[darkmatic]

Dear collegues and all,

I do have a question regarding the shrinkage of polymers.
Like it is known, thermoharding polymers like polyester and polymethylmetacrylate shrinks when they are cured.

Can someone tell me the way how to determinate this shrinkage and to calculat it?
Does someone has a manual regarding this problematic question?

Thank you a lot
Roel

[Dude]

A large portion of the shrinkage comes from thermal contraction.  It can be calculated by using the volumetric coefficient of thermal expansion (in most Physics books).  Assuming that the polymer is thermoplastic, the thermal expansion effect is the only factor.  If the material goes into the mold in a carrier solvent or as a "reactive oligomer", there will be other effects causing a volume change (evaporation, chemical change).  

[darkmatic]

Yes, that's true,  

but I'm searching a method for measuring the cure shrinkage of thermoharding polymers, and not the thermal expansion...

A few minutes ago, I found an method, but I don't know if it is reliable?

Shrinkage in % = density of the liquid resin minus density of the cured resin times 100
 or
shrinkage in % = (d liquid - d solid) * 100

Lets assume tha the density of the resin is 1,074 and the density of the cured piece is 1,15, then the shrinkage is minus 7,6 (-7,6)
Would this mean that there is an shrinkage of 7,6 % or that there is an expansion of 7,6 % ??

Thanks all of you