Aliphatic-aromatic polyester having elevated whiteness index

Abstract

The present invention relates to an aliphatic-aromatic polyester having a whiteness index according to ASTM E 313-73 of at least 25, to a process for preparation thereof and to the use of the aliphatic-aromatic polyester for production of polyester fibers (PF). The present invention further relates to the polyester fibers (PF) comprising the aliphatic-aromatic polyester.

Claims

1. An aliphatic-aromatic polyester obtainable by condensation at least of components (A), (B), (C) and optionally (D): (A) 40 to 70 mol %, based on components (A) and (B), of adipic acid and/or at least one adipic acid derivative, (B) 30 to 60 mol %, based on components (A) and (B), of at least one aromatic 1,ω-dicarboxylic acid and/or at least one 1,ω-dicarboxylic acid derivative, (C) 98 to 102 mol %, based on components (A) and (B), of at least one aliphatic 1,ω-diol, and (D) 0% to 5% by weight, based on the total weight of components (A) to (C), of at least one chain extender, wherein the aliphatic-aromatic polyester has a whiteness index according to ASTM E 313-73 of at least 25, and wherein the condensation comprises the four stages i) to iv): i) a continuous esterification, ii) a precondensation, iii) a postcondensation, and iv) a polyaddition reaction, wherein 0.03% to 0.04% by weight of a phosphorus compound is added to the precondensation product obtained in the second stage after process step ii) and before and/or during process step iii), based on the total weight of the precondensation product.

2. An aliphatic-aromatic polyester according to claim 1, wherein the aliphatic-aromatic polyester has a whiteness index according to ASTM E 313-73 of 25 to 40.

3. An aliphatic-aromatic polyester according to claim 1, wherein the aliphatic-aromatic polyester has an acid number measured according to DIN EN ISO 2114:2002-06 in the range from 1.1 to 1.4 mg KOH/g.

4. An aliphatic-aromatic polyester according to claim 1, wherein the aliphatic-aromatic polyester has a viscosity number according to DIN 53728 in the range from 100 to 300 cm.sup.3/g.

5. An aliphatic-aromatic polyester according to claim 1, wherein the aliphatic-aromatic polyester is obtainable by condensation at least of components (A), (B), (C) and optionally (D): (A) 45 to 65 mol %, based on components (A) and (B), of adipic acid and/or at least one adipic acid derivative, (B) 35 to 55 mol %, based on components (A) and (B), of at least one aromatic 1,ω-dicarboxylic acid and/or at least one 1,w-dicarboxylic acid derivative, (C) 99 to 101 mol %, based on components (A) and (B), of at least one aliphatic 1,ω-diol, and (D) 0.01% to 5% by weight, based on the total weight of components (A) to (C), of at least one chain extender.

6. An aliphatic-aromatic polyester according to claim 1, wherein component (B) is terephthalic acid and/or a terephthalic acid derivative.

7. An aliphatic-aromatic polyester according to claim 1, wherein component (C) is propane-1,3-diol and/or butane-1,4-diol.

8. An aliphatic-aromatic polyester according to claim 1, wherein component (D) is hexamethylene diisocyanate.

9. An aliphatic-aromatic polyester according to a claim 1, wherein the glass transition temperature (T.sub.G) of the aliphatic-aromatic polyester is in the range from −50 to 0° C.

10. A process for preparing an aliphatic-aromatic polyester according to claim 1, wherein i) in a first stage a mixture comprising components (A), (B) and (C) is continuously esterified in the presence of a catalyst to obtain an esterification product, ii) in a second stage the esterification product obtained in the first stage is continuously precondensed up to a viscosity number according to DIN 53728 of 20 to 70 cm.sup.3/g to obtain a precondensation product, iii) in a third stage the precondensation product obtained in the second stage is continuously postcondensed up to a viscosity number according to DIN 53728 of 60 to 170 cm.sup.3/g to obtain a postcondensation product, and iv) in a fourth stage the postcondensation product obtained in the third stage is continuously reacted in a polyaddition reaction with the at least one chain extender (D) up to a viscosity number according to DIN 53728 of 100 to 300 cm.sup.3/g to obtain the aliphatic-aromatic polyester, where 0.03% to 0.04% by weight of a phosphorus compound is added to the precondensation product obtained in the second stage after process step ii) and before and/or during process step iii), based on the total weight of the precondensation product.

11. The process according to claim 10, wherein stages i) and ii) are conducted in the presence of a titanium catalyst.

12. The process according to claim 10, wherein the phosphorus compound is phosphorous acid.

13. Polyester fibers (PF) each comprising, based on the total weight of the polyester fibers (PF), 80% to 99% by weight of at least one terephthalate polyester, 1% to 20% by weight of at least one aliphatic-aromatic polyester according to claims 1 to 9, and 0% to 5% by weight of at least one additive (E), wherein the polyester fibers (PF) have a whiteness index according to CIE 15.3 of at least 65.

14. Polyester fibers (PF) according to claim 13, wherein the at least one terephthalate polyester is polyethylene terephthalate (PET) and/or polybutylene terephthalate (PBT).

15. An aliphatic-aromatic polyester obtainable by a process according to claim 10.

Description

EXAMPLES

(1) Test Methods

(2) The viscosity number was determined according to DIN 53728 (Part 3, Jan. 3, 1985). The solvent used was the mixture of phenol/dichlorobenzene in a weight ratio of 50/50.

(3) The molecular weights (M.sub.w and M.sub.n) were determined according to ASTM D4001. The solvent used was 1,1,1,3,3,3-hexafluoro-2-propanol against narrow-distribution polymethylmethacrylate (PMMA) standards.

(4) The melt volume flow rate (MVR) was determined according to ISO 1133. The testing temperature is 190° C. and the test load is 2.19 kg. The melting time is 4 minutes.

(5) The acid number is determined according to DIN EN ISO 2114:2002-06. The solvent mixture used for 1 g of polymer is 15 mL of 1,2-dichlorobenzene, in which the polyester is dissolved at 180° C. and then diluted with 20 mL of pyridine. Cooling to 60° C. and addition of 50 mL of tetrahydrofuran (THF), 5 mL of water and 40 mL of ethanol are followed by potentiographic titration with 0.1 M ethanolic potassium hydroxide solution with an end point indicator.

(6) The whiteness index is determined on the granules, which have a grain size of 2.5 to 4.4 g/100 of particles, according to ASTM E 313-73 by means of a Minolta CM-5 spectrophotometer. Three measurements are conducted, from which the mean is determined. A glass cuvette (from Minolta) is filled with the granular material to be analyzed (fill height at least 3 cm). The granular material is compacted by pressure from the measurement head of the Minolta instrument.

(7) The whiteness index of the polyester fibers is measured using a Datacolor DC650, according to ISO 18314-1. For this purpose, the polyester fibers in an opaque cluster are analyzed 3 times each against a white and black background. Between the measurements, the specimen is rotated by 90° in each case. The average of the 6 measurements is used to ascertain the tristimulus values X, Y, Z according to ISO 11664-1. Using these, firstly the yellowness index according to ASTM-E313 and secondly the whiteness index according to CIE 15.3 are determined.

(8) Preparation of the Aliphatic-Aromatic Polyester

Inventive Example (I1)

(9) For preparation of the aliphatic-aromatic polyester, 180 kg/h of adipic acid (component (A)), 200 kg/h of terephthalic acid (component (B)) and 290 kg/h of butane-1,4-diol (component (C)) are physically mixed at 35° C. Subsequently, the mixture is transferred continuously to an esterification tank (for example designed as a hydrocyclone as described, for example, in WO 03/042278 A1).

(10) Stage i)

(11) With addition of a further 140 kg/h of butane-1,4-diol (component (C)) and 0.4 kg/h of tetrabutyl orthotitanate (TBOT), the mixture is continuously esterified at a temperature of 240° C. and a pressure of 0.85 bar for a residence time of 1.5 h to obtain an esterification product. The water condensation product that arises and portions of the excess of butane-1,4-diol (component (C)) are distilled off.

(12) Stage ii)

(13) Subsequently, the esterification product obtained in stage i) is guided through a downflow cascade (as described, for example, in WO 03/042278 A1) at a temperature rising from 250 to 260° C. and at a pressure falling from 300 mbar to 10 mbar for a residence time of 2 h, and the predominant portion of excess butane-1,4-diol (component (C)) is distilled off. This precondenses the esterification product obtained in stage i) to obtain a precondensation product.

(14) Stage iii)

(15) After addition of 0.2 kg/h of phosphorous acid dissolved in butane-1,4-diol (component (C)), the precondensation product is transferred in stage iii) into a polycondensation reactor (as described, for example, in EP 0719582) and postcondensed at a temperature of 245° C. and at a pressure of 1 mbar for a further 45 minutes to obtain a postcondensation product. The remaining excess of butane-1,4-diol (component (C)) is distilled off.

(16) Stage iv)

(17) After stage iii), 4 kg/h of hexamethylene diisocyanate (HDI) are metered into the postcondensation product at 240° C. using a static mixing system, and the aliphatic-aromatic polyester is obtained in a polyaddition reaction. The residence time here is 8 minutes. The aliphatic-aromatic polyester is pelletized using underwater pelletization and dried.

(18) The aliphatic-aromatic polyester has a viscosity number of 185 cm.sup.3/g and molecular weights M.sub.w and M.sub.n of 128 000 and 34 000 g/mol respectively. In addition, the aliphatic-aromatic polyester has an acid number of 1.2 mg KOH/g. The whiteness index measured according to ASTM E 313-73 of the aliphatic-aromatic polyester is 33.

Comparative Example (C1)

(19) The preparation is analogous to the inventive example (I1), except that the amount of phosphorous acid is lowered to 0.16 kg/h.

(20) The aliphatic-aromatic polyester has a viscosity number of 182 cm.sup.3/g and molecular weights M.sub.w and M.sub.n of 127 000 and 33 000 g/mol respectively. In addition, the aliphatic-aromatic polyester has a melt volume flow rate of 3.8 cm.sup.3/10 min and an acid number of 0.8 mg KOH/g. The whiteness index measured according to ASTM E 313-73 of the aliphatic-aromatic polyester is 18.

(21) TABLE-US-00001 TABLE 1 Whiteness index according to ASTM E313-73 (higher values = whiter/better) Whiteness index ASTM Example E313-73 I1 33 C1 18

(22) By virtue of the higher addition of phosphorous acid in the preparation of the inventive polyester I1, it thus has a higher whiteness index than the polyester from comparative example C1.

(23) Production of the Polyester Fibers

(24) The terephthalate polyester used in all fiber tests was a polyethylene terephthalate (PET) from Invista of the “RT 20” type, which is abbreviated in the examples to the name “PET RT 20”.

Inventive Example (I2)

(25) Prior to the spinning, the aliphatic-aromatic polyester according to I1 is dried at a temperature of 80° C. for 8 hours. Prior to the spinning, the PET RT 20 is precrystallized at 120° C. for 8 hours and dried at 160° C. overnight.

(26) PET RT 20 is mixed with an aliphatic-aromatic polyester of the invention which has been obtained by condensation of adipic acid (component (A)), terephthalic acid (component (B)) and butane-1,4-diol (component (C)) according to example 11, and melted in an extruder to obtain a homogeneous melt. The homogeneous melt is subsequently extruded through a 24-hole nozzle with a standard sieve (300 μm) of the extruder, giving polyester fibers (PF).

(27) The amount of the polyethylene terephthalate (PET) used is 94% by weight, and the amount of the aliphatic-aromatic polyester used is 6% by weight, based on the total weight of the PET RT 20 and of the aliphatic-aromatic polyester. The spinning temperature is 280° C.

(28) The color values determined on the fibers 12 obtained are collated in table 2.

Comparative Example (C2)

(29) Prior to the spinning, the aliphatic-aromatic polyester according to C1 is dried at a temperature of 80° C. for 8 hours. Prior to the spinning, the PET RT 20 is precrystallized at 120° C. for 8 hours and dried at 160° C. overnight.

(30) PET RT 20 is mixed with the aliphatic-aromatic polyester C1 which has been obtained by condensation of adipic acid (component (A)), terephthalic acid (component (B)) and butane-1,4-diol (component (C)) according to comparative example C1, and melted in an extruder to obtain a homogeneous melt. The homogeneous melt is subsequently extruded through a 24-hole nozzle with a standard sieve (300 μm) of the extruder, giving polyester fibers (PF).

(31) The amount of the polyethylene terephthalate (PET) used is 94% by weight, and the amount of the aliphatic-aromatic polyester used is 6% by weight, based on the total weight of the polyethylene terephthalate (PET) and of the aliphatic-aromatic polyester. The spinning temperature is 280° C.

(32) The color values determined on the fibers C2 obtained are collated in table 2.

Comparative Example (C3)

(33) Fibers were produced without addition of an aliphatic-aromatic polyester based on PET RT 20.

(34) Prior to the spinning, the PET RT 20 was precrystallized at 120° C. for 8 hours and dried at 160° C. overnight.

(35) PET RT 20 was melted in an extruder to obtain a homogeneous melt. The homogeneous melt was subsequently extruded through a 24-hole nozzle with a standard sieve (300 μm) of the extruder, giving the polyester fibers (PF). The spinning temperature is 290° C.

(36) TABLE-US-00002 TABLE 2 Whiteness index and yellowness index of the polyester fibers from examples I2 and C2 and C3. Whiteness index according to CIE 15.3 Yellowness index Example (2004) according to ASTM E 313 I2 74.2 3.8 C2 60.7 8.5 C3 81.6 2.1

(37) The polyester fibers (I2) that are produced with the aliphatic-aromatic polyester (I1) of the invention have only a slight deterioration in the whiteness index and the yellowness index compared to the pure polyester fibers from C3. By contrast, the polyester fibers (C2) produced with the aliphatic-aromatic polyester (C1) are much more intensely colored, which can be seen from the significant rise in the yellowness index and the lower whiteness index. In visual terms as well, there is also a distinctly perceptible resultant yellow color in the fiber C2, which is unacceptable for industrial use. Compared to the pure PET fibers C3, the inventive polyester fibers I2 have only a slight deterioration in the whiteness index.