CN113005560B - Flexible silk fibroin/polyvinyl alcohol composite fiber and preparation method thereof - Google Patents
Flexible silk fibroin/polyvinyl alcohol composite fiber and preparation method thereof Download PDFInfo
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- CN113005560B CN113005560B CN202110312949.5A CN202110312949A CN113005560B CN 113005560 B CN113005560 B CN 113005560B CN 202110312949 A CN202110312949 A CN 202110312949A CN 113005560 B CN113005560 B CN 113005560B
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Abstract
The invention relates to a flexible silk fibroin/polyvinyl alcohol composite fiber and a preparation method thereof, the method comprises the steps of firstly preparing silk fibroin aqueous solution by taking old silk floss as a raw material, then blending the silk fibroin aqueous solution with the polyvinyl alcohol aqueous solution according to a certain proportion to obtain silk fibroin/polyvinyl alcohol composite spinning aqueous solution, and then preparing the silk fibroin/polyvinyl alcohol composite fiber by adopting a dry-jet wet spinning process; in the coagulating bath of the dry-jet wet spinning process, the content of a beta-folding structure of the silk fibroin is improved from 37-39% to 40-42%; the molecular chain orientation degree of the prepared flexible silk fibroin/polyvinyl alcohol composite fiber measured by Raman spectroscopy is 0.69-1.26. The flexible silk fibroin/polyvinyl alcohol composite fiber has elongation at break of 329-528%, breaking strength of 0.17-0.27 cN/dtex, and diameter of 70-108 μm. The method has the advantages of simple process, environmental protection, and large elongation and good flexibility of the prepared composite fiber.
Description
Technical Field
The invention belongs to the technical field of composite materials, and relates to a flexible silk fibroin/polyvinyl alcohol composite fiber and a preparation method thereof.
Background
The silk floss produced in China every year is as many as ten million, however, after the silk floss is used for a certain time, the elasticity of the silk floss is reduced, the phenomena of aging, yellowing and the like exist, the use value is lost and is directly abandoned, a large amount of old silk floss not only causes the non-negligible environmental pressure but also causes the great waste of silk floss resources, the silk is used as natural protein fiber and consists of fibroin and sericin, and the silk fibroin has no toxicity, no stimulation effect and no allergy, has excellent biocompatibility and biodegradability, and has wide application in the fields of textile clothing and biomedicine. At present, no research related to regenerated silk fibroin materials using old silk floss as raw materials is found, and the invention of a material preparation technology capable of developing and utilizing the old silk floss with high value is necessary.
In the existing research of preparing regenerated silk fibroin composite materials by taking common silk as a raw material, water-soluble polymer polyvinyl alcohol is usually used for preparing silk fibroin/polyvinyl alcohol composite fiber (membrane) materials because of no toxicity, no odor, good biocompatibility and chemical stability and better fiber forming property.
The patent CN1818163A and the article "preparation of silk fibroin-polyvinyl alcohol blended modified electrospun membrane" both use silk fibroin/polyvinyl alcohol blended solution as raw material to prepare silk fibroin/polyvinyl alcohol nanofiber membrane by means of electrostatic spinning. However, the nanofiber composite membrane has poor mechanical properties, and the application range is limited.
In the study on fibroin nano-silver/PVA blended fiber prepared by microfluid spinning, a microfluid spinning technology is adopted, formic acid is used as a solvent, a fibroin solution, nano-silver and polyvinyl alcohol are blended to be used as a spinning solution, a glass slide which moves in a balanced and reciprocating manner is used as a receiving device, and the fibroin nano-silver/polyvinyl alcohol composite fiber with an antibacterial function and a uniform diameter is prepared.
CN1062934A mixes polyvinyl alcohol aqueous solution and fibroin nitrate salt solution, adds non-ionic surfactant, adopts wet spinning method, uses ammonium sulfate or sodium sulfate as coagulating bath, prepares silk protein/polyvinyl alcohol composite fiber with skin-core structure. However, the maximum temperature required for dissolving silk fibroin in the method reaches 110 ℃, thermal degradation of silk fibroin is easily caused, silk fibroin is obviously degraded due to the fact that silk peptide bonds are broken by an acid solvent, mechanical properties of the subsequently prepared composite fiber are not affected, the coagulation bath has certain requirements on temperature, and energy consumption and process complexity in the spinning process are increased.
Therefore, the research on the silk fibroin composite filament with good mechanical property and simple preparation method has very important significance.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a flexible silk fibroin/polyvinyl alcohol composite fiber and a preparation method thereof; aims to fully utilize the old silk floss and solve the problems of small extension, easy brittle fracture and the like of the regenerated silk fibroin composite fiber and develop the old silk floss fibroin composite fiber filament with high flexibility. The method specifically comprises the steps of preparing a silk fibroin aqueous solution by using old silk floss as a raw material, blending the silk fibroin aqueous solution with a polyvinyl alcohol aqueous solution, and selecting a ratio with relatively stable compatibility to prepare a silk fibroin/polyvinyl alcohol composite spinning aqueous solution by adjusting the ratio of the silk fibroin to the polyvinyl alcohol; the silk fibroin/polyvinyl alcohol composite fiber is prepared by adopting a dry-jet wet spinning technology. The ethanol is used as the coagulating bath, so that the defect of slow diffusion of the aqueous solution can be overcome due to the high coagulating speed of the ethanol, and the ethanol has low cost, is nontoxic and harmless, has no requirement on temperature and is simple in process. The prepared composite fiber has uniform diameter and elongation at break as high as 337-526%, overcomes the defects of poor elongation capability and easy brittle failure of regenerated silk fiber, and can recycle the old silk floss material with high value.
In order to achieve the purpose, the invention adopts the following scheme:
a preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the steps of firstly preparing silk fibroin aqueous solution by using old silk floss as a raw material, blending the silk fibroin aqueous solution with polyvinyl alcohol aqueous solution according to a certain proportion to obtain silk fibroin/polyvinyl alcohol composite spinning aqueous solution, and then preparing the silk fibroin/polyvinyl alcohol composite fiber by adopting a dry-jet wet spinning process;
in the coagulating bath of the dry-jet wet spinning process, the content of a beta-folding structure of the silk fibroin is improved from 37 to 39 percent to 40 to 42 percent.
The spinning solution using pure water solution as solvent is more green and environment-friendly and can reduce the damage to the performance of silk fibroin, but the aqueous solution of silk fibroin is difficult to complete the forming conversion from liquid state to solid state due to poor volatility of the aqueous solution in air or low diffusion efficiency in a coagulating bath, so that the spinning process is very difficult in terms of difficulty and easiness. And the regenerated silk fibroin fiber has the defect of brittleness at present. The prior spinning process mainly comprises wet spinning, dry-jet wet spinning, electrostatic spinning and microfluidic spinning. The latter two have relatively small yield, and the former three are common traditional spinning modes. The dry spraying wet method is a preparation process combining dry spinning and wet spinning, i.e. the spinning solution is primarily solidified and obtains a certain drafting by utilizing an air section, so as to promote the molecular chain arrangement of the solution to have a certain orientation, then the filament is completely solidified and formed by utilizing a solidification bath, and the molecular chain is further directionally arranged under the combined action of a godet roller and winding tension.
Particularly, the fiber elongation at break obtained by preparing regenerated silk fibroin fiber in the prior art is very low, mainly because silk fibroin rapidly forms a beta-folding structure in a coagulation bath, the stable microcrystalline structure is helpful for improving the rigidity of the fiber, but the rest molecular structures of the internal silk fibroin are rapidly stabilized in a disordered state, and a complex multi-layer structure is not formed in sufficient time, so that the fiber has no good flexibility characteristic, and the mechanical property of the regenerated silk fibroin fiber is very unfavorable.
As a preferable technical scheme:
according to the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the coagulating bath in the dry-jet wet spinning process is ethanol.
The alcohol is a coagulation bath common to silk fibroin and polyvinyl alcohol, methanol or ethanol can be selected in the alcohol, although the coagulation effect of the methanol is good, the methanol is toxic and harmful, and the ethanol is selected as the coagulation bath. However, the fibers obtained by using alcohols as a coagulation bath to prepare the regenerated silk fibroin fibers have very low breaking elongation, because the regenerated silk fibroin fibers in an alcohol solvent have too high reaction speed, other molecular structures of the internal silk fibroin are stabilized in a disordered state, and the mechanical properties of the regenerated silk fibroin fibers are very unfavorable, so that ethanol is low in cost, non-toxic and harmless, but the ethanol is not a good choice as the coagulation bath.
After silk fibroin solution and polyvinyl alcohol are blended, due to the existence of the polyvinyl alcohol solution, the molecular conformation of silk fibroin is gradually converted to an extended beta-folding structure in a solution state, which is beneficial to the gradual formation of directional arrangement and the formation of an ordered crystalline structure of a molecular chain. And in the coagulating bath, the spinning solution begins to solidify gradually from the surface, moisture is continuously separated out from the spinning solution, ethanol permeates into the inside of the spinning solution gradually in the coagulating bath, and a double diffusion process is completed.
According to the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the certain proportion means that the mass ratio of the silk fibroin to the polyvinyl alcohol is 5:5-3:7.
The silk fibroin aqueous solution and the polyvinyl alcohol aqueous solution are easy to phase separate when being blended, because the regenerated silk fibroin molecules are promoted to agglomerate due to strong interaction, and the acting force between the silk fibroin and the polyvinyl alcohol molecules is smaller than the agglomeration. In the literature, a cosolvent is used to hinder the interaction between a fibroin molecular chain and a polyvinyl alcohol molecular chain and facilitate the movement of the molecular chains, so that the hydrogen bond combination between the fibroin molecular chain and the polyvinyl alcohol molecular chain is enhanced, and the aim of improving the compatibility of the fibroin molecular chain and the polyvinyl alcohol molecular chain is fulfilled.
According to the invention, by researching the blending condition of fibroin and polyvinyl alcohol solutions under different proportioning conditions, the solution with high polyvinyl alcohol content has spinnability and the solution blending condition is stable, and the spinning requirement can be met without adding a compatibilizer under the proportioning conditions of 5,4. Rheological property tests show that the polyvinyl alcohol solution has better viscoelasticity, while the silk fibroin solution has better fluidity, because the polyvinyl alcohol has small molecular weight size distribution and more regular and compact structure, and the silk fibroin has large molecular weight size distribution range and sparse structure, the friction in the solution is small. With the ratio of the two adjusted, blending the solutionMolecular structureGradually forming a stable network structure. And according to the results of the rheological tests, when the content of the polyvinyl alcohol is more than half of the content, the solution is blended withThe higher degree of microstructural similarity of the pure polyvinyl alcohol solution indicates that the blended solution indeed forms a more stable structure under these preparations.
According to the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the concentration of the silk fibroin aqueous solution is 18-20 wt%, and the concentration of the polyvinyl alcohol aqueous solution is 18-20 wt%.
The preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following steps: and extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution, sequentially passing through an air section, a coagulating bath, a godet roller in the coagulating bath and a balance reciprocating yarn guide device, further drafting by a winding device, and finally collecting. The fiber is led out of the coagulation bath from the godet roller in the coagulation bath through traction, and passes through the balance reciprocating yarn guide device.
According to the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the distance of the air section is 2-2.5 cm, the length of the coagulating bath is 77-173 cm, and the winding speed of the winding device is 9.8-17.2 rpm. When the silk fibroin/polyvinyl alcohol composite spinning aqueous solution is extruded, the advancing speed of the solution is 2ml/h, and the inner diameter of a needle head used for extrusion is 0.21mm;
furthermore, after the regenerated silk fibroin fibers are solidified by ethanol, the regenerated silk fibroin fibers can be quickly formed and are irreversible after the structure is stable, so that the regenerated silk fibroin is very brittle and cannot be stretched.
The preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following steps of:
putting old silk floss into 0.25wt% sodium carbonate aqueous solution according to the proportion of 1.
In the prior art, the adopted acid solvent can break silk peptide bonds, so that the silk fibroin is obviously degraded, the mechanical property of the subsequently prepared composite fiber is adversely affected, the acid chemical reagent is toxic and harmful to a human body, and can corrode process equipment to cause equipment loss, and related steps of removal and inspection are required to be added to avoid residual acid toxic substances in a finished product, so that the process complexity is increased.
According to the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000 (medium polymerization degree and low molecular weight).
The invention also provides the flexible silk fibroin/polyvinyl alcohol composite fiber prepared by the preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber, the material is a mixture of silk fibroin and polyvinyl alcohol, and the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by Raman spectroscopy is 0.69-1.26.
As a preferred technical scheme:
the flexible silk fibroin/polyvinyl alcohol composite fiber has the elongation at break of 329-528%, the breaking strength of 0.17-0.27 cN/dtex and the diameter of 70-108 μm.
The principle of the invention is as follows:
the invention takes old silk floss as raw material, prepares silk fibroin aqueous solution, and blends with polyvinyl alcohol aqueous solution, and selects the proportion of stable compatibility to prepare silk fibroin/polyvinyl alcohol composite spinning aqueous solution by adjusting the proportion of silk fibroin and polyvinyl alcohol; the silk fibroin/polyvinyl alcohol composite fiber is prepared by adopting a dry-jet wet spinning technology. As the beta-folding is used as a regular secondary structure in the silk fibroin, the crystallinity and the orientation degree of a silk fibroin molecular chain can be effectively improved, and macroscopically, the mechanical property of the fiber is improved. In the prior art, alcohol can induce silk fibroin to be rapidly converted into a beta-folded structure so as to form a crystalline region, but the molecular structure which does not form the crystalline region is stabilized in a disordered state and is not enough to form a multi-layer structure for supporting the flexibility of the fiber, so that the brittle fracture of the fiber is caused, and the mechanical property of the regenerated silk fibroin fiber is not favorable, so that ethanol is low in cost, non-toxic and harmless, but is not a good choice as a coagulating bath. The invention adopts a dry-jet wet spinning process, controls the content of a beta-folding structure of silk fibroin in a coagulation bath to be increased from 37-39% to 40-42%, effectively slows down the speed of transforming the silk fibroin into the beta-folding structure, gradually transforms the molecular conformation of the silk fibroin to the stretching beta-folding structure in a solution state, is beneficial to gradually forming directional arrangement of molecular chains and forming an ordered crystalline structure, and thus improves the mechanical property.
In the invention, ethanol is used as a coagulating bath in a dry-jet wet spinning process, spinning solution is gradually coagulated from the surface, water in the spinning solution is continuously separated out, the ethanol in the coagulating bath gradually permeates into the spinning solution to finish a double diffusion process, at the stage, because the fiber forms a skin layer on the surface firstly, the double diffusion speed in the coagulating bath is gradually reduced, the concentration of the spinning solution is gradually increased along with the separation of water, and polyvinyl alcohol is easy to form gel under high concentration, and the double diffusion process is further reduced under the expansion state. Thereby achieving the effect of slowing down the ethanol on the fibroin solution, namely obviously slowing down the effect of the ethanol on the fiber, and the obtained composite fiber can meet the requirement of subsequent processing.
Advantageous effects
(1) According to the flexible silk fibroin/polyvinyl alcohol composite fiber, the old silk floss material is developed and utilized in a high-value mode, the sustainable development concept is met, compared with the common regenerated silk fibroin fiber, the flexible silk fibroin/polyvinyl alcohol composite fiber has good spinnability, the prepared composite fiber is large in elongation and good in flexibility, and the defect that the regenerated silk fibroin fiber is brittle is overcome; both the silk fibroin and the polyvinyl alcohol material have good biocompatibility, and the obtained composite fiber has great application prospect in the biomedical field;
(2) The preparation method of the flexible silk fibroin/polyvinyl alcohol composite fiber is simple in process, adopts a pure water solution as a solvent of a spinning solution, avoids the degradation effect of an organic solvent on silk fibroin, constructs a green ecological processing process, is green and environment-friendly in production process, and realizes a dry-jet wet spinning technology for continuously and stably producing the silk fibroin/polyvinyl alcohol composite fiber.
Drawings
FIG. 1 is a process flow diagram of a method for preparing a flexible silk fibroin/polyvinyl alcohol composite fiber according to the present invention;
FIG. 2 is a drawing curve of the flexible silk fibroin/polyvinyl alcohol composite fiber of the present invention; the curves a to f are respectively stretching curves corresponding to six embodiments, wherein a is 1,b, 2,c, 3,d, 4,e, 5,f and 6;
FIG. 3 is the flexible silk fibroin/polyvinyl alcohol composite fiber prepared in example 5; wherein, (a) a longitudinal electron microscope image of the fiber, and (b) a cross-sectional electron microscope image of the fiber;
in the figure, 1-flow pump, 2-needle cylinder, 3-spinning guide tube, 4-needle head, 5-coagulating bath, 6-godet roller, 7-balance reciprocating yarn guide device and 8-winding device.
Detailed Description
The invention will be further illustrated with reference to specific embodiments. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention can be made by those skilled in the art after reading the teaching of the present invention, and these equivalents also fall within the scope of the claims appended to the present application.
Fig. 1 is a process flow diagram of a preparation method of a flexible silk fibroin/polyvinyl alcohol composite fiber of the invention, which specifically comprises the following steps: the spinning solution is placed in a needle cylinder 2, passes through a spinning guide pipe 3 under the uniform-speed extrusion action of a flow pump 1, is extruded out by a needle head 4, enters a coagulating bath 5 after passing through an air section, is gradually formed, passes through a godet roller 6 in the coagulating bath, is immediately pulled out of the coagulating bath, passes through a balance reciprocating yarn guide device 7, is further drawn under the action of a winding device 8 and is finally collected into a cylinder.
W/v in the present invention means a mass-to-volume ratio.
Example 1
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9.3M lithium bromide aqueous solution according to the mass-volume ratio of 1 (w/v) to 10 (w/v) at 60 ℃ for 4h, putting into a dialysis bag, dialyzing with deionized water for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain a silk fibroin aqueous solution with the concentration of 20 wt%;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 20wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 4:6 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2) by adopting a dry-jet wet spinning process, sequentially passing through an air section with the distance of 2cm, a coagulating bath with the length of 77cm, a godet roller in the coagulating bath and a balance reciprocating yarn guide device, further drafting by a winding device with the winding speed of 9.8rpm, and finally collecting to obtain flexible silk fibroin/polyvinyl alcohol composite fibers;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is increased from 39 percent to 42 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has elongation at break of 528%, breaking strength of 0.26cN/dtex and diameter of 108 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.78.
Comparative example 1
A method for preparing silk fibroin fibers, which is basically the same as that in example 1, and is different from the method in that the step (2) is omitted, the silk fibroin solution prepared in the step (1) is directly spun by a dry-jet wet spinning process, and in a coagulation bath, the content of a beta-folded structure of the silk fibroin is improved from 32% to 38%.
The prepared silk fibroin fiber has the elongation at break of 6 percent, the breaking strength of 0.11cN/dtex and the diameter of 75 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.5.
Comparing comparative example 1 with example 1, the elongation at break and the strength at break of comparative example 1 are lower than those of example 1, and the content of β -sheet structure in example 1 is higher when entering the coagulation bath, because the content of β -sheet structure in the silk fibroin in the composite solution is increased to some extent due to the addition of polyvinyl alcohol, so that the initial value of the content of β -sheet structure in the coagulation bath of pure silk fibroin spinning solution is lower than that of the composite spinning solution. In addition, compared with the beta-sheet of the fibroin in the coagulating bath in the example 1, the beta-sheet structure is improved by 3%, and in the comparative example 1, the beta-sheet structure is improved by 6% rapidly, the stable microcrystalline structure is helpful for improving the fiber rigidity, but the rest molecular structures of the fibroin in the fiber are stabilized in a disordered state due to rapid coagulation, and a complex multi-layer structure is not formed in sufficient time, so that the fiber has no good flexibility characteristic, and is easy to brittle fracture in the stretching process.
Example 2
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9.3M lithium bromide aqueous solution according to the proportion of 1 (w/v) to 10 at 60 ℃ for 4h, putting into a dialysis bag, dialyzing with deionized water for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain a silk fibroin aqueous solution with the concentration of 19 wt%;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 19wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 5:5 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2) by adopting a dry-jet wet spinning process, sequentially passing through an air section with the distance of 2cm, a coagulating bath with the length of 96cm, a godet roller in the coagulating bath and a balanced reciprocating yarn guide device, further drafting by a winding device with the winding speed of 12.3rpm, and finally collecting to obtain flexible silk fibroin/polyvinyl alcohol composite fibers;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is improved from 38 percent to 41 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has the elongation at break of 355%, the breaking strength of 0.21cN/dtex and the diameter of 92 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.74.
Example 3
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9.3M lithium bromide aqueous solution according to the proportion of 1 (w/v) to 10 at 60 ℃ for 4h, putting into a dialysis bag, dialyzing with deionized water for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain the silk fibroin aqueous solution with the concentration of 18 wt%;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 18wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 3:7 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2) by adopting a dry-jet wet spinning process, sequentially passing through an air section with the distance of 2cm, a coagulating bath with the length of 115cm, a godet roller in the coagulating bath and a balanced reciprocating yarn guide device, and finally further drafting by a winding device with the winding speed of 14.7rpm and finally collecting to obtain flexible silk fibroin/polyvinyl alcohol composite fibers;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is improved from 38 percent to 42 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has elongation at break of 414%, breaking strength of 0.27cN/dtex and diameter of 88 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 1.26.
Example 4
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9.3M lithium bromide aqueous solution according to the proportion of 1 (w/v) to 10 at 60 ℃ for 4h, putting into a dialysis bag, dialyzing with deionized water for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain a silk fibroin aqueous solution with the concentration of 19 wt%;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 19wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 4:6 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2) by adopting a dry-jet wet spinning process, sequentially passing through an air section with the distance of 2cm, a coagulation bath with the length of 135cm, a godet roller in the coagulation bath and a balance reciprocating yarn guide device, and finally further drafting by a winding device with the winding speed of 17.2rpm and finally collecting to obtain flexible silk fibroin/polyvinyl alcohol composite fibers;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is improved from 37 percent to 40 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has the elongation at break of 329 percent, the breaking strength of 0.17cN/dtex and the diameter of 74 mu m; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.69.
Example 5
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9M lithium bromide aqueous solution at 65 deg.C for 2h according to 1:5 (w/v), dialyzing with deionized water in dialysis bag for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain 18wt% silk fibroin aqueous solution;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 18wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 3:7 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Adopting a dry-jet wet spinning process, extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2), sequentially passing through an air section with the distance of 2cm, a coagulation bath with the length of 154cm, a godet roller in the coagulation bath and a balanced reciprocating yarn guide device, and finally further drafting by a winding device with the winding speed of 12.8rpm and finally collecting to obtain the flexible silk fibroin/polyvinyl alcohol composite fiber;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is improved from 37 percent to 41 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has the elongation at break of 446%, the breaking strength of 0.25cN/dtex and the diameter of 70 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.99.
Example 6
A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber comprises the following specific steps:
(1) Dissolving old silk floss with 9.2M lithium bromide aqueous solution at 70 deg.C for 3h according to 1:7 (w/v), placing into dialysis bag, dialyzing with deionized water for 3 days, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain 20wt% silk fibroin aqueous solution;
(2) Blending the silk fibroin aqueous solution prepared in the step (1) with a polyvinyl alcohol aqueous solution with the concentration of 20wt% (the hydrolysis degree of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000) according to the mass ratio of 5:5 to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution;
(3) Extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution prepared in the step (2) by adopting a dry-jet wet spinning process, sequentially passing through an air section with the distance of 2cm, a coagulating bath with the length of 87cm, a godet roller in the coagulating bath and a balance reciprocating yarn guide device, further drafting by a winding device with the winding speed of 14.7rpm, and finally collecting to obtain flexible silk fibroin/polyvinyl alcohol composite fibers;
wherein, the coagulating bath of the dry-jet wet spinning process is ethanol, and the content of the beta-folding structure of the silk fibroin in the coagulating bath is improved from 37 percent to 40 percent.
The prepared flexible silk fibroin/polyvinyl alcohol composite fiber has the elongation at break of 331%, the breaking strength of 0.21cN/dtex and the diameter of 83 μm; the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by raman spectroscopy was 0.69.
FIG. 2 is a drawing curve of the flexible silk fibroin/polyvinyl alcohol composite fiber of the present invention; wherein, the curves a to f are respectively tensile curves corresponding to the embodiments 1 to 6; it can be known from the figure that, in the initial stage of the tensile test, the partial molecular chains in the fiber generate the change of bond length and bond angle under the action of external force, and generate elastic deformation, the borne stress is rapidly increased, and then reaches an inflection point, the hydrogen bonds of the semi-crystalline part in the fiber begin to break, and a yield point is generated, the non-crystalline part molecular chains are straightened and form new bonding bonds between the molecular chains, and the semi-crystalline structure is gradually loosened under the action of the tensile force, so that a section of area with gradually reduced or unchanged stress is generated under the condition of continuous increase of tensile strain, after the semi-crystalline area is completely stretched and unfolded, the tensile force begins to act on a more stable crystalline area in the fiber, and the borne stress of the fiber is greatly increased, until the acting force overcomes the bonding force of the crystalline area, and macroscopic fiber breaks. It is worth mentioning that when stretching to stretch the amorphous or semi-crystalline regions to a fully extended state, if these structures are weak, the forces may not be transmitted to the crystalline regions in time, i.e. the phase of stress rise does not occur, and the fibers break immediately, as can be seen from the curves in the figure, the amorphous or semi-crystalline regions of the composite fibers in the examples of the present invention provide good support for the flexibility of the fibers during the fiber forming process, and all six fibers have good elongation at break; the breaking strength of the prepared composite fiber is 0.17-0.27 cN/dtex, and the elongation at break is up to 329-528%.
Claims (7)
1. A preparation method of flexible silk fibroin/polyvinyl alcohol composite fiber is characterized by comprising the following steps: firstly, preparing a silk fibroin aqueous solution by taking old silk floss as a raw material, blending the silk fibroin aqueous solution with a polyvinyl alcohol aqueous solution according to a certain proportion to obtain a silk fibroin/polyvinyl alcohol composite spinning aqueous solution, and then preparing silk fibroin/polyvinyl alcohol composite fibers by adopting a dry-jet wet spinning process;
the certain proportion refers to the mass ratio of the silk fibroin to the polyvinyl alcohol is 5:5-3:7;
the coagulating bath in the dry-jet wet spinning process is ethanol;
in the coagulating bath of the dry-jet wet spinning process, the content of a beta-folding structure of the silk fibroin is improved from 37-39% to 40-42%;
the flexible silk fibroin/polyvinyl alcohol composite fiber has elongation at break of 329-528%, breaking strength of 0.17-0.27 cN/dtex, and diameter of 70-108 μm.
2. The method for preparing the flexible silk fibroin/polyvinyl alcohol composite fiber according to claim 1, wherein the concentration of the silk fibroin aqueous solution is 18-20 wt%, and the concentration of the polyvinyl alcohol aqueous solution is 18-20 wt%.
3. The method for preparing the flexible silk fibroin/polyvinyl alcohol composite fiber according to claim 1, wherein the dry-jet wet spinning process comprises the following steps: and extruding the silk fibroin/polyvinyl alcohol composite spinning aqueous solution, sequentially passing through an air section, a coagulating bath, a godet roller in the coagulating bath and a balance reciprocating yarn guide device, further drafting by a winding device, and finally collecting.
4. The method as claimed in claim 3, wherein the distance of the air section is 2-2.5 cm, the length of the coagulation bath is 77-173 cm, and the winding speed of the winding device is 9.8-17.2 rpm.
5. The method for preparing the flexible silk fibroin/polyvinyl alcohol composite fiber according to claim 1, wherein the process for preparing the silk fibroin aqueous solution by using old silk floss as a raw material comprises the following steps:
dissolving old silk floss with 9.0-9.3M lithium bromide water solution at the temperature of 60-70 ℃ for 2-4h according to the proportion of 1:5-1 (w/v), putting the old silk floss into a dialysis bag for dialysis for 3 days by deionized water, centrifuging the dialyzed solution to remove impurities, and concentrating to obtain the silk fibroin water solution.
6. The method for preparing a flexible silk fibroin/polyvinyl alcohol composite fiber according to claim 1, wherein the degree of hydrolysis of polyvinyl alcohol is 95%, and the molecular weight distribution is 85000-124000.
7. The method for preparing a flexible silk fibroin/polyvinyl alcohol composite fiber according to any one of claims 1 to 6, wherein the molecular chain orientation degree in the flexible silk fibroin/polyvinyl alcohol composite fiber measured by Raman spectroscopy is 0.69 to 1.26.
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