I have a really hard time finding a D-Limolene supplier in Europe (D-Limolene is a solvent that dissolves HIPS plastic used as 3D printing material ) so my next best option is ABS . I want to print a mold core and after lamination to dissolve it , if i print in ABS i have to use acetone to dissolve it . I  must soak my core in acetone for an hour max , would this be enough to ruin my part ? I dipped a small part i made in acetone for couple of hours and i notice some small softening of the surface part but nothing major ,as far as i can see. Since i want my part to take loads i don't feel really comfortable using acetone . What is your view on this?

HIPS is one route but you can’t get a solvent, then how about PVA. PVA will dissolve in water.

I have tried PVA :
1) extremely expensive  80euros per kilo
2) its almost flexible so in order to print a rigid enough core that can stand vacuum then you have to print thicker walls with more infill that comes to no1
the only good thing is that dissolves super easy leaving no residue.if money is no object then is a good solution , but for me is no option .thanks anyway!