Compressive characteristics of cellular solids produced using vacuum-microwave, freeze, vacuum and hot air dehydration methods

Dried cellular solids were produced using different hydrocolloids such as locust bean gum, low methoxy pectin, methyl cellulose and tapioca starch. They were dried to less than 5% (w.b) moisture content using freeze-drying, vacuum drying, vacuum microwave drying or air-drying methods. The dry cellular solids were subjected to uniaxial compression using a Texture analyzer to study the compressive characteristics. True stress-strain relationship curves were developed for the dry cellular solids produced by different drying methods. Hencky's strain was calculated for true strain. Comparisons of samples dried by different drying methods were done in terms of their compressive characteristics at various water activities. No matter the type of drying, the dried materials were brittle at low water activity, plastic at medium water activity and elastomeric at higher water activity levels. Due to non-uniformity in air-dried samples and more closed pores in vacuum dried samples as well as less mechanical strength, these two were considered inferior for production of strong elastomeric foams. Microwave vacuum dried foams were mechanically the strongest. All the microwave vacuum dried samples were close in their Young's modulus. Increases in microwave power did not make any appreciable changes in pore structures although higher microwave power levels resulted in faster drying.