Preparation method of waste chromium tanning leather scrap composite material and application thereof

Abstract

This invention discloses a method for preparing a composite material from waste chrome-tanned leather scraps and its application, belonging to the field of solid waste resource utilization technology. The method first pre-treats the leather scraps with a deep eutectic solvent to modify them; then, it uses liquid nitrogen embrittlement to destroy the internal structure of the fibers, followed by directional ball milling in a specific pattern to refine the fibers while maintaining their structural integrity; finally, the treated leather scraps are mixed with a specially formulated styrene-butadiene rubber composite adhesive in a certain proportion, and then molded to obtain the composite material. This invention, through multi-stage processing, solves problems such as poor interfacial bonding between leather scraps and weakly polar adhesives, insufficient material flexibility, and poor air permeability and water absorption. The resulting composite material has suitable tensile strength, high elongation at break, excellent bursting properties, air permeability, and water absorption, making it suitable for the preparation of functional insoles, sports shoe midsoles, and medical linings that require high flexibility and comfort.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically a method for preparing a composite material of waste chrome-tanned leather scraps and its application. Background Technology

[0002] The leather industry generates a large amount of solid waste during production, among which waste chrome-tanned leather scraps account for a very high proportion. These waste chrome-tanned leather scraps are rich in collagen. Traditional resource utilization methods, such as extracting collagen or manufacturing recycled leather, generally have problems such as complex processes, secondary pollution, or low product added value.

[0003] Currently, some technologies utilize waste chrome-tanned leather scraps to prepare rigid or semi-rigid sheets. For example, Chinese invention patent CN111925656B discloses a method for preparing chrome leather scrap composite sheets, which involves blending chrome leather scraps with pineapple leaf fibers and natural latex, followed by hot pressing to form the sheet. However, this technology still has certain limitations: First, the resulting sheets are relatively rigid, hard and brittle, and have low elongation at break, making them unsuitable for applications requiring high flexibility, such as insoles or shoe soles. Second, natural latex is expensive. If cheaper styrene-butadiene rubber is used to treat the leather scraps to reduce costs, its weaker polarity leads to poor interfacial bonding with the leather fibers, thus affecting the material's mechanical properties and hydrophilicity. Finally, if pineapple leaf fibers are omitted to pursue flexibility, the material's breathability and water absorption will be significantly insufficient, making it difficult to meet applications requiring high material comfort.

[0004] Furthermore, if waste chrome-tanned leather scraps are directly used to prepare composite materials, their coarse particle size, poor dispersibility, and low surface activity will affect the uniformity and performance stability of the materials. Although mechanical ball milling can refine the particles, it is still difficult to improve the interfacial compatibility between leather scraps and adhesives, and excessive grinding may also damage the collagen fiber structure, limiting its application in flexible composite materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a composite material of waste chrome-tanned leather scraps and its application. By pretreatment with a deep eutectic solvent, liquid nitrogen embrittlement and ball milling, the surface activity of the waste chrome-tanned leather scraps is improved. Then, by combining it with a composite adhesive with styrene-butadiene rubber as the main component, a composite material with balanced tensile strength, elongation at break, bursting properties, air permeability and water absorption is obtained. It is suitable for the production of pads or shoe soles and other products with high flexibility requirements.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a composite material of waste chrome-tanned leather scraps includes the following steps performed sequentially:

[0008] S1. Pretreatment with eutectic solvent: Immerse waste chrome-tanned leather scraps in eutectic solvent and treat at 60~80℃ for 2~3 hours to obtain leather scrap residue;

[0009] S2. Liquid nitrogen embrittlement treatment: Take dried leather scraps, immerse them in liquid nitrogen for 8-12 minutes to obtain embrittled leather scraps;

[0010] S3. Directional ball milling treatment: The brittle leather scraps are treated with an intermittent bidirectional ball milling method at a speed of 200~400 r / min for 30~60 min to obtain polished leather scraps;

[0011] S4. Composite material molding: Take abrasive leather scraps and styrene-butadiene rubber composite adhesive with a weight ratio of 100:20~35, mix them evenly, and mold them at 60~80℃ and 1~3MPa for 3~8min to obtain waste chrome tanned leather scraps composite material.

[0012] The styrene-butadiene rubber composite adhesive comprises styrene-butadiene rubber, polar resin, and plasticizer.

[0013] As a limitation of the present invention, the waste chrome-tanned leather scraps are obtained by taking waste chrome-tanned leather, removing impurities, and crushing it to 8-30 mesh.

[0014] As a further limitation of the present invention, the deep eutectic solvent is composed of choline chloride and a hydrogen bond donor;

[0015] The hydrogen bond donor is selected from urea, lactic acid, or oxalic acid;

[0016] The molar ratio of choline chloride to hydrogen bond donor is 1:1~2.

[0017] As a further limitation of the present invention, the intermittent bidirectional rotation involves rotating the ball mill in one direction for at least 10 minutes, stopping for 4 to 8 minutes, and then rotating the ball mill in the opposite direction until the directional ball milling process is completed.

[0018] Preferably, the ball mill is rotated clockwise for 20 minutes, stopped for 5 minutes, and then rotated counterclockwise for 20 minutes.

[0019] As a further limitation of the present invention, the styrene-butadiene rubber composite adhesive is made by mixing styrene-butadiene rubber, polar resin and plasticizer in a weight ratio of 50~85:10~30:5~15;

[0020] The polar resin is an acrylate resin or a polyvinyl alcohol resin;

[0021] The plasticizer is a citrate ester plasticizer or an epoxy vegetable oil plasticizer.

[0022] As a further limitation of the present invention, the directional ball milling process uses steel large balls, medium balls and small balls in a ratio of 3:5:2;

[0023] The diameter of the large sphere is 10~15mm;

[0024] The diameter of the middle sphere is 6~9mm;

[0025] The diameter of the ball is 3-5 mm.

[0026] The present invention also provides a composite material of waste chrome-tanned leather scraps prepared by the above preparation method.

[0027] This invention also provides an application of waste chrome-tanned leather scraps composite material in the preparation of functional insoles, sports shoe midsoles, or medical linings.

[0028] By adopting the above technical solution, the technical progress achieved by this invention compared with the prior art is as follows:

[0029] This invention significantly improves the surface activity and dispersibility of waste chrome-tanned leather scrap fibers through a multi-step synergistic treatment process involving deep eutectic solvent pretreatment, liquid nitrogen embrittlement, and directional ball milling, making their internal structure easier to bond with adhesives. The deep eutectic solvent treatment conditions are mild, effectively cleaning and activating the leather scrap surface, while liquid nitrogen embrittlement enhances ball milling efficiency. The intermittent bidirectional ball milling mode, combined with multi-sized grinding balls, ensures moderate abrasion of the leather scrap fibers, avoiding over-grinding that damages the structure.

[0030] This invention produces a specialized composite adhesive by compounding a polar resin and an environmentally friendly plasticizer into styrene-butadiene rubber (SBR). This adhesive retains the cost advantages of SBR, enhances the interfacial bonding with treated leather fibers through the polar resin, and improves flexibility through the plasticizer, thereby solving the problems of brittleness and poor bonding in composite materials.

[0031] The process of this invention is clear and easy to operate. The resulting composite material has excellent comprehensive properties, including high mechanical strength, good flexibility, good air permeability and moisture absorption. It overcomes the shortcomings of traditional chrome tanned leather scraps, such as hardness, brittleness and poor comfort, and broadens the application of waste chrome tanned leather scraps in the field of high-value flexible composite materials.

[0032] This invention enables the high-value utilization of waste chrome-tanned leather scraps. The entire process is environmentally friendly, with no emissions of toxic or harmful substances. The resulting products can be directly used in fields requiring high flexibility and comfort, such as insoles, soles, and linings. Attached Figure Description

[0033] Figure 1 This is an appearance diagram of the waste chrome-tanned leather scrap composite material E1 prepared in Example 1 of the present invention;

[0034] Figure 2 The image shows an electron microscope image of the waste chrome-tanned leather scraps composite material E1 in the experimental example of the present invention.

[0035] Figure 3 The image shown is an electron microscope image of the leather scrap composite material C1 in the experimental example of the present invention.

[0036] Figure 4 The graph shows the water vapor permeability test results of the leather shavings composite material C1 in the experimental example of the present invention; Detailed Implementation

[0037] The present invention will be further described in detail below through specific embodiments. It should be understood that the described embodiments are only for explaining the present invention and do not limit the present invention.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods in the art. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0039] Example 1

[0040] A method for preparing a composite material of waste chrome-tanned leather scraps includes the following steps:

[0041] S0. Raw material preparation: Remove impurities from waste chrome-tanned leather and crush it to about 20 mesh for later use.

[0042] S1. Eutectic solvent pretreatment: Weigh choline chloride and urea (molar ratio 1:2) and mix them, stirring at 80℃ to form a clear and transparent eutectic solvent. Take 100g of crushed leather scraps and add them to 500g of the above eutectic solvent, stirring at 70℃ for 2.5h. After treatment, filter to separate the solids, wash three times with deionized water, and dry at 80℃ to constant weight to obtain pretreated leather scrap residue.

[0043] S2. Liquid nitrogen embrittlement treatment: Take 20g of dried pre-treated leather scraps and quickly immerse them in liquid nitrogen for 10 minutes. After removal, allow them to return to room temperature to obtain embrittled leather scraps.

[0044] S3. Directional ball milling treatment: Place the brittle leather shavings into a ball mill jar, adding steel balls with diameters of 12mm, 8mm, and 4mm in a ratio of 3:5:2. Set the ball mill speed to 300 r / min, using an intermittent bidirectional mode: first rotate clockwise for 20 minutes, stop for 5 minutes; then rotate counterclockwise for 20 minutes, for a total time of 45 minutes. After ball milling, pass the shavings through a 100-mesh sieve to obtain ground leather shavings.

[0045] S4. Composite material molding:

[0046] Take 70 parts of styrene-butadiene rubber, 20 parts of acrylic resin, and 10 parts of epoxidized soybean oil by weight ratio, and mix them evenly at 60°C to obtain styrene-butadiene rubber composite adhesive.

[0047] Weigh 100g of abrasive leather scraps and add 25g of the above-mentioned composite adhesive, then mix thoroughly. Place the mixture in a mold and press it at 70℃ and 2MPa for 5 minutes. Demold and cool to obtain a waste chrome-tanned leather scrap composite material, denoted as Waste Chrome-Tanned Leather Scraps Composite Material E1. Figure 1 .

[0048] Example 2

[0049] A method for preparing a composite material of waste chrome-tanned leather scraps includes the following steps:

[0050] S0. Raw material preparation: Remove impurities from waste chrome-tanned leather and crush it to about 30 mesh for later use.

[0051] S1. Eutectic solvent pretreatment: Weigh choline chloride and lactic acid (molar ratio 1:1.5) and mix to prepare a eutectic solvent. Take 100g of crushed leather scraps and add them to 500g of solvent. Stir at 60℃ for 3 hours. After treatment, filter, wash, and dry in a forced-air oven at 70℃ to obtain pretreated leather scrap residue.

[0052] S2. Liquid nitrogen embrittlement treatment: Take 20g of dried leather scraps, immerse them in liquid nitrogen for 8 minutes, and then remove them to return to room temperature.

[0053] S3. Directional ball milling treatment: The brittle leather shavings are ball-milled using steel balls with diameters of approximately 14mm, 7mm, and 3mm (in a ratio of 3:5:2) at a speed of 200 rpm. First, rotate clockwise for 12 minutes, stop for 4 minutes, then rotate counterclockwise for 12 minutes, for a total time of 28 minutes. After ball milling, the sieving process is complete.

[0054] S4. Composite Material Molding: Mix 60g of styrene-butadiene rubber, 25g of polyvinyl alcohol resin, and 15g of tributyl acetylacetate to prepare an adhesive. Take 100g of abrasive leather scraps, add 30g of the adhesive, and mix well. Mold at 65℃ and 1.5MPa for 8 minutes, demold, and cool to obtain a waste chrome-tanned leather scrap composite material, denoted as Waste Chrome-Tanned Leather Scraps Composite Material E2.

[0055] Comparative Example 1

[0056] Steps S1 and S2 of Example 1 are omitted. The dried leather scraps are directly ball-milled in the same way, and then molded in the same proportion and under the same conditions with the same composite adhesive according to the method of Example 1 to obtain leather scrap composite material C1.

[0057] Comparative Example 2

[0058] Perform steps S1, S2, and S3 of Example 1 to obtain modified fibers. Then, use pure styrene-butadiene latex containing non-polar resin and plasticizer as an adhesive, and mold it according to the same addition amount and conditions as in Example 1 to obtain leather scrap composite material C2.

[0059] Comparative Example 3

[0060] Perform steps S1, S2, and S3 of Example 1 to obtain modified fibers. Then, use pure chloroprene latex as an adhesive and mold it according to the same addition amount and conditions as the adhesive in Example 1 to obtain leather scrap composite material C3.

[0061] Effect Experiment Example

[0062] (I) Microscopic morphology observation and results:

[0063] The microstructure of the composite material E1 made from waste chrome-tanned leather scraps was observed using scanning electron microscopy, and electron micrographs were taken. The results are as follows: Figure 2 The microstructure of the leather scrap composite material C1 was observed using scanning electron microscopy, and electron micrographs were taken. The results are as follows. Figure 3 .

[0064] Compare Figure 2 and Figure 3 It can be seen that in the waste chrome tanned leather scrap composite material E1, the fibers and adhesive are connected into blocks and the bonding is tighter, while the leather scrap composite material C1 exhibits a flocculent state, and the tensile strength of the corresponding leather scrap composite material C1 may be lower.

[0065] (II) Performance Testing and Results:

[0066] The water vapor permeability, contact angle, tensile strength and elongation at break of the leather shavings composite materials prepared in Examples 1, 2 and Comparative Examples 1 to 3 were tested one by one. Professional evaluators were invited to conduct a hand feel evaluation to comment on the softness, hardness and elasticity related hand feel. The results are shown in Table 1.

[0067] Among them, the water vapor permeability test results of leather shavings composite material C1 are as follows: Figure 4 .

[0068] Table 1 Performance test results of each sample

[0069]

[0070] The results showed that the waste chrome-tanned leather scrap composites E1 and E2 prepared in Examples 1 and 2 exhibited superhydrophilicity, high moisture permeability, high flexibility, and good strength. However, the comparative sample C1 indicated that leather scrap fibers without deep eutectic solvent pretreatment and liquid nitrogen embrittlement synergistic modification could not achieve ideal performance even when using the same composite adhesive. The comparative sample C2 showed that using styrene-butadiene rubber alone resulted in poor performance due to weak interfacial bonding and brittle adhesive film. The comparative sample C3 showed that, with the same pretreatment, using the more expensive neoprene rubber resulted in a lower elongation at break compared to the styrene-butadiene rubber composite system of this invention.

[0071] Example 3

[0072] A method for preparing a composite material of waste chrome-tanned leather scraps includes the following steps:

[0073] S0. Raw material preparation: Remove impurities from waste chrome-tanned leather and crush it to about 8 mesh for later use.

[0074] S1. Eutectic solvent pretreatment: Weigh choline chloride and oxalic acid (molar ratio 1:1) and mix to prepare a eutectic solvent. Take 100g of crushed leather scraps and add them to 500g of solvent. Stir at 80℃ for 2 hours. After treatment, filter, wash, and dry in a forced-air oven at 75℃ to obtain pretreated leather scrap residue.

[0075] S2. Liquid nitrogen embrittlement treatment: Take 20g of dried leather scraps, immerse them in liquid nitrogen for 12min, and then remove them to return to room temperature.

[0076] S3. Directional ball milling treatment: The brittle leather shavings are ball-milled using steel balls with diameters of approximately 10mm, 6mm, and 5mm (in a ratio of 3:5:2) at a speed of 400 rpm. First, rotate clockwise for 20 minutes, stop for 8 minutes, then rotate counterclockwise for 20 minutes, for a total time of 48 minutes. After ball milling, the sieving process is complete.

[0077] S4. Composite Material Molding: Mix 85g of styrene-butadiene rubber, 10g of acrylate resin, and 5g of citrate plasticizer to prepare an adhesive. Take 100g of abrasive leather scraps, add 20g of adhesive, and mix well. Mold at 80℃ and 3MPa for 3min, demold, and cool to obtain a composite material of waste chrome-tanned leather scraps.

[0078] Example 4

[0079] Waste chrome-tanned leather scraps composite material was prepared according to the method in Example 1 and pulverized into 3-5 mm particles. The waste chrome-tanned leather scraps composite material particles, AC foaming agent, and elastomer modifier were mixed in a ratio of 100:15:5 and placed in a mixer, where they were thoroughly mixed at 80°C. The mixture was then injected into a sports shoe midsole mold and molded at 165°C and 15 MPa for 8 minutes. After demolding, it was cured for 24 hours to obtain the sports shoe midsole preform. After edge trimming and surface embossing, it can be assembled with the shoe upper.

[0080] Testing revealed that the resulting athletic shoes have a moderate midsole density, high rebound rate, and excellent energy return and cushioning performance. They also offer good breathability, meeting the needs of moderate-intensity activities such as running and training.

[0081] The waste chrome-tanned leather scraps composite material obtained by this invention can also be used to prepare other mat products that require flexibility, breathability, and moisture absorption, such as outdoor cushions, instrument and equipment cushioning linings, and pet mats, by adjusting the proportion of composite adhesive, changing molding parameters, or performing surface treatment, and can all give full play to its material properties.

[0082] In other embodiments, the present invention can be achieved by using different process parameters or material selections. For example, in some embodiments, the particle size of the waste chrome-tanned leather scraps can be 10 mesh, 15 mesh or 25 mesh. In step S1, the hydrogen bond donor of the deep eutectic solvent can also be a mixture of urea and lactic acid. The molar ratio of choline chloride to the hydrogen bond donor can be 1:1.2 or 1:1.8. The treatment temperature can be 65°C or 75°C. The treatment time can be 2.2h or 2.8h.

[0083] In step S2, the liquid nitrogen treatment time can be 9 min or 11 min.

[0084] In step S3, the ball milling speed can be 250 r / min or 350 r / min; the unidirectional ball milling time can be 18 min or 25 min; the stop interval time can be 6 min or 7 min; the diameter of the large ball can be 11 mm or 14 mm; the diameter of the medium ball can be 6.5 mm or 8 mm; and the diameter of the small ball can be 3.5 mm or 4.5 mm.

[0085] In step S4, the weight ratio of abrasive leather scraps to styrene-butadiene rubber (SBR) composite adhesive can be 100:22, 100:28, or 100:32. In the SBR composite adhesive, the polar resin can also be specific acrylate resins such as polymethyl acrylate and polymethacrylate, or specific polyvinyl alcohol resins such as polyvinyl butyral. The plasticizer can also be specific citrate esters such as triethyl acetylglucosyl citrate and tributyl citrate, or specific epoxidized vegetable oils such as epoxidized soybean oil and epoxidized linseed oil. The SBR content is 55 parts by weight or 75 parts by weight; the polar resin content is 15 parts by weight or 28 parts by weight; the plasticizer content is 8 parts by weight or 12 parts by weight; the molding temperature is 65℃ or 78℃; the molding pressure is 1.2 MPa or 2.5 MPa; and the molding time is 4 min or 6 min.

[0086] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still modify the technical solutions described in the above embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a composite material of waste chrome-tanned leather scraps, characterized in that, This includes the following steps performed sequentially: S1. Pretreatment with eutectic solvent: Immerse waste chrome-tanned leather scraps in eutectic solvent and treat at 60~80℃ for 2~3 hours to obtain leather scrap residue; S2. Liquid nitrogen embrittlement treatment: Take dried leather scraps, immerse them in liquid nitrogen for 8-12 minutes to obtain embrittled leather scraps; S3. Directional ball milling treatment: The brittle leather scraps are treated with an intermittent bidirectional ball milling method at a speed of 200~400 r / min for 30~60 min to obtain polished leather scraps; S4. Composite material molding: Take abrasive leather scraps and styrene-butadiene rubber composite adhesive with a weight ratio of 100:20~35, mix them evenly, and mold them at 60~80℃ and 1~3MPa for 3~8min to obtain waste chrome tanned leather scraps composite material. The styrene-butadiene rubber composite adhesive comprises styrene-butadiene rubber, polar resin, and plasticizer.

2. The method for preparing a composite material of waste chrome-tanned leather scraps according to claim 1, characterized in that, The waste chrome-tanned leather scraps are obtained by taking waste chrome-tanned leather, removing impurities, and crushing it to 8-30 mesh.

3. The method for preparing a composite material of waste chrome-tanned leather scraps according to claim 2, characterized in that, The deep eutectic solvent is composed of choline chloride and a hydrogen bond donor; The hydrogen bond donor is selected from urea, lactic acid, or oxalic acid; The molar ratio of choline chloride to hydrogen bond donor is 1:1~2.

4. The method for preparing a composite material of waste chrome-tanned leather scraps according to claim 3, characterized in that, Intermittent bidirectional rotation involves rotating the ball mill in one direction for at least 10 minutes, stopping for 4-8 minutes, and then rotating the ball mill in the opposite direction until the directional ball milling process is complete.

5. The method for preparing a composite material of waste chrome-tanned leather scraps according to claim 4, characterized in that, The styrene-butadiene rubber composite adhesive is made by mixing styrene-butadiene rubber, polar resin and plasticizer in a weight ratio of 50~85:10~30:5~15; The polar resin is an acrylate resin or a polyvinyl alcohol resin; The plasticizer is a citrate ester plasticizer or an epoxy vegetable oil plasticizer.

6. The method for preparing a composite material of waste chrome-tanned leather scraps according to claim 5, characterized in that, Directional ball milling uses steel large, medium, and small balls in a ratio of 3:5:

2. The diameter of the large sphere is 10~15mm; The diameter of the middle sphere is 6~9mm; The diameter of the ball is 3-5 mm.

7. A composite material of waste chrome-tanned leather scraps prepared by any one of claims 1 to 6.

8. The application of the waste chrome-tanned leather scraps composite material as described in claim 7 in the preparation of functional insoles, sports shoe midsoles, or medical linings.

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