ToDyeForMicroscaleVatDyeingwithIndigo对微型还原染料靛蓝染料

1、.To Dye For: Microscale Vat Dyeing with IndigoIntroduction:The preparation of dyes and the process of dyeing fabric are two of the oldest chemical processes developed by humans. The use of dyes is an ancient art that was first practiced in Egypt, Persia, China, and India more than 5500 years ago. In

2、digo was originally extracted from the Indigofere Sumatrana plant found primarily in India and later from the Isatis Tinctoria plant in Europe. Due to the demand of this supply of blue dye, a trade route between India and Europe was established.The first synthetic dye was generated in 1856, when Wil

3、liam Henry Perkin, a student at the Royal College of Chemistry (England) accidentally discovered a synthetic mauve dye. This in turn, led to the first commercial development of an organic compound. In the 1880s, Adolph von Baeyer undertook the study of indigo and determined its molecular structure a

4、nd synthetic routes. For this work, von Baeyer received the Nobel Prize in chemistry in 1905. It was commercially available until after 1900 due to the problems faced when trying to mass produce the invention. However, by WWI, almost all the worlds manufactured dyes were produced in Germany and synt

5、hetic dyes had almost entirely replaced the extraction of dyes from natural sources. Dyeing with Indigo:To fully understand the process of indigo dyeing, we must first look at the chemistry behind it. Indigo dye (indigotin) is derived from indican, which is a water-soluble, colorless substance prese

6、nt in indigo-bearing plants. When indigo-bearing plants are crushed and placed in water the indican is released into the solution through bacterial action. When air is beaten into the solution, the indican combines with oxygen to produce indigotin or “indigo blue.” Indigo blue is insoluble and settl

7、es out of the solution to produce the blue indigo dyestuff. Indigo is insoluble in water but is easily reduced by sodium dithionite (sodium hydrosulfite, Na2S2O4) in a strong alkaline solution to produce a water-soluble leucoindigo. This leuco base is strongly attracted to cellulose because they hav

8、e large pores into which the dye molecules easily fit. Upon exposure to the oxygen in the air, the dye molecule rapidly oxidizes to its insoluble form, but by then it has already been trapped inside the cellulose fiber; due to its immense size, it cannot be removed at all easily. When a fiber is pla

9、ced in the indigo white solution, the indigo white penetrates into the fibers and makes loose chemical combination which is oxidized back to the insoluble indigo blue. The colors from this dyeing process, the vat method, are very resistant to washing because the dye is insoluble in water. However, s

10、ynthetic fibers are not good candidates for vat dyeing because they have tightly packed fibers not easily penetrable by dye molecules. For this lab we will be using cotton which is a natural organic polymer consisting of >95% pure cellulose, a linear polymer of glucose.H2OEquipment and Materials:

11、Each Group Needs1 Paper Clip125-mL graduated cylinder1 Sheet of Weigh PaperPairs of Gloves1 Large Weigh Boat1Stirring Rod1 2 X 3 inch piece of aluminum foil1600-mL beaker4 Shoestrings1Small Weigh Boat1125-mL Erlenmeyer Flask1Hot plate with stirring rodProcedure:1. Put on your gloves, Indigo will sta

12、in your skin.2. Fill a large beaker 2/3 full with water. (Warm if Available)3. Add both pairs of shoestrings to the water.Note: This will remove any sizing material that could interfere with the dye adhering to the fabric.4. Add 75 mL of water to the Erlenmeyer flask.Note: For the second set of shoe

13、 strings, you may need to replenish the water; make sure there is the full amount of water in the Erlenmeyer flask each time.5. Add 15 mL sodium hydroxide solution to the same Erlenmeyer flask.6. Mass 0.12-0.14 g of indigo on weigh paper and add it to the flask.7. Carefully add a magnetic stirrer. D

14、o this by tilting the flask and allowing the stirrer to slide down the wall of the flask until it is on the bottom.8. Cover the top with a small square of foil.9. Straighten out the paper clip. Use the end to poke two small holes in the foil top.10. Mass 1 g of sodium dithionite on the small weigh b

15、oat and set aside.11. Turn on the hot plate and stirrer, and gently heat the flask to near boiling over medium heat (5-10 minutes). If necessary, turn up the heat.12. Remove the foil from the Erlenmeyer flask. From the small weigh boat, add the sodium dithionite until the indigo dissolves and a clea

16、r yellow solution appears.Note: If the solution does not turn yellow, add more sodium dithionite in 0.05 g increments.13. Immediately replace the foil.14. Continue heating for 2 minutes. Then, remove, the flask from the heat.15. Remove one pair of shoestrings from the beaker. Wring any excess water

17、out of the shoestrings. Note: For a “tie dye” effect, loosely tie slipknots along the length of the shoestring before immersing it in the dye bath. 16. Turn off the magnetic stirrer. Do not turn off the heat.17. Gently swirl the flask, then remove the foil cover from the flask and add one set of sho

18、estrings.18. Leave the shoestrings in the dye bath for 5 minutes.19. Label the weigh boat with your names.20. Remove the shoestrings from the dye bath and place them in the weigh boat.Note: If the solution turns blue during the dyeing process or after you remove the shoestrings, and then add more so

19、dium dithionite solution in 0.5 g increments until the solution becomes clear and yellow. Also, slightly increase the heat.21. Allow the shoestrings to dry overnight.22. Repeat steps 15-21 for the second set of shoestrings. Add more water if necessary as noted in Step 4.Additional Notes: 20% sodium