METHOD FOR CRYSTALLIZING A POLYESTER COMPRISING AT LEAST ONE 1,4:3,6-DIANHYDROHEXITOL UNIT

Abstract

The invention relates to the field of polymers and relates to a process for crystallizing polyester. More particularly, this is a crystallization process comprising a step of provision of a polyester comprising at least one 1,4:3,6-dianhydrohexitol unit, a step of provision of a coalescence-preventing additive, and a step of crystallization of said semicrystalline polyester. The process according to the invention makes it possible to greatly limit, indeed even to eliminate, the phenomenon of agglomeration of the polyester granules during the crystallization.

Claims

1. A process for crystallizing a polyester comprising at least one 1,4:3,6-dianhydrohexitol unit, comprising the steps of: providing a semicrystalline polyester comprising at least one 1,4:3,6-dianhydrohexitol unit, providing a coalescence-preventing additive, and crystallizing said polyester.

2. The crystallization process as claimed in claim 1, wherein the coalescence-preventing additive is chosen from talc, sodium benzoate, fumed silica, optionally treated with dimethyldichlorosilane, and terephthalic acid.

3. The crystallization process as claimed in claim 1, wherein the coalescence-preventing additive is added in a proportion of between 100 and 25 000 ppm relative to the total weight of polyester.

4. The process as claimed in claim 1, wherein the 1,4:3,6-dianhydrohexitol unit is isosorbide.

5. The process as claimed in claim 1, wherein the polyester provided is a semicrystalline thermoplastic polyester comprising: at least one 1,4:3,6-dianhydrohexitol unit (A), at least one diol unit (B), which is different from the 1,4:3,6-dianhydrohexitol unit (A), and at least one aromatic dicarboxylic acid unit (C).

6. The process as claimed in claim 5, wherein the diol unit (B) of said polyester, which is different from the 1,4:3,6-dianhydrohexitol unit (A), is an alicyclic diol unit selected from the group comprising 1,4-cyclohexanedimethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, spiroglycol, tricyclo[5.2.1.0.sup.2,6]decanedimethanol (TCDDM), 2,2,4,4-tetramethyl-1,3-cyclobutanediol, tetrahydrofurandimethanol (THFDM), furandimethanol, 1,2-cyclopentanediol, 1,3-cyclopentanediol, 1,2-cyclohexanediol, dioxane glycol (DOG), norbornanediols, adamanthanediols, pentacyclopentadecanedimethanols or a mixture of these diols, preferably 1,4-cyclohexanedimethanol.

7. The process as claimed in claim 5, wherein the diol unit (B) of said polyester, which is different from the 1,4:3,6-dianhydrohexitol (A), is a saturated linear non-cyclic aliphatic diol selected from the group comprising ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol and/or 1,10-decanediol, preferably ethylene glycol.

8. The process as claimed in claim 5, wherein the diol unit (C) of said polyester is selected from the group comprising derivatives of naphthalates, terephthalates, furanoates, thiophene dicarboxylate, pyridine dicarboxylate, of isophthalates or mixtures thereof.

9. The process as claimed in claim 1, also comprising a step of increasing the molar mass of said polyester after the crystallization step.

10. The process as claimed in claim 9, wherein the increase in molar mass of said polyester is carried out by solid-state post-condensation (SSP).

11. A process for increasing the molar mass of a polyester comprising at least one 1,4:3,6-dianhydrohexitol unit, comprising the steps of: providing a semicrystalline polyester comprising at least one 1,4:3,6-dianhydrohexitol unit, providing a coalescence-preventing additive, crystallizing said polyester, and increasing of the molar mass by solid-state post-condensation of said crystallized polyester.

Description

FIGURES

[0075] FIG. 1: Change in the molar mass of Polyester 1 as a function of SSP time at 227° C. with the addition of various additives.

[0076] FIG. 2: Flexural and tensile moduli of Polyester 1 with the addition of various additives.

[0077] FIG. 3: Elongation at break of Polyester 1 with the addition of various additives.

[0078] FIG. 4: Change in the optical properties of Polyester 1 with the addition of various additives.

EXAMPLES

[0079] In all of the examples, the wording “nnor/o/diols” refers to the mol % of isosorbide relative to the diols.

[0080] The reduced viscosity in solution (tired) is evaluated using an Ubbelohde capillary viscometer at 35° C. in an of ortho-chlorophenol after dissolving the polymer at 135° C. with magnetic stirring. For these measurements, the polymer concentration introduced is 5 g/l.

[0081] Tg: Glass transition temperature

[0082] Mp: melting point

[0083] For the illustrative examples presented below, the following reactants were used: [0084] Isosorbide (purity >99.5%) Polysorb® P—Roquette Freres [0085] 1,4-Cyclohexanedinnethanol (99% purity, mixture of cis and trans isomers) [0086] Terephthalic acid (purity 99-F %)—Accros [0087] Cobalt acetate tetrahydrate (99.999%)—Sigma Aldrich [0088] Ethylene glycol (purity>99.8%)—Sigma-Aldrich [0089] Antioxidant: Irganox 1010—BASF SE [0090] Antioxidant: Hostanox P-EPQ—Clariant [0091] Irgamod 195—BASF SE [0092] Polymerization additive for limiting etherification reactions: tetraethylammonium hydroxide as a 20% by weight solution in water—Sigma Aldrich [0093] Germanium dioxide (>99.99%)—Sigma Aldrich [0094] Dimethyltin oxide (99%)—Sigma Aldrich [0095] Sodium acetate (>99%) Sigma Aldrich [0096] Talc Imerys 00S F [0097] Sodium benzoate (>99%) Sigma Aldrich [0098] Fumed silica: [0099] Fumed silica treated with dimethyldichlorosilane: Aerosil R972

[0100] Synthesis of the Polyesters

[0101] In this example, two polyesters (1 and 2) for use according to the invention were synthesized.

[0102] Polyester 1

[0103] 21.05 kg of terephthalic acid, 6.4 kg of isosorbide and 13.8 kg of cyclohexanedimethanol are introduced into a 100 l reactor. Then, 12 g of dimethyltin oxide (catalyst) and 17.4 g of Irgamod 195 are also added to the paste.

[0104] The reaction mixture is then heated gradually to 250° C. under a pressure of 5 bar absolute and with constant stirring. The water formed by esterification is continuously removed during the reaction. The degree of esterification is estimated from the mass of distillate collected. After approximately 5 hours of esterification, the pressure in the reactor is reduced to atmospheric pressure and the temperature is brought to 260° C. The pressure is then reduced to 0.7 mbar absolute over 1 hour 30 minutes according to a logarithmic ramp and the temperature is brought to 280° C. After 190 minutes, the polymer is poured into a water tank and chopped in the form of cylindrical granules.

[0105] The properties of the final polyester are as follows: ηred=51.8 ml/g (35° C., 5 g/l, ortho-chlorophenol), Tg=116° C.

[0106] The polyester also has an isosorbide content measured by .sup.1H NMR of 25.0 mol %/diols, a mass per 100 granules=0.91 g, and a water content of 0.43%.

[0107] The granules have a diameter of 1.7±0.2 mm, and a length of 3.3±0.5 mm.

[0108] Polyester 2

[0109] 29.0 kg of terephthalic acid, 3.7 kg of isosorbide and 11.4 kg of ethylene glycol are introduced into a 100 l reactor. Then, 11.6 g of germanium oxide, 2.7 g of cobalt acetate, 17.7 g of Hostanox PEPQ, 17.7 g of Irganox 1010 and 6.2 g of an aqueous solution (20% by weight) of tetraethylammonium hydroxide are also added to the paste.

[0110] The reaction mixture is then heated gradually to 250° C. under a pressure of 3 bar absolute and with constant stirring. The water formed by esterification is continuously removed during the reaction. The degree of esterification is estimated from the mass of distillate collected. After approximately 3 hours 30 minutes of esterification, the pressure in the reactor is reduced to atmospheric pressure over 15 minutes. The pressure is then reduced to 0.7 mbar absolute over 30 minutes according to a logarithmic ramp and the temperature is brought to 265° C. After 110 minutes, the polymer is poured into a water tank and chopped in the form of cylindrical granules.

[0111] The properties of the final polyester are as follows: ηred=47.7 ml/g (35° C., 5 g/l, ortho-chlorophenol), Tg=91° C.

[0112] The polyester also has an isosorbide content measured in .sup.1H NMR of 10.2 mol %/diols, a mass per 100 granules=1.17 g, and a water content of 0.47%.

[0113] The granules have a diameter of 1.7±0.1 mm, and a length of 3.1±0.2 mm.

[0114] Demonstration of the Absence of Coalescence During the Crystallization.

[0115] The aim of this example is to demonstrate and to evaluate the phenomenon of the absence of coalescence during a step of crystallization of a polyester containing isosorbide.

[0116] General Test Procedure:

[0117] The tests were carried out in a laboratory rotary evaporator. A 500 ml fluted round-bottom flask is immersed into an oil bath at an angle of 45° such that the part of the flask containing the granules is completely submerged when the oil is at the test temperature. The flask is stirred at 40 rpm with nitrogen inertization of 0.5 to 2 Ihnin. The polymer granules and any additives are placed into the round-bottom flask and rapidly heated to their glass transition temperature. The bath is then heated at 1° C./min up to the crystallization temperature. After crystallization, the flask is taken out of the bath to be cooled to ambient temperature. The adhesion to the wall and the agglomeration of the granules were observed throughout the tests.

Example 1

[0118] 75 g of granules of Polyester 1 are placed into the round-bottom flask with various additives: fumed silica (aggregates of 0.2 to 0.3 pm), Aerosil R972, talc, sodium benzoate or sodium stearate. The efficacy of the treatment is shown in table 1 for each test.

TABLE-US-00001 TABLE 1 % of granules Presence Amount % of granules agglomerated of static Additive (ppm) in motion on cooling electricity — —  0% 5% Yes Talc 2000  100% 0% No Sodium 7000  100% 0% No benzoate Fumed silica 150  33% 2% Yes Fumed silica 250 100% 0% Yes Aerosil R972 250 100% 0% Yes Terephthalic 20 000   100% 0% No acid

[0119] Talc, sodium benzoate and silica (fumed silica or Aerosil at 250 ppm) make it possible to crystallize the polyester 1 while eliminating the problem of agglomeration. Silica has the drawback of not eliminating the static electricity, which may pose problems with homogeneity in the kinetics of crystallization, diffusion and increase in molar mass.

Example 2

[0120] The example was repeated with polyester 2 and the addition of certain additives: talc, sodium benzoate, fumed silica (aggregates of 0.2 to 0.3 μm) or terephthalic acid (PTA). The efficacy of the treatment is shown in table 2 for each test.

TABLE-US-00002 TABLE 2 % of granules Presence Amount % of granules agglomerated of static Additive (ppm) in motion on cooling electricity — —  0% 15%  Yes Talc 2000 100% 0% No Sodium 7000 100% 0% No benzoate Fumed silica  250 100% 0% Yes Terephthalic 5000  10% 2% No acid Terephthalic 20 000   100% 0% No acid

[0121] The conclusions of example 1 are valid for PE.sub.10T. PTA at 2000 ppm also makes it possible to eliminate the problem of agglomeration.

Example 3

[0122] The tests of example 1 were repeated on a larger scale for the additives which work. 500 g of granules of Polymer 1 (PI.sub.25Tg) were placed into a 2 l round-bottom flask. The addition of talc and sodium benzoate makes it possible to eliminate the problem of agglomeration. On the other hand, the addition of 250 ppm of fumed silica (0.2-0.3 μm) does not work as well as in example 1. Approximately 50% of the granules remain in motion throughout the crystallization, but the other half is stuck and agglomerated on cooling. The same observations as in table 1 were made for a test without additive.

Example 4

[0123] The materials obtained at the end of the tests of example 3 were used to confirm the benefit of the additives in SSP. The granules are brought to 227° C. (material temperature) for several hours with a nitrogen stream of 2 l/min and stirring at 20 rpm. The kinetics of the molar mass increases are shown in FIG. 1.

[0124] FIG. 1 shows that the addition of the anticaking agents has little impact on the SSP kinetics.

[0125] At the end of SSP, it is observed that the anticaking agent is incorporated into the polymer. There is no residual powder in the reactor.

[0126] The polymers were then injection molded. The mechanical and optical characterizations of the final pieces are shown in FIGS. 2 and 3.

[0127] These figures show that the addition of talc and fumed silica do not greatly modify the mechanical and optical characteristics of the final material.