| MadSci Network: Chemistry |
“I have heard that cotton FABRIC shrink when washed, but do the cotton FIBER itself shrink?”
According to Cotton Incorporated (the US cotton marketing association), the shrinkage in cotton fabric is due to a release in the tension of the cotton threads when you wash it, especially for the first time. So initially, cotton fabric is like a piece of stretched elastic; the shrinkage that occurs on washing is analogous to the relaxation of the elastic. Wool fibers, on the other hand, do shrink.
In their words:
Why do cotton and wool shrink when you wash them?
There are two kinds of shrinkage. Progressive shrinkage occurs when the
fiber itself shrinks. Wool fiber shrinks a little more each time it is
washed, which is why wool is usually dry cleaned. Relaxation shrinkage is
when the fabric shrinks. It is caused by the tension applied to yarns and
fabrics during construction. The tension is released when the fabric is
washed or steam pressed, causing it to shrink to its natural size. Most
cotton fabric shrinkage occurs during the first wash.
http://www.cottoninc.com/DidYouKnow/
“Another thing is that from this website:
http://www.cottoninc.com/CottonFiberChart/?Pg=8
It says that cotton has excellent resistance to sunlight. However, as far as I know, prolonged exposure of sunlight will weaken the cotton fabric. So how can cotton have "excellent sunlight resistance"? I think it should be "moderate" or could I be wrong?”
I think that what they really mean is that cotton has excellent sunlight resistance relative to other common textiles. The damaging component in sunlight it ultraviolet radiation (UV). According to an expert, “UV-radiation is one of the major causes of degradation of textile materials because of photo oxidation”. (Ibrahim, et al., UV-protecting and antibacterial finishing of cotton knits, Journal of Applied Polymer Science, Volume 112, Issue 6, pages 3589–3596, 15 June 2009). UV is capable of damaging many types of materials.
Good luck with your studies!
Rafael
**The author is answering this question on his own behalf, and this answer should not be interpreted as a statement originating from his employer.**
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