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Degree

Doctor of Philosophy, University of Akron, Polymer Engineering, 2005.

Abstract

Polyimide foams have emerged as high performance cellular materials with great potential for applications in aerospace due to their excellent mechanical, chemical and electrical properties. A novel technology in the development of polyimide foams consists of solid precursors in the form of powders with embedded blowing agent that can be converted by simple thermal treatment into single polymeric spherical microstructures or inflated together to produce foams with varying ranges of density and properties. This technology is hereafter referred to as solid-state powder foaming. Solid-state foaming from poly(amic acid) precursor particles was studied by examining concurrent and competitive phenomena that determine the morphology and physical properties of resulting polyimide microstructures. Phenomenological analysis of morphological relations, as well as physicochemical processes provided a comprehensive understanding of the governing principles by which potential particle inflation is achieved. Resulting polyimide microstructures present morphologies that are the result of the combined effect of morphological features on the precursor particles, blowing agent concentration and processing conditions exerted on the powders during the inflation process. A strong interrelation was found between different controlling factors such as precursor morphology and processing conditions. The balance between local temperature and concentration inside the particles can be manipulated by these controlling factors in such a way that a particle under a certain set of conditions might experience multiple bubble growth, while under slightly different conditions might present single bubble inflation or no inflation at all. Results from the phenomenological analysis served as the basis of a numerical model and corresponding parametric study where the different parameters of the governing phenomena were evaluated and studied. This parametric study provided a comprehensive understanding of the interrelation of different parameters and conditions which govern the inflation of powdered precursors. By having separated each of the different phenomena, as well as their sources and effects, future research in the field of powder foaming can center on specific issues where optimization or fundamental understanding is required. The comprehensive understanding achieved from the present work lays the groundwork for further optimization of the powder foaming process towards better control of foam properties and novel application development.

Subject Headings

Chemistry, Polymer

Keywords

Polyimide; Foams; Powder; Microspheres

Committee / Advisors

Thein Kyu (Advisor)
R. Byron Pipes (Advisor)

Pages

276p.

Document number: akron1123710711
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=akron1123710711

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