Novel possibilities in chemical pretreatment and finishing of cotton fabrics
Chemical or wet processing of textiles can be basically divided to three stages: pretreatment, dyeing and finishing. Raw cotton fibers have to be treated through several chemical, physical and biological processes before dyeing to obtain desirable properties and become suitable for use or for further treatments. These processes are known as “pretreatment processes”. The aim of the cotton pretreatment is to remove the undesired substances from raw cotton, which are brought to material in the form of natural and process-related attendant substances, by application of processes such as singeing, desizing, scouring and bleaching. Finishing provides extra properties for textiles that customers will value. In the other word, finishing is completing the fabric’s performance by providing special functions. The most conventional and important chemical finishing processes are: softening finishing, hand building finishing, easy-care and durable press finishing of cellulosic fabrics, repellent finishing, soil-release finishing, flame retardant finishing, non-slip finishing, antistatic finishing, anti-pilling finishing, elastomeric finishing, ultraviolet protection finishing, antimicrobial finishing, insect resist and mite protection finishing and etc. The main trend of development in chemical processes of textiles is shortening and simplification of pretreatment processes through combination of two or more stages. The important processes, such as desizing, scouring and bleaching are usually carried out in separate stages in the conventional pretreatment processes. Also consumption of large amount of energy and water is the other aspect of the conventional preparation of textiles. It has been already known that, to minimize the energy and water consumption the combination of several stages of the pretreatment processes by lowering the number of operations or reducing the time of reaction is absolutely necessary. Also, textile industry tends to utilize combination of the finishing processes in a single bath or at least reducing number of the necessary stages to decrease the costs of production. Using multifunctional finishing seems as one of the most attractive fields in textile industry. This idea has been investigated by some researchers to provide more effects in a finished fabric just in a single bath. In this study, it has been tried to combine some important pretreatment processes of cotton fabric by means of enzymes and also create several finishing effects on the cotton fabric through a novel multifunctional finishing process. Thus, the first part of this study has been dedicated to prove the possibility of simultaneous acid-demineralization and enzymatic desizing of cotton fabric in acidic conditions (pH 2) by using industrial acid stable enzymes. Acid-demineralization is necessary to remove undesired cationic metals and earth alkalis. The obtained results show that by use of a mixture of two appropriate enzymes, a glucoamylase (Multifect GA 10L) and an a-amylase (Optisize Next) in a solution of citric acid and presence of a chelating agent, enzymatic desizing, and acid-demineralization is successfully carried out at the same time. Therefore, two processes of pretreatment are integrated into a single process, which effectively reduce time and costs for textile industry. In the second part, multifunctional finishing of cotton through synthesis and employment of a novel polycarboxylic acid was studied to produce a fabric with several functional properties: easy-care, flame retardant and antimicrobial; without any extra finishing process. By this way, it is possible to combine three separate finishing processes into a single stage. This goal is achieved by carboxylation of polyvinylamine (PVAm), resulting to form a polyamino carboxylic acid as a novel polycarboxylic acid. This product was used for crosslinking of cotton fabric by pad-dry-cure process. The reaction between the carboxylic groups of polyamino carboxylic acid and the hydroxyl groups of cellulose in cotton forms ester links. It makes durable press effect, reduces the flammability of treated cotton and creates biostatic properties. Moreover, due to presence of free amino groups the treated cotton with the polyamino carboxylic acid improves dyeability of cotton with reactive dyes and enables a salt-free dyeing process.