Polyvinyl alcohol fibers and fiber products

Abstract

A method for manufacturing polyvinyl alcohol fibers, comprising the steps of: providing a polyvinyl alcohol composition comprising: a homo-polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight of 14,000 to 22,000; 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, propionic acid, and mixtures thereof; melting the composition at a temperature of 200 DEG C to 230 DEG C to form a molten polymer; extruding the molten composition to form an extrudate; forming the extrudate into molten fibers; and solidifying the molten fibers to form solid fibers.

Description

[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, but not exclusively, relates to products comprising nonwoven polyvinyl alcohol fibers, methods of making nonwoven polyvinyl alcohol fibers, and products incorporating such fibers.

[0002] Polyvinyl alcohol has many advantages over polymers traditionally used to make nonwoven fiber products. Polyvinyl alcohol is soluble in water, especially when heated, which facilitates recycling, reuse and environmental degradation.

[0003] Polyvinyl alcohol is made by hydrolysis of homopolymers or copolymers of polyvinyl acetate. Polyvinyl alcohol made 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 (LD) of hydrolysis is easy to process, but its mechanical and chemical properties are poor. Homopolymer polyvinyl alcohol with a high degree (HD) of hydrolysis, for example, a degree of hydrolysis of 85% or more, has excellent properties, but it is not processable without degradation under the conditions of equipment used for the manufacture of polyolefin nonwoven fibers.

[0004] Polyvinyl alcohol is soluble in water, and conventionally, polyvinyl alcohol with a low degree (LD) of hydrolysis is used to make fibers by solution spinning.

[0005] 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.

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

[0007] WO2022 / 008521 discloses a method for producing a processable polyvinyl alcohol having a degree of hydrolysis of 93% to 98% or more.

[0008] WO2022 / 008516 discloses a method for producing plasticized polyvinyl alcohol having a degree of hydrolysis of 93% to 98% or more.

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

[0010] A polyvinyl alcohol composition is provided, comprising:

[0011] Homopolymer polyvinyl alcohol having a degree of hydrolysis of 88% to 98% or more and a weight average molecular weight of 14,000 to 35,000;

[0012] A plasticizer 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 trimethylolpropaneformal, rosin ester, erucamide, and mixtures thereof; and

[0013] 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;

[0014] melting the composition at a temperature of 190° C. to 250° C. to form a molten polymer;

[0015] extruding the molten composition to form an extrudate;

[0016] forming the extrudate into molten fibers; and

[0017] The molten fibers are solidified to form solid fibers.

[0018] The molten fibers may be drawn to form individual solid fibers or a bundle of solid fibers.

[0019] Alternatively, the method may include the following steps:

[0020] forming the molten fibers into a molten or partially solidified nonwoven fiber product; and

[0021] The product is allowed to solidify to form a solid nonwoven fibrous product.

[0022] In embodiments, the degree of hydrolysis may be from 90% to 95%, preferably from 93% to 95%.

[0023] The molecular weight of the homopolymeric polyvinyl alcohol may be from 14,000 to 35,000.

[0024] The molecular weights in this specification are weight average molecular weights and are measured using conventional liquid chromatography techniques.

[0025] The composition may be melted at a temperature of 220°C to 240°C.

[0026] The melt flow index (MFI) of the polyvinyl alcohol composition 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.

[0027] The polyvinyl alcohol composition is preferably stable at the temperatures at which it is melted and extruded. Polyvinyl alcohol without the plasticizers and stabilizers disclosed herein, particularly highly hydrolyzed homopolymers, may decompose at the temperatures required for melt and extrusion processing.

[0028] The advantageous polyvinyl alcohol fibers of the present invention can be processed on a commercial scale using conventional fiber processing equipment.

[0029] 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 to form a series of nonwoven products.

[0030] Advantageously, the polyvinyl alcohol fibers of the present invention can be processed on a commercial scale, for example using equipment operating at 4,500 m / min.

[0031] The stable polyvinyl alcohol polymer used in the present invention can be produced according to WO2022 / 008516 and WO2022 / 008521; the disclosures of these international application publications are incorporated herein by reference for all purposes.

[0032] The polyvinyl alcohol composition can be produced by a method comprising the following steps:

[0033] introducing a polyvinyl alcohol polymer having a degree of hydrolysis of 88 wt % to 98 wt % or more into a mixing reactor, the polyvinyl alcohol polymer comprising homopolymeric polyvinyl alcohol or a blend thereof;

[0034] wherein the mixing reactor comprises a blending chamber having a main inlet, a main outlet and at least two intermeshing components extending between the main inlet and the main outlet, the components being arranged to exert shear forces on the polymer as it is conveyed therethrough from the inlet through the reaction zone to the outlet;

[0035] one or more secondary inlets disposed downstream of the primary inlet for introducing reactants including a processing aid, a plasticizer, and optionally a reactive stabilizer into the chamber to form a reaction mixture;

[0036] wherein the plasticizer is selected from the group disclosed above;

[0037] Wherein the reactive stabilizer, when present, is selected from the group consisting of:

[0038] Sodium stearate, potassium oleate, sodium benzoate, calcium stearate, stearic acid, dimethylpropionic acid and mixtures thereof;

[0039] wherein the blending chamber comprises a plurality of heating zones arranged such that the mixture is subjected to a temperature profile such that the temperature increases from the inlet to the outlet;

[0040] a secondary outlet located between the reaction zone and the primary outlet, the secondary outlet being arranged to allow removal of a processing aid from the chamber;

[0041] reacting a processing aid, a plasticizer, and a polymer in a reaction zone to produce a plasticized polymer; and

[0042] The plasticized polymer is passed through the main outlet.

[0043] The use of a reactive mixing device, typically an extruder, according to the present invention allows the processing aid and plasticizer to react with the polyvinyl alcohol or its blend without decomposing the polymer, followed by removal of all or most of the processing aid from a secondary outlet to obtain plasticized polyvinyl alcohol or its blend.

[0044] The use of a reactive stabilizer can advantageously reduce the degree of degradation during melt processing. This allows homopolyvinyl alcohols with a high degree of hydrolysis, such as 88 wt% or more, to be processed to form fibers or pellets, from which fibers can be formed by extrusion.

[0045] 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 %.

[0046] The reactive stabilizers of the present invention can reduce the degree of degradation of the polymer during processing. Homopolymer polyvinyl alcohol is difficult to process because it degrades at the high temperatures required. This tendency to degrade 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 polymer. Sodium benzoate has been found to be particularly effective.

[0047] It is particularly advantageous to use homopolymeric polyvinyl alcohol. In an embodiment of the invention, homopolymeric polyvinyl alcohol is produced by the hydrolysis of homopolymeric polyvinyl acetate, with a degree of hydrolysis of 90 wt% or more. Polyvinyl alcohol copolymers produced by the hydrolysis of polyvinyl acetate copolymers have inferior properties compared to homopolymeric polyvinyl alcohol. Homopolymeric polyvinyl alcohol may exhibit advantageous properties.

[0048] The homopolymeric polyvinyl alcohol polymer fibers of the present invention can have high tensile strength and flexibility compared to previously available polyvinyl alcohol fibers.

[0049] Polyvinyl alcohol can be produced by hydrolysis of homopolymeric polyvinyl acetate, wherein the degree of hydrolysis is 88 wt % to 98 wt %, such as 90 wt % to 95 wt %.

[0050] 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.

[0051] Blends of polyvinyl alcohols 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 having molecular weights of 22,000 to 38,000, a first polymer having a low degree of hydrolysis and a second polymer having a high degree of hydrolysis, may be blended in a weight ratio of 40:60 to 60:40, such as about 50:50.

[0053] The blend of polymers of different molecular weights used is selected based on the physical properties required of the finished product. These 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.

[0054] The use of a blend allows the viscosity of the polymer to be controlled. The selection of a stabilizer according to the invention allows the use of a blend having a desired viscosity without sacrificing other properties. Alternatively, the use of a blend 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.

[0055] The 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 cost and environmental reasons, water is preferably used.

[0056] Two or more plasticizers may be used.

[0057] When mixtures of plasticizers are used, binary mixtures may be preferred.

[0058] 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.

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

[0060] 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.

[0061] The method of the present invention provides many advantages. The method allows the formation of heat-processable polyvinyl alcohol, which can be used to make both economical and highly functional fibers while also eliminating plastic pollution. Polyvinyl alcohol is water-soluble, non-toxic to the environment, and is biodegradable in nature. Hydrophilic polymers such as polyvinyl alcohol degrade faster than hydrophobic polymers in the environment and do not show bioaccumulation. Thermoplastic polyvinyl alcohol can be mechanically recycled into pellets for repeated use.

[0062] The fibers of the present invention can exhibit advantageous chemical resistance, particularly to alcohols, acids, and bases.

[0063] The fibers of the present invention can have advantageously smaller diameters than previously available polyvinyl alcohol fibers. Fibers with smaller diameters have greater surface area, which can be advantageous for air filtration, such as in a face mask. Finer fibers can also be softer in texture. In addition, finer fibers can also have an increased biodegradation rate after use.

[0064] According to a second aspect of the present invention there is provided a heat processable polyvinyl alcohol fibre produced according to the first aspect of the present invention.

[0065] According to a third aspect of the present invention, there is provided a heat processable nonwoven fibrous product comprising fibres produced according to the method of the first aspect of the present invention.

[0066] The heat-processable polyvinyl alcohol of the present invention can be formed into fibers by various methods.

[0067] Filament extrusion can be used to form both monofilament and multifilament fibers.

[0068] Spunbond can be used to form nonwoven fabrics.

[0069] Meltblowing can be used to form nonwoven fabrics.

[0070] ISO 9092 defines nonwoven products as engineered fiber assemblies which are primarily planar and to which an engineered level of structural integrity is imparted by physical and / or chemical means excluding weaving, knitting or papermaking.

[0071] 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 these 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 desirable single material structure that does not suffer from this disadvantage.

[0072] The nonwoven products comprising the polyvinyl alcohol fibers of the present invention and combined with cellulose pulp fibers, viscose fibers and mixtures thereof have excellent flushability, for example according to the flushability certification (UK Water Fine to Flush) WIZ 4-02-06 issued by the UK Water Association. The wet wipes made with the nonwoven fibers of the present invention exhibit excellent dry tensile strength and wet tensile strength.

[0073] By extruding the filament of molten polyvinyl alcohol polymer through the spinneret with apertures such as the aperture of 0.25mm in diameter, fiber of the present invention can be made.The heated roller that can be called as godet roller rotating at different speeds can be used to pull out these extruded filaments and form a multifilament bundle.This multifilament bundle can be curled by heating, then formed using a toothed or grooved roller, and cut using a rotating blade, to provide the fiber of the desired length.Use specific fiber length to give compatibility with various nonwoven fiber processing technologies.

[0074] The following extrusion and stretching conditions may be employed.

[0075] The extrusion temperature employed may be from 200° C. to 247° C., preferably from 210° C. to 220° C. Within these ranges, higher extrusion temperatures may be used to process polymers with a higher degree of hydrolysis.

[0076] The number of filaments in the fiber can be from 24 to 72. Using a fiber or yarn containing a bundle of a larger number of filaments can advantageously increase the overall diameter and increase the cohesion of the bundle of filaments during the stretching process, and can also allow a higher stretch ratio to be used. A larger number of filaments allows the tension applied during the stretching process to be distributed among a larger number of filaments.

[0077] The speed of the first godet (Godet 1) may be 200 to 400 mpm (m / min). Using a Godet 1 speed above 400 mpm may increase the frequency of melt fracture. The optimum speed of Godet 1 may be about 391 mpm. The speed of Godet 5 may be 350 to 1665 mpm. The speeds of Godets 2 to 4 may be intermediate. Using 72 filaments may result in higher draw ratios, resulting in thinner fibers of 3 dtex or greater at a Godet 5 speed of 500 rpm or more.

[0078] Spin finish may be applied to the filaments before the fibers pass through the godet rolls. Non-aqueous spin finishes such as Tallopol DT, Tallopon Biocone or Vystat may be used. At a spin finish pump speed of 4 to 15 rpm, a spin finish content of 0.4 wt% to 4.7 wt% may be used.

[0079] A minimum of 0.4 wt% spin finish may be used to provide sufficient cohesion between the filaments for drawing and winding.

[0080] The fibers according to the present invention may be laid by various methods including carding, air laying or wet laying to form a nonwoven layer or web. The fibers in the web may be combined by a method selected from the group consisting of hydroentanglement, needle punching, chemical or adhesive bonding and thermal bonding.

[0081] In the carding process, carding needles are used to separate and differentiate the fiber bundles to produce an oriented fiber network structure. Crimped polyvinyl alcohol fibers can be used.

[0082] The use of the heat processable fibers of the present invention allows for the manufacture of fiber products consisting of or comprising homopolymeric polyvinyl alcohol on a commercial scale.

[0083] Blends of polyvinyl alcohol (PVOH) fibers with sustainable fibers, such as biopolymers such as Lyocell, polylactic acid (PLA), and mixtures thereof, may be used.A variety of fibers may be used.

[0084] A blending ratio of PVOH:Lyocell of 70wt%:30wt% to 90wt%:10wt%, preferably 80wt%:20wt%, or a ratio of PVOH:PLA of 70wt%:30wt% to 90wt%:10wt%, preferably 80wt%:20wt% may be adopted.

[0085] The surface density of the carded web can be between 60 and 40 g / m 2 , for example about 50g / m 2 .

[0086] In one embodiment, a carded web of 100% PVOH and 80 wt% PVOH:Lyocell:20 wt% may be needle punched at a penetration depth of 9 mm, hydroentangled at 30 bar, or chemically bonded using an adhesive such as ethylene vinyl acetate (EVA).

[0087] Hot air bonding, in which hot air is forced through the web, for example by convection, may be used to melt the adhesive to avoid excessive compression.

[0088] In one embodiment, a carded web of 80 wt%:20 wt% PVOH:PLA may be hot-air bonded at 120°C for 2 min.

[0089] An air-laying process may be employed, in which a turbulent gas flow is used to produce an isotropic fiber network.

[0090] In one embodiment, the crimped polyvinyl alcohol fibers may be cut into 5 mm lengths and blended with pulp fibers (about 2 mm), such as Georgia Pacific (GP) cellulose.

[0091] The ratio of polyvinyl alcohol to cellulose may be 80 wt %:20 wt % to 20 wt %:80 wt %, for example about 50 wt %:50 wt %.

[0092] The surface density can be about 50g / m 2 , depending on the application, such as single or multiple use application.

[0093] The airlaid web may be hydroentangled and then dried.

[0094] The fibers of the present invention have the advantage that a web containing polyvinyl alcohol fibers can be converted into a high strength hydroentangled airlaid nonwoven fabric. It has been found that the fibers, especially those containing warm water soluble polyvinyl alcohol, partially dissolve during the hydroentanglement process, thereby forming a strong but stiff fabric.

[0095] The wet laying process can be used to form nonwoven fabrics containing hot water soluble polyvinyl alcohol fibers. In this process, the polyvinyl alcohol fibers are dispersed in water and transferred to a foraminous conveyor belt, through which the water is removed to deposit the fiber web.

[0096] In embodiments, the fibers may be cut to a suitable length, such as 5 mm, and blended with pulp fibers, such as Sodra Black, in a ratio of polyvinyl alcohol:pulp of 50 wt%:50 wt% to 20 wt%:80 wt%.

[0097] Lyocell fibers (1.4 dtex / 5 mm) may be blended in a ratio of polyvinyl alcohol:pulp of 50 wt %:50 wt % to 20 wt %:80 wt %.

[0098] The surface density can be about 60g / m 2 This density can be used in the manufacture of flushable wipes.

[0099] The wet-laid web may be hydroentangled and dried at 100°C for 30 seconds.

[0100] The tensile strength is comparable to that of commercially available products. A blend of polyvinyl alcohol:pulp:lyocell in a ratio of 40 wt%:40 wt%:20 wt% may exhibit a relatively high tensile strength of 11 to 13 N, typically about 12 N.

[0101] The hydroentangled wet-laid fabric of the present invention, which is mixed with pulp, has relatively good tensile strength. Pulp fibers generally have a high ability to absorb liquid. After hydroentanglement, the wet-laid web remains saturated, causing the polyvinyl alcohol fibers to partially dissolve during the drying stage. The polyvinyl alcohol fibers act as a binder together with the hydrogen bonds formed between the pulp fibers.

[0102] The increase in specific energy during the hydroentanglement process can increase the dry tensile strength of fabrics incorporating lyocell fibers.

[0103] Percentages and other amounts referred to in this specification are by weight unless otherwise indicated and are selected from any cited ranges to total 100%.

[0104] The present invention is further described by way of example but not in any limiting sense and with reference to the accompanying drawings,

[0105] In the figure:

[0106] Figure 1 is a schematic diagram of a fiber extrusion apparatus according to the present invention.

[0107] In an embodiment of the present invention, the following polyvinyl alcohol homopolymer compositions may be used.

[0108] Polymer composition A

[0109]

[0110] Polymer composition B

[0111]

[0112] Polymer composition C

[0113]

[0114] Polymer composition D

[0115]

[0116] Polymer composition E

[0117]

[0118] Polymer composition F

[0119]

[0120] Polymer composition G

[0121]

[0122]

[0123] Figure 1 An extrusion apparatus for polyvinyl alcohol fibers according to the present invention is shown. A feed hopper (1) supplies pellets of a polyvinyl alcohol composition to an extruder (2). From the extruder, the molten polymer is delivered to a melt pump (3), which meters the polymer to a spinning assembly (4). The spinning assembly (4) rotates the fiber (10) through a quench chamber (5), which is supplied with cooling air by a fan (11). A spinning finish applicator (6) applies a coating to the fiber (10). The fiber is then delivered by a roller (7) to a series of godet rollers (8), which produce stretched fibers. These stretched fibers are then collected on a winder (9).

[0124] Example 1

[0125] Multifilament polyvinyl alcohol fibers were extruded using the following parameters.

[0126]

[0127]

[0128] The fibers were crimped with the following operating parameters: IR heater temperature of 220°C, speed of 1.4 m / min, sawtooth roll temperature of 100°C, and production rate of 17 g / h.

[0129] The results show that the recipe can be adjusted to a higher ratio to form finer fibers with a thickness of 2 dtex. Higher melt strength is achieved.

[0130] The following properties were observed using polyvinyl alcohol (PVOH), Lyocell, and polylactic acid (PLA).

[0131]

[0132] The properties of the air-laid hydroentangled polyvinyl alcohol (PVOH) web are as follows.

[0133]

[0134]

[0135] The properties of the wet-laid hydroentangled PVOH web are as follows.

[0136]

[0137] In other embodiments, the properties of the wet-laid hydroentangled PVOH web are as follows.

[0138]

[0139] Example 2

[0140] The tensile strength of the web comprising the polyvinyl alcohol / pulp blend was compared to the tensile strength of commercially available flushable wipes.

[0141] The tensile strength was compared to that of lotion saturated wipes. The commercial wipes were squeezed by hand to remove excess lotion. The polyvinyl alcohol product of the present invention was saturated with excess lotion at an absorption of 200 to 300 wt%.

[0142] The wet-laid web hydroentangled at high specific energy (30 bars x 2 / 50 bars x 4) exhibited higher wet tensile strength compared to the baseline flushable wipes and the wet-laid web hydroentangled at low specific energy (30 bars x 2 / 50 bars x 2). The increase in specific energy had a positive impact on the wet tensile strength of the wet-laid hydroentangled fabric, increasing it by about 100% to 170%.

[0143] There was no significant difference in wet strength between the 50:50 PVA:Lyocell fabric and the 80:20 PVA:Lyocell fabric hydroentangled at high specific energy (p>0.05).

[0144] Example 3

[0145] The polyvinyl alcohol / pulp blend and a commercially available flushable wipe were compared for dispersibility in drain lines.

[0146] Tests were performed to determine dispersibility in sewer systems. Commercially available wipes showed low dispersibility, with less than 60% passing through a 5.6 mm screen.

[0147] The hydroentangled polyvinyl alcohol wet-laid fabric at low specific energy (30 bars x 2 / 50 bars x 2) showed relatively good dispersibility, with >70 wt% passing through a 5.6 mm screen. Reducing the length of the lyocell fibers from 5 mm to 3 mm had a positive effect on dispersibility.

[0148] The dispersibility of wet-laid hydroentangled fabrics decreases with the increase of specific energy (30 bars×2 / 50 bars×4). The fibers are more closely connected, thus promoting fiber rope formation.

[0149] After the dispersibility test, the hydroentangled wet-laid web at high specific energy showed a fragment size of < 4 cm, which is one of the alternative requirements to be met in order to achieve the dispersibility index in sewer systems.

[0150] Polyvinyl alcohol fibers were successfully converted into wet-laid hydroentangled fabrics. Fabrics incorporating pulp fibers showed good dry tensile strength, wet tensile strength and dispersibility, while the incorporation of lyocell fibers increased the wet tensile strength but reduced the dispersibility of the hydroentangled wet-laid fabrics.

[0151] The commercially available flushable wipes passed the dispersibility test in the drain line with over 50 wt% passing the 12.5 mm screen.

[0152] The wet laid hydroentangled web containing polyvinyl alcohol showed excellent results with over 80 wt% passing the 12.5 mm screen.

[0153] Example 4

[0154] A hydroentangled wet-laid polyvinyl alcohol / pulp nonwoven fabric was compared to a commercially available flushable wipe.

[0155] Commercially available flushable wipes showed low dispersibility with less than 60 wt% passing a 5.6 mm screen. A hydroentangled wet-laid fabric incorporating 20 wt% polyvinyl alcohol fibers and 80 wt% pulp showed excellent results with 90 wt% passing a 5.6 mm screen.

[0156] The web comprising polyvinyl alcohol, pulp and viscose / lyocell fibers showed better dispersibility compared to commercially available flushable wipes.

[0157] The use of polyvinyl alcohol fibers in hydroentangled wet-laid fabrics mixed with pulp fibers improves dry tensile strength. The incorporation of viscose or lyocell fibers improves the wet strength of the fabric. Using 40wt% polyvinyl alcohol, 40wt% pulp and 20wt% viscose fibers, an excellent combination of wet strength and dispersion properties is achieved.

Claims

1. A method for manufacturing polyvinyl alcohol fibers, which comprises the following steps: providing a polyvinyl alcohol composition, the polyvinyl alcohol composition comprising: a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88 wt% to 98 wt% 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, erucamide and mixtures thereof; and optionally a 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 250°C to form a molten polymer; extruding the molten composition to form an extrudate; forming the extrudate into molten fibers; and solidifying the molten fibers to form solid fibers.

2. The method according to claim 1, wherein the degree of hydrolysis is 90 wt% to 98 wt%.

3. The method according to claim 2, wherein the degree of hydrolysis is 95 wt% to 98 wt%.

4. The method according to any one of the preceding claims, wherein the melt flow index of the polyvinyl alcohol composition is 30 to 80.

5. The method according to any one of the preceding claims, wherein the melt flow index of the polyvinyl alcohol composition is 50 to 75.

6. The method according to any one of the preceding claims, wherein the melt flow index of the polyvinyl alcohol composition is 70 to 75.

7. The method according to any one of the preceding claims, wherein the plasticizer is selected from two or more of the group consisting of: diglycerol, triglycerol, xylose, D-mannitol, triacetin, dipentaerythritol, 1,4-butanediol, 3,3-dimethyl-1,2-butanediol and caprolactam.

8. The method according to any one of claims 1 to 7, wherein the polymer composition is a blend of two or more polyvinyl alcohol homopolymers having the same degree of hydrolysis and different molecular weights.

9. A polyvinyl alcohol fiber manufactured according to any one of the preceding claims.

10. A non-woven fiber product manufactured according to any one of claims 1 to 8.

11. The non-woven fiber product according to claim 10, wherein the product is a disposable wipe.

12. A non-woven fiber comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88 wt% or higher.

13. A non-woven fiber product comprising a homopolymer polyvinyl alcohol having a degree of hydrolysis of 88 wt% or higher.

14. The non-woven fiber product according to claim 13, wherein the product is a disposable wipe.

Images