A lyocell ultrafine fiber preparation method based on supercritical carbon dioxide induced fibrillation

Abstract

This invention belongs to the field of textile materials technology, and relates to a lyocell ultrafine fiber based on supercritical carbon dioxide-induced fibrillation and its preparation method. This invention combines supercritical carbon dioxide finishing with mechanical finishing, achieving efficient and controllable ultrafine lyocell fiber processing by controlling the temperature (50-70℃), pressure (28-32MPa), treatment time (90-120min), and depressurization rate (30-60s) of supercritical CO2. The entire lyocell fiber splits into countless ultrafine fibers, and the microcracks generated inside the fibers are fine and uniform, while maximizing the preservation of the fiber's inherent strength.

Description

Technical Field

[0001] This invention belongs to the field of textile materials technology, and specifically relates to a method for preparing lyocell microfiber based on supercritical carbon dioxide-induced fibrillation. Background Technology

[0002] Lyocell fiber is an environmentally friendly regenerated cellulose fiber, widely popular for its excellent strength, hand feel, moisture absorption, and biodegradability. One of its key characteristics is its tendency to "fibrillate" under wet and mechanical conditions, where individual fibers split into fine cilia. This characteristic was once considered a processing challenge; however, it has also been utilized to produce unique fabrics with a peach-skin texture, which, after fibrillation, are more fluffy, soft, drapey, have a delicate, skin-friendly feel, and a slightly cool touch.

[0003] Traditional fibrillation methods primarily rely on intense mechanical action, such as prolonged treatment in hydroentangling, airflow, or turbulent dye vats. These methods have significant drawbacks: The process is difficult to control precisely: it can easily lead to over-fiberization or uneven fibrillation, affecting fabric quality.

[0004] Severe fiber damage: Strong external forces can damage the main structure of the fibers, resulting in a significant decrease in fabric strength and easy generation of lint.

[0005] High energy consumption and low efficiency: Achieving the ideal fibrillation effect requires a long processing time and a high energy input.

[0006] Therefore, there is an urgent need in this field for a new method that can controllably and efficiently achieve lyocell fiber splitting while maximizing the preservation of fiber strength in order to prepare high-performance ultrafine fibers. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing ultrafine lyocell fibers with controllable diameter down to the submicron level. This method combines supercritical carbon dioxide finishing with mechanical finishing, utilizes the fibrillation characteristics of lyocell fibers, and optimizes the parameter range to achieve efficient and controllable ultrafine lyocell fiber processing.

[0008] This invention provides a method for preparing lyocell microfibers based on supercritical carbon dioxide-induced fibrillation. Under certain temperature and pressure, the concentration difference of supercritical carbon dioxide inside and outside the fiber promotes its penetration. The temperature is then further increased and maintained for a period of time, causing the supercritical carbon dioxide in the fiber to reach a supersaturated state, achieving phase separation. Subsequently, rapid pressure release causes the supercritical carbon dioxide dissolved inside the fiber to rapidly vaporize and expand due to the sudden pressure drop, creating microcracks and micropores in the cross-section of the lyocell fiber from the inside, forming a pre-split structure. The supercritical carbon dioxide-treated lyocell material is then mechanically finished, and through physical action, the microcracked fibers are completely split into microfiber bundles. The method includes the following steps: Step 1: Supercritical carbon dioxide infiltration. Place the Lyocell material in a high-pressure reactor, introduce carbon dioxide, and heat to 50-70℃. The pressure inside the reactor should be increased to 28-32MPa to bring the carbon dioxide to a supercritical state. Maintain this state for a period of time, usually 90-120 minutes, to allow the supercritical CO2 to fully penetrate and swell the amorphous regions of the Lyocell fiber.

[0009] Step 2: Supercritical carbon dioxide supersaturation state. Utilizing the characteristics of supercritical carbon dioxide, the supercritical carbon dioxide that has penetrated into Lyocell fibers undergoes phase separation by increasing the temperature.

[0010] Step 3: Rapid depressurization, reducing the pressure inside the reactor to atmospheric pressure in a short time. The depressurization time is preferably less than 60 seconds, and more preferably instantaneous (30-60 seconds) depressurization.

[0011] Step 4: Post-treatment, including one or more of the following: hydroentangling treatment, mechanical kneading treatment, airflow impact treatment, or dynamic stirring treatment in an aqueous solution.

[0012] The beneficial effects achieved by this invention are: (1) This invention overcomes the problems of uneven fibrillation and large damage to fiber strength caused by traditional methods. By precisely controlling the temperature (50-70℃), pressure (28-32MPa), action time (90-120min) and pressure release rate (30-60s) of supercritical CO2, the density and depth of microcracks inside the fiber can be precisely controlled, thereby achieving precise design of fibrillation degree and final fineness.

[0013] (2) The present invention utilizes supercritical carbon dioxide to pre-split inside the fiber, so that fibrillation occurs simultaneously in the fiber cortex and core, reducing the chance of fibrillation recurring during subsequent use, and long-term use will not affect the fabric's hand feel, wrinkle resistance, drape and other wearing properties.

[0014] (3) This invention utilizes internal "air explosion" energy to achieve splitting, and subsequent fibrillation can be completed with only gentle physical action, preserving the integrity and mechanical properties of the fiber to the greatest extent, resulting in a stronger and more durable product. This method significantly shortens the time required for subsequent mechanical fibrillation and reduces energy consumption.

[0015] The ultrafine lyocell fiber obtained by this invention splits a whole lyocell fiber into countless ultrafine fibers. The microcracks generated inside the fiber are fine and uniform overall, while maximizing the preservation of the fiber's inherent strength. It can be used in high-value-added fields such as high-adsorption filtration, biomedical textiles, and battery separators, and has broad application prospects. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a scanning electron microscope image of the cross-section of Lyocell fiber after supercritical CO2 treatment in Example 4. As can be seen from 1, there are microcracks inside the fiber, and the cracks are fine and uniform overall. Figure 2 These are optical microscope images of the fibers split into ultrafine fibers after being treated with a roller friction machine in Example 4. Figure 2 You can see the entire lyocell fiber split into countless ultrafine fibers; Figure 3 The image shows a scanning electron microscope (SEM) image of the cross-section of Lyocell fiber after supercritical CO2 treatment in Comparative Example 1. The cracks are more obvious at the fiber edges, and the cracks are deep but have low density. Detailed Implementation

[0017] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0018] Example 1 Take 100g of Lyocell plain weave fabric, wind it onto a porous roller, place it in a 1L supercritical treatment vessel, fill it with CO2, heat it to 70℃, pressurize it to 28 MPa, and maintain it for 90min to allow the supercritical CO2 to fully penetrate into the fiber and reach saturation solubility within the fiber; raise the temperature at a rate of 10℃ / min to reach a high temperature of 150℃, allowing the supercritical fluid dissolved in the fiber to achieve phase separation and maintain the phase separation time for 60min; open the valve at the bottom of the reactor to instantly release the pressure to atmospheric pressure within 30 seconds.

[0019] The fabric was placed in an overflow dyeing machine and treated for 50 minutes under a water pressure of 0.3 MPa and a mechanical rubbing condition of 40 times / minute.

[0020] Example 2 Take 100g of Lyocell plain weave fabric, wind it onto a porous roller, place it in a 1L supercritical treatment vessel, fill it with CO2, heat it to 70℃, pressurize it to 32 MPa, and maintain it for 90min to allow the supercritical CO2 to fully penetrate into the fiber and reach saturation solubility within the fiber; raise the temperature at a rate of 20℃ / min to reach a high temperature of 150℃, allowing the supercritical fluid dissolved in the fiber to achieve phase separation and maintain the phase separation time for 60min; open the valve at the bottom of the reactor to instantly release the pressure to atmospheric pressure within 45 seconds.

[0021] The fabric was placed in an overflow dyeing machine and treated for 60 minutes under a water pressure of 0.3 MPa and a mechanical rubbing condition of 40 times / minute.

[0022] Example 3 Take 100g of Lyocell plain weave fabric, wind it onto a porous roller, place it in a 1L supercritical treatment vessel, fill it with CO2, heat it to 50℃, pressurize it to 28MPa, and maintain it for 120min to allow the supercritical CO2 to fully penetrate into the fiber and reach saturation solubility within the fiber; raise the temperature at a rate of 10℃ / min to reach a high temperature of 150℃, allowing the supercritical fluid dissolved in the fiber to achieve phase separation and maintain the phase separation time for 60min; open the valve at the bottom of the reactor to instantly release the pressure to atmospheric pressure within 60 seconds.

[0023] The fabric was placed in an overflow dyeing machine and treated for 50 minutes under a water pressure of 0.5 MPa and a mechanical rubbing condition of 30 times / minute.

[0024] The test results are shown in Table 1. Table 1 Test results of Examples 1-3 Table 1 shows the subjective evaluation method of the fibrillation index. Reference: Yang Xuhong. Evaluation of the fibrillation degree of Lyocell fiber [J]. Silk, 2000(8):14-16. Example 4 Lyocell fiber yarn was placed in a supercritical reactor and treated for 120 minutes at 50°C and 28 MPa supercritical CO2. The temperature was then raised to 150°C and held for 60 minutes. The pressure was then instantly released to atmospheric pressure within 60 seconds before the yarn was removed. Electron microscopy revealed the formation of a uniform microcrack network within the fiber.

[0025] After being lightly ground in a tumbler for 5 minutes, the resulting ultrafine fibers had a diameter distribution of 0.5-1.0 µm, an increase in specific surface area of ​​about 3 times, and a moisture regain of 16%. Referring to GB / T 14337-2008 "Test Method for Tensile Properties of Chemical Fibers Short Fibers", the fiber strength of Lyocell fibers before and after supercritical and tumbler friction treatment was tested using a single fiber strength tester. The strength retention rate reached 85% of that of untreated fibers.

[0026] Example 5 Lyocell fiber yarn was placed in a supercritical reactor and treated for 90 minutes at 60°C and 32 MPa supercritical CO2. The temperature was then raised to 150°C and held for 60 minutes. The pressure was then released instantaneously to atmospheric pressure within 30 seconds before the yarn was removed. Electron microscopy revealed a decrease in the uniformity of microcrack distribution within the fiber, with cracks only becoming more pronounced at the fiber edges. The cracks deepened, but their density decreased.

[0027] After being lightly ground in a roller friction mill for 8 minutes, the resulting ultrafine fibers had a diameter distribution of 0.5-0.8µm, an increase in specific surface area of ​​about 3.5 times, and a moisture regain of 18%. The fiber strength was tested using a single fiber strength tester in accordance with GB / T 14337-2008 "Test Method for Tensile Properties of Chemical Fibers Short Fibers". The strength retention rate was 80% of that of untreated fibers.

[0028] Comparative Example 1 (10s instantaneous pressure release) The only difference between this comparative example and Example 1 is that the decompression time is set to 10 seconds for instantaneous decompression; all other processes are exactly the same.

[0029] Comparative Example 2 (Traditional Chemical Method) The same Lyocell fabric was treated with a 10% NaOH solution at 95°C for 60 minutes. After treatment, the fabric strength decreased by 28%, the fiber surface was severely corroded but the splitting was uneven, and an internal network structure could not be formed.

[0030] Comparative Example 3 (Simple SC-CO2 treatment, without rapid decompression) The fibers were treated under the same SC-CO2 conditions, but without rapid depressurization; only a slow depressurization was performed. No obvious microcracks were observed after treatment, making effective fiber splitting impossible during subsequent mechanical finishing.

[0031] Comparative Example 4 (Simply Mechanical Method) Lyocell fabrics were subjected to only strong mechanical brushing treatment (without SC-CO2 pre-splitting). After treatment, the fabric surface showed increased hairiness, low and uneven fiber splitting, and a strength loss of up to 35%.

[0032] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation, characterized in that, Includes the following steps: Supercritical carbon dioxide infiltration: First, under certain temperature and pressure, the concentration difference of supercritical carbon dioxide inside and outside the fiber is used to promote the infiltration of supercritical carbon dioxide into the fiber. Then, the temperature is further increased and maintained for a period of time, so that the supercritical carbon dioxide in the fiber reaches a supersaturated state, achieving phase separation. Then, the pressure is rapidly released, causing the supercritical carbon dioxide dissolved inside the fiber to rapidly vaporize and expand due to the sudden drop in pressure. This causes microcracks and micropores to be generated in the cross section of the Lyocell fiber from the inside, forming a pre-split structure. Mechanical finishing: Next, the lyocell material treated with supercritical carbon dioxide is mechanically finished, and the fibers that have developed microcracks are completely split into ultrafine fiber bundles through physical action.

2. The method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation as described in claim 1, characterized in that, When supercritical carbon dioxide is introduced, the Lyocell material is placed in a high-pressure reactor, carbon dioxide is introduced, the temperature is raised to 50-70℃, and the pressure inside the reactor is raised to 28-32MPa, so that the carbon dioxide reaches the supercritical state.

3. The method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation as described in claim 2, characterized in that, Maintain the supercritical state for 90-120 minutes to allow supercritical CO2 to fully penetrate and swell the amorphous regions of the Lyocell fiber.

4. The method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation as described in claim 1, characterized in that, Rapid decompression time ≤ 60 seconds.

5. The method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation as described in claim 4, characterized in that, 30 seconds ≤ rapid decompression time ≤ 60 seconds.

6. The method for preparing lyocell ultrafine fibers based on supercritical carbon dioxide-induced fibrillation as described in claim 1, characterized in that, Mechanical finishing includes one or more of the following: hydroentangling, mechanical kneading, airflow impact treatment, or dynamic stirring treatment in an aqueous solution.

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