Biodegradable filter cloth and preparation method thereof

Abstract

The invention relates to the technical field of new materials, in particular to biodegradable filter cloth and a preparation method thereof.The biodegradable filter cloth is prepared from, by weight, polybutylene terephthalate, modified starch, polybutylene adipate, bamboo fibers, maleic anhydride grafted polyolefin elastomer and a lubricant; through the synergistic effect of all the components and the preparation process, the performance of the filter cloth can be optimized, the component compatibility problem is solved through cooperation of the modified starch and the compatilizer, the uniformity and compactness of the material structure are guaranteed through the bamboo fiber pretreatment and gradient melting process, the pore characteristics of the filter cloth are optimized through the segmented spinning and weaving process, and the filter cloth has the advantages of being high in practicability and high in practicability. Finally, the filter cloth simultaneously has excellent mechanical properties, efficient filtering performance and good biodegradability, is suitable for industrial production, and has wide application prospects in the fields of industrial filtration, environment-friendly treatment and the like.

Description

Technical Field

[0001] This invention relates to the field of new materials technology, specifically to a biodegradable filter cloth and its preparation method. Background Technology

[0002] As a key material in industrial filtration and environmental remediation, the performance of filter cloth directly affects filtration efficiency and operating costs. Traditional filter cloths are mostly made of non-degradable synthetic polymer materials. These filter cloths are difficult to decompose naturally after use, and large-scale accumulation can cause serious environmental pollution, which does not meet the current needs of green development.

[0003] To address environmental issues, biodegradable filter cloths have gradually become a research hotspot. Current technologies often involve blending biodegradable components such as starch with synthetic polymers to prepare filter cloths. However, the compatibility between ordinary starch and synthetic polymers is poor, resulting in poor mechanical properties of the filter cloth, making it prone to damage during use and leading to a short service life.

[0004] In addition, some biodegradable filter cloths increase the proportion of synthetic polymers in pursuit of mechanical properties, but reduce the biodegradability; or they overemphasize degradability, resulting in insufficient filtration efficiency, making it difficult to achieve a synergistic improvement in mechanical properties, filtration performance and biodegradability.

[0005] Therefore, developing a filter cloth with a reasonable combination of components and a scientific manufacturing process that can simultaneously meet the requirements of mechanical strength, filtration efficiency and biodegradability has become an urgent problem to be solved in the industry. Summary of the Invention

[0006] The purpose of this invention is to provide a biodegradable filter cloth.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A biodegradable filter cloth is composed of the following components in parts by weight: 45-55 parts of polybutylene terephthalate, 15-20 parts of modified starch, 10-15 parts of polybutylene adipate, 5-8 parts of bamboo fiber, 3-5 parts of maleic anhydride-grafted polyolefin elastomer, and 2-4 parts of lubricant.

[0008] As a further technical solution, the modified starch is an acrylate-grafted-nano hydroxyapatite synergistic modified starch, and its preparation method includes the following steps: (1) Pretreatment of nano hydroxyapatite: Add nano hydroxyapatite with a particle size of 50-100nm to a 1%-2% mass fraction of silane coupling agent KH550 ethanol solution, ultrasonically disperse at 200-300W power for 30-40min, filter, and dry at 80-90℃ to constant weight for later use. (2) Grafting reaction: Corn starch or cassava starch is mixed with deionized water at a mass ratio of 1:3-5, heated to 85-95℃ and gelatinized for 30-40 minutes. After cooling to 45-55℃, 5%-8% of acrylate monomer, 0.3%-0.5% of initiator and 2%-3% of pretreated nano-hydroxyapatite are added. The mixture is reacted under nitrogen protection for 2-3 hours. After the reaction is completed, the mixture is centrifuged to dehydrate, dried at 80-100℃ to constant weight, and pulverized through an 80-120 mesh sieve to obtain modified starch.

[0009] As a further technical solution, the initiator is ammonium persulfate or potassium persulfate; the acrylate monomer is methyl methacrylate or butyl acrylate.

[0010] As a further technical solution, the bamboo fiber is pretreated by means of: soaking the bamboo fiber in a sodium hydroxide solution with a mass fraction of 2%-3% at 60-70℃ for 1-2 hours, rinsing it with deionized water until neutral, and then drying it at 80-90℃ to constant weight.

[0011] As a further technical solution, the lubricant is calcium stearate or vinyl bis-stearamide.

[0012] As a further technical solution, the thickness of the filter cloth is 0.1-0.3 mm.

[0013] A method for preparing biodegradable filter cloth includes the following steps: (1) Preparation of modified starch: Preparation of acrylate-grafted-nanohydroxyapatite synergistic modified starch; (2) Gradient melt composite: The modified starch prepared in step (1) is mixed with polybutylene terephthalate in the weight ratio mentioned above, preheated and dried at a vacuum of -0.08~-0.06MPa and 120-130℃ for 2-3h, and then added to a twin-screw extruder with a length-to-diameter ratio of 35-40:1. The mixture is melt-blended at the following temperature gradient: Zone 1 180-190℃, Zone 2 200-210℃, Zone 3 220-230℃, Zone 4 230-240℃, and die head 230-240℃. The screw speed is 300-350r / min and the feeding speed is 50-80kg / h to obtain the composite substrate. (3) Mixing and mixing: The composite substrate obtained in step (2) is mixed with polybutylene adipate, pretreated bamboo fiber, maleic anhydride grafted polyolefin elastomer and lubricant in the weight ratio described above, and stirred at a speed of 200-300 r / min for 15-25 min under nitrogen protection to obtain the mixture. (4) Segmented spinning: The mixture obtained in step (3) is added to the spinning machine and segmented temperature-controlled spinning is adopted. The spinning machine barrel is 200-210℃ in zone 1, 210-220℃ in zone 2, and 220-230℃ in zone 3. The spinneret temperature is 225-235℃, the spinneret orifice diameter is 0.2-0.3mm, and the spinning speed is 800-1000m / min. Inert gas of 0.1-0.2MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and stretched. The cooling temperature is 25-35℃ and the stretching ratio is 2.5-3.5 times to obtain biodegradable fibers. (5) Weaving and finishing: The biodegradable fibers obtained in step (4) are warped, woven and heat-set to obtain biodegradable filter cloth.

[0014] As a further technical solution, the inert gas in step (4) is nitrogen or argon.

[0015] As a further technical solution, the warping process parameters in step (5) are: warping speed 50-80m / min, warping tension 20-30cN; the weaving method is plain weave or twill weave, the weaving density is 30-40 warp yarns / cm, weft yarns 25-35 weft yarns / cm, and the weft tension during the weaving process is 15-25cN.

[0016] As a further technical solution, the heat setting treatment is carried out in a hot air circulating oven at a temperature of 120-130℃ for 20-30 minutes and an oven wind speed of 1-2 m / s. The heat-set filter cloth is then cut and edge-locked with a width of 0.5-1.0 cm.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes acrylate-grafted nano-hydroxyapatite synergistic modification of starch. The grafted groups on the molecular chain can form a good interfacial bond with synthetic polymers such as polybutylene terephthalate and polybutylene adipate. Simultaneously, the filling effect of nano-hydroxyapatite enhances the structural stability of the starch matrix, thereby improving the compatibility between starch and synthetic polymers, avoiding the problem of easy agglomeration of ordinary starch, and thus solving the problem of decreased mechanical properties of filter cloth after the addition of biodegradable components. After pretreatment with sodium hydroxide, bamboo fiber surface impurities are removed, fiber dispersibility is improved, and active sites are formed on the pretreated fiber surface, enabling interaction with other components to form a uniform reinforcing network in the filter cloth. This further enhances the tensile strength and tear strength of the filter cloth, ensuring that the filter cloth is not easily damaged in complex filtration environments.

[0018] 2. Maleic anhydride-grafted polyolefin elastomer, acting as a compatibilizer, has polar groups on its molecular chains that interact with polar starch, bamboo fiber, and non-polar synthetic polymers, reducing interfacial tension between components and ensuring uniform dispersion of all components within the system. This results in a dense composite material, thereby improving the overall uniformity of the filter cloth. The addition of lubricant reduces frictional resistance during processing, ensuring smooth melt bonding and spinning processes, optimizing the surface smoothness of the filter cloth, and reducing fluid resistance during filtration. The gradient melt bonding process achieves complete melting of each component through gradual heating, avoiding localized overheating or insufficient melting. Segmented spinning, aided by temperature control and inert gas, ensures stable fiber forming quality.

[0019] 3. The synergistic effect of the components and preparation process of this invention can optimize the performance of the filter cloth: the combination of modified starch and compatibilizer solves the problem of component compatibility, the pre-treated bamboo fiber and gradient melting process ensure the uniformity and density of the material structure, and the segmented spinning and weaving process optimizes the pore characteristics of the filter cloth. In the end, the filter cloth has excellent mechanical properties, high efficiency filtration performance and good biodegradability, making it suitable for industrial production and with broad application prospects in industrial filtration, environmental protection and other fields. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a biodegradable filter cloth and its preparation method. The biodegradable filter cloth is composed of the following components in parts by weight: 45-55 parts of polybutylene terephthalate, 15-20 parts of modified starch, 10-15 parts of polybutylene adipate, 5-8 parts of bamboo fiber, 3-5 parts of maleic anhydride-grafted polyolefin elastomer, and 2-4 parts of lubricant. With the help of a proprietary preparation process, it achieves a synergistic improvement in both excellent performance and biodegradability.

[0022] Raw materials include: Polybutylene terephthalate: Industrial grade polybutylene terephthalate with uniform molecular weight distribution and good melt flowability is selected; commercially available conventional products are sufficient.

[0023] Modified starch: It is an acrylate-grafted nano-hydroxyapatite synergistic modified starch, which is obtained through a specific preparation process. The specific preparation steps are as follows.

[0024] Polybutylene adipate: Industrial grade polybutylene adipate has good flexibility and biodegradability, and commercially available conventional products can meet the requirements.

[0025] Bamboo fiber: Select natural bamboo fibers of uniform length, which are used after pretreatment. The pretreatment method is as follows.

[0026] Maleic anhydride-grafted polyolefin elastomer: an industrial-grade product used as a compatibilizer to enhance the interfacial bonding between components; suitable for commercially available conventional products.

[0027] Lubricant: Use calcium stearate or vinyl bis-stearamide, industrial grade purity, commercially available products are sufficient.

[0028] Preparation of modified starch: Pretreatment of nano-hydroxyapatite: Add nano-hydroxyapatite with a particle size of 50-100nm to a 1%-2% (w / w) ethanol solution of silane coupling agent KH550, ultrasonically disperse at 200-300W power for 30-40min, filter, and dry at 80-90℃ to constant weight for later use.

[0029] Grafting reaction: Corn starch or cassava starch is mixed with deionized water at a mass ratio of 1:3-5, heated to 85-95℃ for 30-40 minutes for gelatinization, cooled to 45-55℃, and then 5%-8% of acrylate monomer, 0.3%-0.5% of initiator, and 2%-3% of pretreated nano-hydroxyapatite are added. The mixture is reacted under nitrogen protection for 2-3 hours. After the reaction, the starch is centrifuged to remove water, dried at 80-100℃ to constant weight, and pulverized through an 80-120 mesh sieve to obtain modified starch.

[0030] The initiator is preferably ammonium persulfate or potassium persulfate; the acrylate monomer is preferably methyl methacrylate or butyl acrylate.

[0031] Pretreatment of bamboo fiber: Soak bamboo fibers in a 2%-3% sodium hydroxide solution at 60-70℃ for 1-2 hours. After soaking, rinse with deionized water until neutral, and then dry at 80-90℃ to constant weight for later use.

[0032] The preparation method of biodegradable filter cloth includes: Preparation of modified starch: Following the above-described steps for preparing modified starch, acrylate-grafted nano-hydroxyapatite synergistic modified starch was prepared.

[0033] Gradient melt composite: The prepared modified starch and polybutylene terephthalate are mixed in a specific weight ratio, preheated and dried at a vacuum of -0.08~-0.06MPa and 120-130℃ for 2-3 hours, and then added to a twin-screw extruder with an aspect ratio of 35-40:1. The mixture is melt-blended at the following temperature gradient: Zone 1 180-190℃, Zone 2 200-210℃, Zone 3 220-230℃, Zone 4 230-240℃, and Die head 230-240℃. The screw speed is 300-350r / min, and the feeding speed is 50-80kg / h to obtain the composite matrix.

[0034] Mixing and formulation: The obtained composite substrate is mixed with polybutylene adipate, pretreated bamboo fiber, maleic anhydride grafted polyolefin elastomer and lubricant in a specific weight ratio, and stirred at a speed of 200-300 r / min for 15-25 min under nitrogen protection to obtain the mixture.

[0035] Segmented spinning: The mixture is added to a spinning machine, and segmented temperature-controlled spinning is adopted. The temperature of the spinning machine barrel is 200-210℃ in zone 1, 210-220℃ in zone 2, and 220-230℃ in zone 3. The spinneret temperature is 225-235℃, the spinneret orifice diameter is 0.2-0.3mm, and the spinning speed is 800-1000m / min. An inert gas of 0.1-0.2MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and drawn at a cooling temperature of 25-35℃ and a draw ratio of 2.5-3.5 times to obtain biodegradable fibers. Nitrogen or argon is preferred as the inert gas.

[0036] Weaving and Finishing: Biodegradable fibers are warped, woven, and heat-set to obtain biodegradable filter cloth. Warping parameters are: warping speed 50-80 m / min, warping tension 20-30 cN; weaving method is plain weave or twill weave, weaving density is 30-40 warp yarns / cm, weft yarns 25-35 weft yarns / cm, and weft tension during weaving is 15-25 cN; heat setting is carried out in a hot air circulating oven at a temperature of 120-130℃ for 20-30 min, with an oven air velocity of 1-2 m / s; after heat setting, the filter cloth is cut and edge-locked with an edge width of 0.5-1.0 cm.

[0037] In this invention, the thickness of the biodegradable filter cloth is preferably 0.1-0.3 mm.

[0038] Compared with existing technologies, the biodegradable filter cloth provided by this invention achieves synergistic effects among its components through a reasonable ratio of core components such as polybutylene terephthalate, modified starch, and polybutylene adipate, combined with a proprietary preparation process for modified starch, bamboo fiber pretreatment and gradient melt composite, segmented spinning, and other specific preparation steps. This not only endows the filter cloth with good mechanical and filtration properties but also ensures excellent biodegradability, solving the problems of traditional filter cloths being difficult to degrade and causing environmental pollution. At the same time, the preparation process is stable and controllable, and the product has good dimensional consistency, making it suitable for industrial production.

[0039] To further illustrate the present invention, detailed descriptions are provided below through examples, comparative examples, and experiments.

[0040] Example 1: Preparation of modified starch: Pretreatment of nano-hydroxyapatite: Nano-hydroxyapatite with a particle size of 50 nm was added to a 1% (w / w) ethanol solution of silane coupling agent KH550, and ultrasonically dispersed at 200 W for 30 min. After filtration, it was dried at 80 °C to constant weight for later use.

[0041] Grafting reaction: Corn starch and deionized water were mixed at a mass ratio of 1:3, heated to 85℃ and gelatinized for 30 min, cooled to 45℃, and then 5% methyl methacrylate, 0.3% ammonium persulfate and 2% pretreated nano-hydroxyapatite were added. The mixture was reacted under nitrogen protection for 2 h. After the reaction was completed, the starch was centrifuged to dehydrate, dried at 80℃ to constant weight, and pulverized through an 80-mesh sieve to obtain modified starch.

[0042] Bamboo fiber pretreatment: Soak bamboo fibers in a 2% sodium hydroxide solution at 60°C for 1 hour. After soaking, rinse with deionized water until neutral and then dry at 80°C to constant weight for later use.

[0043] Gradient melt compounding: 15 parts of modified starch and 45 parts of polybutylene terephthalate were mixed and preheated and dried at 120°C under vacuum of -0.08MPa for 2 hours. The mixture was then added to a twin-screw extruder with a length-to-diameter ratio of 35:1 and melt-blended at the following temperature gradients: Zone 1 180°C, Zone 2 200°C, Zone 3 220°C, Zone 4 230°C, and Die head 230°C. The screw speed was 300 r / min and the feeding speed was 50 kg / h to obtain the composite matrix.

[0044] Mixing ingredients: Mix the composite substrate with 10 parts of polybutylene adipate, 5 parts of pretreated bamboo fiber, 3 parts of maleic anhydride-grafted polyolefin elastomer, and 2 parts of calcium stearate. Stir at 200 r / min for 15 min under nitrogen protection to obtain the mixture.

[0045] Segmented spinning: The mixture is added to the spinning machine, and segmented temperature-controlled spinning is adopted. The spinning machine barrel is 200℃ in zone 1, 210℃ in zone 2, and 220℃ in zone 3. The spinneret temperature is 225℃, the spinneret orifice diameter is 0.2mm, and the spinning speed is 800m / min. Nitrogen gas at 0.1MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and stretched at a cooling temperature of 25℃ and a stretching ratio of 2.5 times to obtain biodegradable fibers.

[0046] Weaving and Finishing: The biodegradable fibers are warped, woven, and heat-set. The warping speed is 50 m / min and the warping tension is 20 cN. The weaving method is plain weave, with a weaving density of 30 warp yarns / cm and 25 weft yarns / cm. The weft tension during the weaving process is 15 cN. The heat-setting treatment is carried out in a hot air circulating oven at a temperature of 120℃ for 20 minutes, with an oven air velocity of 1 m / s. After heat setting, the filter cloth is cut and edge-locked with a 0.5 cm overlock width to obtain a biodegradable filter cloth with a thickness of 0.1 mm.

[0047] Example 2: Preparation of modified starch: Pretreatment of nano-hydroxyapatite: Nano-hydroxyapatite with a particle size of 80 nm was added to a 1.5% (w / w) ethanol solution of silane coupling agent KH550, ultrasonically dispersed at 250 W for 35 min, filtered, and dried at 85 °C to constant weight for later use.

[0048] Grafting reaction: Cassava starch and deionized water were mixed at a mass ratio of 1:4, heated to 90℃ and gelatinized for 35 min, cooled to 50℃, and then 6.5% butyl acrylate, 0.4% potassium persulfate and 2.5% pretreated nano-hydroxyapatite were added. The reaction was carried out under nitrogen protection for 2.5 h. After the reaction was completed, the starch was dehydrated by centrifugation, dried to constant weight at 90℃, and pulverized through a 100-mesh sieve to obtain modified starch.

[0049] Bamboo fiber pretreatment: Soak bamboo fibers in a 2.5% sodium hydroxide solution at 65°C for 1.5 hours. After soaking, rinse with deionized water until neutral and then dry at 85°C to constant weight for later use.

[0050] Gradient melt composite: 18 parts of modified starch and 50 parts of polybutylene terephthalate were mixed and preheated and dried at 125°C under vacuum of -0.07MPa for 2.5 hours. The mixture was then added to a twin-screw extruder with a length-to-diameter ratio of 38:1 and melt-blended at the following temperature gradients: Zone 1 185°C, Zone 2 205°C, Zone 3 225°C, Zone 4 235°C, and Die head 235°C. The screw speed was 320 r / min and the feeding speed was 65 kg / h to obtain the composite matrix.

[0051] Mixing ingredients: Mix the composite substrate with 12 parts of polybutylene adipate, 6 parts of pretreated bamboo fiber, 4 parts of maleic anhydride-grafted polyolefin elastomer, and 3 parts of vinyl bis-stearamide. Stir at 250 r / min for 20 min under nitrogen protection to obtain the mixture.

[0052] Segmented spinning: The mixture is added to the spinning machine, and segmented temperature-controlled spinning is adopted. The spinning machine barrel is 205℃ in zone 1, 215℃ in zone 2, and 225℃ in zone 3. The spinneret temperature is 230℃, the spinneret orifice diameter is 0.25mm, and the spinning speed is 900m / min. Argon gas at 0.15MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and stretched at a cooling temperature of 30℃ and a stretching ratio of 3.0 times to obtain biodegradable fibers.

[0053] Weaving and Finishing: The biodegradable fibers are warped, woven, and heat-set. The warping speed is 65 m / min and the warping tension is 25 cN. The weaving method is twill weaving, with a weaving density of 35 warp yarns / cm and 30 weft yarns / cm. The weft tension during the weaving process is 20 cN. The heat-setting treatment is carried out in a hot air circulating oven at a temperature of 125℃ for 25 minutes, with an oven air velocity of 1.5 m / s. After heat setting, the filter cloth is cut and edge-locked with a 0.8 cm edging width to obtain a 0.2 mm thick biodegradable filter cloth.

[0054] Example 3: Preparation of modified starch: Pretreatment of nano-hydroxyapatite: Nano-hydroxyapatite with a particle size of 100 nm was added to a 2% (w / w) ethanol solution of silane coupling agent KH550, and ultrasonically dispersed at 300 W for 40 min. After filtration, it was dried at 90 °C to constant weight for later use.

[0055] Grafting reaction: Corn starch and deionized water were mixed at a mass ratio of 1:5, heated to 95℃ and gelatinized for 40 min, cooled to 55℃, and then 8% methyl methacrylate, 0.5% ammonium persulfate and 3% pretreated nano-hydroxyapatite were added. The mixture was reacted for 3 h under nitrogen protection. After the reaction was completed, the starch was centrifuged to remove water, dried at 100℃ to constant weight, and pulverized through a 120-mesh sieve to obtain modified starch.

[0056] Bamboo fiber pretreatment: Soak bamboo fibers in a 3% sodium hydroxide solution at 70°C for 2 hours. After soaking, rinse with deionized water until neutral and then dry at 90°C to constant weight for later use.

[0057] Gradient melt compounding: 20 parts of modified starch and 55 parts of polybutylene terephthalate were mixed and preheated and dried at 130°C under vacuum of -0.06MPa for 3 hours. The mixture was then added to a twin-screw extruder with a length-to-diameter ratio of 40:1 and melt-blended at the following temperature gradients: Zone 1 190°C, Zone 2 210°C, Zone 3 230°C, Zone 4 240°C, and Die head 240°C. The screw speed was 350 r / min and the feeding speed was 80 kg / h to obtain the composite matrix.

[0058] Mixing ingredients: Mix the composite substrate with 15 parts of polybutylene adipate, 8 parts of pretreated bamboo fiber, 5 parts of maleic anhydride-grafted polyolefin elastomer, and 4 parts of calcium stearate. Stir at 300 r / min for 25 min under nitrogen protection to obtain the mixture.

[0059] Segmented spinning: The mixture is added to the spinning machine, and segmented temperature-controlled spinning is adopted. The spinning machine barrel is 210℃ in zone 1, 220℃ in zone 2, and 230℃ in zone 3. The spinneret temperature is 235℃, the spinneret orifice diameter is 0.3mm, and the spinning speed is 1000m / min. Nitrogen gas at 0.2MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and stretched at a cooling temperature of 35℃ and a stretching ratio of 3.5 times to obtain biodegradable fibers.

[0060] Weaving and Finishing: The biodegradable fibers are warped, woven, and heat-set. The warping speed is 80 m / min and the warping tension is 30 cN. The weaving method is plain weave, with a weaving density of 40 warp yarns / cm and 35 weft yarns / cm. The weft tension during the weaving process is 25 cN. The heat-setting treatment is carried out in a hot air circulating oven at a temperature of 130℃ for 30 minutes, with an oven air velocity of 2 m / s. After heat setting, the filter cloth is cut and edge-locked with a 1.0 cm overlock width to obtain a biodegradable filter cloth with a thickness of 0.3 mm.

[0061] Comparative Example 1: The difference from Example 2 is that no modified starch was used, only ordinary corn starch was used as a substitute, while the other raw material ratios and preparation steps were the same as in Example 2.

[0062] Comparative Example 2: The difference from Example 2 is that the bamboo fiber was used directly without pretreatment, while the proportions of other raw materials and preparation steps were the same as in Example 2.

[0063] Comparative Example 3: The difference from Example 2 is that maleic anhydride-grafted polyolefin elastomer was not added, while the other raw material ratios and preparation steps were the same as in Example 2.

[0064] Comparative Example 4: The difference from Example 2 is that the gradient melt composite process was not used in the preparation process, the temperature of each zone of the twin-screw extruder was set to 220°C, and the remaining raw material ratios and preparation steps were the same as in Example 2.

[0065] Performance verification test Experiment 1: Mechanical property testing; Breaking strength and elongation at break: Five samples each with warp and weft dimensions of 300mm × 50mm were cut. The edges of the samples were sealed to prevent yarn fraying. The clamping length was 200mm, the stretching speed was 100mm / min, and the pre-tension was 0.5% of the breaking strength of the sample. The breaking strength and elongation at break of each sample were recorded, and the average value was taken. The results are as follows: Table 1

[0066] As can be seen from Table 1, the mechanical properties of Examples 1-3 are significantly better than those of the comparative examples, indicating that the mechanical properties of the examples are excellent.

[0067] Experiment 2: Biodegradability test; The sample was cut into 10mm × 10mm pieces, and 5g of sample (dry weight) was accurately weighed after removing non-fibrous impurities. This sample was then mixed with compost substrate (a mixture of garden soil, well-rotted organic fertilizer, and sawdust in a mass ratio of 5:3:2, a carbon-to-nitrogen ratio of 25:1, a moisture content of 55%, and a pH of 7.0 ± 0.5) that had been acclimated for two weeks and placed in a laboratory-scale composting reactor (effective volume 5L). The reaction temperature was controlled at 58 ± 2℃, the oxygen concentration at ≥10% (volume fraction), and the moisture content of the compost substrate was maintained at 55% ± 5%. Exhaust gases were collected periodically, and the carbon dioxide concentration was measured using an infrared gas analyzer to calculate the cumulative carbon dioxide release. A blank control group (compost substrate only) and a reference control group (cellulose filter paper) were also set up. The carbon dioxide release of the blank control group was subtracted, and the theoretical maximum carbon dioxide release of the reference control group was compared to obtain the biodegradation rate of the sample. The experiment lasted 180 days, with three parallel experiments for each sample. The average value was taken, and the results are as follows: Table 2

[0068] As can be seen from Table 2, the biodegradability of Examples 1-3 all exceeded 78%, which meets the requirements for biodegradable materials.

[0069] Experiment 3: Filtration performance test; A suspension with a concentration of 10 g / L was prepared using silica particles with a particle size of 5 μm (purity ≥99%, particle size distribution deviation ≤±0.5 μm). The suspension medium was deionized water, and the particles were ultrasonically dispersed for 30 min to ensure uniform dispersion. A flat-plate filter with a filtration area of ​​10 cm² was used.2 A pressure stabilizing valve is installed between the feed tank and the filtration device to control the filtration pressure at 0.1 MPa (relative pressure). The filter cloth sample is laid flat on the support mesh of the filtration device and pressed tightly to prevent leakage. The suspension is introduced at an initial flow rate of 5 mL / min. After continuously filtering 100 mL of suspension, suspension samples are collected before and after filtration. The concentration of 5 μm particles in the samples is determined using a laser particle size analyzer. The filtration efficiency is calculated using the formula: "Filtration efficiency = (particle concentration before filtration - particle concentration after filtration) / particle concentration before filtration × 100%". The total time for filtering 100 mL of suspension is also recorded and converted to an average filtration rate. Each sample is tested three times. The device is cleaned after each test to avoid cross-contamination. The average value is taken. The results are as follows: Table 3

[0070] As can be seen from Table 3, Examples 1-3 exhibit excellent filtration performance, with filtration efficiencies all exceeding 92% and filtration rates maintained above 4.2 mL / min. This achieves a balance between high-efficiency filtration and low resistance, meeting the needs of industrial and civilian filtration scenarios.

[0071] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A biodegradable filter cloth, characterized in that, It is composed of the following components in parts by weight: 45-55 parts of polybutylene terephthalate, 15-20 parts of modified starch, 10-15 parts of polybutylene adipate, 5-8 parts of bamboo fiber, 3-5 parts of maleic anhydride-grafted polyolefin elastomer, and 2-4 parts of lubricant.

2. The biodegradable filter cloth according to claim 1, wherein, The modified starch is an acrylate-grafted nano-hydroxyapatite synergistic modified starch, and its preparation method includes the following steps: (1) Pretreatment of nano hydroxyapatite: Add nano hydroxyapatite with a particle size of 50-100nm to a 1%-2% mass fraction of silane coupling agent KH550 ethanol solution, ultrasonically disperse at 200-300W power for 30-40min, filter, and dry at 80-90℃ to constant weight for later use. (2) Grafting reaction: Corn starch or cassava starch is mixed with deionized water at a mass ratio of 1:3-5, heated to 85-95℃ and gelatinized for 30-40 minutes. After cooling to 45-55℃, 5%-8% of acrylate monomer, 0.3%-0.5% of initiator and 2%-3% of pretreated nano-hydroxyapatite are added. The mixture is reacted under nitrogen protection for 2-3 hours. After the reaction is completed, the mixture is centrifuged to dehydrate, dried at 80-100℃ to constant weight, and pulverized through an 80-120 mesh sieve to obtain modified starch.

3. The biodegradable filter cloth according to claim 2, characterized in that, The initiator is ammonium persulfate or potassium persulfate; the acrylate monomer is methyl methacrylate or butyl acrylate.

4. The biodegradable filter cloth according to claim 1, characterized in that, The bamboo fiber is pretreated by immersing it in a 2%-3% sodium hydroxide solution at 60-70°C for 1-2 hours, rinsing it with deionized water until neutral, and then drying it at 80-90°C to constant weight.

5. The biodegradable filter cloth according to claim 1, characterized in that, The lubricant is calcium stearate or vinyl bis-stearamide.

6. The biodegradable filter cloth according to claim 1, characterized in that, The thickness of the filter cloth is 0.1-0.3 mm.

7. A method for preparing a biodegradable filter cloth as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of modified starch: Preparation of acrylate-grafted-nanohydroxyapatite synergistic modified starch; (2) Gradient melt composite: The modified starch prepared in step (1) is mixed with polybutylene terephthalate in the weight ratio mentioned above, preheated and dried at a vacuum of -0.08~-0.06MPa and 120-130℃ for 2-3h, and then added to a twin-screw extruder with a length-to-diameter ratio of 35-40:

1. The mixture is melt-blended at the following temperature gradient: Zone 1 180-190℃, Zone 2 200-210℃, Zone 3 220-230℃, Zone 4 230-240℃, and die head 230-240℃. The screw speed is 300-350r / min and the feeding speed is 50-80kg / h to obtain the composite substrate. (3) Mixing and mixing: The composite substrate obtained in step (2) is mixed with polybutylene adipate, pretreated bamboo fiber, maleic anhydride grafted polyolefin elastomer and lubricant in the weight ratio described above, and stirred at a speed of 200-300 r / min for 15-25 min under nitrogen protection to obtain the mixture. (4) Segmented spinning: The mixture obtained in step (3) is added to the spinning machine and segmented temperature-controlled spinning is adopted. The spinning machine barrel is 200-210℃ in zone 1, 210-220℃ in zone 2, and 220-230℃ in zone 3. The spinneret temperature is 225-235℃, the spinneret orifice diameter is 0.2-0.3mm, and the spinning speed is 800-1000m / min. Inert gas of 0.1-0.2MPa is introduced through the annular air channel around the spinneret to assist spinning. The spun fibers are cooled and stretched. The cooling temperature is 25-35℃ and the stretching ratio is 2.5-3.5 times to obtain biodegradable fibers. (5) Weaving and finishing: The biodegradable fibers obtained in step (4) are warped, woven and heat-set to obtain biodegradable filter cloth.

8. The biodegradable filter cloth according to claim 7, characterized in that, The inert gas in step (4) is nitrogen or argon.

9. The biodegradable filter cloth according to claim 7, characterized in that, The warping process parameters in step (5) are: warping speed 50-80m / min, warping tension 20-30cN; the weaving method is plain weave or twill weave, the weaving density is 30-40 warp yarns / cm, weft yarns 25-35 weft yarns / cm, and the weft tension during the weaving process is 15-25cN.

10. The preparation method according to claim 7, characterized in that, The heat setting process is carried out in a hot air circulating oven at a temperature of 120-130℃ for 20-30 minutes, with an oven wind speed of 1-2 m / s. After heat setting, the filter cloth is cut and edge-locked with a width of 0.5-1.0 cm.

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