DESC:Field of Invention

The present disclosure relates to a modified regenerated cellulose fiber and a continuous process for preparation of said modified regenerated cellulose fiber. Particularly, the present disclosure relates to a modified regenerated cellulose fiber which are fibril free or have a reduced fibrillation tendency.

Background

Regenerated cellulose fiber like natural fibers such as cotton and hemp have been a key material in textile industry. This is predominantly because of its superior moisture absorbing property and biodegradability along with soft to touch and drapability. However, regenerated cellulose fiber has certain defects such as poor water resistance leading to high degree of swelling in water and shrinkage percentage after washing and whitening due to fibrillation. Fibrillation is a phenomenon in which a filament or fiber shows evidence of smaller-scale fibrous structure by a longitudinal raveling of the filament under rapid, excessive tensile or shearing stress, giving rise to frosted appearance on dyed fabrics.

Amongst all known regenerated cellulose fiber, lyocell fiber is of high significance. Lyocell fiber shows some key advantageous characteristics over other cellulosic fibers, for instance, a high dry and wet tenacity and high wet modulus. However, the fiber also shows an extensive tendency to fibrillate in the wet state. This tendency to fibrillate has been attributed to the spinning process, which causes the formation of longer and more oriented crystalline regions and smaller but more oriented amorphous regions in the fiber structure. Additionally, mechanical abrasions in wet processing (such as scouring, dyeing etc.) in commercial dye houses, which are also high temperature and longtime processes, cause more damage to the fabric.

Researchers have attempted to reduce the fibrillation tendency of lyocell fiber by dope modification and use of cross linkers/resins at fibre as well as fabric finish stage. Crosslinkers are small molecules containing a plurality of functional groups capable of reacting with the hydroxyl groups in cellulose to form crosslinks.

Various crosslinking agents have been reported to reduce fibrillation tendency of regenerated cellulose fiber. In one of the conventional methods, crosslinking agent is a low formaldehyde resin such as N-methylol resin, urea formaldehyde resin. However, formaldehyde based crosslinking agents are not suitable as they release formaldehyde from fiber even after downstream processing to fabric and multiple laundry washes.

Further, bifunctional and trifunctional (and higher) crosslinking agents have been reported in literature for reducing the fibrillation of lyocell fiber to expected level. However, such crosslinking agents have disadvantages such as they tend to reduce the elongation and tenacity of fiber considerably due to constrained spatial structure of the cellulose-cross-linked network or need very high dosage and hence affects elongation. Also, they can only partially reduce the fibrillation due to inherent instability of crosslinks under scouring and acidic/alkaline dyeing conditions.

Bates et al., Coloration Tech. 2004, 120:293-300 discloses application of colourless, water soluble, anionic cross-linking agent, 2,4-diacrylamidobenzenesulphonic acid to lyocell by a pad–steam method for the protection of lyocell against fibrillation. However, such crosslinking agent could only partially reduce the fibrillation.

EP0538977B1 and US5310424 describe usage of colorless chlorotriazine compounds with 2 or higher reactive arms, such as Sandospace R, for fibrillation reduction on lyocell fiber. However, the use of these chemical reagents is not commercially viable due to inherent instability of the chlorotriazine compounds.

US5779737 discloses usage of triazine based acrylamide compounds such as, 1,3,5-Triacryloylhexahydro-1,3,5-triazine (by TCI chemical) in presence of inorganic alkali, for fibrillation reduction at fiber stage. This class of compounds are reported significantly toxic and the crosslinks formed are partially stable to alkaline hydrolysis and also prone to release formaldehyde under downstream processing conditions.

There are other cross-linkers such as polyfunctional aziridines (“PZ-28”, “PZ-33” from Polaziridine LLC.), (N-methoxymethyl) melamines (“Rucon-DMO” from Rudolf and “RA-65” from Dalian Richon), Poly(isobutylene-alt-maleic anhydride), Poly[(isobutylene-alt-maleimide)-co-(isobutylene-alt-maleic anhydride)] (by Sigma Aldrich), L-Lysine Triisocyanate (by ABCR GmBH & Co. KG), Carbonyl-bis-caprolactam (by Atul Ltd.), Trimethylolpropanetriacrylate, Pentaerythritol triacrylate (by Sigma Aldrich), Polyamide-epichlorohydrin resin (“Polycup 172” from Solenis), multifunctional polycarbodiimides ( “Picassian XL 702 & 705” from Stahl), blocked polyisocyanates ( “Bayhydur BL XP 2706, BL 5335” from Covestro), which are devoid of generating additional hydroxyl groups or active dye binding sites/functional groups. Such crosslinking agents make the fiber stiff and also affect the reactive dyeing of fiber due to masking of hydroxyl groups (dye binding site) in cellulose. When using such crosslinking agents, use of additional dye binding agents becomes necessary to achieve regular fiber like color strength.

Summary

A modified regenerated cellulose fiber is disclosed. Said modified regenerated cellulose fiber comprises of regenerated cellulose crosslinked with a modifier, wherein the modifier comprises a crosslinking agent having a formula I or II:
(I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5.

A process for preparing a modified regenerated cellulose fiber is also disclosed. Said process comprises treating a never-dried regenerated cellulose fiber with a modifier comprising a crosslinking agent having a formula I or II:

(I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5.

After said treatment, the treated regenerated cellulose fiber is cured at a temperature between 100-160°C to obtain the modified regenerated cellulose fiber.

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.

As used herein, “never-dried regenerated cellulose fiber” is intended to refer to a regenerated cellulose fiber obtained using any known process, that has not been dried using heat or other thermal energy during the various stages of processing of regenerated cellulose fiber, such as tow, staple or yarn filament.

In its broadest scope, the present disclosure relates to a modified regenerated cellulose fiber which are fibril free or have a reduced fibrillation tendency. Specifically, said modified regenerated cellulose fiber comprises of regenerated cellulose fiber crosslinked with a modifier, wherein the modifier comprises a crosslinking agent having a formula I or II:
(I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5.

A continuous process for preparing said modified regenerated cellulose fiber is also disclosed. Said process comprises treating a never-dried regenerated cellulose fiber with the modifier comprising a crosslinking agent having a formula I or II:

a. (I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5.

After the treatment of the regenerated cellulose fiber with the modifier, the treated regenerated cellulose fiber is cured at a temperature between 100-160°C to obtain the modified regenerated cellulose fiber.

The present inventors found that the disclosed modified regenerated cellulose fibers exhibits sufficient degree of fibrillation resistance. It was further found that the modified regenerated cellulose fibers exhibit tenacity and elongation comparable to regenerated cellulose fibers which have not been modified. Specifically, it was observed that when never-dried regenerated cellulose fiber is treated with the modifier of present disclosure, the fibrillation resistance expressed as wet abrasion number (WAN) improved and there was no negative effect on fiber properties like tenacity and elongation loss as seen in case of conventional crosslinking agents reported in literature.

In accordance with an embodiment, the modified regenerated cellulose fiber comprises the modifier in an amount ranging between 1-25% by weight of cellulose. In some embodiments, the modified regenerated cellulose fiber comprises the modifier in an amount ranging between 5-18% by weight of cellulose.

In accordance with an embodiment, the modifier is an epoxy-based crosslinking agent having the formula I or II or a halohydrin-based crosslinking agent having the formula I or II.

In accordance with an embodiment, the epoxy-based crosslinking agents having a formula I or II comprises epoxy-based agents with multiple epoxy rings, selected from the group of short to medium chain water insoluble or sparingly soluble reactive diluents or polyglycidyl ethers of polyhydric alcohols. In accordance with some embodiments, epoxy-based crosslinking agents are trifunctional epoxy compounds such as trimethylolpropane triglycidyl ether – TMPTGE (“Epotec RD113” from Aditya Birla Chemicals, tetrafunctional pentaerythritol based polyglycidyl ether (“Epotec RD129” from Aditya Birla Chemicals), sorbitol polyglycidyl ethers (“Denacol EX-614, EX-622” from Nagase Chemtex), Glycerol/polyglycerol polyglycidyl ethers (“Denacol EX-313, EX-314, EX-421, EX-512, EX-521” from Nagase Chemtex. Suitable glycidyl amines derivatives can also be used but have lesser bath stability due to self-crosslinking (“Erisys GA 240” from CVC Thermoset specialties). Presence of amine-based catalysts/curing agents (“Anquamine 728, 287, 721” from Evonik, “Lupasol-P” from BASF, “Danfix PAA” from Nittobo) should be avoided in order to facilitate bath stability for continuous process; however, short duration usage of such one-pot system of epoxy-based agent and curing agent can also be used.

Mention may be made of the following epoxy-based crosslinking agents having formula I or II:

In accordance with an embodiment, precursors of above-mentioned epoxy compounds which are halohydrin-based crosslinking agents having a formula I or II comprises polymeric halohydrins with 3 or more halohydrin groups per repeat unit with/without pendant hydroxyl group. Herein, halohydrin-based crosslinking agent gets converted to reactive epoxide in situ, which further reacts with cellulose hydroxyl groups. This reaction can be controlled by proper selection of pH, catalyst system, curing assembly type and curing temperature. Thus, similar to epoxy-based cross-linking agents, the halohydrin-based crosslinking agents are capable of making stable ether crosslinks between hydroxyl groups of cellulose fiber under alkaline conditions of pH 9-13. In accordance with some embodiments, the halohydrin-based crosslinking agents comprise water soluble/miscible chlorohydrin compounds which are derivatives of polychlorohydrin ether of polyhydric alcohols with pendent chlorohydrin functional groups.

In accordance with an embodiment, the modifier further comprises one or more of a solvent, inorganic alkali/alkaline earth hydroxides/carbonates/phosphates, metal fluoroborates etc. Optionally, the modifier further comprises of one or more of a phase transfer catalyst, lubricating/non-ionic surface-active agent, reactive cationization agent, and an exhaustion agent. In accordance with an embodiment, the exhaustion agent is selected from the group consisting of alkali salts, alkaline earth salts and the combination thereof. In some embodiments, the alkali salt is selected from the group consisting of sodium chloride, sodium sulphate and mixtures thereof. In some embodiments, the alkaline earth salt is selected from the group consisting of magnesium sulphate, magnesium carbonate, calcium sulphate and mixtures thereof.

In accordance with an embodiment, the modifier is an alkaline solution of 3-20% (w/v) of crosslinking agent having a formula I or II. In accordance with an embodiment, the modifier is prepared in an aqueous solution at pH 9-13, or a solvent mixture such as 10-40 % water and 50-95% alcohol selected from the group consisting of methanol, ethanol and isopropyl alcohol, or a surfactant mixture and/or polymeric dispersion (or emulsion) at pH 9-13.

In accordance with an embodiment, the moisture content of never-dried regenerated cellulose fiber is in a range of 70-300% by weight of cellulose. In accordance with an embodiment, the incoming fiber tow has a moisture content of 80-300%. In some embodiments, the incoming fiber tow has a moisture content of 90-150%. In some embodiments, the incoming fiber tow has a moisture content of 100-130%.

In accordance with an embodiment, the modifier is applied to a never-dried regenerated cellulose fiber in the application bath at a temperature in a range of 25-45°C. In some embodiments, the modifier is applied at an ambient temperature in a range of 25-35°C. In accordance with an embodiment, the treatment of tow/ fiber bed is carried out in application bath for a time period of 3-300 seconds, for efficient wetting and moisture replacement. In some embodiments, the treatment is carried out for 60-120 seconds.

In accordance with an embodiment, curing is carried out at a temperature between 100-160°C to induce covalent crosslinking. In some embodiments, curing is carried out at the temperature between 120-140°C. In some embodiments, the curing is carried out for 5-120 minutes. In some embodiments, curing is carried out for 10-20 minutes.

After curing, the modified regenerated cellulose fiber is further subjected to one or more of washing, neutralization, bleaching, lubricating and drying steps.

In accordance with an embodiment, the modified regenerated cellulose fiber is subjected to a washing step.

In accordance with an embodiment, the modified regenerated cellulose fiber is subjected to a neutralization step for removal of residual catalyst and crosslinking agent. Neutralization agents for inorganic alkali can be dilute organic acids, and neutralization agents for traces of epoxy can be known polymeric amines/imines. The dilute organic acids are selected from the group consisting of acetic acid, citric acid, lactic acid and mixtures thereof.

In accordance with an embodiment, the washed and neutralized fiber is bleached to desired whiteness, neutralized to pH 6-7 with dilute aqueous organic acid followed by bleaching, spin finish application and drying.

In accordance with an embodiment, organic route is used for application of modifier. In this route, organic solvents are used to form the modifier. The coupling of epoxide with cellulose hydroxyl groups is carried out in a base catalyzed condition at temperature 80°C-150°C. In some embodiments, said coupling is carried out at 100-145°C. In some embodiments, said coupling is carried out at 110-140°C using dry heat, saturated steam or super-heated steam. In accordance with an embodiment, the modifier in the organic route comprises of a phase transfer catalyst such as tetraethylammoniumbromide (TEAB) or cationic polymers such as Poly(DADMAC) in the application bath for faster penetration and better reaction. This fiber upon curing is washed using the same solvent in multiple baths followed by hot water wash and using aqueous acid neutralization to remove unreacted crosslinking agent and catalyst, and the solvent can be recovered easily for reuse by distillation as it doesn’t interfere with the crosslinking agent having very high boiling point. Also, the removal of solvent by suction from the treated fiber prior to entering dryer is possible, hence eliminating any fire hazard in a continuous drying set up. The removal of traces of crosslinking agent can be ascertained by washing with dilute solution of polymeric amines such as Polyallylamine (“Danfix PAA” series from Nittobo), polethylenimine ( “Lupasol” from BASF), Polyvinylamines etc., as they react with free epoxy at room temperature thereby removing the remnant epoxy, without causing any disturbance to crosslinked structure.

In accordance with an embodiment, aqueous route is used for application of modifier. In this route, aqueous solvents are used to form the modifier. For aqueous applications, suitable halohydrin/epoxy compound containing water loving pendant groups are dissolved/dispersed in water at room temperature, followed by elevating the pH of bath with alkali to 11-12.5. In accordance with an embodiment, the application bath contains an exhaustion agent for uniform exhaustion. In accordance with an embodiment, suitable non-ionic/cationic surfactant blends, alkali/alkaline earth metal salts or polymeric quats (such as Poly(DADMAC)) are added to avoid inter-fiber entanglement during drying process. In accordance with an embodiment, for higher dye pick up, suitable dye pick up enhancing agents that are reactive to cellulose can be used in the application bath (“Quat 188”, “CR2000”, “Ecofast Pure” from Dow chemicals and “Cationon KCN” from Lion specialty chemicals). Caution should be taken when selecting these dyeing strength boosting agents, not to interfere with the crosslinking reaction because of competing reactions, and can be judiciously chosen by a person skilled in the art.

In accordance with an embodiment, epoxy agents that are insoluble in water are dispersed in surfactant blends selected from the group consisting of branched secondary alcohol ethoxylates (“Tergitol TMN-6, Tergitol TMN-10” from Dow), Octylphenol ethoxylates (“Triton X-405” from Sigma Aldrich), alkylpolyglycosides (“Elotant milcoside 200/300” from LG chemicals and additionally polymeric thickeners selected from the group of polysaccharides (such as sodium carboxymethylcellulose), without allowing the ring opening of epoxide (as caused by regular anionic and Hydroxylated nonionic surfactants). The surfactant blend of epoxide is dispersed in water by stirring and pH adjusted with NaOH, prior to application as explained above, but at slightly higher temperature 30-50 °C.

In accordance with an embodiment, the regenerated cellulose fiber of the present disclosure is lyocell fiber and a known N-methylmorpholine-N-oxide (NMMO) dissolution method or lyocell process is used to prepare disclosed modified regenerated cellulose fiber. In accordance with an embodiment, said process comprises the steps of:

a. dissolving the cellulose in amine oxides or ionic liquids as solvents such as NMMO, followed by extruding of dope from a multiplicity of fine apertured spinnerets into air.
b. washing of fiber to remove the solvent therefrom;
c. passing the tow/fiber bed in application bath comprising the modifier;
d. adjusting wet pick up of the fiber;
e. optionally, removing the residual solvent for recycling;
f. curing followed by drying of the fiber to a predetermined moisture content;
g. washing followed by neutralizing of the fiber.

In accordance with an embodiment, in step (b) removal of the solvent from fiber is carried out in multiple aqueous baths. NMMO reacts with the crosslinking agent by ring opening, hence removal of traces of NMMO from wet tow/fiber is must to maintain bath stability in a continuous process.

In accordance with an embodiment, in step (c) the tow/fiber bed is passed through the application bath multiple times for uniform wetting with/without intermittent squeeze.

Examples:

In order that this invention may be better understood, the following examples are set forth. These examples are for the purpose of illustration only and the exact compositions, methods of preparation and embodiments shown are not limiting of the invention, and any obvious modifications will be apparent to one skilled in the art.

Also described herein are method for characterizing the modified fibers, formed using embodiments of the claimed process.

Characterization methods:

1. Measurement of fibrillation behaviour expressed as Wet Abrasion Number (WAN)

The wet abrasion number was determined in a wet abrasion testing machine FNP02 from SMK Präzisionsmechanik GmbH. In this method, a fiber is clamped under a fixed pretention of 70mg, over an abrasive shaft tightly wrapped with a tube fabric in wet form (with demineralized water) and number of rotations are counted till fracture of the fiber. The number of rotation sustained is the Wet Abrasion Number. The rotational speed of fabric wrapped shaft is fixed at 400 RPM, with angle of contact 45°.

2. Epoxide estimation and % loading

For water insoluble epoxy-based crosslinking agent, purity of epoxide starting material was determined by non-aqueous epoxide titration. Active epoxide content in liquor and % loading on fiber were estimated by non-aqueous titration with adaptation from ASTM D 1652-04.

3. Chloride estimation, bath monitoring and loading on fiber

For halohydrin-based crosslinking agents, the alkaline bath concentration was monitored by a standardized AgNO3 titration (against starting material). The chemical loading on cured unwashed fiber was estimated by direct titration of fiber by similarly adapted method. In a controlled reaction set up, chloride titration in combination with a gravimetric method before and after washing of fiber gave extent of reaction completion and bound chemical on fiber.

Example 1: Effect of modifier on fibrillation resistance and tensile properties of modified regenerated cellulose fiber: sequential treatment in methanol-water

Never-dried lyocell fiber filament (before complete NMMO removal and spin finish application) was used for the study. Fiber/tow was washed in fresh hot water followed by cold water to remove residual NMMO. Residual NMMO should be < 0.1% as measured by Kjeldahl N analyzer. Filament containing 90-120% moisture was passed through a bath containing 7g/L NaOH solution at 1:10 liquor ratio and squeezed to 100-110% pick up. The alkaline filament was passed through a bath containing 2.5-10% trimethylolpropanetriglycidyl ether (TMPTGE) and 0.4% tetraethylammonium bromide (TEAB) in 90% methanol aqueous at room temperature (30-35°C). After padding at 100% wet pick up, filament was cured at 140-145°C for 25-30 minutes in hot air. The filament was washed with methanol:water at 80:20 ratio once followed by washing in water at 60°C, followed by cold wash to remove unreacted crosslinking agent. Alkalinity was removed by 1-2 g/L glacial acetic acid rinse followed by water wash, and finally spin finish application on staple form and dried.

The various parameters of the fiber were measured, as indicated in Table 1. In Experiments 1A-1D the loading of TMPTGE was varied to see effect on crosslinking and fibrillation resistance expressed in terms of WAN, while keeping all other conditions same, such as, catalyst type, pH, curing type/temperature and subsequent washing. The result of the modified fiber was compared with the standard lyocell fiber.

Observation: WAN increased with increase in % loading of TMPTGE. Additionally, while there was a drop in elongation at 10% loading, tenacity of fiber remained unaffected.

Parameter/Property Experiment no. Standard lyocell fiber (In-house)
1A 1B 1C 1D
Pick up of TMPTGE 2.5% 5% 7.5% 10%
Application bath pH 12.5 12.8 12.5 12.5
Curing temp. (°C) & time (min) 145, 20 145, 20 145, 20 145, 20
WAN 65 229 419 699
Denier (den) 1.07 1.12 1.16 1.24
Dry tenacity (g/den) 5.25 4.78 4.82 4.41
Dry elongation (%) 10.91 10.49 8.65 12.49

Table 1: Effect of modifier concentration on WAN and tensile properties, in a sequential treatment condition

Example 2: Effect of high temperature curing

Example 1 was repeated except that the curing is done in a hot air oven at 165°C for 15 minutes. Effect of higher temperature of curing was investigated at chemical loading of 2.5-10% (Experiments 2A-2C), as indicated in Table 2.

Observation: WAN of the modified fiber upon curing at 165°C for 15 minutes was found to be comparable to that of the modified fiber 145°C curing for 25-30 minutes (1A, 1B, 1D).

Parameter/Property Experiment no.
2A 2B 2C
Pick up of TMPTGE 2.5% 5% 10%
Application bath pH 12.6 12.5 12.5
Curing temp. (°C) & time (min) 165, 15 165, 15 165, 15
WAN 75 216 721

Table 2: Effect of higher curing temperature on WAN in a sequential treatment condition

Example 3: Treatment with purer grade of TMPTGE

Example 1 was repeated except that trimethylolpropanetriglycidyl ether (TMPTGE) available from Sigma Aldrich was used as a much purer grade, as indicated in Table 3.

Observation: The WAN increased as compared to commercially available chemical (experiment 1C), at same % loading.

Experiment no. 3
Pick up of TMPTGE 7.5%
Application bath pH 12.3
Curing temp. (°C) & time (min) 150, 20
WAN 638

Table 3: Result of a sequential treatment of fiber with purer grade of TMPTGE
Example 4: Effect of modifier on bleaching: Single bath treatment in methanol-water

Never-dried lyocell filament was washed as in Example 1. Filament containing 90-120% moisture was passed through a bath containing 2.5-10% trimethylolpropanetriglycidyl ether in a mixture of 90% methanol + 10% water at room temperature (30-35°C). The bath contained 2-3g/L sodium hydroxide and 0.2-0.3% tetraethylammonium bromide (TEAB). After padding at 100% wet pick up, filament was cured at 140-145°C for 15-20 minutes in hot air. The filament was washed with methanol once followed by water at 60°C, followed by cold wash to remove unreacted crosslinking agent. Alkalinity is removed by 1 g/L glacial acetic acid rinse in filament form followed by water wash, and finally spin finish application on staple form and dried. WAN and other parameters were measured. Same fiber was checked for stability towards 1-2g/L sodium hypochlorite - 4.5%aq bleaching at room temperature, as indicated in Table 4.

Observation: The modified regenerated cellulose fibre showed complete stability towards bleaching.
Experiment no. 4
Pick up of TMPTGE 7.5%
Curing temp. (°C) & time (min) 145-150, 20
WAN 435
WAN after sodium hypochlorite bleaching 463

Table 4: Effect of epoxy-based cross-linking agent concentration on WAN and tensile properties in a single bath treatment condition.

Example 5: Single bath treatment in ethanol or ethanol-water

Example 4 was repeated except that the solvent was 50-90% ethanol aqueous, instead of methanol. The bath comprised of 7.5% TMPTGE, 0.2-0.4% TEAB and 3g/L NaOH in respective alcohol:water mixture. Table 5 shows the result of Experiments 5A-5C in which alcohol concentration was varied.

Observation: 90% ethanol showed lesser crosslinking reaction as indicated by lower WAN in Experiment 5A than 90% methanol in Experiment 4. When moving from 80% ethanol to 50% ethanol, the solubility of the crosslinking agent is reduced indicated by haziness of bath, and it has clear impact on crosslinking reaction, as indicated by lowering in WAN. Antifibrillation results are acceptable till 80% ethanol-water blend.

Parameter/Property Experiment no.
5A 5B 5C
Pick up of TMPTGE 7.5% 7.5% 7.5%
Solvent system in application bath 90% ethanol 80% ethanol 50% ethanol
TEAB (% o.w.f.) 0.4 0.4 0.4
Curing temp. (°C) & time (min) 150, 20 150, 20 150, 20
WAN 343 354 191
WAN after sodium hypochlorite bleaching 344 345 182

Table 5: Treatment with epoxy-based crosslinking agent in ethanol-water mixture of varied concentration.

Example 6: Single bath treatment in water

10-15% of a Polychlorohydrin ether of polyhydric alcohol, hereafter named as Poly(CH-O-PHA) (as exemplified in Figure 1) was dissolved in water at room temperature to obtain a clear-to-slightly hazy solution, followed by elevating the pH of bath with 45% NaOH under continuous mixing and pH monitoring. The bath pH is maintained at 11.5-12.5. Lubricating agent is added and mixed well. The conversion to reactive epoxide is ensured by no sudden drop in pH. Washed and never-dried lyocell filament is passed through the application bath with residence time of 1.5-3 s and squeezed to desired wet uptake before entering the curing chamber. The drying and curing is complete in 15-20 minutes at 125-145°C, while higher curing time has no negative impact. The treated tow is washed, cut, bleached to desired whiteness, neutralized to pH 6-7 with dilute aqueous organic acid followed by spin finish application and drying.

Above experiment was repeated with never-dried staple fibers (not seeing any abrasion earlier) with similar results. The above crosslinking study was also repeated with additional 10-30g/L of CR2000 (cationization agent) in application bath to achieve higher dye pick up crosslinked fiber without much hampering the anti-fibrillation property. Experiments 6A-6C are without dye pick-up enhancing agent, and 6D-6E are with dye pick up enhancing agent.

Parameter/Property Experiment no.
6A 6B 6C 6D 6E
Pick up of Poly(CH-O-PHA) (o.w.f.) 9.3% 11.16% 14% 11.16% 11.16%
pH of bath 12.50 12.25 12.46 12.25 12.20
Pick up of CR2000 (o.w.f.) 0 0 0 1.3 2
WAN before bleaching and WI 354 568 (WI 54.5) 682 443 397
Denier (den) 1.32 1.19
Dry tenacity (g/den) 4.89 4.52
Dry elongation (%) 11.24 9.16
WAN after hypochlorite bleaching and final whiteness index (WI) 338 566 (WI 69.1)

Table 6: Effect of concentration of chlorohydrin based crosslinking agent on WAN and tensile properties in a single bath treatment condition, cured at 140°C/30 min and stability towards bleaching (WI – Berger Whiteness Index)

Observation: At same crosslinking agent uptake of 11.16% (in Experiment no. 6B, 6D and 6E), the WAN decreases gradually with increase in cationization agent. An uptake of >10% crosslinking agent seems to give satisfactory result in terms of fibrillation removal, while producing a fiber with optimum whiteness. Tensile properties did not deteriorate at similar uptake level.

Example 7: Estimation of chemical uptake as function of treatment duration, prior to curing

Example 4 was repeated and in Experiment 4A and 4C, the residence time of cellulose filament in application bath was maintained at 5 minutes and 20 minutes respectively.

Observation: Uptake of TMPTGE from methanol is almost uniform at both immediate (5 minutes) and longer duration (120 minutes). No advantage of longer contact time seen at lower bath concentration, as indicated in Table 7. However, permeability increased slightly at long duration for higher bath concentration.
Expt. No. reference Targeted % TMPTGE (o.w.f.) Time of soaking treatment (min) % Epoxide (o.w.f.) % Loading of TMPTGE (o.w.f.)
4A 5 5 1.32 4.31
5 120 1.32 4.31
4C 7.5 5 2.47 8.06
7.5 120 2.60 8.48

Table 7: Estimation of chemical loading on wet fiber against targeted pick up by padding

Example 8: Reaction efficiency - Estimation of bound crosslinking agent on the basis of free epoxide

The crosslinking agent used contains multiple epoxy groups and same was quantified by adaptation of existing non-aqueous titration method on as is fiber and washed fiber, to estimate the extent of reaction- indicates almost complete reaction. Also, washing removes the traces completely, as indicated in Table 8.

Expt. No. reference Target loading of TMPTGE (% o.w.f.) Type of fiber % Epoxide Unreacted %TMPTGE on fiber (o.w.f.)
1B 5 Unwashed 0.125 0.41
Washed 0.043 0.14
1C 7.5 Unwashed 0.041 0.13
Washed 0 0
1D 10 Unwashed 0.124 0.40
Washed 0 0

Table 8: Estimation of residual chemical and bound chemical on fiber

Example 9: Single bath treatment in water using surfactant blend

A dispersion of 7.5% trimethylolpropanetriglycidyl ether (TMPTGE) in water was prepared in presence of 1-2% Tergitol TMN 6 with 3% Triton X405 or 3% Sorbelon MN or 1% C12-16 alkyl benzoate. To the dispersion was added 0.4% TEAB and 0.2% NaOH(s) at room temperature (30-35°C) under constant agitation. Similar to example 1, filament containing 90-120% moisture was passed through an application bath containing above dispersion at 35-45°C. After padding at 100% wet pick up, filament was cured at 145-150°C for 22-25 minutes in hot air. The filament was washed with hot water followed by cold wash to remove unreacted crosslinking agent. Alkalinity was removed by 1g/L acetic acid rinse followed by water wash, cut int staple form and applied spin finish followed by drying. Similar experiments with higher concentrations of TMPTGE and surfactants can achieve higher WAN by a person skilled in the art. Experiment 9A-9C are at same dosage level of crosslinking agent- TMPTGE but with various surfactant blends as explained earlier. WAN and other parameters were measured. The results have been tabulated in Table 9.

Observation: All experiments resulted in similar WAN. Further, full fibrillation removal could not be obtained at 7.5% dosage. It was observed that higher dosage of crosslinking agent will be necessary to obtain similar WAN as that of Example 1 and 4.

Chemical % (o.w.f.)
Experiment No. 9A 9B 9C
TMPTGE 7.5 7.5 7.5
Tergitol TMN6 1 1 2
Triton X-405 3 0 0
Sorbelon MN 0 3 0
C12-16 alkyl benzoate 0 0 1
TEAB 0.4 0.4 0
Water q.s.to 100
WAN (without bleach) 249 226 264
Denier (den) Not measured 1.37 Not measured
Dry tenacity (g/den) 4.60
Dry elongation (%) 11.14

Table 9: Effect of modifier on WAN and tensile properties, in a single bath treatment condition. (q.s. – quantity sufficient)
Example 10: Acid and alkali stability of WAN

Protocol for acid stability: 5g crosslinked fiber treated at 1:20 MLR in dilute acetic acid solution at pH 4-4.5, at 130°C for 30 minutes, followed by washing in plain DM water and drying at 105°C. WAN was measured.

Protocol for scouring or alkaline stability: 5g crosslinked fiber treated at 1:20 MLR in a solution containing 2g/L NaOH, 1g/L soda ash, hydrogen peroxide with stabilizer 3g/L, sequestering agent 1gL at 90-95°C for 30 minutes, followed by washing in hot DM water thoroughly, neutralizing and drying at 105°C. WAN was measured. The results have been tabulated in Table 10.
Experiment No. Fiber type WAN
as is WAN
after acidic treatment WAN
after scouring (alkaline treatment + peroxide bleach)
4 7.5% TMPTGE treated in methanol + water 419 410 415
9A 7.5% TMPTGE treated in water + surfactant blend 249 226 277
6A 10% Poly(CH-O-PHA) treated in water 354 383 421
6C 15% Poly(CH-O-PHA) treated in water 682 739 765

Table 10: Results of acid and alkali stability analysis

Observation: Acid and alkali stability analysis of crosslinked fibers show complete stability under cellulosic or polyester blend conditions.

Example 11: Dyeing behavior towards reactive dyes

Control and crosslinked fibers were scoured, and dyed with three reactive dyes separately: Reactive red F3B – 3% o.w.f., Reactive red HE3BI – 3% o.w.f. and Blue HERDI- 4% o.w.f. (Reactive red F3B with C.I. 181055, Reactive red HE3BI with C.I. 292775, and Reactive blue HERDI with C.I. 137160). Dye bath comprised of 70g/L sodium sulphate and 18g/L soda ash for red dye, and 80g/L sodium sulphate as well as 20g/L soda ash for blue dye. Dyeing was carried out at 60°C for 45 min, followed by water wash, 2g/L non-phosphate ECE detergent at 60°C for 30 min, hot water wash, cold water wash and then drying at 105°C.
Also, dyeing of bleached fiber was done similarly where the bleaching was done by 2-5g/L sodium hypochlorite - 4.5% aq. at 50-55°C followed by 1g/L acetic acid wash. The dyed crosslinked fibers were checked for fibrillation under SEM, which showed almost no fibrillation. The dyeing study was repeated with 100% lyocell knit fabric made with crosslinked fibers using same dyes, followed by washing performance test at 40 °C for 10 home laundry (washing + tumble drying) using ECE detergent. The results have been tabulated in Table 11A-C. Further, visual inspection showed no sign of fibrillation, which was confirmed by SEM analysis.

Fiber dyed with blue dye L* a* b* K/S St. (Max)
Control lyocell 38.4 -1.5 -31.2 100
Example 4 39.6 -2.3 -30.7 91.9
Example 4 bleached 39.7 -2.0 -30.9 91.0

Table 11A: Dyeing results with Reactive Blue HERDI dye – 4% o.w.f. shows negligible impact on color strength

Fiber dyed with red dye L* a* b* K/S St. (Max)
Control lyocell 37.2 57.1 2.5 100
Example 4 39.2 59.8 2.1 97.4
Example 4 bleached 38.4 58.5 1.7 98.1

Table 11B: Dyeing results with Reactive Red F3B dye – 3% o.w.f. shows no impact on color strength

Fiber dyed with red dye L* a* b* K/S St. (Max)
Control lyocell 43.0 58.7 5.8 100
Example 6A 45.7 62.6 7.7 92.6

Table 11C: Dyeing results with Reactive Red HE3BI dye – 3% o.w.f. shows negligible impact on color strength and tone.

Industrial Applicability
The disclosed modified regenerated cellulose fibre exhibits improved fibrillation resistance expressed as wet abrasion number (WAN) and has similar or improved mechanical properties such as elongation and tenacity as compared to fiber without said modification.

The disclosed modified regenerated cellulose fiber exhibits sufficient degree of fibrillation resistance expressed as wet abrasion number (WAN) and the tenacity and elongation in desired range. This was confirmed on both fiber (after wet abrasion test) and fabric surface by SEM before and after home laundering. The disclosed modified regenerated cellulose fiber exhibits anti-fibrillation property even after downstream processing like commercial scouring, dyeing processes and multiple home laundering (washes).

The present disclosure provides a process for the preparation of fabric obtained from various regenerated cellulose fibers, in particular, lyocell fibers having reduced fibrillation, which is simple and cost-effective. The disclosed process of preparing said modified regenerated cellulose fibers is a continuous process. It is cost effective and environmentally sustainable. Specifically, neither the modifier nor the dispersants/catalysts of the modifier have the tendency to liberate toxic formaldehyde, which has remained a major concern for most of the formaldehyde-based resins/cross-linkers used in fiber/textile industry.

The disclosed method provides safer crosslinking chemistry for reducing the fibrillating tendency of fiber. The modifier used in the present method is non-volatile, do not need a high temperature dissolution process for application onto wet lyocell tow/staple fiber in a batch/continuous set up, and has the ability to undergo almost complete reaction from alcoholic solvent/aqueous approach under continuous drying and curing conditions.

Additionally, the organic solvents used in the present disclosure have widely separated boiling points from water and can easily be completely removed by vacuum without altering the homogeneous distribution of the high boiling cross-linker in the cellulose domain, prior to entering dryer and can be recycled back. The ease of solvent removal by vacuum further makes the process safe in terms of curing condition in a continuous process.

The modifier of the present disclosure also does not negatively affect the dye binding ability of the fiber. This is understood to be due to free –OH sites generated after ring opening of epoxide groups on the modifier, thereby keeping the reactive dyeing tendency of fibers almost intact both in acidic and alkaline environments.
,CLAIMS:1. A modified regenerated cellulose fiber comprising of regenerated cellulose fiber crosslinked with a modifier, wherein the modifier comprises a crosslinking agent having a formula I or II:

(I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5.

2. The modified regenerated cellulose fiber as claimed in claim 1, wherein the modifier is an epoxy-based crosslinking agent having a formula I or II or a halohydrin-based crosslinking agent having a formula I or II.

3. The modified regenerated cellulose fiber as claimed in claim 1, wherein the modified regenerated cellulose fiber comprises the modifier in an amount ranging between 1-25% by weight of cellulose.

4. The modified regenerated cellulose fiber as claimed in claim 1, wherein the modified regenerated cellulose fiber comprises the modifier in the amount ranging between 5-18% by weight of cellulose.
5. The modified regenerated cellulose fiber as claimed in any of the preceding claims, wherein the regenerated cellulose fiber is lyocell fiber.

6. A continuous process for preparing a modified regenerated cellulose fiber, said process comprising:

a. treating a never-dried regenerated cellulose fiber with a modifier comprising a crosslinking agent having a formula I or II:
(I)
(II)
wherein
each A is independently H, CH3, , or ;
each B is independently H, OH, O-A, CH2OH, CH2O-A, or
C is H or OH;
Y is O or (CH2)n;
a is an integer in the range of 0-6;
b is an integer in the range of 0-4;
m is an integer in the range of 0-3;
n is an integer in the range of 1-5;

b. curing the treated regenerated cellulose fiber treated at a temperature between 100-160°C to obtain the modified regenerated cellulose fiber.

7. The process as claimed in claim 6, wherein the never-dried regenerated cellulose fiber is in a form selected from the group consisting of tow, staple or filament yarn.

8. The process as claimed in claim 6, wherein the modifier is prepared in an alkaline solution, aqueous solution, water-alcohol mixture, surfactant mixture or dispersion.

9. The process as claimed in claim 6, wherein the modifier further comprises one or more of a solvent, inorganic alkali or alkaline earth hydroxides, carbonates, phosphates and metal fluoroborates.

10. The process as claimed in claim 6, wherein the modifier further comprises of one or more of a phase transfer catalyst, lubricating/non-ionic surface-active agent, reactive cationization agent, and an exhaustion agent.

11. The process as claimed in claim 10, wherein the exhaustion agent is selected from the group consisting of alkali salts, alkaline earth salts and the combination thereof.

12. The process as claimed in claim 6, wherein the modifier is applied to a never-dried regenerated cellulose fiber in an application bath at temperature in a range of 25-45°C.

13. The process as claimed in claim 6 or 12, wherein the treatment of never-dried regenerated fiber with modifier composition is carried out in the application bath for a time period of 3-300 seconds.

14. The process as claimed in claim 6, wherein the curing is carried out for a time period of 5 -120 minutes.

15. The process as claimed in claim 6 or 14, wherein the curing is carried out using one of dry heat, saturated steam or super-heated steam.

16. The process as claimed in claim 6, wherein the process further comprises a neutralization step using an organic acid selected from the group consisting of acetic acid, citric acid, lactic acid and mixtures thereof.

17. The process as claimed in any of the preceding claims, wherein the never-dried regenerated cellulose fiber is obtained from N-methyl morpholine-N-oxide dissolution method.