Biodegradable polypropylene nonwoven fabric and method for producing the same

Abstract

The application discloses a kind of biodegradable polypropylene non-woven fabrics and preparation method thereof, belong to biodegradable polypropylene non-woven fabric technical field, the preparation method includes: preparation degradable master batch, preparation anti-aging master batch, mix, spinning draft;The preparation degradable master batch, polypropylene, polycaprolactone, erucic acid amide, maleic anhydride grafted polypropylene, first modified cellulose nanocrystal, second modified cellulose nanocrystal, stearic acid, 3-aminopropyl trimethoxysilane are added into high-speed mixer and mixed uniformly, then melt extrusion, granulation is carried out in twin-screw extruder, and degradable master batch is obtained;The application can improve the degradability of biodegradable polypropylene non-woven fabric, while improving the strength of non-woven fabric, elongation at break, spinnability, ultraviolet resistance, high temperature resistance, aging resistance.

Description

Technical Field

[0001] This invention relates to the field of biodegradable polypropylene nonwoven fabric technology, specifically to a biodegradable polypropylene nonwoven fabric and its preparation method. Background Technology

[0002] Polypropylene nonwoven fabrics are used in many fields such as medical care, hygiene, protection, and daily life, bringing many conveniences to people's lives. However, the waste of polypropylene nonwoven fabrics takes hundreds of years to completely decompose under natural conditions, which places a great burden on the environment and is a pain point in the development of the polypropylene nonwoven fabric industry.

[0003] Bio-based plastics are plastic-like products made from biomass such as corn, sugarcane, bamboo, or other plant cellulose. They are divided into biodegradable and non-biodegradable types. Bio-based plastics are made from renewable carbon sources in nature, which is different from the carbon chain of traditional petroleum-based plastics. Bio-based plastics can reduce the consumption of petrochemical products by the plastics industry and reduce the environmental pollution caused by petrochemical products during the manufacturing process, thus achieving the dual benefits of saving petroleum resources and protecting the environment.

[0004] To improve the biodegradability of nonwoven fabrics, more and more nonwoven fabric manufacturers are starting to use biodegradable bio-based plastics as raw materials. Among them, the most commonly used biodegradable bio-based plastic is polylactic acid (PLA). PLA degrades through bulk erosion. Specifically, when PLA is immersed in an aqueous medium or implanted in the body, the aqueous medium penetrates into the PLA, causing the PLA molecular chains to loosen, the ester bonds to hydrolyze, the molecular weight to decrease, and it gradually degrades into oligomers. In addition, the terminal carboxyl groups in PLA catalyze the hydrolysis of PLA. As hydrolysis proceeds, the number of terminal carboxyl groups increases, the degradation rate accelerates, and an autocatalytic effect is produced.

[0005] As can be seen from the degradation principle of polylactic acid (PLA) described above, the degradation conditions of PLA are harsh, and the degradation rate is greatly affected by temperature, moisture, acidity, alkalinity, etc. It can only achieve rapid degradation under specific conditions. Otherwise, because PLA responds to photo-oxidative degradation much more readily than traditional petroleum-based plastics, it is easier to form PLA microplastics in a short period of time. PLA microplastics cannot be completely degraded under natural water and soil conditions. If PLA microplastics are not treated in time, they will continue to accumulate in the environment, causing environmental pollution.

[0006] To achieve complete degradation of polylactic acid (PLA), composting is required. However, composting necessitates separating PLA from other waste and treating it separately, which significantly increases the costs associated with waste sorting and composting. Other commonly used biodegradable bio-based plastics, such as polybutylene terephthalate (PET) and polyhydroxyalkanoates (PHA), also face the same degradation challenges as PLA.

[0007] According to the "Research Report on Environmental Impact Assessment and Policy Support of Biodegradable Plastics" jointly released by the School of Environment of Tsinghua University and Sinopec on September 26, 2022, 97% of biodegradable plastic products are incinerated or landfilled after disposal, 3.1% are directly leaked into the environment after disposal, 0.006% undergo anaerobic fermentation after disposal, and only 0.001% are industrial composted after disposal. Therefore, although biodegradable bio-based plastics are used in the preparation of non-woven fabrics in order to protect the environment, the high degradation requirements and costs of existing biodegradable bio-based plastics, coupled with the imperfect existing degradation treatment processes, mean that non-woven fabrics made from biodegradable bio-based plastics not only cannot be completely degraded, but also aggravate microplastic pollution in the environment.

[0008] Furthermore, experiments revealed the following problems with nonwoven fabrics made from existing biodegradable bio-based plastics: The preparation of nonwoven fabrics requires compounding biodegradable bio-based plastics with other materials, such as polypropylene and polyethylene. However, the poor compatibility between biodegradable bio-based plastics and materials like polypropylene and polyethylene affects the strength, elongation at break, and spinnability of the prepared nonwoven fabric; the poor UV resistance of biodegradable bio-based plastics affects the UV resistance of the prepared nonwoven fabric; the poor high-temperature resistance of biodegradable bio-based plastics affects the high-temperature resistance of the prepared nonwoven fabric; and the poor aging resistance of biodegradable bio-based plastics affects the aging resistance of the prepared nonwoven fabric. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a biodegradable polypropylene nonwoven fabric and its preparation method, which can improve the biodegradability of the biodegradable polypropylene nonwoven fabric while also improving the nonwoven fabric's strength, elongation at break, spinnability, UV resistance, high temperature resistance, and aging resistance.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0011] A method for preparing biodegradable polypropylene nonwoven fabric includes: preparing biodegradable masterbatch, preparing anti-aging masterbatch, mixing, and spinning and stretching.

[0012] The preparation of the biodegradable masterbatch involves adding polypropylene, polycaprolactone, erucamide, maleic anhydride-grafted polypropylene, first modified cellulose nanocrystals, second modified cellulose nanocrystals, stearic acid, and 3-aminopropyltrimethoxysilane into a high-speed mixer and mixing them evenly. Then, the mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion and pelletizing to obtain the biodegradable masterbatch.

[0013] In the preparation of the biodegradable masterbatch, the weight ratio of polypropylene, polycaprolactone, erucamide, maleic anhydride-grafted polypropylene, first modified cellulose nanocrystals, second modified cellulose nanocrystals, stearic acid, and 3-aminopropyltrimethoxysilane is 30-40:8-10:10-12:5-7:4-5:3-5:2-3:0.5-1.

[0014] The screw temperature of the twin-screw extruder is 190-220℃;

[0015] The polypropylene has a melt flow index of 35-40 g / 10 min at 230℃ and 2.16 kg.

[0016] The maleic anhydride-grafted polypropylene has a melt index of 100-120 g / 10 min at 230°C and 2.16 kg.

[0017] The preparation method of the first modified cellulose nanocrystals is as follows: cellulose nanocrystals, 3-glycidylpropyltrimethoxysilane, and tetrahydrofuran are mixed and ultrasonically dispersed. The ultrasonic dispersion frequency is controlled at 20-30 kHz for 30-40 min. Then, while stirring at 200-400 rpm at 60-70℃, hydrochloric acid aqueous solution is added dropwise. After the addition is completed, stirring is continued for 7-8 h. The mixture is then centrifuged at 7000-8000 rpm for 8-10 min. The precipitate is then washed with tetrahydrofuran 3-4 times and freeze-dried at -40℃ to -30℃ for 20-25 h to obtain the first modified cellulose nanocrystals.

[0018] In the preparation of the first modified cellulose nanocrystals, the weight-volume ratio of cellulose nanocrystals, 3-glycidylpropyltrimethoxysilane, tetrahydrofuran, and hydrochloric acid aqueous solution is 9-10g:100-110mL:1200-1500mL:45-50mL.

[0019] The concentration of the hydrochloric acid aqueous solution is 38-40 g / L;

[0020] The hydrochloric acid aqueous solution was added at a rate of 5-8 mL / min.

[0021] The preparation method of the second modified cellulose nanocrystals is as follows: cellulose nanocrystals, hexadecyltrimethoxysilane, anhydrous ethanol, and water are ultrasonically dispersed at a frequency of 20-30 kHz for 20-30 min. Then, while stirring at 200-400 rpm at 60-70℃, hydrochloric acid aqueous solution is added dropwise until the pH reaches 5.5-6. Stirring continues for 2.5-3.5 h. The mixture is then centrifuged at 7000-8000 rpm for 8-10 min. The precipitate is then washed 3-4 times with anhydrous ethanol and 3-4 times with water. Finally, it is freeze-dried at a temperature of -40℃ to -30℃ for 20-25 h to obtain the second modified cellulose nanocrystals.

[0022] The second modified cellulose nanocrystal preparation method involves a weight-to-volume ratio of cellulose nanocrystals, hexadecyltrimethoxysilane, anhydrous ethanol, and water of 9-10 g: 20-25 mL: 350-400 mL: 60-70 mL.

[0023] The concentration of the hydrochloric acid aqueous solution is 38-40 g / L;

[0024] The hydrochloric acid aqueous solution was added at a rate of 1-2 mL / min.

[0025] The preparation method of the cellulose nanocrystals in the first and second modified cellulose nanocrystals is as follows: microcrystalline cellulose, citric acid aqueous solution, and sulfuric acid aqueous solution are mixed and stirred at 75-85℃ with a stirring speed of 200-400 rpm for 7-8 hours. Sodium hydroxide aqueous solution is added to adjust the pH to 7. The mixture is then centrifuged at a speed of 9000-10000 rpm for 8-10 minutes. The precipitate is then washed with water 3-4 times and freeze-dried at a temperature of -40℃ to -30℃ for 20-25 hours to obtain cellulose nanocrystals.

[0026] In the preparation of the first and second modified cellulose nanocrystals, the weight-volume ratio of microcrystalline cellulose, citric acid aqueous solution, and sulfuric acid aqueous solution is 90-100g:3200-3300mL:400-600mL.

[0027] The concentration of citric acid aqueous solution is 1000-1200 g / L;

[0028] The concentration of the sulfuric acid aqueous solution is 800-900 g / L;

[0029] The concentration of the sodium hydroxide aqueous solution is 300-350 g / L;

[0030] The preparation of the anti-aging masterbatch involves, by weight, adding polypropylene, filler, light stabilizer, antioxidant, polyethylene wax, stearic acid, and 3-aminopropyltrimethoxysilane into a high-speed mixer and mixing them evenly. Then, the mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion and pelletizing. The screw temperature is controlled at 200-230℃ to obtain the anti-aging masterbatch.

[0031] In the preparation of the anti-aging masterbatch, the weight ratio of polypropylene, filler, light stabilizer, antioxidant, polyethylene wax, stearic acid, and 3-aminopropyltrimethoxysilane is 70-80:7-8:6-7:3-4:3-4:1.5-2:1-2.

[0032] The polypropylene has a melt flow index of 35-40 g / 10 min at 230℃ and 2.16 kg.

[0033] The light stabilizer is one or more of light stabilizer 2020, light stabilizer 119, and light stabilizer 770;

[0034] The method for preparing the filler includes: silane modification, citric acid grafting, and calcium ionization;

[0035] The silane modification involves ultrasonically dispersing mica powder, 3-aminopropyltrimethoxysilane, anhydrous ethanol, and water at a frequency of 20-30 kHz for 20-30 min, followed by stirring at 40-50 °C for 4-5 h, centrifugation at 6000-7000 rpm for 5-7 min, washing the precipitate 3-4 times with anhydrous ethanol, washing it 3-4 times with water, and then freeze-drying at -40 °C to -30 °C for 20-25 h to obtain silane-modified mica powder.

[0036] In the silane modification, the weight-to-volume ratio of mica powder, 3-aminopropyltrimethoxysilane, anhydrous ethanol, and water is 50-60g:60-80mL:600-700mL:100-120mL.

[0037] The particle size of the mica powder is 100-200 nm;

[0038] The citric acid grafting process involves mixing citric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, and water in an ice-water bath, stirring at 100-300 rpm for 10-20 minutes, followed by ultrasonic oscillation at a frequency of 20-30 kHz for 1-1.5 hours. Then, silane-modified mica powder is added, and the mixture is stirred at 100-300 rpm at 20-40°C for 4-5 hours. The mixture is then centrifuged at 6000-7000 rpm for 5-7 minutes. After washing the precipitate 3-4 times with water, it is freeze-dried at -40°C to -30°C for 20-25 hours to obtain the primary filler.

[0039] In the citric acid grafting process, the weight-to-volume ratio of citric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, water, and silane-modified mica powder is 25-30g:25-30g:25-30g:700-1000mL:60-65g.

[0040] The calcium ionization process involves mixing the primary packing material, calcium chloride, and water, stirring at 100-300 rpm for 10-15 minutes at 20-40°C, centrifuging at 6000-7000 rpm for 5-7 minutes, and freeze-drying at -40°C to -30°C for 20-25 hours to obtain the packing material.

[0041] In the calcium ionization process, the weight-to-volume ratio of primary filler, calcium chloride, and water is 80-100g:10-12g:500-600mL.

[0042] The mixing process involves adding polypropylene, biodegradable masterbatch, and anti-aging masterbatch to a high-speed mixer and mixing them evenly to obtain a mixture.

[0043] In the mixture, the weight ratio of polypropylene, biodegradable masterbatch, and anti-aging masterbatch is 96-97.4:0.6-1.5:2-2.5.

[0044] The polypropylene has a melt flow index of 35-40 g / 10 min at 230℃ and 2.16 kg.

[0045] The spinning and drawing process involves adding the mixture to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion, then filtering through a filter, metering by a metering pump, and spinning into continuous fibers through a die. After cold air drawing, the fibers are evenly spread on a mesh belt to form a web, and then passed through upper and lower pressure rollers and hot-rolled by a hot rolling mill to obtain biodegradable polypropylene nonwoven fabric.

[0046] The screw temperature is 230-240℃, the metering pump speed is 5-8 rpm, and the die temperature is 250-270℃; the cold air temperature during cold air drawing is 10-15℃, the conveyor belt speed is 400-450 m / min, the hot rolling mill roll temperature is 150-170℃, and the pressure is 100-120 daN / cm.

[0047] A biodegradable polypropylene nonwoven fabric prepared by the aforementioned method.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] (1) The biodegradable polypropylene nonwoven fabric prepared by the present invention has a different degradation principle from that of conventional biodegradable nonwoven fabric. Conventional biodegradable nonwoven fabric adopts a combination of chemical degradation and biodegradation during degradation. In the early stage of degradation, chemical degradation is carried out. Under light or heat aging, the molecular chains break down to form low molecular weight degradation products with a molecular weight of less than 5000 Daltons, thereby ensuring that the molecular weight is low enough for biodegradation. In the later stage of degradation, microbial degradation is carried out. The digestive enzymes secreted by microorganisms in the environment can convert the low molecular weight degradation products into carbon dioxide, water, and biomass. Therefore, conventional biodegradable nonwoven fabric has poor UV resistance and high temperature resistance. The biodegradable polypropylene nonwoven fabric prepared by this invention forms a biofilm composed of microorganisms on its surface under anaerobic conditions. This biofilm is formed by acids and enzymes secreted by the microorganisms. The enzymes make the polypropylene nonwoven fabric "hydrophilic," promoting its hydrolysis. As the microorganisms secrete enzymes and water, the accumulation of water expands the polypropylene nonwoven fabric chains, allowing the microorganisms to consume the polypropylene chains from start to finish, breaking them down into amino acids, fatty acids, and sugars. The microorganisms also secrete signaling molecules to attract other microorganisms, creating a feeding effect. The final residues of this degradation process are only biogas and humic matter (organic matter), with no toxins or microplastic residues. The biogas can be collected and used to form clean biofuel. Furthermore, the biodegradable polypropylene nonwoven fabric prepared by this invention has strong degradation capabilities, capable of biodegrading in landfills and naturally decomposing under composting conditions, achieving natural degradation within a few years.

[0050] (2) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the biodegradability of the biodegradable polypropylene nonwoven fabric. The biodegradability of the polypropylene nonwoven fabric prepared by the present invention was tested according to GB / T 33797-2017 standard. The biodegradability was 0.89-1.08% after 15 days, 2.80-3.03% after 30 days, 4.60-5.25% after 38 days, and 5.28-5.65% after 45 days.

[0051] (3) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the strength and elongation at break of the biodegradable polypropylene nonwoven fabric. The biodegradable polypropylene nonwoven fabric prepared by the present invention has a CD strength of 48.0-49.9 N / 5cm, an MD strength of 92.8-95.2 N / 5cm, a CD elongation of 85.2-95.1%, and an MD elongation of 89.3-96.7%.

[0052] (4) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the spinnability of the biodegradable polypropylene nonwoven fabric. The biodegradable polypropylene nonwoven fabric prepared by the present invention spins normally during spinning and drawing.

[0053] (5) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the UV resistance of the biodegradable polypropylene nonwoven fabric. The biodegradable polypropylene nonwoven fabric prepared by the present invention is tested for UV resistance according to ASTM G154, specifically using a UVB-313 ultraviolet lamp with an irradiance of 28W / m. 2 After 8 hours at a blackboard temperature of 70℃, 4 hours at a condensation temperature of 50℃, and 210 hours at a blackboard temperature of 50℃, the strength retention rate of CD was 81.24-84.11%, the strength retention rate of MD was 91.41-94.05%, the elongation retention rate of CD was 56.80-59.07%, and the elongation retention rate of MD was 60.28-63.76%.

[0054] (6) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the high temperature resistance of the biodegradable polypropylene nonwoven fabric. When the biodegradable polypropylene nonwoven fabric prepared by the present invention is subjected to high temperature treatment at 60°C for 30 days, the CD strength retention rate is 79.51-82.89%, the MD strength retention rate is 80.20-89.12%, the CD elongation retention rate is 42.77-60.31%, and the MD elongation retention rate is 47.52-58.31%.

[0055] (7) The preparation method of the biodegradable polypropylene nonwoven fabric of the present invention can improve the aging resistance of the biodegradable polypropylene nonwoven fabric. When the biodegradable polypropylene nonwoven fabric prepared by the present invention is aged at room temperature for 90 days, the CD strength retention rate is 87.53-89.78%, the MD strength retention rate is 88.36-92.10%, the CD elongation retention rate is 80.26-87.14%, and the MD elongation retention rate is 82.12-84.87%. Attached Figure Description

[0056] Figure 1 These are microscopic images of the polypropylene nonwoven fabric after 45 days of degradation experiment in Experiment Example 6 and after 45 days of exposure to room temperature air. Detailed Implementation

[0057] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0058] Example 1

[0059] A method for preparing biodegradable polypropylene nonwoven fabric, specifically comprising:

[0060] 1. Preparation of biodegradable masterbatch: By weight, 30 parts polypropylene, 8 parts polycaprolactone, 10 parts erucamide, 5 parts maleic anhydride-grafted polypropylene, 4 parts first modified cellulose nanocrystals, 3 parts second modified cellulose nanocrystals, 2 parts stearic acid, and 0.5 parts 3-aminopropyltrimethoxysilane were added to a high-speed mixer and mixed evenly. Then, the mixture was added to a twin-screw extruder with an aspect ratio of 40:1 for melt extrusion and pelletizing. The screw temperature was controlled at 190℃ to obtain biodegradable masterbatch.

[0061] The polypropylene has a melt flow index of 35 g / 10 min at 230°C and 2.16 kg.

[0062] The maleic anhydride-grafted polypropylene has a melt index of 100 g / 10 min at 230°C and 2.16 kg.

[0063] The preparation method of the first modified cellulose nanocrystals is as follows: 9g of cellulose nanocrystals, 100mL of 3-glycidylpropyltrimethoxysilane, and 1200mL of tetrahydrofuran are mixed and ultrasonically dispersed. The ultrasonic dispersion frequency is controlled at 20kHz for 30min. Then, while stirring at 200rpm at 60℃, 45mL of 38g / L hydrochloric acid aqueous solution is added dropwise at a rate of 5mL / min. After the addition is completed, stirring is continued for 7h. The mixture is then centrifuged at 7000rpm for 8min. The precipitate is then washed three times with tetrahydrofuran and freeze-dried at -40℃ for 20h to obtain the first modified cellulose nanocrystals.

[0064] The preparation method of the second modified cellulose nanocrystals is as follows: 9g of cellulose nanocrystals, 20mL of hexadecyltrimethoxysilane, 350mL of anhydrous ethanol, and 60mL of water are ultrasonically dispersed at a frequency of 20kHz for 20min. Then, while stirring at 200rpm at 60℃, a 38g / L hydrochloric acid aqueous solution is added dropwise at a rate of 1mL / min until the pH reaches 5.5. After stirring for 2.5h, the mixture is centrifuged at 7000rpm for 8min. The precipitate is then washed three times with anhydrous ethanol and three times with water. Finally, the mixture is freeze-dried at -40℃ for 20h to obtain the second modified cellulose nanocrystals.

[0065] The preparation method of the cellulose nanocrystals in the first and second modified cellulose nanocrystals is as follows: 90g of microcrystalline cellulose, 3200mL of citric acid aqueous solution with a concentration of 1000g / L, and 400mL of sulfuric acid aqueous solution with a concentration of 800g / L are mixed and stirred at 75℃ with a stirring speed of 200rpm for 7h. A sodium hydroxide aqueous solution with a concentration of 300g / L is added to adjust the pH to 7. The mixture is then centrifuged at a speed of 9000rpm for 8min. The precipitate is then washed with water three times and freeze-dried at a temperature of -40℃ for 20h to obtain cellulose nanocrystals.

[0066] 2. Preparation of anti-aging masterbatch: By weight, 70 parts polypropylene, 7 parts filler, 6 parts light stabilizer, 3 parts antioxidant, 3 parts polyethylene wax, 1.5 parts stearic acid, and 1 part 3-aminopropyltrimethoxysilane are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion and pelletizing. The screw temperature is controlled at 200℃ to obtain the anti-aging masterbatch.

[0067] The polypropylene has a melt flow index of 35 g / 10 min at 230°C and 2.16 kg.

[0068] The light stabilizer is light stabilizer 2020;

[0069] The method for preparing the filler is as follows:

[0070] (1) Silane modification: 50g mica powder, 60mL 3-aminopropyltrimethoxysilane, 600mL anhydrous ethanol and 100mL water were ultrasonically dispersed. The ultrasonic dispersion frequency was controlled at 20kHz and the time was 20min. Then, the mixture was stirred at 40℃ for 4h and centrifuged. The centrifugation speed was controlled at 6000rpm and the time was 5min. The precipitate was washed 3 times with anhydrous ethanol and 3 times with water. Then, the mixture was freeze-dried. The freeze-drying temperature was controlled at -40℃ and the time was 20h to obtain silane-modified mica powder.

[0071] The mica powder has a particle size of 100 nm;

[0072] (2) Citric acid grafting: In an ice-water bath, 25g of citric acid, 25g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 25g of N-hydroxysuccinimide and 700mL of water were mixed and stirred at 100rpm for 10min. Ultrasonic oscillation was then performed at a frequency of 20kHz for 1h. Then, 60g of silane-modified mica powder was added and stirred at 100rpm for 4h at 20℃. The mixture was then centrifuged at 6000rpm for 5min. The precipitate was washed with water three times and then freeze-dried at -40℃ for 20h to obtain the primary filler.

[0073] (3) Calcium ionization: Mix 80g of primary packing material, 10g of calcium chloride and 500mL of water, stir at 100rpm for 10min at 20℃, centrifuge at 6000rpm for 5min, freeze dry at -40℃ for 20h to obtain the packing material.

[0074] 3. Mixing: By weight, add 97.4 parts polypropylene, 0.6 parts biodegradable masterbatch, and 2 parts anti-aging masterbatch to a high-speed mixer and mix evenly to obtain a mixture;

[0075] The polypropylene has a melt flow index of 35 g / 10 min at 230°C and 2.16 kg.

[0076] 4. Spinning and drawing: The mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion, then filtered by a filter, metered by a metering pump, and spun into continuous fibers through a die; after cold air drawing, the fibers are evenly spread on a mesh belt to form a web, and then passed through upper and lower pressure rollers and hot rolled by a hot rolling mill to obtain biodegradable polypropylene nonwoven fabric.

[0077] The screw temperature is 230℃, the metering pump speed is 5rpm, and the die temperature is 250℃; the cold air temperature during cold air drawing is 10℃, the mesh belt speed is 400m / min, the roll temperature of the hot rolling mill is 150℃, and the pressure is 100daN / cm.

[0078] This embodiment also provides a biodegradable polypropylene nonwoven fabric prepared by the aforementioned method, with a basis weight of 32 gsm.

[0079] Example 2

[0080] A method for preparing biodegradable polypropylene nonwoven fabric, specifically comprising:

[0081] 1. Preparation of biodegradable masterbatch: By weight, 35 parts polypropylene, 9 parts polycaprolactone, 11 parts erucamide, 6 parts maleic anhydride-grafted polypropylene, 4.5 parts first modified cellulose nanocrystals, 4 parts second modified cellulose nanocrystals, 2.5 parts stearic acid, and 0.7 parts 3-aminopropyltrimethoxysilane were added to a high-speed mixer and mixed evenly. Then, the mixture was added to a twin-screw extruder with an aspect ratio of 40:1 for melt extrusion and pelletizing. The screw temperature was controlled at 200℃ to obtain biodegradable masterbatch.

[0082] The polypropylene has a melt flow index of 35 g / 10 min at 230°C and 2.16 kg.

[0083] The maleic anhydride-grafted polypropylene has a melt index of 100 g / 10 min at 230°C and 2.16 kg.

[0084] The preparation method of the first modified cellulose nanocrystals is as follows: 9.5g of cellulose nanocrystals, 105mL of 3-glycidylpropyltrimethoxysilane, and 1400mL of tetrahydrofuran are mixed and ultrasonically dispersed. The ultrasonic dispersion frequency is controlled at 25kHz and the time is 35min. Then, while stirring at 300rpm at 65℃, 48mL of 39g / L hydrochloric acid aqueous solution is added dropwise at a rate of 7mL / min. After the addition is completed, stirring is continued for 7.5h. The mixture is then centrifuged at 7500rpm for 9min. The precipitate is then washed three times with tetrahydrofuran and freeze-dried at -35℃ for 22h to obtain the first modified cellulose nanocrystals.

[0085] The preparation method of the second modified cellulose nanocrystals is as follows: 9.5g of cellulose nanocrystals, 22mL of hexadecyltrimethoxysilane, 370mL of anhydrous ethanol, and 65mL of water are ultrasonically dispersed at a frequency of 25kHz for 25min. Then, while stirring at 300rpm at 65℃, a 39g / L hydrochloric acid aqueous solution is added dropwise at a rate of 1mL / min until the pH reaches 5.5. After stirring for 3h, the mixture is centrifuged at 7500rpm for 9min. The precipitate is then washed three times with anhydrous ethanol and three times with water. Finally, the mixture is freeze-dried at -35℃ for 22h to obtain the second modified cellulose nanocrystals.

[0086] The preparation method of the cellulose nanocrystals in the first and second modified cellulose nanocrystals is as follows: 95g of microcrystalline cellulose, 3250mL of citric acid aqueous solution with a concentration of 1100g / L, and 500mL of sulfuric acid aqueous solution with a concentration of 850g / L are mixed and stirred at 300rpm for 7.5h at 80℃. Sodium hydroxide aqueous solution with a concentration of 320g / L is added to adjust the pH to 7. The mixture is then centrifuged at 9500rpm for 9min. The precipitate is then washed with water three times and freeze-dried at -35℃ for 22h to obtain cellulose nanocrystals.

[0087] 2. Preparation of anti-aging masterbatch: By weight, 75 parts polypropylene, 7.5 parts filler, 6.5 parts light stabilizer, 3.5 parts antioxidant, 3.5 parts polyethylene wax, 1.7 parts stearic acid, and 1.5 parts 3-aminopropyltrimethoxysilane are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion and pelletizing. The screw temperature is controlled at 220℃ to obtain the anti-aging masterbatch.

[0088] The polypropylene has a melt flow index of 38 g / 10 min at 230°C and 2.16 kg.

[0089] The light stabilizer is light stabilizer 119;

[0090] The method for preparing the filler is as follows:

[0091] (1) Silane modification: 55g mica powder, 70mL 3-aminopropyltrimethoxysilane, 650mL anhydrous ethanol and 110mL water were ultrasonically dispersed. The ultrasonic dispersion frequency was controlled at 25kHz and the time was 25min. Then, the mixture was stirred at 45℃ for 4.5h, centrifuged at 6500rpm for 6min, and then the precipitate was washed three times with anhydrous ethanol and three times with water. Finally, the mixture was freeze-dried at -35℃ for 22h to obtain silane-modified mica powder.

[0092] The mica powder has a particle size of 100 nm;

[0093] (2) Citric acid grafting: In an ice-water bath, 28g of citric acid, 28g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 28g of N-hydroxysuccinimide and 900mL of water were mixed and stirred at 200rpm for 15min. Ultrasonic oscillation was performed at a frequency of 25kHz for 1.2h. Then, 62g of silane-modified mica powder was added and stirred at 200rpm for 4.5h at 30℃. The mixture was centrifuged at 6500rpm for 6min. The precipitate was washed with water three times and then freeze-dried at -35℃ for 22h to obtain the primary filler.

[0094] (3) Calcium ionization: 90g primary packing, 11g calcium chloride and 550mL water were mixed and stirred at 200rpm for 12min at 30℃. The mixture was then centrifuged at 6500rpm for 6min and freeze-dried at -35℃ for 22h to obtain the packing.

[0095] 3. Mixing: By weight, add 96.8 parts polypropylene, 1 part biodegradable masterbatch, and 2.2 parts anti-aging masterbatch to a high-speed mixer and mix evenly to obtain a mixture;

[0096] The polypropylene has a melt flow index of 40 g / 10 min at 230°C and 2.16 kg.

[0097] 4. Spinning and drawing: The mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion, then filtered by a filter, metered by a metering pump, and spun into continuous fibers through a die; after cold air drawing, the fibers are evenly spread on a mesh belt to form a web, and then passed through upper and lower pressure rollers and hot rolled by a hot rolling mill to obtain biodegradable polypropylene nonwoven fabric.

[0098] The screw temperature is 235℃, the metering pump speed is 6 rpm, and the die temperature is 260℃; the cold air temperature during cold air drawing is 12℃, the mesh belt speed is 420 m / min, the roll temperature of the hot rolling mill is 160℃, and the pressure is 110 daN / cm.

[0099] This embodiment also provides a biodegradable polypropylene nonwoven fabric prepared by the aforementioned preparation method, with a basis weight of 30 gsm.

[0100] Example 3

[0101] A method for preparing biodegradable polypropylene nonwoven fabric, specifically comprising:

[0102] 1. Preparation of biodegradable masterbatch: By weight, 40 parts polypropylene, 10 parts polycaprolactone, 12 parts erucamide, 7 parts maleic anhydride-grafted polypropylene, 5 parts first modified cellulose nanocrystals, 5 parts second modified cellulose nanocrystals, 3 parts stearic acid, and 1 part 3-aminopropyltrimethoxysilane were added to a high-speed mixer and mixed evenly. Then, the mixture was added to a twin-screw extruder with an aspect ratio of 40:1 for melt extrusion and pelletizing. The screw temperature was controlled at 220℃ to obtain biodegradable masterbatch.

[0103] The polypropylene has a melt flow index of 40 g / 10 min at 230°C and 2.16 kg.

[0104] The maleic anhydride-grafted polypropylene has a melt index of 120 g / 10 min at 230°C and 2.16 kg.

[0105] The preparation method of the first modified cellulose nanocrystals is as follows: 9-10g of cellulose nanocrystals, 110mL of 3-glycidylpropyltrimethoxysilane, and 1500mL of tetrahydrofuran are mixed and ultrasonically dispersed. The ultrasonic dispersion frequency is controlled at 30kHz for 40min. Then, while stirring at 70℃ and 400rpm, 50mL of 40g / L hydrochloric acid aqueous solution is added dropwise at a rate of 8mL / min. After the addition is completed, stirring is continued for 8h. The mixture is then centrifuged at 8000rpm for 10min. The precipitate is then washed four times with tetrahydrofuran and freeze-dried at -30℃ for 25h to obtain the first modified cellulose nanocrystals.

[0106] The preparation method of the second modified cellulose nanocrystals is as follows: 10g of cellulose nanocrystals, 25mL of hexadecyltrimethoxysilane, 400mL of anhydrous ethanol, and 70mL of water are ultrasonically dispersed at a frequency of 30kHz for 30min. Then, while stirring at 400rpm at 70℃, a 40g / L hydrochloric acid aqueous solution is added dropwise at a rate of 2mL / min until the pH reaches 6. After stirring for 3.5h, the mixture is centrifuged at 8000rpm for 10min. The precipitate is then washed four times with anhydrous ethanol and four times with water. Finally, the mixture is freeze-dried at -30℃ for 25h to obtain the second modified cellulose nanocrystals.

[0107] The preparation method of the cellulose nanocrystals in the first and second modified cellulose nanocrystals is as follows: 100g of microcrystalline cellulose, 3300mL of citric acid aqueous solution with a concentration of 1200g / L, and 600mL of sulfuric acid aqueous solution with a concentration of 900g / L are mixed and stirred at 85℃ with a stirring speed of 400rpm for 8h. A sodium hydroxide aqueous solution with a concentration of 350g / L is added to adjust the pH to 7. The mixture is then centrifuged at a speed of 10000rpm for 10min. The precipitate is then washed with water 4 times and freeze-dried at a temperature of -30℃ for 25h to obtain cellulose nanocrystals.

[0108] 2. Preparation of anti-aging masterbatch: By weight, 80 parts polypropylene, 8 parts filler, 7 parts light stabilizer, 4 parts antioxidant, 4 parts polyethylene wax, 2 parts stearic acid, and 2 parts 3-aminopropyltrimethoxysilane are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion and pelletizing. The screw temperature is controlled at 230℃ to obtain the anti-aging masterbatch.

[0109] The polypropylene has a melt flow index of 40 g / 10 min at 230°C and 2.16 kg.

[0110] The light stabilizer is light stabilizer 770;

[0111] The method for preparing the filler is as follows:

[0112] (1) Silane modification: 60g mica powder, 80mL 3-aminopropyltrimethoxysilane, 700mL anhydrous ethanol and 120mL water were ultrasonically dispersed. The ultrasonic dispersion frequency was controlled at 30kHz and the time was 30min. Then, the mixture was stirred at 50℃ for 5h and centrifuged. The centrifugation speed was controlled at 7000rpm and the time was 7min. The precipitate was washed 4 times with anhydrous ethanol and 4 times with water. Then, the mixture was freeze-dried. The freeze-drying temperature was controlled at -30℃ and the time was 25h to obtain silane-modified mica powder.

[0113] The mica powder has a particle size of 200 nm;

[0114] (2) Citric acid grafting: In an ice-water bath, 30g of citric acid, 30g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 30g of N-hydroxysuccinimide and 1000mL of water were mixed and stirred at 300rpm for 20min. Ultrasonic oscillation was performed at a frequency of 30kHz for 1.5h. Then, 65g of silane-modified mica powder was added and stirred at 300rpm for 5h at 40℃. The mixture was centrifuged at 7000rpm for 7min. The precipitate was washed with water 4 times and then freeze-dried at -30℃ for 25h to obtain the primary filler.

[0115] (3) Calcium ionization: Mix 100g of primary packing material, 12g of calcium chloride and 600mL of water, stir at 300rpm for 15min at 40℃, centrifuge at 7000rpm for 7min, freeze dry at -30℃ for 25h to obtain the packing material.

[0116] 3. Mixing: By weight, add 96 parts polypropylene, 1.5 parts biodegradable masterbatch, and 2.5 parts anti-aging masterbatch to a high-speed mixer and mix evenly to obtain a mixture;

[0117] The polypropylene has a melt flow index of 40 g / 10 min at 230°C and 2.16 kg.

[0118] 4. Spinning and drawing: The mixture is added to a twin-screw extruder with a length-to-diameter ratio of 40:1 for melt extrusion, then filtered by a filter, metered by a metering pump, and spun into continuous fibers through a die; after cold air drawing, the fibers are evenly spread on a mesh belt to form a web, and then passed through upper and lower pressure rollers and hot rolled by a hot rolling mill to obtain biodegradable polypropylene nonwoven fabric.

[0119] The screw temperature is 240℃, the metering pump speed is 8 rpm, and the die temperature is 270℃; the cold air temperature during cold air drawing is 15℃, the mesh belt speed is 450 m / min, the roll temperature of the hot rolling mill is 170℃, and the pressure is 120 daN / cm.

[0120] This embodiment also provides a biodegradable polypropylene nonwoven fabric prepared by the aforementioned method, with a basis weight of 29 gsm.

[0121] Comparative Example 1

[0122] The technical solution of this embodiment is an adjustment to the preparation method of biodegradable polypropylene nonwoven fabric in Example 2. Specifically, in the preparation of biodegradable masterbatch in step 1, the addition of the first modified cellulose nanocrystals and the second modified cellulose nanocrystals is omitted.

[0123] Comparative Example 2

[0124] The technical solution of this embodiment is an adjustment to the preparation method of biodegradable polypropylene nonwoven fabric in Example 2. The specific adjustment is as follows: in the preparation of filler in the second step of preparing anti-aging masterbatch, the citric acid grafting and calcium ionization in step (2) are omitted, that is, the silane-modified mica powder obtained by silane modification in step (1) is added to the anti-aging masterbatch as filler.

[0125] Experimental Example 1

[0126] The CD strength, MD strength, CD elongation, and MD elongation of the polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 were tested, and the test results are as follows:

[0127]

[0128] Experimental Example 2

[0129] The spinnability during the spinning draw in step 4 of Examples 1-3 and Comparative Examples 1-2 was recorded, and the results are as follows:

[0130]

[0131] Experimental Example 3

[0132] The UV resistance of the polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The test methods and results are as follows:

[0133] UV resistance was tested according to ASTM G154, specifically using a UVB-313 ultraviolet lamp with an irradiance of 28 W / m². 2The blackboard temperature was 70℃ for 8 hours, the condensation temperature was 50℃ for 4 hours, and the blackboard temperature was 50℃ for 210 hours. Then, the CD strength, MD strength, CD elongation, and MD elongation of the polypropylene nonwoven fabric were tested, and the retention rate was calculated. Three parallel tests were performed, and the average value was taken. The average retention rate is as follows:

[0134]

[0135] Test Example 4

[0136] The polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to high-temperature resistance tests. The test methods and results are as follows:

[0137] The polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to high-temperature treatment at 60°C. After continuous treatment for 1, 3, 5, 7, 15, and 30 days, the CD strength, MD strength, CD elongation, and MD elongation of the polypropylene nonwoven fabrics were tested, and the retention rate was calculated. The results are as follows:

[0138] After 1 day of continuous processing:

[0139]

[0140] After 3 days of continuous processing:

[0141]

[0142] After 5 days of continuous treatment:

[0143]

[0144] After 7 days of continuous treatment:

[0145]

[0146] After 15 days of continuous treatment:

[0147]

[0148] After 30 days of continuous treatment:

[0149]

[0150] Experimental Example 5

[0151] The polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to aging resistance tests. The test methods and results are as follows:

[0152] The polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to aging treatment at room temperature. After continuous treatment for 3d, 7d, 15d, 30d, and 90d, the CD strength, MD strength, CD elongation, and MD elongation of the polypropylene nonwoven fabrics were tested, and the retention rate was calculated. The calculation results are as follows:

[0153] After 3 days of continuous processing:

[0154]

[0155] After 7 days of continuous treatment:

[0156]

[0157] After 15 days of continuous treatment:

[0158]

[0159] After 30 days of continuous treatment:

[0160]

[0161] After 90 days of continuous treatment:

[0162]

[0163] Experimental Example 6

[0164] The biodegradability of the polypropylene nonwoven fabrics prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The biodegradability rate was tested according to GB / T33797-2017 standard. The specific test method is as follows:

[0165] The test material was exposed to a methanogenic inoculum, which was anaerobic digested sewage sludge from Kimpur, Mumbai, India, mixed with municipal solid waste, which had been pre-cultured at 53°C for one week.

[0166] During testing, 1000g of inoculum (at least 20% dry solids) was added to a container, followed by 15g of the test sample (polypropylene nonwoven fabric prepared in the examples) or the reference sample (polylactic acid nonwoven fabric). The mixture was stirred for 2 minutes to obtain the test sample. A blank control was prepared by adding only 1000g of inoculum (at least 20% dry solids) to a container and stirring for 2 minutes. The weights of the test sample and the blank control were then measured separately. The samples were then added separately to flasks, spread evenly, and compacted. The samples were then placed in the dark at 53°C for degradation experiments. The generated biogas was collected during the experiment. The volume of collected gas and the total carbon content were measured after 15, 30, 38, and 45 days of degradation. The total carbon weight and the theoretical carbon weight in the test sample and reference sample were calculated. The total carbon weight was subtracted from the total carbon weight of the blank control to obtain the increase in total carbon weight. This increase was divided by the theoretical carbon weight to obtain the biodegradation rate. The calculated biodegradation rates after 15, 30, 38, and 45 days of degradation are as follows:

[0167]

[0168] Furthermore, after 45 days of degradation experiments, the surfaces of the polypropylene nonwoven fabrics prepared in Examples 1 and 2 were observed under a microscope, and microscopic images were recorded. The polypropylene nonwoven fabrics prepared in Examples 1 and 2 were also placed in room temperature air for 45 days before microscopic observation and recording of the microscopic images. The obtained microscopic images are shown below. Figure 1 As shown, Figure 1 Figure A is a microscopic image of the polypropylene nonwoven fabric of Example 1 after 45 days of degradation experiment; Figure B is a microscopic image of the polypropylene nonwoven fabric of Example 2 after 45 days of degradation experiment; Figure C is a microscopic image of the polypropylene nonwoven fabric of Example 1 after 45 days of exposure to room temperature air; and Figure D is a microscopic image of the polypropylene nonwoven fabric of Example 2 after 45 days of exposure to room temperature air.

[0169] Depend on Figure 1 It can be seen that bacteria have grown on the surface of the polypropylene nonwoven fabrics of Examples 1 and 2 after 45 days of degradation experiment, while no bacteria have grown on the surface of the polypropylene nonwoven fabrics of Examples 1 and 2 after 45 days of being placed in room temperature air environment.

[0170] The results of Experiments 1-6 show that adding first and second modified cellulose nanocrystals to the preparation of biodegradable masterbatch can improve the CD strength, MD strength, CD elongation, MD elongation, spinnability, UV resistance, high temperature resistance, and aging resistance of the prepared polypropylene nonwoven fabric. Furthermore, by grafting silane-modified mica powder with citric acid and ionizing it with calcium during the preparation of fillers in the preparation of anti-aging masterbatch, the CD strength, MD strength, CD elongation, MD elongation, UV resistance, high temperature resistance, aging resistance, and biodegradability of the prepared polypropylene nonwoven fabric can be improved.

[0171] The first modified cellulose nanocrystal added to the preparation of the biodegradable masterbatch is branched polysilane-grafted cellulose nanocrystal. The presence of branched polysilane not only improves the dispersibility of the cellulose nanocrystal and its compatibility with polypropylene and maleic anhydride-grafted polypropylene, but also improves the compatibility between polypropylene and maleic anhydride-grafted polypropylene. Furthermore, it increases the crosslinking density of the prepared biodegradable polypropylene nonwoven fabric, thereby improving its strength, elongation, UV resistance, high-temperature resistance, and aging resistance. The second modified cellulose nanocrystal is long-chain alkyl-grafted cellulose nanocrystal. The presence of long-chain alkyl groups acts as a lubricant, improving spinnability; furthermore, it enables crosslinking between the long-chain alkyl groups and polypropylene and maleic anhydride-grafted polypropylene in the biodegradable polypropylene nonwoven fabric, thus improving the strength, elongation, UV resistance, high-temperature resistance, and aging resistance of the prepared biodegradable polypropylene nonwoven fabric. Furthermore, by using branched polysilanes and hexadecyl groups for grafting, it is possible to avoid mutual interference during grafting that could lead to a decrease in the grafting rate.

[0172] In the preparation of anti-aging masterbatch, the filler is grafted with citric acid and ionized with calcium, specifically by further grafting calcium citrate onto silane-modified mica powder. During filler preparation, 3-aminopropyltrimethoxysilane is first used for surface modification to introduce amino groups, resulting in silane-modified mica powder. Then, 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide are used to activate the carboxyl groups in citric acid, which then react with the amino groups in the silane-modified mica powder to graft citric acid. Finally, it is reacted with chlorinated... The calcium reacts with the unreacted carboxyl groups in the grafted citric acid to obtain calcium citrate-grafted mica powder. On the one hand, calcium citrate can further improve the compatibility between silane-modified mica powder and polypropylene, thereby improving the strength, elongation, UV resistance, high temperature resistance, and aging resistance of the prepared biodegradable polypropylene nonwoven fabric. On the other hand, during degradation, calcium citrate-grafted mica powder can coat the surface of polypropylene, promoting the degradation of polypropylene and thus improving the biodegradability of the biodegradable polypropylene nonwoven fabric.

[0173] Unless otherwise stated, all percentages used in this invention are weight percentages.

[0174] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing biodegradable polypropylene nonwoven fabric, characterized in that, include: Preparation of biodegradable masterbatch, preparation of anti-aging masterbatch, mixing, spinning and drawing; The preparation of the biodegradable masterbatch involves adding polypropylene, polycaprolactone, erucamide, maleic anhydride-grafted polypropylene, first modified cellulose nanocrystals, second modified cellulose nanocrystals, stearic acid, and 3-aminopropyltrimethoxysilane to a high-speed mixer and mixing them evenly. Then, the mixture is added to a twin-screw extruder for melt extrusion and pelletizing to obtain the biodegradable masterbatch. In the preparation of the biodegradable masterbatch, the weight ratio of polypropylene, polycaprolactone, erucamide, maleic anhydride-grafted polypropylene, first modified cellulose nanocrystals, second modified cellulose nanocrystals, stearic acid, and 3-aminopropyltrimethoxysilane is 30-40:8-10:10-12:5-7:4-5:3-5:2-3:0.5-1. The preparation method of the first modified cellulose nanocrystals is as follows: cellulose nanocrystals, 3-glycidylpropyltrimethoxysilane and tetrahydrofuran are mixed and ultrasonically dispersed. Then, while stirring at 60-70℃, hydrochloric acid aqueous solution is added dropwise. After the addition is completed, stirring is continued, centrifugation is performed, the precipitate is washed and freeze-dried to obtain the first modified cellulose nanocrystals. The preparation method of the second modified cellulose nanocrystals is as follows: cellulose nanocrystals, hexadecyltrimethoxysilane, anhydrous ethanol, and water are ultrasonically dispersed, and then hydrochloric acid aqueous solution is added dropwise while stirring at 60-70℃ until the pH is 5.5-6. After stirring, the mixture is centrifuged, the precipitate is washed, and freeze-dried to obtain the second modified cellulose nanocrystals. To prepare the anti-aging masterbatch, polypropylene, filler, light stabilizer, antioxidant, polyethylene wax, stearic acid, and 3-aminopropyltrimethoxysilane are added to a high-speed mixer and mixed evenly. Then, the mixture is added to a twin-screw extruder for melt extrusion and pelletizing to obtain the anti-aging masterbatch. The method for preparing the filler includes: silane modification, citric acid grafting, and calcium ionization; The silane modification involves ultrasonically dispersing mica powder, 3-aminopropyltrimethoxysilane, anhydrous ethanol, and water, then stirring at 40-50°C, centrifuging, washing the precipitate, and freeze-drying to obtain silane-modified mica powder. The citric acid grafting process involves mixing citric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, and water in an ice-water bath, stirring, and then ultrasonically vibrating. Silane-modified mica powder is then added, and the mixture is stirred at 20-40°C, centrifuged, and the precipitate is washed and freeze-dried to obtain the primary filler. The calcium ionization process involves mixing primary packing material, calcium chloride, and water, stirring at 20-40°C, centrifuging, washing the precipitate, and freeze-drying to obtain the packing material.

2. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 1, characterized in that, In the preparation of the biodegradable masterbatch, the screw temperature of the twin-screw extruder is 190-220℃.

3. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 1, characterized in that, In the preparation of the first modified cellulose nanocrystals, the weight-volume ratio of cellulose nanocrystals, 3-glycidylpropyltrimethoxysilane, tetrahydrofuran, and hydrochloric acid aqueous solution is 9-10g:100-110mL:1200-1500mL:45-50mL. The concentration of the hydrochloric acid aqueous solution is 38-40 g / L; The hydrochloric acid aqueous solution was added at a rate of 5-8 mL / min.

4. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 3, characterized in that, The second modified cellulose nanocrystal preparation method involves a weight-to-volume ratio of cellulose nanocrystals, hexadecyltrimethoxysilane, anhydrous ethanol, and water of 9-10 g: 20-25 mL: 350-400 mL: 60-70 mL. The concentration of the hydrochloric acid aqueous solution is 38-40 g / L; The hydrochloric acid aqueous solution was added at a rate of 1-2 mL / min.

5. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 4, characterized in that, The preparation method of the cellulose nanocrystals in the first and second modified cellulose nanocrystals is as follows: microcrystalline cellulose, citric acid aqueous solution and sulfuric acid aqueous solution are mixed and stirred at 75-85℃, sodium hydroxide aqueous solution is added to adjust the pH to 7, centrifuged, the precipitate is washed and freeze-dried to obtain cellulose nanocrystals; In the preparation of the first and second modified cellulose nanocrystals, the weight-volume ratio of microcrystalline cellulose, citric acid aqueous solution, and sulfuric acid aqueous solution is 90-100g:3200-3300mL:400-600mL. The concentration of citric acid aqueous solution is 1000-1200 g / L; The concentration of the sulfuric acid aqueous solution is 800-900 g / L; The concentration of the sodium hydroxide aqueous solution is 300-350 g / L.

6. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 1, characterized in that, In the preparation of the anti-aging masterbatch, the weight ratio of polypropylene, filler, light stabilizer, antioxidant, polyethylene wax, stearic acid, and 3-aminopropyltrimethoxysilane is 70-80:7-8:6-7:3-4:3-4:1.5-2:1-2. The light stabilizer is one or more of light stabilizer 2020, light stabilizer 119, and light stabilizer 770; The screw temperature of the twin-screw extruder is 200-230℃.

7. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 1, characterized in that, In the silane modification, the weight-to-volume ratio of mica powder, 3-aminopropyltrimethoxysilane, anhydrous ethanol, and water is 50-60g:60-80mL:600-700mL:100-120mL. In the citric acid grafting process, the weight-to-volume ratio of citric acid, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, water, and silane-modified mica powder is 25-30g:25-30g:25-30g:700-1000mL:60-65g. In the calcium ionization process, the weight-to-volume ratio of primary filler, calcium chloride, and water is 80-100g:10-12g:500-600mL.

8. The method for preparing biodegradable polypropylene nonwoven fabric according to claim 1, characterized in that, The mixing process involves adding polypropylene, biodegradable masterbatch, and anti-aging masterbatch to a high-speed mixer and mixing them evenly to obtain a mixture. In the mixture, the weight ratio of polypropylene, biodegradable masterbatch, and anti-aging masterbatch is 96-97.4:0.6-1.5:2-2.

5. The spinning and drawing process involves adding the mixture to a twin-screw extruder for melt extrusion, then filtering it through a filter, metering it with a metering pump, and spinning it into continuous fibers through a die. After cold air drawing, the fibers are evenly spread on a mesh belt to form a web, which is then passed through upper and lower pressure rollers and hot-rolled in a hot rolling mill to obtain biodegradable polypropylene nonwoven fabric.

9. A biodegradable polypropylene nonwoven fabric, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

Images