WO2016176113A1

WO2016176113A1 - Polyamide composition with improved chemical resistance

Info

Publication number: WO2016176113A1
Application number: PCT/US2016/028737
Authority: WO
Inventors: Vikram Gopal; Mathur SUMIT; Mark Elkovitch
Original assignee: Invista North America S.A.R.L.
Priority date: 2015-04-29
Filing date: 2016-04-22
Publication date: 2016-11-03

Abstract

A heat-conditioned polyamide composition comprising polyhydric alcohol additives that is acid-resistant without adversely affecting mechanical properties of articles molded therefrom is provided.

Description

POLYAMIDE COMPOSITION WITH IMPROVED CHEMICAL RESISTANCE

FIELD OF INVENTION

[0001] The present application relates to a polyamide having improved chemical resistance with the preservation of mechanical properties. More particularly, the present application relates to polyamide compositions comprising a polyhydiic alcohol, which demonstrate excellent acid resistance after heat treatment and without adversely affecting mechanical properties. An acid- resistant polyamide, an article or part therefrom, is particularly suitable for engineering plastics that require chemical compatibility.

BACKGROUND OF THE INVENTION

[0002] The present application relates to polyamides having excellent acid resistance after heat treatment.

[0003] U.S Patent No. 4, 822,373 A discloses fibrous polyamide substrates, such as nylon carpet, having resistance to staining by acid colorants comprising fibrous polyamide substrate having applied thereto (a) a partially sulfonated novolak resin and (b) polymethacryiic acid, copolymers of methacrylic acid, or combinations of said polymethacryiic acid and said copolymers of methacrylic acid.

[0004] U.S Patent No. 3,673,277A relates to articles and coatings made from thermosetting plastics which are manufactured by mixing together polyamides and polycarboxylic acids, followed by heating and forming.

[0005] U.S Patent Application Publication No. 2011/0210050A1 relates to the use of a novolac resin for increasing the acid resistance of a polyamide composition.

[0006] European Patent Specification No. EP0659799B1 discloses a polyamide comprising an aromatic dicarboxylic acid component and an aliphatic diamine component and having far better moldability and having excellent properties. [0007] In many commercial applications where polyamides are used, it is desirable to have high mechanical strength, and also, high chemical resistance, Resistance from corrosive chemicals, such as acids, would be of interest in applications.

[00083 The problem of poor acid resistance of polyamide materials is solved by providing a polyamide composition comprising a polyhydric alcohol, which upon heat treatment significantly improves the acid resistance without adversely affecting the mechanical properties.

SUMMARY OF THE INVENTION

[0009] Accordingly, an object of the present application relates to a heat-conditioned polyamide composition comprising a polyamide resin and a polyhydric alcohol, wherein the polyamide composition is chemically resistant to an acid medium.

[0010] In one aspect of the present application, said polyamide composition comprises from 0.1 to 15 % by weight of polyhydric alcohol, relative to the total weight thereof.

[0011] In one aspect of the present application, said polyamide composition comprises from 0.25 to 10 % by weight of polyhydric alcohol, relative to the total weight thereof.

[0012] In one aspect of the present application, said polyamide composition comprises from 0.5 to 6 % by weight of polyhydric alcohol, relative to the total weight thereof.

[0013] In one aspect of the present application, said polyhydric alcohol is chosen from a group consisting of neo-pentyl polyhydric polyol.

[0014] In one aspect of the present application, said polyhydric alcohol is chosen from a group consisting of neo-pentyl glycol (NPG), trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol (DPE), tripentaeiythritol and tetrapentaerythritol.

[0015] In one aspect of the present application, said polyhydric alcohol is dipentaerythritol.

[0016] In one aspect of the present application, the polyamide resin is chosen from a group consisting of Nylon 6, Nylon 6,6, Nylon 6,6/6, Nylon 6,12, Nylon 4,6, Nylon 6,10, Nylon 7, Nylon 10, Nylon 10, 10, Nylon 12, Nylon 12, 12, Nylon 6T, Nylon 6T/6I, Nylon 6T/DT, Nylon MXD-6 and combinations thereof.

[0017] In one aspect of the present application, the polyamide resin is PA66 or PA6.

[0018] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium.

[0019] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 1 hour.

[0020] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 24 hours.

[0021] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 100 hours.

[0022] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 250 hours.

[0023] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 500 hours.

[0024] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 750 hours.

[0025] In one aspect of the present application, said polyamide composition is preserved in the presence of an acid medium for at least 1000 hours.

[0026] In one aspect of the present application, the acid medium comprises an organic, an inorganic acid, and mixtures thereof.

[0027] In one aspect of the present application, the acid medium comprises an acid chosen from a group consisting of formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, carbonic acid, and mixtures thereof.

[0028] In one aspect of the present application, the acid medium contains formic acid. [0029] In one aspect of the present application, the acid medium contains sulfuric acid.

[0030] In one aspect of the present application, an article of manufacture, at least a portion of which is molded from said polyamide composition.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Polyamides (nylons) find very many applications in today's engineered plastics and thermoplastics. The most common polyamides used in the textile and plastics industries are polycaproamide (PA6) and polyhexamethyleneadipamide (PA66). These crystalline, aliphatic polyamides are widely used in industrial applications mainly due to their high mechanical strength and rigidity. Applications include carpet and textile fibers, films, laminates, articles and molded parts.

[0032] PA66 (or N66) find "under the hood" applications in automotive industry such as radiator end tanks, covers, in-take manifolds, oil pans, and other structural parts such as ball bearing cages, electro-insulating elements, pipes, and various machine parts such as conveyor belts, hoses, etc. Most of these and many other applications require articles and parts to provide high chemical resistance and also high mechanical properties for parts durability. As an example, tubing and pipes, which come in direct contact with the corrosive environment in chemical and petrochemical industries, must be able to withstand corrosiveness, and at the same time, provide sufficient mechanical strength. However, that is not the case at present.

[0033] A common industrial problem with these polyamides is that articles and fibers made from polyamides show poor chemical resistance, especially in a corrosive acid environment. For example, a sample of PA6 dissolves in an acidic medium. The drawback of chemical attack on the polyamide is that it undoubtedly compromises the mechanical strength, further increasing its failure probability. Applications with increased failure probability for articles and parts means inferior performance, increased environmental and safety incidents, lost productivity, higher maintenance costs, and overall, an inefficient system and/or operation. A polyamide composition with improved chemical resistance with uncompromised mechanical properties is an unmet need that is satisfied by the present disclosure. [0034] It has been unexpectedly found that the addition of a polyhydric alcohol to polyamide enhances and improves the chemical resistance after heat treatment. Fiuther, addition of the polyhydric alcohol followed by heat treatment does not adversely affect the mechanical properties of articles and parts molded from the heat-treated polyamide.

[0035] It is possible, for example, to use a polyamide composition comprising from about 0.1 to about 15 % by weight of polyhydric alcohol, relative to the total weight of the composition. In some embodiments, the polyhydric alcohol may be present in an amount from about 0.1 to about 12 % by weight, relative to the total weight of the composition. In other embodiments, the polyhydric alcohol may be present in an amount from about 0.25 to about 10 % by weight, relative to the total weight of the composition. In some other embodiments, the polyhydric alcohol may be present in an amount from about 0.5 to about 8 % by weight, relative to the total weight of the composition. In some embodiments, the polyhydric alcohol may be present in an amount from about 0.5 to about 6 % by weight, relative to the total weight of the composition.

[0036] In some embodiments, a polyamide composition comprising a polyhydric alcohol may contain glass fiber in an amount from about 10 to about 60 % by weight, relative to the total weight of the composition. In other embodiments, a polyamide composition comprising a polyhydric alcohol may contain glass fiber in an amount from about 15 to about 50 % by weight, relative to the total weight of the composition. In some other embodiments, a polyamide composition comprising a polyhydric alcohol may contain glass fiber in an amount from about 20 to about 40 % by weight, relative to the total weight of the composition. A 35 wt% glass fiber filled polyamide composition comprising a polyhydric alcohol may be preferred.

[0037] In an exemplary embodiment of the present application, the polyamide composition further comprises additives such as lubricants, glass fillers, mineral fillers, plasticizers, pigments, dyes, antioxidants, heat stabilizers, hydrolysis stabilizers, nucleating agents, flame retardants, blowing agents and combinations thereof.

[0038] In another embodiment, the mineral fillers are selected from the group consisting of kaolin, clay, talc, and wollastonite, diatominte, titanium dioxide, mica, amorphous silica and combinations thereof. [0039] In another embodiment, the glass fillers are selected from the group consisting of glass fiber, glass flakes, glass beads and combinations thereof.

[0040] In another embodiment, the glass fillers are hydrolysis resistant glass fibers coated with a sizing composition and organosilane coupling agents.

[0041] In another embodiment, the heat stabilizers are selected from the group consisting of hindered phenols, amine antioxidants, hindered amine light stabilizers (HALS), aryl amines, phosphorus based antioxidants, copper heat stabilizers, etc.

[0042] In one exemplary embodiment, the polyamide composition of the present application is formed by adding a polyhydric alcohol and other additives package to a polyamide resin and mixing the polyhydric alcohol, additives and polyamide resin to form an acid-resistant polyamide. Suitable equipment for blending the polyamide resin, polyhydric alcohol and other additives include a twin-screw extruder, melt kneader or batch mixer. The polyamide composition is suitable for compounding or for use as a masterbatch.

[0043] Suitable polyamide resins that may be used in the present application include any known polyamides in the ait. These include aliphatic, semicrystalline, aromatic or semiaromatic nylon resins. The nylon resins are those prepared from starting materials of essentially a lactam or a diamine, and an aliphatic, semiaromatic or aromatic dicarboxylic acid. Suitable lactams include caprolactam and laurolactam. Suitable amines include tetramethylenediamine, hexamethylenediamine (HMD), 2-methylpentamethyIenediamine, undecamethylenediamine, dodecamethylenediamine, 2,4-/2 ,4,4-trimethylhexamethy lenediamine, 5 - methylnonamethylenediamine, metaxylylenediamine (MXD), paraxylylenediamine and 2- Memyl-l,5-pentamemylenediamine (MPMD). Suitable dicarboxylic acids such include adipic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid (DDDA), terephthalic acid (TPA), isophthalic acid (IPA), 2-chloroterephthalic acid, 2-methylterephthalic acid, 5- methylisophthahc acid, 5-sodium-sulfoisophthalic acid, hexahydroterephthalic acid and hexahydroisophthalic acid. In the present application, nylon homopolymers or copolymers to be derived from those starting materials are used either singly or as their mixtures.

[0044] Specific examples of polyamide resins that are suitable for the present application are polycapramide (nylon 6), polyundecanamide (nylon 11), polylauramide (nylon 12), polyhexamethylenadipamide (nylon 66), polytetramethyienadipamide (nylon 46), polyhexamethylenesebacamide (nylon 610), polyhexamethylenedodecamide (nylon 612), polyhexamethyleneterephthalamide/polycapramide copolymer (nylon 6T/6), polyhexamethyleneterephthalamide/polydodecanamide copolymer (nylon 6T/12), polyhexamettylenadipamide/polyhexamethyleneterephthalamide copolymer (nylon 66/6T), polyhexamethylenadipamide/polyhexamethylenisophthalamide copolymer (nylon 66/61), polyhexameiiiylenadlpamide/polyhexamethylenisophthalamide/-polycapramide copolymer (nylon 66/61/6), polyhexamethylenadipamide/polyhexamethyleneterephthalamide

/polyhexamethylenisophthalamide copolymer (nylon 66/6T/6I), polyhexamethyleneterephmdamide/-polyhexamemylenisophtha lamide copolymer (nylon 6T/6I), polyhexamethylenetereplitlialamide/poly(2-methylpent-imethyle ne)terephthalamide copolymer (nylon 6T/M5T), polyhexamethyleneterephthalamideApolyhexametliylenesebacam ide/polycapramide copolymer (nylon 6T/610/6), polyhexamethyleneterephthalamide/polydodecanamide/ -polyhexamethylenadipamide copolymer (nylon 6T/ 12/66), polyhexamethyleneterephtlialamide/polydodecanamide/ polyhexamethylenisophthalamide copolymer (nylon 6T/12/6I), poly m-xylylenadipamide (nylon MXD6), as well as their mixtures and copolymers, etc.

[0045] Especially preferred are nylon resins suitable for the present application are Nylon 6, Nylon 6,6, Nylon 6,6/6, Nylon 6,12, Nylon 4,6, Nylon 6,10, Nylon 7, Nylon 10, Nylon 10, 10, Nylon 12, Nylon 12, 12, Nylon 6T, Nylon 61, Nylon DT, Nylon DI, Nylon MXD-6 and combinations or copolymers thereof. In another exemplary embodiment of the present application the polyamide resin is Nylon 6,6.

[0046] In some embodiments, the polyhydric alcohol used in the present application may include, but are not limited to, a polyalcohol with more than one hydroxyl (-OH) groups that are attached to carbon in a hydrocai'bon chain. In other embodiments, the polyhydric alcohol used in the present application may be chosen from a class of neo-pentyl polyhydric polyols. The neo- pentyl polyhydric polyols may have any suitable number of hydroxyl groups. In one embodiment, the neo-pentyl polyhydric polyol used in the present application may include about 2 or 4 to about 12 or 8 hydroxyl groups. Commercially available polyols of this type are, for example, neo-pentyl glycol (NPG), trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol (DPE), tripentaerytliritol and tetrapentaerythritol. The preferred polyol may be dipentaerythritol (DPE), although other polyols and mixtures thereof may be used.

[0047] In some embodiments, the polyamides of the present disclosure can be used in applications where resistance to low-molecular weight organic and inorganic acids is required. In other embodiments, the polyamides of the present disclosure may be preserved in the presence of an acid. In one embodiment, the acid may be low-molecular weight, short-chain, linear acid. In another embodiment, the acid may be from a class of common industrial acids, such as but not limited to, formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, carbonic acid, etc.

[0048] In one embodiment, a heat-treated (hot air aging at 210°C) polyamide sample of the present disclosure did not dissolve even after it has been fully immersed in formic acid at room temperature for extended time.

[0049] Articles and parts, having the desired shape and form, may be produced by applying conventional molding and forming techniques to the polyamides and polyamide compositions of the present disclosure. These techniques may include injection molding, blow molding, molding by extrusion, vacuum or compression forming and like. Therefore, the molded articles or parts meeting the design specification could be used as engineered thermoplastic pieces in installations and assemblies. Fuither, films, laminates and fibers could also be formed and suitably used in the field of industrial materials and household goods.

[0050] In some embodiments, the polyamide composition of the present disclosure may comprise one or more other polymers, preferably thermoplastic polymers such as polyamide, polyester, poly olefin, or ABS.

[0051] In some embodiments, the composition according to the present disclosure may comprise functional additives that are typically employed during the manufacture. Examples of functional additives include, but not limited to, lubricants, chain extenders, antifoam agents, flame retardants, plasticizers, nucleants, modifiers, colorants, catalysts, light and/or heat stabilizers, antioxidants, antistatic agents, dyes, pigments, matting agents, molding aids and other conventional additives. [0052] In some embodiments, fillers and additives may be added to the polyamide via conventional means suitable for each additive. These may be added either, before, during or after the polymerization process.

[0053] In some embodiments, the polyamide composition of the present application may be heat-conditioned via conventional means, such as but not limited to, conventional oven, vacuum oven, corona treatment, flame treatment, ultrasound methods, electron-beaming, radiation methods, and other industrial methods. In other embodiments, the polyamide composition of the present application may be heat-conditioned by surrounding the polyamide composition with an environment of hot, fluid medium at desired temperature and for set time period. Any fluidic medium may be used so long as it is inert to the polyamide composition.

TEST AND ANALYTICAL METHODS

[0054] The following test methods are used for the polyamide property determinations:

ISO 527 determination of tensile strength, tensile modulus, and elongation at break,

IS O 188 Method of heat aging used for test samples

[0055] Test sample bars (e.g.: dogbones) are molded using conventional methods and from individual polyamide compositions prepared in each example.

EXAMPLES

[0056] A commercially available feedstock of PA6 is compounded with commercially available glass-fiber and used in the below examples.

[0057] An INVISTA product, TORZEN^® U4800 NCOl, is used as a PA66 base resin. The natural PA66 resin is suitable for compounding, injection molding, and extrusion applications. A technical datasheet is available at the website - http://ep.invista.com/en/index.html.

[0058] The polyhydric alcohol, dipentaerythiitol or "DPE" (CioH₂₂0₇; Chemical Abstracts Registry Number CAS No. 126-58-9), as used herein, is purchased from Perstorp Holding AB (Sweden). The DPE product data sheet for Charmor™ DP40 is available at the Perstorp company website - https://www.perstorp.conVen/products/charmor dp40. Charmor™ DP40 has a sales specification of minimum 90% di-pentaerythritol content.

[0059] The formic acid, as used herein, is obtained from EMD Chemicals. A typical composition of the formic acid is 90 % by weight

[0060] The sulfuric acid, as used herein, is obtained from Sigma Aldrich. A typical composition of the sulfuric acid is 95-98 % by weight.

Example 1 (comparative)

[0061] A test sample of conventionally heat-stabilized, 35% glass-filled PA66 base resin is heat- conditioned in the presence of air using an oven set temperature 210 °C for 500 hrs and immersed in formic acid. The test sample dissolved completely overnight showing no acid resistance.

Example 2

[0062] A test sample of conventionally heat-stabilized 35% glass-filled PA66, comprising a polyhydric alcohol (dipentaerythritol or DPE) in the amount 2 wt% of the total weight of the composition, is heat-conditioned in the presence of air using an oven set temperature 210 °C for 500 hrs and immersed in formic acid. The test sample did not dissolve overnight showing improved acid resistance.

Example 3

[0063] A test sample of 35% glass-filled PA6 resin, comprising a polyhydric alcohol (dipentaerythritol or DPE) in the amount 2 wt% of the total weight of the composition, is heat- conditioned in the presence of air using an oven set temperature 210 °C for 500 hrs and immersed in formic acid. The test sample soaked up some free acid and did not dissolve overnight showing improved acid resistance.

Examples 4-S

[0064] Individual test samples of conventionally heat-stabilized, 35% glass-filled PA66 base resin, are heat-conditioned as in Example 1. A control sample of the same is not heat- conditioned and used as is. The samples are exposed to a 1:5 (w:w) sulfuric acid: water medium at room temperature. The mechanical strength of the test sample is measured at 25 Oh, 500h, 750h and lOOOh along with the starting unexposed test sample. Table 1 below gives the mechanical strength data for the test samples of these examples.

TABLE 1

Examples 6-8

[0065] Individual test samples of conventionally heat-stabilized 35% glass-filled PA66, comprising a polyhydric alcohol (dipentaerythritol or DPE) in the amount 2 wt% of the total weight of the composition are heat-conditioned in the presence of air using an oven set temperature 210 °C for 500 hrs. A control sample of the same is not heat-conditioned and used as is. The samples are exposed to a 1:5 (w:w) sulfuric acid:water medium at room temperature. Also, individual test samples of 35% glass-filled PA6 resin, comprising a polyhydric alcohol (dipentaerythritol or DPE) in the amount 2 wt% of the total weight of the composition are heat conditioned in the presence of air using an oven set temperature 210 °C for 500 hrs and exposed to the 1:5 (wrw) sulfuric acid:water medium at room temperature. The mechanical strengths of these test samples are measured at 250h, 500h, 75 Oh and lOOOh along with the unexposed test samples. [0066] Table 2 represents the mechanical strength comparison for not heat-conditioned and heat- conditioned PA66 test samples along with the data for each of the starting unexposed sample.

TABLE 2

[0067] Table 3 represents the mechanical strength comparison for not heat-conditioned and heat- conditioned 35% glass-filled PA6 + DPE test samples versus the Example 6 (Control) test samples. Table 3 also provides the mechanical strength data for each of the unexposed samples.

[0068] For the heat-conditioned test samples of Example 8 that are acid-exposed for 1000 hrs, the % Retentions of Tensile Strength at break, Elongation at break and Tensile Modulus show improvements over those of the Example 6 (Control) samples.

TABLE 3

[0069] In addition, the present application provides articles of manufacture, at least a portion of which is molded from a polyamide composition comprising a polyamide resin and a polyhydric alcohol in accordance with the present application.

[0070] The present application is illustrated by the above examples. It is to be understood that the examples are for illustration purposes only and are not used to limit the present application thereto.

Claims

What is Claimed is:

1. A polyamide composition comprising a polyaraide resin and a polyhydric alcohol, said polyamide composition being heat- conditioned and chemically resistant to an acid medium.

2. The polyamide composition of claim 1 wherein the polyamide composition is heat-conditioned by a means selected from the group consisting of a conventional oven, vacuum oven, corona treatment, flame treatment, ultrasound method, electron- beaming, radiation method and industrial method.

3. The polyamide composition of claim 1 wherein the polyamide composition is heat-conditioned by surrounding the polyamide composition with an environment of hot, fluid medium at a selected temperature and for a selected time period.

4. The polyamide composition of claim 1 wherein the polyamide composition is heat-conditioned in the presence of air using an oven set temperature 210 ^*C for 500 hours.

5. The polyamide composition of any of the preceding claims comprising from 0.1 to 15 % by weight of polyhydric alcohol, relative to the total weight thereof.

6. The polyamide composition of any of claims 1, 2, 3 or 4 comprising from 0.25 to 10 % by weight of polyhydric alcohol, relative to the total weight thereof.

7. The polyamide composition of any of claims 1, 2, 3 or 4 comprising from 0.5 to 6 % by weight of polyhydric alcohol, relative to the total weight thereof.

8. The polyamide composition of any of the preceding claims wherein the polyhydric alcohol comprises a neo-pentyl polyhydric polyol.

9. The polyamide composition of any of claims 1, 2, 3, 4, 5, 6, or 7 wherein the polyhydric alcohol is selected from the group consisting of neo-pentyl glycol, trimethylolpropane, trimethyloethane, pentaerythritol, dipentaerythritol,

tripentaerythritol and tetrapentaerythritol .

10. The polyamide composition of any of claims 1, 2, 3, 4, 5, 6, or 7 wherein the polyhydric alcohol is dipentaerythritol.

11. The polyamide composition of any of the preceding claims wherein the polyamide resin is selected from the group consisting of: nylon 6; nylon 6,6; nylon 6,6/6; nylon 6,12;

nylon 4,6; nylon 6,10; nylon 7; nylon 10; nylon 10,10; nylon 12; nylon 12,12; nylon 6T; nylon 6T/6I; nylon 6T/DT; and nylon MXD-6 and combinations thereof.

12. The polyamide composition of claim 11 wherein the polyamide resin is nylon 6 or nylon 6,6 or a combination

thereof.

13. The polyamide composition of any of the preceding claims which is chemically resistant to an acid medium for at least one hour up to at least 1000 hours.

14. The polyamide composition of claim 13 wherein the acid medium comprises an organic acid, an inorganic acid, or a mixture thereof.

15. The polyamide composition of claim 13 wherein the acid medium is selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid and carbonic acid and mixtures thereof.

16. An article of manufacture comprising at least a portion molded from the polyamide composition of any of the preceding claims .

17. A method for increasing chemical resistance of a polyamide composition to an acid medium, said method comprising heat-conditioning a polyamide composition comprising a polyamide resin and a polyhydric alcohol.

18. The method of claim 17 wherein the polyamide

composition is heat-conditioned by a means selected from the group consisting of a conventional oven, vacuum oven, corona treatment, flame treatment, ultrasound method, electron-beaming, radiation method and industrial method.

19. The method of claim 17 wherein the polyamide

composition is heat-conditioned by surrounding the polyamide composition with an environment of hot, fluid medium at a selected temperature and for a selected time period.

20. The method of claim 17 wherein the polyamide

composition is heat-conditioned in the presence of air using an oven set temperature 210 ^*C for 500 hours.

21. The method of claims 17, 18, 19 or 20 wherein the polyamide composition comprises from 0.1 to 15 % by weight of polyhydric alcohol, relative to the total weight thereof.

22. The method of claims 17, 18, 19 or 20 wherein the polyamide composition comprises from 0.25 to 10 % by weight of polyhydric alcohol, relative to the total weight thereof.

23. The method of claims 17, 18, 19 or 20 wherein the polyamide composition comprises from 0.5 to 6 % by weight of polyhydric alcohol, relative to the total weight thereof.

24. The method of any of claims 17, 18, 19, 20, 21, 22 or 23 wherein the polyhydric alcohol comprises a neo-pentyl

polyhydric polyol.

25. The method of any of claims 17, 18, 19, 20, 21, 22 or 23 wherein the polyhydric alcohol is selected from the group consisting of neo-pentyl glycol, trimethylolpropane,

trimethyloethane, pentaerythritol, dipentaerythritol,

tripentaerythritol and tetrapentaerythritol.

26. The method of any of claims 17, 18, 19, 20, 21, 22 or 23 wherein the polyhydric alcohol is dipentaerythritol.

27. The method of any of claim 17, 18, 19, 20, 21, 22, 23, 24, 25 or 26 wherein the polyamide resin is selected from the group consisting of: nylon 6; nylon 6,6; nylon 6,6/6; nylon 6,12; nylon 4,6; nylon 6,10; nylon 7; nylon 10; nylon 10,10; nylon 12; nylon 12,12; nylon 6T; nylon 6T/6I; nylon 6T/DT; and nylon MXD-6 and combinations thereof.

28. The method of claim 27 wherein the polyamide resin is nylon.6 or nylon 6,6 or a combination thereof.

29. The method of claims 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27 or 28 wherein the polyamide composition is chemically resistant to an acid medium for at least one hour up to at least 1000 hours.

30. The method of claim 29 wherein polyamide composition is chemically resistant to an acid medium comprising an organic acid, an inorganic acid, or a mixture thereof.

31. The method of claim 29 wherein polyamide composition is chemically resistant to an acid medium selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid and carbonic acid and mixtures thereof.