JP7576833B2 - Reed microfibers, their spun yarns, and nonwoven fabrics - Google Patents

Description

The present invention relates to reed fine fibers extracted from the vascular bundle sheath of reeds, spun yarns using only reed fine fibers, blended yarns of reed fine fibers and other natural fibers, and nonwoven fabrics using reed fine fibers.

Thin, long natural fibers that can be spun are available from a variety of plants. Cotton is a seed fiber that is divided into individual fibers. Its maximum length is about 60 mm, but its average diameter is very thin, less than 20 μm, making it suitable for spun yarn. Very fine spun yarns of less than 40 cotton count can also be obtained from cotton.

On the other hand, hemp such as jute is a bast fiber. Bast fibers are thick single fibers (also called elementary fibers, often called pulp in the paper industry) with a diameter of 30 μm to 50 μm, but several to several dozen of them are bundled together by adhesive substances such as pectin and lignin, and they become long while overlapping in the longitudinal direction. Therefore, the spun yarns are thick and stiff. Therefore, the types of hemp used for clothing are limited to flax and ramie. Spun yarns of Manila hemp, which is a leaf vein fiber, are also thick and stiff, and cannot be used as they are to obtain yarns for clothing.

The right side of Figure 1 is an SEM photograph of a bamboo cross section, showing its microstructure. Vascular bundle sheaths, which are made up of sclerotial cells that become single fibers, surround the xylem and phloem. The aggregate of single fibers, xylem, and phloem is called a vascular bundle. Parenchyma cells are present around the vascular bundles. The cells are bonded to each other by adhesive substances such as pectin and lignin. Vascular bundles run vertically through the bamboo (Non-Patent Document 1), so vascular bundle sheath fibers longer than the bamboo stem can be obtained by chemical retching treatment in which the fibers are immersed in an alkaline aqueous solution such as sodium hydroxide, or by blasting (Non-Patent Document 2), (Patent Document 1). As shown in Figure 1, the cross section of the vascular bundle sheath fiber is not round, so the size of the cross section can be appropriately expressed by its maximum width and maximum thickness.

As is clear from Figure 1, the cross section of the bamboo vascular bundle sheath is large. Although the yield is extremely low at less than 1%, the maximum width and thickness of the bamboo vascular bundle sheath fiber cross section can be narrowed to about 50 μm by mechanical fiber splitting. However, the length is short at less than 20 mm, and it cannot be spun using bamboo fiber alone.

To obtain spun yarn, it must be blended with fine fibers such as cotton (Patent Document 2). Patent Document 2 states that "Bamboo fibers are used that have an average fiber length of 15 mm to 70 mm and a maximum cross-sectional width and thickness of 30 μm to 70 μm after defibration," but the diameter of a single bamboo fiber is 15 μm or more in the case of Moso bamboo and Madake bamboo, and the maximum cross-sectional width and thickness of the bamboo vascular bundle sheath fiber is 30 μm, so it is extremely difficult to practically obtain thin fibers from bamboo that are spun and have a length of 30 mm or more.

Reeds, which grow on the shores of lakes, marshes, and rivers, are of the same family as bamboo, the Gramineae. They are perennial plants, but the stems above ground, which grow in six months, die in winter. The stems above ground correspond to the trunks of bamboo. The underground stems do not die and grow the following year. The size of the vascular bundles is less than one-third that of bamboo, and the number of sclerenchyma cells (the cells that make up b in Figure 1, p are parenchyma cells) is also less than that of bamboo.

The size of the sclerenchyma cells is smaller than that of madake and moso bamboo. The size of the vessels in the vascular bundles and the vascular bundle sheaths around the phloem fibers (b in Figure 1) are also small. Therefore, the reed fine fibers that can be spun and are as thin as or thinner than flax and ramie can be obtained from the reed vascular bundle sheaths.

Since reeds finish growing in six months, reed filaments have lumens (holes) that are not found in mature bamboo filaments. This gives them better insulation than solid bamboo fibers or cotton, and the surface area of reed microfibers is larger, so they also have better moisture absorption and odor absorption properties.

Mechanically extracted "reed fiber" has been used as a reinforcing material for injection-molded products of polylactic acid, a biodegradable resin (Non-Patent Document 3). However, this reed fiber is a spiny reed made by mechanically crushing dried reeds, and is not made by separating and splitting the fibers from the vascular bundle sheaths of reeds into fine fibers. Until now, there has been no reed fine fiber that can be used for thin spun yarn for clothing.

JP2008229933A-Method for extracting bamboo fibers No. 2017-057519 Bamboo fiber blended yarn and its manufacturing method

"Learn about composite materials from bamboo", Toru Fujii, Jianye Jiang: Journal of the Textile Machinery Society of Japan, Vol. 52, No. 8, pp. 334-340, August 1999 "Tensile strength properties of bamboo fibers extracted by explosion method" Hitoshi Takagi, Takaki Takura, Yohei Ichihara, Shinji Ochi, Hiroaki Misawa, and Yu Niki: Zairyo (Japan Society of Materials Science), Vol. 52, No. 4, pp. 353-356, April 2003 "Study on the melt viscoelasticity of reed fiber/biodegradable polyester composite material" Tetsuyuki Gun, Kazuo Kitagawa, and Yasui Hamada; Molding and Processing (Preprint of the 16th Annual Meeting of the Society of Molding and Processing), pp. 197-198, May 2005

The demand for clothing is increasing with economic growth and population growth in developing countries. In addition, the need to reduce carbon dioxide emissions, one of the greenhouse gases, has led to a demand for industrial textile products to use sustainable renewable natural resources.

As a result, there is a growing concern that supplies of existing natural fibers such as cotton and hemp will be strained, creating a need for new natural fiber resources.

Reeds are a renewable natural resource found abundantly around the world. However, apart from harvesting the stalks and using them as roofing material, reed mats, or as a raw material for pulp, there have been few other effective uses for them.

The vascular bundle sheaths of reed stems are thin and long, making them a potential source of yarn for industrial textile products and clothing. However, mechanical crushing of reeds does not produce fine reed fibers suitable for spinning.

Also, reed stems have the same microstructure as bamboo stems, but despite being in the same grass family, reeds have not been shown to have antibacterial properties.

Therefore, the present invention provides reed vascular bundle sheath fine fibers (hereinafter referred to as "reed fine fibers") (reed fine fibers A) extracted from reed stems, having a maximum cross-sectional width and thickness of 100 μm or less and a length of 10 mm or more. The aspect ratio of the fiber (the ratio of the maximum cross-sectional length of the fiber to the fiber length) is 100 or more.

The reed microfibers obtained above are immersed in an antibacterial extract liquid extracted from bamboo epidermis or an aqueous solution of a wood-based antibacterial agent, hinokitiol, to provide antibacterial reed microfibers (reed microfibers B), and in a softening agent to provide flexible reed microfibers (reed microfibers C).

Also provided are spun yarns in which only reed fine fibers A, reed fine fibers B, or reed fine fibers C are twisted together, and blended yarns in which the reed fine fibers are mixed with natural fibers other than the reed fine fibers, such as cotton.

In addition, a nonwoven fabric is provided which is made of only reed fine fibers A, or reed fine fibers B, or reed fine fibers C, or is compounded with polypropylene or polyethylene fibers.

First, a method for producing reed fine fibers will be described below.

Reeds that are at least three months old are cut down and pretreated in the following manner to facilitate separation of the vascular bundle sheaths.

The reeds are soaked in running water or still water below 40°C for one day to one month for bioretching. If using water, change the water every day to prevent odors caused by bacterial growth from adhering to the reed microfibers. Instead of still water, the reeds can be soaked in hot water above 40°C.

Chemical retching may be performed by adding lye, potassium carbonate, sodium carbonate, or an aqueous solution of sodium hydroxide to water or hot water.

The pretreatment may be carried out by steaming with superheated steam at 200° C. or less, or by explosion.

In either pretreatment, the treated reed stems are washed with water.

It is better to crush the reeds with a hammer or roller before pre-treating, as this will shorten the pre-treating time.

If the reed stems are less than six months old and are soft, they do not need to be pretreated.

The pretreated reed stalks are crushed by two rollers rotating in opposite directions to separate the reed vascular bundle sheath from the parenchyma cells and the xylem and phloem in the vascular bundles. If passing the reed stalk through the two rollers once is not enough to separate the reed vascular bundle sheath from the parenchyma cells and the xylem and phloem in the vascular bundles, the reed stalk is passed through the rollers multiple times. By passing the reed stalks through the rollers more times, the vascular bundle sheath is also finely split vertically, allowing thin and long reed microfibers to be extracted in the subsequent process. The process of passing the reed stalk through the two rollers is shown in Figure 2.

Even if the reed stalk is crushed in the two-roller process and the vascular bundle sheath is finely split vertically inside, the vascular bundle sheath is not completely separated from the parenchyma cells and the xylem and phloem in the vascular bundle. Also included are reed vascular bundle sheath fibers with a maximum cross-sectional width and thickness of 100 μm or more.

Therefore, the reed vascular bundle sheath fibers that are separated by the two roller process but still bonded to each other are cut into 30-100 mm pieces and separated into fibers by a depilator, carding machine, or a fiberizer with a similar mechanism. This process is shown in Figure 3. This produces reed fine fibers with a maximum cross-sectional width and thickness of 100 μm or less and a length of 10 mm or more.

Instead of the fiberizer, a disc refiner as shown in FIG. 4 may be used.

For separating reed fine fibers, a linen carding machine used for flax hackling, as shown in Figure 5, may be used. In this case, the reed stalks that have been through the two-roller process are passed through the carding machine without being cut into short pieces.

Reeds belong to the same family as bamboo, the Gramineae, and their cross-sectional structures are very similar, but neither the stems nor the bundle sheaths have been recognized as having antibacterial properties. Therefore, reed microfibers can be immersed in bamboo antibacterial extracts extracted from the bamboo epidermis using hot water, steam, or ethanol to give the reed microfibers antibacterial properties.

Instead of the bamboo antibacterial extract liquid, the material may be immersed in an aqueous solution of hinokitiol, a wood-based antibacterial agent.

The antibacterial activity obtained by immersion in a bamboo antibacterial extract liquid or an aqueous solution of hinokitiol was maintained at 80% even after 10 water washes.

Since reed microfibers have a larger cross section than cotton, they are more rigid than cotton. Therefore, if the reed microfibers are soaked in fabric softener before spinning, they can be softened.

When the maximum cross-sectional width and thickness of the reed fine fibers is 50 μm or less and the fibers are long, such as 30 mm or more, they can be twisted together to produce a reed spun yarn.

Also, regardless of the maximum cross-sectional width and thickness and length of the reed microfiber, blended yarns can be obtained by blending the reed microfiber with natural fibers such as cotton, silk, wool, and hemp.

Reed fine fiber/TPF nonwoven fabric is obtained by combining reed fine fiber with thermoplastic fiber (hereinafter referred to as "TPF") such as polypropylene or low melting point polyethylene fiber and going through the nonwoven fabric process shown in Figure 6. Figure 6 shows an example of the manufacturing process of reed fine fiber/TPF nonwoven fabric using a super blender, a weighing hopper, a carding machine, a cross layer, and a drafter. A mat-like nonwoven fabric is finished by needle punching.

The nonwoven fabric can also be made into a preboard by a double belt press, in which case the needle punching step may be omitted.

Instead of using a carding machine and cross-layering, the nonwoven fabric may be produced by an air-laid method.

The present invention provides an abundant, continuously renewable source of reeds that can be spun into yarn that can be used to weave clothing, thereby easing the tight supply of natural fibers for clothing.

In addition, reed microfibers can be used in combination with TPF to make nonwoven fabrics for automobile interior materials, such as ceilings and rear partitions, which will ease the supply shortage of natural fibers for industrial nonwoven fabrics, such as kenaf.

Nonwoven fabric made from reed microfibers that have been given antibacterial properties is also used for the inner soles of shoes.

In chemical retching using an aqueous solution of sodium hydroxide, one of the pretreatment processes, the immersion time is reduced to less than one tenth of that required for simple immersion in still water. When using sodium hydroxide, its concentration should be 10% or less, preferably 2% or less, and the aqueous solution temperature should be 60°C or less. The immersion time is affected by the growth period of the reeds. For a growth period of 9 months, the immersion time is 15 hours with a sodium hydroxide concentration of 2% and an aqueous solution temperature of 60°C.

By crushing the reeds with rollers, the time required for pretreatment processes such as bioretching and soaking in alkaline solution is reduced by one-third.

By crushing the reed stalks with rollers before the pretreatment process, the amount of reeds in the soaking vessel can be increased by up to three times and the soaking time can be halved.

The pretreatment step makes it easy to remove the vascular bundle sheaths in the subsequent separation step by crushing them with two rollers. Without the pretreatment step, many parenchyma cells would be attached to the divided vascular bundle sheaths, and it would be impossible to create cracks in the vascular bundle sheaths that cross the cross section.

These cracks make it easier to carry out the fiber splitting process using a de-piling machine after the vascular bundle sheath splitting process using two rollers, and even if the maximum cross-sectional width and thickness are 50 μm or less, long and thin fine fibers exceeding 30 mm in length can be obtained.

By using this fine reed fiber, fine reed spun yarn of 10 cotton count (28 hemp count) or more can be obtained using the same process as for spun yarn of cotton or other materials.

After the fiber splitting process using a wool splitter, many short reed fine fibers with a length of less than 30 mm are obtained, even if the maximum cross-sectional width and thickness are reduced to 50 μm or less. In this case, it is not possible to spin the reed fine fibers alone. In addition, thick reed fine fibers with a maximum cross-sectional width and thickness of 50 μm or more are also obtained.

Therefore, by blending it with cotton, silk, wool, and even hemp, it is possible to obtain fine reed spun yarn with a cotton count of 18 or more (hemp count of 50) that contains 20% reed fiber by weight and can be used for clothing such as T-shirts.

Reed vascular bundle sheath microfibers have large voids (lumens) in the center of the single fibers that compose them. Therefore, reed microfiber spun yarn (hereinafter referred to as reed spun yarn) has a high thermal insulation effect in the lateral direction of the yarn. When comparing the thermal conductivity of cotton spun yarn and reed spun yarn of the same weight per unit length, the reed spun yarn is 70% or less than that of cotton spun yarn. Therefore, cloth woven with reed spun yarn has high thermal insulation. In the case of reed/other natural fiber blended yarn, the thermal insulation increases depending on the blending ratio of reed microfibers.

Reed microfiber has lumens and a large surface area per unit weight, so it has high heat insulation and high moisture absorption compared to bamboo fiber etc. When the weight is the same, the moisture absorption rate of reed microfiber is 30% higher than that of bamboo fiber.

In the case of cotton, the diameter of a single fiber is approximately 12 to 20 μm, which is extremely thin, 1/2 to 1/3 that of reed microfibers. Therefore, when it is blended with cotton, the reed microfibers are wrapped around the cotton in the spun yarn, creating a cavity in the spun yarn, which increases the heat retention.

Natural fibers such as kenaf are combined with TPF to form a nonwoven fabric, which is then hot pressed to form a preboard for use in automobile ceilings and rear partitions. Bamboo has thick vascular bundle sheath fibers, which results in a lower bending stiffness than a kenaf fiber/PTF nonwoven board of the same weight. On the other hand, when reed microfibers are used in automobile preboards, the weight of the preboard can be reduced by 5% while still achieving the same performance as a preboard using kenaf fiber.

Cross-sectional SEM images of a Moso bamboo (right) and a reed stem (left). Both are at the same magnification. The structures of the two are very similar. In both cross sections, diamond-shaped vascular bundles (composed of vessels, sieve tubes, and vascular bundle sheaths) can be seen. The black areas are where the posterior wall cells are densely packed, and are called vascular bundle sheaths. A diagram showing the process of separating the vascular bundle sheath from the parenchyma cells by pressing the pretreated reed stem (stem) between two large-diameter steel rollers rotating in opposite directions. The two large-diameter rollers are driven synchronously by an electric motor. The crushing force of the reed stem is controlled by the pressing spring of the upper roller. A diagram showing the process of separating reed stalks, in which the vascular bundle sheaths are mostly separated from the parenchyma cells by two rollers, into fibers by a dehairing machine. Either a flat-top type or a roller-top type dehairing machine can be used. The thinnest wire is used. Photo showing the disc refiner A photo showing a linen carding machine A diagram showing the manufacturing process of reed microfiber/TPF nonwoven fabric using a super blender, weighing hopper, carding machine, cross layer, and drafter.

A first embodiment of the present invention will now be described.

After growth, reeds that grew naturally on the west shore of Lake Biwa and were cut down after 10 months were used to extract reed microfibers. First, the reed stalks were passed through a two-roller separator to crush them. At this time, the spring force was set to 50 kg on one side. Then, the reed stalks were immersed in a 2% aqueous sodium hydroxide solution (temperature 20°C) for 10 hours, washed with water, lightly drained, and passed through a two-roller separator three times. After drying to a moisture content of 40%, a roller top type sample carding machine was used as a wool recovery machine to extract reed microfibers separated from the vascular bundle sheath. In one fiber separation process, 30% by weight of microfibers with a maximum fiber cross-sectional width and thickness of 50 μm or less were obtained. The lengths were widely distributed from 5 to 50 mm, and the average length was 32 mm. Using these reed microfibers, a blended yarn (20 cotton count) with cotton was obtained. The weight content of reed microfibers was 30%. The tensile strength of the blended yarn was 550 g.

Next, a second embodiment of the present invention will be described.

Reed microfibers with an average fiber span of 80 μm and an average fiber length of 42 mm and polypropylene fiber (PPF) were passed through a sample carding machine three times and mixed to produce a 20 cm wide web, which was then cut into 20 cm pieces and stacked alternately at right angles, and then hot pressed (200°C) to produce a preboard. For comparison, a kenaf fiber/PPF board was also produced, and the weights of both boards were compared when their bending stiffness was the same. As a result, it was found that the reed microfiber/PPF preboard was 5% lighter.

Claims (1)

A method for producing reed vascular bundle sheath fine fibers mechanically extracted from the vascular bundle sheath of a reed stem that is 3 to 6 months old after growth, the maximum cross-sectional width and thickness of which are 100 μm or less and the length of which is 10 mm or more, the aspect ratio of the reed vascular bundle sheath fine fibers (the ratio of the maximum cross-sectional length of the fiber to the fiber length) being 100 or more,
The reed stalks are crushed by a roller without being softened through a retching process as a pretreatment, and then the reed fine fibers are mechanically taken out.