Polyvinyl alcohol fiber and spunbond fiber products

Abstract

A method for producing a nonwoven product comprising polyvinyl alcohol fibers, the method comprising the steps of: combining 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 with a cellulose acetate copolymer containing 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 glycols, caprolactam, tricyclic trimethylolpropane, methyl cellulose, methyl ... 1. A method for spunbonding a polyvinyl alcohol web, comprising the steps of: providing a polyvinyl alcohol composition comprising a plasticizer selected from the group consisting of methylformam, rosin ester, erucamide, 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 190°C to 240°C to form a molten polymer; extruding the polymer through a die having a spinneret to form fibers of the molten polymer; drawing the fibers using an air stream, depositing them on a moving collector, and solidifying them to form a spunbond 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 spunbond polyvinyl alcohol fibers, methods of making spunbond 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 polymer through a die having a spinneret to form fibers of the molten polymer; The fibers are stretched using an air stream, deposited on a moving collector, and solidified to form a spunbond nonwoven fibrous web. It is spunbonded by

[0008] The spunbonding process is a continuous conversion technique for converting thermoplastic polymers into nonwoven fabrics. Polymer pellets are melted and the melt is extruded by a spin pump through a special spinneret with multiple holes. At the exit of the spinneret, the molten polymer is cooled and stretched by blowing air at high pressure to give strength to the individual filaments. The attenuation and stretching result in molecular orientation of the polymer during the formation of continuous filaments. The filaments can then be randomly intertwined on a conveyor belt to form a continuous filament nonwoven fabric. Thermal bonding or calendaring can be used to bond the spunbond web. In spunbond applications, the degree of hydrolysis can be 93% to 98%, for example, 93% to 97%, for example, 93% to 95%.

[0009] 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, such as from 93% to less than 98% by weight, for example from 93% to 97% by weight, for example from 93% to 95% by weight.

[0010] For spunbond 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.

[0011] Molecular weights herein are weight average molecular weights and are determined using conventional liquid chromatography techniques.

[0012] In embodiments, the composition may be melted at a temperature of from 220°C to 240°C.

[0013] The polyvinyl alcohol composition of the present invention may have a melt flow index (MFI) of 30 to 70 g / 10 min, e.g., 30 to 60 g / 10 min, e.g., 30 to 50 g / 10 min. The melt flow index referred to herein is determined at 230°C using a 10 kg weight by conventional techniques.

[0014] 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.

[0015] The present invention provides an economical one-step process for forming spunbond homopolymer nonwoven polyvinyl alcohol products directly from the extrusion of a polymer composition.

[0016] The advantageous polyvinyl alcohol fibers of the present invention can be processed on an industrial scale using conventional spunbonding equipment. The filaments can be heat-treated after solidification. Heat treatment can be performed to adjust the crystallinity of the filaments. Controlling the crystallinity can allow for control of the tensile strength of the fibers and fabrics made from the fibers. The sensitivity of the fibers or fabrics to exposure to water during use can also be reduced.

[0017] The heat treatment may be provided by calendering the fiber or fabric by passing the fiber or fabric between rollers maintained at a predetermined temperature range. The temperature of the rollers or calendering temperature may range from 100°C to 150°C, such as from 105°C to 145°C, for example from 108°C to 142°C.

[0018] The polyvinyl alcohol composition is preferably 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, tend to decompose at the temperatures required for melting and extrusion processing.

[0019] The polyvinyl alcohol of the present invention can be processed into filaments or fibers, which can be converted by crimping and cutting into stable fibers suitable for carding, wet laying, and air laying to form a variety of nonwoven products.

[0020] The advantageous polyvinyl alcohol fibers of the present invention have a fiber length of, for example, 4,500 m.min. -1 It is possible to process it on an industrial scale using equipment operating at 1000kJ / cm2.

[0021] 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.

[0022] 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 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:

[0023] 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.

[0024] 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 extruded and formed into spunbond webs.

[0025] The reactive stabilizer may be used in an amount of about 0.1% to about 5% by weight, for example, about 0.1% to about 3% by weight, for example, 0.1% to about 1.5% by weight, for example, about 0.2% to about 0.5% by weight, for example, about 0.25% by weight. The reactive stabilizer 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.

[0026] 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 93% 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.

[0027] The spunbond polyvinyl alcohol polymer fibers of the present invention can have high tensile strength and flexibility.

[0028] 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.

[0029] Blends of polyvinyl alcohols with 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. For fiber production, a blend of two polyvinyl alcohol polymers with molecular weights ranging from 22,000 to 38,000, one polymer with a low degree of hydrolysis and the other with a high degree of hydrolysis, can be mixed in a ratio of 40:60 to 60:40 by weight, for example, about 50:50.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] More than one plasticizer may be used.

[0034] When mixtures of plasticizers are used, two-component mixtures may be preferred.

[0035] In one embodiment, the one or more plasticizers 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.

[0036] The total amount of plasticizer in the formulation can be from about 15% to about 30% by weight.

[0037] The polymer compositions of the present invention may be free of, or free of significant amounts of, water-soluble salts, waxes, oils, or ethylene homopolymers or copolymers.

[0038] 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.

[0039] The spunbond 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.

[0040] According to a second aspect of the present invention, there is provided a spunbond homopolymer polyvinyl alcohol fiber having a degree of hydrolysis of 88% to 98% by weight or more and a molecular weight of 14,000 to 35,000. The fiber may be made according to the first aspect of the present invention.

[0041] According to a third aspect of the present invention, there is provided a spunbond nonwoven fibrous product comprising homopolymer polyvinyl alcohol fibres having a degree of hydrolysis of 88% to 98% by weight or more and a molecular weight of 14,000 to 35,000. The product may be made according to the method of the first aspect of the present invention.

[0042] 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.

[0043] 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.

[0044] The following is a summary of exemplary spunbond parameters according to the present invention: Polymer compositions A through G (see below) may be particularly advantageous.

[0045] The die temperature can range from 205°C to 240°C. Increasing the die temperature can reduce the viscosity of the polyvinyl alcohol polymer. Each grade of polyvinyl alcohol polymer has a threshold temperature in the range of 230°C to 250°C above which the polymer can crosslink and cause spinneret blockage.

[0046] The aspirator air pressure can be 50-110 kPa. Air pressure can have a positive effect on filament fineness. Air pressure can be increased to produce finer filaments. However, there is an optimum value to prevent melt breakage. This parameter can be influenced by both the intrinsic properties of the polymer, such as molecular weight, linearity, and crystallinity, as well as other processing parameters.

[0047] The distance between the aspirator and the collector can be 0.15 to 0.20 m. The distance between the aspirator and the collector can be optimized to achieve good collection of the filaments.

[0048] The extrusion rate can range from 2.42 to 0.97 kg / h, depending on the equipment used. Exemplary polyvinyl alcohol compositions according to the present invention can be processed successfully at high and low extrusion rates. Higher extrusion rates may result in coarser filament diameters.

[0049] The filaments may be collected on a moving conveyor, and the collected filaments may be calendered by passing them through a nip between compression rollers and then calendered between heated rollers before collection on a winder.

[0050] Calendering temperatures can range from 108° C. to 142° C. Increasing the calendering temperature can improve the tensile strength of the fabric and reduce the sensitivity of the fabric to exposure to water.

[0051] The polyvinyl alcohol spunbond fabric of the present invention exhibits a filament diameter within the range of typical spunbond fabrics and has high air permeability. The fabric exhibits swelling and partial dissolution upon contact with water. The fabric is utilized in the manufacture of dry wipes, sanitary topsheets and core wraps, filtration, and personal protective equipment, such as face masks. Percentages and other amounts referred to herein are by weight unless otherwise specified, and are selected from any range to total 100%. [Brief explanation of the drawings]

[0052] 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 spunbonding apparatus according to the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0053] The apparatus includes two extruders (3) driven by an extruder drive (1). A polymer hopper (2) feeds polymer pellets to the extruders (3). The extruders (3) feed molten polymer to a filter (4) and a pump (5). The pump feeds the polymer to a spin pack (6), which extrudes the melt-spun fibers (10) through an air quench unit (7) and an attenuator / aspirator (8). The spun fibers are deposited as a nonwoven web on a moving forming belt (11). The forming belt is an endless conveyor positioned on guide rollers (13). Edge guides (12) are provided. The belt (11) passes between a pair of compression rollers (14) and then two heated calendering rollers (15). The finished nonwoven web is collected in a winder (16).

[0054] In embodiments of the present invention, the following polyvinyl alcohol homopolymer compositions may be used:

[0055] 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%

[0056] Polymer Composition B PVOH; Hydrolysis degree 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%

[0057] 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%

[0058] 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%

[0059] 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%

[0060] 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%

[0061] 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% [Example]

[0062] Example 1 A spunbond nonwoven fabric was produced as disclosed herein. Polymer composition A was used. The following properties were observed:

[0063] Surface density is 52 to 62 g / m 2 The fabrics of the present invention had a medium to high areal density compared to typical spunbond fabrics composed of polyolefin fibers.

[0064] The thickness was 0.25-0.32 mm. The fabrics produced had thicknesses in the typical range of spunbond fabrics (0.2-1.5 mm). The filament diameters were in the range of 10-31 μm. The filament diameters were in the typical range of spunbond fabrics (15-35 μm).

[0065] Air permeability at 200Pa is 2,242~4,876lm -2 s -1 The spunbond fabrics of the present invention exhibited high air permeability. The fabrics of the present invention exhibit good breathability and low pressure drop during use. The tensile strength, MD, ranged from 5 to 13 N / 25 mm. The tensile strength of the polyvinyl alcohol nonwoven fabric was sufficient to enable conversion processes and wipe applications. Filament drawing can be increased to improve tensile strength.

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 polymer through a die having a spinneret to form fibers of molten polymer; the fibers are stretched using an air stream, deposited on a moving collector, and solidified to form a spunbond nonwoven fibrous web. The method is spunbonded by

2. The method of claim 1, wherein the nonwoven fibrous web is calendered at a temperature ranging from 100°C to 150°C.

3. The method of claim 2, wherein the nonwoven fibrous web is calendered at a temperature ranging from 108°C to 142°C.

4. The method of any one of claims 1 to 3, wherein the molten polymer is extruded from a die having a temperature in the range of 205°C to 227°C.

5. The method according to any one of claims 1 to 4, wherein the air flow is from an aspirator, and the air pressure in the aspirator is between 50 and 110 kPa.

6. The method according to any one of claims 1 to 5, wherein the air flow is from an aspirator and the distance between the aspirator and the collector is between 0.15m and 0.20m.

7. A spunbond nonwoven fabric comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% by weight or greater and a molecular weight in the range of 14,000 to 35,000.

8. A spunbond nonwoven homopolymer polyvinyl alcohol fabric made by the method of any one of claims 1 to 6.

9. 9. An article of manufacture incorporating the spunbond fabric of claim 7 or 8.

10. 10. An article of manufacture incorporating the spunbond fabric of any one of claims 7 to 9, wherein the article is selected from the group consisting of dry wipes, sanitary topsheets and core wraps, filters, face masks, and personal protective equipment.

11. A spunbond nonwoven polyvinyl alcohol fabric, wherein the polyvinyl alcohol is a homopolymer and has a degree of hydrolysis of 88% to 98% by weight or more.

12. 12. An article of manufacture incorporating the spunbond fabric of claim 11, wherein the article is selected from dry wipes, sanitary topsheets and core wraps, filters, face masks, and personal protective equipment.

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