الفهرس 
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Abstract
Viscose is one of the most common materials used in the textile field worldwide. Viscose is manufactured by treating cellulose with caustic soda, a carbon disulfide solution, and then neutralizing it with acid to adjust the pH. Because viscose fibers are regenerated fibers, a sub-group of man-made fibres, they are naturally clean. So, their pretreatment processes are not complex like cotton but are sensitive. The dyeing process is done after pretreatments for viscose.
Pretreatment processes for sized viscose before dyeing are considered important operations, the goal of which is.
1- Removing the starch (desizing processes) using the alpha-amylase enzyme.
2- Removal of sulfur residues that may be present in viscose and lead to problems in the dyeing process, by bleaching (oxidation) bath, which can be done using hydrogen peroxide.
After that, the dyeing processes start. All these processes require a large amount of water and take time, leading to an increase in the cost of viscose dyeing.
This work aims to optimize the pretreatments and dyeing processes in one bath, which may reduce the time needed in the dyeing process, and therefore, a reduction in the cost, and consumption of energy (water–electricity-gas) used. In addition to that, it is decreasing the percentage of (COD). This idea could be achieved using alpha-amylase enzyme with a wetting agent and a medium-active oxidizing agent that prevents the reactive dyes from being reduced by sulfur residues in the raw material.
Seven reactive dyes having different reactive groups were used which can be classified into three classes:
1- Monofunctional Reactive group (Monochlorotriazine or vinyl sulfone)
2- Homo bifunctional Reactive groups (dichlorotriazine or di vinyl sulfone)
3- Hetero bifunctional Reactive groups (Monochlorotriazine with vinyl sulfone)
Using the classes mentioned above, the following two methods were applied:
1- First method
Conv- method dyeing: This consists of the removal of the starch by alpha-amylase enzyme in the first bath, followed by an oxidation bath, and then a dyeing bath.
2- Second method
Bio- method dyeing: This consists of dyeing in one bath by combining the removing of starch and pretreatment in the dyeing bath, which leads to reducing time, increasing production, reducing the amount of water used and reducing the percentage of pollution in the wastewater.
Several factors were studied on the seven dyes by this method. These factors are:
1-Effect of enzyme concentration (g/L).
2- Effect of dye concentration.
3- Effect of wetting agent concentration(g/L).
The depth of color and its fastness on dyed fabrics by the Conv- and the Bio- methods were measured. The results showed that using the Bio- method is feasible when using dyes that contain bifunctional reactive groups of two different types (vinyl sulfone- monochlorotriazine), such as red 195, followed by dyes that contain dyes with homogeneous binary dyes (vinyl sulfone) such as black 5.
As for dyes that contain binary groups of the type (monochlorotriazine), such as orange 84, they gave a relatively lower color in terms of color intensity due to the large size of their molecules, while dyes that contain one active group, whether monochlorotriazine or vinyl sulfone, have a lower color intensity. from an environmental point of view, the percentage of COD at the end of the dyeing bath was measured.
The results showed that the Bio-dyeing method therefore gave a much lower percentage than the conv-dyeing method. from the environmental point of view, the use of this method is more favorable. In this study, dyes with polyfunctional reactive groups, which are a modern type of dyes and dyes with bifunctional reactive groups were utilized. Three colors were obtained (olive, maroon and brown) and dyeing was done by the Bio- and Conv- methods. The results showed that the color intensity was higher with polyfunctional reactive dyes than with bifunctional reactive groups. Also, the intensity of color using the Bio-method with both types of dyestuffs was more than that with Conv-method.
from an economic point of view, the Bio-method seems to be of lower cost (less chemicals - lower processes time) than the Conv- method. Also, the amount of water used in the Bio-method is much less than that used in the conv-method. It is well known that saving water is a universal demand since most nations are expected to suffer from a water crisis. Therefore, the COD measured was less in a Bio-method by a significant value.
The fastness properties (washing-light-rubbing) were measured on the dyed viscose fabrics by the two methods, and the results revealed no difference in the degrees of color fastness by the two methods.
1. INTRODUCTION
Cellulosic fibers are broadly categorized as natural and regenerated man-made fibres (Häemmerle, 2011). The global demand for cellulosic fibers production value reached five million metric tons in 2020. The demand for these fibres is expected to increase at a growth rate of 8% per year by 2025 and it is forecast to reach 133.5 million tons by 2030 (Häemmerle, 2011; Eichinger, 2012; Hummel, et al., 2015; Gillian, 2020). The term regenerated cellulosic fibers (RCF) covers a variety of sub-types of fibers that are commercially known as rayon or sub-type brands of viscose, Lyocell, Modal, etc. These fibers represent the second biggest cellulosic fiber group after cotton. Viscose rayon is regarded as the dominant regenerated cellulose fibers with an estimated textile market share of around 79% of all RCF with a production volume of around 5.63 million tons in 2019. Lyocell rayon represents the third rank after viscose and acetate, and its market share is valued at around 4.3% with a production volume of 0.3 million tons. Modal fibers had a market share of around 2.8% of the total RCF market in 2019, with a production volume of around 0.2 million tons. Cupro has a market share of less than 1% of the total RCF market. There is only one provider of Cupro, manufacturing 17,000 tons in 2019 (Textile Exchanges, 2020). Lyocell fibers are expected to grow faster than the other RCF. The main starting material for regenerated cellulosic fibers is high-grade wood pulp or plant fibers. The length of wood pulp fibers is too small for textile use, the fibers need to be dissolved and processed using continuous spinning and regenerating techniques (Navard, 2013). The manufacturing process of regenerated cellulosic fibers is a multi-step process. These fibers have a soft and lustrous silk-like shape, combined with the excellent water absorption capacity of cotton. Therefore, these fibers are used in the most diverse textile garments, alone or combined with other natural or synthetic fibers, due to their characteristic mechanical and physical properties (Karthik, and Rathinamoorthy, 2017).
On the other hand, viscose fabrics are commonly dyed with reactive dyes, which are very popular because of their brilliance, wide range of hues, and excellent color fastness properties. Attempts to maximize the reactive dye uptake and fixation yield to viscose via its chemical bonding have included the application of bifunctional reactive dyes. These dyes can react more readily with viscose, showing better dye exhaustion and fixation than the monofunctional types, resulting in improved dye fixation yields. the conventional exhaust method is one of the viscose fibres most important dyeing methods. However, the large water consumption makes this process particularly unattractive on ecological grounds. In order to achieve an effective production process, the fabric requires a separate pretreatment bath to render the fabric having satisfactory levels of wettability, swelling and reduction of fibrillation tendency, which in turn, leads to a better dye uptake and increases the forces of dye-fiber interactions (Lewis, 2014; Youssef, et al., 2005; Mohamed and Youssef, 2012; Hebeish, et al., 2013; El-Sedik, et al., 2019; Mohamed, et al., 2020). Moreover, several attempts have been made to shorten the conventional exhaust two-bath processes of pretreatment and dyeing viscose into one-bath process. In this context, there is a growing interest in the issues of textile productivity and process optimization using innovative, eco-friendly, and sustainable dyeing methods to reduce the amount of water, energy consumption and hazardous colored effluent discharge (Alamand Hossain, 2018; EL-Defrawy, 2002; Mousa, et al., 2019). Recently, applying one-bath pretreatment and dyeing of viscose fabric with enzymes in the cold pad-batch method has greatly saved chemicals and energy and reduced environmental pollution with an optimized production process (Zhu, et al., 2018). An alternative of viscose fabric pretreatment and dyeing method by the exhaustion technique in one bath is also growing interest. However, there is still needs to be more research on the combined exhaust process of raw viscose like cotton fabrics. Several attempts had been reported on the pretreatment and dyeing cotton in a single bath and stages of conventional and biotreatment of raw cotton using enzymes and carrying out dyeing in the same bath (Losonczi, et al., 2004; Kokol and Golob, 2004; Harane, et al., 2014). Also, a new process of combined pretreatment and reactive dyeing of cotton in a single bath was investigated. The process was completed almost in half of the conventional dyeing time (Öner and Sahinbaskan, 2011). As a part of the ongoing interest to challenge the conventional dyeing process of reactive dyes, the present work optimizes the enzymatic pretreatment of raw viscose fabric with subsequent dyeing in the same bath using different reactive dyes. The results were compared with those obtained by the conventional process in separate baths.