3.3 Dyeing
There are different procedures for the dyeing of clothes or yarns, being the desired colour an important factor to be considered due to different chemical consumption related to each colour. lt must be also taken into consideration that dyeing can be performed over the finished clothes, but also directly to the yarns before weaving. Table 5 shows the environmental impacts categories involved in different dyeing studies. GWP data ranges from 7.0 to 17.3 kg co2 eq, which are almost one order of magnitude higher than those obtained in cultivation steps. The other impacts evaluated show a low variability and they are in the same order than those found for cultivation of cotton with values ranging from 0.037 to 0.997 kg so2 eq for AP, from 0.010 to 0.017kg NO3- eq for AEP, from 0.47 to 0.60kg NO3- eq for TEP, and from 0.00083 to 000870 kg PO43- eq or from 0.010 to 0.018 kg NO3- eq for EP. LCI data for cotton dyeing procedures founded in the literature(see Table 2) shows that energy consumption ranges from 0.3 to 12.1 MJ of electricity, and from 3.2 to 126.0MJ of steam. Water use in dyeing technologies are in the 23-186 kg range, while chemical consumption data are highly heterogeneous ranging from 0.0018 to 0.088o kg for dyes, from 0.0004 to 0.0118kg for wetting agents, from to 0.010 to 0.028 kg for soaps, and from 0.024 to 0.216 kg for softeners. The generated air emissions were in the range of 7.84-12.33 kg for co2, 0.004-0.095 kg for NOx , and 0.0078-0.0135 kg for SO2. Water emisions can be really problematic, considering the high toxicity of dye residues, with a wastewater production in the 21.7-175.8 kg range.
The use of both, conventional and organic cotton, comprises a dyeing step to obtain the desired colour. However, in the case of Recover technology, the appropriate selection of coloured cutting scarps defines the final colour of the fibre to be obtained. Thus, there is no need to any dyeing step and consequently all impacts related to this process can be reduced to nil. This factor added to those given by the absence of cotton cultivation make relevant the production of Recover cotton as an environmentally friendly alternative to standard textile production procedures. In addition, the use of industrial wastes moves from a disposal or incineration raw material to an added value starting point of the production of a new generation of cotton yarn with extremely reduced environmental impacts as compared with those processes which start from virgin cotton.