I am performing mechanical testing with epoxy polymer. The problem that I am facing is that most of the samples contain trapped air bubbles, which work as stress concentration points in the mechanical testing. I use Epon 828 with DETA curing agent (12 phr) and cure at 40 C for one hour. I tried vacuum degassing, but it resulted in even larger bubbles.
We faced this problem before (read my conference papers).
The best method lies in the mixing method.
Therefore, I recommend the use of a high speed mixer for homogeneous mixing and elimination of air bubbles
One method to solve your problem of air entrapment during mixing is to use disposable static mixers. Depending on the viscosity, you could choose a right type of mixer.
In case the air bubble formation is due to exothermic reaction during the mixing process, you may have to think of cooling down the components prior to mixing, though this will affect the setting time and working time.
To avoid air bubbles in solutions and suspensions of low and medium viscosity, vacuum degassing is most usefull tool (desiccator or freeze dryer (without freezing)). But as you wrote for to high viscositys the bubbles are not able to reach the surface. An other (or additional) oppertunity is to centrifuge the non hardened sample, which forces the resin or what ever to fill empty spaces.
The best solution may be to stop using such resins. Better to use a very low viscosity methymethacrylate monomer, which, even then, is best to vacuum. This way, all samples for all time will be conditioned the same, and you don't have to worry about the bubbles.
try cooling slow setting reduces hotspots that produce gas, takes more time
wishing success Stephan
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