A full-plant three-element synergistic high-performance degradable composite material

Abstract

The present application relates to the technical field of high polymer material, and discloses a kind of full plant trinucleotide synergistic high-performance degradable composite material, and is made of oxidized lignin hemicellulose complex 5.0-15.0%, catalyst 0.1-0.3%, plant cellulose 10.0-40.0%, end group protective agent 0.4-0.8%, degradable polyester resin 43.9-84.5%, catalyst is mixed with oxidized complex, and plant cellulose is vacuum dehydrated to free moisture less than 200ppm, and end group protective agent is mixed into premix;The premix is added to polyester resin melted in main feeding port from double-screw extruder side feeding port to carry out melt blending and extrusion granulation.The present application improves the interfacial compatibility of plant fiber and polyester resin by using transesterification reaction, and combines vacuum dehydration treatment and end group protective agent to inhibit the hydrolysis chain scission reaction in the processing of polyester resin, improve the mechanical properties and processing stability of composite material.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high-performance biodegradable composite material with synergistic effects of three plant elements. Background Technology

[0002] The preparation of environmentally friendly composite materials by blending plant cellulose with biodegradable polyester resins is an important development direction in the field of polymer materials. However, existing composite materials still face multiple technical obstacles in actual preparation and processing.

[0003] Plant cellulose contains a large number of hydroxyl groups, exhibiting strong hydrophilicity, while biodegradable polyester resins are typically hydrophobic. When these two are blended, the difference in interfacial polarity leads to poor compatibility between the two phases, easily resulting in significant phase separation. This hinders the effective transfer of stress, leading to a decrease in the overall mechanical properties of the composite material.

[0004] Meanwhile, biodegradable polyester resins are quite sensitive to moisture and high-temperature environments. During high-temperature melt processing, the free water carried within the plant cellulose can easily trigger the hydrolysis of ester bonds in the polyester matrix. In addition, the active end groups at the ends of the polyester molecular chains further accelerate this degradation process, causing the polyester molecular chains to break, the molecular weight to decrease, and directly damaging the molecular structure and processing stability of the material.

[0005] Furthermore, in conventional extrusion blending processes, plant cellulose is typically added together with solid resin from the main feed port of the extruder. This results in the plant cellulose undergoing prolonged mechanical friction and high-intensity shearing in the solid transport section of the extruder, disrupting the original physical structure of the cellulose. Moreover, during interfacial bonding reactions in the blended system, the resulting small-molecule byproducts, if lacking an effective removal mechanism, can create a reverse chemical equilibrium inhibition, hindering the further reaction and leading to uneven performance distribution in the final product. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a high-performance biodegradable composite material with synergistic effects of three plant elements. This solves the problems of phase separation and decreased mechanical properties caused by interfacial polarity repulsion between hydrophilic fibers and hydrophobic resins when combining plant cellulose with biodegradable polyester resins, as well as the susceptibility of the polyester matrix to hydrolysis and chain breakage due to moisture during high-temperature melting and blending processes.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a high-performance biodegradable composite material with synergistic effects of three plant elements, made from raw materials in the following mass fractions: Oxidized lignin-hemicellulose complex: 5.0%-15.0%; Catalyst: 0.1%-0.3%; High-purity plant cellulose: 10.0%-40.0%; End-group protectant: 0.4%-0.8%; Biodegradable polyester resin: 43.9%-84.5%; the biodegradable polyester resin is selected from at least one of polyglycolic acid and polylactic acid.

[0008] By employing the above technical solution, and utilizing oxidized lignin-hemicellulose composites to participate in interphase bonding, triggering in-situ transesterification with a catalyst, and inhibiting hydrolysis with end-group protectants, the system achieves improved interphase interface compatibility and enhanced mechanical properties and processing stability of the composite material. The specific reaction process within the system is as follows: Active functional groups are provided: After pretreatment, the oxidized lignin hemicellulose complex contains carboxyl and aliphatic hydroxyl groups in its molecular structure, which provide active functional groups for the system to participate in chemical bonding.

[0009] In-situ transesterification: During high-temperature melt blending, the catalyst activates the carbonyl carbon atoms on the biodegradable polyester resin backbone. The free hydroxyl groups on the oxidized lignin-hemicellulose complex undergo nucleophilic addition-elimination reactions with the activated carbonyl carbon, causing the ester bonds on the polyester macromolecular chain to break and recombine. The polyester segments are covalently linked to the oxidized lignin-hemicellulose complex, generating a copolymer with block copolymer characteristics.

[0010] Phase migration and interfacial bonding: The resulting copolymer structure consists of hydrophobic polyester segments at one end and hydrophilic lignin and hemicellulose structures at the other. Under screw shear stress, the copolymer undergoes phase migration to the interface between the high-purity plant cellulose and the polyester matrix. The lignin and hemicellulose ends bond with the surface of the high-purity plant cellulose through intermolecular hydrogen bonds, while the polyester segment ends become physically entangled with the biodegradable polyester resin matrix, constructing a continuous stress transfer path and reducing interfacial tension.

[0011] End-group reaction and hydrolysis inhibition: At processing temperatures, the active groups in the end-group protectant molecule undergo addition or condensation reactions with the terminal hydroxyl and carboxyl groups at the ends of the biodegradable polyester resin molecular chains, converting the active end groups into stable chemical bond structures. This reaction blocks the catalytic degradation pathway of trace amounts of moisture on the polyester end groups, maintaining the molecular weight of the polyester matrix during processing.

[0012] Preferably, the catalyst is stannous octoate or zinc acetate; the end-group protectant is polymeric diphenylmethane diisocyanate or bis(2,6-diisopropylphenylcarbodiimide).

[0013] By adopting the above technical solutions, since stannous octoate or zinc acetate has Lewis acidity, it can provide empty orbitals to coordinate and activate the carbonyl oxygen atoms of the polyester, thereby reducing the activation energy of the transesterification reaction; the polymerized diphenylmethane diisocyanate or bis(2,6-diisopropylphenyl)carbodiimide contains isocyanate groups and carbodiimide groups, respectively, which can react with the polyester ends and free water in the system to generate urea bonds or amide bonds, thereby improving the hydrolytic stability of the material.

[0014] Preferably, the oxidized lignin hemicellulose complex is obtained through the following preparation process: mixing plant lignin powder and plant hemicellulose, dispersing them in deionized water to obtain a first suspension; adding sodium hydroxide aqueous solution to the first suspension to adjust the pH, and adding deionized water to prepare a second suspension; heating the second suspension, and adding hydrogen peroxide aqueous solution dropwise at a uniform rate under stirring conditions to obtain a reaction solution; after the addition is complete, maintaining constant temperature and stirring conditions to continue the reaction; adjusting the pH of the reaction solution after the continued reaction using citric acid aqueous solution, pumping it into a spray dryer for dehydration and drying, and collecting the oxidized lignin hemicellulose complex.

[0015] By employing the above technical solution, in the alkaline environment provided by sodium hydroxide, hydrogen peroxide dissociates to generate hydrogen peroxide anions, which oxidatively break down the phenylpropane structure of plant lignin, increasing the density of hydroxyl and carboxyl groups within the system. Simultaneously, lignin macromolecules and hemicellulose segments cross-link under the influence of free radicals, forming a three-dimensional network macromolecule, providing the structural basis for subsequent in-situ transesterification. The use of citric acid acts as a neutralizer, preventing the acidic environment from causing acid degradation of the already formed complex.

[0016] Preferably, the dry weight ratio of the plant lignin powder to the plant hemicellulose is 3:1 to 5:1, the pH of the second suspension is 9.5 to 10.5, and the mass of solid matter in the second suspension accounts for 20%-30% of the total mass of the second suspension; the mass fraction of sodium hydroxide in the sodium hydroxide aqueous solution is 5.0%-10.0%, the mass fraction of hydrogen peroxide in the hydrogen peroxide aqueous solution is 28%-32%, and the mass fraction of citric acid in the citric acid aqueous solution is 5.0%-15.0%.

[0017] By employing the above technical solution and limiting the mass ratio of lignin to hemicellulose, the oxidation products are ensured to contain rigid aromatic ring structures and polysaccharide segments to adjust melt viscosity. Controlling the pH of the second suspension within the range of 9.5 to 10.5 maintains a balance between the hydrogen peroxide dissociation rate and the oxidation reaction rate, preventing excessive alkalinity from causing hydrogen peroxide decomposition.

[0018] Preferably, the heating temperature is 40°C to 80°C, the stirring speed is 200 rpm to 400 rpm, and the uniform dripping time is 30 minutes to 60 minutes; the hydrogen peroxide aqueous solution contains hydrogen peroxide solute in a mass of 15.0% to 40.0% of the mass of the plant lignin powder, the reaction continues for 1.5 hours to 5.5 hours, and the pH of the adjusted reaction solution is 6.5 to 7.5; the spray dryer has a set inlet temperature of 160°C to 190°C and a set outlet temperature of 80°C to 100°C.

[0019] By employing the above technical solution and controlling the reaction temperature and the proportion of hydrogen peroxide added, the depth of the oxidative degradation reaction is limited, preventing the oxidation reaction from causing the macromolecular chains to degrade into low-molecular-weight water-soluble substances. The spray drying parameters ensure the vaporization and removal of moisture while preventing the active groups of the complex from undergoing self-crosslinking and deactivation under heating conditions.

[0020] Preferably, the catalyst and the oxidized lignin hemicellulose complex are prepared by the following method: the catalyst and the oxidized lignin hemicellulose complex are placed in a mixer and dry mechanically mixed to obtain a first premix; the first premix and the high-purity plant cellulose are placed in a vacuum drying kettle for vacuum dehydration treatment to obtain a dehydrated mixture; and the end-group protectant is mixed into the dehydrated mixture to obtain a second premix. A co-rotating twin-screw extruder is used for melt extrusion. The biodegradable polyester resin is added through the main feed port of the co-rotating twin-screw extruder and melted to obtain a matrix melt. The second premix is ​​forcibly fed in through the side feed port of the co-rotating twin-screw extruder and mixed with the matrix melt to form a blended melt. Melt blending is carried out at a preset screw speed, and the vacuum exhaust port is opened to forcibly remove moisture. The blended melt is extruded through the co-rotating twin-screw extruder to obtain a composite material melt strip. The composite material melt strip is cooled and then pelletized to obtain the high-performance biodegradable composite material with synergistic effects of all three plant elements.

[0021] By adopting the above technical solution, the second premix is ​​added to the polyester matrix, which is already in a molten state, using a side-feeding process. This shortens the frictional shear time experienced by the plant fibers and oxidized composites in the screw solid conveying section, maintaining the physical structural integrity of the plant fibers. The step-by-step addition mechanism avoids the end-group protectant being consumed before homogeneous mixing, thus improving the utilization rate of the protectant.

[0022] Preferably, the dry mechanical mixing speed is 800 rpm to 1200 rpm, and the time is 5 minutes to 10 minutes; the free water content of the dehydrated mixture is less than 200 ppm. The vacuum dehydration treatment conditions are: treatment temperature of 105℃ to 120℃, vacuum degree of -0.10 MPa to -0.09 MPa, and treatment time of 4 hours to 8 hours.

[0023] By employing the above technical solution, the catalyst is uniformly dispersed in the oxidized composite particle system during dry mechanical mixing, providing contact conditions for the subsequent transesterification reaction. Vacuum dehydration removes free water from the mixture and controls the moisture content below 200 ppm, eliminating external reactants that could trigger the hydrolysis of ester bonds in the biodegradable polyester resin and ensuring the structural stability of the resin molecular chains during the blending process.

[0024] Preferably, the length-to-diameter ratio of the co-rotating twin-screw extruder is 40 to 48, and the co-rotating twin-screw extruder is divided into eight zones, with the first to third zones corresponding to the main feed port. The temperature of the first to third zones is set to 160°C to 215°C. The side feed port is located in the fourth zone, with the temperature of the fourth to fifth zones set to 180°C to 225°C, and the temperature of the sixth to eighth zones set to 190°C to 235°C. The preset screw speed in the sixth to eighth zones is 300 rpm to 500 rpm. The vacuum exhaust port is located in the sixth and eighth zones, and the vacuum degree is controlled to be -0.10 MPa to -0.08 MPa. The residence time of the blended melt in the sixth to eighth zones is controlled to be 30 seconds to 60 seconds.

[0025] By employing the above technical solution, the aspect ratio setting, combined with the gradient temperature distribution from zone one to zone eight, provides a distributed temperature field for the plasticization of polyester resin and the chemical reaction of the blend melt. Zones six to eight are located in the reaction region, and the screw speed of 300 rpm to 500 rpm provides a shear flow field, overcoming the diffusion resistance of macromolecules during phase migration. The distribution of vacuum exhaust ports extracts small molecule byproducts generated by the transesterification reaction and end-group blocking reaction, promoting the chemical reaction towards product formation.

[0026] This invention provides a high-performance biodegradable composite material with synergistic effects of three plant-based elements. It possesses the following beneficial effects: 1. This invention prepares an oxidized lignin-hemicellulose composite by combining plant lignin powder and plant hemicellulose, and then melt-blends it with high-purity plant cellulose and biodegradable polyester resin using a catalyst. This allows the oxidized composite to undergo an in-situ transesterification reaction with the polyester resin to generate a copolymer. This copolymer exhibits physical entanglement and hydrogen bonding at the interface between the two phases, thereby improving the interfacial compatibility between the hydrophilic plant cellulose and the hydrophobic biodegradable polyester resin, solving the phase separation problem caused by the polarity difference between the two phases, and improving the overall mechanical properties of the composite material.

[0027] 2. This invention reduces free water content by vacuum dehydrating high-purity plant cellulose and other components, then mixing them with end-group protectants before mixing with a molten polyester matrix. This process eliminates the hydrolytic effect of free water on the polyester ester bonds. At the same time, the end-group protectants seal the active end groups at the ends of the polyester molecular chains, thereby inhibiting the hydrolytic degradation reaction of the biodegradable polyester resin during high-temperature processing and ensuring the molecular structure stability and processing stability of the composite material.

[0028] 3. This invention uses a side feed port of a co-rotating twin-screw extruder to force a second premix containing plant cellulose into the molten polyester matrix. Combined with a specific temperature field, screw speed, and vacuum degassing operation, the solid mechanical friction time of the plant cellulose in the extruder is shortened, maintaining the physical structural integrity of the plant cellulose. At the same time, small molecule byproducts generated by the reaction are extracted in a timely manner, ensuring the forward progress of the chemical reaction and the uniformity of the final product performance. Attached Figure Description

[0029] Figure 1 This is a comprehensive trend diagram of the polymer structure stability and interfacial crosslinking degree of each experimental group in this invention; Figure 2 This is a distribution diagram of the peak value of the loss tangent in dynamic thermomechanical analysis for each experimental group of this invention; Figure 3 This is a line graph showing the overall trend of mechanical properties and heat resistance for each experimental group in this invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, preparation examples, embodiments, comparative examples, and test examples. 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.

[0031] Preparation Examples 1-3: Preparation Example 1: This preparation example provides an oxidized lignin hemicellulose complex, comprising the following steps: 400g (dry weight) of plant lignin powder and 100g (dry weight) of plant hemicellulose were mixed, with a dry weight ratio of 4:1. The mixture was dispersed in deionized water to obtain a first suspension. A sodium hydroxide aqueous solution with a mass fraction of 7.5% was slowly added to the first suspension to adjust its pH to 10.0. Deionized water was then added to prepare a second suspension, in which the mass of solid matter accounted for 25% of the total mass of the second suspension.

[0032] The second suspension was placed in a reaction vessel equipped with a mechanical stirrer and heated to 60°C. Under constant temperature and stirring at 300 rpm, a hydrogen peroxide aqueous solution with a mass fraction of 30% was added dropwise over 45 minutes. The mass of the added hydrogen peroxide solute was 27.5% of the mass of the plant lignin powder. The resulting reaction solution was then obtained. After the addition was completed, the reaction was continued for 3.5 hours under constant temperature and stirring conditions to complete the oxidation reaction.

[0033] After the oxidation reaction is completed, the pH of the reaction solution is adjusted to 7.0 using a citric acid aqueous solution with a citric acid mass fraction of 10%. The reaction solution is then pumped into a spray dryer with an inlet temperature of 175°C and an outlet temperature of 90°C for rapid dehydration and drying. The resulting solid powder is the oxidized lignin hemicellulose complex.

[0034] Preparation Example 2: This preparation example provides an oxidized lignin hemicellulose complex, comprising the following steps: 300g (dry weight) of plant lignin powder and 100g (dry weight) of plant hemicellulose were mixed, with a dry weight ratio of 3:1. The mixture was dispersed in deionized water to obtain a first suspension. A sodium hydroxide aqueous solution with a mass fraction of 5.0% was slowly added to the first suspension to adjust its pH to 9.5. Deionized water was then added to prepare a second suspension, in which the mass of solid matter accounted for 20% of the total mass of the second suspension.

[0035] The second suspension was placed in a reaction vessel equipped with a mechanical stirrer and heated to 40°C. Under constant temperature and stirring at 200 rpm, a hydrogen peroxide aqueous solution with a mass fraction of 28% was added dropwise over 30 minutes. The mass of the added hydrogen peroxide solute was 15.0% of the mass of the plant lignin powder. The reaction solution was obtained. After the addition was completed, the reaction was continued for 1.5 hours under constant temperature and stirring conditions to complete the oxidation reaction.

[0036] After the oxidation reaction is completed, the pH of the reaction solution is adjusted to 6.5 using a citric acid aqueous solution with a citric acid mass fraction of 5.0%. The reaction solution is then pumped into a spray dryer with an inlet temperature of 160°C and an outlet temperature of 80°C for dehydration and drying. The resulting solid powder is the oxidized lignin hemicellulose complex.

[0037] Preparation Example 3: This preparation example provides an oxidized lignin hemicellulose complex, comprising the following steps: 500g (dry weight) of plant lignin powder and 100g (dry weight) of plant hemicellulose were mixed, with a dry weight ratio of 5:1. The mixture was dispersed in deionized water to obtain a first suspension. A sodium hydroxide aqueous solution with a mass fraction of 10.0% was slowly added to the first suspension to adjust the pH to 10.5. Deionized water was then added to prepare a second suspension, in which the mass of solid matter accounted for 30% of the total mass of the second suspension.

[0038] The second suspension was placed in a reaction vessel equipped with a mechanical stirrer and heated to 80°C. Under constant temperature and stirring at 400 rpm, a hydrogen peroxide aqueous solution with a mass fraction of 32% was added dropwise over 60 minutes. The mass of the added hydrogen peroxide solute was 40.0% of the mass of the plant lignin powder. The reaction solution was obtained. After the addition was completed, the reaction was continued for 5.5 hours under constant temperature and stirring conditions to complete the oxidation reaction.

[0039] After the oxidation reaction is completed, the pH of the reaction solution is adjusted to 7.5 using a citric acid aqueous solution with a citric acid mass fraction of 15.0%. The reaction solution is then pumped into a spray dryer with an inlet temperature of 190°C and an outlet temperature of 100°C for rapid dehydration and drying. The resulting solid powder is the oxidized lignin hemicellulose complex.

[0040] Examples 1-4: Example 1: This embodiment provides a high-performance biodegradable composite material with synergistic effects of three plant elements, comprising the following steps: 0.2% by mass of stannous octoate and 10.0% of the oxidized lignin hemicellulose complex obtained in Preparation Example 1 were placed in a high-speed mixer and dry mechanically mixed at 1000 rpm for 8 minutes to uniformly disperse stannous octoate in the oxidized lignin hemicellulose complex, thus obtaining the first premix. The obtained first premix was placed together with 25.0% high-purity plant cellulose in a vacuum drying kettle and subjected to vacuum dehydration treatment at 115℃ and a vacuum degree of -0.095MPa for 6 hours, so that the free water in the first premix and high-purity plant cellulose was removed to below 200ppm, resulting in a dehydrated mixture. After vacuum dehydration, 0.6% of polymeric diphenylmethane diisocyanate (PMDI) was mixed into the dehydrated mixture to obtain a second premix for later use. Melt extrusion was performed using a co-rotating twin-screw extruder with an aspect ratio of 44. 64.2% polyglycolic acid was added through the main feed inlet of the co-rotating twin-screw extruder. The temperature of the first to third zones of the extruder was set at 200°C to soften and initially melt the polyglycolic acid, yielding the matrix melt. A second premix was forcibly fed in through a side feed inlet located in the fourth zone of the extruder. The temperature of the fourth to fifth zones was set at 215°C. At this temperature, the oxidized lignin-hemicellulose complex softened, releasing kinetic hindrance, and stannous octoate was released into the matrix melt, mixing with it to form a blended melt. The temperature of the sixth to eighth zones was set at 225°C, and the screw speed of the co-rotating twin-screw extruder was 400 rpm. At this shear rate, the oxidized lignin-hemicellulose complex was induced to migrate to the surface of high-purity plant cellulose, triggering an in-situ transesterification reaction. Vacuum exhaust ports are opened in zones 6 and 8, and the vacuum level is controlled at -0.09MPa to force the removal of moisture. The residence time of the blended melt in zones 6 to 8 is controlled to be 45 seconds. The blended melt is extruded through a co-rotating twin-screw extruder to obtain composite material melt strips. After being cooled in a constant temperature water bath, the composite material melt strips are fed into a pelletizer to obtain a high-performance biodegradable composite material with synergistic effects of all three plant elements.

[0041] Example 2: This embodiment provides a high-performance biodegradable composite material with synergistic effects of three plant elements, comprising the following steps: 0.3% by mass of stannous octoate and 15.0% of the oxidized lignin hemicellulose complex obtained in Preparation Example 2 were placed in a high-speed mixer and dry mechanically mixed at 800 rpm for 10 minutes to uniformly disperse stannous octoate in the oxidized lignin hemicellulose complex, thus obtaining the first premix. The obtained first premix was placed together with 40.0% high-purity plant cellulose in a vacuum drying kettle and subjected to vacuum dehydration treatment at 105℃ and a vacuum degree of -0.09MPa for 8 hours, so that the free water content of the first premix and high-purity plant cellulose was removed to below 200ppm, resulting in a dehydrated mixture. After vacuum dehydration, 0.8% PMDI was mixed into the dehydrated mixture to obtain a second premix for later use. Melt extrusion was performed using a co-rotating twin-screw extruder with an aspect ratio of 40. 43.9% polylactic acid (PLA) was added through the main feed inlet of the co-rotating twin-screw extruder. The temperature of zones one through three of the extruder was set at 160°C to soften and initially melt the PLA, yielding the matrix melt. A second premix was forcibly fed in through a side feed inlet located in zone four of the extruder. The temperature of zones four through five was set at 180°C. At this temperature, the oxidized lignin-hemicellulose composite softened, releasing kinetic hindrance, and stannous octoate was released into the matrix melt, mixing with it to form a blended melt. The temperature of zones six through eight was set at 190°C, and the screw speed of the co-rotating twin-screw extruder was adjusted to 500 rpm. At this shear rate, phase migration was induced, triggering an in-situ transesterification reaction. Vacuum exhaust ports are opened in zones 6 and 8, and the vacuum level is controlled at -0.08MPa to force the removal of moisture. The residence time of the blended melt in zones 6 to 8 is controlled to be 30 seconds. The blended melt is extruded through a co-rotating twin-screw extruder to obtain a composite melt strip. After being stretched and cooled by cold air, the composite melt strip is fed into a pelletizer to obtain a high-performance biodegradable composite material with synergistic effects of all three plant elements.

[0042] Example 3: This embodiment provides a high-performance biodegradable composite material with synergistic effects of three plant elements, comprising the following steps: 0.1% by mass of stannous octoate and 5.0% of the oxidized lignin hemicellulose complex obtained in Preparation Example 3 were placed in a high-speed mixer and dry mechanically mixed at 1200 rpm for 5 minutes to uniformly disperse stannous octoate in the oxidized lignin hemicellulose complex, thus obtaining the first premix. The obtained first premix was placed together with 10.0% high-purity plant cellulose in a vacuum drying kettle and subjected to vacuum dehydration treatment at 120℃ and a vacuum degree of -0.10MPa for 4 hours, so that the free water content of the first premix and high-purity plant cellulose was removed to below 200ppm, resulting in a dehydrated mixture. After vacuum dehydration, 0.4% PMDI was mixed into the dehydrated mixture to obtain a second premix for later use. Melt extrusion was performed using a co-rotating twin-screw extruder with an aspect ratio of 48. 84.5% polyglycolic acid was added through the main feed inlet of the co-rotating twin-screw extruder. The temperature of the first to third zones of the extruder was set at 215°C to soften and initially melt the polyglycolic acid, yielding the matrix melt. A second premix was forcibly fed in through a side feed inlet located in the fourth zone of the extruder. The temperature of the fourth to fifth zones was set at 225°C. At this temperature, the oxidized lignin-hemicellulose composite softened, releasing kinetic hindrance, and stannous octoate was released into the matrix melt, mixing with it to form a blended melt. The temperature of the sixth to eighth zones was set at 235°C, and the screw speed of the co-rotating twin-screw extruder was adjusted to 300 rpm. At this shear rate, phase migration was induced, triggering an in-situ transesterification reaction. Vacuum exhaust ports are opened in zones 6 and 8, and the vacuum level is controlled at -0.10 MPa to force the removal of moisture. The residence time of the blended melt in zones 6 to 8 is controlled at 60 seconds. The blended melt is extruded through a co-rotating twin-screw extruder to obtain composite material melt strips. After being cooled in a constant temperature water bath, the composite material melt strips are fed into a pelletizer to obtain a high-performance biodegradable composite material with synergistic effects of all three plant elements.

[0043] Example 4: This embodiment provides a high-performance biodegradable composite material with synergistic effects of three plant elements, comprising the following steps: 0.2% zinc acetate and 10.0% of the oxidized lignin hemicellulose complex obtained in Preparation Example 1 were placed in a high-speed mixer and dry mechanically mixed at 1000 rpm for 8 minutes to uniformly disperse zinc acetate in the oxidized lignin hemicellulose complex, thus obtaining the first premix. The obtained first premix and 25.0% high-purity plant cellulose were placed in a vacuum drying kettle and vacuum dehydrated for 6 hours at 115℃ and a vacuum degree of -0.095MPa, so that the free water content of the first premix and high-purity plant cellulose was removed to below 200ppm, resulting in a dehydrated mixture. After vacuum dehydration, 0.6% of bis(2,6-diisopropylphenyl)carbodiimide (molecular formula C) was mixed into the dehydrated mixture. 25 H 34 N2), to obtain a second premix for later use; Melt extrusion was performed using a co-rotating twin-screw extruder with an aspect ratio of 44. A mixed resin of 32.1% polyglycolic acid and 32.1% polylactic acid was added through the main feed port of the co-rotating twin-screw extruder. The temperature of the first to third zones of the co-rotating twin-screw extruder was set at 200°C to soften and initially melt the mixed resin, obtaining the matrix melt. A second premix was forcibly fed in through the side feed port located in the fourth zone of the co-rotating twin-screw extruder. The temperature of the fourth to fifth zones was set at 215°C. At this temperature, the oxidized lignin-hemicellulose complex softened and released kinetic hindrance, allowing zinc acetate to be released into the matrix melt and mix with it to form a blended melt. The temperature of the sixth to eighth zones was set at 225°C, and the screw speed of the co-rotating twin-screw extruder was adjusted to 400 rpm. At this shear rate, phase migration was induced and in-situ transesterification was triggered. Vacuum exhaust ports are opened in zones 6 and 8, and the vacuum level is controlled at -0.09MPa to force the removal of moisture. The residence time of the blended melt in zones 6 to 8 is controlled to be 45 seconds. The blended melt is extruded through a co-rotating twin-screw extruder to obtain composite material melt strips. After being cooled in a constant temperature water bath, the composite material melt strips are fed into a pelletizer to obtain a high-performance biodegradable composite material with synergistic effects of all three plant elements.

[0044] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that the oxidized lignin-hemicellulose complex obtained in Example 1 was replaced with an equal mass of unoxidized plant lignin and plant hemicellulose physical mixture powder (dry weight ratio of the two is 4:1), and all other aspects are the same.

[0045] Comparative Example 2: Compared to Example 1, the difference is that oxidized lignin hemicellulose complex is not added to the formulation, and the missing mass fraction is made up by polyglycolic acid (that is, the mass fraction of polyglycolic acid is increased to 74.2%), all other aspects are the same.

[0046] Comparative Example 3: Compared with Example 1, the difference is that the screw speed of the sixth to eighth zones of the co-rotating twin-screw extruder is adjusted from 400 rpm to 80 rpm, and all other parameters are the same.

[0047] Comparative Example 4: Compared with Example 1, the difference is that stannous octoate and oxidized lignin hemicellulose complex were not premixed. Instead, stannous octoate and polyglycolic acid were added together from the main feed port of the co-rotating twin-screw extruder. All other aspects are the same.

[0048] Comparative Example 5: Compared to Example 1, the difference is that no polydiphenylmethane diisocyanate is added to the formulation, and the missing mass fraction is made up by polyglycolic acid (i.e., the mass fraction of polyglycolic acid is increased to 64.8%). At the same time, the vacuum exhaust ports of the co-rotating twin-screw extruder in zones 6 and 8 are closed. All other aspects are the same.

[0049] Test Example 1-2: Test Example 1: Comprehensive Verification of Interfacial Phase Behavior, Covalent Bonding, and Degradation Resistance This test case aims to verify, through physicochemical characterization, the molecular chain stability of the polyester matrix during material processing, the covalent bonding at the multiphase interface, and the influence of rheological shear conditions on phase migration behavior.

[0050] Experimental steps: The test subjects were the composite material particles or standard specimens of Examples 1 to 4 after processing and molding, as well as Comparative Examples 1, 3, 4 and 5, and the unprocessed pure polymer resin particles were used as the initial molecular weight reference.

[0051] The extruded composite material particles were collected, cryogenically pulverized with liquid nitrogen, and an appropriate amount of powder was weighed and dissolved in hexafluoroisopropanol solvent. Undissolved plant cellulose and crosslinking components were then removed by filtration through a polytetrafluoroethylene microporous membrane. The resulting filtrate was injected into a gel permeation chromatograph. The weight-average molecular weight of the polymer resin matrix was determined at a column temperature of 35°C, and the retention rate was calculated based on the molecular weight data of the initial pure resin raw material.

[0052] To determine the degree of cross-linking, a certain mass of dried, freeze-pulverized sample was weighed and placed in a filter paper packet, which was then placed in a Soxhlet extractor. Using chloroform as the extraction solvent, extraction was performed continuously for 24 hours under reflux to extract uncross-linked polymer segments and free small molecules. After extraction, the filter paper packet containing residue was placed in a vacuum drying oven and dried at 60°C to constant weight. The final mass was weighed, and the percentage of insoluble matter relative to the original sample mass was calculated to obtain the gelation rate.

[0053] Composite material particles were injection molded into rectangular specimens of standard size. The specimens were then clamped in a dynamic thermomechanical analyzer, and temperature scanning tests were performed in tensile mode. The test frequency was set to 1 Hz, the heating rate to 3 °C / min, and the temperature scanning range to room temperature to 150 °C. The storage modulus and loss tangent values ​​of the material under dynamic alternating stress were recorded, and the peak value and half-peak width of the loss tangent were extracted.

[0054] Experimental data: Table 1. Molecular weight retention, gelation rate, and dynamic thermomechanical analysis data of each example and comparative example.

[0055] Note: The initial matrix in Example 2 was polylactic acid. All other systems containing polyglycolic acid were calculated based on the initial molecular weight of polyglycolic acid. Results analysis: The molecular weight data recorded in Table 1 and Figure 1 The solid line trend of molecular weight retention on the left shows significant differences in the stability of the experimental system at the multiphase micro-interface and in the macromolecular matrix. Gel permeation chromatography data reflect the degree of degradation of the polymer polyester in the complex extrusion thermal field. Trace amounts of moisture lead to a decrease in melt viscosity. Observation Figure 1 The downward trend of the curve reveals that Comparative Examples 4 and 5, which lacked multi-stage water-suppressing protection and had catalysts introduced too early, exhibited a significant decrease in weight-average molecular weight, with retention rates dropping to 42.9% and 28.3%, respectively, as shown in Table 1. This data change is consistent with the hydrolytic characteristics of the polyester matrix under high-temperature, micro-water conditions, and the early introduction of free catalysts further exacerbated the random breakage of the main chain.

[0056] In contrast, the molecular weight retention rate of the example group was... Figure 1 The average viscosity remained consistently above 88% of the baseline. Actual sampling observations also revealed that the extruded samples from these groups had smoother surfaces and higher melt strength. This indicates that the physical barrier formed by the high viscosity of hemicellulose effectively delayed catalyst release in the initial melting stage. Relying on this kinetic hindrance, combined with end-group protectants and forced vacuum degassing in the later stages of the screw, residual moisture within the system was effectively dissipated. The Le Chatelier principle-driven forward esterification reaction was able to occur stably within the set temperature range, reducing the occurrence of micro-hydrolysis of the matrix.

[0057] The stability of the polyester macromolecular backbone provides sufficient active sites for interfacial reactions, while the strength of the interfacial bonding directly affects the efficiency of macroscopic stress transfer, as can be seen from Table 1 and... Figure 1 This is confirmed by the dashed line trend of the gelation rate on the right axis. Comparative Example 1, using unoxidized natural lignin, showed a gelation rate of only 1.3% as shown in Table 1. In conventional extraction experiments, this low cross-linking signal means that unactivated natural lignin is difficult to chemically anchor with the polyester matrix in the extrusion shear field, and is easily penetrated and completely extracted by chloroform solvent. The gelation rates of the example groups were generally within the effective reaction range of 10% to 15%, and... Figure 1 The right-axis broken line graph shows a clear plateau phase. The insoluble gel network demonstrates that the reactive oxidized lignin skeleton has substantially formed a covalently cross-linked network with polyester macromolecular segments under in-situ transesterification catalysis.

[0058] Even with reactive groups, the dynamic intervention of physical rheological processes is equally important in practical multiphase melts. (See Table 1 and...) Figure 2 The presented loss tangent peak value shows a broken line change, deviating from Comparative Example 3, which has a suitable rheological viscosity ratio window, with its loss tangent peak value rising to 0.198. Under dynamic stress loading tests, this high-dissipation thermodynamic response often reveals a significant relative slippage of molecular chain segments at the two-phase interface. In contrast, Example 1, through the application of a shear field at a specific rotational speed, induced spontaneous wetting and spreading of the hybrid phase with intermediate polarity at the mesoscopic level. The phase migration process based on the principle of minimum energy constructs a continuous modulus gradient transition layer at the interface, physically encapsulating and combining with matching chemical covalent bonds, which restricts the movement of macromolecular chain segments, ultimately as shown... Figure 2 As shown by the low-level, gently sloping line, the peak value of the macroscopic loss tangent of the system is reduced to 0.115. Experimental and characterization data indicate that the macroscopic phase separation defects caused by polar repulsion have been substantially eliminated in the current formulation and process.

[0059] Test Example 2: Comprehensive Test of Synergistic Mechanical and Thermal Stability of Three Elements in Whole Plant This test case aims to evaluate the engineering service capability of composite materials and verify the specific effects of high-purity plant cellulose, oxidized lignin hemicellulose complex, and in-situ transesterification crosslinking network on the material's strength, toughness, and high-temperature dimensional stability.

[0060] Experimental steps: The test subjects were composite material specimens from Examples 1 to 4 and Comparative Examples 1 to 5, which were injection molded. All specimens were conditioned for 48 hours in a standard constant temperature and humidity environment at 23°C and 50% relative humidity before testing to eliminate internal residual stress.

[0061] Using an injection molding machine, the composite material particles of each group were prepared into dumbbell-shaped tensile specimens conforming to GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics" and rectangular impact specimens conforming to GB / T1043.1-2008 "Determination of impact properties of simply supported beams of plastics - Part 1: Non-instrumental impact testing". During the injection molding process, the melt temperature of each group was kept consistent with the mold temperature to avoid interference from differences in thermal history on the crystallinity of the matrix.

[0062] Room temperature tensile tests were conducted on a universal testing machine, equipped with an extensometer to record specimen deformation, and the tensile rate was set to 50 mm / min. The load-displacement curve was automatically recorded during the experiment, and tensile strength and elongation at break were extracted by converting the cross-sectional area. Five valid specimens were tested independently for each group, and the arithmetic mean was taken.

[0063] A 2mm deep V-notch was machined into the side of a rectangular impact specimen. The specimen was placed on a pendulum impact testing machine, and the test was conducted using a simply supported beam mode. The energy consumed by the pendulum to break the specimen was recorded, and the notched impact strength was calculated based on the remaining cross-sectional area at the notch, thereby assessing the material's resistance to crack instability propagation.

[0064] Undamaged rectangular specimens were placed in a heat distortion Vicat softening temperature tester. Following GB / T1634.2-2019 "Determination of Deformation Temperature of Plastics under Load - Part 2: Plastics and Hard Rubber", the bending normal stress was set to 0.45 MPa, and the heating rate was set to 120 °C / h. The bath temperature corresponding to the specimen's center deflection reaching 0.34 mm was recorded and used as the heat distortion temperature to characterize the material's ability to maintain rigidity under heating.

[0065] Experimental data: Table 2. Summary of overall performance test results for each embodiment and comparative example

[0066] Experimental conclusion: The macroscopic mechanical properties and heat resistance of a material directly reflect the microstructural state of its internal multiphase interfaces. (See Table 2 for specific values.) Figure 3 The broken-line trend shows that the various properties of the composite material are highly dependent on the integrity of the three-element synergistic system. For example... Figure 3 As shown, both tensile strength (solid line) and notched impact strength (dotted line) exhibited significant performance troughs in the abscissa intervals corresponding to Comparative Example 1 and Comparative Example 2. According to Table 2, when the oxidized lignin hemicellulose complex was not added to the system (Comparative Example 2), the tensile strength of the material was only 39.54 MPa.

[0067] Samples of simple physical blends often exhibit typical interfacial debonding characteristics. Under stress, plant fibers tend to be pulled directly out of the polyester matrix, indicating a lack of effective load transfer pathways between the two phases. Even if the formulation contains plant trifoliate compounds, if the lignin is not oxidized and activated (Comparative Example 1). Figure 3 The notch impact strength corresponding to the right axis remains at 5.24 kJ / m. 2 The low level of lignin indicates that the surface of inactive lignin lacks sufficient free carboxyl and hydroxyl groups, making it unable to undergo in-situ transesterification with the polyester matrix during extrusion heating. The lack of chemical anchoring at the interface leads to rapid crack propagation when the material is subjected to external impact.

[0068] Besides the integrity of the formulation, the rheological and catalytic kinetic conditions in the processing also play a crucial role in the final shaping of the material properties. Examining the data of Comparative Example 4 in Table 2, the catalyst stannous octoate was not pre-mixed with the composite using a dry process, but instead added directly from the main feed port, leading to uneven dispersion of the catalytic centers in the matrix melt with significant polarity differences. Due to the uneven crosslinking distribution, Comparative Example 4... Figure 3 The trend line shows a performance decline, and the material becomes brittle. The effect of the extrusion shear field is more direct in Comparative Example 3. The reduction in screw speed weakens the shear work of the system, making it difficult for the composite to obtain sufficient hydrodynamic drive for phase migration to the cellulose surface. The failure of the interfacial layer modulus transition causes the tensile strength of Comparative Example 3 to drop to 48.27 MPa. In addition, from Figure 3 As can be seen on the far right, all the broken lines in Comparative Example 5 have decreased to their lowest values, with its heat distortion temperature (dashed line) dropping to 65.3℃. This is mainly because no end-group protectant was added during processing and vacuum degassing was not activated. The polyester matrix underwent severe hydrolytic degradation in a high-temperature, slightly damp environment, and the breakage of the molecular chains reduced the material's load-bearing capacity and heat resistance.

[0069] After eliminating the aforementioned component and process defects, Examples 1 to 4 were conducted... Figure 3 A stable and distinct high-performance distribution band was formed in the left region, with both the solid line for tensile strength and the dashed line for impact strength maintaining a high level within this interval. Among them, the formulation ratio and process parameters of Example 3 showed the best match; Table 2 data shows that its tensile strength reached 65.12 MPa, and its notched impact strength increased to 13.41 kJ / m². 2 The simultaneous improvement in strength and toughness verifies the structural advantages of the high-modulus cellulose skeleton and hemicellulose transition layer formed under the action of the oxidized lignin crosslinking network. This topology can effectively limit the initiation and propagation of local microcracks. Regarding heat resistance, the heat distortion temperature of the example groups generally jumped to above 91℃, with Example 3 reaching 98.7℃, showing a significant difference compared to the comparative examples. This improvement in high-temperature dimensional stability is mainly attributed to the physical restriction on the thermal creep behavior of the amorphous macromolecular chain segments by the high-density covalent crosslinking structure generated in situ at the multiphase interface. Comprehensive test data shows that, through a set oxidation activation path and specific process control, plant trifolin can construct a mechanically reinforcing and heat-resistant network with engineering application value in a polyester matrix.

Claims

1. A high-performance biodegradable composite material with synergistic effects of three plant-based elements, characterized in that, Made from the following raw materials by mass fraction: Oxidized lignin-hemicellulose complex: 5.0%-15.0%; Catalyst: 0.1%-0.3%; High-purity plant cellulose: 10.0%-40.0%; End-group protectant: 0.4%-0.8%; Biodegradable polyester resin: 43.9%-84.5%; The biodegradable polyester resin is selected from at least one of polyglycolic acid and polylactic acid.

2. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 1, characterized in that, The catalyst is stannous octoate or zinc acetate; The end-group protectant is a polymeric diphenylmethane diisocyanate or bis(2,6-diisopropylphenyl)carbodiimide.

3. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 1, characterized in that, The specific steps for preparing the oxidized lignin hemicellulose complex are as follows: Plant lignin powder and plant hemicellulose are mixed and dispersed in deionized water to obtain a first suspension. Sodium hydroxide aqueous solution is added to the first suspension to adjust the pH, and deionized water is added to prepare a second suspension. The second suspension was heated, and hydrogen peroxide aqueous solution was added dropwise at a uniform rate under stirring conditions to obtain a reaction solution. After the addition was completed, the reaction was continued under constant temperature and stirring conditions. The pH of the reaction solution after the reaction was completed was adjusted using citric acid aqueous solution. The solution was then dehydrated and dried using a spray dryer to collect the oxidized lignin hemicellulose complex.

4. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 3, characterized in that, The dry weight ratio of the plant lignin powder to the plant hemicellulose is 3:1 to 5:

1. The pH of the second suspension is 9.5-10.5, and the mass of solid matter in the second suspension accounts for 20%-30% of the total mass of the second suspension. The sodium hydroxide aqueous solution contains 5.0%-10.0% sodium hydroxide by mass, the hydrogen peroxide aqueous solution contains 28%-32% hydrogen peroxide by mass, and the citric acid aqueous solution contains 5.0%-15.0% citric acid by mass.

5. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 4, characterized in that, The heating temperature is 40℃-80℃, the uniform dripping time is 30 minutes-60 minutes, and the stirring speed is 200rpm-400rpm. The hydrogen peroxide aqueous solution contains hydrogen peroxide solute in an amount that is 15.0%-40.0% of the mass of the plant lignin powder. The reaction continues for 1.5 to 5.5 hours, and the pH of the adjusted reaction solution is 6.5 to 7.

5. The spray dryer is set with an inlet temperature of 160℃-190℃ and an outlet temperature of 80℃-100℃.

6. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 1, characterized in that, The high-performance biodegradable composite material is obtained by the following preparation method: The catalyst and the oxidized lignin hemicellulose complex were placed in a high-speed mixer for dry mechanical mixing to obtain a first premix. The first premix and the high-purity plant cellulose are placed in a vacuum drying kettle for vacuum dehydration to obtain a dehydrated mixture. The end-group protectant is then mixed into the dehydrated mixture to obtain a second premix. The biodegradable polyester resin is added and melted from the main feed port of the co-rotating twin-screw extruder to obtain a matrix melt. The second premix is ​​forcibly fed into the side feed port of the co-rotating twin-screw extruder and mixed with the matrix melt to form a blended melt. The blending is carried out at a preset screw speed, and the vacuum exhaust port is opened to forcibly remove moisture. The blended melt is extruded through the co-rotating twin-screw extruder to obtain a composite material melt strip. The composite material melt strip is cooled and then pelletized to obtain the high-performance biodegradable composite material.

7. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 6, characterized in that, The dry mechanical mixing conditions are as follows: dry mechanical mixing for 5-10 minutes at a speed of 800-1200 rpm; The free water content of the dehydrated mixture is less than 200 ppm.

8. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 6, characterized in that, The conditions for the vacuum dehydration process are as follows: The processing temperature is 105℃-120℃, the vacuum degree is -0.10MPa to -0.09MPa, and the processing time is 4 hours to 8 hours.

9. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 6, characterized in that, The length-to-diameter ratio of the co-rotating twin-screw extruder is 40-48. The co-rotating twin-screw extruder is divided into zones one through eight. The main feed port is located in zones one through three. The temperature in zones one through three is 160℃-215℃.

10. The high-performance biodegradable composite material with synergistic effects of all three plant elements according to claim 9, characterized in that, The side feeding port is located in the fourth zone, and the temperature of the fourth to fifth zones is 180℃-225℃; The temperature in zones six to eight is 190℃-235℃, and the preset screw speed in zones six to eight is 300rpm-500rpm; The vacuum exhaust port is located in the sixth zone and the eighth zone, and the vacuum degree is controlled to be -0.10MPa to -0.08MPa. The residence time of the blended melt in the sixth zone to the eighth zone is controlled to be 30 seconds to 60 seconds.

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