Degradable cigarette filter tow and method of making

Abstract

The application relates to the technical field of material preparation, and discloses a degradable cigarette filter tow and a preparation method thereof. The degradable cigarette filter tow is twisted from modified plant fibers and polylactic acid fiber tows, the modified plant fibers are obtained by compounding basalt fibers after semi-carbonization and low-temperature plasma treatment of plant fibers, and the modified plant fibers are used as supports to be compounded with the polylactic acid fiber tows, and the basalt fibers on the surfaces of the modified plant fibers are used to ensure sufficient distance between the tows, so that the problems of insufficient hardness and easy adhesion of the polylactic acid fibers when used alone are solved.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a biodegradable cigarette filter tow and its preparation method. Background Technology

[0002] In existing cigarette products on the market, the filter tip is crucial for reducing harmful substances in cigarette smoke. The filter tip traps some of the particles and harmful substances in the smoke, thus reducing the amount of harmful substances in the inhaled smoke. Currently, most cigarette filters use cellulose acetate as the filter material. Cellulose acetate filters have excellent trapping effects on harmful components in cigarette smoke and are widely used. However, cellulose acetate is difficult to degrade under natural conditions, causing a significant environmental impact. The organic solvents used in its production cause serious environmental pollution and can easily remain in the filter tip, harming the health of cigarette consumers.

[0003] Polylactic acid (PLA) tow, due to its advantages of wide availability, complete biodegradability, short degradation cycle, and good processing performance, and the abundance of polar groups on its surface, exhibits excellent adsorption properties for polar substances in flue gas, making it a promising alternative to cellulose acetate. However, in practical applications, the insufficient hardness of PLA fibers leads to inadequate filter hardness when used alone. Furthermore, under the high temperatures of flue gas, PLA fibers melt, causing them to adhere and clog the filter rod, increasing suction resistance and negatively impacting the vaping experience. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a biodegradable cigarette filter tow and its preparation method, which uses modified plant fiber as support and is compounded with polylactic acid fiber bundles, thus solving the problems of insufficient hardness and easy adhesion of polylactic acid fiber when used alone.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] A biodegradable cigarette filter tow, wherein the tow is made of modified plant fiber and polylactic acid fiber tow twisted together, wherein the modified plant fiber is made by first semi-carbonizing the plant fiber and then treating it with low-temperature plasma, and then combining it with basalt fiber.

[0007] Semi-carbonization and low-temperature plasma treatment can increase the surface roughness of plant fibers and the content of active groups on the surface of plant fibers, which is more conducive to subsequent composite with basalt fibers. The basalt fibers further increase the surface roughness of plant fibers, which is more conducive to the composite between modified plant fibers and polylactic acid fiber bundles. At the same time, due to the presence of basalt fibers, when plant fibers and polylactic acid fiber bundles are composited and aggregated into a filter, the basalt fibers can provide a certain support for the entire filter. On the other hand, the presence of basalt fibers creates gaps between the fiber bundles, which is conducive to the passage of flue gas, thereby preventing the fiber bundles from sticking together and reducing the impact on the suction resistance of the filter rod.

[0008] Furthermore, the basalt fiber includes a first basalt fiber and a second basalt fiber, wherein the first basalt fiber has a diameter of 0.5-1.0 μm and an aspect ratio of 1-2, and the second basalt fiber has a diameter of 1.5-3 μm and an aspect ratio of 1-1.5.

[0009] By using two different sizes of basalt fibers, protrusions of varying heights are formed on the surface of the modified plant fibers, thereby increasing the contact area between the modified plant fibers and polylactic acid fibers. During the composite process of basalt fiber modified plant fibers and polylactic acid fiber bundles, the polylactic acid fiber bundles can be constrained to a certain extent, improving the stability of the bundle twisting.

[0010] Furthermore, the mass ratio of the first basalt fiber to the second basalt fiber is 3:(1-1.5).

[0011] Furthermore, the diameter of the modified plant fiber is 20-45 μm.

[0012] Furthermore, the method for preparing the modified plant fiber is as follows:

[0013] Semi-carbonization: Take the pretreated plant fiber and place it in a muffle furnace. Pour nitrogen gas into the furnace and keep it at 200-250℃ for 60-90 minutes under nitrogen atmosphere. Cool it to room temperature to obtain semi-carbonized plant fiber.

[0014] Softening: Sorbitol anhydride fatty acid ester polyoxyethylene ether and dioctadecyl dimethyl ammonium chloride were stirred and mixed at 50-60℃ for 30-45 min. Deionized water preheated to 50-60℃ was added, and stirring and mixing were continued for 20-30 min. Acetic acid was added to adjust the pH of the solution to 5-6 to obtain a mixed solution. Semi-carbonized plant fibers were placed in a ball mill and ground for 30-45 min. Impurities were removed and sieved out. The plant fibers were added back to the ball mill, and the mixed solution was added again. The mixture was ball milled for 45-90 min. The mixture was then removed and heated to 65-80℃ under stirring. The reaction was continued for 1-2 h. After the reaction was completed, the mixture was filtered. The filter cake was washed with deionized water until neutral and dried to obtain softened plant fibers.

[0015] Composite: Basalt fibers were added to a 1% (w / w) silane coupling agent solution and soaked for 4-5 hours. After soaking, the fibers were dried at 110-120℃ for 2-3 hours and ultrasonically dispersed in a 0.07 mol / L maleic anhydride solution to obtain a suspension for later use. The softened plant fibers were added to a low-temperature plasma device for low-temperature plasma treatment and then immediately immersed in the suspension. Benzoyl peroxide was added dropwise and the mixture was stirred for 2-3 hours. The mixture was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. The filtered cake was then dried to obtain the modified plant fibers.

[0016] Semi-carbonization of plant fibers carbonizes the surface while maintaining the fibrous structure and toughness inside. Grinding then partially removes the carbon deposits from the fibers, increasing the surface roughness. The semi-carbonized plant fibers also enhance their ability to adsorb harmful substances in cigarette smoke. Combined with softening treatment, the plant fibers become relatively softer, thus meeting the hardness requirements of cigarette filter rods.

[0017] Furthermore, the plant fiber is any one of flax fiber, ramie fiber, mulberry bark fiber, and coconut shell fiber.

[0018] Furthermore, the pretreatment of the plant fiber is as follows: the plant fiber is soaked in deionized water at 25-40℃ for 1-2 days, expandable graphite nanosheets are added, ultrasonic treatment is performed for 20-30 minutes, the fiber is taken out and placed in a microwave oven, treated for 10-20 seconds at a microwave power of 100-300W, cooled to room temperature, taken out, and washed in deionized water by shaking 3-5 times, and then dried for later use.

[0019] Plant fiber molecules generally have a relatively compact structure, high crystallinity and orientation, and a flat, non-curled surface, making them unsuitable for composite with polylactic acid fibers. Pre-treating plant fibers with expandable graphite nanosheets under microwave conditions causes the nanosheets to expand, and the water in the plant fibers absorbs microwave energy, resulting in volume changes. This swelling of the plant fibers causes the hydrogen bonds inside the fibers to break, reducing crystallinity and making the fibers looser, which is more conducive to subsequent processing.

[0020] Furthermore, the low-temperature plasma treatment uses air as the working gas, with a discharge power of 150-170W and a treatment time of 3-5 minutes.

[0021] Furthermore, this invention also discloses a method for preparing the above-mentioned biodegradable cigarette filter tow. The specific preparation method is as follows: polylactic acid fiber tow is placed in deionized water, 1-2 wt% formic acid solution and 3-5 wt% chloroacetic acid solution are added, the pH is adjusted to 7-7.5, dimethylamine is added, and the reaction is carried out at 40-70℃ for 60-90 min. After that, the polylactic acid fiber tow is taken out, dried at 40-50℃ for 20-30 min, soaked in water-based polyurethane adhesive solution for 5-15 min, taken out, heated to 90-110℃, and then thermally twisted with modified plant fiber. After drying at 70-90℃, the biodegradable cigarette filter tow is obtained.

[0022] The beneficial effects of this invention are:

[0023] 1. The biodegradable cigarette filter tow of the present invention is obtained by combining modified plant fiber and polylactic acid fiber tow. The plant fiber serves as a supporting skeleton to support the polylactic acid fiber tow, while the basalt fiber on the surface of the modified plant fiber ensures sufficient distance between the tows, thereby preventing the polylactic acid fiber tows from sticking together. This allows the filter to meet the requirements for hardness and draw resistance. At the same time, both the plant fiber and polylactic acid fiber used have good biodegradability, are environmentally friendly, and reduce environmental pollution.

[0024] 2. The biodegradable cigarette filter tow of the present invention is prepared by first reacting polylactic acid tow with formic acid, chloroacetic acid, dimethylamine and other substances under weak alkaline conditions to methylate it. The methylated polylactic acid not only has better adhesion, but also better adsorption of harmful substances in the smoke. After being soaked in an aqueous polyurethane adhesive solution and heated to a slightly molten state, the surface exhibits high adhesion. After being thermally twisted with modified plant fibers, the polylactic acid fibers and modified plant fibers are tightly compounded and are not easy to loosen and fall off, thus improving the stability of use. Detailed Implementation

[0025] The technical solutions of the embodiments 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.

[0026] This invention discloses a biodegradable cigarette filter tow, which is made by twisting modified plant fiber and polylactic acid fiber tow. The modified plant fiber is prepared by first semi-carbonizing and then treating the plant fiber with low-temperature plasma, followed by compounding with basalt fiber. The basalt fiber includes a first basalt fiber and a second basalt fiber. The first basalt fiber has a diameter of 0.5-1.0 μm and an aspect ratio of 1-2, while the second basalt fiber has a diameter of 1.5-3 μm and an aspect ratio of 1-1.5. The specific preparation method is as follows:

[0027] Example 1

[0028] Preparation of modified plant fibers

[0029] In this embodiment, ramie fiber is selected as the plant fiber, and the specific preparation method is as follows:

[0030] The pretreatment process is as follows: take ramie fibers with a diameter of 20-30μm and soak them in deionized water at 25℃ for 2 days. Add expandable graphite nanosheets with a mass of 0.1 times that of the ramie fibers and sonicate for 20 minutes. Take them out and place them in a microwave oven. Treat them for 15 seconds at a microwave power of 200W. After cooling to room temperature, take them out and place them in deionized water to shake and wash 3-5 times. Dry them for later use.

[0031] Semi-carbonization: Pretreated ramie fibers are placed in a muffle furnace, nitrogen is introduced, and the furnace is kept at 200°C for 80 minutes under a nitrogen atmosphere. After cooling to room temperature, semi-carbonized ramie fibers are obtained.

[0032] Softening: Sorbitan fatty acid ester polyoxyethylene ether and dioctadecyl dimethyl ammonium chloride were stirred and mixed at 50°C for 30 min. Deionized water preheated to 50°C was added. The mass ratio of sorbitan fatty acid ester polyoxyethylene ether, dioctadecyl dimethyl ammonium chloride and deionized water was 10:2:5. The mixture was stirred and mixed for another 25 min. Acetic acid was added to adjust the pH of the solution to 5-6 to obtain a mixed solution. Semi-carbonized ramie fibers were placed in a ball mill and ground for 30 min. Impurities were removed and sieved out. The ramie fibers were added back into the ball mill, and 10 times the mass of the mixed solution of ramie fibers was added. The mixture was ball milled for 90 min and then removed. The temperature was raised to 65°C under stirring and the reaction was continued for 2 h. After the reaction was completed, the mixture was filtered. The filter cake was washed with deionized water until neutral and dried to obtain softened ramie fibers.

[0033] Composite process: First basalt fibers with a diameter of 0.5-1.0 μm and an aspect ratio of 1-2, and second basalt fibers with a diameter of 1.5-3 μm and an aspect ratio of 1-1.5 are weighed at a mass ratio of 3:1.2. After ball milling and mixing, basalt fibers are obtained. The basalt fibers are then added to a prepared 1% (w / w) silane coupling agent solution, soaked for 5 hours, removed, and dried at 110℃ for 3 hours. The resulting product is then processed with 20 g / L of... The solid-liquid ratio was ultrasonically dispersed in a 0.1 mol / L maleic anhydride solution to obtain a suspension for later use. The prepared softened ramie fibers were added to a low-temperature plasma device, with air as the working gas, and subjected to low-temperature plasma treatment for 5 min at a discharge power of 150 W. Immediately afterward, the fibers were immersed in the suspension, and 0.05 times the mass of the softened ramie fibers was added dropwise. The mixture was stirred and reacted for 2 h. After filtration, the filter cake was washed with deionized water until the washing liquid was neutral, and then dried to obtain modified ramie fibers.

[0034] Preparation of biodegradable cigarette filter tow

[0035] Polylactic acid fiber tow was placed in deionized water, and 2 wt% formic acid solution and 3 wt% chloroacetic acid solution were added to adjust the pH to 7-7.5. Then dimethylamine was added, and the mixture was reacted at 50°C for 80 min. The polylactic acid fiber tow was then removed, dried at 50°C for 25 min, soaked in an aqueous polyurethane adhesive solution for 5 min, and then removed. After being heated to 110°C, it was thermally twisted with modified ramie fiber and dried at 90°C to obtain biodegradable cigarette filter tow.

[0036] Example 2

[0037] Preparation of modified plant fibers

[0038] In this embodiment, coconut shell fiber is selected as the plant fiber, and the specific preparation method is as follows:

[0039] The pretreatment process is as follows: take coconut shell fibers with a diameter of 35-45μm and soak them in deionized water at 40℃ for 1 day. Add expandable graphite nanosheets with a mass of 0.2 times that of ramie fibers, sonicate for 30 minutes, take them out and place them in a microwave oven. Treat them for 10 seconds at a microwave power of 300W. After cooling to room temperature, take them out and place them in deionized water to shake and wash 3-5 times. Dry them for later use.

[0040] Semi-carbonization: Pretreated coconut shell fiber is placed in a muffle furnace, nitrogen is introduced, and the temperature is kept at 220°C for 90 minutes under nitrogen atmosphere. After cooling to room temperature, semi-carbonized coconut shell fiber is obtained.

[0041] Softening: Sorbitan fatty acid ester polyoxyethylene ether and dioctadecyl dimethyl ammonium chloride were stirred and mixed at 55°C for 45 min. Deionized water preheated to 55°C was added. The mass ratio of sorbitan fatty acid ester polyoxyethylene ether, dioctadecyl dimethyl ammonium chloride and deionized water was 12:3:8. The mixture was stirred and mixed for another 30 min. Acetic acid was added to adjust the pH of the solution to 5-6 to obtain a mixed solution. Semi-carbonized coconut shell fiber was placed in a ball mill and ground for 40 min. Impurities were removed and sieved out. The coconut shell fiber was added back into the ball mill, and 10 times the mass of the mixed solution of coconut shell fiber was added. The mixture was ball milled for 60 min and then removed. The temperature was raised to 80°C under stirring and the reaction was continued for 1 h. After the reaction was completed, the mixture was filtered. The filter cake was washed with deionized water until neutral and dried to obtain softened coconut shell fiber.

[0042] Composite: First basalt fibers with a diameter of 0.5-1.0 μm and an aspect ratio of 1-2, and second basalt fibers with a diameter of 1.5-3 μm and an aspect ratio of 1-1.5, are mixed at a ratio of 3:1.5. The first and second basalt fibers were weighed out by mass ratio and mixed by ball milling to obtain basalt fibers. The basalt fibers were added to a prepared 1% silane coupling agent solution, soaked for 4 hours, and then dried at 120℃ for 3 hours. The basalt fibers were ultrasonically dispersed in a 0.1 mol / L maleic anhydride solution at a solid-liquid ratio of 18 g / L to obtain a suspension for later use. The prepared softened coconut shell fibers were added to a low-temperature plasma device, and air was used as the working gas. The low-temperature plasma treatment was carried out for 3 minutes under a discharge power of 170W. The fibers were then immediately immersed in the suspension, and 0.05 times the mass of the softened coconut shell fibers of benzoyl peroxide was added dropwise. The mixture was stirred and reacted for 3 hours. The mixture was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. The mixture was then dried to obtain modified coconut shell fibers.

[0043] Preparation of biodegradable cigarette filter tow

[0044] Polylactic acid fiber tow was placed in deionized water, and 1 wt% formic acid solution and 5 wt% chloroacetic acid solution were added to adjust the pH to 7-7.5. Then dimethylamine was added, and the mixture was reacted at 70℃ for 60-90 min. The polylactic acid fiber tow was then removed, dried at 40℃ for 30 min, soaked in an aqueous polyurethane adhesive solution for 12 min, removed, heated to 100℃, and then thermally twisted with modified plant fibers. The mixture was then dried at 90℃ to obtain biodegradable cigarette filter tow.

[0045] Example 3

[0046] Preparation of modified plant fibers

[0047] In this embodiment, mulberry bark fiber is selected as the plant fiber, and the specific preparation method is as follows:

[0048] The pretreatment process is as follows: Soak mulberry bark fibers with a diameter of 30-40 μm in deionized water at 35℃ for 1 day, add expandable graphite nanosheets with a mass of 0.15 times that of ramie fibers, sonicate for 25 minutes, take them out and place them in a microwave oven, treat them for 20 seconds at a microwave power of 100W, cool them to room temperature, take them out and place them in deionized water to shake and wash 3-5 times, and dry them for later use.

[0049] Semi-carbonization: Take the pretreated mulberry bark fiber and place it in a muffle furnace. Pour nitrogen into the furnace and keep it at 250°C for 60 minutes under nitrogen atmosphere. Cool it to room temperature to obtain semi-carbonized mulberry bark fiber.

[0050] Softening: Sorbitan fatty acid ester polyoxyethylene ether and dioctadecyl dimethyl ammonium chloride were stirred and mixed at 60°C for 40 min. Deionized water preheated to 60°C was added. The mass ratio of sorbitan fatty acid ester polyoxyethylene ether, dioctadecyl dimethyl ammonium chloride and deionized water was 15:1:8. The mixture was stirred and mixed for another 20 min. Acetic acid was added to adjust the pH of the solution to 5-6 to obtain a mixed solution. Semi-carbonized mulberry bark fiber was placed in a ball mill and ground for 45 min. Impurities were removed and sieved out. The mulberry bark fiber was added back to the ball mill, and 10 times the mass of the mixed solution of mulberry bark fiber was added. The mixture was ball milled for another 45 min. The mixture was then removed and heated to 70°C under stirring. The reaction was continued for 2 h. After the reaction was completed, the mixture was filtered. The filter cake was washed with deionized water until neutral and dried to obtain softened mulberry bark fiber.

[0051] Composite: Take first basalt fibers with a diameter of 0.5-1.0 μm and an aspect ratio of 1-2, and second basalt fibers with a diameter of 1.5-3 μm and an aspect ratio of 1-1.5, and mix them in a 3:1 ratio. The first and second basalt fibers were weighed out by mass ratio and mixed by ball milling to obtain basalt fibers. The basalt fibers were added to a prepared 1% silane coupling agent solution, soaked for 4 hours, and then dried at 115℃ for 2 hours. The basalt fibers were ultrasonically dispersed in a 0.1mol / L maleic anhydride solution at a solid-liquid ratio of 15g / L to obtain a suspension for later use. The prepared softened mulberry bark fibers were added to a low-temperature plasma device, and air was used as the working gas. The low-temperature plasma treatment was carried out at a discharge power of 160W for 4 minutes. The fibers were then immediately immersed in the suspension. Benzoyl peroxide with a mass of 0.05 times that of the softened mulberry bark fibers was added dropwise. The mixture was stirred and reacted for 2-3 hours. The mixture was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. The mixture was then dried to obtain modified mulberry bark fibers.

[0052] Preparation of biodegradable cigarette filter tow

[0053] Polylactic acid fiber tow was placed in deionized water, and 2 wt% formic acid solution and 4 wt% chloroacetic acid solution were added to adjust the pH to 7-7.5. Then dimethylamine was added, and the mixture was reacted at 40°C for 60-90 min. The polylactic acid fiber tow was then removed, dried at 50°C for 30 min, soaked in an aqueous polyurethane adhesive solution for 15 min, and then removed. After being heated to 90°C, it was thermally twisted with modified coconut shell fiber and dried at 80°C to obtain biodegradable cigarette filter tow.

[0054] Comparative Example 1

[0055] The difference between this comparative example and Example 1 is that the filter tip in this comparative example is made of pure polylactic acid fiber tow.

[0056] Comparative Example 2

[0057] The difference between this comparative example and Example 1 is that the modified plant fiber in this comparative example is not composite with basalt fiber.

[0058] The hardness of the cigarette filters prepared in Example 1, Comparative Example 1, and Comparative Example 2, as well as the draw resistance during the first, third, fifth, and seventh puffs, were tested. The test results are shown in Table 1.

[0059] Table 1. Hardness and suction resistance test results

[0060]

[0061] As can be seen from the data in the table above, the filter rod prepared using the tow of the present invention has a hardness that better meets the hardness requirements of cigarette filter rods. At the same time, the draw resistance of the filter rod will not be affected as the smoking time increases.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A biodegradable cigarette filter tow, characterized in that, The filament bundle is made of modified plant fiber and polylactic acid fiber bundle twisted together. The modified plant fiber is made by first semi-carbonizing and then treating the plant fiber with low-temperature plasma, and then combining it with basalt fiber. The method for preparing the modified plant fiber is as follows: Semi-carbonization: Take the pretreated plant fiber and place it in a muffle furnace. Pour nitrogen gas into the furnace and keep it at 200-250℃ for 60-90 minutes under nitrogen atmosphere. Cool it to room temperature to obtain semi-carbonized plant fiber. Softening: Sorbitol anhydride fatty acid ester polyoxyethylene ether and dioctadecyl dimethyl ammonium chloride were stirred and mixed at 50-60℃ for 30-45 min. Deionized water preheated to 50-60℃ was added, and stirring and mixing were continued for 20-30 min. Acetic acid was added to adjust the pH of the solution to 5-6 to obtain a mixed solution. Semi-carbonized plant fibers were placed in a ball mill and ground for 30-45 min. Impurities were removed and sieved out. The plant fibers were added back to the ball mill, and the mixed solution was added again. The mixture was ball milled for 45-90 min. The mixture was then removed and heated to 65-80℃ under stirring. The reaction was continued for 1-2 h. After the reaction was completed, the mixture was filtered. The filter cake was washed with deionized water until neutral and dried to obtain softened plant fibers. Composite: Basalt fibers were added to a 1% (w / w) silane coupling agent solution and soaked for 4-5 hours. After soaking, the fibers were dried at 110-120℃ for 2-3 hours and ultrasonically dispersed in a 0.07 mol / L maleic anhydride solution to obtain a suspension for later use. The softened plant fibers were added to a low-temperature plasma device for low-temperature plasma treatment and then immediately immersed in the suspension. Benzoyl peroxide was added dropwise and the mixture was stirred for 2-3 hours. The mixture was filtered, and the filter cake was washed with deionized water until the washing liquid was neutral. The filtered cake was then dried to obtain the modified plant fibers.

2. The biodegradable cigarette filter tow according to claim 1, characterized in that, The basalt fiber includes a first basalt fiber and a second basalt fiber. The first basalt fiber has a diameter of 0.5-1.0 μm and an aspect ratio of 1-2. The second basalt fiber has a diameter of 1.5-3 μm and an aspect ratio of 1-1.

5.

3. The biodegradable cigarette filter tow according to claim 2, characterized in that, The mass ratio of the first basalt fiber to the second basalt fiber is 3:(1-1.5).

4. The biodegradable cigarette filter tow according to claim 3, characterized in that, The modified plant fiber has a diameter of 20-45 μm.

5. The biodegradable cigarette filter tow according to claim 4, characterized in that, The plant fiber is any one of flax fiber, ramie fiber, mulberry bark fiber, and coconut shell fiber.

6. The biodegradable cigarette filter tow according to claim 5, characterized in that, The pretreatment of the plant fiber is as follows: the plant fiber is soaked in deionized water at 25-40℃ for 1-2 days, expandable graphite nanosheets are added, ultrasonic treatment is performed for 20-30 minutes, the fiber is taken out and placed in a microwave oven, and treated for 10-20 seconds at a microwave power of 100-300W. After cooling to room temperature, the fiber is taken out and placed in deionized water for 3-5 oscillation washes, and then dried for later use.

7. The biodegradable cigarette filter tow according to claim 6, characterized in that, The low-temperature plasma treatment uses air as the working gas, with a discharge power of 150-170W and a treatment time of 3-5 minutes.

8. A method for preparing a biodegradable cigarette filter tow according to any one of claims 5-7, characterized in that, The specific preparation method is as follows: polylactic acid fiber tow is placed in deionized water, 1-2 wt% formic acid solution and 3-5 wt% chloroacetic acid solution are added, the pH is adjusted to 7-7.5, dimethylamine is added, and the reaction is carried out at 40-70℃ for 60-90 min. After that, the polylactic acid fiber tow is taken out and dried at 40-50℃ for 20-30 min. After that, it is soaked in water-based polyurethane adhesive solution for 5-15 min and then taken out. After being heated to 90-110℃, it is thermally twisted with modified plant fiber and dried at 70-90℃ to obtain biodegradable cigarette filter tow.

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