Method for producing nanocellulose-containing fiber or silk, nanocellulose-containing fiber or silk, and silkworm bait

Abstract

The technical problem of the present invention is to provide: a method for producing fibers or filaments containing nanocellulose from which practical and high-strength fibers or filaments can be obtained; a practical and high-strength nanocellulose-containing fibers or filaments; and a silkworm bait for obtaining practical and high-strength fibers or filaments. The solution of the present invention is to obtain nanocellulose-containing fibers or silks by causing silkworms to ingest a bait containing cellulose nanofibers, taking out silks from cocoons spitted by the silkworms, and refining the silks to remove sericin.

Description

Technical Field

[0001] The present invention relates to a method for producing fibers or silks containing nanocellulose, fibers or silks containing nanocellulose, and bait for silkworms. Background Art

[0002] Silk fibers extracted from silkworm cocoons are composed of fibroin (about 70%) and sericin (about 30%), and have a structure in which two strands of fibroin are covered by sericin. In the past, in order to improve the strength of the silk fibers, the inventors of the present application developed a method for producing composite silk in which cellulose nanofibers are dispersed in silk fibers by making silkworms ingest a feed containing cellulose nanofibers and extracting silk from the cocoons spit out by the silkworms (for example, see Patent Document 1).

[0003] Here, cellulose nanofiber is a kind of nanocellulose, light and high strength and high elasticity. In addition, because cellulose nanofiber is derived from plant fiber, the environmental load during production or disposal is small, and biocompatibility is excellent. In the silk obtained by the method of recording in patent document 1, the cellulose nanofiber dispersed in the silk fiber is arranged along the fiber direction, and the strength ratio is larger than the existing raw silk of the undispersed cellulose nanofiber.

[0004] In addition, previous reports have pointed out that experiments were conducted in which silkworms were fed a feed prepared by mixing ceramic powder with artificial feed and the cocoons obtained from the silkworms were observed. The results showed that although ceramic particles were contained in the sericin layer of the cocoon silk, no ceramic particles were observed on the surface of the refined silk fibroin (for example, refer to non-patent document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2020-97807

[0008] Non-patent literature

[0009] Non-patent document 1: Yoichi Kamishi, Fukuju Miyazawa, and Naoto Kasawa, "A study on the use of セラミックス powder mixed with artificial feed to feed silkworm cocoons", Journal of the Silk Manufacturing Research Association, 1999, Vol. 8, p. 53-56 Summary of the invention

[0010] 1. Technical issues to be resolved

[0011] When silk fibers or silk threads are used for clothing purposes, silk from which sericin is removed by refining cocoon silk or raw silk taken out of cocoons is usually used in consideration of gloss, texture, dyeing, etc. However, in the method for manufacturing composite silk described in Patent Document 1, since the obtained composite silk is not refined, it contains sericin, which still has a technical problem of being impractical. In addition, in the method for manufacturing composite silk described in Patent Document 1, cellulose nanofibers are confirmed to be dispersed on the surface of the obtained composite silk, that is, in the part of sericin covering two silk fibroin, but it is not confirmed whether the cellulose nanofibers are dispersed in the silk fibroin. Therefore, the method for manufacturing composite silk described in Patent Document 1 has a technical problem that even if the obtained composite silk is refined, it is not clear what degree of strength the refined fiber or silk has.

[0012] The present invention is completed with a focus on the above-mentioned technical problems, and its purpose is to provide a method for producing fibers or silk containing nanocellulose that can obtain practical and strong fibers or silk, practical and strong fibers or silk containing nanocellulose, and bait for silkworms for obtaining practical and strong fibers or silk.

[0013] (II) Technical solution

[0014] In order to achieve the above-mentioned purpose, the method for producing fibers or silks containing nanocellulose of the present invention is characterized in that silkworms are allowed to ingest bait containing cellulose nanofibers, silk is taken out from the cocoons spun by the silkworms, and the silk is refined to remove sericin, thereby obtaining fibers or silks containing nanocellulose.

[0015] According to the method for producing fibers or silks containing nanocellulose of the present invention, it is possible to produce fibers or silks in which cellulose nanofibers are dispersed in silk fibroin after refining to remove sericin. In Non-Patent Literature 1, when silkworms were fed with bait in which ceramic powder was mixed in artificial feed, although the sericin layer of the cocoon silk taken out from the cocoon spit out by the silkworms contained ceramic particles, no ceramic particles were observed on the surface of the refined silk fibroin. Therefore, when using bait containing cellulose nanofibers, it is possible that the silk fibroin does not contain nanocellulose. However, according to the method for producing fibers or silks containing nanocellulose of the present invention, cellulose nanofibers can be dispersed in the refined silk fibroin.

[0016] The fiber or silk produced by the method for producing the fiber or silk containing nanocellulose of the present invention has greater strength than the existing refined fiber or silk in which the cellulose nanofibers are not dispersed because the cellulose nanofibers are dispersed in the silk core protein. In addition, the produced fiber or silk is practical because the sericin is removed by refining. The produced fiber or silk can be used as a functional material in, for example, clothing, medical fields, sports goods such as the gut of a tennis racket or the net of a football goal, fishing line, nets for fisheries, filters, sheets, fiber-reinforced resins, electrode materials, etc.

[0017] The silk refined by the method for producing fibers or silks containing nanocellulose of the present invention is preferably cocoon silk extracted from cocoons spun by silkworms or raw silk formed by combining multiple cocoon silks, but it can also be silk in a state of making raw silk into cloth. Refining can be any method as long as it is a method that can remove sericin such as enzyme refining, acid refining, alkali refining, soap refining, high-pressure refining, etc. In the method for producing fibers or silks containing nanocellulose of the present invention, it is preferred that impurities other than sericin are also removed by refining. In addition, it is preferred that all contaminants such as sericin or impurities are removed by refining, but these contaminants may remain in the form of unavoidable impurities.

[0018] In the method for producing the fiber or silk containing nanocellulose of the present invention, the bait preferably contains 3 to 10 wt.% of the cellulose nanofiber, and particularly preferably contains 5 to 7.5 wt.% of the cellulose nanofiber. In addition, the bait may contain more than 7 wt.% and less than 10 wt.% of the cellulose nanofiber. In this case, it is particularly possible to obtain fibers with a small cross-sectional area, and to obtain fibers or silks with high rigidity and high strength.

[0019] The method for producing fibers or silks containing nanocellulose of the present invention can make silkworms ingest bait containing less than 3wt.% of cellulose nanofibers or bait containing more than 7wt.% and less than 10wt.% of cellulose nanofibers, and extract silk from the cocoons spit out by the silkworms. In this case, fibers or silks with high rigidity and high strength can be obtained from unrefined fibers or silks.

[0020] The nanocellulose-containing fibers or threads of the present invention are characterized in that they are composed of silk fibroin and cellulose nanofibers dispersed in the silk fibroin, or are composed of the silk fibroin, the cellulose nanofibers and inevitable impurities.

[0021] The fiber or silk containing nanocellulose of the present invention is suitable for being manufactured by the manufacturing method of the fiber or silk containing nanocellulose of the present invention. Since the fiber or silk containing nanocellulose of the present invention has cellulose nanofibers dispersed in the fibroin, it has greater strength than the existing refined fiber or silk in which the cellulose nanofibers are not dispersed. In addition, the fiber or silk containing nanocellulose of the present invention does not contain sericin, or even if it contains sericin, it contains a small amount of sericin in the form of inevitable impurities, so it is practical.

[0022] In the fiber or silk containing nanocellulose of the present invention, the cellulose nanofibers are preferably arranged along the fiber direction of the silk core protein. In this case, the strength is particularly large. The fiber or silk containing nanocellulose of the present invention is preferably composed of a cross-sectional area of ​​220 to 260 μm 2 At this time, since the cross-sectional area of ​​each fiber is relatively small, the rigidity is high and the strength is large.

[0023] The bait for silkworms of the present invention is characterized in that it contains more than 7wt.% and less than 10wt.% of the cellulose nanofibers. The bait for silkworms of the present invention may be, for example, a commercially available bait for silkworms mixed with cellulose nanofibers, or a commercially available bait for silkworms mixed with mulberry leaves and cellulose nanofibers.

[0024] The bait for silkworms of the present invention is suitable for use as bait in the method for producing fibers or silks containing nanocellulose of the present invention, and can obtain fibers or silks in which cellulose nanofibers are dispersed in sericin and fibroin. The obtained fibers or silks may be unrefined fibers or silks or refined fibers or silks, and since cellulose nanofibers are dispersed, the strength is greater than that of existing fibers or silks in which cellulose nanofibers are not dispersed. In addition, the refined fibers or silks are practical because sericin is removed by refining.

[0025] (III) Beneficial effects

[0026] According to the present invention, there can be provided a method for producing fibers or silks containing nanocellulose that can obtain practical and strong fibers or silks, practical and strong fibers or silks containing nanocellulose, and bait for silkworms for obtaining practical and strong fibers or silks. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1(a) is a scanning electron microscope (SEM) image showing a cross-section of cocoon silk before refining (before removal of sericin) obtained from silkworms fed a feed having a weight fraction of cellulose nanofibers (CNF) of 0 wt.% in the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention; (b) is a scanning electron microscope (SEM) image showing a cross-section of cocoon silk before refining (before removal of sericin) obtained from silkworms fed a feed having a weight fraction of cellulose nanofibers (CNF) of 5 wt.% in the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention; (c) is a scanning electron microscope (SEM) image showing a cross-section of cocoon silk before refining (before removal of sericin) obtained from silkworms fed a feed having a weight fraction of cellulose nanofibers (CNF) of 12.5 wt.% in the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention.

[0028] Figure 2 (a) is a graph showing the cross-sectional area of ​​cocoon silk before refining (before removing sericin) obtained by the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention, relative to the weight fraction of CNF; (b) is a graph showing the cross-sectional area of ​​silk after refining (after removing sericin) obtained by the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention, relative to the weight fraction of CNF.

[0029] Figure 3 The present invention relates to a method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention, wherein (a) is a phase detection image obtained by using a scanning probe microscope (SPM) of silkworms that have been refined by feeding a feed containing 0 wt.% CNF; and (b) is a phase detection image obtained by enlarging the vicinity of the center of (a).

[0030] Figure 4 This is a phase detection image obtained using a scanning probe microscope (SPM) of silkworm cocoons obtained from silkworms fed a feed having a CNF weight fraction of 7.5 wt.% in the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention, after refining the silk.

[0031] Figure 5 (a) is to use the cantilever of the scanning probe microscope to contact Figure 4 Phase detection image when the contact pressure is set to weak within the range of circle 1 shown; (b) is a phase detection image when the cantilever of the scanning probe microscope is contacted Figure 4 Phase detection image when the contact pressure is set to medium within the range of circle 1 shown; (c) is a phase detection image when the cantilever of the scanning probe microscope is contacted Figure 4The phase detection image when the contact pressure in the range within the frame of circle 1 is set to be strong.

[0032] Figure 6 (a) is to use the cantilever of the scanning probe microscope to contact Figure 4 Phase detection image when the contact pressure is set to weak when the contact pressure is within the range of circle 2 shown; (b) is a phase detection image when the cantilever of the scanning probe microscope is contacted Figure 4 The phase detection image shown in the frame range of circle 2 is when the contact pressure is set to be strong.

[0033] Figure 7 The present invention is a plan view of a test piece for a tensile test showing cocoon silk before refining and silk after refining (test sample) obtained by the method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention.

[0034] Figure 8 (a) shows the cocoon silk before refining obtained by silkworms fed with a feed containing 0 wt.% and 5 wt.% CNF by weight, using Figure 7 (a) is a stress-strain curve of the tensile test result of the test piece shown; (b) is a stress-strain curve of the refined silk obtained by the silkworm fed with a feed having a weight fraction of CNF of 0 wt.%, 5 wt.%, and using Figure 7 The stress-strain curve of the tensile test results of the test specimens is shown.

[0035] Fig. 9 (a) is a graph showing the Young's modulus of the cocoon silk before refining obtained by the method for producing fibers or silks containing nanocellulose using an embodiment of the present invention, relative to the weight fraction of CNF; (b) is a graph showing the tensile strength of the cocoon silk before refining obtained by the method for producing fibers or silks containing nanocellulose using an embodiment of the present invention, relative to the weight fraction of CNF.

[0036] Fig.10 (a) is a graph showing the Young's modulus of the refined silk obtained by the method for producing fibers or silks containing nanocellulose using an embodiment of the present invention, relative to the weight fraction of CNF; (b) is a graph showing the tensile strength of the refined silk obtained by the method for producing fibers or silks containing nanocellulose using an embodiment of the present invention, relative to the weight fraction of CNF. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described based on examples and the like.

[0038] The method for producing fibers or silks containing nanocellulose according to an embodiment of the present invention can produce fibers or silks containing nanocellulose as follows. That is, first, silkworms are made to ingest a bait containing cellulose nanofibers, and cocoon silk is extracted from the cocoons spit out by the silkworms. In this case, the bait for silkworms may be, for example, a commercially available bait for silkworms mixed with cellulose nanofibers, or a commercially available bait for silkworms mixed with mulberry leaves and cellulose nanofibers.

[0039] Next, the obtained cocoon silk or raw silk formed by combining a plurality of cocoon silks or a product in a state of fabric made from the raw silk is refined to remove sericin. At this time, the refining may be any method such as enzyme refining, acid refining, alkali refining, soap refining, high pressure refining, etc., as long as it is a method capable of removing sericin. In addition, it is preferred that impurities other than sericin are also removed by refining, but contaminants such as sericin or impurities may also remain in the form of unavoidable impurities. In this way, fibers or silks in which cellulose nanofibers are dispersed in the refined silk fibroin can be manufactured.

[0040] The fibers or silks produced by the method for producing fibers or silks containing nanocellulose according to the embodiment of the present invention have cellulose nanofibers dispersed in the fibroin, so they are stronger than the conventional refined fibers or silks in which the cellulose nanofibers are not dispersed. In addition, the sericin in the produced fibers or silks is almost completely removed by refining, which is practical.

[0041] In addition, the method for producing nanocellulose-containing fibers or silks according to an embodiment of the present invention may not purify the silk extracted from the cocoons spun by silkworms. In this case, the unrefined fibers or silks can be used to produce fibers or silks in which cellulose nanofibers are dispersed in sericin and fibroin.

[0042] The fiber or silk containing nanocellulose of the embodiment of the present invention is suitable for manufacturing by the method for manufacturing the fiber or silk containing nanocellulose of the embodiment of the present invention. In addition, the bait for silkworms of the embodiment of the present invention is suitable for use as the bait of the method for manufacturing the fiber or silk containing nanocellulose of the embodiment of the present invention.

[0043] Example 1

[0044] The method for manufacturing fibers or silks containing nanocellulose according to the embodiment of the present invention is used to manufacture silks containing nanocellulose, and experiments are conducted to investigate the characteristics thereof. In the experiment, the larvae of silkworms were divided into 6 groups, and after the larvae of the silkworms reached the 4th instar, they began to be given bait containing cellulose nanofibers (hereinafter also referred to as "CNF"). The larvae of the silkworms used were Jinqiu Zhonghe, which is a hybrid of Japanese and Chinese species. In addition, CNF was a 5wt.% aqueous solution slurry ("BiNFi-sIMa-10005" manufactured by SUGINO MACHINE LIMITED) using a raw material after pulping and made by a water jet method (WJ method). The diameter of the CNF in the slurry is about 10~50nm. In addition, the bait used was a slurry of an aqueous solution of 5 wt.% of CNF mixed with a commercially available bait ("Insecta LFM" manufactured by Nosan Corporation) at a predetermined weight ratio, and further mixed so that the ratio of the commercially available bait to water was 1:3, and then heated in a microwave oven and adjusted to a tubular shape. Six types of baits corresponding to six groups of silkworm larvae were prepared, and the weight fractions of CNF relative to the commercially available bait were 0, 2.5, 5, 7.5, 10, and 12.5 wt.%, and were given to the silkworm larvae of each corresponding group.

[0045] In the experiment, silkworms were raised in a breeding room maintained at 25°C and 60% humidity, and the larvae were allowed to make cocoons. The cocoons were harvested after two weeks. The harvested cocoons were heated at 130°C for two hours in a vacuum drying oven ("DP200" manufactured by Yamato Scientific Co., Ltd.) to kill the pupae inside the cocoons. Then, the cocoons were boiled at 80°C to 90°C using a heating plate ("Isotemp" manufactured by Fisherbrand), and the cocoon silk was extracted from the cocoons and wound.

[0046] The wound silk cocoons were alkali-refined using sodium bicarbonate (Hayashi Pure Chemical Ind., Ltd.) to remove sericin. Pure water and sodium bicarbonate were mixed in a weight ratio of 25:1, and the silk cocoons were boiled at 80°C to 90°C for 5 to 6 hours to perform refining. The refined silk was dyed with picric acid-carmine to confirm the removal of sericin.

[0047] First, using a scanning electron microscope (SEM; "S-3400N" manufactured by Hitachi High-Tech Corporation), the cross-sectional structure of the cocoon silk obtained from each group of silkworm larvae before refining and after refining was observed and the cross-sectional area was measured. SEM images of the cross-sectional cocoon silk obtained from silkworms fed with a CNF weight fraction of 0 wt.%, 5 wt.%, and 12.5 wt.% are shown in FIG. Figure 1 (a)~(c). Figure 1 As shown in (a) to (c) of FIG. 1 , it was confirmed that each cocoon silk had a structure in which sericin surrounded two fibroin strands. In addition, the diameter of each fibroin strand was about 10 μm to 15 μm.

[0048] Next, the cross-sectional areas of the cocoon silk before refining (before removing sericin) and the silk after refining (after removing sericin) of each group were calculated from the respective SEM images and are shown in FIG. Figure 2 and Table 1. In addition, the cross-sectional area is the average value of the measured values ​​of each of the four samples in each group.

[0049] [Table 1]

[0050]

[0051] like Figure 2 As shown in (a) and Table 1, it was confirmed that when the weight fraction of CNF in the bait was 5 wt.%, the cross-sectional area of ​​the cocoon silk before removing the sericin was the smallest at 253 μm. 2 , as CNF increases and decreases from 5wt.%, the cross-sectional area becomes larger. In addition, Figure 2 As shown in (b) and Table 1, it was confirmed that when the weight fraction of CNF in the bait was 7.5 wt.%, the cross-sectional area of ​​the silk after removing the sericin was the smallest at 241 μm. 2 , as CNF increases and decreases from 7.5wt.%, the cross-sectional area becomes larger.

[0052] In addition, it was confirmed that when using a bait mixed with 10wt.% or less of CNF, the cross-sectional area of ​​the silk before and after the removal of sericin tended to decrease compared to when using a bait without CNF (0wt.%). It is believed that this is because the mixed bait of CNF hinders the growth of silkworms and shrinks the silk gland, which is the organ that spits out silk. In addition, it was confirmed that the cross-sectional area of ​​the bait with 12.5wt.% CNF increased compared to when using a bait without CNF (0wt.%). It is believed that this is because the increased amount of CNF condenses and forms gaps in the silk.

[0053] Next, a scanning probe microscope (SPM; "SPM-9700HT" manufactured by Shimadzu Corporation) was used to observe the surface of the refined silk obtained from silkworms fed with a CNF weight fraction of 0wt.%, 7.5wt.%. The observation was performed in the air, and a phase detection image (pixel; 256×256) was obtained using the phase detection mode. For the phase detection image, in order to make it easier to identify, the curved surface of the silk shape was flattened by digital correction. The phase detection images when CNF was 0wt.% and 7.5wt.% are shown in FIG. Figure 3 and Figure 4 .

[0054] like Figure 3 As shown in FIG. 1 , when CNF is 0 wt.%, even after refining, a small amount of sericin remains, and the presence of microfibrils constituting silk fibroin is confirmed underneath. Figure 4 As shown, when the CNF content was 7.5 wt.%, long and thin fibers extending along the fiber direction of the fibroin were confirmed within the dotted-line frames of circles 1 and 2 in the fibroin.

[0055] In order to confirm whether each fiber was CNF, the contact pressure of the cantilever of the scanning probe microscope was gradually increased when it was in contact with the range including each fiber. The results are shown in Figure 5 and Figure 6 .like Figure 5 and Figure 6 As shown in FIG. 1 , it was confirmed that when the contact pressure was gradually increased, the fiber indicated by the arrow in each figure deformed less than its surroundings. Since the compressive elastic modulus of CNF is larger than that of silk fibroin, Figure 5 and Figure 6 Based on the results, it is believed that the fibers indicated by arrows in each figure are CNFs.

[0056] Next, the cocoon silk obtained from each group of silkworm larvae before refining and the refining silk were subjected to a tensile test. The tensile test was conducted using a 20N micro-load tester ("MST-1" manufactured by Shimadzu Corporation) at room temperature and a relative humidity of 50 to 70%. Figure 7As shown, in the tensile test, the cocoon silk before refining and the refined silk trimmed to 30 mm in length are used as test samples 1. Each test sample 1 is placed in the center of a paper sheet 2 of 30 mm × 5 mm in length direction of the paper sheet 2, and the 5 mm at both ends are fixed to the tabs 3 formed at both ends of the paper sheet 2 with an adhesive. The tabs 3 at both ends are respectively installed on the two grips of the testing machine, and just before the tensile test is started, the paper sheet 2 is cut only in the width direction near one grip. The crosshead speed (tensile speed) is set to 20 mm / min by stroke control, and the tensile test is thus performed.

[0057] For each group of silk before refining and silk after refining, stress-strain curves were obtained by tensile tests, and Young's modulus and tensile strength were obtained from the respective curves. When calculating Young's modulus and tensile strength, the values ​​in Table 1 were used as the cross-sectional area of ​​each silk. As an example, the stress-strain curves of silk before refining and silk after refining obtained from silkworms fed with a CNF weight fraction of 0 wt.% and 5 wt.% are shown in Table 1, respectively. Figure 8 In addition, the Young's modulus and tensile strength of the cocoon silk before refining of each group obtained from the stress-strain curve are shown in Fig. 9 (a) and (b) show the Young's modulus and tensile strength of the refined silk of each group. Fig.10 In addition, the Young's modulus and tensile strength of each group are the average values ​​of 8 samples.

[0058] like Fig. 9 As shown in (a), it was confirmed that when the weight fraction of CNF in the bait was 7.5wt.%, the Young's modulus of the cocoon silk before removing the sericin protein was the largest, and as the CNF increased and decreased from 7.5wt.%, the Young's modulus decreased. In addition, it was confirmed that when CNF was 10wt.%, the Young's modulus decreased compared to when CNF was not mixed (0wt.%). In addition, as Fig. 9 As shown in (b), it was confirmed that when the weight fraction of CNF in the bait was 5wt.%, the tensile strength was the largest, and as CNF increased and decreased from 5wt.%, the tensile strength decreased. In addition, it was confirmed that when CNF was 10wt.% and 12.5wt.%, the tensile strength was almost the same as when CNF was not mixed (0wt.%).

[0059] according to Fig. 9 The results of (a) and (b) indicate that when the bait contains 10 wt.% or less of CNF, the strength of the cocoon silk before the removal of sericin increases, and in most cases, the rigidity also increases. In addition, it is believed that when the bait contains 2.5 to 7.5 wt.% of CNF, the rigidity is particularly high and the strength increases. Figure 2 (a) and the results in Table 1 show that, considering the dispersion of the measured values, the silk before removing the sericin has a cross-sectional area of ​​240 to 320 μm 2 The fiber is composed of fibers or their aggregates, and the cross-sectional area of ​​the fibers becomes slightly smaller.

[0060] like Fig.10 As shown in (a) and (b), it was confirmed that when the weight fraction of CNF in the bait was 7.5wt.%, the Young's modulus and tensile strength of the silk after removing sericin were both the maximum, and as CNF increased and decreased from 7.5wt.%, the Young's modulus and tensile strength decreased. In addition, it was confirmed that compared with the case where CNF was not mixed (0wt.%), when CNF was 2.5wt.% and 12.5wt.%, the Young's modulus and tensile strength decreased.

[0061] according to Fig.10 The results of (a) and (b) indicate that when the bait contains 3 to 10 wt.% CNF, the silk after removing the sericin has high rigidity and increased strength. In addition, when the bait contains 5 to 7.5 wt.% CNF, the rigidity is particularly high and the strength is increased. Figure 2 (b) and the results in Table 1 show that, considering the dispersion of the measured values, the silk after removing the sericin has a cross-sectional area of ​​220 to 260 μm 2 The fiber is composed of fibers or their aggregates, and the cross-sectional area of ​​the fibers is relatively small.

[0062] Through Fig. 9 and Fig.10 Comparison confirmed that the Young's modulus and tensile strength after refining were smaller than those before refining. This is believed to be caused by the damage of silk fibroin due to heating during refining and the action of sodium bicarbonate aqueous solution. In addition, after refining to remove sericin, it can be confirmed that the Young's modulus and tensile strength change according to the weight fraction of CNF, so it can be seen that CNF is dispersed not only in sericin but also in silk fibroin.

[0063] Description of Reference Numerals

[0064] 1: Test specimen; 2: Paper; 3: Handle.

Claims

1. A method for producing fibers or filaments containing nanocellulose, characterized in that: Silkworms are made to ingest a feed containing cellulose nanofibers, silk is taken out from the cocoons produced by the silkworms, and the silk is refined to remove sericin, thereby obtaining fibers or silk containing nanocellulose.

2. The method for producing fibers or filaments containing nanocellulose according to claim 1, characterized in that: The bait contains 3 to 10 wt.% of the cellulose nanofibers.

3. The method for producing fibers or filaments containing nanocellulose according to claim 1, characterized in that: The bait contains more than 7 wt.% and less than 10 wt.% of the cellulose nanofibers.

4. A method for producing fibers or filaments containing nanocellulose, characterized in that: Silkworms are made to ingest a feed containing less than 3 wt.% of cellulose nanofibers or a feed containing more than 7 wt.% and less than 10 wt.% of cellulose nanofibers, and silk is extracted from cocoons spun by the silkworms.

5. A fiber or filament comprising nanocellulose, characterized in that The invention is composed of silk fibroin and cellulose nanofibers dispersed in the silk fibroin, or is composed of the silk fibroin, the cellulose nanofibers and inevitable impurities.

6. The fiber or filament comprising nanocellulose according to claim 5, characterized in that The cellulose nanofibers are arranged along the fiber direction of the silk fibroin.

7. The fiber or filament comprising nanocellulose according to claim 5 or 6, characterized in that The cross-sectional area ranges from 220 to 260 μm 2 fibers or their aggregates.

8. A bait for silkworms, characterized in that: The cellulose nanofibers are contained in an amount of more than 7 wt.% and less than 10 wt.%.

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