Ultrafine collagenous fiber as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of tanning waste processing, and discloses a superfine collagenous fiber as well as a preparation method and application thereof. The preparation method comprises the following steps: drying the tanned leather trimming material, dissociating fibers into small particles, infiltrating the small particles with a rewetting liquid prepared from urea and an oxidizing agent until the water content is 5-120%, and finely dissociating the fibers. According to the method, urea and an oxidizing agent are used for cooperatively treating the dried and fiber-dissociated tanned leather trimming material, hydrogen bonds in the tanned leather trimming material are fundamentally prevented from being regenerated, the dispersibility of the collagen fiber is remarkably improved, and the superfine collagen fiber is prepared. The average diameter of the superfine collagenous fiber provided by the invention is less than 1200 nm, and the superfine collagenous fiber has better strength and thermal stability, is used for preparation, modification and other treatments of a composite material, and can improve the strength, rigidity and other properties of the composite material.

Description

Technical Field

[0001] The invention belongs to the technical field of leather waste processing, and particularly relates to ultra-fine collagen fibers, a preparation method and applications thereof. Background Art

[0002] Tanned leather trimmings are a common solid waste from leather processing. These semi-finished products, already tanned but not yet retanned and fatliquored, can be crushed to produce collagen fibers that can be used to prepare composite materials such as spunlace-based regenerated leather, thereby realizing resource utilization. However, tanned leather trimmings retain a multi-layered structure similar to leather, consisting of collagen fibers, fiber bundles, and fiber bundle networks. This structure collapses during water evaporation, and hydrogen bonding forces cause the collagen fibers to gradually adhere together. Consequently, direct crushing yields only coarse fiber bundles, resulting in composite materials with poor mechanical properties and strength. Pretreatment of tanned leather trimmings with acidic or alkaline reagents can improve the dispersion of collagen fibers, but can also cause detanning, reducing the mechanical properties and thermal stability of the composite material. Pretreatment of tanned leather trimmings with enzyme preparations can also yield fine collagen fibers, but this carries the risk of generating wastewater with high nitrogen content, and the enzyme inactivation process also generates new saline wastewater. Furthermore, enzyme preparations are generally expensive, making their practical application in the treatment of leather processing solid waste difficult.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing ultrafine collagen fibers, which utilizes urea and an oxidant to synergistically improve the dispersibility of collagen fibers, thereby obtaining ultrafine collagen fibers.

[0005] The present invention also aims to provide the ultra-fine collagen fibers and applications thereof.

[0006] The first technical solution adopted in the present invention is: The method for preparing ultra-fine collagen fibers comprises the following steps: After the tanned leather trimmings are dried and the fibers are dissociated into small particles, they are soaked with a rewetting solution prepared with urea and an oxidant to a moisture content of 5-120%, and then the fibers are finely dissociated; Wherein, the oxidant is selected from one or more of sodium percarbonate, ozone, sodium hypochlorite or hydrogen peroxide.

[0007] Preferably, the amount of urea used is 1-20% of the mass of the small particles.

[0008] Preferably, the amount of urea used is 5-10% of the mass of the small particles.

[0009] Preferably, the amount of the oxidant is 1-20% of the mass of the small particles.

[0010] Preferably, the amount of the oxidant is 5-10% of the mass of the small particles.

[0011] Preferably, the small particles are soaked to a water content of 10-40%.

[0012] Preferably, the tanned leather trimming material is dried to a moisture content of ≤15%.

[0013] The second technical solution adopted in the present invention is: The ultrafine collagen fibers are prepared according to any of the above methods for preparing ultrafine collagen fibers.

[0014] The third technical solution adopted in the present invention is: Application of the ultrafine collagen fibers in composite materials.

[0015] The fourth technical solution adopted by the present invention is: Application of the ultra-fine collagen fibers in spunlace regenerated leather.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention utilizes urea and an oxidant to collaboratively treat the tanned leather trimmings after drying and fiber dissociation. While urea destroys hydrogen bonds, the oxidant oxidizes substances that are prone to hydrogen bonds, directly and fundamentally preventing the regeneration of hydrogen bonds, significantly improving the dispersibility of collagen fibers in the tanned leather trimmings, and facilitating the preparation of extremely fine collagen fibers.

[0017] 2. The ultrafine collagen fibers provided by the present invention have an average fiber diameter of less than 1200 nm and have good strength and thermal stability.

[0018] 3. The ultrafine collagen fibers provided by the present invention can be used in the preparation, modification and other treatments of composite materials, and can improve the strength, stiffness and other properties of the composite materials.

[0019] 4. The ultra-fine collagen fibers provided by the present invention are used in spunlace regenerated leather, which can ensure that the spunlace regenerated leather has a better web-surface rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 is a stereomicroscope image of the collagen fibers prepared in Example 4; Figure 2Stereomicroscope image of collagen fibers prepared in the blank example. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments.It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention.In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.Unindicated specific conditions in the embodiment are carried out according to the conditions of normal conditions or manufacturer's advice.Reagents used or instruments that are not indicated by manufacturers are conventional products that can be purchased commercially.

[0023] The first embodiment provided by the present invention is: The method for preparing ultra-fine collagen fibers comprises the following steps: After the tanned leather trimmings are dried and the fibers are dissociated into small particles, they are soaked with a rewetting liquid prepared with urea and an oxidant to a moisture content of 5-120%, and then the fibers are finely dissociated.

[0024] The key to the embodiment of the present invention lies in the use of a rewetting liquid. Urea, when used alone, can destroy the hydrogen bonds in the tanning leather trimming material in an aqueous solution and disperse its collagen fibers. However, once it dries or the fibers dissociate, the urea will be thermally decomposed, the hydrogen bonds will be restored, and the collagen fibers in the tanning leather trimming material will gradually stick together again, and the dispersibility will decrease. The oxidant can improve the dispersibility of the collagen fibers by oxidizing substances that produce hydrogen bonds in the tanning leather trimming material, such as hydroxyl groups, amino groups on serine or threonine, but the improvement effect when used alone is also limited. The present invention uses a rewetting liquid prepared by urea and an oxidant to treat the tanning leather trimming material after fiber dissociation. While the urea destroys the hydrogen bonds, the oxidant oxidizes groups such as hydroxyl groups and amino groups that are prone to hydrogen bonds, converting these groups into carbonyl groups, nitro groups, etc., directly and fundamentally preventing the hydrogen bonds from being generated again, significantly improving the dispersibility of the collagen fibers in the tanning leather trimming material, and facilitating the preparation of extremely fine collagen fibers.

[0025] The oxidant described herein has an oxidizing power weaker than ozone (inclusive) but stronger than sodium percarbonate (inclusive), such as one or more of sodium percarbonate, ozone, sodium hypochlorite, or hydrogen peroxide. Hydrogen peroxide herein refers to a 30-35% aqueous hydrogen peroxide solution. Sodium percarbonate is preferred for its ease of storage. If the oxidizing power of the oxidant is too weak, it will affect the hydrogen bond breaking effect of the tanning trimming material; however, if the oxidizing power is too strong, it will damage the structure of collagen fibers.

[0026] The rewetting liquid is prepared with water as solvent and urea and oxidant as solute. The amount of urea and oxidant in the rewetting liquid is determined based on the mass of the small particles after fiber dissociation. The amount of urea used is 1-20% of the mass of the small particles, preferably 5-10%. When the amount of urea is too low, it cannot achieve the purpose of destroying the hydrogen bonds in the tanning trimming material; when the amount is too high, the structural damage to the collagen fibers will be too strong, the self-assembly structure of the collagen molecules will be destroyed, and the morphology of the fibers cannot be retained. The amount of oxidant used is 1-20% of the mass of the small particles, preferably 5-10%. When the amount of oxidant is too low, the groups that are prone to hydrogen bonds cannot be fully oxidized, and the hydrogen bonds will be regenerated in subsequent operations, affecting the effect of fiber dissociation; when the amount is too high, the oxidant will not only attack these hydrogen bond groups, but also affect the main chain of the molecule, affecting the fiber structure.

[0027] One of the functions of water in the rewetting fluid is to regulate the concentration of urea and oxidant, and the second function is to provide solvation, facilitating the penetration and reaction of urea and oxidant in the interfiber gaps. Generally speaking, the amount of water used is determined according to the water content of the small particles, and it is sufficient to infiltrate the small particles to a water content of 5-120%. Preferably, it is infiltrated to a water content of 10-40%. If the amount of water used is too high, the concentration of urea and oxidant will be diluted, affecting the reaction effect; if the amount is too low, the urea and oxidant will not be able to effectively penetrate into the collagen fiber network, affecting their effect. Therefore, in the actual preparation of the rewetting fluid, the amount of water used needs to be adjusted according to the amount of urea and oxidant used.

[0028] In general, the amounts of urea, oxidant, and water in the rewetting fluid jointly influence the dispersion of collagen fibers in the tanned leather trimmings and the structure of the resulting ultrafine collagen fibers. When the amounts of the three are within the aforementioned ranges, the yield of ultrafine collagen fibers is over 95%, the average fiber diameter is less than 1200 nm, and when used to prepare spunlace regenerated leather, the fiber web coverage rate exceeds 92%. Furthermore, when the amounts of the three are within the preferred ranges, the yield of ultrafine collagen fibers is over 96%, the average fiber diameter is less than 450 nm, and when used to prepare spunlace regenerated leather, the fiber web coverage rate exceeds 95%.

[0029] In an embodiment of the present invention, the tanned leather trimming material needs to be dried to a moisture content of ≤15%, and then the fibers are dissociated into small particles. The moisture content of the small particles will be further reduced during the fiber dissociation process, even below 5%. Drying, fiber dissociation, and fine fiber dissociation are all conventional treatment methods for leather and its waste. Drying can be carried out by common dynamic or static drying methods, such as blast drying and fluidized bed drying, and the tanned leather trimming material is dried to a moisture content of ≤15%. Fiber dissociation can be carried out by one of the common fiber dissociation methods such as defibration, fiber opening, and crushing to obtain small particles smaller than 2 cm*2 cm and larger than 0.5 cm*0.5 cm. Fine fiber dissociation can be carried out by one of the common fiber dissociation methods such as opening, licking-in, and combing, and the parameters are set according to conventional textile processes to obtain the required extremely fine collagen fibers.

[0030] The second embodiment provided by the present invention is: The ultra-fine collagen fibers were prepared according to the above preparation method.

[0031] The ultrafine collagen fibers according to the embodiment of the present invention have an average fiber diameter of less than 1200 nm and have good strength and thermal stability.

[0032] The third embodiment provided by the present invention is: Application of ultra-fine collagen fibers in composite materials.

[0033] The ultrafine collagen fibers of the embodiment of the present invention can be used in the preparation, modification and other processes of composite materials, and can improve the strength, stiffness and other properties of the composite materials.

[0034] The fourth embodiment provided by the present invention is: Application of ultra-fine collagen fibers in spunlace regenerated leather.

[0035] The strength of the ultrafine collagen fibers in the embodiment of the present invention is maintained, and when used in spunlace regenerated leather, it can ensure that the spunlace regenerated leather has a better web-surface rate.

[0036] To further illustrate the technical solution of the present invention, examples for implementing the present invention and corresponding comparative examples will be disclosed below to demonstrate the relevant technical effects of the present invention.

[0037] Example 1 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 12% and crushed into small particles of 2 cm*2 cm; Take 10% urea and 10% sodium percarbonate by mass of the small particles, prepare urea-sodium percarbonate rewetting liquid with water, soak the small particles to a water content of 15%, and then comb to obtain extremely fine collagen fibers.

[0038] Example 2 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 15% and then defibrated into small particles of 0.5 cm*2 cm; Take 5% urea and 5% sodium percarbonate by mass of the small particles, prepare urea-sodium percarbonate rewetting solution with water, soak the small particles to a water content of 10%, and then loosen them to obtain extremely fine collagen fibers.

[0039] Example 3 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 10% and then opened into small particles of 1 cm*2 cm; Take 3% urea and 20% sodium percarbonate by weight of the small particles, prepare urea-sodium percarbonate rewetting solution with water, soak the small particles to a water content of 40%, and then use a licker-in roller to obtain extremely fine collagen fibers.

[0040] Example 4 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 3% and crushed into small particles of 1 cm*1 cm; Take 20% urea and 5% sodium percarbonate by weight of the small particles, prepare urea-sodium percarbonate rewetting solution with water, soak the small particles to a water content of 5%, and then comb to obtain extremely fine collagen fibers.

[0041] Example 5 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 10% and crushed into small particles of 1 cm*1 cm; Take 10% urea and 20% sodium percarbonate by mass of the small particles, prepare urea-sodium percarbonate rewetting solution with water, soak the small particles to a water content of 120%, and then loosen them to obtain extremely fine collagen fibers.

[0042] Example 6 Preparation of ultra-fine collagen fibers The tanned leather trimmings were dried to a moisture content of 15% and crushed into small particles of 0.5 cm*0.5 cm; Take 15% urea and 1% sodium percarbonate by weight of the small particles, prepare urea-sodium percarbonate rewetting solution with water, soak the small particles to a water content of 15%, and then comb to obtain extremely fine collagen fibers.

[0043] Example 7 Preparation of ultra-fine collagen fibers The preparation method is the same as that of Example 1, except that sodium percarbonate is replaced by an equal amount of sodium hypochlorite.

[0044] Blank example The tanned leather trimmings are dried to a moisture content of 15% and broken into fine fibers.

[0045] Comparative Example 1 The preparation method is the same as that of Example 1, except that urea is not used.

[0046] Comparative Example 2 The preparation method is the same as that of Example 1, except that sodium percarbonate is not used.

[0047] Comparative Example 3 The preparation method is the same as that of Example 1, except that the amount of urea used is 40% of the mass of the small particles.

[0048] Comparative Example 4 The preparation method is the same as that of Example 1, except that the amount of sodium percarbonate used is 40% of the mass of the small particles.

[0049] Comparative Example 5 The preparation method is the same as that of Example 1, except that sodium percarbonate is replaced by an equal amount of potassium permanganate.

[0050] Figure 1 and Figure 2 The following are stereomicroscope images of collagen fibers obtained in Example 4 and the blank example respectively. Figure 1 and Figure 2 It can be seen that the blank example obtained thick fiber bundles, while Example 4 obtained extremely fine collagen fibers prepared according to the preparation method of the present invention.

[0051] The yield, average diameter and thermal stability of the collagen fibers obtained in the above examples, blank examples and comparative examples, as well as the web-surfacing rate of the spunlace regenerated leather, were measured as follows: Yield: Measure the mass of the final collagen fibers and the solid mass of the initial tanned leather trimmings and calculate the ratio; Average diameter: Scanning electron microscopy was used to measure the diameters of 500 collagen fibers using Nano Measurer (version 1.2) and the average value was calculated. Thermal stability: A thermogravimetric analyzer (TG209F1, Leitz, Germany) was used to measure the starting temperature of the first stage of thermal weight loss, excluding water evaporation, at a heating rate of 10°C / min under a nitrogen atmosphere. Web surfing rate: Collagen fibers with a mass of m1 and a moisture content of ω1 are evenly spread on a polyester base fabric with a significantly larger area, a mass of m2, and a moisture content of ω2. After the hydroentanglement operation, the material is mixed with 25°C clean water at a material-to-liquid ratio of 1:10 and placed in the drum of conventional leather manufacturing equipment. After rotating and washing for 30 minutes, the material is taken out, dried, and weighed. The mass is m3. The web surfing rate is then calculated according to the following formula: .

[0052] When collagen fibers are used to make hydroentangled regenerated leather, their diameter and strength both affect their web-penetration efficiency. Too thick a diameter makes it difficult to penetrate the fabric; too weak a strength causes the fibers to be broken down by the water during spunlace, becoming smaller and shorter fibers. Even if they do penetrate the fabric, they are easily washed out during subsequent rinsing.

[0053] The results of collagen fiber index determination in different treatment groups are shown in Table 1.

[0054] Table 1 Collagen fiber index determination results of different treatment groups .

[0055] The results of the indices measured in Table 1 indicate that each example, using the process of the present invention, achieved efficient collagen fiber dissociation, producing extremely fine collagen fibers with ideal mechanical properties. These fibers, when used to prepare spunlace regenerated leather, were able to withstand the impact of high-pressure water jets under spunlace conditions. When unsuitable conditions were used to treat tanned leather trimmings (Comparative Examples 1-3), the resulting collagen fibers also exhibited good mechanical properties, but the fiber bundles were coarse, resulting in a reduced web-surface rate when used to prepare spunlace regenerated leather, making subsequent operations ineffective. However, when the oxidation was too intense (Comparative Examples 4 and 5), the fiber structure of the tanned leather trimmings was completely destroyed, resulting in a low collagen fiber yield and poor mechanical properties. These collagen fibers were unable to withstand the impact of high-pressure water jets under spunlace conditions, resulting in a web-surface rate of less than 50% when used to prepare spunlace regenerated leather, similarly hindering subsequent operations.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing ultrafine collagen fibers, characterized in that: The following steps are involved: After the tanned leather trimmings are dried and the fibers are dissociated into small particles, they are soaked with a rewetting solution prepared with urea and an oxidant to a moisture content of 5-120%, and then the fibers are finely dissociated; Wherein, the oxidant is selected from one or more of sodium percarbonate, ozone, sodium hypochlorite or hydrogen peroxide.

2. The preparation method according to claim 1, wherein The amount of urea used is 1-20% of the mass of the small particles.

3. The preparation method according to claim 1, wherein The amount of urea used is 5-10% of the mass of the small particles.

4. The preparation method according to claim 1, wherein The amount of the oxidant used is 1-20% of the mass of the small particles.

5. The preparation method according to claim 1, wherein The amount of the oxidant used is 5-10% of the mass of the small particles.

6. The preparation method according to claim 1, wherein Small particles are soaked to a water content of 10-40%.

7. The preparation method according to claim 1, wherein The tanned leather trimmings are dried to a moisture content ≤ 15%.

8. The ultrafine collagen fibers prepared by the method for preparing ultrafine collagen fibers according to any one of claims 1 to 7.

9. Use of the ultrafine collagen fibers as claimed in claim 8 in composite materials.

10. Use of the ultrafine collagen fiber according to claim 8 in spunlace regenerated leather.

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