by Katie Acken
The Chemistry of Tie-Dye
If you’ve tie-dyed before, then you’ve actually set up a chemical reaction! This fun summertime activity works so well because of some awesome chemistry. In order to tie-dye you just need fabric, dye, the right pH (acid or base level), and a little chemistry know-how.
Fabric
If you’ve tie-dyed before, you probably were told to use 100% cotton fabric – but why? Well, this is because the chemical structure of the fabric affects how it interacts with the dye. Specifically, you need a fabric that is composed of a chemical called cellulose. Cellulose is a polymer that plants use to build their cell walls. Polymers are long chains of repeating units, called monomers, linked together. In cellulose, these monomers are actually glucose (sugar!) molecules linked together. The way that these glucose molecules are linked, or bonded, together makes these chains very strong and flexible and unable to be digested by humans. These properties make cellulose very useful. Cellulose fibers can be harvested from plants like cotton, hemp, and flax and used to make fabrics like cotton, hemp, and linen. Another common fabric, rayon, is made synthetically, but it is also composed of cellulose.
Dye
The most common dye used for tie-dying is a type of dye called fiber reactive dye. This dye actually forms a covalent bond with the cellulose fibers in the fabric. Covalent bonds are strong because the atoms share electrons, which links them together. This is why tie-dye is permanent and doesn’t wash out of your clothes like a mustard stain might!
The right pH
The final factor that makes a successful tie-dye project is having the right pH, which is necessary for the dye to bind to the cellulose fibers. pH is a scale used to measure how acidic or basic a solution is. A solution is a liquid mixture containing a solute dissolved in a solvent. For example, salt water is a solution of salt (or sodium chloride, the solute) dissolved in water (the solvent). Solutions with a pH between 0 and 7 are considered acidic (like lemon juice), while solutions with a pH between 7 and 14 are considered basic or alkaline (like bleach). A pH around 7 is considered neutral (like pure water).
Putting it all together
Before dyeing, fabric is soaked in a basic solution for about 10 minutes. This solution usually contains soda ash (sodium carbonate) and water. Baking soda (sodium bicarbonate) can be used instead, but it makes a weaker basic solution so the dye won’t stick as well. As the fabric sits in the basic solution, the sodium carbonate activates the cellulose so that the dye can bind and form a chemical bond. After soaking, you squeeze out your fabric and apply the dye in whatever pattern you like! After you’re done applying the dye, your creation needs to sit for up to 24 hours. Waiting is hard, but if you want vibrant colors you need to give all the dye enough time to finish bonding to the fabric. Finally, the next day you rinse out your fabric to remove all of the unbound dye. Be careful though; even though your tie-dye masterpiece has absorbed as much dye as it can, this excess dye can still stain you and whatever you’re wearing. Now, after a quick spin in the washing machine (by itself), your new tie-dye creation is ready to wear!
