Freeze-drying method for making semi-interpenetrating polymer networks and their fiber reinforced composites

The freeze-drying method, employed in processing food and pharmaceutical products, was used to make semi-IPNs with less phase separation than their conventional solution processed counterparts. Mathematical models for the batch operation as well as for the continuous casting were proposed and simulated. Unlike most previous studies found in the literature, the sublimation interface temperatures are no longer assumed to be constants in these models. Experimental Studies of several polyimide semi-IPNs made by the freeze drying method were also conducted. It was found that the degree of phase separation for a freeze-drying process semi-IPN is lower than its solution processed counterpart.This phenomenon has been proved through various test methods.Those freeze-drying processed semi-IPNs also have higher glass transition temperatures and their fiber reinforced composites have better thermal mechanical properties than the solution processed ones. Fracture toughness values of several semi-IPN specimens were also tested and were found to be higher than their unmodified counterparts.