Glycerol in comparison with ethanol in alcohol-assisted dyeing

The dyeing processes can be reformulated to reduce the environmental pollution with economic advantages by the substitution of most auxiliary products with low cost, non-toxic and biodegradable products derived from natural sources. In a previous work a chemical substitution study was carried out with ethanol and the results showed a favorable effect of ethanol addition, at about 1-3% v/v, on the dye uptake, with some differences depending on fiber nature and dye class. In the present study glycerol was considered as alternative to ethanol due to the very low volatility and high boiling point which make safer its use in industry. The effect of glycerol introduction without other additives in isothermal dyeing of various fiber yarns (wool, cotton, polyester, nylon 6 and acrylic) was experimented and compared with that of ethanol. Moreover the equilibrium data obtained were correlated with contact angle measurements of water glycerol solutions on the yarns. Glycerol, like ethanol, is able to improve the dye uptake. In the case of synthetic fibers the wetting effect was confirmed by a minimum of interfacial tension in the range 1-3% v/v of glycerol in water. However in the case of wool and cotton other effects should be considered, involving the glycerol penetration into the fiber structure favored by hydrogen bonds formation. Finally environmental benefits and cost savings arising from substitution of auxiliary agents with glycerol were considered and some advantages of glycerol in comparison with ethanol were highlighted. (C) 2012 Elsevier Ltd. All rights reserved.