A method for preparing breathable and odor-resistant insoles

Abstract

This invention relates to the field of polymer composite materials technology and discloses a method for preparing breathable and odor-resistant insoles. The method includes: impregnating kudzu root fibers with an aqueous solution of matrine extract and drying at low temperature to obtain a matrine-kudzu root fiber composite; mixing bamboo charcoal powder and kaolin to obtain a bamboo charcoal-kaolin composite powder; melt-blending and granulating plant tannic acid powder and PLA granules to obtain a plant tannic acid-modified PLA matrix; and hot-pressing a mixture of Juncao fiber, matrine-kudzu root fiber composite, bamboo charcoal-kaolin composite powder, and the plant tannic acid-modified PLA matrix to obtain a breathable and odor-resistant insole. This invention uses a dual-pathway synergistic deodorization of bamboo charcoal and kaolin, and uses plant tannic acid cross-linking modification of PLA to inhibit hydrolysis during use and restore PLA's degradability through laccase degradation under composting conditions, thus solving the technical problem of the contradiction between durability and degradability in fully degradable insoles.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and more specifically, to a method for preparing a breathable and odor-resistant insole. Background Technology

[0002] Insoles are constantly exposed to the enclosed, high-temperature, and humid microenvironment of the feet. Foot sweat continuously soaks the insole material, providing a warm and humid environment for bacteria and fungi to multiply. Bacterial metabolism produces odor-causing gases such as ammonia and organic sulfides, which are the main sources of shoe odor. Traditional polymer foam insoles (such as EVA (ethylene-vinyl acetate copolymer), polyurethane, etc.) are mainly closed-cell structures with poor breathability, preventing effective drainage of foot sweat, which accumulates inside the material, further aggravating bacterial and fungal growth and leading to a persistent and worsening odor. Existing odor-resistant insoles mostly rely on activated carbon particles for physical adsorption and deodorization, but their adsorption capacity is limited, and their ability to adsorb polar odor components such as ammonia is insufficient. Once the odor adsorption is saturated, the odor-resistant function rapidly declines, resulting in a short-lasting effect. Some products use chemically synthesized antibacterial agents (such as silver ion preparations and quaternary ammonium salts), whose antibacterial effect is mainly against bacteria, offering limited protection against common foot pathogenic fungi (dermatophytes, Candida albicans, etc.) that cause athlete's foot, and posing safety risks associated with long-term skin contact.

[0003] However, under the combined effects of the slightly acidic nature of foot sweat (pH 4-6) and the temperature of the sole (approximately 35-40°C), the ester bonds of degradable polymer insoles, represented by polylactic acid (PLA), undergo accelerated hydrolysis, resulting in a rapid decline in mechanical properties and an actual service life far below the required usage. If synthetic crosslinking agents are introduced to increase hydrolysis resistance, the full degradability of PLA is compromised. There is a fundamental contradiction between durability and degradability after disposal, which has become the core obstacle to the industrialization of fully degradable functional insoles. Summary of the Invention

[0004] This invention provides a method for preparing breathable and odor-resistant insoles, solving the technical problem of the contradiction between durability and degradability in fully degradable insoles in related technologies.

[0005] This invention provides a method for preparing a breathable and odor-resistant insole, comprising the following steps: Step 1: Mix and impregnate the matrine extract aqueous solution with kudzu fiber, filter and dry to obtain matrine-kudzu fiber complex with matrine loaded on the inner wall of the microporous channel of kudzu fiber; Step 2: Mix bamboo charcoal powder and kaolin powder at a mass ratio of (1-3):1 to obtain bamboo charcoal-kaolin composite powder; Step 3: After dry mixing of plant tannic acid powder and polylactic acid granules, melt blending is carried out at 170-190℃, so that the polyphenolic hydroxyl groups of plant tannic acid form intermolecular hydrogen bonds with the ester carbonyl groups on the polylactic acid molecular chain, and undergo esterification condensation with the terminal carboxyl groups of the polylactic acid molecular chain to form covalent ester bonds. After cooling and granulation, plant tannic acid modified polylactic acid matrix is ​​obtained. Step 4: Mix the Juncao fiber, the matrine-kudzu fiber composite, the bamboo charcoal-kaolin composite powder and the plant tannic acid modified polylactic acid matrix evenly, and hot press at 170-190℃ and 5-15 MPa. Demold and cool to obtain the breathable and odor-resistant insole.

[0006] Preferably, the amounts of each raw material are as follows, by weight: 50-65 parts polylactic acid, 10-20 parts Juncao fiber, 8-15 parts matrine-kudzu fiber composite, 10-20 parts bamboo charcoal-kaolin composite powder, and 3-8 parts plant tannins.

[0007] Preferably, in step one, the mass concentration of the matrine extract aqueous solution is 5-15 wt%, and the mass ratio of the matrine extract aqueous solution to kudzu fiber is (8-15):1; the soaking temperature is 20-25℃, and the soaking time is 2-4h; after filtration, the kudzu fiber is dried at 60-75℃ until the moisture content of the kudzu fiber is less than 5%.

[0008] Preferably, in step three, the melt blending time is 10-20 min; the amount of plant tannin is 5%-16% of the weight of polylactic acid.

[0009] Preferably, in step four, the hot pressing time is 10 to 20 minutes.

[0010] Preferably, the polylactic acid has a melt flow rate of 5–20 g / 10 min, and the test conditions are a temperature of 190°C and a load of 2.16 kg.

[0011] Preferably, the length of the kudzu fiber is 3-10 mm, and the total polyphenol content, calculated as gallic acid equivalent, is not less than 5 mg / g dry weight; the length of the kudzu fiber is 3-10 mm.

[0012] Preferably, the total mass fraction of matrine and oxymatrine in the matrine extract is not less than 30 wt%.

[0013] Preferably, the bamboo charcoal powder has a particle size of 100-200 mesh and a BET specific surface area of ​​not less than 300 m². 2 / g; the kaolin powder is natural kaolin that has not been calcined at high temperature, with a kaolinite content of not less than 85% dry weight and a particle size of 200-400 mesh; the purity of the plant tannins is not less than 85%, and they are derived from chestnut shell extract or pomegranate peel extract.

[0014] The beneficial effects of this invention are as follows: (1) The combination of Juncao fiber and Kudzu fiber in the PLA matrix forms a double-fiber porous interconnected skeleton, giving the insole excellent breathability and moisture-wicking properties, continuously reducing foot temperature and humidity, and inhibiting the reproduction of bacteria and fungi from the source.

[0015] (2) The three natural antibacterial components, matrine extract, kudzu fiber natural plant antibacterial components and plant tannins, work together to cover Gram-positive bacteria, Gram-negative bacteria and common pathogenic fungi of the feet (dermatophytes, Candida albicans, etc.), with a broad antibacterial spectrum, no synthetic chemical antibacterial agent residue, and are safe for human skin; matrine is continuously released through the porous channels of kudzu fiber, and the deodorizing effect is maintained for a long time.

[0016] (3) The synergistic effect of bamboo charcoal microporous physical adsorption and kaolin surface active hydroxyl chemical adsorption has the ability to adsorb both non-polar organic odor and polar ammonia. The dual-pathway deodorization effect is better than single activated carbon adsorption, and the deodorization is more comprehensive and lasting.

[0017] (4) Plant tannic acid modifies the PLA matrix through a dual mechanism of hydrogen bond crosslinking and covalent crosslinking, effectively inhibiting the hydrolysis of PLA under the slightly acidic, hot and humid environment of the foot, and ensuring the service life of the insole; after disposal, laccase degrades the tannic acid under composting conditions, the crosslinking network disintegrates, and PLA restores its normal biodegradability, fundamentally solving the technical problem of the contradiction between durability and degradability of fully degradable insoles.

[0018] (5) All components are derived from natural renewable raw materials. Agricultural waste (chestnut shells, pomegranate peels, etc.) are used as the source of tannic acid. It is safe for human skin and can be completely biodegraded under composting conditions after disposal, eliminating environmental pollution caused by the disposal of polymer insoles. Plant tannic acid simultaneously serves as both a PLA crosslinking modifier and a natural antibacterial component, allowing one material to play multiple roles and reduce raw material costs. Attached Figure Description

[0019] Figure 1 This is a bar chart comparing the diameters of the inhibition zones of the three strains for each sample of the present invention; Figure 2 This is a line graph showing the change in the adsorption effect of ammonia on each sample of the present invention over time. Figure 3 This is a line graph comparing the tensile strength retention rate at different stages of foot immersion in a simulated environment, as presented in this invention. Detailed Implementation

[0020] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0021] Example 1 This embodiment discloses a method for preparing a breathable and odor-resistant insole, which includes the following steps: Step 1: Preparation of matrine-pueraria fiber complex Matrine extract (total mass fraction of matrine and oxymatrine is 35 wt%) was dissolved in water to prepare an aqueous solution of matrine extract with a mass concentration of 10 wt%. Ten parts by weight of kudzu root fiber with a length of 5 mm were added to the aqueous solution (100 parts by weight), with a mass ratio of matrine extract aqueous solution to kudzu root fiber of 10:1. The solution was soaked at 22°C for 3 h to allow matrine to penetrate into the microporous channels of kudzu root fiber and be adsorbed onto the inner wall of the fiber pores. Excess solution was removed by filtration, and the solution was dried at 70°C until the moisture content of kudzu root fiber was less than 5%, yielding 12 parts by weight of matrine-kudzu root fiber composite.

[0022] Step 2: Preparation of bamboo charcoal-kaolin composite powder Bamboo charcoal powder (particle size 150 mesh, BET specific surface area 350 m²) 2 Bamboo charcoal-kaolin composite powder (6g) and natural kaolin powder (uncalcined at high temperature, kaolinite content 88%, particle size 300 mesh) are dry mechanically mixed at a mass ratio of 2:1 until the two are evenly dispersed to obtain 15 parts by weight of bamboo charcoal-kaolin composite powder.

[0023] Step 3: Preparation of Plant Tannin-Modified PLA Matrix Five parts by weight of plant tannic acid powder (derived from chestnut shell extract, purity 92%) were dry-mixed with 55 parts by weight of PLA granules (melt flow rate 10 g / 10 min, test temperature 190℃, load 2.16 kg) to ensure uniform adhesion of the plant tannic acid powder to the surface of the PLA granules. The mixture was then melt-blended at 180℃ for 15 min to allow the polyphenolic hydroxyl groups of the plant tannic acid to form hydrogen bonds and covalent ester bonds with the PLA molecular chains. After cooling and granulation, 60 parts by weight of plant tannic acid-modified PLA matrix were obtained. The amount of plant tannic acid used was 9.1% of the weight of PLA.

[0024] Step 4: Hot pressing of insoles 15 parts by weight of Juncao fiber with a total polyphenol content of 8 mg / g dry weight (determined by the Folin-phenol method) and a length of 5 mm, 12 parts by weight of matrine-kudzu fiber composite obtained in step one, 15 parts by weight of bamboo charcoal-kaolin composite powder obtained in step two, and 60 parts by weight of plant tannic acid modified PLA matrix obtained in step three were dry mechanically mixed evenly, placed in a mold, and hot-pressed at 180℃ and 10 MPa for 15 min; after demolding and cooling to room temperature, a breathable and odor-resistant insole was obtained.

[0025] Example 2 This embodiment discloses a method for preparing a breathable and odor-resistant insole, which includes the following steps: Step 1: Preparation of matrine-pueraria fiber complex Matrine extract (total mass fraction of matrine and oxymatrine of 30 wt%) was dissolved in water to prepare an aqueous solution of matrine extract with a mass concentration of 5 wt%. Seven parts by weight of kudzu fiber with a length of 3 mm were added to the aqueous solution (56 parts by weight), with a mass ratio of matrine extract aqueous solution to kudzu fiber of 8:1. The solution was soaked at 20°C for 2 h to allow matrine to penetrate into the microporous channels of kudzu fiber and be adsorbed onto the inner wall of the fiber pores. Excess solution was removed by filtration, and the solution was dried at 60°C until the moisture content of the kudzu fiber was less than 5%, yielding eight parts by weight of matrine-kudzu fiber composite.

[0026] Step 2: Preparation of bamboo charcoal-kaolin composite powder Bamboo charcoal powder (particle size 100 mesh, BET specific surface area 320 m²) 2 Bamboo charcoal-kaolin composite powder (6g) and natural kaolin powder (uncalcined at high temperature, kaolinite content 85%, particle size 200 mesh) are dry mechanically mixed at a mass ratio of 1:1 until the two are evenly dispersed to obtain 10 parts by weight of bamboo charcoal-kaolin composite powder.

[0027] Step 3: Preparation of Plant Tannin-Modified PLA Matrix Three parts by weight of plant tannic acid powder (derived from pomegranate peel extract, purity 88%) were dry-mixed with 50 parts by weight of PLA granules (melt flow rate 5 g / 10 min, test temperature 190℃, load 2.16 kg) to ensure uniform adhesion of the plant tannic acid powder to the surface of the PLA granules. The mixture was then melt-blended at 170℃ for 10 min to allow the polyphenolic hydroxyl groups of the plant tannic acid to form hydrogen bonds and covalent ester bonds with the PLA molecular chains. After cooling and granulation, 53 parts by weight of plant tannic acid-modified PLA matrix were obtained. The amount of plant tannic acid used was 6% of the weight of PLA.

[0028] Step 4: Hot pressing of insoles Ten parts by weight of Juncao fiber with a total polyphenol content of 6 mg / g dry weight (determined by the Folin-phenol method) and a length of 3 mm, eight parts by weight of matrine-kudzu fiber composite obtained in step one, ten parts by weight of bamboo charcoal-kaolin composite powder obtained in step two, and 53 parts by weight of plant tannic acid modified PLA matrix obtained in step three were dry mechanically mixed evenly, placed in a mold, and hot-pressed at 170℃ and 5 MPa for 10 min; after demolding and cooling to room temperature, a breathable and odor-resistant insole was obtained.

[0029] Example 3 This embodiment discloses a method for preparing a breathable and odor-resistant insole, which includes the following steps: Step 1: Preparation of matrine-pueraria fiber complex Matrine extract (total mass fraction of matrine and oxymatrine of 40 wt%) was dissolved in water to prepare an aqueous solution of matrine extract with a mass concentration of 15 wt%. 12 parts by weight of kudzu fiber with a length of 10 mm were added to the aqueous solution (180 parts by weight), with a mass ratio of matrine extract aqueous solution to kudzu fiber of 15:1. The solution was soaked at 25°C for 4 h to allow matrine to penetrate into the microporous channels of kudzu fiber and adsorb onto the inner wall of the fiber pores. Excess solution was removed by filtration, and the solution was dried at 75°C until the moisture content of the kudzu fiber was less than 5%, yielding 15 parts by weight of matrine-kudzu fiber composite.

[0030] Step 2: Preparation of bamboo charcoal-kaolin composite powder Bamboo charcoal powder (particle size 200 mesh, BET specific surface area 420 m²) 2 Bamboo charcoal-kaolin composite powder (6g) and natural kaolin powder (uncalcined at high temperature, kaolinite content 92%, particle size 400 mesh) are dry mechanically mixed at a mass ratio of 3:1 until the two are evenly dispersed to obtain 20 parts by weight of bamboo charcoal-kaolin composite powder.

[0031] Step 3: Preparation of Plant Tannin-Modified PLA Matrix Eight parts by weight of plant tannic acid powder (derived from chestnut shell extract, 90% purity) were dry-mixed with 65 parts by weight of PLA granules (melt flow rate 20 g / 10 min, test temperature 190℃, load 2.16 kg) to ensure uniform adhesion of the plant tannic acid powder to the surface of the PLA granules. The mixture was then melt-blended at 190℃ for 20 min to allow the polyphenolic hydroxyl groups of the plant tannic acid to form hydrogen bonds and covalent ester bonds with the PLA molecular chains. After cooling and granulation, 73 parts by weight of plant tannic acid-modified PLA matrix were obtained. The amount of plant tannic acid used was 12.3% of the weight of PLA.

[0032] Step 4: Hot pressing of insoles 20 parts by weight of Juncao fiber with a total polyphenol content of 12 mg / g dry weight (determined by the Folin-phenol method) and a length of 10 mm, 15 parts by weight of matrine-kudzu fiber composite obtained in step one, 20 parts by weight of bamboo charcoal-kaolin composite powder obtained in step two, and 73 parts by weight of plant tannic acid modified PLA matrix obtained in step three were dry mechanically mixed evenly, placed in a mold, and hot-pressed at 190℃ and 15 MPa for 20 min; after demolding and cooling to room temperature, a breathable and odor-resistant insole was obtained.

[0033] Example 4 This embodiment provides a method for preparing a breathable and odor-resistant insole. The amounts of each raw material are as follows by weight: 55 parts of PLA (polylactic acid), 15 parts of Juncao fiber, 12 parts of matrine-kudzu fiber composite, 15 parts of bamboo charcoal-kaolin composite powder, and 5 parts of plant tannic acid; the mass ratio of bamboo charcoal to kaolin in the bamboo charcoal-kaolin composite powder is 2:1.

[0034] The specifications for each raw material are as follows: PLA (polylactic acid) melt flow rate (MFR, test temperature 190℃, load 2.16 kg) is 10 g / 10 min; the length of the Juncao fiber is 5 mm, and the total polyphenol content in the Juncao fiber (calculated as gallic acid equivalent, determined by the Folin-phenol method) is ≥5 mg / g (dry weight); the length of the kudzu fiber used to prepare the matrine-kudzu fiber composite is 5 mm; the particle size of the bamboo charcoal powder is 150 mesh, and the BET specific surface area (determined by the nitrogen adsorption method according to GB / T 19587) is ≥300 m². 2 / g; Kaolin powder is made from natural kaolin (uncalcined at high temperature), kaolinite ( The content of matrine is ≥85% (dry weight), and the particle size is 300 mesh; the total mass fraction of matrine and oxymatrine in the matrine extract is ≥30 wt%; the plant tannins are obtained from chestnut shell extract, and the purity is ≥85% (calculated as tannin mass fraction).

[0035] Step 1: Preparation of matrine-pueraria fiber complex Matrine extract is loaded directly onto the microporous channels of kudzu fiber, and the matrine is enriched in the inner wall of the fiber channel. When the insole is worn, the matrine is slowly dissolved as the foot sweat moistens the fiber channel. The greater the amount of sweat, the faster the dissolution rate. Kudzu fiber is a natural biodegradable material, so there is no need to introduce synthetic wall materials.

[0036] The specific steps are as follows: (1) Dissolve matrine extract in water to prepare an aqueous solution of matrine extract with a mass concentration of 10 wt%; (2) Add kudzu fiber to the aqueous solution of matrine extract, the mass ratio of the aqueous solution of matrine extract to kudzu fiber is 10:1, and soak at room temperature for 3 h, so that matrine can penetrate into the micropores of kudzu fiber with water molecules and be adsorbed on the inner wall of the fiber pores. (3) After impregnation, filter to remove excess solution, and dry the kudzu fiber loaded with matrine at 70°C until the moisture content of the kudzu fiber is less than 5% to obtain matrine-kudzu fiber composite.

[0037] The drying temperature is limited to 70℃ (upper limit below 75℃): The melting point of matrine is 75~77℃. Limiting the drying temperature to 75℃ ensures that matrine remains solid and is retained on the inner wall of the pores of kudzu fiber during the drying process, preventing matrine from melting and flowing out of the pores after exceeding the melting point. The chemical structure of matrine and other alkaloids remains stable and does not decompose at 60~75℃. This temperature range effectively removes moisture from the fiber while preserving the solid state and antibacterial activity of matrine.

[0038] Matrine has a melting point of 75–77°C and is in a liquid state at the hot-pressing temperature (180°C) in step four. The retention of matrine in the matrine-kudzu fiber composite during hot pressing depends on the following physical confinement process: the micropores of kudzu fiber are small, confining the liquid matrine within the fiber's internal channels; during hot pressing, the molten plant tannin-modified PLA matrix flows rapidly and coats the outer surface of the kudzu fiber, sealing the outer openings of the fiber channels and preventing the liquid matrine from migrating outwards; after cooling following hot pressing, the PLA matrix solidifies, and the matrine remains in a solid state within the kudzu fiber channels, releasing again through sweat dissolution during insole wear.

[0039] Step 2: Preparation of bamboo charcoal-kaolin composite powder Bamboo charcoal powder (particle size 100-200 mesh, BET specific surface area ≥300 m²) 2 Bamboo charcoal-kaolin composite powder (6g) and natural kaolin powder (uncalcined at high temperature, kaolinite content ≥85%, particle size 200-400 mesh) are mixed by dry mechanical mixing at a mass ratio of 2:1 until the two are evenly dispersed, to obtain 15 parts by weight of bamboo charcoal-kaolin composite powder.

[0040] Bamboo charcoal powder has a well-developed microporous network, which allows for the physical adsorption of odor molecules such as ammonia and organic sulfides through these micropores; kaolin is a natural aluminosilicate mineral, and its particle surface is rich in active hydroxyl groups (…). The process involves surface chemical adsorption of polar odor molecules such as ammonia by surface-active hydroxyl groups, fixing these molecules onto the surface of kaolin particles. When bamboo charcoal and kaolin are mixed in the aforementioned proportion, the microporous physical adsorption of organic odors by bamboo charcoal synergizes with the surface chemical adsorption of polar odors by kaolin. The resulting composite powder exhibits adsorption capacity for both non-polar organic odors and polar ammonia, overcoming the deficiency of single activated carbon in its insufficient adsorption of polar odor components.

[0041] Step 3: Preparation of Plant Tannin-Modified PLA Matrix Using tannic acid derived from natural plants as a crosslinking modifier for PLA, the polyphenolic hydroxyl groups of tannic acid simultaneously form hydrogen bonds and covalent ester bonds with the PLA molecular chain, increasing the density of the PLA matrix and increasing the resistance to water molecule penetration into the matrix, thereby effectively inhibiting the hydrolysis of PLA under slightly acidic, hot and humid conditions. After disposal, under composting conditions, polyphenol oxidases such as laccase secreted by microorganisms oxidize and degrade tannic acid, breaking the hydrogen bonds and covalent ester bonds between tannic acid and the PLA molecular chain, restoring PLA to normal biodegradability, and achieving the dual goals of durability during use and biodegradability after disposal.

[0042] The specific steps are as follows: (1) The plant tannic acid powder (taken from chestnut shell or pomegranate peel extract, 5 parts by weight) is dry-mixed with PLA granules (55 parts by weight) so that the plant tannic acid powder is evenly attached to the surface of the PLA granules. (2) The above mixture was melt-blended at 180°C for 15 min. At this temperature, the polyphenolic hydroxyl groups of plant tannins ( ) and the ester carbonyl group on the PLA molecular chain ( Intermolecular hydrogen bonds are formed between tannic acid and the terminal carboxyl group of the PLA molecular chain; at the same time, the phenolic hydroxyl group of tannic acid forms an intermolecular hydrogen bond with the terminal carboxyl group of the PLA molecular chain. Under hot-melting conditions, partial esterification and condensation reactions occur, forming covalent ester bonds. The combined effect of hydrogen bonds and covalent ester bonds increases the density of the PLA matrix and the resistance to water molecule penetration into the matrix. As a result, under slightly acidic conditions (pH 4-6) and warm conditions (approximately 35-40°C), fewer water molecules reach the PLA ester bonds, and the hydrolysis rate is effectively suppressed. (3) After melt blending, the PLA matrix modified with plant tannic acid is obtained by cooling and granulation, which is modified PLA granules formed by hydrogen bonds and covalent ester bonds between tannic acid and PLA molecular chains.

[0043] The amount of plant tannins used is approximately 9.1% of the PLA weight (5 parts tannins / 55 parts PLA): below this amount, the crosslinking point density in the modified PLA matrix is ​​insufficient, resulting in limited inhibition of PLA hydrolysis; above this amount, the modified PLA matrix becomes more brittle, leading to a decrease in the mechanical properties of the insole; at this amount, the modified PLA matrix maintains the required flexibility of the insole while ensuring the hydrolysis resistance of PLA.

[0044] Step 4: Hot pressing of insoles The following materials were mixed evenly by dry mechanical mixing: 15 parts of Juncao fiber, 12 parts of matrine-kudzu fiber composite obtained in step 1, 15 parts of bamboo charcoal-kaolin composite powder obtained in step 2, and 60 parts of plant tannic acid modified PLA matrix obtained in step 3 (prepared by blending 55 parts of PLA and 5 parts of plant tannic acid). The mixture was placed in a mold and hot-pressed at 180℃ and 10 MPa for 15 min. After demolding, the mixture was cooled to room temperature to obtain a breathable and odor-resistant insole.

[0045] Experimental verification Experiment 1: Test on the broad-spectrum antibacterial properties of breathable and odor-resistant insoles 1. Experimental Objective The invention verifies that the breathable and odor-resistant insole has broad-spectrum antibacterial activity against Gram-positive bacteria, Gram-negative bacteria, and common pathogenic fungi of the feet. The focus is on verifying its inhibitory effect on fungi such as dermatophytes that are difficult to effectively combat with existing chemically synthesized antibacterial agents.

[0046] 2. Preparation of experimental samples Test sample (S1): A 20 mm diameter circular piece with a thickness of 3 mm was taken from the breathable and odor-resistant insole prepared according to Example 1.

[0047] Comparative Sample 1 (C1): Pure PLA hot-pressed insole, made by hot-pressing 55 parts by weight of PLA granules (MFR=10 g / 10 min) at 180℃ and 10 MPa for 15 min. The size is the same as S1, and it does not contain any antibacterial components.

[0048] Comparative Sample 2 (C2): Commercial silver ion antibacterial insole, a circular piece of the same size was cut from a commercially available product.

[0049] 3. Experimental conditions Test strains: Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 8739), and Trichophyton rubrum (ATCC 28188). Incubation temperatures: 37°C for bacteria, 28°C for Trichophyton rubrum. Bacterial culture medium: Nutrient agar (NA). Fungal culture medium: Sabouraud dextrose agar (SDA).

[0050] 4. Experimental Procedure (1) Prepare bacterial suspension according to GB / T 20944.1 agar diffusion method, and adjust the concentration to 0.5%. CFU / mL (bacteria) or CFU / mL (fungi).

[0051] (2) Spread the bacterial suspension evenly on the surface of the corresponding culture medium plate.

[0052] (3) Place each sample disc in the center of the plate with bacterial solution, cover and incubate at the corresponding temperature (24h for bacteria, 168h (7 days) for fungi).

[0053] (4) After the culture is completed, use a vernier caliper to measure the diameter (mm) of the inhibition zone around the sample. Each group is tested in parallel 3 times and the average value is taken.

[0054] 5. Experimental Results Table 1. Diameter of inhibition zone (mm) for each sample against the three bacterial strains

[0055] Figure 1 The bar chart shows the comparison of the inhibition zone diameters of each sample against the three strains. This chart visually reflects the broad-spectrum antibacterial effect of S1 against bacteria and Trichophyton rubrum, as well as the significant deficiency of C2 (silver ions) in inhibiting fungi.

[0056] 6. Analysis and Summary From Table 1 and Figure 1 It can be seen that the inhibition zone diameters of S1 (Example 1) against Staphylococcus aureus, Escherichia coli and Trichophyton rubrum were 18.2 mm, 15.6 mm and 16.4 mm, respectively, all of which were significantly larger than those of C1 (pure PLA, no inhibition zone).

[0057] Compared with C2 (commercial silver ions), S1 has a comparable inhibitory effect on bacteria, but the diameter of the inhibition zone of S1 against Trichophyton rubrum (16.4 mm) is much larger than that of C2 (2.1 mm). This indicates that the synergistic effect of matrine extract in S1 with the natural antibacterial components of Juncao fiber and plant tannins can effectively cover pathogenic fungi of the feet that are difficult to deal with by existing silver ion antibacterial agents.

[0058] Experiment 2: Test on the ammonia adsorption and deodorization performance of breathable and odor-resistant insoles 1. Experimental Objective The study verified that the dual-pathway adsorption and deodorization effect of bamboo charcoal-kaolin composite powder is better than that of single bamboo charcoal adsorption, and focused on verifying the synergistic contribution of the active hydroxyl groups on the surface of kaolin to the chemical adsorption of polar ammonia.

[0059] 2. Preparation of experimental samples Test sample (S1): A 50 mm × 50 mm × 3 mm piece of the breathable and odor-resistant insole prepared according to Example 1, weighing about 3 g.

[0060] Comparison Sample 1 (C1): Pure PLA hot-pressed insole (same as Experiment 1 C1), same size.

[0061] Comparative Sample 3 (C3): Single bamboo charcoal composite insole, in which the bamboo charcoal-kaolin composite powder in the formulation of Example 1 was replaced with an equal weight of pure bamboo charcoal powder (particle size 150 mesh, BET specific surface area 350 m²). 2 / g), the remaining components and processes are exactly the same as in Example 1, and a comparative insole is prepared.

[0062] 3. Experimental conditions Sealed container volume: 5 L. Initial ammonia concentration: 100 mg / m³ 3 (Simulated upper limit of odor concentration in the wearing environment). Ambient temperature: 37℃. Ammonia concentration detection: Nessler's reagent spectrophotometry (HJ 533), detection wavelength 420 nm. Detection time points: 0, 30, 60, 90, 120, 180, 240 min.

[0063] 4. Experimental Procedure (1) Place each sample in a 5 L sealed container and inject ammonia gas into the container to an initial concentration of 100 mg / m³. 3 .

[0064] (2) Maintain the container temperature at 37℃, and extract gas samples from the sealed container at the above-mentioned time points. Bubble the extracted gas into 5 mL of 0.01 mol / L dilute sulfuric acid absorption solution to ensure that the ammonia in the gas is fully absorbed by the absorption solution. Perform colorimetric treatment on the absorption solution using the HJ533 Nessler's reagent spectrophotometric method, and measure the absorbance at 420 nm using a spectrophotometer. Convert the absorbance to ammonia concentration (mg / mL). 3 ).

[0065] (3) Each group was tested in parallel 3 times, and the average value was taken to calculate the change of ammonia concentration over time.

[0066] 5. Experimental Results Table 2. Ammonia concentration in the container of each sample at different time points (mg / m³) 3 )

[0067] Figure 2 The graph shows the ammonia concentration of each sample over time. This graph visually reflects that the ammonia adsorption rate and final adsorption capacity of S1 are superior to those of C3 (single bamboo charcoal) and C1 (pure PLA).

[0068] 6. Analysis and Summary From Table 2 and Figure 2 It can be seen that at 240 min, the ammonia concentration in S1 decreased to 5.2 mg / m³. 3 The ammonia removal rate reached 94.8%; C3 (single bamboo charcoal) had an ammonia removal rate of 79.9%; C1 (pure PLA) had almost no ammonia removal effect (ammonia removal rate of only 9.4%).

[0069] S1 showed significantly better ammonia removal performance than C3, indicating that the chemical adsorption of polar ammonia by the active hydroxyl groups on the surface of kaolin provided an effective supplement to the microporous physical adsorption of bamboo charcoal. The dual-pathway synergistic adsorption of bamboo charcoal and kaolin significantly improved the overall deodorization capacity.

[0070] Experiment 3: Hydrolysis Resistance Test of Plant Tannin-Modified PLA Matrix 1. Experimental Objective The study verified that crosslinking modification of PLA by plant tannins through hydrogen bonds and covalent ester bonds can effectively inhibit the hydrolysis of PLA under simulated foot wearing environment (slightly acidic, warm, and humid), proving that the insole of the present invention has mechanical durability during use. At the same time, it was verified that the biodegradability of PLA can be restored under waste composting conditions.

[0071] 2. Preparation of experimental samples Test sample (S1): The breathable and odor-resistant insole prepared according to Example 1 was cut into dumbbell-shaped tensile strips (total length 150 mm, gauge length 50 mm × narrow section width 10 mm, thickness 3 mm) according to GB / T 1040.2 1B type specifications, with 5 strips per group.

[0072] Comparative Sample 4 (C4): Tannic acid-free PLA composite insole. The plant tannic acid in the formulation of Example 1 was removed, and the dosage and hot pressing process of the remaining components (PLA 55 parts, Juncao fiber 15 parts, Matrine-Kueraria fiber composite 12 parts, Bamboo charcoal-Kaolin composite powder 15 parts) were exactly the same as those in Example 1, and the comparative sample was prepared.

[0073] 3. Experimental conditions Immersion solution: Acetic acid-sodium acetate buffer solution with a pH of 5.0 (simulating the slightly acidic environment of foot sweat). Immersion temperature: 37℃ (simulating foot temperature). Immersion duration: 0, 1, 2, 4, 6, and 8 weeks. Tensile test according to GB / T 1040.2, tensile rate 50 mm / min, test temperature 23℃. Degradability test: Several S1 and C4 samples were placed in composted soil at 55℃ and 60% moisture content, soaked for 8 weeks, and then removed to determine the mass loss rate (%).

[0074] 4. Experimental Procedure (1) Soak the S1 and C4 samples in a buffer solution at 37℃ and pH 5.0, and replace the solution every 48 h.

[0075] (2) Take out the corresponding time nodes at weeks 0, 1, 2, 4, 6 and 8, rinse with distilled water and dry at 60℃ to constant weight, and determine the tensile strength (MPa) according to GB / T 1040.2.

[0076] (3) Calculate the tensile strength retention rate (%) at each time point: retention rate = tensile strength at a certain time point / initial tensile strength × 100%.

[0077] (4) Composting degradation experiment: Take 3 pieces of S1 and C4 each (size 50 mm × 50 mm × 3 mm, initial weight), bury them in simulated compost soil at 55℃ and 60% moisture content, take them out after 8 weeks, rinse them with distilled water, dry them at 60℃ to constant weight, and calculate the mass loss rate.

[0078] 5. Experimental Results Table 3 Tensile strength and retention rate of each sample after immersion in a simulated foot environment for different times.

[0079] Table 4. Mass loss rates of S1 and C4 under simulated composting conditions over 8 weeks.

[0080] Figure 3 The graph shows the change in tensile strength retention rate of S1 and C4 with soaking time. This graph visually reflects the protective effect of plant tannic acid crosslinking modification on the hydrolysis resistance of PLA matrix.

[0081] 6. Analysis and Summary From Table 3 and Figure 3 It was found that after soaking for 8 weeks at 37℃ and pH 5.0, the tensile strength retention rate of S1 was 74.2%, while that of C4 (without plant tannins) was only 25.6%, indicating that S1's hydrolysis resistance was significantly better than that of C4. This demonstrates that the hydrogen bond and covalent ester bond cross-linking network formed by plant tannins and PLA molecular chains effectively increased the penetration resistance of the PLA matrix to water molecules, significantly slowing down the hydrolysis rate of PLA under simulated slightly acidic and humid conditions of the foot, thus maintaining sufficient mechanical strength of the insole throughout its service life.

[0082] Table 4 shows that after 8 weeks under simulated composting conditions (55℃, 60% moisture content), the mass loss rates of S1 and C4 were 39.8% and 32.7%, respectively, both showing significant degradation. This indicates that the biodegradability of PLA under waste composting conditions was not lost due to the cross-linking modification of plant tannins. The mass loss rate of S1 (39.8%) was slightly higher than that of C4 (32.7%). The main reason for this is that the tannin component in S1 (accounting for approximately 4.9% of the total mass of S1, i.e., 5 parts tannin / 102 parts total ratio) can be directly degraded by composting microorganisms, directly contributing to the additional mass loss of S1. In addition, polyphenol oxidases such as laccase secreted by composting microorganisms oxidize and degrade tannins, causing partial disintegration of the hydrogen bonds and covalent ester bonds between tannins and PLA molecular chains, increasing the accessibility of PLA chain segments, and further promoting the biodegradation of PLA components.

[0083] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for preparing a breathable and odor-resistant insole, characterized in that, Includes the following steps: Step 1: Mix and impregnate the matrine extract aqueous solution with kudzu fiber, filter and dry to obtain matrine-kudzu fiber complex with matrine loaded on the inner wall of the microporous channel of kudzu fiber; Step 2: Mix bamboo charcoal powder and kaolin powder at a mass ratio of (1-3):1 to obtain bamboo charcoal-kaolin composite powder; Step 3: After dry mixing of plant tannic acid powder and polylactic acid granules, melt blending is carried out at 170-190℃, so that the polyphenolic hydroxyl groups of plant tannic acid form intermolecular hydrogen bonds with the ester carbonyl groups on the polylactic acid molecular chain, and undergo esterification condensation with the terminal carboxyl groups of the polylactic acid molecular chain to form covalent ester bonds. After cooling and granulation, plant tannic acid modified polylactic acid matrix is ​​obtained. Step 4: Mix the Juncao fiber, the matrine-kudzu fiber composite, the bamboo charcoal-kaolin composite powder and the plant tannic acid modified polylactic acid matrix evenly, and hot press at 170-190℃ and 5-15 MPa. Demold and cool to obtain the breathable and odor-resistant insole.

2. The preparation method according to claim 1, characterized in that, The amounts of each raw material by weight are as follows: polylactic acid 50-65 parts, Juncao fiber 10-20 parts, matrine-kudzu fiber composite 8-15 parts, bamboo charcoal-kaolin composite powder 10-20 parts, and plant tannic acid 3-8 parts.

3. The preparation method according to claim 1, characterized in that, In step one, the mass concentration of the matrine extract aqueous solution is 5-15 wt%, and the mass ratio of the matrine extract aqueous solution to kudzu fiber is (8-15):1; the soaking temperature is 20-25℃, and the soaking time is 2-4 h; after filtration, it is dried at 60-75℃ until the moisture content of the kudzu fiber is less than 5%.

4. The method of claim 1, wherein, In step three, the melt blending time is 10 to 20 minutes; the amount of plant tannic acid used is 5% to 16% of the weight of polylactic acid.

5. The preparation method according to claim 1, characterized in that, In step four, the hot pressing time is 10 to 20 minutes.

6. The method of claim 1, wherein, The polylactic acid had a melt flow rate of 5–20 g / 10 min, and the test conditions were a temperature of 190 °C and a load of 2.16 kg.

7. The preparation method according to claim 1, characterized in that, The length of the Juncao fiber is 3-10 mm, and the total polyphenol content, calculated as gallic acid equivalent, is not less than 5 mg / g dry weight; the length of the Kudzu root fiber is 3-10 mm.

8. The preparation method according to claim 1, characterized in that, The total mass fraction of matrine and oxymatrine in the matrine extract is not less than 30 wt%.

9. The preparation method according to claim 1, characterized in that, The bamboo charcoal powder has a particle size of 100-200 mesh and a BET specific surface area of ​​not less than 300 m². 2 / g; the kaolin powder is natural kaolin that has not been calcined at high temperature, with a kaolinite content of not less than 85% dry weight and a particle size of 200-400 mesh; the purity of the plant tannins is not less than 85%, and they are derived from chestnut shell extract or pomegranate peel extract.

10. An air-permeable odor-controlling insole, characterized by It is prepared by any one of claims 1 to 9.

Images