Abstract: C.I. Acid Blue 113 and C.I. Acid Blue 168 were applied to dyeing of soybean/casein/polyvinyl alcohol blend fiber (short for double protein fiber) and soybean/polyvinyl alcohol blend fiber (short for soybean protein fiber). The absorption thermodynamics performance of acid dyes on double protein fiber and soybean protein fiber were compared by Langmuir and Langmuir+Nerst absorption equations. The thermodynamics parameters of Langmuir+Nerst equation were also investigated. The difference of absorption properties between double protein fiber and soybean protein fiber were also analysed. It was found that Langmuir+Nerst equation can better fitted the absorption of acid dyes on double protein fiber and soybean protein fiber. The equilibrium absorption of acid dyes on double protein fibers was higher than that of soybean protein fibers. The electrostatic interaction force between C.I. Acid Blue 113 and regenerated protein fiber was stronger than C.I. Acid Blue 168.

Key words: soybean protein, casein, regenerated protein fiber, absorption, dyeing, acid dyes