To dye green and clean

Abstract

Textile industry is obliged to adapt to ecological legislation because classical processes have a great environmental impact caused by operations included in preparation, dyeing and printing of textile materials, specially those containing cotton. Removal of hydrophobic impurities and starches, using surfactants, alkalis and oxidants at high temperatures is normally made with important consequences at ecological level, with problematic effluents and higher costs. CORONA is a non- pollutant technique based in physical means of production of plasma at ambience pressure, which can be applied to reduce ecological and economical cost factors in textile industry. The term plasma means an ionized gas, formed by a complex mixture of electrons, neutral particles, ions, photons and radicals produced by an electric discharge or by radiation in electromagnetic fields able to produce ionization. When the fabric runs betweenelectrodes and an electric discharge is made at ambience temperature and pressure, with a high voltage of more than 10 000 V and a frequency between 20-40 kHz, the treatment is known as CORONA. In the medium, free electrons lose energy when collide with neutral molecules. This energy transfer produces new very reactive particles and with capacity to be involved in other reactions, responsible for the formation of new compounds and changes of fibre’s superficial properties. CORONA technology is not industrially used in textiles yet, but it has a wide application in the case of other polymeric products like plastics in order to achieve a better degree of cohesion between printing inks and materials. Its application in textiles has been thought in order to take practical advantage of the possibility to work continuously at ambience conditions. CORONA effects in the structure of cotton’s surface were already studied and the creation of channels for water penetration was proved, together with the oxidation of fatty matters, which are the mechanisms responsible for the fast increase in hidrophility after CORONA treatment. This fact is decisive in what concerns all the chain of wet processes for cotton transformation. Studies were previously made about CORONA effects in textile printing. These studies led to very good results related to the reinforcement of links in the system fibre-pigment together with surface changes caused by the discharge which are responsible for an increase in the wet/dry rubbing fastness. It is possible to have a fastness improvement of one point, which means an optimal result for pigment printing quality. In the present work, the extension of these results to preparation and dyeing of cotton has been made. Shorter, cleaner and easier processes are possible, including direct dyeing of raw cotton materials. Depending on final use for textile dyed products, results for a completely “Green Process” are presented, where the presence of husks and seeds not removed by any chemical treatment can be seen as a kind of quality certification.