WO1993005097A1

WO1993005097A1 - A process for controlling the melt viscosity of polyamides during melt processing

Info

Publication number: WO1993005097A1
Application number: PCT/US1992/007254
Authority: WO
Inventors: Yash P. Khanna; Kevin R. Slusarz; Annemarie C. Reimschuessel; Ronald A. F. Moore
Original assignee: Allied-Signal Inc.
Priority date: 1991-09-03
Filing date: 1992-08-27
Publication date: 1993-03-18
Also published as: CN1070660A; MX9205041A; AU2505092A

Abstract

A process for controlling the melt viscosity of a polyamide which comprises forming a molten mixture polyamide and an effective amount of water thereby reducing or decreasing the melt viscosity of said polyamide.

Description

A PROCES8 FOR CONTROLLING THE MELT VISCOSITY OF POLYAMIDES DURING MELT PROCESSING

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for controlling (increasing or decreasing) the melt viscosity of polyamide compositions in the melt by controlling the moisture content of said polyamide compositions. A more preferred embodiment of this invention relates to a process of reversibly increasing or decreasing the melt viscosity of the polyamide during melt processing of a polyamide into molded articles. Polyamide compositions treated in accordance with the process of this invention are capable of being fabricated into useful shaped articles of manufacutre, e.g., filaments, both mono- and multifilament, films, tapes, ribbons, rods, laminates, and the like. 2. Description of the Prior Art

Polyamide compositions are disclosed in the prior art as having many and varied uses in industrial and commercial applications. For example, these polymers can be formed into filaments in which the polymer chains are oriented along the filament axis. Such filaments have many uses, in commerical applications as for example in the production of fibers for tire cord, textiles and the like. Similarly, these polymers can be fabricated into other useful shaped articles, as for example, gears, lawn mower housings, skate boards and the like.

The melt viscosity of polyamide compositions provides an indication of the molecular weight of the polyamides. In general, polymers having low melt viscosities are desirable because of improved properties of fibers and other shaped articles made therefrom. For example, fibers made from polymers of

B TITUTESHEET relatively high melt viscosities have increased tensile strength, durability and impact resistance. These properties are very desirable, especially in fibers used in reinforcement for pneumatic automobile tires. Several processes have been proposed in the prior art for increasing the viscosity and molecular weight of polyamides, as for example poly(hexamethylene adipamide) . One such process is set forth in U.S. Patent No. 3,763,113 which discloses a process for increasing the molecular weight of polyamides having recurring -CONH- alkylene-NHCO-alkylene units, such as poly(hexamethylene adipamide) by heating the polyamide with a phosphonic acid derivative in the presence of an inert gas, such as nitrogen. Similarly, U.S. Patent Nos. 3,551,548 and 3,763,113, each broadly describes a process for increasing the relative viscosity of polyamides, generally, and poly(hexylmethyleneadipamide) , specifically, by sweeping a molten mixture of the polyamide and a phosphorous compound with an inert gas.

Each of these processes provides various adverse effects. For example, in each of the processes an inert gas is employed, which in high concentrations causes uneven finishing, i.e. a variation in the degree of polymerization, throughout the polyamide, which results in a non-uniform polymer. Furthermore, inert gas is expensive, and requires additional equipment and monitoring which can increase the cost of commerializa ion of the process, even though the inert gas is used in small amounts.

U.S. Patent No. 4,417,032 discloses a process for forming quasi-random copolya ides from two or more homo polyamides. In this process, the homo polyamides are melt blended in the presence of a phosphite promoter. U.S. Patent no. 3,509,107 discloses a process for increasing the relative viscosity of fibers formed from polyamides or copolyamides by incorporating a phosphorous or phosphite compound into the polyamide or copolyamide under an inert gas atmosphere. The primary object of U.S. Patent No. 3,509,107 is to provide a process for increasing the viscosity of polyamide or copolyamide yarn and cord which requires a minimum amount of gas. U.S. Patent No. 3,551,548 describes various optimizing procedures for the process of U.S. Patent No. 3,509,107. The described patents are each directed to a process of producing polyamide yarn with increased viscosity via incorporating a phosphorous or phosphite compound into the yarn, and then heating said yarn in the presence of inert gas. British Patent No. 569,184 discloses a process for producing a random copolymer from nylon 6 and nylon 6,6. The process comprises heating a mixture of nylon 6 and nylon 6,6 which results in interchange between various sections of the respective polymer molecules with the final product being a random copolymer of nylon 6 and nylon 6,6. In order to produce a random copolymer of nylon 6 and nylon 6,6, British Patent No. 569,184 teaches that it is necessary to heat the mixture of homopolymers for periods of time up to 8 hr. at 285*C without any catalyst.

U.S. Patent No. 4,390,667 discloses a process for decreasing the melt index and increasing the viscosity of polyamide fibers via incorporating a phosphate compound into the polyamide and heating the polyamide until the desired changes in the melt index and viscosity occur. The phosphate utilized in U.S. Patent No. 4,390,667 include substituted aryl phosphtes which satisfy certain Hammett sigma values.

U.S. Patent No. 4,417,031 discloses a process for preparing block and graft copolymers. The

SUBSTITUTESHEET described process involves reacting two or more polyamides, polyesters, or homopolymers of β- unsaturated carboxylic acids in order to form a graft and/or block copolymer. Included in the patent are copolymers formed from poly(caproamide) and poly(hexamethylene adipamide) .

U.S. Patent No. 4,946,909 describes a process for forming random copolymers which comprises forming a polymer melt containing one or more polyamides and one or more aryl phosphoryl azide compounds, such as diphenyl phosphoryl azide; and heating said melt for a period of time sufficient to form the desired amount of the copolymer.

U.S. Patent No. 4,906,708 describes a process for decreasing the melt index, and increasing the melt viscosity and melt elasticity of a polyamide by adding thereto an effective amount of an aryl phosphoryl azide compound as for example diphenyl phosphoryl azide, and thereafter heating the composition until the desired changes in melt index, melt viscosity and melt elasticity are attained.

BRIEF DESCRIPTION OF THE INVENTION In general, this invention relates to a process for controlling the melt viscosity of a molten polyamide. This process comprises forming a molten mixture comprising a polyamide and water wherein the amount of water in said mixture in such that the viscosity of said polyamide is equal to a predetermined value.

A preferred aspect of this invention relates to an improved process for melt processing a polyamide. More particularly, the improved melt processing process of this invention comprises the steps of: a. forming a molten mixture comprising a polyamide and water, wherein the amount of water in said mixture is such that the viscosity of said mixture is equal to a predetermined value; and b. melt processing said molten mixture. Another more preferred aspect this invention relates to a process for melt processing a polyamide into an article. This process comprises the steps of: a. forming a molten mixture comprising a polyamide and water, wherein the amount of water in said mixture is such that the viscosity of said mixture is equal to a predetermined value; b. placing said mixture into the shape of an article to form a molten preform having the shape of said article; and c. cooling said molten mixture to form said article.

In this embodiment of the invention, the mixture can be placed into the shape of an article by any number of methods as for example by extrusion such as extrusion through a die or spinnerette to form a fiber; film or the like injection molding as for example injection of the mixture into a mold having the shape of the article. Other useful procedures for placing the molten mixture into the shape of an article include blow molding to form hollow articles as for example by placing the mixture into a mold having the shape of a hollow article, and introducing a gas into the mold to form a hollow molten preform having the shape of the article. Yet another more preferred aspect of this invention is a polymer blending process which comprises forming a molten mixture of two or more polymers at least one of which is a polyamide and an amount of water sufficient to increase or decrease the melt viscosity of said polyamide thereby decreasing the

SUBSTITUTESHEET difference between the melt viscosity of said polyamide and the melt viscosity of at least one other polymer in said blend.

As used herein, "melt viscosity" denotes the internal friction, i.e. fluidity of the polyamide, and is well known in the art. A wide variety of viscometers is available for measurement of viscosity, such as capillary, rotational, orifice, falling ball, and oscillatory types. They are described in Barr, "A Monograph of Viscometry," Oxford, NY (1931) and Kirk and Othmer, "Encyclopedia of Chemical Technology," Vol. 14, pp. 756-775 the Interscience Encyclopedia, Inc., New York (1955) .

By way of this invention large changes in the melt viscosity of polyamides can be produced by controlling the moisture content of the resin within certain limits without significantly affecting the chemical nature of the resin e.g. extractable content and molecular weight. Surprisingly, it has been discovered that the melt viscosity of a polyamide in the melt can be reversibly change, either raised or lowered, when the polymer is in the melt. Several advantages flow from this invention. Melt viscosity plays a key role in polymer processing operations. The lower the melt viscosity of the molten polyamide the more easily the polymer can be processed in extrusion and injection molding processes. On the other hand, in blow molding process relatively higher melt viscosities are desired. Moreover, polymer blending is impacted significantly by differences in the melt viscosities of the polymers forming the blend. In general, the greater the difference in melt viscosity, the more difficult the blending process, and conversel, the smaller the difference in melt viscosity, the easier the blending process. Through use of this invention the rheology

TUTESHEET and morphology of polymer blends can be controlled by decreasing the viscosity mis-match of the individual components. For the blends involving polyamides, the melt viscosity of the polyamide can be adjusted through the use of this invention to provide for improved polymer blending. By equilibrating the polyamide (pellets, powders etc) with moisture under different conditions of temperature, time and vacuum, a suitable combination of these variables can yield a moisture content of the resin as for example between 0.001 and 1.0%. Such resins will show a dramatic variation in melt viscosity but only in the melt.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing changes in melt viscosity as a function of drying temperature or in other words the amount of moisture.

DETAILED DESCRIPTION OF THE INVENTION The first step of the process of this invention comprises forming a molten mixture comprising an appropriate polyamide, and an effective amount of water. As used herein, "molten mixture" is a mixture which has been heated to a temperature which is equal to or greater than the melting point of at least one of the polyamide components of the mixture. The manner in which the molten mixture is formed is not critical and conventional methods can be employed. Methods and apparatus for forming molten polyamide mixtures are well known in the art and will not be described herein in great detail. For example, the molten mixture can be formed through use of conventional polymer and additive blending means in which at least one of the polymer components of the mixture such as the polyamide component, is heated to a temperature equal to or

SUBSTITUTESHEET greater than its melting point and below the degradation temperature of the components of the mixture. In a particularly preferred embodiment of this invention, the mixture is heated above the melting point of the polyamide in the mixture.

The manner in which water is added to the molten mixture may vary widely, and the water can be introduced by a wide variety of methods. For example, the effective amount of water can be added to the polymer after melting or during melting or may be added to the polymer components collectively or individually prior to melting. For example, an effective amount of water can be added by drying the polyamide such that the final moisture content is within the desired concentration range. Where the original polyamide sample is moist, effective moisture control can be provided by drying a moist sample of the polyamide at various combinations of temperature (as for example from 23"C to 165"C), using varying heating times (from a few minutes to days depending on the amount of moisture) and/or employing varying pressures during the drying step (usually about 10"⁶ to about 760 mm Hg) . In those instances where the original polyamide sample includes little water, the amount of water can be increased to the desired extent by the direct addition of water or by absorption by exposing the polyamide sample to an atmosphere of humidity.

Surprisingly, it has been discovered that the amount of water present in the molten molten affects the melt viscosity of the polyamide in the mixture without modifying the structure of the polymer i.e. molecular weight or weight percent of extractable. In general, melt viscosity increases with decreasing water content and melt viscosity decreases with increasing water content. In the practice of this invention, the amount of water employed is varied to the extent necessary to provide the desired melt viscosity. For example, in certain polymer blending applications to insure proper of the polymeric components, it is preferred that the melt viscosities of various polymeric components of the mixture are of the same order of magnitude. Through use of this invention, the viscosity of the polyamide component, can be varried as required to achieve the desired match in viscosities. Similarly, in various molding precedures the melt vicosity of relatively high molecular weight polyamides can be reduced to the extent necessary to allow extrusion and injection molding.

In general, an effective amount of water is employed in forming the mixture. In the preferred embodiments of the invention, the amount of water employed is in the range of more than 0% to about 1% based on the total weight of the polyamide. The amount of water employed within the range will vary widely depending on the particular application. For example, in those applications where a relatively high melt viscosity is required, as for example blow molding, best results are obtained when the amount of water is near the lower end of the range, as for example below about 0.05% by weight of the polyamide. Applications where a relatively low melt viscosity is required as for example extrusion and injection molding, best results are obtained where the amount of water is near the higher of the range as for example equal to or greater than about 0.05% by weight of the polyamide. In these applications, the amount of water employed is preferably from greater than 0% to about 0.05 weight % by weight of the polyamide. In the particularly preferred embodiments of this invention, the amount of water is from greater than about 0% to about 0.01

SUBSTITUTESHEET weight % by weight of the polyamide, and most preferably from greater than 0% to about 0.005 weight % by weight of the polyamide, with those embodiments of in which, the amount of water is from about 0.0005 to about 0.003 weight % by weight of the polyamide being those of choice.

In those applications where relatively low melt viscosity is required as for example extrusion and injection molding, best results are obtained when the amount of water is near the high end of the range as for example equal to or greater than about 0.05% by weight of the polyamide. In this application the amount of water employed in preferably from about 0.05% to about 0.5% by weight more preferably from about 0.05 to about 0.1% by weight and most preferably from about 0.05 to about 0.08% by weight of the polyamide.

Polymers which are useful in the conduct of this invention are polyamides. Polyamides are polymers in which the recurring monomeric units are linked by amide linkages. Any polyamide can be used in the practice of this invention. Illustrative of useful polyamides are those characterized by the presence of recurring carbonamide groups as an integral part of the polymer chain which are separated from one another by at least two carbon atoms. These polyamides are those prepared by reaction of diamines and diacids having the recurring unit represented by the general formula:

NHCORCOHNHR¹ in which R is an alkylene group of at least about two carbon atoms, preferably from about 2 to about 10 carbon atoms, or an arylene group, and R^l is R or aryl. Exemplary of such materials are poly(hexamethylene adipamide) (nylon 6,6) poly(hexamethylene sebacamide) (nylon 6,10), poly(hexamethylene isophthalamide) , poly(hexamethylene terephthalamide) ,

HEET poly(heptamethylene pimelamide) (nylon 7,7) poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9) poly(decamethylene sebacamide) (nylon 10,10), poly[bis(4-amino cyclohexyl)-methane-1,10- decanecarboxamide) ] (Quiana) , poly(m-xylylene adipamide), poly(p-xylene sebacamide), poly(2,2,2- trimethylhexamethylene tere- phthalamide) , poly(piperazine sebacamide), poly(p-phenylene terephthalamide) , poly(metaphenylene isophthalamide) and the like.

Other useful polyamides are those formed by polymerization of amino acids and derivatives thereof, as for example lactams. Illustrative of these useful polyamides are poly(4-aminobutyric acid) (nylon 4), poly(6-aminohexanoic acid (nylon 6) , poly(7-amino- heptanoic acid) (nylon 7) , poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(ll- aminoundecanoic acid) (nylon 11) , poly (12- aminododecanσic acid) (nylon 12) and the like.

Preferred polyamides for use in the practice of this invention are polycaprolactam and poly(hexamethylene adipamide) . The particularly preferred polyamide is polycaprolactam.

The number average molecular weight of the polyamide can vary widely and is determined by conventional procedures as for example analytical determination of end-groups, osmotic pressure, vapour pressure lowering and ebulliometry or cryoscopy. As used herein, the number average molecular weight, M., is defined as follows:

SUBSTITUTE SHEET

wherein the summation

represents the total number of molecules in a sample, N- represents the number of molecules of molecular weight M; and the summation

iN

represents the total weight of the sample.

In the preferred embodiments of the invention, the polyamide is of article forming number average molecular weight. As used herein, "article forming molecular weight" is a molecular weight such that the polyamide can be used to form an article of manufacture such as a molded part, a film, a fiber and the like. Through use of this invention, polyamides of various article forming molecular weights can be melt processed more easily because of the decrease or increase in melt viscosity. In general, the number average molecular weight is at least about 1000. Preferably, the number average molecular weight of the polyamide is from about 1,000 to about 1,000,000. More preferably, the number average molecular weight of the polyamide is from about 3,000 to about 100,000 and is most preferably from about 50,000 to about 5,000. In the particularly preferred embodiments of the invention, the number average molecular weight of the polyamide is from about 8,000 to about 30,000.

Various other optional ingredients, which are normally included in polymer compositions, may be added to the mixture at an appropriate time during the conduct of the process. For example, these optional ingredients can be added either prior to or after melting of the polyamide in the first step of the process of this invention; or after the conduct of the second step in which the desired melt viscosity has been attained. Such optional components include fillers, plasticizers, impact modifers, colorants, mold release agents, antioxidants, ultraviolet light stabilizers, lubricants, antistatic agents, fire retardants, and the like. These optional components are well known to those of skill in the art, accordingly, only the preferred optional components will be described herein in detail.

A particulate filler is preferably included in the molten mixture. The filler functions to increase the modulus and stiffness of the composition, and provides a more economical composition. Any conventional filler can be employed provided that it provides all or a portion of the above-identified functions, and does not otherwise have a deleterious effect on the polamide. The fillers may optionally be treated with various coupling agents or adhesion promoters as is known to those skilled in the art. Useful fillers may be selected from a wide variety of minerals, metals, metal oxides, siliceous materials, metal salts, and mixtures thereof. Examples of such useful fillers include glass fibers, alumina, aluminum hydrates, feldspar, asbestos,

SUBSTITUTESHEET talc, calcium carbonate, clay, carbon black, glass quartz, novaculite and other forms of silica, kaolinite, bentonite, garnet, mica, saponite, beidellite, calcium oxide, calcium hydroxide, and the like. Such fillers are well-known materials and are readily available. The foregoing recited fillers are illustrative only and are not meant to limit the scope of the fillers that can be employed in this invention. In the preferred embodiments of this invention, fibrous materials are the fillers of choice, and glass fiber is the filler of choice in the particularly preferred embodiments of this invention.

The quantity of filler employed is not critical and can be varied widely as desired. In the preferred embodiments of this invention, the quantity of filler is up to about 150 wt % based on the total weight of the polyamide, and in the particularly preferred embodiment is in the range of from about 30 to 90 wt % on the same basis. It is also very desirable to include a plasticizer of the type known in the art for use with polyamide composition. Useful plasticizers will depend on various factors including the type of polyamide employed, and include caprolactam, mixtures of ortho-toluene and para- toluene ethyl sulfonamides, and the like.

In the second step of the process, the molten mixture having increased or decreased melt visocity is processed in the molten state. Because of the increased or decreased melt viscosity, polyamides can be more easily melt processed using a procedure where the increased or decreased melt viscosity is of some benefit. As used herein, "melt processing" means that the molten polymer is subjected to some treatment or processing in the molten state. Melt processing is well known to those of skill in the polymer processing art, and includes various processes for melt processing polyamides into useful products. For example, such melt processes include extrusion, casting or injection molding of the polyamides into articles such fibers, films, and parts. In these processes, the molten polyamide mixture is placed in the form of the mold to form a molten preform which is then cooled solidifying the molten polyamide to form the desired article.

Melt processing also includes polymer blending in which two or more polymers at least one of which is a polyamide are processed into blends. For example, in these melt processes an amount of water is included in the molten mixture which is sufficient to decrease the difference in melt viscosities of the polyamide and at least one other polymer the mixture. The mixture is then mixed to form a blend of the desired homogenity.

Useful melt processing procedures also include conventional blow molding techniques such as extrusion blow molding, injection blow molding, stretch blow molding, multi-layer blow molding and the like. For example, a single extrusion blow molding procedure can be used in which a parison (a round hollow tube is extruded from the molten polyamide mixture) is entrapped between two halves of a mold. The parison is expanded with a gas such as air or steam against the cavity of the mold to form the parts having the configuration of the mold. The blown part is then cooled, removed from the mold and excess flash is trimmed from the part and reclaimed for further use. In the preferred embodiments of this invention, the molten polyamide having a decreased melt viscosity is used in melt processing processes where melt viscosity of the melt is critical. These include extrusion molding, injection molding and blow molding, more preferably extrusion and injection molding.

SUBSTITUTESHEET Articles formed in the process of this invention can vary widely. For example, the process of this invention is useful in the fabrication of films. Films produced in accordance with this invention may be employed as packaging materials, incorporated in laminates and diffusion barrier, cooking bags, cable insulation and the like.

The process of this invention is also useful in the preparation of mono and multi-filament fibers. Such fibers can be used for conventional purposes as for example as tire cord in pneumatic tires, carpets and the like.

The process of this invention can also be used in the fabrication of molded articles. Examples of such moldings are components for technical equipment, apparatus casting, household equipment, sports equipment, components for the electrical and electronics industries and electrical insulations, car components, circuits, and semi-finished products which can be shaped by machining. The use of the materials for coating articles by means of immersion or powder coating processes is also possible as is their use as hot-melt adhesives.

The process of this invention is also suitable for the production of sheets and panels. The sheets and panels prepared by the process of this invention are suitable as coating materials for other materials comprising, for example, wood, glass, ceramic, metal or other plastics. The sheets and panels can also be laminated with other plastic films which is preferably affected by joint extrusion, the sheets being bonded in the molten state. The surfaces of the sheets and panels, including those in the embossed form, can be improved or finished by conventional methods, as for example, by lacquering or by the application of

T protective films.

The following examples are presented to better illustrate the invention in detail and should not be construed as limitations thereto. EXAMPLE I

A series of experiments were carried out to determine the effect of water concentration on the melt viscosity of nylon 6 resin A. The procedure employed is as follows: 1. Sample Conditioning

Nylon 6 resin A was in pellet (chip) form. The samples, unless otherwise specified, were dried in a vacuum oven (=-0.05mm Hg) for 17 hours at a temperature between 22^*C and 165^*C. In some cases, duplicate samples were simultaneously dried, one for rheology and the other for the following sequence of tests: moisture analysis → solution viscosity → extractables analysis.

2. Melt Viscosity The melt viscosity was measured on an Instron Capillary Rheometer at 260'C. The sample from the vacuum oven was quickly transferred(< 30 sec) to the rheometer pre-set at 260^*C and equilibrated for 10 minutes prior to measurements. The melt viscosity values (i_.^) are reported at a shear rate of 16.4 sec¹ unless otherwise specified. For each nylon 6 resin sample used, the solution viscosity was measured prior to melt rheology and after the melt rheology in order to ensure that no significant changes in molecular weight were occurring during either drying or in the rheometer.

3. Solution Viscosity

The intrinsic viscosity [77] was measured at a concentration of 0.52% of nylon 6 resin in m-cresol at 25*C. The intrinsic viscosity was obtained by

SUBSTITUTESHEET extrapolation from a single concentration using established calibration curves. In one example, the extrapolation to [77] was obtained using three concentrations.

4. Moisture Content

The moisture content was measured with the commercially available, DuPont Moisture Analyzer. The sample from the vacuum oven was quickly sealed and loaded onto the sample holder of the instrument. The moisture given-off at 150°C - 30 min. by the sample was quantitatively analyzed by the instrument. In one example, moisture was also analyzed by the standard Karl-Fisher method.

The results are set forth in the following Table I.

TABLE I

¹ By DuPont Moisture Analyzer.

² From Single Concentration.

Data in Table I for a nylon 6 resin A shows that as the drying temperature increases, the moisture content decreases, and the melt viscosity increases. Neither the caprolactam content nor the total extractables content changed upon drying. Table I shows that the solution intrinsic viscosity [rj] changes slightly from 1.18 to 1.24 when the drying temperature increases from 50 to 140*C. The following relationship (equation 3) predicts that an increase in [ η ] from 1.18 to 1.24 should increase the melt viscosity (-7_m-,.) by about 28%; the actual increase being 51%. This is attributed to the decrease in moisture content.

(1)

soln (3)

EXAMPLE II Using the procedure of EXAMPLE I, the melt viscosity of a nylon 6 resin B was evaluated as a function of drying temperature and moisture content. The results are set forth in the following Table II.

SUBSTITUTESHEET TABLE II

¹ By DuPont Moisture Analyzer

² From Single Concentration

Data in Table II for a nylon 6 resin B clearly demonstrates that the melt viscosity increases with an increase in drying temperature and, thus with decreasing moisture content. In this case, the increase in [17] from 1.34 to 1.39 should increase the melt viscosity by 20%; however, the actual increase is 134% and points out the role of moisture content.

BSTITUTESHEET EXAMPLE III Using the procedure of EXAMPLE I, the relationship between melt viscosity of nylon 6 resin C and moisture content was evaluated. The result as set forth in the following Table III.

TABLE III

By DuPont Mo sture Analyzer ²From Single Concentration

Data shown in Table III for a nylon 6 resin C shows that for an increase in [η ] from 1.65 to 1.68, the corresponding increase in melt viscosity should be 9% while the actual increase is 159%. This is again assigned to the lower moisture content at higher drying temperature.

EXAMPLE IV

Using the procedure of EXAMPLE I, the relationship between melt viscosity of nylon 6 resin D and moisture content was evaluated. The results as set forth in the following Table IV.

SUBSTITUTESHEET TABLE IV

¹ By DuPont Mositure Analyzer

² By Extrapolation of Three Concentrations.

Data shown in Table IV for a nylon 6 resin D suggests that an increase of 218% in melt viscosity is observed while the [η ] does not change. (see also FIG.

1).

EXAMPLE V Using the procedure of EXAMPLE I, the effect of moisture content on the melt viscosity of nylon 6 resin D was evaluated. The results are set forth in the following Table V.

HEET TABLE V

^!By Karl-Fisher Method

EXAMPLE VI Using the procedure of EXAMPLE I, experiments were carried out to determine if the melt viscosity of nylon 6 resin C could be decreased by re-equilibrating with moisture and subsequent drying at a lower temperature. The results are set forth in the following Table VI.

SUBSTITUTESHEET TABLE VI

Experiment Drying History 7-._ 16.4 sec'¹ Pa°S No.

Two samples dried under 1365 identical conditions, i.e., 150°C/17h/Vacuum

One Sample Analyzed for melting 591 viscosity the other sample equilibrated at 50% releative humidity for 24 hours & then dried at 50°/17h/Vacuum. Melt Viscosity subsequently measured

Two samples dried under 1605 identical conditions, i.e. 160°C/17h/Vacuum. One sample analyzed for melt viscosity

The other sample equilibrated 880 at 93% relative humidity for 7 hours and then dried at 50°C/17h/ Vacuum. Melt Viscosity subsequently measured.

Data in Table VI for a nylon 6 resin D reveals an important aspect of this invention i.e. melt viscosity can not only be increased but also decreased by re- equilibrating with moisture and subsequently by drying at a lower temperature.

ITUTE SHEET

Claims

WHAT IS CLAIMED IS:

1. A process of controlling the melt viscosity of a polyamide which comprises forming a molten mixture, comprising a polyamide and an effective amount of water said polyamide having a melt viscosity greater than or less than that of the polyamide in the absence of said amount of water.

2. The process of claim 1 which further comprises the step of melt processing said mixture.

3. A process according to claim 2 wherein said melt processing comprises the steps of: placing said mixture into a mold having a predetermined shape to form a molten preform having the shape of said mold; and cooling said molten preform solidifying said molten mixture to form an article having the shape of said mold.

4. A process according to claim 3 wherein said polyamide is selected from the group consisting of nylon 6 and nylon 6,6.

5. A process according to claim 3 which further comprises introducing a gas into said mold to form a hollow molten mixture preform and cooling said hollow molten mixture preform to form a hollow article having the shape of said mold.

6. A process according to claim 1 wherein the amount of water is from greater than about 0 wt % to about 0.10 wt % based on the total weight of the mixture.

7. A process according to claim 6 wherein said amount is less than about 0.05 wt %.

8. A process according to claim 7 wherein said amount is less than about .01 wt %.

9. A process according to claim 8 wherein said amount is less than about 0.005 wt.

10. A process according to claim 9 wherein said amount is equal to or less than about 0.002 wt %.