PREPARATION METHOD OF POLYESTER

Abstract

A preparation method of a polyester is provided. The method includes the following steps: allowing a raw material including a diacid and a diol to contact a monoclinic nano-TiO2 (namely, TiO2(B)) catalyst, and conducting an esterification reaction and a polycondensation reaction sequentially to obtain the polyester. The method can efficiently catalyze the synthesis of the polyester and avoid from yellowing of the polyester. Meanwhile, nano-TiO.sub.2(B) is polymerized in situ in the polyester, such that a structure of nano-TiO.sub.2(B) can adjust the structure and properties of a polyester matrix and effectively improve the mechanical, thermal, and barrier properties of the polyester.

Claims

1. A preparation method of a polyester, comprising the following steps: allowing a raw material comprising a diacid and a diol to contact a catalyst, and conducting an esterification reaction and a polycondensation reaction sequentially to obtain the polyester, wherein the catalyst is nano-TiO.sub.2(B).

2. The preparation method according to claim 1, wherein the diacid is selected from at least one of furandicarboxylic acid (FDCA) and terephthalic acid (TPA).

3. The preparation method according to claim 1, wherein the diol is a C.sub.2-4 diol.

4. The preparation method according to claim 1, wherein the diol is selected from at least one of ethylene glycol (EG), 1,3-propanediol, and 1,4-butanediol.

5. The preparation method according to claim 1, wherein the nano-TiO.sub.2(B) is selected from one of a zero-dimensional (0D) nanomaterial, a one-dimensional (1D) nanomaterial, a two-dimensional (2D) nanomaterial, and a three-dimensional (3D) nanomaterial; the 0D nanomaterial is a nanoparticle; the 1D nanomaterial is a nanowire; the 2D nanomaterial is a nanosheet; and the 3D nanomaterial is a nanoporous sphere.

6. The preparation method according to claim 1, wherein a molar ratio of the diol to the diacid is (1.4-3.0):1; and a molar amount of the catalyst is 0.5% to 10% of a molar amount of the diacid.

7. The preparation method according to claim 1, wherein the esterification reaction is conducted in an inactive atmosphere.

8. The preparation method according to claim 7, wherein the inactive atmosphere is a nitrogen atmosphere.

9. The preparation method according to claim 1, wherein the esterification reaction is conducted at 190? C. to 220? C.; and the esterification reaction is conducted for 1 h to 4 h.

10. The preparation method according to claim 1, wherein the polycondensation reaction is conducted at 220? C. to 250? C.; and the polycondensation reaction is conducted for 1 h to 8 h.

11. A polyester prepared by the preparation method according to claim 1.

12. The polyester according to claim 11, wherein the polyester has a chromaticity b of less than or equal to 11.2, an intrinsic viscosity of 0.92 dL/g to 1.36 dL/g, a tensile strength of 62 MPa to 120 MPa, an oxygen barrier coefficient of 0.5?10.sup.?13 to 8.2?10.sup.?12, and an elongation at break of 27% to 266%.

13. The polyester according to claim 11, wherein in the preparation method, the diacid is selected from at least one of FDCA and TPA.

14. The polyester according to claim 11, wherein in the preparation method, the diol is a C.sub.2-4 diol.

15. The polyester according to claim 11, wherein in the preparation method, the diol is selected from at least one of EG, 1,3-propanediol, and 1,4-butanediol.

16. The polyester according to claim 11, wherein in the preparation method, the nano-TiO.sub.2(B) is selected from one of a 0D nanomaterial, a 1D nanomaterial, a 2D nanomaterial, and a 3D nanomaterial; the 0D nanomaterial is a nanoparticle; the 1D nanomaterial is a nanowire; the 2D nanomaterial is a nanosheet; and the 3D nanomaterial is a nanoporous sphere.

17. The polyester according to claim 11, wherein in the preparation method, a molar ratio of the diol to the diacid is (1.4-3.0):1; and a molar amount of the catalyst is 0.5% to 10% of a molar amount of the diacid.

18. The polyester according to claim 11, wherein in the preparation method, the esterification reaction is conducted in an inactive atmosphere.

19. The polyester according to claim 18, wherein the inactive atmosphere is a nitrogen atmosphere.

20. The polyester according to claim 11, wherein in the preparation method, the esterification reaction is conducted at 190? C. to 220? C.; and the esterification reaction is conducted for 1 h to 4 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 is an electron microscopy (EM) image of a 0D TiO.sub.2(B) nanoparticle in Examples 1 and 10;

[0040] FIG. 2 is an EM image of a 1D TiO.sub.2(B) nanowire in Example 2;

[0041] FIG. 3 is an EM image of a 2D TiO.sub.2(B) nanosheet in Examples 3, 5 to 9, and 11 to 14;

[0042] FIG. 4 is an EM image of a 3D TiO.sub.2(B) nanoporous sphere in Example 4;

[0043] FIG. 5 is a cross-sectional EM image of a PEF/TiO.sub.2(B) nanocomposite polyester in Example 1;

[0044] FIG. 6 is a cross-sectional EM image of a PTF/TiO.sub.2(B) nanocomposite polyester in Example 14;

[0045] FIG. 7 is a cross-sectional EM image of a PBF/TiO.sub.2(B) nanocomposite polyester in Example 13;

[0046] FIG. 8 is a cross-sectional EM image of a PET/TiO.sub.2(B) nanocomposite polyester in Example 5;

[0047] FIG. 9 is a cross-sectional EM image of a PTT/TiO.sub.2(B) nanocomposite polyester in Example 12; and

[0048] FIG. 10 is a cross-sectional EM image of a PBT/TiO.sub.2(B) nanocomposite polyester in Example 11.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] The present application will be described in detail below with reference to examples, but the present application is not limited to these examples.

[0050] To illustrate the present application clearly, the present application will be further described below with reference to preferred examples. Those skilled in the art should understand that the content described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present application.

[0051] Unless otherwise specified, the raw materials and catalysts in the examples of the present application all are purchased from commercial sources.

[0052] Wherein, FDCA is prepared in accordance with the method of Example 1 in the patent CN201810442696.1, TPA is purchased from Innochem, and other raw materials are purchased from Sinopharm.

[0053] The nano-TiO.sub.2(B) catalysts used in the examples of the present application are prepared according to the following preparation methods, respectively: [0054] (1) A preparation method of a TiO.sub.2(B) nanoparticle: through liquid-phase chemical precipitation method, 5 mL of TiCl.sub.4 is added as a titanium source to 200 mL of a mixed solvent of water and EG (wherein a volume ratio of EG to water is 10:1), and a resulting mixture is heated to allow a reaction under reflux for 0.2 h, such that TiCl.sub.4 is hydrolyzed; and a resulting reaction system is centrifuged, and a resulting precipitate is washed with absolute ethanol to obtain the TiO.sub.2(B) nanoparticle. [0055] (2) A preparation method of a TiO.sub.2(B) nanowire: through chemical precipitation and hydrothermal synthesis method, 2 mL of butyl titanate is hydrolyzed in 20 mL of a mixed solvent of water and ethanol (where a volume ratio of water to ethanol is 1:1) to obtain 20 nm particles, then the particles are subjected to a hydrothermal reaction at 160? C. for 4 h in 20 mL of a 10 mol/L KOH solution, and then K is replaced with 0.1 M dilute nitric acid to obtain a titanic acid nanowire; and then the titanic acid nanowire is calcined in a 350? C. muffle furnace for 2 h to obtain the 1D TiO.sub.2(B) nanowire. [0056] (3) A preparation method of a TiO.sub.2(B) nanosheet: through liquid-phase chemical precipitation method, 5 mL of TiCl.sub.4 is added as a titanium source to 200 mL of a mixed solvent of EG and water (where a volume ratio of EG to water is 10:1), EG is added as a structure-directing agent, and a resulting mixture is heated to allow reaction under reflux for 2 h, such that TiCl.sub.4 is hydrolyzed, where the structure-directing agent EG may be combined with a c axis of a TiO.sub.2 unit cell to inhibit the growth of the unit cell along the c axis, such that the unit cell grows along a and b axes to be the 2D TiO.sub.2(B) nanosheet. [0057] (4) A preparation method of a TiO.sub.2(B) nanoporous sphere: through liquid-phase chemical precipitation, hydrothermal synthesis, and high-temperature calcination method, 5 mL of butyl titanate is subjected to the alcoholysis in 100 mL of ethanol with 1.5 mL of long-chain oleamine as a structure-directing agent to obtain a titanium alkoxide nanosphere assembled from nanoparticles; the titanium alkoxide nanosphere is subjected to a hydrothermal reaction at 180? C. for 6 h in 20 mL of a 10 mol/L NaOH solution to obtain sodium titanate; then replacement is conducted with 0.1 M dilute HCl (Na is replaced by H.sup.+) to obtain metatitanic acid; and the metatitanic acid is calcined at 350? C. for 4 h to obtain the TiO.sub.2(B) nanoporous sphere assembled from nanowires.

[0058] In the examples of the present application, a chromaticity is measured by a 3nh colorimeter (NR200) and an intrinsic viscosity is measured by a Zhongwang UbbeloHde viscometer (IVS100); and the viscosity and chromaticity are measured according to the test methods in the standard GB/T 14190-2017. A tensile strength and an elongation at break are measured by an Instron Electronic Universal Material Testing Machine (Instron-1121). A tensile test is conducted at 25? C. by an Instron-1121 testing machine according to requirements in ASTM D638, with a tensile speed of 5 mm/min. A dumbbell-shaped sample with a width of 3.18 mm and a thickness of 3.2 mm is prepared through injection molding by an injection molding machine and tested for the tensile strength and elongation at break. An oxygen transmission coefficient is tested by a Labthink's oxygen transmission rate test system (VAC-V2) according to a test method of the standard GB/T 1038-2000.

Example 1

[0059] With a TiO.sub.2(B) nanoparticle as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanoparticle (an EM image of the TiO.sub.2(B) nanoparticle was shown in FIG. 1) was 5% of a molar amount of the FDCA. A resulting product polyethylene 2,5-furandicarboxylate (PEF) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 2

[0060] With a TiO.sub.2(B) nanowire as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanowire (an EM image of the TiO.sub.2(B) nanowire was shown in FIG. 2) was 5% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 3

[0061] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 4

[0062] With a TiO.sub.2(B) nanoporous sphere as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanoporous sphere (an EM image of the TiO.sub.2(B) nanoporous sphere was shown in FIG. 4) was 5% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 5

[0063] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of TPA and 0.25 mol of EG (a molar ratio of EG to TPA was 2.5) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 250? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the TPA. A resulting product polyethylene terephthalate (PET) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 6

[0064] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 2.5% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 7

[0065] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 1% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 8

[0066] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of TPA and 0.3 mol of EG (a molar ratio of EG to TPA was 3) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 250? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 1% of a molar amount of the TPA. A resulting product PET was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 9

[0067] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of TPA and 0.25 mol of EG (a molar ratio of EG to TPA was 2.5) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 4 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the TPA. A resulting product PET was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 10

[0068] With a TiO.sub.2(B) nanoparticle as a catalyst, 0.1 mol of TPA and 0.3 mol of EG (a molar ratio of EG to TPA was 3) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 250? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanoparticle (an EM image of the TiO.sub.2(B) nanoparticle was shown in FIG. 1) was 5% of a molar amount of the TPA. A resulting product PET was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 11

[0069] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of TPA and 0.24 mol of 1,4-butanediol (a molar ratio of 1,4-butanediol to TPA was 2.4) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 4 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the TPA. A resulting product polybutylene terephthalate (PBT) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 12

[0070] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of TPA and 0.14 mol of 1,3-propanediol (a molar ratio of 1,3-propanediol to TPA was 1.4) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 0.5% of a molar amount of the TPA. A resulting product polytrimethylene terephthalate (PTT) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 13

[0071] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of FDCA and 0.25 mol of 1,4-butanediol (a molar ratio of 1,4-butanediol to FDCA was 2.5) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the FDCA. A resulting product polybutylene 2,5-furandicarboxylate (PBF) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Example 14

[0072] With a TiO.sub.2(B) nanosheet as a catalyst, 0.1 mol of FDCA and 0.16 mol of 1,3-propanediol (a molar ratio of 1,3-propanediol to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 240? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TiO.sub.2(B) nanosheet (an EM image of the TiO.sub.2(B) nanosheet was shown in FIG. 3) was 5% of a molar amount of the FDCA. A resulting product polypropylene 2,5-furandicarboxylate (PTF) was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Comparative Example 1

[0073] With tetrabutyl titanate (TBT) as a catalyst, 0.1 mol of FDCA and 0.16 mol of EG (a molar ratio of EG to FDCA was 1.6) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 250? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TBT was 5% of a molar amount of the FDCA. A resulting product PEF was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

Comparative Example 2

[0074] With TBT as a catalyst, 0.1 mol of TPA and 0.25 mol of EG (a molar ratio of EG to TPA was 2.5) were adopted as raw materials and subjected to an esterification reaction at each of 190? C., 200? C., 210? C., and 220? C. for 1 h and then to a polycondensation reaction at 250? C. for 2 h under protection of nitrogen, and then the reaction was terminated, where a molar amount of the TBT was 5% of a molar amount of the TPA. A resulting product PET was tested for chromaticity and viscosity, and the resulting product was crushed and injection-molded, and then subjected to mechanical and barrier performance tests. Results were shown in Table 1.

TABLE-US-00001 TABLE 1 Oxygen transmission Intrinsic Tensile Elongation coefficient viscosity strength at break cm.sup.3 .Math. cm/cm.sup.2 .Math. Product Chromaticity dL/g MPa % s .Math. cm Hg Example 1 PEF b: 11.2 1.25 107 42 1.9 ? 10.sup.?13 Example 2 PEF b: 6.5 1.19 109 31 2.8 ? 10.sup.?13 Example 3 PEF b: 7.7 1.36 116 45 0.5 ? 10.sup.?13 Example 4 PEF b: 9.1 1.22 120 27 8.1 ? 10.sup.?13 Example 5 PET b: 0.5 1.25 71 166 3.5 ? 10.sup.?12 Example 6 PEF b: 9.6 1.28 111 36 5.2 ? 10.sup.?13 Example 7 PEF b: 5.1 1.32 118 51 4.6 ? 10.sup.?13 Example 8 PET b: 1.2 1.17 78 157 3.3 ? 10.sup.?12 Example 9 PET b: 1.6 1.05 65 134 8.1 ? 10.sup.?12 Example 10 PET b: 3.6 0.92 64 139 6.6 ? 10.sup.?12 Example 11 PBT b: 0.1 0.96 85 141 8.2 ? 10.sup.?12 Example 12 PTT b: 0.1 1.13 62 185 6.4 ? 10.sup.?12 Example 13 PBF b: 5.2 1.22 62 266 9.1 ? 10.sup.?13 Example 14 PTF b: 6.7 1.19 76 39 1.4 ? 10.sup.?12 Comparative PEF b: 26.8 0.86 84 9 3.9 ? 10.sup.?12 Example 1 Comparative PET b: 8.5 0.66 56 34 9.4 ? 10.sup.?12 Example 2

[0075] Generally, in a nano-compounding process, the introduction of a small amount of a nanomaterial can affect a structure of a polymer, thereby affecting mechanical properties of the polymer. Common toughening mechanisms of polymer nanocomposites are as follows: debonding and pull-out, crack deflection, crack pinning, and crack bridging. In a polymerization process of a polyester, appropriate weak interfacial bonding is formed between the catalyst nano-TiO.sub.2(B) and a polymer matrix instead of strong interfacial bonding, and under an action of an external force load, the nanomaterial is prone to cavitation phenomena such as debonding, crack propagation direction deflection, and nanomaterial pull-out in the polymer matrix, where an interface will play a role of blocking the crack propagation and consume an additional energy, which can increase a total fracture energy, make the material to be toughened, and bring improvement of other properties. It can be seen from Examples 1 to 4, Examples 6 to 7, and Comparative Example 1 that, a product PEF obtained with the nano-TiO.sub.2(B) as a catalyst has a better tensile strength and elongation at break than those of a product PEF obtained with TBT as a catalyst, that is, when the nano-TiO.sub.2(B) is used as a catalyst, the obtained product PEF has improved toughness.

[0076] It can be seen from Examples 1 to 4, Examples 6 to 7, and Comparative Example 1 that, at a same polyester synthesis temperature, the polyester obtained in Comparative Example 1 has a lower viscosity than that of the polyester obtained with TiO.sub.2(B) as a catalyst; the polyester obtained in Comparative Example 1 has a higher chromaticity value b than that of the polyester prepared in the example of the present application; and the polyester obtained in Comparative Example 1 has a higher oxygen transmission coefficient than that of the polyester prepared in the example of the present application. That is, at a same synthesis temperature, the preparation of a polyester with TiO.sub.2(B) as a catalyst in the present application can obtain a polyester with an improved viscosity, a reduced value b, and improved barrier properties.

[0077] It can be seen from Example 5, Examples 8 to 10, and Comparative Example 2 that, at a same polyester synthesis temperature, the polyester obtained in Comparative Example 2 has a lower viscosity than that of the polyester obtained with TiO.sub.2(B) as a catalyst; the polyester obtained in Comparative Example 2 has a higher chromaticity value b than that of the polyester prepared in the example of the present application; and the polyester obtained in Comparative Example 2 has a higher oxygen transmission coefficient than that of the polyester prepared in the example of the present application. That is, at a same synthesis temperature, the preparation of a polyester with TiO.sub.2(B) as a catalyst in the present application can obtain a polyester with an improved viscosity, a reduced value b, and improved barrier properties.

[0078] It can be seen from Example 5, Examples 8 to 10, and Comparative Example 2 that, a product PET obtained with the nano-TiO.sub.2(B) as a catalyst has a better tensile strength and elongation at break than those of a product PET obtained with TBT as a catalyst, that is, when the nano-TiO.sub.2(B) is used as a catalyst, the obtained product PET has improved toughness.

[0079] FIG. 5 to FIG. 10 show cross-sectional EM images of the prepared composite polyester. It can be seen from FIG. 5 to FIG. 10 that, there is no obvious agglomeration phenomenon in a matrix of the composite polyester, indicating that the catalyst is dispersed in situ in the polyester matrix and the dispersibility is very well.

[0080] The above examples are merely few examples of the present application, and do not limit the present application in any form. Although the present application is disclosed as above with preferred examples, the present application is not limited thereto. Some changes or modifications made by any technical personnel familiar with the profession using the technical content disclosed above without departing from the scope of the technical solutions of the present application are equivalent to equivalent implementation cases and fall within the scope of the technical solutions.