DOPE COMPOSITION FOR PRODUCING LIGNOCELLULOSE FIBER, HIGHLY STRETCHED LIGNOCELLULOSE FIBER PRODUCED THEREFROM, AND METHOD FOR PRODUCING THE SAME

Description

DESCRIPTION OF GOVERNMENT-SPONSORED RESEARCH AND DEVELOPMENT

This research was conducted at the Korea Institute of Science and Technology under the supervision of the National Research Foundation of Korea, which is under the Ministry of Science and ICT, the research business title is Korea Institute of Science and Technology Research Operating Expenses Support (Major Project Expenses), and the research project title is Development of the source technology for Electro Super Cellulose Composite Material (Project Identification No.: 2710034017, Project No.: 2E33200).

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2024-0186101, filed Dec. 13, 2024, the entire contents of which are hereby incorporated by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present disclosure discloses a dope composition for producing a lignocellulose fiber, a highly stretched lignocellulose fiber produced therefrom, and a method for producing the same.

Further, this research was conducted at SH-INT Co., Ltd. under the supervision of the Korea Institute for Advancement of Technology, which is under the Ministry of Trade, Industry and Energy, the research business title is Automotive Industry Technology Development, and the research project title is Development of Technology for High-Heat Resistance Carbon-Recycling Composite Materials for Future Automotive Parts with Biomass Content of 95% and Heat Distortion Temperature of 160° C. or More. (Project Identification No.: 2410005585, Project No.: 00507722).

Description of the Related Art

Industries such as automobiles, drones, and fiber-reinforced composite materials are facing a situation where the industries must respond to current and future social needs, such as environmental issues, CO₂ reduction, weight reduction, and improved fuel efficiency.

The required physical properties for low-cost carbon fiber are physical properties with a tensile strength of 1.7 GPa or more and an elastic modulus of 170 GPa or more, which are much lower than those of general-purpose carbon fiber, but the price needs to be sufficiently low. However, currently, a precursor fiber for a low-cost carbon fiber has not yet been developed, and thus have not yet been commercialized worldwide.

Biomass, particularly, lignocellulose (wood-based material) containing lignin, which is a carbon-neutral carbon source as an alternative to petroleum, capable of avoiding conflict with food in order to respond to climate change and maintain civilization, is very promising as a precursor fiber material.

A cellulose fiber made using high-purity pulp for fiber has been commercially produced and used as high-quality fabric materials for a very long period of time. Although this cellulose fiber has been used to prepare carbon fiber, the cellulose fiber is only used to produce specialty carbon fiber due to its extremely low carbonization yield. Lignin, which accounts for 25% to 35% of the total wood components, is generated during the pulping process that extracts cellulose and is used only as a solid fuel. Although lignin has a much higher carbonization yield than cellulose, the physical properties of lignin fiber are so poor due to its extremely low molecular weight that the lignin cannot be used to produce carbon fiber.

Although attempts have been made to produce a composite fiber by blending pulp for fiber and lignin to date, poor fiber-forming ability has become a major problem due to phase separation between cellulose and lignin. In particular, lignocellulose obtained from papermaking pulp or biorefineries contains many impurities such as hemicellulose and lignin, and thus has poor fiber-forming ability, making it impossible to produce a commercial fiber from the components.

SUMMARY OF THE INVENTION

In one aspect, an object of the present disclosure is to provide a dope composition for producing a lignocellulose fiber.

In another aspect, an object of the present disclosure is to provide a lignocellulose fiber formed from the dope composition for producing a lignocellulose fiber.

In still another aspect, an object of the present disclosure is to provide a carbon fiber formed from the lignocellulose fiber.

In yet another aspect, an object of the present disclosure is to provide a method for producing the lignocellulose fiber.

In one aspect, the present disclosure provides a dope composition for producing a lignocellulose fiber, including lignin; and pulp and having a pH of 7.5 or more.

In an exemplary embodiment, the composition may include alkali lignin, may include alkali pulp, or may include an alkali compound.

In an exemplary embodiment, the alkali compound may include one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, sodium sulfide, and sodium hydrosulfide.

In an exemplary embodiment, the lignin and the pulp may be mixed in a weight ratio of 4:1 to 1:4.

In an exemplary embodiment, the lignin may be alkali lignin obtained by evaporating black liquor.

In an exemplary embodiment, the pulp may contain 60 wt % or more of cellulose, 5 wt % or more of hemicellulose, and 5 wt % or more of lignin, based on the total weight of the pulp.

In an exemplary embodiment, the composition may include a tertiary amine oxide solution.

In an exemplary embodiment, the tertiary amine oxide solution may include 13.3 to 20 wt % of water based on the total weight of the solution.

In an exemplary embodiment, the composition may further include a phosphate salt.

In an exemplary embodiment, the phosphate salt may include one or more selected from the group consisting of ammonium phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

In another aspect, the present disclosure provides a lignocellulose fiber formed from the dope composition for producing a lignocellulose fiber.

In an exemplary embodiment, the lignocellulose fiber may have a draw ratio of 10 or more.

In still another aspect, the present disclosure provides a carbon fiber formed from the lignocellulose fiber.

In yet another aspect, the present disclosure provides a method for producing the lignocellulose fiber, the method including: spinning the dope composition for producing a lignocellulose fiber to obtain a highly stretched alkali lignocellulose gel fiber; neutralizing the highly stretched alkali lignocellulose gel fiber in an acid bath to obtain a neutralized lignocellulose gel fiber; and coagulating the neutralized lignocellulose gel fiber in a coagulation bath and washing the coagulated fiber with water to obtain a lignocellulose fiber.

In an exemplary embodiment, the spinning may be air-gap spinning.

In an exemplary embodiment, the acid bath may further include a phosphate salt.

In an exemplary embodiment, the coagulation bath may include an aqueous tertiary amine oxide solution.

In an exemplary embodiment, the production method may further include impregnating the lignocellulose fiber with an aqueous acidic solution after the water washing.

In an exemplary embodiment, the production method may further include impregnating the lignocellulose fiber with an aqueous solution containing a phosphate salt after the water washing.

In an exemplary embodiment, the production method may further include producing a carbon fiber from the lignocellulose fiber.

In one aspect, a technology disclosed in the present disclosure has an effect of providing a dope composition for producing a lignocellulose fiber.

The dope composition has excellent fiber-forming ability and has an effect of providing high stretch and high productivity.

The dope composition has an effect of providing a highly stretched alkali lignocellulose gel fiber capable of producing a lignocellulose fiber with high physical properties using inexpensive low-purity papermaking pulp.

In addition, the dope composition contributes to giving high-added value to lignin and utilizing low-purity pulp, and has an effect of providing a lignocellulose fiber with excellent mechanical properties.

In another aspect, a technology disclosed in the present disclosure has an effect of providing a lignocellulose fiber formed the dope composition for producing a lignocellulose fiber.

The lignocellulose fiber has excellent mechanical properties, and thus has an effect of being used as a lignocellulose fiber-reinforced composite material or a low-cost precursor fiber for carbon fiber.

In yet another aspect, a technology disclosed in the present disclosure has the effect of providing a carbon fiber formed from the lignocellulose fiber.

In yet another aspect, a technology disclosed in the present disclosure has an effect of providing a method for producing the lignocellulose fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow chart of producing a fiber using a dope composition for producing a lignocellulose fiber according to an example.

FIG. 2 shows a set of photographs of a dope composition for producing a lignocellulose fiber according to a comparative example.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present disclosure will be described in detail.

The terms used in the present specification are used only to describe specific embodiments, and are not intended to limit the present disclosure. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, it will be appreciated that the term “include” “have”, or the like is intended to designate the presence of characteristics, numbers, steps, operations, constituent elements, parts described in the specification or combinations thereof, and does not exclude in advance the possibility of the existence or addition of one or more other characteristics, numbers, steps, operations, constituent elements, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person with ordinary skill in the art to which the present disclosure pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the relevant art and should not be interpreted in an ideal or overly formal sense unless explicitly defined in the present specification.

In one aspect, the present disclosure provides a dope composition for producing a lignocellulose fiber, including lignin; and pulp and having a pH of 7.5 or more, or 8 or more.

In an exemplary embodiment, the composition may have a pH of 7.5 to 12.

In an exemplary embodiment, the composition may have a pH of 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more, or 11.5 or more, and 12 or less, 11.5 or less, 11 or less, 10.5 or less, 10 or less, 9.5 or less, 9 or less, 8.5 or less, or 8 or less.

In an exemplary embodiment, the composition may include alkali lignin, may include alkali pulp, or may include an alkali compound.

In the related art, a dope containing tertiary amine oxide, in which cellulose and lignin are mixed, has a decline in fiber-forming ability due to phase separation, so that it has not been possible to stretch the gel fiber at a high magnification. In addition, the spinning speed was slow, making it impossible to produce a fiber with high physical properties and provide high fiber productivity. In contrast, the present disclosure has an effect of providing the high stretch and high spinning speed of the gel fiber by adding an alkali compound to alkali pulp, alkali lignin, or dope to use an alkali dope with a pH of 7.5 or more, thereby suppressing phase separation.

In an exemplary embodiment, the lignin may be alkali lignin.

In an exemplary embodiment, the alkali lignin may be treated with an alkali compound.

In an exemplary embodiment, the alkali lignin may be immersed in an aqueous alkali solution.

In an exemplary embodiment, the alkali lignin may have a pH of 7.5 or more, or 8 or more.

In an exemplary embodiment, the alkali lignin may have a pH of 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more, or 11.5 or more, and 12 or less, 11.5 or less, 11 or less, 10.5 or less, 10 or less, 9.5 or less, 9 or less, 8.5 or less, or 8 or less.

In an exemplary embodiment, the lignin may be alkali lignin obtained by evaporating black liquor. The present disclosure has an effect in which alkali lignin obtained from black liquor can be used without neutralization, and the water content of tertiary amine oxide may be increased using the alkali lignin.

In an exemplary embodiment, the lignin may be a powder.

In an exemplary embodiment, the pulp may be alkali pulp.

In an exemplary embodiment, the alkali pulp may be treated with an alkali compound.

In an exemplary embodiment, the alkali pulp may be immersed in an aqueous alkali solution.

In an exemplary embodiment, the alkali pulp may have a pH of 7.5 or more, or 8 or more.

In an exemplary embodiment, the alkali pulp may have a pH of 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more, or 11.5 or more, and 12 or less, 11.5 or less, 11 or less, 10.5 or less, 10 or less, 9.5 or less, 9 or less, 8.5 or less, or 8 or less.

In an exemplary embodiment, the pulp may be a powder.

In an exemplary embodiment, the composition may include an alkali compound.

In an exemplary embodiment, the alkali compound may include one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, sodium sulfide, and sodium hydrosulfide.

In an exemplary embodiment, the lignin and the pulp may be mixed in a weight ratio of 4:1 to 1:4, or a weight ratio of 4:1 to 1:1.

In an exemplary embodiment, the pulp may include 60 wt % or more of cellulose, 5 wt % or more of hemicellulose, and 5 wt % or more of lignin, based on the total weight of the pulp.

In an exemplary embodiment, the pulp may include 60 to 90 wt % of cellulose, 5 to 20 wt % of hemicellulose, and 5 to 30 wt % of lignin, based on the total weight of the pulp.

In an exemplary embodiment, the pulp may include 60 wt % or more, 65 wt % or more, 70 wt % or more, 75 wt % or more, 80 wt % or more, or 85 wt % or more, and 90 wt % or less, 85 wt % or less, 80 wt % or less, 75 wt % or less, 70 wt % or less, or 65 wt % or less of cellulose, based on the total weight of the pulp.

In an exemplary embodiment, the pulp may include 5 wt % or more, 10 wt % or more, or 15 wt % or more, and 20 wt % or less, 15 wt % or less, or 10 wt % or less of hemicellulose, based on the total weight of the pulp.

In an exemplary embodiment, the pulp may include 5 wt % or more, 10 wt % or more, 15 wt % or more, 20 wt % or more, or 25 wt % or more, and 30 wt % or less, 25 wt % or less, 20 wt % or less, 15 wt % or less, or 10 wt % or less of lignin, based on the total weight of the pulp.

In an exemplary embodiment, the pulp may be a low-purity pulp containing 10 wt % or more, 15 wt % or more, or 20 wt % or more of impurities other than cellulose.

In an exemplary embodiment, the pulp may be a low-purity pulp containing 10 wt % or more, 15 wt % or more, 20 wt % or more, or 25 wt % or more, and 30 wt % or less, 25 wt % or less, 20 wt % or less, or 15 wt % or less of impurities other than cellulose.

In an exemplary embodiment, the impurities may include hemicellulose and lignin.

In an exemplary embodiment, the composition may include a tertiary amine oxide solution.

In an exemplary embodiment, it may be preferred that the tertiary amine oxide solution includes 13.3 to 20 wt % of water based on the total weight of the solution to dissolve cellulose.

In an exemplary embodiment, the tertiary amine oxide may be N-methylmorpholine N-oxide (NMMO).

In an exemplary embodiment, the composition may further include a phosphate salt.

In an exemplary embodiment, the phosphate salt may include one or more selected from the group consisting of ammonium phosphate, diammonium hydrogen phosphate, and triammonium phosphate. By adding a phosphate salt to the composition, a precursor fiber may be converted into a chemically, physically, thermally, and structurally stable carbon fiber.

In an exemplary embodiment, the composition may be prepared by mixing lignin and pulp with a tertiary amine oxide solution having a water content of 13.3 to 20 wt %, followed by heat treatment at 120° C. or less to homogenize the mixture.

In an exemplary embodiment, the composition may be prepared by immersing lignin and pulp in a tertiary amine oxide solution having a water content of 20 to 50 wt %, evaporating water while allowing the solution to swell, and finally concentrating the tertiary amine oxide solution to a water content of 13.3 to 20 wt %.

The present disclosure may provide a dope composition having a pH of 7.5 or more by using alkali lignin, or by using alkali pulp, or by adding an alkali compound, in the process of dissolving lignin and pulp in tertiary amine oxide. The dope composition provides excellent fiber-forming ability by suppressing phase separation, and provides an effect of increasing the stretchability of a lignocellulose gel fiber, improving fiber properties, and increasing production speed.

In addition, low-purity papermaking pulp containing 15 wt % or more of impurities in the related art or refined wood obtained as a by-product in the wood biorefinery process could not be used to produce a high stretched gel fiber. The dope composition of the present disclosure has an effect of providing excellent fiber-forming ability and high stretch by adjusting the pH to 7.5 or more, even though low-purity cellulose, that is, papermaking pulp or refined wood is used.

In another aspect, the present disclosure provides a lignocellulose fiber formed from the dope composition for producing a lignocellulose fiber.

In an exemplary embodiment, the lignocellulose fiber may be a precursor fiber for carbon fiber.

In an exemplary embodiment, the lignocellulose fiber may have a draw ratio of 10 or more, or 10 to 80.

In still another aspect, the present disclosure provides a carbon fiber formed from the lignocellulose fiber.

In yet another aspect, the present disclosure provides a method for producing a lignocellulose fiber, the method including preparing a dope composition including lignin; and pulp and having a pH of 7.5 or more.

In yet another aspect, the present disclosure provides a method for producing the lignocellulose fiber, the method including: spinning the dope composition for producing a lignocellulose fiber to obtain a highly stretched alkali lignocellulose gel fiber; neutralizing the highly stretched alkali lignocellulose gel fiber in an acid bath to obtain a neutralized lignocellulose gel fiber; and coagulating the neutralized lignocellulose gel fiber in a coagulation bath and washing the coagulated fiber with water to obtain a lignocellulose fiber.

In an exemplary embodiment, the production method may be stretching the neutralized lignocellulose gel fiber with a stretching roller and then coagulating the fiber in a coagulation bath.

In an exemplary embodiment, the spinning may be air-gap spinning.

In an exemplary embodiment, the spinning may be spinning through a spinning nozzle.

In an exemplary embodiment, the alkali lignocellulose gel fiber may be highly stretched. A gel fiber to be formed in the air layer can be stretched at a high magnification by subjecting the dope composition to an air-gap spinning. The present disclosure has an effect of producing a high strength fiber without an additional thermal stretching process.

In an exemplary embodiment, the highly stretched alkali lignocellulose gel fiber may have a draw ratio of 10 or more, or 10 to 80.

In an exemplary embodiment, the alkali lignocellulose gel fiber may have a pH of 7.5 or more, or 8 or more.

In an exemplary embodiment, the alkali lignocellulose gel fiber may have a pH of 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more, or 11.5 or more, and 12 or less, 11.5 or less, 11 or less, 10.5 or less, 10 or less, 9.5 or less, 9 or less, 8.5 or less, or 8 or less.

In an exemplary embodiment, the alkali lignocellulose gel fiber may include an alkali compound.

In an exemplary embodiment, the alkali compound may include one or more selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide, calcium hydroxide, barium hydroxide, strontium hydroxide, sodium sulfide, and sodium hydrosulfide.

In an exemplary embodiment, the alkali lignocellulose gel fiber may include tertiary amine oxide.

In an exemplary embodiment, the tertiary amine oxide may be N-methylmorpholine N-oxide.

In an exemplary embodiment, the alkali lignocellulose gel fiber may further include a phosphate salt.

In an exemplary embodiment, the phosphate salt may include one or more selected from the group consisting of ammonium phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

In an exemplary embodiment, the alkali lignocellulose gel fiber may be obtained by extruding, through a nozzle, a dope composition obtained by dissolving alkali lignin in an aqueous tertiary amine oxide solution, the alkali lignin obtained from pulp and black liquor generated in a wood pulping process.

In an exemplary embodiment, the acid bath may include an aqueous acidic solution, and the aqueous acidic solution may include 10 wt % or less, or more than 0 wt % to 10 wt % or less, of an acid based on the total weight of the aqueous solution.

In an exemplary embodiment, the acid may include one or more selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, and chloric acid.

In an exemplary embodiment, the aqueous acidic solution may further include a phosphate salt.

In an exemplary embodiment, the phosphate salt may include one or more selected from the group consisting of ammonium phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

In an exemplary embodiment, the coagulation bath may include an aqueous tertiary amine oxide solution.

In an exemplary embodiment, the aqueous tertiary amine oxide solution may include 30 wt % or less, or more than 0 wt % to 30 wt % or less, of the tertiary amine oxide based on the total weight of the aqueous solution. A high concentration of tertiary amine oxide contained in the gel fiber may be slowly removed in a coagulation bath containing a low concentration of an aqueous tertiary amine oxide solution.

In an exemplary embodiment, the tertiary amine oxide may be N-methylmorpholine N-oxide.

In an exemplary embodiment, the production method may include removing tertiary amine oxide from the neutralized lignocellulose gel fiber in a coagulation bath.

In an exemplary embodiment, the lignocellulose fiber may be highly stretched.

In an exemplary embodiment, the lignocellulose fiber may have a draw ratio of 10 or more, or 10 to 80.

In an exemplary embodiment, the production method may further include drying after the water washing.

In an exemplary embodiment, the production method may further include impregnating the lignocellulose fiber with an aqueous acidic solution without a drying process after the water washing.

In an exemplary embodiment, the production method may further include impregnating the lignocellulose fiber with an aqueous acidic solution without a drying process after the water washing, and the aqueous acidic solution may include 5 to 30 wt %, preferably 5 to 15 wt %, of acid based on the total weight of the aqueous solution.

In an exemplary embodiment, the aqueous acidic solution may include one or more selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, hydrobromic acid, hydroiodic acid, perchloric acid, and chloric acid.

In an exemplary embodiment, the aqueous acidic solution may further include a phosphate salt.

In an exemplary embodiment, the production method may further include impregnating the lignocellulose fiber with an aqueous acidic solution containing a phosphate salt without a drying process after the water washing.

In an exemplary embodiment, the phosphate salt may include one or more selected from the group consisting of ammonium phosphate, diammonium hydrogen phosphate, and triammonium phosphate.

In an exemplary embodiment, the production method may further include producing a carbon fiber from the lignocellulose fiber.

In an exemplary embodiment, the carbon fiber may be obtained by thermally stabilizing the lignocellulose fiber at 100 to 370° C. and then subjecting the fiber to a carbonization reaction.

In an exemplary embodiment, the carbon fiber may be obtained by irradiating the lignocellulose fiber with an electron beam, thermally stabilizing the fiber at 100 to 370° C., and then subjecting the fiber to a carbonization reaction.

In an exemplary embodiment, the carbon fiber may be produced from a lignocellulose fiber impregnated with the acidic aqueous solution or a lignocellulose fiber impregnated with an aqueous solution including a phosphate salt.

FIG. 1 shows a flow chart of producing a fiber using a dope composition for producing a lignocellulose fiber according to an example.

The alkali dope composition according to the present disclosure provides excellent fiber-forming ability (spinnability). In air-gap spinning through an acidic neutralization bath (A), a gel fiber (B) is neutralized and highly stretched by a stretching roller (C), thereby forming a highly stretched lignocellulosic gel fiber (D). The highly stretched lignocellulosic gel fiber (D) is then transferred to a coagulation/washing bath (3) under minimal tension and without further stretching. Such transfer of the gel fiber under minimal tension prevents the loss of elongation properties resulting from excessive stretching of the lignocellulosic fiber.

The highly stretched lignocellulosic gel fiber (D) is washed with water and then dried (4) to yield a highly stretched lignocellulosic fiber (5). Alternatively, after the water washing, the gel fiber is passed through an aqueous acidic solution bath (or an aqueous phosphate salt solution bath) (6) to form an undried highly stretched lignocellulosic fiber containing an acid or a phosphate salt (7), which is then continuously subjected to stabilization and carbonization (8) to produce a carbon fiber (9).

Hereinafter, the present disclosure will be described in more detail through examples. These examples are only for exemplifying the present disclosure, and it will be obvious to those of ordinary skill in the art that the scope of the present disclosure should not be construed as being limited by these examples.

Experimental Example 1

After a dope composition having a pH of 7 was prepared according to the composition in the following Table 1, the dope composition was then heated and pressurized under the conditions in the following Table 2, and then air-gap spun through a nozzle, and the resulting product was allowed to pass through an acid bath, a stretching roller, and a coagulation bath and took up to produce a highly stretched lignocellulose fiber. The content of water in the aqueous NMMO solution was 13.3 wt %. The spin draw ratio and the fiber diameter are shown in Table 2.

	TABLE 1
	Dope compositions (wt. %)

	Neutral	Pulp for fiber
	Lignin	(Sappi)	NMMO•H2O

	Comparative	0	11	89
	Example 1
	Comparative	40	0	60
	Example 2
	Comparative	37.5	2.5	60
	Example 3
	Comparative	25	5	70
	Example 4
	Comparative	20	5	75
	Example 5
	Comparative	15	7.5	77.5
	Example 6
	Comparative	10	10	80
	Example 7

TABLE 2
						After NMMO

Soften-

removal

	ing	Spinning	Take up		Fiber
	Point	conditions	Speed	Draw	Mor-	Diameter

	(° C.)	(° C.)	(psi)	(m/min)	Ratio	phology	(μm)

Comparative	108	115	40	110	80	retain	11.2
Example 1
Comparative	52	130	65	125	80	non	—
Example 2
Comparative	120	130	50	25	10	non	—
Example 3
Comparative	117	125	50	30	15	non	—
Example 4
Comparative	111	120	45	52	16	retain	14.9
Example 5
Comparative	108	115	25	59	43	retain	13.7
Example 6
Comparative	88	115	45	65	51	retain	12.7
Example 7

As a result, the dope composition containing high-purity pulp for fiber (Comparative Example 1) had excellent fiber-forming ability and could produce a fiber at a high draw ratio. In contrast, the dope composition containing 40 wt % of neutral lignin (Comparative Example 2) had excellent fiber-forming properties and could be spun at a high draw ratio, but due to the low molecular weight of the lignin, fiber morphology could not be retained after NMMO removal (see FIG. 2).

It was confirmed that in the case of the dope compositions (Comparative Examples 3 and 4) in which a small amount of pulp with excellent fiber-forming ability was added to neutral lignin, spinnability was poor due to phase separation, as in the related art. In addition, it was found that in the case of the dope compositions (Comparative Examples 5 to 7) in which the pulp content was further increased, spinnability was improved and fiber morphology was retained after NMMO removal. However, it was confirmed that spin draw ratio was significantly lower than those of the dope compositions containing high-purity pulp for fiber (Sappi) or neutral lignin alone (Comparative Examples 1 and 2).

Experimental Example 2

A highly stretched lignocellulose fiber was produced in the same manner as in Experimental Example 1, except that alkali lignin was used instead of neutral lignin, and the fiber was produced under the conditions shown in the following Tables 3 and 4. In this experimental example, a dope composition having a pH of 10 was prepared using alkali lignin and used, and the alkali lignin is a powder obtained by removing water by evaporating strongly alkaline black liquor generated as a by-product in the process of producing pulp from wood.

	TABLE 3
	Dope compositions (wt. %)

	Alkali	Pulp for fiber
	Lignin	(Sappi)	NMMO•H2O

	Example 1	37.5	2.5	60
	Example 2	25	5	70
	Example 3	20	5	75
	Example 4	15	7.5	77.5
	Example 5	10	10	80

TABLE 4
	Soften-					After NMMO

ing

Spinning

Take up

removal

Point

conditions

Speed

Draw

Fiber

Diameter

	(° C.)	(° C.)	(psi)	(m/min)	Ratio	Morphology	(μm)

Example	115	130	45	35	20	non	—
1
Example	115	125	45	45	29	non	—
2
Example	108	120	45	60	45	retain	13.8
3
Example	105	115	20	75	62	retain	12.4
4
Example	84	115	40	80	75	retain	11.8
5

As a result, it was confirmed that spinnability can be significantly improved using an alkaline dope composition. Specifically, it was found that in Examples 1 and 2, in which a small amount of pulp was added to alkali lignin, spin draw ratio was increased almost 2-fold compared to Comparative Examples 3 and 4, in which neutral lignin was used. However, in Examples 1 and 2, the content of pulp with excellent fiber-forming ability was so low that fiber morphology could not be retained after NMMO removal.

It was confirmed that in Examples 3 to 5, in which the pulp content was further increased, spin draw ratio was significantly increased compared to Comparative Examples 5 to 7, in which neutral lignin was used, and fiber morphology was retained after NMMO removal. In particular, it was found that in Example 5, in which alkali lignin and pulp were used in a ratio of 1:1, spin draw ratio was almost similar to that of the dope composition containing pulp alone (Comparative Example 1).

Experimental Example 3

To produce fibers in the related art, high-purity pulp for fiber had to be used because the fiber-forming ability (spinnability) needs to be excellent. However, in the case of papermaking pulp, the cellulose in the pulp itself is used as it is, so that there is an advantage of being much cheaper than pulp for fiber because the pulp does not need to be refined to a high purity in the pulping process.

The following Table 5 shows the composition according to the type of pulp. The following Table 5 shows that pulp for fiber has a cellulose content of about 92% and is low in hemicellulose content and lignin content, whereas MP for papermaking has a much lower purity. In addition, it can be seen that in the case of OP for papermaking, which has only been subjected to the previous step treatment of MP for papermaking, the cellulose content is much lower than that of pulp for fiber, and a large amount of hemicellulose and lignin remain as impurities.

A highly stretched lignocellulose fiber was produced in the same manner as in Experimental Example 1, but produced using the pulp in the following Table 5 under the conditions shown in Tables 6 and 7. In this experimental example, when alkali lignin was used, a dope composition having a pH of 10 was prepared and used, and when alkali lignin was not used, a dope composition having a pH of 7 was prepared and used. The alkali lignin is a powder obtained by removing water by evaporating strongly alkaline black liquor generated as a by-product in the process of producing pulp from wood.

	TABLE 5
	Pulp compositions (wt. %)

Pulp (cellulose)

Hemi-

Use	Type	Cellulose	cellulose	Lignin

For	Oxygen	Oxygen	68.0	10.1	21.9
papermaking	Pulp	bleaching
(low-	(OP)	pre-
purity)		treatment
	Market	Oxygen/alkali	81.4	11.7	6.9
	Pulp	bleaching
	(MP)	pre-
		treatment
For fiber	Sappi	Pulp for	91.9	0.8	7.2
(high-	Pulp	fiber
purity)	(SP)

	TABLE 6
	Type	Dope compositions (wt. %)

	Pulp/Lignin	Pulp	Lignin	NMMO•H2O

Comparative	Sappi	11	0	89
Example 8
Example 6	Market pulp (MP)	10	0	90
Example 7	Oxygen pulp (OP)	11	0	89
Example 8	OP/Neutral lignin	9.1	2.9	88
Example 9	OP/Neutral lignin	8	4	88
Example 10	OP/Alkali lignin	9.1	2.9	88
Example 11	OP/Alkali lignin	8	4	88

TABLE 7
	Soften-					After NMMO

ing

Spinning

Take up

removal

Point

conditions

Speed

Draw

Fiber

Diameter

	(° C.)	(° C.)	(psi)	(m/min)	Ratio	Morphology	(μm)

Com-	108	115	30	75	78	retain	10.5
parative
Example
8
Example	110	115	60	70	65	retain	10.9
6
Example	105	115	50	50	52	retain	11.8
7
Example	100	115	50	45	35	retain	12.4
8
Example	96	110	50	25	30	retain	15.9
9
Example	98	115	50	75	69	retain	10.8
10
Example	94	105	50	65	55	retain	11.2
11

As a result, it was found that in the case of the dope compositions using papermaking pulp (MP) and insufficiently refined papermaking pulp (OP) (Examples 6 and 7), spin draw ratio was low due to impurities, unlike Comparative Example 8, in which high-purity pulp for fiber was used. It was confirmed that in the case of the dope composition in which neutral lignin was added to such papermaking pulp (Examples 8 and 9), spinnability further deteriorated, and thus spin draw ratio was reduced compared to Examples 6 and 7. In contrast, it was confirmed that in the case of dope compositions in which alkali lignin was added to insufficiently refined, low-purity papermaking pulp (OP) (Examples 10 and 11), the spinnability was rather improved, and thus a high spin draw ratio was shown compared to a dope composition containing papermaking pulp (MP) alone. Therefore, in the present disclosure, it was confirmed that, using alkali lignin, lignocellulose fibers for papermaking can be produced from cheaper, low-purity papermaking pulp.

TABLE 8
Mechanical properties of highly stretched
lignocellulose fiber dried yarns

	Tensile	Elastic
	strength	modulus	Elongation
	(g/d)	(g/d)	(%)

Comparative	Neutral lignin/SP (2/1)	3.1	206	3.9
Example 6
Comparative	Neutral lignin/SP (1/1)	3.7	256	4.1
Example 7
Comparative	Sappi Pulp (SP)	5.1	313	5.5
Example 8
Example 4	Alkali lignin/SP (2/1)	3.5	268	4.2
Example 5	Alkali lignin/SP (1/1)	4.1	301	4.9
Example 6	MP	3.6	307	4.5
Example 7	OP	4.5	346	4.9
Example 8	Neutral lignin/OP	2.8	232	4.5
	(2.9/9.1)
Example 9	Neutral lignin/OP (4/8)	2.1	180	4.3
Example 10	Alkali lignin/OP	4.6	340	5.0
	(2.9/9.1)
Example 11	Alkali lignin/OP (4/8)	3.4	295	5.1

As described above, it was confirmed that in the case of a dope in which pulp and lignin are mixed, a highly stretched gel fiber cannot be obtained due to phase separation, but the alkaline dope according to the present disclosure is improved in fiber-forming ability (spinnability), and thus can produce a highly stretched gel fiber, and has an effect of providing high physical properties and high productivity.

In particular, since not only papermaking pulp but also low-purity papermaking pulp that is insufficiently refined contain impurities such as hemicellulose, and thus have even poorer fiber-forming ability than high-purity pulp, the fiber-forming ability is remarkably lower than that of high-purity pulp when lignin is mixed. However, it was confirmed that the alkaline dope according to the present disclosure can produce a highly stretched lignocellulose gel fiber from a mixture of low-purity pulp and lignin, and not only can obtain excellent lignocellulose fiber properties, but also can increase the spinning speed to improve productivity.

Although the specific part of the present disclosure has been described in detail, it will be apparent to those of ordinary skill in the art that such a specific description is just a preferred embodiment and the scope of the present disclosure is not limited thereby. Therefore, the substantial scope of the present disclosure will be defined by the appended claims and equivalents thereof.