Patent ID: 7563830

Claim:
A method of producing a thick-walled biodegradable foamed product, the method comprising the steps of: a) extruding a starch-based biodegradable polymeric base material containing water as a blowing agent, at a temperature below the flash point of water and with a level of shear which causes only medium levels of macromolecular degradation of the composition, to obtain a product with a water content of between 20% and 50%; b) conditioning the extrudate of step (a) at a controlled temperature and humidity to obtain a conditioned extrudate with a moisture content between 5% and 20%, wherein the moisture content of the conditioned extrudate is less than that of extrudate of step a) and with viscoelastic properties which are high enough to prevent rupture of the extrudate during heating and low enough to prevent shrinkage post heating; c) transferring the conditioned extrudate of step b to a mold; and d) heating the conditioned extrudate of step b using microwaves from a microwave heating device producing microwaves at a frequency of 2450 MHz characterized by the steps of: i) preheating by applying said microwaves in a first heating step to the conditioned extrudate in the device of step d to a temperature immediately below the flash point of the blowing agent to achieve uniform temperature distribution throughout the extrudate; ii) and then in a second heating step different from said first heating step and after achieving said uniform temperature distribution throughout the extrudate, by controlled rapid heating of the preheated conditioned extrudate of step d(i) by applying said microwaves in the device of step d through the flash point of the blowing agent; thereby forming an expanded foam product with a uniform closed cell structure, a medium density and resilient properties.