THE EFFECT OF MOISTURE-CONTENT ON THE MECHANICAL-PROPERTIES OF EXTRUDED FOOD FOAMS

The mechanical properties of extrusion-cooked foams have been measured as a function of density and moisture content. Extrusion conditions were varied to give a range of densities for which the flexural strength and modulus increased with density. The increase of density by low levels of water absorption caused little change in this response. However, the density increase by absorption of greater quantities of water resulted in a decrease in mechanical properties. This has been largely attributed to the changes in the foam wall mechanical properties which are discussed in terms of plasticization of polymers. There is some evidence that compared to the flexural test method, the higher strain rate of impact testing requires a higher level of water addition in order to cause a decrease in strength.