MXPA01013391A - Extruded products from polyethylene terephthalate with reduced acetaldehyde content and process of their production. - Google Patents

Abstract

Polyols with at least one primary hydroxy function and at least one other primary, secondary or tertiary hydroxy function in the 2 and/or 3 position are used as additives in concentrations from 50 ppm to 5,000 ppm in order to reduce the acetaldehyde content of extruded products of polyetheylene terephthalate. Sugar alcohols, such as sorbitol, mannitol or xylitol, are preferably used. Additionally, ionic compounds, preferably easily soluble ionic compounds, such as alkali compounds, can be admixed in amounts from 0.05 ppm to 50 ppm. According to the present invention, aqueous polyol solutions are sprayed onto polyethylene terephthalate pellets after polycondensation or after the second polycondensation stage, also known as solid state polymerization, or said pellets are produced through extrusion with a polyol content of less than or equal to 25 percent by weight, pelletized, and admixed as a masterbatch with a polyester prior to processing.

Description

PRODUCTS EXTRUDED FROM POLYETHYLENE TERTHTALATE WITH REDUCED ACETALDEHYDE CONTENT, AND PROCESS FOR ITS PRODUCTION The invention relates to extruded products of polyethylene terephthalate with a reduced acetaldehyde content, such as bottles or films, and to a process for producing them. Polyethylene terephthalate is widely used as a raw material to produce packaging materials, such as bottles. Especially the use of polyethylene terephthalate in the production of bottles for mineral water, requires a very high degree of purity of this polyester. Because thermal decomposition of polyethylene terephthalate occurs when this compound is processed into extruded products, decomposition products will be found in the processed polyester in any case. The free acetaldehyde content is of particular importance for use as a receptacle for mineral water, because even ultramicro-traces of this substance affect the taste of the mineral water. Acetaldehyde is formed during hydrolysis or alcoholysis of vinyl esters of terephthalic acid that have been formed in a purely thermal process, and is also a product of oxidative degradation of polyester. Basically, there are three preferred resolutions for this problem. A first option is to stabilize polyester for high processing temperatures. It is known that phosphorus compounds are used as stabilizers (Patents Numbers JP 58 047 024, JP 53 026 893, JP 62 199 648, WO 97 44 376, EP 826 713, JP 101 82 805, and US Pat. North American Number 5,874,517), and heterocycles have also been described (Japanese Patent Number JP 57 049 620). A second option includes the largely complete decomposition of vinyl esters in the second stage of polycondensation, also known as solid state polymerization (SSP). This is achieved through treatment with water or aliphatic alcohols. Examples of these methods are found in Patent Numbers JP 07 053 698; JP 04 211 424; CH 655 938; Patent of the United States of America Number 4,591,629; BE 896 505 and JP 56 055 426. A third option is to "trap" free acetaldehyde with appropriate chemical compounds. Among others, polyamides based on xylo-lendiamine (Japanese Patent Numbers JP 62 181 336; (JP 62 050 328; and US Pat. No. 5,258,233), commercial polyamides, have been used as "trappers". Nylon (Patents Numbers EP 714,832, ch 684,537; (WO 97 01 427), or special polyamides of terephthalic acid, bis (hydroxymethyl) cyclohexane and bis (aminomethyl) cydohexane (International Publication Number WO 97 28 218). inorganic materials, such as zeolites (U.S. Patent No. 4,391,971, and International Publication Number WO 94 29 378.) The use of polyamides has proven to be the most efficient option, however, these substances have the drawback that They cause an undesirable yellow coloration in the polyester.The known acetaldehyde scavengers are added just before the polyester is processed, that is, immediately before the polyester is processed. oduce the preforms. This causes feeding problems. It is the object of the present invention to clearly reduce the content of free acetaldehyde in the products of extruded polyethylene terephthalate, which results from the processing process, by the addition of "trappers" approved for use with food materials, without affecting other parameters of the extruded product, such as color or mechanical properties, to an unacceptable degree. Furthermore, it is critical that this addition has no negative influence on the conditions under which the modified polyester is being processed, and that the modified polymer can be processed as known and without additional processing steps. In a surprising way, it has been found that the acetaldehyde content of the products can be clearly reduced by the addition of polyols to the polyethylene terephthalate before, or during, the extrusion, without affecting the processing criteria or the properties of the product. In addition, it was established that specifically the polyols with at least one primary hydroxyl function, and one or more primary, secondary, or tertiary hydroxyl functions in the 2 and / or 3 position, are qualified as acetaldehyde trappers for the processing parameters specified. Sugar alcohols of a relatively low melting point, such as sorbitol, mannitol, or xylitol are especially suitable. In addition, it has been found that the free acetaldehyde content in the polyester after processing can be clearly reduced by spraying an aqueous solution of polyol onto the crystalline granules of the polyethylene terephthalate after the second stage of polycondensation, which is also known as polymerization in solid state. Without this application of an aqueous polyol solution, a drastic reduction of the molecular weight of the polyester through hydrolysis during processing occurs. The modified polyesters can subsequently be processed according to known processes. The aerosol application of the aqueous polyol solutions immediately following the solid state polymerization provides a simple method for modifying the polyester, in such a way that free acetaldehyde, which is generated through processing, is reduced. The amount of added polyol is between 50 ppm and 2,000 ppm, preferably between 200 ppm and 1,000 ppm. The concentration of the aerosol solutions is between 5 percent by weight and 70 percent by weight, preferably between 10 percent by weight and 50 percent by weight. The aqueous polyol solution is sprayed onto the granules at temperatures between 0 ° C and 300 ° C, preferably between 20 ° C and 220 ° C. In addition, polyethylene terephthalate with a polyol content of up to 25 percent by weight can be made through extrusion, and can be granulated. Surprisingly, the degradation of the polyester through alcoholysis under the given process conditions in the presence of multivalent alcohols can be reduced to a degree where a modified polyester of a viscosity suitable for granulation is obtained, through a selection of appropriate process conditions, such as retention time and temperature.

A preferred use is made of sugar alcohols, such as sorbitol, mannitol, or xylitol. According to the present invention, the retention time is from 20 seconds to 450 seconds, preferably from 30 seconds to 150 seconds, with temperatures from 225 ° C to 300 ° C, preferably from 230 ° C to 285 ° C. In the processing step, the polyester, which has been modified through extrusion, can be added to the polyester resin as a masterbatch in order to reduce the free acetaldehyde content. In addition, it was found that adding 0.05 ppm to 50 ppm of ionic compounds (relative to polyester) increased the efficiency of the polyols as aldehyde trappers, while at the same time the slight discoloration of the the extruded products that were treated with polyols. Preferred ionic compounds are readily soluble ionic compounds, more specifically alkaline compounds. With as little as 0.1 ppm to 5.0 ppm of these ionic compounds, the acetaldehyde content of the extruded products can be reduced by another approximately 5 to 25 percent. An especially favorable processing method is to spray the aqueous polyol solutions containing the ionic compounds as additional additives onto crystalline polyethylene terephthalate granules after the second polycondensation stage. The invention is explained with the modalities found below. The generation of acetaldehyde during processing of the polyethylene terephthalate was measured according to the following method: The polyester was processed in an injection molding machine ES 200-50 by Angel Company, with a screw of 30 millimeters in diameter, and a proportion of the length to the diameter of 20. The components, ie the polyethylene terephthalate and the dry polyols, were mixed in a stainless steel vessel by vigorous stirring, and then fed into the hopper of molding machine material by injection, to which a nitrogen curtain was applied. This mixture was processed (melted and homogenized) at temperatures between 270 ° C and 300 ° C. Then this fusion was injected in a mol-of cooled under the parameters of processing under pressure: Drying Instrument: circulating air drying oven UT20 by Heraeus Instruments. Temperature: 120 ° C Duration: 12 hours Injection molding Machine: ES 200-50, by Engel Company Cylinder temperatures: 211/211/211/11 ° C Screw speed: 42 rpm Cooling time: 10 seconds Residence time pressure: 10 seconds Retention time of the melting: 2.5 minutes The acetaldehyde content of the resins produced as written above, was determined according to the following method: At the beginning, the different materials were ground with a mesh of 1 millimeter in a centrifugal mill of Retsch Company (ZM 1) in the presence of liquid nitrogen. Approximately 0.1 grams to 0.3 grams of ground material was placed in a 22 ml-liter sample vial, and sealed with a polytetrafluoroethylene seal. The sample bottles were heated in a temperature controlled upper space oven (HS-40 XL, Perkin Elmer top space autosampler) at 150 ° C for 90 minutes, and subsequently analyzed by gas chromatography ( XL GC AutoSystem by Perkin Elmer) with an external standard. The calibration curve was prepared by a complete evaporation of the aqueous solutions of different acetaldehyde contents. The equipment specifications for the determination of acetaldehyde are as follows: Conditions of the Upper Space Autosampler: Oven temperature 150 ° C Needle temperature 160 ° C Transfer temperature 170 ° C Retention time 90 minutes Gas Chromatographic Conditions : Column Stainless steel 1.8 m by 3.175 mm. Packaging Porapack Q, 80/100 mesh nitrogen carrier gas, 30 ml / minute. Hydrogen gas fuel Synthetic air Air column temperature 140 ° C Detector temperature 220 ° C The following examples will explain the effect of adding solid polyol to polyethylene terephthalate before processing in extruded products. Tables I and II show the significant reduction of the acetaldehyde content of the modified polyethylene terephthalate, compared to the polyesters to which polyol was not added, and to which respectively commercial stabilizers were added. It is interesting to note that polyvinyl aleonol with exclusively secondary alcohol functions can generate acetaldehyde by alcoholysis of vinyl esters, but can not bind to the aldehyde released. Table 1 Acetaldehyde Content of Polyethylene Terephthalate Extruded Products as a Function of Aggregate Solid Additives Table II provides an overview of the dependence of the acetaldehyde content on the concentration of solid polyols added.

Table II Acetaldehyde content of Polyethylene Terephthalate Extruded Products as a Concentration Function of Aggregate Solid Additives Behavior as a "comonomer" during processing is of critical importance for the use of the appropriate polyols. For this reason, the molecular weight distribution of the processed resins was determined. To characterize the polyethylene terephthalate samples, 200 milligrams of the ground resin was dissolved in 5 milliliters of 1,1,1,3,3,3-hexafluoroisopropanol. Once the polyester was completely dissolved, 100 microliters of this solution was adjusted with chloroform in a 2 milliliter graduated glass flask. These solutions were filtered and analyzed under the following conditions: Instruments: Sizing chromatography unit with an HPLC pump from Polymer Laboratories (PL), LC 1120. Injector Spark Holland Basic Marathon Degasys DG 1210 Degassing Detector UV / VIS detector , PL LC 1200 Column Oven K5 (Tech Lab) Conditions: Column of separation: 2 columns with Mixed Gel B PL, 10 microns (300 by 7.5 millimeters) Elution solvent: chloroform Temperature: 35 ° C Detection: 263 nm Analysis time: 25 minutes Volume injected: 50 microliters Software: Calibration software PL Calibration: External calibration with polystyrene standards (PL) The following Table III shows the values for the extruded polyethylene terephthalate products, determined by molecular weight determination.

Table III Determination of Molecular Weight for Modified Polyethylene Terephthalate Resins From Table III, it becomes obvious that there is only a slight reduction in the viscosity of the polyester during processing, due to the degradation of the chain caused by the alcoholysis for a polyol addition to about 1,000 ppm. There is no limitation for the processing of modified products. No gel formation was observed, i.e., the formation of a branched polyester, even when much more than 3,000 ppm polyol was added in any case. Some examples illustrating the processes according to the invention for producing polyethylene terephthalate products with a reduced content of acetaldehyde by aerosol application of aqueous polyol solutions are described below. The following examples are for illustrative purposes only, and are not intended to limit the scope of this invention. Unless otherwise indicated, all parts and percentages are by weight.

Example 1 (reference) 1 kilogram of polyethylene terephthalate granules with an intrinsic viscosity (IV) of 0.76 deciliters / gram, was processed according to the above method, in the Engel machine. The resulting polyester resin had a free acetaldehyde (AA) content of 10.5 ppm. Example 2 (according to the invention) 3 milliliters of an aqueous 10% sorbitol solution was sprayed on one kilogram of polyethylene terephthalate granules with an intrinsic viscosity of 0.76 deciliters / gram, by means of a manual spray for chromatography thin layer (TLC), at a temperature of 25 ° C. The polyester resin obtained from the subsequent processing in the Engel machine had a free acetaldehyde content of 6.5 ppm (approximately 62 percent of the acetaldehyde contained in the reference).

Example 3 (according to the invention) In a manner similar to mode 2), 5 milliliters of an aqueous 10% sorbitol solution was sprayed on 1 kilogram of polyethylene terephthalate granules with an intrinsic viscosity of 0.76 deciliters. -gram, at a temperature of 25 ° C. After the polyester was processed in the Engel machine, a free acetaldehyde content of 5.7 ppm (approximately 54 percent of the content of the reference) was detected. Table IV below shows the acetaldehyde content of the polyester resins as a function of the amount and concentration of the aqueous sugar alcohol solution. In addition, the molecular weight of polyethylene terephthalate is shown after processing.

Table IV Content of Acetaldehyde in Polyethylene Terephthalate After Extrusion Processing as a Function of the Amount of Aggregate Additive and Concentration of Aqueous Additive Solution * weight average molar mass measured with size exclusion chromatography. ** average molar mass in number measured with size exclusion chromatography Table IV illustrates that the acetaldehyde content of the polyester resins after processing can be significantly reduced by spraying aqueous polyol solutions thereon, specifically sugar alcohol solutions, without appreciably reducing their molecular weight, which would affect the properties of the extruded product. Another option for producing polyethylene terephthalate products with a low acetaldehyde content is by adding a masterbatch containing polyol to the processed polyester. The following tests were conducted to produce polyethylene terephthalate containing polyol 1. Composition by means of ZSK 30 The polyethylene terephthalate used to produce the sorbitol batch was dried at a temperature of 120 ° C for 20 hours, in a drying plant SOMOS TF 100 (by Mann und Hummel Pro Tec GmbH), with air of drying in a closed circuit.

The sorbitol batch was produced in the ZSK 30, a two-bar laboratory kneading extruder with co-rotating screws counterclockwise, made by Werner und Pfleiderer Company. The diameter of the screw is 30.7 millimeters, and the length of the screw is 1.241 millimeters, which is equal to 40.4 D. The process of plasticization, mixing, and dispersion is presented by means of three blocks of kneading elements in the compression zones and measurement introduction. The measured introduction zone is provided with a vacuum degassing opening. The product was discharged through the orifice nozzles. The d-sorbitol was fed together with the polyethylene terephthalate granules by means of the feeder 1, to which a permanent nitrogen curtain was applied, or towards the compression zone by means of the lateral feeder 2. An accurate measured introduction of the individual components through the use of electronic differential measuring scales. The addition of more than 20 percent sorbitol by the side feeder was not feasible, because the melting of polyethylene terephthalate could not absorb the sorbitol (liquid) that had melted into the wall of the hot funnel to a large degree . The processing parameters are shown in the following Table V. Table V Processing parameters - sorbitol batch Machine: ZSK 30 2__ Composition by means of DSK 42/6 Drying of polyethylene terephthalate: The polyethylene terephthalate was dried in a drying oven with circulating air from Binder Company, to which a nitrogen curtain was applied. Drying temperature: 160 ° C Drying time: 6 hours The sorbitol batch was made in the DSB 42/6 by Brabender Company, an internal double-rotating counter-rotating mixer. The diameter of the screw was 43 millimeters, and the length of the 6D process. Forced transport and a narrow retention time range are provided by the direction of rotation of the machine. D-sorbitol was added together with the polyethylene terephthalate by means of the nitrogen-purged screw-in measurement unit with speed control. For concentrations above 3 percent sorbitol, a uniform feed to the twin screw mixer was not achieved by means of the measured insert screws, due to the polyethylene terephthalate / sorbitol bond. Adjusted processing parameters: Cylinder temperatures: 265 ° C / 270 ° C / 275 ° C Screw speed DSK: 80 rpm Measuring speed of the screw: 5 rpm Production: 3 kg / hour. 3. Composition in the kneading and measuring chamber W50 EHT Drying of polyethylene terephthalate: The polyethylene terephthalate was dried in a circulating air drying oven of Binder Company, to which a nitrogen curtain was applied. Drying temperature: 160 ° C Drying time: 6 hours. The addition of sorbitol to polyethylene terephthalate was simulated by means of the W50 EHT measuring mixer from Brabender Company. Measuring kneaders are used to test the processes, such as mixing, composition or plasticizing of polymers, chemical products or additives, under the conditions of the production gears. The dry polyethelene terephthalate was fed to the kneading chamber together with the D-sorbitol, and a nitrogen blanket was applied during the kneading. Concentrations above 40 percent of D-sorbitol could not be added to polyethylene terephthalate under the following experimental conditions. A separate molten sorbitol was also found when the kneading chamber was opened to remove the material.

Volume of the kneading chamber: 55 cm3 Temperature of the kneading machine: 240 ° C Temperature of the dough: 247 ° C Speed of the kneading blades: 60 rpm Table VI shows the results obtained from the generation of acetaldehyde achieved at through the addition of a batch of polyethylene terephthalate / sorbitol during polyester processing. Table VI Use of Polyethylene Terephthalate Containing Sorbitol as a Master Batch to Reduce Acetaldehyde Generation During Polyester Processing These tests illustrate that the acetaldehyde content can be significantly reduced by adding polyethylene-containing polyethylene terephthalate to the polyester to be processed. Table VII shows the results for the reduction of the acetaldehyde content by spraying polyol solutions, to which ionic compounds were further mixed, on the polyester, at room temperature. Table VII illustrates the effect of ionic compounds in the range of 1 ppm to 50 ppm. If the polyethylene terephthalate is treated with aqueous polyol solutions at higher temperatures, the polyols will be less efficient in reducing the acetaldehyde content of the extruded products, and the processed polyesters will be slightly colored. The addition of ionic compounds will increase the efficiency of the polyols, and will reduce the slight coloration of the processed polyesters. Table VIIT summarizes these results, and illustrates the surprising effect of the ionic mixtures with respect to the color of the processed polyesters, and the efficiency of the polyols as aldehyde trappers. The addition of polyols is a simple method for significantly reducing the acetaldehyde content of extruded products made of polyethylene te-reftalate resins. Surprisingly, it was found that the addition of ionic compounds in the range of 0.1 ppm to 100 ppm, further increases the efficiency of the polyols as aldehyde trappers, and that the slight colorations can be reduced by spraying aqueous solutions of these Additives on polyethylene terephthalate granules at higher temperatures. Naturally, the present process for reducing the acetaldehyde content in the polyethylene terephthalate extrudates can be used alone, or together with other methods to reduce the acetaldehyde content, such as the inclusion of comonomers to reduce the processing temperatures, the use of special catalysts, or the deactivation of catalysts. In addition, combinations of different acetaldehyde scavengers, such as polyol / polyamide, can be used to reduce the acetaldehyde content in the extruded products made of polyethylene terephthalate.

Table VII Acetaldehyde Content of the Polyester Resins On Which Aqueous Solutions of Polyol / Additive were Sprayed at Room Temperature fifteen Table VIII Acetaldehyde Content of the Polyester Resins Upon Which Aqueous Solutions of Polyol / Additive were Sprayed at 100 ° C fifteen

Claims (16)

1. CLAIMS 1. Extruded products with a reduced content of acetaldehyde, characterized in that they comprise a mixture of polyethylene terephthalate with a polyol having at least one primary hydroxyl function, and at least one other primary or secondary or tertiary hydroxyl function, in the position 2/3, in a concentration of 50 ppm to 5,000 ppm in relation to polyethylene terephthalate, are used as additives to reduce the content of acetaldehyde, optionally, further mixed with 0.05 ppm to 50 ppm (relative to terephthalate) polyethylene) of at least one ionic compound.
2. 2. The extruded products according to claim 1, characterized in that the polyol additives are sugar alcohol, such as sorbitol, mannitol, or xylitol.
3. 3. The extruded products according to claims 1 and 2, characterized in that the polyols are preferably used in concentrations of 100 ppm to 2,000 ppm in relation to polyethylene terephthalate.
4. 4. The extruded products according to claim 1, characterized in that they are mixed from 0.1 ppm to 5.0 ppm of ionic compounds, in relation to polyethylene terephthalate.
5. 5. The extruded products according to claims 1 and 2, characterized in that at least one ionic compound is an easily soluble compound, preferably an easily soluble sodium compound.
6. 6. A process for producing extruded products of polyethylene terephthalate with a reduced content of acetaldehyde, characterized in that aqueous polyol solutions are sprayed with which the ionic compounds can be mixed on granules of polyethylene terephthalate.
7. 7. A process for producing polyethylene terephthalate extrudates according to claim 6, characterized in that aqueous polyol solutions are sprayed onto crystalline granules of polyethylene terephthalate after condensation.
8. 8. A process for producing polyethylene terephthalate extrudates according to claims 6 and 7, characterized in that aqueous solutions of polyol are sprayed onto the polyethylene terephthalate granules at temperatures between 0 ° C. and 300 ° C, preferably between 20 ° C and 260 ° C.
9. 9. A process for producing polyethylene terephthalate extrudates according to claims 6 to 8, characterized in that the aqueous polyol solution is an aqueous solution of sorbitol, mannitol, or xylitol, or combinations thereof. same.
10. 10. A process for producing polyethylene terephthalate extrudates according to claims 6 to 9, characterized in that the amount of added polyol is in the range of 50 ppm to 2,000 ppm, preferably 200 ppm. to 1,000 ppm in relation to the amount of polyethylene terephthalate.
11. 11. A process for producing polyethylene terephthalate extrudates according to claims 6 to 10, characterized in that the concentration of the aqueous polyol aerosol solution is in the range of 5 percent by weight to 70 percent by weight. 100 percent by weight, preferably 10 percent by weight to 50 percent by weight.
12. 12. A process for producing extruded products of polyethylene terephthalate with a reduced acetaldehyde content, characterized in that the polyethylene terephthalate granules with a polyol content of up to or equal to 25 weight percent are produced by extrusion, and granulated and mixed as a masterbatch with a polyester before processing.
13. 13. A process for producing extruded products of polyethylene terephthalate with a reduced acetaldehyde content according to claim 12, characterized in that retention times of 20 seconds to 450 seconds, preferably 30 seconds, are used. to 150 seconds, to prepare the batch.
14. 14. A process for producing extruded products of polyethylene terephthalate with a reduced acetaldehyde content according to claims 12 and 13, characterized in that the processing temperatures are in the range of 225 ° C to 300 ° C, preferably from 230 ° C to 285 ° C.
15. 15. A process for producing extruded products of polyethylene terephthalate with a reduced acetaldehyde content according to claims 12 to 14, characterized in that sugar alcohols, such as sorbitol, mannitol, or xylitol, are used as the polyol.
16. 16. A process for producing extruded products of polyethylene terephthalate with a reduced acetaldehyde content according to claims 12 to 15, characterized in that polyols are used in the range of 0.5 percent by weight to 50 percent by weight. weight in relation to the amount of polyethylene terephthalate.