Research On Dyeing And Fixing Process Of Plant Indigo Dye

In recent years,synthetic dyes have been widely used due to its low price,complete chromatogram and high color fastness. In the process of being made and usded,it can not only cause some health problems,but also cause damage to the environment. The study of natural dyes to solve this problem is of great significance. The use of natural indigo plant can not only dye fabric,but also has a good artistic value and medicinal value. For a long time,the process of plants indigo dyeing is immature,especially in that colour can not be deep and fastness is not good,which seriously affects its industrialization.In the dyeing of cotton fabric with indigo, the key is the process of the reducing,dyeing and fixing process of plant indigo dyeing cotton fabric. Plant indigo is a kind of vat dye,which needs to be reduced to leuco. Leuco is soluble in water and has affinity to cotton fiber,it will access to inside of the cotton fabric and be reoxided to deposite on the fabric. Therefore, this process will be dinvestigated separately in two stages. With K/S value as the evaluation criteria, process parameters which affect the reducing process, such as the concentration of sodium hydroxide, the concentration of sodium hydrosulfite, reduction temperature, reduction time are optimized to increase the extent of reduction.After the detemination of a good reduction process, process parameters which affect the dyeing process, such as the dyeing temperature, dyeing time, the concentration of sodium chloride are optimized. Dye the cotton fabric with the optimized reducing and dyeing process,and test colour fastness to washing and colour fastness to rubbing.As to disqualified colour fastness,try to choose suitable fixing agent for fixing.The results are as follows:(1) Single factor experiments for reduction pHase shows that K/S value with the increase of the concentration of sodium hydroxide has been increased,but it has a greater reduction up to 4g/L. K/S value increases gradually with increasing concentration of sodium hydrosulfite,and it changes little up to 20g/L;K/S value with the increase of reduction temperature has been increased and when the temperature reaches 80℃,K/S value becomes stable; K/S value with the increase of reduction time has been increased and when the time reaches 15min,K/S value becomes stable.Orthogonal experimental results based on single factor experiments show that only reduction time significantly affects K/S value, so that the interactions between various factors exist. Design orthogonal experiments with interaction. According to the analysis, the interaction affects K/S values,and the impact is greater than both the concentration of sodium hydrosulfite and reduction time.Considering the interaction, the best reduction process is identified as the concentration of sodium hydroxide concentration 6g/L,the concentration of sodium hydrosulfite 15g/L,reduction temperature 65℃,reduction time 10min.(2) The method of plant indigo dyeing on cotton fabric is leuco dye method,using sodium chloride as the promoting agent. With K/S value as the evaluation criteria, do single-factor experiments on dyeing temperature, dyeing time and the concentration of sodium chloride. The results show that K/S value with the increase of dyeing temperature has been increased,but it has a greater reduction up to 30℃; K/S value with the increase of dyeing time has been increased and when the time reaches 35min, K/S value becomes stable; K/S value with the increase of the concentration of sodium chloride has been increased and when the concentration reaches 40g/L, K/S value becomes stable.Based on single-factor experiments,orthogonal experiments are arranged. After the intiutive analysis,K/S value is best when dyeing temperature is 30℃,dyeing time is 30 minutes,and the concentration of sodium chloride is 50g/L. According the square-difference analysis, dyeing temperature and the concentration of sodium chloride have significant impact on K/S value, and the affection of dyeing time on K/S value is not very significant.(3) On the basis of best reduction process and dyeing process using plant indigo dyeing cotton fabric in last two chapters, color fastness to washing and color fastness to rubbing are tested.The result shows that color fastness to washing is good,with fading and staining fastness reaching grade 4 or 4 above. Color fastness to dry rubbing grades 3-4,and color fastness to wet rubbing grades 3. Use fixing agent called fixing DC for fixing.Color fastness to dry rubbing and wet rubbing are improved by 1 grade to 4-5 grade and 4 grade.