Ask A Scientist Materials Science Archive

name         Peter
status       other
grade        other
location     N/A

Question -   I like to wear shirts in the office, which I do not need
to iron after washing, so called non-iron shirts. Unfortunately after a
few washing cycles this property gets lost, they become wrinkled and need
to iron them. I wonder, what kind of technique (chemical and/or physical
treatment) is applied by the shirt manufacturers to achieve this effect
and what can I do at home to make it non-iron again
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Peter,

I'm not certain but I believe the perma-press or non-iron pants and shirts 
are cotton blends with polyester. If so, and if the textile material has 
enough polyester in the blend, then the structural properties (integrity, 
strength, stiffness) of the material is controlled by the temperature at 
which polyester softens (a thing called "glass transition temperature").

So if I were to guess, I would say that repeated washing at high 
temperatures will bring the polyester past this glass-transition -become 
rubbery instead of glassy- and the press (structure) that was developed in 
the clothing during its production becomes gradually lost. By the way, the 
glass-transition temperature is not an established number; it also depends 
on the environment (water or solvents), stress (the washing cycle), etc.

Ironing (bringing the textile material past its glass-transition 
temperature) and then allowing it to cool with the structure desired 
(wrinkle free and with ironing seams) allows the clothing to regain its 
original pressed look.

Cotton does not have this ability because cotton fibers interact well with 
water and allows the fibers to be deformed.

So: you have a few choices, (a) wash the material at lower temperature 
settings, low stress cycle, weaker detergents - to reduce loss of 
structure (b) find clothing with more polyester in it - to strengthen 
structures, or (c) iron every now and then and making sure that the 
clothing cools in a dry, pressed state - to regain structures.

Greg (Roberto Gregorius)
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