Degradable polypropylene short fiber and preparation method thereof

Abstract

The invention relates to the field of polypropylene materials, and particularly discloses a degradable polypropylene short fiber and a preparation method thereof. Wherein the polypropylene short fiber comprises the following raw materials: 100-130 parts of polypropylene; 5 to 15 parts of maleic anhydride grafted polypropylene; 15 to 35 parts of hydrophobic modified lignin; 5 to 10 parts of alkylated cyclodextrin; 3-6 parts of a plasticizer; 1-5 parts of a lubricant; and the cyclodextrin contains 6 to 8 D-glucopyranose units. The polypropylene short fiber disclosed by the invention has excellent biodegradability, and meanwhile, the polypropylene short fiber has relatively outstanding performance in fiber strength and toughness.

Description

Technical Field

[0001] The present application relates to the field of polypropylene materials, and in particular to a biodegradable polypropylene staple fiber and a preparation method thereof. Background Art

[0002] Polypropylene staple fibers, due to their excellent physical and mechanical properties, chemical stability, and low cost, are widely used in numerous fields, including textiles, construction, healthcare, and personal hygiene products. However, with growing awareness of environmental protection, the environmental impact of discarded traditional polypropylene staple fibers has become increasingly prominent. Specifically, due to the inherent chemical stability of polypropylene, it is difficult to degrade naturally, resulting in not only a waste of resources but also serious environmental pollution. Consequently, the market is placing higher demands on the biodegradability of fiber materials.

[0003] Adding natural organic compounds, such as lignin, to polypropylene resin is an effective means of improving the biodegradability of polypropylene staple fibers. Lignin, a natural polymer with good biodegradability and environmental friendliness, could theoretically significantly enhance the degradation properties of polypropylene fibers. However, in practice, the incorporation of large amounts of lignin has been found to reduce the extrudability and mechanical properties of polypropylene staple fibers, particularly increasing fiber brittleness and reducing flexibility. This has undoubtedly limited its potential for application in high-performance fibers.

[0004] To address the issue of decreased mechanical properties of polypropylene staple fibers caused by the introduction of lignin, patent application CN105754209A discloses a lignin / polypropylene composite material. Specifically, it relates to a well-compatible lignin / polypropylene composite prepared by adding a compatibilizer and a plasticizer. The composite material comprises the following components by weight: 100 parts polypropylene, 10-50 parts lignin, 0-20 parts compatibilizer, 0-10 parts plasticizer, and 0.1-1 part coupling agent. The compatibilizer is maleic anhydride grafted polypropylene with a grafting ratio of 0.8% to 1.2%, and the plasticizer is selected from triphenyl phosphate, dibutyl phthalate, or dioctyl phthalate. The addition of the compatibilizer and plasticizer achieves good solubility in the lignin / polypropylene blend, improving the mechanical properties of the composite material. However, as a small molecule, the plasticizer can migrate and precipitate in the polypropylene resin, limiting its effect on improving the mechanical properties of the polypropylene staple fibers. Summary of the Invention

[0005] The present application provides a degradable polypropylene staple fiber and a preparation method thereof, which can effectively alleviate the problem of decreased mechanical properties of the degradable polypropylene staple fiber caused by the doping of lignin and polypropylene.

[0006] In a first aspect, the present application provides a biodegradable polypropylene staple fiber, comprising the following raw materials in parts by weight: 100-130 parts of polypropylene; 5-15 parts of maleic anhydride grafted polypropylene; 15-35 parts of hydrophobically modified lignin; 5-10 parts of alkylated cyclodextrin; 3 to 6 parts of plasticizer; 1 to 5 parts of lubricant; The cyclodextrin contains 6 to 8 D-pyranose units.

[0007] The increased brittleness caused by lignin doping is primarily due to the high number of polar groups in lignin, which results in low solubility in polypropylene. This makes effective dispersion of lignin difficult, leading to agglomeration. Furthermore, the polar groups form physical or chemical crosslinks in polypropylene, restricting the movement of the polypropylene molecular chains, thereby increasing the rigidity of the polypropylene material and reducing its flexibility. To address this issue, the present invention, on the one hand, hydrophobically modifies the lignin to improve its compatibility with the polypropylene substrate and reduce the formation of agglomerates that cause stress concentration. Secondly, the present invention incorporates a liquid plasticizer and an alkylated cyclodextrin. The plasticizer, while simultaneously plasticizing, reduces the melt viscosity of the polypropylene and improves its extrudability. Alkylated cyclodextrin is a low-molecular-weight cyclodextrin with an alkyl group grafted onto its surface. It has good solubility in polypropylene and can be used to reduce the interactions between polypropylene molecules or between lignin molecules, acting as a plasticizer. It can replace some small-molecule liquid plasticizers, reducing the rigidity of polypropylene and increasing its flexibility. Furthermore, cyclodextrin itself is easily degradable, and its addition can improve the degradability of polypropylene staple fibers. More importantly, since cyclodextrin is a cyclic compound with an inner cavity structure, its interior can be coated with small molecular substances such as plasticizers. Its surface can adsorb antioxidants through hydrogen bonding, which plays a certain sustained-release role, helping to reduce the precipitation of plasticizers to the fiber surface and ensure product quality.

[0008] It should be noted that the cyclodextrin of the present application contains 6, 7 or 8 repeating D-pyranose units to control its molecular weight and ensure a good plasticizing effect.

[0009] The hydrophobic modification of lignin in the present application can be achieved by alkylation or grafting of organosilicon segments.

[0010] The polypropylene staple fiber raw material disclosed herein may be added with other processing aids according to the actual processing needs, including but not limited to stabilizers, reinforcing agents, flame retardants, antistatic agents, nucleating agents, fillers, antioxidants, ultraviolet absorbers, and pigments. The amounts used are all conventional amounts, or may be adjusted according to the actual requirements.

[0011] Preferably, the antioxidant is a hindered phenol antioxidant and / or a phosphite antioxidant, preferably a hindered phenol antioxidant and a phosphite antioxidant in a mass ratio of 1:1. Exemplarily, the hindered phenol antioxidant is antioxidant 1010 and / or antioxidant 1076; the phosphite antioxidant is antioxidant 168 and / or antioxidant 626.

[0012] Preferably, the lubricant includes at least one of an internal lubricant and an external lubricant, and more preferably the mass ratio of the internal lubricant to the external lubricant is 0.5-1:0.5-1.

[0013] Exemplarily, the internal lubricant is distearamide and / or stearic acid acetamide; the external lubricant is at least one of polyethylene wax, oxidized polyethylene wax, and fatty acid amide.

[0014] Preferably, the plasticizer is selected from one or more of phthalates, fatty acid glycol esters, epoxy soybean oil, citrates, and phosphates.

[0015] Preferably, the alkylated cyclodextrin is prepared by dissolving cyclodextrin in an alkaline aqueous solution, then adding a C1-C6 alkyl halide, and reacting at 50-80° C. for 10-20 hours.

[0016] Alkylation modification of cyclodextrin improves its solubility in polypropylene substrates and enhances its ability to reduce intermolecular forces, resulting in a superior plasticizing effect. It should be noted that grafted alkyl halides with carbon atoms of 1-12, and more preferably 2-6, exhibit superior plasticizing properties.

[0017] C2 haloalkanes include but are not limited to dichloroethane, bromoethane, and iodoethane; C3 haloalkanes include but are not limited to 1,2-dichloropropane, 1-bromopropane, 2-bromopropane, 1-iodopropane, and 2-iodopropane; C4 haloalkanes include but are not limited to tetrafluorobutane, tetrachlorobutane, 1-bromobutane, 2-bromobutane, 1-iodobutane, and 2-iodobutane; C5 haloalkanes include but are not limited to pentafluoropentane, pentachloropentane, 1,2-dichloropentane, 1-bromopentane, 2-bromopentane, 1-iodopentane, and 2-iodopentane; C6 haloalkanes include but are not limited to hexafluorohexane, hexachlorohexane, 1,2-dichlorohexane, 1-bromohexane, 2-bromohexane, 1-iodohexane, and 2-iodohexane.

[0018] Preferably, the molar ratio of the cyclodextrin to the alkyl halide is 1:10-20.

[0019] Preferably, the cyclodextrin is α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin.

[0020] Preferably, during the preparation of the alkylated cyclodextrin, the molar ratio of the base added to the alkaline water to the cyclodextrin is 2 to 4:1.

[0021] Preferably, the raw materials of the hydrophobically modified lignin include lignin and a vinyl silane coupling agent in a mass ratio of 100:1-5.

[0022] Preferably, the vinyl silane coupling agent is vinyl trimethoxy silane and / or vinyl triethoxy silane.

[0023] Preferably, the raw material of the hydrophobically modified lignin further includes polycaprolactone-modified hydroxyethyl acrylate, and the mass ratio of the vinyl silane coupling agent to the caprolactone-modified hydroxyethyl acrylate is 1-5:30-50.

[0024] Preferably, the preparation method of the hydrophobically modified lignin is as follows: adding lignin and a vinyl silane coupling agent into ethanol and mixing them to react to obtain vinyl-modified lignin; Under the action of an initiator, vinyl modified lignin and polycaprolactone modified hydroxyethyl acrylate undergo free radical copolymerization to obtain the product.

[0025] Preferably, the initiator is azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl hydroperoxide, diisopropyl oxydicarbonate, potassium persulfate, sodium persulfate or ammonium persulfate.

[0026] Preferably, the amount of the initiator is 0.5% to 1% of the total mass of the vinyl-modified lignin and the polycaprolactone-modified hydroxyethyl acrylate.

[0027] Lignin and a vinyl silane coupling agent can introduce organosilicon segments onto its surface, reducing its polarity and improving its compatibility with polypropylene. The introduction of vinyl functional groups also allows for further copolymerization with polycaprolactone-modified hydroxyethyl acrylate monomers to produce polycaprolactone-grafted lignin. Because polycaprolactone is a semicrystalline, biodegradable material, the modified lignin exhibits enhanced biodegradability. More importantly, the hydroxyl groups in the polycaprolactone-modified hydroxyethyl acrylate segments can bond with maleic anhydride-grafted polypropylene during melt processing, further improving the biodegradability of the polypropylene substrate.

[0028] In a second aspect, the present application provides a method for preparing degradable polypropylene staple fibers, comprising the following steps: According to the ratio of any of the above fibers, polypropylene, maleic anhydride grafted polypropylene, hydrophobically modified lignin, plasticizer, alkylated cyclodextrin and lubricant are weighed and added into a blender and mixed evenly to prepare a premix; The premix is passed into a screw extruder and extruded into filaments through a spinning orifice plate, followed by drawing and stretching, cooling and solidification, curling and shaping, and cutting and packaging to obtain polypropylene staple fibers; the temperatures of the six temperature zones of the extruder are set as follows: zone one 160-170°C, zone two 175-185°C, zone three 185-195°C, zone four 195-205°C, zone five 205-215°C, and zone six 205-215°C.

[0029] In summary, this application has the following beneficial effects: This application uses silane-modified lignin in combination with alkylated cyclodextrin to effectively alleviate the problems of increased brittleness and decreased flexibility of polypropylene staple fibers caused by the addition of lignin. While achieving improved degradability of polypropylene staple fibers, it also ensures a balance between their strength and flexibility, and does not cause the problem of plasticizer precipitation. Furthermore, this application further improves the degradability of polypropylene staple fibers by introducing polycaprolactone segments onto the surface of lignin and bonding them to maleic anhydride-grafted polypropylene. DETAILED DESCRIPTION

[0030] Preparation Example Preparation Example Raw material selection: Kraft lignin; caprolactone-modified hydroxyethyl acrylate was obtained from Hunan Juren New Materials, model HAM3, molecular weight 358 g / mol, hydroxyl value 157 KOHmg / g.

[0031] Preparation Example 1-1, hydrophobically modified lignin, was prepared according to the following steps: 100g of hydroxylated lignin was added to 1L of ethanol and ultrasonically dispersed for 10 minutes. Then, 3.6g of vinyltriethoxysilane was added dropwise to the ethanol solution with stirring. After the addition was complete, the reaction was stirred at room temperature for 8 hours. The product was isolated, filtered and washed three times with ethanol, and then dried at 50°C for 12 hours to obtain vinyl-modified lignin.

[0032] Sodium dodecylbenzenesulfonate was added to deionized water to prepare an emulsion with a concentration of 3 wt%. The above-mentioned vinyl-modified lignin, 42 g of polycaprolactone-modified hydroxyethyl acrylate, and 1.0 g of benzoyl peroxide were added to the emulsion. The temperature was raised to 72°C and the reaction was stirred for free radical copolymerization. After 8 hours, the product was filtered out, washed twice with deionized water, and dried at 50°C to constant weight.

[0033] Preparation Example 1-2, hydrophobically modified lignin, was prepared according to the following steps: 100g of hydroxylated lignin was added to 1L of ethanol and ultrasonically dispersed for 10 minutes. Then, 1.3g of vinyltrimethoxysilane was added dropwise to the ethanol solution with stirring. After the addition was complete, the reaction was stirred at room temperature for 6 hours. The product was isolated, filtered and washed three times with ethanol, and then dried at 50°C for 12 hours to obtain vinyl-modified lignin.

[0034] Fatty alcohol polyoxyethylene ether was added to deionized water to prepare an emulsion with a concentration of 2 wt%, and the above-mentioned vinyl-modified lignin, 35 g of polycaprolactone-modified hydroxyethyl acrylate and 1.0 g of sodium persulfate were added to the emulsion. The temperature was raised to 65°C and the reaction was stirred for free radical copolymerization. After 8 hours, the product was filtered out, washed twice with deionized water, and dried at 50°C to constant weight.

[0035] Preparation Example 1-3, hydrophobically modified lignin, was prepared according to the following steps: 100g of hydroxylated lignin was added to 1L of ethanol and ultrasonically dispersed for 10 minutes. Then, 5.0g of vinyltriethoxysilane was added dropwise to the ethanol solution with stirring. After the addition was complete, the reaction was stirred at room temperature for 8 hours. The product was isolated, filtered and washed three times with ethanol, and then dried at 50°C for 12 hours to obtain vinyl-modified lignin.

[0036] Sodium dodecylbenzenesulfonate was added to deionized water to prepare an emulsion with a concentration of 3 wt%. The above-mentioned vinyl-modified lignin, 46 g of polycaprolactone-modified hydroxyethyl acrylate and 1.2 g of benzoyl peroxide were added to the emulsion. The temperature was raised to 72°C and the reaction was stirred for free radical copolymerization. After 10 hours, the product was filtered out, washed twice with deionized water, and dried at 50°C to constant weight.

[0037] Preparation Example 1-4, hydrophobically modified lignin, was prepared according to the following steps: 100g of hydroxylated lignin was added to 1L of ethanol and ultrasonically dispersed for 10 minutes. Then, 3.6g of vinyltriethoxysilane was added dropwise to the ethanol solution with stirring. After the addition was complete, the reaction was stirred at room temperature for 8 hours. The product was isolated, filtered and washed three times with ethanol, and then dried at 50°C for 12 hours.

[0038] Preparation Example 2-1, alkylated cyclodextrin, was prepared according to the following method: Weigh 12g of sodium hydroxide and add it to 1000mL of deionized water to prepare an alkaline aqueous solution. Add 126.1g (0.1mol) of β-cyclodextrin and stir to dissolve. Heat to 75°C. Then, add 135.6g (1.2mol) of 1,2-dichloropropane dropwise over 5 hours. Stir and react for 10 hours to obtain the reaction product. The reaction product is then neutralized with 10wt% hydrochloric acid to a pH of 7 and extracted with 1200g of chloroform. After phase separation, the organic phase is separated and the solvent is distilled off under standard pressure to produce the alkylated cyclodextrin.

[0039] Preparation Example 2-2, alkylated cyclodextrin, was prepared according to the following method: 8g of sodium hydroxide was added to 800mL of deionized water to prepare an alkaline aqueous solution. 144.1g (0.1mol) of γ-cyclodextrin was added and stirred to dissolve. The temperature was raised to 60°C. 218g (2mol) of ethyl bromide was then added dropwise to the solution over 5 hours. After the addition was complete, the mixture was stirred and reacted for 12 hours to obtain the reaction product. The reaction product was then neutralized with 15wt% hydrochloric acid to a pH of 7 and extracted with 1000g of chloroform. After phase separation, the organic phase was separated and the solvent was distilled off under standard pressure to obtain the alkylated cyclodextrin.

[0040] Preparation Example 2-3, alkylated cyclodextrin, was prepared according to the following method: Weigh 16g of sodium hydroxide and add it to 1200mL of deionized water to prepare an alkaline aqueous solution. Add 126.1g (0.1mol) of β-cyclodextrin and stir to dissolve. Heat to 80°C, then add 247.5g (1.5mol) of 1-bromohexane dropwise to the solution over 7 hours. Stir and react for 12 hours after the addition is complete to obtain the reaction product. The reaction product is then neutralized with 10wt% sulfuric acid to a pH of 7 and extracted with 1500g of chloroform. After phase separation, the organic phase is separated and the solvent is distilled off under standard pressure to produce the alkylated cyclodextrin.

[0041] Preparation Example 2-4, alkylated cyclodextrin, differs from Preparation Example 2-3 in that 108.1 g (0.1 mol) of α-cyclodextrin is used instead of β-cyclodextrin.

[0042] Preparation Example 2-5, alkylated cyclodextrin, differs from Preparation Example 2-3 in that 2450 g (15 mol) of 1-chlorooctane is used instead of 1-bromohexane.

[0043] Preparation Example 2-6, alkylated cyclodextrin, differs from Preparation Example 2-3 in that 1-bromohexane is replaced by 3360 g (15 mol) of 1-bromododecane.

[0044] Example Raw material selection in the embodiment: polypropylene was selected as polypropylene homopolymer (Juzhengyuan PPH-T03); maleic anhydride grafted polypropylene was selected as Dow FUSABOND P613; dioctyl phthalate was selected as plasticizer; and stearic acid acetamide and oxidized polyethylene wax (molecular weight 3000-4000, softening point 102-106°C) were selected as lubricant in a mass ratio of 1:0.5.

[0045] Example 1: A biodegradable polypropylene staple fiber is prepared according to the following steps: 10 kg of polypropylene, 0.8 kg of maleic anhydride grafted polypropylene, 2.4 kg of the hydrophobically modified lignin of Preparation Example 1-1, 0.5 kg of plasticizer, 0.72 kg of the alkylated cyclodextrin of Preparation Example 2-1 and 0.3 kg of lubricant were weighed and added into a blender, and mixed uniformly at 120° C. to prepare a premix.

[0046] The premix is passed into a twin-screw extruder and extruded into filaments through a spinning orifice plate, pulled and stretched, cooled and solidified, curled and shaped, and sheared to obtain polypropylene staple fibers; the temperatures of the six temperature zones of the extruder are set as: zone one 160°C, zone two 175°C, zone three 190°C, zone four 200°C, zone five 215°C, and zone six 210°C.

[0047] Example 2: A degradable polypropylene staple fiber is prepared according to the following steps: 10 kg of polypropylene, 0.6 kg of maleic anhydride grafted polypropylene, 1.8 kg of the hydrophobically modified lignin of Preparation Example 1-2, 0.36 kg of plasticizer, 0.55 kg of the alkylated cyclodextrin of Preparation Example 2-2 and 0.2 kg of lubricant were weighed and added into a blender, and mixed uniformly at 120° C. to prepare a premix.

[0048] The premix is passed into a twin-screw extruder and extruded into filaments through a spinning orifice plate, which are then pulled and stretched, cooled and solidified, and sheared to obtain polypropylene staple fibers; the temperatures of the six temperature zones of the extruder are set as follows: 160°C in zone one, 180°C in zone two, 185°C in zone three, 200°C in zone four, 210°C in zone five, and 205°C in zone six.

[0049] Example 3: A biodegradable polypropylene staple fiber is prepared according to the following steps: 10 kg of polypropylene, 1.5 kg of maleic anhydride grafted polypropylene, 3.3 kg of the hydrophobically modified lignin of Preparation Example 1-3, 0.6 kg of plasticizer, 1 kg of the alkylated cyclodextrin of Preparation Example 2-3 and 0.5 kg of lubricant were weighed and added into a blender, and mixed uniformly at 120° C. to prepare a premix.

[0050] The premix is passed into a twin-screw extruder and extruded into filaments through a spinning orifice plate, pulled and stretched, cooled and solidified, and sheared to obtain polypropylene staple fibers; the temperatures of the six temperature zones of the extruder are set as: 170°C in zone one, 185°C in zone two, 195°C in zone three, 205°C in zone four, 215°C in zone five, and 210°C in zone six.

[0051] Example 4, a degradable polypropylene staple fiber, differs from Example 3 in that the hydrophobically modified lignin of Preparation Example 1-3 is replaced by an equal amount of the hydrophobically modified lignin of Preparation Example 1-4.

[0052] Example 5, a degradable polypropylene staple fiber, differs from Example 3 in that the alkylated cyclodextrin in Preparation Example 2-3 is replaced by an equal amount of the alkylated cyclodextrin in Preparation Example 2-4.

[0053] Example 6, a degradable polypropylene staple fiber, differs from Example 3 in that the alkylated cyclodextrin in Preparation Example 2-3 is replaced by an equal amount of the alkylated cyclodextrin in Preparation Example 2-5.

[0054] Example 7, a degradable polypropylene staple fiber, differs from Example 3 in that the alkylated cyclodextrin in Preparation Example 2-3 is replaced by an equal amount of the alkylated cyclodextrin in Preparation Example 2-6.

[0055] Comparative Example Comparative Example 1, a degradable polypropylene staple fiber, differs from Example 3 in that the alkylated cyclodextrin in Preparation Example 2-3 is replaced by an equal amount of β-cyclodextrin.

[0056] Comparative Example 2, a degradable polypropylene staple fiber, differs from Example 3 in that the alkylated cyclodextrin in Preparation Example 2-3 is replaced by an equal amount of dioctyl phthalate.

[0057] Comparative Example 3, a degradable polypropylene staple fiber, differs from Example 3 in that dioctyl phthalate is replaced by an equal amount of the alkylated cyclodextrin of Preparation Example 2-3.

[0058] Comparative Example 4, a degradable polypropylene staple fiber, differs from Example 3 in that the hydrophobically modified lignin in 1-3 is replaced by an equal amount of Kraft lignin.

[0059] Performance testing Test 1: Determine the elongation at break and breaking strength of polypropylene staple fibers in accordance with GB / T 14344-2008 “Test method for tensile properties of chemical filaments”.

[0060] Test 2: Compost the biodegradable polypropylene staple fiber samples described above according to ASTM D5338. Record the biodegradation rates after 10, 30, and 60 days of composting. Compost temperature was 58°C ± 2°C, and each compost sample weighed 20g.

[0061] Test 3: Place the polypropylene staple fiber sample in an oven at 50°C and heat it for 48 hours to observe whether there is obvious plasticizer precipitation on the surface of the polypropylene staple fiber.

[0062] Table 1. Performance test results As can be seen from Table 1, compared with Comparative Examples 1 to 4, Examples 1 to 7 use hydrophobically modified lignin in combination with a plasticizer and an alkylated cyclodextrin to produce polypropylene staple fibers with a relatively balanced rigidity and toughness. When any one component is missing, the optimal performance balance cannot be achieved.

[0063] As shown in Table 1, Example 4 exhibits poor biodegradability compared to Example 1. This may be because, in Example 1, the reaction of polycaprolactone-modified hydroxyethyl acrylate with vinyl-modified lignin introduces highly biodegradable polycaprolactone segments and hydroxyl groups into the lignin, enabling the polyester segments to be further grafted onto polypropylene through an esterification reaction, thereby improving the biodegradability of the polypropylene staple fibers.

[0064] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A degradable polypropylene staple fiber, characterized in that: Including the following raw materials by weight: 100-130 parts of polypropylene; 5-15 parts of maleic anhydride grafted polypropylene; 15-35 parts of hydrophobically modified lignin; 5-10 parts of alkylated cyclodextrin; 3 to 6 parts of plasticizer; 1 to 5 parts of lubricant; The cyclodextrin contains 6 to 8 D-pyranose units.

2. The fiber according to claim 1, characterized in that The alkylated cyclodextrin is prepared by dissolving cyclodextrin in an alkaline aqueous solution, then adding a C1-C6 alkyl halide, and reacting at 50-80° C. for 10-20 hours.

3. The fiber according to claim 2, characterized in that The molar ratio of the cyclodextrin to the alkyl halide is 1:10-20.

4. The fiber according to claim 2, characterized in that The cyclodextrin is α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin.

5. The fiber according to claim 1, characterized in that The raw materials of the hydrophobically modified lignin include lignin and a vinyl silane coupling agent in a mass ratio of 100:1-5.

6. The fiber according to claim 5, characterized in that The raw material of the hydrophobically modified lignin further comprises polycaprolactone-modified hydroxyethyl acrylate, and the mass ratio of the vinyl silane coupling agent to the caprolactone-modified hydroxyethyl acrylate is 1-5:30-50.

7. The fiber according to claim 6, characterized in that The preparation method of the hydrophobically modified lignin is as follows: adding lignin and a vinyl silane coupling agent into ethanol and mixing them to react to obtain vinyl-modified lignin; Under the action of an initiator, vinyl modified lignin and polycaprolactone modified hydroxyethyl acrylate undergo free radical copolymerization to obtain the product.

8. The fiber according to claim 1, characterized in that The lubricant includes an internal lubricant and an external lubricant in a mass ratio of 0.5-1:0.5-1.

9. The fiber according to claim 1, characterized in that The antioxidant is a combination of a hindered phenol antioxidant and a phosphite antioxidant.

10. A method for preparing degradable polypropylene staple fibers, characterized in that: The steps include: According to the ratio of the fiber according to any one of claims 1 to 9, polypropylene, maleic anhydride grafted polypropylene, hydrophobically modified lignin, plasticizer, alkylated cyclodextrin and lubricant are weighed and added into a blender and mixed uniformly to prepare a premix; The premix is passed into a screw extruder and extruded into filaments through a spinning orifice plate, followed by drawing and stretching, cooling and solidification, curling and shaping, and cutting and packaging to obtain polypropylene staple fibers; the temperatures of the six temperature zones of the extruder are set as follows: zone one 160-170°C, zone two 175-185°C, zone three 185-195°C, zone four 195-205°C, zone five 205-215°C, and zone six 205-215°C.

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