PBAT / bamboo powder biodegradable composite master batch, preparation method thereof and composite film

Abstract

The invention belongs to the technical field of biodegradable materials, and relates to a PBAT / bamboo powder biodegradable composite master batch and a preparation method thereof, and a composite film, the composite master batch comprises the following raw materials by mass: 100 parts of PBAT, 10-30 parts of modified bamboo powder, 5-10 parts of a compatibilization grafting agent, 0.5-1 part of a retardant, 20-30 parts of a blocking agent, and 0.2-0.4 part of a chain extender; the modified bamboo powder is obtained by impregnating bamboo powder with inorganic alkali liquor and modifying with an acyl halide reagent; the compatibilization grafting agent is obtained by grafting and modifying PBAT (poly (butylene adipate-co-terephthalate)) through ultraviolet light of a grafting agent, and the grafting agent is compounded by carboxyl-containing acrylate and unsaturated fatty acid glycidyl ester according to the mass ratio of 1: (1-2). According to the invention, the bamboo powder is modified and a novel compatibilization grafting agent is introduced, so that the hydrophobicity, dispersity and compatibility with PBAT of the bamboo powder are improved, and the prepared composite film has good appearance, high water and oxygen barrier property and better mechanical properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of biodegradable materials, and particularly relates to a PBAT / bamboo powder biodegradable composite masterbatch, a preparation method thereof, and a composite film. Background Art

[0002] Poly(butylene adipate-co-terephthalate) (PBAT), as a biodegradable aliphatic-aromatic copolyester, has attracted much attention due to its good processing properties, mechanical properties, and biocompatibility. In many fields, especially in the packaging and agricultural mulch film industries, PBAT has shown considerable application prospects. However, the manufacturing cost of PBAT is relatively high, and constructing a composite system with other low-cost and environmentally friendly materials is an effective way to reduce costs. Bamboo powder has the advantages of wide sources, renewability, and degradability. The use of bamboo powder and PBAT to prepare PBAT-based composite materials can effectively reduce costs and make full use of the remaining bamboo forest resources. However, there are still the following problems in the composite of bamboo powder and PBAT: 1) For the matrix PBAT, the compatibility and dispersibility of bamboo powder are poor, which affects the mechanical properties of the composite material; 2) Bamboo powder is prone to thermal-oxidative degradation during high-temperature processing, and a series of complex reactions occur to generate brown polymers, making the color of the prepared PBAT-based composite material darker, seriously affecting the appearance quality of the product; 3) Bamboo powder has good water absorption, while PBAT itself has poor water and oxygen barrier properties, and the water and oxygen barrier properties of the product prepared by the composite of bamboo powder and PBAT are even worse; 4) In view of the above problems, the effective addition amount of bamboo powder in the prior art is generally low, and the real comprehensive utilization of bamboo powder has not been achieved.

[0003] Patent CN111548611A discloses a high-density bamboo powder / PBAT / polylactic acid biodegradable plastic and a preparation method thereof. It uses a high-speed grinder to prepare ultra-fine bamboo powder with a particle size of 5000-7000 mesh to improve its dispersibility and compatibility in PBAT, but does not give quantitative particle size distribution data of bamboo powder, and the appearance quality and mechanical properties of the prepared composite material are poor; secondly, the process of grinding bamboo powder to 5000-7000 mesh in this patent is energy-consuming and will increase the manufacturing cost. Patent CN118599297A discloses a degradable plastic prepared from marine recycled plastics and a preparation method thereof. This patent does not pay attention to the compatibility problem of bamboo powder. Summary of the Invention

[0004] In view of the problems in the prior art that the compatibility between bamboo powder and PBAT is poor, the effective addition amount of bamboo powder is low, the color of the product is relatively dark, and the water and oxygen barrier properties of the material are poor, the present invention provides a PBAT / bamboo powder biodegradable composite masterbatch, its preparation method and composite film. By modifying the bamboo powder and introducing a new compatibilizing grafting agent, and through the synergistic effect with other additives, a PBAT / bamboo powder biodegradable composite masterbatch with a high bamboo powder addition amount is prepared, and then a film product with good mechanical properties, appearance and high water and oxygen barrier rate is prepared.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A PBAT / bamboo powder biodegradable composite masterbatch, comprising the following raw materials in parts by mass: 100 parts of PBAT, 10 - 30 parts of modified bamboo powder, 5 - 10 parts of compatibilizing grafting agent, 0.5 - 1 part of retarder, 20 - 30 parts of barrier agent, 0.2 - 0.4 part of chain extender, The modified bamboo powder is obtained by successively impregnating ultrafine bamboo powder with an inorganic alkali solution and modifying it with an acyl halide reagent; the compatibilizing grafting agent is obtained by grafting PBAT with ultraviolet light using a grafting agent, and the grafting agent is a compound of an acrylic ester containing a carboxyl group and a glycidyl unsaturated fatty acid ester in a mass ratio of 1:(1 - 2).

[0006] Further, the particle size of the ultrafine bamboo powder is 800 - 1000 mesh, the inorganic alkali solution is an aqueous solution of NaOH and / or KOH, the concentration is 4 - 7 wt%, and the mass ratio of the ultrafine bamboo powder to the inorganic alkali solution is 1:(2 - 5); the conditions for the impregnation treatment are: impregnation at 20 - 30 °C for 10 - 30 min, then filtration, washing with water until neutral, and drying at 60 - 80 °C to constant weight. After the impregnation and etching of the inorganic alkali solution, the surface active sites of the ultrafine bamboo powder increase, which is beneficial to the subsequent modification with the acyl halide reagent.

[0007] Further, the ultrafine bamboo powder is obtained by successively impregnating bamboo raw powder with an inorganic salt solution, steam explosion, and pulverization; the particle size D50 of the bamboo raw powder is 100 - 200 mesh, the inorganic salt solution is an aqueous solution of NaCl with a concentration of 0.5 - 2.0 wt%, the solid-liquid ratio of the bamboo powder to the inorganic salt solution is 1 g:(10 - 15) mL, and the conditions for the impregnation with the inorganic salt solution are: impregnation at 20 - 30 °C for 1 - 2 h; the conditions for the steam explosion are: explosion pressure 1.5 - 2.0 MPa, pressure holding time 10 - 25 min; the pulverization is air pulverization. After the steam explosion and pulverization treatment, the surface roughness and specific surface area of the bamboo powder increase.

[0008] Furthermore, the dosage of the acyl halide reagent is 4-6 wt% of the ultrafine bamboo powder; the acyl halide reagent is at least one of benzoyl chloride, 2-isopropoxybenzoyl chloride, 4-chlorobenzoyl bromide, 3-bromo-5-trifluoromethylbenzoyl chloride, 2-bromo-4,5-dimethoxy-benzoyl chloride, trifluoromethylbenzoyl chloride, p-trifluoromethoxybenzenesulfonyl chloride, 5-bromo-2-isopropoxybenzoyl chloride.

[0009] Furthermore, the conditions for modification with the acyl halide reagent are: reaction at 80-100 °C for 2-4 h under a vacuum environment of 0.05-0.08 Mpa. The acyl halide group in the acyl halide reagent undergoes an acylation reaction with the hydroxyl group in the bamboo powder to form an ester group, thereby introducing the acyl halide reagent into the side chain of the bamboo powder, improving the hydrophobicity and dispersibility of the bamboo powder, and increasing the effective addition amount of the bamboo powder in PBAT; at the same time, the graft modification destroys the regularity of the cellulose molecular chain of the bamboo powder, reduces the crystallinity and imparts partial thermoplasticity. At the same time, the ester group generated by the acylation reaction during modification has a better polarity match with the main chain of PBAT, enhancing the interfacial compatibility; in addition, other groups in the bamboo powder such as acetyl groups are easily oxidized to form aldehydes and ketones during hot processing, and quinone substances are generated, resulting in color deepening. The acyl halide reagent can cover the active sites or react with these groups to reduce oxidation discoloration during hot processing and cooperate with the blocker to solve the serious problem of color change during the processing of bamboo powder-based composites.

[0010] Furthermore, the dosage of the grafting agent is 10-20 wt% of PBAT.

[0011] Furthermore, the carboxyl-containing acrylate can be commercially available or self-made, and is selected from at least one of mono(2-acryloyloxyethyl) succinate, mono-2-(methacryloyloxy)ethyl succinate, mono-2-acryloyloxyethyl maleate, mono-2-(methacryloyloxy)ethyl maleate, mono-2-acryloyloxyethyl fumarate, mono-2-(methacryloyloxy)ethyl fumarate, mono-2-(methacryloyloxy)ethyl itaconate.

[0012] Furthermore, the unsaturated fatty acid glycidyl ester is at least one of glycidyl acrylate and glycidyl methacrylate. The carboxyl-containing acrylate and the unsaturated fatty acid glycidyl ester are used to carry out an ultraviolet grafting reaction on PBAT to form a new type of compatibilizing grafting agent containing carboxyl and epoxy groups. This compatibilizing grafting agent has good reaction compatibility with PBAT; at the same time, the active carboxyl and epoxy groups in this compatibilizing grafting agent can interact or react with the active groups on the surface of the bamboo powder, significantly improving the compatibility of the bamboo powder in the composite material system, enhancing the interfacial adhesion force, and further increasing the effective addition amount of the bamboo powder in PBAT.

[0013] Further, the conditions for ultraviolet grafting are: ultraviolet light with a wavelength of 200-400 nm is irradiated for 10-30 min.

[0014] Further, the compatibilizing grafting agent is prepared by a preparation method including the following steps: PBAT, a grafting agent, and an initiator are dissolved in a solvent together, and a grafting reaction is carried out under ultraviolet irradiation. After the reaction is completed, the compatibilizing grafting agent is obtained through filtration, washing, and drying.

[0015] Preferably, the dosage of the initiator is 5-8 wt% of PBAT, and the initiator is at least one of benzophenone, α-dimethoxybenzil ketal, 1-hydroxycyclohexyl phenyl ketone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone; the solvent is chloroform or tetrahydrofuran, and its dosage is 4-6 times the mass of PBAT; the washing is carried out with ethanol and / or pure water, and the drying is vacuum drying at 50-70 °C until constant weight.

[0016] Further, the weight-average molecular weight of the PBAT is 200,000-400,000.

[0017] Further, the retarder is at least one of calcium sulfite, sodium sulfite, magnesium sulfite, and sodium bisulfite. The retarder has strong reducibility and preferentially reacts with oxygen during hot processing to block the oxidation path of phenolic substances in bamboo powder; secondly, the metal ions in the retarder help to improve the thermal stability of bamboo powder and weaken the discoloration during processing; the synergistic effect of the retarder and the bamboo powder modifier solves the discoloration problem during the processing of bamboo powder-based composites.

[0018] Further, the barrier agent is a polycarbonate copolymer, such as PPC-P can be selected; the chain extender is at least one of 2,4-toluene diisocyanate, pyromellitic dianhydride, glycidyl methacrylate, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

[0019] Further, the raw materials further include 0.1-1 part of a weathering agent and 0.1-1 part of a mildew-proof agent; the weathering agent is at least one of bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, 3-benzotriazole-5-tert-butyl-4-hydroxyphenyl propionate, 2-(2-hydroxy-3-cumyl-5-tert-octylphenyl) benzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, and 2-hydroxy-4-n-octyloxybenzophenone; the mildew-proof agent is at least one of dimethyl fumarate, iodopropargyl n-butylcarbamate, dodecyl dimethyl benzyl ammonium chloride, and dichlorodidecyl dimethyl ammonium chloride.

[0020] Second aspect, the present invention also provides a method for preparing the above PBAT / bamboo powder biodegradable composite masterbatch, comprising the following steps: mixing the above raw materials and then performing melt extrusion, followed by water cooling, pelletizing, and drying to obtain the PBAT / bamboo powder biodegradable composite masterbatch.

[0021] Further, the conditions for the melt extrusion are: melting and pelletizing in a twin-screw extruder, with a melting temperature of 150 - 250 °C and a screw rotation speed of 150 - 300 rpm; the drying is carried out at 60 - 80 °C for 12 - 24 h.

[0022] Third aspect, the present invention also provides a composite film, which is formed by blowing the aforementioned PBAT / bamboo powder biodegradable composite masterbatch with a blown film machine.

[0023] Further, the rotation speed of the blown film machine is 70 - 120 rpm, the temperature is set at 165 - 185 °C, the blow-up ratio is 2 - 3.5, and the traction speed is 3 - 7 m / min. Adjust the above parameters according to the required thickness of the composite film.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By modifying the bamboo powder and introducing a new compatibilizing grafting agent, the present invention improves the dispersion and compatibility of the bamboo powder in the PBAT matrix through polarity matching and chemical reactions, enhances the interfacial adhesion between the bamboo powder and PBAT, breaks through the technical bottleneck of the bamboo powder addition amount, and the composite film products can still maintain excellent comprehensive performance and good appearance when the bamboo powder addition amount is as high as 30%.

[0025] 2. By modifying the bamboo powder, the present invention is beneficial to improving the color of the product, and in synergistic effect with the blocker, solves the problem of color change during the processing of the bamboo powder-based composite material, thereby obtaining products with lighter colors.

[0026] 3. By modifying the bamboo powder to improve its hydrophobicity and combining with the synergistic effect of the barrier agent, the finally prepared film products have good water and oxygen barrier properties. Specific Embodiments

[0027] The present invention will be further described below with reference to specific embodiments. In the following embodiments, unless otherwise specified, the parts are all parts by mass.

[0028] The raw bamboo powder is selected from Lu'an Xingzhu New Materials Technology Co., Ltd., and the particle size is 100 mesh.

[0029] The PBAT powder is selected from Dongguan Kadar Plastic Raw Materials Co., Ltd., the particle size is about 400 mesh, and the weight average molecular weight is about 248,000.

[0030] The polycarbonate copolymer PPC-P, selected from Shandong Lianxin Environmental Protection Technology Co., Ltd., has a weight-average molecular weight of approximately 152,000.

[0031] Example 1 (S1) The bamboo raw powder was placed into an aqueous NaCl solution (concentration 1 wt%) at a solid-liquid ratio of 1 g:10 mL and impregnated at 25 °C for 1.5 h to form a mixed material. Then, the mixed material was placed into a steam explosion tank, and saturated steam was introduced for steam explosion. The explosion pressure was 1.7 MPa, and the pressure holding time was 15 min. After explosion, the material was collected, washed with water, dried at 90 °C for 12 h to obtain dry material, and then the dry material was pulverized by air flow to a particle size of 800 - 1000 mesh to obtain ultrafine bamboo powder. (S2) 100 parts of the ultrafine bamboo powder were placed into 400 parts of an aqueous KOH solution (concentration 4 wt%) and impregnated under ultrasonic conditions at 25 °C for 20 min. The ultrasonic frequency was 50 kHz. After impregnation, it was filtered, washed with pure water until neutral, and dried at 60 °C for 24 h to obtain pretreated ultrafine bamboo powder. The pretreated ultrafine bamboo powder and 4 parts of 4-chlorobenzoyl bromide were put into a vacuum high-speed mixer. The vacuum degree was set to 0.05 Mpa, and they were kneaded and modified at 80 °C and a rotation speed of 200 rpm for 2 h. After the reaction ended, modified bamboo powder was obtained. (S3) 100 parts of PBAT powder, 10 parts of a grafting agent [a compound of succinic acid mono(2-acryloyloxyethyl ester) and glycidyl acrylate in a mass ratio of 1:1], and 6 parts of the initiator benzophenone were jointly dissolved in 400 parts of chloroform, and then placed into an ultraviolet reactor. Ultraviolet light with a wavelength of 360 nm was irradiated for 20 min. After the reaction ended, it was filtered, washed with absolute ethanol, and vacuum dried at 70 °C for 12 h to obtain a compatibilizing grafting agent. (S4) The modified bamboo powder, compatibilizing grafting agent, and other raw materials prepared in the above steps were mixed evenly according to the following parts by mass: PBAT 100 parts, Modified bamboo powder 10 parts, Compatibilizing grafting agent 5 parts, The retarder calcium sulfite 0.5 part, The barrier agent PPC-P 20 parts, The chain extender 2,4-toluene diisocyanate 0.2 part, The weathering agent bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate 0.1 part, The mildew-proof agent dimethyl fumarate 0.1 part, The above-mentioned mixed raw materials were placed into a twin-screw extruder, melted and extruded, water-cooled, and pelletized. The melting temperature was set to 165 °C, the extrusion temperature was set to 155 °C, the screw extrusion rotation speed was 150 rpm, and the deashing vacuum degree was set to 0.06 Mpa. The pelletized material was dried at 60 °C for 24 h to obtain a PBAT / bamboo powder biodegradable composite masterbatch.

[0032] Example 2 The rest is the same as in Example 1, except that: in step (S2), 4.5 parts of p-trifluoromethoxybenzenesulfonyl chloride are used to replace 4 parts of 4-chlorobenzoyl bromide; in step (S3), succinic acid mono(2-acryloyloxyethyl ester) and glycidyl acrylate are compounded in a mass ratio of 1:1.5; in step (S4), 0.6 part of sodium sulfite is used to replace 0.5 part of calcium sulfite.

[0033] Example 3 The rest is the same as in Example 1, except that: in step (S2), 6 parts of 3-bromo-5-trifluoromethylbenzoyl chloride are used to replace 4 parts of 4-chlorobenzoyl bromide; in step (S3), succinic acid mono(2-acryloyloxyethyl ester) and glycidyl acrylate are compounded in a mass ratio of 1:2; in step (S4), 0.7 part of magnesium sulfite is used to replace 0.5 part of calcium sulfite.

[0034] Example 4 The rest is the same as in Example 1, except that: in step (S3), the dosage of the grafting agent is 15 parts.

[0035] Example 5 The rest is the same as in Example 1, except that: in step (S3), the dosage of the grafting agent is 20 parts.

[0036] Example 6 The rest is the same as in Example 1, except that: in step (S3), the grafting agent is a compound of fumaric acid mono-2-(methacryloyloxy)ethyl ester and glycidyl methacrylate in a mass ratio of 1:1.

[0037] Example 7 The rest is the same as in Example 1, except that: in step (S4), the mass parts of each raw material are: 100 parts of PBAT, 20 parts of modified bamboo powder, 8 parts of compatibilizing grafting agent, 0.8 part of blocker sodium sulfite, 25 parts of barrier agent PPC-P, 0.4 part of chain extender 2,4-toluene diisocyanate, 0.5 part of weathering agent bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, 0.5 part of mildew-proof agent dimethyl fumarate.

[0038] Example 8 The rest is the same as in Example 1, except that: in step (S4), the mass parts of each raw material are: 100 parts of PBAT, 30 parts of modified bamboo powder, 10 parts of compatibilizing grafting agent, 1 part of retarder magnesium sulfite, 30 parts of barrier agent PPC-P, 0.4 part of chain extender 2,4-toluene diisocyanate, 0.5 part of weathering agent bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate, 0.5 part of mildew-proof agent dimethyl fumarate.

[0039] Comparative Example 1 The rest is the same as in Example 1, except that: steps (S2) and (S3) are omitted, ultrafine bamboo powder is used to replace the modified bamboo powder in step (S4), and the compatibilizing grafting agent is not used.

[0040] Comparative Example 2 The rest is the same as in Example 8, except that: steps (S2) and (S3) are omitted, ultrafine bamboo powder is used to replace the modified bamboo powder in step (S4), and the compatibilizing grafting agent is not used.

[0041] Comparative Example 3 The rest is the same as in Example 1, except that: step (S2) is omitted, and ultrafine bamboo powder is used to replace the modified bamboo powder in step (S4).

[0042] Comparative Example 4 The rest is the same as in Example 1, except that: step (S3) is omitted, and the compatibilizing grafting agent is not used in step (S4).

[0043] Comparative Example 5 The rest is the same as in Example 1, except that: maleic anhydride is used to replace the compound of succinic acid mono(2-acryloyloxyethyl ester) and glycidyl acrylate with a mass ratio of 1:1 in step (S3).

[0044] Application Example 1 The PBAT / bamboo powder biodegradable composite masterbatch prepared in Example 1 was put into a blown film machine, the processing temperature was set at 175 °C, the blow-up ratio was 2.5, after forming, it was cooled by an air ring, the height of the condensation line was controlled at 2 cm, the traction speed was 4 m / min, and then it was cut and wound to obtain a composite film.

[0045] Application Examples 2-8 The rest is the same as in Application Example 1, except that the composite masterbatches are prepared in Examples 2-8 respectively.

[0046] Comparative Application Examples 1-5 The rest is the same as in Application Example 1, except that the composite masterbatches are prepared in Comparative Examples 1-5 respectively.

[0047] Testing and Analysis The composite films prepared from the above application examples and comparative application examples were respectively subjected to the following performance tests: Tensile properties: According to the relevant provisions of the standard GB / T 1040.3-2006, the prepared composite films were subjected to tensile tests using a universal testing machine to test the tensile strength and elongation at break. Five groups of parallel tests were conducted, and the test results were averaged.

[0048] Color difference: Five samples were cut from different positions on the prepared composite films. The samples were placed on the surface of a white standard plate, and the color of the samples was measured using a color difference meter. The brightness (L*), chromaticity (a* and b*) of the samples were measured. By comparing with the standard white plate, the total color difference (ΔE) of the film samples was calculated. The calculation formula is as follows: ; where ΔL is the brightness difference, Δa is the red-green axis color difference, and Δb is the yellow-blue axis color difference. The smaller the total color difference value, the lighter the color of the film product and the better the appearance quality.

[0049] Water permeability: Five samples were cut from different positions of the prepared composite films. According to the standard GB / T 26253-2010, the water vapor permeability of the samples was measured using a water vapor permeability tester. The test conditions were: 25°C, 90% relative humidity, and the results were averaged from the data of 5 samples. The lower the water permeability, the better the water barrier property.

[0050] Oxygen permeability: Five samples were cut from different positions of the prepared composite films. According to the standard GB / T 19789-2021, the oxygen permeability of the samples was measured using an oxygen permeability tester. The test temperature was 23°C, and the results were averaged from the data of 5 samples. The lower the oxygen permeability, the better the oxygen barrier property.

[0051] The above test results are shown in Table 1.

[0052] Table 1 Performance Tests of Composite Films 。

[0053] As can be seen from the data in Table 1, the total color difference of the composite film obtained by blow molding the PBAT / bamboo powder biodegradable composite masterbatch prepared in the present invention is small (indicating that the overall color of the product is light), not exceeding 35, and it has good water and oxygen barrier properties and good mechanical properties. Especially in Example 8, when the addition amount of the modified bamboo powder is as high as 30% of PBAT, the film product still has good comprehensive properties. Compared with Application Example 1 where the bamboo powder was not modified (the addition amount of bamboo powder was 10% of PBAT) and no compatibilizing graft was used, the color difference value of its film product was much higher than that of Example 1, and the mechanical properties were much lower than those of Example 1, and the water and oxygen barrier properties were also poor. Compared with Application Example 2 where the bamboo powder was not modified (the addition amount of bamboo powder was 30% of PBAT) and no compatibilizing grafting agent was used, both the product color and mechanical properties of its film product were much worse than those of Example 8, unable to meet the daily use requirements, and the water and oxygen barrier properties were also poor. Compared with Application Example 3 where the bamboo powder was not modified, the comprehensive properties of its film product were significantly lower than those of Example 1. Compared with Application Example 4 where the self-made compatibilizing graft was not used, although the color of its film product was not deep, the mechanical properties were worse than those of Example 1. Compared with Application Example 5, although the water and oxygen barrier properties of its film product were good and the color was not deep, the mechanical properties were also worse than those of Example 1.

[0054] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A PBAT / bamboo powder biodegradable composite masterbatch, characterized in that: The invention comprises the following raw materials in parts by weight: PBAT 100 shares, 10~30 parts of modified bamboo powder, 5~10 parts of the grafting agent, Blocker 0.5~1 part, 20~30 parts of barrier agent, Chain extender 0.2~0.4 parts, The modified bamboo powder is obtained by sequentially impregnating ultrafine bamboo powder with inorganic alkali solution and then modifying it with an acyl halide reagent; the volume-increasing grafting agent is obtained by modifying PBAT with a grafting agent using ultraviolet light, and the grafting agent is a compound of carboxyl-containing acrylate and unsaturated fatty acid glycidyl ester in a mass ratio of 1: (1-2).

2. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The particle size of the ultrafine bamboo powder is 800-1000 mesh, the inorganic alkali solution is a NaOH aqueous solution and / or a KOH aqueous solution, the concentration is 4-7wt%, and the mass ratio of the ultrafine bamboo powder to the inorganic alkali solution is 1:(2-5); the conditions of the immersion treatment are: immersion at 20-30°C for 10-30min, followed by filtering, washing with water to neutrality, and drying at 60-80°C to constant weight; and / or The ultrafine bamboo powder is obtained by sequentially soaking bamboo raw powder in an inorganic salt solution, steam-exploding and pulverizing.

3. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The amount of the acyl halide reagent is 4-6wt% of the ultrafine bamboo powder; the acyl halide reagent is at least one of benzoyl chloride, 2-isopropoxybenzoyl chloride, 4-chlorobenzoyl bromide, 3-bromo-5-trifluoromethylbenzoyl chloride, 2-bromo-4,5-dimethoxy-benzoyl chloride, trifluoromethylbenzoyl chloride, p-trifluoromethoxybenzenesulfonyl chloride, and 5-bromo-2-isopropoxybenzoyl chloride; and / or The conditions for modification of the acyl halide reagent are: reacting at 80-100° C. for 2-4 hours under a vacuum environment of 0.05-0.08 MPa.

4. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The amount of the grafting agent is 10-20wt% of PBAT; and / or The carboxyl-containing acrylate is selected from at least one of mono(2-acryloyloxyethyl)succinate, mono-2-(methacryloyloxy)ethyl succinate, mono-2-acryloyloxyethyl maleate, mono-2-(methacryloyloxy)ethyl maleate, mono-2-(methacryloyloxy)ethyl fumarate and mono-2-(methacryloyloxy)ethyl itaconate; and / or The unsaturated fatty acid glycidyl ester is at least one of glycidyl acrylate and glycidyl methacrylate; and / or The conditions for the ultraviolet light grafting are: irradiation with ultraviolet light having a wavelength of 200-400 nm for 10-30 minutes.

5. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The volume-increasing grafting agent is prepared by a preparation method comprising the following steps: dissolving PBAT, a grafting agent and an initiator in a solvent, carrying out a grafting reaction under ultraviolet light irradiation, and obtaining the volume-increasing grafting agent after filtering, washing and drying after the reaction is completed.

6. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 5, characterized in that: The amount of the initiator is 5-8wt% of PBAT, and the initiator is at least one of benzophenone, α-dimethoxybenzil ketal, 1-hydroxycyclohexyl benzophenone, and 2-hydroxy-2-methyl-1-phenyl-1-propanone; the solvent is chloroform or tetrahydrofuran, and its amount is 4-6 times the mass of PBAT; the washing is ethanol and / or pure water washing, and the drying is vacuum drying at 50-70°C to constant weight.

7. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The weight average molecular weight of the PBAT is 200,000 to 400,000; and / or The blocker is at least one of calcium sulfite, sodium sulfite, magnesium sulfite and sodium bisulfite; and / or The barrier agent is a polycarbonate copolymer; the chain extender is at least one of 2,4-toluene diisocyanate, pyromellitic anhydride, 2,3-glycidyl methacrylate, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

8. The PBAT / bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that: The raw materials also include 0.1 to 1 parts of a weathering agent and 0.1 to 1 parts of a mildew preventer; the weathering agent is at least one of bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate, 3-benzotriazole-5-tert-butyl-4-hydroxyphenylpropionate, 2-(2-hydroxy-3-cumyl-5-tert-octylphenyl)benzotriazole, 2-(3,5-di-tert-butyl-2-hydroxyphenyl)-5-chlorobenzotriazole, and 2-hydroxy-4-n-octyloxybenzophenone; the mildew preventer is at least one of dimethyl fumarate, iodopropynyl n-butylcarbamate, dodecyl dimethyl benzyl ammonium chloride, and didecyl dimethyl ammonium chloride.

9. The method for preparing the PBAT / bamboo powder biodegradable composite masterbatch according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: mixing the above raw materials and then performing melt extrusion, and then water cooling, pelletizing and drying to obtain PBAT / bamboo powder biodegradable composite masterbatch.

10. A composite film, characterized in that: The PBAT / bamboo powder biodegradable composite masterbatch according to any one of claims 1 to 8 is formed by film blowing by a film blowing machine.