Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/05—Alcohols; Metal alcoholates
  • C08K5/053—Polyhydroxylic alcohols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
  • C08K5/098—Metal salts of carboxylic acids

Definitions

• the invention relates to extruded products of polyethylene terephthalate with a reduced acetaldehyde content, such as bottles or films, and to a process to produce the same.
• Polyethylene terephthalate is largely used as a raw material to produce packaging materials, such as bottles.
• packaging materials such as bottles.
• polyethylene terephthalate in producing bottles for mineral water requires a very high degree of purity of this polyester.
• thermal decomposition of the polyethylene terephthalate occurs when this compound is processed into extruded products, breakdown products will be found in the processed polyester in any case.
• the free acetaldehyde content is of particular importance for the use as a receptacle for mineral water as even ultramicro-traces of this substance would affect the taste of the mineral water.
• Acetaldehyde forms during the hydrolysis or alcoholysis of vinyl esters of the terephthalic acid that have formed in a purely thermal process, and is also a product of oxidative polyester degradation. Basically, there are three preferred resolutions to this problem.
• a first option is to stabilize the polyester for high processing temperatures. It is known that phosphor compounds are used as stabilizers (JP 58 047 024, JP 53 026 893, JP 62 199 648, WO 97 44 376, EP 826 713, JP 101 82 805, U.S. Patent 5,874,517), and heterocycles have been described as well (JP 57 049 620).
• a second option includes the largely complete decomposition of the vinyl esters in the second polycondensation stage, also known as the solid state polymerization (SSP). This is achieved through treatment with water or aliphatic alcohols. Examples of such procedures are found in JP 07 053 698; JP 04 21 1 424; CH 655 938; U.S. Patent 4 591 629; BE 896 505 and JP 56 055 426.
• SSP solid state polymerization
• a third option is to "catch" the free acetaldehyde with appropriate chemical compounds.
• polyamides based on xylylene diamine JP 62 181 336, JP 62 050 328, U.S.
• Patent 5 258 233 commercial polyamides, such as nylon (EP 714 832, CH 684 537, WO 97 01 427), or special polyamides of terephthalic acid, bis(hydroxymethyl)cyclohexane and bis(aminomethyl)cyclohexane (WO 97 28 218) have been used as "catchers”.
• acetaldehyde content of the products can be clearly reduced by adding polyols to polyethylene terephthalate prior to, or during extrusion without affecting the processing criteria or product properties. It was further established that specifically polyols with at least one primary hydroxy function and one more primary, secondary or tertiary hydroxy function in the 2 and/or 3 position qualify as acetaldehyde catchers for the specified processing parameters.
• Relatively low-melting sugar alcohols such as sorbitol, mannitol or xylitol
• sorbitol mannitol
• xylitol Relatively low-melting sugar alcohols
• spraying an aqueous polyol solution onto crystalline polyethylene terephthalate pellets after the second polycondensation stage which is also known as solid state polymerization.
• a drastic reduction of the molecular weight of the polyester through hydrolysis during processing occurs.
• the added polyol amount is between 50 ppm and 2,000 ppm, preferably between 200 ppm and 1 ,000 ppm.
• the concentration of the spray 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 pellets at temperatures between 0°C and 300°C, preferably between 20°C and 220°C.
• polyethylene terephthalate with a polyol content of up to 25 percent by weight can be made through extrusion, and pelletized.
• the degradation of the polyester through alcoholysis under the given process conditions in the presence of multivalent alcohols can be reduced to an extent whereby a modified polyester of a viscosity adequate for pelletization is obtained, through a selection of appropriate process conditions, such as retention time and temperature.
• the retention time is 20 seconds to 450 seconds, preferably between 30 seconds and 150 seconds, with temperatures ranging from 225°C to 300°C, preferably from 230°C to 285°C.
• the polyester which has been modified through extrusion, can be added to the polyester resin as masterbatch in order to reduce the free acetaldehyde content.
• ionic compounds are readily soluble ionic compounds, more specifically alkali compounds.
• An especially favorable processing method is to spray aqueous polyol solutions containing the ionic compounds as additional additives onto crystalline polyethylene terephthalate pellets after the second polycondensation stage.
• the acetaldehyde generation during the processing of polyethylene terephthalate was measured according to the following method:
• the polyester was processed on an ES 200-50 injection molding machine by Engel Company, with a screw 30 mm in diameter/and a length-diameter ratio of 20.
• the components that is dried polyethylene terephthalate and the polyols, were mixed in a stainless steel vessel through intense stirring, and then fed to the material hopper of the injection molding machine, to which a nitrogen curtain was applied. This mixture was processed (melted and homogenized) at temperatures between 270°C and 300°C. This melt was then injected into a cooled mold under pressure processing parameters:
• the acetaldehyde content of the resins produced as described above was determined according to the following method: At first, the various materials were ground with a 1 mm screen in a centrifugal mill by Retsch Company (ZM 1) in the presence of liquid nitrogen. Approximately 0.1 g to 0.3 g of the ground material was put in a 22 mL sample bottle, and sealed with a polytetrafluoroethylene seal.
• sample bottles were heated in a temperature-controlled, headspace oven (HS-40 XL headspace autosampler by Perkin Elmer) at 150°C for 90 minutes, and subsequently analyzed through gas chromatography (XL GC AutoSystem by Perkin Elmer) with an external standard.
• HS-40 XL headspace autosampler by Perkin Elmer XL headspace autosampler by Perkin Elmer
• gas chromatography XL GC AutoSystem by Perkin Elmer
• the calibration curve was prepared through complete evaporation of aqueous solutions of different acetaldehyde contents.
• Tables I and II show the significant reduction of the acetaldehyde content of the modified polyethylene terephthalate as compared to polyesters to which no polyol was added or to which commercial stabilizers were added respectively. It is interesting to note that polyvinyl alcohol with exclusively secondary alcohol functions can generate acetaldehyde through alcoholysis of the vinyl esters, but that it cannot bond the liberated aldehyde.
• Table II provides an overview of the dependence of the acetaldehyde content on the concentration of added solid polyols.
• Separating column 2 columns with PL Gel Mixed B, 10 ⁇ m, (300 by 7.5 mm )
• Table III shows the values for the extruded products of polyethylene terephthalate determined through molecular weight determination.
• the polyester resin obtained from subsequent processing on the Engel machine had a free acetaldehyde content of 6.5 ppm (approximately 62 percent of the acetaldehyde contained in the reference).
• Example 3 Similar to embodiment 2), 5 mL of a 10 percent aqueous sorbitol solution were sprayed onto 1 kg of polyethylene terephthalate pellets with a intrinsic viscosity of 0.76 dl_/g at a temperature of 25°C.
• Table IV shows the acetaldehyde content of the polyester resins as a function of the amount and concentration of the aqueous sugar alcohol solution. The molecular weight of the polyethylene terephthalate after processing is shown in addition. Table IV
• Table IV illustrates that the acetaldehyde content of polyester resins after processing can be significantly reduced by spraying aqueous polyol solutions on them, specifically sugar alcohol solutions, without considerably reducing their molecular weight, which would affect the properties of the extruded product.
• Another option to produce products of polyethylene terephthalate with a low acetaldehyde content is through adding a polyol-containing masterbatch to the processed polyester.
• the polyethylene terephthalate used to produce the sorbitol batch was dried at a temperature of 120°C for 20 hours in a SOMOS drying plant TF 100 (by Mann und Hummel ProTec GmbH) with dry air in a closed circuit.
• the sorbitol batch was produced on the ZSK 30, a two-shaft laboratory kneading extruder with co-rotating anticlockwise screws, made by Werner und Pfleiderer Company.
• the screw diameter is 30.7 mm and the screw length is 1 ,241 mm, which equals 40.4 D.
• the plasticizing, mixing and dispersing process occurs via 3 kneading element blocks in the compression and metering zones.
• the metering zone is provided with a vacuum degassing opening.
• the product was discharged via orifice nozzles.
• the d-sorbitol was fed together with the polyethylene terephthalate pellets via feeder 1 to which a permanent nitrogen curtain is applied, or into the compression zone via sidefeeder 2. Precise metering of the individual components was achieved through the use of electronic differential metering balances. Adding more than 20 percent of sorbitol via the sidefeeder was not feasible as the polyethylene terephthalate melt could not absorb the (liquid) sorbitol which had molten at the hot funnel wall to a large extent.
• the polyethylene terephthalate was dried in a circulated-air drying oven by Binder Company, to which a nitrogen curtain was applied. Drying temperature: 160°C
• the sorbitol batch was made on the DSK 42/6 by Brabender Company, an internal counter-rotating twin-screw compounder.
• the screw diameter was 43 mm, and the process length 6D. Forced conveying and a narrow retention time range are provided by the sense of rotation of the machine. D-sorbitol was added together with the polyethylene terephthalate via the nitrogen-purged screw metering unit with speed control.
• the polyethylene terephthalate was dried in a circulated-air drying oven by Binder Company, to which a nitrogen curtain was applied.
• sorbitol was simulated by means of the W50 EHT measuring kneader by Brabender Company. Measuring kneaders are used to test processes, such as mixing, compounding or plasticizing of polymers, chemicals or additives, under production-geared conditions.
• the dried polyethylene terephthalate was fed to the kneading chamber together with the d-sorbitol, and a nitrogen curtain was applied during kneading.
• Kneading chamber volume 55 cm 3 Kneading machine temperature: 240°C Mass temperature: 247°C Kneading blade speed: 60 rpm
• Table VI shows the results gained from acetaldehyde generation achieved through the addition of a polyethylene terephthalate /sorbitol batch during polyester processing.
• Table VI Use of Sorbitol-Containing Polyethylene Terephthalate as a Masterbatch to Reduce the Acetaldeh de Generation Durin ol ester Processin .
• Table VII shows the results for the reduction of the acetaldehyde content through spraying polyol solutions, to which additionally ionic compounds were admixed, onto the polyester at room temperature.
• Table VII illustrates the effect of ionic compounds in the range from 1 ppm to 50 ppm.
• 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. Adding ionic compounds will increase the efficiency of the polyols and reduce the slight coloring of the processed polyesters.
• Table VIII summarizes these results and illustrates the surprising effect of ionic admixtures with regard to the color of the processed polyesters and the efficiency of the polyols as aldehyde catchers.
• the addition of polyols constitutes a simple method of significantly reducing the acetaldehyde content of extruded products made of polyethylene terephthalate resins.
• ionic compounds in the range from 0.1 ppm to 100 ppm further increases the efficiency of the polyols as aldehyde catchers and that the slight colorings can be reduced by spraying aqueous solutions of these additives on the polyethylene terephthalate pellets at higher temperatures.
• the subject process to reduce the acetaldehyde content in extruded products of polyethylene terephthalate 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.
• combinations of different acetaldehyde catchers, such as polyol/polyamide, can be used to reduce the acetaldehyde content in extruded products made of polyethylene terephthalate.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Extrusion Moulding Of Plastics Or The Like (AREA)

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• 2000
  • 2000-06-29 AU AU63397/00A patent/AU6339700A/en not_active Abandoned
  • 2000-06-29 WO PCT/US2000/017996 patent/WO2001000724A1/en not_active Application Discontinuation
  • 2000-06-29 CA CA002377237A patent/CA2377237A1/en not_active Abandoned
  • 2000-06-29 EP EP00950271A patent/EP1196490A1/de not_active Withdrawn
  • 2000-06-29 AR ARP000103298A patent/AR024614A1/es unknown
  • 2000-06-29 MX MXPA01013391A patent/MXPA01013391A/es not_active Application Discontinuation
  • 2000-06-29 JP JP2001506731A patent/JP2003503573A/ja active Pending

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