Bamboo-derived nanocellulose-filled degradable composites and methods of making the same

Abstract

This invention provides a bamboo-derived nanocellulose-filled biodegradable composite material and its preparation method. Choline chloride and urea are mixed and stirred under heating to obtain a eutectic solvent. Bamboo powder is added to the eutectic solvent and reacted under heating to obtain coarse bamboo cellulose. The coarse bamboo cellulose is then placed in a ball mill with an ionic liquid [BMIM]Cl, and citric acid, a crosslinking agent, and a catalyst are added and mixed. The mixture is then ball-milled under heating and vacuum conditions. The product is further processed to obtain esterified nanocellulose. The esterified nanocellulose is then treated with PLA, PBAT, and additives to obtain the bamboo-derived nanocellulose-filled biodegradable composite material. The ball milling-esterification step in the preparation method of the bamboo-derived nanocellulose-filled biodegradable composite material of this invention eliminates several intermediate steps such as transfer, weighing, and reactor reassembly, thus improving production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of composite materials, and in particular relates to a bamboo-derived nanocellulose-filled biodegradable composite material and its preparation method. Background Technology

[0002] Currently, various biodegradable composite materials have gradually entered people's production and daily life. However, their large-scale industrialization is still constrained by factors such as cost and performance. Biomass, as a clean and inexpensive raw material, is also gradually being used to fill biodegradable materials. Although it can reduce some costs, its tensile properties will further decline compared with materials such as polypropylene (PP) and polyethylene (PE). my country is rich in bamboo resources, and bamboo has a fast growth rate and short growth cycle. However, due to cutting losses and scrap waste during bamboo processing, the comprehensive utilization rate of bamboo is less than 70%. Bamboo contains 40-60 wt% cellulose, but due to lignin encapsulation (content 15-30 wt%) and high crystallinity (XRD value 55-65%), it has poor compatibility with the polylactic acid (PLA) / polybutylene adipate-butylene terephthalate copolymer (PBAT) system.

[0003] Chinese invention patent application number 2021107891469 directly pulverizes bamboo and wood fibers to 3mm, softens them with ammonium sulfate and glycerol, then mixes them with raw materials PLA, PBAT, and polybutylene succinate (PBS), followed by twin-screw extrusion granulation and finally injection molding to form a composite material. Although this reduces production costs and increases productivity, its tensile strength is low and cannot meet current market competition. Chinese invention patent application number 2024101728541 grinds bamboo pulp in a ball mill, followed by enzymatic hydrolysis with citrate buffer and ultrasonic treatment to obtain nanocellulose. Although nanocellulose is prepared, the subsequent processing is cumbersome and only utilizes the mechanical function of the ball mill. Chinese invention patent application number 2020105636254 treats bamboo fibers with citric acid, which increases the filling capacity, but the cellulose esterification substitution degree is low, resulting in a large fluctuation range in the tensile strength of the composite material, and difficulty in balancing degradation performance and mechanical strength. Summary of the Invention

[0004] In view of this, the present invention aims to overcome the defects in the prior art and proposes a bamboo-derived nanocellulose-filled biodegradable composite material and its preparation method.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0007] Step 1 involves mixing choline chloride and urea, stirring under heating conditions to obtain a eutectic solvent.

[0008] Step 2 involves adding bamboo powder to the eutectic solvent and reacting it under heating conditions. After the reaction is complete, the mixture is filtered, washed, and dried to obtain coarse bamboo cellulose.

[0009] Step 3 involves placing the coarse bamboo cellulose and the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) into a ball mill jar, adding zirconium oxide beads, citric acid, crosslinking agent, and catalyst, mixing them, preheating, and then ball milling under heating and vacuum conditions. After the reaction is completed, the product is dried, pulverized, washed, and freeze-dried to obtain esterified nanocellulose.

[0010] Step 4 involves mixing the esterified nanocellulose with PLA, PBAT, and additives, then extruding and hot-pressing the mixture to obtain the bamboo-derived nanocellulose-filled biodegradable composite material.

[0011] Furthermore, the bamboo powder in step 2 is produced by the following steps: cutting bamboo into strips, washing, drying once, pulverizing, and drying a second time to obtain the bamboo powder; the pulverizer speed in the pulverizing step is 2500-3000 rpm; the temperature of the first drying step is 40-70℃; the temperature of the second drying step is 80℃; the particle size of the bamboo powder in step 2 is 800-1200 mesh, and the moisture content is <5.0%.

[0012] Furthermore, the molar ratio of choline chloride to urea in step 1 is 1:1-5; and the heating temperature in step 1 is 80-100℃.

[0013] Furthermore, in step 2, the solid-liquid ratio of bamboo powder to eutectic solvent is 1 g: 10-15 mL; the heating temperature in step 2 is 80-100℃; the reaction time in step 2 is 4-6 hours; the washing temperature in step 2 is 80-90℃; and the drying temperature in step 2 is 60-80℃ for 6-8 hours.

[0014] Furthermore, in step 3, the mass ratio of coarse bamboo cellulose to ionic liquid [BMIM]Cl is 1:2-3; the molar ratio of coarse bamboo cellulose to citric acid in step 3 is 1:2-3.5; the amount of crosslinking agent added in step 3 is 2-6% of the mass of coarse bamboo cellulose; the amount of catalyst added in step 3 is 2-4% of the mass of coarse bamboo cellulose; the crosslinking agent in step 3 is 1,6-hexanediol; and the catalyst in step 3 is p-toluenesulfonic acid.

[0015] Furthermore, in step 3, the ball-to-material weight ratio in the ball milling step is 12-15:1; the ball milling speed in step 3 is 300-600 r / min, and the ball milling time is 4-8 h; the heating temperature in step 3 is 70-90℃; the vacuum degree of the vacuuming (nitrogen purging) in step 3 is <0 MPa; and the preheating temperature in step 3 is 75-80℃, and the time is 10-15 min.

[0016] Furthermore, the drying temperature in step 3 is 120-150℃; the washing steps in step 3 are performed 3 times (with residual acidity below 0.2%).

[0017] Further, in step 4, the mass ratio of esterified nanocellulose, PLA, PBAT to the additives is 5-40:5-25:15-75:5-15; the additives in step 4 are at least one of compatibilizer, chain extender, compatibilizer, dispersant, lubricant, or plasticizer; the additives in step 4 include the following raw materials in parts by weight: 7-10 parts of polybutylene adipate-terephthalate grafted maleic anhydride (PBAT-g-MA), 1-2 parts of ADR4368, 0.2-0.5 parts of tributyl acetylcitrate, 0.4-0.5 parts of maleic anhydride, 0.2-1 parts of polyethylene wax, 0.1-0.2 parts of white oil, 0.2-1 parts of glycerin, and 0.2-0.8 parts of ethylene glycol.

[0018] Furthermore, in step 4, the extrusion step employs a co-rotating twin-screw extruder (L / D=40:1) with zoned temperature control: zone 1 150-155℃, zone 2 155-160℃, zone 3 160-165℃, die head 165-170℃, screw speed 150-400rpm, feed rate 5-8kg / h, and masterbatch intrinsic viscosity 0.8-1.2dL / g; in step 4, the hot pressing step has an upper plate temperature of 160-170℃, a lower plate temperature of 170-180℃, and a pressure of 6-10MPa; and the thickness of the bamboo-derived nanocellulose-filled biodegradable composite material in step 4 is 0.05-0.15mm.

[0019] The present invention also provides a bamboo-derived nanocellulose-filled biodegradable composite material prepared by the aforementioned preparation method.

[0020] This invention selectively removes lignin from bamboo powder to extract cellulose, and then produces esterified nanocellulose through the synergistic effect of ball milling and esterification. This method introduces citric acid, crosslinking agent, and catalyst during low-temperature heated ball milling, enabling mechanical and thermal energy to drive the esterification reaction, achieving mechanochemical coupling, improving reaction kinetic efficiency, reducing energy consumption, and forming highly crosslinked, highly grafted cellulose, which significantly improves interfacial compatibility with PLA / PBAT. The composite material is extruded and granulated using a melt blending process, followed by hot pressing in a flat vulcanizing machine. While ensuring biodegradability, the comprehensive mechanical properties of the composite material meet the application requirements of future high-end markets.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The method for preparing bamboo-derived nanocellulose-filled biodegradable composite materials described in this invention eliminates multiple intermediate steps such as transfer, weighing, and reactor reassembly in the ball milling-esterification step, reducing operation time. Furthermore, the low-temperature heated ball milling process achieves mechanochemical coupling, improving reaction kinetic efficiency and thus production efficiency. The ball milling-esterification step is completed in a sealed vacuum ball mill jar, with activation and reaction initiation occurring under a controlled atmosphere (vacuum nitrogen), significantly reducing material loss and external contamination. [BMIM]Cl, as an expensive ionic liquid, acts as both an activator (swelling cellulose) and a reaction medium throughout the process, ensuring its full utilization. The resulting biodegradable composite material exhibits excellent properties, with a tensile strength of 34 MPa, an elongation at break of up to 600%, and a crystallinity reduced to 48.9%. Compared to the traditional PLA / PBAT hybrid system, both tensile strength and elongation at break are improved by more than 70%.

[0023] The low eutectic solvent in the bamboo-derived nanocellulose-filled biodegradable composite material of the present invention selectively removes lignin from bamboo powder and extracts cellulose, with a lignin residue rate of less than 5%. Attached Figure Description

[0024] Figure 1 The X-ray diffraction (XRD) spectrum of the esterified nanocellulose described in Example 3 of this invention;

[0025] Figure 2 The Fourier transform infrared absorption spectrum (FTIR) of the esterified nanocellulose described in Example 3 of this invention is shown.

[0026] Figure 3 This is a schematic diagram of the stress and strain of the composite material described in Embodiment 3 of the present invention. Detailed Implementation

[0027] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0028] The present invention will be described in detail below with reference to the embodiments.

[0029] Example 1

[0030] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0031] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1200 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0032] (2) Mix choline chloride and urea in a molar ratio of 1:1 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0033] (3) Add coarse bamboo cellulose and [BMIM]Cl to the ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of coarse bamboo cellulose:citric acid = 1:2. Simultaneously add 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1. The weight ratio of zirconia balls with diameters of 10, 5, 2, and 1 mm is 4:3:2:1. The ball mill jar containing the added materials is... Preheat in an 80℃ oven for 10 min (to dissolve and impregnate the cellulose with the ionic liquid), then evacuate and purge with nitrogen (repeated 3 times) to a vacuum of -0.1 MPa. Then place in a temperature-controlled planetary ball mill at 300 r / min and 70℃ for 4 h. First, spread the product flat and dry it in a 120℃ oven for 2 h. Then, pulverize the dried product and wash it three times with ethanol (residual acid less than 0.2%). Freeze-dry at -50℃ and a vacuum of 5 Pa to obtain esterified nanocellulose.

[0034] (4) Mix 10 parts of esterified nanocellulose, 20 parts of PLA and 60 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.4 parts of tri-n-butyl acetylacetic acid, 0.4 parts of polyethylene wax, 0.2 parts of white oil, 0.2 parts of glycerol, 0.3 parts of ethylene glycol and 0.5 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw speed. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0035] (5) During the hot pressing process, the upper plate die head temperature is 170℃ and the lower plate temperature is 180℃. The film is pressed under a pressure of 8MPa, and the resulting film thickness is 0.1±0.01mm.

[0036] Example 2

[0037] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0038] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1200 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0039] (2) Mix choline chloride and urea in a molar ratio of 1:1 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0040] (3) Add coarse bamboo cellulose and [BMIM]Cl to the ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of coarse bamboo cellulose:citric acid = 1:2. Simultaneously add 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 15:1. The weight ratio of zirconia balls with diameters of 10, 5, 2, and 1 mm is 4:3:2:1. The ball mill jar containing the added materials is... Preheat in an 80℃ oven for 10 min (to dissolve and impregnate the cellulose with the ionic liquid), then evacuate and purge with nitrogen (repeated 3 times) to a vacuum of -0.1 MPa. Then place in a temperature-controlled planetary ball mill at 300 r / min and 70℃ for 4 h. First, spread the product flat and dry it in a 120℃ oven for 2 h. Then, pulverize the dried product and wash it three times with ethanol (residual acid less than 0.2%). Freeze-dry at -50℃ and a vacuum of 5 Pa to obtain esterified nanocellulose.

[0041] (4) Mix 15 parts of esterified nanocellulose, 20 parts of PLA and 50 parts of PBAT and add 10 parts of PBAT-g-MA, 2 parts of ADR4368, 0.5 parts of tri-n-butyl acetylacetic acid, 0.4 parts of polyethylene wax, 0.2 parts of white oil, 0.8 parts of glycerol, 0.6 parts of ethylene glycol and 0.5 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, and 170°C at the die head. Set the screw speed to 300 rpm, the feeding rate to 6 kg / h, and the intrinsic viscosity of the masterbatch to 1.0 dL / g.

[0042] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0043] Example 3

[0044] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0045] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0046] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0047] (3) Add coarse bamboo cellulose and [BMIM]Cl to the ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of coarse bamboo cellulose:citric acid = 1:2. Simultaneously add 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1. The weight ratio of zirconia balls with diameters of 10, 5, 2, and 1 mm is 4:3:2:1. The ball mill jar containing the added materials is... Preheat in an 80℃ oven for 10 min (to dissolve and impregnate the cellulose with the ionic liquid), then evacuate and purge with nitrogen (repeated 3 times) to a vacuum of -0.1 MPa. Then place in a temperature-controlled planetary ball mill at 400 r / min and 70℃ for 4 h. First, spread the product evenly in a 120℃ oven and dry for 1 h. Then, pulverize the dried product and wash it three times with ethanol (residual acid less than 0.2%). Freeze-dry at -50℃ and a vacuum of 5 Pa to obtain esterified nanocellulose.

[0048] (4) Mix 10 parts of esterified nanocellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0049] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0050] Comparative Example 1

[0051] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0052] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0053] (2) Add bamboo powder and [BMIM]Cl to the ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of bamboo powder:citric acid = 1:2. At the same time, add 1,6-hexanediol (2% of the total mass of bamboo powder and citric acid) and p-toluenesulfonic acid (2% of the total mass of bamboo powder and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1. The weight ratio of zirconia balls with diameters of 10, 5, 2, and 1 mm is 4:3:2:1. The ball mill jar containing the added materials is dried at 80°C. In the chamber, preheat for 10 minutes (to dissolve and wet the bamboo powder with ionic liquid), then evacuate and purge with nitrogen (repeated 3 times) to a vacuum of -0.1 MPa. Then place it in a temperature-controlled planetary ball mill at 300 r / min and 70℃ for 4 hours. First, spread the product evenly in a 120℃ oven and dry for 1 hour. Then, pulverize the dried product and wash it three times with ethanol (with residual acid content below 0.2%). Freeze-dry the product at -50℃ and 5 Pa to obtain esterified bamboo powder.

[0054] (3) Mix 10 parts of esterified bamboo powder, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial double-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0055] (4) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0056] Comparative Example 2

[0057] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0058] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0059] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0060] (3) Mix 10 parts of coarse bamboo cellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0061] (4) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0062] Comparative Example 3

[0063] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0064] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0065] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0066] (3) Add coarse bamboo cellulose and [BMIM]Cl to a ball mill jar at a mass ratio of 1:2.5, and add distilled water at a ratio of 1 g:1 mL according to the amount of cellulose added. At the same time, add zirconia balls with a ball-to-material weight ratio of 12:1 and a weight ratio of 4:3:2:1 for zirconia balls with diameters of 10, 5, 2 and 1 mm. Mill the cellulose in a planetary ball mill at a speed of 400 r / min for 4 h. Centrifuge and wash the cellulose (the filtrate can be recovered by rotary evaporation). Freeze-dry the cellulose at a temperature of -50℃ and a vacuum of 5 Pa to obtain nanocellulose.

[0067] (4) Add nanocellulose and citric acid in a ratio of 0.5:2 (molar ratio). First, add citric acid to a three-necked flask and add 1,6-hexanediol (2% of the total mass of nanocellulose and citric acid). React at 120℃ and 200rpm for 30min. Then add nanocellulose and p-toluenesulfonic acid (2% of the total mass of nanocellulose and citric acid). Keep the conditions unchanged and react for 3 hours. Wash the product three times with ethanol (residual acid less than 0.2%). Freeze-dry at -50℃ and 5Pa vacuum to obtain esterified nanocellulose.

[0068] (5) Mix 5 parts of esterified nanocellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetyl citrate, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0069] (6) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0070] Comparative Example 4

[0071] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0072] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0073] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0074] (3) Crude bamboo cellulose and citric acid were mixed in a ratio of 0.5:2 (molar ratio). First, citric acid was added to a three-necked flask, and 1,6-hexanediol (2% of the total mass of crude bamboo cellulose and citric acid) was added at the same time. The mixture was reacted at 120℃ and 200rpm for 30min. Then, crude bamboo cellulose and p-toluenesulfonic acid (2% of the total mass of crude bamboo cellulose and citric acid) were added. The mixture was reacted for 3 hours under the same conditions. The product was washed three times with ethanol (the residual acid was less than 0.2%). The product was freeze-dried at -50℃ and 5Pa to obtain esterified cellulose.

[0075] (4) Mix 10 parts of esterified cellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0076] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0077] Comparative Example 5

[0078] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0079] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0080] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0081] (3) Add coarse bamboo cellulose and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) to the ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of coarse bamboo cellulose:citric acid = 1:2. At the same time, add 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1 and a zirconia ball weight ratio of 4:3:2:1 with diameters of 10, 5, 2, and 1 mm. The material was added to a ball mill jar and preheated in an 80℃ oven for 10 minutes (to dissolve and wet the cellulose with the ionic liquid). A vacuum was then created and purged with nitrogen (repeated 3 times) to a vacuum level of -0.1 MPa. The jar was then placed in a temperature-controlled planetary ball mill at 300 r / min and 70℃ for 4 hours. The product was then spread out and dried in a 120℃ oven for 1 hour. The dried product was then pulverized and washed three times with ethanol (residual acid content less than 0.2%). Finally, it was freeze-dried at -50℃ and a vacuum level of 5 Pa to obtain esterified nanocellulose.

[0082] (4) Mix 10 parts of esterified nanocellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0083] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0084] Comparative Example 6

[0085] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0086] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0087] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0088] (3) Add coarse bamboo cellulose and [BMIM]Cl to a ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of 1:2, along with 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1 and a weight ratio of 4:3:2:1 for zirconia balls with diameters of 10, 5, 2, and 1 mm. Vacuum the ball mill with nitrogen (repeated 3 times) to a vacuum degree of -0.1 MPa. Then, mill the ball mill for 4 hours at a speed of 400 r / min in a temperature-controlled planetary ball mill. First, spread the product flat and dry it in a 120℃ oven for 1 hour. Then, pulverize the dried product and wash it three times with ethanol (residual acid less than 0.2%). Freeze-dry the product at a temperature of -50℃ and a vacuum degree of 5 Pa to obtain esterified nanocellulose.

[0089] (4) Mix 10 parts of esterified nanocellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0090] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0091] Comparative Example 7

[0092] A method for preparing a bamboo-derived nanocellulose-filled biodegradable composite material includes the following steps:

[0093] (1) Cut bamboo into strips 5cm wide and 10cm long, wash with deionized water to remove surface dust and impurities, and then dry at 70℃. Then, pulverize the dried bamboo at 2500rpm to obtain bamboo powder with a particle size of 1000 mesh. Take 500g of powder and dry it in an oven at 80℃ for 4 hours until the moisture content of the bamboo powder drops to 5.0%.

[0094] (2) Mix choline chloride and urea in a molar ratio of 1:2 and stir at 80°C for 1 h to obtain a eutectic solvent. Add the obtained bamboo powder to the eutectic solvent with a solid-liquid ratio of 1 g: 10 mL and stir at 80°C for 4 h. After the reaction is completed, filter, wash with deionized water multiple times until neutral (pH=7), and dry at 60°C to obtain coarse bamboo cellulose.

[0095] (3) Add coarse bamboo cellulose and [BMIM]Cl to a ball mill jar at a mass ratio of 1:2.5, and add citric acid at a molar ratio of 1:2, along with 1,6-hexanediol (2% of the total mass of coarse bamboo cellulose and citric acid) and p-toluenesulfonic acid (2% of the total mass of coarse bamboo cellulose and citric acid). Finally, add zirconia balls with a ball-to-material weight ratio of 12:1 and a weight ratio of 4:3:2:1 for zirconia balls with diameters of 10, 5, 2, and 1 mm. Ball mill at a speed of 400 r / min for 4 h. First, spread the product flat and dry it in an oven at 120℃ for 1 h. Then, pulverize the dried product and wash it three times with ethanol (residual acid less than 0.2%). Freeze-dry it at a temperature of -50℃ and a vacuum of 5 Pa to obtain esterified nanocellulose.

[0096] (4) Mix 10 parts of esterified nanocellulose, 15 parts of PLA and 65 parts of PBAT and add 7 parts of PBAT-g-MA, 1 part of ADR4368, 0.2 parts of tri-n-butyl acetylacetic acid, 0.2 parts of polyethylene wax, 0.1 parts of white oil, 0.2 parts of glycerol, 0.2 parts of ethylene glycol and 0.4 parts of maleic anhydride. Stir for 20 minutes at 150°C and 2000 rpm in a coaxial twin-core mixer. Set the temperature of the twin-screw extruder to 155°C in zone 1, 160°C in zone 2, 165°C in zone 3, 170°C at the die head, and 300 rpm for the screw. The feeding rate is 6 kg / h and the intrinsic viscosity of the masterbatch is 1.0 dL / g.

[0097] (5) During the hot pressing process, the temperature of the upper plate die head is 170℃ and the temperature of the lower plate is 180℃. The film is pressed under a pressure of 8MPa, and the thickness of the film is 0.08±0.003mm.

[0098] The films obtained in each embodiment and each comparative example were tested, and the results are shown in Table 1.

[0099] Table 1 Test Results

[0100]

[0101] As shown in Table 1, in Examples 1-3, increasing the required milling speed and ball-to-material ratio increases the degree of esterification. Comparatively, the milling speed has a greater impact on the system than the ball-to-material ratio (when the milling speed exceeds 500 r / min, black spots and charring occur in the material). A 10% addition of esterified nanocellulose significantly enhances the performance of the composite material. The optimal example is Example 3. Figure 3 Its tensile strength is 34 MPa, and its elongation at break is 608%. Figure 1 ( Figure 1 The red line in the image represents the extracted, unmodified nanocellulose. It shows that the crystallinity decreased from 73.1% (nanocellulose) to 48.9% (esterified cellulose), indicating a significant decrease in crystallinity. The peak at 14°-17° became flatter, and the intensity of the 22.6° peak decreased markedly, suggesting that not only surface esterification occurred but the internal crystal structure may also have undergone some esterification. With a significant increase in cellulose content, all properties of the composite material decrease. Figure 2 It can be seen that 1720cm -1 The presence of a carbonyl functional group indicates successful esterification.

[0102] Compared to Example 3: In Comparative Example 1, because the bamboo powder did not have lignin removed, its structure was dense, making ball milling very difficult and resulting in a low degree of esterification, leading to a decrease in performance; in Comparative Example 2, no ball milling was performed, and the cellulose was directly subjected to subsequent steps. Due to the larger particle size of the cellulose compared to the others, the performance decreased; Comparative Example 3 involved ordinary chemical modification, and its performance differed significantly from that of Example 3; Comparative Example 4 involved direct esterification without ball milling. Although there was a degree of esterification, there were also significant stress defects, resulting in a further decrease in the tensile strength and elongation at break of the prepared material; Comparative Example 5 used the ionic liquid [BMIM]BF4. Because the chloride ions in [BMIM]Cl are extremely strong hydrogen bond acceptors, they can effectively disrupt the hydrogen bond network between and within cellulose molecular chains, causing the cellulose lattice to expand or even dissolve. Meanwhile, the large-volume anions [BF4] in [BMIM]BF4... - The poor solubility / swelling ability of cellulose leads to a decrease in the degree of esterification. Comparative Examples 6 and 7 were ball milling-esterification without heating and without vacuuming, respectively. The esterification degrees of the prepared materials were not significantly different and were very low. This is because, during ball milling at room temperature, since [BMIM]Cl is a solid, more mechanical energy will be converted into ineffective frictional heat, and local carbonization may even occur due to frictional overheating. Furthermore, since there is no liquid phase involved, the chemical esterification degree will be very low.

[0103] Heating and vacuum can be performed synergistically. Heating provides activation energy, effectively opening the tight hydrogen bond network of cellulose and promoting ionic liquid formation. Vacuum promotes the forward reaction; the boiling point of water, a byproduct of esterification, is lowered under vacuum conditions and it is removed in real time, overcoming the concentration limitations of reversible reactions and significantly increasing the degree of substitution (DS) of cellulose esterification. In addition, vacuum effectively removes oxygen from the system, inhibiting the thermal oxidative degradation of biomass components at high temperatures and ensuring the color and structural stability of the product.

[0104] In summary, the superior results achieved by ball milling-esterification synergistic modification of bamboo-based cellulose lie in the continuous synergistic effect of mechanical activation and chemical esterification in the [BMIM]Cl ionic liquid medium. The ball milling process, through high-energy impact and shearing, mechanically and chemically depolymerizes the coarse bamboo cellulose, instantly reducing its crystallinity, breaking micron-sized fiber bundles, and generating numerous lattice defects, thereby maximizing the exposure of hydroxyl groups and the reactivity of the cellulose surface. In this process, all materials are first preheated in the ball mill jar, causing the [BMIM]Cl ionic liquid to transform into a liquid state that wets and swells the cellulose, and allowing any moisture in the system to evaporate, making vacuuming easier. Then, the frictional heat generated by ball milling (along with external low-temperature heating and vacuum environment assistance), combined with the swelling effect of the [BMIM]Cl ionic liquid, drives the esterifying agent citric acid and the catalyst p-toluenesulfonic acid to be forcibly and uniformly mixed with the activated cellulose at the micro-nano scale, rapidly initiating the reaction. The subsequent esterification reaction forms a covalent ester bond structure on this highly active surface. This not only inhibits the retraction and re-aggregation of hydrogen bonds between cellulose molecules after ball milling, thus stabilizing the nanofiber morphology, but also imparts hydrophobic modification to cellulose. Thus, ball milling provides activation, energy, and efficient mass transport, while esterification provides structural stability and functional modification. The two reinforce each other, forming a synergistic enhancement effect far superior to activation or heating esterification alone.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bamboo-derived nanocellulose-filled degradable composite material, characterized by: Includes the following steps: Step 1 involves mixing choline chloride and urea, stirring under heating conditions to obtain a eutectic solvent. Step 2 involves adding bamboo powder to the eutectic solvent and reacting it under heating conditions. After the reaction is complete, the mixture is filtered, washed, and dried to obtain coarse bamboo cellulose. Step 3 involves placing the coarse bamboo cellulose and ionic liquid [BMIM]Cl into a ball mill jar, adding zirconium oxide beads, citric acid, crosslinking agent, and catalyst, mixing them, preheating, and then ball milling under heating and vacuum conditions. After the reaction is complete, the product is dried, pulverized, washed, and freeze-dried to obtain esterified nanocellulose. Step 4 involves mixing the esterified nanocellulose with PLA, PBAT, and additives, extruding, and hot-pressing to obtain the bamboo-derived nanocellulose-filled biodegradable composite material. In step 3, the mass ratio of coarse bamboo cellulose to ionic liquid [BMIM]Cl is 1:2-3; the molar ratio of coarse bamboo cellulose to citric acid in step 3 is 1:2-3.5; the amount of crosslinking agent added in step 3 is 2-6% of the total mass of coarse bamboo cellulose and citric acid; the amount of catalyst added in step 3 is 2-4% of the total mass of coarse bamboo cellulose and citric acid; the crosslinking agent in step 3 is 1,6-hexanediol; and the catalyst in step 3 is p-toluenesulfonic acid. The heating conditions in step 3 are 70-90℃.

2. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: The bamboo powder in step 2 is produced by the following steps: cutting bamboo into strips, washing, drying once, pulverizing, and drying a second time to obtain the bamboo powder; the pulverizer speed in the pulverizing step is 2500-3000 rpm; the temperature of the first drying step is 40-70℃; the temperature of the second drying step is 80℃; the particle size of the bamboo powder in step 2 is 800-1200 mesh, and the moisture content is <5.0%.

3. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: The molar ratio of choline chloride to urea in step 1 is 1:1-5; the heating temperature in step 1 is 80-100℃.

4. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: In step 2, the solid-liquid ratio of bamboo powder to eutectic solvent is 1 g: 10-15 mL; the heating temperature in step 2 is 80-100℃; the reaction time in step 2 is 4-6 hours; the washing temperature in step 2 is 80-90℃; and the drying temperature in step 2 is 60-80℃ for 6-8 hours.

5. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: The ball-to-material weight ratio in step 3 is 12-15:1; the ball milling speed in step 3 is 300-600 r / min, and the ball milling time is 4-8 h; the preheating temperature in step 3 is 75-80℃, and the time is 10-15 min.

6. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: The drying temperature in step 3 is 120-150℃; the washing steps in step 3 are performed 3 times.

7. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: In step 4, the mass ratio of esterified nanocellulose, PLA, PBAT to the additives is 5-40:5-25:15-75:5-15. The additives in step 4 include the following raw materials in parts by weight: PBAT-g-MA 7-10 parts, ADR4368 1-2 parts, tributyl acetylacetic acid 0.2-0.5 parts, maleic anhydride 0.4-0.5 parts, polyethylene wax 0.2-1 parts, white oil 0.1-0.2 parts, glycerin 0.2-1 parts, and ethylene glycol 0.2-0.8 parts.

8. The method for preparing the bamboo-derived nanocellulose-filled biodegradable composite material according to claim 1, characterized in that: The extrusion step in step 4 uses a co-rotating twin-screw extruder with an L / D ratio of 40:1 and zoned temperature control: zone 1 150-155℃, zone 2 155-160℃, zone 3 160-165℃, die head 165-170℃, screw speed 150-400rpm, and feeding rate 5-8kg / h. The hot pressing step in step 4 has an upper plate temperature of 160-170℃, a lower plate temperature of 170-180℃, and a pressure of 6-10MPa. The thickness of the bamboo-derived nanocellulose-filled biodegradable composite material in step 4 is 0.05-0.15mm.

9. A bamboo-derived nanocellulose-filled biodegradable composite material prepared by the preparation method according to any one of claims 1-8.

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