Water-soluble modified polyvinyl alcohol and its preparation method and application

Abstract

The application discloses water-soluble modified polyvinyl alcohol and a preparation method and application thereof, and belongs to the technical field of non-woven materials. The water-soluble modified polyvinyl alcohol is obtained by blending, extruding, polyvinyl alcohol, a composite polyol plasticizing system, a melt blowing process stabilizing additive and an auxiliary additive, so that the polyvinyl alcohol is converted from a high-crystalline and high-brittle resin which cannot be directly melt blown into a water-soluble modified polyvinyl alcohol with melt flowability, drawability and thermal stability. The melt blown non-woven fabric is prepared by using the obtained water-soluble modified polyvinyl alcohol as raw material, and the stable processing of the polyvinyl alcohol under the melt blowing process condition is realized for the first time. The prepared melt blown non-woven fabric maintains the low-temperature water-soluble property of the polyvinyl alcohol, and therefore can be widely used in medical protection, industrial isolation or radioactive dust trapping scenes.

Description

Technical Field

[0001] This invention belongs to the field of nonwoven materials technology, specifically relating to a water-soluble modified polyvinyl alcohol, its preparation method, and its application. Background Technology

[0002] Currently, high-efficiency filtration disposable products such as protective clothing, air filtration materials, and medical isolation materials are usually made of nonwoven fabrics prepared from thermoplastic polymers such as polypropylene through meltblowing or composite melt spinning processes. These materials have high filtration efficiency and certain mechanical strength, but there are two prominent problems: (1) Traditional materials are not water-soluble and cannot be rapidly degraded. After use, they often need to be disposed of centrally by high-temperature incineration or chemical decomposition, which generates additional energy consumption and environmental burden. (2) The disposal process usually requires the overall collection and high-temperature destruction of pollutants (including bacteria, virus carriers, suspended particles, dust, and even radioactive particles) as solid hazardous waste. The process is complex, costly, and carries the risk of secondary exposure.

[0003] Polyvinyl alcohol (PVA) is a polymer with good hydrophilicity and water solubility, theoretically possessing the potential to be used as a base material for environmentally friendly disposable protective / filtration materials. However, conventional PVA has high crystallinity and a narrow thermal processing window; its melting temperature range is very close to its thermal degradation temperature range. Under high-temperature conditions, the melt is prone to cross-linking, charring, scaling, and even spinneret blockage, making it difficult to stably extrude and continuously stretch under the high-temperature, high-shear conditions of meltblown processes. Therefore, current technologies cannot directly use PVA to prepare microfiber nonwoven fabrics via meltblown processes, especially not nonwoven fabrics that combine microfiber structure, filtration and barrier properties, and rapid dissolution in low-temperature water. In other words, traditional meltblown nonwoven fabrics possess structural properties but are not suitable for aqueous treatment; PVA materials possess water solubility and environmental potential but lack meltblown processability and stability. Current technologies have not disclosed a method for modifying PVA to be meltblownable, further forming a controllable microfiber network structure, while maintaining rapid dissolution in low-temperature water.

[0004] Therefore, there is an urgent need for a new technical solution that enables polyvinyl alcohol materials to be processable, continuously web-forming, and capable of forming fine fiber porous structures under melt-blowing conditions, and to achieve rapid disposal with low energy consumption and low secondary hazards by direct dispersion and dissolution in low-temperature water after use. Summary of the Invention

[0005] The purpose of this invention is to provide a water-soluble modified polyvinyl alcohol, its preparation method, and its applications. By co-extruding polyvinyl alcohol, a composite polyol plasticizing system, a meltblown processing stabilizer, and auxiliary additives, polyvinyl alcohol is transformed from a highly crystalline and brittle resin that cannot be directly meltblown into a water-soluble modified polyvinyl alcohol with melt flowability, stretchability, and thermal stability.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] One technical solution of the present invention provides a water-soluble modified polyvinyl alcohol, obtained by co-extrusion of polyvinyl alcohol, a composite polyol plasticizing system, a meltblown processing stabilizer, and auxiliary additives; the composite polyol plasticizing system is composed of tris(hydroxymethyl)aminomethane (Tris) and other polyols, wherein the mass ratio of Tris(hydroxymethyl)aminomethane to other polyols is 1:(1-5), and the other polyols are at least one of glycerol, diethylene glycol, and 1,4-butanediol; the meltblown processing stabilizer includes silicone oil, stearic acid, polydimethylsiloxane, etc. At least one of polyethylene wax and fluorinated surfactant; the auxiliary additives include antioxidant / heat-stabilizing additives; the polyvinyl alcohol accounts for 70% to 90% of the water-soluble modified polyvinyl alcohol by mass; the composite polyol plasticizing system accounts for 5% to 25% of the water-soluble modified polyvinyl alcohol by mass; the meltblown processing stabilizer accounts for 0.1% to 5% of the water-soluble modified polyvinyl alcohol by mass; and the auxiliary additives account for 0.1% to 3% of the water-soluble modified polyvinyl alcohol by mass.

[0008] The water-soluble modified polyvinyl alcohol prepared by this invention has a melt index of 60-200 g / 10 min at 210-230°C.

[0009] In the water-soluble modified polyvinyl alcohol provided by this invention, the composite polyol plasticizing system interacts with the polyvinyl alcohol molecular chains through multi-point hydrogen bonding, reducing the regularity and crystallinity of the polyvinyl alcohol chain segments. This allows the polyvinyl alcohol to exhibit a flowable melt state within a temperature range below its conventional melting point, significantly widening the melt processing window of the polyvinyl alcohol and providing the necessary melt flowability for subsequent meltblown processing. The meltblown processing stabilizer provides interfacial lubrication and inhibits local thermal degradation in the high-temperature, high-shear region of the meltblown spinneret, reducing the risk of coking and scaling caused by local overheating at the spinneret, preventing spinneret breakage and spinneret blockage, thereby ensuring continuous and stable spinneret production and controllable refinement of molten polyvinyl alcohol during the high-temperature, high-speed gas flow drawing process. This invention, through the combination of its components, enables the resulting water-soluble modified polyvinyl alcohol melt to exhibit controlled shear-thinning behavior within the meltblown shear rate range. It can be drawn into ultrafine continuous fibers by high-speed hot airflow and rapidly shaped into a web after cooling. While achieving meltblown spinnability of the polyvinyl alcohol system, it maintains its water-soluble properties, thus achieving environmentally friendly disposal.

[0010] The water-soluble modified polyvinyl alcohol provided by this invention can be continuously sprayed out in a molten state at 200-240°C, and can be stretched into ultrafine fibers by high-speed hot airflow without significant charring.

[0011] Preferably, the degree of polymerization of the polyvinyl alcohol is 300-1700, more preferably 400-600, and the degree of hydrolysis is 80%-99%, more preferably 85%-90%.

[0012] Preferably, the antioxidant / heat stabilizing system additives include hindered phenolic antioxidants and phosphite heat stabilizers.

[0013] Optionally, the hindered phenolic antioxidant is selected from at least one of 2,6-di-tert-butyl-4-methylphenol (BHT), pentaerythritol tetratetra[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010), and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076); the phosphite heat stabilizer is selected from at least one of tris(2,4-di-tert-butylphenyl) phosphite, tris(nonylphenyl) phosphite, and tris(isodecylphenyl) phosphite.

[0014] Preferably, the auxiliary additives further include thioester auxiliary antioxidants.

[0015] Optionally, the thioester auxiliary antioxidant is selected from at least one of distearyl thiodipropionate and dilauryl thiodipropionate.

[0016] The second technical solution of the present invention provides a method for preparing the above-mentioned water-soluble modified polyvinyl alcohol, comprising the following steps:

[0017] Polyvinyl alcohol, a composite polyol plasticizing system, meltblown processing stabilizer and auxiliary additives are blended and melt-extruded to obtain the water-soluble modified polyvinyl alcohol.

[0018] Preferably, the temperature of the melt extrusion is 210–230°C.

[0019] The third technical solution of the present invention provides a polyvinyl alcohol-based meltblown nonwoven fabric, which is prepared by using the above-mentioned water-soluble modified polyvinyl alcohol as raw material and through conventional meltblown nonwoven fabric preparation process.

[0020] Preferably, the average fiber diameter of the polyvinyl alcohol-based meltblown nonwoven fabric is 0.5–5 μm, more preferably 1–3 μm.

[0021] Fourth technical solution of the present invention: A method for preparing polyvinyl alcohol-based meltblown nonwoven fabric, comprising the following steps:

[0022] The water-soluble modified polyvinyl alcohol is melt-extruded, and the melt is stretched by hot air to form a fiber web. The fiber web is then hot-pressed to obtain the polyvinyl alcohol-based meltblown nonwoven fabric.

[0023] Preferably, the water-soluble modified polyvinyl alcohol is dried before melt extrusion, and the drying temperature does not exceed 100°C for 8 to 30 hours.

[0024] The purpose of drying is to reduce the moisture content of water-soluble modified polyvinyl alcohol, so as to avoid bubbling, filament breakage or unstable stretching under subsequent high temperature conditions.

[0025] Preferably, the temperature of the melt extrusion is 200–240°C, more preferably 210–230°C, and the time is no more than 30 minutes.

[0026] This invention sets the residence time of the melt in the spinning device to no more than 30 minutes, which ensures that the thermal weight loss of the melt under melt-blowing shear conditions does not exceed 2wt%, thereby suppressing coking, scaling and fiber breakage in the spinning area, and ensuring the continuous formation of an ultrafine fiber network structure and stable web formation under high-speed hot airflow stretching.

[0027] Preferably, the temperature of the hot airflow is 190–240°C and the flow velocity is 100–300 m / s.

[0028] Preferably, the temperature of the hot pressing does not exceed 170°C.

[0029] The fifth technical solution of the present invention provides an application of polyvinyl alcohol-based meltblown nonwoven fabric in the preparation of protective clothing, air filter materials, medical dressings or disposable isolation products.

[0030] Protective clothing includes medical protective suits; air filtration materials include mask filter layers, air purification filter elements, industrial dust removal filter materials, or disposable air filter curtains; disposable isolation supplies include outer layers for nuclear / radioactive dust isolation or contaminated isolation sheets.

[0031] The polyvinyl alcohol-based meltblown nonwoven fabric provided by this invention is water-soluble, so it does not require high-temperature incineration or strong oxidizing chemical treatment during disposal.

[0032] The beneficial technical effects of the present invention are as follows:

[0033] The water-soluble modified polyvinyl alcohol provided by this invention, through the compounding of raw materials, not only reduces the crystallinity of polyvinyl alcohol but also broadens its melt processing window. This allows the modified polyvinyl alcohol to achieve controllable melt flowability within a temperature range below its conventional melting point and maintain continuous extrusion under melt-blowing conditions. This represents the first time that stable processing of polyvinyl alcohol under melt-blowing process conditions has been achieved.

[0034] The meltblown nonwoven fabric prepared from the water-soluble modified polyvinyl alcohol provided by this invention can be rapidly dispersed or dissolved in low-temperature water, thus making it suitable for applications such as medical protection, industrial isolation, and radioactive dust capture. This meltblown nonwoven fabric can carry away the material itself along with the adsorbed or blocked pollutant particles, microorganisms, or harmful dust. After use, it can be directly transferred and disposed of in aqueous media, avoiding high-temperature incineration or chemical decomposition. This successfully reduces the difficulty of downstream hazardous waste treatment and the risk of secondary exposure in scenarios such as medical protection, industrial isolation, and radioactive dust capture. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 The melt index is the TPVA prepared in Example 1.

[0037] Figure 2 The image shows the surface microstructure of the fiber web before hot pressing in Example 2.

[0038] Figure 3The surface microstructure of the polyvinyl alcohol-based meltblown nonwoven fabric prepared in Example 2 is shown.

[0039] Figure 4 The cross-sectional microstructure of the polyvinyl alcohol-based meltblown nonwoven fabric prepared in Example 2 is shown. Detailed Implementation

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] Example 1

[0046] Preparation of water-soluble modified polyvinyl alcohol (TPVA) particles:

[0047] Polyvinyl alcohol (degree of polymerization 400, degree of hydrolysis 88%), Tris, glycerol, diethylene glycol, polydimethylsiloxane, antioxidant 1010, and tris(2,4-di-tert-butylphenyl) phosphite were added to an extrusion apparatus in a mass ratio of 87:4.5:2.5:2.5:1.5:1.5:0.5 for blending and plasticizing. The mixture was then melt-extruded at 230°C, cooled, and pelletized to obtain TPVA granules.

[0048] The melt index of the TPVA prepared in Example 1 is shown in the figure. Figure 1 .

[0049] Depend onFigure 1 It can be seen that the melt index of TPVA at 210℃, 220℃ and 230℃ are 73.6g / 10min, 111g / 10min and 120.8g / 10min respectively, indicating that the melt has good fluidity.

[0050] Example 2

[0051] Preparation of polyvinyl alcohol-based meltblown nonwoven fabric:

[0052] The TPVA particles obtained in Example 1 were dried in a vacuum oven at 90°C for 24 hours to remove moisture. The dried particles were then melt-extruded in an extrusion spinning device. The temperature zones of the extrusion spinning device were set sequentially to 190°C, 210°C, 215°C, 220°C, and 220°C, and the time from melting to extrusion was controlled to be no more than 15 minutes. The extruded melt was stretched by a hot airflow in the molten state, so that the melt was stretched into ultrafine fibers and formed a fiber web under the action of high temperature and high speed airflow. The hot airflow temperature was 210°C and the flow rate was 200 m / s. Then, the formed fiber web was hot-pressed at 140°C to obtain polyvinyl alcohol-based meltblown nonwoven fabric.

[0053] The surface microstructure of the fiber web before hot pressing in Example 2 is shown below. Figure 2 .

[0054] The surface microstructure of the polyvinyl alcohol-based meltblown nonwoven fabric prepared in Example 2 is shown in the figure. Figure 3 .

[0055] The cross-sectional microstructure of the polyvinyl alcohol-based meltblown nonwoven fabric prepared in Example 2 is shown in [reference needed]. Figure 4 .

[0056] Depend on Figures 2 to 4 It is known that the diameter of TPVA fibers is between 1.5 and 3.5 μm. After meltblowing, the fiber web is relatively loose. After hot rolling, the TPVA meltblown nonwoven fabric fibers are tightly bonded, forming a three-dimensional structure.

[0057] Comparative Example 1

[0058] Preparation of polyvinyl alcohol-based meltblown nonwoven fabric:

[0059] Compared with Example 2, the only difference in the preparation of TPVA used compared with Example 1 is that Tris is replaced with an equal mass of glycerol and diethylene glycol in a mass ratio of 2.5:2.5. All other process parameters are the same as in Example 2.

[0060] Comparative Example 2

[0061] Preparation of polyvinyl alcohol-based meltblown nonwoven fabric:

[0062] Compared with Example 2, the only difference in the preparation of TPVA used in Example 1 is that glycerol and diethylene glycol are replaced with an equal mass of Tris, while other process parameters are the same as in Example 2.

[0063] Comparative Example 1 used only glycerol / diethylene glycol without adding Tris, and the result was that the TPVA prepared in Comparative Example 1 had a narrow meltblown window and severe yellowing.

[0064] Using only glycerol / diethylene glycol as a modifier (without Tris), the material melts in the twin-screw extruder and the melt is pale yellow and transparent. There is no obvious abnormal noise when it is extruded from the die head, but the melt output stability is poor, and there are occasional alternating phenomena of "interruption-surge". After the extruded strip cools, the surface is slightly rough and has no obvious luster.

[0065] Under conditions of 215℃ and 2.16kg load, the average melt flow rate (MFR) was 15.8 g / 10min, with significant fluctuations during the test, a standard deviation of 2.3 g / 10min (standard test three times, data were 13.2, 18.5, and 15.7 g / 10min respectively). This was attributed to melt degradation at high temperatures leading to unstable flowability. The TPVA prepared in Comparative Example 1 could only be spun into short-term continuous fibers within a spinneret temperature range of 213–217℃ and a hot air velocity range of 0.9–1.1 m / s, with a window temperature range of only 4℃ and a wind speed range of only 0.2 m / s. Furthermore, the window stability at high temperatures was extremely poor, and the continuous spinning time did not exceed 5 minutes. When the spinneret temperature rose to 220℃, the melt color rapidly deepened, changing from pale yellow to dark yellow. When the temperature reached 230℃, the melt showed signs of carbonization and could not form a fiber web at all.

[0066] Comparative Example 2 used only Tris without any other polyols, and the result was that the TPVA melt prepared in Comparative Example 2 had abnormal viscosity and poor spinnability.

[0067] After the material is added to the twin-screw extruder, obvious agglomeration still occurs in Zone 1 (190℃). After being pushed into Zone 2 (210℃), it gradually melts, but the melt is milky white and opaque with extremely poor fluidity. When the melt reaches the die head (220℃), a severe "stagnant flow" phenomenon occurs, and the screw load suddenly increases from the normal 80A to 160A (the upper limit of the rated load of the equipment), accompanied by sharp friction noise. The extruded strip is irregularly columnar with deep grooves on the surface. After cooling, it is as hard as glass and easily broken.

[0068] Under conditions of 215℃ and 2.16kg load, the average MFR was 0.5g / 10min. During the test, the melt could not flow continuously, and the data repeatability was extremely poor. Only one out of three tests yielded valid data, and the other two tests were interrupted due to melt clogging the test port. High temperature did not effectively improve its fluidity. The spinneret clogging rate reached 95%. After cleaning and retesting, the clogging rate still exceeded 90%, indicating that high temperature exacerbated the adhesion and clogging between the melt and the spinneret.

[0069] At spinning temperatures of 200–240°C, the synergistic effect of Tris and glycerol / diethylene glycol in the thermoplastic modification of PVA is more critical: Although glycerol / diethylene glycol can reduce melt viscosity to a certain extent at high temperatures, its thermal stability defects are amplified when used alone, resulting in a narrower meltblown window, more severe yellowing and degradation; Tris can improve the thermal stability of PVA at high temperatures, but due to the lack of synergistic plasticizing effect of polyols, the problem of abnormally high melt viscosity is not improved, and the spinnability is extremely poor. Only by using the two in combination can stable processing performance and product quality be achieved in this temperature range.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A water-soluble modified polyvinyl alcohol, characterized in that, This product is obtained by co-extrusion of polyvinyl alcohol, a composite polyol plasticizing system, a meltblown processing stabilizer, and auxiliary additives. The composite polyol plasticizing system is composed of tris(hydroxymethyl)aminomethane and other polyols, with a mass ratio of tris(hydroxymethyl)aminomethane to other polyols of 1:(1-5), wherein the other polyols are glycerol and diethylene glycol. The meltblown processing stabilizer includes at least one of silicone oil, stearic acid, polydimethylsiloxane, polyethylene wax, and fluorinated surfactants. The auxiliary additives are antioxidant / heat-stabilizing additives. The polyvinyl alcohol comprises 70%-90% of the water-soluble modified polyvinyl alcohol by mass; the composite polyol plasticizing system comprises 5%-25% of the water-soluble modified polyvinyl alcohol by mass; the meltblown processing stabilizer comprises 0.1%-5% of the water-soluble modified polyvinyl alcohol by mass; and the auxiliary additives comprise 0.1%-3% of the water-soluble modified polyvinyl alcohol by mass. The degree of polymerization of the polyvinyl alcohol is 300–1700, and the degree of alcoholysis is 80%–99%.

2. The water-soluble modified polyvinyl alcohol according to claim 1, characterized in that, The antioxidant / heat stabilizing system additives include hindered phenolic antioxidants and phosphite heat stabilizers.

3. A method for preparing the water-soluble modified polyvinyl alcohol according to claim 1 or 2, characterized in that, Includes the following steps: Polyvinyl alcohol, a composite polyol plasticizing system, meltblown processing stabilizer and auxiliary additives are blended and melt-extruded to obtain the water-soluble modified polyvinyl alcohol.

4. The method for preparing water-soluble modified polyvinyl alcohol according to claim 3, characterized in that, The temperature of the melt extrusion is 210–230°C.

5. A polyvinyl alcohol-based meltblown nonwoven fabric, characterized in that, It is prepared using the water-soluble modified polyvinyl alcohol as described in claim 1 or 2 as raw material through a conventional meltblown nonwoven fabric preparation process.

6. The polyvinyl alcohol-based meltblown nonwoven fabric according to claim 5, characterized in that, The average fiber diameter of the polyvinyl alcohol-based meltblown nonwoven fabric is 0.5–5 μm.

7. A method for preparing the polyvinyl alcohol-based meltblown nonwoven fabric according to claim 5 or 6, characterized in that, Includes the following steps: The water-soluble modified polyvinyl alcohol is melt-extruded, and the melt is stretched by hot air to form a fiber web. The fiber web is then hot-pressed to obtain the polyvinyl alcohol-based meltblown nonwoven fabric.

8. The method for preparing polyvinyl alcohol-based meltblown nonwoven fabric according to claim 7, characterized in that, Includes the following steps: The water-soluble modified polyvinyl alcohol is dried before melt extrusion at a temperature not exceeding 100°C for 8 to 30 hours.

9. The method for preparing polyvinyl alcohol-based meltblown nonwoven fabric according to claim 7, characterized in that, Includes the following steps: The temperature of the melt extrusion is 200–240°C and the time is no more than 30 min; and / or the temperature of the hot gas flow is 190–240°C and the flow rate is 100–300 m / s; and / or the temperature of the hot pressing is no more than 170°C.

10. The use of the polyvinyl alcohol-based meltblown nonwoven fabric according to claim 5 or 6 in the preparation of protective clothing, air filtration materials, medical dressings or disposable isolation products.

Images