(a) Low or ultra low formaldehyde easy care finishing:
Washing of cured fabric reduces the chances of released formaldehyde from the finished fabric.
Washing removes free formaldehyde as well as untreated N-mehylol groups which may decompose to form formaldehyde. The PH during washing plays an important role in the formaldehyde release properties of finished fabrics. Generally the PH range for best formaldehyde release properties is between PH 4 to PH 5 (11). The temperature of the wash bath has little or no effect on the amount of formaldehyde released from DMDHEU finished fabrics, consequently a low temperature or room temperature washing is preferable. A considerable amount of water and heat energy is needed to redry the fabric after washing which increases the production costs and this is the major draw-back of the process.
To decrease the amount of formaldehyde of the fabrics finished with N-methylol compounds, a process which is based on the spraying of urea on to the cured fabrics has been developed. The process is called the BASF fog-chamber technique. This technique is very efficient for reducing the amount of formaldehyde liberated during the storage of finished fabrics. In most cases a 10-30% solution of urea has proved satisfactory, while an atomized spray for low wet pick-up of 5-10% is sufficient.
Methylated DMDHEU reactants can reduce the formaldehyde release to an ultra-low level. A two-step
production sequence of methylated DMDHEU was developed (12). The methylated DMDHEU treated fabric has exceptional performance as evidenced by superior chlorine resistance and enhanced wash durability.
(b) Formaldehyde free easy care finishing:
Due to the increasing public awareness of formaldehyde hazards, in recent years there has been a trend to avoid the use of formaldehyde and thus to eliminate any possible formaldehyde release from the finished fabrics. The resin finishing industry has researched extensively a non-formaldehyde easy care finishing treatment to provide high quality and high safety clothing for practical use.
Glyoxal with aluminum sulfate catalyst can impart a high degree of wrinkle resistance and smooth drying qualities to cotton fabric. A considerable amount of strength loss was observed at high curing temperature (145-155°) but by using aluminum dihyderoxy acetate as buffer the fabric can be treated with high curing temperature (145-160 °C) for 15 seconds and that imparts a very good easy care effect comparable to that of a conventional pad-dry-cure treatment with DMDHEU (13).
Among the new non formaldehyde finishes being developed, poly-carboxylic acids appear to have a number of advantages over other reagents (14). Recently a process was developed using monosodium phosphates as the curing catalyst for easy care finishing with 1, 2, 3, 4-butanetetrcarcarboxylic acid. The process is suitable for simple pad-dry-cure techniques. After padding with polycarboxylic acid, catalyst and softener, the fabrics was dried at 80°C and then cured at 180°C for 90 Seconds. The cured fabric was rinsed in 50°C in running water for 30 minutes and finally dried at 85°C for 5 mins. The finished fabric demonstrated an excellent easy care finishing effect, a high level of smooth drying properties, good laundry durability and no yellowing effects. Breaking and tearing strength retention is somewhat higher than in DMDHEU treatment catalyzed by magnesium chloride.
More recently sodium hydrosulphite has proven to be the most active curing catalyst for easy care finishing with 1, 2, 3, 4- butaneteracarboxylic acid. By using sodium hypophosphite as catalyst it is possible to reduce the curing time to as low as 15 seconds at a temperature of 205-215°C, thus making high speed fabric finishing possible. Additives have also been found which increase the easy care finishing performance of cotton fabric treated with BTCA catalysed by hypophosphite. The addition of 2-3% N, N-disubstituted amides will produce the following effects:
Increased easy care performance
Increased durability to alkaline laundering
Decrease in the concentration of sodium hypophosphite and BTCA required and thus lower the chemical cost.
Due to the harmful effect of formaldehyde and increasing public awareness of formaldehyde hazards, BTCA could be the effective cross-linking agent for high quality cotton fabric.