Introduction

During the 90s the fashion trend was for garments made from the natural fibers with softer handle and greater comfort during wear. Easy-care products range from commodity to niche or from simple resin finish to highly developed performance packages. Dimethyloldihydroxyethylene urea -- DMDHEU and modified DMDHEU are the most commonly used easy-care finishing agents in the textile industry. However, this type of compound releases formaldehyde which is a known irritant to mucous membranes and is also carcinogenic. Further, its constant exposure to human body and skin results in dermatitis and respiratory problems. During the last few years health and safety as well as environmental pressures have reflected on technology. Easy-care resins must leave no or low formaldehyde residues on fabric. The limit of formaldehyde on textiles is specified as per end use viz., outer clothing, close to skin and baby clothing. There is a great concern about replacement of formaldehyde-based resins with formaldehyde free resins especially for baby clothing and close to skin where limiting values are 25 and 75 ppm respectively. Since the conventional cross-linking agent releases formaldehyde, efforts have been made to replace the traditional DMDHEU cross-linking agent by formaldehyde-free cross-linking agents for cellulosic fabrics. Multifunctional carboxylic acids, polycarboxylic acids with suitable catalyst have been reported as formaldehyde free cross-linking agents. However, these types of agent form ester linkage with cotton fabric and thereby stability of bond to washing is lower than that of DMDHEU type of products. Further, these types of product are applied at higher temperature to effect cross-linking to the cotton fabric and consequently the mechanical strength of the treated fabric is inferior and also treated fabrics show tendency to yellow. When these products applied to dyed fabric, the change in shade is more pronounced. In order to overcome the difficulty of the formaldehyde-free polycarboxylic type of cross-linking agent, in the present study, a speciality cross-linking agent Primafin NF and evaluated for different properties. Studies have also been carried out with respect to change in shade of the treated fabrics dyed with different classes of reactive dyes.

Experimental

Fabric
Mill bleached with mercerized cotton fabric with reeds X picks, 132 X 72 threads / inch and counts 40S X 40S.

Dyes
1. Hetero-bifunctional reactive dyes viz. C. I. Reactive Yellow 160, Red 195, Orange 122, Blue 222 and Black HFGR. 2. Homo-bifunctional reactive dyes viz. C. I. Reactive Yellow 84, Red 152, Orange 84 A, Green 19 A and Blue 171 3.Sulphatoehtylsulphone reactive dyes viz. C. I. Reactive Yellow 77, Red 35, Orange 16, Blue 21 and Black 5

Methods of dyeing

All reactive dyes were dyed as per methods recommended by the manufacturers. Dyed samples were thoroughly washed with 1 g/l Sorbecol PNN to remove unfixed as well as hydrolyzed dye.

Finishing procedure

Undyed and dyed cotton fabrics were padded with Primafin NF -- non formaldehyde cross-linking agent with built in catalyst viz. 100 g/l at 80 percent expression and dried at 90 degrees C for 1 min and cured at 120, 130 and 140 degree C for 2 to 4 min. Cotton fabric was also finished with conventionally used 100 g/l DMDHEU -- built in catalyst in similar manner and dried at 90 degrees C and cured at 150 Degrees C for 3 min. Finished samples were evaluated for different properties.

Whiteness index and color measurement - Whiteness index, color depth and change in shade was measured on Premier Colorscan.

Wrinkle Recovery Angle - As per AATCC test method No. 66-1968 on Monsalo tester, wrinkle recovery angle was measured.

Breaking strength - Raveled strip method as per ASTM D 5035 of Stech Engg. Co.

Tear strength - Tear force was determined by single rip test as per ASTM D 1424-81 ON Elmendorf tester of Ameet Trading Co.

Results and discussions

Cotton fabrics finished with Primafin NF as a cross-linking agent at different temperature. Efforts to develop formaldehyde-free butanetetracarboxylicacid or citric acid with suitable catalyst have been reported. In the present study, formaldehyde free cross-linking agent has been developed which can be cured at low temperature and which does not impair whiteness of the treated fabric. Further, this product is based on aldehydic/ketonic group thereby it forms ether linkage with the hydroxyl group of cellulose. In general, ether linkage comparatively more stable than ester linkage normally forms when finished with polycarboxylic acid. Results of the study indicate that incase of cotton fabric finished with Primafin NF and cured at 120 - 140 degrees C for 2 to 4 min, whiteness of finished fabric is marginally lower as compared with that of unfinished fabric. Yellowness index goes hand-in-hand with whiteness index. In case of cotton fabric finished with conventionally used cross-linking agent DMDHEU, decrease in whiteness index is slightly lower as compared with Primafin NF-finished or unfinished fabric. Wrinkle recovery angle of cotton fabric finshed with Primafin NF is fund to be 270 degrees irrespective of the temperature and time of treatment and comparable to that for conventionally used DMDHEU cross-linked fabric. Tear and tensile strength retention values are found to be marginally better in case of Primafin NF as compared with DMDHEU cross-linked fabric (table 2).

Cross-linking of cotton fabric dyed with diffrent classes of reactive dyes.

Dyeing of cotton fabric was carried out with homo- and hetero-bi-functional amd vinyl sulphone dyes. K/S of cotton fabric dyed with different classes of dyes and finished with cross linking agent are not much different as compared with the unfinished fabric. However, color difference depends on type of dye and finishing agent. In case of homo-bifunctional reactive dyes, color difference ranges from 0.29 to 0.94 for Primafin NF while in case of conventially used DMDHEU finished fabric the color diffrence is between 0.2 to 1.2 at different depth of shade and chromophore (0.5 - 4% shade) (fig 1). In case of hetero-bifunctional reactive dyed and finished fabrics similar behaviours is observed. The color difference for Primafin NF is between 0.2 to 1.0, while for DMDHEU finished fabric is between 0.2 to 1.1 (fig 2). For vinyl sulphone dyes, color difference is between 0.19 - 0.45 for Red 195, Blue 227 and Black HFGR and Orange 122 Primafin NF finished fabric, and DMDHEU-finished as well as for Primafin NF (fig 3).