Preparation method of supercritical fluid foaming thermoplastic fiber and prepared foam fiber

Abstract

The invention discloses a supercritical fluid foaming thermoplastic fiber preparation method and a prepared foam fiber. According to the invention, the supercritical fluid permeates into the thermoplastic fiber and is mutually soluble with the high polymer for forming the fiber, and a certain solvent content is achieved. In the reaction, by adjusting thermodynamic conditions, namely temperature and pressure conditions, the supercritical fluid dissolved in the fiber is subjected to phase separation, so that a potential foaming point is formed in a loose structure part such as an amorphous region in the fiber. The temperature is adjusted, so that the thermoplastic fibers can generate moderate rheology; the pressure is adjusted to form a proper pressure difference inside and outside the fibers, so that foaming is realized, and a large amount of micro-nano-scale foam is formed by the fibers. The prepared series of foaming fiber products can realize low density, high buoyancy and high heat retention property, light rays are frequently reflected on the bubble wall surfaces in the fibers, a good visual shielding effect is achieved, the thermal resistance is improved by 50-300%, the light weight and high heat preservation effects of the fibers are realized, and the foaming fiber is a heat preservation material with a novel structure and outstanding functions.

Description

Technical Field

[0001] The invention relates to a method for preparing supercritical fluid foamed thermoplastic fibers and the prepared foam fibers, belonging to the field of functional fiber processing and application. Background Art

[0002] When the material contains air, it can provide the product with functional effects such as light weight, heat insulation, buoyancy and rigidity. The microbubbles of air in the polymer material can also stop the cracks that have already occurred and improve its strength. Cotton fiber and kapok fiber have natural hollow structures in textile fibers; viscose fiber can be formed into bamboo-shaped cavities by chemical foaming method; thermoplastic synthetic fibers such as polyester and nylon can be formed into one or more through cavities by using special-shaped spinnerets or aerated composite spinning methods; the newly developed parallel composite elastic fiber containing cavities has made some well-known outdoor thermal clothing brands very profitable. However, the existing hollow fiber cavity is concentrated in the core, and its radial size is several microns. The contained air is still easy to flow, and the heat insulation effect of static air is not achieved; especially for fibers with large hollowness (such as kapok), it is very easy to flatten and crack during processing and use; therefore, its warming effect is difficult to meet the warming needs of clothing in plateau cold areas, especially in special low-temperature environments such as the North and South Poles and space; when the warming effect is improved by increasing the thickness and layers of clothing, the heavy clothing will affect the human body's function and sports skills. Hollow synthetic fibers with continuous channel-shaped cavities cannot form a closed airbag structure because they are open at both ends, so it is difficult to provide buoyancy to help drowning people get rescued; and ordinary hollow fibers only have two more interfaces between air and polymer materials inside the fiber than solid core fibers, and the reflection phenomenon of light passing through the fiber does not increase significantly, so it is difficult to form a good shading effect.

[0003] Therefore, forming a foam structure inside the fiber, especially controlling the size of the foam unit at the nanometer-micrometer scale, and forming a static air unit is an ideal structure for providing lightweight warmth, buoyancy, and increased light-shielding effects for textiles. However, the existing technology cannot form a foam fiber with micro-nano cell size during the spinning process.

[0004] Plastics, rubber and other polymer materials can be processed by applying chemical foaming agents that can generate gas, or physical foaming agents that can be gasified due to phase change at appropriate temperature and pressure, to produce foam plastics and rubber (or rubber-plastic composite materials) with a foam size of more than tens of microns. Supercritical fluid SCF (Supercritical Fluid) is applied to plastics / rubbers by screw extrusion and other methods to mix them evenly and carefully, and then extruded in a plasticized state and gradually expanded under heat preservation conditions to form micro-nanostructured pores inside plastic / rubber parts.

[0005] However, when thermoplastic synthetic fibers are melt-spinned, when the spinning fluid is extruded from the spinneret outlet, in order to meet the drawing requirements and enable the fibers to obtain appropriate orientation and thus sufficient strength, the spinning melt is in a low melt viscosity state that is easy to flow and deform, and the melt strength is also relatively low. The presence of impurities, especially bubbles, inside the fiber can easily lead to melt rupture, especially in the presence of bubbles with expansion effects, which can more easily aggravate the expansion effect of the spinneret outlet, leading to melt rupture, and causing a large amount of the spinning melt to adhere to the spinneret plate surface, making the spinning process impossible.

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

[0007] The present invention aims to solve the technical status quo that the finished thermoplastic synthetic fiber cannot be expanded and foamed by using supercritical fluid in the prior art, and provides a supercritical fluid foamed thermoplastic fiber microporous foam material and a preparation method thereof.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0009] In order to overcome the problems of existing hollow fibers being too large in hollow size, the air contained inside being able to flow, resulting in excessive thermal conductivity of the fibers, and insufficient thermal insulation performance of the fiber aggregate, the present invention adopts supercritical fluid (SCF) to infiltrate the interior of thermoplastic synthetic fibers, achieve mutual solubility with the fiber-forming polymer and reach a certain content; adjust the thermodynamic conditions, i.e., temperature and pressure conditions, so that the supercritical fluid dissolved in the fiber achieves phase separation, and forms potential foaming points in the loosely structured parts such as the amorphous area inside the fiber; adjust the temperature so that the thermoplastic fiber can undergo moderate rheology; and adjust the pressure so that an appropriate pressure difference is formed inside and outside the fiber to achieve foaming.

[0010] The amount of supercritical fluid dissolved and the foaming process (temperature, pressure, time and time curve of changes) are controlled to control the number, size and shape of the pores in the fiber, including whether the pores are closed pores, open pores, or partially open pores.

[0011] The penetration of supercritical fluid (SCF) into the fiber is a time-consuming process. It is necessary to establish a method to accelerate the penetration of SCF from the perspective of thermodynamics and surface physicochemistry.

[0012] 1) From the perspective of thermodynamics, select the conditions for forming high-density SCF: for example, SCF has a higher density at a lower temperature, and the SCF penetration rate can be accelerated under the condition of a large density gradient inside and outside the fiber;

[0013] (2) Using pulse pressure to form penetration pressure pulses inside and outside the fiber through the speed difference of pressure transmission, thereby increasing the penetration speed of SCF;

[0014] (3) Use special additives to adjust the polarity of SCF and the additives as a whole to the fiber-forming polymer, make the polarity of the solvent and the solute as consistent as possible, increase the dissolution rate of SCF in various specific fiber materials, and facilitate SCF to enter the fiber.

[0015] Supercritical fluid (SCF) can be selected from a combination of CO2 and N2, or other subcritical and lower pressure compressed gases can also be considered to increase the penetration rate while increasing the penetration amount and volume expansion capacity.

[0016] The present invention provides a technology and a series of foamed fiber products that form a large amount of micro-nano-scale foams by infiltrating supercritical fluid into the amorphous region or pre-set foaming point in thermoplastic synthetic fibers, and then rapidly releasing pressure when the fibers are at a temperature at which flow deformation can occur, so that the supercritical fluid at the fiber foaming point expands. The foamed fibers thus prepared can achieve low density, high buoyancy and high warmth retention, and can frequently reflect light on the bubble wall inside the fibers, achieving a good visual shielding effect.

[0017] First, a working environment suitable for the supercritical fluid to penetrate into the fiber and reach saturated solubility should be established, so that the supercritical fluid has the highest saturated solubility inside the fiber; after reaching saturated solubility, the temperature should be increased to destroy the thermodynamic equilibrium state of the fiber-forming polymer dissolved with the supercritical fluid, so that the supercritical fluid changes from a homogeneous state dissolved in the fiber-forming polymer to a phase separation state, SCF aggregation points appear, and a foaming and expanding center is formed; another important function of heating is to make the fiber reach a state where plastic deformation can occur, while avoiding the melting or adhesion of the fiber, so that the fiber has the maximum plastic deformation ability; then, after the foaming and expanding center is formed, the pressure should be quickly released to reduce the SCF pressure in the high-pressure chamber, so as to highlight the SCF pressure difference inside and outside the fiber, and under the temperature condition where the fiber is at which plastic deformation can occur, the number of micro-nano-scale bubbles inside the fiber and the distribution of bubble size that meet the design requirements are formed under the action of the SCF pressure difference inside and outside the fiber, so as to obtain a suitable foaming fiber density in terms of macroscopic effect, as well as the thermal insulation, buoyancy and visual shielding effects of the fiber after being made into textiles.

[0018] Secondly, the foaming effect needs to be regulated. Due to the differences in the types of thermoplastic synthetic fibers, their chemical structures lead to different solubility of supercritical fluids inside them, the differences in aggregate structures lead to different sizes and numbers of amorphous regions that can accommodate supercritical fluids, and the differences in materials also lead to different plastic deformation capabilities. Therefore, various conventional finished fibers such as polyester, nylon, polypropylene, and polylactic acid fibers often cannot directly achieve the foaming effect through supercritical fluid processing. It is necessary to apply processing aids (such as methanol, ethanol, butanol, polyethylene glycol, triethanolamine and their compound formulas) during the supercritical fluid processing to change the accessibility of the infiltrated substance or change the deformation ability of the fiber-forming polymer and the feel of the fiber; it is necessary to perform blending modification during spinning processing, add powder materials or cellular materials with micro-nano structures, and provide more effective gas storage points and expansion centers for the fibers; it is also necessary to blend or copolymerize the fiber-forming polymer to improve the deformation ability of the fiber or adjust the softening point of the fiber; according to the specific fiber-forming polymer type, fiber specifications of the cellular fiber, pore size and pore density and other product technical requirements, by selecting processing aids, blending and copolymerization spinning, and forming the corresponding supercritical fluid process, the foaming effect of different types of fibers can be controlled. After foaming, the fiber usually becomes thicker and the feel is easy to become hard. The fiber feel is adjusted by applying a toughening agent to soften it.

[0019] In view of the fact that the raw material selection, foaming process determination, and product processing technology of foamed fibers and their products for different purposes are different, and the market demands vary greatly, it is difficult to obtain better results and quickly meet the technical difficulties of user requirements by determining the process based on experience. The present invention proposes: (1) using the theory of sensory engineering, the fiber foaming process is regarded as having two levels of independent variables: ① raw material parameters, such as fiber type, fineness, length, etc.; fluid type, physical property parameters, additive type and dosage; ② parameter selection of the foaming process, such as temperature, pressure, time and its changes; and one level of dependent variables: density, linearity, and so on of the foamed fiber; density, cell size and morphology, etc., and on this theoretical basis, participate in the deep learning technology of artificial intelligence, especially the use of neural network technology, to calculate the nonlinear regression relationship between these independent variables and dependent variables, especially by using the causal relationship established by AI technology, it is possible to quickly determine the raw materials and processing technology according to market needs; (2) on the basis of the above AI system, extend the independent variables to the flake processing technology, namely ③ fiber ratio, combing process, pressing process, oiling process; extend the dependent variable to ② thermal resistance, compression elasticity, fluffiness, etc. of the flakes, and establish the relationship between the flake performance and the aforementioned processing technology;

[0020] (3) Continue to extend to the subsequent independent variables of foamed fibers, such as ④ spinning process such as mixing ratio, linear density, yarn count, etc., ⑤ weaving process such as density, organization, loom type, weft insertion rate, etc.; ⑥ knitting process such as density, organization, napping process, etc. (knitting can also be single-row), and their relationship with dependent variables such as fabric thermal resistance and square meter weight.

[0021] In addition, the size and number of micro- and nano-scale pores in the fiber cross section can be tested by image analysis methods of electron microscope photographs.

[0022] Aiming at the problem that the idle period of the intermittent foaming process affects the unit production capacity and thus increases the cost, the present invention proposes the following solution:

[0023] (1) Establish a satellite processing system, with a low-pressure chamber as the center, and build 4 to 10 high-pressure chambers around the low-pressure chamber. Through the artificial intelligence control system, these high-pressure chambers are in the process of completing the foaming task in stages. When a high-pressure chamber enters the pressure release and foaming stage, the high-pressure chamber is quickly connected to the low-pressure chamber through a quick-opening valve, and the SCF is quickly transferred to the low-pressure chamber for recycling. After the SCF in the low-pressure chamber is recycled, the quick-opening valve connected to the high-pressure chamber is closed, and the next high-pressure chamber is quickly opened and connected to the low-pressure chamber.

[0024] (2) The above-mentioned alternating pressure release process, taking into account the difference in actual operation time due to different types of fibers under different foaming requirements, is controlled by artificial intelligence (AI) technology.

[0025] The beneficial effects achieved by the present invention are:

[0026] The present invention is the first to form a new technology for micro-nano-scale foaming of thermoplastic polymer materials using supercritical fluids; compared with the original fibers not processed by SCF technology, the fibers made of foamed fibers have a 100g / m 2 After the flakes are added, the thermal resistance is increased by 50-300%, achieving the lightweight and high thermal insulation effect of the fiber; and according to the needs of the product, it can be compounded with other fiber materials to make more cost-effective products, providing thermal insulation materials with new structures and outstanding functions for scientific activities such as human moon landing, space travel, polar exploration, operations in cold and extreme cold regions, and winter insulation for ordinary people.

[0027] Conventional thermoplastic synthetic fibers such as PET, PTT, PBT, PA6, PA66, PBS, PLA, PP, and PE can all be processed using SCF technology to form closed-cell bubbles or open-cell bubbles, reducing the fiber density by 3 to 70%. The still air stored in a large number of micro-nanoscale cavities inside the fibers enables the fibers and their aggregates to achieve significant thermal insulation effects, thereby improving the thermal insulation properties and floating and shielding effects of conventional fiber materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 A buffer heat exchange auxiliary device to offset the jet cooling effect;

[0030] Figure 2 It is the technical roadmap for supercritical fluid foaming processing system. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0032] Example 1

[0033] Preparation method of supercritical fluid foamed thermoplastic fiber microporous foam material:

[0034] Feeding: Add the processed fiber into the high-pressure chamber;

[0035] Sealing: Close the inlet and outlet valves of the high-pressure chamber;

[0036] Expel air: Slowly inject CO2 from the top of the high-pressure chamber. Using the characteristic that CO2 has a higher specific gravity than air, the air is squeezed to the outlet at the bottom of the high-pressure chamber and pressed into the separation tank for separation, and the CO2 is recovered into the CO2 storage tank;

[0037] Use a pump (preferably a plunger pump) to pump CO2 at a relatively low temperature into the high-pressure chamber until the set CO2 penetration pressure (such as 20-32 MPa) is reached. According to different varieties, select an appropriate length of time (such as 30-150 minutes) to penetrate the supercritical fluid to achieve saturated solubility in the fiber;

[0038] The temperature is raised at a rate of 5 to 15°C / min to a high temperature state 25 to 45°C lower than the melting point of the fiber, so that the supercritical fluid dissolved in the fiber can achieve phase separation. A dispersed pressure center is formed. Since sufficient phase separation takes a long time, a phase separation time of 30 to 120 minutes is required. The length of the phase separation time can be used to control the size of the foamed fiber pores and the density of the pores;

[0039] After the pressure is released, the fiber should still be kept at the original temperature, and the supercritical fluid inside the fiber forms a gathering point to exert external pressure to achieve microporous foaming. Because the fiber-forming polymer undergoes plastic deformation very slowly under the conditions of preventing melt adhesion, a longer time (30 to 180 minutes) is required for foaming after the pressure is released.

[0040] Selection of fiber types. All thermoplastic synthetic fibers can be foamed under SCF, including but not limited to polyester fibers (PET, PTT, PBT, PLA, PBS, etc.), polyamide fibers (PA6, PA66, PA10, PA, etc.), polyolefin fibers (PE, PP, UHMWPE, etc.), and thermoplastic elastic fibers such as TPU and TPEE. Among them, fibers with lower melting points such as PLA, PE, and PP are convenient for foaming under supercritical fluid at lower temperatures, and thermoplastic fibers with low melt viscosity and high melt strength are easy to form foams;

[0041] Adjustment of aggregate structure. Supercritical fluid can only exist in the crystalline region, so when the crystallinity is low, it is easy to dissolve the supercritical fluid in the amorphous region, establish a pressure center after phase separation, form a higher foaming ratio, and make the fiber have a lower density; the reasonable eutectic of multiple fiber-forming polymer materials can reduce the crystallinity of alloy fibers and increase the foaming ratio; for conventional fiber-forming polymers, a bimodal polymer with a normal molecular weight and a low molecular weight appropriately blended is used for spinning, and the obtained fiber is conducive to improving the ability of local plastic deformation and is easy to form a foam structure;

[0042] Aiming at the technical problem that ordinary thermoplastic fibers only foam in extremely small amorphous areas or local areas with loose structures when using supercritical fluids, which affects the distribution of foaming positions, cell density and cell shape, and ultimately affects the thermal insulation effect of the foamed fibers and the ability to generate buoyancy after falling into water, the present invention mixes general inorganic particles into the fiber-forming polymer. Supercritical fluid can be stored at the interface between the inorganic particles and the fiber-forming polymer, establishing more foaming points and increasing the foaming ratio;

[0043] Inorganic particles can be selected from materials with tiny voids, such as SiO2 aerogel powder, organic framework materials COFs, organic-inorganic hybrid framework materials MOFs, molecular sieves, zeolites; and conventional additives without significant pore structures, such as matting agent TiO2, inorganic flame retardants, etc. When mixed with fiber-forming polymers, bubbles will remain in the cross section. These tiny voids that appear inside and at the boundaries of the additives will serve as storage points for supercritical fluids after phase transition, and will become foaming points. Under appropriate temperature and pressure conditions, bubbles will be generated at fixed points, and the desired foaming effect can be achieved by selecting the type and quantity of additives and combining them with the foaming process.

[0044] Two polymer materials with different foaming abilities are made 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 abilities of the different materials on both sides, the morphological changes of the double-sided structural fibers can be expanded, a more obvious three-dimensional curved fiber appearance can be produced, and the thermal resistance and compression elasticity of the fiber assembly can be improved. In view of the technical difficulties that PET / PTT parallel composite elastic fibers are difficult to comb and more difficult to comb after foaming processing, and cannot exert their high elastic effect, the present invention proposes that PET / PTT parallel composite elastic fibers and PTT short fibers can be pre-mixed and combed uniformly, so that the PET / PTT parallel composite elastic fibers are distributed between the PTT fibers, and the PTT fibers and the PTT components in the parallel composite elastic fibers can be foamed, and the elastic fibers have more significant curling and better compression elasticity after foaming.

[0045] The processing technology of supercritical fluid foaming includes the configuration of temperature, pressure, time, setting of pressure release rate, fiber loading amount and temperature uniformity of various parts of the fiber (including temperature changes caused by jet cooling), etc. The realization of the process requires equipment with corresponding functions.

[0046] Apply processing aids. During supercritical fluid processing, penetrants and toughening agents (such as methanol, ethanol, butanol, polyethylene glycol, triethanolamine, etc. and their compound formulas) need to be applied to change the accessibility of supercritical fluid to penetrate into the fiber, improve flexibility and thus improve foaming ability.

[0047] When as much supercritical fluid as possible is dissolved inside the fiber, it is easy to form dense gas storage points inside the fiber, and it is possible to form a sufficiently large pressure difference inside and outside the fiber, which is convenient for fiber foaming. According to the thermodynamic theory of supercritical fluid, the density of supercritical fluid is related to temperature and pressure, and the main driving force for SCF to penetrate into the fiber is the SCF concentration difference inside and outside the fiber, that is, the density difference of supercritical fluid. Therefore, to increase the SCF density of the processing environment, the highest possible pressure and the lowest possible temperature after exceeding the critical point should be selected. Obviously, the infiltration processing of supercritical fluid at a relatively low temperature can also reduce the operating cost. According to different fiber types, it is necessary to achieve a saturated dissolved state of supercritical fluid inside the fiber within a suitable infiltration time and dissolve enough supercritical fluid.

[0048] The supercritical fluid dissolved in the fiber is evenly distributed in the amorphous region of the fiber in a homogeneous structure, and does not form a pressure center for generating bubbles. Therefore, it is necessary to change the thermodynamic state so that the supercritical fluid dissolved in the fiber can achieve phase separation and form a foaming point. The measure to change the thermodynamic state can be to change the pressure or the temperature. However, because the aforementioned process of infiltrating the supercritical fluid is carried out at a relatively low temperature, and the subsequent foaming requires the temperature of the fiber to reach a higher temperature that can achieve plastic deformation, at least to the softening point of the fiber material, the method of increasing the temperature can achieve phase separation and form a foaming center while allowing the fiber to reach the high temperature state required for plastic deformation.

[0049] The supercritical fluid increases its temperature through a heat exchanger and heats the fiber in a spray flow manner in the fiber. In order to ensure that the temperature rise of the fiber is uniform, the heating rate should not be too fast, and the temperature should be raised at a rate of 5 to 15°C / min (preferably 8 to 12°C / min) to reach a high temperature state 25 to 45°C lower than the melting point of the fiber (preferably 30 to 40°C lower than the melting point of the fiber); during this heating process, the supercritical fluid pressure in the system will increase, so part of the supercritical fluid should be diverted to the storage tank through the pressure control system of the equipment to ensure that the pressure in the high-pressure chamber where the fiber is located is within the pressure range that the equipment can withstand, and act on the fiber in conjunction with the temperature, so that the fiber is in an appropriate state where plastic deformation can occur, and the pressure at the foaming point inside the fiber after the pressure in the high-pressure chamber is released can promote the fiber to undergo plastic deformation and form a foam state, and ensure that the fiber surface does not appear in a sticky state, let alone melt bonding, so as not to damage the textile processing performance of the fiber.

[0050] Example 2

[0051] When the fiber is in a state of storing foaming gas and the fiber itself has the temperature conditions for plastic deformation, there are many ways to quickly release the pressure in the high-pressure chamber to achieve fiber microporation. If the pressure release rate is not fast enough, the supercritical fluid will leak from the gaps formed by the free volume of the polymer material and fail to establish a sufficiently large external pressure difference, which will not promote fiber expansion; however, rapid pressure release will form a jet cooling effect, which will significantly reduce the fiber temperature near the pressure release port and prevent expansion.

[0052] The first method is to use an electrically controlled partial explosion type large-size valve to connect the high-pressure chamber and the large-size low-pressure chamber.

[0053] A quick-opening valve with a large cross-sectional size (such as an inner diameter of 6 to 12 inches) is connected to the wall of the high-pressure chamber, and a low-pressure chamber with a temperature of 10 to 50 times the volume of the high-pressure chamber is set at the other end of the quick-opening valve. When the quick-opening valve opens in less than 1 second, the fibers in the high-pressure chamber quickly pass through the quick-opening valve and enter the low-pressure chamber at the temperature of the chamber, which can quickly form a pressure difference between the inside and outside of the fiber and still maintain a temperature condition suitable for the expansion and deformation of the fiber. The advantage of this processing method is that the jet cooling effect is not significant when the large-diameter quick-opening valve passes through the fiber, and the fiber will not be cooled, and the fiber expansion conditions will not be destroyed; the disadvantage is that the purchase cost of the large-diameter quick-opening valve is high, and after the quick-opening valve passes through the fiber, there will be fibers left near the valve port, and special tools and methods are required for cleaning to reset the quick-opening valve to the closed state.

[0054] The second method is to set 4 to 10 small-caliber (such as 1 to 2 inch inner diameter) quick-opening valves on the high-pressure chamber, open all the quick-opening valves at a rate of 85% of the high-pressure chamber pressure within 1 second, and quickly release the supercritical fluid into the low-pressure chamber connected to the quick-opening valve (the volume of the low-pressure chamber is still 10 to 40 times that of the high-pressure chamber; the processed fiber is intercepted by the metal filter in front of the quick-opening valve and is not transferred to the low-pressure chamber, but foamed in situ in the high-pressure chamber. This method weakens the jet cooling effect by dispersing the flow rate of the supercritical fluid, which can avoid the local fiber temperature caused by the jet cooling being lower than the plastic deformation temperature, affecting the foaming effect. Add a baffle at the pressure release port facing the fiber sample to avoid jet cooling directly facing the fiber.

[0055] The third method is to use a medium-caliber quick-opening valve (3 to 6 inches in diameter) to avoid the problem of using large-caliber quick-opening valves with excessively high unit prices; it can also avoid the problem of equipment processing difficulties caused by multiple pressure relief ports. The specific measure is to install an auxiliary device with buffering and compensation functions in the high-pressure chamber before the medium-caliber quick-opening valve.

[0056] The fourth method is to set a breathable heating element (such as metal such as foamed aluminum) at the pressure release port. When the pressure is about to be released, the heating element is preheated so that the heat loss caused by the jet can be compensated by the heating element.

[0057] At the position where the quick-opening valve is connected in the foaming tank, an inverted trapezoidal heat exchanger can be set, which is composed of foam aluminum sheets and PTFE foam sheets stacked alternately, wherein the PTFE foam is an insulating layer and the foam aluminum is an electric heating layer with appropriate resistance. Adjacent foam aluminum discs are electrically connected at a certain position of the circle, but are electrically connected to another adjacent layer in the 180° direction of the circle, thereby establishing a heater with appropriate resistance and thus appropriate heating power to supplement the heat carried away by the jet.

[0058] After obtaining the energy value that needs to be replenished according to the foaming process and the pressure release rate, the startup program of the heat exchanger is entered in advance to allow the heat exchanger to obtain heat storage; and according to the volume of the foaming tank, the fiber processing amount, the foaming process and the pressure release process, as well as the implemented temperature signal of the temperature sensor in the foaming tank, the heating current of the heat exchanger is controlled to achieve precise heating, effectively offset the energy generated by the jet refrigeration, and keep the processed fiber within the conditions for plastic processing.

[0059] In order to prevent the heat exchanger from heating the processed fiber and causing the fiber to melt due to approaching the melting point, a layer of PTFE fiber flakes is placed above the heat exchanger to act as a temperature damper.

[0060] No matter which pressure release method is used, the fiber after pressure release, whether it is still in the high-pressure bin or has been transferred to the low-pressure bin, still needs to have enough pressure release and foaming time to ensure that the high pressure at the foaming point in the fiber can overcome the high viscosity of the fiber-forming polymer and achieve sufficient foaming. The volume of the low-pressure bin needs to be large enough to quickly establish a pressure difference between the inside and outside of the fiber after connecting with the high-pressure bin, but the construction cost will be greatly increased if the volume of the low-pressure bin is too large. The volume of the low-pressure bin can also be saved by evacuating the low-pressure bin. Vacuum equipment can be installed in the low-pressure bin. When the low-pressure bin is in standby state, a vacuum pump is used to reduce the air pressure. When the high-pressure bin is depressurized through the quick-opening valve, a pressure difference between the inside and outside of the fiber is quickly generated. When there is no need to build a large-volume low-pressure bin, the pressure difference requirement can be quickly achieved.

[0061] Example 3

[0062] In the density test of foamed fiber, bubbles are adsorbed on the fiber surface, affecting the test accuracy. For thermoplastic fibers processed by microporation, the linear density after expansion can be tested by airflow meter method, and the specific surface area can be tested by inert gas infiltration method, but it is impossible to intuitively obtain a simple indicator to express the degree of fiber foaming - density. After the fiber is processed by supercritical fluid to achieve the purpose of foaming, it can first be expressed in the reduction of fiber density, but when the fiber density is tested by buoyancy method, when the fiber is sunk into water, ethanol and other test medium fluids, the fluid pressure fails to remove the air adsorbed on the surface of the fiber assembly, which becomes part of the volume of the fiber assembly. This kind of bubble will be mixed with the gas in the closed pores inside the fiber and the gas stored in the open foam around the fiber, making it difficult to obtain accurate test results for fiber density; similar test methods such as density gradient tube method have the problem of more bubbles adsorbed on the fiber surface, which affects the test accuracy of foamed fiber density.

[0063] The electric field method is used to remove the problem of bubbles adsorbed on the fiber surface in the foam fiber density test. After weighing the dry mass of the extracted fiber sample (including the original sample that has not been treated with supercritical fluid), the sample is placed in a small beaker (e.g., 50 mL), covered with a round metal plate or printed circuit substrate as an electrode, and connected to the terminal of a high-voltage power supply; the small beaker containing the fiber sample and the grounding plate on the top are placed in another slightly larger beaker (e.g., 100 mL), and the liquid used in the density test (e.g., distilled water, ethanol, xylene, etc.) is injected into the slightly larger beaker to submerge the electrode; a piece of insulating material such as polyester film is added to the bottom of the slightly larger beaker, and a metal sheet at least larger than the bottom area of ​​the beaker is placed below it as another electrode, and the electrode lead is connected to another terminal of the power supply, and the point is grounded. The outside of the slightly larger beaker of the entire device is dry. The power supply used is direct current or industrial frequency alternating current, and the voltage is higher than 10,000 volts. When a direct current power supply is used, the negative pole of the power supply is grounded. When high voltage is applied, the bubbles attached to the fiber surfaces inside and outside the fiber assembly will gradually merge small bubbles into large bubbles, and the buoyancy generated by the large bubbles will float up and detach from the liquid to reach the liquid surface, thus achieving the purpose of bubble separation. When using AC high voltage, the alternating electric field generated by the industrial frequency AC high voltage causes the bubbles to vibrate, making it easier for tiny bubbles to merge into large bubbles and float up. Since the entire system has no high temperature and no oxygen, it is still safe despite the strong electric field and the use of ethanol as the density test fluid. After eliminating the bubbles, move the fiber in the small beaker to the liquid tank of the density meter without contact with air (the fiber sample can be moved to the liquid tank together with the small beaker to immerse it, and then the fiber and the liquid can be poured onto the weighing plate in the liquid tank, and the small beaker can be taken out. The liquid in the liquid tank must be deducted from the capacity of the small beaker in advance to ensure that the liquid level does not change), and the mass after deducting the buoyancy is weighed; the difference between the dry mass and the wet mass is the buoyancy, from which the displacement, that is, the volume, can be calculated, and the fiber density can be obtained. After eliminating the bubbles adsorbed on the fiber surface, the accurate fiber density value will be obtained.

[0064] Example 4

[0065] The processed supercritical fluid foamed thermoplastic fiber microporous foam material can be directly used to process yarn, fabric and clothing, and can also be used to prepare thermal insulation flakes. The thermal insulation effect of existing thermal insulation flakes is usually not as good as that of down flakes, but down flakes have problems such as being afraid of moisture, not resistant to pressure, and having odor. A new formula containing foamed fibers is designed to achieve the thermal insulation performance of down products while avoiding the problems of down products.

[0066] The design of the thermal insulation flakes is as follows:

[0067] Hollow coarse denier foamed fiber / 1.5d~3d foamed fiber / 1d or less foamed fiber (or ordinary ultra-fine fiber) / PET-based ES fiber;

[0068] PET / PTT parallel composite hollow fiber / 1.5d~3d foam fiber / 1d or less foam fiber (or ordinary ultrafine fiber) / PET-based ES fiber;

[0069] PET / PTT parallel composite hollow fiber / 1.5d~3d foam fiber / 1d or less foam fiber (or ordinary ultrafine fiber) / PTT-based ES fiber;

[0070] PET / PTT parallel composite foamed short fibers (or PET / COPET parallel composite foamed short fibers, both using PTT hybrid foaming process) / multi-hollow coarse denier foamed fibers / 1.5d~3d foamed fibers / 1d or less foamed fibers (or ordinary ultra-fine fibers) / PET-based (or PTT-based) ES fibers;

[0071] PET / PTT parallel composite elastic foam filament / 1.5d~3d foam fiber / 1d or less foam fiber (or ordinary ultra-fine fiber) / PET-based (or PTT-based) ES fiber (to solve the problem that elastic staple fibers are not easy to comb, but it also needs equipment patents to cooperate, and it is expected to adopt air-variable blowing spinning)

[0072] Down, cashmere, rabbit hair, silk, etc. are added to the above formula, and the surface is mainly applied with foamed fibers to make lightweight and highly warm fabrics.

[0073] The scheme of using foamed fibers to make lightweight and highly warm fabrics is as follows:

[0074] 1) The foamed filaments are made into knitted fabrics, which are then napped and polarized to make fleece or polar fleece fabrics; or ordinary fabrics containing synthetic fibers are subjected to SCF foaming processing to generate a large number of micro-nano-scale pores inside the synthetic fibers during the process, thereby improving warmth retention;

[0075] (2) Foamed filaments, or yarns spun from foamed staple fibers, either pure or blended with other common fibers, used as warp yarns, weft yarns, or warp and weft yarns to weave woven fabrics;

[0076] (3) Foamed filaments or foamed staple fibers are spun pure or blended with other common fibers to form yarns, which are used as raw materials for warp knitted fabrics or weft knitted fabrics to be woven into warp knitted fabrics or weft knitted fabrics.

[0077] The dyeing properties of the foamed fibers are improved, and the processing and experimental properties are not much different from those of the corresponding raw material fibers.

[0078] The existing flame retardant fibers have poor thermal insulation effects, which affects the thermal insulation effects of firefighters when working at fire scenes.

[0079] The present invention performs a foaming process based on supercritical carbon dioxide on flame-retardant fibers such as nylon, polyphenylene sulfide PPS, and flame-retardant modified PVA fibers (flame-retardant vinyl). On the one hand, the flame-retardant powder can store gas to become a gas storage point, and on the other hand, CO2 is stored inside the fiber. When there is an appropriate amount of pore density, the contained CO2 gas is beneficial to the fiber to achieve gas-phase flame retardancy, thereby improving the flame retardant performance. At the same time, when the fiber contains a large number of pores, the thermal insulation effect can be improved.

[0080] After existing textiles fall into water, it is difficult to offset their own weight by relying on their displacement, and no net buoyancy is generated, which makes it difficult to rescue people who fall into water. However, when a large number of closed pores are present inside the fiber obtained by the present invention and the overall fiber density is less than 1, net buoyancy is provided for people who fall into water. When the fiber density is significantly reduced, more buoyancy can be provided (for example, when a garment with a mass of 1 kg is worn and the fiber density is reduced from 1.38 to 0.6, the buoyancy increases by 0.78 kg, which can keep a person who is not carrying any weight basically floating).

[0081] Existing synthetic fiber textiles lack hydrophilic polar groups and are not easy to absorb water, which makes people feel stuffy when sweating; applying a hydrophilic agent can temporarily improve the hydrophilicity but it is not durable. The present invention uses foaming to produce a large number of micro-nano-scale pores in the fiber and makes the pores into an open structure, which can absorb water by relying on the surface tension of the micro-nano-scale pores, so that the synthetic fiber textile has a good sweat-absorbing and hydrophilic effect, overcoming the problem that synthetic fibers do not absorb moisture but absorb sweat, and have poor wearing comfort.

[0082] Ordinary textiles only have the interface between the overall surface of the fiber and the air, and there are too few interfaces that can form light reflection, which leads to the common problems of poor shielding effect of thin fabrics and exposure of underwear and body contours; after light-colored, especially white clothing falls into water, the interface between the fiber and the air is replaced by the interface between the fiber and the water, and the difference in the refractive index of the two is smaller, and the light is less likely to reflect, so the clothing loses the shielding effect. The present invention uses foaming processing to make the fiber produce a large number of micro-nano-scale bubbles, and a large number of interfaces between air and fiber materials appear in the dry state, and the refractive index of both is large (the refractive index of air is about 1, and the refractive index of fiber is about 1.5), so a good shielding effect can be maintained; textiles made of foamed fibers still maintain internal closed bubbles after falling into water to prevent water from entering, except that the refractive index at the surface contacting water is changed from the refractive index of air 1 to the refractive index of water 1.33, and there are still a large number of interfaces between air and fiber materials inside, so a good shielding effect is still maintained. Therefore, foamed fibers can be used to manufacture textile fabrics such as swimsuits with good shielding effect, which still maintain good body shielding effect after the wearer falls into water, or summer thin light-colored and white fabrics.

[0083] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing supercritical fluid foamed thermoplastic fibers, characterized in that: By infiltrating the supercritical fluid into the thermoplastic fiber, it is miscible with the fiber-forming polymer and reaches a certain solvent content; the thermodynamic conditions, namely the temperature and pressure conditions, are adjusted to make the supercritical fluid dissolved in the fiber achieve phase separation, and form potential foaming points in the loose structure part inside the fiber; the temperature is adjusted to make the thermoplastic fiber undergo moderate rheology; the pressure is adjusted to form an appropriate pressure difference between the inside and outside of the fiber to achieve foaming, so that the fiber forms a series of foamed fiber products with a large amount of micro-nano scale foam.

2. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: The modification is carried out by using any one or more auxiliary agents selected from methanol, ethanol, butanol, polyethylene glycol and triethanolamine.

3. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: The thermoplastic synthetic fibers include, but are not limited to, polyester fibers, polyamide fibers, polyolefin fibers, TPU and TPEE.

4. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: The specific steps include: Feeding: Add the processed fiber into the high-pressure chamber; Sealing: Close the inlet and outlet valves of the high-pressure chamber; Use a pump to pump the foaming gas at a lower temperature into the high-pressure chamber until the set foaming gas penetration pressure is reached. According to different varieties, choose an appropriate length of time to infiltrate the supercritical fluid to achieve saturated solubility in the fiber; The temperature is raised at a rate of 5 to 15°C / min to reach a high temperature state 25 to 45°C lower than the melting point of the fiber, so that the supercritical fluid dissolved in the fiber can achieve phase separation; a dispersed pressure center is formed; since a long time is required for sufficient phase separation to occur, a phase separation time of 30 to 120 minutes is required, and the length of the phase separation time can be used to control the size of the pores of the foamed fiber and the density of the pores; After pressure release, the fiber should still be kept at the original temperature condition, and the external pressure formed by the aggregation points formed by the supercritical fluid inside the fiber can be used to achieve microporous foaming; because the fiber-forming polymer undergoes plastic deformation very slowly under the condition of preventing melt adhesion, a longer time is required for foaming after pressure release.

5. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: Any one or more inorganic particles selected from SiO2 aerogel powder, organic framework material COFs, organic-inorganic hybrid framework material MOFs, molecular sieves, zeolites, matting agent TiO2, and inorganic flame retardants are mixed into the fiber-forming polymer.

6. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: The fibers are made of two polymer materials with different foaming abilities in a parallel composite manner, such as PET / PTT parallel composite fibers, PET / PBT parallel composite fibers and COPET / PET parallel composite fibers.

7. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: The temperature is increased by a heat exchanger, and the fiber is heated in a spray flow manner at a rate of 5 to 15°C / min.

8. The method for preparing supercritical fluid foamed thermoplastic fibers according to claim 1, characterized in that: An inverted trapezoidal heat exchanger formed by alternately stacking foam aluminum sheets and PTFE foam sheets is arranged at a position connected to a quick-opening valve in the foaming tank; The electric field method is used to remove the problem of bubbles adsorbed on the fiber surface in the foamed fiber density test; after removing the bubbles, the fibers in the small beaker are moved to the liquid tank of the density meter without contacting the air, and the mass after deducting the buoyancy is weighed; the difference between the dry mass and the wet mass is the buoyancy, from which the displacement, that is, the volume, can be calculated to obtain the fiber density. After removing the bubbles adsorbed on the fiber surface, an accurate fiber density value will be obtained.

9. A series of foamed fiber products prepared by the method for preparing supercritical fluid foamed thermoplastic fibers according to any one of claims 1 to 8.

10. Use of the series of foamed fiber products according to claim 9 in processing yarns, fabrics and garments.

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