Authors Meram S. Abdelrahman, Sahar H. Nassar, Hamada Mashaly, Safia Mahmoud, Dalia Maamoun, Tawfik A. Khattab
Thickeners have been used as a significant component in textile printing pastes. They are characterized with high molecular weight, high viscosity in an aqueous medium, good storage, long hydration time consistent with other printing paste components and being colorless. They impart plasticity and stickiness to the print paste with the ability to introduce designs without bleeding. The major function of printing pastes is to hold, adhere and transfer the dyestuff onto the targeted fabric. There have been various well known synthetic and natural thickeners. Color is a major significant factor in textile manufacturing and application employing either natural or synthetic dyestuffs for conventional or smart textiles. Thickeners are known as thick materials which can impart gumminess and plasticity to the printing pastes so that it can be applied on the cloth surface with a specific design outline and without bleeding or scattering. Hence, thickeners are generally functioning with the following advantages: To provide the essential viscosity to the print paste, to carry the printing ingredients into the fabric surface, to prevent premature interaction between the printing ingredients. There are four important approaches to generate thickeners: low concentration of high molecular weight polymers, high concentration low molecular weight materials, emulsion of two immiscible fluids, dispersion of finely divided solids (e.g. Bentonite). Quality of printing paste depends on the following desirable properties of thickeners: Printing paste stability to storage, pressure and temperature, properties of produced dry film, effects on color yield (e.g. diffusion and fixation), preparation simplicity, removal from fabric surface, low price and easily obtained, easy to remove by washing after drying, homogeneous distribution of printing paste, environmental impacts, styles and techniques of printing, type of fabric used, compatibility and stability to different printing ingredients including dyes and auxiliaries, provide sharp outlines without bleeding or spreading, good mechanical properties, to prevent dusting of dry film, good diffusion to provide maximum color yield, good absorption of condensed water to guarantee free space for dye and water, molecules to penetrate into the fibers, It should not hold the colorant or keep it away from fabric, good drying to prevent spreading and wetting, transparency and good solubility, to avoid fish-eyes. Therefore, a variety of polysaccharides derivatives, synthetic polymeric materials, and emulsion thickening agents were developed. Those developed thickening agents were characterized by plasticity and stickiness to clothing with sharp outlines. The choice of a thickening agent largely depends on the type of dye and style of printing. According to compatibility between both of dye and thickener, broad rules for the choice of thickener have been laid. For example, reactive dyes are used with Sodium Alginates which comprise fewer crosslinking properties, while pigments were used with synthetic thickeners, in addition to binder. The choice of a thickening agent also depends on the fabric characteristics. Thickeners function as a carrier of coloring matter, chemicals, solvents, and auxiliaries, bringing it into close contact with fabric surface during the coloration process. Thickeners are expected to create acceptable adhesion and consistent distribution of the printing pastes to fabric surface. Thickeners prevent the separation of the dye to occur which results in level prints with sharp outlines; at the same time as thickeners should possess the required physical and chemical properties (e.g. viscosity and flow property). The storage stability of the thickener paste must be high enough. It should be compatible and inert to dyes and other auxiliaries included in the printing paste. They should possess the ability to absorb steaming water without flushing. They are expected to have high-quality thermal and photo-stability without film break during the high temperature steam or thermal fixation. The removal of the thickener from the fabric surface after fixation should be straightforward. Among the commonly known thickening agents are biological polymers, chemically customized biological polymers such as sodium alginate, starch or customized starch, galactomannan or customized galactomannan, and carboxymethyl cellulose.
