Hydrolysis-resistant compositions comprising polyethylene terephthalate (PET)

Abstract

The invention relates to hydrolysis-resistant compositions comprising polyethylene terephthalate (PET), production processes, and use of the said compositions.

Claims

1-18. (canceled)

19. A process for producing a purified monomeric carbodiimide, comprising recrystallizing in a solvent a monomeric carbodiimide of the formula (I) ##STR00006## where R.sup.1, R.sup.2, R.sup.4 and R.sup.6 are mutually independently C.sub.3-C.sub.6-alkyl, and R.sup.3 and R.sup.5 are mutually independently C.sub.1-C.sub.3-alkyl, wherein the solvent is a mixture of methanol and ethanol at a ratio ranging from 1:3 to 3:1, and wherein the purified monomeric carbodiimide has less than 1000 ppm content of urea compounds of the formulae (II) and (III) ##STR00007## where n is 1 to 100 and R.sup.1, R.sup.2, R.sup.4 and R.sup.6 are mutually independently C.sub.3-C.sub.6-alkyl and R.sup.3 and R.sup.5 are mutually independently C.sub.1-C.sub.3-alkyl.

20. The process of claim 19, wherein the purified monomeric carbodiimide has less than 500 ppm content of the urea compounds of the formulae (II) and (Ill).

21. The process of claim 19, wherein the moieties R.sup.1 to R.sup.6 are isopropyl.

22. The process of claim 19, further comprising, before recrystallization, producing the monomeric carbodiimide of the formula (I) by the reaction of trisubstituted benzene isocyanates of the formula (IV) ##STR00008## where R.sup.1, R.sup.2, R.sup.4 and R.sup.6 are mutually independently C.sub.3-C.sub.6-alkyl, and R.sup.3 and R.sup.5 are mutually independently C.sub.1-C.sub.3-alkyl, at temperatures of 40° C. to 200° C. in the presence of at least one catalyst and with elimination of carbon dioxide.

23. The process of claim 19, wherein the recrystallization comprises dissolving the monomeric carbodiimide of the formula (I) in the solvent at a temperature ranging from 40° C. to 80° C. to form a recrystallization mixture.

24. The process of claim 23, further comprising cooling the recrystallization mixture to a temperature ranging from 10° C. to 25° C.

25. A process for producing a polyethylene terephthalate (PET) composition, comprising producing a purified monomeric carbodiimide according to the process of claim 1, and mixing the purified monomeric carbodiimide with PET.

26. The process according to claim 25, wherein the purified monomeric carbodiimide is present in the PET composition in an amount ranging from 0.5 to 5% by weight.

27. The process according to claim 25, wherein the purified monomeric carbodiimide is present in the PET composition in an amount ranging from 1.5 to 2.5% by weight.

28. The process according to claim 25, wherein the purified monomeric carbodiimide and PET are mixed in an extruder.

Description

EXAMPLES

[0046] 1) Specimen B: a monomeric carbodiimide with about 8.7% by weight NCN content based on 2,4,6-triisopropylphenyl isocyanate, corresponding to the formula (I)

##STR00004##  where R.sup.1 to R.sup.6 are isopropyl, with 3000 ppm content of urea compounds of the formula (II) and formula (III). [0047] 2) Specimen C: a monomeric carbodiimide with about 8.7% by weight NCN content based on 2,4,6-triisopropylphenyl isocyanate, corresponding to the formula (I)

##STR00005##  where R.sup.1, R.sup.2, R.sup.4 and R.sup.6 are isopropyl, with <100 ppm content of urea compounds of the formula (II) and formula (III). [0048] 3) Polyethylene terephthalate (PET) obtainable as NOVAPET SPRIT H11 from Novapet S.A: with intrinsic viscosity about 0.8 dl/g.

Production of Specimen B and Specimen C:

[0049] 400 g of 2,4,6-triisopropylphenyl isocyanate were charged and heated to 140° C. under a current of nitrogen in a scalded nitrogen-filled 500 ml flask with flat ground flange. 400 mg of 1-methylphospholene oxide were added, and then the reaction mixture was heated to 160° C. within a period of 5 hours. The reaction was then continued at 160° C. until NCO content<1% (corresponding to conversion>95%) had been achieved. The crude product thus obtained was: [0050] a) purified by means of distillation at temperature 220° C. under a pressure of 0.1 mbar. The product obtained (specimen B) was a pale yellow liquid with viscosity 700 mPas at 25° C. (see EP 2671912). The content of urea compounds of the formula (II) and formula (III) was 3000 ppm. [0051] b) purified by means of recrystallization in methanol/ethanol mixture (1:1) (see experimental description below). The product obtained (specimen C) was a solid with white to pale yellow crystals and melting point about 50° C. (DSC peak maximum). The content of urea compounds of the formula (II) and formula (III) was <100 ppm.

Recrystallization (Specimen C)

[0052] After carbodiimidation, specimen C was dissolved in ethanol and methanol in the ratio 1:1 in a glass beaker. The mixture was then stirred at 50° C. for 15 min. It was then cooled, with continuous stirring, to a temperature between 18 and 20° C., and again stirred at 18-20° C. for 15 minutes. The resultant crystals were then isolated by suction filtration by way of a suction funnel and dried at 40° C. and 10 mbar in a vacuum drying oven for 8 hours until constant mass was achieved.

Hydrolysis Resistance in Polyethylene Terephthalate (PET)

[0053] For evaluation of the hydrolysis-resistance effect in PET, the stabilizers used in each Example (specimens B and C) were dispersed in the quantities mentioned in Table 1 in PET by means of a ZSK 25 laboratory twin-screw extruder from Werner & Pfleiderer, and the test described below was then carried out. F3 standard test specimens for measurement of ultimate tensile strength were then produced from the resultant granulates in an Arburg Allrounder 320 S 150-500 injection-moulding machine.

[0054] For the hydrolysis test, these F3 standard test specimens were stored in water vapour at a temperature of 110° C., and their relative ultimate tensile strength was measured in %.

[0055] Table 1 shows the relative tensile strength as percentage, beginning with 100% at day 0:

TABLE-US-00001 TABLE 1 Relative ultimate Ex. 1 Ex. 2 (Comp.) Ex. 3 (Inv.) tensile strength (Comp.) PET, specimen B PET, specimen C (%) PET 0.2% NCN 0.2% NCN 0 days 100 100 100 1 day 66 85 94 2 days 5 55 88 3 days 0 35 70 4 days 3 37 5 days 0 17 Comp. = Comparative example, Inv. = nventive

[0056] The results show that specimen C of the invention has much better hydrolysis resistance than specimen B. Direct comparison of specimen C reveals the importance of the low content of urea contents of the formula (II) and formula (III).