Investigations into the Sequential Application of Crease Resist Finish, Tannin and Cationic Reactant to Improve the Resistance of Sulphur Dyes to Oxidation

The importance of sulphur dyes are realized due to the fact that they offer an economical method of achieving dyeing of good color strength and acceptable fastness on cellulosic substrates. However, the main limitations associated with this class of dye are the lack of availability of bright colors and it’s fading on exposure to laundering with detergent and perborates/peroxides formulations. In order to meet the growing requirements of customers regarding the higher wash fastness, garment traders are in turn demanding their suppliers to achieve these properties against single and multiple washes. In this study, sulphur black 1 dyed cotton fabric has been aftertreated with Fixapret CP, Bayprotect Cl and CC (Choline Chloride) with various sequential combinations to improve the wash fastnesss of the dyed fabric against the aggressive ISO-1O5 CO9 washing system. Sequential application of Bayprotect Cl followed by CC was found to offer a significant improvement causing a 12% reduction in percentage colour loss relating to the untreated fabric, which was comparable to the independent application of Fixapret CP with minimum deleterious effects on the hue, chroma and tensile strength of the fabric.


INTRODUCTION
possesses moderate to good fastness which allows them to broadly satisfy the needs of industry, however, with the increasing performance demands of garment suppliers and customers, the use of these dyes is gradually declining as they are getting replaced by other dye classes [2]. A major reason for their continuing unpopularity is the environmental impact that is created by the use of the conventional reducing agent sodium sulphide, which is highly toxic to marine life and sewerage systems. CO9 washing protocol [3].
Cellulosic goods dyed with sulphur dyes are particularly affected by bleach-containing washing powders. The purpose of bleach (such as sodium perborate) is to help remove the stains produced by tea, coffee, fruit juice etc. and the addition of a bleach activator (such as TAED) facilitates the low temperature removal of these stains [4].
One of the most important aspects of this work was to design an after treatment formulation to improve the wash down of sulphurdyeings when exposed to aggressive washing system of ISO-1O5 CO9. The work done so far has produced potential solutions to improve the resistance of sulphur dyed cotton fabric against ISO-1O5 CO6 treatments. However, the effect of ISO-1O5 CO9 washing is far more degradative to the colour, hence a further protective system is needed to be developed which could safeguard the dyed material from the highly oxidative environment produced by this washing regime. For this purpose, the sequential applications of crease resist finish (Fixapret CP), cationic reactant (CC) and tannin (Bayprotect Cl) have been explored.  [1] raised to 98 o C at a gradient of 4 o C/min and maintained at the boil for 60 minutes. The temperature was then reduced to 50 o C.

Materials
Dyeings were washed thoroughly with cold water to remove any unfixed surface dye. The dyed fabric was then oxidised with 5 g/L hydrogen peroxide and 1 g/L soda ash at 40-45 o C for 15 minutes. It was then finally soaped with 1g/L of non-ionic detergent at the boil for 20 minutes and then rinsed with warm and cold water. The L:R employed for oxidation and soaping was 10:1.

After Treatment with Bayprotect Cl
Sulphur dyed fabrics were after treated with a liquor containing 4% omf Bayprotect Cl and 100 g/L sodium sulphate. A pH of 3.5 was maintained with citric acid. The samples along with the liquor were treated at 98 o C for 20 minutes with liquor to goods ratio of 10:1. The finished fabric was finally rinsed with warm and cold water and air dried. The application method is shown in Fig. 3.

After Treatment with Choline Chloride
CC was applied on its own and also added in different concentrations to the liquor containing Fixapret CP and magnesium chloride. The application method is the same as described above in section 2.4.

Colour Analysis
The colorimetric data of the dyed and after treated cotton  DMDHEU based resins are produced as a result of the reaction between glyoxal, urea, and formaldehyde and react with the cellulose by etherifying the hydroxyl groups in the amorphous phase. The N-methylol groups in DMDHEU react with the cellulose, and a crosslinking net is formed [6][7]. Application of crease resist finish to cotton involves padding the material with a solution containing a condensation polymer precursor and a suitable

Investigations into the Sequential Application of Crease Resist Finish, Tannin and Cationic Reactant to Improve the Resistance of Sulphur Dyes to Oxidation
polymerisation catalyst followed by drying and curing.
As a result of heating, the polymer precursor either reacts with hydroxyl groups in the cellulose to form crosslinks between adjacent polymer chains, or it polymerises in the amorphous regions of the fibres [5]. Crease resist finish after treatment of sulphur dyed cotton produces crosslinked cellulose fabric and the crosslinking treatment serves to "lock" the dye in the fabric, so increasing the wash fastness [8]. After treatments with the tannin, Bayprotect Cl also showed slight improvements, that is, a reduction of % color loss to 54 and 55% for AC 3 and AC4, respectively.
It is quite obvious that an increase in % concentration of the applied finish did not significantly reduce the color loss, indicating that 4% omf was an optimum quantity for the after treatment.
To enhance the effect of the fixatives on the wash fastness of the dyeings, the sequential application of Bayprotect

Investigations into the Sequential Application of Crease Resist Finish, Tannin and Cationic Reactant to Improve the Resistance of Sulphur Dyes to Oxidation
partly untreated cotton. The fabric was dyed with different dyes and under different pH conditions to produce twocolor and contrasting tonal effects. The purpose of using a reactive additive in the crosslinking system was to produce additional properties in the crosslinked fabric other than resiliency and shrinkage control [9].
Previous work on modification of electrical resistivity of durable press finishes showed that cationic groups could

COMPOSITION AND APPLICATION PARAMETERS FOR SEQUENTIAL APPLICATION OF BAYPROTECT CL, FIXAPRET CP AND CHOLINE CHLORIDE ON CI LEUCO SULPHUR BLACK 1 DYED COTTON FABRIC
chloride and Fixapret CP after tannin treatment did not considerably enhance the wash fastness of the dyed samples (AC 9-AC 11, Table 4 (Table 5).
On applying various combinations of the aforementioned fixatives, only slight improvements were observed, as shown in Table 6. Hence, the co-application of CC with relative proportions of Fixapret CP was not found to be much significant for improving the resistance of the dyes to oxidation against perborate based laundering.

DYED COTTON FABRIC AFTERTREATED WITH BAYPROTECT CL, FIXAPRET CP AND CHOLINE CHLORIDE
As shown in Table 8, AC-19 and AC-20 indicated that the combined application of Fixapret CP and CC following Bayprotect Cl treatment did not yield any significant effect on the wash durability to the CO9 test. On the other hand, when CC was applied after Bayprotect Cl (AC-21), it produced results comparable to the individual application of Fixapret CP (AC-12).
However, on increasing the concentration of CC from 10-20 g/l, no decrease in % color loss was observed indicating that 10 g/l is an optimum quantity. It was estab lished that sequential ap plication of 4% omfBayprotect Cl and 10 g/l of CC would produce improved results in terms of increased fastness to laundering.     Table 9). However, it can be seen that after treatment with

Mechanism
The wash fastness of acid dyes on nylon can be improved by a back-tanning process in which the dyed fabric is first treated with tannic acid and then tartar emetic. The anionic tannic acid is adsorbed onto the surface of nylon by forces of attraction between the anionic tannic acid and cationic ammonium ion groups at the ends of the polymer chains of nylon. Further, on the application of tartar emetic, a film of the insoluble antimony salt of tannic acid is produced that restricts desorption of the dyes.
Hence, the insoluble anionic tannic acid repels dye anions on a nylon surface after back tanning [5].
Syntans (synthetic tanning agents) are also used in place of tannins as they are less expensive and environmentally friendly. The mechanism by which syntans improve the wash fastness of acid dyes on nylon is slightly different. The anionic syntans do not form a layer like the tannic acid/tartar emetic combination, instead, they are substantive to nylon.
The syntan molecules adsorb on the surface by interaction with ammonium ion sites but they cannot penetrate into the polymer because of their large molecular size. The large sized adsorbed syntan on the nylon surface inhibits the dye leakage d uring laundering [5]. Another theory favours the aromatic attraction of dyestuff and syntan, thus hindering the dyestuff molecules from migrating out of the fibre [12].
In the case of improved wash fastness of sulphur dyed fabric, there is a potential for the formation of large molecular size complexes with low aqueous solubility between the anionic tannin and the cationic reactant arising from the electrostatic forces of attraction between the anionic groups in the dye or the tannin and the cations. For this to occur, the dye must contain anionic group similar to the sulphonated groups in the direct dye.
In spite of the fact that only little is known about the exact chemistry of the sulphur dyes, it has been proposed that some sulphur dyes may contain sulphonic acid groups [13]. Hence, the large surface area may lead to maximizing the cumulative effect of weak intermolecular forces and also the physical entrapment.
Since the process involves the sequential application of tannin and a cationic reactant, it is postulated that the application of an aromatic carboxylic acid derivative (anionic tannin) introduces anionic sites on cellulose as depicted in Fig. 4. Sequential application of cationic reactant, in turn, introduces positive charges which form complexes with the negative charges as shown in Fig. 5.
The suggested reason for the improved wash fastness is that the sequential application of the tannin and cationic reactant has a tendency to produce complexes which inhibit the dissolution of dye molecules and protects the dye against ISO-1O5 CO9 washing regime based on modern detergent formulation.

FIG. 4. FORMATION OF A LAYER OF NEGATIVE CHANGESN OF TANNIN ON THE SIRFACE OF FABRIC
Negative charges produced by Bayprotect Cl

CONCLUSIONS
The sequential application of Fixapret CP and Bayprotect Cl was beneficial in terms of achieving an improved wash fastness against ISO-1O5 CO9 washing, but Fixapret CP was found to have deleterious effects on the tensile strength, wet crocking and chroma of the fabric.