Annealing process of PS&PP ??

Hi,
To relieve the residual stress, I will have to thermal anneal my PS&PP
panels. At the same time, I want to keep the original geometry shape
untouched, i.e. still a good flat panel.
I never done this before. Could anyone here tell me the right process to
conduct it? e.g. What temperature, how long etc. Or, is there standard for
annealing process, where can I find it?
Thanks a lot!
BTW
This is for thesis, there is only small amount of them.