Development of eco-friendly, energy saving and cost-effective textile pretreatment dyeing and finishing

Abstract

Conventional wet processing of textile system is responsible for consumption of huge utility (water, gas and electricity), high effluent load and excessive chemical cost. Lots of alternatives have been suggested for the modifications of different steps of the whole wet process sequence. The current job was attempted to propose such an innovative way that will control the total steps. The main modification was done on the first stage, pretreatment, which affected second and third stage, dyeing and finishing. During dyeing, some more essential changes was also done. The main focus was how to avoid the major chemicals used during these processes. The common and mostly used sequence of entire wet processing for cotton is as follows: Reactive dyeing with SALT PRETREATMENT for increasing absorbency (using CAUSTIC SODA) and whiteness (using HYDROGEN PEROXIDE) Common Finishing using SOFTENER Natural dyeing with MORDANT At pretreatment stage, firstly major chemicals, caustic soda and hydrogen peroxide, were avoided, and after that completely chemical-free pretreatment was performed. During reactive dyeing salt was avoided, and for natural dyeing (in this work, dyeing with Swietenia mahagoni), mordant was eliminated. Eventually finishing was achieved without softener. Pretreatment without major chemicals was performed on the cotton fabric at high temperature. Detergent along with wetting agent were applied at 105°C, 120°C and 130°C to attain the targeted pretreatment outcome in regard to optimal coloration performance. Soon it was found that only high temperature was enough to receive the expected goal. Chemical-free pretreatment approach was found to influence dyeing and common finishing process. 120 GSM cotton knit fabric was pretreated in water at higher temperature (105°C, 120°C, 130°C) than the commonly practiced temperature ranges from 80°C to 100°C. Sample treated at 130°C for 20 min exhibited CMC pass value for 0.5% depth of shade dyeing. Medium shade expressed as 1%, for example, and deep shade expressed as 1.5%, for example, received CMC pass value in case of samples treated at 120°C, or even at 105°C for 20-40 min. Both single and combined shades (Red, Yellow, Blue and Combined) experienced the CMC pass result effectively. CIE xxii Lab values confirmed the CIE lightness of the dyed samples that resemble with the color difference expressed by CMC ΔE value. FTIR results demonstrated that weakening of the characteristic peaks (1000-1740cm-1) for wax, pectin and fat ester of the treated samples were close to that of conventionally pretreated fabrics. Still sufficient absorbency and CIE lightness index were achieved for the accepted color difference. The remaining wax content was helpful to retain fabric comfort and softness and hence the use of softener could be eliminated. Coloration fastness properties (wash, perspiration and light) of the treated cotton showed grade 4 and 4-5 in the scale of 5, which are same as the conventional samples. Promisingly K/S value of the treated cotton exhibited higher values compared to the conventional ones, which affirmed the reduction of dyes and chemicals cost, and effluent load in turn. The chemical-free pretreated fabric was also tried to develop the dyeing systems of mordantless natural coloration and salt-free reactive coloration on cotton. Conventional reactive dyeing on cotton was performed without salt. The salt-free approach demonstrated successful by using alkali in an increased amount proportionally. Random trials were made to match the CMC values for different identical shade percentages (0.5%, 1%, 1.5%) of conventional and salt-free dyed samples. No deviations were observed for the dyed samples regarding color fastness properties. Individual (Red, Yellow, Blue) and combined both types of dyeing at different depth of shades were tried with detailed CIE Lab values. Exhaustion-fixation curves of the conventional and salt-free dyed samples proved that although the initial exhaustion peak was absent from the salt-free dyed samples, eventually the terminal part of the fixation curve met each other. This way scope of a new pathway for salt-free reactive dyeing curve analysis was settled. Regarding mordantless natural dyeing, Swetenia mahagoni was applied on cotton knit fabric without using any mordant. FTIR curves of mahagony leave extract dyed cotton confirmed the characteristic peak in the region of 1190-1210cm-1 which provided the evidence for dye-fibre bonding of C-O-C stretching. Glycoside link was developed between alcohols of triterpenoid of mahagony leaf extract and β-glucose of cellulose. Because of the dye-fibre bonding, K/S value attained the satisfactory level, which is very close to the value while using mordant. Coloration fastness properties of the colored cotton were almost 4 to 4-5 in the scale of 5 which is inspiring. Color evenness was investigated by computing average CMC color difference values of specific dyed zones, which reported negligible deviation. Mordantless natural dyeing xxiii was also performed on the chemical-free pretreated fabric. Increased K/S value was experienced for this type of fabric, which indicated more dye uptake onto fabric and less effluent load. Combined reactive-mahagony leaf extract dyes were applied on cotton as both of the dyes have the scope of getting same bonding nature with cotton. Their fastness properties, dye uptake, evenness of shade along with FTIR characterization all were satisfactory and were explained at an understanding mode. As per the mentioning about development of finishing part, it was actually about the elimination of mostly used softener after reactive dyeing of cotton knit fabric. Previously it was unveiled that during chemical-free high temperature pretreatment, degree of removal of wax, pectin and fat was less than the conventional samples. It facilitated the retention of that much amount of monohydric as well as tri-hydric alcoholic esters, that was responsible for the surface smoothness as well as softness of cotton. Comfortability of the samples were judged by Fabric Touch Tester (FTT) by dint of fourteen parameters. The grading of the resultant comfortability, revealed as softness, smoothness, warmth and active-passive touch feel were mostly same for the conventional and chemical-free pretreated samples with minor deviation for smoothness data. The chemical-free pretreated samples retained more strength than the conventionally treated samples sensibly, as formation of oxy-cellulose did not occur due to absence of hydrogen peroxide. Dimensional stability-check parameters, GSM, shrinkage and spirality exhibited improved results than the conventional samples. This was possible due to the sufficient reduction of processing stages and washing cycles employed. As a whole, the conventional textile wet processing system was exchanged with chemical-free pretreatment, salt-free reactive dyeing, mordantless natural dyeing and softener free finishing. This way, innumerable energy saving (around 55%), less time consuming (approximately 55%) and eco-friendly processing with reduced cost (8.15tk per kg) were possible with this innovative approach. Considering dyes and chemicals, utilities, overhead cost, process loss and effluent, the summation of cost saving per kg of cotton knit fabric is 37.63 BDT which is 29.28% of the whole production cost per kg of fabric.