A method for the directed enzymatic closed-loop recycling of ester-bond cross-linked plant fiber materials

Abstract

The application discloses a kind of ester bond crosslinking plant fiber material's directional enzymolysis closed loop recycling method, it is mainly related to fiber material technical field.The ester bond crosslinking plant fiber material's directional enzymolysis closed loop recycling method includes the following steps: ester bond crosslinking plant fiber material is mixed with the enzymatic hydrolysis liquid of composite enzyme, and enzymolysis reaction is carried out;Solid-liquid separation is obtained recycled plant fiber and recycled polycarboxylic acid monomer;Specific aliphatic esterase of enzyme activity 16-20U / L is used as composite enzyme, endo-type cellulase of enzyme activity 8-10U / L, the temperature of the enzymatic hydrolysis liquid is 45-50 ℃, and the pH value of the enzymatic hydrolysis liquid is 4.5-5.5.The recycled plant fiber and recycled polycarboxylic acid monomer obtained by the directional enzymolysis closed loop recycling method are used as raw materials for recycling, and the tensile strength retention rate of ester bond crosslinking plant fiber material prepared by 5 times of raw material recycling is greater than 85%, which realizes directional depolymerization and material closed loop recycling of ester bond crosslinking plant fiber material.

Description

Technical Field

[0001] This invention relates to the field of fiber materials technology, and in particular to a method for the directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials. Background Technology

[0002] Existing plant fiber-based plastic substitutes typically combine plant fibers with biodegradable polymers such as PLA and PBAT through physical blending or chemical crosslinking. Physical blending is a simpler process, but it results in poor interfacial compatibility between plant fibers and polymers, leading to insufficient mechanical strength and easy water absorption and swelling in the finished product. While chemical crosslinking can improve strength and water resistance, it is difficult to degrade and recycle after disposal. Polycarboxylic acid esterification crosslinking can improve the water resistance and strength of plant fiber materials, but current processes usually focus more on strength improvement during the service life, without fully considering targeted dismantling and high-value recycling during the disposal stage.

[0003] In terms of recycling, existing plant fiber-based materials mainly rely on strong acid and alkali chemical recycling, industrial composting, incineration, landfilling, or mechanical crushing for reuse. Strong acid and alkali chemical recycling methods are demanding, severely damaging the cellulose backbone and significantly reducing the degree of polymerization of the recycled fibers, making them unsuitable for the reprocessing of high-strength materials. Industrial composting has a long cycle and converts biomass carbon sources into carbon dioxide and water, making it difficult to achieve high-value recycling of raw materials. Incineration and landfilling involve resource waste or environmental burden. Mechanical crushing for reuse easily damages the fiber aspect ratio, reducing the strength of the recycled material. Therefore, how to achieve targeted recycling of materials in a mild and controllable manner after disposal is a pressing technical problem to be solved in the industrial application of plant fiber-based plastic substitutes. Summary of the Invention

[0004] This invention proposes a directional enzymatic hydrolysis closed-loop recycling method for ester-linked plant fiber materials, which solves the technical problems of difficult degradation and recycling of plant fiber materials after disposal and low recycling rate.

[0005] To achieve the above objectives, this invention proposes a method for the targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials. The method includes the following steps: Ester-linked cross-linked plant fiber materials are mixed with the enzymatic hydrolysate of a composite enzyme and subjected to enzymatic hydrolysis to obtain a depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers. The depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers is subjected to solid-liquid separation to obtain recovered plant fibers and recovered polycarboxylic acid monomers. The complex enzyme includes a specific aliphatic esterase and an endoglucanase. The specific aliphatic esterase has an enzyme activity of 16-20 U / L, the endoglucanase has an enzyme activity of 8-10 U / L, the temperature of the enzymatic hydrolysate is 45-50℃, and the pH of the enzymatic hydrolysate is 4.5-5.5.

[0006] In one embodiment, the preparation method of the enzymatic hydrolysate of the complex enzyme is as follows: prepare an aqueous phase system with a temperature of 45-50°C and a pH buffer between 4.5 and 5.5, and add a specific aliphatic esterase and an endoglucanase to the aqueous phase system.

[0007] In one embodiment, the mass ratio of the ester-linked plant fiber material to the enzymatic hydrolysate of the complex enzyme is 1:8-15.

[0008] In one embodiment, the solid-liquid separation includes the following steps: First-stage coarse separation: centrifuge at 2500-3500 rpm for 4-6 minutes to separate large particles of undeaggregated residue; Secondary fine separation involves centrifugation at 7500-8500 rpm for 8-12 minutes to separate the recovered high-quality active plant microfibers. Three-stage purification: centrifugation at 10,000-15,000 rpm for 10-20 min to separate the liquid product of plant fiber residue and the liquid product containing polycarboxylic acid monomers.

[0009] In one embodiment, the ester-linked cross-linked plant fiber material is prepared by the following steps: Alkali treatment of plant fibers yields a highly active plant fiber matrix. The highly active plant fiber matrix was mixed with a crosslinking solution and then ultrasonically treated to obtain the mixture. The mixture is poured into a mold and subjected to esterification reaction through hot pressing curing to obtain ester-linked plant fiber materials.

[0010] In one embodiment, the crosslinking liquid comprises the following components: a polycarboxylic acid crosslinking agent, a catalyst, and deionized water.

[0011] In one embodiment, the hot pressing set temperature is 140-180°C, and the hot pressing applied pressure is 10-15 MPa.

[0012] In one embodiment, the plant fiber is at least one of wheat straw fiber, wood fiber, bamboo fiber, and hemp fiber.

[0013] In one embodiment, the polycarboxylic acid crosslinking agent is at least one of citric acid, fumaric acid, malic acid, tartaric acid, and bio-based succinic acid.

[0014] In one embodiment, the catalyst is at least one of sodium hypophosphite and p-toluenesulfonic acid.

[0015] This invention provides a method for the targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials, comprising the following steps: mixing the ester-linked plant fiber material with an enzymatic hydrolysate of a composite enzyme for enzymatic hydrolysis; performing solid-liquid separation to obtain recovered plant fiber and recovered polycarboxylic acid monomers; the composite enzyme used is specifically a specific aliphatic esterase with an activity of 16-20 U / L and an endoglucosidase with an activity of 8-10 U / L; the temperature of the hydrolysate is 45-50℃, and the pH value of the hydrolysate is 4.5-5.5. This invention solves the technical problems of difficult degradation and recycling of waste plant fiber materials and low recycling rates through the targeted enzymatic hydrolysis and closed-loop recovery method of the ester-linked plant fiber material. The recovered plant fiber and recovered polycarboxylic acid monomers obtained by the targeted enzymatic hydrolysis and closed-loop recovery method are recycled and tested. The ester-linked plant fiber material prepared after five cycles of raw material recycling exhibits a tensile strength retention rate of greater than 85%, achieving targeted depolymerization and closed-loop recovery of the ester-linked plant fiber material. Compared with existing technologies, the solution provided by this invention can achieve rapid depolymerization and raw material recycling in the waste stage of ester-linked plant fiber materials through mild enzymatic hydrolysis conditions. It provides a solution to the problem that existing plant fiber plastic substitutes are difficult to balance high strength and durability with closed-loop recycling. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. 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.

[0017] Current plant fiber-based materials mainly rely on strong acid and alkali chemical recycling, industrial composting, incineration, landfilling, or mechanical pulverization for reuse. While strong acid and alkali chemical recycling can break ester bonds, the harsh reaction conditions cause severe irreversible degradation of the cellulose backbone, leading to a significant decrease in the degree of polymerization of the recycled fibers, making it unsuitable for the reprocessing of high-strength materials. Physical mechanical pulverization can only reduce particle size, failing to achieve directional depolymerization of the cross-linked network and graded recovery of individual components, resulting in low-quality pulverized material with limited recycling value. Industrial composting and microbial degradation routes can dispose of waste, but the degradation cycle is long, and high-quality separate recovery of plant fibers and polycarboxylic acid monomers is impossible, resulting in a complete waste of valuable biomass resources. Incineration and landfilling methods do not conform to the concept of a green circular economy and bring additional carbon emissions and environmental burden. Therefore, how to achieve directional and efficient depolymerization of ester-linked plant fiber materials under mild conditions, while simultaneously achieving high-quality graded recovery of plant fiber components and polycarboxylic acid monomers, and then recycling the recovered materials in a closed loop for the preparation of new materials, is a core technical challenge that urgently needs to be overcome in this field.

[0018] In view of this, the present invention proposes a method for the targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials, the method comprising the following steps: Ester-linked cross-linked plant fiber materials are mixed with the enzymatic hydrolysate of a composite enzyme and subjected to enzymatic hydrolysis to obtain a depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers. The depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers is subjected to solid-liquid separation to obtain recovered plant fibers and recovered polycarboxylic acid monomers. The complex enzyme includes a specific aliphatic esterase and an endoglucanase. The specific aliphatic esterase has an enzyme activity of 16-20 U / L, the endoglucanase has an enzyme activity of 8-10 U / L, the temperature of the enzymatic hydrolysate is 45-50℃, and the pH of the enzymatic hydrolysate is 4.5-5.5.

[0019] Ester-linked plant fiber materials were mixed with the enzymatic hydrolysate of the composite enzyme for enzymatic hydrolysis. The specific aliphatic esterase exhibited high selectivity for citrate bonds, with a hydrolysis rate more than 8.5 times that of acetate bonds, achieving directional shearing of cross-linked nodes while maintaining the integrity of the cellulose backbone. Simultaneously, an endoglucanase helped relax the hydrogen bond network between fiber aggregates, reducing enzyme-substrate mass transfer resistance and allowing the aliphatic esterase to more easily reach deeper ester bond sites. The synergistic effect of the two enzymes achieved complete directional disintegration of the material. The hydrolysate temperature was set at 45-50℃ and the pH at 4.5-5.5. Under these conditions, the conformation of the specific aliphatic esterase's active site closely matched the spatial accessibility of the ester bonds, with the carbonyl carbon atom of the ester bond within a reasonable distance (approximately 3-5 Å) for nucleophilic attack by the enzyme molecule, resulting in the highest catalytic efficiency. A pH deviation from the 4.5-5.5 range also led to enzyme activity loss and decreased substrate accessibility. Finally, the activity of specific aliphatic esterase was limited to 16-20 U / L and that of endo-cellulase to 8-10 U / L. Within this range, the two formed the best synergistic depolymerization effect, and the depolymerization products were short-cut micro / nanofibers with a length retention rate of >85% and polycarboxylic acid monomers that could be recycled in high purity. If the enzyme activity was lower than this range, the depolymerization was insufficient and the recovery rate decreased. If it was higher than this range, the enzyme protein would cause non-specific erosion of the cellulose backbone, the quality of the recycled fiber would be significantly reduced, and the mechanical properties of the recycled material would be affected.

[0020] In one embodiment, the preparation method of the enzymatic hydrolysate of the complex enzyme is as follows: prepare an aqueous phase system with a temperature of 45-50℃ and a pH buffer between 4.5 and 5.5, and add a specific aliphatic esterase and an endoglucosidase to the aqueous phase system.

[0021] The preparation of the compound enzyme hydrolysate involves controlling the temperature of the aqueous phase system at 45-50℃ and the pH at 4.5-5.5, followed by the addition of specific aliphatic esterase and endoglucanase. The temperature of 45-50℃ and the weakly acidic pH of 4.5-5.5 maintain the specific aliphatic esterase and endoglucanase within their optimal activity range. Within this pH range, strong acids, strong alkalis, or high-temperature chemical recycling can prevent severe damage to the degree of fiber polymerization. Within this temperature range, the α / β hydrolytic folding conformation of the specific aliphatic esterase's active site is highly stable. Below 45℃, the thermal motion of the enzyme molecules weakens, and the substrate activity frequency decreases. Above 50℃, the stability of disulfide bonds and hydrogen bonds in the hydrophobic core decreases, and the active site gradually unfolds and becomes inactive.

[0022] In one embodiment, the mass ratio of the ester-linked plant fiber material to the enzymatic hydrolysate of the complex enzyme is 1:8-15.

[0023] Within this mass ratio range, the broken ester-linked plant fiber material is ensured to be fully wetted and dispersed by the enzymatic hydrolysate, providing sufficient diffusion space for the composite enzyme on the particle surface and in the pores. If the mass ratio is too low, the system viscosity is high, and solid particles tend to accumulate, making it difficult for enzyme molecules to uniformly contact the ester-linked nodes, resulting in incomplete depolymerization. If the mass ratio is too high, although mass transfer resistance decreases, the amount of enzyme solution and buffer system increases, raising the burden of subsequent separation and concentration, which is detrimental to the economic efficiency of industrial closed-loop recycling. The 1:8-15 mass ratio range specified in this invention achieves a balance between enzymatic hydrolysis efficiency and subsequent processing workload.

[0024] In one embodiment, the solid-liquid separation includes the following steps: First-stage coarse separation: centrifuge at 2500-3500 rpm for 4-6 minutes to separate large particles of undeaggregated residue; Secondary fine separation involves centrifugation at 7500-8500 rpm for 8-12 minutes to separate the recovered high-quality active plant microfibers. Three-stage purification: centrifugation at 10,000-15,000 rpm for 10-20 min to separate the liquid product of plant fiber residue and the liquid product containing polycarboxylic acid monomers.

[0025] The solid-liquid separation employs a three-stage separation mode, enabling graded recovery based on the particle size, density, and dispersion state of different components in the depolymerized slurry. The first-stage coarse separation uses a low rotation speed to remove large, undepolymerized residue particles, preventing them from entering the subsequent fine separation stage and causing equipment wear or affecting the purity of the recovered material. The second-stage fine separation uses medium-to-high rotation speeds to enrich reusable active plant microfibers. These fibers retain a certain aspect ratio and surface-active hydroxyl groups, and can be washed, dried, and recycled as remanufacturing raw materials. The third-stage purification uses even higher rotation speeds to further remove fine suspended impurities, making the polycarboxylic acid monomers and oligomers in the liquid phase more suitable for vacuum concentration and recovery. By introducing a three-stage centrifugal separation technology—first-stage coarse separation, second-stage fine separation, and third-stage purification—fiber damage and component mixing caused by single-stage separation can be reduced, improving the overall recovery rate of plant fiber residues and polycarboxylic acid monomers.

[0026] In one embodiment, the ester-linked cross-linked plant fiber material is prepared by the following steps: Alkali treatment of plant fibers yields a highly active plant fiber matrix. The highly active plant fiber matrix was mixed with a crosslinking solution and then ultrasonically treated to obtain the mixture. The mixture is poured into a mold and subjected to esterification reaction through hot pressing curing to obtain ester-linked plant fiber materials.

[0027] The preparation method constructs a directionally enzymatically hydrolyzable ester crosslinking network through three steps: alkali treatment, crosslinking solution infiltration, and hot-press curing. Alkali treatment opens the pores of plant fibers, exposing more cellulose hydroxyl groups to obtain a highly active plant fiber matrix. The cavitation effect of ultrasound drives the polycarboxylic acid crosslinking agent and catalyst in the crosslinking solution to uniformly penetrate into the micropores and amorphous regions of the plant fibers. Finally, hot-press curing under high temperature and pressure promotes the dehydration and activation of the polycarboxylic acid, leading to esterification with the hydroxyl groups.

[0028] In one embodiment, the crosslinking liquid comprises the following components: a polycarboxylic acid crosslinking agent, a catalyst, and deionized water.

[0029] The polycarboxylic acid crosslinking agent is an aliphatic organic acid containing two or more carboxyl groups. Under catalytic and hot-pressing conditions, it undergoes esterification with the hydroxyl groups of plant fibers to form an inter-fiber aliphatic ester bond crosslinking structure. Compared with aromatic or heterocyclic crosslinking systems, the ester bonds formed by polycarboxylic acid crosslinking have less steric hindrance, and the carbonyl carbon is in an open molecular conformation, allowing the specific aliphatic esterase Cutinase to depolymerize under specific conditions, thereby achieving directional enzymatic hydrolysis. The introduction of the catalyst can promote the rapid intramolecular dehydration of the polycarboxylic acid crosslinking agent under high temperature and high pressure to form an activated anhydride intermediate, which then undergoes deep esterification with the hydroxyl groups on the cellulose surface, improving the crosslinking density and the mechanical strength of the material. Deionized water is used as a solvent medium to ensure that the polycarboxylic acid crosslinking agent and catalyst are uniformly dispersed in the cellulose matrix. Combined with ultrasonic dispersion, the crosslinking solution penetrates into the amorphous region and micropores of the fiber, resulting in a uniform distribution of ester bonds and a porous microstructure after hot pressing. This provides a stable spatial channel for enzyme molecules to subsequently enter the substrate and fully contact the ester bond sites.

[0030] In one embodiment, the hot pressing set temperature is 140-180°C, and the hot pressing applied pressure is 10-15 MPa.

[0031] Under these hot-pressing temperature and pressure conditions, the dehydration and activation of polycarboxylic acids can be promoted, leading to esterification with hydroxyl groups. If the temperature is too low, the degree of dehydration of polycarboxylic acids to form active intermediates is insufficient, resulting in incomplete esterification and limited improvement in material strength and water resistance. If the temperature is too high, plant fibers may undergo thermal degradation or darken in color, and excessive cross-linking will reduce subsequent targeted enzymatic hydrolysis and ring-closing recovery. Controlling the pressure at 10-15 MPa helps to remove excess moisture, increase the contact area between fibers, and promote the fixation of the cross-linking solution in the fiber pores.

[0032] In one embodiment, the plant fiber is at least one of wheat straw fiber, wood fiber, bamboo fiber, and hemp fiber.

[0033] Different fiber sources have varying aspect ratios, lignin content, hemicellulose content, and crystallinity, catering to different application scenarios: wheat straw fiber is widely available and low-cost, making it suitable for packaging and disposable plastic substitutes; wood fiber offers good molding stability, making it suitable for boards and molded parts; bamboo and hemp fibers have high aspect ratios, enhancing material reinforcement. Different fiber sources can be selected based on the specific application requirements.

[0034] In one embodiment, the polycarboxylic acid crosslinking agent is at least one of citric acid, fumaric acid, malic acid, tartaric acid, and bio-based succinic acid.

[0035] Citric acid, fumaric acid, malic acid, tartaric acid, and bio-based succinic acid all contain two or more carboxyl groups, which can undergo esterification reactions with the hydroxyl groups of plant fibers under catalytic and thermo-pressing conditions, forming ester bonds that cross-link between fibers or on the fiber surface. All of the above polycarboxylic acids are aliphatic organic acids, and the ester bonds they form with the hydroxyl groups of cellulose are aliphatic ester bonds. These bonds have a high substrate specificity matching with specific aliphatic esterases and can be depolymerized by specific aliphatic esterases (Cutinase) under set enzymatic hydrolysis temperatures (45-50℃) and pH conditions (4.5-5.5).

[0036] In one embodiment, the catalyst is at least one of sodium hypophosphite and p-toluenesulfonic acid.

[0037] Sodium hypophosphite and p-toluenesulfonic acid can both serve as catalysts for the esterification reaction of polycarboxylic acids with cellulose hydroxyl groups. The introduction of catalysts makes the cross-linking reaction more complete and uniform, reducing the loss of unreacted polycarboxylic acids. Sodium hypophosphite can promote the rapid intramolecular dehydration of polycarboxylic acid cross-linking agents under high temperature and high pressure to form activated anhydrides, which then undergo a deep esterification reaction with the hydroxyl groups on the cellulose surface, assembling a dense ester bond cross-linking network in situ within the material. P-Toluenesulfonic acid, as an acidic catalyst, can increase the esterification reaction rate between carboxyl and hydroxyl groups.

[0038] Experimental materials The specific aliphatic esterase Cutinase was purchased from Novozym (China) Biotechnology Co., Ltd., model Novozym 51016.

[0039] The endo-cellulase was purchased from Novozym (China) Biotechnology Co., Ltd., model Novozym 47601.

[0040] Solid-liquid separation includes the following steps: First-stage coarse separation: centrifugation at 3000 rpm for 5 min separates large particles of undeaggregated residue; Secondary fine separation: centrifugation at 8000 rpm for 10 min to separate the recovered high-quality active plant microfibers; Three-stage purification was performed, and the mixture was centrifuged at 12,000 rpm for 15 min to separate the liquid product of plant fiber residue and the liquid product containing polycarboxylic acid monomers.

[0041] Example 1 A method for the targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials includes the following steps: S10. The ester-linked cross-linked plant fiber material is mechanically crushed into particles with a particle size of less than 5 mm to obtain the crushed ester-linked cross-linked plant fiber material. The crushed ester-linked cross-linked plant fiber material is mixed with the enzymatic hydrolysate of the composite enzyme at a mass ratio of 1:10 and stirred at 1200 rpm. The enzymatic hydrolysis reaction is carried out at a temperature of 48°C and a pH of 5.0 to obtain a depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers. The preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor. 18 U of specific aliphatic esterase and 8 U of endo-cellulase are added to each liter of the aqueous phase system. S20. The depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers is subjected to solid-liquid separation to recover the liquid phase product of plant fiber residues and the liquid phase product of polycarboxylic acid monomers, respectively. The liquid phase products are dried to obtain the recovered plant fibers and recovered polycarboxylic acid monomers.

[0042] Example 2 The difference between Example 2 and Example 1 is only that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 16U of specific aliphatic esterase and 10U of endoglucosidase are added to each liter of the aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0 for the enzymatic hydrolysate.

[0043] Example 3 The difference between Example 3 and Example 1 is only that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 20U of specific aliphatic esterase and 6U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0 for the enzymatic hydrolysate.

[0044] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 14U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0.

[0045] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 22U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0.

[0046] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 4U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0.

[0047] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 12U of endoglucosidase are added to each liter of the aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0 for the enzymatic hydrolysate.

[0048] Example 4 The difference between Example 4 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 45°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 45°C and a pH of 5.0.

[0049] Example 5 The difference between Example 5 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 55°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out at a temperature of 50°C and a pH of 5.0.

[0050] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 40°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 40°C and a pH of 5.0 for the enzymatic hydrolysate.

[0051] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 60°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out at a temperature of 55°C and a pH of 5.0.

[0052] Example 6 The difference between Example 6 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 4.5 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 4.5.

[0053] Example 7 The difference between Example 7 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.5 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.5.

[0054] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 4.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of the aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 4.0.

[0055] Comparative Example 8 The only difference between Comparative Example 8 and Example 1 is that the preparation method of the enzymatic hydrolysate of the composite enzyme is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 6.0 is prepared in an industrial reactor, and 18U of specific aliphatic esterase and 8U of endoglucosidase are added to each liter of aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 6.0.

[0056] Comparative Example 9 The only difference between Comparative Example 9 and Example 1 is that the preparation method of the enzymatic hydrolysate is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 26U of specific aliphatic esterase is added to each liter of the aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0 for the enzymatic hydrolysate.

[0057] Comparative Example 10 The only difference between Comparative Example 10 and Example 1 is that the preparation method of the enzymatic hydrolysate is as follows: an aqueous phase system with a temperature of 48°C and a pH buffer of 5.0 is prepared in an industrial reactor, and 26 U of endoglucosidated cellulase is added to each liter of the aqueous phase system; enzymatic hydrolysis is carried out under the conditions of a temperature of 48°C and a pH of 5.0 for the enzymatic hydrolysate.

[0058] The differences between Examples 1-7 and Comparative Examples 1-10 are shown in Table 1.

[0059] Table 1

[0060] Application examples The recovered plant fibers and recovered polycarboxylic acid monomers obtained by the directional enzymatic hydrolysis and closed-loop recovery method of the ester-linked plant fiber materials described in Examples 1-7 and Comparative Examples 1-10 were used as raw materials for the re-preparation of ester-linked plant fiber materials.

[0061] The ester-linked cross-linked plant fiber material is prepared by the following steps: M1. Alkali treatment of fresh bamboo fiber: crush fresh bamboo fiber through a 100-mesh sieve, place it in a 4wt% sodium hydroxide aqueous solution, stir at 60℃ for 2 hours, filter, wash with water until neutral and dry to obtain a highly active bamboo fiber matrix. M2. First, mix 50g of the highly active bamboo fiber matrix with 50g of recycled plant fiber, then mix with the crosslinking solution, and sonicate to obtain a mixture. Sonicate the mixture at 40kHz frequency and 200W power for 30 minutes. The crosslinking solution is prepared by mixing 20g of recycled polycarboxylic acid monomer crosslinking agent, 6g of sodium hypophosphite catalyst and 180g of deionized water, and stirring at room temperature for 30 minutes. M3. After the mixture is air-dried for 12 hours for preliminary dehydration, it is put into a mold and placed in a hot press. The esterification reaction is carried out by hot pressing curing treatment. The hot pressing temperature is set at 160℃, the hot pressing pressure is 12MPa, and the pressure is held for 3 minutes to obtain ester-linked plant fiber material.

[0062] Test Example 1 The recovered plant fibers and recovered polycarboxylic acid monomers obtained by the directional enzymatic hydrolysis closed-loop recovery method of the ester-linked plant fiber materials described in Examples 1-7 and Comparative Examples 1-10 were used to prepare ester-linked plant fiber materials according to steps M1-M3 in the application examples; the above operation was repeated 5 times to obtain ester-linked plant fiber materials of the 1st, 2nd, 3rd, 4th and 5th cycles.

[0063] Tensile strength tests were conducted on ester-crosslinked plant fiber materials in the 0th, 1st, 2nd, 3rd, 4th and 5th cycles according to the national standard GB / T 1040.1-2018 "Determination of tensile properties of plastics". The ester-crosslinked plant fiber material in the 0th cycle was ester-crosslinked plant fiber material that had not undergone directional enzymatic hydrolysis.

[0064] The tensile strength of the ester-linked plant fiber material after the 0th cycle was determined to be 35.2 MPa through tensile strength testing. Using this as a standard, the tensile strength retention rate was calculated for each cycle. The formula for calculating the tensile strength retention rate is as follows: Tensile strength retention rate (%) = 1 - {(Tensile strength of material in the 0th cycle - Tensile strength of material in the nth cycle) / Tensile strength of material in the 0th cycle} · 100%, where the tensile strength of the material in the 0th cycle is 35.2 MPa, and n = 1-5. Five samples were taken from each of Examples 1-7 and Comparative Examples 1-10, and the average value was taken. The test data are summarized in Table 2.

[0065] Table 2

[0066] As shown in Table 2, the ester-linked plant fiber materials prepared after five closed-loop cycles from the recycled plant fibers and recycled polycarboxylic acid monomers obtained in Examples 1-7 still maintained a high tensile strength retention rate, all greater than 85%. Specifically, the tensile strength retention rates for the first to fifth cycles in Example 1 were 97.8%, 95.6%, 93.4%, 91.6%, and 88.2%, respectively, and remained above 85% after the fifth cycle. This indicates that under the conditions of 18 U / L specific aliphatic esterase, 8 U / L endo-cellulase, enzymatic hydrolysis temperature of 48℃, and pH of 5.0, the composite enzyme can act relatively accurately on the ester-linked nodes, achieving directional depolymerization of the material while minimizing excessive damage to the main structure of the plant fiber.

[0067] In Examples 2-3, after adjusting the activities of the two enzymes, the retention rate was greater than 87% in the 5th cycle, indicating that the specific aliphatic esterase can maintain a good recycling effect within the range of 16-20 U / L and the endopeptidase can maintain a good recycling effect within the range of 6-10 U / L.

[0068] In Comparative Examples 1-4, the enzyme activity exceeded the limit, and the retention rate was less than 85% in the 5th cycle. This indicates that insufficient enzyme activity leads to incomplete depolymerization of the cross-linked network, while excessive enzyme activity may cause non-specific erosion of the fiber structure.

[0069] Compared to Example 1, Examples 4-5 and 6-7, with changes in the temperature or pH of the enzymatic hydrolysate, still maintained a retention rate of over 85% after the 5th cycle, indicating that the synergistic depolymerization effect of the complex enzyme can be well maintained within the range of 45-50℃ and pH 4.5-5.5. In Comparative Examples 5-8, the temperature or pH of the enzymatic hydrolysate exceeded the specified range, and the retention rate after the 5th cycle further decreased, indicating that an unsuitable enzymatic hydrolysis environment reduces the enzyme's selectivity for ester bonds and its depolymerization stability.

[0070] Compared to Example 1, Comparative Examples 9 and 10, using only a single enzyme, showed a retention rate of less than 70% in the fifth cycle, significantly lower than Examples 1-7. This indicates that using either a specific aliphatic esterase or an endonuclease alone is insufficient to simultaneously achieve directional ester bond breaking and fiber structure protection. The overall data from Example 1 demonstrates that this invention, through the synergistic effect of a specific aliphatic esterase and an endonuclease, combined with suitable enzyme activity, temperature, and pH conditions, can achieve directional enzymatic hydrolysis and recovery of ester-linked plant fiber materials. Simultaneously, it ensures that the recovered plant fibers and recovered polycarboxylic acid monomers maintain high mechanical properties after multiple cycles of reprocessing. This solves the technical problems of difficult degradation and recycling of plant fiber materials after disposal, and low recycling rates in existing technologies.

[0071] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for the directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials, characterized in that, Includes the following steps: Ester-linked cross-linked plant fiber materials are mixed with the enzymatic hydrolysate of a composite enzyme and subjected to enzymatic hydrolysis to obtain a depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers. The depolymerization slurry containing plant fiber residues and polycarboxylic acid monomers is subjected to solid-liquid separation to obtain recovered plant fibers and recovered polycarboxylic acid monomers. The complex enzyme includes a specific aliphatic esterase and an endoglucanase. The specific aliphatic esterase has an enzyme activity of 16-20 U / L, the endoglucanase has an enzyme activity of 8-10 U / L, the temperature of the enzymatic hydrolysate is 45-50℃, and the pH of the enzymatic hydrolysate is 4.5-5.

5.

2. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 1, characterized in that, The preparation method of the enzymatic hydrolysate of the complex enzyme is as follows: prepare an aqueous phase system with a temperature of 45-50℃ and a pH buffer between 4.5 and 5.5, and add specific aliphatic esterase and endo-cellulase to the aqueous phase system.

3. The method for targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 1, characterized in that, The mass ratio of the ester-linked plant fiber material to the enzymatic hydrolysate of the composite enzyme is 1:8-15.

4. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 1, characterized in that, The solid-liquid separation includes the following steps: First-stage coarse separation: centrifuge at 2500-3500 rpm for 4-6 minutes to separate large particles of undeaggregated residue; Secondary fine separation involves centrifugation at 7500-8500 rpm for 8-12 minutes to separate the recovered high-quality active plant microfibers. Three-stage purification: centrifugation at 10,000-15,000 rpm for 10-20 min to separate the liquid product of plant fiber residue and the liquid product containing polycarboxylic acid monomers.

5. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 1, characterized in that, The ester-linked cross-linked plant fiber material is prepared by the following steps: Alkali treatment of plant fibers yields a highly active plant fiber matrix. The highly active plant fiber matrix was mixed with a crosslinking solution and then ultrasonically treated to obtain the mixture. The mixture is poured into a mold and subjected to esterification reaction through hot pressing curing to obtain ester-linked plant fiber materials.

6. The method for targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 5, characterized in that, The crosslinking liquid comprises the following components: polycarboxylic acid crosslinking agent, catalyst, and deionized water.

7. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 5, characterized in that, The hot pressing temperature is set at 140-180℃, and the hot pressing pressure is 10-15MPa.

8. The method for targeted enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 5, characterized in that, The plant fiber is at least one of wheat straw fiber, wood fiber, bamboo fiber, and hemp fiber.

9. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 6, characterized in that, The polycarboxylic acid crosslinking agent is at least one of citric acid, fumaric acid, malic acid, tartaric acid, and bio-based succinic acid.

10. The method for directional enzymatic hydrolysis and closed-loop recovery of ester-linked plant fiber materials as described in claim 6, characterized in that, The catalyst is at least one of sodium hypophosphite and p-toluenesulfonic acid.

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