Citric Acid Anti-wrinkle Finishing The Main Problems And Countermeasures

Citric acid as a formaldehyde-free crease-resistant finishing agent is available, low-cost and nontoxic. But there are some defects by using it for cotton fabric finishing, including serious strength loss, yellowing easily and not very high wrinkle recovery angle (WRA) of the treated fabric. So the solutions to these questions are studied in this research.Both cellulose hydrolysis accelerated by acid and crosslinks within fibers are the main reasons to strength loss of fabric. And the quantity of strength loss coming from cellulose acidic hydrolysis is half of the total strength loss. Therefore, some alkaline chemicals are used to raise the pH value to diminish strength loss, such as NaOH, ammonia and 4-Dimethylaminopyridine. Three performances of treated fabric, i.e. strength, whiteness and WRA, could be balanced if the pH value is controlled in the range of 2.3~2.7, although NaOH and ammonia have some negative effect on WRA. 4-Dimethylaminopyridine has the best effect on the fabric performances among these alkaline chemicals, for it markedly improves not only strength but also WRA. Polybasic alcohol and β-cyclodextrin are also utilized to improve fabric's strength not for their raising pH but for their ability of crosslinking with citric acid and cellulose.It is found that aconitic acid which produced from citric acid pyrolytic dehydration is the main factor causing yellow of fabric. Then studies in two aspects are performed: restraining citric acid to dehydrate and eliminate yellowing of fabric. The results show that as a citric acid modifying product for restraining citric acid dehydration, acetocitric acid does not have thermal stability due to its tert-butyl acetate structure which is much easier to rupture producing a new unsaturated acid than citric acid itself does. Triethanolamine, boric acid and sodium tetraborate are very good auxiliaries for restraining citric acid to dehydrate although they also have some negative action on other performances. The negative action can be cut down to the least when adding proper amount of these auxiliaries respectively. For eliminating yellowing, we develop a new procedure of pad-dry-curing-steaming. It can not only improve the whiteness of fabric obviously, but also increase the crease-resistant performance, and have no affect on strength.Adding sodium citrate into finish bath as a co-reactive catalyst is studied in this research. WRA, whiteness and strength are all improved in this new technique under optimizing process. The other performances of finished cotton fabric are also studied, especially with hygroscopicity and soiling. The result suggests that the more crosslinking exist, the more serious strength loss. Fabric soiling is related with the quantity of carboxyl group on fabric, the more quantity present, the easier soiling appears.