MXPA99001694A - Process for improving the flavor retaining property of polyester/polyamide blend containers for ozonated water - Google Patents

Abstract

The present invention relates to a process for minimizing the formation of undesirable byproducts in ozonated liquids comprising the steps of providing a container comprising a polyester comprising repeat units from a dicarboxylic acid component comprising at least about 85 mole percent terephthalic acid, 2,6-naphthalenedicarboxylic acid or a mixture thereof and at least about 85 mole percent ethylene glycol, and from about - to about - weight%of at least one polyamide which displays a melting point below that of said polyester, and filling said container with an ozonated liquid.

Description

PROCESS TO IMPROVE THE FLAVOR RETENTION PROPERTIES OF POLYESTER / POLYAMIDE MIXTURE CONTAINERS FOR OZONIZED WATER Field of the Invention The market for polyester containers for carbonated and even mineral waters, as well as for other liquid products, requires exceptionally low levels of acetaldehyde (AA) and / or other flavor-affecting compounds, which may contribute to flavors. undesirable. Ozonation through treatments with free ozone, which is frequently used to purify such liquid products, especially water, can result in the formation of these compounds that affect flavor, as byproducts of the ozonation process. The present invention relates to containers capable of preventing the generation of AA or other flavorings that result as a by-product from the ozonation processes.

BACKGROUND OF THE INVENTION AA is an inherent by-product that is generated during the molten phase of polymerization and the subsequent processing of PET and other polyesters on their way to useful articles such as containers. Some residual AA may remain in the finished items. The amount of the residual AA level depends in part on the conditions used in the process. For example, poly (ethylene terephthalate) (PET) resin prepared using dimethyl terephthalate (DMT) typically leads to 9-10 ppm of AA in bottle walls, however, PET resins based on terephthalic acid (PTA) lead to much lower AA levels in the walls of the bottles, that is, 5-6 ppm. Despite significant improvements in PTA-based resins, this level of AA is still perceived as too high. In effect, taste tests with customers have indicated that consumers can detect differences in AA of approximately 20 ppb. As a result, there has been a significant interest from customers in reducing the residual AA content as much as possible. Because some water can contain several contaminants, disinfection before bottling is desirable. Chlorination and ozonation are two common methods to disinfect water from springs. The ozonation process leaves residual ozone in the water that is subsequently bottled. Ozonated water that is stored in conventional PET containers may acquire an undesirable taste due to the presence of various flavorings such as acetaldehyde and / or other compounds, some of which may be the byproduct of the ozonation process. Therefore, it is highly desirable to provide containers for use with ozonated water that have acceptable flavor retention and clarity properties. The U.S. Patent No. 5,258,233 discloses the use of a mixture of a low molecular weight polyamide with PET to reduce acetaldehyde. In this patent, it is established that less than 2% polyamide should be used to reduce color and haze. In a symmetrical form, the US Pat. No. 5,266,233 discloses the use of a mixture of low molecular weight polyamide with PET copolyethers to reduce the acetaldehyde content. The U.S. Patent No. 5,340,884 describes the technique of mixing the polyamide with polyesters to create a concentrate that can be diluted with a polyester and still produce the desired properties. Jammes et al describes the formation and behavior of some keto acids and aldehydes in water treatment processes for drinking, which include an ozonation stage (Rev. Sci. Eau (1995), 8 (3), 333-54). . Specific disinfection byproducts can also induce immediate deterioration of water quality due to objectionable organoleptic properties. Anderson et al described in Can. Proc. Water Qual. Technol. Conf. (1994), Pt. 1, 871-908 the formation of ozone byproducts in three different types of surface water. The by-products of ozonation that were examined in this study included acetaldehyde, propanol, butanol, pentanol, hexanol, heptanol, octanol, benzaldehyde, glyoxal and methyl glyoxal, oxalic acid, pyruvic acid, oxalacetic acid and similar organic compounds. The U.S. Patent No. 5,362,784 discloses polyalkylene imine (PAI) compositions. Particularly polyethylene imine and polyester polymers, including copolymers and derivatives thereof, such compositions can be used in the production of films and devices that are capable of cleaning undesirable aldehydes. However, there is no description regarding the use of ozonated water in containers made from resin mixtures. J. Poly. Sci .: Part A Polymer Chemistry, 34, 3573 (1996) describes the use of N-dialkyl amides, particularly dimethyl acetamide as ozone killing cleaners, in the preparation of functional polystyrene. The publication does not disclose the use of polyamides either separately or in combination with polyesters.

In addition, there is no indication that dialkyl amides improve the taste of ozonated water packaged in polyester containers. JP 92-317959 921 104 describes the use of ozone to disinfect water, a typical process of interest known in the industry. The patent does not disclose the use of polyamides as a method to improve the taste of ozonated water. J. Dairy Sci. (1994), 74 (1), 96-9 describes the described effects of ozone on the taste of water packed in poly (ethylene) containers. The "desaborization" generated during ozonation could be controlled by treating the containers with butylated hydrotoluene (BHT, 185 ppm). The publication does not describe the "desaborización" in containers of polyester, nor the use of polyamides to improve the flavor of the water.

Detailed Description of the Invention The present invention relates to a process for reducing the formation of undesirable by-products in ozonized liquids, which comprises the steps of: Provide a container comprising a polyester comprising repeating units of a dicarboxylic acid component comprising at least about 85 mole percent terephthalic acid, 2,6-naphthalendicarboxylic acid or a mixture thereof and at least about 85 mole percent of ethylene glycol; and from about 0.05 to about 2% by weight of at least one polyamide that displays a melting point below said polyester, and filling said container with an ozonated liquid. We have surprisingly discovered that the presence of certain additives in polyester-based beverage containers reduces the "de-blistering" that is imparted to a liquid such as water by a disinfection process such as ozonation.

Polyesters The polyester, component, of the present invention is a polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) resin. Copolyesters and mixtures of PET and PEN can also be used. The polyethylene terephthalate resin contains repeating units of at least 85 percent mol dß terephthalic acid and at least 85 mol percent of ethylene glycol, while the PEN resin contains repeating units of at least 85 mol percent of acid 2,6- naphthalenedicarboxylic acid and at least 85% ethylene glycol, based on 100 mol percent dicarboxylic acid and 100 mol percent diol. The dicarboxylic acid component of the polyester can be optionally modified with up to about 15 mole percent of one or more other dicarboxylic acids other than terephthalic acid or suitable synthetic equivalents such as dimethyl terephthalate. Said additional dicarboxylic acids include aromatic dicarboxylic acids preferably having from 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having from 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having from 8 to 12 carbon atoms. Examples of dicarboxylic acids to be included with the terephthalic acid are phthalic acid, isophthalic acid, naphthalenedicarboxylic acid (including, but not limited to the 2,6- isomer), cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid , succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. Examples of dicarboxylic acids to be included with naphthalene-2,6-dicarboxylic acid are phthalic acid, terephthalic acid, isophthalic acid, other isomers of naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-acid dicarboxylic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, and the like. The polyesters can be prepared from two or more of the above dicarboxylic acids. It should be understood that the use of the corresponding acid anhydrides, esters and acid chlorides of these acids is included in the term "dicarboxylic acid." further, the polyester component may optionally be modified with up to about 15 mole percent of one or more other diols other than ethylene glycol. Said additional diols include cycloaliphatic diols preferably having from 6 to 20 carbon atoms or aliphatic diols preferably having from 3 to 20 carbon atoms. Examples of such diols included with ethylene glycol are diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,2-diol, pentane-1,5-diol, hexane-1,6-diol. , 3-Methylpentanediol- (2,4), 2-methylpentanediol- (1, 4), 2,2,4-trimethylpentane-diol- (1,3), 2-ethylhexanediol- (1,3), 2,2 -diethylpro-ano-diol- (1,3), hexanediol- (1, 3), 1,4-di- (hydroxyethoxy) -benzene, 2,2-bis- (4-hydroxy-cyclohexyl) -propane, , 4-dihydroxy-1,1, 3,3-tetramethylcyclobutane, 2,2-bis- (3-hydroxyethoxyphenyl) -propane, and 2,2-bis- (4-hydroxypropoxyphenyl) -propane. The polyesters can be prepared from two or more of the above diols. The polyethylene terephthalate resin may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylolpropane, pyromellitic dianhydride, pentatritritol, and other polyesters or polyester polyols that are generally known in the art. Preferably said PET polyesters comprise at least about 90 mol% of terephthalic acid or dimethyl terephthalate and about 90 mol% of ethylene glycol residues.

The polyethylene terephthalate-based polyesters of the present invention can be prepared by conventional polycondensation procedures quite well known in the art. Such processes include direct condensation of the dicarboxylic acid (s) with the diol (s) or by ester exchange using a dialkyl dicarboxylate. For example, a dialkyl terephthalate such as dimethyl terephthalate is subjected to an exchange of ester with the diol (s) at elevated temperatures in the presence of a catalyst. The polyesters can also be subjected to solid state polymerization methods. The PEN polyesters can also be prepared by well-known polycondensation processes. Many other ingredients can be added to the compositions of the present invention to improve the performance properties of polyesters. For example, crystallization aids, impact modifiers, surface lubricants, anti-caking agents, stabilizers, antioxidants, ultraviolet light absorbing agents, metal deactivators, colorants, nucleating agents, fillers and the like can be added. All of these additives and many others, as well as their uses are well known in the art and do not require extensive explanation. Therefore, reference will be made only to a limited number, it being understood that any of these compounds can be used as long as they do not prevent the present invention from achieving its objectives.

Ozone Cleansing Compounds Applicants have surprisingly found that a number of compounds known to reduce residual AA in polyesters also act as ozone scavengers when incorporated into containers for ozonized substances. Suitable ozone scavenging compounds include high molecular weight polyamides such as those described in U.S. Pat. No. 4,837,115; polyamides, polyalkylene phenylene ester and polyalkylene phenylene ethers thereof such as those described in U.S. Pat. No. 4,052,481; Polyalkylene mines, particularly polyethylene mines such as those described in U.S. Pat. No. 5,362,784; and low molecular weight polyamides such as those described in U.S. Pat. No. 5,340,884. Compounds having superior ozone cleaning capabilities and which are compatible with polyesters are preferred. Suitable ozone cleaning compounds have a melting point below the melting point of polyester (PEN, PET or mixtures thereof). Preferably said ozone cleaner compound is a polyamide and more preferably is a polyamide selected from the group consisting of partially aromatic, low molecular weight polyamides having an average molecular weight of less than 15,000, low molecular weight aliphatic polyamides having an average molecular weight of less than 7,000 and fully aromatic polyamides. Combinations of such polamides are also included within the scope of the invention. By "partially aromatic polyamide" is meant that the amide bond of the partially aromatic polyamide contains at least one aromatic ring and one non-aromatic species. The partially aromatic polyamides have an I.V. of less than about 0.8 dLJg. Preferably the I.V. of the partially aromatic polyamides is less than about 0.7 dLJg and the average molecular weight is less than about 12,000. The aliphatic polyamides have an I.V. of less than about 1.1 dL / g. Preferably I.V. of other aliphatic polyamides is less than about 0.8 dL / g and the average molecular weight is less than about 6,000. Fully aromatic polyamides comprise at least 70 mol% of m-xylylene diamine-derived structural units or a mixture of xylylene diamine comprising m-xylylene and up to 30% p-xylylene diamine and an acid in the molecule chain. ae-aliphatic dicarboxylic having 6 to 10 carbon atoms, which is further described in Japanese Patent Publications Nos. 1156/75, 5751/75, 5735/75 and 10196/75 and the Open Description of Patent Application of Japan Patent No. 29697/75. Preferably the ozone cleaners of the present invention are selected from the low molecular weight polyamides described in US Pat. No. 5,340,884. Low molecular weight polyamides formed from isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, meta- or paraxylylene diamine, 1,3- or 1,4-cyclohexane (bis) m.thylamine, aliphatic diacids with from 6 to 12 can also be used. carbon atoms, aliphatic amino acids or lactams with 6 to 12 carbon atoms, aliphatic diamines with 4 to 12 carbon atoms, and other polyamide forming acids and diamines which are generally known. The low molecular weight polyamides may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, pyromellitic dianhydride, or other polyamides and polyamide-forming polyamines that are known in the art. Partially aromatic, low molecular weight polyamides, which are preferred include: poly (m-xylylene adipamide), poly (hexamethylene isophthalamide), poly (hexamethylene adi amide-co-isophthalamide), poly (hexamethylene adipamide- co-teraphthalamide), and poly (hexamethylene isophthalamide-co-terephthalamide). The partially aromatic, low molecular weight polyamide most preferred is poly (m-xylylene adipamide) with an average molecular weight of about 4,000 to about 7,000 and an inherent viscosity of about 0.3 to about 0.6 dL / g. Preferred low molecular weight aliphatic polyamides include poly (hexamethylene adipamide) and poly (caprolactam). The most preferred low molecular weight aliphatic polyamide is poly (hexamethylene adipamide) with an average molecular weight of about 3,000 to about 6,000 and an inherent viscosity of 0.4 to 0.9 dL / g. Partially aromatic, low molecular weight polyamides are preferred over aliphatic polyamides wherein clarity and dispersibility are crucial. Low molecular weight aliphatic polyamides include polycapramide (nylon 6), poly-α-aminoheptanoic acid (nylon 7), poly-α-aminonanoic acid (nylon 9), polyundßkane-amide (nylon 1 1), polyaurillactam (nylon '12 ), polyethylene-adipamide (nylon 2,6), polytetramethylene-adipamide (nylon 4,6), polyhexamethylene-adipamide (nylon 6,6), polyhexamethylene-sebacamide (nylon 6,10), polyhexamethyl-dodecamide (nylon 6,12) ), polyoctamethylene adipamide (nylon 8.6), polydecamethylene adipamide (nylon 10.6), polidodecamethylene adipamide (nylon 12.6) and polidodecamstylene sebacamide (nylon 12.8). The low molecular weight polyamides are generally prepared by melt phase polymerization from a diacid diamine complex which can be prepared either in situ or in a separate step. In any method, diacid and diamine are used as starting materials. Alternatively, an ester form of the diacid may be used, preferably the dimethyl ester. If the ester is used, the reaction should be carried out at a relatively low temperature, generally 80 to 120 ° C, until the ester is converted to an amide. The mixture is then heated to the polymerization temperature. In the case of polycaprolactam, either caprolactam or 6-aminocaproic acid can be used as the starting material and the polymerization can be catalyzed by the addition of adipic acid / hexamethylene diamine salt resulting in a copolymer of nylon 6/66. When the diacid diamine complex is used, the mixture is heated to melting and stirred until equilibrium. The molecular weight is controlled by the diacid diamine ratio. An excess of diamine produces a higher concentration of terminal amino groups. If the diacid-diamine complex is prepared in a separate step, an excess of diamine is added before polymerization. The polymerization can be carried out either at atmospheric pressure or at high pressures. The composition or articles of the present invention may contain up to about two percent by weight of the low molecular weight polyamides, preferably between about 0.05 to about 2% by weight of the polyester and more preferably less than about one percent by weight. It has been determined that the use of polyamides at more than two weight percent based on the weight of the polyester causes undesirable levels of haze.

Ozone cleaners can be added directly to the polyester or they can be added through the use of a concentrate. The process of preparing blends of polyester / polyamide blends of the present invention involves the preparation of the low molecular weight polyester and polyamide, respectively, by processes such as those mentioned above. The polyester and polyamide are dried in an atmosphere of dry air or dry nitrogen, or under reduced pressure. The polyester and the polyamide are mixed and subsequently intermixed in molten form, for example, in a single screw or twin screw extruder. The melting temperatures should be at least as high as the melting point of the polyester and are typically in the range of 260-310 ° C. Preferably, the melt temperature in the molten phase is kept as low as possible within said range. After completion of the melt phase intermixing, the extrudate is obtained in the form of a filament, and recovered according to the usual manner such as by cutting. In substitution of the melt-phase intermixing, the polyester and polyamide can be either dry-mixed and hot-molded or formed directly into plastic articles. The polyamide can be added in the manufacturing stages of the polyester. For example, the polyamide can be mixed with the molten polyester while it is removed from the polycondensation reactor, before its granulation. This method, however, is not desirable if the polyester / polyamide blend will be subjected to polymerization in the solid state since undesirable color and / or haze can develop over extended periods of time at elevated temperatures. The ozone cleaning compound can be added directly to the polyester or as a concentrate. Where the ozone cleaner compound is added as a concentrate, the ozone cleaner compound is added to a carrier resin which may be, for example, polycarbonate, polyester copolymer, polyolefin and the like. Generally the concentrate comprises from about 1 to about 99% by weight of a carrier resin comprising a dicarboxylic acid component comprising repeating units of at least about 60 mole percent of aromatic dicarboxylic acid selected from the group consisting of terephthalic acid, naphthalenedicarboxylic acid and mixtures of these, and a diol component comprising repeating units of at least about 50 mole percent of ethylene glycol, based on 100 mole percent dicarboxylic acid and 100 mole percent diol and about 1 to about 99% by weight of a polyamide described above. More preferably the carrier resin is about 20 to about 99 and more preferably about 50 to about 99 weight percent. Generally between about 1 and about 20 weight percent of the concentrate is added to the base resin. More preferably about 1 to about 10 weight percent of the concentrate is added. It should be understood that the base resin may contain small amounts of the ester form of the acid component, as long as the total amount of the ester form of the polyester / polyamide mixture does not exceed about 20% by weight, and preferably not more than about 10% by weight. % in weigh. It should also be understood that the polyamide resin could be added directly to the polymerization melt in a single step, as opposed to the addition of subsequent processing steps.

Ozonation Process Ozonation is used for the purpose of disinfecting a liquid such as water that has been released from its large impurities to improve its odor and taste, and to remove dissolved organic matter by means of oxidation and micro-flocculation. The residual ozone in the disinfected water varies from 0.1 ppm to 30 ppm of ozone, and generally decays in a very short period of time due to its inherent instability (high reactivity) of the ozone molecule. ((The FirstInternational Symposium on Ozone for Water and Wastewater Tratmßnt, Vol. 1, Dßc. 2-5, 1973. The International Ozone Institute, Inc. Rice & Browning).

EXAMPLES Example 1 - 9921 W Eastpak® PET (Eastman Chemical Company, I.V. = 0.80) was dried for 6 hours at 150 ° F in a Patterson dryer. The polyamide base additive (25% by weight of polyhexamethylene adipamide (0.43 IV) prepared as described in Example 1 of US Patent No. 5,258,233 mixed in PET 9921 W Eastpak® in a ratio of 25: 75% by weight) was dried at 65 ° C for 8 hours. 100 parts of Eastpak 9921 W Eastpak resin were mixed with 1 part of polyamide base additive, so that a homogeneous mixture of "salt and pepper" granules was obtained. The mixed granules were fed to the extruder of a "HUSKY" injection molding machine and the preforms were injection molded using an 8-cavity mold of 54 g. All the preforms for this study were selected from the same cavity in the mold. A temperature of 277 ° C was maintained for injection molding and a total cycle time of 27.44 seconds. The preforms were blown to form two liter bottles using a SIDEL SB02-3 RBM machine. The bottles were covered immediately. The bottles were filled with ozonated water containing 0.4 ppm of ozone and stored at 20 ° C. The AA was measured using a GC analysis as follows. A gas chromatographic method of head space gas in equilibrium (static) (EHS-GC) was used to determine the parts per billion (ppb) of AA levels in water. 5 gm of a water sample was placed in a sealed headspace flask in the presence of 2 gm of sodium chloride and heated at 80 ° C for 90 minutes using an automatic headspace sampler. A portion of the headspace gas was injected onto a GC megabore GC-Q capillary column (J &W Scientific). The concentration of AA was then determined by a flame ionization detector (FID). An HP GC model 5890A was used. The acetaldehyde (AA) in the water was 3 ppb after 60 days of storage.

This is a truly low level of AA and is acceptable for bottled water without AA flavor problems.

Example 2 (Control) - In this example, PET 9921 W Eastpak resin bottles were made without polyamide additive and in glass. The processing conditions for the PET control were the same as for Example 1. A bottle of the same size and geometry was also made of glass. These bottles were filled with ozonated water containing 0.4 ppm of ozone and stored as in Example 1. After 60 days of storage, the AA level in the water stored in PET was 14 ppb and the AA level in the stored water. in glass it was less than 3 ppb. The AA values are summarized from Table 1 below.

Example 3 - Bottles made as in Examples 1 and 2 were filled with ozonated water (0.4 ppm ozone) and stored at 55 ° C for 8 days. The acetaldehyde (AA) levels in the water are shown in Table 1 below.

Table 1 AA (ppb) AA (ppb) Bottle Type 60 days @ 80 days @ Taste 20 ° C. 55 ° C PET 14 Undesirable PET + additive < 3 3 None Glass < 3 < 3 None Measured levels of AA in containers with ozone scavenging compound at both ambient and elevated temperatures are dramatically (5 times) lower than those in unmodified PET. The AA level is surprisingly low, given the high storage temperatures.

Example 4 - The above examples were repeated using water without ozonation. In both storage conditions the measured AA levels were less than 3 ppm in all three containers (glass, PET and PET with additive). Therefore, because the AA is not generated in any of the glass containers or in any of the containers filled with water without ozonation, it is clear that the source of AA is an undesirable reaction between unmodified PET and ozone. This is totally. Therefore, prior to the recognition of the reaction between ozonated liquids and polyester containers, it was totally unexpected that conventional AA additives would block the undesirable reaction between ozone and PET. Clearly the presence of ozone is in some way responsible for the generation of AA in the water.

Claims (13)

1. Novelty of the Invention 1. A process for reducing the formation of undesirable by-products in ozonized liquids, which comprises the steps of: providing a container comprising a polyester comprising repeating units of a dicarboxylic acid component comprising at least about 85 mol percent of terephthalic acid, 2,6-naphthalenedicarboxylic acid or a mixture thereof and at least about 85 mole percent of ethylene glycol; and from about 0.05 to about 2% by weight of at least one polyamide having a melting point below said polyester, and filling said container with an ozonated liquid.
2. 2. The process of claim 1, wherein the dicarboxylic acid component further comprises up to about 15 mole percent of at least one second dicarboxylic acid selected from the group consisting of aromatic dicarboxylic acids having from 8 to 14 carbon atoms, aliphatic dicarboxylic acids having from 4 to 12 carbon atoms, cycloaliphatic dicarboxylic acids having from 8 to 12 carbon atoms, and mixtures thereof.
3. 3. The process of claim 2, wherein said second dicarboxylic acid is selected from the group consisting of phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, succinic acid, glutaric acid, Adipic acid, azelaic acid, sebacic acid, and mixtures thereof.
4. 4. The process of claim 1, wherein said polyester further comprises up to about 15 mole percent of at least one additional diol.
5. 5. The process of claim 4, wherein said additional diol is selected from the group consisting of cycloaliphatic diols having from 6 to 20 carbon atoms and aliphatic diols having from 3 to 20 carbon atoms.
6. 6. The process of claim 5, wherein said additional diol is selected from the group consisting of diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,2-diol, pentane-1, 5- diol, hexane-1,6-diol, 3-methyl pentanediol- (2,4), 2-methylpentanediol- (1, 4), 2,2,4-trimethylpentane-diol- (1, 3), 2-methylhexanediol- (1, 3), 2,2-di-ethylpropane-diol- (1, 3), hexanediol- (1, 3), 1,4-di- (hydroxyethoxy) -benzene, 2,2-bis- (4-hydroxy) -cyclohexyl) -propane, 2,4-dihydroxy-1,1, 3,3-tetramethylcyclobutane, 2,2-bis- (3-hydroxyethoxyphenyl) -propane, 2,2-bis- (4-hydroxypropoxyphenyl) -propane and mixtures of them.
7. 7. The process of claim 1, wherein said polyamide is selected from the group consisting of partially aromatic, low molecular weight polyamides having an average molecular weight of less than 15,000, low molecular weight aliphatic polyamides having an average molecular weight of less than 7,000 fully aromatic polyamides and mixtures thereof.
8. 8. The process of claim 7, wherein said polyamide comprises a partially aromatic, low molecular weight polyamide selected from the group consisting of poly (m-xylylene adipamide), poly (hexamethylene isophthalamide), poly (hexamethylene adipamide-co -isophthalamide), poly (hexamethylene adipamide-co-teraphthalamide), and poly (hexamethylene isophthalamide-co-terephthalamide) and mixtures thereof.
9. 9. The process of claim 8, wherein said partially aromatic, low molecular weight polyamide is poly (m-xylylene adipamide) with an average molecular weight of about 4,000 to about 7,000 and an inherent viscosity of about 0.3 'to about 0.6. dL / g.
10. 10. The process of claim 7, wherein said polyamide comprises at least one low molecular weight aliphatic polyamide selected from the group consisting of polycapramide (nylon 6), poly-α-aminoheptanoic acid (nylon 7), poly-α-aminonanoic acid ( nylon 9), polyundecano-amide (nylon 11), polyaurillactam (nylon 12), polystyrene-adipamide (nylon 2,6), polytetramistile-adipamide (nylon 4,6), polyhexamethylene-adipamide (nylon 6,6), polyhexamethylene- sebacamide (nylon 6.10), polyhexamethylene-dodecamide (nylon 6.12), polyoctamethylene-adipamide (nylon 8.6), polydecamethylene-adipamide (nylon 10.6), polidodecamethylene-adipamide (nylon 12.6) and polidodecamethylene- sebacamide (nylon 12.8).
11. 11. The process of claim 7, wherein said polyamide comprises a low molecular weight aliphatic polyamide selected from the group consisting of poly (hexamethylene adipamide), poly (caprolactam) and mixtures thereof.
12. 12. The process of claim 7, wherein said polyamide comprises poly (hexamethylene adipamide) with an average molecular weight of about 3,000 to about 6,000 and an inherent viscosity of about 0.4 to about 0.9 dL / g.
13. 13. A container comprising a polyester comprising repeating units of a dicarboxylic acid component comprising at least about 85 mole percent terephthalic acid, 2,6-naphthalenedicarboxylic acid or a mixture thereof and at least about 85 mole percent ethylene glycol; and from about 0.05 to about 2% by weight of at least one polyamide having a melting point below said polyester, wherein said container is filled with a liquid containing no more acetaldehyde than a non-ozonated liquid in a vessel formed from said polyester.