36 in response to a change in pressure or an opening of the extrusion valve. In one aspect, the cutting speed module can modulate the cutting speed in response to changes in pressure and an opening of the extrusion valve. In still another embodiment, the extrusion valve module 90 can modulate the extrusion valve 34 in response to a change in the cutting speed or pressure. In one aspect, the extrusion valve module can modulate the extrusion valve in response to changes in the cutting speed and pressure. As such, the present modules can work in concert via the process controller to adjust the processing parameters during casting in a manner sufficient to provide consistent and uniform polyamide pellets.

As a further note, in order to assist in determining an appropriate level of activity for a process parameters, e.g., pressure, valve opening, and cutter speed, throughput can be estimated based on any of a number of techniques, including estimations using optics, estimations using weight and/or volume (in the vessel and/or after extrusion), estimates based on energy transfer with respect to the casting water surrounding the extruded polymer, or the like. With specific reference to the energy transfer technique, such a casting process can include the use of a casting throughput estimate or dynamic value profile to use for adjusting process parameters in the production of the polyamide pellets. For example, estimating the casting throughput can include measuring temperatures of the casting water and flow rates such that the heat transfer is calculated and then correlated to the casting throughput. As a further note, some of the functional units described in this

specification have been labeled as "modules," in order to more particularly emphasize their implementation independence. For example, a "module" may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. Modules may also be implemented in software for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more blocks of computer instructions, which may be organized as an object, procedure, or function.

Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which comprise the module and achieve the stated purpose for the module when joined logically together.

Indeed, a module of executable code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices. The modules may be passive or active, including agents operable to perform desired functions.

EXAMPLES

Example 1 - Autoclave with Traditional Cycling

A commercial autoclave with capacity to produce 1200 kg of nylon-6,6 per cycle is charged with an aqueous solution of adipic acid and hexamethylene diamine. The temperature is raised from 150 °C to 280 °C. The commercial autoclave is equipped with a pressure control valve emptying into a vent line. When the pressure of the autoclave reaches 300 psia, the control valve opens sufficiently to maintain the pressure at 300 psia kPa. Both the water of solution and the water evolved by the condensation reaction of adipic acid and hexmethylene diamine are controllably released from the autoclave through the control valve into the vent line.

Example 2 - Comparative Cycle Times for Target RV of 38.5

Example 1 is repeated to produce nylon-6,6 having RV of 38.5. In the pre- casting cycle, the absolute pressure is reduced from 16 psia to 12 psia.

Comparing the times for the pre-casting cycle, the desired RV is achieved 4 minutes faster at the reduced pressure.

Example 3 - Comparative Cycle Times for Target RV of 40 with Non-Inhibiting

Additives

Example 1 is repeated to produce nylon-6,6 having RV of 40 with non- inhibiting additives such as: catalysts, optical brighteners, and anti-foaming additives. The term "non-inhibiting additives" means that the additives are not those that the ordinary skilled person would select for the purpose of inhibiting polymerization. In the pre-casting cycle, the absolute pressure is reduced from 13 psia to 7 psia. Comparing the times for the pre-casting cycle, the desired RV is achieved 6 minutes faster at the reduced pressure.

Example 4 - Comparative Cycle Times for Target RV of 52 with Polymerization- Inhibiting Additives

Example 1 is repeated to produce nylon-6,6 having RV of 45 with polymerization-inhibiting additives. Examples of such additives include the following: hydroquinon, p-methoxypheno!, cresoi, t-butylcatechoL 3,5-di-t-butyl-4- hydroxyto!uene, 2,2'-methyIenebis(4-methy!-6-t-butyipheno!), 2,2'- methylenebis(4-ethyl-6-t-butylphenol), 4,9'-thiobis(3-methyl-6-t-butyiphenol); a thioether type such as phenothiazine, distearylthiodipropionate; an amine type such as p-phenylenediamine, 4-aminodiphenylamine, N,N'-diphenyi-p- phenylenediamine, N-i-propyl-N'-phenyl-p-phenylenediamine, N~(1 .3- dimethylbutyl)-N'-phenyl-p-phenylenediamine, N,N'-di-2-naphthyl-p- pheny!enediamine, diphenylamine, N-phenyl-f -naphthylamine, 4,4'-dicumyl- diphenylamine, 4,4 ^, -diocty1-diphenylamine; a nitroso compound such as N- nitrosodiphenylamine, N-nitrosophenylnaphthyiamine, N-nitrosodinaphiyiamine, p-nitrosopheno!, nitrosobenzene, p-nitrosodiphenylamine, a-nitroso-p-naphtol; a nitrite such as ammonium nitrite, sodium nitrite, potassium nitrite, copper nitrite, iron nitrite, trimethylammonium nitrite, n~hexy! nitrite, 1 -octyl nitrite and esters thereof; nitroxide such as piperidine-1 -oxyl, pyrrolidine-1 -oxyi, 2,2,8,6- tetramethyi-4-oxopiperidine-1 -oxy!, 2,2,6,6-tetramethyipiperidine-l -oxyi; a copper salt such as copper dimethy!dithiocarbamate, copper diethyldithiocarbamate, copper dibutyldithiocarbamate, copper acetate, copper salicylate, copper thiocyanate, copper sulfate and copper chloride; a chromium compound such as chromium acetate and chromium oxide; a thiourea compound such as thiourea, 1 ,3-dimethylthiourea, 1 ,3~diethy!thiourea, 1 ,3-di-i-propy!thiourea, 1 ,3- dibutylthiourea and dimethylolthiourea; iodine, iodide such as lithium iodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide and titanium iodide; bromide such as lithium bromide, sodium bromide, potassium bromide and cesium bromide or the like. The term "polymerization-inhibiting additives" means those additives that the ordinary skilled person would select for the purpose of inhibiting polymerization. In the pre-casting cycle, the absolute pressure is reduced from 8 psia to 5 psia. Comparing the times for the pre- casting cycle, the desired RV is achieved 7 minutes faster at the reduced pressure.

Although the subject matter has been described in language specific to structural features and/or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the described technology.