TW202421868A - Polyvinyl alcohol fibres and meltblown fibrous products - Google Patents

Abstract

A method of manufacture of a nonwoven product comprising polyvinyl alcohol fibres, the method comprises the steps of: providing a polyvinyl alcohol composition comprising homopolymeric polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or greater; and a weight average molecular weight in the range from 14,000 to 22,000; a plasticiser 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-1,2-butanediol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide, and mixtures thereof; and an optional stabilizer selected from the group consisting of: sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethyl pentane diol, propionic acid and mixtures thereof; melting the composition at a temperature from 200 DEG C to 230 DEG C to form a molten polymer; wherein the molten polymer is meltblown by the steps of: extrusion of the molten polymer through a die having a spinneret to form molten fibres of the polymer; the fibres being blown from the die and attenuated by a flow of heated air to form attenuated molten fibres, the attenuated fibres being deposited on a moving collector and allowed to solidify to form a melt blown nonwoven fibre web.

Description

Polyvinyl alcohol fiber and melt-blown fiber products

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, but not exclusively, relates to products containing melt-blown polyvinyl alcohol fibers, methods of making melt-blown polyvinyl alcohol fibers, and products incorporating such fibers.

Polyvinyl alcohol has many advantages over polymers traditionally used to make non-woven fiber products. Polyvinyl alcohol is soluble in water, especially when heated, which facilitates recycling, reuse and environmental degradation.

Polyvinyl alcohol is made 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 polyvinyl alcohol or homopolymeric polyvinyl alcohol with a low degree (LD) of hydrolysis is easy to process, but its mechanical and chemical properties are poor. Homopolymeric polyvinyl alcohol with a high degree (HD) of hydrolysis, for example 85% or more, has excellent properties, but it is not processable without degradation using equipment used for polyolefin nonwoven fiber manufacturing.

Polyvinyl alcohol is soluble in water, and traditionally, polyvinyl alcohol with a low degree (LD) of hydrolysis is used to make fibers by solution spinning.

In order to improve water resistance, a thermal step such as a heat stretching step and a chemical step such as an acetylation step are required.

WO2017/046361 discloses a method for producing a processable polyvinyl alcohol having a degree of hydrolysis greater than or equal to 98%.

WO2022/008521 discloses a method for producing processable polyvinyl alcohol having a degree of hydrolysis of 93% to 98% or higher.

WO2022/008516 discloses a method for producing plasticized polyvinyl alcohol having a degree of hydrolysis of 93% to 98% or higher.

According to the first aspect of the present invention, a method for manufacturing a nonwoven product containing polyvinyl alcohol fibers comprises the following steps: Providing a polyvinyl alcohol composition, the polyvinyl alcohol composition comprising homopolymer polyvinyl alcohol having a hydrolysis degree of 88% to 98% or more and a weight average molecular weight of 14,000 to 35,000; Plasticizers selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propylene glycol, 1,4-butylene glycol, 2-hydroxy-1,3-propylene glycol, 3-methyl-1,3-butylene glycol, 3,3-dimethyl-1,2-butylene glycol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclic trimethylolpropane formal, rosin esters, erucamide and mixtures thereof; and 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 aforementioned composition at a temperature of 190°C to 240°C to form a molten polymer; Wherein the aforementioned molten polymer is melt-sprayed by the following steps: Extruding the aforementioned molten polymer through a die having a nozzle to form molten fibers of the polymer; Blowing the aforementioned fibers out of the aforementioned die and attenuating them by heated air flow to form attenuated molten fibers; and depositing the aforementioned attenuated fibers on a moving collector and solidifying them to form a melt-sprayed nonwoven fiber web.

Meltblowing is a "single-step process" for converting melt-processable polymers, particularly the polyvinyl alcohol composition of the present invention, into nonwoven fabrics. The polymer pellets can be melted and the melt is forced through a nozzle having a plurality of small holes by a spinning pump. The extruded polymer chains are attenuated with a hot air stream immediately after the die. Subsequently, the attenuated filaments are placed on a collector to form a meltblown web, thereby forming a self-bonded meltblown web composed of fine polyvinyl alcohol composition filaments. Meltblown nonwoven fabrics are characterized by having very fine filaments, typically 1 to 5 µm.

For melt blowing applications, the degree of hydrolysis can be 90% to 95%, ideally 93% to 95%.

For melt blowing applications, the molecular weight of the homopolymeric polyvinyl alcohol may be from 14,000 to 22,000, such as from 15,000 to 20,000, such as from 16,000 to 20,000.

The molecular weights in this specification are weight average molecular weights and are measured using conventional liquid chromatography techniques.

In a specific embodiment, the aforementioned composition can be melted at a temperature of 220°C to 240°C.

The melt flow index (MFI) of the polyvinyl alcohol composition of the present invention may be 30 to 80 g/10 min, such as 50 to 75 g/10 min, such as 70 to 75 g/10 min. The melt flow index mentioned in this specification is measured by conventional techniques at 230°C using a 10 kg weight.

The polyvinyl alcohol composition of the present invention is stable at the temperature at which it is melted and extruded. Polyvinyl alcohol without the plasticizer and stabilizer disclosed in this specification, specifically a homopolymer with a high degree of hydrolysis, may decompose at the temperature required for melting and extrusion processing.

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

The stable polyvinyl alcohol polymer used in the present invention can be produced according to WO2022/008516 and WO2022/008521; for all purposes, the disclosures of these international application publication documents are incorporated into this specification by reference.

The aforementioned polyvinyl alcohol composition can be manufactured by a method comprising the following steps: Introducing a polyvinyl alcohol polymer having a hydrolysis degree of 88wt% to 98wt% or higher into a mixing reactor, the polyvinyl alcohol polymer comprising homopolymer polyvinyl alcohol or a blend thereof; Wherein, the aforementioned mixing reactor comprises a mixing chamber, the mixing chamber having a main inlet, a main outlet and at least two mutually enveloping components extending between the aforementioned main inlet and the main outlet, the aforementioned components being arranged to apply shear force to the polymer when it is transported from the aforementioned inlet through the reaction zone to the aforementioned outlet; One or more secondary inlets located downstream of the main inlet are used to introduce reactants including processing aids, plasticizers and optional reactive stabilizers into the aforementioned chamber to form a reaction mixture; Wherein, the aforementioned plasticizer is selected from the group disclosed above; Wherein, when the aforementioned reactive stabilizer is present, it is selected from the group consisting of the following substances: Sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethyl propionic acid and mixtures thereof; Wherein, the aforementioned mixing chamber includes a plurality of heating zones arranged to subject the mixture to a temperature change whereby the temperature increases from the inlet to the outlet; A secondary outlet located between the reaction zone and the main outlet, the secondary outlet being arranged to allow the removal of a processing aid from the aforementioned chamber; Allowing the processing reagent, plasticizer and polymer to react in the reaction zone to produce a plasticized polymer; and Allowing the aforementioned plasticized polymer to pass from the main outlet.

According to the reactive mixing apparatus of the present invention, usually an extruder is used to react the processing aid and plasticizer with the 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 plasticized polyvinyl alcohol or its blend.

The use of a reactive stabilizer can advantageously reduce the degree of degradation during melt processing. This allows homopolymeric polyvinyl alcohol with a high degree of hydrolysis, such as 88 wt % or more, to be processed to form fibers or pellets, which can be formed from the pellets by extrusion.

The reactive stabilizer may be used in an amount of about 0.1 wt % to about 5 wt %, such as about 0.1 wt % to about 3 wt %, such as 0.1 wt % to about 1.5 wt %, such as about 0.2 wt % to about 0.5 wt %, such as about 0.25 wt %.

The reactive stabilizer of the present invention can reduce the degree of degradation of the aforementioned polymers during processing. Homopolymer polyvinyl alcohol is difficult to process because it degrades at the required high temperatures. This degradation tendency leads to the use of polyvinyl alcohol copolymers with the attendant loss of engineering properties. This can be seen by UV spectroscopy analysis of the amount of conjugation in the aforementioned polymers. Sodium benzoate has been found to be particularly effective.

The use of homopolymeric polyvinyl alcohol is particularly advantageous. In a specific embodiment of the invention, homopolymeric polyvinyl alcohol is produced by hydrolysis of homopolymeric polyvinyl acetate, with a degree of hydrolysis of 90 wt% or more. Polyvinyl alcohol copolymers produced by hydrolysis of polyvinyl acetate copolymers have inferior properties compared to homopolymeric polyvinyl alcohol. Homopolymeric polyvinyl alcohol can exhibit advantageous properties.

The polyvinyl alcohol polymer of the present invention can have high tensile strength and flexibility.

Polyvinyl alcohol can be produced by hydrolysis of homopolymerized polyvinyl acetate, wherein the degree of hydrolysis is 88 wt % to 98 wt %, such as 90 wt % to less than 95 wt %.

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.

Blends of polyvinyl alcohols with the same molecular weight and different degrees of hydrolysis can be combined. Blending different grades of polyvinyl alcohol can improve the properties of the resulting polymer, such as melt strength.

For fiber production, two polyvinyl alcohol polymers with molecular weights of 14,000 to 22,000, 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.

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

The use of blends allows the viscosity of the polymer to be controlled. The selection of stabilizers according to the present invention allows the use of blends with the desired viscosity without sacrificing other properties. Alternatively, the use of blends allows the use of polyvinyl alcohol with one or more stabilizers while maintaining viscosity or other properties to enable the manufacture of pellets or films.

The aforementioned processing aid is preferably water. Alternatively, the processing aid may include 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 reasons of cost and environment, it is desirable to use water.

Two or more plasticizers may be used.

When mixtures of plasticizers are used, binary mixtures may be preferred.

In a specific embodiment, the plasticizer 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.

The total amount of plasticizer in the formulation may be from about 15 wt % to about 30 wt %.

The polymer compositions and fibers of the present invention may not contain any or any substantial amounts of water-soluble salts, oils, waxes, or ethylene homopolymers or copolymers.

The process of the present invention provides numerous advantages. The process allows the formation of heat-processable polyvinyl alcohol, which can be used to make economical and highly functional fibers, while also eliminating plastic pollution. Polyvinyl alcohol is water-soluble, non-toxic to the environment, and biodegradable in nature. Hydrophilic polymers such as polyvinyl alcohol degrade faster in the environment than hydrophobic polymers and do not exhibit bioaccumulation. Thermoplastic polyvinyl alcohol can be mechanically recycled into pellets for repeated use.

The homopolymeric polyvinyl alcohol fibers of the present invention offer numerous advantages over previously available polyvinyl alcohol-containing fibers. The fibers of the present invention and products made from such fibers exhibit improved tensile strength, barrier properties, water solubility, and biodegradability. Homopolymeric polyvinyl alcohol fibers 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 a desired single material structure that does not suffer from such drawbacks.

The fibers of the present invention can exhibit advantageous chemical resistance, particularly to alcohols, acids and bases.

The meltblown fibers of the present invention may have advantageously smaller diameters. Fibers with smaller diameters have larger surface areas, which may be advantageous for air filtration, such as in a face mask. Finer fibers may also be softer in texture. In addition, finer fibers may also have an increased biodegradation rate after use.

According to a second aspect of the present invention, a melt-blown homopolymerized polyvinyl alcohol fiber is provided, wherein the degree of hydrolysis of the melt-blown homopolymerized polyvinyl alcohol fiber is 88 wt % to 98 wt % or higher. The fiber can be manufactured according to the first aspect of the present invention.

According to a third aspect of the present invention, a meltblown nonwoven fiber product is provided, the product comprising homopolymerized polyvinyl alcohol fibers having a degree of hydrolysis of 88 wt % to 98 wt % or more. The product can be manufactured according to the method of the first aspect of the present invention.

ISO9092 defines nonwoven products as engineered fiber components that are primarily planar, and the design standards given are based on the overall structure of the engineered fiber component obtained by physical and/or chemical means that do not include weaving, knitting or papermaking.

The areal density may be about 50 g/ ^m2 , depending on the application, such as single or multiple use applications.

In a specific embodiment, the surface density may be about 60 g/m ^2. Nonwoven fabrics having such a density may be used in the manufacture of flushable wipes.

The following process parameters can be used.

The mold temperature may be 200° C. to 230° C. The optimum mold temperature may be 220° C. Melt fracture may be observed at higher temperatures.

The air flow rate may be 2,000 to 7,000 l/min, for example 5,900 to 6,900 l/min. A higher air flow rate of 7,000 l/min may result in greater stretching of the polymer stream and may reduce the average filament diameter from 14.1 µm to 12.6 µm.

The air temperature at the mold may be 200°C to 280°C, such as 245°C to 280°C. An ideal air temperature may be 220°C to 240°C. Increasing the air temperature at the mold to a higher temperature may result in more frequent melt fractures. The distance from the mold to the collector used may be 0.1 to 0.25 m, such as 0.24 m.

The melt-blown polyvinyl alcohol nonwoven fabric of the present invention has many applications, and these applications utilize the unique properties of homopolymer polyvinyl alcohol.

The percentages and other amounts mentioned in this specification are by weight unless otherwise stated and are selected from any of the listed ranges and total 100%.

In a specific embodiment of the present invention, the following polyvinyl alcohol (PVOH) homopolymer composition can be used.

Polymer composition A PVOH; hydrolysis degree 98%; low viscosity                           35.97% PVOH; hydrolysis degree 89%; low viscosity                             35.97% Trihydroxymethylpropane                                                                                           14.37% Sodium benzoate                                                                                                     0.21% Glycerin                                                                                                 4.29% Water                                                                                 9.20%

Polymer composition B PVOH; hydrolysis degree 99%; high viscosity                           7.193% PVOH; hydrolysis degree 98%; low viscosity                             64.737% Trihydroxymethylpropane       ...

Polymer composition C PVOH; hydrolysis degree 98%; low viscosity                           35.87% PVOH; hydrolysis degree 89%; low viscosity                             35.87% Dipentaerythritol       ...

Polymer composition D PVOH; hydrolysis degree 98%; low viscosity                           22.61% PVOH; hydrolysis degree 97%; medium viscosity                                 52.76% Dipentaerythritol                                                                     4.99% Sodium benzoate                                                                                                             0.25% Triacetin     ...

Polymer composition E PVOH; hydrolysis degree 98%; low viscosity                           25.20% PVOH; hydrolysis degree 98%; low viscosity                                   5.20% PVOH; hydrolysis degree 89%; low viscosity                               25.21% Dipentaerythritol       ...

Polymer composition F PVOH; hydrolysis degree 98%; low viscosity                           27.33% PVOH; hydrolysis degree 98%; low viscosity                             27.33% PVOH; hydrolysis degree 89%; low viscosity                           27.33% Dipentaerythritol       ...

Polymer composition G PVOH; hydrolysis degree 98%; low viscosity                           72.45% PVOH; hydrolysis degree 99%; high viscosity                                                 9.20% Dipentaerythritol                                                                       7.95% Methylpentanediol                                                       5.63% Glycerin                                                                                                 4.50% Sodium benzoate                                                                                             0.27%

Figures 1 and 2 show a meltblowing apparatus used according to the present invention.

The extruder (1) supplies the molten polyvinyl alcohol composition to the gear pump (2), and the gear pump (2) supplies the aforementioned polymer to the mold (3). The air manifold (4) supplies a high-speed primary airflow to the mold outlet (5), so that the primary airflow surrounds the mold outlet (6) of the polymer feed port (7). The primary airflow generates a molten fiber flow (8) toward a rotating cylindrical collector (9). The secondary airflow (10) is used to cool the molten polymer fiber flow to promote its solidification when the polymer flow contacts the collector (9), thereby forming a solidified nonwoven web (11). The solidified web (11) is pulled out of the collector (9) and wound on a rotating winder (12). [Example]

Example 1 Melt-blown polyvinyl alcohol fibers were extruded using the following parameters.

The following parameters were used to melt-blow the polyvinyl alcohol composition of the present invention. Polymer composition A was used.

Melt spraying parameters Parameters Extrusion Zone 1 180℃ Extrusion Zone 2 200℃ Extrusion zone 3 205℃ Mold temperature 210℃ to 220℃ Air temperature 240℃ to 280℃ Air flow 6900 l/min Distance from mold to collector 0.1 to 0.3 m Extrusion speed 6 to 16 rpm Die hole diameter 0.25mm Air Angle 45° Air knife gap 0.7 to 1.4 mm

Advantageous polyvinyl alcohol polymers for forming melt-blown fabrics have a degree of hydrolysis of 94%, trihydroxymethylpropane is used as a plasticizer and glycerol is added.

The melt-blown fabric had an area density of 60.88 g/m ² and a thickness of 0.51 mm. The filament diameter was 12.61 µm. Before thermal bonding, the air permeability at 200 Pa was 3,536 l·min ^-2 s ^-1 and the tensile strength MD was 0.44 l/25 mm.

A large proportion (65%) of the filaments measured 5 to 14µm in diameter, with an average filament diameter of 12.6µm. At an air flow rate of 6,200 l/min, the air velocity was 6,900 l/min, and a large proportion of the filaments were 10 to 14µm in diameter, with an average filament diameter of 14.12µm. The higher air velocity thinned the aforementioned polymer into fine filaments.

1: Extruder 2: Gear Pump 3: Die 4: Air Manifold 5: Die Outlet 6: Die Outlet for Polymer Feed 7: Polymer Feed 8: Molten Fiber Stream 9: Collector 10: Secondary Air Stream 12: Winder

The present invention is further described by way of examples and with reference to the drawings, but is not intended to be limiting of the present invention. In the drawings: [Figure 1] is a schematic diagram of a meltblowing apparatus according to the present invention; and [Figure 2] is a cross-sectional view of a mold of the apparatus shown in Figure 1

Claims (19)

A method for manufacturing a nonwoven product containing polyvinyl alcohol fibers, the method comprising the following steps: Providing a polyvinyl alcohol composition, the polyvinyl alcohol composition comprising homopolymer polyvinyl alcohol having a hydrolysis degree of 88% to 98% or more and a weight average molecular weight of 14,000 to 35,000; Plasticizers selected from the group consisting of diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, methylpentanediol, 1,2-propylene glycol, 1,4-butylene glycol, 2-hydroxy-1,3-propylene glycol, 3-methyl-1,3-butylene glycol, 3,3-dimethyl-1,2-butylene glycol, polyethylene glycol 300, polyethylene glycol 400, alkoxylated polyethylene glycol, caprolactam, tricyclotrihydroxymethylpropane methyl acetal, rosin ester, erucamide and mixtures thereof; and 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 molten polymer is melt-blown by the following steps: Extruding the molten polymer through a die having a nozzle to form molten fibers of the polymer; Blowing the fibers out of the die and thinning them by a heated air flow to form thinned molten fibers, which are deposited on a moving collector and solidified to form a melt-blown nonwoven fiber web. The method as described in claim 1, wherein the degree of hydrolysis is 90% to 95%. The method as described in claim 2, wherein the degree of hydrolysis is 93% to 95%. The method as described in any one of claims 1 to 3, wherein the molecular weight of the homopolymer polyvinyl alcohol is 14,000 to 22,000. The method as described in claim 4, wherein the molecular weight of the homopolymer polyvinyl alcohol is 15,000 to 20,000. The method as described in claim 5, wherein the molecular weight of the homopolymer polyvinyl alcohol is 16,000 to 20,000. The method of claim 6, wherein the composition is melted at a temperature in the range of 220°C to 230°C. The method as described in any one of claims 1 to 7, wherein the melt flow index of the polyvinyl alcohol composition is 30 to 80 g/10 min. The method as described in claim 8, wherein the melt flow index of the polyvinyl alcohol composition is 50 to 75 g/10 min. The method as described in claim 9, wherein the melt flow index of the polyvinyl alcohol composition is 70 to 75 g/10 min. A method as described in any one of claims 1 to 10, wherein the molten polymer is extruded from a die at a temperature in the range of 200°C to 220°C. A method as described in any one of claims 1 to 11, wherein the air temperature at the mold is 200°C to 280°C. A method as described in any one of claims 1 to 12, wherein the air pressure at the mold is 50 to 110 kPa. A method as described in any one of claims 1 to 13, wherein the fiber diameter is 12 to 15 µm. A melt-blown polyvinyl alcohol fiber produced according to the method as described in any one of claims 1 to 14. A meltblown nonwoven fabric comprises homopolymerized polyvinyl alcohol having a hydrolysis degree of 88 wt % to 98 wt % or more. A meltblown nonwoven fabric is composed of homopolymerized polyvinyl alcohol having a hydrolysis degree of 88 wt % to 98 wt % or higher. A meltblown nonwoven homopolymer polyvinyl alcohol fabric produced by the method as described in any one of claims 1 to 14. A product blended with the meltblown fabric as described in any one of claims 16 to 18, wherein the product is selected from the group consisting of dry wipes, hygiene top sheets and core wraps, filters, face masks, and personal protective equipment.