Modeling inflation and growth in polyimide foam processing

Derek Matthew Sanderson, Purdue University

Abstract

Polyimide foams produced from poly(amic acid) precursors are currently used in aerospace and military applications for their high thermal stability, inflammability, and desirable mechanical properties. They are used despite fundamental knowledge of the phenomena governing their growth. A numerical model was previously developed to predict the inflation behavior of a single poly(amic acid) particle subjected to linearly increasing temperatures. This model was modified in order to handle non-linear thermal cycles and to remedy inconsistencies discovered in the course of the present work. A parametric study was conducted to investigate the effect of initial particle dimensions, blowing agent concentration, and thermal cycle on the bubble growth in a single particle. The heating rate and particle dimensions were all found to produce a local maximum value of final particle radius because of competing diffusion and kinetic phenomena. It was then shown that this inflation model can be used as a subfunction to predict density in a foam growth model that describes the transfer of heat throughout a layer of expanding precursor. The effect of the imposed heat treatment and initial thickness of precursor layer on the final density profile was studied. Regions of increased inflation were observed in the interior of the foam. These regions were caused by an increase in the period of time spent in the range of temperatures that permit inflation. Observations from these studies were then used to develop a heat treatment process that improves uniformity in the density of the foam. These customized processing conditions demonstrate the improvements made possible by the growth model and open the door to further improvements in polyimide foam processing.

Degree

M.S.M.S.E.

Advisors

Krane, Purdue University.

Subject Area

Materials science

COinS