WO2021105809A1

WO2021105809A1 - Regenerated cellulose fiber and a process for preparing the same

Info

Publication number: WO2021105809A1
Application number: PCT/IB2020/060562
Authority: WO
Inventors: Saurabh Singh; Sagar Deshpande; Rupesh Arun Khare; Manzoor SHAIKH; Vishal VALSE
Original assignee: Grasim Industries Limited
Priority date: 2019-11-29
Filing date: 2020-11-10
Publication date: 2021-06-03

Abstract

The present disclosure relates to an acid regenerated cellulose fiber having wet tenacity of at least 1.7 grams per denier; conditioned tenacity of at least 3.0 grams per denier; and degree of polymerization of less than 300.

Description

REGENERATED CELLULOSE FIBER AND A PROCESS FOR PREPARING THE SAME

FIELD OF INVENTION

The present disclosure, in general, relates to an acid regenerated cellulose fiber and a process for preparing the same. Particularly, it relates to an acid regenerated cellulose fiber, which is similar to conventional modal fiber in terms of properties such as enhanced tenacity and modulus yet has a lower degree of polymerization compared to the conventional modal or High Wet Modulus (HWM) cellulosic fibers.

BACKGROUND

Recent years have seen an increase in demand for regenerated cellulose fibers due to the increasing price of cotton, and global fashion trends. They possess several qualities such as excellent drape, better dyeability, color retention, and high moisture absorbency. They are also comfortable to wear. These qualities make them fibers of choice. Examples of such fibers include viscose rayon or viscose, modal, and lyocell. Fabrics made from regenerated cellulosic fibers are versatile materials having wide applications in textiles, apparel, and other industrial sectors. However, these fibers have certain limitations.

The regenerated cellulose fibers, such as viscose, tend to suffer from low tenacity and high deformation in wet conditions. One of the major factors influencing the tenacity of the fibers is the degree of polymerization. It is known that among other things a higher degree of polymerization is required to achieve high tenacity. For example, modal fibers exhibit higher tenacity and lower deformation in wet conditions in comparison to viscose fibers. However, they have a higher degree of polymerization. Due to the higher degree of polymerization, the process to produce the modal fibers requires higher alkali to cellulose ratio, reduced dissolution temperature (-4 to 0^°C), and the addition of a higher amount of carbon disulfide. Further, the process requires higher stretch-bath temperature, which leads to reduced recovery of carbon disulfide. Due to these reasons, the process for producing modal fibers is uneconomical and unsustainable. Lyocell fibers are a recent addition to the family of regenerated cellulose fabrics. Lyocell is obtained by a solvent spinning process (US patent no. 4,246,221), which was originally commercialized by Courtaulds. These fibers have excellent tenacity in both dry and wet conditions but have higher fibrillation and degree of polymerization, in fact, more than that of the modal fiber.

Polynosic fibers are modified viscose fibers that exhibit higher tenacity and lower deformation in wet conditions. However, they suffer from easy fibrillation and less water-imbibing capacity. Further, the process of producing them is also less productive. Also, they are required to be treated with special finishing agents to be advantageous.

SUMMARY

The present disclosure also relates to a process for preparing an acid regenerated cellulose fibe. The process comprises preparing a dope solution by dissolving cellulose xanthate in an aqueous alkali solution, the dope solution comprising cellulose in the range of 8-10 wt.%, alkali to cellulose content in the range of 0.45-0.7 and ball fall in the range of 40-110; spinning the dope solution by pressing it through a spinneret into a spin bath comprising sulfuric acid in the range of 70-120 grams per liter, sodium sulfate in the range of 280-360 grams per liter, and zinc sulfate in the range of 10-50 grams per liter to obtain a filament; and stretching the filament in the range of 70-105% to obtain the fiber. The stretching comprises subjecting the filament to a single stretch or multiple stretches. If the filament is subjected to a single stretch, then zinc sulfate is in the range of 20-45 grams per liter; and if the filament is subjected to multiple stretches then zinc sulfate is in the range of 10-45 grams per liter. BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts the stretching of a filament through a spinning roll in accordance with an embodiment of the present disclosure.

FIG. 2 shows a comparison of the properties of the known fibers with the fiber in accordance with the present disclosure.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.

Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The present disclosure relates to a novel acid regenerated cellulose fiber. The acid regenerated cellulose fiber has wet tenacity of at least 1.7 grams per denier, conditioned tenacity of at least 3.0 grams per denier, and degree of polymerization of less than 300. In accordance with an embodiment of the present disclosure, the wet tenacity of the disclosed fiber is in the range of 1.7-2.6 grams per denier.

In accordance with an embodiment, wherein the conditioned tenacity of the fiber is in the range of 3.0-4.2 grams per denier.

In accordance with an embodiment, the degree of polymerization of the fiber is in the range of 250 to 300.

In accordance with an embodiment, wet modulus of the fiber is greater than 0.5 grams per denier. In a preferred embodiment, the wet modulus of the fiber is in the range of 0.5 -1.0 grams per denier.

The cross-section of the fiber can be serrated, non-serrated, or bean-shaped depending upon regeneration kinetics, which can be modified by modifying spinning conditions and/or by the type of modifier or quantity or type of surfactant used while making the fiber.

The present disclosure also relates to a product comprising or made from the disclosed fiber. Examples of the product include but are not limited to a fabric and a yam. The fabric may be knitted, woven, or non- woven. The fiber may be used alone or may be blended with other fibers. The other fibers may be cellulosic fibers, for example, cotton, or non-cellulosic fibers, for example, polyester.

The present disclosure further relates to a process of preparing an acid regenerated cellulose fiber. The process comprises preparing a dope solution by dissolving cellulose xanthate in an aqueous alkali solution, the dope solution comprising cellulose in the range of 8-10 wt.%, alkali to cellulose content in the range of 0.45-0.7 and ball fall in the range of 40-110; spinning the dope solution by pressing it through a spinneret into a spin bath comprising sulfuric acid in the range of 70-120 grams per liter, sodium sulfate in the range of 280-360 grams per liter, and zinc sulfate in the range of 10-50 grams per liter to obtain a filament; and stretching the filament in the range of 70-105% to obtain the fiber, wherein the stretching comprises subjecting the filament to a single stretch or multiple stretches; and wherein if the filament is subjected to a single stretch, then zinc sulfate is in the range of 20-45 grams per liter; and if the filament is subjected to multiple stretches then zinc sulfate is in the range of 10-45 grams per liter.

FIG. 1 shows the stretching of the filament [102] through rollers of a spinning roll [100] in accordance with an embodiment of the present disclosure. Here, the filament is shown being stretched through a first roller [104], a second roller [106], and a third roller [108]

The expression ‘single stretch’ as used herein means when there the speed of the second roller [106], is equal to the third roller [108].

The expression ‘multiple stretches’ as used herein means two or more stretches. In case of multiple stretches each subsequent roller has a speed higher than the previous roller.

The expression “double or two stretches” as used herein means when the speed of the third roller [108] is higher than the second roller [106] which in turn is higher than the first roller [104].

A person skill in the art may change the stretch in various permutations to arrive at same total ratio of stretches between the rollers by adjusting the speeds.

The process of preparing the cellulose xanthate is well known. In a conventional process, cellulose pulp is steeped in an aqueous alkali solution resulting in the formation of alkali cellulose. The alkali cellulose so obtained is pressed and shredded to depolymerize. Thereafter, the depolymerized alkali cellulose is subjected to pre-aging by oxidative hydrolysis, followed by xanthation with carbon disulfide. This results in the formation of yellow to brown cellulose xanthate crumbs. Any suitable starting material may be used to obtain the cellulose pulp. Examples of suitable starting material include but are not limited to cotton, hardwood, softwood, and bamboo. The aqueous alkali solution may be an aqueous solution of sodium hydroxide.

The dope solution may be subjected to ripening before subjecting it to the spinning. In accordance with an embodiment, the dope is ripened and/or filtered before subjecting it to the spinning.

In accordance with an embodiment, cellulose in the dope solution is in the range of 8.5-9.5 wt%.

In accordance with an embodiment, the alkali to cellulose content in the dope solution is in the range of 0.5-0.65.

In accordance with an embodiment, the ball fall of the dope solution is in the range of 50-70.

In an embodiment, the spin bath comprises sulfuric acid in the range of 75-110 grams per liter. In an embodiment, the spin bath comprises sodium sulfate in the range of 300-350 grams per liter.

In accordance with an embodiment, the filament is subjected to two or double stretches.

The temperature of the spin bath is in the range of 40 to 60°C. In accordance with an embodiment, the temperature is in the range of 45 to 55°C.

The spinning is performed at a speed in the range of 20 to 80 meters per minute. In accordance with an embodiment, the spinning is performed at a speed in the range of 30 to 60 meters per minute. The stretching may be carried out by passing the filament through air, hot air, or a hot stretch bath. The temperature of the hot air is in the range of 25-50 C. The temperature of the hot stretch bath is in the range of 50-90 C. In a specific embodiment, stretching is carried out by passing the filament through a hot stretch bath at least once. In an embodiment, the filament is stretched in the range of 70-90%.

The fiber so obtained may be collected in a staple form, a filament form, or film form. In accordance with an embodiment, the process comprises cutting the fiber to obtain the fiber in staple form. In accordance with an embodiment, the fiber obtained by the disclosed process has properties as disclosed above.

In accordance with an embodiment, the process further comprises subjecting the fiber obtained to post-processing. The post-processing includes washing, desulfurizing, bleaching, finishing, and drying the fiber in a conventional manner.

EXAMPLES

Example 1: Preparation of dope solutions - Cellulose xanthate was obtained by a conventional process, which included steeping, pressing, shredding, pre-aging, and xanthation. Cellulose xanthate so obtained was used to prepare dope solutions for various types of fibers i.e. viscose, modal and inventive fibers A to G. The compositions of the dope solution for viscose, modal and inventive fibers A to G respectively are provided in Table 1.

Table 1: Compositions of the Dope Solution

Example 2 - Preparation of Viscose Fiber: The dope solution prepared for viscose fiber was spun to form viscose filaments by extruding the dope through orifices of a spinneret into a spinning bath containing 110 to 120 grams per liter (gpl) of sulfuric acid, 10 to 11 gpl of zinc sulfate, and 330 to 350 gpl of sodium sulfate. The filaments were withdrawn from the bath, passed over a first godet to a spinning roll, and subjected to a single stretch to achieve a stretch of about 60% to obtain viscose fiber. The spinning speed was 60 meters per minute. The viscose fibers so obtained were washed, desulfurized, and finished with a lubricant. The finished fibers were dried by usual methods. The viscose fibers had an average linear density in the range of 1.0 to 1.5 denier depending on flow and spinning role settings. The Degree of Polymerization (DP) of the viscose fibers was in the range of around 220 to 250. Example 3: Preparation of Modal Fiber - The dope solution prepared for modal fiber was spun to form modal filaments by extruding the dope through orifices of a spinneret into a spinning bath containing 80 to 85 gpl of sulfuric acid, 45 gpl of zinc sulfate, and 110 to 120 gpl of sodium sulfate. The filaments were withdrawn from the bath, passed over a first godet to a second hot bath called a stretch bath. The filaments were subjected to a single stretch. During the passage of the filaments through the stretch bath, they were stretched approximately in the range of 90-110% to obtain modal fiber. The modal fibers so obtained were washed, desulfurized, and finished with a lubricant. The finished fibers were dried by usual methods. The modal fibers had an average linear density in the range of 1.0- 1.5 denier. The DP of the modal fibers was more than 350.

Example 4 - Preparation of Inventive Fibers IF -A to IF-G: The dope solutions for the inventive fibers IF-A to IF-G were spun to form filaments by extruding the dope solutions through orifices of a spinneret into a spinning bath containing 80 to 120 gpl of sulfuric acid, 10-45 gpl of zinc sulfate, and 280 to 350 gpl of sodium sulfate. The coagulation, dewatering as well as regeneration rates were controlled such that an optimum state of the filament was obtained for stretching. The filaments were subjected to a single stretch or two (double) stretches to obtain the inventive fibers IF-A to IF-G. The filaments were stretched in the range of 70-105% depending on the composition of the dope as well as spinning parameters and conditions. In some cases, filaments were subjected to multiple stretches. The filaments were air stretched and/or stretched by passing the filaments through a hot stretch bath. The spinning speed was in the range of 30-60 meters per minute. The fibers so obtained were washed, desulfurized, and finished with a lubricant. The finished fibers were dried by usual methods. The fibers had an average linear density in the range of 1.0- 1.5 denier. The DP of the inventive fibers IF- A-IF-G was 250.

Tables 2 and 3 below provide spinning parameters and conditions for Example 2-4. Table 2: Comparison of the Spinning Parameters

Table 3: Spinning Conditions

Example 5: Comparison of the properties of the fibers

The properties of viscose fiber, modal fiber, and IF-A to IF-G obtained in Examples 2, 3, and 4 respectively were compared. Vibrodyn 500-Staple Fiber Testing-Lenzing Instrument was used to measure the wet tenacity of the fibers according to the standard test methods. The comparison is provided in Tables 4 and 5.

Table 4: Comparison of the Properties of the Fibers

Table 5: Comparison of the Properties of the Fibers

FIG. 2 shows a comparison of the properties (wet tenacity and DP) of viscose, modal, and lyocell fibers with the inventive fiber.

INDUSTRIAL APPLICABILITY

The disclosed fiber exhibits high tenacity while having a low degree of polymerization (less than 300). The disclosed fiber is similar to conventional modal fiber in terms of properties such as enhanced tenacity and modulus yet has a lower degree of polymerization compared to the conventional modal or High Wet Modulus (HWM) cellulosic fibers. The fiber is suitable for all types of applications such as for making dyed or greige, woven, or non-woven fabrics. It can be used in blends with other fibers including and not limited to cotton, polyester, and other fibers.

The disclosed process is a continuous process for manufacturing high tenacity regenerated cellulosic fibers, with a lower degree of polymerization (less than 300). The process is economical and environment-friendly with higher productivity. The process has a significantly lower carbon footprint. Also, the process utilizes a lower amount of sodium hydroxide compared to the standard processes for making conventional modal or viscose fibers.

Claims

We Claim:

1. An acid regenerated cellulose fiber having: wet tenacity of at least 1.7 grams per denier; conditioned tenacity of at least 3.0 grams per denier; and degree of polymerization of less than 300.

2. The fiber as claimed in claim 1, wherein the wet tenacity is in the range of 1.7 -2.6 grams per denier.

3. The fiber as claimed in claim 1, wherein the conditioned tenacity is in the range of 3.0-4.2 grams per denier.

4. The fiber as claimed in claim 1 , wherein the degree of polymerization is in the range of 250 to 300.

5. The fiber as claimed in claim 1, wherein wet modulus of the fiber is greater than 0.5 grams per denier, preferably in the range of 0.5- 1.0 grams per denier.

6. A yam comprising the fiber as claimed in any one of claims 1-5.

7. A fabric comprising the fiber as claimed in any one of claims 1-5.

8. A process of preparing an acid regenerated cellulose fiber, the process comprising: preparing a dope solution by dissolving cellulose xanthate in an aqueous alkali solution, the dope solution comprising cellulose in the range of 8-10 wt.%, alkali to cellulose content in the range of 0.45-0.7 and ball fall in the range of 40- 110; spinning the dope solution by pressing it through a spinneret into a spin bath comprising sulfuric acid in the range of 70-120 grams per liter, sodium sulfate in the range of 280-360 grams per liter, and zinc sulfate in the range of 10-50 grams per liter to obtain a filament; and stretching the filament in the range of 70-105% to obtain the fiber, wherein the stretching comprises subjecting the filament to a single stretch or multiple stretches; and wherein if the filament is subjected to single stretch, then zinc sulfate is in the range of 20-45 grams per litre; and if the filament is subjected to multiple stretches then zinc sulfate is in the range of 10-45 grams per litre.

9. The process as claimed in claim 8, wherein the cellulose is in the range of 8.5-9.5 wt%.

10. The process as claimed in claim 8, wherein the alkali to cellulose content is in the range of 0.5-0.65.

11. The process as claimed in claim 8, wherein the ball fall is in the range of 50-70.

12. The process as claimed in claim 8, wherein sulfuric acid is in the range of 75-110 grams per liter.

13. The process as claimed in claim 8, wherein sodium sulfate is in the range of 300- 350 grams per liter.

14. The process as claimed in claim 8, wherein the temperature of the spin bath is in the range of 40 to 60°C.

15. The process as claimed in claim 8, wherein the filament is stretched in the range of 70-90%.

16. The process as claimed in claim 8, wherein stretching is carried out by passing the filament through air, hot air, or a hot stretch bath.

17. The process as claimed in claim 8, wherein the filament is subjected to multiple stretching.

18. A process of preparing an acid regenerated cellulose fiber as claimed in claim 1, the process comprising: preparing a dope solution by dissolving cellulose xanthate in an aqueous alkali solution, the dope solution comprising cellulose in the range of 8-10 wt.%, alkali to cellulose content in the range of 0.45-0.7 and ball fall in the range of 40-

110; spinning the dope solution by pressing it through a spinneret into a spin bath comprising sulfuric acid in the range of 70-120 grams per liter, sodium sulfate in the range of 280-360 grams per liter and zinc sulfate in the range of 10-50 grams per liter to obtain a filament; and stretching the filament in the range of 70-105% to obtain the fiber wherein the stretching comprises subjecting the filament to a single stretch or multiple stretches; and wherein if the filament is subjected to single stretch, then zinc sulfate is in the range of 20-45 grams per litre; and if the filament is subjected to multiple stretches then zinc sulfate is in the range of 10-45 grams per litre.