Optimization of Mercerizing conditions for enhanced cotton Fabric Dye ability

Abstract

Pretreatment of cotton fabrics prior to dyeing involves a number of processes consisting of desizing, scouring, bleaching and mercerisation. Mercerisation process is among the pretreatment processes that have a great impact on dyeing properties of cotton fabrics. The mercerisation process is the treatment of cotton fabric with strong sodium hydroxide solution. The dyed fabrics at Rivatex, Kenya presented uneven dyeing faults and the absorbance preliminary study confirmed that the practical cause was improper mercerisation. The main aim of this study was to optimize mercerizing conditions for enhanced fabric dyeability by mercerizing the cotton fabric with varying conditions of sodium hydroxide concentration and treatment time; determining optimum mercerizing conditions for enhanced fabric dyeability and eventually analysing and comparing dye exhaustion and colour fastness properties of mercerized and un-mercerized fabric. This was accomplished by pretreatment of the cotton fabric using 3% o.w.f hydrogen peroxide and 5% o.w.f sodium hydroxide at a temperature of 800C for 2 hours. The pretreated samples were then subjected to mercerization experiments in slack state. A two-variable, five level circumscribed central composite design with two replicates which yielded 26 experiments was used. The variables were; sodium hydroxide concentration in a range of 13%-27% w/v and treatment time in a range of 2-7 minutes at room temperature. After mercerization, the samples were measured for absorbance. Un-mercerized (control) and mercerized samples were dyed using similar dyeing conditions. The samples were dyed with a reactive red HE 3B dye using 3% shade (o.w.f), 20g/L sodium carbonate, 55g/L sodium sulphate, 0.5g/L sodium hydroxide and 2ml/l wetting agent. The dyed samples were tested for dye exhaustion and colour fastness. The results were subjected to statistical analysis to establish the appropriate sodium hydroxide concentration and treatment time. The combined pretreatment process gave acceptable values of absorbance of wetting time of 78 seconds and sinking time of 108 seconds. The experimental data was used to develop regression models to establish the relationship between the mercerizing conditions and the fabric properties. The model for dye exhaustion of mercerised samples yielded a coefficient of determination (R2) value of 0.64, a P value of less than 0.05 and an optimum exhaustion of 64.4%. This showed a realistic improvement in comparison to the unmercerised dyed samples which yielded 34% dye exhaustion. On the other hand, mercerized dyed samples highlighted a substantial improvement in colour fastness as they yielded acceptable colour fastness rates of 4 to 4/5 for washing and rubbing and 7 light colour fastness as compared to 2/3 to 3 for unmercerised samples Statistically, the optimum conditions were established as 23.4% sodium hydroxide and 4.9 minutes treatment time. From the results of this study, it was concluded that the optimal conditions of mercerization can yield improved dye uptake and uniform dyeing. However, to maximize the full research potential, there is a need for further investigations about; the effect of mercerisation on the fibre surface morphology, effect of mercerisation on natural dyeing, mercerisation study using cotton blended fabric and a study which involve variation of mercerizing temperature are recommended.