A method for preparing a silk composite nanofiber and a pu synthetic leather comprising the same

Abstract

The application discloses a preparation method of silk composite nanometer artificial fiber and PU synthetic leather containing the fiber, relates to the field of fiber modification, and comprises the following steps: S1, silk fibroin is sequentially subjected to degumming, enzymolysis and functionalization treatment to obtain a modified silk protein solution; S2, the modified silk protein solution is mixed with nanometer materials, a solvent is added for dispersion, ultrasonic-microwave synergistic treatment is carried out, silk sericin is added, stirring and dispersion are carried out, and a composite spinning solution is formed; S3, the composite spinning solution is spun through an electrostatic spinning process to obtain a composite fiber, the composite fiber is placed in glutaraldehyde vapor for crosslinking, and the silk composite nanometer artificial fiber is obtained. Through precise matching of a multi-level structure and material function, modification treatment of silk fibroin and introduction of nanometer materials, the natural characteristics of silk fibroin are retained, the mechanical properties, functional diversity and interlayer bonding strength of the fiber are comprehensively improved, and the performance of the fiber and the PU synthetic leather is synergistically optimized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fiber modification, in particular to high-performance fibers, and specifically to a silk composite nanometer artificial fiber preparation method and PU synthetic leather containing the same. BACKGROUND

[0002] In recent years, polyurethane (PU) synthetic leather has been widely used in shoe materials, luggage, automotive interiors and other fields due to its strong plasticity and low cost. Traditional PU synthetic leather has the defect of generally low air permeability and moisture permeability due to its dense structure. The dense structure hinders the effective diffusion of water vapor, which can easily cause a stuffy feeling and hygiene problems during long-term use. At the same time, the extensive use of petroleum-based raw materials makes it difficult for traditional synthetic leather to meet the increasingly stringent environmental requirements, and its lack of biocompatibility also limits its expansion in the medical, wearable devices and other fields. Although natural leather has excellent moisture permeability and biocompatibility, its production relies on animal resources, which has problems such as unstable supply chain, ethical controversy and processing pollution.

[0003] In the prior art, the air permeability can be partially improved by introducing a nanofiber membrane as a functional layer, but the mechanical properties of conventional nanofibers (such as polyacrylonitrile and polyvinyl alcohol) are weak, which makes it difficult to meet the application requirements in high-load scenarios, and the interfacial bonding strength with the PU matrix is insufficient, which can easily cause interlayer peeling. In addition, the increasing scarcity of natural leather resources has prompted the industry to explore sustainable alternative materials, and silk protein has attracted attention due to its excellent biocompatibility and rich amino acid composition. However, the beta-sheet crystal of natural silk fibroin gives it a certain rigidity, but its low elongation at break and single function limit its direct application in the synthetic leather field.

[0004] Therefore, it is necessary to improve the prior art to solve the above problems. SUMMARY

[0005] The present application overcomes the shortcomings of the prior art and provides a silk composite nanometer artificial fiber preparation method and PU synthetic leather containing the same.

[0006] To achieve the above purpose, the technical solution adopted by the present application is as follows: a silk composite nanometer artificial fiber preparation method, comprising the following steps:

[0007] S1, silk fibroin is sequentially subjected to degreasing, enzymatic hydrolysis and functionalization treatment to obtain a modified silk protein solution;

[0008] S2, the modified silk protein solution is mixed with nanometer materials at a mass ratio of 100:5-20, a solvent is added for dispersion, and ultrasonic-microwave synergistic treatment is performed for 30-60 min, silk glue protein is added, and magnetic stirring is performed for 20-40 min for dispersion to form a composite spinning solution;

[0009] S3, spinning the composite spinning solution by an electrospinning process to obtain composite fibers with a diameter of 200-500 nm, and placing the composite fibers in 5-8 wt% glutaraldehyde vapor for crosslinking for 4-8 h to obtain silk composite nanometer artificial fibers.

[0010] In a preferred embodiment of the present application, in the step of S1:

[0011] The degumming treatment specifically comprises: placing the silk fibroin in an alkaline solution with a pH value of 9.5-10.5, treating at a temperature of 95-100 ℃ for 30-60 min to obtain degummed silk fibroin.

[0012] The enzymatic treatment specifically comprises: dissolving the degummed silk fibroin in an acetic acid buffer solution, adding a protease solution, and reacting at 40-45 ℃ for 1-3 h to obtain a silk fibroin peptide segment.

[0013] The functionalization treatment specifically comprises: adding 5-10 wt% of a double-bond-containing monomer solution to the enzymatic product, and reacting at 60-70 ℃ under nitrogen protection for 4-6 h to obtain a modified silk fibroin solution.

[0014] In a preferred embodiment of the present application, the alkaline solution is a mixed solution of Na2CO3 / NaHCO3 with an equal volume, and the concentration is 0.05-0.5 mol / L; the mass ratio of the silk fibroin to the alkaline solution is 1:3-5.

[0015] In a preferred embodiment of the present application, the protease is one of trypsin, papain or neutral protease, and the concentration is 0.5-1.5 wt%; the mass ratio of the degummed silk fibroin, the acetic acid buffer solution and the protease solution is 1:4-7:1-3.

[0016] In a preferred embodiment of the present application, the double-bond-containing monomer is one of glycidyl methacrylate, acrylic acid or methyl methacrylate; and the addition amount of the monomer solution is 10-50 % of the enzymatic product.

[0017] In a preferred embodiment of the present application, in the step of S2, the nanomaterials comprise ZnO-TiO2 heterojunction nanoparticles and cellulose nanocrystals with a mass ratio of 1:0.4-0.8; the molar ratio of Zn to Ti in the ZnO-TiO2 heterojunction nanoparticles is 1:1-3, the particle size is 30-50 nm, and the specific surface area is 50-90 m² / g; the diameter of the cellulose nanocrystals is 10-30 nm, the aspect ratio is 30-50, and the crystallinity is ≥70 %.

[0018] In a preferred embodiment of the present application, in the step of S2, the mass ratio of the modified silk fibroin solution to the solvent is 1:1-4, and the solvent is 8-12 wt% calcium chloride solution; the ultrasonic-microwave synergistic treatment parameters are: ultrasonic frequency 20-60 kHz, power density 0.5-2.0 W / mL, and microwave power 600-1000 W.

[0019] In a preferred embodiment of the present application, in the step of S2, the mass ratio of the modified silk fibroin solution to the sericin is 1:0.2-0.5.

[0020] In a preferred embodiment of the present application, in the step of S3, the electrospinning parameters are: voltage 25-35 kV, receiving distance 15-25 cm, and rotating speed of receiving device 2000-4000 rpm.

[0021] The present application provides a PU synthetic leather comprising the silk composite nanofiber prepared by any one of the above methods, wherein the PU synthetic leather comprises:

[0022] The functional surface layer is a porous membrane formed by hot pressing the silk composite nanofiber, with a thickness of 50-100 μm, a pore size of 0.5-2 μm, and a porosity of 70-85 %.

[0023] The base layer is a PU foam body with a density of 0.3-0.5 g / cm³ and a foaming pore size of 100-300 μm.

[0024] The hot pressing forming conditions are: temperature 140-160 ℃, pressure 5-8 MPa, and time 30-60 s.

[0025] The present application solves the defects in the background art and has the following beneficial effects:

[0026] (1) The present application provides a preparation method of a silk composite nanofiber and a PU synthetic leather comprising the same, which realizes precise matching of multi-level structure and material function, utilizes modification treatment of silk fibroin to provide a mechanical skeleton for subsequent compounding by retaining the beta-sheet crystal structure, and significantly improves the tensile strength and toughness of the fiber by introducing nanomaterials through rigid reinforcement and interface effect, thereby forming a gradient permeation network in PU synthetic leather compounding by the porous structure of the fiber membrane and the through channels of the PU foaming layer, water molecules can quickly escape along the continuous channels constructed by the hydrophilic groups of the silk fibroin, and the photocatalytic antibacterial activity of the nanoparticles endows the material with persistent protection capability, and the chemical bonding between the polar groups on the fiber surface and the substrate can significantly enhance the interlayer bonding strength, thereby realizing comprehensive improvement of the mechanical properties, functional diversity, and interlayer bonding strength of the fiber while retaining the natural properties of silk fibroin, and achieving synergistic optimization of the performance of the fiber and the PU synthetic leather.

[0027] (2) In the application, by modifying the silk fibroin, the selective hydrolysis in alkaline environment can strip the disordered structure of sericin, so that the beta-fold crystal domain of silk fibroin is fully exposed, the regular hydrophobic region formed by the glycine-alanine repeat sequence forms an anchor base for subsequent nanocomposite, and the specific cleavage of protease on arginine / lysine residues converts long-chain silk fibroin into a peptide segment with an active end, and then the newly generated amino and carboxyl groups at the breakage can significantly improve the reactivity of the molecular chain, so that the epoxy group containing double bond monomer can be covalently bonded with the primary amine group of the silk peptide chain, and a cross-linked network is constructed between the molecular chains, so that the modified silk fibroin has the mechanical stability of the natural structure and the functional adjustability of the synthetic polymer, which lays a good foundation for high-performance fibers.

[0028] (3) In the application, through the synergy of the nanocomposite system, the zinc ions on the surface of ZnO can be combined with the carboxyl groups of silk fibroin through coordination bonds, and the hydroxyl groups of TiO2 form a hydrogen bond network with the carboxyl groups of CNC. The coupling of the two interfaces makes the nanoparticles uniformly dispersed in the fiber matrix, and the rigidity of the ZnO-TiO2 heterojunction converts the external stress into a local electric field through the piezoelectric effect of ultrasound, inducing the CNC to align along the fiber axis, forming a "reinforced frame" reinforcing structure, and the recombination of sericin can not only form hydrogen bonds and electrostatic interactions with the polar groups on the surfaces of silk protein, ZnO-TiO2 and CNC, but also fill the micro gaps in the "reinforced frame", and then form a "reinforced-concrete" composite structure, thereby further improving the mechanical properties and functionality of the material.

[0029] (4) In the application, through the ultrasound-microwave synergy when silk protein is combined with nanomaterials, the micro-jet and shock wave generated by the ultrasonic cavitation effect can strip the agglomerates of nanoparticles, and the dielectric heating of microwaves promotes the conformational relaxation of silk peptide chains, exposing more binding sites. The synergistic effect of the two energy fields breaks the van der Waals force agglomeration of nanoparticles, so that the active surface of the ZnO-TiO2 heterojunction forms directional bonding with the silk peptide chain, and the long axis direction of the cellulose nanocrystal tends to be consistent with the stretching direction of the electric field, finally forming an anisotropic reinforcing network structure, thereby ensuring efficient expression of functional properties.

[0030] (5) In the present application, by glutaraldehyde vapor crosslinking post-treatment of the fiber, Schiff base reaction occurs between the dialdehyde group in the glutaraldehyde molecule and the lysine residue epsilon-amino group of the silk fibroin peptide chain, dynamic covalent crosslinking is constructed between adjacent molecular chains, vapor phase reaction avoids fiber swelling caused by liquid phase crosslinking, diffusion and penetration of aldehyde groups make the crosslinking points uniformly distributed in the fiber, the three-dimensional crosslinking network not only fixes the ordered arrangement of the beta-sheet crystal region to maintain the fiber rigidity, but also endows the material with deformation recovery ability through the reversible rupture-recombination of dynamic bonds, and then the residual aldehyde groups on the surface of the crosslinked fiber can further react with the isocyanate groups of the PU prepolymer to form chemical bridges at the fiber / PU interface, thereby better strengthening the interlayer bonding force. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0032] Figure 1 is a flow chart of a silk composite nanometer artificial fiber preparation method of a preferred embodiment of the present application;

[0033] Figure 2 is a PU synthetic leather three-dimensional structure schematic diagram of a preferred embodiment of the present application;

[0034] In the figure: 1, functional surface layer; 2, base layer. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0036] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, therefore, the scope of protection of the present application is not limited by the specific embodiments disclosed below.

[0037] SUMMARY OF THE APPLICATION

[0038] Despite the significant progress made in nanofiber technology in recent years, there are still many limitations. Currently, the strength of many nanofibers is relatively low, often less than 1.5 cN / dtex, limiting their use in scenarios that require high strength applications.

[0039] Among them, silk protein as a kind of natural polymer material, because of its unique beta sheet structure (content > 30 %), rich amino acid composition (a total of 18 kinds) and natural antibacterial properties (bacteriostatic rate > 90 %) and attention. However, the tensile strength and toughness of silk protein are relatively poor, which limits its application in high-strength and high-toughness materials.

[0040] In order to overcome the shortcomings of traditional PU synthetic leather and nanofiber technology, a lot of exploration has been made in the prior art. In the aspect of fiber modification, improving the performance of fibers through chemical modification, physical compounding and other means has become an important way. However, the applicant found that the existing modification method is often difficult to simultaneously realize the significant improvement of fiber strength, toughness, functionality and interfacial bonding force, thereby difficult to meet its direct application in the field of synthetic leather.

[0041] The present application aims at the above technical bottleneck, and proposes a new type of silk composite nanofiber preparation method and its application in PU synthetic leather, which realizes the synergistic regulation of multi-level structure and interface, and comprehensively improves the mechanical properties, functional diversity and interfacial bonding strength of the fiber while retaining the natural properties of silk protein.

[0042] It should be noted that: the raw materials, equipment and reagents used in the present application can be purchased from the market or prepared by the preparation method of the prior art, and the preparation of raw materials is as follows:

[0043] Silk fibroin: CAS No. 96690-41-4, purchased from Hubei Shengeng Chemical; glycidyl methacrylate: CAS No. 106-91-2, molecular weight 142.15, purity ≥ 99%, purchased from Jinan Shengda Chemical; acrylic acid: CAS No. 79-10-7, molecular weight 72.063, density 1.051 g / cm3, purchased from Shandong Kejian Chemical; methyl methacrylate: CAS No. 80-62-6, density 0.944 kg / cm3, purity ≥ 99%, purchased from Shandong Kejian Chemical; ZnO-TiO2 heterojunction nanoparticles: CAS No. 1314-13-2 (ZnO) / 13463-67-7 (TiO2), molar ratio Zn:Ti = 1:2, particle size 40 ± 5 nm, specific surface area 85 ± 5 m2 / g, purchased from Aldrich Reagent; cellulose nanocrystals: diameter 20 ± 5 nm, crystallinity ≥ 75%, purchased from CelluForce Company, USA; sericin: CAS No. 60650-88-6, purchased from Hubei Xinyu Hong Biological Medicine; trypsin: CAS No. 9002-07-7, activity ≥ 2500 U / mg, purchased from Shanghai Yuanye Bioengineering; papain: CAS No. 9001-73-4, molecular weight 226.23246, purity ≥ 99%, purchased from Guangdong Mingtong Biological; neutral protease: CAS No. 9068-59-1, purity ≥ 99%, purchased from Jiangsu Yuanyuan Biological.

[0044] As shown in Figure 1 A method for preparing silk composite nanofiber, comprising the following steps:

[0045] S1, silk fibroin is sequentially subjected to degumming, enzymatic hydrolysis and functionalization treatment to obtain a modified silk protein solution;

[0046] S2, the modified silk protein solution is mixed with nanomaterials at a mass ratio of 100:5-20, a solvent is added for dispersion, and ultrasonic-microwave synergistic treatment is performed for 30-60 min, sericin is added, and magnetic stirring is performed for 20-40 min for dispersion to form a composite spinning solution;

[0047] S3, the composite spinning solution is spun by an electrospinning process to obtain a composite fiber with a diameter of 200-500 nm, and the composite fiber is placed in 5-8 wt% glutaraldehyde vapor for crosslinking for 4-8 h to obtain a silk composite nanofiber.

[0048] In some specific embodiments, in the step of S1:

[0049] The degumming treatment specifically comprises: placing the silk fibroin in an alkaline solution with a pH value of 9.5-10.5, and treating at a temperature of 95-100 ℃ for 30-60 min to obtain degummed silk protein;

[0050] The enzymatic treatment specifically includes: dissolving the degummed silk protein in an acetic acid buffer solution, adding a protease solution, and reacting at 40-45 °C for 1-3 h to obtain a silk protein peptide segment;

[0051] The functional treatment specifically includes: adding 5-10 wt% of a double-bond-containing monomer solution to the enzymatic product, and reacting at 60-70 °C for 4-6 h under nitrogen protection to obtain a modified silk protein solution.

[0052] In some specific embodiments, the alkaline solution is a mixed solution of Na2CO3 / NaHCO3 with a concentration of 0.05-0.5 mol / L, and the mass ratio of the silk fibroin to the alkaline solution is 1:3-5.

[0053] In some specific embodiments, the protease is one of trypsin, papain, or neutral protease, and the concentration is 0.5-1.5 wt%, and the mass ratio of the degummed silk protein, the acetic acid buffer solution, and the protease solution is 1:4-7:1-3.

[0054] In some specific embodiments, the double-bond-containing monomer is one of glycidyl methacrylate (GMA), acrylic acid (AA), or methyl methacrylate (MMA), and the amount of the monomer solution added is 10-50% of the enzymatic product.

[0055] In some specific embodiments, in the step of S2, the nanomaterials include ZnO-TiO2 heterojunction nanoparticles and cellulose nanocrystals (CNC) with a mass ratio of 1:0.4-0.8; the molar ratio of Zn to Ti in the ZnO-TiO2 heterojunction nanoparticles is 1:1-3, the particle size is 30-50 nm, and the specific surface area is 50-90 m² / g; the cellulose nanocrystals have a diameter of 10-30 nm, an aspect ratio of 30-50, and a crystallinity of ≥70%.

[0056] In some specific embodiments, in the step of S2, the mass ratio of the modified silk protein solution to the solvent is 1:1-4, and the solvent is a 8-12 wt% calcium chloride (CaCl2) solution; the ultrasonic-microwave synergistic treatment parameters are: ultrasonic frequency 20-60 kHz, power density 0.5-2.0 W / mL, and microwave power 600-1000 W.

[0057] In some specific embodiments, in the step of S2, the mass ratio of the modified silk protein solution to the sericin is 1:0.2-0.5.

[0058] In some specific embodiments, in the step of S3, the electrospinning parameters are: voltage 25-35 kV, receiving distance 15-25 cm, and rotating speed of the receiving device 2000-4000 rpm.

[0059] AsFigure 2 As shown, the present application provides a PU synthetic leather comprising the silk composite nanofiber prepared by any one of the above methods, wherein the PU synthetic leather comprises:

[0060] Functional surface layer 1: porous membrane formed by hot pressing of the silk composite nanofiber, thickness 50-100 μm, pore size 0.5-2 μm, porosity 70-85 %;

[0061] Matrix layer 2: PU foam, density 0.3-0.5 g / cm³, foaming pore size 100-300 μm;

[0062] Hot pressing molding conditions: temperature 140-160 ℃, pressure 5-8 MPa, time 30-60 s.

[0063] To further make the purpose and effect of the present application simple and easy to understand, the present application is further described in combination with examples and comparative examples.

[0064] Example 1

[0065] A method for preparing a silk composite nanofiber, comprising the following steps:

[0066] S1, silk fibroin modification treatment:

[0067] a. The silk fibroin is placed in a Na2CO3 / NaHCO3 mixed solution with a pH value of 10.0 (Na2CO3 / NaHCO3 is mixed in equal volume with a concentration of 0.3 mol / L), treated at a temperature of 98 ℃ for 45 min to obtain degummed silk fibroin, wherein the mass ratio of silk fibroin to Na2CO3 / NaHCO3 mixed solution is 1:4;

[0068] b. The degummed silk fibroin is dissolved in an acetic acid buffer solution, and a trypsin solution with a concentration of 1 wt% is added, and reacted at 45 ℃ for 2 h to obtain a silk protein peptide segment, wherein the mass ratio of degummed silk fibroin, acetic acid buffer solution and trypsin solution is 1:5:2;

[0069] c. A GMA solution with a concentration of 8 wt% is added to the enzymatic product, and reacted at 65 ℃ for 5 h under nitrogen protection to obtain a modified silk protein solution, wherein the addition amount of GMA solution is 30 % of the enzymatic product;

[0070] S2, the modified silk fibroin solution and the nanomaterial (ZnO-TiO2: CNC = 1:0.6) were mixed in a mass ratio of 100:12, a CaCl2 solvent with a concentration of 10 wt% was added, and ultrasonic-microwave synergistic treatment was performed at an ultrasonic frequency of 40 kHz, a power density of 1.2 W / mL, and a microwave power of 800 W for 40 min, silk glue protein was added, and magnetic stirring was performed at a rotating speed of 800 rpm for 30 min to form a composite spinning solution, wherein the mass ratio of the modified silk fibroin solution to the CaCl2 solvent was 1:2, the mass ratio of the modified silk fibroin solution to the silk glue protein was 1:0.3, and the aspect ratio of the CNC was 38;

[0071] S3, the composite spinning solution was spun by an electrospinning process, the electrospinning parameters were as follows: a voltage of 305 kV, a receiving distance of 20 cm, and a receiving device rotating speed of 3000 rpm, a composite fiber with a diameter of 350 nm was prepared, and was placed in 6 wt% glutaraldehyde vapor for crosslinking for 6 h to obtain a silk composite nanometer artificial fiber.

[0072] Example 2

[0073] This example is basically the same as Example 1, except that the amount of the nanomaterial is different, specifically, in the step S2, the mass ratio of the modified silk fibroin solution to the nanomaterial (ZnO-TiO2: CNC = 1:0.6) is 100:5.

[0074] Example 3

[0075] This example is basically the same as Example 1, except that the amount of the nanomaterial is different, specifically, in the step S2, the mass ratio of the modified silk fibroin solution to the nanomaterial (ZnO-TiO2: CNC = 1:0.6) is 100:20.

[0076] Example 4

[0077] This example is basically the same as Example 1, except that the aspect ratio of the CNC is different, specifically, in the step S2, the aspect ratio of the CNC is 30.

[0078] Example 5

[0079] This example is basically the same as Example 1, except that the aspect ratio of the CNC is different, specifically, in the step S2, the aspect ratio of the CNC is 50.

[0080] Example 6

[0081] This example is basically the same as Example 1, except that the ultrasonic-microwave synergistic treatment time is different, specifically, in the step S2, the ultrasonic-microwave synergistic treatment time is 30 min.

[0082] Example 7

[0083] This example is basically the same as Example 1, except that the time of ultrasonic-microwave synergistic treatment is different, specifically, in the step of S2, the time of ultrasonic-microwave synergistic treatment is 60 min.

[0084] Example 8

[0085] This example is basically the same as Example 1, except that the amount of sericin is different, specifically, in the step of S2, the mass ratio of modified silk protein solution to sericin is 1:0.2.

[0086] Example 9

[0087] This example is basically the same as Example 1, except that the amount of sericin is different, specifically, in the step of S2, the mass ratio of modified silk protein solution to sericin is 1:0.5.

[0088] Comparative Example 1

[0089] Commercially available: PLGA (poly-lactic-co-glycolic acid) silk fibroin nanofiber, fiber diameter 350 nm, purity >95%, brand: JDFS-10011, purchased from Xi'an Hao Ran Biology.

[0090] Comparative Example 2

[0091] This comparative example is basically the same as Example 1, except that the functional treatment is not performed in the modification treatment of silk fibroin, and the step of S1 is specifically:

[0092] a. The silk fibroin is placed in a Na2CO3 / NaHCO3 mixed solution with a pH value of 10.0 (Na2CO3 / NaHCO3 is mixed in equal volume, and the concentration is 0.3 mol / L), and treated at a temperature of 98℃ for 45 min to obtain degummed silk fibroin, wherein the mass ratio of silk fibroin to Na2CO3 / NaHCO3 mixed solution is 1:4;

[0093] b. The degummed silk fibroin is dissolved in an acetic acid buffer solution, and a trypsin solution with a concentration of 1 wt% is added, and reacted at 45℃ for 2 h to obtain a modified silk protein solution, wherein the mass ratio of degummed silk fibroin, acetic acid buffer solution and trypsin solution is 1:5:2.

[0094] Comparative Example 3

[0095] The comparative example is basically the same as the embodiment 1, and the difference is that the amount of the nanomaterial is different. Specifically, in the step S2, the mass ratio of the modified silk protein solution to the nanomaterial (ZnO-TiO2: CNC = 1:0.6) is 100:3.

[0096] Comparative example 4

[0097] The comparative example is basically the same as the embodiment 1, and the difference is that the amount of the nanomaterial is different. Specifically, in the step S2, the mass ratio of the modified silk protein solution to the nanomaterial (ZnO-TiO2: CNC = 1:0.6) is 100:25.

[0098] Comparative example 5

[0099] The comparative example is basically the same as the embodiment 1, and the difference is that the CNC is not added. Specifically, in the step S2, the modified silk protein solution and the nanomaterial (ZnO-TiO2) are mixed in a mass ratio of 100:12, and a 10 wt% CaCl2 solvent is added for dispersion. The ultrasonic-microwave synergistic treatment is performed for 40 min at an ultrasonic frequency of 40 kHz, a power density of 1.2 W / mL, and a microwave power of 800 W. The sericin protein is added for magnetic stirring at a speed of 800 rpm for 30 min to form a composite spinning solution. The mass ratio of the modified silk protein solution to the CaCl2 solvent is 1:2, and the mass ratio of the modified silk protein solution to the sericin protein is 1:0.3.

[0100] Comparative example 6

[0101] The comparative example is basically the same as the embodiment 1, and the difference is that the aspect ratio of the CNC is different. Specifically, in the step S2, the aspect ratio of the CNC is 25.

[0102] Comparative example 7

[0103] The comparative example is basically the same as the embodiment 1, and the difference is that the aspect ratio of the CNC is different. Specifically, in the step S2, the aspect ratio of the CNC is 54.

[0104] Comparative example 8

[0105] The comparative example is basically the same as the embodiment 1, and the difference is that the ultrasonic-microwave synergistic treatment is not performed. Specifically, in the step S2, the modified silk protein solution and the nanomaterial (ZnO-TiO2: CNC=1:0.6) are mixed at a mass ratio of 100:12, the CaCl2 solvent with a concentration of 10 wt% is added and dispersed by magnetic stirring at a speed of 800 rpm for 40 min, the sericin is added and stirred at a speed of 800 rpm for 30 min to form a composite spinning solution, wherein the mass ratio of the modified silk protein solution to the CaCl2 solvent is 1:2, the mass ratio of the modified silk protein solution to the sericin is 1:0.3, and the aspect ratio of the CNC is 38.

[0106] Comparative example 9

[0107] The comparative example is basically the same as the embodiment 1, and the difference is that the ultrasonic-microwave synergistic treatment time is different. Specifically, in the step S2, the ultrasonic-microwave synergistic treatment time is 17 min.

[0108] Comparative example 10

[0109] The comparative example is basically the same as the embodiment 1, and the difference is that the ultrasonic-microwave synergistic treatment time is different. Specifically, in the step S2, the ultrasonic-microwave synergistic treatment time is 45 min.

[0110] Comparative example 11

[0111] The comparative example is basically the same as the embodiment 1, and the difference is that the sericin is not added. Specifically, in the step S2, the modified silk protein solution and the nanomaterial (ZnO-TiO2: CNC=1:0.6) are mixed at a mass ratio of 100:12, the CaCl2 solvent with a concentration of 10 wt% is added and dispersed, and the ultrasonic-microwave synergistic treatment is performed at an ultrasonic frequency of 40 kHz, a power density of 1.2 W / mL, and a microwave power of 800 W for 40 min to form a composite spinning solution, wherein the mass ratio of the modified silk protein solution to the CaCl2 solvent is 1:2, and the aspect ratio of the CNC is 38.

[0112] Comparative example 12

[0113] The comparative example is basically the same as the embodiment 1, and the difference is that the amount of the sericin is different. Specifically, in the step S2, the mass ratio of the modified silk protein solution to the sericin is 1:0.1.

[0114] Comparative example 13

[0115] The comparative example is basically the same as the embodiment 1, and the difference is that the amount of the sericin is different. Specifically, in the step S2, the mass ratio of the modified silk protein solution to the sericin is 1:0.6.

[0116] Comparative Example 14

[0117] This comparative example is basically the same as Example 1, except that the composite fiber is not post-treated, specifically: in the step of S3, the composite spinning solution is spun by electrospinning process, and the electrospinning parameters are: voltage 305 kV, receiving distance 20 cm, receiving device rotating speed 3000 rpm, to obtain a silk composite nanometer artificial fiber with a diameter of 350 nm.

[0118] Performance detection: the silk composite nanometer artificial fibers obtained in Examples 1-9 and Comparative Examples 2-14, and the PLGA silk fibroin nanofiber commercially available in Comparative Example 1, are respectively subjected to performance test of fiber mechanical properties.

[0119] Fiber mechanical properties: refer to GB / T 14344-2022 “Chemical fiber Filament tensile property test method”.

[0120] At the same time, the silk composite nanometer artificial fibers obtained in Examples 1-9 and Comparative Examples 2-14, and the PLGA silk fibroin nanofiber commercially available in Comparative Example 1, are formed into a porous membrane with a thickness of 80 μm, a pore size of 1.2 μm, and a porosity of 79 % on a PU foam with a density of 0.4 g / cm³ and a foaming pore size of 200 μm, at a temperature of 150 ℃, a pressure of 6 MPa, and a hot pressing time of 50 s, to prepare a PU synthetic leather with a thickness of 2.6 mm, and then sequentially perform performance tests of moisture permeability, antibacterial rate, and interfacial bonding force.

[0121] PU synthetic leather moisture permeability: refer to GB / T 12704.1-2009 “Textiles Permeability test method for textiles Part 1: hygroscopic method”.

[0122] PU synthetic leather antibacterial rate: refer to GB / T 20944.3-2008 “Evaluation of antibacterial properties of textiles Part 3: oscillation method”, and the bacteria are Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 25922).

[0123] Fiber / PU synthetic leather interfacial bonding force: refer to GB / T 2791-1995 “Adhesive peel strength test method”.

[0124] The performance test results of fiber mechanical properties and PU synthetic leather moisture permeability, PU synthetic leather antibacterial rate, and fiber / PU interfacial bonding force are shown in Table 1.

[0125] Table 1: Performance test results of fibers and PU synthetic leather of Examples 1-9 and Comparative Examples 1-14

[0126]

[0127]

[0128] From Table 1:

[0129] From the comparison of Examples 1-9, it can be seen that the present application removes sericin in silk fibroin through degumming treatment, fully exposes the beta-sheet crystal domain, and provides a mechanical skeleton for subsequent nanocomposites. Enzymatic hydrolysis converts long-chain silk fibroin into peptide segments with active ends, improving the reactivity of the molecular chain. Functionalization further constructs a cross-linked network through covalent bonding of double-bond-containing monomers with silk peptide chains, enhancing the mechanical stability and functional adjustability of the fiber. The introduction of ZnO-TiO2 heterojunction nanoparticles and cellulose nanocrystals further improves the tensile strength and toughness of the fiber through rigidity enhancement and interface effect. At the same time, the compounding of sericin not only enhances the interaction within the fiber, but also improves the interlaminar bonding strength of the fiber and the PU matrix. Thus, the tensile strength of the silk composite fiber (3.22 cN / dtex) is increased by 122% compared to traditional materials, the moisture permeability (5234 g / m²·24h) is increased by 148%, the antibacterial rate (>99%) reaches the medical grade standard, and the interfacial bonding force (36.4 N / cm) breaks through the interface bottleneck of traditional PU leather.

[0130] From the comparison of Example 1 and Comparative Example 1, it can be seen that traditional PLGA fibers lack the beta-sheet crystal skeleton of silk protein and nanocomposite system, the molecular chain is mainly in random coil, lacks rigid skeleton support, and the molecular chain is mainly synthetic polymer, resulting in insufficient antibacterial rate and loose interface bonding. In addition, the hydrophilicity of PLGA is poor, hindering the directional transmission of water molecules in PU synthetic leather, resulting in significantly lower tensile strength (1.45 cN / dtex) and moisture permeability (2100 g / m²·24h) than Example 1 (3.22 cN / dtex, 5234 g / m²·24h).

[0131] From the comparison of Example 1 and Comparative Example 2, it can be seen that without functionalization treatment, the silk protein molecular chain lacks the cross-linking of GMA epoxy groups, resulting in the inability to form a dynamic covalent network within the fiber. The amino group of silk peptide is not reacted with GMA, and the molecular chains only rely on natural hydrogen bonding, which is insufficient in mechanical stability. At the same time, it reduces the chemical bonding ability of the fiber and the PU matrix, and the interfacial bonding force (15.6 N / cm) is less than 50% of Example 1 (36.4 N / cm), and the antibacterial rate is reduced due to the lack of photocatalytic active sites.

[0132] From the comparison of Examples 1-3 and Comparative Examples 3-4, it can be seen that an appropriate amount of nanomaterials can significantly improve the performance of the fiber. Comparative Example 3 has too little nanomaterials to form a continuous reinforcing network, and the Zn²+ The coordination bond density with the carboxyl group of silk fibroin is insufficient, and the piezoelectric effect of ZnO-TiO2 and the orientation arrangement of CNC are limited, resulting in a decrease in stress transfer efficiency and a decrease in tensile strength; and the comparative example 4 has an interface bonding force (24.8 N / cm) which is decreased by 32% than that of the example 1 due to the agglomeration of excessive nanoparticles which hinders the orientation arrangement of the silk fibroin molecular chain. The example of the application realizes the uniform dispersion of the heterojunction and CNC by optimizing the ratio, forms a “reinforced concrete” composite structure, and gives consideration to mechanics and function.

[0133] It can be known from the comparison of the example 1 and the example 4-5 and the comparative examples 5-7 that: the comparative example 5 has a significant decrease in fiber tensile strength due to the lack of rigid support of cellulose nanocrystals and the dependence on the piezoelectric effect of ZnO-TiO2. The comparative example 6 has a short rod-like structure of CNC which cannot be effectively arranged along the fiber axis and cannot effectively bridge the stress transfer between the silk fibroin molecular chains due to the excessively short size of the nanocrystals. The comparative example 7 has a decrease in performance due to the excessively large aspect ratio of the nanocrystals which are easy to entangle in the spinning process and are easy to hinder the dispersion of the nanoparticles. The example of the application realizes the synergy of hydrogen bond network and stress transfer by optimizing the size of CNC.

[0134] It can be known from the comparison of the example 1 and the example 6-7 and the comparative examples 8-10 that: when the ultrasonic-microwave synergistic treatment is not performed, the nanomaterials are agglomerated due to van der Waals force, the piezoelectric and microwave effects cannot be synergized, and the interface bonding sites of ZnO-TiO2 and silk peptide chains are reduced, resulting in a decrease in tensile strength; the comparative example 9 has an insufficient treatment time and the CNC cannot be fully arranged along the fiber axis due to the ultrasonic-microwave synergistic treatment; and the comparative example 10 has a decrease in performance due to the overheating of the microwave which causes the silk fibroin to be partially denatured, the molecular chain to be broken, and the fiber to be thermally degraded or the nanoparticles to be excessively agglomerated. The example of the application realizes the directional bonding of the nanomaterials by using the ultrasonic cavitation to strip the agglomerates and the microwave intermediate heat to promote the stretching of the molecular chain through the appropriate treatment time, and the moisture permeability and the antibacterial rate are both optimal.

[0135] It can be known from the comparison of the example 1 and the example 8-9 and the comparative examples 11-13 that: the comparative example 11 (without sericin protein) has a lower bonding force (19.5 N / cm) due to the lack of polar groups of sericin which fill the gaps of the “reinforced frame” and the fiber / PU interface only relies on chemical bonding, lacking the hydrogen bond and electrostatic interaction of the polar groups. The comparative example 12 has a decrease in mechanical strength due to the insufficient amount of sericin protein which cannot completely cover the surface of the nanoparticles and cannot fully fill the gaps of the “reinforced frame”. The comparative example 13 has an excessive amount of sericin protein which covers the surface of the nanomaterials and hinders the functional expression. The example of the application realizes the construction of the “reinforced concrete” composite structure by optimizing the addition ratio and fully filling the sericin, and forms the hydrogen bond / electrostatic network of the hydroxyl and carboxyl groups to improve the interface bonding force to 36.4 N / cm.

[0136] From the comparison of Example 1 and Comparative Example 14, it can be seen that the glutaraldehyde vapor crosslinking post-treatment can significantly improve the mechanical properties and interlayer bonding force of the fiber, and is the key to constructing a stable fiber network. The uncrosslinked fiber relies only on physical entanglement between molecular chains, and chain slippage easily occurs during hot pressing, so the moisture permeation amount is only 3293 g / m²·24h, and the interfacial bonding force also decreases. The dynamic covalent network formed by the vapor crosslinking of the present application example 1 not only maintains the fiber rigidity, but also strengthens the interlayer bonding through the reaction of the residual aldehyde group with the PU isocyanate group.

[0137] The above is based on the ideal embodiments of the present application, and for those skilled in the art, the present application is not limited to the details of the above exemplary embodiments, and can be realized in other specific forms without departing from the spirit or basic characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0138] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for preparing filament composite nanofibers, characterized in that, Includes the following steps: S1. Silk fibroin is subjected to degumming, enzymatic hydrolysis, and functionalization treatment in sequence to obtain a modified silk fibroin solution; the functionalization treatment specifically involves adding 5-10 wt% of a monomer solution containing double bonds to the enzymatic hydrolysis product and reacting it at 60-70 ℃ for 4-6 h under nitrogen protection to obtain a modified silk fibroin solution; the monomer containing double bonds is glycidyl methacrylate. S2. The modified silk fibroin solution and nanomaterials are mixed at a mass ratio of 100:5-20, dispersed in solvent, and subjected to ultrasonic-microwave synergistic treatment for 30-60 min. Then, sericin is added, and the mixture is magnetically stirred for 20-40 min to disperse, forming a composite spinning solution. The nanomaterials include ZnO-TiO2 heterojunction nanoparticles and cellulose nanocrystals at a mass ratio of 1:0.4-0.

8. The ultrasonic-microwave synergistic treatment parameters are: ultrasonic frequency 20-60 kHz, power density 0.5-2.0 W / mL, and microwave power 600-1000 W. S3. The composite spinning solution is spun by electrospinning to obtain composite fibers with a diameter of 200-500 nm, and then crosslinked in 5-8 wt% glutaraldehyde vapor for 4-8 h to obtain composite nanofibers.

2. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: In step S1: The degumming process specifically involves placing silk fibroin in an alkaline solution with a pH of 9.5-10.5 and treating it at a temperature of 95-100 °C for 30-60 min to obtain degummed silk fibroin. The enzymatic hydrolysis process specifically involves dissolving degummed silk fibroin in acetate buffer, adding protease solution, and reacting at 40-45 ℃ for 1-3 h to obtain silk fibroin peptides.

3. The method for preparing a silk composite nanofiber according to claim 2, characterized in that: The alkaline solution is an equal volume of Na2CO3 / NaHCO3 mixture with a concentration of 0.05-0.5 mol / L, and the mass ratio of the silk fibroin to the alkaline solution is 1:3-5.

4. The method for preparing a silk composite nanofiber according to claim 2, characterized in that: The protease is trypsin with a concentration of 0.5-1.5 wt%, and the mass ratio of the degummed silk protein, the acetate buffer, and the protease solution is 1:4-7:1-3.

5. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: The amount of monomer solution added is 10-50% of the enzymatic hydrolysis product.

6. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: In step S2, the molar ratio of Zn to Ti in the ZnO-TiO2 heterojunction nanoparticles is 1:1-3, the particle size is 30-50 nm, and the specific surface area is 50-90 m² / g; the diameter of the cellulose nanocrystals is 10-30 nm, the aspect ratio is 30-50, and the crystallinity is ≥70%.

7. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: In step S2, the mass ratio of the modified silk protein solution to the solvent is 1:1-4, and the solvent is 8-12 wt% calcium chloride solvent.

8. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: In step S2, the mass ratio of the modified silk protein solution to the sericin is 1:0.2-0.

5.

9. The method for preparing a silk composite nanofiber according to claim 1, characterized in that: In step S3, the electrospinning parameters are: voltage 25-35 kV, receiving distance 15-25 cm, and receiving device rotation speed 2000-4000 rpm.

10. A PU synthetic leather, characterized in that: The PU synthetic leather comprises the silk composite nanofiber prepared according to any one of claims 1-9, wherein the PU synthetic leather comprises: Functional surface layer: The porous membrane formed by hot pressing of the filament composite nanofibers has a thickness of 50-100 μm, a pore size of 0.5-2 μm, and a porosity of 70-85%. Substrate layer: PU foam, density 0.3-0.5 g / cm³, foam pore size 100-300 μm; Hot pressing conditions: temperature 140-160 ℃, pressure 5-8 MPa, time 30-60 s.

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