Natural Dyes PDF Edited by E. Perrin Akçakoca Kumbasar

Contents

Preface
As it is known dyes are colored materials that have an affinity to the substrate. Textile materials without colorants cannot be imagined and according to archaeological evidence dyeing has been widely used for over 5000 years. In the past, dyes were obtained from plants, animals or minerals. After the discovery of the first synthetic dye by W. H. Perkin in 1856, many thousands of synthetic dyes have been found and by the 1870s commercial dyeing with natural dyes was in the decline. For textile finishing processes first stage is pre-treatment. In general, dyeing and printing, chemical and mechanical finishing processes follow pre-treatment. With the development of chemical industry all finishing processes of textile materials are developing continuously and, ecological and sustainable production methods are very important nowadays. So some researchers show the ecological values of natural dye.

The first section of the book “Natural Dyes” considers eco-friendly pre-treatments. The application of natural dyes and approach to ecological dyeing with natural dyes is discussed in the following section. As it is known, the efficiency of finishing treatments can change with chemical properties. Accordingly, in the last Chapter, the importance of surface modification of wool fibers is evaluated.

Eco-Friendly Pretreatment of Cellulosic Fabrics with Chitosan and Its Influence on Dyeing Efficiency
Mohamed Abd el-moneim Ramadan, Samar Samy,
Marwa abdulhady and Ali Ali Hebeish
Textile Research Division, National Research centre, Dokki, Giza Egypt

1. Introduction
Wet processing of textiles uses large quantities of water, and electrical and thermal energy. Most of these processes involve the use of chemicals as assisting, accelerating or retarding their rates and are carried out at elevated temperatures to transfer mass from processing liquid medium across the surface of textile material in a reasonable time. So, we can use some natural materials and some physical tools to reduce the chemicals, water, energy and pollution. This tools and natural material can use also to improvement the fabrics surface via introduce new active groups on its. Improvement of the fabrics surface can increase the efficiency of bleaching, dyeing and finishing processes.

Chitin, a major component of the shell of crab and shrimp is one of the most abundant natural polysaccharides with a large unexplored commercial potential. Chitosan is partially or completely N-deacetylated chitin and mainly consists of B-(1,4)- linked 2- amino-2-deoxy- B-D-glucopyranose. In recent years, a number of investigations have been carried out to exploit the potential applicability of chitosan(1). Chitosan have many applications in the medical and textile fields.

Cellulose which has been known to have good physical properties has been widely used as construction material, paper and clothes. Cellulosic fabrics can be oxidized by several oxidizing agents such as hydrogen peroxide (H2O2), sodium persulphate (Na2S2O8) and potassium periodate (KIO3). Oxidation of cellulosic fabric using sodium metaperiodate (NaIO4) has been extensively investigated in the literature, since it leads to selective cleavage at the C2 and C3 vicinal hydroxyl groups to yield a product with 2,3-dialdehyde units along the polymer chain(2). The latter is an important functional polymer for further derivatisation to specialized products.

As a naturally deriving substances, chitosan and cellulose share several common beneficial properties such as being nontoxic and biodegradable. Structurally, chitosan is slightly different from cellulose as the monosaccharide in chitosan chain is 2-amino-2-dehydroxy-Dglucose instead of D-glucose. The presence of amino group is responsible for the complete solubility of chitosan in a diluted aqueous acidic solution as a polycationic polymer whereas cellulose is totally insoluble. This polycationic nature makes chitosan very appealing as a surface treating agent for cellulose fabrics to improve its dyeability to reactive and acid dyes. Chitosan used for surface modification of cellulose fabrics. Direct padding or exhausting chitosan solution onto cotton fiber was reported to show significant improvement in dyeability of the fiber with some reactive dyes (3). Oxidations of cotton fiber or fabric prior to the treatment of chitosan have been reported. Chitosan was applied after oxidation of cotton fabric by H2O2 show improved dyeability with reactive dyes (4). Potassium periodate is known to selectivity convert 1,2-dihydroxyl groups to a pair of aldehyde groups without significant side reaction and is widely used in structural analysis of carbohydrates(2). This oxidizing agent was used successfully for surface oxidation of cotton fiber prior to the treatment with chitosan to produce chitosan coated cotton fiber.

We undertake this work with a view to establish appropriate conditions for synthesis of cotton fabric containing chitosan. We plan to incorporate chitosan in the molecular structure of cotton surface through strong interaction between chitosan molecules and cotton molecules. To achieve the goal, creation of functional groups such as aldehyde groups is effected by NaIO4 oxidation and thus obtained oxidized cotton is treated with chitosan. This is ratter a two-step process for producing cotton fabrics containing chitosan. A novel onestep process is also devised for preparation of the same modified fabrics; the fabric is treated in an aqueous solution containing the oxidant and chitosan. All modified fabrics are monitored for fixed amount of chitosan expressed as nitrogen content, carbonyl content, dyeability, strength properties and IR spectra.