Method for producing cocoon filaments with fine fineness

Abstract

To develop a safe and inexpensive agent suppressing the growth of a larva and enabling the miniaturization of the larva by feeding the agent to the fifth instar larva of a silkworm and to stably obtain a cocoon filament having a fine fineness for a long time by allowing the larva to produce a cocoon.SOLUTION: When using a powder containing natural silica produced by physically pulverizing rice husks so that an X-ray diffraction peak near a diffraction angle 2 θ = 35 degrees in wide-angle X-ray diffraction measurement of the contained natural silica disappears or the peak intensity of the diffraction is reduced to such an extent that only the peak position of the diffraction can be determined, or when using a powder containing regenerated silica obtained by subjecting bamboo leaf plant opal to alkali extraction once and then precipitating in an acidic bath, and further when using a powder of synthetic silica, It has been found that it is possible to reduce the size of silkworm larvae and to stably obtain long cocoon filaments of fine fineness from the cocoons of the larvae.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to the discovery that feeding silica powder to silkworm larvae raised in the sericulture industry during the fifth instar stage can suppress the growth of the larvae and reduce their size at will, and the development of a method for producing cocoon thread that enables the stable production of fine cocoon thread over a long period of time by having the reduced size larvae produce cocoons. [Background technology]

[0002] To improve the texture and feel of silk products, there has been a demand for finer cocoon threads. The only way to achieve this is to breed silkworms, which requires a great deal of effort, time, and expense. Patent Document 1 revealed that by feeding silkworms an inducer that modifies the silkworm's spinning movement, silkworms that normally produce cocoon threads of approximately 3 denier can be made to produce cocoon threads of less than 1 denier. However, the fineness of the cocoon threads in the early stages of spinning is 3-4 denier, and tends to decrease rapidly as spinning progresses. Therefore, in order to consistently produce finer threads for a long period of time, it became necessary to develop a rearing method that would reduce the size of silkworm larvae. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Toshio Watanabe, Yutaka Kawahara, Patent Publication No. 2023-115873, Modulation inducer of silkworm spinning movement and virus disease preventive agent. [Non-patent literature] [Non-Patent Document 1] Hamamura, Y., Feeding mechanism of silkworms and artificial diets. Chemistry and Biology, Vol. 1, No. 7, pp. 364-370, 1963. [Non-patent document 2] O. Tsutsui, R. Sakamoto, M. Obayashi, S. Yamakawa, T. Handa, D. Nishio-Hamane, I. Matsuda, Light and SEM observation of opal phytoliths in the mulberry leaf. Flora, vol. 218, pp. 44-50 (2016). [Non-patent document 3] Ken Takahashi, Epidemiological Study on the Carcinogenicity of Silica, Aerosol Research, Vol. 16, No. 4, pp. 280-284, 2001. Summary of the Invention [Problem to be solved by the invention]

[0004] We have developed a safe and inexpensive agent that can be fed to fifth-instar silkworm larvae, thereby suppressing their growth and allowing them to be made smaller at will.Furthermore, by making the smaller larvae produce cocoons, we have made it possible to stably obtain fine cocoon thread for a long period of time. [Means for solving the problem]

[0005] Although silica has no nutritional value, it has been reported that silkworm larvae, particularly silkworms, continuously consume cellulose coated with silica gel (SiO₂·nH₂O) (Non-Patent Document 1). Meanwhile, analysis of mulberry leaves, the primary food source of silkworm larvae, has confirmed the accumulation of phytoliths (amorphous silica) on the leaf surface (Non-Patent Document 2). Furthermore, when the thermally denatured silica described in Patent Document 1 was applied to mulberry leaves and fed to fifth-instar silkworm larvae, the larvae became smaller due to the excessive intake of non-nutritional thermally denatured silica. However, they were still able to spin and produce cocoons at the same time as normal rearing. Similarly, experiments were conducted in which fifth-instar silkworm larvae were fed mulberry leaves coated with powders such as natural silica, regenerated silica, and synthetic silica. Growth was examined, and it was found that regardless of the silica powder used, the silkworm larvae did not die from silica overconsumption and were able to spin and produce cocoons at the same time as normal rearing. Furthermore, since neither type of silica has any nutritional value, excessive consumption of silica caused silkworm larvae to become smaller.

[0006] When silkworm larvae were overfed with a powder containing thermally denatured silica (Comparative Example 2), they became smaller, but the fineness of the cocoon filaments significantly decreased from the outer layer to the inner layer, making it impossible to stably produce fine filaments for a long period of time. Consequently, we conducted extensive research into the optimal silica properties. As shown in Examples 1-3, we found that it is possible to use powder containing natural silica produced by physically crushing rice husks (rice husks) to eliminate the X-ray diffraction peak at a diffraction angle of 2θ = 35 degrees in wide-angle X-ray diffraction measurements of the natural silica contained therein, or to reduce the intensity of the X-ray diffraction peak to such an extent that only the position of the X-ray diffraction peak can be distinguished. We also found that powder containing regenerated silica obtained by first extracting bamboo leaf plant opal with alkali and then precipitating it in an acid bath, and synthetic silica powder are also possible. This led to the present invention. The silica used in breeding should not contain crystalline silica (cristobalite), which shows a strong crystalline diffraction peak at a diffraction angle of approximately 2θ = 22 degrees in wide-angle X-ray diffraction measurements. Crystalline silica was classified as a carcinogen by the International Agency for Research on Cancer in 1997 (Non-Patent Document 3). [Effects of the Invention]

[0007] By feeding silica to fifth-instar silkworm larvae based on the rearing method of the present invention, even with conventional silkworm varieties, without the need for breeding improvement, it is possible to stably obtain long, fine-fiber threads. Furthermore, by using this cocoon thread, it is possible to improve the texture and feel of silk fiber products, which is expected to lead to the development of the silk textile industry. [Brief explanation of the drawings]

[0008] [Figure 1] This figure shows the change in the fineness of the cocoon filaments in the longitudinal direction from the outside to the inside of the cocoon obtained from fifth-instar silkworm larvae that were fed powder containing natural silica produced by physically crushing rice husks (rice husks), thereby eliminating the X-ray diffraction peak at a diffraction angle of around 2θ = 35 degrees in wide-angle X-ray diffraction measurement of the natural silica contained therein, or by reducing the intensity of the X-ray diffraction peak to an extent that only the position of the X-ray diffraction peak can be distinguished. (Example 1) [Figure 2] This figure shows the change in the fineness of the cocoon filaments from the outside to the inside of the cocoon obtained from fifth-instar silkworm larvae that were fed powder containing regenerated silica derived from bamboo that was sprinkled directly on mulberry leaves (Example 2). [Figure 3] This figure shows the change in the fineness of the cocoon filaments from the outside to the inside of the cocoon obtained from 5th instar silkworm larvae that were fed synthetic silica gel powder sprinkled directly on mulberry leaves (Example 3). [Figure 4] 1 is a graph showing the disappearance of peaks derived from natural silica by heat treatment of rice husk at 500° C. (Comparative Example 1). [Figure 5]This figure shows the change in the lengthwise fineness of the cocoon filaments from the outside to the inside of the cocoon obtained from 5th instar silkworm larvae that were fed an artificial diet containing 10 weight percent of rice husk powder heat-treated at 500°C (Comparative Example 1). [Figure 6] This figure shows the change in the lengthwise fineness of the cocoon filaments from the outside to the inside of the cocoon obtained from fifth-instar silkworm larvae that had been fed mulberry leaves that had been sprinkled directly on rice husk powder that had been heat-treated at 500°C (Comparative Example 2). [Figure 7] This is a graph showing the change in the fineness of the cocoon filaments in the longitudinal direction from the outside to the inside of the cocoon obtained by normal rearing of silkworm larvae fed only mulberry leaves from the 4th to 5th instars (Comparative Example 3). DETAILED DESCRIPTION OF THE INVENTION [Example]

[0009] Rice husks were physically crushed to eliminate the X-ray diffraction peak near 2θ = 35 degrees in wide-angle X-ray diffraction measurements of the natural silica contained therein, or to reduce the intensity of the X-ray diffraction peak to the point where the peak position could only be discerned. This powder containing natural silica was then sprinkled directly onto mulberry leaves and fed to 50 fifth-instar larvae (variety: Gunma 200), which matured and produced cocoons. None of the silkworms died during rearing. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer to inner layers was measured, yielding the results shown in Figure 1. [Example]

[0010] Powder containing regenerated silica derived from bamboo was sprinkled directly onto mulberry leaves and fed to 50 fifth-instar larvae (variety name: Gunma 200), which then matured and produced cocoons. None of the silkworms died during rearing. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer layer to the inner layer was measured, yielding the results shown in Figure 2. [Example]

[0011] Synthetic silica gel powder was sprinkled directly onto mulberry leaves and fed to 50 5th instar larvae (variety name: Gunma 200), which then matured and produced cocoons. None of the silkworms died during rearing. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer layer to the inner layer was measured, yielding the results shown in Figure 3. Comparative Example 1

[0012] When rice husks are heat-treated at 500°C, the two characteristic peaks at diffraction angles of 9° and 35°, which are derived from natural silica, are thermally denatured and disappear, as shown in Figure 4, while the diffraction peak at a diffraction angle of around 3° increases dramatically. The pyrolysis residue of rice husks containing this heat-denatured silica was physically crushed as needed and mixed with 10% by weight of commercially available artificial feed for silkworm larvae (product name: Kuwanahana for second-stage silkworms). This was then fed to fifth-stage larvae (variety: Gunma 200), which matured the silkworms and allowed them to produce cocoons. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer to inner layers was measured, yielding the results shown in Figure 5. Because the fineness of the cocoon filaments decreased significantly from the outer to inner layers, it was not possible to stably produce thin filaments for long periods. Comparative Example 2

[0013] The thermal decomposition residue of rice husk containing heat-modified silica, which was heat-treated at 500°C and had the two characteristic peaks at diffraction angles of 9 and 35 degrees, which are specific to natural silica, disappear due to thermal modification, while the diffraction peak around a diffraction angle of 3 degrees is extremely increased, was physically crushed appropriately, and sprinkled directly on mulberry leaves, which were then fed to 5th-instar larvae (variety: Gunma 200), which matured the silkworms and allowed them to produce cocoons. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer to the inner layer was measured, resulting in the results shown in Figure 6. Cocoons were produced in which the fineness of the cocoon filaments decreased significantly from the outer to the inner layer, but it was not possible to stably produce thin filaments for long periods. Comparative Example 3

[0014] Silkworm larvae (variety: Gunma 200) were reared from the fourth to fifth instar on a diet of mulberry leaves only, and allowed to mature and produce cocoons. The cocoons were boiled as usual, and the change in the lengthwise fineness of the cocoon filaments from the outer to the inner layer of the cocoon was measured, yielding the results shown in Figure 7. Cocoons were obtained in which the fineness of the cocoon filaments gradually decreased from the outer to the inner layer, but it was not possible to stably produce thin filaments of 2-3 denier for a long period of time.

Claims

1. This method for producing cocoon thread involves feeding amorphous silica powder to fifth-instar silkworm larvae, thereby suppressing the growth of the larvae and, as a result, reducing the diameter of the larvae's spinning orifice, thereby enabling the production of finer cocoon thread.

2. The method for producing cocoon thread according to claim 1, wherein the amorphous silica described in claim 1 is produced from plant opal of plants such as rice chaff, rice stalks, wheat stalks, and bamboo leaves, and the amorphous silica derived from the plant opal is used.

3. The amorphous silica according to claim 1 is synthesized by a sol-gel method using an addition reaction of water to tetraethyl orthosilicate, and the method for producing cocoon filament according to claim 1 uses the chemically synthesized amorphous silica.

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