Bamboo-based material, preparation method and application thereof

Abstract

The application relates to the technical field of bamboo-based material preparation, and discloses a bamboo-based material, a preparation method and application of the bamboo-based material, which is made of bamboo powder, a hydrophilic ionic liquid, titanium dioxide, diatomite, an aluminate coupling agent, polypropylene powder and an additive. The preparation method comprises the following steps: firstly, the bamboo powder, the ionic liquid and the titanium dioxide are mixed at high speed to soften the bamboo powder by mechanical-chemical action; then, the diatomite is added to adsorb free liquid and moisture, so that the material is in the form of dry powder; the coupling agent is sprayed to perform interface hydrophobic modification; finally, the base resin is added, and one-step extrusion molding is performed through a large-length-diameter-ratio double-screw extruder. Through the gradient modification process of ionic liquid plasticization and diatomite adsorption, the agglomeration and adhesion problems of high-filling bamboo powder are solved, the one-step molding reduces the thermal history, and the prepared plate has high toughness, high strength and excellent appearance quality.

Description

Technical Field

[0001] This invention relates to the field of bamboo-based material preparation technology, specifically to a bamboo-based material, its preparation method, and its application. Background Technology

[0002] Bamboo-plastic composites are widely used in packaging boards and building formwork due to their green, environmentally friendly, renewable, and low-cost characteristics. However, maintaining the mechanical properties and processing stability of the material with high bamboo powder filler content has always been a challenge in the industry. Bamboo powder is mainly composed of cellulose and lignin, contains a large number of surface hydroxyl groups, is highly polar and rigid, while matrix resins such as polypropylene are non-polar. The interfacial compatibility between the two is naturally poor.

[0003] To improve processing performance, existing technologies often employ coupling agents such as aluminates and silanes for surface treatment. These methods primarily improve interfacial adhesion but cannot fundamentally alter the rigidity of the bamboo powder cellulose chains, thus offering limited improvement in plasticizing properties. Some technologies attempt to introduce liquid plasticizers or solvents for pretreatment of bamboo powder to achieve softening.

[0004] However, in existing bamboo-based material preparation technologies, the addition of liquid additives often leads to adhesion or agglomeration of the dry mixture due to capillary forces, deteriorating powder flowability and easily forming bridging at the extruder feed inlet, resulting in unstable feeding. Free liquid or moisture adhering to the surface of the bamboo powder can occupy the reaction sites of the coupling agent, causing the coupling agent to hydrolyze and become ineffective, significantly reducing the interface modification effect. In terms of processing technology, the current mainstream method is a two-step process of granulation followed by extrusion. Bamboo powder is a heat-sensitive biomass material with poor heat resistance. Granulation and molding require two high-temperature shearing processes. Repeated thermal history easily leads to thermal degradation or carbonization of bamboo fibers, not only causing the product to turn black and deteriorate in appearance, but also producing a large amount of small-molecule volatiles, causing porosity defects inside the board. Therefore, this invention provides a bamboo-based material, its preparation method, and its applications to address the shortcomings of existing technologies. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a bamboo-based material, its preparation method, and its application. It solves the problems of high-filler bamboo-plastic composite materials, such as the high polarity and easy agglomeration caused by the large number of hydroxyl groups on the surface of bamboo powder during the preparation process, and the fact that bamboo powder needs to undergo two thermal histories of granulation and molding in the traditional melt blending process, resulting in thermal degradation of cellulose, poor processing rheological properties, and low interfacial bonding strength.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The first aspect of this invention provides a bamboo-based material, which adopts the following technical solution:

[0008] A bamboo-based material is made from the following raw materials in parts by weight: 40-80 parts bamboo powder; 2-4 parts hydrophilic ionic liquid; 1-2 parts titanium dioxide; 1.5-3 parts diatomaceous earth; 1.5-2.5 parts aluminate coupling agent; 14-54 parts polypropylene powder; 4-6 parts maleic anhydride-grafted polypropylene; 5-7 parts lubricant; and 0.6-1.0 parts antioxidant compound.

[0009] By adopting the above technical solution, hydrophilic ionic liquids are used to disrupt the hydrogen bonds between cellulose chains in bamboo powder, and the frictional assistance of titanium dioxide particles is combined to achieve plasticization of high-content bamboo powder. The porous structure of diatomaceous earth is used to adsorb ionic liquids, solving the adhesion problem after modification. The synergistic effect of each component improves the processing fluidity and mechanical properties of the material while ensuring high filling content.

[0010] Preferably, the hydrophilic ionic liquid is 1-butyl-3-methylimidazolium chloride; the lubricant is composed of polyethylene wax and zinc stearate, wherein the weight ratio of polyethylene wax to zinc stearate is 2.8-3.2:1; the antioxidant compound is composed of antioxidant 1010 and antioxidant 168, wherein the weight ratio of antioxidant 1010 to antioxidant 168 is 0.8-1.2:1.

[0011] By adopting the above technical solutions, a specific ionic liquid achieves swelling of bamboo powder, the lubricant ratio balances the internal and external frictions during processing, and reduces heat accumulation; the antioxidant compound system inhibits the thermal oxidative degradation of bamboo powder during processing, and maintains the material's color and strength.

[0012] Preferably, the preparation method of the hydrophilic ionic liquid includes the following steps: adding N-methylimidazolium and 1-chlorobutane to a reaction vessel; heating to 75-85°C under a protective atmosphere and maintaining the reflux reaction for 46-50 hours; cooling and separating the layers after the reaction, taking the lower layer of liquid and washing it with ethyl acetate to remove unreacted raw materials; drying the washed product under vacuum to obtain a pale yellow transparent viscous liquid.

[0013] By adopting the above technical solutions, the synthesis process parameters and post-processing can be controlled to improve the purity of ionic liquids and reduce the interference of impurities on interfacial reactions.

[0014] The second aspect of this invention provides a method for preparing bamboo-based materials, employing the following technical solution:

[0015] A method for preparing bamboo-based materials includes the following steps:

[0016] S1. Bamboo powder, hydrophilic ionic liquid, and titanium dioxide are put into a mixer and mechanical-chemical synergistic dissociation is carried out by high-speed shearing and heating to remove moisture and soften the bamboo powder.

[0017] S2. Reduce the speed of the mixer and add diatomaceous earth. Utilize the mesoporous structure of diatomaceous earth to adsorb and fix free hydrophilic ionic liquids and residual moisture, so that the material is transformed into a dry powder state.

[0018] S3. Spray an aluminate coupling agent into the dry powder obtained in step S2 to carry out an interfacial hydrophobic modification reaction.

[0019] S4. Add polypropylene powder, maleic anhydride-grafted polypropylene, lubricant and antioxidant compound, and cool and mix to obtain modified bamboo-plastic dry mix;

[0020] S5. Add the modified bamboo-plastic dry mixture to the extruder, and obtain the bamboo-based material through one-step extrusion molding, vacuum shaping, cooling and cutting.

[0021] By adopting the above technical solution, the present invention achieves interface modification and molding through a stepwise gradient process, as detailed below:

[0022] In step S1, a hydrophilic ionic liquid is used to penetrate into the bamboo powder fiber under high temperature and shear field, opening the hydrogen bonds between cellulose molecular chains and realizing the plasticization of the fiber surface. Titanium dioxide particles provide micro-friction during the mixing process, which helps the bamboo powder to dissociate and promotes the evaporation of water, so that the bamboo powder is transformed from rigid particles into thermoplastic microfiber bundles.

[0023] In step S2, to address the stickiness and residual moisture on the surface of bamboo powder after ionic liquid treatment, the mesoporous structure of diatomaceous earth is utilized to adsorb the free ionic liquid and precipitated moisture into the pores. This step eliminates liquid bridging forces between particles, prevents material adhesion, provides a dry reaction interface for subsequent chemical grafting, and prevents the coupling agent from hydrolyzing.

[0024] In step S3, after the material is restored to a dry powder state, an aluminate coupling agent is added. The coupling agent molecules chemically bond with the hydroxyl groups on the surface of the bamboo powder. Since the previous step removed the interference of free water, the coupling agent forms a hydrophobic layer on the surface of the bamboo powder, improving the interfacial compatibility between the bamboo powder and the polypropylene matrix.

[0025] In step S5, a high aspect ratio twin-screw extruder with a forced feeding system is used to directly extrude the dry mixture. This process eliminates the granulation step, reduces the thermal history of the bamboo powder, and preserves the length and strength of the bamboo fibers; combined with multi-stage vacuum degassing to remove volatiles, it reduces porosity in the finished product.

[0026] Preferably, step S1 further includes: turning on the stirring blades to a linear velocity of 20-25 m / s, using the self-generated heat from material friction to raise the temperature to 105-115℃, maintaining high-speed stirring for 4-5 minutes, and turning on the exhaust device during this period.

[0027] By adopting the above technical solution, the shear energy provided by the linear velocity is matched with the temperature, ensuring the wetting and softening of bamboo powder by the ionic liquid, and removing the adsorbed water inside the bamboo powder through the exhaust device.

[0028] Preferably, step S2 further includes: reducing the mixer speed to a linear velocity of 10-15 m / s, adding diatomaceous earth at a temperature of 100-110°C and continuing to stir for 60-120 seconds until the material is free of liquid bridges and adhesion.

[0029] By adopting the above technical solutions, reducing the rotation speed and maintaining the temperature are beneficial to the dispersion and adsorption of diatomaceous earth, preventing excessive shearing from damaging the pore structure of diatomaceous earth, and ensuring that the material is transformed into a free-flowing powder state.

[0030] Preferably, in step S3, the interfacial hydrophobic modification reaction is carried out by stirring at a medium speed for 2-3 minutes; in step S4, the discharge temperature of the cooled mixture is controlled at 40-50℃.

[0031] By adopting the above technical solution, the reaction time is controlled to allow the coupling agent to complete the coating; the discharge temperature is controlled to prevent material agglomeration and to provide a suitable bulk density.

[0032] Preferably, in step S5, the modified bamboo-plastic dry mixture is added to the extruder and extruded in one step using a co-rotating parallel twin-screw extruder. The length-to-diameter ratio of the extruder is greater than or equal to 44:1, and a vertical forced feeder is used for feeding. The feeding screw runs synchronously with the main screw or the speed of the feeding screw is higher than the synchronous speed of the main screw.

[0033] By adopting the above technical solutions, the large aspect ratio provides the residence time required for plasticization and degassing; the vertical forced feeding and synchronous overspeed strategy solve the feeding bridging problem of low-density bamboo powder and improve the stability of extrusion output.

[0034] Preferably, in step S5, the middle part of the extruder barrel and the metering section are respectively provided with vacuum exhaust ports, and the vacuum degree is controlled between -0.08MPa and -0.09MPa; the temperature setting range of each zone of the extruder is 160-195℃, and the temperature setting range of the die head is 165-175℃.

[0035] By adopting the above technical solution, two-stage vacuum exhaust removes water vapor and volatiles; segmented temperature control ensures the melting of polypropylene and the plasticization of bamboo powder, avoiding local overheating that could lead to the degradation of bamboo powder.

[0036] This invention provides an application of bamboo-based materials, employing the following technical solution:

[0037] The above-mentioned bamboo-based materials are used in the preparation of woven yarns, woven bags, corrugated boards and corrugated boxes.

[0038] By adopting the above technical solution, the bamboo-based material has high rigidity and toughness, and the resulting woven yarns, woven bags, corrugated boards and corrugated boxes have low water absorption and high compressive strength, meeting the requirements for the durability of packaging materials.

[0039] This invention provides a bamboo-based material, its preparation method, and its applications. It offers the following advantages:

[0040] 1. This invention introduces hydrophilic ionic liquid and titanium dioxide, utilizing the swelling effect of the ionic liquid on cellulose to break hydrogen bonds, combined with the micro-friction effect of titanium dioxide, to achieve in-situ plasticization of bamboo powder with high filling content. After diatomaceous earth adsorbs excess liquid, aluminate coupling agent is grafted onto the surface to construct a hydrophobic modified layer, which improves the interfacial compatibility between bamboo powder and polypropylene matrix, so that the material maintains high tensile strength and flexural modulus even with high bamboo powder filling content.

[0041] 2. This invention employs a one-step extrusion molding process, eliminating the traditional granulation-then-molding step. This reduces the thermal history experienced by bamboo powder and lowers the risk of thermal degradation and discoloration of cellulose due to repeated high-temperature processing. Combined with the shearing plasticization and multi-stage vacuum degassing of a high aspect ratio twin-screw extruder, it can directly convert dry blends into dense sheets, simplifying the production process and reducing energy consumption while ensuring the appearance, color, and physical properties of the finished product.

[0042] 3. This invention solves the problem of adhesion and agglomeration that easily occurs in bamboo powder modified by ionic liquids. By adding diatomaceous earth with a mesoporous structure, free ionic liquids and deeply precipitated water are adsorbed into the pores, eliminating liquid bridging forces between particles. This treatment transforms the material into a well-dispersed powder state, ensuring the effective progress of the subsequent coupling agent grafting reaction and improving the conveying stability of the mixture in the extruder feeding section, preventing bridging and clogging. Attached Figure Description

[0043] Figure 1 The following are comparative diagrams of the dry-mixed powder characteristics test of the present invention; wherein, (a) is a comparative diagram of the angle of repose of the dry-mixed powder, and (b) is a diagram of the filter paper imprinting oil penetration test.

[0044] Figure 2 The following are comparative graphs of the real-time monitoring curves of the main extrusion process current of the present invention; wherein, (a) is the current curve of Example 2, and (b) is the current curve of Comparative Example 5.

[0045] Figure 3 This is a schematic diagram verifying the mechanical properties and synergistic effect of the modified bamboo-plastic composite board of the present invention; wherein, (a) is a biaxial comparison diagram of tensile strength and elongation at break, and (b) is a comparison diagram of flexural modulus and notched impact strength.

[0046] Figure 4The diagram shows a comparison of the structural performance and weather resistance of the finished packaging board of the present invention; wherein, (a) is a comparison of flat crush strength; and (b) is a comparison of water absorption rate and yellowing index. Detailed Implementation

[0047] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0049] The polypropylene powder used is isotactic polypropylene homopolymer, CAS number 9003-07-0, with a melt flow rate (230℃, 2.16kg) of 2.0g / 10min to 3.0g / 10min and a density of 0.90g / cm³. 3 The isotacticity is greater than 96%, and the particle size distribution of the powder is between 30 mesh and 60 mesh.

[0050] Bamboo powder is made from moso bamboo that is over three years old. It is mechanically crushed and screened, with a particle size ranging from 200 mesh to 400 mesh. Before use, it is dried with hot air to reduce the moisture content to below 8%.

[0051] The titanium dioxide used is titanium dioxide, CAS number 13463-67-7, with an average native particle size of 0.20μm to 0.30μm, and the surface is treated with an inorganic aluminum coating.

[0052] Diatomaceous earth's main chemical component is amorphous silicon dioxide, with CAS number 61790-53-2, a mesh size of 1250 mesh, and an oil absorption value (DOP) of 60ml / 100g to 65ml / 100g.

[0053] The aluminate coupling agent is DL-411; maleic anhydride-grafted polypropylene (PP-g-MAH), CAS number 25722-45-6, has a grafting rate of 0.8% to 1.2% and a melt flow rate (230℃, 2.16kg) of 40g / 10min to 60g / 10min; the lubricant and antioxidant are all commercially available general plastic processing aids, including polyethylene wax CAS number 9002-88-4, zinc stearate CAS number 557-05-1, antioxidant 1010 (CAS number 6683-19-8) and antioxidant 168 (CAS number 31570-04-4).

[0054] Preparation Example 1:

[0055] This preparation example provides a method for preparing the hydrophilic ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), including the following steps:

[0056] In a reaction vessel equipped with a reflux condenser, thermometer, and magnetic stirrer, 82 parts by mass of N-methylimidazole and 102 parts by mass of 1-chlorobutane were added. Under a nitrogen atmosphere, stirring was started and the reaction system was heated to 80°C and refluxed for 48 hours. After the reaction was completed, the reaction solution was cooled to room temperature and allowed to stand for separation. The supernatant was removed, and the lower layer of pale yellow viscous liquid was retained. The lower liquid was washed three times with 200 parts by mass of ethyl acetate. After each wash, the mixture was allowed to stand for separation and the supernatant was removed to remove unreacted raw materials. Finally, the washed product was placed in a vacuum drying oven and dried at 80°C and a vacuum of -0.09 MPa for 24 hours to obtain a pale yellow transparent viscous liquid, which is the target product.

[0057] Example 1:

[0058] This embodiment provides a method for preparing bamboo-based materials, including the following steps:

[0059] S1. Weigh 40 parts bamboo powder, 2 parts 1-butyl-3-methylimidazolium chloride, and 1 part titanium dioxide by mass and put them into a high-speed mixer with a pneumatic exhaust valve. Turn on the stirring blades to a linear velocity of 20 m / s and use the friction of the materials to generate heat to raise the temperature to 105℃. Keep stirring at high speed for 4 minutes, and open the exhaust valve to continuously discharge water vapor during this period.

[0060] S2. Reduce the mixer speed to a linear velocity of 10m / s, add 1.5 parts of diatomaceous earth, keep the material temperature at 100℃ and continue stirring for 90 seconds to make the material into a dry powder state.

[0061] S3. Keep stirring at medium speed, spray in 1.5 parts of aluminate coupling agent, and continue the reaction for 2 minutes;

[0062] S4. Then add 54 parts of polypropylene powder, 4 parts of maleic anhydride grafted polypropylene, 5 parts of polyethylene wax and zinc stearate compound lubricant (mass ratio 2.8:1), and 0.6 parts of antioxidant compound (antioxidant 1010 and antioxidant 168 mass ratio 0.8:1). Discharge the material into a cold mixer to cool and mix to 45°C before discharging to obtain modified bamboo-plastic dry mix.

[0063] S5. Add the above dry mixture to the vertical forced feeder of the co-rotating parallel twin-screw extruder. Set the forced feed screw to run synchronously with the main screw. Extrude the material in one step using an extruder with a length-to-diameter ratio of 44:1. Set the temperatures of each zone of the extruder to 160℃, 175℃, 180℃, 185℃, 180℃, 175℃, and 170℃, and the die head temperature to 165℃. Open the vacuum exhaust system with a vacuum degree of -0.08MPa in the middle of the barrel and the metering section. Extrude the melt through the hollow plate mold, cool and shape it on the vacuum shaping table, and then cut it to obtain a high-toughness bamboo-plastic packaging board.

[0064] Example 2:

[0065] This embodiment provides a method for preparing bamboo-based materials, including the following steps:

[0066] S1. Weigh 60 parts bamboo powder, 3 parts 1-butyl-3-methylimidazolium chloride, and 1.5 parts titanium dioxide by mass and put them into a high-speed mixer with a pneumatic exhaust valve. Turn on the stirring blades to a linear velocity of 22 m / s and use the friction of the materials to generate heat to raise the temperature to 110°C. Maintain high-speed stirring for 5 minutes, and open the exhaust valve to continuously discharge water vapor during this period.

[0067] S2. Reduce the mixer speed to a linear velocity of 12m / s, add 2 parts of diatomaceous earth, keep the material temperature at 105℃ and continue stirring for 60 seconds to make the material into a dry powder state.

[0068] S3. Keep stirring at medium speed, spray in 2 parts of aluminate coupling agent, and continue to react for 3 minutes;

[0069] S4. Then add 34 parts of polypropylene powder, 5 parts of maleic anhydride grafted polypropylene, 6 parts of polyethylene wax and zinc stearate compound lubricant (mass ratio 3:1), and 0.8 parts of antioxidant compound (1010 and 168 mass ratio 1:1). Discharge the material into a cold mixer to cool and mix to 50°C before discharging to obtain modified bamboo-plastic dry mix.

[0070] S5. Add the above dry mixture to the vertical forced feeder of the co-rotating parallel twin-screw extruder. Set the forced feed screw to run synchronously with the main screw. Extrude the material in one step through the extruder with a length-to-diameter ratio of 44:1. Set the temperatures of each zone of the extruder to 165℃, 180℃, 185℃, 190℃, 185℃, 180℃, and 175℃, and the die head temperature to 170℃. Open the vacuum exhaust with a vacuum degree of -0.085MPa in the middle of the barrel and the metering section respectively. The melt is extruded through the hollow plate mold, cooled and shaped by the vacuum shaping table, and then traction-cut to obtain a general-purpose bamboo-plastic packaging board.

[0071] Example 3:

[0072] This embodiment provides a method for preparing bamboo-based materials, including the following steps:

[0073] S1. Weigh 80 parts bamboo powder, 4 parts 1-butyl-3-methylimidazolium chloride, and 2 parts titanium dioxide by mass and put them into a high-speed mixer with a pneumatic exhaust valve. Turn on the stirring blades to a linear velocity of 25 m / s and use the friction of the materials to generate heat to raise the temperature to 115°C. Maintain high-speed stirring for 5 minutes, and open the exhaust valve to continuously discharge water vapor during this period.

[0074] S2. Reduce the mixer speed to a linear velocity of 15m / s, add 3 parts of diatomaceous earth, and continue stirring for 120 seconds while maintaining the material temperature at 110℃ to ensure that the high-content ionic liquid is completely adsorbed and locked.

[0075] S3. Keep stirring at medium speed, spray in 2.5 parts of aluminate coupling agent, and continue the reaction for 3 minutes;

[0076] S4. Then add 14 parts of polypropylene powder, 6 parts of maleic anhydride grafted polypropylene, 7 parts of polyethylene wax and zinc stearate compound lubricant (mass ratio 3.2:1), and 1.0 part of antioxidant compound (1010 and 168 mass ratio 1.2:1). Discharge the materials into a cold mixer to cool and mix to 40°C before discharging to obtain modified bamboo-plastic dry mix.

[0077] S5. Add the above dry mixture to the vertical forced feeder of the co-rotating parallel twin-screw extruder. Set the forced feed screw speed slightly higher than the synchronous speed of the main screw to improve the filling and compaction. Extrude the material in one step using an extruder with a length-to-diameter ratio of 48:1. Set the temperatures of each zone of the extruder to 165℃, 185℃, 190℃, 195℃, 190℃, 185℃, and 180℃, and the die head temperature to 175℃. Open a powerful vacuum exhaust system with a vacuum degree of -0.09MPa in the middle of the barrel and the metering section. Extrude the melt through the hollow plate mold, cool and shape it on the vacuum shaping table, and then cut it to obtain a high-rigidity bamboo-plastic packaging board.

[0078] Comparative Example 1:

[0079] Compared to Example 2, the difference lies in the following: the mixing process is changed, and all raw materials, including bamboo powder, PP powder, ionic liquid, titanium dioxide, and coupling agent, are added to the high-speed mixer at once, with the mixing temperature controlled to not exceed 80°C. Diatomaceous earth is not added to the formula. The types and amounts of other raw materials remain the same.

[0080] Comparative Example 2:

[0081] Compared to Example 2, the difference lies in the molding process: the dry mixture prepared in Example 2 is fed into a twin-screw extruder for melt granulation, followed by water-cooled pelletizing, drying, and then the pellets are fed into a single-screw extruder to extrude sheets. All other formulations and parameters remain the same.

[0082] Comparative Example 3:

[0083] The difference from Example 2 is that 1-butyl-3-methylimidazolium chloride is not added to the formulation, but all other aspects are the same.

[0084] Comparative Example 4:

[0085] Compared with Example 2, the difference is that titanium dioxide is not added to the formula, and an equal mass of nano-calcium carbonate (Mohs hardness 3.0, much lower than titanium dioxide) is used instead, while the rest are the same.

[0086] Comparative Example 5:

[0087] Compared with Example 2, the difference is that diatomaceous earth is not added to the formula, step S2 is omitted, and the rest are the same.

[0088] Comparative Example 6:

[0089] Compared with Example 2, the difference is that the feeding order is changed. In step S1, the aluminate coupling agent and the hydrophilic ionic liquid are simultaneously added to the mixer, and there is no step-by-step processing. All other aspects are the same.

[0090] Test Example 1:

[0091] Test Description: This experiment aims to evaluate the physical state of the modified bamboo-plastic dry blend before it enters the extruder, and to verify the locking ability of the porous adsorbent for ionic liquids and the flowability of the system. Test samples were taken from the cold mixer outlets of Examples 1 to 3 and Comparative Examples 1 and 5, with the sample temperature maintained between 40°C and 45°C.

[0092] Test steps:

[0093] 1. Take 500g of freshly discharged dry-mixed powder and place it in the feed funnel of a BT-1000 powder comprehensive characteristic tester. The height of the bottom of the funnel from the base plate is fixed at 80mm. Turn on the vibrating feeder to allow the powder to fall naturally and accumulate into a cone until the top of the cone touches the bottom of the funnel. Measure the average diameter and height of the cone's base and calculate the angle of repose. Repeat the test 5 times for each sample and take the arithmetic mean.

[0094] 2. Take a quantitative filter paper (pore size 15-20μm) and lay it flat on a glass plate. Weigh 20g of hot dry-mixed powder and pile it in the center of the filter paper. Cover it with another layer of filter paper of the same specification. Apply a static pressure of 2kg using a standard cylindrical weight and maintain it for 5 minutes.

[0095] 3. Remove the weights and powder, and observe the oil penetration of the bottom filter paper. Use calipers to measure the maximum diameter of the oil stains. If multiple points are distributed, calculate the total area percentage. At the same time, observe the clumping of the powder after being compressed, and determine whether there are liquid bridges between the powder particles by rubbing them between your fingers.

[0096] The test data is shown in Table 1:

[0097] Table 1: Data Records of Flowability and Oil Leakage Tests for Dry Mixtures of Each Formulation

[0098]

[0099] According to the appendix Figure 1 Analysis of the data in Table 1 shows that the angles of repose in Examples 1 to 3 are concentrated between 33° and 38°, and the filter paper test showed virtually no oil stains. This indicates that even under extreme conditions with a bamboo powder filling amount as high as 80 parts and an ionic liquid content increased to 4 parts, diatomaceous earth still effectively adsorbs the ionic liquid, whose viscosity decreases at high temperatures, into the mesoporous structure. At this point, the powder surface exhibits a dry state dominated by coupling agents and lubricants, with moderate interparticle friction. This not only eliminates the risk of bridging caused by liquid phase adhesion but also provides a rheological basis for subsequent high-density solid conveying in the forced feeder.

[0100] The angle of repose in Comparative Example 1 was as high as 66.4°, and the powder was in a damp and agglomerated state. This was mainly because the low-temperature mixing (80°C) failed to effectively remove the moisture contained in the bamboo powder, and no adsorbent was added. As a result, the moisture and ionic liquid formed a liquid bridge with high surface tension on the powder surface, causing the particles to agglomerate. The material in this state could not pass through the feed throat of the twin-screw extruder.

[0101] Comparative Example 5 showed an angle of repose of 52.8°, and a noticeable oil spot with a diameter of 28.4 mm appeared on the filter paper. Although this group underwent high-temperature drying to remove moisture, the lack of diatomaceous earth locking allowed free ionic liquid to accumulate on the surface of the bamboo powder and resin particles. This oil-rich surface acted as excessive lubrication at the microscopic level, and macroscopically manifested as sticky powder with a large angle of repose (due to high viscous resistance). This free liquid formed a slip layer on the screw surface, causing a sharp decrease in solid conveying efficiency and triggering fluctuations in the main unit current.

[0102] Test Example 2:

[0103] Test Description: This experiment evaluates the solids conveying efficiency and melt stability of different formulation systems in a twin-screw extruder by monitoring the main unit's operating parameters and the appearance quality of the extruded product. The experimental equipment is a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 44:1, equipped with a quantitative vertical forced feeding system and a high-frequency data acquisition module.

[0104] Experimental steps:

[0105] 1. Adjust the extruder process parameters to the settings of the corresponding embodiment or comparative example. After each temperature zone reaches the set temperature and is held at that temperature for 30 minutes, start the main unit. Set the main unit screw speed to 300 rpm, and gradually increase the forced feeder speed until the main unit torque reaches 75% to 85% of the rated value. After the extrusion output is continuous and the die pressure is stable, start recording data.

[0106] 2. The main unit current (Amps), melt pressure (MPa), and actual feeder speed are continuously recorded using sensors at a sampling frequency of 1Hz for 60 minutes. For samples experiencing severe feeding interruptions or main unit torque alarm shutdowns, the operating data and fault symptoms before the shutdown time are recorded.

[0107] 3. During data acquisition, take a sample of the sheet material approximately 1 meter long every 10 minutes. Observe the surface flatness of the sheet material under standard light, focusing on checking for sharkskin-like defects, flow marks, unplasticized particles, or ruptured air bubbles. Simultaneously, weigh the total extrusion volume over 60 minutes and calculate the average production capacity.

[0108] The test data is shown in Table 2:

[0109] Table 2: Record of Main Machine Current Fluctuation and Product Appearance in One-Step Extrusion Process

[0110]

[0111] (Note: Comparative Example 2 uses particle feed, which has excellent fluidity and therefore the lowest volatility; Comparative Example 1 had severe slippage and vent blockage, requiring multiple adjustments to the feeding speed during the process, and the data was calculated based on the stable period.)

[0112] According to the appendix Figure 2 The data in Table 2, and the differences in processing stability between the examples and the comparative examples, confirm the decisive role of friction coefficient control within the system in one-step extrusion.

[0113] Example 2 maintained a low current fluctuation rate of 2.12% at a high fill rate of 60%, and achieved a production capacity of 198.7 kg / h. This indicates that the adsorption-locked dry mix established a stable frictional shear mechanism in the solid conveying section of the screw. Diatomaceous earth locks the ionic liquid within the pores, ensuring a sufficient coefficient of dynamic friction between the material and the inner wall of the barrel. This allows the material to be effectively propelled forward by the screw ridges, rather than slipping in place.

[0114] Comparative Example 5 (without diatomaceous earth) exhibited a current fluctuation rate as high as 15.66%, and its average current value (126.7A) was lower than that of Example 2 (155.6A). This decrease in current value does not necessarily indicate reduced energy consumption, but rather a loss of screw gripping ability. Free ionic liquid migrates to the barrel wall under high temperature and pressure, forming a low-viscosity lubricating film, causing severe wall slippage of the material within the screw channel. This slippage prevents the extrusion pressure from being established, manifesting as periodic drops in current and a decrease in output. Furthermore, the "bamboo-like" stripes appearing on the sheet surface are precisely due to melt fracture caused by extrusion speed pulsations.

[0115] Comparative Example 1 recorded nearly 30% of drastic fluctuations and numerous bubble defects. This was attributed to the failure of low-temperature mixing to effectively remove the bound water from the bamboo powder. In the high-temperature section of the extruder, residual moisture instantly vaporized and expanded in volume, leading to melt pressure instability. Simultaneously, water vapor mixed with unadsorbed ionic liquid to form an emulsion layer, further exacerbating the "bridging" and "return" phenomena in the feeding section, confirming the necessity of the initial high-temperature dissociation drying process.

[0116] Although Comparative Example 3 showed smaller current fluctuations, the average current was as high as 178.9 A, and transverse cracks appeared on the surface of the product. This is because the lack of chemical softening effect from ionic liquids resulted in excessive rigidity of the bamboo powder and extremely high melt viscosity, leading to a significant increase in processing torque. Under high shear force, the hard bamboo powder particles acted as stress concentration points, causing brittle fracture of the melt surface and making it difficult to obtain acceptable appearance quality.

[0117] Test Example 3:

[0118] Test Description: This experiment aims to determine the physical and mechanical properties of the plates prepared in the examples and comparative examples, and to analyze the synergistic reinforcement mechanism between components and the influence of the process on the material properties through data comparison.

[0119] Test steps:

[0120] 1. Using a CNC engraving machine, cut test specimens along the extrusion direction from the upper surface of each group of finished sheet materials. Prepare Type IV dumbbell-shaped tensile specimens conforming to ASTM D638, 80mm×10mm×4mm rectangular bending specimens conforming to ASTM D790, and 80mm×10mm×4mm notched impact specimens conforming to ISO 179. Prepare 7 specimens for each test item for each formulation, and after removing the maximum and minimum values, take the arithmetic mean of the remaining 5 valid data.

[0121] 2. Place all prepared specimens in a constant temperature and humidity test chamber and condition them for 48 hours at a temperature of 23±2℃ and a relative humidity of 50±5% to eliminate residual stress during specimen preparation and differences in moisture content caused by different storage environments.

[0122] 3. Tensile and bending tests were performed using a universal testing machine equipped with a 50kN force sensor. The tensile test speed was set to 50mm / min, and the tensile yield strength and elongation at break were recorded. The bending test span was set to 64mm, the loading speed was 2mm / min, and the bending modulus was recorded. A pendulum impact testing machine was used to perform notched impact tests on simply supported beams. The pendulum energy was 2J, the notch depth was 2mm (Type A notch), and the impact strength was recorded.

[0123] The test data is shown in Table 3:

[0124] Table 3: Mechanical property test data of bamboo-plastic composite boards for each group

[0125]

[0126] According to the appendix Figure 3 And the data in Table 3:

[0127] Due to the different bamboo powder filling ratios in Examples 1 to 3, the prepared boards exhibited distinct performance grading characteristics:

[0128] In Example 1, the bamboo powder addition of 40 parts was relatively low, and the polypropylene matrix maintained a good continuous phase structure. The elongation at break in this set of data reached 45.6%, and the notched impact strength reached 8.9 kJ / m. 2 It exhibits excellent deformation absorption and impact resistance, and is a high-toughness formula suitable for applications with high requirements for shock absorption and cushioning.

[0129] In Example 3, the bamboo powder addition of 80 parts reached the maximum, with a large amount of rigid bamboo fiber forming a dense reinforcing skeleton in the system. The tensile yield strength of this set of data reached 43.1 MPa, and the flexural modulus was as high as 4.88 GPa. The material exhibited outstanding resistance to deformation and load-bearing capacity, and is a high-rigidity formula suitable for structural components with strict requirements for stiffness and support strength.

[0130] In Example 2, the bamboo powder addition of 60 parts was moderate, resulting in a tensile strength of 38.7 MPa, an elongation at break of 12.4%, and an impact strength of 6.2 kJ / m. 2 Both are at a balanced level. It balances the material's load-bearing capacity and flexibility, and is a universal formula that meets the requirements for use in the preparation of woven yarns, woven bags, corrugated boards, and corrugated boxes.

[0131] Example 2 showed a tensile strength of 38.7 MPa, an elongation at break of 12.4%, and an impact strength of 6.2 kJ / m. 2Compared to Comparative Example 3 (without ionic liquid), although Comparative Example 3 retained titanium dioxide, its elongation at break was only 3.4% due to the lack of swelling and softening effect of the ionic liquid, exhibiting obvious brittle fracture characteristics. This indicates that in unsoftened rigid bamboo powder, hard particles cannot embed into the cell wall for splitting, but instead act as impurities, causing stress concentration.

[0132] Compared to Comparative Example 4 (calcium carbonate replacing titanium dioxide), although Comparative Example 4 contained ionic liquid, its elongation at break (7.2%) and flexural modulus (2.75 GPa) were both lower than those of Example 2. This indicates that with only chemical softening and lacking the microscopic shearing and grinding of high-hardness particles (titanium dioxide), bamboo powder cannot achieve effective fiberization and remains in the form of particulate filler, without improving the aspect ratio, thus limiting the reinforcing and toughening effect. The excellent comprehensive performance of Example 2 confirms that both "ionic liquid softening" and "titanium dioxide micro-grinding" are indispensable, jointly realizing the structural transformation of bamboo powder from "particulate filler" to "fiber reinforcement".

[0133] Comparing Example 2 and Comparative Example 2 (two-step method), Example 2 showed a higher elongation at break (12.4%) and impact strength than Comparative Example 2 (8.5%). This is because the two-step process involves two high-temperature shearing processes (granulation + extrusion), leading to partial thermal degradation and carbonization of hemicellulose and lignin in the bamboo fiber, thus damaging the fiber's inherent strength. In contrast, the one-step process of this invention shortens the material's thermal history through low-temperature adsorption-locking technology, maximizing the preservation of the natural fiber's intrinsic strength.

[0134] The mechanical properties of Comparative Example 6 (with a changed feeding order) were generally lower than those of Example 2, with the tensile strength decreasing by approximately 13%. This confirms the necessity of "gradient interface construction." If ionic liquids, adsorbents, and coupling agents are added simultaneously, diatomaceous earth will competitively adsorb the coupling agent, resulting in a reduced coupling coverage on the bamboo powder surface, weakened interfacial bonding, and difficulty in forming an effective stress transfer layer between the matrix resin and bamboo fibers.

[0135] Test Example 4:

[0136] Test Description: Specific tests are conducted on the structural stiffness, moisture resistance, and thermal stability of the packaging sheet material. The impact of the one-step process on reducing thermal history on the material's appearance, and the contribution of "gradient interface construction" to barrier performance are evaluated.

[0137] 1. Flat crush strength test: A sample of 64.5 cm² area was cut from the board using a sampler. 2A circular specimen (90.6 mm in diameter) was placed between the upper and lower plates of a compression testing machine. The platen running speed was set to 12.5 mm / min. Pressure was applied along the thickness direction of the plate until the specimen was crushed. The maximum yield force value was recorded. Ten specimens were tested for each formula, and the average value was taken to characterize the load-bearing capacity of the packaging box under stacking conditions.

[0138] 2. Water Absorption Test: Cut the board into 50mm × 50mm square samples. Smooth the cut surfaces with 400-grit sandpaper to remove burrs. Place the samples in a 50℃ oven to dry for 24 hours until constant weight, and weigh the dry weight (m1). Then, completely immerse the samples in distilled water at 23℃ for 24 hours. After removal, blot the visible water droplets with filter paper and immediately weigh the wet weight (m2). The calculation formula is (m2...). m1) / m1×100%. This index is used to evaluate the integrity of the coupling agent's coating on hydrophilic bamboo powder.

[0139] 3. Yellowing Index (YI) Test: The CIE Lab colorimetric value of the board surface was measured using a spectrophotometer under a D65 light source and a 10° field of view. The yellowing index YI was calculated according to the ASTM E313 standard. This index directly reflects the degree of thermal degradation of bamboo powder during processing. The higher the YI value, the more severe the carbonization of the material and the greater the fiber damage.

[0140] The experimental data are shown in Table 4:

[0141] Table 4: Test data on structural performance and weather resistance of finished packaging boards

[0142]

[0143] According to the appendix Figure 4 And the data in Table 4:

[0144] In terms of compressive strength, Example 3 achieved 915.8 kPa, far exceeding the standard for conventional plastic hollow boards. This is attributed to the microfiber network formed after the "mechanical-chemical synergistic dissociation" of the high-filler bamboo powder. This high aspect ratio structure constructs a skeleton similar to reinforced concrete in the core layer of the board, improving the compressive stiffness in the vertical direction. Compared with Example 2 (692.5 kPa) and Comparative Example 2 (610.4 kPa), although the raw material composition and ratio are the same, the strength of Example 2 is increased by about 13%. The reason is that the secondary melt shearing in the two-step method causes some long fibers to break, weakening their reinforcing effect, while the one-step method effectively preserves the morphological integrity of the fibers.

[0145] Regarding water absorption, Examples 1 to 3 all maintained below 1%, exhibiting excellent hydrophobicity. In contrast, Comparative Example 6 had a water absorption rate as high as 2.15%. This directly confirms the importance of the order of material addition in the "gradient interface construction" mechanism. In Comparative Example 6, because the aluminate coupling agent, ionic liquid, and adsorbent were added simultaneously, the porous diatomaceous earth competitively adsorbed some of the coupling agent, and the presence of the ionic liquid on the bamboo powder surface interfered with the condensation reaction between the coupling agent and hydroxyl groups, resulting in incomplete hydrophobic modification of the bamboo powder surface, allowing water to easily penetrate along hydrophilic channels. In contrast, the examples strictly followed the order of "adsorption-locking followed by coupling modification," ensuring that the coupling agent acted on the "dry and clean" outer layer of the fiber, forming a dense hydrophobic barrier.

[0146] Regarding the yellowing index (YI), Example 2 (24.6) was lower than Comparative Example 2 (45.8). The dark brown color of Comparative Example 2 indicates that the lignin and hemicellulose in the bamboo powder underwent severe thermal degradation and oxidative discoloration after experiencing two high-temperature processes of granulation and extrusion. This degradation not only affects the appearance but also involves the breakage of polymer chains and a decrease in mechanical properties. Example 2 solved the screw feeding problem through diatomaceous earth adsorption technology, successfully achieving direct extrusion of powder and avoiding heat accumulation during the intermediate granulation process. Thus, while obtaining high-strength physical properties, it maintained the lighter color and natural texture of the bamboo-plastic material.

[0147] 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 method for preparing bamboo-based materials, characterized in that, The bamboo-based material is made from the following raw materials in parts by weight: Bamboo powder: 40-80 parts; Hydrophilic ionic liquid: 2-4 parts; Titanium dioxide: 1-2 parts; Diatomaceous earth: 1.5-3 parts; Aluminate coupling agent: 1.5-2.5 parts; Polypropylene powder: 14-54 parts; Maleic anhydride-grafted polypropylene: 4-6 parts; Lubricant: 5-7 parts; Antioxidant compound: 0.6-1.0 parts; The hydrophilic ionic liquid is 1-butyl-3-methylimidazolium chloride; The method for preparing the bamboo-based material includes the following steps: S1. Bamboo powder, hydrophilic ionic liquid, and titanium dioxide are put into a high-speed mixer with a pneumatic exhaust valve. The mixture undergoes mechanical-chemical synergistic dissociation through high-speed shear heating to remove moisture and soften the bamboo powder. S2. Reduce the mixer speed and add diatomaceous earth. Utilize the mesoporous structure of diatomaceous earth to adsorb and lock free hydrophilic ionic liquids and residual moisture, so that the material is transformed into a dry powder state. S3. Spray an aluminate coupling agent into the dry powder obtained in step S2 to carry out an interfacial hydrophobic modification reaction. S4. Add polypropylene powder, maleic anhydride-grafted polypropylene, lubricant and antioxidant compound, and cool and mix to obtain modified bamboo-plastic dry mix; S5. Add the modified bamboo-plastic dry mixture to the extruder, and obtain the bamboo-based material by one-step extrusion molding, vacuum shaping, cooling and cutting. Step S1 further includes: Turn on the stirring blades to a linear velocity of 20-25 m / s, and use the material friction to generate heat to raise the temperature to 105-115℃. Maintain high-speed stirring for 4-5 minutes, and turn on the exhaust device during this period. Step S2 further includes: Reduce the mixer speed to a linear velocity of 10-15 m / s, add diatomaceous earth at a temperature of 100-110℃ and continue stirring for 60-120 seconds until the material is free of liquid bridges and adhesion.

2. The method for preparing bamboo-based materials according to claim 1, characterized in that, The lubricant is composed of polyethylene wax and zinc stearate, wherein the weight ratio of polyethylene wax to zinc stearate is 2.8-3.2:1; the antioxidant compound is composed of antioxidant 1010 and antioxidant 168, wherein the weight ratio of antioxidant 1010 to antioxidant 168 is 0.8-1.2:

1.

3. The method for preparing bamboo-based materials according to claim 2, characterized in that, The preparation method of the hydrophilic ionic liquid includes the following steps: Add 82 parts by mass of N-methylimidazole and 102 parts by mass of 1-chlorobutane to the reaction vessel; Heat to 85°C under a protective atmosphere and maintain reflux for 48 hours; After the reaction is complete, the mixture is cooled and separated into layers. The lower layer is then washed with ethyl acetate to remove unreacted reactants. The washed product was dried under vacuum to obtain a pale yellow, transparent, viscous liquid.

4. The method for preparing bamboo-based materials according to claim 1, characterized in that, In step S3, the interfacial hydrophobic modification reaction is carried out by stirring at a medium speed for 2-3 minutes; in step S4, the discharge temperature of the cooled mixture is controlled at 40-50℃.

5. The method for preparing bamboo-based materials according to claim 1, characterized in that, In step S5, the modified bamboo-plastic dry mixture is added to the extruder and extruded in one step using a co-rotating parallel twin-screw extruder with a length-to-diameter ratio of 44:

1. A vertical forced feeder is used for feeding, and the feeding screw runs synchronously with the main screw or the feeding screw speed is higher than the synchronous speed of the main screw.

6. The method for preparing bamboo-based materials according to claim 1, characterized in that, In step S5, the middle part of the extruder barrel and the metering section are respectively provided with vacuum exhaust ports, and the vacuum degree is controlled between -0.08MPa and -0.09MPa; the temperature setting range of each zone of the extruder is 160-195℃, and the temperature setting range of the die head is 165-175℃.

7. The application of the bamboo-based material prepared by the method of any one of claims 1-6 in the preparation of woven yarns, woven bags, corrugated boards and corrugated boxes.

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