Modeling the effect of formulation on the properties of extruded corn flour-based foamed plastic

The effects of formulation on resiliency, unit density and thermal conductivity of an extruded corn flour-based foamed plastic were studied. A central composite design was used to establish the levels of corn flour, water, sodium bicarbonate, soy protein and polystyrene used to develop the individual models. Three separate multiple regression models were developed to predict resiliency, unit density and thermal conductivity as functions of formulation ingredient levels. The models were used to isolate the formulations that produced the minimum unit density, maximum resiliency and minimum thermal conductivity. These optimal formulations were extruded using a commercial scale extruder. The results produced extrudates those resiliency, unit density and thermal conductivity were 89.9%, 0.041 $\rm g/cm\sp3$ and 0.045 $\rm W/(m{\cdot}C),$ respectively. The unit density and thermal conductivity were within the range of commercial rigid cellular polystyrene. The resiliency was 5% less than commercial polystyrene loose-fill. A foamed sheet product was also successfully extruded using, the formulations developed. A computer based data acquisition and control system, used with the thermal probe, was developed to measure thermal conductivity of the extrudates. Errors due to short test times and differences in thermal mass of the probe and sample were determined. A multiple regression equation was developed to allow convenient calculation of those values required to assess the error associated with short test times and differences in thermal mass. A method to calculate the error was developed and used to correct the measured thermal conductivity values.