Preparation method of heat-resistant full-biodegradable bamboo-plastic composite material

Abstract

The application discloses a preparation method of a heat-resistant full-biodegradable bamboo-plastic composite material and belongs to the technical field of degradable polymer composite materials. In view of the technical problems of a poor interfacial compatibility of a polylactic acid, polybutylene glycol terephthalate adipate and polybutylene succinate blending system, weak combination of bamboo powder and a matrix, poor processing fluidity and insufficient heat resistance, the bamboo powder is treated by an alkaline solution, washed, dried and then modified by reacting with a silane coupling agent solution; heavy calcium carbonate and the modified bamboo powder are respectively subjected to aluminum ester coupling agent activation treatment; the polylactic acid, the polybutylene glycol terephthalate adipate and the polybutylene succinate are used as matrix raw materials, and the activated calcium carbonate, the activated bamboo powder, a polylactic acid nucleating agent and a chain extender are mixed; a melt blend is obtained through banburying; and the melt blend is placed into a mold and is pressed into a shape. The application can be applied to the fields of catering utensils, packaging materials, household supplies and lightweight structural parts.

Description

Technical Field

[0001] This invention relates to the field of biodegradable polymer composite materials technology, and more specifically, to a method for preparing a heat-resistant, fully biodegradable bamboo-plastic composite material. Background Technology

[0002] Polylactic acid (PLA), polybutylene adipate terephthalate (PBAT), and polybutylene succinate (PBS) are currently common fully biodegradable polymer materials with broad application prospects in replacing traditional petroleum-based plastics. However, single-component materials often have shortcomings in terms of mechanical properties, heat resistance, and processing performance. For example, PLA has high rigidity but poor toughness and insufficient heat resistance; PBAT has good toughness but low modulus and low heat distortion temperature; and PBS has good heat resistance but is expensive. Therefore, blending these three materials to improve overall performance has become an important research direction in this field.

[0003] Currently, there is considerable research on the blending of ternary systems of polylactic acid, polybutylene adipate terephthalate, and polybutylene succinate. For example, Chinese patent document CN113337088B discloses the preparation of biodegradable composite plastic materials using PBAT, PBS, PLA, bamboo fiber, and other raw materials. However, most studies still face the problem of poor interfacial compatibility between biomass fillers such as bamboo powder and hydrophobic polyester matrices. The surface of bamboo powder contains a large number of polar hydroxyl groups, which do not match well with the weakly polar polyester matrix. If not systematically treated, direct blending easily leads to filler agglomeration. When bamboo powder and fillers such as calcium carbonate are introduced into the system, the stress concentration caused by agglomeration increases the brittleness of the composite material, making it difficult to stably improve tensile strength and elastic modulus. Ultimately, this results in large fluctuations in the mechanical properties of the product, failing to meet the stability requirements of industrial production. At the same time, the insufficient heat resistance of this type of biodegradable bamboo-plastic composite material is also a key shortcoming restricting its application range. Especially in systems primarily composed of polylactic acid and polybutylene adipate terephthalate, the material often undergoes significant softening and deformation when exposed to high-temperature environments.

[0004] Furthermore, existing technologies for improving the compatibility between bamboo powder and the matrix mostly focus on modification with a single coupling agent or the addition of nucleating agents and chain extenders. However, these individual methods often fail to balance processing fluidity, mechanical properties, and cost. To achieve ideal results, existing processes often require multiple complex mixing and pretreatment steps, leading to high overall production costs and making biodegradable bamboo-plastic composites less economically competitive with ordinary plastics. For example, while existing technologies, such as Chinese patent document CN115403908A, propose improving the crystallinity and heat resistance of polylactic acid-based composites by introducing nano-nucleating agents, they do not fully address the systematic treatment of the interface between bamboo powder and high-proportion inorganic fillers. Under conditions of high bamboo powder and calcium carbonate filler content, there is still considerable room for improvement in compatibility and heat resistance. Therefore, existing technologies still lack a comprehensive solution to simultaneously address the aforementioned issues of interface compatibility, heat resistance, and cost control. Summary of the Invention

[0005] One objective of this invention addresses the following problem: In biodegradable bamboo-plastic composites, the large difference in interfacial polarity between bamboo powder and the polyester matrix leads to poor compatibility, making them prone to agglomeration and a decrease in mechanical properties. Simultaneously, polylactic acid-based systems generally suffer from insufficient heat resistance, easily softening and deforming at high temperatures.

[0006] To achieve these objectives of the present invention, the present invention provides a method for preparing a heat-resistant, fully biodegradable bamboo-plastic composite material, comprising the following steps: Step 1: Immerse bamboo powder in an alkaline solution and stir at 70-90 ℃ for 1.5-3 h. After washing and drying, immerse it in a solution containing silane coupling agent and stir at 30-50 ℃ for 1.5-3 h. After drying, the modified bamboo powder is obtained. Step 2: The heavy calcium carbonate and the modified bamboo powder obtained in Step 1 are activated with an aluminate coupling agent, respectively. The mass ratio of heavy calcium carbonate to aluminate coupling agent is 100:(2-5), and the mass ratio of modified bamboo powder to aluminate coupling agent is 100:(1-2.5). The mass fraction of aluminate coupling agent corresponding to heavy calcium carbonate is greater than that corresponding to modified bamboo powder. After stirring and activation, activated calcium carbonate and activated bamboo powder are obtained respectively. Step 3: Dry polylactic acid, polybutylene adipate terephthalate, and polybutylene succinate separately and use them as matrix raw materials; then add activated calcium carbonate and activated bamboo powder obtained in Step 2; then add 0.2-1.0% polylactic acid nucleating agent relative to the mass of polylactic acid and 0.5-2.0% chain extender relative to the mass of polylactic acid, mix evenly, and obtain a mixture. Step 4: The mixture obtained in Step 3 is kneaded at 175-185℃ and a rotor speed of 25-40 r / min for 8-12 min to obtain a melt blend. Step 5: Place the molten blend obtained in Step 4 into a mold preheated to 175-185℃, apply a mold closing pressure of 5-20 MPa and hold the pressure for 3-6 min; then transfer the mold to a cold press, cool and solidify under pressure for 3-8 min, and demold to obtain the heat-resistant fully biodegradable bamboo-plastic composite material.

[0007] Preferably, in the matrix raw materials of step 3, the mass ratio of polylactic acid, polybutylene adipate terephthalate, and polybutylene succinate is 2:1:2; and the mass ratio of activated calcium carbonate to activated bamboo powder is 4:1.

[0008] Preferably, the alkaline solution in step 1 is a 3% sodium hydroxide aqueous solution, and the silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. After immersing the bamboo powder in the alkaline solution and stirring, it is filtered and washed with deionized water until the washing solution is neutral. Then, it is dried at 60-90 °C to constant weight and then immersed in a solution containing the silane coupling agent for reaction.

[0009] Preferably, the independent coupling agent activation treatment of heavy calcium carbonate and modified bamboo powder in step 2 involves placing heavy calcium carbonate and 2%-5% of an aluminate coupling agent by mass of heavy calcium carbonate, and modified bamboo powder and 1%-2.5% of an aluminate coupling agent by mass of modified bamboo powder, into a high-speed mixer for separate stirring and activation, and completing the differential coating of the two at 100-110 ℃.

[0010] Preferably, the polylactic acid nucleating agent in step 3 is an organic carboxylic acid nucleating agent, and the chain extender is a chain extender containing multiple epoxy groups.

[0011] Preferably, in step 3, the matrix raw material, activated calcium carbonate, activated bamboo powder, polylactic acid nucleating agent and chain extender are placed in a high-speed mixer and mixed at a speed of 300-500 r / min for 3-5 min to obtain the mixture.

[0012] Preferably, in step 4, the mixture obtained in step 3 is placed in an internal mixer, the rotor speed of the internal mixer is 30 r / min, and the mixing time is 10 min.

[0013] Preferably, in step 5, after the molten blend is hot-pressed and held under pressure in the mold, the mold is immediately transferred to a cold press while maintaining the mold closing pressure, and the mold is cooled and shaped under the same pressure.

[0014] Preferably, the bamboo powder is 200-400 mesh moso bamboo powder prepared by grinding, and the heavy calcium carbonate is heavy calcium carbonate with a particle size of 1500 mesh.

[0015] Preferably, when used to prepare a customized equipment buffer liner, after obtaining the melt blend in step 4, hollow glass microspheres pretreated with an aluminate coupling agent are added to the melt blend and mixed evenly to obtain a composite melt; a molding die is formed using the three-dimensional shape data of the target object to be coated, the target object is placed in the inner cavity of the molding die, and the composite melt is injected or transferred into the gap between the target object and the molding die. A mold closing pressure is applied at 175-185°C and held for 3-6 minutes to shape the composite melt according to the surface contour of the target object. Subsequently, it is cold-pressed, shaped, and demolded to obtain a customized buffer liner that perfectly fits the shape of the target object.

[0016] Preferably, after the mixing in step 4 is completed, the resulting melt blend is placed in a calender at 140-160°C and pressed into a sheet with a thickness of 1.0-1.5 mm; the sheet is cut into multiple sheets of equal size, and the sheets are cross-layered with the fiber orientation of adjacent sheets at an angle of 30°-90° to obtain a laminated preform; the laminated preform is placed between the inner cavity of the forming mold and the target object, and the laminated preform is melt-compositely formed in the hot pressing process in step 5 to obtain a customized buffer liner with an internal cross-interlocked fiber skeleton.

[0017] The present invention has at least the following beneficial effects: This invention enables the preparation of bamboo-plastic composite materials with certain mechanical strength and heat resistance through two-step chemical modification of bamboo powder, differential coupling activation treatment of dual fillers, selection of composition and ratio of plastic matrix, and coordination of process temperature and process flow. At the same time, it has certain advantages in terms of raw material cost and processing efficiency.

[0018] In the treatment of bamboo powder, the bamboo powder is first heat-treated in an alkaline solution, which can reduce the content of wax, pectin, and free hydroxyl groups on the surface of the bamboo powder to a certain extent, thereby reducing the polarity and hydrophilicity of the bamboo powder. Subsequently, the bamboo powder is grafted with a silane coupling agent solution. The silanol groups generated by the hydrolysis of the silane coupling agent undergo a condensation reaction with the residual hydroxyl groups on the surface of the bamboo powder, introducing organic functional groups into the surface of the bamboo powder. This helps to improve the interfacial compatibility between the bamboo powder and the polyester matrix. After the above two-step modification, the bamboo powder is more uniformly distributed in the matrix, and is less prone to early failure caused by stress concentration under stress, which has a positive effect on the stability of the tensile strength of the composite material.

[0019] Regarding filler activation, both heavy calcium carbonate and modified bamboo powder were activated with aluminate coupling agents, with the amount of coupling agent used for calcium carbonate being higher than that used for bamboo powder. After treatment with the aluminate coupling agent, heavy calcium carbonate forms chemical bonds on its surface, which helps reduce its dispersed particle size in the matrix and improves the bonding between the inorganic filler and the organic matrix. Bamboo powder, on the other hand, uses a lower amount of coupling agent than calcium carbonate to avoid the formation of a multilayer on the bamboo powder surface due to excessive coupling agent, which could lead to agglomeration. Activating the two fillers with different amounts of coupling agent ensures a more suitable dispersion of the filler in the matrix, helping to reduce the risk of brittle cracking caused by localized agglomeration within the composite material.

[0020] In terms of the plastic matrix, polylactic acid (PLA), polybutylene adipate terephthalate (PBT), and polybutylene succinate (PBS) are combined in a mass ratio of 2:1:2. PLA provides a certain degree of rigidity and strength, PBT provides good processability, and PBS, due to its high softening temperature, enhances the composite material's ability to maintain its shape at higher temperatures. Furthermore, PLA nucleating agents and chain extenders are added. Nucleating agents promote PLA crystallization, increasing the crystallization rate and crystallinity to some extent during processing, thus improving the material's heat resistance. Chain extenders react with the broken molecular chain end groups of PLA caused by heat processing, restoring some molecular weight and maintaining relatively stable melt strength during processing, contributing to the density of the internal structure of the hot-pressed product.

[0021] In terms of processing technology, internal mixing of each component at a temperature of 175-185 ℃ helps the matrix resin to fully melt and achieve interfacial contact with the filler. Direct hot pressing followed by cooling molding reduces the need for intermediate cooling and granulation, which helps maintain the dispersion of the components and makes the process more compact. Maintaining the clamping pressure during hot pressing and transferring it to a cold press for cooling reduces residual stress caused by uneven temperature drops before demolding, thus improving the smoothness and dimensional stability of the finished product.

[0022] The composite material prepared by the above method, with a total mass ratio of inorganic filler and biomass filler exceeding 50%, exhibits a tensile strength of over 24 MPa and an elastic modulus exceeding 1200 MPa. Its appearance remains relatively stable after immersion in an 80°C water bath for 30 minutes. This comprehensive performance under high-filling conditions differs from the effects obtained through single modifiers or conventional blending combinations in existing technologies. This difference is mainly due to the systematic coordination of bamboo powder surface treatment, filler activation scheme, and matrix ratio in this method. Furthermore, the use of a large proportion of calcium carbonate and bamboo powder to replace a portion of the synthetic resin reduces raw material costs to some extent, making it suitable for industrial-scale production.

[0023] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0024] Figure 1 The images show the heat-resistant, fully biodegradable bamboo-plastic composite material samples prepared in Example 1 of this invention; where a is a front view of a sheet sample with a thickness of 0.3 mm, b is a side view of a sheet sample with a thickness of 0.3 mm, c is a front view of a sample with a thickness of 1.0 mm, and d is a side view of a sample with a thickness of 1.0 mm. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to examples, so that those skilled in the art can implement it based on the description. It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0026] Example 1 200-400 mesh bamboo powder was immersed in a 3% sodium hydroxide aqueous solution and stirred for 2 hours in a constant temperature oil bath at 80℃. The alkaline solution etched the surface of the bamboo powder, systematically removing wax, pectin, and water-soluble extracts covering the fiber surface, and significantly reducing the number of free hydroxyl groups in the bamboo powder cell walls, thereby lowering the surface polarity of the bamboo powder. After the reaction, the bamboo powder was vacuum filtered and washed until the filtrate was neutral, and then dried to constant weight in an 80℃ forced-air oven. Subsequently, the dried alkaline-treated bamboo powder was immersed in a 2% γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) ethanol solution and stirred for 2 hours at 40℃. The silanol groups generated by the hydrolysis of KH-560 condensed and grafted with the residual hydroxyl groups of the bamboo powder, forming an organic hydrophobic layer on its surface and introducing epoxy functional groups. After the reaction, the mixture was filtered and dried at low temperature to obtain modified bamboo powder.

[0027] Take the above-mentioned heavy calcium carbonate powder and add 2% (by weight of calcium carbonate) of aluminate coupling agent; separately take the above-mentioned modified bamboo powder and add 1% (by weight of bamboo powder) of aluminate coupling agent. Place both in a high-speed mixer and activate them at 105 °C for 10 min by high-speed stirring. The inorganic-affinity end of the aluminate reacts with the surface of inorganic calcium carbonate to form chemical bonds, and at the same time combines with the polar groups on the surface of bamboo powder, to obtain activated calcium carbonate and activated bamboo powder respectively.

[0028] PLA, PBAT, and PBS were dried in an oven at 80 ℃ for 24 h. The matrix raw materials were weighed according to a PLA:PBAT:PBS mass ratio of 2:1:2, and the two activated fillers were weighed according to an activated calcium carbonate:activated bamboo powder mass ratio of 4:1. 0.5% of PLA nucleating agent LAK-301 and 1% of chain extender ADR-4468 (relative to PLA mass) were added to the mixture. All components were added to a high-speed mixer and mixed at 300 r / min for 3 min at room temperature to obtain the mixture.

[0029] The mixture is transferred into an internal mixer, and the mixing temperature is set to 180 ℃, the rotor speed is set to 30 r / min, and the mixing time is set to 10 min, so that the matrix can be fully melted and interfacially bonded with the filler to obtain a melt blend.

[0030] The molten blend was cut into small pieces. Molds with dimensions of 25×25×0.3 mm, 25×25×0.5 mm, and 25×25×1.0 mm were preheated to 180 °C. A release agent was applied to the inner wall of the mold, and the small pieces of blend were evenly spread into the mold cavity. The mold was then placed into the working area of ​​a flatbed vulcanizing press, and a clamping pressure of 15 MPa was applied and held for 4 minutes. After hot pressing, while maintaining the clamping pressure, the mold was immediately moved to a cold press and cold pressed for 5 minutes while maintaining the clamping pressure. After depressurization, the heat-resistant, fully biodegradable bamboo-plastic composite material was obtained.

[0031] like Figure 1 As shown, a) is a front view of a 0.3 mm thick sheet sample, b) is a side view of a 0.3 mm thick sheet sample, c) is a front view of a 1.0 mm thick sample, and d) is a side view of a 1.0 mm thick sample. The prepared sheet samples exhibit a uniform light beige or light yellowish-brown color at room temperature. The 0.3 mm thick sheet sample has a matte texture and is generally smooth, with extremely fine granular texture visible under light reflection; the surface is free of bubbles and voids, and there are no cracks at the edges. When laid flat, it fits tightly against the table without warping or deformation, indicating that the pressure-holding and cooling process effectively suppressed the generation of internal gas, while the differentiated coupling treatment and appropriate cooling rate eliminated the internal stress of the product. The 1.0 mm thick sample is slightly darker in color than the sheet, but still maintains a uniform wheat bran color. When viewed from the side, there is no layering, the edge lines are clear, and there are no obvious burrs or flash, indicating that the bamboo powder and plastic matrix achieved good micro-mixing and dispersion during the mixing process, and the mold closing pressure was precisely controlled. The sample has a slightly frosted feel to the touch, and exhibits good rigidity and flexibility when lightly folded.

[0032] Example 2 The preparation steps in this embodiment are basically the same as those in Example 1, except that in step 3, the mass ratio of PLA:PBAT:PBS is strictly controlled to be 2:1:2, and the mass ratio of activated calcium carbonate:activated bamboo powder is strictly controlled to be 4:1.

[0033] Example 3 The preparation steps in this embodiment are basically the same as those in Example 1. The only difference is that in step 1, after the bamboo powder is treated in a 3% sodium hydroxide solution at 80°C for 2 hours, it must be filtered and washed with deionized water until the washing solution is neutral. Then, it is dried at 60-90°C to constant weight and then strictly reacted with KH-560 ethanol solution at 40°C for 2 hours.

[0034] Example 4 The preparation steps of this embodiment are basically the same as those of Example 1. The difference is that in step 2, heavy calcium carbonate and 2%-5% of aluminate coupling agent by mass of calcium carbonate, and modified bamboo powder and 1%-2.5% of aluminate coupling agent by mass of bamboo powder are placed in a high-speed mixer and stirred and activated in a temperature range of 100-110 ℃ to achieve differentiated coating of the two.

[0035] Example 5 The preparation steps in this embodiment are basically the same as those in Example 1. The difference is that the polylactic acid nucleating agent used in step 3 is clearly an organic carboxylic acid nucleating agent (LAK-301), and the chain extender used is clearly a chain extender containing multiple epoxy groups (ADR-4468).

[0036] Example 6 The preparation steps in this embodiment are basically the same as those in Example 1. The difference lies in the mixing step in step 3. The matrix raw materials, activated calcium carbonate, activated bamboo powder, polylactic acid nucleating agent and chain extender are placed in a high-speed mixer and mixed at a speed of 300-500 r / min for 3-5 min to obtain a mixture.

[0037] Example 7 The preparation steps in this embodiment are basically the same as those in Embodiment 1. The difference is that in step 4, the mixture is placed in an internal mixer, the rotor speed is set to 30 r / min, and the mixing time is set to 10 min.

[0038] Example 8 The preparation steps in this embodiment are basically the same as those in Embodiment 1. The difference is that in step 5, after the molten blend is hot-pressed and held under pressure in the mold, the mold is immediately transferred to the cold press while maintaining the mold closing pressure. The mold closing pressure is maintained throughout the process for cooling and shaping.

[0039] Example 9 The preparation steps of this embodiment are basically the same as those of Example 1. The difference is that the bamboo powder used in step 1 is specifically limited to 200-400 mesh moso bamboo powder that has been ground, and the heavy calcium carbonate used in step 2 is specifically limited to heavy calcium carbonate with a particle size of 1500 mesh.

[0040] Comparative Example 1 This comparative example is used to verify the effectiveness of the conventional process after excluding PBS. In this comparative example, the PBS component was removed from the raw material ratio, and the PLA to PBAT ratio was adjusted to 1:1 by mass. The remaining components (calcium carbonate, bamboo powder, nucleating agent, coupling agent, chain extender) and preparation steps were completely consistent with Example 1.

[0041] Comparative Examples 2-1 to 2-4 This comparative example is to verify the effect of excluding other plastic matrix compounding ratios. The preparation steps are exactly the same as in Example 1, except that the mass ratio of the matrix plastic in step 3 is changed: Control sample 2-1: PLA:PBAT:PBS = 2:2:2; Control sample 2-2: PLA:PBAT:PBS = 1:1:3; Comparative samples 2-3: PLA:PBAT:PBS = 1:3:1; Comparative samples 2-4: PLA:PBAT:PBS = 3:1:1.

[0042] Comparative Example 3 This comparative example is used to verify the effect of process temperature. The preparation steps are exactly the same as in Example 1, except that the internal mixer temperature setting in step 4 is changed: Comparative sample 3-1: The mixing temperature was 170 ℃; Comparative sample 3-2: The mixing temperature was 190 ℃.

[0043] Comparative Example 4 This comparative example is used to verify the effect of differentiated coupling rather than uniform addition. The preparation steps are exactly the same as in Example 1, except that the amount of aluminate coupling agent added in step 2 is changed: Comparative sample 4-1: Both calcium carbonate and bamboo powder contain 1% of their own weight of aluminate coupling agent. Comparative sample 4-2: Both calcium carbonate and bamboo powder contain 2% by weight of aluminate coupling agent.

[0044] Performance Testing and Results Analysis All mechanical property tests in this invention were conducted according to the national standard GB / T1040.1-2018, and the test samples were standard dumbbell-shaped Type I specimens. For Examples 1 to 9, the molds used were all flat molds with a length of 25 mm and a width of 25 mm, resulting in square plates of varying thicknesses. Plates with a thickness of 1.0 mm were selected as the test substrates, and before testing, these plates were cut into dumbbell-shaped tensile specimens conforming to standard dimensions using a cutter or a special cutting machine. All samples from each example underwent rigorous inspection before tensile testing to ensure that the specimen surface was free of bubbles, pores, and cracks, thus avoiding stress concentration that could lead to distorted results. Five valid specimens were tested in each group, and the final tensile strength and elastic modulus were taken as their arithmetic mean.

[0045] The mechanical and heat resistance properties of the composite material samples prepared in Examples 1 to 9 and the comparative examples were tested, and the test results are summarized in Table 1 and Table 2, respectively.

[0046] Table 1. Results of mechanical and heat resistance properties of the composite materials prepared in Examples 1 to 9 The test data in Table 1 show that the tensile strength of Examples 1 to 9 is stably distributed between 24.11 MPa and 24.58 MPa, and the elastic modulus is stably distributed between 1241.30 MPa and 1253.20 MPa. Further observation of Example 8 reveals its significant process characteristics. In Example 8, after hot pressing and holding, the mold closing pressure is maintained and the mold is directly transferred into a cold press to complete the shaping. This cold pressing transfer method results in better flatness and dimensional stability of the product after demolding compared to other examples. This proves that continuous cooling under mold closing pressure can effectively eliminate the internal stress rebound caused by the sudden change of thermoplastic resin from high temperature to low temperature, and avoid warping deformation caused by premature pressure release.

[0047] Table 2. Results of mechanical and heat resistance properties of the composite materials prepared in the comparative examples. Based on the data in Table 2, in Comparative Example 1, the removal of the polybutylene succinate component resulted in a sharp drop in tensile strength to 19.64 MPa, and the composite material exhibited significant softening deformation in 80 °C hot water. This indicates that the high softening point of polybutylene succinate, along with its synergistic effect with the nucleating agent, is an indispensable component for achieving the composite material's performance in medium- and high-temperature applications.

[0048] Comparative Examples 2-1 to 2-4 had their mass ratios of the three plastic matrices readjusted. In Comparative Example 2-3, the proportion of polybutylene adipate terephthalate was too high, causing the material to soften and deform rapidly in hot water, with a significant drop in tensile strength to 11.43 MPa. In Comparative Example 2-4, the proportion of polylactic acid was too high; although the tensile strength barely reached 20.20 MPa, its elastic modulus was only 757.18 MPa, indicating insufficient material rigidity and a high susceptibility to brittle deformation.

[0049] Comparative Examples 3-1 and 3-2 varied the mixing temperature. When the mixing temperature was set to 170 °C, the matrix polyester did not completely melt, leaving unmelted particles on the sample surface, and the tensile strength only reached 17.85 MPa. When the temperature was set to 190 °C, although the matrix completely melted, the excessively high processing temperature caused the polylactic acid to undergo a thermo-oxidative degradation reaction, resulting in a yellowing of the sample surface and a drop in tensile strength to 20.32 MPa. Therefore, the mixing temperature range of 175 °C to 185 °C represents the equilibrium window for the abrupt performance changes of this system at different temperatures.

[0050] Comparative Examples 4-1 and 4-2 adjusted the coupling agent addition ratio of calcium carbonate and bamboo powder to a uniform ratio. In Comparative Example 4-1, both were added at 1%, which resulted in insufficient interfacial bonding between calcium carbonate and the matrix. The material softened after immersion in hot water, and the tensile strength decreased to 20.15 MPa. In Comparative Example 4-2, both were added at 2%. Although the material strength recovered somewhat, excessive coupling agent content on the bamboo powder surface led to localized agglomeration, resulting in stress concentration and cracks on the surface of the molded sample. These two sets of comparative data demonstrate that a differentiated activation addition scheme using 2% calcium carbonate and 1% bamboo powder is essential. It is crucial to maintain a higher proportion of calcium carbonate coupling agent than bamboo powder to ensure optimal interfacial dispersion for the two fillers with different polarities, while avoiding performance degradation caused by a single ratio.

[0051] Based on the test results in Tables 1 and 2 above, it can be seen that the complete technical solution of this invention, formed by two-step bamboo powder impurity removal and grafting modification, differential activation with dual fillers, critical ratio of ternary plastic matrix, and integrated temperature-controlled hot pressing molding, enables the material to maintain a tensile strength of no less than 24.11 MPa and an elastic modulus of over 1241 MPa even under high-filling conditions where the total proportion of inorganic and natural fillers exceeds 50%, and ensures that it does not deform or soften after continuous immersion in 80 ℃ hot water for 30 minutes. This comprehensive performance, which combines high filling, high strength, and high heat resistance, cannot be obtained by simply adding a single modifier or conventional material combinations in existing technologies.

[0052] Application Example 10 This application example uses the exact same steps as Example 1 to prepare the melt blend.

[0053] To address the instrument's buffer protection requirements, hollow glass microspheres with a particle size of 30-50 micrometers were placed in a high-speed mixer, and an aluminate coupling agent accounting for 2% of the mass of the glass microspheres was added. The mixture was stirred and activated at 105 °C for 20 min to allow the coupling agent to be fully grafted onto the surface of the glass microspheres, thus obtaining modified hollow glass microspheres.

[0054] Prepare a solid metal counterweight with dimensions of 90 mm × 60 mm × 18 mm as a simulation of the target to be covered. Use a 3D scanner to obtain the shape data of the counterweight, and based on the data, process an aluminum alloy forming mold whose inner cavity completely fits the shape of the counterweight, leaving a 3 mm gap.

[0055] The molten blend obtained in step 4 is cooled to a plastic state and then fed into an internal mixer at a mass ratio of 100:5 of the molten blend to the modified hollow glass microspheres. The mixture is then mixed at low speed at 175°C for 3 minutes to uniformly disperse the microspheres and obtain a composite melt containing microspheres.

[0056] The solid metal counterweight is placed in the inner cavity of an aluminum alloy mold, the mold is closed, and a pre-drilled injection hole is provided. The composite melt is injected into the gap between the counterweight and the mold cavity using a molding transfer method. The mold temperature is controlled at 180°C, and a mold-closing pressure of 12 MPa is applied and held for 4 minutes. After holding the pressure, while maintaining the mold-closing pressure, the mold is transferred to a cold press for cooling and shaping for 5 minutes. After demolding, the counterweight is removed. The composite material has solidified according to the shape and contour of the counterweight, forming a customized inner protective shell with uniform thickness, perfect fit, and buffering energy absorption effect.

[0057] Comparative Example 10-1 The difference between this comparative example and application example 10 is that hollow glass microspheres are not added when preparing the composite melt. Instead, the pure melt blend obtained in example 1 is used to directly coat the counterweight. The remaining process parameters and coating molding steps are exactly the same as in application example 10.

[0058] Comparative Examples 10-2 The difference between this comparative example and application example 10 is that the hollow glass microspheres used are not subjected to activation pretreatment with aluminate coupling agent before intensive mixing. They are directly intensively mixed with the molten blend in their original state and then injected into the mold. The remaining process parameters and coating molding steps are exactly the same as those in application example 10.

[0059] Effect Experiment 10 The metal counterweights with customized liners prepared in Application Example 10, Comparative Example 10-1, and Comparative Example 10-2 were subjected to quasi-static compression tests on a universal testing machine. During the test, a flat indenter was placed directly above the counterweight, and the compression rate was set to 5 mm per minute. The load value borne by the liner material when the compression deformation reached 2 mm was recorded. Simultaneously, to simulate accidental drops during daily use, these three sets of lined counterweights were subjected to free-fall drop tests from a height of 1 meter above the surface of a hardened steel plate. Each test was repeated three times. After the drops, the cracking of the liner and the deformation of the counterweight surface were inspected.

[0060] To verify the service stability of the inner liner shell in actual use environments, before the compression test, three sets of samples were placed in a constant temperature forced-air oven at 80℃ for 4 hours to simulate the heating state of the equipment in a sealed cabin or vehicle-mounted high-temperature environment. After the heat preservation was completed, the samples were immediately taken out for the above compression and drop tests, and the appearance and dimensional changes of the inner liner material before and after the high temperature were observed simultaneously.

[0061] Test results show that, in terms of heat resistance stability, after being kept at 80 ℃ for 4 h in Application Example 10, the inner liner shell did not show any softening deformation, blistering, or warping, and the dimensional shrinkage rate was less than 0.5%. This is due to the excellent heat resistance of the matrix material prepared in claim 1, whose internal bamboo powder and calcium carbonate, through differentiated coupling and ternary matrix ratio, construct a solid rigid skeleton. In contrast, Comparative Examples 10-1 and 10-2 showed slight reduction in gloss and slight edge warping after high-temperature treatment, reflecting structural loosening of the base material at high temperatures.

[0062] In terms of mechanical and cushioning performance, Application Example 10 achieved a load value of 412 N when compressed to 2 mm. Due to the excellent elastic modulus of the substrate, its rigid support allowed the hollow microspheres to be tightly compressed and absorb impact energy in the initial stage of stress. After the drop test, the customized liner surface was smooth and crack-free, and the surface of the internal counterweight remained intact. In contrast, Comparative Example 10-1, without the addition of microspheres, although the substrate had high rigidity, lacked energy dissipation units, resulting in a load value as high as 611 N under the same compression conditions. Excessive rigidity caused the impact force to be directly transmitted to the interior, and the edges of the counterweight showed significant deformation after the drop. Comparative Example 10-2 achieved a load value of 534 N during compression deformation. Because its microspheres were not activated by aluminate coupling, there were obvious defects at the interface between the beads and the substrate. After the drop test, the liner showed obvious glass microsphere peeling and matrix cracking at the stressed bending points, resulting in a sharp drop in cushioning efficiency.

[0063] Based on the above comparative verifications, the bamboo-plastic substrate prepared by this invention not only possesses excellent mechanical modulus and heat resistance dimensional stability at 80℃, but also provides a strong chemical bonding interface and rigid support for functional microspheres. This synergistic effect of the highly heat-resistant and rigid matrix and the activated microspheres enables the final customized inner liner shell to simultaneously overcome the triple technical challenges of high-temperature softening and collapse, excessive rigidity leading to equipment damage, and interface debonding causing structural failure. This achieves comprehensive performance gains in terms of heat resistance, high strength, and precise cushioning protection.

[0064] Application Example 11 This application example uses the exact same steps as Example 1 to prepare the melt blend.

[0065] To address the instrument's buffering and protection requirements, hollow glass microspheres with a particle size of 30 to 50 micrometers were pre-placed in a high-speed mixer, and an aluminate coupling agent at a mass ratio of 2% of the glass microspheres was added. The mixture was stirred and activated at 105°C for 20 minutes to obtain modified hollow glass microspheres. The molten blend obtained in step 4 was cooled to a plastic state and then fed into an internal mixer at a mass ratio of 100:5 of the molten blend to the modified hollow glass microspheres. The mixture was then mixed at low speed at 175°C for 3 minutes to obtain a composite melt containing microspheres.

[0066] The composite melt was placed in a calender at 140°C and pressed into a sheet with a thickness of 1.2 mm. After the sheet cooled naturally to room temperature, it was cut into sheets with dimensions of 90 mm x 60 mm using a cutter. Three sheets were taken and cross-laminated at a 45° angle between the long sides of adjacent sheets to obtain a laminated preform with a total thickness of 3.6 mm.

[0067] Prepare a solid metal counterweight with dimensions of 90 mm x 60 mm x 18 mm as a simulation of the target object to be covered. Use a 3D scanner to obtain the shape data of the counterweight and process a high-precision aluminum alloy forming mold with an inner cavity that fits perfectly with the shape of the counterweight and leaves a three-millimeter gap.

[0068] The aforementioned laminated preform was placed in the inner cavity of an aluminum alloy mold, and a counterweight was placed on top of the preform. After mold closing, mold closing pressure was applied using a die-pressing transfer method, controlling the mold temperature at 180℃, applying a mold closing pressure of 12 MPa, and holding the pressure for 4 minutes. During this hot pressing process, the three layers of cross-stacked sheets were heated and remelted, fusing together into a single unit. After holding the pressure, the mold was transferred to a cold press for cooling and shaping for 5 minutes while maintaining the mold closing pressure. After demolding, the counterweight was removed. The composite material had been solidified according to the shape of the counterweight, and a multi-layered interlocking skeleton structure composed of cross-arranged bamboo powder fibers had been formed inside the product, resulting in a customized cushioning inner liner shell.

[0069] Comparative Example 11-1 The difference between this comparative example and application example 11 is that, while both involve pressing the composite melt into thin sheets and cutting them into sheets, when taking three sheets, all three are laid in parallel with the same fiber orientation direction, rather than being laid in a cross-laminated manner. The parallel-laminated sheets are then placed into the mold cavity for hot-pressing composite. All other process parameters, counterweights, and mold specifications are exactly the same as in application example 11.

[0070] Effect Experiment 11 The metal counterweights with customized liners prepared in Application Example 11, Application Example 10, and Comparative Examples 11-2 were placed in a constant-temperature forced-air drying oven at 60°C. A constant static load of 20 kg was applied above the liner shell to simulate the pressure environment of multiple pieces of equipment stacked in a warehouse. After 15 days of continuous pressure, the load was removed, and the thickness of each liner shell in the pressure direction was measured and recorded using a digital micrometer. The permanent deformation rate was calculated, which is the percentage of the thickness that cannot spring back to its original thickness after being compressed.

[0071] The test results show that: Application Example 11, after 15 days of high-temperature static pressing at 60°C, exhibited a permanent deformation rate of only 1.8%, with uniform wall thickness around the inner liner and no signs of shaking in the internal counterweight. Application Example 10, under the same testing conditions, showed a permanent deformation rate as high as 7.9%, with a significantly thinner inner liner wall after demolding and noticeable gaps and loosening of the counterweight within the shell. Comparative Example 11-1, under the same testing conditions, achieved a permanent deformation rate of 5.6%. Although the calendering orientation suppressed deformation in some directions, the lack of fiber cross-layout resulted in significant localized plastic slippage in the non-oriented directions, leading to asymmetrical slight warping at the edges of the inner liner.

[0072] The above results indicate that hot pressing of unidirectional sheets with consistent bamboo fiber orientation cross-laminated can form a multi-layered interlocking physical skeleton structure inside the final product. This structure effectively inhibits the slippage of polymer chains in the compressive direction at the microscopic level, significantly reducing the creep behavior of the composite material under long-term high temperature and static pressure.

[0073] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Further modifications can be readily implemented by those skilled in the art.

Claims

1. A method for preparing a heat-resistant, fully biodegradable bamboo-plastic composite material, characterized in that, Includes the following steps: Step 1: Immerse bamboo powder in an alkaline solution and stir at 70-90℃ for 1.5-3 hours. After washing and drying, immerse it in a solution containing silane coupling agent and stir at 30-50℃ for 1.5-3 hours. After drying, the modified bamboo powder is obtained. Step 2: The heavy calcium carbonate and the modified bamboo powder obtained in Step 1 are activated with an aluminate coupling agent, respectively. The mass ratio of heavy calcium carbonate to aluminate coupling agent is 100:(2-5), and the mass ratio of modified bamboo powder to aluminate coupling agent is 100:(1-2.5). The mass fraction of aluminate coupling agent corresponding to heavy calcium carbonate is greater than that corresponding to modified bamboo powder. After stirring and activation, activated calcium carbonate and activated bamboo powder are obtained respectively. Step 3: Dry polylactic acid, polybutylene adipate terephthalate, and polybutylene succinate separately and use them as matrix raw materials; then add activated calcium carbonate and activated bamboo powder obtained in Step 2; then add 0.2-1.0% polylactic acid nucleating agent relative to the mass of polylactic acid and 0.5-2.0% chain extender relative to the mass of polylactic acid, mix evenly, and obtain a mixture. Step 4: The mixture obtained in Step 3 is kneaded at 175-185 ℃ and a rotor speed of 25-40 r / min for 8-12 min to obtain a melt blend. Step 5: Place the melt blend obtained in step 4 into a mold preheated to 175-185 ℃, apply a mold closing pressure of 5-20 MPa and hold the pressure for 3-6 min. The mold is then transferred to a cold press and cooled and shaped under pressure for 3-8 minutes. After demolding, the heat-resistant, fully biodegradable bamboo-plastic composite material is obtained.

2. The preparation method according to claim 1, characterized in that: In step 3, the mass ratio of polylactic acid, polybutylene adipate terephthalate, and polybutylene succinate in the matrix raw materials is 2:1:2; the mass ratio of activated calcium carbonate to activated bamboo powder is 4:

1.

3. The preparation method according to claim 1, characterized in that: The alkaline solution in step 1 is a 3% sodium hydroxide aqueous solution, and the silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane. After immersing bamboo powder in the alkaline solution and stirring, it is filtered and washed with deionized water until the washing solution is neutral. Then, it is dried at 60-90 °C to constant weight and then immersed in a solution containing the silane coupling agent for reaction.

4. The preparation method according to claim 1, characterized in that: Step 2 involves the separate activation treatment of heavy calcium carbonate and modified bamboo powder using coupling agents. This is achieved by placing heavy calcium carbonate and 2%-5% (by weight of heavy calcium carbonate) of aluminate coupling agent, and modified bamboo powder and 1%-2.5% (by weight of modified bamboo powder) of aluminate coupling agent, into a high-speed mixer for separate stirring and activation. The differential coating of the two is then completed at 100-110 °C.

5. The preparation method according to claim 1, characterized in that: The polylactic acid nucleating agent in step 3 is an organic carboxylic acid nucleating agent, and the chain extender is a chain extender containing multiple epoxy groups.

6. The preparation method according to claim 1, characterized in that: In step 3, the matrix raw materials, activated calcium carbonate, activated bamboo powder, polylactic acid nucleating agent and chain extender are placed in a high-speed mixer and mixed at a speed of 300-500 r / min for 3-5 min to obtain a mixture. In step 4, the mixture obtained in step 3 is placed in an internal mixer with a rotor speed of 30 r / min and a mixing time of 10 min.

7. The preparation method according to claim 1, characterized in that: In step 5, after the molten blend is hot-pressed and held under pressure in the mold, the mold is immediately transferred to the cold press while maintaining the mold closing pressure, and the mold is cooled and shaped under the same pressure.

8. The preparation method according to claim 1, characterized in that: The bamboo powder is 200-400 mesh Nanmu bamboo powder made by grinding, and the heavy calcium carbonate is heavy calcium carbonate with a particle size of 1500 mesh.

9. The preparation method according to claim 1, when used to prepare a customized equipment buffer liner, is characterized in that, After obtaining the melt blend in step 4, hollow glass microspheres pretreated with aluminate coupling agent are added to the melt blend and mixed evenly to obtain a composite melt. A molding die is formed using the three-dimensional shape data of the target object to be coated. The target object is placed in the inner cavity of the molding die, and the composite melt is injected or transferred into the gap between the target object and the molding die. A mold closing pressure is applied at 175-185 ℃ and held for 3-6 min to shape the composite melt according to the surface contour of the target object. Then, it is cold-pressed, shaped, and demolded to obtain a customized cushioning liner that perfectly fits the shape of the target object.

10. The preparation method according to claim 9, characterized in that: After the mixing in step 4 is completed, the resulting melt blend is placed in a calender at 140-160 ℃ and pressed into a sheet with a thickness of 1.0-1.5 mm. The sheet is then cut into multiple sheets of equal size, and the sheets are cross-laminated with the fiber orientation of adjacent sheets at an angle of 30°-90° to obtain a laminated preform. The laminated preform is placed between the inner cavity of the forming mold and the target object, and in the hot pressing process in step 5, the laminated preform is melt-laminated to obtain a customized buffer liner with an internal cross-interlocked fiber skeleton.

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