Abstract
Low density composites of sodium montmorillonite and poly(amide-imide) polymers have been created using an ice templating method, which serves as an alternative to the often-difficult foaming of high temperature/high performance polymers. The starting polymer was received in the poly(amic acid) form which can be cured using heat, into a water insoluble amide-imide copolymer. The resulting materials have densities in the 0.05 g/cm3 range and have excellent mechanical properties. Using a tertiary amine as a processing aid provides for lower viscosity and allows more concentrated polymer solutions to be used. The concentration of the amine relative to the acid groups on the polymer backbone has been found to cause significant difference in the mechanical properties of the dried materials. The synthesis and characterization of low density versions of two poly(amide-imide) polymers and their composites with sodium montmorillonite clay are discussed in the present work.
Highlights
Polymer aerogel represent a family of low density materials which are typically produced by either supercritical or freeze drying of wet gels [1,2]
The supercritical drying process developed from early work by Kistler [3], who showed that colloidal silica could be generated via a sol-gel process in an alcohol, solvent exchanged with acetone, dried using supercritical carbon dioxide
A great advantage of the supercritical drying approach is that the exquisite structure generated in the wet gel state can be preserved in the finished aerogel, producing materials of high surface area and nanoporosity, leading to material with exceptional thermal insulative properties
Summary
Polymer aerogel represent a family of low density materials which are typically produced by either supercritical or freeze drying of wet gels [1,2]. The supercritical drying process developed from early work by Kistler [3], who showed that colloidal silica could be generated via a sol-gel process in an alcohol, solvent exchanged with acetone, dried using supercritical carbon dioxide. Because the materials produced using such an ice templating method are coarser than those generated using supercritical drying, they tend to possess lower surface areas, lack nanoporosity, and exhibit typical polymer foam-like thermal conductivities [7]. The freeze drying process benefits from the use of water as solvent and simplicity in the freeze drying process, and is amenable to a wide range of polymers, such as poly(vinyl alcohol) [8]
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