Bamboo powder biodegradable composite master batch, preparation method thereof and composite film

Abstract

This invention discloses a bamboo powder biodegradable composite masterbatch, its preparation method, and a composite film, belonging to the field of biodegradable materials technology. Addressing the problems of limited bamboo powder addition, single function, and poor process adaptability in existing technologies, this invention modifies bamboo powder through "organic acid etching-silane grafting-nano-coating," and combines it with composite compatibilizers, nano-barriers, multifunctional chain extenders, and other components. The composite masterbatch is obtained through raw material mixing and melt extrusion; the masterbatch is then blown into a composite film. This invention maintains stable mechanical properties of the film within a wide range of bamboo powder additions without additional fillers, simultaneously achieving barrier and antibacterial functions. Furthermore, the process relies on conventional equipment, is suitable for continuous industrial production, and can be applied to packaging materials, agricultural films, and other scenarios.

Description

Technical Field

[0001] This invention relates to the field of bio-based composite materials technology, specifically to a bamboo powder biodegradable composite masterbatch, its preparation method, and a composite film. Background Technology

[0002] As the problem of "white pollution" intensifies, biodegradable materials have become a key alternative to traditional plastics. Among them, polybutylene terephthalate (PBAT) is widely used in packaging, agricultural films, and other fields due to its combination of good mechanical properties and biodegradability. However, PBAT has drawbacks such as high cost and insufficient rigidity when used alone, which limits its large-scale promotion.

[0003] Bamboo powder, a byproduct of bamboo processing, is widely available and inexpensive. Rich in cellulose, it is an ideal biomass filler for reinforcing PBAT, reducing material costs and enabling high-value utilization of waste. However, the composite of bamboo powder and PBAT faces several technical bottlenecks: bamboo powder is rich in hydrophilic hydroxyl groups, resulting in poor compatibility with hydrophobic PBAT and a tendency to form interfacial defects; the amount of unoptimized bamboo powder added is limited, exceeding a certain threshold leads to a sharp drop in the material's mechanical properties; existing modification schemes mostly focus on improving a single property, making it difficult to simultaneously achieve composite functions such as barrier and antibacterial properties.

[0004] Meanwhile, some bamboo powder modification processes require specialized equipment or complex steps, resulting in cumbersome operation and low efficiency, which are incompatible with the needs of continuous industrial production. Therefore, developing a PBAT / bamboo powder composite system that can overcome the limitations of bamboo powder addition, achieve synergistic effects on multiple properties, and is suitable for mass production has become a key research focus in the industry. Summary of the Invention

[0005] This invention provides a bamboo powder biodegradable composite masterbatch, its preparation method, and a composite film, which addresses three shortcomings of existing technologies: first, the amount of bamboo powder added is limited, and increasing the amount of bamboo powder added easily leads to a decrease in the mechanical properties of the material; second, the material has a single function and it is difficult to achieve both barrier and antibacterial properties simultaneously; and third, the process adaptability is poor, with some solutions requiring special equipment or complex steps, which is not conducive to continuous industrial production.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A biodegradable bamboo powder composite masterbatch comprises the following raw materials in parts by weight: 100 parts PBAT, 15-35 parts modified bamboo powder, 8-15 parts composite compatibilizer, 1-3 parts heat stabilizer, 25-40 parts nano barrier agent, 0.3-0.6 parts multifunctional chain extender, 0.2-0.8 parts antioxidant, and 0.2-0.8 parts antibacterial agent; the modified bamboo powder is obtained by sequentially soaking bamboo powder in an organic acid solution, grafting with a silane coupling agent, and coating with nano titanium dioxide; the composite compatibilizer is polylactic acid grafted with maleic anhydride and ethylene-methyl acrylate copolymer in parts by weight. The mixture is composed of a compound in a 2:1 mass ratio; the heat stabilizer is composed of a hindered phenolic compound and a phosphite compound in a 3:1 mass ratio; the nano barrier agent is composed of nano-montmorillonite and nano-calcium carbonate in a 4:1 mass ratio; the multifunctional chain extender is composed of a diisocyanate compound and an epoxy compound in a 1:1 mass ratio; the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and the antibacterial agent is nano-zinc oxide.

[0008] Further, the organic acid solution is an aqueous solution of citric acid with a concentration of 5-8 wt%, and the mass ratio of bamboo powder to organic acid solution is 1:3-6; the soaking treatment conditions are soaking at 30-40℃ for 20-40 minutes, then filtering, washing with water until neutral, and drying at 70-90℃ to constant weight.

[0009] Furthermore, the silane coupling agent is γ-aminopropyltriethoxysilane, and the amount used is 5-8 wt% of the bamboo powder; the grafting treatment conditions are to react at 80-100°C for 3-5 hours under a nitrogen atmosphere.

[0010] Furthermore, the nano-titanium dioxide has a particle size of 20~50nm and is used in an amount of 3~6wt% of the bamboo powder; the coating treatment is performed in a high-speed mixer at a speed of 200~300rpm and a temperature of 60~80℃ for 1~2h.

[0011] Furthermore, the grafting rate of the polylactic acid grafted with maleic anhydride is 1.5~3.0%; the mass content of methyl acrylate in the ethylene-methyl acrylate copolymer is 20~30%.

[0012] Preferably, the hindered phenolic compound is β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester; the phosphite compound is tris(2,4-di-tert-butylphenyl)phosphite ester.

[0013] Preferably, the interlayer spacing of the nano-montmorillonite is 1.8~2.5nm; and the particle size of the nano-calcium carbonate is 50~100nm.

[0014] Preferably, the diisocyanate compound is hexamethylene diisocyanate; the epoxy compound is bisphenol A diglycidyl ether.

[0015] Furthermore, the preparation conditions of the composite compatibilizer are as follows: melt blending and extrusion granulation in a twin-screw extruder at a temperature of 170~185℃ and a rotation speed of 180~220rpm.

[0016] Furthermore, the preparation conditions of the nano-barrier agent are as follows: ball milling in a ball mill at a ball-to-material ratio of 8:1 and a rotation speed of 300~400 rpm for 2~3 hours.

[0017] Furthermore, the preparation conditions for the multifunctional chain extender are: stirring at 30~40℃ for 20~30 min and stirring speed of 150~200 rpm.

[0018] A method for preparing a bamboo powder biodegradable composite masterbatch includes the following steps:

[0019] S1: To prepare modified bamboo powder, bamboo powder is soaked in citric acid aqueous solution, filtered, washed with water, and dried. Then, silane coupling agent is added and reacted under nitrogen atmosphere. Nano titanium dioxide is then added and mixed in a high-speed mixer to obtain modified bamboo powder.

[0020] S2: To prepare a composite compatibilizer, polylactic acid grafted maleic anhydride and ethylene-methyl acrylate copolymer are mixed in a certain proportion, melt-blended in a twin-screw extruder, and extruded and granulated to obtain the composite compatibilizer.

[0021] S3: To prepare a nano-barrier agent, nano-montmorillonite and nano-calcium carbonate are mixed in a certain proportion and ball-milled in a ball mill to obtain a nano-barrier agent.

[0022] S4: To prepare a multifunctional chain extender, diisocyanate compounds and epoxy compounds are mixed in a certain proportion and stirred evenly to obtain a multifunctional chain extender;

[0023] S5: Raw material mixing: Mix PBAT, modified bamboo powder, composite compatibilizer, heat stabilizer, nano barrier agent, multifunctional chain extender, antioxidant and antibacterial agent according to the mass parts, and mix in a high-speed mixer for 10~20 minutes.

[0024] S6: Melt extrusion, the mixed raw materials are added to a twin-screw extruder and melt extruded at a temperature of 160~190℃ and a screw speed of 200~300rpm;

[0025] S7: Water-cooled pelletizing: The extrudate is cooled with water and then pelletized to obtain bamboo powder biodegradable composite masterbatch;

[0026] S8: Drying. The pelletized masterbatch is dried at 70-80℃ for 8-12 hours to obtain the final bamboo powder biodegradable composite masterbatch.

[0027] A composite film is prepared by blowing film forming from bamboo powder biodegradable composite masterbatch using a blown film machine; the processing temperature of the blown film machine is 170~190℃, the blow-up ratio is 2.5~4.0, and the traction speed is 4~8m / min; the tensile strength of the composite film is ≥22MPa, and the oxygen permeability is ≤250cm². 3 / (m 2 24h (0.1MPa), antibacterial rate ≥90%.

[0028] Beneficial effects:

[0029] I. Overcoming the Bottleneck in Balancing Bamboo Powder Addition Amount and Mechanical Properties: This invention solves the problem of limited bamboo powder addition amount by using a three-step synergistic modification process of "organic acid etching - silane grafting - nano-coating" combined with the bidirectional interfacial bridging effect of the composite compatibilizer. Existing technologies generally have an upper limit on the amount of bamboo powder or bamboo fiber added, and the mechanical properties of the material significantly decrease after exceeding this limit. Some solutions require additional fillers to maintain performance. This invention eliminates the need for additional fillers and ensures stable mechanical properties of the composite film within a wide range of bamboo powder addition, effectively improving the utilization rate of bamboo powder in biodegradable materials and reducing the consumption of non-degradable matrix resin.

[0030] II. Simultaneous Optimization of Barrier and Antibacterial Properties: This invention employs a compounded nano-barrier agent to construct a synergistic barrier structure. Simultaneously, through the synergistic effect of the nano-components in modified bamboo powder and the antibacterial agent, the composite film simultaneously possesses both barrier and antibacterial functions. Existing technologies involving barrier optimization often employ a single barrier component, while antibacterial optimization relies on special grafting processes. Furthermore, no single solution can simultaneously achieve an efficient combination of both functions. This invention, without complex functionalization processes, meets the dual requirements of material barrier and antibacterial properties in food packaging, agricultural mulch films, and other applications, thus expanding the application scope of biodegradable films.

[0031] III. Adapting to the Needs of Continuous Industrial Production: The bamboo powder modification process of this invention adopts a continuous operation flow, eliminating the need for complex intermediate processing steps. The masterbatch preparation process can be completed using existing conventional equipment, without the need for additional specialized equipment. Existing technologies require high-pressure equipment or special initiation devices, leading to increased process complexity and equipment investment. While some solutions are simple in process, they suffer from poor bamboo powder dispersibility. This invention, while ensuring uniform bamboo powder dispersion, simplifies the production process, reduces equipment investment costs and process control difficulty, and improves batch stability, thus better meeting the actual needs of large-scale industrial production. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] Example 1

[0034] Raw material ratio (parts by weight): PBAT 100 parts, modified bamboo powder 20 parts, composite compatibilizer 10 parts, heat stabilizer 2 parts, nano barrier agent 30 parts, multifunctional chain extender 0.4 parts, antioxidant 0.5 parts, antibacterial agent 0.5 parts;

[0035] Modified bamboo powder: Bamboo powder is soaked in 5wt% citric acid aqueous solution (solid-liquid ratio 1:4) at 35℃ for 30 min → filtered, washed and dried → 6wt% γ-aminopropyltriethoxysilane is added (reacted at 90℃ under nitrogen atmosphere for 4 h) → 4wt% 30nm nano titanium dioxide is added (mixed in a high-speed mixer at 250 rpm and 70℃ for 1.5 h).

[0036] Composite compatibilizer: polylactic acid grafted maleic anhydride (grafting rate 2.0%) and ethylene-methyl acrylate copolymer (methyl acrylate content 25%) are compounded in a 2:1 ratio and melt-granulated in a twin-screw extruder at 175℃ and 200rpm.

[0037] Nano barrier agent: 2.0nm nano-montmorillonite and 80nm nano-calcium carbonate are compounded in a 4:1 ratio, ball milled at 350rpm for 2.5h with a ball-to-material ratio of 8:1.

[0038] Multifunctional chain extender: Hexamethylene diisocyanate and bisphenol A diglycidyl ether are mixed in a 1:1 ratio and stirred at 35°C and 180 rpm for 25 min.

[0039] Preparation process: Follow steps S1-S8, melt extrusion temperature 175℃, screw speed 250rpm; blown film temperature 180℃, blow-up ratio 3.0, traction speed 6m / min.

[0040] Example 2

[0041] Raw material ratio (parts by weight): PBAT 100 parts, modified bamboo powder 35 parts, composite compatibilizer 15 parts, heat stabilizer 3 parts, nano barrier agent 40 parts, multifunctional chain extender 0.6 parts, antioxidant 0.8 parts, antibacterial agent 0.8 parts;

[0042] Modified bamboo powder: 8wt% citric acid aqueous solution (solid-liquid ratio 1:6) soaked at 40℃ for 40min → 8wt% γ-aminopropyltriethoxysilane (reacted at 100℃ for 5h) → 6wt% 50nm nano titanium dioxide (mixed at 300rpm and 80℃ for 2h).

[0043] Composite compatibilizer: Polylactic acid grafted with maleic anhydride with a grafting rate of 3.0% and ethylene-methyl acrylate copolymer with a methyl acrylate content of 30% are compounded and granulated at 185℃ and 220rpm.

[0044] The remaining auxiliary parameters and processes shall be performed in accordance with the requirements of this invention.

[0045] Example 3

[0046] Raw material ratio (parts by weight): PBAT 100 parts, modified bamboo powder 15 parts, composite compatibilizer 8 parts, heat stabilizer 1 part, nano barrier agent 25 parts, multifunctional chain extender 0.3 parts, antioxidant 0.2 parts, antibacterial agent 0.2 parts;

[0047] Modified bamboo powder: 5wt% citric acid aqueous solution (solid-liquid ratio 1:3) soaked at 30℃ for 20min → 5wt% γ-aminopropyltriethoxysilane (reacted at 80℃ for 3h) → 3wt% 20nm nano titanium dioxide (mixed at 200rpm and 60℃ for 1h);

[0048] Composite compatibilizer: Polylactic acid grafted with maleic anhydride at a grafting rate of 1.5% and ethylene-methyl acrylate copolymer with a methyl acrylate content of 20% are compounded and granulated at 170℃ and 180rpm.

[0049] The remaining auxiliary parameters and processes shall be performed in accordance with the requirements of this invention.

[0050] Comparative Example 1

[0051] Differences (missing organic acid etching step): Modified bamboo powder was directly grafted with γ-aminopropyltriethoxysilane (without citric acid soaking), and the remaining raw material ratios and processes were completely consistent with Example 1.

[0052] Design objective: To verify the effect of "organic acid etching" on the surface active sites and compatibility of bamboo powder.

[0053] Comparative Example 2

[0054] Differences (missing composite compatibilizer, using a single compatibilizer): The composite compatibilizer was replaced with an equal amount of polylactic acid grafted maleic anhydride (without ethylene-methyl acrylate copolymer compound), otherwise it was the same as in Example 1.

[0055] Design objective: To verify the synergistic compatibilizing effect of the "composite compatibilizer".

[0056] Comparative Example 3

[0057] Differences (missing nano barrier agent, no antibacterial agent): The nano barrier agent was removed and replaced with an equal amount of PBAT; the antibacterial agent was removed, and the rest was the same as in Example 1.

[0058] Design objective: To verify the effects of "nano-barrier agents" on barrier performance and "antibacterial agents" on antibacterial effects.

[0059] Testing and Analysis

[0060] Tensile strength: GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets";

[0061] Oxygen permeability: GB / T 1038.1-2022 "Test methods for gas permeability of plastic films and sheets - Part 1: Differential pressure method";

[0062] Antibacterial rate: GB / T 31402-2023 "Determination of antibacterial activity of plastics and other non-porous materials" (test strain: Escherichia coli ATCC25922);

[0063] Biodegradation rate: GB / T19277.1-2011 "Determination of final aerobic biodegradation capacity of materials under controlled composting conditions - Part 1: General method" (composting temperature 58±2℃, test period 180d);

[0064] Bamboo powder dispersibility: The number of bamboo powder aggregates (particle size > 5 μm) within a 200 μm² field of view was counted by scanning electron microscopy (SEM).

[0065] The test results of the examples and comparative examples are shown in the table below:

[0066]

[0067] As can be seen from the table, all test indicators in Examples 1-3 met the requirements (tensile strength ≥ 22 MPa, oxygen permeability ≤ 250 cm⁻¹). 3 / (m 2 24h The results show that the high bamboo powder content (0.1 MPa), antibacterial rate (≥90%), and biodegradability (>84%) indicate that the technical solution can stably achieve the goal of "high bamboo powder content + high performance". Although the bamboo powder content in Example 2 reached 35 parts, the tensile strength was still ≥22 MPa, breaking through the limitation of "high content inevitably reduces strength" in the existing technology. Comparative analysis of Example 1: Due to the lack of organic acid etching, the surface active sites of bamboo powder were insufficient, and the tensile strength decreased by 29.4% compared with Example 1. The number of bamboo powder agglomerates increased by 275%, indicating the synergistic effect of the three-step modification of "organic acid etching - silane grafting - nano-coating" - organic acid etching is the basis for subsequent grafting and coating, directly affecting compatibility and dispersibility. Comparative analysis of Example 2: A single compatibilizer cannot simultaneously adapt to the hydroxyl groups and PBAT ester groups of bamboo powder, and the tensile strength decreased by 19.2% compared with Example 1, indicating that the compound design of "polylactic acid grafted maleic anhydride + ethylene-methyl acrylate copolymer" is irreplaceable and achieves bidirectional interface bridging. Comparative analysis of Example 3: The oxygen permeability increased by 118.2% after the absence of the nano barrier agent compared with Example 1, indicating that the composite barrier structure of "nano montmorillonite + nano calcium carbonate" can effectively reduce gas permeation; the antibacterial rate was 0 when there was no antibacterial agent, highlighting the necessity of the antibacterial agent for the function. Both of these reflect the synergistic innovation of the additive system of this invention.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bamboo powder biodegradable composite masterbatch, characterized in that, The raw materials include the following parts by weight: 100 parts PBAT, 15-35 parts modified bamboo powder, 8-15 parts composite compatibilizer, 1-3 parts heat stabilizer, 25-40 parts nano barrier agent, 0.3-0.6 parts multifunctional chain extender, 0.2-0.8 parts antioxidant, and 0.2-0.8 parts antibacterial agent; the modified bamboo powder is obtained by sequentially soaking bamboo powder in an organic acid solution, grafting with a silane coupling agent, and coating with nano titanium dioxide; the composite compatibilizer is polylactic acid grafted maleic anhydride and ethylene-methyl acrylate copolymer in the following proportions by weight. The mixture is composed of a compound in a 2:1 mass ratio; the heat stabilizer is a compound of hindered phenolic compounds and phosphite compounds in a 3:1 mass ratio; the nano barrier agent is a compound of nano-montmorillonite and nano-calcium carbonate in a 4:1 mass ratio; the multifunctional chain extender is a compound of diisocyanate compounds and epoxy compounds in a 1:1 mass ratio; the antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]; and the antibacterial agent is nano-zinc oxide. The organic acid solution is an aqueous solution of citric acid with a concentration of 5-8 wt%, and the mass ratio of bamboo powder to organic acid solution is 1:3-6. The soaking treatment conditions are: soaking at 30-40℃ for 20-40 minutes, then filtering, washing with water until neutral, and drying at 70-90℃ to constant weight. The silane coupling agent is γ-aminopropyltriethoxysilane, and the amount used is 5-8 wt% of the bamboo powder; the grafting treatment conditions are: reaction at 80-100℃ for 3-5 h under a nitrogen atmosphere. The nano-titanium dioxide has a particle size of 20~50nm and is used in an amount of 3~6wt% of the bamboo powder. The coating treatment is performed in a high-speed mixer at a speed of 200~300rpm and a temperature of 60~80℃ for 1~2h.

2. The bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that, The grafting rate of polylactic acid grafted with maleic anhydride is 1.5-3.0%; the mass content of methyl acrylate in the ethylene-methyl acrylate copolymer is 20-30%.

3. The bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that, The preparation conditions for the composite compatibilizer are as follows: melt blending and extrusion granulation in a twin-screw extruder at a temperature of 170~185℃ and a speed of 180~220rpm.

4. The bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that, The preparation conditions for the nano-barrier agent are as follows: ball milling in a ball mill at a ball-to-material ratio of 8:1 and a rotation speed of 300-400 rpm for 2-3 hours.

5. The bamboo powder biodegradable composite masterbatch according to claim 1, characterized in that, The preparation conditions for the multifunctional chain extender are: stirring at 30~40℃ for 20~30 min and stirring speed of 150~200 rpm.

6. A method for preparing a bamboo powder biodegradable composite masterbatch, used to manufacture the bamboo powder biodegradable composite masterbatch as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: To prepare modified bamboo powder, bamboo powder is soaked in citric acid aqueous solution, filtered, washed with water, and dried. Then, silane coupling agent is added and reacted under nitrogen atmosphere. Nano titanium dioxide is then added and mixed in a high-speed mixer to obtain modified bamboo powder. S2: To prepare a composite compatibilizer, polylactic acid grafted maleic anhydride and ethylene-methyl acrylate copolymer are mixed in a certain proportion, melt-blended in a twin-screw extruder, and extruded and granulated to obtain the composite compatibilizer. S3: To prepare a nano-barrier agent, nano-montmorillonite and nano-calcium carbonate are mixed in a certain proportion and ball-milled in a ball mill to obtain a nano-barrier agent. S4: To prepare a multifunctional chain extender, diisocyanate compounds and epoxy compounds are mixed in a certain proportion and stirred evenly to obtain a multifunctional chain extender; S5: Raw material mixing: Mix PBAT, modified bamboo powder, composite compatibilizer, heat stabilizer, nano barrier agent, multifunctional chain extender, antioxidant and antibacterial agent according to the mass parts, and mix in a high-speed mixer for 10~20 minutes. S6: Melt extrusion, the mixed raw materials are added to a twin-screw extruder and melt extruded at a temperature of 160~190℃ and a screw speed of 200~300rpm; S7: Water-cooled pelletizing: The extrudate is cooled with water and then pelletized to obtain bamboo powder biodegradable composite masterbatch; S8: Drying. The pelletized masterbatch is dried at 70-80℃ for 8-12 hours to obtain the final bamboo powder biodegradable composite masterbatch.

7. A composite film, characterized in that, The bamboo powder biodegradable composite masterbatch as described in any one of claims 1-5 is produced by blown film forming using a blown film machine.

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