Bio-based polypropylene composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of plastic bottle materials, and particularly relates to a bio-based polypropylene composite material as well as a preparation method and application thereof. The bio-based polypropylene composite material prepared from polypropylene, modified nanocellulose, maleic anhydride grafted polypropylene, functionally modified enzyme microcapsules, antioxidant and other raw materials can be applied to the technical field of plastic bottle packaging materials, and has the advantages of good mechanical properties, excellent degradation performance, ecological environmental protection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic bottle materials, and more specifically relates to a bio-based polypropylene composite material, a preparation method thereof, and applications thereof. Background Art

[0002] Plastic products made of polypropylene are currently widely used in the packaging of food, beverages, and daily necessities due to their light weight, good chemical resistance, and manageable costs. Their mechanical properties are superior to those of polyethylene, and their production cost is lower than that of polyethylene terephthalate, making them both practical and economical. However, as the global annual production of plastics continues to grow, the environmental risks of polypropylene, the second-largest general-purpose plastic in the world, are gradually becoming apparent. Due to the chemical stability of polypropylene materials, they are difficult to degrade in the natural environment and can only be physically broken down into microplastics. After natural weathering, polypropylene microplastics migrate through soil erosion and water bodies, penetrating widely into the bottom of the ecological chain. Limited by technical issues such as the attenuation of the mechanical properties of recycled polypropylene materials, the actual global recycling rate of polypropylene plastics is low, and a large amount of discarded packaging materials continues to accumulate in the environment, posing a serious threat to human health through bioaccumulation.

[0003] Currently, the biodegradable plastics on the market mainly include polylactic acid, polybutylene succinate, and polyhydroxyalkanoates. Polylactic acid uses lactic acid as its raw material and has the characteristics of good heat resistance and biocompatibility, but its toughness is poor and degradation requires high-temperature composting; polybutylene succinate has good heat resistance, but poor storage stability and is easily hydrolyzed, resulting in a rapid decline in mechanical properties; polyhydroxyalkanoates are synthesized by microorganisms and have outstanding barrier and biodegradability, but their processing performance is narrow and they are only suitable for high-value-added fields such as medical treatment. Compared with the above completely alternative biodegradable materials, the biodegradable modification technology of polypropylene materials has attracted much attention in the industry. This is mainly because polypropylene is the second largest general-purpose plastic variety in the world, with excellent mechanical properties, a large industrial base and mature processing equipment. If the functionalization of the material can be improved through controllable blending modification or additives, there is no need to repurchase production equipment and restructure the supply chain system, thereby significantly reducing the cost of transformation technology iteration and the technical prospects are broad.

[0004] The biodegradable modification technologies of polypropylene mainly include physical blending, chemical blending and additive chemical degradation. The physical blending method introduces biomass fillers such as starch and coffee grounds and utilizes their biodegradable properties to improve the environmental friendliness of the polypropylene matrix. However, the poor interfacial compatibility between the filler and polypropylene leads to a decrease in mechanical properties and a decrease in processing performance. The chemical blending method is to add polylactic acid to the polypropylene material to improve its degradation performance, but due to compatibility issues, the addition of polylactic acid will cause a significant decrease in mechanical properties. The chemical degradation method uses photosensitizers to induce the oxidation and chain breakage of polypropylene molecular chains to form low molecular weight fragments to promote microbial metabolism. It has the advantages of controllable degradation cycles, but the process may release toxic intermediates or change the soil microbial community. Therefore, it is urgent to develop polypropylene composite materials with excellent mechanical properties, ecological sustainability and controllable degradation characteristics to fill the gaps in research and development and application in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects in mechanical properties, ecological sustainability and degradation performance of degradable polypropylene composite materials in the prior art, and to provide a bio-based polypropylene composite material with excellent performance.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned bio-based polypropylene composite material.

[0007] Another object of the present invention is to provide an application of the above-mentioned bio-based polypropylene composite material in the preparation of plastic bottle materials.

[0008] The above-mentioned purpose of the present invention is achieved through the following technical solutions: The invention provides a bio-based polypropylene composite material, which is prepared by comprising the following raw materials calculated in parts by weight: 100-500 parts of polypropylene, 5-20 parts of modified nanocellulose, 3-10 parts of maleic anhydride grafted polypropylene, 2-8 parts of functionalized modified enzyme microcapsules and 0.5-5 parts of antioxidant; wherein the modified nanocellulose is prepared by modifying nanocellulose with a silane coupling agent; and the functionalized modified enzyme microcapsules are prepared by microencapsulation after co-precipitation and encapsulation of a metal organic framework material and CRL lipase.

[0009] In the bio-based polypropylene composite material of the present invention, by adding nanocellulose modified with a silane coupling agent, the compatibility with polypropylene in the composite material is improved, thereby improving the mechanical properties of the material as a whole. The silane coupling agent constructs an organic siloxane interface layer on the surface of the nanocellulose, while reducing the surface polarity and constructing a chemical bridge with the hydrophobic polypropylene matrix, effectively suppressing particle agglomeration and interfacial stress. In addition, the nanocellulose itself has the characteristics of an aspect ratio and a rigid crystal structure, which allows the modified nanocellulose to form a dispersed reinforced network in the polypropylene group. The tensile strength of the composite material is improved through interfacial stress transfer and mechanical interlocking effects. At the same time, as a heterogeneous nucleating agent, it can significantly increase the crystallization rate of the polypropylene substrate, thereby synergistically improving the impact resistance.

[0010] Modifying the polypropylene matrix by adding maleic anhydride-grafted polypropylene to the system improves the composite's interfacial compatibility and enhances the breakability of its molecular chains. During melt blending, the anhydride groups in the maleic anhydride-grafted polypropylene form a physical crosslinked network with the pure polypropylene matrix through molecular chain entanglement and interfacial effects of the grafted segments. This improves the compatibility between the composite phases and avoids interfacial debonding defects caused by polarity differences. After coextrusion, the anhydride groups undergo hydrolysis under certain conditions to generate carboxylic acid groups. The introduction of polar groups disrupts the local crystalline regularity of the molecular chains. Simultaneously, the hydrophilic carboxylic acid groups absorb water and swell, inducing microcracks at the interface. This in turn accelerates the penetration of water molecules and the diffusion of microbial metabolites, gradually destroying the continuous network structure of the polypropylene composite and accelerating the degradation rate.

[0011] The metal-organic framework (MOF) within the microcapsule's core stabilizes the enzyme's molecular conformation through coordination. The outer nano-silica layer forms a cross-linked network with the epoxy resin, creating a thermal barrier that provides short-term resistance to polypropylene processing temperatures and ensures the enzyme maintains its initial activity during melt extrusion or injection molding. During exposure to natural environments, exposure to certain humidity conditions triggers epoxy resin swelling and hydrolysis of hydroxyl groups on the silica surface, triggering a gradient release of the enzyme, ultimately achieving controlled degradation.

[0012] The present invention improves the controllable degradation of bio-based polypropylene composite materials through the synergistic effect between the components. The anhydride groups in maleic anhydride grafted polypropylene can react with the hydroxyl groups on the surface of nanocellulose modified by silane coupling agents to form a small amount of ester bonds, providing specific catalytic sites for biological enzymes. When the microcapsules release highly active enzymes in a target environment in a timely manner, due to the specificity of the released enzymes, they can combine with a small amount of ester bonds to form enzyme-substrate complexes, significantly reducing the activation energy of the hydrolysis reaction, promoting the cleavage of ester bonds and initiating the depolymerization of polypropylene molecular chains to form low-molecular-weight fragments. The low-molecular-weight fragments are further decomposed into carbon dioxide and water by soil microorganisms, thereby improving and controlling the degradation rate of the material and eliminating microplastic residues.

[0013] Furthermore, the functionalized enzyme microcapsules contain a metal-organic framework (MOF) and a microcapsule structure. This structural design not only enables uniform dispersion within the system but also effectively transfers stress, significantly improving its mechanical properties. Furthermore, the MOF structure possesses a high specific surface area and abundant surface active sites, properties that optimize interfacial bonding between components. Through coordination, the MOF enhances load transfer, further improving mechanical properties.

[0014] Furthermore, the raw materials calculated by weight may also include 1 to 5 parts of humic acid.

[0015] Existing biodegradable polypropylene is prone to leaving microplastics in the natural environment. In addition, the use of traditional additives such as photosensitizers may release toxic intermediates or change the soil microbial community. By introducing humic acid into the polypropylene matrix in the system, the dual functions of material degradation regulation and environmental pollution prevention and control can be synergistically achieved. Due to the rich active functional groups in humic acid molecules, they can efficiently capture nitrogen-containing intermediates and dissolved organic nitrogen released during the degradation of polypropylene through coordination, complexation and hydrogen bonding. In addition, the three-dimensional network porous structure formed by humic acid self-assembly can physically intercept small molecular pollutants and inhibit their migration to the environmental medium with the leachate, thereby reducing the pollution generated by intermediates during the decomposition of polypropylene and maintaining the ecological safety of the degradation process. In addition, the quinone group of humic acid acts as an electron shuttle to promote the oxidation-enzymatic decomposition coupling reaction, forming a local high-concentration enzyme microenvironment, thereby synergistically achieving the material degradation rate regulation.

[0016] In addition, the quinone group of humic acid acts as an electron shuttle to promote the oxidation-enzymatic decomposition coupling reaction, forming a local high-concentration enzyme microenvironment, which can further promote microbial metabolism and the overall disintegration of the material. At the same time, it can also combine with degradation intermediates to form stable complexes to avoid soil nitrogen imbalance.

[0017] Furthermore, the polypropylene has a melt mass flow rate measured at 2.16 kg and 230° C. of 10-15 g / 10 min.

[0018] Preferably, the bio-based polypropylene composite material is prepared by including the following raw materials calculated by weight: 250 parts of polypropylene, 10 parts of modified nanocellulose, 6 parts of maleic anhydride grafted polypropylene, 5 parts of functionalized modified enzyme microcapsules, 3 parts of humic acid and 2 parts of antioxidant.

[0019] Furthermore, the preparation process of the modified nanocellulose is as follows: stirring the nanocellulose and the acidic reagent at 45-60°C for 60-90 minutes; centrifuging and washing until the supernatant is neutral; adding deionized water, and high-pressure homogenizing at 100-150 MPa to obtain a suspension; adding a silane coupling agent to the suspension, adjusting the pH to 5-5.5, and ultrasonically dispersing for 20-30 minutes; stirring at 40-60°C for 60-120 minutes; centrifuging; and vacuum drying to obtain the modified nanocellulose.

[0020] Furthermore, the modified nanocellulose is prepared by including the following raw materials calculated in parts by weight: 10-40 parts of nanocellulose, 50-200 parts of acidic reagent, 200-500 parts of water, and 2-5 parts of silane coupling agent.

[0021] Furthermore, the nanocellulose is one or a combination of cellulose nanocrystals and cellulose nanofibers.

[0022] Preferably, the nanocellulose is cellulose nanofibers.

[0023] Furthermore, the acidic reagent is sulfuric acid or hydrochloric acid.

[0024] Optionally, the silane coupling agent is at least one of an aminosilane coupling agent and an epoxysilane coupling agent.

[0025] Preferably, the silane coupling agent is an aminosilane coupling agent.

[0026] Nanocellulose is modified with an aminosilane coupling agent, resulting in the grafting of hydrophilic amino groups onto the nanocellulose surface. The alkyl chains enhance the compatibility between nanocellulose and polypropylene. The hydrophilic properties of the amino groups also promote water penetration, which acts as an enzyme reaction medium and substrate diffusion carrier, accelerating the contact between the enzyme and substrate, further increasing the degradation rate. Furthermore, the aminosilane coupling agent can form a more effective interfacial bond with the maleic anhydride-grafted polypropylene in the system through hydrogen bonding or physical adsorption. The synergistic compatibilization effect of the amino groups is particularly significant when polypropylene is blended with maleic anhydride-grafted polypropylene.

[0027] Furthermore, the aminosilane coupling agent is one or more of γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane.

[0028] Furthermore, the epoxy silane coupling agent is γ-glycidyloxypropyltrimethoxysilane.

[0029] Furthermore, the mass ratio of the nanocellulose to the silane coupling agent is 1:(0.125~0.25).

[0030] Furthermore, the maleic anhydride grafted polypropylene is of a type selected from the group consisting of Bynel 50E803, Exxelor PO 1020, and ADMER AT3115E.

[0031] Furthermore, the antioxidant is one or a combination of antioxidant 1010 and antioxidant 168.

[0032] Preferably, the antioxidant is antioxidant 1010.

[0033] The metal organic framework materials commonly used in the art can be used in the present invention.

[0034] Preferably, the metal organic framework material is a ZIF type. The metal organic framework material selected from the ZIF type has better stability, is easier to process, and has lower cost.

[0035] Furthermore, the metal organic framework material is ZIF-8 or ZIF-14.

[0036] Furthermore, the preparation process of the functionalized modified enzyme microcapsules is as follows: dissolving the metal source in methanol, adding CRL lipase, and stirring at room temperature for 30 to 45 minutes; dropping the ligand and stirring for 24 to 36 hours; centrifuging; washing; and drying to obtain a functionalized modified enzyme complex; dissolving the emulsifier in deionized water, adding the functionalized modified enzyme complex and nano-silica, ultrasonically dispersing for 20 to 40 minutes, and after drying, adding to epoxy resin, stirring at 30 to 50 degrees Celsius for 30 to 60 minutes, adding a curing agent, and curing; crushing and sieving to obtain functionalized modified enzyme microcapsules.

[0037] Furthermore, the functionalized modified enzyme microcapsules are prepared by including the following raw materials calculated by weight: 1 to 5 parts of CRL lipase, 5 to 30 parts of ligand, 2 to 10 parts of metal source, 100 to 500 parts of methanol, 10 to 30 parts of nano-silica, 0.5 to 3 parts of emulsifier, 5 to 20 parts of curing agent and 50 to 300 parts of epoxy resin.

[0038] Preferably, the functionalized modified enzyme microcapsules are prepared by including the following raw materials calculated by weight: 3 parts of CRL lipase, 18 parts of ligand, 8 parts of metal source, 300 parts of methanol, 20 parts of nano-silica, 2 parts of emulsifier, 12 parts of curing agent and 150 parts of epoxy resin.

[0039] Furthermore, the ligand is one or a combination of 2-methylimidazole and 2-ethylimidazole.

[0040] Preferably, the ligand is 2-methylimidazole.

[0041] Furthermore, the metal source is a zinc salt, and the zinc salt is zinc nitrate hexahydrate or zinc nitrate dihydrate.

[0042] Preferably, the metal source is zinc nitrate hexahydrate.

[0043] Furthermore, the emulsifier is one or more of polyethylene glycol 400, polyethylene glycol 600, and Tween 80.

[0044] Preferably, the emulsifier is polyethylene glycol 400.

[0045] Furthermore, the epoxy resin is Dow DER736 epoxy resin.

[0046] Furthermore, the curing agent is one or a combination of methyltetrahydrophthalic anhydride and methylhexahydrophthalic anhydride.

[0047] The present invention also provides a method for preparing a bio-based polypropylene composite material, comprising the following steps: The raw materials except the functionalized modified enzyme microcapsules are pre-mixed according to the formula, and are added to the extruder through the main feeding port. The temperature is controlled in sections, the screw speed is 150-180 rpm, the feeding rate is 10-12 kg / h, and the residence time is 1-3 minutes. The functionalized modified enzyme microcapsules are injected through the side feeding port at 80-100°C, and the mixture is extruded through the die head at 160-170°C, and then granulated by water cooling and air drying.

[0048] The present invention protects the use of the aforementioned bio-based polypropylene composite material in the preparation of plastic bottle materials.

[0049] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention prepares a bio-based polypropylene composite material by synergistically preparing nanocellulose modified with a silane coupling agent, maleic anhydride grafted polypropylene, polypropylene, and functionalized modified enzyme microcapsules. The system has good compatibility, excellent mechanical properties, and a high degradation rate, and can avoid the risk of secondary pollution caused by microplastics and traditional additives such as photosensitizers.

[0050] 2. This invention utilizes a silane-modified nanocellulose, maleic anhydride-grafted polypropylene, polypropylene, and functionalized enzyme microcapsules to create a bio-based polypropylene composite. The modified nanocellulose, modified with a silane coupling agent, significantly enhances the material's mechanical strength at low addition levels. Furthermore, the functionalized enzyme microcapsules and other components are uniformly dispersed throughout the system, forming a stable structure that reduces material density while maintaining overall performance. DETAILED DESCRIPTION

[0051] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0052] The CRL lipase used in the examples and comparative examples of the present invention was purchased from Hangzhou Chuangke Biotechnology Co., Ltd.; antioxidant 1010 and antioxidant 168 were produced by BASF.

[0053] Example 1 Preparation of a bio-based polypropylene composite material Example 1 provides a bio-based polypropylene composite material, the amounts of the components (in parts by weight, the same below) and the preparation method are as follows: S1. Preparation of modified nanocellulose: 10 parts of cellulose nanocrystals (Nanjing Tianlu, TL-003) were added to 50 parts of 64 wt% sulfuric acid and stirred in a water bath at 60°C for 60 min; the mixture was taken out and centrifuged at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the supernatant was repeatedly washed until the supernatant was neutral; the above product was taken out, 200 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 2 parts of γ-aminopropyltrimethoxysilane were added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 20 min; stirring was performed at 40°C for 120 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 12 h to obtain modified nanocellulose; S2. Preparation of functionalized modified enzyme microcapsules: 2 parts of zinc nitrate hexahydrate were dissolved in 100 parts of methanol, 1 part of CRL lipase was added, and the mixture was stirred at room temperature for 30 min; 5 parts of 2-methylimidazole was added and the mixture was stirred for 24 h; the mixture was centrifuged at 8000 rpm / min for 10 min; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 h to obtain a functionalized modified enzyme complex; 0.5 parts of emulsifier polyethylene glycol 400 was dissolved in deionized water, 10 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 20 min. After drying, the mixture was added to 50 parts of Dow DER736 epoxy resin, stirred at 30°C for 60 min, and cured by adding 5 parts of methyltetrahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules; S3. Preparation of composite material: 100 parts of polypropylene (Borstar® HE345FB), 5 parts of modified nanocellulose obtained in step S1, 3 parts of maleic anhydride grafted polypropylene (Bynel 50E803), 1 part of humic acid (NJDULY, R1606) and 0.5 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The first zone was 160°C, the second zone was 170°C, the third zone was 180°C, the fourth zone was 180°C, the die was 170°C (forced water cooling), the screw speed was 150 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute; 2 parts of the functionalized modified enzyme microcapsules obtained in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 6 h to obtain the bio-based polypropylene composite material of Example 1.

[0054] Example 2 Preparation of a bio-based polypropylene composite material Example 2 provides a bio-based polypropylene composite material, the amounts of the components and the preparation method are as follows: S1. Preparation of modified nanocellulose: 40 parts of cellulose nanofibers (Nanjing Tianlu, TL-012) were added to 200 parts of 64 wt% sulfuric acid and stirred in a water bath at 45°C for 90 min; the mixture was taken out and centrifuged at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the supernatant was repeatedly washed until the supernatant was neutral; the above product was taken out, 500 parts of deionized water were added, and high-pressure homogenization was performed at 150 MPa for 5 cycles to obtain a suspension; 5 parts of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane were added to the suspension, the pH was adjusted to 5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 30 min; the mixture was stirred at 60°C for 60 min; the solid was collected by centrifugation; and vacuum dried at 50°C for 16 h to obtain modified nanocellulose; S2. Preparation of functionalized modified enzyme microcapsules: 10 parts of zinc nitrate hexahydrate were dissolved in 500 parts of methanol, 5 parts of CRL lipase were added, and the mixture was stirred at room temperature for 45 min; 30 parts of 2-ethylimidazole were added and the mixture was stirred for 36 h; the mixture was centrifuged at 8000 rpm / min for 10 min; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 h to obtain a functionalized modified enzyme complex; 3 parts of emulsifier polyethylene glycol 600 were dissolved in deionized water, 30 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 40 min. After drying, the mixture was added to 300 parts of Dow DER736 epoxy resin, stirred at 50°C for 30 min, and cured by adding 20 parts of methylhexahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules; S3. Preparation of composite material: 500 parts of polypropylene (H110MA), 20 parts of modified nanocellulose obtained in step S1, 10 parts of maleic anhydride grafted polypropylene (Exxelor PO 1020), 5 parts of humic acid (NJDULY, R1606) and 5 parts of antioxidant 168 were pre-mixed and added to the extruder through the main feed port. The first zone was 170°C, the second zone was 180°C, the third zone was 185°C, the fourth zone was 185°C, the die was 175°C (forced water cooling), the screw speed was 180 rpm, the feed rate was 12 kg / h, and the residence time was 2 minutes; 8 parts of the functionalized modified enzyme microcapsules obtained in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 6 h to obtain the bio-based polypropylene composite material of Example 2.

[0055] Example 3 Preparation of a bio-based polypropylene composite material Example 3 provides a bio-based polypropylene composite material, the amounts of the components and the preparation method are as follows: S1. Preparation of modified nanocellulose: 16 parts of cellulose nanocrystals (Nanjing Tianlu, TL-003) were added to 80 parts of 64 wt% sulfuric acid and stirred in a water bath at 50°C for 80 min; the mixture was taken out and centrifuged at 8000 rpm / min for 20 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the washing was repeated until the supernatant was neutral; the above product was taken out, 400 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 4 parts of N-phenyl-γ-aminopropyltrimethoxysilane were added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 25 min; stirring was performed at 45°C for 80 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 10 h to obtain modified nanocellulose; S2. Preparation of functionalized modified enzyme microcapsules: 9 parts of zinc nitrate hexahydrate were dissolved in 300 parts of methanol, 4 parts of CRL lipase were added, and the mixture was stirred at room temperature for 35 minutes; 20 parts of 2-ethylimidazole were added and the mixture was stirred for 30 hours; the mixture was centrifuged at 8000 rpm / min for 15 minutes; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 hours to obtain a functionalized modified enzyme complex; 1 part of emulsifier Tween 80 was dissolved in deionized water, 15 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 30 minutes. After drying, the mixture was added to 100 parts of Dow DER736 epoxy resin, stirred at 40°C for 40 minutes, and cured by adding 10 parts of methylhexahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules. S3. Preparation of composite materials: 300 parts of polypropylene (Borstar® HE345FB), 8 parts of modified nanocellulose obtained in step S1, 5 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 2 parts of humic acid (NJDULY, R1606) and 1 part of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The first zone was 160°C, the second zone was 170°C, the third zone was 175°C, the fourth zone was 180°C, the die was 175°C (forced water cooling), the screw speed was 160 rpm, the feed rate was 12 kg / h, and the residence time was 1 minute; 4 parts of the functionalized modified enzyme microcapsules obtained in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 6 h to obtain the bio-based polypropylene composite material of Example 3.

[0056] Example 4 Preparation of a bio-based polypropylene composite material Example 4 provides a bio-based polypropylene composite material, the amounts of the components and the preparation method are as follows: S1. Preparation of modified nanocellulose: 20 parts of cellulose nanofibers (Nanjing Tianlu, TL-013) were added to 100 parts of 64 wt% sulfuric acid and stirred in a water bath at 50°C for 80 min; the mixture was taken out and placed in a centrifuge for centrifugation at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the washing was repeated until the supernatant was neutral; the above product was taken out, 500 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 5 parts of γ-aminopropyltrimethoxysilane was added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 25 min; stirring was performed at 45°C for 80 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 12 h to obtain modified nanocellulose; S2. Preparation of functionalized modified enzyme microcapsules: 8 parts of zinc nitrate hexahydrate were dissolved in 300 parts of methanol, 3 parts of CRL lipase were added, and the mixture was stirred at room temperature for 40 min; 18 parts of 2-methylimidazole were added and the mixture was stirred for 30 h; the mixture was centrifuged at 8000 rpm / min for 15 min; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 h to obtain a functionalized modified enzyme complex; 2 parts of emulsifier polyethylene glycol 400 were dissolved in deionized water, 20 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 30 min. After drying, the mixture was added to 150 parts of Dow DER736 epoxy resin, stirred at 30°C for 30 min, and cured by adding 12 parts of methyltetrahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules; S3. Preparation of composite material: 250 parts of polypropylene (Borstar® HE345FB), 10 parts of modified nanocellulose obtained in step S1, 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The first zone was 160°C, the second zone was 170°C, the third zone was 180°C, the fourth zone was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute; 5 parts of the functionalized modified enzyme microcapsules obtained in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 h to obtain the bio-based polypropylene composite material of Example 4.

[0057] Example 5 Preparation of a bio-based polypropylene composite material Example 5 provides a bio-based polypropylene composite material, which differs from Example 4 in that the silane coupling agent γ-aminopropyltrimethoxysilane of the modified nanocellulose in the bio-based polypropylene composite material formula is replaced by γ-glycidyloxypropyltrimethoxysilane, and its special steps, number of components, and conditions are the same as those in Example 4.

[0058] Example 6 Preparation of a bio-based polypropylene composite material Example 6 provides a bio-based polypropylene composite material, which differs from Example 4 in that humic acid is not added to the bio-based polypropylene composite material formula, and the other steps, component quantities, and conditions are consistent with Example 4.

[0059] Example 7 Preparation of a bio-based polypropylene composite material Example 7 provides a bio-based polypropylene composite material, which differs from Example 4 in that humic acid is not added to the bio-based polypropylene composite material formula, and is replaced by an equal amount of functionalized modified enzyme microcapsules, that is, the amount of functionalized modified enzyme microcapsules added is 8 parts, and the other steps, the number of components, and the conditions are the same as in Example 4.

[0060] Comparative Example 1 Preparation of a polypropylene composite material Comparative Example 1 provides a polypropylene composite material, which differs from Example 4 in that modified nanocellulose is not added to the polypropylene composite material formula, that is, the amounts of the components and the preparation method are as follows: S1. Preparation of functionalized modified enzyme microcapsules: 8 parts of zinc nitrate hexahydrate were dissolved in 300 parts of methanol, 3 parts of CRL lipase were added, and the mixture was stirred at room temperature for 40 min; 18 parts of 2-methylimidazole were added and the mixture was stirred for 30 h; the mixture was centrifuged at 8000 rpm / min for 15 min; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 h to obtain a functionalized modified enzyme complex; 2 parts of emulsifier polyethylene glycol 400 were dissolved in deionized water, 20 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 30 min. After drying, the mixture was added to 150 parts of Dow DER736 epoxy resin, stirred at 30°C for 30 min, and cured by adding 12 parts of methyltetrahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules. S2. Preparation of a composite material: 250 parts of polypropylene (Borstar® HE345FB), 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The first zone was 160°C, the second zone was 170°C, the third zone was 180°C, the fourth zone was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute; 5 parts of the functionalized modified enzyme microcapsules prepared in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 h to obtain the polypropylene composite material of Comparative Example 1.

[0061] Comparative Example 2 Preparation of a polypropylene composite material Comparative Example 2 provides a polypropylene composite material, which differs from Example 4 in that no silane coupling agent is used to modify the nanocellulose in the polypropylene composite material formulation, that is, the amounts of the components and the preparation method are as follows: Preparation of Nanocellulose: 100 parts of 64 wt% sulfuric acid were added to 20 parts of cellulose nanofibers (Nanjing Tianlu, TL-013), and stirred in a water bath at 50°C for 80 min. The mixture was removed and centrifuged at 8000 rpm / min for 15 min, the supernatant was discarded, and the mixture was washed with deionized water and centrifuged. The supernatant was discarded, and the washing process was repeated until the supernatant was neutral. The mixture was then vacuum dried at 60°C for 12 h to obtain nanocellulose. S2. Preparation of functionalized modified enzyme microcapsules: 8 parts of zinc nitrate hexahydrate were dissolved in 300 parts of methanol, 3 parts of CRL lipase were added, and the mixture was stirred at room temperature for 40 min; 18 parts of 2-methylimidazole were added and the mixture was stirred for 30 h; the mixture was centrifuged at 8000 rpm / min for 15 min; the mixture was washed twice with methanol; and the mixture was vacuum dried for 12 h to obtain a functionalized modified enzyme complex; 2 parts of emulsifier polyethylene glycol 400 were dissolved in deionized water, 20 parts of nano-silica and the functionalized modified enzyme complex were added, and the mixture was ultrasonically dispersed for 30 min. After drying, the mixture was added to 150 parts of Dow DER736 epoxy resin, stirred at 30°C for 30 min, and cured by adding 12 parts of methyltetrahydrophthalic anhydride. The mixture was then crushed through a 100-mesh sieve to obtain functionalized modified enzyme microcapsules; S3. Preparation of a composite material: 250 parts of polypropylene (Borstar® HE345FB), 10 parts of nanocellulose obtained in step S1, 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feeding port. The temperature of zone 1 was 160°C, zone 2 was 170°C, zone 3 was 180°C, zone 4 was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feeding rate was 10 kg / h, and the residence time was 1 minute; 5 parts of the functionalized modified enzyme microcapsules obtained in step S2 were added through the side feeding port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 h to obtain the polypropylene composite material of Comparative Example 2.

[0062] Comparative Example 3 Preparation of a polypropylene composite material Comparative Example 3 provides a polypropylene composite material, which differs from Example 4 in that maleic anhydride grafted polypropylene is not added to the polypropylene composite material formula, and the other steps, component parts, and conditions are consistent with Example 4.

[0063] Comparative Example 4 Preparation of a polypropylene composite material Comparative Example 4 provides a polypropylene composite material, which differs from Example 4 in that no functionally modified enzyme microcapsules are added to the polypropylene composite material formula, that is, the amounts of the components and the preparation method are as follows: S1. Preparation of modified nanocellulose: 20 parts of cellulose nanofibers (Nanjing Tianlu, TL-013) were added to 100 parts of 64 wt% sulfuric acid and stirred in a water bath at 50°C for 80 min; the mixture was taken out and placed in a centrifuge for centrifugation at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the washing was repeated until the supernatant was neutral; the above product was taken out, 500 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 5 parts of γ-aminopropyltrimethoxysilane was added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 25 min; stirring was performed at 45°C for 80 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 12 h to obtain modified nanocellulose; S2. Preparation of a composite material: 250 parts of polypropylene (Borstar® HE345FB), 10 parts of modified nanocellulose obtained in step S1, 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The temperature of zone 1 was 160°C, zone 2 was 170°C, zone 3 was 180°C, zone 4 was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute. After extrusion through the die at 170°C, the mixture was water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and then air-dried at 50°C for 8 h to obtain the polypropylene composite material of Comparative Example 4.

[0064] Comparative Example 5 Preparation of a polypropylene composite material Comparative Example 5 provides a polypropylene composite material, which differs from Example 4 in that the functionalized modified enzyme microcapsules in the polypropylene composite material formula are replaced with unmodified CRL lipase, that is, the amounts of the components and the preparation method are as follows: S1. Preparation of modified nanocellulose: 20 parts of cellulose nanofibers (Nanjing Tianlu, TL-013) were added to 100 parts of 64 wt% sulfuric acid and stirred in a water bath at 50°C for 80 min; the mixture was taken out and placed in a centrifuge for centrifugation at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the washing was repeated until the supernatant was neutral; the above product was taken out, 500 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 5 parts of γ-aminopropyltrimethoxysilane was added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 25 min; stirring was performed at 45°C for 80 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 12 h to obtain modified nanocellulose; S2. Preparation of a composite material: 250 parts of polypropylene (Borstar® HE345FB), 10 parts of modified nanocellulose obtained in step S1, 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The temperature of zone 1 was 160°C, zone 2 was 170°C, zone 3 was 180°C, zone 4 was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute; 5 parts of CRL lipase were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 h to obtain the polypropylene composite material of Comparative Example 5.

[0065] Comparative Example 6 Preparation of a Polypropylene Composite Material Comparative Example 6 provides a polypropylene composite material, which differs from Example 4 in that the functionalized modified enzyme microcapsules in the polypropylene composite material formula are replaced with functionalized modified enzyme complexes, that is, they are not microencapsulated. The amounts and preparation methods of the components are as follows: S1. Preparation of modified nanocellulose: 20 parts of cellulose nanofibers (Nanjing Tianlu, TL-013) were added to 100 parts of 64 wt% sulfuric acid and stirred in a water bath at 50°C for 80 min; the mixture was taken out and placed in a centrifuge for centrifugation at 8000 rpm / min for 15 min, the supernatant was discarded, deionized water was added for washing and centrifugation was performed, the supernatant was discarded, and the washing was repeated until the supernatant was neutral; the above product was taken out, 500 parts of deionized water were added, and high-pressure homogenization was performed at 100 MPa for 5 cycles to obtain a suspension; 5 parts of γ-aminopropyltrimethoxysilane was added to the suspension, the pH was adjusted to 5.5 with acetic acid, and ultrasonic dispersion was performed at 50°C for 25 min; stirring was performed at 45°C for 80 min; the solid was collected by centrifugation; and vacuum drying was performed at 60°C for 12 h to obtain modified nanocellulose; S2. Preparation of a functionalized enzyme complex: 8 parts of zinc nitrate hexahydrate were dissolved in 300 parts of methanol, 3 parts of CRL lipase were added, and the mixture was stirred at room temperature for 40 minutes; 18 parts of 2-methylimidazole were added, and stirring was continued for 30 hours; the mixture was centrifuged at 8000 rpm / min for 15 minutes; the mixture was washed twice with methanol, and vacuum dried for 12 hours to obtain a functionalized enzyme complex; S3. Preparation of a composite material: 250 parts of polypropylene (Borstar® HE345FB), 10 parts of modified nanocellulose obtained in step S1, 6 parts of maleic anhydride grafted polypropylene (ADMER AT3115E), 3 parts of humic acid (NJDULY, R1606) and 2 parts of antioxidant 1010 were pre-mixed and added to the extruder through the main feed port. The first zone was 160°C, the second zone was 170°C, the third zone was 180°C, the fourth zone was 180°C, the die was 175°C (forced water cooling), the screw speed was 170 rpm, the feed rate was 10 kg / h, and the residence time was 1 minute; 5 parts of the functionalized modified enzyme complex obtained in step S2 were added through the side feed port at 80°C, and the mixture was extruded through the die at 170°C, then water-cooled and pelletized (the die outlet was connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 h to obtain the polypropylene composite material of Comparative Example 6.

[0066] Comparative Example 7 Polypropylene plastic pellets Comparative Example 7 is pure polypropylene plastic pellets.

[0067] Comparative Example 8 Preparation of a Polylactic Acid / Polypropylene Composite Material Comparative Example 8 is a polylactic acid / polypropylene composite material, and the amount and preparation method of each component are as follows: 250 parts of polypropylene (Borstar® HE345FB), 75 parts of polylactic acid (NatureWorks 7001D), 10 parts of compatibilizer ethylene-acrylic acid copolymer (EAA 5000) and 2 parts of antioxidant 1010 are pre-mixed and added to the extruder through the feeding port, zone 1 is 160°C, zone 2 is 170°C, zone 3 is 180°C, zone 4 is 180°C, the die head is 175°C (forced water cooling), the screw speed is 170 rpm, the feeding rate is 10kg / h, and the residence time is 1 minute; then, the mixture is extruded through the die head at 170°C and water-cooled to form strands (the die head outlet is connected to a circulating water cooling jacket and cooled to <50°C), and air-dried at 50°C for 8 hours to obtain the polylactic acid / polypropylene composite material of Comparative Example 8.

[0068] Comparative Example 9 Preparation of a Polypropylene Composite Material Comparative Example 9 provides a polypropylene composite material, which differs from Example 4 in that: functionalized modified enzyme microcapsules are not added to the polypropylene composite material formula (correspondingly, step S2 of Example 4 is not performed), and an equal amount of humic acid is used instead, that is, the amount of humic acid added is 8 parts. The other steps, the number of components, and the conditions are the same as those in Example 4.

[0069] Experimental Example 1 Mechanical Properties Test of Polypropylene Material 1. Test materials: Test samples of polypropylene materials prepared in Examples 1 to 7 and Comparative Examples 1 to 9 of the present invention.

[0070] 2. Test Method: The polypropylene materials prepared in Examples 1 to 7 and Comparative Examples 1 to 9 were injection molded to form standard specimens, and the tensile strength and impact strength of the materials were tested; the tensile strength was measured according to ASTM D638, and the impact strength was measured according to ASTM D256, using the cantilever beam method.

[0071] 3. Test results: The test results are shown in Table 1.

[0072] Table 1 Mechanical properties test results of the polypropylene material of the present invention

[0073] From the results in Table 1, it can be seen that the polypropylene composite material prepared by the present invention has excellent mechanical properties, specifically tensile strength ≥33.6 MPa, impact strength ≥11.5 kJ / m 2 , among which, Example 4 performs better.

[0074] As can be seen from Table 1, the mechanical properties of the polypropylene composite material of Comparative Example 1, which does not include modified nanocellulose, are greatly reduced compared to those of Example 4. The core reason is that modified nanocellulose has extremely high specific strength and specific modulus. After being evenly dispersed in the polypropylene matrix, it can effectively transfer loads through strong interfacial bonding and bear external stress, thereby significantly improving tensile strength. During the impact process, nanocellulose can hinder crack propagation, induce plastic deformation of the matrix, and absorb impact energy. Without the addition of modified nanocellulose, the polypropylene matrix loses the support of the rigid reinforcement phase, the interaction force between the molecular chains is weak, and it is easy to slip or break when subjected to stress, resulting in a significant decrease in tensile strength. At the same time, the lack of nanocellulose's inhibitory effect on crack propagation means that impact energy cannot be effectively dissipated, and cracks tend to expand rapidly in the matrix, resulting in a significant reduction in impact strength.

[0075] The polypropylene composite material formula of Comparative Example 2 does not use a silane coupling agent to modify the nanocellulose. As a result, its mechanical properties are slightly lower than those of Example 4. Due to the reduced interfacial compatibility between the surface of the unmodified nanocellulose and the hydrophobic polypropylene matrix, it is unevenly dispersed in the matrix. At the same time, the fiber and the matrix lack chemical bonding or physical anchoring, resulting in weak interfacial bonding. When stressed, stress cannot be effectively transferred to the nanocellulose through the interface. Instead, stress concentration points are formed at the fiber-matrix interface, causing microcracks and rapid expansion. This leads to a decrease in tensile strength and impact strength.

[0076] The maleic anhydride grafted polypropylene is not added in the polypropylene composite material formula of Comparative Example 3, and its mechanical property declines more obviously compared with Example 4, and this is because the interface compatibility lacks and causes. The group on the maleic anhydride grafted polypropylene molecular chain can chemically bond or hydrogen bond with modified nano cellulose etc., can significantly improve the interface combination of non-polar polypropylene matrix and other additives. If this component is not added in the system, a weak interface is formed between modified nano cellulose and the polypropylene matrix because of polarity difference, causing stress transfer efficiency to reduce, easily causing interface debonding or crack propagation in the stretching process, and tensile strength significantly declines and impact strength drops sharply.

[0077] The polypropylene composite material formulation of Comparative Example 4 does not include functionalized enzyme microcapsules; the functionalized enzyme microcapsules in the polypropylene composite material formulation of Comparative Example 5 are replaced with unmodified CRL lipase; and the functionalized enzyme microcapsules in the polypropylene composite material formulation of Comparative Example 6 are replaced with functionalized modified enzyme complexes, i.e., they are not microencapsulated. As shown in Table 1, the tensile strength and impact strength mechanical properties of all three are reduced compared to those of Example 4. Compared to Example 4, Comparative Example 6 does not microencapsulate the functionalized modified enzyme complexes, and its tensile strength and impact strength are slightly reduced. This is because the functionalized enzyme microcapsules added in Example 4 contain a metal-organic framework structure and a microcapsule structure, which can be uniformly dispersed within the system, effectively transfer stress, and improve interfacial binding capacity, thereby improving its mechanical properties. The difference between Comparative Example 5 and Example 4 is that Comparative Example 5 directly adds unmodified CRL lipase, which has poor dispersibility in the polypropylene system and easily agglomerates, thereby reducing its mechanical properties. The difference between Comparative Example 4 and Example 4 is that Comparative Example 4 does not directly add functionalized modified enzyme microcapsules, and its tensile strength and impact strength decrease. This is because Comparative Example 4 does not add functionalized modified enzyme microcapsules, and the metal-organic framework structure and microcapsule structure of the functionalized modified enzyme microcapsules cannot disperse and transmit stress.

[0078] Comparative Example 7 uses pure, unmodified polypropylene, while Comparative Example 8 uses a polylactic acid / polypropylene composite modified with polylactic acid, a common modification method for biodegradable polypropylene in the prior art. Table 1 shows that the tensile strength of Comparative Examples 7 and 8 is significantly lower than that of Example 4. The tensile strength of the polylactic acid-modified polypropylene composite is significantly lower than that of pure polypropylene.

[0079] Comparative Example 9 differs from Example 4 in that the functionalized enzyme microcapsules are omitted from the polypropylene composite formulation (correspondingly, step S2 of Example 4 is omitted). Instead, an equal amount of humic acid, namely 8 parts of humic acid, is added. As shown in Table 1, the tensile strength and impact strength of the composite are lower than those of Example 4.

[0080] Experimental Example 2 Degradation Performance Test of Polypropylene Material 1. Test materials: Test samples of polypropylene materials prepared in Examples 1 to 7 and Comparative Examples 1 to 9 of the present invention.

[0081] 2. Test Method: The polypropylene materials prepared in Examples 1-7 and Comparative Examples 1-9 were injection molded to form standard specimens for testing. Agricultural soil (0-20 cm) was selected, and after removing stones and plant roots, it was ground and passed through a 2 mm sieve. Water was added to adjust the humidity to 70%, and the container was sealed and equilibrated for 24 hours. A standard specimen was taken, wiped dry with anhydrous ethanol, and weighed using an analytical balance to record the initial mass. A 5 cm thick layer of the adjusted humidity soil was spread across the bottom of a glass container. The specimen was placed horizontally, then covered with a 5 cm thick layer of the same soil and gently compacted. The container was covered with gauze and placed in a constant temperature and humidity incubator at 25 ± 2°C, protected from direct sunlight. The humidity at the depth of the specimen was monitored every two days using a soil moisture meter. If the humidity was below 65%, water was added to 70% using a sprayer. The samples were taken out at 30 days and 90 days respectively. The soil on the surface of the samples was carefully peeled off with tweezers. The residual particles were cleaned with a soft brush and then gently rinsed with deionized water three times. The samples were placed in a vacuum drying oven and dried to constant weight. The samples were weighed, the mass after degradation was recorded, and the weight loss rate was calculated.

[0082] 3. Test results: The test results are shown in Table 2.

[0083] Table 2 Degradation performance test results of the polypropylene material of the present invention

[0084] As shown in Table 2, the polypropylene composite material prepared in this application has excellent degradation efficiency, specifically, a 30-day weight loss rate of ≥36.2% and a 90-day weight loss rate of ≥67.3%. Among them, Example 4 performs even better.

[0085] As can be seen from Table 2, the weight loss rate of the polypropylene composite material of Comparative Example 1, in which modified nanocellulose is not added, is lower than that of Example 4. The reason is that the anhydride groups in the maleic anhydride grafted polypropylene can react with the hydroxyl groups on the surface of the modified nanocellulose to form a small amount of ester bonds, providing specific catalytic sites for the biological enzymes to form enzyme-substrate complexes, significantly reducing the activation energy of the hydrolysis reaction and increasing the degradation rate. When modified nanocellulose is not added to the formula, the activation energy of the degradation reaction increases, resulting in a decrease in the degradation rate.

[0086] In the polypropylene composite material formula of Comparative Example 2, no silane coupling agent is used to modify the nanocellulose, and the weight loss rate is slightly lower than that of Example 4. This is because when the nanocellulose is not modified with a silane coupling agent, its poor dispersibility in the polypropylene matrix, weak interfacial bonding and changes in the matrix structure together lead to a decrease in the degradation reaction rate.

[0087] In the polypropylene composite material formula of Comparative Example 3, maleic anhydride grafted polypropylene is not added, and the weight loss rate is slightly lower than that of Example 4. On the one hand, filler agglomeration, interface defects and matrix densification jointly lead to an increase in degradation resistance, which in turn leads to a significant decrease in the weight loss rate. On the other hand, because maleic anhydride grafted polypropylene is not added, the hydroxyl groups on the surface of the modified nanocellulose fail to react with it to form a small amount of ester bonds, providing specific catalytic sites for the biological enzyme, thereby increasing the reaction activation energy and slowing down the degradation rate.

[0088] The polypropylene composite material formulation of Comparative Example 4 did not include functionalized enzyme microcapsules; the functionalized enzyme microcapsules in the polypropylene composite material formulation of Comparative Example 5 were replaced with unmodified CRL lipase; and the functionalized enzyme microcapsules in the polypropylene composite material formulation of Comparative Example 6 were replaced with a functionalized enzyme complex, i.e., without microencapsulation. The weight loss rates of these composite materials were significantly reduced compared to Example 4. In particular, the 90-day weight loss rate of Comparative Example 4 was only 8.2%, demonstrating that the functionalized enzyme microcapsules of the present invention significantly contribute to improving the degradation rate of the polypropylene composite material. In the polypropylene composite material formula of Comparative Example 5, the functionalized modified enzyme microcapsules are replaced with unmodified CRL lipase; in the polypropylene composite material formula of Comparative Example 6, the functionalized modified enzyme microcapsules are replaced with functionalized modified enzyme complexes. Although the weight loss rate of Comparative Example 6 is higher than that of Comparative Example 5, both are significantly lower than that of Example 4. This is because the unmodified CRL lipase and the functionalized modified enzyme complex have lost some activity during the high-temperature granulation or injection molding process, indicating that the functionalization and microencapsulation of the lipase in the present invention can achieve active protection in a high-temperature processing environment. During the exposure stage in the natural environment, the epoxy resin swells and the hydroxyl groups on the silica surface are hydrolyzed under certain humidity conditions, triggering the gradient release of the enzyme molecules, thereby achieving its controlled release and degradation.

[0089] Comparative Example 7, a pure polypropylene material, shows a 90-day weight loss rate of only 0.9%, indicating that polypropylene has extremely poor degradation under natural conditions. Comparative Example 8, a polylactic acid-modified polypropylene / polypropylene composite, is the primary modification method for degradable polypropylene in the prior art. Table 2 shows that its degradation rate is significantly improved compared to pure polypropylene. However, Table 1 shows that the addition of polylactic acid significantly reduces the mechanical properties of the polylactic acid / polypropylene composite.

[0090] Furthermore, Example 4 demonstrated superior degradation performance compared to Example 7. This is because the quinone groups in humic acid act as electron shuttles to promote the coupled oxidation-enzymatic degradation reaction, creating a localized high-enzyme microenvironment and synergistically regulating the degradation rate. However, the addition of functionalized enzyme microcapsules containing only a single component, without synergistic action with humic acid, resulted in slightly reduced degradation performance.

[0091] In Comparative Example 9, when the functionalized enzyme microcapsules were replaced with an equal amount of humic acid, the degradation performance was significantly reduced. This phenomenon further confirms that the functionalized enzyme microcapsules are the core functional unit that dominates the degradation efficiency and also demonstrates the synergistic mechanism of humic acid and functionalized enzyme microcapsules.

[0092] In summary, the present invention synthesizes a bio-based polypropylene composite material by synergistically combining nanocellulose modified with a silane coupling agent, maleic anhydride-grafted polypropylene, polypropylene, and functionalized enzyme microcapsules. The silane coupling of the modified nanocellulose significantly enhances the material's mechanical strength at low addition levels. Furthermore, the functionalized enzyme microcapsules and other components are uniformly dispersed throughout the system, forming a stable structure that reduces material density while maintaining overall performance.

[0093] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A bio-based polypropylene composite material, characterized in that: The invention comprises the following raw materials calculated in parts by weight: 100-500 parts of polypropylene, 5-20 parts of modified nanocellulose, 3-10 parts of maleic anhydride grafted polypropylene, 2-8 parts of functionalized modified enzyme microcapsules and 0.5-5 parts of antioxidant; wherein the modified nanocellulose is prepared by modifying nanocellulose with a silane coupling agent; and the functionalized modified enzyme microcapsules are prepared by microencapsulation after co-precipitation and encapsulation of a metal organic framework material and CRL lipase.

2. The bio-based polypropylene composite material according to claim 1, characterized in that: The raw materials calculated by weight may further include 1 to 5 parts of humic acid.

3. The bio-based polypropylene composite material according to claim 1, characterized in that: The functionalized modified enzyme microcapsules are prepared from the following raw materials calculated by weight: 1 to 5 parts of CRL lipase, 5 to 30 parts of ligand, 2 to 10 parts of metal source, 100 to 500 parts of methanol, 10 to 30 parts of nano-silicon dioxide, 0.5 to 3 parts of emulsifier, 5 to 20 parts of curing agent and 50 to 300 parts of epoxy resin.

4. The bio-based polypropylene composite material according to claim 1, characterized in that: The modified nanocellulose is prepared by including the following raw materials calculated in parts by weight: 10-40 parts of nanocellulose, 50-200 parts of acidic reagent, 200-500 parts of water, and 2-5 parts of silane coupling agent.

5. The bio-based polypropylene composite material according to claim 1, characterized in that: The silane coupling agent is at least one of an aminosilane coupling agent and an epoxysilane coupling agent.

6. The bio-based polypropylene composite material according to claim 1, characterized in that: The preparation method of the modified nanocellulose comprises the following steps: Nanocellulose and an acidic reagent are stirred at 45-60°C for 60-90 min; centrifuged and washed until the neutral supernatant is neutral; deionized water is added and high-pressure homogenized at 100-150 MPa to obtain a suspension; a silane coupling agent is added to the suspension, the pH is adjusted to 5-5.5, and ultrasonically dispersed for 20-30 min; stirred at 40-60°C for 60-120 min; centrifuged and vacuum dried to obtain modified nanocellulose.

7. The bio-based polypropylene composite material according to claim 1, characterized in that: The preparation method of the functionalized modified enzyme microcapsules comprises the following steps: The metal source was dissolved in methanol, CRL lipase was added, and the mixture was stirred at room temperature for 30 to 45 minutes; the ligand was added and stirred for 24 to 36 hours; the mixture was centrifuged, washed, and dried to obtain a functionalized modified enzyme complex; the emulsifier was dissolved in deionized water, the functionalized modified enzyme complex and nano-silica were added, ultrasonically dispersed for 20 to 40 minutes, and after drying, the mixture was added to epoxy resin, stirred at 30 to 50°C for 30 to 60 minutes, a curing agent was added, and the mixture was cured; the mixture was crushed and sieved to obtain functionalized modified enzyme microcapsules.

8. The bio-based polypropylene composite material according to claim 3, characterized in that: The emulsifier is one or more of polyethylene glycol 400, polyethylene glycol 600 and Tween 80.

9. A method for preparing the bio-based polypropylene composite material according to any one of claims 1 to 8, characterized in that: The steps include: The raw materials except the functionalized modified enzyme microcapsules are pre-mixed according to the formula, and are added to the extruder through the main feeding port. The temperature is controlled in sections, the screw speed is 150-180 rpm, the feeding rate is 10-12 kg / h, and the residence time is 1-3 minutes. The functionalized modified enzyme microcapsules are injected through the side feeding port at 80-100°C, and after being extruded through the die head at 160-170°C, water-cooled strand granulation is performed, and air drying is performed.

10. Use of the bio-based polypropylene composite material according to claims 1 to 8 in the preparation of plastic bottle materials.

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