Preparation method for supercritical fluid foamed fiber, and foamed fiber prepared by preparation method

Abstract

A preparation method for a supercritical fluid (SCF) foamed fiber, and a foamed fiber prepared by the preparation method. The preparation method comprises a fiber preparation step, an SCF infiltration step, a foaming point formation step, and a viscous flow, plastic deformation and foaming step. The fiber finished product and the fiber product are allowed to be directly subjected to SCF foaming processing, and the obtained foamed fiber has controllable cell density, micro-nano scale and closed state, and has an improved thermal insulation effect, occlusion effect, net buoyancy, flame retardant effect, deep dyeing effect, and wearing comfort.

Description

Preparation method of supercritical fluid foamed fiber and foamed fiber prepared therefrom Technical Field

[0001] This invention relates to a method for preparing supercritical fluid foamed fibers and the foamed fibers prepared therefrom, belonging to the field of functional fiber processing and application. Background Technology

[0002] When materials contain air, they can provide functional effects such as lightweight, thermal insulation, increased buoyancy, and stiffness. Air bubbles within polymer materials can also terminate existing cracks, improving their strength. Cotton and kapok fibers in textiles have natural hollow structures; viscose fibers can be chemically foamed to form slub-like cavities; thermoplastic synthetic fibers such as polyester and nylon can be spun into one or more through-hole structures using shaped spinnerets or air-assisted composite spinning. The newly developed parallel composite elastic fibers containing cavities have generated significant profits for some well-known outdoor thermal clothing brands. However, the cavities of existing hollow fibers are concentrated in the core, with radial dimensions on the micrometer scale. This allows air to easily flow within the fibers, failing to achieve the insulation effect of still air. Especially for fibers with high hollowness (such as kapok), they are easily flattened and cracked during processing and use. Therefore, their warmth retention is insufficient for clothing in high-altitude, cold regions, particularly in extreme low-temperature environments like the Arctic, Antarctic, and space. Increasing clothing thickness and layers to improve warmth can be cumbersome, hindering physical function and motor skills. Hollow synthetic fibers with continuous channel-like cavities, being open at both ends, cannot form a closed air pocket structure, making it difficult to provide buoyancy to help drowning victims. Furthermore, ordinary hollow fibers only have two additional interfaces between air and polymer materials compared to solid fibers; the reflection of light passing through the fiber is not significantly increased, making it difficult to achieve a good light-blocking effect.

[0003] Therefore, forming a foam-like structure within the fiber, especially controlling the size of the foam units to the nanometer-micrometer scale, to create stationary air units, is an ideal structure for providing textiles with lightweight warmth, buoyancy, increased light-blocking effect, and improved dyeing depth. However, current technology cannot yet create foamed fibers with micro- and nano-scale pores during the spinning process.

[0004] Polymer materials such as plastics and rubber can be processed by adding chemical foaming agents that generate gas, or physical foaming agents that can vaporize due to phase change at appropriate temperatures and pressures, to create foamed plastics and rubber (or rubber-plastic composites) with foam sizes of tens of micrometers or larger. Applying supercritical fluid (SCF) to plastics / rubber using methods such as screw extrusion and mixing it uniformly and finely, then extruding it in a plasticized state and gradually expanding it under heat preservation conditions, can form micro-nano structured pores inside plastic / rubber parts.

[0005] However, when thermoplastic synthetic fibers are melt-spun, the spinning fluid is in a low melt viscosity state when it is extruded from the spinneret. In order to meet the stretching requirements and obtain the appropriate degree of orientation of the fiber and thus obtain sufficient strength, the spinning melt is in a state of easy flow and deformation, and the melt strength is also relatively low. When there are impurities (especially air bubbles) inside the fiber, it is easy to cause the melt to break down. In particular, when there are air bubbles with an expansion effect, it is easier to aggravate the expansion effect at the spinneret outlet, leading to melt breakage and causing a large amount of spinning melt to adhere to the surface of the spinneret, making the spinning process impossible.

[0006] Therefore, although supercritical fluid technology can be used in the plastics and rubber fields to make foam materials containing micro- and nano-pores from polymer materials, existing technologies have not yet been able to directly produce microporous foam fibers with micro- and nano-scale dimensions from thermoplastic polymer materials during the spinning process. Summary of the Invention

[0007] The present invention aims to address the current technical limitations of supercritical fluid foaming processing of thermoplastic synthetic fiber products, and provides a method for preparing supercritical fluid foamed fibers and the foamed fibers prepared therefrom.

[0008] To overcome the problems of excessively large hollow fiber dimensions, internal air flow leading to excessively high thermal conductivity, and insufficient thermal insulation performance of fiber assemblies, this invention employs supercritical fluid (SCF) to penetrate the interior of thermoplastic synthetic fibers, achieving miscibility with the fiber-forming polymer and reaching a certain content. By adjusting thermodynamic conditions, namely temperature and pressure, the supercritical fluid dissolved in the fibers undergoes phase separation, forming potential foaming points in the amorphous regions and other loosely structured parts within the fibers. Temperature is adjusted to allow the thermoplastic fibers to undergo moderate viscous flow plastic deformation. Pressure is adjusted to create an appropriate pressure difference between the inside and outside of the fiber, achieving foaming.

[0009] The number, size, and shape of cells appearing in the fiber can be controlled by controlling the amount of supercritical fluid dissolved and the foaming process (temperature, pressure, time, and the time curve of change), including whether the cells are closed cells, open cells, or partially open cells.

[0010] The penetration of SCF into the fiber is a relatively time-consuming process, and it is necessary to accelerate the penetration rate of SCF from the perspectives of thermodynamics and surface physicochemistry.

[0011] (1) From a thermodynamic point of view, select the conditions for forming high-density SCF: such as SCF having a higher density at a lower temperature, which can accelerate the SCF penetration rate under the condition that there is a large SCF density gradient inside and outside the fiber.

[0012] (2) By using pulsed pressure, the speed difference of pressure transmission forms a penetration pressure pulse inside and outside the fiber, thereby increasing the penetration speed of SCF;

[0013] (3) Special additives are used to adjust the overall polarity of SCF and additives on fiber-forming polymers, so that the polarity of solvent and solute is as consistent as possible, thereby increasing the dissolution rate of SCF on various fiber materials and facilitating the entry of SCF into the fiber interior.

[0014] This invention involves infiltrating supercritical fluid into the amorphous regions or pre-placed foaming points of thermoplastic synthetic fibers. Rapid pressure release at a temperature where the fiber can undergo flow deformation causes the supercritical fluid in the foaming points to expand, ultimately forming foamed fibers with numerous micro- and nano-scale pores. The resulting foamed fibers achieve low density, high buoyancy, high warmth retention, high visual opacity, and the ability to be dyed in dark colors.

[0015] First, a suitable working environment must be established for the supercritical fluid to penetrate and reach saturation solubility within the fiber, ensuring the highest possible solubility of the supercritical fluid inside the fiber. Once saturation is achieved, the temperature must be increased to disrupt the thermodynamic equilibrium of the fiber-forming polymer containing the supercritical fluid. This causes the supercritical fluid to separate from the homogeneous state dissolved in the fiber-forming polymer, resulting in SCF aggregation points and forming foaming and swelling centers. Another crucial function of this heating is to bring the fiber to a state where it can undergo plastic deformation, maximizing its plastic deformation capacity while preventing melting or adhesion. Then, after the formation of foaming and swelling centers, the pressure inside the high-pressure chamber must be rapidly released to reduce the SCF pressure, highlighting the SCF pressure difference between the inside and outside of the fiber. Under these plastic deformation temperature conditions and the SCF pressure difference, the fiber internally forms the required number and size distribution of micro / nanoscale cells, achieving the desired foam fiber density and, macroscopically, the insulation, buoyancy, visual masking, and enhanced dyeing depth effects of the textile made from the fiber.

[0016] Secondly, the foaming effect needs to be controlled. Due to differences in varieties, thermoplastic synthetic fibers have different chemical structures, resulting in different solubility of supercritical fluids within them; differences in aggregate structure lead to different sizes and numbers of amorphous regions that can accommodate supercritical fluids; and differences in material also lead to different plastic deformation capabilities. Therefore, conventional finished fibers such as polyester, nylon, polypropylene, and polylactic acid fibers often cannot achieve foaming effects directly through supercritical fluid processing. Processing aids (such as methanol, ethanol, butanol, polyethylene glycol, or triethanolamine) need to be applied during supercritical fluid processing to alter the accessibility of the infiltrated substances, or to change the deformability of the fiber-forming polymer and the feel of the fiber. Alternatively, blending modification can be performed during spinning by adding powder materials or porous materials with micro / nano structures to provide more effective air storage points and expansion centers for the fiber. Blending or copolymerization modification of the fiber-forming polymer can also improve the fiber's deformability or adjust its softening point. Depending on the specific type of fiber-forming polymer, the fiber specifications, pore size, and pore density of the porous fiber, the foaming effect of different fiber varieties can be controlled by selecting processing aids, blending and copolymer spinning, and forming corresponding supercritical fluid processes. After foaming, the fibers usually become coarser, which can make them feel stiff. The feel of the fibers can be adjusted by applying toughening agents to soften them.

[0017] Based on the above technical concepts, the present invention provides the following technical solution:

[0018] The first aspect of the present invention relates to a method for preparing supercritical fluid foamed fibers, the method comprising the following steps:

[0019] Step 1: Fiber preparation steps;

[0020] Step 2: Supercritical fluid infiltration step, in which supercritical fluid is infiltrated into the fiber to be foamed and reaches a certain content;

[0021] Step 3: Foaming point formation step, in which the temperature of the fiber is increased, so that the supercritical fluid that has penetrated into the fiber can achieve phase separation and form potential foaming points inside the fiber;

[0022] Step 4: Viscous flow plastic deformation and foaming step. In this step, the temperature is controlled to soften the fiber, generate plastic deformation ability, and reduce the pressure of the environment in which the fiber is located to form a pressure difference between the inside and outside of the fiber, so as to achieve foaming.

[0023] In a preferred embodiment of the present invention, the fiber in step 1 is a fiber form selected from short fibers, filaments, or a fiber aggregate form selected from yarns, fabrics, and wadding.

[0024] In a preferred embodiment of the present invention, the fiber in step 1 is a thermoplastic fiber, which is preferably selected from polyester (polyethylene terephthalate PET, polypropylene terephthalate PTT, polybutylene terephthalate PBT, polylactic acid PLA, polybutylene succinate PBS) fiber, polyamide (polyamide PA6, polyamide PA66, polyamide PA10, polyamide PA56) fiber, polyolefin (polyethylene PE, polypropylene PP, ultra-high molecular weight polyethylene UHMWPE) fiber, thermoplastic polyurethane elastomer TPU fiber, thermoplastic polyester elastomer TPEE fiber, polyvinyl alcohol PVA fiber, polyphenylene sulfide PPS fiber, and polyimide PI (thermoplastic polyamide-imide PAI and polyetherimide PEI) fiber, or any one or more of these fibers.

[0025] In a preferred embodiment of the present invention, the fiber in step 1 is a fiber modified with particulate matter, wherein the particulate matter is preferably selected from any one or more of aerogel powder, covalent organic framework materials (COFs), metal-organic framework materials (MOFs), molecular sieves, zeolites, matting agents, kaolin, ZrO2, ZrC, and inorganic flame retardants.

[0026] In a preferred embodiment of the present invention, the fiber in step 1 is a fiber obtained by blending and spinning two or more fiber-forming polymers with different molecular weights.

[0027] In a preferred embodiment of the present invention, the fiber in step 1 is a composite fiber made by combining two or more fiber-forming polymers with different foaming capabilities in a parallel compounding manner.

[0028] In a preferred embodiment of the present invention, step 1 includes: placing the fiber to be foamed in a material cart, and the entire material cart entering a vacuum drying device for drying, with drying conditions of 105-125°C for 15-25 min and vacuum degree of -0.11 to -0.14 MPa; preferably 110-120°C for 18-22 min and vacuum degree of -0.12 to 0.13 MPa.

[0029] In a preferred embodiment of the present invention, the supercritical fluid in step 2 is selected from CO2, N2, or a combination thereof.

[0030] In a preferred embodiment of the present invention, step 2 further introduces an auxiliary agent, which is selected from any one or more of methanol, ethanol, butanol, polyethylene glycol, and triethanolamine.

[0031] In a preferred embodiment of the present invention, step 2 includes:

[0032] Step 2-1: Feeding step, in which the fibers prepared in step 1 are fed into the high-pressure chamber;

[0033] Step 2-2: Sealing step, in which the inlet and outlet valves of the high-pressure chamber are closed;

[0034] Step 2-3: Supercritical fluid introduction step. In this step, supercritical fluid is pumped into the high-pressure chamber, starting from atmospheric pressure, and reaches the set supercritical fluid infiltration pressure P1 (8-30 MPa, preferably 12-28 MPa) within the initial time t0 (10-40 min, preferably 15-30 min). At the same time, the equipment temperature is increased so that the fiber also reaches the set supercritical fluid infiltration temperature T1 (40-80℃, preferably 50-70℃) within t0, and continues for a certain infiltration time t1 (20-100 min, preferably 30-80 min) to allow the supercritical fluid to penetrate into the fiber to be foamed and reach a certain content.

[0035] In a preferred embodiment of the present invention, step 3 includes:

[0036] Step 3-1: After the penetration time t1 is reached, a heating step for phase separation is started. In this step, the temperature is increased at a rate of 3 to 15 °C / min (preferably 5 to 10 °C / min). After a heating time t2 (10 to 50 min, preferably 15 to 35 min), the phase separation temperature T2 is reached. This phase separation temperature T2 is 20 to 45 °C lower than the fiber melting temperature (preferably 25 to 40 °C lower).

[0037] Step 3-2: Maintain the phase separation time t3 (20-100 min, preferably 30-80 min) at the phase separation temperature T2 to complete the phase separation and form potential foaming points inside the fiber.

[0038] In a preferred embodiment of the present invention, step 4 includes:

[0039] Step 4-1: Decompression step, in which the phase separation temperature T2 at the end of step 3-2 is maintained, and the pressure on the fiber is reduced to the foaming background low pressure P2 (0.3-3 MPa, preferably 0.5-1.2 MPa) over a decompression time t4 (1s-20min, preferably 10s-15min);

[0040] Step 4-2: The holding step, in which the foaming background low pressure P2 and phase separation temperature T2 at the end of step 4-1 are maintained for a foaming time t5 (20-80 min, preferably 30-60 min) to achieve foaming.

[0041] A second aspect of the invention relates to supercritical fluid foamed fibers obtained by the preparation method of the invention.

[0042] A third aspect of the invention relates to the use of the supercritical fluid foamed fibers of the invention in the processing of wadding, yarn, fabrics and garments.

[0043] The beneficial effects achieved by this invention are:

[0044] This invention allows for direct supercritical fluid foaming of finished fiber products, eliminating the problem of melt rupture caused by foaming during spinning, which prevents the spinning process from proceeding.

[0045] Compared with the original fibers that have not been processed by the method of this invention, the method of this invention can form a large number of micro- and nano-scale closed-cell and open-cell bubbles inside the fiber, resulting in foamed fibers with reduced density and increased thermal resistance, while also achieving lightweight and high heat insulation effects.

[0046] The method of this invention creates numerous micro- and nano-scale cavities within the fibers, storing still air that does not flow. This prevents the fibers from being flattened or cracked during processing and use. Furthermore, the still air imparts significant thermal insulation to the fibers and their aggregates. The fibers obtained by this method can be blended with other fiber materials to create more cost-effective products. This provides novel structural and functional thermal insulation materials for scientific activities such as lunar landings, space travel, and polar exploration, as well as for operations in cold and extremely cold regions and for general public winter insulation.

[0047] Ordinary textiles only have an interface between the overall fiber surface and the air, resulting in too few interfaces that can form light reflection. This leads to poor shading effect and exposure of underwear and body contours in ordinary thin fabrics. When light-colored, especially white, clothing gets wet, the interface between the fiber and air changes to that between the fiber and water. The difference in refractive index between the two is smaller, resulting in less light reflection loss, and thus the clothing loses its shading effect. This invention uses a foaming process to create a large number of micro- and nano-scale pores inside the fiber. In the dry state, there are a large number of interfaces between the air and fiber material, and the difference in refractive index between the two is large (air refractive index is about 1.0, and fiber refractive index is about 1.5), so it can maintain a good shading effect. Textiles made of foamed fibers retain their internal closed pores and prevent water from entering even after getting wet. Except for the surface refractive index changing from air refractive index 1.0 to water refractive index 1.33 at the water contact point, there are still a large number of interfaces between the air and fiber material inside, so it still maintains a good shading effect. Therefore, the foamed fibers of this invention can be used to manufacture textile fabrics such as swimsuits that provide good coverage and maintain good body covering even after the wearer falls into the water, or lightweight light-colored or white fabrics for summer.

[0048] Existing textiles, once submerged in water, cannot compensate for their own weight through water displacement, thus failing to generate net buoyancy and lacking rescue capability for those who fall into the water. The foamed fibers obtained by the method of this invention contain numerous closed-cell structures with air pockets, providing net buoyancy for those who fall into the water. Furthermore, the foamed fibers of this invention have a significantly lower density, providing greater buoyancy (e.g., for a 1kg garment, with a fiber density of 1.38g / cm³). 3 Reduced to 0.60 g / cm 3 At that time, the buoyancy increases by 0.78 kg, which can keep an unloaded human body basically floating.

[0049] If the method of this invention is used to perform supercritical carbon dioxide-based foaming processing on flame-retardant fibers such as acrylonitrile, polyphenylene sulfide (PPS), and flame-retardant modified PVA fibers (flame-retardant vinylon), on the one hand, the flame retardant powder can provide more effective gas storage points and expansion centers for the fibers, storing more CO2 gas inside the fibers to improve the heat preservation effect; on the other hand, the CO2 gas contained therein is conducive to the fibers achieving gas-phase flame retardancy, further improving the flame retardant performance, thereby achieving a synergistic effect with the original flame retardant mechanism.

[0050] Existing synthetic fiber textiles lack hydrophilic polar groups, making them difficult to absorb moisture and resulting in a stuffy feeling when sweating. Applying hydrophilic agents can temporarily improve hydrophilicity, but this effect is not durable. The foamed fibers obtained by the method of this invention form a large number of micro- and nano-scale closed-cell and open-cell bubbles inside. The open-cell bubbles can adsorb moisture through their surface action, improving the sweat absorption and hydrophilicity effect and wearing comfort.

[0051] The foamed fiber obtained by the method of the present invention has a large number of micro- and nano-scale pores inside, which increases the specific surface area of ​​the fiber and can significantly improve the dyeing depth and fastness at the same time.

[0052] The effects of this invention are not limited to those described above. It should be understood that the effects of this invention include all effects that can be inferred from the description of this invention. Attached Figure Description

[0053] 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:

[0054] Figure 1 shows a process flow diagram of the method for preparing SCF foamed fiber of the present invention;

[0055] Figure 2 shows an electron microscope image of the foamed fibers obtained according to Example 1 of the present invention;

[0056] Figure 3 shows an electron microscope image of the foamed fibers obtained according to Example 2 of the present invention;

[0057] Figure 4 shows an electron microscope image of the foamed fibers obtained according to Example 3 of the present invention;

[0058] Figure 5 shows an electron microscope image of the foamed fibers obtained according to Example 4 of the present invention;

[0059] Figure 6 shows an electron microscope image of the foamed fibers obtained according to Example 5 of the present invention;

[0060] Figure 7 shows an electron microscope image of the foamed fibers obtained according to Example 6 of the present invention;

[0061] Figure 8 shows an electron microscope image of the foamed fibers obtained according to Example 7 of the present invention;

[0062] Figure 9 shows an electron microscope image of the foamed fibers obtained according to Example 8 of the present invention;

[0063] Figure 10 shows an electron microscope image of the foamed fibers obtained according to Example 9 of the present invention;

[0064] Figure 11 shows the changes in the thermal conductivity of single fibers of different materials before and after SCF foaming;

[0065] Figure 12 shows the changes in fiber dyeing effect under different degrees of foaming.

[0066] It is understood that the accompanying drawings are not necessarily drawn to scale, and show, to some extent, simplified representations of various features illustrating the basic principles of the invention. Specific design features of the invention disclosed herein (including, for example, specific dimensions, orientations, positions, and shapes) will be determined in part by the specific intended application and environment of use.

[0067] In the accompanying drawings, reference numerals throughout the various figures refer to the same or equivalent parts of the invention. Detailed Implementation

[0068] Various embodiments of the invention will now be described in detail, examples of which are shown in the accompanying drawings and described below. Although the invention will be described in conjunction with exemplary embodiments thereof, it should be understood that this specification is not intended to limit the invention to these exemplary embodiments. Rather, the invention is intended to cover not only the exemplary embodiments thereof, but also various alternatives, modifications, equivalents, and other embodiments that may be included within the spirit and scope of the invention as defined by the appended claims.

[0069] Throughout the accompanying drawings, the same reference numerals will refer to the same or similar components. For clarity, the dimensions of the structures are depicted as larger than their actual dimensions. It should be understood that although terms such as "first" and "second" may be used herein to describe the various components, these components are not limited by these terms. These terms are used only to distinguish one component from another. For example, a "first" component discussed below may be referred to as a "second" component without departing from the scope of the invention. Similarly, a "second" component may also be referred to as a "first" component. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise.

[0070] It will also be understood that, when used in this specification, the terms “comprising,” “including,” “having,” etc., indicate the presence of the stated features, values, steps, operations, elements, components, or combinations thereof, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, or combinations thereof.

[0071] Unless otherwise stated, all figures, numerical values, and / or expressions used herein to represent the amounts of components, reaction conditions, polymer compositions, and mixtures should be considered approximations that include various uncertainties (particularly those inherent in obtaining these values ​​and affecting the measurements), and are therefore to be understood as being modified in all cases by the term "about". Furthermore, when numerical ranges are disclosed in this specification, unless otherwise stated, the range is continuous and includes all values ​​from the minimum to the maximum of the range. Additionally, when such ranges involve integer values, unless otherwise stated, all integers from the minimum to the maximum value will be included.

[0072] Any numerical interval represented by the expression "a~b" represents the range of values ​​extending from "a" to "b" (i.e., including the strict limits a and b), while any numerical interval represented by the expression "greater than a and less than b" represents the range of values ​​greater than "a" and less than "b" (i.e., excluding the limits a and b).

[0073] The supercritical fluid foaming process of this invention includes the configuration of temperature, pressure, and time, the setting of the depressurization rate, the fiber loading amount, and the temperature uniformity of the fibers (including temperature changes caused by jet cooling), etc. The implementation of this process also requires equipment with corresponding functions. The following will describe each step of the method of this invention in detail.

[0074] As shown in Figure 1, the method of the present invention includes: ① fiber preparation step; ② supercritical fluid infiltration step; ③ foaming point formation step; ④ viscous flow plastic deformation and foaming step.

[0075] Step 1: Fiber Preparation Steps

[0076] In this step, the fibers to be foamed are prepared. The fibers can be in fiber form or fabric form. Regarding the choice of fiber type, all thermoplastic synthetic fibers can be foamed under supercritical fluid (SCF), including but not limited to polyester fibers (polyethylene terephthalate PET, polypropylene terephthalate PTT, polybutylene terephthalate PBT, polylactic acid PLA, polybutylene succinate PBS, etc.), polyamide fibers (polyamide PA6, polyamide PA66, polyamide PA10, polyamide PA56, etc.), polyolefin fibers (polyethylene PE, polypropylene PP, ultra-high molecular weight polyethylene UHMWPE, etc.), and thermoplastic elastic fibers such as thermoplastic polyurethane elastomer (TPU) and thermoplastic polyester elastomer (TPEE). Among these, fibers with lower melting points, such as PLA, PE, and PP, are easier to foam under supercritical fluid conditions at lower temperatures. Thermoplastic fibers with low melt viscosity and high melt strength are also more likely to form foam.

[0077] Supercritical fluids can only exist in the non-crystalline region of fibers. Therefore, when the fiber crystallinity is low, supercritical fluids can easily penetrate into the amorphous region. After phase separation, pressure centers are established, resulting in a higher foaming ratio and giving the fiber a lower density.

[0078] To address the technical problem that when ordinary thermoplastic fibers are foamed using supercritical fluids, foaming only occurs in extremely small amorphous regions or loosely structured localized areas, affecting the distribution of foaming locations, cell density, and cell shape, ultimately impacting the thermal insulation performance and buoyancy of the foamed fibers after they fall into water, this invention utilizes fibers obtained through blending and spinning of particles with a diameter of less than 0.5 micrometers. By incorporating microparticles, especially those with microporous structures, into the fiber-forming polymer, SCF can be stored within the particles or at the interface between the particles and the fiber-forming polymer, establishing more foaming points and increasing the foaming ratio.

[0079] The particulate matter can be selected from substances containing micropores, such as SiO2 aerogel powder, covalent organic framework materials (COFs), metal-organic framework materials (MOFs), molecular sieves, and zeolites; as well as conventional additives without significant porous structures, such as matting agents TiO2, kaolin, ZrO2, ZrC, and inorganic flame retardants. When these particulate matter is mixed with fiber-forming polymers, a loose structure remains at the interface. These micropores or loose structures appearing inside and at the boundaries of the additives can serve as storage points after phase separation of the supercritical fluid, becoming foaming points, and will generate bubbles at specific locations under appropriate temperature and pressure conditions. By selecting the types and quantities of additives and combining them with the foaming process, the desired foaming effect can be achieved.

[0080] In addition, the rational co-melting of multiple fiber-forming polymers can also reduce the crystallinity of the fiber and increase the foaming ratio. Blending and spinning two or more fiber-forming polymers with different molecular weights can improve the fiber's ability to undergo localized plastic deformation, making it easier to form a foam structure. Blending and spinning bimodal polymers of the same material but with different molecular weights can utilize the characteristic that lower molecular weight polymers easily achieve lower flow viscosity, thus appropriately increasing cell size and optimizing spinnability.

[0081] The fibers of this invention can be made by combining two or more polymeric materials with different foaming capabilities in a parallel composite manner, such as PET / PTT parallel composite fibers, PET / PBT parallel composite fibers, and COPET / PET parallel composite fibers. Due to the different foaming capabilities of the materials on both sides, the composite fibers can amplify the morphological differences between the two sides of the structural fibers, producing a more pronounced three-dimensional curved fiber appearance and improving the thermal resistance and compressive elasticity of the fiber assembly. Addressing the technical challenge of PET / PTT parallel composite elastic fibers being difficult to comb, and even more difficult to comb after foaming, thus failing to achieve their high elasticity, this invention proposes pre-combing PET / PTT parallel composite elastic fibers with PTT short fibers, distributing the PET / PTT parallel composite elastic fibers among the PTT fibers. Furthermore, both the PTT fibers and the PTT component in the parallel composite elastic fibers can be foamed, resulting in more significant crimping and better compressive elasticity of the elastic fibers after foaming.

[0082] Synthetic fibers such as polyester, which are prone to hydrolysis under high temperatures and moisture content, are susceptible to hydrolysis during SCF foaming, leading to a reduction in molecular weight and significant damage to fiber strength. Therefore, drying is necessary before foaming. Specifically, the fibers loaded into a cart are placed into a vacuum drying equipment and dried at 105–125°C for 15–25 minutes under a vacuum of -0.11–-0.14 MPa (preferably 110–120°C for 18–22 minutes under a vacuum of -0.12–-0.13 MPa) until the fiber moisture content is less than [a certain value is missing]. After that, the fiber preparation work is completed. The fiber or finished product can be loaded into the high-pressure chamber by the material cart and put into the chamber for SCF foaming processing.

[0083] Step 2: Supercritical fluid infiltration step

[0084] The supercritical fluid used in this invention can be selected from CO2, N2, or a combination thereof.

[0085] When a large amount of supercritical fluid is dissolved inside the fiber, dense gas storage points are easily formed within the fiber, and a sufficiently large pressure difference may be created inside and outside the fiber, facilitating fiber foaming. According to the thermodynamic theory of supercritical fluids, the density of supercritical fluids is related to temperature and pressure, and the main driving force for SCF penetration into the fiber is the SCF concentration difference inside and outside the fiber, i.e., the density difference of the supercritical fluid. Therefore, to increase the SCF density in the processing environment, the highest possible pressure and the lowest possible temperature after exceeding the critical point should be selected. Obviously, performing supercritical fluid penetration processing at a lower temperature can also reduce operating costs. Secondly, adding periodically varying pressure pulses to the selected working pressure can assist SCF penetration into the fiber. Furthermore, using special additives (such as methanol, ethanol, and polyethylene glycol) to adjust the compatibility of SCF with the fiber-forming polymer can also increase the mutual solubility rate of SCF in the fiber material, facilitating SCF entry into the fiber interior.

[0086] Depending on the type of fiber and the final foaming requirements, the supercritical fluid needs to reach a saturated dissolution state inside the fiber within a suitable infiltration time to allow sufficient supercritical fluid to infiltrate.

[0087] To improve the penetration rate of SCF and reduce the required penetration time t1, a double-acting plunger pump can be used to apply a pulse pressure wave of ±(0.5~3.0)MPa with a pulse period of 2~8min (preferably 1.0~2.5MPa with a pulse period of 3~5min), which can shorten the penetration time by 15~35%. Adding special processing aids (such as methanol, ethanol, polyvinyl alcohol, etc.) that adjust the compatibility between SCF and fiber-forming polymers when pumping CO2 fluid into the high-pressure chamber can also accelerate the penetration process of SCF.

[0088] Step 3: The phase separation process of SCF, i.e., the formation of the foaming point.

[0089] The supercritical fluid penetrating the fiber is uniformly distributed in the amorphous region of the fiber and the interior and periphery of the blended particles in a homogeneous structure. However, it cannot form pressure centers for bubble formation. Therefore, it is necessary to change the thermodynamic state to achieve phase separation of the supercritical fluid penetrating the fiber and form foaming points. Changing the thermodynamic state can be achieved by altering the pressure or temperature. However, since the aforementioned supercritical fluid penetration process takes place at a relatively low temperature, and subsequent foaming requires the fiber temperature to reach a high enough level to achieve plastic deformation—at least reaching the softening point of the fiber material—raising the temperature is adopted. This allows for phase separation and the formation of foaming centers while simultaneously bringing the fiber to the high temperature required for plastic deformation.

[0090] In the foaming point formation step, the temperature is increased at a rate of 3–15°C / min (preferably 5–10°C / min) to reach a phase separation temperature T2 that is 20–45°C (preferably 25–40°C) lower than the fiber melting temperature. This allows the SCF dissolved in the fiber to undergo phase separation, forming dispersed pressure centers. Since sufficient phase separation requires a relatively long time, a phase separation time t3 of 20–100 min (preferably 30–80 min) is needed. The length of this phase separation time t3 can affect the size of the foamed fiber pores.

[0091] To ensure uniform temperature throughout the fibers within the high-pressure chamber, SCF is controlled by flow channels and flows through all parts of the fibers. Furthermore, the heating process causes an increase in SCF pressure within the system; therefore, the equipment's pressure control system diverts a portion of the SCF to a storage tank to ensure that the pressure within the high-pressure chamber containing the fibers remains within the process requirements and the equipment's tolerance range.

[0092] Step 4: Viscous Flow Plastic Deformation and Foaming Steps

[0093] As mentioned earlier, in step 3, the fiber temperature is increased to the phase separation temperature T2, causing the SCF that has penetrated the fiber to separate and form potential foaming points inside the fiber. The high temperature applied to the fiber keeps its temperature above the softening point but below the melting temperature, thus placing it in a suitable state where it can undergo plastic deformation. After the high-pressure chamber is depressurized and the pressure reaches the depressurization pressure P2, the fiber remains at the original phase separation temperature (i.e., foaming temperature) T2. The various pressure accumulation points formed by the SCF inside the fiber push outward to undergo plastic deformation, achieving microporous foaming. This ensures that the fiber surface does not stick together or melt bond, so as not to damage the fiber's textile processing properties.

[0094] Example

[0095] Table 1 below shows the materials and process parameters used in each embodiment.

[0096] Example 1

[0097] 1.33dtex×38mm fully dull PET fibers produced by Yizheng Chemical Fiber Co., Ltd. were loaded into a trolley and vacuum dried at 115℃ / 20min / -0.12MPa before entering a high-pressure chamber for SCF-CO2 foaming. Anhydrous ethanol, a processing aid to facilitate SCF penetration, was added to the SCF at 3% of the fiber mass and entered the high-pressure chamber with the SCF. Within the initial time t0 = 20min, the pressure was increased from room temperature and pressure to penetration pressure P1 and penetration temperature T1 (28MPa and 45℃), and pressure pulses of ±1.5MPa were applied every 3min. The penetration time was maintained at t1 = 40min to ensure that the SCF fully penetrated into the fiber. Then, within a heating time t2 = 30 min, the temperature is raised to the phase separation temperature T2 = 230℃, while maintaining the infiltration pressure P1 constant and the phase separation time t3 = 30 min. This allows the SCF, which has infiltrated the fiber and is miscible with the fiber-forming polymer, to achieve phase separation. The SCF fluid then transfers to the amorphous region of the fiber and the loosely structured area at the interface between the matting agent TiO2 and the polymer, forming gas storage points. Next, a 12-inch quick-opening valve is opened, and within a pressure release time t4 = 10 s, the fiber is rapidly transported to a low-pressure chamber with a volume 45 times that of the high-pressure chamber, a foaming background low pressure P2 of 0.68 MPa, and a temperature that is the same as the pressure chamber. The fiber gas storage points begin to form bubbles due to the internal and external pressure difference. Because the fiber-forming polymer deforms relatively slowly at temperatures where adhesion has not occurred, a foaming time of 30 min t5 is required to form the bubbles shown in Figure 2. The density of the foamed PET fiber is reduced to 0.83 g / cm³. 3 The thermal conductivity of the single fiber decreased to 66.9% of that of the original fiber, and its strength decreased by 14.1% compared to the original fiber, but it still maintained good textile processing performance. This foamed PET fiber and modal fiber were spun and woven into knitted fabric by Qingdao Jifa Group Co., Ltd. in a 50 / 50 ratio. Compared with cotton fabric of the same square meter weight, the thermal resistance increased by 43.4% (refer to Table 2), demonstrating the significant thermal insulation performance of the foamed fiber and the outstanding warmth retention effect after being made into knitted fabric. The characteristics of this embodiment are sufficient SCF penetration, ample air storage, and appropriate decompression time, resulting in high cell density and slightly irregular cell shape without open-cell formation. The SCF foamed fiber exhibits good warmth retention, pressure resistance, and buoyancy generation.

[0098] Example 2

[0099] Based on Example 1, 1.33dtex×38mm fully dull PET fiber produced by Yizheng Chemical Fiber Co., Ltd. was still used for foaming. During the SCF-CO2 infiltration stage, no processing aid ethanol was applied, and no pressure pulse was added. Within the initial time t0 = 20 min, the infiltration pressure P1 and infiltration temperature T1 were adjusted to 20 MPa and 70℃, which are slightly weaker infiltration capacity, and after a 40 min infiltration time t1 and a 30 min heating time t2, the phase separation state was entered. The process of the SCF phase separation stage was 230℃ / 20 MPa / 30 min, but during the depressurization stage, the depressurization time t4 was extended to 10 min, and a 12-inch diameter quick-opening valve was still used to transport the high-pressure fluid and fiber to a low-pressure chamber with a volume 45 times that of the high-pressure chamber, a foaming background low pressure P2 of 0.68 MPa, and a temperature that had been reached. Under the action of the internal and external pressure difference, the fiber gas storage points formed the cells shown in Figure 3 after a 30 min foaming time t5. Under process conditions that reduce SCF infiltration and moderate expansion, the resulting foamed fiber has small pore size (average approximately 100 nm) and round pores. The fiber density is 1.03 g / cm³. 3 The strength loss is 6.1%. Due to the small cell size, its thermal insulation performance is significantly improved. This process is suitable for processing foamed fibers with low inherent strength but requiring spinning and high-strength napping processes, ensuring processability while obtaining good thermal insulation performance.

[0100] Example 3

[0101] Based on Example 1, no processing aid ethanol or pressure pulse is applied during the SCF infiltration stage. The infiltration pressure P1 and infiltration temperature T1 remain at 28 MPa / 45°C with a 20-minute initial infiltration time t0, but the infiltration time t1 is halved to 20 minutes to reduce the infiltration volume. The phase separation temperature T2 = 230°C is reached via a 30-minute heating time t2, while the pressure remains constant at the infiltration pressure P1 = 28 MPa, but the phase separation time t3 is shortened to 20 minutes. The pressure release time t4 is shortened to 1 second, and two 4-inch diameter quick-opening valves are used for simultaneous pressure release. Temperature compensation is activated to ensure that the fiber does not deviate from its rheological state due to jet cooling. The low-pressure chamber volume remains 45 times that of the high-pressure chamber, but due to the change in pipeline volume, the final foaming background low pressure P2 is 0.64 MPa, and the foaming time t5 remains 30 minutes. The resulting fibers (as shown in Figure 4) exhibited a lower SCF infiltration rate compared to Example 1. However, due to the extremely rapid pressure release, a high proportion of laterally open channels were observed at the fiber edges in the cross-section. Furthermore, due to insufficient SCF infiltration, small and dense gaps existed between the fibrils within the fiber cross-section, resulting in a fibrillation state not typically found in synthetic fibers. This also led to a decrease in fiber density, with a measured density of 1.12 g / cm³. 3The fiber strength loss was 7.6%. Due to the presence of open cells, the equilibrium moisture regain of PET fiber increased from 0.4% to 1.04%, significantly improving the comfort of PET fiber.

[0102] Example 4

[0103] 1.67 dtex × 38 mm far-infrared polyester fiber from Taiji Stone (Shanghai) Technology Co., Ltd. was vacuum dried at 110℃ / 25 min / -0.14 MPa and then placed in a high-pressure chamber for SCF-N2 foaming. Methanol and butanol (1.5% by weight of fiber) were added to the SCF as processing aids (methanol and butanol were fully recovered in the SCF separation unit, with no leakage or contamination). The pressure was increased from room temperature and pressure to penetration pressure P1 and penetration temperature T1 (24 MPa and 55℃) within the initial time t0 = 26 min; the penetration time t1 = 40 min was maintained to allow the SCF to penetrate into the fiber; then, the temperature was increased to the phase separation temperature T2 = 232℃ and the pressure... Maintaining a constant infiltration pressure P1, the SCF that has infiltrated and become miscible with the fiber-forming polymer undergoes phase separation. This phase separation is maintained for t3 = 45 min, allowing the SCF fluid to transfer to the amorphous region of the fiber and the loosely structured interface between the far-infrared powder ZrO2 and the polymer, forming gas storage points. Then, within a depressurization time t4 = 4 min, the high-pressure fluid is released into a low-pressure chamber (30 times the volume of the high-pressure chamber), leaving the fiber in the high-pressure chamber where the pressure has been reduced to 1.2 MPa. The foaming time is maintained for t5 = 50 min. The resulting fiber cross-section is shown in Figure 5. It can be seen that although SCF-N2 has lower permeation and expansion capabilities than SCF-CO2, by applying appropriate processing aids, providing a longer phase separation time, and employing a relatively slow depressurization method and a relatively long foaming time, a relatively uniform cell diameter can be ensured, and all cells are closed-cell structures. The measured density of the obtained foamed fiber is 0.97 g / cm³. 3 The thermal conductivity of the single fiber decreased by 64.5% compared to the unfoamed virgin fiber; the strength decreased by 11.1% compared to the virgin fiber. This product, consisting of 40% foamed PET fiber, 20% 1.33dtex×38mm foamed PET fiber and 20% 5.5dtex×64mm foamed PET fiber obtained through a similar process, and 20% hot-melt bonded fiber, was blended with these fibers to produce a chemical fiber wadding sheet by Yuyue Home Textiles Co., Ltd. Due to the low thermal conductivity of the SCF foamed fiber and the high radiative heat effect of the ZrO2 contained in the fiber, the thermal resistance of the wadding sheet, calculated on the same square meter weight, was increased by 148.0% compared to chemical fiber wadding sheets obtained from conventional PET under a similar formulation (Table 3).

[0104] Example 5

[0105] 1.67dtex×38mm ordinary PLA fibers produced by Anhui Fengyuan Bio-fiber Co., Ltd. are directly fed into a high-pressure chamber for SCF-CO2 foaming. Within an initial time t0 = 15 minutes, the pressure rises from room temperature and atmospheric pressure to an infiltration pressure P1 = 14MPa and an infiltration temperature T1 = 65℃, and the infiltration time is maintained at t1 = 50 minutes, allowing SCF to penetrate into the interior of the PLA fibers. Then, within a heating time t2 = 15 min, the temperature is raised to the phase separation temperature T2 = 116℃, while the pressure remains constant at the infiltration pressure P1. This phase separation is continued for a period t3 = 40 min, allowing the SCF, which has infiltrated the fiber and is miscible with the fiber-forming polymer, to undergo phase separation. This allows the SCF fluid to transfer to the amorphous region of the fiber, forming gas storage points. Because PLA has low flow viscosity and low melt strength, a slower depressurization rate is used. Within a depressurization time t4 = 5.5 min, the fluid from the high-pressure chamber is transferred to a low-pressure chamber with a volume 35 times that of the high-pressure chamber. The pressure in the high-pressure chamber decreases uniformly to the foaming background low pressure P2 = 1.2 MPa, subjecting the fiber gas storage points to a gradually increasing internal and external pressure difference, slowly generating bubbles. Foaming is completed within a foaming time t5 = 60 min. The resulting foamed PLA fiber (as shown in Figure 6) exhibits numerous bubbles with a diameter less than 100 nm in the cross-section, and bubbles can also be seen beneath the fiber surface in the longitudinal direction of the fiber. The density of foamed PLA fibers was reduced to 1.08 g / cm³. 3 The thermal conductivity of the single fiber decreased to 55.1% of that of the original fiber (Figure 11), and its strength decreased by 12.3% compared to the original fiber, yet it still maintained normal textile processing performance. The wadding made of 60% foamed PLA fiber, 20% ordinary hollow polyester, and 20% bonded fiber, compared to ordinary chemical fiber wadding of the same weight per square meter produced by Yuyue Home Textiles Co., Ltd., showed a 33.4% increase in thermal resistance (Table 3), indicating that SCF foamed fiber can significantly improve the warmth retention of wadding and other textiles.

[0106] Example 6

[0107] Ningbo Dafeng New Materials Co., Ltd. produces 2.2 dtex × 51 mm blended flame-retardant PET fibers, which are vacuum dried at 110℃ / 25 min / -0.14 MPa and then foamed with SCF-CO2 in a high-pressure chamber. Because the blended flame-retardant fiber has a relatively loose structure, processing aids and pressure pulses are not required for effective SCF infiltration. Within an initial time t0 = 30 min, the temperature and pressure rise from room temperature and pressure to an infiltration temperature T1 = 70℃ and an infiltration pressure P1 = 18 MPa. After an infiltration time t1 = 35 min, sufficient SCF infiltrates the fiber. Then, within a heating time t2 = 30 min, the temperature is raised to the phase separation temperature T2 = 204℃, while the pressure remains constant at the infiltration pressure P1. This phase separation is continued for a period t3 = 30 min, allowing the SCF, which has infiltrated the fiber and is miscible with the fiber-forming polymer, to undergo phase separation. This allows the SCF fluid to transfer to the amorphous region of the fiber and the loosely structured areas of the flame retardant particles within the fiber-forming polymer, forming gas storage points. Then, within a depressurization time t4 = 12 s, the fiber is rapidly transported to a low-pressure chamber (45 times the volume of the high-pressure chamber, already at the same temperature) (the low-pressure P2 in the foaming background is 0.71 MPa), and foaming begins. After a foaming time t5 = 40 min, the cells shown in Figure 7 are formed. Because the blended flame-retardant PET fiber easily infiltrates the SCF and forms large gas storage points near the flame retardant particles, and because the flame-retardant polyester has a low melt temperature and low flow viscosity, a large expansion force is generated within a short 12 s depressurization time. Therefore, large-sized and irregularly shaped pores appear on the fiber cross-section. However, the transversely flattened pore shape is related to the pressure applied to the sample during slicing. The density of the foamed flame-retardant PET fiber is reduced to 0.91 g / cm³. 3 The strength decreased by 17.3% compared to the original fiber, which still meets the requirements for textile processing. Flame-retardant PET samples and foamed flame-retardant PET fibers were prepared into fiber bundles of 0.5g each, 15cm long, bound with 0.7mm diameter fine iron wire at 1cm intervals. The limiting oxygen indices (LOIs) were measured to be 27.7% and 29.6%, respectively. Using the same method, the limiting oxygen indices (LOIs) of ordinary polyester fiber and foamed polyester fiber were measured to be 19.5% and 22.4%, respectively. This indicates that CO2 gas applied inside the fiber promotes the flame-retardant effect for both flame-retardant PET and ordinary PET.

[0108] Example 7

[0109] The 111dtex / 72f polyester DTY filament containing 0.5% covalent organic framework material (COFs), developed by Suzhou Baolidi Materials Technology Co., Ltd., was processed using a loose winding method to achieve a filament winding density of 0.41 g / cm³. 3Metal cylindrical tubes are densely packed in a trolley equipped with a tube rack and dried under vacuum at 115℃ / 20min / -0.12Mpa before entering a high-pressure chamber for SCF-CO2 foaming. Due to the blending and addition of COFs, SCF can easily penetrate into the fiber interior, so there is no need to apply processing aids such as ethanol to promote penetration, nor is it necessary to apply pressure pulses. The high-pressure chamber rises directly from room temperature and pressure to an infiltration pressure of 12 MPa and an infiltration temperature of 65°C over an initial time of t0 = 25 min, and maintains this infiltration time for t1 = 25 min to allow SCF to infiltrate into the COF-containing PET filaments. Then, after a heating time of t2 = 34 min, the temperature is raised to the phase separation temperature of 228°C, while the pressure remains constant at the infiltration pressure. During the phase separation time of t3 = 38 min, the SCF, which has infiltrated the fiber and is miscible with the fiber-forming polymer, undergoes phase separation, allowing the SCF fluid to transfer to the amorphous region of the fiber and the micropores inside the COFs, forming gas storage points. Then, within a depressurization time of t4 = 25 s, the high-pressure fluid is discharged into a low-pressure chamber with a volume 40 times that of the high-pressure chamber and has reached the same temperature (low pressure P2 = 0.64 MPa in the foaming background). The gas storage points in the fiber begin to generate bubbles under the influence of the internal and external pressure difference, and foaming is completed after a foaming time of 40 min t5. Because COFs have a large gas storage space, while the gas content stored in the amorphous region is relatively small, the resulting cell size is not very uniform (as shown in Figure 8). The density of the foamed PET filaments obtained in this way is 0.91 g / cm³. 3 The fleece woven by Shanghai Jialinjie Textile Technology Co., Ltd. has a thermal resistance that is 38.0% higher than that of ordinary polyester fleece of the same structure and specifications, and is also fluffy and soft to the touch.

[0110] Example 8

[0111] 1.56dtex×51mm fully dull PET fibers produced by Yizheng Chemical Fiber Co., Ltd. were loaded into a trolley and vacuum dried at 113℃ / 25min / -0.14MPa before entering a high-pressure chamber for SCF-CO2 foaming. Anhydrous ethanol, a processing aid to facilitate SCF penetration, was added to the SCF at 4% of the fiber mass and simultaneously introduced into the high-pressure chamber. Within the initial time t0 = 28min, the pressure increased from room temperature and atmospheric pressure to penetration pressure P1 = 25MPa and penetration temperature T1 = 48℃. On this basis, pressure pulses of ±1.5MPa were applied every 2.5min. The penetration time was maintained at t1 = 45min to ensure that the SCF fully penetrated into the fiber. Then, within a heating time t2 = 32 min, the temperature is raised to the phase separation temperature T2 = 232℃, while maintaining the infiltration pressure P1 constant, and the phase separation time t3 = 32 min is maintained. This allows the SCF, which has infiltrated the fiber and is miscible with the fiber-forming polymer, to achieve phase separation. The SCF fluid then transfers to the amorphous region of the fiber and the loosely structured area at the interface between the matting agent TiO2 and the polymer, forming gas storage points. Next, within a depressurization time t4 = 14 min, the high-pressure fluid is released into a low-pressure chamber (45 times the volume of the high-pressure chamber, already at the same temperature) (the low-pressure P2 in the foaming background is 0.71 MPa). The fiber remains in the high-pressure chamber, and the gas storage points in the fiber begin to expand and foam under the influence of the internal and external pressure difference. After a foaming time t5 of 30 min, the cells shown in Figure 9 are formed. The density of the foamed PET fiber decreases to 0.60 g / cm³. 3 It can be calculated that using 1kg of this foam fiber can provide 0.78kg of net buoyancy, which can keep an unloaded human body basically floating, thus preventing drowning. In addition, the high heat retention effect of the foam fiber can also delay the drop in body temperature of a person who falls into the water.

[0112] Example 9

[0113] 2.6 dtex × 64 mm cationic polyester produced by Jiangsu Jiangnan High Fiber Co., Ltd. was processed into polyester strips and then fed into a high-pressure chamber in the form of fiber balls for direct foaming using SCF-CO2. After an initial time t0 = 18 minutes, the high-pressure chamber temperature reached the infiltration temperature T1 = 60℃ and the infiltration pressure P1 = 20 MPa. After an infiltration time t1 = 22 minutes, SCF was infiltrated into the cationic modified polyester fibers. Then, after a heating time t2 = 18 minutes, the temperature reached the phase separation temperature T2 = 218℃, while the pressure remained constant at the infiltration pressure P1. After a phase separation time t3 = 50 minutes, the SCF infiltrated into the fibers was dispersed in the amorphous regions of the fibers. Although the cationic modified polyester does not have the large gas storage points of blended particles, especially those with porous structures, the copolymerization modification of the cationic modified polyester also increases its amorphous regions, resulting in a higher density of gas storage points after phase separation. After a decompression time of t4 = 12 min, the fluid in the high-pressure chamber slowly decompresses into the low-pressure chamber, which has a volume 30 times that of the high-pressure chamber. Foaming then occurs under a low background pressure of P2 = 0.61 MPa (i.e., foaming time t5 = 40 min). Under this gentle expansion, numerous tiny gaps are created, as shown in Figure 10. This allows for good strength retention (strength loss of 8.9%). When light passes through the fibers, numerous interfaces are generated, leading to an increase in the proportion of reflected light. Shanghai Jialinjie Textile Technology Co., Ltd. blended this foamed fiber strip with 90-count mercerized wool strips in a 60 / 40 polyester / wool ratio to create a high-density variable-weight jersey fabric weighing 155 g per square meter, used to make white T-shirts. Compared to knitted fabrics made from the same material using ordinary cationic polyester, this SCF-containing foamed fiber knitted fabric exhibits a one-level improvement in visual shading performance.

[0114] Example 10

[0115] The yarn, a 32s ordinary ring-spun yarn blended from 65% ordinary polyester and 35% viscose fiber produced by Shandong Hongye Textile Co., Ltd., was loosely wound at Zhejiang Sanyuan Textile Co., Ltd., and produced with a yarn packing density of 0.44 g / cm³ by cross-winding on metal bobbins. 3The material is loosely packaged and then foamed in a high-pressure chamber using a 50 / 50 mixture of CO2 and N2. Since the primary purpose of this process is not insulation, but rather to address the pilling issues of traditional polyester-viscose fabrics and the harsh conditions that damage viscose fibers when dyeing polyester with disperse dyes, the SCF foaming process for this product employs the gentlest possible processing conditions. The initial time t0 is set to 26 min, the high-pressure chamber infiltration temperature T1 to 45℃, and the infiltration pressure P1 = 12 MPa. After an infiltration time of t1 = 34 min, the phase separation temperature T2 is raised to 216℃ within a heating time of t2 = 18 min (pressure P1 remains constant). The foaming point is formed after a phase separation time of t3 = 45 min. Then, the fluid in the high-pressure chamber is released into a low-pressure chamber with a volume 45 times that of the high-pressure chamber at a relatively slow depressurization time of t4 = 2 min. The resulting low-pressure background P2 is 0.71 MPa. After a foaming time of 30 minutes (t5), a polyester-viscose blended yarn with foamed polyester fibers was obtained. This yarn was woven into suit fabric by Zhejiang Sanyuan Textile Co., Ltd. Compared with the same raw material without foaming, its anti-pilling performance was improved by 1 to 1.5 grades. Furthermore, when these two yarns were dyed with disperse / reactive dyes under the same dyeing conditions, the dye uptake rate of three pairs of fabrics of different colors increased by 14 to 17%, the K / S value increased by 4 to 6, the wash fastness increased by 1 grade, and the dry and wet rubbing fastness increased by 1 grade respectively. This indicates that the polyester fibers in the yarn have a looser fiber structure after SCF foaming, which improves the dyeing performance.

[0116] Example 11

[0117] Shanghai Jialinjie Textile Technology Co., Ltd. uses a modified structure jersey fabric woven from 150D / 144F recycled polyester DTY. The fabric is continuously wrapped around a perforated PTFE tube as a skeleton, forming a 30cm diameter roll. The knitted fabric is then loosely bound and secured with PTFE before being loaded into a material cart for SCF foaming. To prevent unevenness due to shrinkage differences under harsh processing conditions, a fast yet gentle processing method is employed. Therefore, SCF-CO2, which has a good expansion effect, was used, and ethanol was added at a ratio of 4% of the fiber mass as a processing aid to help penetration. During the penetration stage, a pressure pulse (±1.5MPa, cycle 3min) was activated to help SCF penetrate faster. The initial time t0 was 18min, the penetration temperature T1 was 60℃, and the penetration pressure P1 = 24MPa. After penetration time t1 (22min), the phase separation temperature T2 was raised to 214℃ within a heating time t2 (20min) (the pressure P1 remained unchanged). After phase separation time t3 = 34min, the foaming point was formed. Then, a 12-inch diameter quick-opening valve was controlled to transport the high-pressure chamber fluid to a low-pressure chamber with a volume 45 times that of the high-pressure chamber within a pressure release time t4 = 25s. The resulting foaming background low pressure P2 was 0.71MPa, and the foaming time entered t5 = 50min. The resulting pure recycled polyester knitted fabric showed an approximately 12% increase in weight per square meter; the thermal resistance of both the original and foamed samples was tested using a flatbed thermal insulation instrument and converted to a uniform value of 100 g / m². 2 The thermal resistance of the foamed recycled polyester knitted fabric increased by 56% compared to the original sample. The foamed knitted fabric sample was slightly uneven and needed to be ironed to restore its original shape, and its thermal resistance remained basically unchanged after ironing.

[0118] Table 2 below shows the degree of improvement in the thermal resistance of the fabric after replacing ordinary fibers of the same material with foamed fibers prepared according to the present invention, and Table 3 shows the degree of improvement in the thermal resistance of the wadding after replacing ordinary fibers of the same material with foamed fibers prepared according to the present invention.

[0119] Table 2

[0120] Table 3

[0121] Example 12

[0122] Using 1.33 dtex × 38 mm fully matte PET fiber produced by Yizheng Chemical Fiber Co., Ltd. and 1.67 dtex × 38 mm ordinary PLA fiber produced by Anhui Fengyuan Bio-fiber Co., Ltd., samples with different degrees of foaming were formed according to different foaming processes. PET foam fiber II was processed according to Example 1. For PET foam fiber I, based on Example 1, no processing aid ethanol was applied during the SCF infiltration stage, no additional pressure pulse was applied, and the infiltration time was reduced from 40 min to 20 min. PLA foam fiber I was processed according to Example 5. For PLA foam fiber II, based on Example 5, 2% methanol + 1.5% ethanol was applied during the SCF infiltration stage, and a pressure pulse of ±2.5 MPa was applied every 2 min.

[0123] Yuyue Home Textiles Co., Ltd. dyed raw PET fibers and two types of foamed PET fibers with different degrees of foaming to navy blue and blue, respectively, under the same dyeing conditions and with the same dye formula. Similarly, raw PLA fibers and PLA fibers with different degrees of foaming were also dyed to navy blue and blue under the same dyeing conditions and with the same dye formula. The computer color measurement results in Table 4 show that as the degree of foaming (i.e., the expansion rate) increases, the L value decreases significantly, indicating a significant deepening of the color. Foamed fibers, whether PET or PLA, and regardless of whether dyeing is done at 95℃, 115℃, or 130℃, exhibit increased dyeing depth and facilitate lowering of the dyeing temperature.

[0124] Table 4

[0125] This invention allows for direct SCF foaming of thermoplastic synthetic fiber finished products, eliminating the problem of melt rupture caused by foaming during spinning, which prevents the spinning process from continuing. Furthermore, it can directly foam thermoplastic synthetic fiber products (such as woven fabrics, knitted fabrics, nonwoven fabrics, and wadding), making the processing method convenient.

[0126] The pore size in the SCF foamed fiber obtained by this invention can be controlled within the range of 20 nanometers to 3.0 micrometers, and the pores are basically evenly distributed in the fiber, forming a honeycomb-like structure. Therefore, it can resist the lateral pressure during textile processing and use, avoiding the defect of aerogel-type thermal insulation materials that are not resistant to compression.

[0127] The SCF foamed fiber obtained by this invention can reduce the fiber density to 40-90% of the original fiber density. (Based on an original density of 1.38 g / cm³) 3 Taking a single PET fiber product as an example, the density of foamed PET fiber after SCF-CO2 foaming is only 0.60 g / cm³. 3 Based on a CO2 density of 0.002 g / cm³ 3It is estimated that the density of foamed fibers is reduced to 56.6% of the original fiber density, which can significantly reduce the weight of textiles.

[0128] The SCF foamed fiber obtained in this invention contains a large number of micro- and nano-scale air bubbles, resulting in a 50% reduction in the thermal conductivity of its single fiber compared to the unfoamed original fiber (Figure 11). This significant reduction in fiber thermal conductivity lays a solid foundation for improving the warmth retention performance of textiles. Replacing 20% ​​of ordinary fibers (such as polyester) of the same material in a fabric with foamed fiber can increase the thermal resistance of the resulting woven or knitted fabric by 20-30%; increasing the replacement amount of foamed fiber to 40% can increase the thermal resistance of the fabric by 40-50% (Table 2); 100g / m² fabric made by replacing 80% of the fiber in the wadding with foamed fiber of the same material... 2 The wadding material increases thermal resistance by 50-200%, while also being lightweight and providing excellent insulation (Table 3). It can provide lightweight and non-bulky cold-weather clothing materials for scientific activities in extremely cold regions, such as human lunar landings, space travel, and polar exploration, as well as for cold-weather operations and for the general public to keep warm in winter.

[0129] The SCF foamed fiber obtained by this invention contains a large number of micro- and nano-sized air bubbles, resulting in a significantly lower density. Textiles made from this fiber can provide greater buoyancy if the wearer falls into water, preventing drowning. Among existing textile fibers, only PE fiber has a density of 0.97 g / cm³. 3 PP fiber density 0.91g / cm³ 3 Besides providing minimal buoyancy in water, most textile fibers have a density greater than that of water; for example, the density of widely used cotton fiber reaches 1.54 g / cm³. 3 It will sink in water. In the aforementioned example, the density of PET fiber after SCF foaming was 1.38 g / cm³. 3 Reduced to 0.60 g / cm 3 It can be calculated that using 1kg of this foam fiber can provide 0.78kg of net buoyancy, which can keep an unloaded human body basically floating, thus preventing drowning. In addition, the high heat retention effect of the foam fiber can also delay the drop in body temperature of a person who falls into the water.

[0130] The SCF foamed fiber obtained by this invention contains flame-retardant gases such as CO2 and N2 in its micro-nano-scale pores. Even foamed polyester made from ordinary fibers such as PET will release flame-retardant gases to achieve "gas-phase flame retardancy" when exposed to flame, thereby delaying combustion. By applying the technology of this invention to flame-retardant modified flame-retardant fibers such as flame-retardant PET, flame-retardant vinylon PVA, and acrylonitrile chlorofiber, as well as thermoplastic intrinsically flame-retardant fibers such as polyphenylene sulfide PPS and polyimide PAI and PEI, foamed fibers can achieve a synergistic effect between the contained flame-retardant gases and the original flame-retardant mechanism, and increase the heat insulation effect, providing flame-retardant and heat-insulating materials for fire rescue clothing.

[0131] The foamed fiber obtained by this invention, due to its rich internal micro- and nano-scale pores, has a large number of interfaces between the fiber-forming polymer and the gas, resulting in frequent light reflection. This enhances the fiber's light-blocking effect, preventing light-colored and lightweight fabrics from exposing the body's contours, and alleviating the exposure problem of light-colored clothing after it gets wet. Since the refractive indices of fiber, air, and water are approximately 1.5, 1.0, and 1.33, respectively, when textiles are dry, the fiber forms an interface with air, and the difference in refractive indices between the two is approximately 0.5, resulting in strong light reflection and a good shielding effect. When textiles get wet, the fiber changes from contact with air to contact with water, and the refractive index difference between the fiber and water interfaces decreases to approximately 0.17. Light can almost directly penetrate the inside of the clothing and continue to transmit the image of the inside, resulting in significant exposure. However, after SCF foamed fiber gets wet, the interface between the gas and the fiber material is still maintained inside the fiber (the refractive indices of CO2 and N2 are basically the same as those of air). Therefore, the abundant interfaces inside the fiber greatly enhance the shielding effect and alleviate the embarrassing situation of light-colored clothing after it gets wet.

[0132] The foamed fiber obtained by this invention has a large number of micro- and nano-scale pores inside, resulting in a loose internal structure that improves dyeability and increases color depth under the same dye usage. Furthermore, the moderately loose structure can also improve the fiber's anti-pilling performance. When the fiber ends are exposed on the surface of the fabric, they can break during friction, thus preventing pilling and improving the fabric's anti-pilling rating by more than 1 level.

[0133] Existing synthetic fiber textiles lack hydrophilic polar groups, making them difficult to absorb moisture and resulting in a stuffy feeling when sweating. Applying hydrophilic agents can temporarily improve hydrophilicity, but this effect is not durable. By using the method of this invention and increasing the pressure difference during foaming to form some open-cell structures, moisture can be absorbed through the surface effect of the open-cell bubbles, improving the sweat absorption and hydrophilicity effect and wearing comfort.

[0134] This invention uses SCFCO2 or N2 for foaming processing, and the entire processing is pollution-free and emission-free, making it green and environmentally friendly; it also makes resource utilization of CO2 generated by other industries, which helps to reduce carbon emissions.

[0135] The above description illustrates specific exemplary embodiments of the invention for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and variations can be made in accordance with the above teachings. The exemplary embodiments were chosen and described to explain certain principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various exemplary embodiments of the invention, as well as their various alternatives and modifications. The scope of the invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A process for the production of supercritical fluid foamed fibers, characterized in that, The method includes the following steps: Step 1: Fiber preparation steps; Step 2: Supercritical fluid infiltration step, in which supercritical fluid is infiltrated into the fiber to be foamed and reaches a certain content; Step 3: Foaming point formation step, in which the temperature of the fiber is increased, so that the supercritical fluid that has penetrated into the fiber can achieve phase separation and form potential foaming points inside the fiber; Step 4: Viscous flow plastic deformation and foaming step. In this step, the temperature is controlled to soften the fiber, generate plastic deformation ability, and reduce the pressure of the environment in which the fiber is located to form a pressure difference between the inside and outside of the fiber, so as to achieve foaming.

2. The process for the production of supercritical fluid-foamed fibers according to claim 1, characterized in that, The fibers in step 1 are selected from short fibers, filaments, or fiber aggregates selected from yarns, fabrics, and wadding.

3. The process for the production of supercritical fluid-foamed fibers according to claim 1, characterized in that, The fiber in step 1 is a thermoplastic fiber, which is selected from any one or more of polyester fiber, polyamide fiber, polyolefin fiber, thermoplastic polyurethane elastomer TPU fiber, thermoplastic polyester elastomer TPEE fiber, polyvinyl alcohol PVA fiber, polyphenylene sulfide PPS fiber, and polyimide PI fiber.

4. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, The fiber in step 1 is a fiber modified with particulate matter, which is selected from any one or more of aerogel powder, covalent organic framework materials (COFs), metal-organic framework materials (MOFs), molecular sieves, zeolites, matting agents, kaolin, ZrO2, ZrC, and inorganic flame retardants.

5. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, The fiber in step 1 is obtained by blending and spinning two or more fiber-forming polymers with different molecular weights.

6. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, The fiber in step 1 is a composite fiber made by combining two or more fiber-forming polymers with different foaming capabilities in a parallel compounding manner.

7. The process for the production of supercritical fluid-foamed fibers according to claim 1, characterized in that, Step 1 includes: placing the fiber to be foamed in a material cart, and the entire material cart is put into a vacuum drying equipment for drying. The drying conditions are 105-125℃, 15-25min, and vacuum degree -0.11 to -0.14MPa.

8. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, The supercritical fluid in step 2 is selected from CO2, N2, or a combination thereof.

9. The process for producing supercritical fluid foamed fibers according to claim 1, wherein Step 2 further introduces an auxiliary agent, which is selected from any one or more of methanol, ethanol, butanol, polyethylene glycol, and triethanolamine.

10. The process for producing supercritical fluid foamed fibers according to claim 1, wherein Step 2 includes: Step 2-1: Feeding step, in which the fibers prepared in step 1 are fed into the high-pressure chamber; Step 2-2: Sealing step, in which the inlet and outlet valves of the high-pressure chamber are closed; Step 2-3: Supercritical fluid introduction step. In this step, supercritical fluid is pumped into the high-pressure chamber, starting from atmospheric pressure, and reaches the set supercritical fluid infiltration pressure P1 within the initial time t0; at the same time, the equipment temperature is increased so that the fiber also reaches the set supercritical fluid infiltration temperature T1 within t0, and continues to infiltrate for a certain period of time t1, so that the supercritical fluid infiltrates into the fiber to be foamed and reaches a certain content.

11. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, Step 3 includes: Step 3-1: After the penetration time t1 is reached, a heating step for phase separation is started. In this step, the temperature is increased at a rate of 3 to 15 °C / min. After the heating time t2, the phase separation temperature T2 is reached. This phase separation temperature T2 is 20 to 45 °C lower than the fiber melting temperature. Step 3-2: Maintain phase separation at phase separation temperature T2 for phase separation time t3 to complete phase separation and form potential foaming points inside the fiber.

12. The process for producing supercritical fluid foamed fibers according to claim 1, characterized by, Step 4 includes: Step 4-1: Decompression step. In this step, the phase separation temperature T2 at the end of step 3-2 is maintained, and the pressure on the fiber is reduced to the foaming background low pressure P2 over a decompression time t4. Step 4-2: The holding step, in which the foaming background low pressure P2 and phase separation temperature T2 at the end of step 4-1 are maintained for foaming time t5 to achieve foaming.

13. Supercritical fluid foamed fiber obtained by any one of claims 1 to 12.

14. Use of the supercritical fluid foamed fiber according to claim 13 in the processing of wadding, yarn, fabric and clothing.

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