Do 100% polyester textiles "scortch" or oxidize (i.e., yellow) under
direct heat @350-400 degrees-F for 1-3 minutes of exposure?  If not,
what causes yellowing under these conditions?

Hi Salvoloveslucy,

theoretically 100% polyester should melt rather than scorch and the
melting point of polyester is over 480F (250C):
( http://www.ril.com/business/polyester/recron/py_ff_glossary.html )


"Synthtic fibers are thermoplastic and will not scorch unless they
contain cotton or cellulosic fibers such as linen, ramie, or rayon.
Instead they will shrink and melt in high heat. Sometimes the surface
of the fabric will be permanently "glazed" by an iron or dryer that is
too hot or left on too long. The glazed area will look shinier than
the rest of the fabric. Sometimes, the fabric will be totally melted
so a hole forms."
http://www.extension.iastate.edu/textiles/faq.html

however sizing chemicals used to alter the feel of polyester can cause
yellowing and it is possible this might well be accelerated by heat.

Any polymer fibre can yellow under excessive heat or natural ageing
e.g. exposure to UV. Most polymers are stabilised against heat and
long term ageing by the use of antioxidants. If you heat them up
repeatedly you use up the antioxidant and eventually they begin to
degrade. Degradation leads to coloured by products typically yellow if
the first colour. However, some antioxidants also produce yellow by
products as a result of their function (staining antioxidants) these
are often limited to use in dark coloured products.

Scorching and yellowing are two different phenomena but have similar results.