A kind of PBAT composite film and its preparation method

Abstract

The application discloses a kind of PBAT composite film and preparation method thereof, the PBAT composite film includes following raw materials, PBAT resin, calcium carbonate, optional PLA and optional other auxiliary agent, wherein, the preparation method of the PBAT resin includes following steps: (1) short straight chain aliphatic dibasic acid is esterified with short branched-chain aliphatic dihydric alcohol, and polyester oligomer A is obtained;(2) adipic acid, terephthalic acid and 1,4-butanediol are esterified and polycondensed, and polyester oligomer B is obtained;(3) polyester oligomer B is added to polyester oligomer A to carry out ester exchange reaction, and PBAT resin is obtained.The application can significantly improve the molecular chain movement ability by reacting with aliphatic polyester oligomer during PBAT polymerization, so that the glass transition temperature and crystallinity of PBAT are significantly reduced, so as to improve the heat sealing effect of composite film.

Description

Technical Field

[0001] This invention belongs to the field of polymer material synthesis, specifically relating to a PBAT composite film with good heat-sealing performance and its preparation method. Background Technology

[0002] With the continuous improvement of people's living standards and the increasing severity of "white pollution" (plastic pollution), PBAT, as a biodegradable plastic, is being used more and more widely in the field of composite film packaging. To prevent leakage and breakage of flexible packaging bags, the composite film needs to have good heat-sealing properties. Heat-sealing performance is one of the key indicators for evaluating the performance of composite films, and its quality mainly depends on the structure of the polymer used in the film substrate. In the molten state, the polymer chains on the plastic sealing surface diffuse, penetrate, and entangle with each other, thus sealing the opening. Therefore, the mobility of polymer molecular chains plays a decisive role in heat sealing.

[0003] Polybutylene adipate (PBAT) combines the degradation properties of aliphatic polyesters with the mechanical properties of aromatic polyesters, exhibiting good ductility and elongation at break, making it widely used in packaging films. However, its mechanical strength is slightly inferior and its cost is relatively high. Therefore, calcium carbonate, PLA, and other additives are commonly added during processing to reduce costs and improve efficiency.

[0004] Patent CN202210035112.5 discloses a method for preparing a PBAT / PLA / CaCO3 fully biodegradable composite material. Without compromising the inherent biodegradability of the raw materials, the introduction of a small amount of PLA imparts high strength to the composite material, while the addition of calcium carbonate significantly reduces production costs while improving strength, thus facilitating industrial production. Patent CN202111531707.1 provides a high-stiffness, high-toughness, fully biodegradable blown film modified material, prepared by blending 0-15 parts PLA, 50-70 parts PBAT, 20-50 parts calcium carbonate, 0.1-1 parts chain extender, and 0.1-10 parts reinforcing phase. However, these patents generally studied the influence of various components on the mechanical properties of the film, but neglected the crucial indicator of composite films as packaging materials—heat-sealing performance. Due to the addition of certain amounts of calcium carbonate, PLA, and other materials, the composite film has a high crystallization temperature and crystallinity, significantly reducing its heat-sealing performance and affecting its application in the packaging field. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, this invention provides a PBAT composite film and its preparation method. During the synthesis of PBAT, the reaction with aliphatic polyester oligomers can significantly improve the molecular chain mobility, thereby significantly reducing the glass transition temperature and crystallinity of PBAT, thus improving the heat sealing effect of the composite film.

[0006] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0007] A PBAT composite film comprises the following raw materials: PBAT resin, calcium carbonate, optional PLA, and optional other additives, wherein the preparation method of the PBAT resin includes the following steps:

[0008] (1) Short-chain aliphatic dicarboxylic acid is esterified with aliphatic diol containing short branches to obtain polyester oligomer A.

[0009] (2) Adipic acid (AA), terephthalic acid (PTA) and 1,4-butanediol (BDO) are subjected to esterification polycondensation reaction to obtain polyester oligomer B;

[0010] (3) Polyester oligomer A was added to polyester oligomer B to carry out transesterification reaction to obtain PBAT resin;

[0011] In step (1), the short straight-chain aliphatic dicarboxylic acid is a straight-chain aliphatic dicarboxylic acid with 4-10 carbon atoms, preferably selected from one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, with adipic acid being the most preferred.

[0012] The short-branched aliphatic diol is an aliphatic diol with a straight-chain alkyl substituent. Preferably, the short-branched aliphatic diol has 3-10 carbon atoms and is preferably selected from one or more of 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, and 1,5-hexanediol, with 1,2-propanediol being the most preferred.

[0013] In step (1), a short-chain aliphatic dicarboxylic acid and aliphatic diol containing short branches undergo esterification in the presence of a catalyst, wherein the catalyst is an organotitanium compound selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate and tetraoctyl titanate, preferably tetrabutyl titanate.

[0014] In step (1), the molar ratio of the short-chain aliphatic dicarboxylic acid to the amount of short-chain aliphatic diol added is 1:1.2-1.5;

[0015] The catalyst added, based on titanium, is 10-80 ppm of the total amount of dicarboxylic acid and diol, preferably 30-60 ppm.

[0016] In this invention, step (2) involves mixing adipic acid, terephthalic acid and 1,4-butanediol in a certain proportion, and then, under the action of a catalyst, performing an esterification reaction at 180-230°C under normal pressure for 2-4 hours, followed by a polycondensation reaction at 220°C-240°C and 2-5 kPa (absolute pressure) for 0.5-2 hours to obtain polyester oligomer B with a certain viscosity.

[0017] In step (2), the catalyst is selected as an organic titanium compound, selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate and tetraoctyl titanate, preferably tetrabutyl titanate;

[0018] In step (2), the molar ratio of the sum of the amounts of adipic acid and terephthalic acid added to the amount of 1,4-butanediol added is 1.35-1.65:1, preferably 1.4-1.6:1;

[0019] The molar ratio of adipic acid to terephthalic acid is 1.0-1.3:1.

[0020] In step (2), the amount of catalyst added, based on titanium, is 10-80 ppm of the total amount of dicarboxylic acid and diol, preferably 30-60 ppm.

[0021] In this invention, step (3) involves adding a certain amount of polyester oligomer A to polyester oligomer B, mixing them evenly, and then carrying out an ester exchange reaction for 2-4 hours under conditions of 0-200 Pa and 230℃-250℃ to obtain modified PBAT resin.

[0022] In step (3), the amount of polyester oligomer A added is 1-5 wt% of the total mass of polyester oligomer A and polyester oligomer B.

[0023] In this invention, the polyester oligomer A has a number average molecular weight between 1000 and 3000 g / mol;

[0024] The polyester oligomer B has a number average molecular weight of 1.0-2.0 × 10⁻⁶. 5 The intrinsic viscosity at 22℃ is between 0.20 and 0.35 dL / g, with a value between g / mol.

[0025] The PBAT resin has a number average molecular weight of 3-6×10⁻⁶. 5 The crystallinity is between g / mol and 2-8 g / 10 min, the glass transition temperature is below -30℃, and the crystallinity is not higher than 20%.

[0026] In this invention, the PBAT composite film material comprises the following raw materials in parts by weight:

[0027] 45-65 parts of PBAT resin, preferably 50-60 parts

[0028] Calcium carbonate 25-45 parts, preferably 30-40 parts

[0029] PLA 0-6 parts, preferably 0.1-4.5 parts

[0030] Other additives: 0-1.5 parts, preferably 0.1-1 parts.

[0031] Preferably, the other additives include antioxidants, opening agents, and chain extenders; wherein the amount of antioxidant added is 0-0.7 parts, the amount of opening agent added is 0-0.5 parts, and the amount of chain extender added is 0-0.3 parts.

[0032] The present invention also provides a method for preparing the PBAT composite film, wherein PBAT resin, calcium carbonate, PLA and other additives are blended, extruded and blown into a film to obtain the PBAT composite film.

[0033] In this invention, a twin-screw extruder is used to extrude and granulate the material at 140℃-240℃, and after drying, a composite film is prepared by blowing film using a blown film extruder.

[0034] In some preferred embodiments of the present invention, under the conditions of heat sealing pressure of 300N, heat sealing time of 0.7s, and heat sealing temperature of 98°C, the heat sealing aging of the PBAT / calcium carbonate / PLA composite film is not less than 120h, and the heat sealing strength is not less than 6N.

[0035] The present invention has found that during the preparation of PBAT resin, the presence of branched aliphatic polyester oligomers can act as an internal plasticizer. The branches on the polyester oligomers can increase the distance between polymer macromolecules, reduce the intermolecular forces, and improve the mobility of molecular chains. This results in a significant decrease in the glass transition temperature and crystallinity of PBAT, thereby improving the heat-sealing effect of the composite film.

[0036] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows:

[0037] This invention significantly reduces the glass transition temperature and crystallinity of PBAT by copolymerizing it with branched aliphatic polyester oligomers during the synthesis process. This results in PBAT / calcium carbonate / PLA composite films with high heat-sealing efficiency and high heat-sealing strength, meeting the requirements of flexible packaging films and achieving good technical results. Detailed Implementation

[0038] The present invention will be further described below with reference to the embodiments. It should be noted that the embodiments do not constitute a limitation on the scope of protection of the present invention.

[0039] The embodiments of the present invention use the following raw materials, but are not limited to these raw materials:

[0040] Raw materials: 1,4-Butanediol, adipic acid, terephthalic acid; succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol;

[0041] Catalysts: Tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate, tetraoctyl titanate;

[0042] Other raw materials: PLA (Mn=5w), calcium carbonate (particle size 1000-3000nm), antioxidant 1618, opening agent erucamide, chain extender ADR-4468;

[0043] All the above raw materials are from commercial purchases. Unless otherwise specified, other raw materials are also common commercially available.

[0044] The main properties of PBAT resin in this embodiment of the invention were tested using the following methods:

[0045] a) Relative molecular mass: The relative molecular mass of the polymer was determined using Waters gel chromatography with chloroform as the mobile phase, an elution rate of 1 mL / min, a temperature of 40 °C, and narrow-distribution polystyrene as the standard sample.

[0046] b) Melt flow index: The melt mass flow rate (MFR) was measured using a GOTTFERT melt flow index tester at 190°C and 2.16 kg.

[0047] c) Intrinsic viscosity: The intrinsic viscosity was measured using a phenol-tetrachloroethane (volume ratio 1:1) solution at 22°C using an Ubbelohde viscometer.

[0048] d) Thermal properties: The melting point of the copolyester was tested using a Perkins Elmer Pyris1 differential scanning calorimeter. The sample was first heated to 180°C at 20°C / min to eliminate thermal history, then cooled to -30°C at a rate of 20°C / min, and then heated up at a rate of 10°C / min to obtain the DSC curve of the sample.

[0049] The main properties of the PBAT / calcium carbonate / PLA composite film in this invention were tested using the following methods:

[0050] a) Blending: Weigh the raw materials according to a certain proportion and mix them thoroughly. Feed the mixture into a twin-screw extruder and set the parameters as follows: screw speed 150 rpm, heating temperatures of zones 1-5 as follows: 160℃, 165℃, 170℃, 175℃, 180℃.

[0051] b) Film preparation: PBAT masterbatch is vacuum dried at 80℃ for more than 3 hours, and then the masterbatch is added to the hopper of the blown film machine. The plasticizing screw temperature of the blown film machine is set at 160-190℃, the speed is 200rpm and the feeding rate is 3. The film bubble is drawn out from the die, passes through the herringbone clamp and the top pressure roller to reach the roll. The cooling air volume of the air ring is gradually increased to stabilize the film bubble. The film width is 25cm and the single layer film thickness is about (25±3)μm.

[0052] c) Film sampling: Refer to the standard "QB / T 2358-1998 Test method for heat-sealing strength of plastic film packaging bags", use a sampling knife to take a sample with a width of (15±0.1) mm and an unfolded length of (100±1) mm, and take 10 samples from each heat-sealed film.

[0053] d) Film heat sealing: The samples were aged at room temperature, and the heat-sealed film without defects was tested every 24 hours. During the test, the film was opened 180° with the heat-sealed part as the center. The clamping distance of the universal tensile testing machine was set to 50 mm. The two ends of the sample were clamped on the two clamps of the universal tensile testing machine, so that the sample axis coincided with the center line of the upper and lower clamps in the longitudinal direction. A tensile force of 200 N was used to perform the tensile property test at a speed of 500 mm / min. The data was transmitted to the computer through the sensor, and the maximum load force F at the fracture of the sample was read. This was repeated 10 times, and the average value was taken as the heat seal strength.

[0054] Examples 1-11 and Comparative Examples 1-4:

[0055]

Example 1

[0056] Preparation of PBAT-modified resin:

[0057] (1) Mix 590.5g succinic acid and 456.6g 1,2-propanediol evenly, and add 0.15g tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low viscosity polyester oligomer A with molecular weight Mn=1320g / mol.

[0058] (2) Mix 876.6g AA, 830g PTA, and 1386g BDO evenly, add 0.44g tetrabutyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 3kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.1×10 5 g / mol, intrinsic viscosity is 0.23 dL / g;

[0059] (3) Add 20g of polyester oligomer A to 1980g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 50Pa and 240℃ for 3h to obtain modified PBAT resin with a molecular weight Mn = 5.8 × 10⁻⁶. 5 g / mol, melt index (MFR) = 2.1 g / 10 min;

[0060]

Example 2

[0061] Preparation of PBAT-modified resin:

[0062] (1) Mix 660.5g of glutaric acid and 585.65g of 1,2-butanediol evenly, and add 0.22g of tetraisopropyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=1443g / mol.

[0063] (2) Mix 876.6g AA, 830g PTA, and 1435.5g BDO evenly, add 0.56g tetrabutyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 3.5kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.3×10 5 g / mol, intrinsic viscosity is 0.21 dL / g;

[0064] (3) Add 40g of polyester oligomer A to 1960g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 100Pa and 240℃ for 3h to obtain modified PBAT resin with a molecular weight Mn = 5.3 × 10⁻⁶. 5 g / mol, melt index (MFR) = 2.6 g / 10 min;

[0065]

Example 3

[0066] Preparation of PBAT-modified resin:

[0067] (1) Mix 730.5g adipic acid with 630.7g 1,3-butanediol evenly, and add 0.26g tetraethyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2099g / mol.

[0068] (2) Mix 876.6g AA, 830g PTA, and 1485g BDO evenly, add 0.61g tetraethyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 3.2kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.3×10 5 g / mol, intrinsic viscosity is 0.24 dL / g;

[0069] (3) Add 60g of polyester oligomer A to 1940g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 110Pa and 240℃ for 3h to obtain modified PBAT resin with a molecular weight Mn = 4.7 × 10⁻⁶. 5 g / mol, melt index (MFR) = 3.4 g / 10 min;

[0070]

Example 4

[0071] Preparation of PBAT-modified resin:

[0072] (1) Mix 800.5g pimelic acid with 781.13g 1,2-pentanediol evenly, and add 0.28g tetramethyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2371g / mol.

[0073] (2) Mix 876.6g AA, 830g PTA, and 1534.5g BDO evenly, add 0.58g tetramethyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 2.8kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.6×10 5 g / mol, intrinsic viscosity is 0.27 dL / g;

[0074] (3) Add 80g of polyester oligomer A to 1920g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 180Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 4.1 × 10⁻⁶. 5 g / mol, melt index (MFR) = 4.2 g / 10 min;

[0075]

Example 5

[0076] Preparation of PBAT-modified resin:

[0077] (1) Mix 870.5g of octanoic acid and 677.0g of 1,3-pentanediol evenly, and add 1.09g of tetraoctyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2846g / mol.

[0078] (2) Mix 876.6g AA, 830g PTA, and 1584.0g BDO evenly, add 2.33g tetraoctyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 3.9kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.8×10 5g / mol, intrinsic viscosity is 0.28 dL / g;

[0079] (3) Add 100g of polyester oligomer A to 1900g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 60Pa and 240℃ for 3h to obtain modified PBAT resin with a molecular weight Mn = 3.2 × 10⁻⁶. 5 g / mol, melt index (MFR) = 4.8 g / 10 min;

[0080]

Example 6

[0081] Preparation of PBAT-modified resin:

[0082] (1) Mix 940.5g of octanoic acid and 677.0g of 1,4-pentanediol evenly, and add 0.8g of tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2975g / mol.

[0083] (2) Mix 876.6g AA, 830g PTA, and 1584.0g BDO evenly, add 1.64g tetrabutyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 4.0kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.9×10 5 g / mol, intrinsic viscosity is 0.33 dL / g;

[0084] (3) Add 50g of polyester oligomer A to 1950g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 40Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 4.9 × 10⁻⁶. 5 g / mol, melt index (MFR) = 4.5 g / 10 min;

[0085]

Example 7

[0086] Preparation of PBAT-modified resin:

[0087] (1) Mix 1010.5g sebacic acid with 768.1g 1,2-hexanediol evenly, and add 0.44g tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=1563g / mol.

[0088] (2) 876.6g AA, 830g PTA, and 1584.0g BDO were mixed evenly, and 0.82g tetrabutyl titanate catalyst was added. The mixture was subjected to esterification at 210℃ under normal pressure for 3 hours, then the pressure was reduced to 3.3kPa, and polycondensation was carried out at 230℃ for 1 hour to obtain polyester oligomer B with a certain viscosity and a molecular weight Mn = 1.2 × 10⁻⁶. 5 g / mol, intrinsic viscosity is 0.23 dL / g;

[0089] (3) Add 70g of polyester oligomer A to 1930g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 100Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 4.4 × 10⁻⁶. 5 g / mol, melt index (MFR) = 4.5 g / 10 min;

[0090]

Example 8

[0091] Preparation of PBAT-modified resin:

[0092] (1) Mix 730.5g adipic acid with 768.1g 1,3-hexanediol evenly, and add 0.48g tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2111g / mol.

[0093] (2) 876.6g AA, 830g PTA, and 1584.0g BDO were mixed evenly, and 1.05g tetrabutyl titanate catalyst was added. The mixture was subjected to esterification at 210℃ under normal pressure for 3 hours, then the pressure was reduced to 2.8kPa, and polycondensation was carried out at 230℃ for 1 hour to obtain polyester oligomer B with a certain viscosity and a molecular weight Mn = 1.3 × 10⁻⁶. 5 g / mol, intrinsic viscosity is 0.25 dL / g;

[0094] (3) Add 90g of polyester oligomer A to 1910g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 110Pa and 240℃ for 3h to obtain modified PBAT resin with a molecular weight Mn = 5.1 × 10⁻⁶. 5 g / mol, melt index (MFR) = 3.4 g / 10 min;

[0095]

Example 9

[0096] Preparation of PBAT-modified resin:

[0097] (1) Mix 730.5g adipic acid with 768.1g 1,4-hexanediol evenly, and add 0.59g tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2416g / mol.

[0098] (2) Mix 876.6g AA, 830g PTA, and 1584.0g BDO evenly, add 1.29g tetrabutyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 2.8kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.5×10 5 g / mol, intrinsic viscosity is 0.25 dL / g;

[0099] (3) Add 70g of polyester oligomer A to 1930g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 150Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 5.0 × 10⁻⁶. 5 g / mol, melt index (MFR) = 3.1 g / 10 min;

[0100]

Example 10

[0101] Preparation of PBAT-modified resin:

[0102] (1) Mix 730.5g adipic acid with 768.1g 1,5-hexanediol evenly, and add 0.48g tetrabutyl titanate catalyst. Esterify at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2393g / mol.

[0103] (2) 876.6g AA, 830g PTA, and 1584.0g BDO were mixed evenly, and 1.05g tetrabutyl titanate catalyst was added. The mixture was subjected to esterification at 210℃ under normal pressure for 3 hours, then the pressure was reduced to 2.7kPa, and polycondensation was carried out at 230℃ for 1 hour to obtain polyester oligomer B with a certain viscosity and a molecular weight Mn = 1.4 × 10⁻⁶. 5 g / mol, intrinsic viscosity is 0.24 dL / g;

[0104] (3) Add 70g of polyester oligomer A to 1930g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 120Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 4.8 × 10⁻⁶. 5 g / mol, melt index (MFR) = 4.0 g / 10 min;

[0105]

Example 11

[0106] Preparation of PBAT-modified resin:

[0107] (1) 730.5g adipic acid and 494.65g 1,2-propanediol were mixed evenly, and 0.39g tetrabutyl titanate catalyst was added. The mixture was subjected to esterification reaction at 230℃ under normal pressure for 3h to obtain low-viscosity polyester oligomer A with molecular weight Mn=2435g / mol.

[0108] (2) Mix 876.6g AA, 830g PTA, and 1584.0g BDO evenly, add 1.05g tetrabutyl titanate catalyst, and perform esterification reaction at 210℃ under normal pressure for 3h. Then reduce the pressure to 2.1kPa and carry out polycondensation reaction at 230℃ for 1h to obtain polyester oligomer B with a certain viscosity and molecular weight Mn=1.6×10 5 g / mol, intrinsic viscosity is 0.29 dL / g;

[0109] (3) Add 70g of polyester oligomer A to 1930g of polyester oligomer B and mix thoroughly. Perform transesterification reaction at 130Pa and 240℃ for 3 hours to obtain modified PBAT resin with a molecular weight Mn = 4.5 × 10⁻⁶. 5 g / mol, melt index (MFR) = 3.5 g / 10 min;

[0110] Comparative Example 1

[0111] The modified PBAT resin was prepared according to the method in Example 11, except that polyester oligomer A was not added in step (3), while all other operations remained unchanged. The resulting modified PBAT resin had a molecular weight Mn = 4.4 × 10⁻⁶. 5 g / mol, melt index (MFR) = 3.6 g / 10 min;

[0112] Comparative Example 2

[0113] The modified PBAT resin was prepared according to the method in Example 11, except that in step (3), 200g of polyester oligomer A was added to 1800g of polyester oligomer B and mixed thoroughly; all other operations remained unchanged. The resulting modified PBAT resin had a molecular weight Mn = 2.8 × 10⁻⁶. 5 g / mol, melt index (MFR) = 7.2 g / 10 min;

[0114] 1000g of the modified PBAT resin obtained in Example 1 was thoroughly mixed with 720g of calcium carbonate, 86g of PLA, 8g of antioxidant 1618, 4g of opening agent erucamide, and 2g of antioxidant ADR-4468. The mixture was then co-extruded and blown into film according to the aforementioned test method to prepare a PBAT / calcium carbonate / PLA composite film. The heat seal strength of the composite film was measured according to the standard "QB / T 2358-1998 Test Method for Heat Seal Strength of Plastic Film Packaging Bags".

[0115] 1166g of the modified PBAT resin obtained in Examples 2-11 and Comparative Examples 1-2 was thoroughly mixed with 720g of calcium carbonate, 100g of PLA, 8g of antioxidant 1618, 4g of opening agent erucamide, and 2g of antioxidant ADR-4468. The mixture was then co-extruded and blown into film according to the aforementioned test methods to prepare a PBAT / calcium carbonate / PLA composite film. The heat seal strength of the composite film was measured according to the standard "QB / T2358-1998 Test Method for Heat Seal Strength of Plastic Film Packaging Bags".

[0116] The glass transition temperature (Tg), crystallization temperature (Tc), crystallinity, heat-sealing aging, and heat-sealing strength of the modified PBAT resins provided in Examples 1-11 and Comparative Examples 1-2 are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A PBAT composite film, characterized in that, Including the following raw materials: The mixture comprises PBAT resin, calcium carbonate, optional PLA, and optional other additives, wherein the method for preparing the PBAT resin includes the following steps: (1) Short-chain aliphatic diacids are esterified with aliphatic diols containing short branches to obtain polyester oligomer A; (2) Adipic acid, terephthalic acid and 1,4-butanediol were subjected to esterification polycondensation reaction to obtain polyester oligomer B; (3) Polyester oligomer A is added to polyester oligomer B to carry out transesterification reaction to obtain PBAT resin; The short-chain aliphatic dicarboxylic acid is a straight-chain aliphatic dicarboxylic acid with 4-10 carbon atoms; The short-branched aliphatic diol is an aliphatic diol with a straight-chain alkyl substituent, and the short-branched aliphatic diol has 3-10 carbon atoms. In step (3), the amount of polyester oligomer A added is 1-5 wt% of the total mass of polyester oligomer A and polyester oligomer B.

2. The composite film according to claim 1, characterized in that, In step (1), the short linear aliphatic dicarboxylic acid is selected from one or more of succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, and sebacic acid.

3. The composite film according to claim 2, characterized in that, In step (1), the short linear aliphatic dicarboxylic acid is adipic acid.

4. The composite film according to claim 1, characterized in that, The short-chain aliphatic diols are selected from one or more of 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, and 1,5-hexanediol.

5. The composite film according to claim 4, characterized in that, The short-chain aliphatic diol is 1,2-propanediol.

6. The composite film according to claim 1, characterized in that, The molar ratio of the short-chain aliphatic dicarboxylic acid to the short-chain aliphatic diol is 1:1.2-1.

5.

7. The composite film according to claim 1, characterized in that, In step (1), a short-chain aliphatic dicarboxylic acid and aliphatic diol containing short branches undergo esterification in the presence of a catalyst.

8. The composite film according to claim 7, characterized in that, The catalyst is an organotitanium compound selected from one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate, and tetraoctyl titanate.

9. The composite film according to claim 8, characterized in that, The catalyst is tetrabutyl titanate.

10. The composite film according to claim 7, characterized in that, The catalyst is added at a rate of 10-80 ppm based on the total amount of the dicarboxylic acid and diol, calculated as titanium.

11. The composite film according to claim 10, characterized in that, The catalyst is added at a rate of 30-60 ppm based on the total amount of the dicarboxylic acid and diol, calculated as titanium.

12. The composite film according to claim 1, characterized in that, Step (2) involves mixing adipic acid, terephthalic acid and 1,4-butanediol evenly, and then, under the action of a catalyst, first performing an esterification reaction at 180-230℃ under normal pressure for 2-4 hours, and then performing a polycondensation reaction at 220℃-240℃ and 2-5kPa for 0.5-2 hours to obtain polyester oligomer B.

13. The composite film according to claim 12, characterized in that, In step (2), the catalyst is selected from organotitanium compounds, specifically one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, tetramethyl titanate, and tetraoctyl titanate.

14. The composite film according to claim 13, characterized in that, In step (2), the catalyst is tetrabutyl titanate.

15. The composite film according to claim 1, characterized in that, In step (2), the molar ratio of the sum of the amounts of adipic acid and terephthalic acid added to the amount of 1,4-butanediol added is 1.35-1.65:

1.

16. The composite film according to claim 15, characterized in that, In step (2), the molar ratio of the sum of the amounts of adipic acid and terephthalic acid added to the amount of 1,4-butanediol added is 1.4-1.6:

1.

17. The composite film according to claim 1, characterized in that, The molar ratio of adipic acid to terephthalic acid is 1.0-1.3:

1.

18. The composite film according to claim 12, characterized in that, In step (2), the amount of catalyst added is 10-80 ppm of the total amount of dicarboxylic acid and diol, calculated as titanium.

19. The composite film according to claim 18, characterized in that, In step (2), the amount of catalyst added is 30-60 ppm of the total amount of dicarboxylic acid and diol, calculated as titanium.

20. The composite film according to claim 1, characterized in that, Step (3) involves adding polyester oligomer A to polyester oligomer B, mixing them evenly, and then carrying out an ester exchange reaction for 2-4 hours under conditions of 0-200 Pa and 230℃-250℃ to obtain modified PBAT resin.

21. The composite film according to claim 1, characterized in that, The polyester oligomer A has a number average molecular weight between 1000 and 3000 g / mol.

22. The composite film according to claim 1, characterized in that, The polyester oligomer B has a number average molecular weight of 1.0-2.0 × 10⁻⁶. 5 The intrinsic viscosity at 22℃ is between 0.20 and 0.35 dL / g, with a value between g / mol and g / mol.

23. The composite film according to claim 1, characterized in that, The PBAT resin has a number average molecular weight of 3-6×10⁻⁶. 5 The crystallinity is between g / mol and 2-8 g / 10 min, the glass transition temperature is below -30℃, and the crystallinity is not higher than 20%.

24. The composite film according to claim 1, characterized in that, The ingredients include the following parts by weight: 45-65 parts of PBAT resin 25-45 parts calcium carbonate PLA0-6 copies, Other adjuvants: 0-1.5 parts.

25. The composite film according to claim 24, characterized in that, The ingredients include the following parts by weight: 50-60 parts of PBAT resin 30-40 parts calcium carbonate PLA 0.1-5 copies Other adjuvants: 0.1-1 part.

26. The composite film according to claim 1, characterized in that, The other additives include antioxidants, opening agents, and chain extenders; wherein the amount of antioxidants added is 0-0.7 parts, the amount of opening agents added is 0-0.5 parts, and the amount of chain extenders added is 0-0.3 parts.

27. A method for preparing the PBAT composite film according to any one of claims 1-26, comprising blending PBAT resin, calcium carbonate, optional PLA and optional other additives, extruding and blowing film to obtain the PBAT composite film.

28. The composite film according to claim 1, characterized in that, A composite film is prepared by extruding and granulating the material using a twin-screw extruder at 140℃-240℃, drying it, and then blowing it into a film using a blown film extruder.

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