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To Dye For (Part II)

A while back I wrote a post about dying yarn. I like to knit so I thought it would be pretty interesting. Well, I got a bit over my head when I realized that artificial and natural yarns are dyed with completely different processes! So the first post was the science behind artificial yarn dyeing and today’s is about natural yarn. I am excited for this one, which I expect to have a littlemore BIO in biochemistry.

Wondering if your yarn is natural or artificial? Try burning a little piece of it. If it melts, it is artificial ūüôā

Natural yarn is made of either plant or animal fibers. Of plant fibers, cotton is the most common. Wool is the most common animal fiber. Let’s get started with dyes used for cotton.

Here’s a refresher of what cotton looks like when it is grown, its fibers, and the cellulose they are composed of.

Cellulose is a made up of chains of glucose molecules, so it is actually a sugar. Before you go and start gobbling up your yarn stash, remember that while our bodies use glucose, we do not have the proper enzymes to digest cellulose. I suppose you would get a good dose of fiber.

The “n” under the cellulose means that this pattern repeats “n” number of times. So imagine this pattern repeated several, several times until a long chain forms.

Zhou et al., 2008. Functional nano-composite oxides synthesized by environmental-friendly auto-combustion within a micro-bioreactor. Materials Research Bulletin. 43: 2248-59.

The “n” under the cellulose means that this pattern repeats “n” number of times. So imagine this pattern repeated 30 thousand times until a long chain forms.

Many of the dyes we learned about in Part I formed ionic bonds with the fiber molecules. In direct dyeing, a common method for dyeing cotton, this is not the case. The affinity of the dye for cotton actually comes from its shape. Direct dyes are planar (flat), allowing them to fit in among the fibers. This allows for Van-Der-Waals, hydrogen, and dipole bonds to form.  See the image below for an example of a direct dye molecule.

There are a couple spots where charges could occur- the sulfonate groups- but these are mainly to give the molecule solubility in water.

Vat dyes are another good method for coloring cotton fiber, but I do not have time to elaborate on them. We must move on to wool!

I know, I know, I already started this post with a goat picture. Just one more!

What is wool made of? What properties of wool can be exploited for dyeing purposes?

Simpson, W.S. & Crawshaw, G.H. (2002) Wool: Science and Technology. Woodhead Publishing.

Simpson, W.S. & Crawshaw, G.H. (2002) Wool: Science and Technology. Woodhead Publishing.

Keratin is a protein, and since a variety of amino acid side chains are charged, we could expect dyes that have a charge to work well. These are called acid dyes. Kool-aid is actually an acid dye, and many people ¬†for dyeing wool. It is also nice to use because it is nontoxic.¬†According to Wikipedia, wool can be used as a fertilizer, since it is made of protein. Maybe that is what I will do with my failed knitting projects….

But what about the cuticle of the hair?? Does it get in the way of the dye and does it need to be removed? According to the book “Wool: Science and Technology,” it is believed that the dye can squeeze in between the scales of the cuticle. However, the condition of the cuticle can have an effect on dye uptake. For example, lipids can be present on the cuticle and prevent the dye from doing its job (hydrophobic lipid, hydrophilic dye). In addition, damage to the cuticle-such as from the sun or chlorine- can affect the way that the wool responds to dye.

One blog I visited said that dreadlocks are basically felted hair. This makes sense. Of course, this blogger was felting her own hair to make a hat or something..

This website  and that website about the chemistry of dye is super awesome, and I recommend you go there if you would like to learn more from the experts.

Ok, just one more cute baby animal pic! How can baby hedgehogs be SO adorable?!


About ilovebraaains

I am on my way to becoming a neuroscientist!

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