Influence of processing variables on the mechanical properties of extruded maize

Maize was extrusion cooked under different conditions of feed moisture and extruder screw speed to produce foams of different bulk density. The foams were tested in tension, com-pression and flexure according to British Standards for plastic materials. A power law corre-lation between mechanical properties and bulk density was used with a density power law index in the range 1.5 to 2.3. This represents a special case of Ashby's treatments of foams where the foam wall properties have not been included. These pore wall properties were a function of processing conditions. A pin identation test was used to obtain localized mech-anical properties and indicated the different deformation behaviour of low- and high-density foams together with the greater strength of the foam surface.