Cellular Solids Based on Biopolymer Nanocomposites

Abstract

The society of Delft Aerospace Rocket Engineering (DARE) aims at launching the Stratos IV sounding rocket to an apogee of 100km; thus cementing their place as one of the few student teams that have had the unique opportunity to design and build a rocket that is capable of reaching the frontiers of space. In doing so, DARE has entered flight supersonic regimes during atmospheric entry. With the development of cryogenic engines in the pipeline, future DARE missions look at reaching the hypersonic velocity regimes resulting in the current cork and carbon fibre composite heat shield design becoming redundant. Thus, hypersonic flight brings with it the challenge of designing new a heat shield; capable of withstanding the elevated temperatures.

Alginate and montmorillonite nanoclay based biopolymer nanocomposites have become a well-researched topic in recent years. This stems from the ability of the nanoclay fillers to align themselves within the suspension to mimic natural materials such as nacre (mother of pearl). The alignment of the nanoclay not only reinforces the biopolymer to provide a high storage modulus but also provides a tortuous path for transport phenomenon such as diffusion to take place; thereby making them flame retardant.

In their native state, the nanocomposites are film-like and offer limited viability. But, simple production practices may be borrowed from culinary disciplines to transform the nanocomposites into foams with different relative densities. The introduction of the gaseous voids should further heighten the thermal characteristics; allowing them to function as heat shields. However, in transforming the nanocomposite to a foam, little is understood about the impact it will have on the mechanics of the native nanocomposite. As multiple analytical and numerical models have been provided over the years to estimate the mechanical properties of foams, a careful assessment of the various literature sources becomes necessary. Once a suitable model is identified, a detailed experimental campaign can be carried out to characterise the biopolymer nanocomposite foams mechanically.