Polyvinyl alcohol fibers and spunbond fiber products

Abstract

A method of making a nonwoven product comprising polyvinyl alcohol fibers, the method comprising the steps of: providing a polyvinyl alcohol composition comprising a homo-polyving akohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight of 14,000 to 35,000; a plasticizer selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methyl pentanediol, 1, 2-propanediol, 1, 4-butanediol, 2-hydroxy-1, 3-propanediol, 3-methyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3, 3-dimethyl-1, 3-butanediol, 3 the component A is prepared from 1, 2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane methylal, abietate, erucyl amide and a mixture of 1, 2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol and caprolactam; and an optional stabilizer selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethyl pentanediol, propionic acid, and mixtures thereof; melting the composition at a temperature of 190 DEG C to 240 DEG C to form a molten polymer; wherein the molten polymer is spun-bonded by: extruding the polymer through a mold having a spinneret to form molten polymer fibers; the fibers are stretched using a gas stream, deposited on a moving collector and allowed to cure to form a spunbonded nonwoven web.

Description

[0001] The present invention relates to polyvinyl alcohol fibers, methods for manufacturing polyvinyl alcohol fibers, and products made from polyvinyl alcohol fibers. The present invention particularly but not exclusively relates to products comprising spunbond polyvinyl alcohol fibers, methods for manufacturing spunbond polyvinyl alcohol fibers, and products incorporating such fibers.

[0002] Compared with polymers conventionally used for manufacturing non-woven fiber products, polyvinyl alcohol has many advantages. Polyvinyl alcohol is soluble in water, especially when heated, which facilitates recycling, reuse, and environmental degradation.

[0003] Polyvinyl alcohol is prepared by hydrolysis of homopolymers or copolymers of polyvinyl acetate. Polyvinyl alcohol made by partial or complete hydrolysis of homopolymeric polyvinyl acetate is called homopolymeric polyvinyl alcohol. The degree of hydrolysis determines the properties of the resulting polymer. Copolymeric or homopolymeric polyvinyl alcohol with low degree (LD) of hydrolysis is easy to process, but its mechanical and chemical properties are poor. Homopolymeric polyvinyl alcohol with high degree (HD) of hydrolysis, such as a degree of hydrolysis of 85% or higher, has excellent properties, but it is not processable without degradation under the conditions of equipment used for manufacturing polyolefin non-woven fibers.

[0004] Polyvinyl alcohol is soluble in water, and fibers are conventionally manufactured from polyvinyl alcohol with low degree (LD) of hydrolysis by solution spinning.

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

[0006] WO2017 / 046361 discloses a method for manufacturing processable polyvinyl alcohol with a degree of hydrolysis greater than or equal to 98%.

[0007] WO2022 / 008521 discloses a method for manufacturing processable polyvinyl alcohol with a degree of hydrolysis of 93% to 98% or higher.

[0008] WO2022 / 008516 discloses a method for manufacturing plasticized polyvinyl alcohol with a degree of hydrolysis of 93% to 98% or higher.

[0009] According to a first aspect of the present invention, a method for manufacturing a non-woven product comprising polyvinyl alcohol fibers comprises the following steps:

[0010] Providing a polyvinyl alcohol composition comprising homopolymeric polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or higher and a weight average molecular weight of 14,000 to 35,000;

[0011] Plasticizers 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 ester, erucamide and mixtures thereof; and

[0012] Optional stabilizers selected from the group consisting of sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpentanediol, propionic acid and mixtures thereof;

[0013] Melting the composition at a temperature of 190 °C to 240 °C to form a molten polymer;

[0014] wherein the spunbonding of the molten polymer is carried out by the following steps:

[0015] Extruding the polymer through a die having a spinneret to form molten polymer fibers;

[0016] Stretching the fibers using an air stream, depositing them on a moving collector and curing them to form a spunbond nonwoven fiber web.

[0017] The spunbond process is a continuous conversion technology for converting thermoplastic polymers into nonwoven fabrics. Polymer pellets are melted and the melt is forced through a special spinneret with a large number of holes by a spinning pump. At the exit of the spinneret, the molten polymer is cooled and stretched by high-pressure blowing air to impart strength to the individual filaments. During the formation of continuous filaments, thinning and elongation result in molecular orientation of the polymer. The filaments can then be randomly laid on a conveyor belt to form a continuous filament nonwoven fabric. Thermal bonding or calendering can be used to bond the spunbond web.

[0018] For spunbond applications, the degree of hydrolysis can be 93% to 98%, such as 93% to 97%, such as 93% to 95%.

[0019] Polyvinyl alcohol can be manufactured by hydrolysis of homopolymeric polyvinyl acetate, wherein the degree of hydrolysis is 88 wt% to 98%, such as 93 wt% to less than 98%, such as 93 wt% to 97%, such as 93 wt% to 95%.

[0020] For spunbond applications, the molecular weight of homopolymeric polyvinyl alcohol can be 14,000 to 22,000, such as 15,000 to 20,000, such as 16,000 to 20,000.

[0021] The molecular weight in this specification is the weight-average molecular weight and is measured using conventional liquid chromatography techniques.

[0022] In an embodiment, the composition may be melted at a temperature of 220 °C to 240 °C.

[0023] The melt flow index (MFI) of the polyvinyl alcohol composition of the present invention may be 30 to 70 g / 10 min, such as 30 to 60 g / 10 min, such as 30 to 50 g / 10 min. The melt flow index mentioned in this specification is determined using a weight of 10 kg at 230 °C by conventional techniques.

[0024] The polyvinyl alcohol composition of the present invention is stable at the temperature at which it is melted and extruded. Polyvinyl alcohol without the plasticizers and stabilizers disclosed herein, specifically homopolymers with a high degree of hydrolysis, may decompose at the temperatures required for melt and extrusion processing.

[0025] The present invention provides an economical "one-step" process that directly forms a spunbonded homopolymer polyvinyl alcohol nonwoven product by extruding the polymer composition.

[0026] The advantageous polyvinyl alcohol fibers of the present invention can be processed on a commercial scale using conventional spunbond equipment.

[0027] The filaments can be heat-treated after curing. Heat treatment can be carried out to change the crystallinity of the filaments. Controlling the crystallinity allows control of the tensile strength of the fibers and the fabric made from the fibers. It can also reduce the sensitivity of the fibers or fabric to exposure to water during use.

[0028] Heat treatment can be provided by passing the fibers or fabric between rolls maintained within a predetermined temperature range to calender the fibers or fabric. The temperature of the rolls or the calendering temperature can be 100 °C to 150 °C, such as 105 °C to 145 °C, such as 108 °C to 142 °C.

[0029] The polyvinyl alcohol composition is preferably stable at the temperature at which it is melted and extruded. Polyvinyl alcohol without the plasticizers and stabilizers disclosed herein, specifically homopolymers with a high degree of hydrolysis, is prone to decomposition at the temperatures required for melt and extrusion processing.

[0030] The polyvinyl alcohol according to the present invention can be processed into filaments or fibers. These filaments or fibers can be converted into short fibers suitable for carding, wet laying, and air laying by crimping and cutting, thereby forming a series of nonwoven products.

[0031] The advantageous polyvinyl alcohol fibers of the present invention can be processed on a commercial scale, for example, using equipment operating at 4,500 m / min.

[0032] The stable polyvinyl alcohol polymers used in the present invention can be manufactured according to WO2022 / 008516 and WO2022 / 008521; for all purposes, the disclosures of these international application publication documents are incorporated herein by reference.

[0033] The polyvinyl alcohol composition can be manufactured by a method comprising the following steps:

[0034] Introduce a polyvinyl alcohol polymer with a degree of hydrolysis of 88 wt% to 98 wt% or higher, which comprises a homopolymer polyvinyl alcohol or its blend, into a mixing reactor.

[0035] Wherein, the mixing reactor comprises a blending chamber, the blending chamber is provided with a main inlet, a main outlet and at least two mutually meshing members extending between the main inlet and the main outlet, and the members are arranged to apply a shearing force to the polymer when transporting the polymer from the inlet through the reaction zone to the outlet.

[0036] One or more secondary inlets provided downstream of the main inlet are used to introduce reactants including processing aids, plasticizers and reactive stabilizers into the chamber to form a reaction mixture.

[0037] Wherein the plasticizer is selected from the group disclosed above;

[0038] Wherein when the reactive stabilizer is present, it is selected from the group consisting of:

[0039] Sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpropanoic acid and their mixtures;

[0040] Wherein, the mixing chamber comprises a plurality of heating zones arranged such that the temperature increases from the inlet to the outlet, so that the mixture undergoes a temperature change.

[0041] A secondary outlet located between the reaction zone and the main outlet, which is arranged to allow the removal of the processing aid from the chamber.

[0042] React the processing aid, plasticizer and polymer in the reaction zone to produce a plasticized polymer; and

[0043] Pass the plasticized polymer through the main outlet.

[0044] According to the reactive mixing equipment of the present invention, usually the use of an extruder enables the processing aid and plasticizer to react with polyvinyl alcohol or its blend without decomposing the polymer, and then all or most of the processing aid is removed from the secondary outlet to obtain a plasticized polyvinyl alcohol or its blend.

[0045] The use of a reactive stabilizer can advantageously reduce the degree of degradation during melt processing. This allows for the processing of homopolymeric polyvinyl alcohol with a high degree of hydrolysis, such as 88 wt% or higher, to form fibers or pellets. Fibers can be extruded from the pellets and formed into a spunbond web.

[0046] The amount of the reactive stabilizer can be from about 0.1 wt% to about 5 wt%, such as from about 0.1 wt% to about 3 wt%, such as 0.1 wt% to about 1.5 wt%, such as from about 0.2 wt% to about 0.5 wt%, such as about 0.25 wt%.

[0047] The reactive stabilizer of the present invention can reduce the degree of degradation of the polymer during processing. Homopolymeric polyvinyl alcohol is difficult to process due to degradation at the required high temperatures. This degradation tendency has led to the use of polyvinyl alcohol copolymers, resulting in a loss of engineering properties. This can be seen by UV spectroscopic analysis of the number of conjugated bonds in the polymer. Sodium benzoate has been found to be particularly effective.

[0048] The use of homopolymeric polyvinyl alcohol is particularly advantageous. In an embodiment of the present invention, the homopolymeric polyvinyl alcohol is manufactured by hydrolysis of homopolymeric polyvinyl acetate, with a degree of hydrolysis of 93 wt% or higher. Polyvinyl alcohol copolymers made by hydrolysis of polyvinyl acetate copolymers have poorer properties compared to homopolymeric polyvinyl alcohol. Homopolymeric polyvinyl alcohol can exhibit advantageous properties.

[0049] The spunbond polyvinyl alcohol polymer fibers of the present invention can have high tensile strength and flexibility.

[0050] Blends of two or more polyvinyl alcohol polymers can be used, such as blends of two polyvinyl alcohol polymers having relatively high molecular weight and relatively low molecular weight, respectively.

[0051] Blends of polyvinyl alcohol having the same molecular weight and different degrees of hydrolysis can be combined. Blending different grades of polyvinyl alcohol together can improve the properties of the resulting polymer, such as melt strength.

[0052] For fiber production, two polyvinyl alcohol polymers with molecular weights of 22,000 to 38,000, namely a first polymer with a low degree of hydrolysis and a second polymer with a high degree of hydrolysis, can be blended in a weight ratio of 40:60 to 60:40, such as about 50:50.

[0053] The blend of polymers with different molecular weights used is selected according to the physical properties required for the finished product. This may require the use of materials with different molecular weights. It may be advantageous to use more than two polymers with different molecular weights. The use of a single molecular weight polymer is not excluded.

[0054] The use of blends allows the control of the viscosity of the polymer. The selection of the stabilizer according to the invention allows the use of blends with the desired viscosity without loss of other properties. Alternatively, the use of blends allows the use of polyvinyl alcohol together with one or more stabilizers while maintaining the viscosity or other properties, making it possible to manufacture pellets or films.

[0055] The processing aid is preferably water. Alternatively, the processing aid may comprise a mixture of water and one or more hydroxy compounds having a boiling point lower than the boiling point or melting point of the plasticizer. For cost and environmental reasons, water is preferably used.

[0056] Two or more plasticizers can be used.

[0057] When using a mixture of plasticizers, a binary mixture can be preferred.

[0058] In one embodiment, one or more plasticizers can 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.

[0059] The total amount of plasticizer in the formulation can be from about 15 wt% to about 30 wt%.

[0060] The polymer composition of the present invention may not contain any or any substantial amount of water-soluble salts, waxes, oils, or ethylene homopolymers or copolymers.

[0061] The method of the present invention offers many advantages. The method allows the formation of thermally processable polyvinyl alcohol while also eliminating plastic pollution. The thermally processable polyvinyl alcohol can be used to manufacture fibers that are both economical and highly functional. Polyvinyl alcohol is water-soluble, non-toxic to the environment, and inherently biodegradable. Hydrophilic polymers such as polyvinyl alcohol degrade faster in the environment than hydrophobic polymers and do not exhibit bioaccumulation. The thermoplastic polyvinyl alcohol can be mechanically recycled into pellets for reuse.

[0062] The spunbond fibers of the present invention can have an advantageously small diameter. Fibers with a smaller diameter have a larger surface area, which can be beneficial for air filtration, such as in face masks. The finer fiber texture can also be softer. In addition, the finer fibers can also have an increased biodegradation rate after use.

[0063] According to a second aspect of the present invention, there is provided a spunbonded homopolymer polyvinyl alcohol fiber having a degree of hydrolysis of 88 wt% to 98 wt% or higher and a molecular weight of 14,000 to 35,000. The fiber can be manufactured according to the first aspect of the present invention.

[0064] According to a third aspect of the present invention, there is provided a spunbond nonwoven fiber product comprising homopolymer polyvinyl alcohol fibers having a degree of hydrolysis of 88 wt% to 98 wt% or higher and a molecular weight of 14,000 to 35,000. The product can be manufactured according to the method of the first aspect of the present invention.

[0065] ISO9092 defines a nonwoven product as an engineered fiber assembly that is predominantly planar and is given a level of structural integrity by physical and / or chemical means that exclude weaving, knitting, or papermaking.

[0066] Compared with previously available fibers containing polyvinyl alcohol, the homopolymer polyvinyl alcohol fibers of the present invention offer many advantages. The fibers of the present invention and products made from these fibers exhibit improved tensile strength, barrier properties, water solubility, and biodegradability. The homopolymer polyvinyl alcohol fibers can unexpectedly exhibit all of these properties. In contrast, copolymers can only compromise and provide one or more of these properties at the expense of other properties. The fibers and products of the present invention have the desired single-material structure that does not suffer from this drawback.

[0067] The following is a summary of exemplary spunbond parameters according to the present invention. Polymer compositions A to G (see below) may be particularly advantageous.

[0068] The die temperature can be 205 °C to 240 °C. Increasing the die temperature may reduce the viscosity of the polyvinyl alcohol polymer. Each grade of polyvinyl alcohol polymer has a threshold temperature range of 230 °C to 250 °C, and the polymer may crosslink outside this threshold temperature range, resulting in spinneret blockage.

[0069] The air pressure at the aspirator can be 50 to 110 kPa. This air pressure may have a positive effect on the filament fineness. The air pressure can be increased to produce finer filaments. However, there is an optimum value to prevent melt fracture. This parameter may be affected by the inherent properties of the polymer such as molecular weight, linearity, and crystallinity and other process parameters.

[0070] The distance from the aspirator to the collector can be 0.15 to 0.20 m. The distance between the aspirator and the collector can be optimized for good filament collection.

[0071] The extrusion speed can be 2.42 to 0.97 kg / h, depending on the equipment used. The exemplary polyvinyl alcohol compositions according to the present invention can be successfully processed at high and low extrusion speeds. Higher extrusion speeds may result in coarser filament diameters.

[0072] The filaments can be collected on a moving conveyor belt. The collected filaments can be calendered through the nip between the compaction rollers and then through the nip between the heating rollers before being collected on a winder.

[0073] The calendering temperature can be from 108 °C to 142 °C. Increasing the calendering temperature can increase the tensile strength of the fabric and reduce the sensitivity of the fabric when exposed to water.

[0074] 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 when in contact with water. The fabric finds applications in the manufacture of dry wipes, hygiene top sheets and core wraps, filtration media and personal protective equipment such as face masks.

[0075] Percentages and other amounts mentioned in this specification are by weight unless otherwise indicated and are selected from any of the recited ranges and total 100%.

[0076] The present invention is further illustrated by way of examples but not in any limiting sense and with reference to the accompanying drawings, in which:

[0077] Figure 1 is a schematic view of a spunbond apparatus according to the present invention.

[0078] The apparatus includes two extruders (3) driven by an extruder drive (1). A polymer hopper (2) supplies polymer pellets to the extruders (3). The extruders (3) supply the molten polymer to a filter (4) and a pump (5). The pump (5) supplies the polymer to a spinning assembly (6) which extrudes the molten spinning fibers (10) through an air quencher (7) and a tapering / draw-off device (8). The spinning fibers (10) are deposited on a moving forming belt (11) in the form of a nonwoven web. The forming belt (11) is an endless conveyor belt located on guide rollers (13). Edge guides (12) are provided. The forming belt (11) passes between a pair of compaction rollers (14) and subsequently between two heated calender rollers (15). The final nonwoven web is collected on a winder (16).

[0079] In an embodiment of the present invention, the following polyvinyl alcohol homopolymer compositions can be used.

[0080] Polymer composition A

[0081]

[0082]

[0083] Polymer composition B

[0084]

[0085] Polymer composition C

[0086]

[0087] Polymer composition D

[0088]

[0089] Polymer composition E

[0090]

[0091]

[0092] Polymer composition F

[0093]

[0094] Polymer composition G

[0095]

[0096] Example 1

[0097] A spunbond nonwoven fabric was manufactured as disclosed in this specification. Polymer composition A was used. The following properties were observed.

[0098] The areal density is 52 to 62 g / m 2 . Compared with a typical spunbond fabric composed of polyolefin fibers, the fabric of the present invention has a medium to high areal density.

[0099] The thickness is 0.25 to 0.32 mm. The thickness of the produced fabric is within the typical range for spunbond fabrics (0.2 to 1.5 mm).

[0100] The filament diameter is 10 to 31 μm. The filament diameter is within the typical range for spunbond fabrics (15 to 35 μm).

[0101] The air permeability at 200 Pa is 2,242 to 4,876 l.m -2 s -1 . The spunbond fabric of the present invention exhibits high air permeability. The fabric of the present invention shows good breathability and low pressure drop in use.

[0102] The tensile strength MD is 5 to 13 N / 25 mm. The tensile strength of the polyvinyl alcohol nonwoven fabric is sufficient to enable it to undergo conversion processes and wipe applications. The filament stretching can be enhanced to increase the tensile strength.

Claims

1. A method for manufacturing a nonwoven product containing polyvinyl alcohol fibers, the method comprising the following steps: providing a polyvinyl alcohol composition comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or higher and a weight average molecular weight 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 ester, erucic acid amide, 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; wherein the spunbonding of the molten polymer is carried out by the following steps: extruding the polymer through a die having a spinneret to form molten polymer fibers; drawing the fibers using an air stream, depositing them on a moving collector and curing them to form a spunbond nonwoven fiber web.

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

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

4. The method according to any one of the preceding claims, wherein the molten polymer is extruded from a die at a temperature of 205 °C to 227 °C.

5. The method according to any one of the preceding claims, wherein the air stream comes from a suction device, and the air pressure at the suction device is 50 to 110 kPa.

6. The method according to any one of the preceding claims, wherein the air stream comes from a suction device, and the distance from the suction device to the collector is 0.15 to 0.20 m.

7. A spunbond nonwoven fabric comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88 wt% to 98 wt% or higher and a molecular weight of 14,000 to 35,000.

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

9. A product incorporating the spunbond fabric according to any one of claims 7 or 8.

10. A product incorporating the spunbond fabric according to any one of claims 7 to 9, wherein the product is selected from the group consisting of: dry wipes, sanitary top sheets and core-spun tapes, filter media, 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 wt% to 98 wt% or higher.

12. A product incorporating the spunbond fabric of claim 11, wherein the product is selected from dry wipes, sanitary topsheets and core-spun tapes, filter media, face masks, and personal protective equipment.

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