Polyimide-Silica Hybrid Aerogels with High Mechanical Strength for Thermal Insulation Applications
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Polyimide-Silica Hybrid Aerogels with High Mechanical Strength for Thermal Insulation Applications Wenting Dong, Wendell Rhine, and Shannon White Aspen Aerogels, Inc., Northborough, MA 01532, USA ABSTRACT High performance polyimides have been widely investigated as materials with excellent thermal, mechanical, and electronic properties due to their highly rigid structures. Aspen has developed an approach to prepare polyimide aerogels which have applications as low dielectric constant materials, separation membranes, catalyst supports and insulation materials. In this paper, we will discuss the preparation of polyimide-silica hybrid aerogel materials with good mechanical strengths and low thermal conductivities. The polyimide-silica hybrid aerogels were made by a two-step process and the materials were characterized to determine thermal conductivity and compressive strength. Results show that compressive moduli of the polyimidesilica hybrid aerogels increase dramatically with density (power law relationship). Thermal conductivity of the aerogels is dependent on the aging conditions and density, with the lowest value achieved so far being ~12 mW/m-K at ambient conditions. The relationship between aerogel density and surface area, thermal stability, porosity and morphology of the nanostructure of the polyimide-silica hybrid aerogels are also described in this paper. INTRODUCTION The exploration of space requires that new technologies be developed for long-term cryogenic propellant storage applications in-space, on the lunar surface, and on the Earth. High performance thermal insulation materials are needed to insulate cryotanks on launch vehicles as well as cryogenic fluid storage tanks in space. Silica aerogels are the best known thermal insulation materials. However, silica aerogels are weak and the mechanical strength of these silica aerogels needs to be improved to meet the requirements of these applications. Thus, this work has focused on improving the strength of aerogels which are the lightest weight and best insulation materials known. Improvements in the strength of aerogels would allow these materials to be used as advanced non-compacting insulation materials capable of retaining structural integrity while accommodating large operating temperatures ranging from 423 ºF and 650 ºF. The mechanical properties of aerogel materials can be increased by reinforcing them with organic polymer crosslinking agents and with fibers. Based on published results for polymer crosslinked aerogels (X-aerogels) [1,2,3,4,5], preparing organic polymer modified silica gels is a viable approach for improving the strength of aerogels. Polyimide materials have been widely investigated for their excellent thermal, mechanical, and electronic properties due to their highly rigid molecular structures [6]. Polyimide based polymer crosslinked silica aerogels are therefore anticipated to have a high modulus and excellent thermal insulation properties. Our objective in this effort is to develop lightweight multifunctional polyimide and silica
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