WO2012137219A2

WO2012137219A2 - A process for making fibril-free lyocell fabrics

Info

Publication number: WO2012137219A2
Application number: PCT/IN2012/000227
Authority: WO
Inventors: Sushil Kumar HADA
Original assignee: Grasim Industries Limited
Priority date: 2011-04-05
Filing date: 2012-03-30
Publication date: 2012-10-11
Also published as: WO2012137219A3

Abstract

This invention relates to a process of making fibril-free lyocell fabric from a fibrillated fabric wherein the fibrillated fabric is contacted with a cross linking agent and metal salt catalyst at 120-210°C for a period ranging from 10 sec to 5 mins to obtain a cross- linked fibrillated fabric, subjecting the cross linked fibrillated fabric to further treatment with an inorganic alkali solution at 60-90°C and 0-10 bar pressure followed by washing with a solution of sodium hexameta phosphate at 60-120°C.

Description

TITLE: A PROCESS FOR MAKING FIBRIL-FREE LYOCELL FABRICS FIELD OF THE INVENTION:

This invention relates to a process for the preparation of lyocell fabric having reduced fibrillation.

BACKGROUND OF THE INVENTION:

Lyocell is the name for the cellulosic fibre made by extrusion of a solution of cellulose in the mixture of organic solvents and water through a spinneret into a coagulating bath, without intermediate formation of a chemical derivative of cellulose. The process of manufacturing of cellulose fibre is called "Solvent Spinning" and cellulose fibre produced thereby is referred to as "Solvent-Spun" cellulose fibre or Lyocell fibre. The solvent most commonly used is N-methylmorpholine N- oxide (NMMO). One such example of solvent- spinning process is disclosed in US4,246,221. In this approach, cellulose is dissolved in a solvent such as an aqueous tertiary amine N-oxide, for example N-methylmorpholine N-oxide. The resulting solution is then extruded through a suitable die into an aqueous bath to produce an assembly of filaments, which is washed in water to remove the solvent and is subsequently dried. Lyocell fibres exhibit a strong tendency to fibrillate, particularly when subjected to mechanical stress in wet condition. Fibrillation refers to partial splitting of individual fibre along the axis, to yield fine fibrils attached to the body of fibre. Fabrics both woven and knitted which comprises such fibre may exhibit fuzzy appearance. Fibrillation occurs during wet processing and is enhanced by alkaline pH, high temperature and high mechanical stress. Fabrics with low yarn twist and open fabric structure, is more prone to fibrillation. Fibrillation is in general considered to be undesirable in textile end uses, and efforts have been made to reduce or eliminate fibrillation tendency by chemical, enzymatic and mechanical after treatments.

The fibrillation of the lyocell fabric gives the fabric surface a peach skin effect, which is desirable for a few applications and undesirable for others. Thus, the lyocell fibre applications are limited due to its strong fibrillation tendency.

The standard procedure followed for lyocell based fabric where the dyed lyocell fabric is subjected to chemical finishing followed by compacting gives rise to a high degree of fibrillation. Several fabric conditions are known to lower the fibrillation, such as high yarn twist, tight setting of the weave, low temperature, low mechanical stress, application of crease avoiding or lubricating systems, singeing, enzymatic treatment with highly specific cellulase treatment and resin finishing with cross linking system which avoid formation of fibrillation completely and durably.

Several patents and patent publications describe methods to reduce the fibrillation tendency of lyocell fibre and fabric. Broadly, they are either based on crosslinking or on polishing wherein the fabric is fibrillated and the fibrils on the surface are removed by treatment.

The crosslinking treatment is described in EP-A-538, 997; EP-0,755,467; GB 2373784; US 5310424; GB 2399064; and WO-A-9424343. The cross- linking agents commonly used are acrylamido compounds, polyhalotriazine compounds, N-methylol Resin, Poly halogenated compounds, Formaldehyde etc. According to this process poly-functional agents are used to form crosslinks between cellulose molecules, which reduces the fibrillation tendency of the fiber. EP0755467 teaches a process according to which cellulose molecules react with acrylamido group such as l,3,5-triacryloyllhexahydro-l,3,5-triazine by Michael addition, thereby cross linking the cellulose molecules. Polyhalotriazine compounds such as 2,4-dichloro-6-hydroxy-l,3,5-triazine react with cellulose under alkaline conditions, thereby crosslinking the cellulose molecules as taught by GB 2373784. N-methylol resin reacts with cellulose molecules in the presence of acid catalysts such as citric acid, tartaric acid etc., thereby cross linking the cellulose (WO 9530043). Poly halogenated compounds which contain two to six reactive functional groups which react with cellulose molecules. Some of these chemical crosslinking agents are dichlorotriazinyl, trichloropyrimidinyl, chlorodiflouropyrimidinyl, dichloropyrimidinyl, and dichloropyridazinyl as described in US 5310424. Formaldehyde also reacts with cellulose molecules thereby crosslinking the cellulosic molecule with formaldehyde and reducing the pill forming tendency of the cellulosic fabric, as taught by US 20010051486. However, crosslinking treatment leads to increase in brittleness of the fibres and hence strength loss.

Another method commonly employed to reduce fibrillation is by polishing. In this approach, the fabric is wet processed to obtain high fibrillation, after which the fabric is treated either enzymatically or mechanically to remove the fibrils from the fabric surface. The two commonly employed methods are bio-polishing and mechanical polishing. The bio-polishing technique involves the use of enzymes such as cellulase to remove the fibrils from the fabric surface. According to a typical bio-polishing process route of lyocell fabric, the Lyocell Fabric is subjected to Fibrillation Generation followed by Bio polishing and Optional post processing.

In this method, the fabric is intentionally fibrillated at processing stage before dyeing, so that the long and loose fibres come on to the surface of the fabric and can be easily removed by giving treatment of enzymatic defibrillation (also termed as Bio-polishing/ Bio washing). The Enzyme used is cellulase enzyme which catalyses the hydrolytic degradation of the cellulose. This gives the fabric a clean surface or a peach-skin effect is achieved. This method is successful in removing the long fibre ends produced in the primary fibrillation from the surface of the fabric but are expensive both in terms of materials cost and processing time. Also, this method generally produces considerable reduction in fabric tensile strength which is also supported by WO 9530043. Such a process is described in US 5916798 and also mentioned in the article entitled "Enzymatic Defibrillation of Lyocell" in Lenzinger Berichte 77/97 at pages 35-41 by R.Breier, Textilchemie Dr. Petry GmbH, D-Reutlingen, Germany.

The other process employed is mechanical polishing, according to which the fibrils present on the fabric surface are removed by mechanical action. This technique involves the use of aero dynamic machines such as air tumbler to remove the fibrils from the fabric surface. In a typical route, the lyocell fabric is subjected to Fibrillation Generation followed by Mechanical polishing and Optional post processing.

In this method, defibrillation is achieved by mechanical action in the air tumbler. This method is expensive and requires high installation cost of aerodynamic machine like air tumbler, and defibrillation is not fully achieved with considerable strength loss of to the fabric. This method is described in the article entitled "Finishing of Easy-care, Non Pilling Knitwear of Lyocell Fibres" in Lenzinger Berichte, 85 (2006) 95-97 by George. Kling.

These processes suffer from the drawback that they result in loss of strength to the fabric or by use of high cost aerodynamic machine, which is not desirable. Hence there is a need for a process that removes the fibrillation of Lyocell fabric without compromising on the strength & at the same time dispensing with the use of expensive aerodynamic machines.

OBJECTS OF THE INVENTION:

It is therefore an object of this invention to propose a process for the preparation of lyocell fabric having reduced fibrillation, which does not reduce the strength of the fabric.

It is a further objection of this invention to propose a process for the preparation of lyocell fabric having reduced fibrillation, which uses available equipments and is easy to operate.

Another object of the invention is to propose a process for the preparation of lyocell fabric having reduced fibrillation, which is simple and cost-effective.

These and other objects and advantages of the invention will be apparent from the ensuing description. At the outset of the description, which follows, it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only an exemplary embodiment and the teachings of the invention are not intended to be taken restrictively.

SUMMARY

A process of making fibril-free lyocell fabric from a fibrillated fabric wherein the fibrillated fabric is contacted with a cross linking agent and metal salt catalyst at 120-210°C for 10 sec -5 mins to obtain a cross- linked fibrillated fabric, the cross linked fibrillated fabric is further treated with an inorganic alkali solution at 60-90°C and 0-10 bar pressure followed by washing with a solution of sodium hexameta phosphate at 60- 120°C.

DETAILED DESCRIPTION OF THE INVENTION:

According to this invention is provided a process for preparation of lyocell fabric having low fibrillation.

In accordance with this invention is provided a process wherein the fibrillated & dyed lyocell fabric is treated with cross linking agent, and a metal salt catalyst, which is then further treated with an inorganic alkali solution and finally washed with Na hexametaphosphate.

The lyocell fabric is a knit or woven fabric containing 10 to 100% lyocell fibres.

In accordance with a preferred embodiment, the fibrillated fabric is generated by treating the fabric at 450 mpm (meters per minutes) with 5gm/l of soda ash and 1 grams per liter of lubricating agent, 1 grams per liter of defoamer at a maximum blower speed for 45 min at 85°C. The fibrillated fabric is contacted with a cross linking agent which is a low formaldehyde resin, and metal salt catalyst at 120-210°C for lOsec-5 mins. The cross linked fibrillated fabric is further treated with an inorganic alkali solution at 60-90°C and 0-10 bar pressure in a confined container and washed with sodium hexameta phosphate of concentration 1 grams per liter at 60-120°C and 0-10 bar pressure.

The cross linking agent is present in a concentration of 5 to 80 grams per liter, preferably 20 to 60 grams per liter, most preferably 40 to 50 grams per liter. The concentration of the metal salt catalyst is 2 to 30 grams per liter preferably 5 to 15 grams per liter. The inorganic alkali is present in a concentration of 5 to 25 grams per liter, preferably 10 to 25 grams per liter, more preferably 15 to 20 grams per liter.

By way of an exemplary embodiment, and without implying any limitation on the scope of the invention, the low formaldehyde resin is selected from Urea formaldehyde resin, N-methylol resin, the metal salt catalyst is selected from Magnesium chloride, Vanadium Oxide and the inorganic alkali is selected from Sodium hydroxide, Sodium Carbonate,Potassium Hydroxide and Sodium silicate.

By way of an exemplary embodiment, and without implying any limitation on the scope of the invention, the defoamer is vitekol K® and the lubricant is azalube®.

The invention will now be explained in greater detail with the help of the following non-limiting examples. Experimental Data:

Example 1:

The Fibrillated fabric is generated by treating the fabric at 450 mpm with 5gm/l of soda ash and 1 grams per liter of lubricating agent, 1 grams per liter of defoamer at a maximum blower speed for 45 min at 85°C.

Example 2:

The fibrillated fabric is contacted with 7.5 gms of N-methylol resin and 3.5 grams of magnesium chloride of metal salt catalyst at 150°C for 15 sec. The cross linked fibrillated fabric is further treated with 15 grams of sodium silicate at 80°C and 0-10 bar pressure in a confined container and washed with sodium hexameta phosphate of concentration 1 gram per liter at 80°C and 0-10 bar pressure.

Example 3:

The fibrillated fabric is contacted with 42.5 gms of Urea formaldehyde and 9 gms of magnesium chloride of metal salt catalyst at 170°C for 30 sec. The cross linked fibrillated fabric is further treated with 15 gms of Sodium silicate at 80°C and 0- 10 bar pressure in a confined container and washed with sodium hexameta phosphate of concentration 1 gram per liter at 80°C and 0-10 bar pressure. Example 4:

The fibrillated fabric is contacted with 45 gms of Urea formaldehyde resin and 10 gms of magnesium chloride of catalyst at 170°C for 20 minutes. The cross linked fibrillated fabric is further treated with 15 gms of Sodium silicate at 110°C and 0-10 bar pressure in a confined container and washed with sodium hexameta phosphate of concentration 1 gpl at 80°C and 0-10 bar pressure.

Example 5:

The fibrillated fabric is contacted 45 gms of Urea formaldehyde resin and 10 gms of magnesium Chloride at 170°C for 20 sec. The cross linked fibrillated fabric is further treated with 15 gms of Sodium silicate at 80°C and 0-10 bar pressure in a confined container and washed with sodium hexameta phosphate of concentration 1 gpl at 60°C and 0-10 bar pressure.

Processing steps such as wetting, dyeing, and chemical finishing, and drying are done as per the standard procedure known to the industry. The treatment of the lyocell fabric with Sodium silicate may be carried out in soft flow dyeing machines. The fibrillated fabric may be prepared by wet treatment containing optionally alkali, lubricating agent and defoamer at 60- 100°C.

The present invention does not involve use of expensive enzymes/ chemicals or equipments and hence is economically more viable to obtain a fibrillation-free fabric and the process can be easily performed on standard processing equipments such as the soft flow and Air flow dyeing machine. The strength loss of the fabric has been measured by standard methods and it was observed that the strength loss of the fabric according to the present invention is sustantially lower in fabrics processed by other procedures such as by standard processes, bio-polishing method, mechanical polishing process etc. The results are presented in Table I.

Therefore, the strength loss of the fabric processed in accordance with the instant invention is 5.6, which is very low compared to other processes.

Claims

WE CLAIM;

1. A process of making fibril- free lyocell fabric from a fibrillated fabric wherein

the fibrillated fabric is contacted with a cross linking agent and metal salt catalyst at 120-210°C for a period ranging from 10 sec to 5 mins to obtain a cross-linked fibrillated fabric,

subjecting the cross linked fibrillated fabric to further treatment with an inorganic alkali solution at 60-90°C and 0-10 bar pressure followed by washing with a solution of sodium hexameta phosphate at 60-120°C.

2. A process as claimed in claim 1 wherein the lyocell fabric is knit or woven fabric containing 10-100% lyocell fibres.

3. A process as claimed in claim 1 wherein the crosslinking agent is a low formaldehyde resin such as N-methylol resin, urea formaldehyde resin.

4. A process as claimed in claim 1 wherein the concentration of crosslinking agent is 5-80 gpl, preferably 20-60 gpl, more preferably 40- 50 gpl.

5. A process as claimed in claim 1 wherein the metal salt catalyst is selected from magnesium chloride, vanadium oxide.

6. A process as claimed in claim 1 wherein the concentration of the catalyst is 2-30 gpl, preferably 5-15 gpl.

7. A process as claimed in claim 1 wherein the inorganic alkali is selected from sodium hydroxide, sodium carbonate, potassium hydroxide and sodium silicate.

8. The process as claimed in claim 1,7 wherein the alkali is preferably sodium silicate.

9. The process as claimed in claim 1 wherein the concentration of the inorganic alkali is 5 to 25 gpl, preferably 10-25 gpl, more preferably 15- 20 gpl.

10. The process as claimed in claim 1 wherein the temperature used for the step of treatment with an alkali solution is preferably 75-85°C.

11. The process as claimed in claim 1 wherein the reaction is conducted in a confined container which is soft flow dyeing maching such as jet dyeing machine and air flow dyeing machine.

12. The process as claimed in claim 1 wherein the temperature of the step of washing is preferably 75-90°C.

13. The process as claimed in claim 1 wherein the temperature of treatment is preferably 60-120°C, more preferably 80-90°C.