PBAT / functional modified cellulose acetate composite membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of high polymer materials and biodegradable materials, and discloses a PBAT / functional modified cellulose acetate composite membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, mixing cellulose acetate with a functional plasticizer containing hydroxyl or epoxy group to obtain functional modified cellulose acetate; s2, dissolving PBAT and functional modified cellulose acetate in an organic solvent, adding a compatilizer, and uniformly stirring to obtain a composite solution; and S3, processing the composite solution into a film, drying, and removing the organic solvent to obtain the PBAT / functional modified cellulose acetate composite film. The functional plasticizer and the compatilizer are cooperatively regulated and controlled to form a stable interface, the flexible tensile strength of the obtained composite film is improved by 35%, the elongation at break is improved by 80%, the oxygen permeation rate is reduced by 50%, and the composite film can be completely degraded under the composting condition.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and biodegradable materials, and more specifically, to a PBAT / functionalized modified cellulose acetate composite membrane, its preparation method, and its application. Background Technology

[0002] With the rapid growth in demand for biodegradable materials, the preparation of biodegradable films by blending PBAT (polybutylene terephthalate) with natural polymers has become a research hotspot. PBAT possesses good flexibility and biodegradability, but its intrinsic mechanical strength and barrier properties are relatively low, making it difficult to meet the requirements of packaging applications with high mechanical properties and water and oxygen resistance. Cellulose acetate (CA), derived from natural cellulose, has high modulus, transparency, and barrier properties, making it an ideal material for enhancing the performance of PBAT films. However, PBAT is an aliphatic-aromatic polyester with weak polarity, while CA is highly polar, resulting in poor compatibility and weak interfacial bonding. Direct blending can easily lead to phase separation, decreased transparency, and degraded mechanical properties. Therefore, improving the interfacial compatibility and overall performance of the PBAT / CA system is an important research direction in this field.

[0003] Existing technologies include composites of cellulose acetate and PBAT. Patent CN115139596A describes a membrane material prepared using a multilayered or adhesive-based composite structure. The upper and lower layers are based on cellulose acetate (CA) and PBAT, respectively, with a polyurethane adhesive used in the middle layer for bonding. Starch or various inorganic nanoparticles are added to enhance barrier and antibacterial properties. While this approach achieves high transparency and some barrier performance improvement, it suffers from complex membrane structures, interface dependence on external adhesives, multi-step film formation processes, and a complex material system with numerous components and cumbersome preparation procedures. Furthermore, this multilayered structure relies on physical bonding, resulting in limited improvement in interfacial compatibility and difficulty in achieving interfacial energy matching at the molecular level. Additionally, this technology primarily improves the performance of the CA layer, while a significant polarity difference remains between the PBAT and CA layers, leading to insufficient synergistic toughening and plasticizing effects. The system's flexibility, mechanical uniformity, and long-term environmental stability still have room for improvement. Summary of the Invention

[0004] To overcome the defects of the prior art, such as poor interfacial compatibility, obvious phase separation, insufficient mechanical and barrier properties, as well as the complex preparation of multilayer stacked structures and the dependence on external binders, the present invention provides a PBAT / functionalized modified cellulose acetate composite membrane. Another objective of this application is to provide a method for preparing a PBAT / functionalized modified cellulose acetate composite membrane; Another objective of this application is to provide an application of a PBAT / functionalized modified cellulose acetate composite membrane.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows: A method for preparing a PBAT / functionalized modified cellulose acetate composite membrane includes the following steps: S1. Mix cellulose acetate with a functionalized plasticizer containing hydroxyl or epoxy groups to obtain functionalized modified cellulose acetate (f-CA). S2. Dissolve PBAT and functionalized modified cellulose acetate in an organic solvent, add a compatibilizer, and stir until homogeneous to obtain a composite solution. S3. The composite solution is processed into a film, dried, and the organic solvent is removed to obtain a PBAT / functionalized modified cellulose acetate composite film.

[0006] Preferably, the cellulose acetate contains 30-40 wt% acetyl groups and 9-10 wt% hydroxyl groups.

[0007] Preferably, the cellulose acetate contains 32.0 wt% acetyl groups and 9.7 wt% hydroxyl groups.

[0008] Preferably, the triethyl citrate has a purity of not less than 99%.

[0009] Preferably, the number-average molecular weight (Mn) of the PBAT is 10,000 to 15,000.

[0010] Preferably, the number-average molecular weight (Mn) of the PBAT is 12000.

[0011] Furthermore, the mass ratio of cellulose acetate to functionalized plasticizers containing hydroxyl or epoxy groups in S1 is 100:15~25.

[0012] Furthermore, the mass ratio of PBAT to functionalized modified cellulose acetate in S2 is 70~85:15~30.

[0013] Preferably, the mass ratio of PBAT to functionalized modified cellulose acetate in S2 is 70~80:20~30.

[0014] Preferably, the mass ratio of PBAT to functionalized modified cellulose acetate in S2 is 75:25.

[0015] Further, in S1, the mixture is stirred at 70-90°C for 1-2 hours to obtain functionalized modified cellulose acetate.

[0016] Further, add 0.2~1 wt% compatibilizer to S2 and stir for 3~5 hours.

[0017] Preferably, 0.4~0.6 wt% of a compatibilizer is added to S2.

[0018] Preferably, 0.5 wt% of a compatibilizer is added to S2.

[0019] Preferably, the organic solvent is dichloromethane.

[0020] Preferably, the composite solution is cast into a film.

[0021] Furthermore, the drying temperature in S3 is 40~60℃, and the drying time is 4~6 hours.

[0022] Preferably, the product is air-dried at room temperature for 12-24 hours, and then dried at 40-60°C for 4-6 hours. Furthermore, the functionalized plasticizer includes triethyl epoxidized citrate and hydroxyl citrate esters.

[0023] Preferably, the hydroxy citrate esters include at least one of monohydroxypropyl citrate, dihydroxypropyl citrate, monohydroxyethyl citrate, dihydroxyethyl citrate, glyceryl citrate, acetylated glyceryl citrate, monopropylene citrate-glycidyl ether, and monoethoxylated glyceryl citrate.

[0024] Furthermore, the compatibilizer includes maleic anhydride-grafted PBAT (PBAT-g-MAH) or maleic anhydride-grafted polylactic acid (PLA-g-MAH).

[0025] Preferably, the grafting rate of PBAT-g-MAH is 0.5%~1.5%, and the number average molecular weight (Mn) is 10000~15000; the grafting rate of PLA-g-MAH is 1.0%~2.0%, and the number average molecular weight (Mn) is 60000~90000.

[0026] Preferably, the grafting rate of PBAT-g-MAH is 1%; the grafting rate of PLA-g-MAH is 1.5%.

[0027] A PBAT / modified cellulose acetate composite membrane is prepared by the method for preparing the PBAT / modified cellulose acetate composite membrane.

[0028] An application of the PBAT / modified cellulose acetate composite membrane to prepare a biodegradable film.

[0029] This invention utilizes a synergistic mechanism between functionalized plasticizers and reactive compatibilizers. The plasticizer not only improves the flexibility of CA (carbohydrate) but also provides active sites that can interact with the polar segments of PBAT, thereby forming a hydrogen bond network or chemical bond at the two-phase interface, significantly enhancing compatibility and composite uniformity. This interface control method differs from existing reinforcement strategies based on lamination, multilayer coating, or inorganic filler systems, achieving the goal of improving PBAT / CA compatibility at the molecular scale.

[0030] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: 1. Significantly improved compatibility: Through the synergistic regulation of functionalized plasticizers and compatibilizers, a stable molecular-level interface transition layer is constructed between the PBAT and CA phases, which weakens the originally obvious phase separation interface and forms a uniform and continuous structure, reducing the oxygen permeability by about 50% compared with the unmodified system.

[0031] 2. Significantly Improved Mechanical and Barrier Properties: Enhanced interfacial bonding makes load transfer between the two phases more efficient, eliminating interfacial fragility points in the unmodified system, thus achieving a significant improvement in mechanical properties. This invention increases tensile strength by 35% and elongation at break by 80%, demonstrating simultaneous enhancement of both strength and flexibility.

[0032] 3. Green, environmentally friendly, and biodegradable: This invention enhances the polarity of CA through functional modification, enabling it to form a more permeable and hydrophilic interface structure with PBAT. This promotes easier penetration of water and microorganisms into the material, thus achieving more continuous degradation. All components of the composite membrane of this invention can be completely degraded under composting conditions, with a degradation rate exceeding 25% after 30 days, reaching a maximum of 37.1%, significantly better than the unmodified system, demonstrating excellent environmental friendliness and compostability. Attached Figure Description

[0033] Figure 1 The tensile strength of the composite membrane; Figure 2 Elongation at break of the composite membrane; Figure 3 The oxygen permeability of the composite membrane. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0035] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0036] The PBAT-g-MAH grafting rate is 0.5%~1.5%, and the number average molecular weight (Mn) is 10000~15000; the PLA-g-MAH grafting rate is 1.0%~2.0%, and the number average molecular weight (Mn) is 60000~90000; the cellulose acetate has 32.0 wt% acetyl groups and 9.7 wt% hydroxyl groups; the triethyl citrate has a purity of 99%; and the PBAT has a number average molecular weight (Mn) of 12000.

[0037] The hydroxy citrate esters include at least one of monohydroxypropyl citrate, dihydroxypropyl citrate, monohydroxyethyl citrate, dihydroxyethyl citrate, glyceryl citrate, acetylated glyceryl citrate, monopropylene citrate-glycidyl ether, and monoethoxylated glyceryl citrate.

[0038] The method for preparing the PBAT / functionalized modified CA composite membrane of the present invention includes the following steps: (1) Preparation of functionalized modified CA: Cellulose acetate and functionalized plasticizers containing hydroxyl or epoxy groups are mixed at a mass ratio of 100:(15~25) and stirred at 70~90℃ for 1~2 hours to obtain functionalized modified cellulose acetate (f-CA).

[0039] (2) Preparation of blended solution: PBAT and f-CA are dissolved in dichloromethane at a mass ratio of (70~85):(15~30), and 0.2~1 wt% compatibilizer (PBAT-g-MAH or PLA-g-MAH) is added and stirred for 3~5 hours.

[0040] (3) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 12-24 hours, and then dried in a vacuum oven at 50°C for 4-6 hours to obtain the PBAT / f-CA composite film.

[0041] Example 1 (1) Preparation of functionalized modified CA: Cellulose acetate and triethyl epoxidized citrate were mixed at a mass ratio of 100:15 and stirred at 80°C for 1 hour to obtain functionalized modified cellulose acetate (f-CA1).

[0042] (2) Preparation of blended solution: PBAT and f-CA were dissolved in dichloromethane at a mass ratio of 75:25, and 0.5 wt% compatibilizer (PBAT-g-MAH) was added and stirred for 4 hours.

[0043] (3) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 20 hours, and then dried in a vacuum oven at 50°C for 5 hours to obtain the PBAT / f-CA1 composite film.

[0044] Example 2 (1) Preparation of functionalized modified CA: Cellulose acetate and triethyl epoxidized citrate were mixed at a mass ratio of 100:20 and stirred at 90°C for 1 hour to obtain functionalized modified cellulose acetate (f-CA2).

[0045] (2) Preparation of blended solution: PBAT and f-CA were dissolved in dichloromethane at a mass ratio of 75:25, and 0.5wt% compatibilizer (PBAT-g-MAH) was added and stirred for 3 hours.

[0046] (3) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 12 hours, and then dried in a vacuum oven at 40°C for 6 hours to obtain the PBAT / f-CA2 composite film.

[0047] Example 3 (1) Preparation of functionalized modified CA: cellulose acetate and epoxy citrate were mixed at a mass ratio of 100:25 and stirred at 70°C for 1 hour to obtain functionalized modified cellulose acetate (f-CA3).

[0048] (2) Preparation of blended solution: PBAT and f-CA were dissolved in dichloromethane at a mass ratio of 75:25, and 0.5 wt% compatibilizer (PLA-g-MAH) was added and stirred for 5 hours.

[0049] (3) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 60°C for 4 hours to obtain the PBAT / f-CA3 composite film.

[0050] Comparative Example 1 (1) Solution preparation: Weigh 10g CA (cellulose acetate), dissolve it in 200g dichloromethane, and stir for 5 hours.

[0051] (2) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 50°C for 4 hours to obtain a CA film.

[0052] Comparative Example 2 (1) Solution preparation: Weigh 10g PB (polybutylene succinate), dissolve it in 50g dichloromethane, and stir for 6 hours.

[0053] (2) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 50°C for 4 hours to obtain a PBAT film.

[0054] Comparative Example 3 (1) Preparation of blended solution: PBAT and CA were dissolved in dichloromethane at a mass ratio of 25:75, and 0.5 wt% compatibilizer (PLA-g-MAH) was added and stirred for 5 hours.

[0055] (2) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 50°C for 4 hours to obtain the PBAT / CA composite film.

[0056] Comparative Example 4 (1) Preparation of blended solution: PBAT and CA were dissolved in dichloromethane at a mass ratio of 50:50, and 0.5 wt% compatibilizer (PLA-g-MAH) was added and stirred for 5 hours.

[0057] (2) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 50°C for 4 hours to obtain the PBAT / CA composite film.

[0058] Comparative Example 5 (1) Preparation of blended solution: PBAT and CA were dissolved in dichloromethane at a mass ratio of 75:25, and 0.5 wt% compatibilizer (PLA-g-MAH) was added and stirred for 5 hours.

[0059] (2) Film formation: The composite solution is cast into a film, naturally dried at room temperature for 24 hours, and then dried in a vacuum oven at 50°C for 4 hours to obtain the PBAT / CA composite film.

[0060] Test methods 1. Tensile property test: Tensile test was conducted using a universal testing machine according to GB / T1040.3-2018. The film was a strip sample with a length of 150 mm and a width of 20 mm, with an initial clamping distance of 50 mm and a tensile speed of 150 mm / min.

[0061] 2. Oxygen barrier performance test: The test was conducted using a VAC-V2 differential pressure gas permeation instrument (Jinan Langguang Electromechanical Technology Co., Ltd.) at 23℃ and 50% relative humidity.

[0062] 3. Soil Degradation Test: 0.5 cm × 0.5 cm membrane samples were evenly buried in the soil, with a coverage thickness of approximately 6 cm. Each group had three replicates. After culturing in outdoor soil for 30 days, all composite films from the culture groups were removed and placed in SDS solution at 180 r·min⁻¹. -1 After 4 hours of oscillating cleaning, the film was rinsed with sterile water and dried at low temperature to constant weight. The mass of the PBAT film before and after degradation was measured using a precision balance, and the degradation rate of the composite film was calculated according to formula (1).

[0063] Composite membrane degradation rate % = (m 初始质量 -m 降解后的质量 ) / m 初始质量 ×100%.

[0064] Analysis and Explanation As shown in Table 1, the physical properties of the composite membrane were improved after functional modification of CA. This is because epoxy citrate (EC) is a key and efficient multifunctional modifier in this composite system. Through chemical reaction and physical action, it optimizes the structure of the material from the molecular level to the microscopic phase level, thereby achieving a synergistic improvement in mechanical properties and barrier properties.

[0065] Table 1 Physical properties of composite membranes

[0066] 1. Mechanical properties like Figure 1 As shown, the tensile strength of the PBAT / CA composite film increases with the modification of CA with epoxy citrate (EC), up to a maximum increase of 43%. This is because CA is a hydrophilic rigid molecule, while PBAT is a hydrophobic flexible polyester. The two are thermodynamically incompatible, and direct blending leads to phase separation, forming a clear interface. Under tensile stress, cracks preferentially originate and propagate at these fragile interfaces, causing the material to fail at relatively low stress. The epoxy groups (-CH-(O)-CH-) in the EC molecule are highly reactive and, under heating conditions, can undergo ring-opening reactions with the hydroxyl groups (-OH) on the CA molecular chain and the carboxyl groups (-COOH) or hydroxyl groups at the ends of the PBAT molecular chain. This is like forming a "chemical anchor point" between CA and PBAT, firmly connecting the two phases through chemical bonds, improving their interfacial compatibility, and thus enhancing the tensile strength of the PBAT / CA composite film.

[0067] like Figure 2 As shown, the elongation at break of the PBAT / CA composite film increased from 128.2% to 289.2% with the addition of epoxy citrate. This is because the reaction between the epoxy groups of EC and the hydroxyl groups of CA introduces larger, more flexible citrate chains. These long chains insert between CA molecular chains, disrupting the original strong hydrogen bond network of CA and increasing the free volume between molecular chains. The increased interchain spacing and weakened interactions make CA molecular chains and segments easier to move, rotate, and rearrange under stress. This means that the originally brittle CA phase becomes more flexible and plastic, thereby improving the elongation at break of the PBAT / CA composite film.

[0068] 2. Interface compatibility like Figure 3 As shown, epoxy citrate modification of CA improved the interfacial compatibility of the PBAT / CA composite membrane, thus enhancing its barrier properties; the oxygen permeability increased from 152.3 cm⁻¹. 3 ·m -2 ·day -1 It dropped to 76.1 cm. 3 ·m -2 ·day -1This is because in incompatible CA / PBAT blends, phase separation results in numerous microscopic interface defects, voids, and pores. These defects provide rapid pathways for small molecules such as water vapor and oxygen, leading to poor barrier properties. The compatibilizing effect of EC (electrolyte-coated polymer) makes CA and PBAT bind more tightly, eliminating micropores and gaps at the phase interface. Small molecules must penetrate through the polymer bulk and cannot take shortcuts, making the path more tortuous.

[0069] 3. Biodegradability As shown in Table 2, in the unmodified PBAT / CA system, with the increase of CA content, the 30-day degradation rate decreased from 28.3% of pure PBAT to only 6.2%, indicating that CA exhibits a significant degradation inhibition effect in the composite membrane. The interfacial phase separation structure makes it difficult for water and microorganisms to fully enter the system, thus preventing PBAT from effectively exerting its degradation ability.

[0070] Table 2 Degradation rate of composite membrane

[0071] In contrast, the PBAT / f-CA composite membrane obtained by modifying CA with functionalized plasticizers in this invention exhibits significantly improved degradation performance. Specifically, the degradation rate in Example 1 reached 37.1%, significantly higher than the 25.8% of the unmodified PBAT / CA (Comparative Example 5) at the same ratio. This result indicates that functionalization improves the polarity and interfacial structure of CA, preventing it from acting as a degradation inhibitor and instead enabling it to synergistically form a more uniform and permeable interfacial network with PBAT. This promotes the connectivity of hydrolysis and microbial pathways, resulting in a significant improvement in the overall degradation performance of the composite membrane.

[0072] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a PBAT / functionalized modified cellulose acetate composite film, characterized in that, The method comprises the following steps: S1, mixing cellulose acetate and a functionalized plasticizer containing hydroxyl or epoxy groups to obtain functionalized modified cellulose acetate; S2, dissolving PBAT and the functionalized modified cellulose acetate in an organic solvent, adding a compatibilizer, stirring uniformly to obtain a composite solution; S3, processing the composite solution into a film, drying and removing the organic solvent to obtain a PBAT / functionalized modified cellulose acetate composite film.

2. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a support to form a film; and (c) drying the film. In S1, the mass ratio of cellulose acetate to the functionalized plasticizer containing hydroxyl or epoxy groups is 100:15-25.

3. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a support to form a film; and (c) drying the film. In S2, the mass ratio of PBAT to the functionalized modified cellulose acetate is 70-85:15-30.

4. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a support to form a film; and (c) drying the film. In S1, stirring at 70-90℃ for 1-2 hours to obtain the functionalized modified cellulose acetate.

5. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a substrate to form a film; and (c) drying the film. In S2, adding 0.2-1 wt% of the compatibilizer and stirring for 3-5 hours.

6. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a substrate to form a film; and (c) drying the film. In S3, the drying temperature is 40-60℃ and the time is 4-6 hours.

7. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a substrate to form a film; and (c) drying the film. The functionalized plasticizer includes epoxidized triethyl citrate and hydroxyl-containing citrate.

8. The method of claim 1, wherein the PBAT / modified cellulose acetate composite film is prepared by the steps of: (a) dissolving PBAT and modified cellulose acetate in a solvent to prepare a solution; (b) coating the solution on a support to form a film; and (c) drying the film. The compatibilizer includes maleic anhydride grafted PBAT or maleic anhydride grafted polylactic acid.

9. A PBAT / modified cellulose acetate composite film, characterized in that, Prepared by the preparation method of the PBAT / modified cellulose acetate composite film according to any one of claims 1-8.

10. Use of the PBAT / modified cellulose acetate composite film according to claim 9, characterized in that, Preparation of a degradable film.

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