Process for the preparation of crimped composite fibers and crimped composite fibers obtained thereby

Abstract

The present invention relates to a method for preparing a crimped composite fiber and a crimped composite fiber obtained thereby, the method comprising the steps of: a) providing a composite fiber comprising a first component and a second component crimped side by side; b) subjecting the composite fiber in step a) to supercritical fluid infiltration; c) foaming and crimping the composite fiber subjected to supercritical fluid infiltration in step b); d) setting the composite fiber foamed and crimped in step c). The crimped composite fiber has improved fiber crimp shrinkage and warmth retention properties.

Description

Technical Field

[0001] This invention relates to a method for preparing crimped composite fibers and the crimped composite fibers obtained therefrom, and particularly to a method for preparing crimped composite fibers based on supercritical fluid foaming technology, which optimizes the fiber crimping structure and significantly improves the thermal insulation performance by controlling temperature and pressure conditions. Background Technology

[0002] Fiber crimp increases the friction and cohesion between fibers, thereby improving the spinnability of short fibers. Simultaneously, crimp increases the transverse space occupied by the fiber and its longitudinal elastic elongation, regulating the permeability, conduction, or insulation of the fiber assembly, thus enhancing its elasticity and warmth retention. Fiber crimp typically originates from two main sources: natural and artificially added. For chemical fibers, artificial crimping can be achieved through thermomechanical deformation processes such as false twisting, weaving and unweaving, stuffing, and gear shaping. Furthermore, composite multifilaments can be used, where two fiber-forming polymer components with different heat shrinkage properties are distributed side-by-side across the fiber cross-section, resulting in a highly fluffy three-dimensional crimped structure upon heating. Among such composite fibers, PTT fibers, due to their inherent excellent properties and their good interfacial compatibility with PET (both being polyester fibers), are widely used in the textile industry due to their superior elasticity and crimp properties. For example, patent CN116971044A discloses a method for producing a bicomponent composite elastic fiber for thermal insulation fabrics. This method involves injecting a certain proportion of warmth-retaining masterbatch into high-viscosity PTT and low-viscosity PET respectively to form a high-viscosity mixture and a low-viscosity mixture, followed by drying and then composite spinning to form a figure-eight shaped bicomponent fiber. CN117983153B discloses a polymerization reactor for high-viscosity PTT and a method for preparing melt-spun high-viscosity PTT / low-viscosity PET bicomponent elastic fibers. However, in traditional processes, the fiber crimp rate is low and the thermal insulation performance is limited due to the difference in properties between the two composite components.

[0003] Supercritical fluids possess gas-like diffusivity and liquid-like solubility; their density-related properties, such as viscosity and solubility, can be easily controlled with variations in temperature and pressure. In recent years, supercritical fluid foaming technology has been used to improve the lightweighting and performance optimization of thermoplastic polymers such as PET, PLA, and PP. However, its application in the foaming of thermoplastic fibers, especially PET / PTT side-by-side composite fibers, is still immature. Therefore, this invention proposes a method combining supercritical fluid foaming technology with the preparation of side-by-side composite fibers, aiming to improve fiber crimp and enhance thermal insulation performance by controlling process parameters. Summary of the Invention

[0004] One aspect of the present invention relates to a method for preparing a crimped composite fiber, the method comprising the following steps:

[0005] a) Provide a composite fiber, said composite fiber comprising a first component and a second component compounded in parallel;

[0006] b) Supercritical fluid infiltration is performed on the composite fibers from step a);

[0007] c) Foam and curl the composite fibers that have been infiltrated by supercritical fluid in step b).

[0008] d) Set the composite fibers that have been foamed and curled in step c) into shape.

[0009] In a preferred embodiment, the first component has a higher softening point than the second component.

[0010] In a preferred embodiment, the first component and the second component are selected from polyesters (polyethylene terephthalate PET, etc.). 5%AF&rsv_pq=9bb2e460000d8acc&oq=PTT%20%E8%81%9A&rsv_t=18e27ZSsBq7qGSrckXI07ENMeu qH7RnytOVZV8+ScyceG5Lw+3 / 23yU0RRaEZxJGSZ9seMURGnE&tn=62095104_9_oem_dg&ie=utf-8" The composite fiber can be made of polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polylactic acid (PLA), polybutylene succinate (PBS), etc., or polyamides (PA6, PA66, PA10, PA56, etc.), provided that the first and second components are homologous and have a difference in intrinsic viscosity of 0.30~1.05 dL / g (preferably 0.45-0.90 dL / g), thus having a certain degree of interfacial compatibility. The first and second components are distributed on both sides of the cross-section of the composite fiber, which can be in the form of locally connected circular cross-sections of equal diameter, connected circular cross-sections of one large and one small, peanut-shaped, etc.

[0011] In a preferred embodiment, the mass ratio of the first component to the second component is 1:0.5-1.2.

[0012] In a preferred embodiment, the supercritical fluid is selected from CO2, N2, or a combination thereof.

[0013] In a preferred embodiment, in step b), the composite fiber is placed in a high-pressure chamber containing supercritical fluid. Starting from atmospheric pressure, the set supercritical fluid infiltration pressure P1 (8~30 MPa, preferably 12~28 MPa) is reached within an initial time t0 (10~40 min, preferably 15~30 min). At the same time, the temperature is increased so that the composite fiber also reaches the set supercritical fluid infiltration temperature T1 (40~80℃, preferably 50~70℃) within t0, and the infiltration continues for a certain period of time t1 (20~100 min, preferably 30~80 min) to allow the supercritical fluid to penetrate into the composite fiber and reach a certain content.

[0014] In a preferred embodiment, step c) includes:

[0015] c-1) After reaching the penetration time t1, the phase separation temperature T2 is reached within the heating time t2 (10~50 min, preferably 15~35 min). The phase separation temperature T2 is lower than the softening point of the first component and higher than the softening point of the second component. The phase separation temperature T2 is also lower than the melting temperature of the second component (preferably 20~45°C lower, more preferably 25~40°C lower).

[0016] c-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 composite fiber;

[0017] c-3) Maintain the phase separation temperature T2 and allow the pressure on the composite fiber to decrease to the foaming background low pressure P2 (0.3-3 MPa, preferably 0.5-1.2 MPa) over a pressure relief time t4 (1s-20min, preferably 10s-15min).

[0018] c-4) Maintain the foaming background low pressure P2 and phase separation temperature T2 for a foaming time t5 (20-80 min, preferably 30-60 min) to achieve foaming.

[0019] In a preferred embodiment, the shaping in step d) is carried out at a temperature of 150~160°C for 10~30 minutes.

[0020] Another aspect of the present invention relates to a crimped composite fiber comprising a first component and a second component compounded in parallel, the second component having a larger pore volume than the first component, such that the composite fiber has a crimped three-dimensional structure.

[0021] In a preferred embodiment, the crimped composite fiber is obtained by the preparation method of the present invention. The crimped composite fiber of the present invention has a crimp rate of 55-65% and a breaking strength of 2.5-3.8 cN / dtex.

[0022] The beneficial effects achieved by this invention are:

[0023] The crimping properties of parallel composite fibers are significantly improved. By using supercritical fluid foaming technology, only the second component of the parallel composite fibers is foamed, which significantly exaggerates the volume of the second component, causing asymmetry on both sides of the parallel composite fibers, thereby forming a highly crimped three-dimensional structure. The method of this invention can increase the fiber crimp rate from the traditional 40% to over 55-65%.

[0024] The thermal insulation performance of parallel composite fibers and their products is enhanced. First, the formation of the crimped structure increases the number of voids between fibers in the fiber assembly. Second, the second component in the parallel composite fibers undergoes supercritical foaming, forming micro-nano-scale, non-interconnected pores within the fibers. This results in lower thermal conductivity of the gas stored within the fibers compared to solids, while also increasing the pathways for heat flow. The decreased fiber density after foaming further reduces the proportion of heat flow pathways, thereby improving the thermal insulation effect of the fibers and their products. Textiles made from the fibers prepared by this invention exhibit thermal insulation performance that is more than 30% higher than that produced using traditional methods.

[0025] The method of this invention has strong process controllability. By precisely controlling the pressure, temperature and processing time of the supercritical fluid, the degree of fiber crimping and foaming effect can be flexibly adjusted to meet the needs of different application scenarios.

[0026] 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.

[0027] 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.

[0028] 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

[0029] 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:

[0030] Figure 1 A process flow diagram of the method for preparing the crimped composite fiber of the present invention is shown;

[0031] Figure 2a and Figure 2b The images show a macroscopic longitudinal view and a microscopic electron microscope image of the crimped composite fiber obtained by the preparation method of the present invention.

[0032] Figure 3a and Figure 3b Electron micrographs of the second and first components in the cross-section of the crimped composite fiber obtained by the preparation method of the present invention are shown respectively.

[0033] 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.

[0034] In the accompanying drawings, reference numerals throughout the various figures refer to the same or equivalent parts of the invention. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 by the term "about" in all cases. 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.

[0039] 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).

[0040] In the preparation method of the crimped composite fiber of the present invention, parallel composite fibers containing a first component and a second component can be produced first using existing twin-screw composite spinning equipment. Then, under certain temperature and pressure, the concentration difference of supercritical fluid inside and outside the fiber is used to promote the penetration of supercritical fluid into the fiber, reaching a certain penetration amount within the parallel composite fiber, forming a homogeneous system with the fiber-forming polymer. The temperature is then further increased, which on the one hand disrupts the thermodynamic equilibrium of the system, causing the supercritical fluid dissolved in the fiber to reach a supersaturated state, achieving phase separation and forming high-pressure fluid aggregation points or bubble nuclei in the amorphous region of the fiber. On the other hand, the fiber temperature is increased, giving it the ability to undergo plastic deformation flow, thereby achieving foaming. During the foaming process of the parallel composite fiber, the difference in thermal properties between the two components in the parallel composite fiber is utilized. By setting the temperature, the second component swells and foams due to reaching its softening point, while the first component, although also infiltrated by supercritical fluid, cannot undergo plastic deformation at the set temperature due to its excessively high softening point and continues to maintain a relatively stable state. The foaming of the second component creates discontinuous, interconnected cells within it, increasing their diameter and significantly expanding the volume of one side of the second component in the parallel composite fibers. This further amplifies the asymmetry between the two sides, given their different thermal shrinkage, resulting in a highly curled, three-dimensional structure. This allows for the creation of more micro-spaces within the fiber and fiber assemblies to increase heat transfer paths, thereby further improving the warmth, bulkiness, and compressive elasticity of the resulting textiles (including woven fabrics, knitted fabrics, nonwoven fabrics, and wadding).

[0041] The method of the present invention includes: a) a composite fiber supply step; b) a supercritical fluid infiltration step; c) a foaming and crimping step; and d) a shaping step.

[0042] a) Composite fiber supply steps

[0043] In this step, a composite fiber to be foamed is provided. The composite fiber comprises a first component and a second component compounded in parallel. There are no specific limitations on the types of the two components, including but not limited to polyester (polyethylene terephthalate PET, etc.). 5%AF&rsv_pq=9bb2e460000d8acc&oq=PTT%20%E8%81%9A&rsv_t=18e27ZSsBq7qGSrckXI07ENMeuqH7RnytOVZV8+ScyceG5Lw+3 / 23yU0RRaEZxJGSZ9seMURGnE&tn=62095104_9_oem_dg&ie=utf-8" \t "_blank" These are thermoplastic fiber-forming polymers such as polypropylene terephthalate (PTT), polybutylene terephthalate (PBT), polylactic acid (PLA), polybutylene succinate (PBS), etc., and polyamides (PA6, PA66, PA10, PA56, etc.). Preferably, the two components belong to the same species, thus having a certain degree of interfacial compatibility, and the intrinsic viscosity of the two components has a certain difference (0.30~1.05 dL / g, preferably 0.45-0.90 dL / g).

[0044] A twin-screw melt spinning machine can be used to melt-spin the first and second components selected from the above materials into parallel composite fibers. When viewed in the cross-section of the parallel composite fibers, the first and second components are located on opposite sides of the cross-section of the composite fibers.

[0045] To further enhance the difference in foaming effect between the two components, the second component can be modified, preferably one or more of the following particle-modified fiber-forming polymers: aerogel powder, covalent organic framework materials (COFs), metal-organic framework materials (MOFs), molecular sieves, zeolites, matting agents, kaolin, ZrO2, ZrC, and inorganic flame retardants.

[0046] 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. Because the different foaming capabilities of the materials on both sides of the composite fiber increase the morphological differences between the two sides of the fiber structure, resulting in a more pronounced three-dimensional curved fiber appearance and improving the thermal resistance and compressive elasticity of the fiber assembly.

[0047] b) Supercritical fluid infiltration steps

[0048] The supercritical fluid used in this invention can be selected from CO2, N2, or a combination thereof.

[0049] 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. 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.

[0050] 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.

[0051] Taking CO2 as an example, the supercritical fluid infiltration step may further include:

[0052] Feeding: The trolley loaded with the fibers or products to be processed is moved along a fixed track into the high-pressure chamber;

[0053] Sealing: Close the inlet and outlet valves of the high-pressure chamber;

[0054] Air removal: CO2 is slowly injected from below the high-pressure chamber. Taking advantage of the fact that CO2 is denser than air, the air is forced to the upper outlet of the high-pressure chamber and then into the separator for separation. The CO2 is then recovered into the CO2 storage tank.

[0055] Simultaneously, the temperature and pressure controllers are activated, and the fluid transport pump (preferably a plunger pump) is turned on to pump CO2 (or N2 or a mixture of both) at a lower temperature into the high-pressure chamber. At the same time, the heater is turned on. Using the temperature and pressure rise curve developed according to AI technology, the temperature and pressure rise simultaneously within the initial time t0 (10~40min, preferably 15~30min) to reach the infiltration temperature T1=40~80℃ (preferably 50~70℃) and the infiltration pressure P1=8~30MPa (preferably 12~28MPa). The infiltration temperature T1 and the infiltration pressure P1 are maintained at this infiltration temperature T1 and the infiltration time t1=20~100min (preferably 30~80min) to ensure that the SCF content in the fiber meets the requirements for subsequent foaming.

[0056] 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 2~8 min (preferably 1.0~2.5 MPa with a pulse period of 3~5 min), 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.

[0057] c) Foaming and curling steps

[0058] The supercritical fluid penetrating the fiber is uniformly distributed in the amorphous region of the fiber in a homogeneous structure, but it cannot form pressure centers for bubble generation. 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 the 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.

[0059] In this step, the temperature is increased at a rate of 3–15 °C / min (preferably 5–10 °C / min) to reach the phase separation temperature T2. This phase separation temperature T2 is lower than the softening point of the first fiber material and higher than the softening point of the second fiber material, and lower than the melting temperature of the second component (preferably 20–45 °C lower, more preferably 25–40 °C lower). This allows the SCF dissolved in the second component 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.

[0060] After phase separation time t3, the SCF that has penetrated the second component achieves phase separation and forms potential foaming points inside the fiber. The phase separation temperature T2 is maintained, ensuring the second component is in a suitable state for plastic deformation. After a depressurization time t4, the high-pressure chamber is depressurized to the foaming background low pressure P2. The foaming background low pressure P2 and phase separation temperature T2 are maintained for a foaming time t5. The pressure accumulation points formed by the SCF inside the fiber push outwards to induce plastic deformation, achieving microporous foaming. This ensures that the fiber surface does not adhere or melt-bond, thus preventing damage to the fiber's textile processing properties.

[0061] d) Shaping steps

[0062] The foamed and crimped fibers are cooled to room temperature and then heat-set to fix the crimped structure. The heat setting process is carried out at 150-160°C for 10-30 minutes, resulting in a parallel composite fiber with high crimp rate and excellent heat retention properties.

[0063] Example 1

[0064] PET chips (intrinsic viscosity 0.49) produced by Yizheng Chemical Fiber Co., Ltd. and full-dull PTT chips (intrinsic viscosity 1.32) from Shenghong Group were intermittently dried in a vacuum drum dryer at a mass ratio of 1:0.6. After drying, the moisture content of both PET and PTT chips was controlled below 30 ppm before melt extrusion. The melt was transported through a melt pipeline and metered by a metering pump to obtain PET and PTT spinning melts. These melts flowed through their respective channels to the parallel composite spinning spinneret of the spinning assembly, where they converged to form a bicomponent composite fiber with interconnected PET and PTT components. The fiber then underwent cooling, oiling, stretching, and winding to obtain the PET / PTT bicomponent parallel composite fiber. The spinning temperature of the PET spinning melt was 295℃, the spinning temperature of the PTT spinning melt was 272℃, the cooling temperature was 23℃, and the winding speed was 2750 m / min. The prepared fibers were then processed in a supercritical carbon dioxide high-pressure chamber. Starting from atmospheric pressure, the pressure and temperature were increased from room temperature and atmospheric pressure to the infiltration pressure P1 and infiltration temperature T1 (20 MPa and 55 °C) within an initial time t0 = 20 min. Under these pressure and temperature conditions, the infiltration time t1 = 80 min was maintained to allow the supercritical carbon dioxide to fully infiltrate the fibers and reach a saturated dissolved state. Next, the temperature was raised to 185 °C and maintained for a phase separation time t3 = 70 min, causing the supercritical carbon dioxide that had infiltrated and dissolved in the second component of the composite fiber to undergo phase separation, forming potential foaming points. Then, maintaining the phase separation temperature, the quick-opening valve is opened, and after a depressurization time t4 = 50s, the high-pressure chamber is depressurized to 0.80 MPa, the low-pressure background P2 of foaming, thus disrupting the thermodynamic equilibrium of supercritical carbon dioxide. The low-pressure background P2 and phase separation temperature T2 are maintained for a foaming time t5 = 25min, achieving foaming of the second component in the parallel composite fiber. The first component, due to its high softening point, has not yet reached the temperature at which plastic deformation easily occurs, so although supercritical fluid has infiltrated, the foaming effect is not significant. After foaming, the fiber is cooled to room temperature and then heat-set at 160℃ for 20 minutes. The characteristic of this embodiment is that sufficient infiltration time ensures adequate storage of supercritical carbon dioxide in the second component. Simultaneously, the matting agent in the second component, acting as a blending modifier, provides more potential gas storage points and bubble nuclei. The relatively slow depressurization rate ensures high pore density, small and uniform size.

[0065] Figure 2a and Figure 2bThe macroscopic longitudinal view and microscopic electron microscope image of the crimped composite fiber obtained in Example 1 are shown respectively. As shown in the figure, from a macroscopic perspective, the fiber exhibits regular and continuous crimping, indicating that stable crimping was achieved through the stress difference at the interface of the two components during the supercritical fluid foaming process. From a microscopic perspective, the fiber surface is smooth and dense, and the three-dimensional crimped morphology is full and three-dimensional, demonstrating the good structural integrity of the composite structure during phase separation and shrinkage. This crimped structure gives the fiber a higher crimp rate, which can significantly improve the warmth and breathability of fiber assemblies (such as nonwoven fabrics and fiber mats). In addition, the elastic recovery effect generated by crimping makes it easier for the fiber to return to its initial shape after being deformed by force, enhancing the flexibility and wrinkle resistance of the fiber in textile processing.

[0066] Figure 3a This is an electron micrograph of the PTT component in the cross-section of the bicomponent composite fiber prepared in Example 1. Figure 3b The figure shows an electron microscope image of the PET component in the cross-section of the bicomponent composite fiber prepared in Example 1. As shown in the figure, the PTT component in the bicomponent composite fiber has a larger foaming ratio than the PET component.

[0067] The PET / PTT bicomponent parallel composite fiber prepared in this embodiment was tested. Its cross-section is a locally connected circular cross-section of equal diameter. The breaking strength is 3.24 cN / dtex, the fiber crimp shrinkage rate is 58.3%, the oil content is 1.0%, and the thermal conductivity decreases to 72.4% of the original. Yuyue Home Textiles Co., Ltd. used this foamed fiber (50%), ordinary polyester hollow fiber (30%), and ES bonding fiber (20%) to make a wadding. Compared with the wadding made using the same proportion of unfoamed bicomponent parallel composite fiber, the thermal resistance increased by 30.5%, and the compression elasticity recovery rate increased by 24.1%. This indicates that the crimp reinforcement and micro / nano-scale cells formed by foaming can significantly improve the warmth retention and compression elasticity of the wadding.

[0068] Example 2

[0069] This embodiment uses the same melt spinning method as Example 1 for preparing bicomponent composite fibers, except that the PTT chips used are far-infrared PTT chips containing zirconium dioxide produced by Suzhou Baolidi Materials Technology Co., Ltd. The mass ratio of PET chips to far-infrared PTT chips is 1:1.2. After vacuum drying, the fibers are placed in a high-pressure chamber for supercritical carbon dioxide foaming. Methanol, a processing aid to facilitate SCF penetration, is added at 1.5% of the fiber mass in the supercritical carbon dioxide. Within an initial time t0 = 20 min, the pressure and temperature are increased from room temperature and pressure to penetration pressure P1 and penetration temperature T1 (28 MPa and 45°C), and pressure pulses of ±1.2 MPa are applied every 3 min. Through the application of the aid and the design of the pressure pulses, the penetration amount and efficiency are further improved, and the penetration time is reduced. The penetration time t1 = 45 min is maintained to ensure sufficient penetration. Next, within a heating time t2 = 30 min, the temperature is raised to the phase separation temperature T2 = 180℃, while maintaining the infiltration pressure P1 = 28 MPa. The phase separation time is then maintained for 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 structurally loose areas of the bicomponent composite fiber, especially the amorphous regions of the second component and the interface areas containing the blended modified zirconium dioxide particles. Then, the quick-opening valve is opened, and within a depressurization time t4 = 10 s, the fiber is rapidly transported to a low-pressure chamber with a foaming background low pressure P2 of 0.78 MPa and a temperature of phase separation temperature T2 = 185℃. The sudden increase in the internal and external pressure difference induces foaming at the supercritical carbon dioxide storage points within the fiber. Foaming is maintained for a certain time t5 = 30 min to complete the foaming process. After the fiber cools, it is then shaped at 150℃ for 20 minutes to complete the processing.

[0070] The PET / PTT bicomponent side-by-side composite fiber prepared in this embodiment was tested. After foaming, the crimp shrinkage rate of the bicomponent composite fiber was 62.7%, the thermal conductivity decreased to 66.1% of the original, and the strength decreased by 12.3% compared with the original fiber. A blended yarn of 60% foamed bicomponent composite fiber and 40% cotton fiber, woven into knitted fabric by Shanghai Jialinjie Textile Technology Co., Ltd., showed an increase in thermal resistance of up to 86.1% compared with cotton fabric of the same square meter weight due to the increased crimp rate, the micro-nano pores inside the PTT component of the fiber, and the effect of zirconium dioxide. Furthermore, the anti-pilling level was improved by 1 to 1.5 grades.

[0071] Example 3

[0072] The fully matte PET / PBT bicomponent parallel composite filaments produced by Tongkun Group Co., Ltd. were vacuum dried at 105℃ / 20min / -0.12MPa and then placed in a high-pressure chamber for supercritical carbon dioxide foaming. Within an initial time t0=18min, the pressure increased from room temperature and pressure to a weaker penetration pressure P1=15MPa and penetration temperature T1=65℃. After a maintenance penetration time t1=30min and a temperature increase time t2=30min, the process entered the supercritical carbon dioxide foaming phase separation stage, with the phase separation conditions being 160℃ / 15MPa / 30min. During the phase separation stage, the supercritical carbon dioxide that had penetrated into the fully matte PET / PTT bicomponent parallel composite filament fibers was transferred to its amorphous region and the loosely structured interface between the matting agent particles and the fiber, forming potential foaming points. Then, the quick-opening valve is opened, and within the pressure release time t4=10min, the supercritical fluid in the high-pressure chamber is released into the low-pressure chamber with a foaming background low pressure P2 of 0.78MPa and a temperature of phase separation temperature T2=160℃. The fiber is still in the high-pressure chamber and begins to expand and foam due to the pressure difference between the inside and outside of the fiber. The foaming is completed after t5=40min.

[0073] After cooling, the fibers undergo heat setting at 150℃ for 18 minutes. Test results showed that the crimp shrinkage rate of the foamed fiber increased by 20.9% compared to the original fiber, while the thermal conductivity decreased by 38.2%. The breaking strength decreased by 5.2%. Jiangsu Jianlu Wool Textile Co., Ltd. used this foamed fiber filament with 80-count wool to create a 60 / 40 polyester / 40 wool core-spun yarn, which was then woven into fabrics for uniforms. Compared to fabrics using ordinary bicomponent fiber core-spun yarn, the woven fabric containing the foamed fiber showed a 35.2% increase in thermal resistance, and the visual opacity of white or light-colored fabrics improved by one level.

[0074] Example 4

[0075] Flame-retardant PET / PTT fibers produced by Jiangsu Guowang High-Tech Fiber Co., Ltd. were directly fed into a high-pressure chamber for supercritical nitrogen foaming. Within an initial time t0 = 35 minutes, the pressure and temperature increased from room temperature and pressure to the penetration pressure P1 and penetration temperature T1 (30 MPa and 55℃). Due to the low permeability of supercritical nitrogen, additives were needed to assist and maintain a long penetration time. Therefore, 2.0% methanol and 1.5% butanol were added according to the fiber weight, and the penetration time was selected as t1 = 80 minutes to allow SCF to penetrate into the fiber. The process begins with raising the temperature to the phase separation temperature T2 = 172℃ within a heating time t2 = 30 min, while maintaining the infiltration pressure P1 constant. The phase separation time is then maintained at t3 = 75 min, allowing the SCF fluid to transfer to the amorphous region of the fiber and the loosely structured area at the interface between the flame retardant particles and the polymer, forming gas storage points. Next, the quick-opening valve is opened, releasing the high-pressure fluid into the low-pressure chamber within a depressurization time t4 = 4 min, while the fiber remains in the high-pressure chamber where the pressure has been reduced to 1.12 MPa. The foaming time is maintained at t5 = 70 min. After cooling, the fiber is set at 155℃ for 25 min.

[0076] The resulting foamed fiber exhibited a 15.5% increase in crimp shrinkage compared to the original fiber, a 24.5% decrease in thermal conductivity per fiber compared to the unfoamed original fiber, and an 8.1% decrease in strength compared to the original fiber. When this foamed DTY fiber was woven into fleece by Jialinjie Textile Technology Co., Ltd., it showed a 28.0% increase in thermal resistance compared to ordinary polyester fleece of the same structure and specifications, while also being lightweight and soft.

[0077] Table 1 below shows the preparation parameters of the crimped composite fibers according to Examples 1-4 of the present invention.

[0078] Table 1

[0079]

[0080] 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 method for preparing crimped composite fibers, characterized in that, The method includes the following steps: a) Provide a composite fiber, the composite fiber comprising a first component and a second component compounded in parallel, wherein the first component of the composite fiber has a higher softening point than the second component; b) Supercritical fluid infiltration is performed on the composite fiber in step a). In step b), the composite fiber is placed in a high-pressure chamber containing supercritical fluid. Starting from atmospheric pressure, the set supercritical fluid infiltration pressure P1 is reached within the initial time t0. At the same time, the temperature is increased so that the composite fiber also reaches the set supercritical fluid infiltration temperature T1 within t0, and the infiltration is continued for a certain time t1, so that the supercritical fluid infiltrates into the interior of the composite fiber and reaches a certain content. c) Foaming and curling the composite fiber infiltrated by supercritical fluid in step b), wherein step c) includes: c-1) reaching the phase separation temperature T2 within a heating time t2 after reaching the infiltration time t1, the phase separation temperature T2 being lower than the softening point of the first component and higher than the softening point of the second component; c-2) maintaining the phase separation temperature T2 for a phase separation time t3 to complete phase separation and form potential foaming points inside the composite fiber; c-3) maintaining the phase separation temperature T2 and reducing the pressure of the composite fiber to the foaming background low pressure P2 over a decompression time t4; c-4) maintaining the foaming background low pressure P2 and the phase separation temperature T2 for a foaming time t5 to achieve foaming, and further increasing the difference between the two components through the difference in expansion rate to enhance curling; d) Set the composite fibers that have been foamed and curled in step c) into shape.

2. The method for preparing crimped composite fibers according to claim 1, characterized in that, The first component and the second component are selected from polyester or polyamide, provided that the first component and the second component are homologous, with an intrinsic viscosity difference of 0.30~1.05 dL / g, and the first component and the second component are distributed on both sides of the cross section of the composite fiber.

3. The method for preparing crimped composite fibers according to claim 1, characterized in that, The mass ratio of the first component to the second component is 1:0.5~1.

2.

4. The method for preparing crimped composite fibers according to claim 1, characterized in that, The supercritical fluid is selected from CO2, N2, or a combination thereof.

5. The method for preparing crimped composite fibers according to claim 1, characterized in that, The setting process in step d) is carried out at a temperature of 150~160℃ for 10~30 minutes.

6. A crimped composite fiber prepared by the preparation method according to any one of claims 1 to 5, characterized in that, The crimped composite fiber includes a first component and a second component, wherein the second component has a larger foaming ratio than the first component, so that the composite fiber has a crimped three-dimensional structure.

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