Improving the Dyeing of Nonpolar Fabrics
Most natural fibers, such as cotton and wool, consist of large molecules that have regions with a partial positive or partial negative charge. These polar molecules have a strong attraction for dyes that contain either polar molecules or ions.
The molecules in some manufactured fibers, such as nylon, are nonpolar molecules. These synthetic fibers are difficult to dye. Molecules of other synthetic fibers, such as polyester and rayon, have only a few polar regions. As you might suspect, polyester and rayon have intermediate attractions for dyes. In this lab, you will investigate a process for improving a fiber's ability to absorb and retain dye.
Problem How can you increase the dyeholding capacity of nonpolar fibers?
Materials
tongs
2 fabric test strips
hot dye bath containing methyl orange
clock or watch
paper towels
scissors
soap
hot iron(II) sulfate solution
Skills Observing, Drawing Conclusions
Procedure
Part A: Dyeing Without Treatment
On a sheet of paper, copy the data table shown.
Use the tongs to immerse a fabric test strip in the methyl orange dye bath. CAUTION The dye bath is hot. Do not touch the glass. The dye will stain skin and clothing.
After 7 minutes, remove the strip from the dye bath. Allow as much of the dye solution as possible to drip back into the bath as shown on page 185. Rinse off the excess dye with water in the sink.
Place the strip on a paper towel to dry. Be careful to avoid splashes when transferring the strip between the dye bath and paper towel. Record your observations in your data table.
After the fabric strip is dry, test it for colorfastness, or the ability to hold dye. Cut the strip in half lengthwise and wash one half of the strip in the sink with soap and water.