ENVIRONMENTAL BEST PRACTICE IN DYEING AND FINISHING OF TENCEL AND LENZING MODAL

Transcription

1 Lenzinger Berichte 89 (11) 3-36 ENVIRONMENTAL BEST PRACTICE IN DYEING AND FINISHING OF TENCEL AND LENZING MODAL Jim Taylor Lenzing AG, Werkstr. 1, 486 Lenzing, Austria Phone: (+43) ; Fax: (+43) ; Presented during the 48 th Man-Made Fibers Congress, Dornbirn, Austria, 9 This paper will report on studies carried out by Lenzing in collaboration with DyStar and Huntsman to investigate the environmental aspects of dyeing processes for TENCEL and Lenzing Modal. It will report results studying the performance of different reactive dye types to Lenzings fibres utilising batchwise and semi-continuous application techniques. The paper will then move on to assess energy, chemical and water consumption in the fibre manufacture through dyeing and finishing processes and draw comparisons with cotton, demonstrating the reduction in environmental damage that can be delivered. The analysis is then extended to investigate the cost savings that are possible as a result of the optimised processing. Keywords: TENCEL, dyeing, finishing, Modal, environment The Requirement for Bleaching and Scouring TENCEL and Lenzing Modal fibres are inherently white and will require no bleaching to achieve the majority of colours. Of course for optical whites and very pale bright pastels, some degree of bleaching may still be necessary. The fibre is also extremely clean and contains very little in the way of impurities. In knitted structures (where this work was concentrated) the fibre contains a very small amount of water soluble spinning lubricant, applied during fibre manufacture, together with low levels of waxes that may have been introduced in the knitting process. For the purposes of calculations made relating to process routes, it was assumed that only a mild detergent scour was required prior to dyeing although in many cases it would be feasible to use scour dye methodologies. Comparisons are drawn with the processing of cotton, where a thorough scouring process is needed to remove its natural impurities and waxes. In contrast to the man-made fibres bleaching is required for many more shades, not just those of high clarity and brightness. is prone to base colour variation and is often bleached regardless of shade being dyed to deliver a more uniform base white. Comparison of Dye Requirements to Achieve Equivalent Shades Exhaust Dyeing Figure 1-4, show the chemical and dyestuff requirements to achieve equivalent shades on cotton, TENCEL,TENCEL A1 and (in one instance) TENCEL LF in an exhaust dyeing process. The shades studied were Dark Brown, Navy, Khaki and Pink dyed using commodity dyes, Remazol RGB or Levafix CA from DyStar and Novacron LS and FN ranges from Huntsman.

2 Lenzinger Berichte 89 (11) Dark Brown Shade DyStar A1 TENCEL LF Figure 1. Dye and salt required for Dark Brown Shade DyStar Navy Shade Huntsman A1 The results show that: (1) TENCEL requires less than half of the amount of dye to achieve the same shade as cotton. () You need only half the amount of salt on TENCEL. (3) Soda ash concentrations are also reduced by similar magnitude. (4) The use of lower dye levels coupled with higher fixation levels means less unfixed dye on TENCEL compared with cotton. (5) TENCEL results in only 3% of the level of residual colour compared with cotton. (6) TENCEL A1 results in only % of the level of residual colour. Comparison of Wash Off Behaviour The figures 5 and 6 show the colour remaining in the dye bath / rinsing baths after dyeing the dark brown shade. Figure. Navy Shade Huntsman. Dye bath 5 C 5 C acid 8 C 98 C 8 C Cold Khaki Shade DyStar A1 Figure 3. Khaki Shade Dystar. Pink Shade DyStar TENCEL A 1 1.7% C.I Reactive Yellow % C.I. Reactive Red 39.51% C.I. Reactive Black 5,74% Total Figure 4. Pink Shade DyStar. A1 35 g/l Na SO 4 7 g/l Soda Figure 5. Wash off behaviour of TENCEL A1. It is clear that much less is needed to be removed from the TENCEL A1, and it should be possible to remove at least one, possibly two washing baths.

3 Lenzinger Berichte 89 (11) 3-36 Cold Pad Batch Dyeing In the assessment of dyeing performance carried out, work concentrated on the results with standard TENCEL as it is most likely to be utilised with this dyeing technique rather than the TENCEL A1 variant which is most likely to be used in knitted fabrics. Once again, the work was carried out over a range of shades, but only two the Navy and Khaki are reported here. Figures 5 and 6 show the results. Dye bath 5 C 5 C acid 1% 3.99% C.I Reactive Yellow % C.I. Reactive Red % C.I. Reactive Black 5 6,39% Total 1 g/l Na SO 4 g/l Soda 8 C 98 C 8 C Cold Figure 6. Wash off behaviour of cotton dyed to the dark brown shade Navy Shade Huntsman A1 Novocron C Alkali Figure 7. Dye and Alkali requirements Navy shade Huntsman Figure 8. Khaki Shade DyStar. The dye yield benefits are not as large as was seen with the exhaust dyeing, but are still valuable. (1) About 7% of the dye is required on TENCEL to achieve the same shade as on cotton. () 15% less alkali is needed. (3) TENCEL results in just 45% of the amount of residual unfixed colour as is seen with cotton. Salt Sensitivity and Effect of Liquor Ratio It is important in dyeing systems that small changes in process parameters do not result in large variations in shade. When dyeing critical shades such as beige, grey or khaki that are based on trichromatic combinations, the more robust the dye combination and fibre being dyed are to process variation, the better right first time performance that could be expected. Work was carried out with DyStar to change the salt and liquor ratio when dyeing the khaki shade and to measure the impact on shade reproducibility. The results show that the impact on shade of variations in salt concentration and liquor ratio, is lower on TENCEL A1 than with cotton. It also shows the improved performance of the Levafix CA dye combination when compared with Commodity dyestuffs (the last four columns are smaller than the first four).

4 Lenzinger Berichte 89 (11) 3-36 It is interesting to note that with TENCEL A1 even a reduction in salt concentration to 5% of its original results, even with commodity dyes, in a shade change of less than DE 1., indicating that salt levels can probably be reduced further. Comparison of Energy, Water and Chemical Consumption in Jet Dyeing the Navy Shade. In order to make these comparisons, a number of assumptions have been made: kg loading 1:1 liquor ratio Cold water at o C No hot fill (all heating done in machine) Liquor retention of x weight of fabric on draining Standard fill / drain no parallel rinsing/draining 1% right first time no additions All hot baths cooled to 6 o C before draining 5% efficiency of heating (steam energy transfer) 5% efficiency of cooling (heat transfer to cold water) No water recycling No use of renewable energy No bleaching needed for TENCEL A1 The results show that water, energy, dye and chemical consumption for a dark shade on TENCEL A1 is half that needed for cotton. Khaki Shade - Process Variations TENCEL A1 Figure 9. Effect of process parameter change on Khaki Shade.

5 Lenzinger Berichte 89 (11) 3-36 Table 1. Comparison of Energy, Water and Chemical Consumption in Jet Dyeing the Navy Shade. Preparation Novocron FN Scour/Bleach at 98 C 8 o C 6 o C Novocron FN TENCEL A1 Detergent scour at 65 o C Remazol RGB Scour/Bleach at 98 C 8 o C 6 o C Remazol RGB TENCEL A1 Detergent scour at 65 o C Remazol RGB TENCEL LF Detergent scour at 65 o C Dyeing Wash off Migration dyeing 8/6 o C 7 o C 8 o C 6 o C Migration dyeing 8/6 o C 7 o C 6 o C Isothermal Dyeing at 6 o C 8 o C 8 o C 5 o C Isothermal Dyeing at 6 o C Isothermal Dyeing at 6 o C Process Time (mins) Bath water (l) Cooling water (l) Total water (l) Water / kg fabric (l) Total Energy (MJ) Energy /kg fabric (MJ) Total Chemicals (kg) Chemicals/k g fabric (kg) Total Dye (kg) Dye / kg fabric (kg)

6 Lenzinger Berichte 89 (11) 3-36 Costs of the Dyeing Process If we use the information from above, it is possible to estimate the costs of the dyeing process. The analysis has been carried out using average prices for gas, electricity and water / effluent in Europe. Gas.45 Euro / m 3 Electricity.5 Euro / kwh Water / effluent.5 Euro / m 3 Dyeing of a black shade on the three fibres indicated demonstrated a 4% better colour yield on TENCEL A1 with a 1% improvement from the modal fabric. Information drawn from a Life Cycle Analysis Study carried out by Dr Martin Patel and Li Chen [1, ], reported at Dornbirn conference in 8, allows us to examine the environmental impact of the three fibre types from fibre production through to the finished fabric in terms of energy usage and water consumption Dye / Chemicals Electricity Gas Water Table. Fibre manufacture, impact per T-shirt (assume 5g) [1]. TENCEL Modal Water litres) A1 Figure 1. Cost comparison cotton with TENCEL A1. The calculations show that TENCEL A1 is significantly more cost effective in processing than cotton. For the example above, based on a Navy shade dyed with Novocron FN dyes, the total reduction in processing cost is 1.33 / kg, made up of saving.59 from power and water, and.74 in dyes and chemicals. Of course, the saving in dyes and chemicals will be reduced in pale shades, so this result is a good case scenario, however it should be borne in mind that the TENCEL A1 process is shorter than that for cotton, so there will be fixed cost savings also that have not been factored in here. The Environmental Cost of Your Black T-Shirt A comparison between cotton, TENCEL A1 and Lenzing Modal Trials at scale have been carried out to verify the results from the lab results reported above. Energy (MJ) CO (kg) Land Use (m) It should also be noted that unless the cotton is certified organic, there will be high levels of pesticides, herbicides and fertilizers used in cotton production also. Note that the land use for cotton growing is of agricultural quality, whereas the land used for growing of the trees is marginal land, generally unsuitable for growing agricultural crops. Yarn Spinning has much higher levels of waste. 3% waste is typical for a combed cotton. This results in a 3% increase in energy requirement for spinning yarn. Typically reducing the energy consumption from 3.7 MJ to.9 Knitting No differences

7 Lenzinger Berichte 89 (11) 3-36 Dyeing Process Table 3. Dying process comparison of cotton, and Modal. TENCEL Modal Energy (MJ) Water (litres) Chemical (g) Dyestuff 1 18 Conclusions In exhaust dyeing, when compared to cotton, TENCEL A1 can be dyed using approximately: Half the amount of dye to achieve the same shade Half the amount of chemicals Half the amount of water Half the amount of energy This is achieved because of very mild scouring/bleaching requirements, high dye fixation and thus less unfixed dye to remove from low salt dye liquors. In cold pad batch dyeing a similar picture emerged for TENCEL compared to cotton: Approx 66% of dye required to achieve same shade Less than half the amount of chemicals Half the amount of water Half the amount of energy Again this is achieved by mild scouring/bleaching requirements, high dye fixation and less unfixed dye to wash off. Taking into account the improved efficiencies of TENCEL in comparison to cotton, if best practice is adopted, the cost differential between cotton and TENCEL will be considerably reduced if not eradicated. Acknowledgements The author wishes to express great thanks to the following for their help in carrying out the work and interpretation of the results: Phil Patterson, Colour Connections Ltd, Peter Collishaw and Roland Schamberger, DyStar, Erwin Miosga and Mike Heaton, Huntsman Textile Effects, Andrew Thompson, CHT for help with calculations. References [1] Li Chen and Martin K. Patel, Lenzinger Berichte 88 (1) [] Li Chen and Martin K. Patel, Lenzinger Berichte 88 (1) The remarkable savings on water, energy, dyes and chemicals in processing mean that the cost of processing of TENCEL and TENCEL A1 are significantly less than the cost of processing cotton. Further studies are needed to assess the true cost of producing a TENCEL garment in comparison to one made of cotton over a wider range of colours.