Polyvinyl alcohol fiber and meltblown fiber products

Abstract

A method for producing a nonwoven product comprising polyvinyl alcohol fibers, the method comprising the steps of: (a) dissolving a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight in the range of 14,000 to 22,000 in a copolymer of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin ester, erucic acid amine, methyl ... 1. A method for producing a meltblown nonwoven fibrous web, comprising the steps of: providing a polyvinyl alcohol composition comprising a plasticizer selected from the group consisting of methyl acrylate and mixtures thereof; and an optional stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpentanediol, propionic acid, and mixtures thereof; melting the composition at a temperature of 200°C to 230°C to form a molten polymer; extruding the molten polymer through a die having a spinneret to form molten fibers of the polymer; the fibers emerging from the die and being attenuated by a stream of heated air to form attenuated molten fibers; and depositing the attenuated fibers on a moving collector and solidifying them to form a meltblown nonwoven fibrous web.

Description

[Technical Field]

[0001] The present invention relates to polyvinyl alcohol fibers, methods of making polyvinyl alcohol fibers, and products made from polyvinyl alcohol fibers. The present invention particularly relates to, but is not limited to, products comprising meltblown polyvinyl alcohol fibers, methods of making meltblown polyvinyl alcohol fibers, and products incorporating such fibers. [Background technology]

[0002] Polyvinyl alcohol has many advantages over polymers traditionally used in the manufacture of nonwoven textiles: it dissolves in water, especially when heated, facilitating recovery, recycling, and environmental degradation.

[0003] Polyvinyl alcohol is produced by hydrolysis of homopolymers or copolymers of polyvinyl acetate. Polyvinyl alcohol produced by partial or complete hydrolysis of homopolymer polyvinyl acetate is called homopolymer polyvinyl alcohol. The degree of hydrolysis determines the properties of the resulting polymer. Copolymer polyvinyl alcohol or homopolymer polyvinyl alcohol with a low degree of hydrolysis (LD) is easy to process but has poor mechanical and chemical properties. Homopolymer polyvinyl alcohol with a high degree of hydrolysis (HD), for example, 85% or more, has excellent properties but cannot be processed without degradation under the conditions of equipment used to produce polyolefin nonwoven fibers.

[0004] Polyvinyl alcohol dissolves in water and fibers are conventionally made by solution spinning methods using polyvinyl alcohol with a low degree of hydrolysis (LD).

[0005] To improve water resistance, heat stretching, such as hot stretching, and chemical processes, such as acetylation, are required.

[0006] WO 2017 / 046361 discloses a method for producing processable polyvinyl alcohol having a degree of hydrolysis of 98% or more. WO 2022 / 008521 discloses a method for producing processable polyvinyl alcohol having a degree of hydrolysis ranging from 93% to 98% or more. WO 2022 / 008516 discloses a method for producing plasticized polyvinyl alcohol having a degree of hydrolysis of 93% to 98% or more. Summary of the Invention [Means for solving the problem]

[0007] According to a first aspect of the present invention, there is provided a method for producing a nonwoven product comprising polyvinyl alcohol fibers, the method comprising: a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight in the range of 14,000 to 35,000; a plasticizer selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide, and mixtures thereof; an optional stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpentanediol, propionic acid, and mixtures thereof; providing a polyvinyl alcohol composition comprising: Melting the composition at a temperature of 190°C to 240°C to form a molten polymer. the molten polymer comprises extruding the molten polymer through a die having a spinneret to form molten fibers of the polymer; The fibers are blown through a die and attenuated by a stream of heated air to form attenuated molten fibers, which are deposited on a moving collector and solidified to form a meltblown nonwoven fibrous web. It is melt-blown by

[0008] Meltblowing is a one-step process for converting melt-processable polymers, particularly the polyvinyl alcohol composition of the present invention, into nonwoven fabrics. Pellets of the polymer are melted, and the melt can be extruded by a spin pump through a spinneret containing multiple small orifices. The extruded polymer chains are attenuated immediately after the die using a stream of hot air. The attenuated filaments are then twisted together on a collector to form a meltblown web, thereby forming a self-bonded meltblown web composed of fine filaments of the polyvinyl alcohol composition. Meltblown nonwoven fabrics are typically characterized as having very fine filaments in the 1-5 μm range. For meltblown applications, the degree of hydrolysis can be 90-95%, preferably 93-95%.

[0009] For meltblown applications, the molecular weight of the homopolymer polyvinyl alcohol may range from 14,000 to 22,000, such as from 15,000 to 20,000, for example from 16,000 to 20,000.

[0010] Molecular weights herein are weight average molecular weights and are determined using conventional liquid chromatography techniques.

[0011] In embodiments, the composition may be melted at a temperature of from 220°C to 240°C.

[0012] The polyvinyl alcohol composition of the present invention may have a melt flow index (MFI) of 30 to 80 g / 10 min, e.g., 50 to 75 g / 10 min, e.g., 70 to 75 g / 10 min. The melt flow index referred to herein is determined at 230°C using a 10 kg weight by conventional techniques.

[0013] The polyvinyl alcohol composition of the present invention is stable at the temperatures at which it is melted and extruded. Polyvinyl alcohols without the plasticizers and stabilizers disclosed herein, especially homopolymers with a high degree of hydrolysis, may tend to decompose at the temperatures required for melting and extrusion processing.

[0014] The advantageous polyvinyl alcohol fibers of the present invention can be processed on an industrial scale using conventional meltblowing equipment.

[0015] The stabilized polyvinyl alcohol polymers used in the present invention may be prepared in accordance with WO 2022 / 008516 and WO 2022 / 008521, the disclosures of which are incorporated herein by reference for all purposes.

[0016] The polyvinyl alcohol composition introducing into a mixing reactor a polyvinyl alcohol polymer comprising a homopolymer polyvinyl alcohol or a blend thereof having a degree of hydrolysis ranging from 88% to 98% by weight or greater, The mixing reactor includes a blending chamber having a first inlet, a first outlet, and at least two interengaging components extending between the first inlet and the first outlet, the components configured to apply a shear force to the polymer while the polymer is conveyed by the components from the inlet through the reaction zone to the outlet; one or more second inlets located downstream of the first inlet for introducing reactants, including processing aids, plasticizers, and optional reaction stabilizers, into the chamber to form a reaction mixture; The plasticizer is selected from the group disclosed above, the reaction stabilizer, when present, is selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpropionic acid, and mixtures thereof; the blending chamber includes a plurality of heating zones configured to subject the mixture to a temperature profile in which the temperature increases from the inlet to the outlet; a second outlet located between the reaction zone and the first outlet configured to allow removal of a processing aid from the chamber; reacting the treating agent, plasticizer, and polymer in a reaction zone to form a plasticized polymer; passing the plasticized polymer through a first outlet; It can be made by a method comprising:

[0017] The use of a reactive mixing device, typically an extruder according to the present invention, allows the processing aids and plasticizers to react with the polyvinyl alcohol or blends thereof without decomposing the polymer, followed by removal of all or most of the processing aids through a second outlet to obtain the plasticized polyvinyl alcohol or blends thereof.

[0018] The use of reactive stabilizers can result in an advantageous reduction in the degree of degradation during melt processing, allowing homopolymer polyvinyl alcohols with high degrees of hydrolysis, for example, 88% by weight or greater, to be processed to form fibers or pellets from which fibers can be formed by extrusion.

[0019] The reaction stabilizer may be used in an amount of about 0.1% by weight to about 5% by weight, for example, about 0.1% by weight to about 3% by weight, for example, 0.1% by weight to about 1.5% by weight, for example, about 0.2% by weight to about 0.5% by weight, for example, about 0.25% by weight.

[0020] The reactive stabilizers of the present invention can reduce the degree of polymer degradation during processing. Homopolymer polyvinyl alcohol has been difficult to process due to its decomposition at the required high temperatures. This susceptibility to degradation has led to the use of polyvinyl alcohol copolymers with consequently reduced engineering properties. This can be seen by UV spectral analysis of the amount of conjugation present in the polymer. Sodium benzoate has been found to be particularly effective.

[0021] The use of homopolymer polyvinyl alcohol is particularly advantageous. Homopolymer polyvinyl alcohol is produced by hydrolysis of homopolymer polyvinyl acetate, and the degree of hydrolysis is 90% by weight or more in an embodiment of the present invention. Polyvinyl alcohol copolymers produced by hydrolysis of polyvinyl acetate copolymers have inferior properties compared to homopolymer polyvinyl alcohol. Homopolymer polyvinyl alcohol can exhibit advantageous properties.

[0022] The polyvinyl alcohol polymers of the present invention can have high tensile strength and flexibility.

[0023] Polyvinyl alcohol may be produced by hydrolysis of the homopolymer polyvinyl acetate, the degree of hydrolysis being in the range of from 88% to 98% by weight, for example from 90% to less than 95% by weight.

[0024] A blend of two or more polyvinyl alcohol polymers may be used, for example, a blend of two polyvinyl alcohol polymers having a relatively high molecular weight and a relatively low molecular weight, respectively.

[0025] Blends of polyvinyl alcohols having the same molecular weight and different degrees of hydrolysis can be combined. Mixing different polyvinyl alcohol grades together can improve the properties of the resulting polymer, such as melt strength.

[0026] For fiber production, a blend of two polyvinyl alcohol polymers having molecular weights in the range of 14,000 to 22,000, the first polymer having a low degree of hydrolysis and the second polymer having a high degree of hydrolysis, can be mixed in a ratio of 40:60 to 60:40 by weight, for example about 50:50.

[0027] The blend of polymers of different molecular weights used is selected depending on the physical properties required for the final product. This may require the use of materials of different molecular weights. The use of three or more polymers of different molecular weights may be advantageous. The use of a single molecular weight polymer is not excluded.

[0028] The use of a blend can allow for control of the viscosity of the polymer. The selection of a stabilizer according to the present invention allows for the use of a blend with a desired viscosity without compromising other properties. Alternatively, the use of a blend can allow for the use of polyvinyl alcohol containing one or more stabilizers while maintaining viscosity or other properties to allow for pellet or film production.

[0029] The processing aid is preferably water. Alternatively, the processing aid may comprise a mixture of water and one or more hydroxyl compounds having a boiling point below the boiling point or melting point of the plasticizer. For cost and environmental reasons, the use of water is preferred.

[0030] More than one plasticizer may be used.

[0031] When mixtures of plasticizers are used, two-component mixtures may be preferred.

[0032] In one embodiment, the plasticizer may be selected from the group consisting of diglycerol, triglycerol, xylose, D-mannitol, triacetin, dipentaerythritol, 1,4-butanediol, 3,3-dimethyl-1,2-butanediol, and caprolactam.

[0033] The total amount of plasticizer in the formulation can be from about 15% to about 30% by weight.

[0034] The polymer compositions and fibers of the present invention may be free of, or free of significant amounts of, water-soluble salts, oils, waxes, or ethylene homopolymers or copolymers.

[0035] The method of the present invention offers many advantages. The method allows for the formation of heat-processable polyvinyl alcohol, which can be used to produce highly functional, economical fibers while eliminating plastic pollution. Polyvinyl alcohol is water-soluble, environmentally harmless, and inherently biodegradable. Hydrophilic polymers, such as polyvinyl alcohol, degrade environmentally faster than hydrophobic polymers and do not exhibit bioaccumulation. Thermoplastic polyvinyl alcohol can be mechanically recycled and pelletized for repeated use.

[0036] The homopolymer polyvinyl alcohol fibers of the present invention offer many advantages over previously available polyvinyl alcohol-containing fibers. The fibers of the present invention and products made from these fibers exhibit improved tensile strength, barrier properties, water solubility, and biodegradability. Homopolymer polyvinyl alcohol fibers can unexpectedly exhibit all of these properties. In comparison, copolymers have only been able to provide one or more of these properties at the expense of others, impairing one or more of these properties. The fibers and products of the present invention have a desirable monomaterial structure that does not suffer from these drawbacks.

[0037] The fibers of the present invention may exhibit advantageous chemical resistance, particularly to alcohols, acids and alkalis.

[0038] The meltblown fibers of the present invention may have an advantageously smaller diameter. Fibers with a smaller diameter have a larger surface area, which may be advantageous for air filtration, for example, in face masks. Finer fibers may also have a softer texture. Furthermore, finer fibers may also have an increased rate of biodegradation after use.

[0039] According to a second aspect of the present invention, there is provided a meltblown homopolymer polyvinyl alcohol fiber having a degree of hydrolysis of 88% to 98% by weight or more, which fiber can be produced according to the first aspect of the present invention.

[0040] According to a third aspect of the present invention, there is provided a meltblown nonwoven fibrous product comprising fibers of a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% by weight or more, which product may be made according to the method of the first aspect of the present invention.

[0041] A nonwoven product is defined by ISO 9092 as an engineered fibrous assembly, primarily planar, given a desired level of structural integrity by physical and / or chemical means, excluding woven, knitted or paper-made fabrics.

[0042] Areal density is approximately 50 gm depending on the application, e.g., single or multiple use applications. -2 It could be.

[0043] In an embodiment, the areal density is about 60 gm -2 A nonwoven fabric having this density can be used to make flushable wipes.

[0044] The following processing parameters may be used:

[0045] The die temperature may range from 200° C. to 230° C. The optimum die temperature may be 220° C. Melt failure may be observed at higher temperatures.

[0046] Air flow volume is 2,000 to 7,000 liters per minute. -1 , for example, 5,900 to 6,900 liters -1 The range can be 7,000 liters per minute. -1 The higher air flow may allow for higher drawing of the polymer stream, allowing the average filament diameter to be reduced from 14.1 μm to 12.6 μm.

[0047] The die air temperature can range from 200 to 280°C, e.g., 245 to 280°C. A preferred air temperature can be 220 to 240°C. Higher die air temperatures can result in more frequent melt breakage. A die-to-collector distance of 0.1 to 0.25 m, e.g., 0.24 m, can be used. The meltblown polyvinyl alcohol nonwoven fabric of the present invention is useful in many applications that take advantage of the unique properties of homopolymer polyvinyl alcohol.

[0048] Percentages and other amounts referred to herein are by weight unless otherwise specified and are selected from any range to add up to 100%. [Brief explanation of the drawings]

[0049] The invention will now be further illustrated by way of example and not by way of limitation with reference to the accompanying drawings, in which: [Figure 1] 1 is a diagrammatic view of a meltblowing apparatus according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a die of the device shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0050] In embodiments of the present invention, the following polyvinyl alcohol (PVOH) homopolymer compositions may be used:

[0051] Polymer Composition A PVOH; degree of hydrolysis 98%; low viscosity 35.97% PVOH; degree of hydrolysis 89%; low viscosity 35.97% Trimethylolpropane 14.37% Sodium benzoate 0.21% Glycerol 4.29% Water 9.20%

[0052] Polymer Composition B PVOH; degree of hydrolysis 99%; high viscosity 7.193% PVOH; degree of hydrolysis 98%; low viscosity 64.737% Trimethylolpropane 14.37% Sodium benzoate 0.21 Glycerol 4.29% Water 9.20%

[0053] Polymer Composition C PVOH; degree of hydrolysis 98%; low viscosity 35.87% PVOH; degree of hydrolysis 89%; low viscosity 35.87% Dipentaerythritol 6.21% Triacetin 12.41% Sodium benzoate 0.25% Water 9.39%

[0054] Polymer Composition D PVOH; degree of hydrolysis 98%; low viscosity 22.61% PVOH; degree of hydrolysis 97%; intermediate viscosity 52.76% Dipentaerythritol 4.99% Sodium benzoate 0.25% Triacetin 10.00% Water 9.39%

[0055] Polymer Composition E PVOH; degree of hydrolysis 98%; low viscosity 25.20% PVOH; degree of hydrolysis 98%; low viscosity 5.20% PVOH; degree of hydrolysis 89%; low viscosity 25.21% Dipentaerythritol 5.00% Triacetin 10.00% Water 9.39%

[0056] Polymer composition F PVOH; degree of hydrolysis 98%; low viscosity 27.33% PVOH; degree of hydrolysis 98%; low viscosity 27.33% PVOH; degree of hydrolysis 89%; low viscosity 27.33% Dipentaerythritol 8.00% Methylpentanediol 5.50% Glycerol 4.50%

[0057] Polymer Composition G PVOH; degree of hydrolysis 98%; low viscosity 72.45% PVOH; Hydrolysis degree 99%; High viscosity 9.20% Dipentaerythritol 7.95% Methylpentanediol 5.63% Glycerol 4.50% Sodium benzoate 0.27%

[0058] 1 and 2 show a meltblowing apparatus used in accordance with the present invention.

[0059] An extruder (1) supplies a molten polyvinyl alcohol composition to a gear pump (2), which delivers the polymer to a die (3). An air manifold (4) delivers a first high-velocity air stream to the die outlet (5) so that the first air stream surrounds the die outlet (6) of the polymer feed (7). The first air stream generates a stream of molten fibers (8) that is directed toward a rotating cylindrical collector (9). A second air stream (10) serves to cool the stream of molten polymer fibers and promotes solidification of the polymer stream as it contacts the collector (9), forming a solidified nonwoven web (11). The solidified web (11) is drawn from the collector and wound onto a rotating winder (12). [Example]

[0060] Example 1 Meltblown polyvinyl alcohol fibers were extruded using the following parameters:

[0061] Melt-blowing of the polyvinyl alcohol composition of the present invention was carried out using the following parameters: Polymer composition A was used.

[0062] [Table 1]

[0063] A preferred polyvinyl alcohol polymer for forming the meltblown fabric had a degree of hydrolysis of 94% using trimethylolpropane as a plasticizer with additional glycerol.

[0064] The resulting meltblown fabric had a weight of 60.88 g / m before thermal bonding. 2 areal density, 0.51 mm thickness, 12.61 μm filament diameter, 3,536 l.min -2 s -1 and a tensile strength, MD, of 0.44 l / 25 mm.

[0065] A significant proportion (65%) of the filament diameters were measured between 5 and 14 μm, with an average filament diameter of 12.6 μm. The air flow rate was 6,200 l / min. -1 6,900 l.min with an air flow of -1 The average filament diameter was 14.12 μm, with a significant proportion of the filaments having a diameter between 10 and 14 μm. The higher air velocity allowed for attenuation of the polymer into finer filaments.

Claims

1. 1. A method for producing a nonwoven product comprising polyvinyl alcohol fibers, comprising: a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight in the range of 14,000 to 35,000; a plasticizer selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide, and mixtures thereof; an optional stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpentanediol, propionic acid, and mixtures thereof; providing a polyvinyl alcohol composition comprising: Melting the composition at a temperature of 190°C to 240°C to form a molten polymer. wherein the molten polymer comprises extruding the molten polymer through a die having a spinneret to form molten fibers of the polymer; the fibers are blown from the die and attenuated by a stream of heated air to form attenuated molten fibers, which are deposited on a moving collector and solidified to form a meltblown nonwoven fibrous web. Meltblown by, method.

2. 2. The method of claim 1, wherein the degree of hydrolysis is 90-95%.

3. 3. The method of claim 2, wherein the degree of hydrolysis is 93-95%.

4. 4. The method of any one of claims 1 to 3, wherein the molecular weight of the homopolymer polyvinyl alcohol ranges from 14,000 to 22,000.

5. 5. The method of claim 4, wherein the molecular weight of the homopolymer polyvinyl alcohol ranges from 15,000 to 20,000.

6. 6. The method of claim 5, wherein the molecular weight of the homopolymer polyvinyl alcohol ranges from 16,000 to 20,000.

7. The method of claim 6, wherein the composition is melted at a temperature in the range of 220°C to 230°C.

8. 8. The method of any one of claims 1 to 7, wherein the polyvinyl alcohol composition has a melt flow index in the range of 30 to 80 g / 10 min.

9. 9. The method of claim 8, wherein the polyvinyl alcohol composition has a melt flow index in the range of 50 to 75 g / 10 min.

10. 10. The method of claim 9, wherein the polyvinyl alcohol composition has a melt flow index in the range of 70 to 75 g / 10 min.

11. A method according to any one of claims 1 to 10, wherein the molten polymer is extruded through a die having a temperature in the range of 200°C to 220°C.

12. The method of any one of claims 1 to 11, wherein the air temperature at the die is in the range of 200°C to 280°C.

13. The method according to any one of claims 1 to 12, wherein the air pressure in the die is between 50 kPa and 110 kPa.

14. The method according to any one of claims 1 to 13, wherein the fibre diameter is in the range of 12 μm to 15 μm.

15. A meltblown polyvinyl alcohol fiber made according to any one of claims 1 to 14.

16. A meltblown nonwoven fabric comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% by weight or more.

17. A meltblown nonwoven fabric comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% by weight or more.

18. A meltblown nonwoven homopolymer polyvinyl alcohol fabric made by the method of any one of claims 1 to 14.

19. 19. An article of manufacture incorporating the meltblown fabric of any one of claims 16-18, wherein the article is selected from the group consisting of dry wipes, sanitary topsheets and core wraps, filters, face masks, and personal protective equipment.

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