Dept. Of fiber and Textile Processing, Udct, Matunga

Textiles have been subjected to chemical pretreatment processes since time immemorial. Human ingenuity and imagination, craftsmanship and resourcefulness are evident in textile products throughout the ages; we are to this day awed by beauty and sophistication of textiles sometimes found in archeological excavations. This paper mainly describes the need of continuous pretreatments its recipe. It also gives the update of new machinery design for continuous pretreatments.

INTRODUCTION

After January 2005 the quota restriction ended and the entire textile sector is now open for foreign direct investment (FDI) with ultimate aim to be par with the new economy information technology (IT) sector. The textile sector Foreign exchange earning amounts to about US$11b a year is about 35% of total foreign exchange earned by the nation. This amounts to approximately Rs. 51700 crore per year (@ Rs47 per dollar). This figure is to be raised 5 fold at US$ 50b per year (Rs 2, 35,000 crore per annum) by the year 2010, a level projected for the Indian IT sector by 2008¹.

To achieve the above shown statistics in todays era of global competition its crucial to produce goods in shortest possible time while consuming least possible amount of energy, materials and water and consequently at lower processing costs. Well a logical approach is to shorten the sequence by combining the three operations-desizing, scouring bleaching which is popularly known as the D-S-B process. Thus efforts have, been made to improve the efficiency of these processes and also to combine these processes to reduce the time consumed and also the energy and water consumption along with incurring lesser cost of production and increased productivity. This also reduces the effect of chemical pre-treatments of textiles on the ecology by reducing substantially the amount of effluent released from the process house.

This paper discusses the single stage preparatory process which combines the desizing, scouring and bleaching operations into a single stage that are carried out in individual unit operations otherwise².

COMBINED PREPARATORY PROCESSES

In a combined process, hydrogen peroxide or sodium hypochlorite can be used as a desizing and bleaching agent and sodium hydroxide can be used as a conventional scouring agent along with a wetting agent at pH of 10.5 11.5 (using soda ash). Various combined processes have been developed in the past using the above chemicals and also using new scourant formulations³.

Some attempts have, also been made to review the various methods of single stage preparatory processes earlier. Preoxygen boosters were considered to be the key compound in developing a DSB process, which can, also, interact with starch and PVA sizes and to act as desize-scour boosters. Processes without peroxygen boosters were, also, developed incorporating higher strength of peroxide bur were not widely accepted. Role of peroxide activators namely tri-sodium phosphate, tetra sodium pyrophosphate, sodium hexameta phosphate, magnesium sulphate and sodium salts of EDTA were analyzed in combination of sodium silicate in the single stage preparatory process³.

PEROXIDE BASED SINGLE STAGE PROCESS

Single stage preparatory process using hydrogen peroxide has been developed successfully in past for starch and acrylic-base sized textile materials, and, also has been used for processing various fabrics. In a combined process, hydrogen peroxide can be used as a conventional scouring agent along with a wetting agent. The treatments can be carried out in the stainless steel containers. Caustic soda provides required alkalinity for scouring and activation of hydrogen peroxide. When activated, hydrogen peroxide degrades the sizing materials at lower temperatures and at higher temperature, bleaching occur along with completion of desizing.