Polypropylene fiber short fiber for automobile wheel cover and preparation method of polypropylene fiber short fiber

Abstract

The invention discloses a polypropylene staple fiber for an automobile wheel casing and a preparation method thereof, and belongs to the technical field of artificial filaments or analogues, the polypropylene staple fiber is prepared from polypropylene resin, an ethylene-propylene-diene terpolymer, maleic anhydride grafted polypropylene, an efficient plasticizer, an antioxidant, a light stabilizer, a nucleating agent and silicone master batch. Compared with the prior art, the high-efficiency plasticizer is introduced, and the elastomer is matched for toughening and interface compatibility improvement, so that the entanglement resistance of a polypropylene molecular chain is reduced, and meanwhile, the stress transfer is optimized, so that the energy dissipation is more uniform when the fiber is stressed or repeatedly bent; the repeated bending fatigue resistance of the fiber is remarkably improved while the fiber is endowed with high elongation at break, and the comprehensive requirements of the automobile wheel cover on the toughness and durability of the material are fully met.

Description

Technical Field

[0001] This invention relates to the field of artificial filaments or similar materials, and in particular to a polypropylene staple fiber for automobile wheel covers and its preparation method. Background Technology

[0002] Polypropylene staple fiber has broad application prospects in automotive parts such as wheel arches due to its advantages of light weight, corrosion resistance, and low cost. However, conventional polypropylene staple fiber generally lacks sufficient toughness and is prone to brittle fracture under repeated bending or impact, making it difficult to meet the dual requirements of high toughness and long service life for automotive wheel arches in actual use. To address this, existing technologies have focused on plasticizer modification, elastomer toughening, and interfacial compatibility improvement, attempting to enhance fiber toughness through single or combined methods.

[0003] Patent document CN121021365A discloses a high-toughness polypropylene staple fiber. It reduces the entanglement resistance between polypropylene molecular chains by introducing a novel plasticizer with a specific structure, making the molecular chains more prone to relative sliding under stress, thereby improving the fiber's tensile and bending resistance. However, this technical solution mainly relies on the molecular lubrication effect of the plasticizer and fails to simultaneously address the interfacial defects caused by polarity differences in the multi-component system within the fiber. It also cannot effectively control the crystallization behavior of polypropylene, resulting in the fiber still easily failing at weak interfaces during repeated bending or impact. The plastics industry publication "Preparation and Performance Study of Glass Fiber / High-Density Polyethylene Composite Material Reinforced with Eucommia Rubber" by Jin Xin reports a method for using natural Eucommia rubber to toughen glass fiber reinforced high-density polyethylene composite materials. This method absorbs impact energy through crazing and shear generation induced by the elastomer dispersed phase. However, this technical solution targets a glass fiber reinforced high-density polyethylene system, which differs significantly from the matrix resin and reinforcement form of polypropylene-based polypropylene staple fiber. Furthermore, the compatibility of Eucommia rubber with polypropylene and its applicability in spinning processes remain unclear. Patent document CN114805787A discloses a cellulose-based polyether polyol fatty acid ester plasticizer and its preparation method. It uses cellulose as a raw material to prepare a bio-based plasticizer with high polarity and good flexibility. However, it is mainly used in polylactic acid systems. Its plasticizing effect in polypropylene fiber systems and its compatibility with polypropylene matrix need further verification.

[0004] In summary, there is currently no existing technology that can systematically improve the toughness of polypropylene staple fibers from three dimensions: molecular chain mobility, interfacial bonding strength, and crystalline structure. In particular, there is a lack of polypropylene staple fibers and their preparation methods that can impart high elongation at break and significantly improve their resistance to repeated bending fatigue, so as to meet the comprehensive requirements of automotive wheel covers for material toughness and durability. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention aims to provide a polypropylene staple fiber for automotive wheel covers and its preparation method.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A type of polypropylene staple fiber for automotive wheel covers comprises the following raw materials in parts by weight: 60-90 parts polypropylene resin, 10-20 parts ethylene-propylene-diene terpolymer, 5-10 parts maleic anhydride-grafted polypropylene, 2-5 parts high-efficiency plasticizer, 1-3 parts antioxidant, 0.2-0.6 parts light stabilizer, 0.1-0.5 parts nucleating agent, and 0.4-0.8 parts silicone masterbatch.

[0008] The raw materials for preparing the high-efficiency plasticizer include the following components: sodium cellulose, dipropylene glycol dimethyl ether, 1,2-epoxybutane, aliphatic modifier, methanesulfonic acid, and toluene;

[0009] The preparation method of the high-efficiency plasticizer is as follows: Sodium cellulose is mixed with dipropylene glycol dimethyl ether, and 1,2-epoxybutane is introduced to react. After neutralization, filtration, and vacuum distillation, a pretreated product is obtained. The pretreated product is then mixed with an aliphatic modifier, methanesulfonic acid, and toluene to react. After vacuum distillation to remove toluene, alkaline washing and neutralization, and vacuum dehydration and drying, a high-efficiency plasticizer is obtained.

[0010] The light stabilizer is at least one of light stabilizer 770, light stabilizer 944, and light stabilizer 622.

[0011] The nucleating agent is at least one of NA-11 and NA-21;

[0012] The antioxidant is at least one of antioxidant 1010, antioxidant 168, and antioxidant 1076.

[0013] Preferably, the antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.5-2:0.5-2.

[0014] The aliphatic modifier is at least one of linoleic acid, stearic acid, lauric acid, ricinoleic acid, cyclohexanecarboxylic acid, and epoxy fatty acid methyl ester.

[0015] Preferably, the aliphatic modifier is composed of epoxy fatty acid methyl ester and ricinoleic acid.

[0016] More preferably, the aliphatic modifier is composed of epoxidized fatty acid methyl ester and ricinoleic acid in a mass ratio of 0.5-2:0.5-2.

[0017] The preparation method of the high-efficiency plasticizer is as follows, in parts by weight:

[0018] S1. Under nitrogen protection, add 2-4 parts of sodium cellulose and 10-20 parts of dipropylene glycol dimethyl ether to a high-pressure reactor, heat to 75-90℃, and continuously introduce 30-50 parts of 1,2-epoxybutane over 1-3 hours, controlling the reaction temperature at 100-130℃. After the addition is complete, maintain the temperature for 0.5-3 hours. After the reaction is complete, cool down and depressurize, add 10-20% hydrochloric acid dropwise to neutralize the reaction solution, filter, and recover the dipropylene glycol dimethyl ether by vacuum distillation at a reactor temperature of 130-150℃ and a vacuum degree of -0.08~-0.095MPa to obtain the pretreated product.

[0019] S2. Take 7-12 parts of the pretreated material from step S1, mix it with 2-6 parts of aliphatic modifier, 0.05-0.2 parts of methanesulfonic acid and 4-8 parts of toluene, and react at 90-105℃ for 5-10 hours. After the reaction is completed, remove the toluene by vacuum distillation at 60-85℃ and a vacuum degree of -0.08 to -0.095 MPa. Wash with 5-10% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 60-90℃ and a vacuum degree of -0.08 to -0.095 MPa to obtain a high-efficiency plasticizer.

[0020] The preparation method of the high-efficiency plasticizer is also as follows, in parts by weight:

[0021] S1. Under nitrogen protection, add 2-4 parts of sodium cellulose and 10-20 parts of dipropylene glycol dimethyl ether to a high-pressure reactor, heat to 75-90℃, and continuously introduce 30-50 parts of 1,2-epoxybutane over 1-3 hours, controlling the reaction temperature at 100-130℃. After the addition is complete, maintain the temperature for 0.5-3 hours. After the reaction is complete, cool down and depressurize, add 10-20% hydrochloric acid dropwise to neutralize the reaction solution, filter, and recover the dipropylene glycol dimethyl ether by vacuum distillation at a reactor temperature of 130-150℃ and a vacuum degree of -0.08~-0.095MPa to obtain the pretreated product.

[0022] S2. The aliphatic modifier is stirred and mixed at 60°C for 30 minutes to obtain a premixed acid component. The aliphatic modifier is composed of epoxy fatty acid methyl ester and ricinoleic acid in a mass ratio of 0.5-2:0.5-2. Take 7-12 parts of the pretreated material from step S1, mix it with the premixed acid component, 0.05-0.2 parts of methanesulfonic acid and 4-8 parts of toluene, and react at 90-105°C for 1-3 hours. Raise the temperature to 105-115°C and continue the reaction for 4-8 hours. After the reaction is completed, remove the toluene by vacuum distillation at 60-85°C and a vacuum degree of -0.08 to -0.095 MPa. Wash with a 5-10% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 60-90°C and a vacuum degree of -0.08 to -0.095 MPa to obtain a high-efficiency plasticizer.

[0023] The method for preparing the polypropylene short fiber for automobile wheel covers is as follows:

[0024] Step 1: Under a nitrogen atmosphere, add polypropylene resin, ethylene-propylene-diene terpolymer, maleic anhydride-grafted polypropylene, high-efficiency plasticizer, antioxidant, light stabilizer, nucleating agent, and silicone masterbatch to a high-speed mixer. Set the stirring speed to 800-1500 r / min, control the mixing temperature to 85-95℃, and the mixing time to 5-15 min to obtain the premixed material.

[0025] Step 2: The above premixed material is fed to a twin-screw extruder, where it is melted and plasticized before being extruded to obtain a spinning melt.

[0026] Step 3: The spinning melt is extruded through the spinning assembly to form a melt stream, and then cooled and solidified by side blowing air at a temperature of 20-30℃ and a wind speed of 0.2-1m / s. The spinning speed is set to 800-1500m / min to obtain nascent fibers.

[0027] Step 4: The nascent fibers undergo two-stage stretching treatment. The first stage stretching is carried out in a water bath at a temperature of 70-80℃ and a stretching ratio of 1.5-2 times. The second stage stretching is carried out in a hot box at a temperature of 80-90℃ and a stretching ratio of 1.5-2 times. Subsequently, heat setting treatment is carried out in hot air at 90-100℃ for 5-30 minutes. The set fibers are then cut into short fibers of 40-100mm and subjected to static elimination and opening and impurity removal processes to obtain polypropylene short fibers for automotive wheel covers.

[0028] In step 2, the temperatures of each heating section of the twin-screw extruder are set as follows: 185-195℃ for the feeding zone, 200-210℃ for the compression zone, 215-225℃ for the homogenization zone, and the melting temperature is controlled at 210-220℃.

[0029] In exploring the toughening modification of polypropylene staple fibers for automotive wheel arches, this invention initially referenced the existing approach of reducing polypropylene molecular chain entanglement resistance by introducing plasticizers with specific structures. However, it was found that while this molecular lubrication mechanism can improve the fiber's elongation at break, it is difficult to simultaneously address the interfacial defects caused by polarity differences in the multi-component system within the fiber, nor can it effectively control the crystallization behavior of polypropylene. This is akin to adding lubricant to a machine while neglecting the precise fit between components and overall structural optimization, making the fiber prone to damage at weak interfaces when subjected to repeated bending or stretching, failing to meet the dual requirements of high toughness and long lifespan for automotive wheel arches in practical use.

[0030] True toughness enhancement requires a systematic design across three dimensions: molecular chain mobility, interfacial bonding strength, and crystalline structure. Therefore, this invention constructs a composite modification system. An ethylene-propylene-diene terpolymer serves as an energy absorption center to disperse impact stress. Maleic anhydride-grafted polypropylene bridges the molecular gaps between components of varying polarities. Nucleating agents are then used to regulate the formation of fine, uniform polypropylene grains. However, the most crucial step is the design of a novel, highly efficient plasticizer. Its molecular skeleton retains long-chain alkyl groups compatible with polypropylene and interacts with some raw materials through ether or ester bonds. More importantly, it was discovered that introducing fatty acid segments with different structures into the plasticizer molecule can endow it with different functions. For example, the additional hydroxyl groups from ricinoleic acid can form hydrogen bond networks with some raw materials, while epoxy fatty acid methyl esters possess the potential for ring-opening crosslinking under acidic conditions.

[0031] Therefore, this invention attempts to combine two aliphatic modifiers with different functions, allowing the epoxy groups of epoxy fatty acid methyl esters and the secondary hydroxyl groups of ricinoleic acid to chemically bond during the reaction, forming a molecular network-like structure. This constructs an elastic network within the fiber that can both absorb energy and limit excessive slippage of molecular chains. Further process optimization involves pre-mixing to ensure sufficient contact between the two aliphatic modifiers, followed by staged heating to ensure the orderly conduct of the esterification and epoxy ring-opening reactions, resulting in a more uniform and complete cross-linked network. This systematic innovation, from molecular design to process optimization, significantly improves the fiber's resistance to repeated bending fatigue while maintaining high elongation at break, truly meeting the comprehensive requirements of automotive wheel covers for material toughness and durability.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] 1) By introducing a highly efficient plasticizer, this invention can simultaneously improve the interfacial bonding of components, reduce the resistance to molecular chain entanglement, and regulate crystallization behavior, thereby achieving a balance between fiber toughness and processing stability.

[0034] 2) This invention uses a compound of epoxy fatty acid methyl ester and ricinoleic acid as an aliphatic modifier. Under the catalysis of methanesulfonic acid, the epoxy group of epoxy fatty acid methyl ester and the secondary hydroxyl group of ricinoleic acid undergo a ring-opening addition reaction to form an ether bond. Simultaneously, the carboxyl group of ricinoleic acid undergoes an esterification reaction with the pretreated material to form an ester bond. These two chemical bonds together construct a microscale chemical cross-linking network. When the fiber is under stress, this network absorbs energy through segmental elastic deformation. At the same time, the cross-linking points effectively limit the excessive slippage of the polypropylene molecular chains, avoiding fatigue damage caused by stress concentration, thereby synergistically improving the fiber's elongation at break and flexural fatigue life.

[0035] 3) The present invention further promotes the orderly progress of each reaction through a staged heating reaction process, which promotes the uniform construction of the cross-linked network. While maintaining the high elongation at break of the fiber, it significantly improves its resistance to repeated bending fatigue, thus meeting the comprehensive requirements of automobile wheel covers for material toughness and durability. Detailed Implementation

[0036] The sources or parameters of some substances are as follows:

[0037] Polypropylene resin, using grade BX3500 produced by SK in South Korea, with a melt flow index (MFR) of 10g / 10min (230℃ / 2.16kg).

[0038] The ethylene-propylene-diene terpolymer is manufactured by Dow Chemical Company of the United States under the brand name Nordel 4770R.

[0039] Maleic anhydride-grafted polypropylene uses Bynel 50E803 manufactured by DuPont, USA.

[0040] The silicone masterbatch used is Dow Corning's MB50-001 grade.

[0041] Sodium cellulose, specifically sodium carboxymethyl cellulose, CAS No.: 9004-32-4, with a degree of substitution of 0.7-0.9, purity ≥99.5%, viscosity range of 1000-3000 mPa·s (1% aqueous solution, 25℃), and moisture content ≤10.0%.

[0042] The methanesulfonic acid used is industrial grade methanesulfonic acid, CAS number 75-75-2, with a purity ≥99.0%, a density of 1.475-1.485 g / mL (20℃), and a moisture content ≤0.5%.

[0043] Linoleic acid, purity ≥95%, CAS No.: 60-33-3.

[0044] Stearic acid, purity ≥98%, CAS No.: 57-11-4.

[0045] Lauric acid, purity ≥98%, CAS No.: 143-07-7.

[0046] Ricinoleic acid, purity ≥85%, hydroxyl value 165mgKOH / g, CAS No.: 141-22-0.

[0047] Cyclohexanecarboxylic acid, purity ≥98%, CAS No.: 98-89-5.

[0048] Epoxy fatty acid methyl ester, epoxy value ≥4.2%, acid value ≤0.8mgKOH / g, CAS No.: 68082-35-9.

[0049] In the embodiments and comparative examples of this invention, all raw materials are commercially available products.

[0050] Example 1

[0051] A method for preparing polypropylene staple fibers for automotive wheel covers is as follows, in parts by weight:

[0052] Step 1: Under a nitrogen atmosphere, add 75 parts of polypropylene resin, 16 parts of ethylene-propylene-diene terpolymer, 7 parts of maleic anhydride-grafted polypropylene, 3.5 parts of high-efficiency plasticizer, 1.8 parts of antioxidant, 0.4 parts of light stabilizer 944, 0.3 parts of nucleating agent NA-11, and 0.6 parts of silicone masterbatch to a high-speed mixer. Set the stirring speed to 1250 r / min, control the mixing temperature to 92℃, and the mixing time to 9 min to obtain the premixed material.

[0053] Step 2: The premixed material is fed to a twin-screw extruder. The temperatures of each heating section of the screw are set as follows: 190°C for the feeding zone, 205°C for the compression zone, and 220°C for the homogenization zone. The melting temperature is controlled at 215°C. After melting and plasticizing, the material is extruded to obtain the spinning melt.

[0054] Step 3: The spinning melt is extruded through the spinning assembly to form a melt stream, and then cooled and solidified by side blowing air at a temperature of 25℃ and a wind speed of 0.6m / s. The spinning speed is set to 1100m / min to obtain nascent fibers.

[0055] Step 4: The nascent fibers undergo two-stage stretching treatment. The first stage stretching is carried out in a water bath at a temperature of 75°C and a stretching ratio of 1.8 times. The second stage stretching is carried out in a hot box at a temperature of 88°C and a stretching ratio of 1.8 times. Subsequently, heat setting treatment is performed in hot air at 95°C for 15 minutes. The set fibers are then cut into 60mm short fibers and subjected to static elimination and opening and impurity removal processes to obtain polypropylene short fibers for automotive wheel covers.

[0056] This invention employs two-stage stretching to gradually apply stress at a lower single-stage stretching ratio, avoiding fiber breakage or internal structural defects caused by excessively high single-stage stretching ratio. At the same time, the two-stage coordination precisely controls the total stretching ratio, ensuring proper orientation of molecular chains without excessive slippage, thereby effectively improving the breaking elongation while ensuring uniform fiber deformation.

[0057] The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1.

[0058] The preparation method of the high-efficiency plasticizer is as follows, in parts by weight:

[0059] S1. Under nitrogen protection, 2.8 parts of sodium cellulose and 14.5 parts of dipropylene glycol dimethyl ether were added to a high-pressure reactor. The temperature was raised to 82°C, and 36.5 parts of 1,2-epoxybutane were continuously introduced over 2 hours. The reaction temperature was controlled at 120°C. After the addition was completed, the reaction was maintained at this temperature for 1 hour. After the reaction was completed, the temperature was lowered and the pressure was released. 15% hydrochloric acid was added dropwise to neutralize the reaction solution. The mixture was filtered, and the dipropylene glycol dimethyl ether was recovered by vacuum distillation at a reactor temperature of 145°C and a vacuum degree of -0.09MPa to obtain the pretreated product.

[0060] S2. Take 9.5 parts of the pretreated material from step S1, mix it with 4.2 parts of aliphatic modifier, 0.1 parts of methanesulfonic acid and 6 parts of toluene, and react at 100℃ for 8 hours. After the reaction is completed, remove the toluene by vacuum distillation at 80℃ and a vacuum degree of -0.095MPa, wash with 8% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 85℃ and a vacuum degree of -0.09MPa to obtain a high-efficiency plasticizer.

[0061] The aliphatic modifier is linoleic acid.

[0062] Example 2

[0063] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is stearic acid.

[0064] Example 3

[0065] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is lauric acid.

[0066] Example 4

[0067] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is ricinoleic acid.

[0068] Example 5

[0069] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is cyclohexanecarboxylic acid.

[0070] Example 6

[0071] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is epoxy fatty acid methyl ester.

[0072] Example 7

[0073] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is composed of epoxy fatty acid methyl ester and ricinoleic acid in a mass ratio of 1:1.

[0074] Example 8

[0075] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier in the preparation method of the high-efficiency plasticizer is composed of stearic acid and linoleic acid in a mass ratio of 1:1.

[0076] Example 9

[0077] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 7, except that the preparation method of the high-efficiency plasticizer is different.

[0078] The preparation method of the high-efficiency plasticizer is as follows, in parts by weight:

[0079] S1. Under nitrogen protection, 2.8 parts of sodium cellulose and 14.5 parts of dipropylene glycol dimethyl ether were added to a high-pressure reactor. The temperature was raised to 82°C, and 36.5 parts of 1,2-epoxybutane were continuously introduced over 2 hours. The reaction temperature was controlled at 120°C. After the addition was completed, the reaction was kept at this temperature for 1 hour until the reaction pressure was constant. After the reaction was completed, the temperature was lowered and the pressure was released. 15% hydrochloric acid was added dropwise to neutralize the reaction solution. The solution was filtered, and the dipropylene glycol dimethyl ether was recovered by vacuum distillation at a reactor temperature of 145°C and a vacuum degree of -0.09MPa to obtain the pretreated product.

[0080] S2. Mix 2.1 parts of epoxy fatty acid methyl ester and 2.1 parts of ricinoleic acid at 60°C for 30 minutes to obtain a premixed acid component; take 9.5 parts of the pretreated material from step S1, mix it with the premixed acid component, 0.1 parts of methanesulfonic acid and 6 parts of toluene, and react at 100°C for 2 hours; raise the temperature to 110°C and continue the reaction for 6 hours. After the reaction is completed, remove the toluene by vacuum distillation at 80°C and a vacuum degree of -0.095MPa, wash with 8% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 85°C and a vacuum degree of -0.09MPa to obtain a high-efficiency plasticizer.

[0081] Comparative Example 1

[0082] The preparation method of polypropylene short fiber for automobile wheel covers is basically the same as that in Example 1, except that the aliphatic modifier is not added in the preparation method of the high-efficiency plasticizer.

[0083] Test Example 1

[0084] The tensile properties of chemical fiber staple fibers were tested according to the national standard GB / T14337-2022 "Test Method for Tensile Properties of Chemical Fibers". Twenty single fibers were randomly selected from the polypropylene staple fiber samples of each example and comparative example as test specimens. These specimens were equilibrated for 24 hours under standard atmospheric conditions of 20℃±2℃ and 65%±5% relative humidity. A single fiber tensile tester was used, with the initial clamp spacing set to 10mm and the tensile speed to 20mm / min. The fiber specimens were placed vertically in the upper and lower clamps and stretched at a constant rate until fiber breakage. The instrument automatically recorded the elongation at break. The elongation at break was calculated using the following formula: Elongation at break (%) = (Elongation at break / Initial clamp spacing) × 100%. Ten valid specimens were tested for each sample, and the arithmetic mean was taken as the final test result. The test results are shown in Table 1.

[0085] Table 1

[0086] Experimental protocol Elongation at break (%) Example 1 398 Example 2 362 Example 3 374 Example 4 406 Example 5 356 Example 6 368 Example 7 428 Example 8 382 Example 9 436 Comparative Example 1 306

[0087] Test Example 2

[0088] Single-wire bending fatigue performance test:

[0089] Twenty single fibers were randomly selected from the polypropylene staple fiber samples to be tested as test specimens and equilibrated for 24 hours under standard atmospheric conditions of 20℃±2℃ and 65%±5% relative humidity. The single fiber specimens were fixed on a reciprocating bending fatigue testing machine, with a bending angle of 90°, a bending frequency of 60 times / minute, and an initial tension of 0.2 cN / dtex. The number of bends at which fiber fracture occurred was recorded. Ten valid specimens were tested for each sample, and the arithmetic mean was taken as the final test result. A higher number of bending fatigue cycles indicates better fiber bending resistance, making it less prone to fatigue fracture due to repeated deformation during use in automotive wheel covers. The relevant test data are summarized in Table 2.

[0090] Table 2

[0091] Experimental protocol Bending fatigue cycles (times) Example 1 2853 Example 2 2121 Example 3 2386 Example 4 3120 Example 5 2456 Example 6 2563 Example 7 3581 Example 8 2682 Example 9 3864 Comparative Example 1 1680

[0092] Compared to Comparative Example 1, the high-efficiency plasticizers introduced in Examples 1-6 possess both long-chain alkyl groups and polar ether or ester bonds compatible with polypropylene. This plasticizer inserts into the polypropylene molecular chains, reducing the resistance to chain entanglement and allowing the molecular chains to undergo elastic deformation and absorb energy during repeated bending, thus preventing fatigue fracture caused by stress concentration. Example 4 uses castor oil acid, whose additional secondary hydroxyl groups can form hydrogen bonds with some raw materials, enhancing interfacial bonding and stress transfer. This results in more uniform energy dissipation during repeated bending, leading to better elongation at break and bending fatigue cycles.

[0093] Example 7 uses a blend of epoxy fatty acid methyl ester and ricinoleic acid. Under acidic catalysis, the epoxy group of the epoxy fatty acid methyl ester undergoes a ring-opening addition reaction with the secondary hydroxyl group of ricinoleic acid to form an ether bond. Simultaneously, the carboxyl group of ricinoleic acid undergoes an esterification reaction with the pretreated product. The two components form a partially cross-linked network structure through chemical bonding. This network can absorb energy through the elastic deformation of the cross-linking points during repeated bending and effectively limit fatigue damage caused by excessive slippage of molecular chains, thereby synergistically improving bending fatigue life. Example 8 uses a blend of stearic acid and linoleic acid. The two components undergo esterification reactions independently with the pretreated product. The product is only a physical mixture, and there is no chemical bonding between the components. Therefore, the bending fatigue life is between that of the two single components, and no synergistic effect is observed.

[0094] Example 9, based on Example 7, first premixes epoxy fatty acid methyl ester and ricinoleic acid at 60°C to allow the two components to fully contact and form an association. Then, a staged heating reaction is employed: first, the esterification reaction is promoted at 100°C, and then the temperature is increased to 110°C to accelerate the epoxy ring-opening addition reaction. This process ensures the orderly conduct of epoxy ring-opening and esterification, improves the collision efficiency between epoxy and hydroxyl groups, and results in a more complete and uniformly distributed cross-linked network structure. This leads to more uniform stress distribution during tensile fracture, absorption of more deformation energy, and more effective energy absorption and inhibition of fatigue damage accumulation during repeated bending, thereby further improving the elongation at break and flexural fatigue life.

Claims

1. A polypropylene staple fiber for automotive wheel covers, characterized in that, The raw materials include the following parts by weight: 60-90 parts polypropylene resin, 10-20 parts ethylene-propylene-diene terpolymer, 5-10 parts maleic anhydride-grafted polypropylene, 2-5 parts high-efficiency plasticizer, 1-3 parts antioxidant, 0.2-0.6 parts light stabilizer, 0.1-0.5 parts nucleating agent, and 0.4-0.8 parts silicone masterbatch; The raw materials for preparing the high-efficiency plasticizer include the following components: sodium cellulose, dipropylene glycol dimethyl ether, 1,2-epoxybutane, aliphatic modifier, methanesulfonic acid, and toluene; The aliphatic modifier is composed of epoxy fatty acid methyl ester and ricinoleic acid.

2. The polypropylene staple fiber for automotive wheel covers as described in claim 1, characterized in that, The light stabilizer is at least one of light stabilizer 770, light stabilizer 944, and light stabilizer 622.

3. The polypropylene staple fiber for automotive wheel covers as described in claim 1, characterized in that, The nucleating agent is at least one of NA-11 and NA-21.

4. The polypropylene staple fiber for automotive wheel covers as described in claim 1, characterized in that, The antioxidant is at least one of antioxidant 1010, antioxidant 168, and antioxidant 1076.

5. The polypropylene staple fiber for automotive wheel covers as described in claim 1, characterized in that, The antioxidant is a compound of antioxidant 1010 and antioxidant 168 in a mass ratio of 0.5-2:0.5-2.

6. The polypropylene staple fiber for automotive wheel covers as described in claim 1, characterized in that, The aliphatic modifier is composed of epoxy fatty acid methyl ester and ricinoleic acid in a mass ratio of 0.5-2:0.5-2.

7. A method for preparing polypropylene staple fibers for automotive wheel covers as described in any one of claims 1-6, characterized in that, The method is as follows: Step 1: Under a nitrogen atmosphere, add polypropylene resin, ethylene-propylene-diene terpolymer, maleic anhydride-grafted polypropylene, high-efficiency plasticizer, antioxidant, light stabilizer, nucleating agent, and silicone masterbatch to a high-speed mixer. Set the stirring speed to 800-1500 r / min, control the mixing temperature to 85-95℃, and the mixing time to 5-15 min to obtain the premixed material. Step 2: The above premixed material is fed to a twin-screw extruder, where it is melted and plasticized before being extruded to obtain a spinning melt; Step 3: The spinning melt is extruded through the spinning assembly to form a melt stream, and then cooled and solidified by side blowing air at a temperature of 20-30℃ and a wind speed of 0.2-1m / s. The spinning speed is set to 800-1500m / min to obtain nascent fibers. Step 4: The nascent fibers undergo two-stage stretching treatment. The first stage stretching is carried out in a water bath at a temperature of 70-80℃ and a stretching ratio of 1.5-2 times. The second stage stretching is carried out in a hot box at a temperature of 80-90℃ and a stretching ratio of 1.5-2 times. Subsequently, heat setting treatment is carried out in hot air at 90-100℃ for 5-30 minutes. The set fibers are then cut into short fibers of 40-100mm and subjected to static elimination and opening and impurity removal processes to obtain polypropylene short fibers for automotive wheel covers.

8. The method as described in claim 7, characterized in that, In step 2, the temperatures of each heating section of the twin-screw extruder are set as follows: 185-195℃ for the feeding zone, 200-210℃ for the compression zone, 215-225℃ for the homogenization zone, and the melting temperature is controlled at 210-220℃.

9. The method as described in claim 7, characterized in that, The preparation method of the high-efficiency plasticizer is as follows, in parts by weight: S1. Under nitrogen protection, add 2-4 parts of sodium cellulose and 10-20 parts of dipropylene glycol dimethyl ether to a high-pressure reactor, heat to 75-90℃, and continuously introduce 30-50 parts of 1,2-epoxybutane over 1-3 hours, controlling the reaction temperature at 100-130℃. After the addition is complete, maintain the temperature for 0.5-3 hours. After the reaction is complete, cool down and depressurize, add 10-20% hydrochloric acid dropwise to neutralize the reaction solution, filter, and recover the dipropylene glycol dimethyl ether by vacuum distillation at a reactor temperature of 130-150℃ and a vacuum degree of -0.08~-0.095MPa to obtain the pretreated product. S2. Take 7-12 parts of the pretreated material from step S1, mix it with 2-6 parts of aliphatic modifier, 0.05-0.2 parts of methanesulfonic acid and 4-8 parts of toluene, and react at 90-105℃ for 5-10 hours. After the reaction is completed, remove the toluene by vacuum distillation at 60-85℃ and a vacuum degree of -0.08 to -0.095 MPa. Wash with 5-10% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 60-90℃ and a vacuum degree of -0.08 to -0.095 MPa to obtain a high-efficiency plasticizer.

10. The method as described in claim 7, characterized in that, The preparation method of the high-efficiency plasticizer is also as follows, in parts by weight: S1. Under nitrogen protection, add 2-4 parts of sodium cellulose and 10-20 parts of dipropylene glycol dimethyl ether to a high-pressure reactor, heat to 75-90℃, and continuously introduce 30-50 parts of 1,2-epoxybutane over 1-3 hours, controlling the reaction temperature at 100-130℃. After the addition is complete, maintain the temperature for 0.5-3 hours. After the reaction is complete, cool down and depressurize, add 10-20% hydrochloric acid dropwise to neutralize the reaction solution, filter, and recover the dipropylene glycol dimethyl ether by vacuum distillation at a reactor temperature of 130-150℃ and a vacuum degree of -0.08~-0.095MPa to obtain the pretreated product. S2. The aliphatic modifier is stirred and mixed at 60°C for 30 minutes to obtain a premixed acid component. The aliphatic modifier is composed of epoxy fatty acid methyl ester and ricinoleic acid in a mass ratio of 0.5-2:0.5-2. Take 7-12 parts of the pretreated material from step S1, mix it with the premixed acid component, 0.05-0.2 parts of methanesulfonic acid and 4-8 parts of toluene, and react at 90-105°C for 1-3 hours. Raise the temperature to 105-115°C and continue the reaction for 4-8 hours. After the reaction is completed, remove the toluene by vacuum distillation at 60-85°C and a vacuum degree of -0.08 to -0.095 MPa. Wash with a 5-10% sodium bicarbonate solution until neutral, and then dehydrate and dry by vacuum distillation at 60-90°C and a vacuum degree of -0.08 to -0.095 MPa to obtain a high-efficiency plasticizer.