Experimental verification of the devolatilization model for AFR700 polyimide composites

A model describing the devolatilization of polyimide composites was developed earlier in order to facilitate fabrication of composites of high quality. Recently, this model was generalized and expanded to accommodate additional condensation polyimide systems like AFR700. The existing model requires specific inputs for the kinetics, mass transfer coefficient and gas phase permeability. These empirical submodels were developed by fitting experimental data to the existing model for several heating rates and vacuum pressures. Subsequently the model was verified by comparing the model outputs for pressure and temperature profiles through the laminate thickness with experimental results for conditions other than those used to fit the submodels. Good agreement between model predictions and experimental results was obtained. As an example pressure profiles were predicted correctly within 0.004-0.012 atm of the experimental pressure profiles with pressures ranging between 0.116 atm and 0.276 atm, temperature profiles were predicted correctly within {dollar}2spcirc C{dollar}-{dollar}3spcirc C{dollar} with experimental temperature profiles (temperature range {dollar}211spcirc C{dollar} to {dollar}236spcirc C){dollar} for a 29-ply laminate heated at {dollar}1spcirc C/min{dollar} heating rate and vacuum of 20 Torr.; By increasing the heating rate for a 15-ply laminate from {dollar}1spcirc C/min{dollar} to {dollar}2spcirc C/min{dollar} at identical vacuum pressure, the average measured maximum of the pressure peaks through the laminate increases by 27%. For a 29-ply laminate the same increase in heating rate causes the increase in the maximum value of the pressure peaks to be more pronounced (an average by 31%). The temperature difference between the tool surface and the bleeder side of the laminate increases with heating rate and laminate thickness.; Model simulations, together with dynamic dielectric measurements, were used to study the polyimidization (polycondensation) reaction and accompanying devolatilization process for unidirectional AFR700/S-2 glass laminates.; For the first time it was possible to explain the dielectric sensor measurements in real processing cycles. Also for the first time the simulation model calculations allow the selection of proper temperature-pressure-time relations for optimal autoclave processing of this polyimide resin system. Unexplained dielectric data during the Air Force Extended cure cycle and Qualitative Process Automation (QPA) cure cycle were clearly explained for first time by the model.