Method for preparing polypropylene fiber aggregate based on instantaneous pressure release spinning method and application thereof

Abstract

The present invention belongs to the field of polypropylene nonwoven fabric preparation and discloses a method for preparing a polypropylene fiber aggregate based on an instantaneous pressure-release spinning process. Polypropylene and a plasticizer are added to a supercritical reactor, stirred, and supercritical carbon dioxide is injected to produce a supercritical fluid. The supercritical fluid is instantaneously released into the spinning environment, where gas-liquid separation occurs in the supercritical state, and the plasticizer and carbon dioxide are replaced into the air in gaseous form. The polypropylene in the supercritical fluid is cooled to obtain solidified polypropylene, which is then drawn under the action of gas pressure flow to form a polypropylene micro-nano fiber aggregate. The present invention also discloses the application of the polypropylene micro-nano fiber aggregate, which is formed into a polypropylene nonwoven fabric after electrostatic fiber opening and hot rolling. The present invention is used to prepare polypropylene micro-nano fiber aggregates with a diameter of 0.5 to 5 μm. The prepared polypropylene nonwoven fabric has performance far superior to polypropylene nonwoven fabric materials produced by meltblown or spunbond, and has great application prospects in the field of protective clothing.

Description

Technical Field

[0001] The present invention belongs to the field of polypropylene nonwoven fabric preparation, and particularly relates to a method for preparing a polypropylene fiber assembly based on an instantaneous pressure release spinning method and its application. Background Art

[0002] The novel coronavirus pneumonia (COVID-19) pandemic broke out globally in 2020. As the pandemic raged, medical protective equipment such as masks and protective clothing remained in short supply, primarily due to a shortage of key filter materials used in protective textiles. To achieve high barrier properties in medical protective materials, electret meltblown nonwovens, electrospun nonwovens, and porous membrane materials are generally used. Electret meltblown nonwoven technology is relatively mature and is used by international companies such as 3M and Honeywell in the large-scale production of N95 masks. While electrospun nonwovens offer excellent filtration performance, they are limited by electrospinning production capacity and are unable to meet the large-scale demand for epidemic prevention. Furthermore, the preparation technology for porous membranes as protective materials remains immature, resulting in significant conflicts between filtration efficiency, air resistance, and cost.

[0003] Currently, achieving uniform, fine fiber diameters in electret meltblown nonwovens relies on the use of high-melt-index polypropylene (PP) resins with excellent processing flow properties. Generally, these resins require a melt index of 1500-2000 g / 10min, significantly higher than the 2-60 g / 10min range of standard PP resins. Currently, the main production routes for high-melt-index PP resins utilize peroxide degradation and metallocene-catalyzed polymerization. The peroxide degradation method suffers from a lengthy production process, high energy consumption, poor product flow stability, and high volatile organic compound (VOC) content. Metallocene-catalyzed PP resins, on the other hand, offer stable flow properties, low VOC levels, and low production costs. However, the core technology for this production has long been limited to LyondellBasell Industries in the Netherlands. Therefore, in order to better respond to the prevention and control of the COVID-19 epidemic and major public health emergencies that may occur in the future, it is of extremely important strategic significance to explore and establish a new technology that is not limited to high melt index PP resin as the basic raw material and can produce microfiber aggregates (including yarns, fabrics, and non-woven fabrics) on a large scale.

[0004] The flash spinning method involves dissolving polyethylene in an organic solvent (such as toluene or xylene) under high temperature and pressure, and producing nonwovens using a dry solution spinning process. This process is plagued by significant solvent contamination and difficulty controlling fiber morphology. Furthermore, DuPont's technology is strictly confidential, and only a few universities and companies have conducted exploratory research. The "flash pressure release" (FPR) spinning method, on the other hand, utilizes phase diagram control of a high-solubility solution under supercritical conditions and vector finite element analysis of the spinning tunnel's temperature, velocity, and pressure to achieve the engineered production of fine polymer fibers and aggregates. Both the production process and the fiber product are calculable and simulated. Therefore, addressing the current challenges of shortages and low efficiency of key filtration raw materials for medical protective materials, the use of flash pressure release spinning to produce conventional polypropylene (PP) nonwovens holds significant scientific significance and application value. Summary of the Invention

[0005] In order to solve the above-mentioned problems existing in the prior art, the present invention provides a method for preparing a polypropylene fiber aggregate based on the instantaneous pressure release spinning method, using a supercritical fluid as the spinning liquid, and generating a polypropylene microfiber aggregate by gas-liquid separation during the ejection process through the spinning assembly;

[0006] Another object of the present invention is to provide an application of the polypropylene fiber aggregate prepared by the instantaneous pressure release spinning method to prepare a polypropylene nonwoven fabric with high filtration efficiency, water resistance, and resistance to synthetic blood penetration.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0008] A method for preparing a polypropylene fiber assembly based on an instantaneous pressure release spinning method comprises the following steps:

[0009] S1. Add polypropylene and plasticizer into a supercritical reactor, and inject supercritical carbon dioxide under stirring to obtain a stable supercritical fluid;

[0010] S2. The supercritical fluid is instantaneously released into the atmosphere, and the supercritical fluid undergoes gas-liquid separation from the supercritical state. The plasticizer and carbon dioxide are replaced into the air in the form of gas. The polypropylene in the supercritical fluid is cooled to obtain solidified polypropylene, and the solidified polypropylene is stretched under the action of air pressure flow to form a polypropylene micro-nano fiber aggregate.

[0011] As a limitation, the polypropylene is isotactic polypropylene or metallocene polypropylene, and the melt index is 20-60 g / 10min; the plasticizer is one of dioxane, cyclohexane, dichloromethane, xylene, and ethylene glycol monomethyl ether.

[0012] As a second limitation, the mass ratio of the polypropylene to the plasticizer is 70~95:30~5.

[0013] As a third limitation, in step S1, the processing temperature of the supercritical reactor is 130-190°C, the pressure after the injection of supercritical carbon dioxide is 8-18 MPa, and the stirring time is 1-3 hours.

[0014] As a fourth limitation, in step S2, the supercritical fluid is instantaneously released into the atmosphere at a speed of 200-300 m / s.

[0015] As a fifth limitation, the diameter of the polypropylene micro-nano fiber assembly is 0.5-5 μm.

[0016] The present invention also provides an application of the above-mentioned polypropylene fiber aggregate prepared based on the instantaneous pressure release spinning method, wherein the polypropylene micro-nano fiber aggregate is used to form a polypropylene non-woven fabric after electrostatic fiber opening and hot rolling.

[0017] As a limitation, the longitudinal tensile breaking strength of the polypropylene nonwoven fabric is 190-220N, and the transverse tensile breaking strength is 110-137N.

[0018] Due to the adoption of the above technical solution, the present invention has achieved the following technical advancements compared with the prior art:

[0019] (1) The instantaneous pressure release spinning method of the present invention uses supercritical fluid as the spinning solution, which can achieve higher spinning pressure difference and spinning speed than the flash evaporation method, and can effectively avoid the recovery and treatment of organic solvents;

[0020] (2) The present invention solves the problems of large solvent pollution and difficult controllable fiber morphology in the production process of flash nonwovens through the instantaneous pressure release spinning method;

[0021] (3) In the present invention, the supercritical fluid undergoes gas-liquid separation during the instantaneous release process to form a polypropylene micro-nano fiber aggregate, which is then electrostatically opened and hot-rolled to form a polypropylene nonwoven fabric with higher filtration efficiency, water resistance, and resistance to synthetic blood penetration;

[0022] (4) The diameter of the polypropylene micro-nano fiber aggregate prepared by the present invention can reach 0.5~5μm.

[0023] The invention belongs to the technical field of polypropylene nonwoven fabrics and is used for preparing polypropylene micro-nano fiber aggregates. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a scanning electron microscope image of the polypropylene micro-nano fiber assembly prepared in Example 1 of the present invention;

[0025] Figure 2 The polypropylene nonwoven fabric is prepared from the polypropylene micro-nano fiber aggregate in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods.

[0027] Example 1 Method for preparing polypropylene fiber aggregates based on instantaneous pressure release spinning method and its application

[0028] This embodiment includes the following steps: adding 70 kg of isotactic polypropylene with a melt index of 20 g / 10 min and 30 kg of cyclohexane into a supercritical reactor at 150° C., injecting supercritical carbon dioxide to 16 MPa under mechanical stirring, and stirring for 2 hours to obtain a stable supercritical fluid; releasing the supercritical fluid into the atmosphere through a circular nozzle at an instantaneous release rate of 200 m / s, during which the supercritical fluid rapidly undergoes gas-liquid separation from the supercritical state, cyclohexane and carbon dioxide escape into the air in the form of gas, and the polypropylene in the supercritical fluid is cooled to obtain solidified polypropylene, which is then stretched under the action of air pressure flow to form a polypropylene micro-nano fiber aggregate.

[0029] like Figure 1 The figure shows a scanning electron microscope image of the polypropylene micro-nano fiber aggregate prepared in the embodiment. The cross section of the formed polypropylene micro-nano fiber aggregate is circular with a diameter of about 0.5-2 μm. The obtained polypropylene micro-nano fiber aggregate is subjected to electrostatic fiber opening and hot rolling to obtain a polypropylene nonwoven fabric, such as Figure 2 Through mechanical property testing, it was found that the longitudinal tensile breaking strength of polypropylene nonwoven fabric reached 201N, and the transverse tensile breaking strength reached 137N.

[0030] Examples 2-7 Method for preparing polypropylene fiber aggregates based on instantaneous pressure release spinning method and its application

[0031] Examples 2 to 7 are respectively a method for preparing a polypropylene fiber assembly based on an instantaneous pressure release spinning method and its application. The preparation method is basically the same as that of Example 1, except that the types and qualities of polypropylene and plasticizer used in the preparation process are different, and the process parameters are different, as shown in Table 1.

[0032] Table 1 Raw materials and process parameters of Examples 2 to 7

[0033]

[0034] In this example, the polypropylene used in Example 2 was isotactic polypropylene, and the plasticizer was dioxane. The resulting polypropylene micro-nanofiber aggregate had a diameter of approximately 0.8 to 5 μm. The resulting polypropylene micro-nanofiber aggregate was subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 190 N and a transverse tensile breaking strength of 125 N.

[0035] In Example 3, the polypropylene used was metallocene polypropylene, and the plasticizer was dichloromethane. The resulting polypropylene micro-nanofiber aggregates had a diameter of approximately 1 to 2.4 μm. The resulting polypropylene micro-nanofiber aggregates were subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 214 N and a transverse tensile breaking strength of 118 N.

[0036] In Example 4, the polypropylene used was metallocene polypropylene, and the plasticizer was xylene. The resulting polypropylene micro-nanofiber aggregates had a diameter of approximately 0.5 to 3 μm. The resulting polypropylene micro-nanofiber aggregates were subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 207 N and a transverse tensile breaking strength of 130 N.

[0037] In Example 5, the polypropylene used was isotactic polypropylene, and the plasticizer was ethylene glycol monomethyl ether. The resulting polypropylene micro-nanofiber aggregates had a diameter of approximately 1.7 to 4.2 μm. The resulting polypropylene micro-nanofiber aggregates were subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 193 N and a transverse tensile breaking strength of 118 N.

[0038] In Example 6, the polypropylene used was isotactic polypropylene, and the plasticizer was cyclohexane. The resulting polypropylene micro-nanofiber aggregates had a diameter of approximately 2.7 to 5 μm. The resulting polypropylene micro-nanofiber aggregates were subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 218 N and a transverse tensile breaking strength of 130 N.

[0039] In Example 7, the polypropylene used was metallocene polypropylene, and the plasticizer was ethylene glycol monomethyl ether. The resulting polypropylene micro-nanofiber aggregates had a diameter of approximately 0.8 to 3.5 μm. The resulting polypropylene micro-nanofiber aggregates were subjected to electrostatic opening and hot rolling to produce a polypropylene nonwoven fabric. Mechanical property testing revealed that the polypropylene nonwoven fabric exhibited a longitudinal tensile breaking strength of 216 N and a transverse tensile breaking strength of 113 N.

[0040] Comparative Example

[0041] In this example, the filtration efficiency and synthetic blood penetration resistance required by the national standard GB19082-2009 (Technical requirements for medical disposable protective clothing) are used as comparative example 1, and the water permeability required by the national standard GB / T4744-1997 (Determination of water permeability of textiles) is used as comparative example 2. The polypropylene nonwoven fabrics obtained in Examples 1 to 7 were compared to perform filtration efficiency, water permeability, and synthetic blood penetration resistance performance tests. The results are shown in Table 2.

[0042] Table 2 Performance test results

[0043]

[0044] As shown in Table 2, compared with Comparative Examples 1 and 2, the polypropylene nonwoven fabric obtained in this embodiment has good filtration efficiency, water resistance, and resistance to synthetic blood penetration, and has great application prospects in the field of protective clothing.

Claims

1. A method for preparing a polypropylene fiber assembly based on an instantaneous pressure release spinning method, characterized in that: The following steps are involved: S1. Add polypropylene and plasticizer into a supercritical reactor, and inject supercritical carbon dioxide under stirring to obtain a stable supercritical fluid; S2. The supercritical fluid is instantaneously released into the atmosphere, whereby the supercritical fluid undergoes gas-liquid separation from the supercritical state, and the plasticizer and carbon dioxide are replaced into the air in the form of gas. The polypropylene in the supercritical fluid is cooled to obtain solidified polypropylene, which is then stretched under the action of air pressure flow to form a circular polypropylene micro-nanofiber aggregate with a diameter of 0.5 to 5 μm. In step S1, the processing temperature of the supercritical reactor is 130-190°C, the pressure after the supercritical carbon dioxide is injected is 8-18 MPa, and the stirring time is 1-3 hours; In step S2, the supercritical fluid is instantaneously released into the atmosphere at a speed of 200-300 m / s; The polypropylene micro-nano fiber aggregate is used to form a polypropylene non-woven fabric after electrostatic fiber opening and hot rolling; The polypropylene nonwoven fabric has a longitudinal tensile breaking strength of 190-220N and a transverse tensile breaking strength of 110-137N; a filtration efficiency greater than 95%, water permeability of 15.4-18.3kPa, and a synthetic blood resistance level of 4.

2. The method for preparing a polypropylene fiber assembly based on instantaneous pressure release spinning according to claim 1, characterized in that: The polypropylene is isotactic polypropylene or metallocene polypropylene, and has a melt index of 20-60 g / 10 min; the plasticizer is one of dioxane, cyclohexane, dichloromethane, xylene, and ethylene glycol monomethyl ether.

3. The method for preparing a polypropylene fiber assembly based on instantaneous pressure release spinning according to claim 1, characterized in that: The mass ratio of the polypropylene to the plasticizer is 70-95:30-5.

4. An application of the instantaneous pressure release spinning method for preparing a polypropylene fiber assembly according to any one of claims 1 to 3, characterized in that: The polypropylene nonwoven fabric is used for producing medical protective materials with high filtration efficiency, water resistance and synthetic blood penetration resistance.

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