High Strength Ultra-thin Biodegradable Film and Preparation Method Thereof

Abstract

A biodegradable film is prepared from a composition that includes a copolyester obtained by extrusion reaction of a branched aliphatic-aromatic copolyester derived from monomer a, monomer b, monomer c and monomer d with an organic peroxide. The film can be completely degraded into small molecular products such as carbon dioxide, water and the like under natural or composting conditions. Moreover, the film can be prepared having a thickness of 4-50 μm as required, and its mechanical properties can reach the same level as or even better than those of LDPE film.

Claims

1. A biodegradable film, which is prepared from a composition comprising: a copolyester obtained by extrusion reaction of a branched aliphatic-aromatic copolyester derived from monomer a, monomer b, monomer c and monomer d with an organic peroxide, wherein the monomer a is an aromatic dibasic acid or an ester derivative thereof, the monomer b is one or more of C.sub.2-C.sub.10 aliphatic dihydric alcohols or C.sub.3-C.sub.10 alicyclic dihydric alcohols; the monomer c is a C.sub.4-C.sub.20 aliphatic dibasic acid or an ester derivative thereof; the monomer d is one or more of polyols with a functionality of more than 2, polycarboxylic acids with a functionality of more than 2, anhydrides with a functionality of more than 2, epoxy compounds or anhydrides with hydroxyl or carboxyl group, glycidyl ester, glycidyl ether, glycidol, lactones or cyclic carbonates with hydroxyl or carboxyl side group; the branched aliphatic-aromatic copolyester is obtained by reacting monomer a, monomer b, monomer c and monomer d under the action of a catalyst system containing a second catalyst, wherein the second catalyst is a compound of RE(R.sup.3).sub.3, wherein RE is a rare earth metal element, R.sup.3 is at least one selected from the group consisting of halogen, alkoxy group, aryloxy group, acetylacetone group and R.sup.4COO— group, wherein R.sup.4 is C.sub.1-C.sub.30 alkyl group.

2. (canceled)

3. The biodegradable film as claimed in claim 1, wherein, in the compound of RE(R.sup.3).sub.3 as the second catalyst, RE is lanthanum, cerium, praseodymium, neodymium, terbium, ytterbium, dysprosium, samarium or scandium; the halogen is chlorine or bromine, the alkoxy group is C.sub.3-C.sub.6 alkoxy group, the aryloxy group is aryloxy group comprising at least one benzene ring and/or naphthalene ring, and R.sup.4 is C.sub.1-C.sub.20 alkyl group.

4. The biodegradable film as claimed in claim 1, wherein the catalyst system further comprises a first catalyst and/or a third catalyst; wherein the first catalyst is one or more selected from the group consisting of an oxide of M, M(OR.sup.1).sub.n and M(OOCR.sup.2).sub.m, wherein M is titanium, antimony or zinc, n and m are each independently the valence of M, R.sup.1 is C.sub.1-C.sub.10 alkyl group, and R.sup.2 is C.sub.1-C.sub.20 alkyl group; the third catalyst is at least one organotin compound.

5. The biodegradable film as claimed in claim 4, wherein the molar ratio of the catalyst in its entirety to the monomer (a+c) is 1:1000-20000, and the molar ratio of the first catalyst to the second catalyst to the third catalyst is 0-20:0.1-10:0-1, preferably 0.1-20:0.1-10:1.

6. The biodegradable film as claimed in claim 1, wherein the amounts of various monomers are as follows: the molar ratio of (a+c) to b is 1:0.8-3, the molar ratio of (a+c) to d is 100-2000:1, the molar ratio of a to c is 0:100-95:5, preferably 0:100-60:40.

7. The biodegradable film as claimed in claim 1, wherein the monomer a is selected from terephthalic acid or dimethyl terephthalate; the monomer b is selected from ethylene glycol, 1,3-propanediol or 1,4-butanediol; the monomer c is selected from succinic acid, succinic anhydride, dimethyl succinate, adipic acid or dimethyl adipate; the monomer d is selected from pyromellitic dianhydride, glycerol, pentaerythritol, glycidyl succinate, glycidyl adipate, glycidyl terephthalate, ethylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, glycidic acid, glycidol, 3-hydroxyphthalic anhydride, 4-hydroxyphthalic anhydride, 3-hydroxymethylcaprolactone, a five-membered or six-membered cyclic carbonate with an alkylhydroxy group or an alkylcarboxyl group.

8. The biodegradable film as claimed in claim 1, wherein the branched aliphatic-aromatic copolyester is prepared as follows: under the action of a catalyst system, monomer a, monomer b, monomer c and monomer d are mixed for esterification or transesterification reaction, or the esterification or transesterification product of monomer a and monomer b and the esterification or transesterification product of monomer c and monomer d are mixed for copolycondensation reaction.

9. The biodegradable film as claimed in claim 1, wherein the branched aliphatic-aromatic copolyester has a melt index of 2-100 g/10 min, preferably 5-100 g/10 min at 190° C. under a load of 2.16 kg.

10. The biodegradable film as claimed in claim 1, wherein the organic peroxide is selected from dialkyl peroxides, diacyl peroxides or peroxyesters.

11. The biodegradable film as claimed in claim 10, wherein the dialkyl peroxide is selected from dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or di(tert-butylperoxyisopropyl)benzene; the diacyl peroxide is selected from benzoyl peroxide or lauroyl peroxide.

12. The biodegradable film as claimed in claim 1, wherein the organic peroxide is used in an amount of 0.01 to 5 wt % based on the amount of the branched aliphatic-aromatic copolyester.

13. The biodegradable film as claimed in claim 1, wherein the copolyester has a melt index of 0.1 to 10 g/10 min at 190° C. under a load of 2.16 kg.

14. The biodegradable film as claimed in claim 1, wherein the composition also comprises additives, and the additives include an antioxidant, a slipping agent, an anti-blocking agent and a nucleating agent.

15. The biodegradable film as claimed in claim 14, wherein the amount of the antioxidant is 0.05-5 parts, the amount of the slipping agent is 0.05-5 parts, the amount of the anti-blocking agent is 0.05-5 parts, and the amount of the nucleating agent is 0.1-20 parts based on 100 parts by weight of the copolyester.

16. The biodegradable film as claimed in claim 14, wherein the antioxidant is a mixture of a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 1:1.

17. The biodegradable film as claimed in claim 16, wherein the hindered phenol antioxidant is selected from antioxidant 1010, antioxidant 1076, antioxidant 245 or antioxidant 246; the phosphite antioxidant is selected from triphenyl phosphate, trimethyl phosphate or antioxidant 168.

18. The biodegradable film as claimed in claim 14, wherein the slipping agent is stearate or organic carboxylic acid amide, wherein the stearate is preferably calcium stearate, and the organic carboxylic acid amide is preferably erucamide or oleamide; the anti-blocking agent is silica or talc; the nucleating agent is selected from hyperbranched polyamides, low density polyethylene or ethylene-methacrylic acid ionomers.

19. A method for preparing the biodegradable film as claimed in claim 1, the method comprising the steps of: 1) preparing a copolyester by extrusion reaction of a branched aliphatic-aromatic copolyester derived from monomer a, monomer b, monomer c and monomer d with an organic peroxide; the monomer a is an aromatic dibasic acid or an ester derivative thereof, the monomer b is one or more of C.sub.2-C.sub.10 aliphatic dihydric alcohols or C.sub.3-C.sub.10 alicyclic dihydric alcohols; the monomer c is a C.sub.4-C.sub.20 aliphatic dibasic acid or an ester derivative thereof, the monomer d is one or more of polyols with a functionality of more than 2, polycarboxylic acids with a functionality of more than 2, anhydrides with a functionality of more than 2, epoxy compounds or anhydrides with hydroxyl or carboxyl group, glycidyl ester, glycidyl ether, glycidol, lactones or cyclic carbonates with hydroxyl or carboxyl side group; the branched aliphatic-aromatic copolyester is obtained by reacting monomer a, monomer b, monomer c and monomer d under the action of a catalyst system containing a second catalyst, wherein the second catalyst is a compound of RE(R.sup.3).sub.3, wherein RE is a rare earth metal element, R.sup.3 is at least one selected from the group consisting of halogen, alkoxy group, aryloxy group, acetylacetone group and R.sup.4COO— group, wherein R.sup.4 is C.sub.1-C.sub.30 alkyl group; 2) extruding and granulating the copolyester obtained in the step 1) to obtain a composition; and 3) blowing the composition to obtain the biodegradable film.

20. (canceled)

21. The method as claimed in claim 19, wherein, in the compound of RE(R.sup.3).sub.3 as the second catalyst, RE is lanthanum, cerium, praseodymium, neodymium, terbium, ytterbium, dysprosium, samarium or scandium; the halogen is chlorine or bromine, the alkoxy group is C.sub.3-C.sub.6 alkoxy group, the aryloxy group is aryloxy group comprising at least one benzene ring and/or naphthalene ring, and R.sup.4 is C.sub.1-C.sub.20 alkyl group.

22. The method as claimed in claim 19, wherein the catalyst system further comprises a first catalyst and/or a third catalyst; wherein the first catalyst is one or more selected from the group consisting of an oxide of M, M(OR.sup.1).sub.n and M(OOCR.sup.2).sub.m, wherein M is titanium, antimony or zinc, n and m are each independently the valence of M, R.sup.1 is C.sub.1-C.sub.10 alkyl group, and R.sup.2 is C.sub.1-C.sub.20 alkyl group; the third catalyst is at least one organotin compound.

23. The method as claimed in claim 22, wherein the molar ratio of the catalyst in its entirety to the monomer (a+c) is 1: 1000-20000, and the molar ratio of the first catalyst to the second catalyst to the third catalyst is 0-20:0.1-10: 0-1, preferably 0.1-20:0.1-10:1.

24. The method as claimed in claim 19, wherein the amounts of various monomers are as follows: the molar ratio of (a+c) to b is 1:0.8-3, the molar ratio of (a+c) to d is 100-2000:1, the molar ratio of a to c is 0:100-95:5, preferably 0:100-60:40.

25. The method as claimed in claim 19, wherein the monomer a is selected from terephthalic acid or dimethyl terephthalate; the monomer b is selected from 1,3-propanediol or 1,4-butanediol; the monomer c is selected from succinic acid, succinic anhydride, dimethyl succinate, adipic acid or dimethyl adipate; the monomer d is selected from pyromellitic dianhydride, glycerol, pentaerythritol, glycidyl succinate, glycidyl adipate, glycidyl terephthalate, ethylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, glycidic acid, glycidol, 3-hydroxyphthalic anhydride, 4-hydroxyphthalic anhydride, 3-hydroxymethylcaprolactone, a five-membered or six-membered cyclic carbonate with an alkylhydroxy group or an alkylcarboxyl group.

26. The method as claimed in claim 19, wherein the branched aliphatic-aromatic copolyester is prepared as follows: under the action of a catalyst system, monomer a, monomer b, monomer c and monomer d are mixed for esterification or transesterification reaction, or the esterification or transesterification product of monomer a and monomer b and the esterification or transesterification product of monomer c and monomer d are mixed for copolycondensation reaction.

27. The method as claimed in claim 19, wherein the branched aliphatic-aromatic copolyester has a melt index of 2-100 g/10 min, preferably 5-100 g/10 min at 190° C. under a load of 2.16 kg.

28. The method as claimed in claim 19, wherein the extrusion temperature in the step 1) is 130-190° C., preferably 150-180° C., and more preferably 160-180° C.

29. The method as claimed in claim 19, wherein the organic peroxide is selected from dialkyl peroxides, diacyl peroxides or peroxyesters.

30. The method as claimed in claim 29, wherein the dialkyl peroxide is selected from dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or di(tert-butylperoxyisopropyl)benzene; the diacyl peroxide is selected from benzoyl peroxide or lauroyl peroxide.

31. The method as claimed in claim 19, wherein the organic peroxide is used in an amount of 0.01 to 5 wt % based on the amount of the branched aliphatic-aromatic copolyester.

32. The method as claimed in claim 19, wherein the copolyester has a melt index of 0.1 to 10 g/10 min at 190° C. under a load of 2.16 kg.

33. The method as claimed in claim 19, wherein the copolyester is also mixed with additives in the step 2), wherein the additives include an antioxidant, a slipping agent, an anti-blocking agent and a nucleating agent.

34. The method as claimed in claim 33, wherein the amount of the antioxidant is 0.05-5 parts, the amount of the slipping agent is 0.05-5 parts, the amount of the anti-blocking agent is 0.05-5 parts, and the amount of the nucleating agent is 0.1-20 parts based on 100 parts by weight of the copolyester.

35. The method as claimed in claim 33, wherein the antioxidant is a mixture of a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 1:1.

36. The method as claimed in claim 35, wherein the hindered phenol antioxidant is selected from antioxidant 1010, antioxidant 1076, antioxidant 245 or antioxidant 246; the phosphite antioxidant is selected from triphenyl phosphate, trimethyl phosphate or antioxidant 168.

37. The method as claimed in claim 33, wherein the slipping agent is stearate or organic carboxylic acid amide, wherein the stearate is preferably calcium stearate, and the organic carboxylic acid amide is preferably erucamide or oleamide; the anti-blocking agent is silica or talc; the nucleating agent is selected from hyperbranched polyamides, low density polyethylene or ethylene-methacrylic acid ionomers.

38. A copolyester, which is obtained by extrusion reaction of a branched aliphatic-aromatic copolyester derived from monomer a, monomer b, monomer c and monomer d with an organic peroxide, wherein the monomer a is an aromatic dibasic acid or an ester derivative thereof, the monomer b is one or more of C.sub.2-C.sub.10 aliphatic dihydric alcohols or C.sub.3-C.sub.10 alicyclic dihydric alcohols; the monomer c is a C.sub.4-C.sub.20 aliphatic dibasic acid or an ester derivative thereof, the monomer d is one or more of polyols with a functionality of more than 2, polycarboxylic acids with a functionality of more than 2, anhydrides with a functionality of more than 2, epoxy compounds or anhydrides with hydroxyl or carboxyl group, glycidyl ester, glycidyl ether, glycidol, lactones or cyclic carbonates with hydroxyl or carboxyl side group: the branched aliphatic-aromatic copolyester is obtained by reacting monomer a, monomer b, monomer c and monomer d under the action of a catalyst system containing a second catalyst, wherein the second catalyst is a compound of RE(R.sup.3).sub.3, wherein RE is a rare earth metal element, R.sup.3 is at least one selected from the group consisting of halogen, alkoxy group, aryloxy group, acetylacetone group and R.sup.4COO— group, wherein R.sup.4 is C.sub.1-C.sub.30 alkyl group.

39. (canceled)

40. The copolyester as claimed in claim 38, wherein, in the compound of RE(R.sup.3).sub.3 as the second catalyst, RE is lanthanum, cerium, praseodymium, neodymium, terbium, ytterbium, dysprosium, samarium or scandium; the halogen is chlorine or bromine, the alkoxy group is C.sub.3-C.sub.6 alkoxy group, the aryloxy group is aryloxy group comprising at least one benzene ring and/or naphthalene ring, and R.sup.4 is C.sub.1-C.sub.20 alkyl group.

41. The copolyester as claimed in claim 8, wherein the catalyst system further comprises a first catalyst and/or a third catalyst; wherein the first catalyst is one or more selected from the group consisting of an oxide of M, M(OR.sup.1).sub.n and M(OOCR.sup.2).sub.m, wherein M is titanium, antimony or zinc, n and m are each independently the valence of M, R.sup.1 is C.sub.1-C.sub.10 alkyl group, and R.sup.2 is C.sub.1-C.sub.20 alkyl group; the third catalyst is at least one organotin compound.

42. The copolyester as claimed in claim 41, wherein the molar ratio of the catalyst in its entirety to the monomer (a+c) is 1: 1000-20000, and the molar ratio of the first catalyst to the second catalyst to the third catalyst is 0-20:0.1-10: 0-1, preferably 0.1-20:0.1-10:1.

43. The copolyester as claimed in claim 38, wherein the amounts of various monomers are as follows: the molar ratio of (a+c) to b is 1:0.8-3, the molar ratio of (a+c) to d is 100-2000:1, the molar ratio of a to c is 0:100-95:5, preferably 0: 100-60:40.

44. The copolyester as claimed in claim 38, wherein the monomer a is selected from terephthalic acid or dimethyl terephthalate; the monomer b is selected from ethylene glycol, 1,3-propanediol or 1,4-butanediol; the monomer c is selected from succinic acid, succinic anhydride, dimethyl succinate, adipic acid or dimethyl adipate; the monomer d is selected from pyromellitic dianhydride, glycerol, pentaerythritol, glycidyl succinate, glycidyl adipate, glycidyl terephthalate, ethylene glycol glycidyl ether, 1,4-butanediol glycidyl ether, glycidic acid, glycidol, 3-hydroxyphthalic anhydride, 4-hydroxyphthalic anhydride, 3-hydroxymethylcaprolactone, a five-membered or six-membered cyclic carbonate with an alkylhydroxy group or an alkylcarboxyl group.

45. The copolyester as claimed in claim 38, wherein the branched aliphatic-aromatic copolyester is prepared as follows: under the action of a catalyst system, monomer a, monomer b, monomer c and monomer d are mixed for esterification or transesterification reaction, or the esterification or transesterification product of monomer a and monomer b and the esterification or transesterification product of monomer c and monomer d are mixed for copolycondensation reaction.

46. The copolyester as claimed in claim 38, wherein the branched aliphatic-aromatic copolyester has a melt index of 2-100 g/10 min, preferably 5-100 g/10 min at 190° C. under a load of 2.16 kg.

47. The copolyester as claimed in claim 38, wherein the organic peroxide is selected from dialkyl peroxides, diacyl peroxides or peroxyesters.

48. The copolyester as claimed in claim 47, wherein the dialkyl peroxide is selected from dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane or di(tert-butylperoxyisopropyl)benzene; the diacyl peroxide is selected from benzoyl peroxide or lauroyl peroxide.

49. The copolyester as claimed in claim 38, wherein the organic peroxide is used in an amount of 0.01 to 5 wt % based on the amount of the branched aliphatic-aromatic copolyester.

50. The copolyester as claimed in claim 38, wherein the copolyester has a melt index of 0.1 to 10 g/10 min at 190° C. under a load of 2.16 kg.

Description

EXAMPLE 1

[0101] A method for preparing the biodegradable film, the method comprising the steps of:

[0102] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO), 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were mixed to react in a reaction kettle (esterification at 150-230° C. and polycondensation at 230-260° C.), the prepared branched aliphatic-aromatic copolyester having a melt index of 23 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0103] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in a German Kekuron zsk25 twin-screw extruder, wherein various sections were at the temperatures of 130-150-170° C., to prepare a copolyester, the prepared copolyester having a melt index of 2.2 g/10 min at 190° C. under a load of 2.16 kg;

[0104] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in a German Kekuron zsk25 twin-screw extruder and granulation, wherein various sections were at the temperatures of 130-150-170° C., to obtain a film blowing material;

[0105] 4) the film blowing material was blown on a German Collin ep30 film blowing machine at the film blowing temperature of 150-190° C., at a blow-up ratio of 5-8, to obtain a film with a thickness of 10 μm.

[0106] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 2

[0107] A method for preparing the biodegradable film, the method comprising the steps of:

[0108] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 570.8 g (7.5 mol) of monomer b 1,3-propanediol, 438.4 g (3 mol) of monomer c dimethyl succinate and 1 g (0.0046 mol) of monomer d pyromellitic dianhydride were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 15 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0109] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 1.8 g/10 min at 190° C. under a load of 2.16 kg;

[0110] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0111] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0112] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0113] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 3

[0114] A method for preparing the biodegradable film, the method comprising the steps of:

[0115] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 679.6 g (3.5 mol) of monomer a dimethyl terephthalate, 570.8 g (7.5 mol) of monomer b 1,3-propanediol, 657.6 g (4.5 mol) of monomer c adipic acid and 0.7 g (0.005 mol) of monomer d pentaerythritol were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 40 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0116] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 2.8 g/10 min at 190° C. under a load of 2.16 kg;

[0117] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material:

[0118] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0119] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0120] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 4

[0121] A method for preparing the biodegradable film, the method comprising the steps of:

[0122] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO), 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 40 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.174 g of tetrabutyl titanate, 0.071 g of dibutyltin oxide, 0.099 g of triphenylhydroxytin and 0.22 g of lanthanum stearate;

[0123] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 5 g of lauroyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 180° C., to prepare a copolyester, the prepared copolyester having a melt index of 2.6 g/10 min at 190° C. under a load of 2.16 kg:

[0124] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 180° C. and granulation, to obtain a film blowing material;

[0125] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0126] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0127] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 5

[0128] A method for preparing the biodegradable film, the method comprising the steps of.

[0129] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid, 570.8 g (7.5 mol) of monomer b 1,3-propanediol, 438.4 g (3 mol) of monomer c dimethyl succinate and 1 g (0.0046 mol) of monomer d pyromellitic dianhydride were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 80 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0130] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 0.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 160° C., to prepare a copolyester, the prepared copolyester having a melt index of 1.5 g/10 min at 190° C. under a load of 2.16 kg.

[0131] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 160° C. and granulation, to obtain a film blowing material;

[0132] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0133] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0134] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 6

[0135] A method for preparing the biodegradable film, the method comprising the steps of:

[0136] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO), 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 25 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0137] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 1.8 g/10 min at 190° C. under a load of 2.16 kg;

[0138] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1.5 g of antioxidant 246, 1.5 g of triphenyl phosphate, 1 g of slipping agent calcium stearate, 1 g of anti-blocking agent talc and 5 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0139] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0140] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0141] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 7

[0142] A method for preparing the biodegradable film, the method comprising the steps of: 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA) and 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO) were subjected to esterification reaction, 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were subjected to esterification reaction, and then the two esterification products were mixed to carry out copolycondensation reaction, the prepared branched aliphatic-aromatic copolyester having a melt index of 42 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0143] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 2.4 g/10 min at 190° C. under a load of 2.16 kg;

[0144] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0145] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0146] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0147] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

EXAMPLE 8

[0148] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA) and monomer b 650 g (7.21 mol) of 1,4-butanediol (BDO) were subjected to esterification reaction, 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were subjected to esterification reaction, and then the two esterification products were mixed to carry out copolycondensation reaction, the prepared branched aliphatic-aromatic copolyester having a melt index of 80 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst was 0.62 g of lanthanum stearate;

[0149] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 3.6 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 3.2 g/10 min at 190° C. under a load of 2.16 kg;

[0150] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material:

[0151] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0152] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0153] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

COMPARATIVE EXAMPLE 1

[0154] A method for preparing the biodegradable film, the method comprising the steps of:

[0155] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO), 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 20 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0156] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0157] 3) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0158] Regarding the conditions and devices in the above steps 1)-3), please refer to the corresponding steps in Example 1.

[0159] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

COMPARATIVE EXAMPLE 2

[0160] A method for preparing the biodegradable film, the method comprising the steps of:

[0161] 1) preparation of an aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO) and 330 g (2.79 mol) of monomer c succinic acid (SA) were mixed to react, the prepared aliphatic-aromatic copolyester having a melt index of 30 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.31 g of lanthanum stearate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0162] 2) 500 g of the aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 5 g/10 min at 190° C. under a load of 2.16 kg;

[0163] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0164] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0165] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0166] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

COMPARATIVE EXAMPLE 3

[0167] A method for preparing the biodegradable film, the method comprising the steps of:

[0168] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA) and 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO) were subjected to esterification reaction, followed by the reaction with 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol, the prepared branched aliphatic-aromatic copolyester having a melt index of 100 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst was 0.45 g of tetrabutyl titanate;

[0169] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 5 g/10 min at 190° C. under a load of 2.16 kg;

[0170] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0171] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0172] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0173] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

COMPARATIVE EXAMPLE 4

[0174] A method for preparing the biodegradable film, the method comprising the steps of:

[0175] 1) preparation of an aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO) and 330 g (2.79 mol) of monomer c succinic acid (SA) were mixed to react, the prepared aliphatic-aromatic copolyester having a melt index of 60 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst was 0.62 g of lanthanum stearate;

[0176] 2) 500 g of the aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester, the prepared copolyester having a melt index of 5 g/10 min at 190° C. under a load of 2.16 kg;

[0177] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0178] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0179] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0180] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

COMPARATIVE EXAMPLE 5

[0181] A method for preparing the biodegradable film, the method comprising the steps of:

[0182] 1) preparation of a branched aliphatic-aromatic copolyester: under the action of a catalyst, 423.8 g (2.55 mol) of monomer a terephthalic acid (PTA), 650 g (7.21 mol) of monomer b 1,4-butanediol (BDO), 330 g (2.79 mol) of monomer c succinic acid (SA) and 1 g (0.01 mol) of monomer d glycerol were mixed to react, the prepared branched aliphatic-aromatic copolyester having a melt index of 20 g/10 min at 190° C. under a load of 2.16 kg, wherein the catalyst contained 0.245 g of tetrabutyl titanate, 0.1 g of dibutyltin oxide and 0.14 g of triphenylhydroxytin;

[0183] 2) 500 g of the branched aliphatic-aromatic copolyester prepared in the step 1) and 2.5 g of benzoyl peroxide were subjected to extrusion reaction in the extruder at the temperature of 170° C., to prepare a copolyester;

[0184] 3) 500 g of the copolyester prepared in the step 2) was mixed with 1 g of antioxidant 1010, 1 g of antioxidant 168, 2.25 g of slipping agent erucamide, 2.25 g of anti-blocking agent silica and 10 g of nucleating agent Dupont Surlyn8920 resin, and subjected to melt extrusion in the twin-screw extruder at the temperature of 170° C. and granulation, to obtain a film blowing material;

[0185] 4) the film blowing material was blown on the film blowing machine, to obtain a film with a thickness of 10 μm.

[0186] Regarding the conditions and devices in the above steps 1)-4), please refer to the corresponding steps in Example 1.

[0187] The obtained film was subjected to performance tests, and the test results of optical property, thermal property, barrier property and aging property were shown in Table 1, and the mechanical properties were shown in Table 2.

TABLE-US-00002 TABLE 1 Nominal strain Glass Water retention rate Light transition permeability/ after 208 hour Density/ Surface Internal transmittance/ Melting temperature/ g .Math. m.sup.−2 .Math. d.sup.−1, xenon lamp g .Math. cm.sup.−3 Haze/% haze/% haze/% % point/° C. ° C. 38° C., 90% RH irradiation (%) Example 1 1.25 40 37 2.8 89 128 −15.0 480 75 Example 2 1.25 38 35 2.9 92 127 −14.2 560 67 Example 3 1.24 41 38 2.7 88 115 −29.6 980 84 Example 4 1.25 39 35 3.6 87 125 −15.2 640 91 Example 5 1.24 42 39 3.1 89 126 −13.8 570 87 Example 6 1.25 39 37 2.3 91 129 −13.6 510 95 Example 7 1.24 37 35 2.2 88 128 −14.5 680 98 Example 8 1.25 38 36 2.3 89 130 −15.6 530 96 Comparative 1.24 45 40 5.4 80 128 −15.2 780 63 Example 1 Comparative 1.25 51 45 5.8 82 125 −14.6 890 62 Example 2 Comparative 1.25 48 44 4.9 88 127 −14.5 850 58 Example 3 Comparative 1.24 47 43 4.5 85 129 −14.6 800 65 Example 4 Comparative 1.25 46 42 5.2 83 126 −14.6 980 54 Example 5

TABLE-US-00003 TABLE 2 Com- Com- Com- Com- Com- par- par- par- par- par- ative ative ative ative ative Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 1 ple 2 ple 3 ple 4 ple 5 Dart impact/g 22 23 21 22 25 24 20 19 18 17 16 19 16 (ASTM method A) Yield MD 21.4 22.3 19.8 22.5 24.8 21.3 20.1 19.5 15 12 13 18 12 point/% TD 17.9 19.2 16.3 20.1 22.3 16.9 16.8 16.5 11 9 10 15 10 Tensile MD 3.1 3.5 2.9 3.3 3.8 3.2 3.0 3.1 2.3 1.8 2.8 3.0 1.5 load/N TD 2.8 3.2 2.7 3.1 3.5 2.9 2.7 2.8 1.9 1.5 2.3 2.8 1.3 (10 mm) Tensile MD 14 15 13 14 18 13 13 12 8 7 8 9 6 strength at TD 10 12 11 11 15 10 10 10 5 5 6 8 4 yield/MPa Tensile MD 24 26 21 25 30 22 23 21 15 13 12 16 10 strength at TD 22 24 19 23 25 19 21 20 13 10 10 14 8 break/MPa Elongation MD 240 300 350 250 320 190 200 190 150 100 120 160 110 at break/% TD 420 450 480 380 480 300 290 250 180 120 140 170 100 Right MD 1.1 13 1.2 1.5 1.5 1.0 1.2 1.1 0.8 0.6 0.7 0.9 0.8 angle tear TD 1.7 2.0 1.8 2.1 1.9 1.5 1.5 1.3 0.9 0.8 0.8 1.0 0.6 load/N

[0188] It can be seen from the data in Table 1 and Table 2 that, compared with Comparative Example 1 which does not include the chain extension and tackifying step and Comparative Example 2 which includes the aliphatic-aromatic copolyester prepared using only three monomers, the films prepared in Examples 1-7 of the invention all have optical properties better than those of Comparative Examples 1 and 2, thermal properties basically equivalent to those of Comparative Examples 1 and 2, barrier properties and aging properties basically better than those of Comparative Examples 1 and 2, and overall mechanical properties better than those of Comparative Examples 1 and 2. Moreover, compared with Comparative Example 3 which includes the aliphatic-aromatic copolyester prepared using only the first catalyst and Comparative Example 4 which includes the aliphatic-aromatic copolyester prepared using only three monomers, the film prepared in Example 8 of the invention has optical property better than those of Comparative Examples 3 and 4, thermal property basically equivalent to those of Comparative Examples 3 and 4, barrier property and aging property better than those of Comparative Examples 3 and 4, and overall mechanical properties basically better than those of Comparative Examples 3 and 4. In addition, compared with Comparative Example 5 which includes the aliphatic-aromatic copolyester prepared using only the first catalyst and the third catalyst, the films prepared in Examples 1-8 of the invention have optical properties better than that of Comparative Example 5, thermal properties basically equivalent to that of Comparative Example 5, and barrier properties, aging properties and overall mechanical properties better than those of Comparative Example 5.

[0189] The examples of the invention have been described above, the above description is exemplary, not exhaustive, and the invention is not limited to the examples. Without departing from the scope and spirit of the examples, many modifications and changes are obvious to those of ordinary skill in the art.