APPLICATIONS OF ULTRAVIOLET RADIATIONS IN DYEING PROCESSES OF YARNS AND FABRICS

Not dyed wool yarns and fabrics were treated by ultraviolet radiations, using a medium pressure Hg lamp, in order to obtain a modification onto fibre surface. As consequence, UV treated wool showed increase in metal ions absorption and hydrophilicity, together with improved kinetics of dye absorption under the same dyeing conditions as untreated wool. The surface modification of wool due to UV radiations was confirmed by FTIR-ATR analysis, nevertheless the fibre morphology by SEM analysis was unaffected. Experimental results showed that different kind of dyes are able to give differential dyeing after irradiation, but not all members of the same dyeing class have similar behaviour. Then, a selection of 1:1 metal-complex dyes was chosen to evidence the maximum of difference between irradiated and not irradiated areas. The main interests on wool fabrics were focused on two effects: a) one shade, double face with different depth, higher on treated side; b) two shades, double face with different colour and depth. Moreover it was found that UV pretreatment can be useful to obtain the same dyeing with lower temperature conditions (85°C). Fastness evaluations towards dry rubbing and machine washing at 50°C were also carried out to confirm the feasibility of this alternative dyeing technique; in all experiments carried out with selected 1:1 metal-complex dyes the same score of conventional premetallized 1:1 dyeings was obtained. Dyed cotton yarns and fabrics were treated by ultraviolet radiations, using a medium pressure Hg lamp, in order to obtain a fading of coloured fibre surface. As consequence, UV-treated dyed cotton showed different resistances to discoloration as a function of the selections of reactive dyes used; a selection of cold-reactive dyes (applicable at 60 ° C on cellulosic fibers), having good contrast between UV treated part and untreated, was presented. Industrial applications for discontinuous and continuous treatments (yarns or fabrics) and new proposal are also presented, with an economical evaluation of the processes (feasibility, reliability and effective costs).