WO2011021220A2

WO2011021220A2 - A process for manufacturing acrylic fibers with noncircular cross section

Info

Publication number: WO2011021220A2
Application number: PCT/IN2010/000542
Authority: WO
Inventors: Anasuya Sahoo; Preeti Lodha; Manoj Gavali
Original assignee: Aditya Birla Science & Technology Co. Ltd.
Priority date: 2009-08-17
Filing date: 2010-08-17
Publication date: 2011-02-24
Also published as: WO2011021220A3

Abstract

A manufacturing process for acrylic fibres with noncircular cross-section is disclosed. The acrylic fibres are prepared by extruding the solution containing acrylic polymer and sodium thiocyanate through circular orifices and coagulating the extruded fibres in a coagulation bath containing a coagulating agent.

Description

A Process For Manufacturing Acrylic Fibers With Noncircular Cross Section.

Field of the Invention

The present invention relates to a process for manufacturing acrylic fibers. The present invention envisages a process for manufacturing acrylic fibers having non-circular cross-section using sodium thiocyanate as a solvent for the acrylic polymer and using circular hole spinneret.

Definition

In the context of this invention the term "acrylic polymer" means polymers containing at least 50 percent acrylonitrile monomer units. The other monomers units can be methyl methacrylate, vinyl acetate, methacrylic acid, acrylic acid, ethyl vinyl ether, vinyl bromide, vinyl chloride, vinylidene chloride, vinyl sulfonic acid, itaconic acid, methylmethacrylate, and sulfonated monomers such as sodium styrene sulfonate, sodium methallyl sulfonate, and sodium sulfophenyl methallyl ether.

Background of the Invention

Acrylic fibers are synthetic fibers containing at least 50% of acrylonitrile monomer. The acrylic fibers are prepared from a polymer Polyacrylonitrile which is obtained by free radical polymerization with an average molecular weight of -100,000. Acrylic is lightweight, soft, and warm, with a wool-like feel. It is resilient, retains its shape, and resists shrinkage and wrinkles. Acrylic fibers are commonly used in sweaters, hand-knitting yarns, rugs, awnings, boat covers, and beanies; the fiber is also used as a precursor for carbon fiber. In recent years, synthetic fiber technology has progressed to the stage wherein the useful properties such as thermal stability, ability to retain perfumes, antibacterial properties can be imparted to synthetic fibers by modifying the cross-sectional configurations of the fiber. These properties are essential in several industrial as well as household applications. The cross sectional configurations which are other than round, include dog-bone or dumbbell cross-sectional configuration (e.g. Vinyon™ or Orion™ from Dimethyl Formamide based process), kidney shaped (e.g. Acrilan™ from Dimethyl acetamide based process). It has been found that the fabrics made of fibers having non-circular cross-section have significantly different appearances and feel as compared to fabrics made of round fibers. Furthermore, fabric made of non-circular fibers possess higher surface area than the corresponding fabrics made of round fibers having equal denier. This affects luster, smoothness, wickability, dyeability, drape and other related properties of the fabrics.

The wet spun acrylic fibers with inorganic solvent based systems are known to have circular i.e. round cross-sections. On the other hand, by employing organic reagent based systems, the acrylic fibers having non-circular cross- sections can be prepared. However, the inorganic solvent based acrylic fibers have lower gloss/luster and softness as compared to the organic solvent based acrylic fibers. Also, because of the volatile nature of some of the organic reagents it becomes difficult to recover the organic reagent and hence the system is not ecofriendly. Various efforts have also been made to make non-circular cross-section by using non-circular spinnerets in the wet- spinning method. However, these methods have not been- successful from an industrial view point since such spinnerets tend to be expensive due to high fabrication cost and in some cases, more prone to damage when used under high pressure.

Prior Art

Japanese Patent 1970/2328 discloses a method of preparing fibers having non-circular cross-sections by using a plastic-made spinneret having non- circular orifices. The above mentioned Japanese patent also provides a method wherein fibers extruded through a metallic spinneret having circular orifices located near to each other, are agglutinated and united to form fibers with non-circular cross-sections. However, the method results into the low productivity because of the spinneret have a low pressure resistance. Further, the unevenness in agglutination between the peripheral and central parts of the spinneret results into the different cross-sectional shapes of the fibers and also fibers of non-united, circular cross-sections are present in the mixture.

US Patent 3676540 and 3760053, disclose a method for making shaped fibers by using rectangular spinneret of low thermal conductivity, such as of plastic material, and unusually high jet stretch.

US3706828 discloses a process for producing acrylonitrile fibre having a non-circular cross-section by extruding from circular orifices using Zinc chloride as the solvent and sequentialstretching. However this process is not reproducible.

US3975486 discloses a process for producing an anti piling acrylic fibre, wherein the steps of coagulation, stretching and relaxing are conducted under particular conditions. US patent 4510111 discloses producing cocoon shaped acrylic fibers by two step coagulation process wherein the first coagulation bath contains an aqueous solution of sodium thiocyanate having concentration 5% -35% at temperature -5°C to 5°C and residence time of d* 1/4 to d seconds (d is the denier of the filament). The second coagulation bath was maintained with aqueous sodium thiocyanate solution of concentration 5-35% at temperature 6°C - 4O⁰C for a time period of more than d second. However, the method disclosed in the abovementioned US Patent does not provide consistent results.

Thus, there is felt a need to develop a process for manufacturing acrylic fibers having non-circular cross-sections without the use of non-circular spinnerets.

Objects of the Invention

It is an object of the present invention to provide a process for manufacturing acrylic fibers with non-circular cross-section which avoids the use of non circular spinnerets.

Another object of the present invention is to provide a process for manufacturing of acrylic fiber with non-circular cross-section having significantly enhanced luster properties.

Yet another object of the present invention is to provide a cost-effective process for manufacturing of acrylic fiber with non-circular cross-section. Still another object of the present invention is to provide a process for manufacturing acrylic fiber with non-circular cross-section wherein the products developed from such fibers have improved smoothness, softness, slipperiness, enhanced wickability, enhanced dyeability and drape due to their non-circular cross-section.

Still further object of the present invention is to provide a process for manufacturing acrylic fiber with non-circular cross-section such that inherent properties of the fibers such as fiber strength, linear density, tenacity, elongation, dyeability and drying properties are not altered.

Summary of the Invention

In accordance with the present invention, there is provided a process for manufacturing acrylic fibers with noncircular cross-section comprising the following steps using sodium thiocyanate as a solvent for acrylic polymer and using circular hole spinnerets.

In preferred embodiment of the present invention, there is provided a process for manufacturing acrylic- fibers with noncircular cross-section comprising the following steps;

a. dissolving an acrylic polymer in an aqueous solution of sodium thiocyanate, to obtain a spinning solution;

b. extruding, said spinning solution through a metallic circular orifice spinneret into a first coagulating bath containing 0.01% to 100% by

. volume an additive, said additve is at least one selected from the group consisting of alcohols, organic acids, ketones, ethers, esters, amides, hydrocarbons and dissociating salts comprising of cations with higher charge density as compared to sodium cation in the sodium thiocyanate solvent, in water;

c. holding the extruded spinning solution in the first coagulating bath maintained at a temperature in the range of -10⁰C to 30⁰C, to obtain coagulated filaments;

d. passing the coagulated filaments through an aqueous bath and stretching in one or more steps , and optionally void collapsing, crimping and heat setting to obtain an acrylic fiber having non circular cross section.

Typically the aqueous solution in step (a) contains 30% to 50% by weight of sodium thiocyanate.

Typically, the alcohol is selected form the group consisting of Methanol, Ethanol, Isopropyl alcohol, n-propanol, butanol, isobutanol, pentanol, t-butyl alcohols, di-ethylene glycol, ethylene glycols, tri-ethylene glycol, glycerol, benzyl alcohol and phenol, organic acid is selected from the group consisting of formic acid, acetic acid, oxalic acids, ether is selected from the group consisting of diethyl ether, tetrahydrofuran, mono and poly- substituted alkyl ethers, ester is selected form the group consisting of dimethyl esters, esters of polyhydric alcohols, esters of ethylene glycol acetates, amide is dimethyl formamide, hydrocarbon is selected form the group consisting of toluene and xylene, ketone is acetone and the dissociating salts consists of at least one cation selected from the group of lithium, zinc, calcium, magnesium, , aluminum, copper, silver, iron ,ammonium, quaternary ammonium and pyridinium, and at least one anion selected from the group consisting of alkyl carboxylates, phosphates, dialkyl phosphates, alkyl phosphonate, sulfates, chlorides, bromides, iodides, nitrates and thiocyanates.

In preferred embodiment of the present invention the additive is at least one selected from the group consisting of alcohols, preferably, methanol, ethanol, isopropyl alcohol, n-propanol and butanol, and dissociating salts preferably, calcium chloride and lithium chloride.

In one aspect of the present invention the additive is alcohol, at least one selected from the group consisting of ethanol and propanol. The alcohol is in the range of 30- to 100% by weight in water and the bath is maintained at temperature in the range of -5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec.

In another aspect of the present invention the additive is dissociating salt selected from the group consisting of calcium chloride and lithium chloride.

Typically, the dissociating salt is in the range of 30% -50% by weight in water and the bath is maintained at a temperature in the range of 5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec.

Brief description of the accompanying drawings

The invention will now be described with reference to the accompanying drawing, in which

Figure 1 illustrates the cross-sectional view of the control acrylic fibers with circular cross-sectional configuration; and Figure 2 illustrates the cross-sectional view of the acrylic fibers prepared using iso-propanol as an additive, shows non-circular cross-sectional configuration.

Figure 3 illustrates the cross-sectional view of the acrylic fibers prepared using calcium chloride as an additive, shows non-circular cross-sectional configuration.

Detailed description of the Invention

Conventionally, the acrylic fibers are prepared by dissolving acrylic polymer in organic solvents like N, N-dimethylformamide (DMF), Dimethyl Sulfoxide, Dimethyl acetamide (DMAc) or inorganic solvents such as aqueous sodium thiocyanate. The solution is then metered through a multi- hole circular spinneret. The filaments are coagulated in an aqueous solution of the same solvent. The resultant filaments are washed, stretched, dried and crimped to obtain acrylic fiber having circular cross-section using inorganic solvents based system.

On the other hand, in the prior art by employing organic solvent based system, the acrylic fibers having non-circular cross-sections can also be prepared. However, these organic solvent based methods suffer from disadvantages which include non-ecofriendly process, toxicity associated with use of organic solvent and costly solvent recovery system. Whereas fibers produced by sodium thiocyanate method overcome all the above mentioned disadvantages but suffer from other disadvantages which include lower gloss/luster, poor wickability and poor drape. A variety of non-circular spinnerets have also been used in the manufacture of non-circular cross-sectional acrylic fibers. But these spinnerets are found to be expensive because of their high fabrication cost, thereby making the process industrially un-economical.

Accordingly, the present invention envisages a process for the manufacturing of acrylic fibers having non-circular cross-section using sodium thiocyanate as the solvent for the acrylic polymer.

The process further avoids the use of expensive non-circular spinnerets thereby making the overall process cost-effective.

Thus, in accordance with this invention, a process for manufacturing of acrylic fibers with non-circular cross-section comprising the following steps. In the first step, acrylic polymer (5-20%) by weight of total solution is dissolved in an aqueous solvent containing an inorganic reagent in the range of 30 to 80% to obtain a spinning solution having a viscosity of about 2000- 5000 centipoises. This spinning solution is maintained at 30-70⁰C and then extruded through a metallic spinneret having 90 circular orifices and diameter of 80 microns into a first coagulating bath. The first coagulating bath contains mainly an additive selected from a group consisting of alcohols, organic acids, ketones, ethers, esters, amides, hydrocarbons and dissociating salts in water, the additive is in the range of about 0.1 to 100% by weight. The first coagulating bath is maintained at a temperature in the range of about -10 to 30⁰C. The spinning solution is held in the first coagulating bath for 0.1 to 10 seconds to obtain coagulated filaments.

In the second step, the freshly formed coagulated filaments are passed through a second coagulating bath containing an aqueous solution of sodium thiocyanate having concentration in the range of 6 to 18% and maintained at a temperature in the range of -10⁰C to 30⁰C. The coagulated filaments are then cold stretched for more than 1.14 times at 0⁰C and more than 2.5 times at a temperature 30⁰C, washed with water at 50⁰C, and then further hot stretched for more than 4.5 times in length at a temperature above 80⁰C. The stretched filaments are then subjected to the post treatment like void collapsing, heat setting at 120⁰C, crimping, finishing and final drying to obtain a acrylic fiber having non-circular cross-section.

Cold stretching is the stretching of fibres by conventional methods at a temperature between -10⁰C to 30⁰C. Hot stretching is the stretching of fibres by conventional methods at a temperature between 70° C to 200° C.

The acrylic polymer consist of at least 50 % acrylonitrile monomer units, the other monomer units may be methacrylate, vinyl acetate, methacrylic acid, acrylic acid, ethyl vinyl ether, vinyl bromide, vinyl chloride, vinylidene chloride, vinyl sulfonic acid, itaconic acid, methylmethacrylate, and sulfonated monomers such as sodium styrene sulfonate, sodium methallyl sulfonate, and sodium sulfophenyl methallyl ether.

The acrylic fiber manufactured in accordance with the present invention has enhanced luster properties. The products developed from such fibers show improved smoothness, enhanced wickability, enhanced dyeability and improved drape due to their non-circular cross-section.

The additive is selected from a group consisting of alcohols, organic acids, ketones, ethers, esters, amides, hydrocarbons and dissociating salts. The alcohol is selected" foτm the group consisting of Methanol, Ethanol, Isopropyl alcohol, n-propanol, butanol, isobutanol, pentanol, t-butyl alcohols, di-ethylene glycol, ethylene glycols, tri-ethylene glycol, glycerol, benzyl alcohol and phenol, organic acid is selected from the group consisting of formic acid, acetic acid, oxalic acids, ether is selected from the group consisting of diethyl ether, tetrahydrofuran, mono and poly- substituted alkyl ethers, ester is selected form the group consisting of dimethyl esters, esters of polyhydric alcohols, esters of ethylene glycol acetates, amide is dimethyl formamide, hydrocarbon is selected form the group consisting of toluene and xylene, ketone is acetone and the dissociating salts consists of at least one cation selected from the group of lithium, zinc, calcium, magnesium, , aluminum, copper, silver, iron , ammonium, quaternary ammonium and pyridinium, and at least one anion selected from the group consisting of alkyl carboxylates, phosphates, dialkyl phosphates, alkyl phosphonate, sulfates, chlorides, bromides, iodides, nitrates and thiocyanates.

The dissociating salts consist of cations with higher charge density as compared to the cation of the sodium thiocyanate.

The alcohols, organic acids, ketones, ethers, esters, amides, hydrocarbons used as additive are low molecular weight water soluble organic reagent (molecular weight less than 500g/mole).

The typical composition of the spinning solution in accordance with the present invention is as follows.

• STC (30-55%): Water (30-60%): Acrylic polymer (10-15%) The uniqueness of the present invention lies in a development of a process to manufacture non-circular cross-section in acrylic fiber withoutjhfi use of non-circular spinnerets using inorganic solvent system^ such as sodium thiocyanate. The fibers manufactured in accordance with the present invention, shows significantly enhanced luster properties as compared to standard sodium thiocyanate process based fibers.

The invention will now be described with respect to the following examples which do not limit the invention in any way and only exemplify the invention.

Example 1

An acrylic polymer (consisting of 91.1% acrylonitrile, 8.5% methyl acrylate and 0.4% sodium methacryl sulfonate) was dissolved in an aqueous solution of sodium thiocyanate, 38% in concentration, to prepare a spinning solution having a viscosity of 3000 centipoises at 3O⁰C. This spinning solution maintained at 50⁰C was extruded through a metallic spinneret having 90 circular orifices, each 80 micron in diameter, into an aqueous 70% (by weight) isopropyl alcohol (IPA) solution maintained at 10⁰C. (1^st coagulating bath) and was held in the bath for 3 seconds. The freshly-formed filaments were then passed through the standard sodium thiocyanate based spinning process. The coagulated spinning^■ solution was further passed into an aqueous 14% sodium thiocyanate solution (2^nd coagulating bath) maintained at -2.3°C with a pull away ratio of 4.7. Then the coagulated filament was cold stretched 1.14 times at 0⁰C and 2.5 times at 30⁰C_. in pure water bath and water washed at a temperature 50⁰C. Further the fiber passed through a water bath at temperature 95°C and -hot wet stretched 4.5 times. The denier of these filaments after the total 13X stretch was 3. The filaments were of non circular configuration.

Example 2

An acrylic polymer (consisting of 91.1% acrylonitrile, 8.5% methyl acrylate and 0.4% sodium methacryl sulfonate) was dissolved in an aqueous solution of sodium thiocyanate, 38% in concentration, to prepare a spinning solution having a viscosity of 3000 centipoises at 30⁰C. This spinning solution was extruded at 50⁰C through 80 micron circular die into an aqueous 50% (by weight) Lithium Chloride (LiCl) solution at 10⁰C with a residence time of 1.5 seconds. The coagulated spinning solution was further passed into an aqueous 14% sodium thiocyanate solution maintained at -5⁰C with a pull away ratio of 5. Then the coagulated filament was cold stretched 1.15 times at O⁰C and 2.5 times at 3O⁰C in pure water bath and water washed at a temperature 50⁰C. Further the fiber passed through a water bath at temperature 95°C and hot wet stretched 4.5 times. The filaments were of non circular configuration.

The following table 1 illustrates the results obtained with the different spinning solution compositions prepared in accordance with the present invention using alcohol and dissociating salts as an additive.

LiCl Lithium Chloride IPA Isopropyl alcohol CaC12Calcium Chloride EtOH Ethanol

The above table indicates that the acrylic fibers having circular cross-section were obtained when the filaments were extruded into the first coagulation bath without the additive. On the other hand, the acrylic fibers with non- circular cross-section were formed when the filaments were passed through the first coagulating bath containing an alcohol or dissociating salt as an additive. The acrylic fibers manufactured in accordance with the present invention show significantly improved luster as compared to regular fiber without any significant loss in the mechanical and physical properties. Test Protocols:

1. Fiber Cross section:

Using a microscope and calibration with a micrometer scale, the cross- section area (in square micron) and perimeter (in micron) were measured for 10 representative fiber specimens for the sample. The data was analyzed using 2 sample t-test at 95% confidence interval and the fiber sample was classified as:

Non-circular

Circular _II_FF

^Densjt>^{r in} s/^cc For example, a 3 -denier acrylic fiber with a density of 1.17 g/cc made using an acrylic polymer (91.1% acrylonitrile, 8.5% methyl acrylate and 0.4% sodium methacryl sulfonate) will be classified as non-circular if its Area to Perimeter ratio is less than 4.76.

2. Luster Measurement:

The fiber tuft board is prepared by aligning the fibers in parallel manually and fixed to a board to prepare a rectangular test piece -of 6 cm X 4.5 cm dimension ensuring that all surface is completely and uniformly covered by the fibers aligned in the 6 cm direction.

The gloss value was measured on the fiber tuft board using a D-410B Mini gloss meter in accordance with the test method of JIS-Z-8741 at 60 degree incidence angle geometry. Here the incident ray will form an angle of 60 deg with the direction of arrangement of the fiber. A total of 5 fiber tuft board were measured for each fiber sample. The fiber sample data was classified into No, Low and high based on the following criteria:

• If (Sample gloss value - Control gloss value) < 0,

o then "No" luster improvement was reported

• If (Sample gloss value - Control gloss value) > 0,

o then "Improved" luster was reported

The above analysis was carried out using 2-sample t-test at 95% confidence interval. The fibers were tested without any finish oil.

3. Mechanical property Measurement: Mechanical Property of the fibers in terms of tenacity (gpd), elongation (%) was measured as per the ISO5079:1995 standard procedure.

Technical advancement

The acrylic fibers with non-circular cross-sections manufactured in accordance with the present invention shows improved lustrous properties as compared to the regular circular fibers without altering the inherent properties of the fibers. Furthermore, the products developed from such fibers also results into an improved smoothness, enhanced wickability, enhanced dyeability and drape due to their non-circular cross section. The abovementioned process also avoids the use of expensive modified spinnerets thereby making the overall process cost-effective.

While considerable emphasis has been placed herein on the specific steps of the preferred process, it will be appreciated that many steps can be made and that many changes can be made in the preferred steps without departing from the principles of the invention. These and other changes in the preferred steps of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Claims

Claims:

1. A process for manufacturing acrylic fibers with non- circular cross- section comprising the following steps using sodium thiocyanate as a solvent for acrylic polymer and using circular hole spinnerets.

2. The process as claimed in claim 1 ,comprising the following steps:

b. extruding , said spinning solution through a metallic circular orifice spinneret into a first coagulating bath containing 0.01% to 100% by volume an additive, said additive is at least one selected from the group consisting of alcohols, organic acids, ketones, ethers, esters, amides, hydrocarbons and dissociating salts comprising of cations with higher charge density as compared to sodium cation in the sodium thiocyanate solvent, in water ;

3. The process as claimed in claim 2, in which the additive is a water soluble low molecular weight (molecular weight is less than 500 g/mole) organic reagent.

4. The process as claimed in claim 2, in which the dissociating salts comprise cations with higher charge density as compared to sodium cation in the sodium thiocyanate solvent and an anion.

5. The process as claimed in claim 2, wherein the alcohol is selected form the group consisting of Methanol, Ethanol, Isopropyl alcohol, n-propanol, butanol, isobutanol, pentanol, t-butyl alcohols, di-ethylene glycol, ethylene glycols, tri-ethylene glycol, glycerol, benzyl alcohol and phenol, organic acid is selected from the group consisting of formic acid, acetic acid, oxalic acids, ether is selected from the group consisting of diethyl ether, tetrahydrofuran, mono and poly-substituted alkyl ethers, ester is selected form the group consisting of dimethyl esters, esters of polyhydric alcohols, esters of ethylene glycol acetates, amide is dimethyl formamide, hydrocarbon is selected form the group consisting of toluene and xylene, ketone is acetone and the dissociating salts consists of at least one cation selected from the group of lithium, zinc, calcium, magnesium, , aluminum, copper, silver, iron ,ammonium, quaternary ammonium and pyridinium, and at least one anion selected from the _.group consisting of alkyl carboxylates, phosphates, dialkyl phosphates, alkyl phosphonate, sulfates, chlorides, bromides, iodides, nitrates and thiocyanates.

6. The process as claimed in claim 2, wherein the additive is at least one selected from the group consisting of alcohols, preferably, methanol, ethanol, isopropyl alcohol, n-propanol and butanol, and dissociating salts preferably, calcium chloride and lithium chloride.

7. The process as claimed in any one of the preceding claims, wherein the additive is at least one alcohol selected from the group consisting of ethanol, methanol and isopropyl alcohol.

8. The process as claimed in any one of the preceding claims, wherein the additive is at least one dissociating salt selected from the group consisting of calcium chloride and lithium chloride.

9. The process as claimed in any one of the preceding claims 2 to 8, wherein the first coagulating bath contains 30% -100% of ethanol in water and the bath is maintained at temperature in the range of -5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec.

10. The process as claimed in claims 2 to 9, wherein the first coagulating bath contains 30%- 100% of isopropanol in water and the bath is maintained at temperature in the range of -5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec .

11. The process as claimed in any one of the preceding claims 2 to 10, wherein the first coagulating bath contains 30% -50% by weight of calcium chloride in water and bath is maintained at a temperature in the range of 5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec.

12. The process as claimed in any one of the preceding claims 2 to 11, wherein the first coagulating bath contains 30%-50% by weight of lithium chloride in water and bath is maintained at a temperature in the range of 5 ⁰C to 25 ⁰C and a residence time of > 0.01 sec .

13. A fiber with high luster manufactured in accordance with a process as claimed in any one of the preceding claims.

14. A woven, nonwoven or knit product made from the acrylic fiber of claim 13.