silicone adhesive whitening

lscheerl

I'm currently doing my thesis on adhesive joints between metal and glass.
I recently did some tension tests with a silicone adhesive.
This adhesive (a film of 1mm) cures due to high temperature (140°C) and a little pressure (0,7MPa) is needed.
During the tension test , it becomes white (first in the middle and than it spreads). When the whole surface is white, the joint breaks.
Does anyone know a reasonable explanation or where I have to start searching?