December 2015
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12 Dec 2015 
Supercritical fluid extrusion is definitely a recent technical development for production of expanded starch-based foams where formation of a microcellular structure is normally achieved by injection of supercritical CO2 into the melt. The great successful plastic pelletizer diffusivity of CO2 in the porous matrix favors escape of the gas to the environment, reducing the amount designed for diffusion into the bubbles, posing a significant challenge thus. This research utilized two approaches to address this problem: increasing the nucleation cost and thus the ultimate bubble density in the foam, and lowering the melt temperature. The former was attained by reducing the nozzle diameter in order to achieve an increased pressure drop rate as the starch-CO2 melt flows through the nozzle. The second way was evaluated by introducing a cooling zone prior to the access of the melt in to the nozzle. Bubble density increased a lot more than once the nozzle radius was decreased from 3 fourfold.00 to at least one 1.50 mm. A higher bubble density led to a larger barrier or level of resistance to diffusion of CO2 to the environment, and increased growth ratio by as much as 160%. Cooling of the melt resulted in a reduction in diffusion coefficient of CO2 in the starch melt, and thus reduced CO2 damage to the environment. The expansion ratio increased by 34% as the melt heat range reduced from 60 to 40°C. The above-mentioned approaches can be handy in enhancing and managing expansion, which determines the textural attributes of the expanded food product ultimately.
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